Information management in DNA replication modeled by directional, stochastic chains with memory

NASA Astrophysics Data System (ADS)

Arias-Gonzalez, J. Ricardo

2016-11-01

Stochastic chains represent a key variety of phenomena in many branches of science within the context of information theory and thermodynamics. They are typically approached by a sequence of independent events or by a memoryless Markov process. Stochastic chains are of special significance to molecular biology, where genes are conveyed by linear polymers made up of molecular subunits and transferred from DNA to proteins by specialized molecular motors in the presence of errors. Here, we demonstrate that when memory is introduced, the statistics of the chain depends on the mechanism by which objects or symbols are assembled, even in the slow dynamics limit wherein friction can be neglected. To analyze these systems, we introduce a sequence-dependent partition function, investigate its properties, and compare it to the standard normalization defined by the statistical physics of ensembles. We then apply this theory to characterize the enzyme-mediated information transfer involved in DNA replication under the real, non-equilibrium conditions, reproducing measured error rates and explaining the typical 100-fold increase in fidelity that is experimentally found when proofreading and edition take place. Our model further predicts that approximately 1 kT has to be consumed to elevate fidelity in one order of magnitude. We anticipate that our results are necessary to interpret configurational order and information management in many molecular systems within biophysics, materials science, communication, and engineering.

Nonlinear information fusion algorithms for data-efficient multi-fidelity modelling.

PubMed

Perdikaris, P; Raissi, M; Damianou, A; Lawrence, N D; Karniadakis, G E

2017-02-01

Multi-fidelity modelling enables accurate inference of quantities of interest by synergistically combining realizations of low-cost/low-fidelity models with a small set of high-fidelity observations. This is particularly effective when the low- and high-fidelity models exhibit strong correlations, and can lead to significant computational gains over approaches that solely rely on high-fidelity models. However, in many cases of practical interest, low-fidelity models can only be well correlated to their high-fidelity counterparts for a specific range of input parameters, and potentially return wrong trends and erroneous predictions if probed outside of their validity regime. Here we put forth a probabilistic framework based on Gaussian process regression and nonlinear autoregressive schemes that is capable of learning complex nonlinear and space-dependent cross-correlations between models of variable fidelity, and can effectively safeguard against low-fidelity models that provide wrong trends. This introduces a new class of multi-fidelity information fusion algorithms that provide a fundamental extension to the existing linear autoregressive methodologies, while still maintaining the same algorithmic complexity and overall computational cost. The performance of the proposed methods is tested in several benchmark problems involving both synthetic and real multi-fidelity datasets from computational fluid dynamics simulations.

Gaussian functional regression for output prediction: Model assimilation and experimental design

NASA Astrophysics Data System (ADS)

Nguyen, N. C.; Peraire, J.

2016-03-01

In this paper, we introduce a Gaussian functional regression (GFR) technique that integrates multi-fidelity models with model reduction to efficiently predict the input-output relationship of a high-fidelity model. The GFR method combines the high-fidelity model with a low-fidelity model to provide an estimate of the output of the high-fidelity model in the form of a posterior distribution that can characterize uncertainty in the prediction. A reduced basis approximation is constructed upon the low-fidelity model and incorporated into the GFR method to yield an inexpensive posterior distribution of the output estimate. As this posterior distribution depends crucially on a set of training inputs at which the high-fidelity models are simulated, we develop a greedy sampling algorithm to select the training inputs. Our approach results in an output prediction model that inherits the fidelity of the high-fidelity model and has the computational complexity of the reduced basis approximation. Numerical results are presented to demonstrate the proposed approach.

Modeling and Compensation of the Internal Friction Torque of a Travelling Wave Ultrasonic Motor.

PubMed

Giraud, F; Sandulescu, P; Amberg, M; Lemaire-Semail, B; Ionescu, F

2011-01-01

This paper deals with the control and experimentation of a one-degree-of-freedom haptic stick, actuated by a travelling wave ultrasonic motor. This type of actuator has many interesting properties such as low-speed operation capabilities and a high torque-to-weight ratio, making it appropriate for haptic applications. However, the motor used in this application displays nonlinear behavior due to the necessary contact between its rotor and stator. Moreover, due to its energy conversion process, the torque applied to the end-effector is not a straightforward function of the supply current or voltage. This is why a force-feedback control strategy is presented, which includes an online parameter estimator. Experimental runs are then presented to examine the fidelity of the interface.

Multi-criteria optimization of chassis parameters of Nissan 200 SX for drifting competitions

NASA Astrophysics Data System (ADS)

Maniowski, M.

2016-09-01

The work objective is to increase performance of Nissan 200sx S13 prepared for a quasi-static state of drifting on a circular path with given constant radius (R=15 m) and tyre-road friction coefficient (μ = 0.9). First, a high fidelity “miMA” multibody model of the vehicle is formulated. Then, a multicriteria optimization problem is solved with one of the goals to maximize a stable drift angle (β) of the vehicle. The decision variables contain 11 parameters of the vehicle chassis (describing the wheel suspension stiffness and geometry) and 2 parameters responsible for a driver steering and accelerator actions, that control this extreme closed-loop manoeuvre. The optimized chassis setup results in the drift angle increase by 14% from 35 to 40 deg.

Development of Adaptive Model Refinement (AMoR) for Multiphysics and Multifidelity Problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Turinsky, Paul

This project investigated the development and utilization of Adaptive Model Refinement (AMoR) for nuclear systems simulation applications. AMoR refers to utilization of several models of physical phenomena which differ in prediction fidelity. If the highest fidelity model is judged to always provide or exceeded the desired fidelity, than if one can determine the difference in a Quantity of Interest (QoI) between the highest fidelity model and lower fidelity models, one could utilize the fidelity model that would just provide the magnitude of the QoI desired. Assuming lower fidelity models require less computational resources, in this manner computational efficiency can bemore » realized provided the QoI value can be accurately and efficiently evaluated. This work utilized Generalized Perturbation Theory (GPT) to evaluate the QoI, by convoluting the GPT solution with the residual of the highest fidelity model determined using the solution from lower fidelity models. Specifically, a reactor core neutronics problem and thermal-hydraulics problem were studied to develop and utilize AMoR. The highest fidelity neutronics model was based upon the 3D space-time, two-group, nodal diffusion equations as solved in the NESTLE computer code. Added to the NESTLE code was the ability to determine the time-dependent GPT neutron flux. The lower fidelity neutronics model was based upon the point kinetics equations along with utilization of a prolongation operator to determine the 3D space-time, two-group flux. The highest fidelity thermal-hydraulics model was based upon the space-time equations governing fluid flow in a closed channel around a heat generating fuel rod. The Homogenous Equilibrium Mixture (HEM) model was used for the fluid and Finite Difference Method was applied to both the coolant and fuel pin energy conservation equations. The lower fidelity thermal-hydraulic model was based upon the same equations as used for the highest fidelity model but now with coarse spatial meshing, corrected somewhat by employing effective fuel heat conduction values. The effectiveness of switching between the highest fidelity model and lower fidelity model as a function of time was assessed using the neutronics problem. Based upon work completed to date, one concludes that the time switching is effective in annealing out differences between the highest and lower fidelity solutions. The effectiveness of using a lower fidelity GPT solution, along with a prolongation operator, to estimate the QoI was also assessed. The utilization of a lower fidelity GPT solution was done in an attempt to avoid the high computational burden associated with solving for the highest fidelity GPT solution. Based upon work completed to date, one concludes that the lower fidelity adjoint solution is not sufficiently accurate with regard to estimating the QoI; however, a formulation has been revealed that may provide a path for addressing this shortcoming.« less

Multi-fidelity stochastic collocation method for computation of statistical moments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Xueyu, E-mail: xueyu-zhu@uiowa.edu; Linebarger, Erin M., E-mail: aerinline@sci.utah.edu; Xiu, Dongbin, E-mail: xiu.16@osu.edu

We present an efficient numerical algorithm to approximate the statistical moments of stochastic problems, in the presence of models with different fidelities. The method extends the multi-fidelity approximation method developed in . By combining the efficiency of low-fidelity models and the accuracy of high-fidelity models, our method exhibits fast convergence with a limited number of high-fidelity simulations. We establish an error bound of the method and present several numerical examples to demonstrate the efficiency and applicability of the multi-fidelity algorithm.

Series Elastic Actuators for legged robots

NASA Astrophysics Data System (ADS)

Pratt, Jerry E.; Krupp, Benjamin T.

2004-09-01

Series Elastic Actuators provide many benefits in force control of robots in unconstrained environments. These benefits include high force fidelity, extremely low impedance, low friction, and good force control bandwidth. Series Elastic Actuators employ a novel mechanical design architecture which goes against the common machine design principal of "stiffer is better." A compliant element is placed between the gear train and driven load to intentionally reduce the stiffness of the actuator. A position sensor measures the deflection, and the force output is accurately calculated using Hooke"s Law (F=Kx). A control loop then servos the actuator to the desired output force. The resulting actuator has inherent shock tolerance, high force fidelity and extremely low impedance. These characteristics are desirable in many applications including legged robots, exoskeletons for human performance amplification, robotic arms, haptic interfaces, and adaptive suspensions. We describe several variations of Series Elastic Actuators that have been developed using both electric and hydraulic components.

The effect of bench model fidelity on fluoroscopy-guided transforaminal epidural injection training: a randomized control study.

PubMed

Gonzalez-Cota, Alan; Chiravuri, Srinivas; Stansfield, R Brent; Brummett, Chad M; Hamstra, Stanley J

2013-01-01

The purpose of this study was to determine whether high-fidelity simulators provide greater benefit than low-fidelity models in training fluoroscopy-guided transforaminal epidural injection. This educational study was a single-center, prospective, randomized 3-arm pretest-posttest design with a control arm. Eighteen anesthesia and physical medicine and rehabilitation residents were instructed how to perform a fluoroscopy-guided transforaminal epidural injection and assessed by experts on a reusable injectable phantom cadaver. The high- and low-fidelity groups received 30 minutes of supervised hands-on practice according to group assignment, and the control group received 30 minutes of didactic instruction from an expert. We found no differences at posttest between the high- and low-fidelity groups on global ratings of performance (P = 0.17) or checklist scores (P = 0.81). Participants who received either form of hands-on training significantly outperformed the control group on both the global rating of performance (control vs low-fidelity, P = 0.0048; control vs high-fidelity, P = 0.0047) and the checklist (control vs low-fidelity, P = 0.0047; control vs high-fidelity, P = 0.0047). Training an epidural procedure using a low-fidelity model may be equally effective as training on a high-fidelity model. These results are consistent with previous research on a variety of interventional procedures and further demonstrate the potential impact of simple, low-fidelity training models.

Development of a High Fidelity Dynamic Module of the Advanced Resistive Exercise Device (ARED) Using Adams

NASA Technical Reports Server (NTRS)

Humphreys, B. T.; Thompson, W. K.; Lewandowski, B. E.; Cadwell, E. E.; Newby, N. J.; Fincke, R. S.; Sheehan, C.; Mulugeta, L.

2012-01-01

NASA's Digital Astronaut Project (DAP) implements well-vetted computational models to predict and assess spaceflight health and performance risks, and enhance countermeasure development. DAP provides expertise and computation tools to its research customers for model development, integration, or analysis. DAP is currently supporting the NASA Exercise Physiology and Countermeasures (ExPC) project by integrating their biomechanical models of specific exercise movements with dynamic models of the devices on which the exercises were performed. This presentation focuses on the development of a high fidelity dynamic module of the Advanced Resistive Exercise Device (ARED) on board the ISS. The ARED module, illustrated in the figure below, was developed using the Adams (MSC Santa Ana, California) simulation package. The Adams package provides the capabilities to perform multi rigid body, flexible body, and mixed dynamic analyses of complex mechanisms. These capabilities were applied to accurately simulate: Inertial and mass properties of the device such as the vibration isolation system (VIS) effects and other ARED components, Non-linear joint friction effects, The gas law dynamics of the vacuum cylinders and VIS components using custom written differential state equations, The ARED flywheel dynamics, including torque limiting clutch. Design data from the JSC ARED Engineering team was utilized in developing the model. This included solid modeling geometry files, component/system specifications, engineering reports and available data sets. The Adams ARED module is importable into LifeMOD (Life Modeler, Inc., San Clemente, CA) for biomechanical analyses of different resistive exercises such as squat and dead-lift. Using motion capture data from ground test subjects, the ExPC developed biomechanical exercise models in LifeMOD. The Adams ARED device module was then integrated with the exercise subject model into one integrated dynamic model. This presentation will describe the development of the Adams ARED module including its capabilities, limitations, and assumptions. Preliminary results, validation activities, and a practical application of the module to inform the relative effect of the flywheels on exercise will be discussed.

A Method of Surrogate Model Construction which Leverages Lower-Fidelity Information using Space Mapping Techniques

DTIC Science & Technology

2014-03-27

fidelity. This pairing is accomplished through the use of a space mapping technique, which is a process where the design space of a lower fidelity model...is aligned a higher fidelity model. The intent of applying space mapping techniques to the field of surrogate construction is to leverage the

A unified, multifidelity quasi-newton optimization method with application to aero-structural designa

NASA Astrophysics Data System (ADS)

Bryson, Dean Edward

A model's level of fidelity may be defined as its accuracy in faithfully reproducing a quantity or behavior of interest of a real system. Increasing the fidelity of a model often goes hand in hand with increasing its cost in terms of time, money, or computing resources. The traditional aircraft design process relies upon low-fidelity models for expedience and resource savings. However, the reduced accuracy and reliability of low-fidelity tools often lead to the discovery of design defects or inadequacies late in the design process. These deficiencies result either in costly changes or the acceptance of a configuration that does not meet expectations. The unknown opportunity cost is the discovery of superior vehicles that leverage phenomena unknown to the designer and not illuminated by low-fidelity tools. Multifidelity methods attempt to blend the increased accuracy and reliability of high-fidelity models with the reduced cost of low-fidelity models. In building surrogate models, where mathematical expressions are used to cheaply approximate the behavior of costly data, low-fidelity models may be sampled extensively to resolve the underlying trend, while high-fidelity data are reserved to correct inaccuracies at key locations. Similarly, in design optimization a low-fidelity model may be queried many times in the search for new, better designs, with a high-fidelity model being exercised only once per iteration to evaluate the candidate design. In this dissertation, a new multifidelity, gradient-based optimization algorithm is proposed. It differs from the standard trust region approach in several ways, stemming from the new method maintaining an approximation of the inverse Hessian, that is the underlying curvature of the design problem. Whereas the typical trust region approach performs a full sub-optimization using the low-fidelity model at every iteration, the new technique finds a suitable descent direction and focuses the search along it, reducing the number of low-fidelity evaluations required. This narrowing of the search domain also alleviates the burden on the surrogate model corrections between the low- and high-fidelity data. Rather than requiring the surrogate to be accurate in a hyper-volume bounded by the trust region, the model needs only to be accurate along the forward-looking search direction. Maintaining the approximate inverse Hessian also allows the multifidelity algorithm to revert to high-fidelity optimization at any time. In contrast, the standard approach has no memory of the previously-computed high-fidelity data. The primary disadvantage of the proposed algorithm is that it may require modifications to the optimization software, whereas standard optimizers may be used as black-box drivers in the typical trust region method. A multifidelity, multidisciplinary simulation of aeroelastic vehicle performance is developed to demonstrate the optimization method. The numerical physics models include body-fitted Euler computational fluid dynamics; linear, panel aerodynamics; linear, finite-element computational structural mechanics; and reduced, modal structural bases. A central element of the multifidelity, multidisciplinary framework is a shared parametric, attributed geometric representation that ensures the analysis inputs are consistent between disciplines and fidelities. The attributed geometry also enables the transfer of data between disciplines. The new optimization algorithm, a standard trust region approach, and a single-fidelity quasi-Newton method are compared for a series of analytic test functions, using both polynomial chaos expansions and kriging to correct discrepancies between fidelity levels of data. In the aggregate, the new method requires fewer high-fidelity evaluations than the trust region approach in 51% of cases, and the same number of evaluations in 18%. The new approach also requires fewer low-fidelity evaluations, by up to an order of magnitude, in almost all cases. The efficacy of both multifidelity methods compared to single-fidelity optimization depends significantly on the behavior of the high-fidelity model and the quality of the low-fidelity approximation, though savings are realized in a large number of cases. The multifidelity algorithm is also compared to the single-fidelity quasi-Newton method for complex aeroelastic simulations. The vehicle design problem includes variables for planform shape, structural sizing, and cruise condition with constraints on trim and structural stresses. Considering the objective function reduction versus computational expenditure, the multifidelity process performs better in three of four cases in early iterations. However, the enforcement of a contracting trust region slows the multifidelity progress. Even so, leveraging the approximate inverse Hessian, the optimization can be seamlessly continued using high-fidelity data alone. Ultimately, the proposed new algorithm produced better designs in all four cases. Investigating the return on investment in terms of design improvement per computational hour confirms that the multifidelity advantage is greatest in early iterations, and managing the transition to high-fidelity optimization is critical.

Constitutive equation of friction based on the subloading-surface concept

PubMed Central

Ueno, Masami; Kuwayama, Takuya; Suzuki, Noriyuki; Yonemura, Shigeru; Yoshikawa, Nobuo

2016-01-01

The subloading-friction model is capable of describing static friction, the smooth transition from static to kinetic friction and the recovery to static friction after sliding stops or sliding velocity decreases. This causes a negative rate sensitivity (i.e. a decrease in friction resistance with increasing sliding velocity). A generalized subloading-friction model is formulated in this article by incorporating the concept of overstress for viscoplastic sliding velocity into the subloading-friction model to describe not only negative rate sensitivity but also positive rate sensitivity (i.e. an increase in friction resistance with increasing sliding velocity) at a general sliding velocity ranging from quasi-static to impact sliding. The validity of the model is verified by numerical experiments and comparisons with test data obtained from friction tests using a lubricated steel specimen. PMID:27493570

Langley Stability and Transition Analysis Code (LASTRAC) Version 1.2 User Manual

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan

2004-01-01

LASTRAC is a general-purposed, physics-based transition prediction code released by NASA for Laminar Flow Control studies and transition research. The design and development of the LASTRAC code is aimed at providing an engineering tool that is easy to use and yet capable of dealing with a broad range of transition related issues. It was written from scratch based on the state-of-the-art numerical methods for stability analysis and modern software technologies. At low fidelity, it allows users to perform linear stability analysis and N-factor transition correlation for a broad range of flow regimes and configurations by using either the linear stability theory or linear parabolized stability equations method. At high fidelity, users may use nonlinear PSE to track finite-amplitude disturbances until the skin friction rise. This document describes the governing equations, numerical methods, code development, detailed description of input/output parameters, and case studies for the current release of LASTRAC.

Creation of a Rapid High-Fidelity Aerodynamics Module for a Multidisciplinary Design Environment

NASA Technical Reports Server (NTRS)

Srinivasan, Muktha; Whittecar, William; Edwards, Stephen; Mavris, Dimitri N.

2012-01-01

In the traditional aerospace vehicle design process, each successive design phase is accompanied by an increment in the modeling fidelity of the disciplinary analyses being performed. This trend follows a corresponding shrinking of the design space as more and more design decisions are locked in. The correlated increase in knowledge about the design and decrease in design freedom occurs partly because increases in modeling fidelity are usually accompanied by significant increases in the computational expense of performing the analyses. When running high fidelity analyses, it is not usually feasible to explore a large number of variations, and so design space exploration is reserved for conceptual design, and higher fidelity analyses are run only once a specific point design has been selected to carry forward. The designs produced by this traditional process have been recognized as being limited by the uncertainty that is present early on due to the use of lower fidelity analyses. For example, uncertainty in aerodynamics predictions produces uncertainty in trajectory optimization, which can impact overall vehicle sizing. This effect can become more significant when trajectories are being shaped by active constraints. For example, if an optimal trajectory is running up against a normal load factor constraint, inaccuracies in the aerodynamic coefficient predictions can cause a feasible trajectory to be considered infeasible, or vice versa. For this reason, a trade must always be performed between the desired fidelity and the resources available. Apart from this trade between fidelity and computational expense, it is very desirable to use higher fidelity analyses earlier in the design process. A large body of work has been performed to this end, led by efforts in the area of surrogate modeling. In surrogate modeling, an up-front investment is made by running a high fidelity code over a Design of Experiments (DOE); once completed, the DOE data is used to create a surrogate model, which captures the relationships between input variables and responses into regression equations. Depending on the dimensionality of the problem and the fidelity of the code for which a surrogate model is being created, the initial DOE can itself be computationally prohibitive to run. Cokriging, a modeling approach from the field of geostatistics, provides a desirable compromise between computational expense and fidelity. To do this, cokriging leverages a large body of data generated by a low fidelity analysis, combines it with a smaller set of data from a higher fidelity analysis, and creates a kriging surrogate model with prediction fidelity approaching that of the higher fidelity analysis. When integrated into a multidisciplinary environment, a disciplinary analysis module employing cokriging can raise the analysis fidelity without drastically impacting the expense of design iterations. This is demonstrated through the creation of an aerodynamics analysis module in NASA s OpenMDAO framework. Aerodynamic analyses including Missile DATCOM, APAS, and USM3D are leveraged to create high fidelity aerodynamics decks for parametric vehicle geometries, which are created in NASA s Vehicle Sketch Pad (VSP). Several trade studies are performed to examine the achieved level of model fidelity, and the overall impact to vehicle design is quantified.

Nonlinear Friction Compensation of Ball Screw Driven Stage Based on Variable Natural Length Spring Model and Disturbance Observer

NASA Astrophysics Data System (ADS)

Asaumi, Hiroyoshi; Fujimoto, Hiroshi

Ball screw driven stages are used for industrial equipments such as machine tools and semiconductor equipments. Fast and precise positioning is necessary to enhance productivity and microfabrication technology of the system. The rolling friction of the ball screw driven stage deteriorate the positioning performance. Therefore, the control system based on the friction model is necessary. In this paper, we propose variable natural length spring model (VNLS model) as the friction model. VNLS model is simple and easy to implement as friction controller. Next, we propose multi variable natural length spring model (MVNLS model) as the friction model. MVNLS model can represent friction characteristic of the stage precisely. Moreover, the control system based on MVNLS model and disturbance observer is proposed. Finally, the simulation results and experimental results show the advantages of the proposed method.

Prediction and validation of the energy dissipation of a friction damper

NASA Astrophysics Data System (ADS)

Lopez, I.; Nijmeijer, H.

2009-12-01

Friction dampers can be a cheap and efficient way to reduce the vibration levels of a wide range of mechanical systems. In the present work it is shown that the maximum energy dissipation and corresponding optimum friction force of friction dampers with stiff localized contacts and large relative displacements within the contact, can be determined with sufficient accuracy using a dry (Coulomb) friction model. Both the numerical calculations with more complex friction models and the experimental results in a laboratory test set-up show that these two quantities are relatively robust properties of a system with friction. The numerical calculations are performed with several friction models currently used in the literature. For the stick phase smooth approximations like viscous damping or the arctan function are considered but also the non-smooth switch friction model is used. For the slip phase several models of the Stribeck effect are used. The test set-up for the laboratory experiments consists of a mass sliding on parallel ball-bearings, where additional friction is created by a sledge attached to the mass, which is pre-stressed against a friction plate. The measured energy dissipation is in good agreement with the theoretical results for Coulomb friction.

Friction of hard surfaces and its application in earthquakes and rock slope stability

NASA Astrophysics Data System (ADS)

Sinha, Nitish; Singh, Arun K.; Singh, Trilok N.

2018-05-01

In this article, we discuss the friction models for hard surfaces and their applications in earth sciences. The rate and state friction (RSF) model, which is basically modified form of the classical Amontons-Coulomb friction laws, is widely used for explaining the crustal earthquakes and the rock slope failures. Yet the RSF model has further been modified by considering the role of temperature at the sliding interface known as the rate, state and temperature friction (RSTF) model. Further, if the pore pressure is also taken into account then it is stated as the rate, state, temperature and pore pressure friction (RSTPF) model. All the RSF models predict a critical stiffness as well as a critical velocity at which sliding behavior becomes stable/unstable. The friction models are also used for predicting time of failure of the rock mass on an inclined plane. Finally, the limitation and possibilities of the proposed friction models are also highlighted.

Reciprocal Sliding Friction Model for an Electro-Deposited Coating and Its Parameter Estimation Using Markov Chain Monte Carlo Method

PubMed Central

Kim, Kyungmok; Lee, Jaewook

2016-01-01

This paper describes a sliding friction model for an electro-deposited coating. Reciprocating sliding tests using ball-on-flat plate test apparatus are performed to determine an evolution of the kinetic friction coefficient. The evolution of the friction coefficient is classified into the initial running-in period, steady-state sliding, and transition to higher friction. The friction coefficient during the initial running-in period and steady-state sliding is expressed as a simple linear function. The friction coefficient in the transition to higher friction is described with a mathematical model derived from Kachanov-type damage law. The model parameters are then estimated using the Markov Chain Monte Carlo (MCMC) approach. It is identified that estimated friction coefficients obtained by MCMC approach are in good agreement with measured ones. PMID:28773359

Teaching elliptical excision skills to novice medical students: a randomized controlled study comparing low- and high-fidelity bench models.

PubMed

Denadai, Rafael; Oshiiwa, Marie; Saad-Hossne, Rogério

2014-03-01

The search for alternative and effective forms of training simulation is needed due to ethical and medico-legal aspects involved in training surgical skills on living patients, human cadavers and living animals. To evaluate if the bench model fidelity interferes in the acquisition of elliptical excision skills by novice medical students. Forty novice medical students were randomly assigned to 5 practice conditions with instructor-directed elliptical excision skills' training (n = 8): didactic materials (control); organic bench model (low-fidelity); ethylene-vinyl acetate bench model (low-fidelity); chicken legs' skin bench model (high-fidelity); or pig foot skin bench model (high-fidelity). Pre- and post-tests were applied. Global rating scale, effect size, and self-perceived confidence based on Likert scale were used to evaluate all elliptical excision performances. The analysis showed that after training, the students practicing on bench models had better performance based on Global rating scale (all P < 0.0000) and felt more confident to perform elliptical excision skills (all P < 0.0000) when compared to the control. There was no significant difference (all P > 0.05) between the groups that trained on bench models. The magnitude of the effect (basic cutaneous surgery skills' training) was considered large (>0.80) in all measurements. The acquisition of elliptical excision skills after instructor-directed training on low-fidelity bench models was similar to the training on high-fidelity bench models; and there was a more substantial increase in elliptical excision performances of students that trained on all simulators compared to the learning on didactic materials.

A multi-fidelity framework for physics based rotor blade simulation and optimization

NASA Astrophysics Data System (ADS)

Collins, Kyle Brian

New helicopter rotor designs are desired that offer increased efficiency, reduced vibration, and reduced noise. Rotor Designers in industry need methods that allow them to use the most accurate simulation tools available to search for these optimal designs. Computer based rotor analysis and optimization have been advanced by the development of industry standard codes known as "comprehensive" rotorcraft analysis tools. These tools typically use table look-up aerodynamics, simplified inflow models and perform aeroelastic analysis using Computational Structural Dynamics (CSD). Due to the simplified aerodynamics, most design studies are performed varying structural related design variables like sectional mass and stiffness. The optimization of shape related variables in forward flight using these tools is complicated and results are viewed with skepticism because rotor blade loads are not accurately predicted. The most accurate methods of rotor simulation utilize Computational Fluid Dynamics (CFD) but have historically been considered too computationally intensive to be used in computer based optimization, where numerous simulations are required. An approach is needed where high fidelity CFD rotor analysis can be utilized in a shape variable optimization problem with multiple objectives. Any approach should be capable of working in forward flight in addition to hover. An alternative is proposed and founded on the idea that efficient hybrid CFD methods of rotor analysis are ready to be used in preliminary design. In addition, the proposed approach recognizes the usefulness of lower fidelity physics based analysis and surrogate modeling. Together, they are used with high fidelity analysis in an intelligent process of surrogate model building of parameters in the high fidelity domain. Closing the loop between high and low fidelity analysis is a key aspect of the proposed approach. This is done by using information from higher fidelity analysis to improve predictions made with lower fidelity models. This thesis documents the development of automated low and high fidelity physics based rotor simulation frameworks. The low fidelity framework uses a comprehensive code with simplified aerodynamics. The high fidelity model uses a parallel processor capable CFD/CSD methodology. Both low and high fidelity frameworks include an aeroacoustic simulation for prediction of noise. A synergistic process is developed that uses both the low and high fidelity frameworks together to build approximate models of important high fidelity metrics as functions of certain design variables. To test the process, a 4-bladed hingeless rotor model is used as a baseline. The design variables investigated include tip geometry and spanwise twist distribution. Approximation models are built for metrics related to rotor efficiency and vibration using the results from 60+ high fidelity (CFD/CSD) experiments and 400+ low fidelity experiments. Optimization using the approximation models found the Pareto Frontier anchor points, or the design having maximum rotor efficiency and the design having minimum vibration. Various Pareto generation methods are used to find designs on the frontier between these two anchor designs. When tested in the high fidelity framework, the Pareto anchor designs are shown to be very good designs when compared with other designs from the high fidelity database. This provides evidence that the process proposed has merit. Ultimately, this process can be utilized by industry rotor designers with their existing tools to bring high fidelity analysis into the preliminary design stage of rotors. In conclusion, the methods developed and documented in this thesis have made several novel contributions. First, an automated high fidelity CFD based forward flight simulation framework has been built for use in preliminary design optimization. The framework was built around an integrated, parallel processor capable CFD/CSD/AA process. Second, a novel method of building approximate models of high fidelity parameters has been developed. The method uses a combination of low and high fidelity results and combines Design of Experiments, statistical effects analysis, and aspects of approximation model management. And third, the determination of rotor blade shape variables through optimization using CFD based analysis in forward flight has been performed. This was done using the high fidelity CFD/CSD/AA framework and method mentioned above. While the low and high fidelity predictions methods used in the work still have inaccuracies that can affect the absolute levels of the results, a framework has been successfully developed and demonstrated that allows for an efficient process to improve rotor blade designs in terms of a selected choice of objective function(s). Using engineering judgment, this methodology could be applied today to investigate opportunities to improve existing designs. With improvements in the low and high fidelity prediction components that will certainly occur, this framework could become a powerful tool for future rotorcraft design work. (Abstract shortened by UMI.)

Nonlinear friction model for servo press simulation

NASA Astrophysics Data System (ADS)

Ma, Ninshu; Sugitomo, Nobuhiko; Kyuno, Takunori; Tamura, Shintaro; Naka, Tetsuo

2013-12-01

The friction coefficient was measured under an idealized condition for a pulse servo motion. The measured friction coefficient and its changing with both sliding distance and a pulse motion showed that the friction resistance can be reduced due to the re-lubrication during unloading process of the pulse servo motion. Based on the measured friction coefficient and its changes with sliding distance and re-lubrication of oil, a nonlinear friction model was developed. Using the newly developed the nonlinear friction model, a deep draw simulation was performed and the formability was evaluated. The results were compared with experimental ones and the effectiveness was verified.

Flight simulator fidelity assessment in a rotorcraft lateral translation maneuver

NASA Technical Reports Server (NTRS)

Hess, R. A.; Malsbury, T.; Atencio, A., Jr.

1992-01-01

A model-based methodology for assessing flight simulator fidelity in closed-loop fashion is exercised in analyzing a rotorcraft low-altitude maneuver for which flight test and simulation results were available. The addition of a handling qualities sensitivity function to a previously developed model-based assessment criteria allows an analytical comparison of both performance and handling qualities between simulation and flight test. Model predictions regarding the existence of simulator fidelity problems are corroborated by experiment. The modeling approach is used to assess analytically the effects of modifying simulator characteristics on simulator fidelity.

An Investigation of the Impact of Aerodynamic Model Fidelity on Close-In Combat Effectiveness Prediction in Piloted Simulation

NASA Technical Reports Server (NTRS)

Persing, T. Ray; Bellish, Christine A.; Brandon, Jay; Kenney, P. Sean; Carzoo, Susan; Buttrill, Catherine; Guenther, Arlene

2005-01-01

Several aircraft airframe modeling approaches are currently being used in the DoD community for acquisition, threat evaluation, training, and other purposes. To date there has been no clear empirical study of the impact of airframe simulation fidelity on piloted real-time aircraft simulation study results, or when use of a particular level of fidelity is indicated. This paper documents a series of piloted simulation studies using three different levels of airframe model fidelity. This study was conducted using the NASA Langley Differential Maneuvering Simulator. Evaluations were conducted with three pilots for scenarios requiring extensive maneuvering of the airplanes during air combat. In many cases, a low-fidelity modified point-mass model may be sufficient to evaluate the combat effectiveness of the aircraft. However, in cases where high angle-of-attack flying qualities and aerodynamic performance are a factor or when precision tracking ability of the aircraft must be represented, use of high-fidelity models is indicated.

Prediction of Sliding Friction Coefficient Based on a Novel Hybrid Molecular-Mechanical Model.

PubMed

Zhang, Xiaogang; Zhang, Yali; Wang, Jianmei; Sheng, Chenxing; Li, Zhixiong

2018-08-01

Sliding friction is a complex phenomenon which arises from the mechanical and molecular interactions of asperities when examined in a microscale. To reveal and further understand the effects of micro scaled mechanical and molecular components of friction coefficient on overall frictional behavior, a hybrid molecular-mechanical model is developed to investigate the effects of main factors, including different loads and surface roughness values, on the sliding friction coefficient in a boundary lubrication condition. Numerical modelling was conducted using a deterministic contact model and based on the molecular-mechanical theory of friction. In the contact model, with given external loads and surface topographies, the pressure distribution, real contact area, and elastic/plastic deformation of each single asperity contact were calculated. Then asperity friction coefficient was predicted by the sum of mechanical and molecular components of friction coefficient. The mechanical component was mainly determined by the contact width and elastic/plastic deformation, and the molecular component was estimated as a function of the contact area and interfacial shear stress. Numerical results were compared with experimental results and a good agreement was obtained. The model was then used to predict friction coefficients in different operating and surface conditions. Numerical results explain why applied load has a minimum effect on the friction coefficients. They also provide insight into the effect of surface roughness on the mechanical and molecular components of friction coefficients. It is revealed that the mechanical component dominates the friction coefficient when the surface roughness is large (Rq > 0.2 μm), while the friction coefficient is mainly determined by the molecular component when the surface is relatively smooth (Rq < 0.2 μm). Furthermore, optimal roughness values for minimizing the friction coefficient are recommended.

Unbiased multi-fidelity estimate of failure probability of a free plane jet

NASA Astrophysics Data System (ADS)

Marques, Alexandre; Kramer, Boris; Willcox, Karen; Peherstorfer, Benjamin

2017-11-01

Estimating failure probability related to fluid flows is a challenge because it requires a large number of evaluations of expensive models. We address this challenge by leveraging multiple low fidelity models of the flow dynamics to create an optimal unbiased estimator. In particular, we investigate the effects of uncertain inlet conditions in the width of a free plane jet. We classify a condition as failure when the corresponding jet width is below a small threshold, such that failure is a rare event (failure probability is smaller than 0.001). We estimate failure probability by combining the frameworks of multi-fidelity importance sampling and optimal fusion of estimators. Multi-fidelity importance sampling uses a low fidelity model to explore the parameter space and create a biasing distribution. An unbiased estimate is then computed with a relatively small number of evaluations of the high fidelity model. In the presence of multiple low fidelity models, this framework offers multiple competing estimators. Optimal fusion combines all competing estimators into a single estimator with minimal variance. We show that this combined framework can significantly reduce the cost of estimating failure probabilities, and thus can have a large impact in fluid flow applications. This work was funded by DARPA.

Teaching Elliptical Excision Skills to Novice Medical Students: A Randomized Controlled Study Comparing Low- and High-Fidelity Bench Models

PubMed Central

Denadai, Rafael; Oshiiwa, Marie; Saad-Hossne, Rogério

2014-01-01

Background: The search for alternative and effective forms of training simulation is needed due to ethical and medico-legal aspects involved in training surgical skills on living patients, human cadavers and living animals. Aims: To evaluate if the bench model fidelity interferes in the acquisition of elliptical excision skills by novice medical students. Materials and Methods: Forty novice medical students were randomly assigned to 5 practice conditions with instructor-directed elliptical excision skills’ training (n = 8): didactic materials (control); organic bench model (low-fidelity); ethylene-vinyl acetate bench model (low-fidelity); chicken legs’ skin bench model (high-fidelity); or pig foot skin bench model (high-fidelity). Pre- and post-tests were applied. Global rating scale, effect size, and self-perceived confidence based on Likert scale were used to evaluate all elliptical excision performances. Results: The analysis showed that after training, the students practicing on bench models had better performance based on Global rating scale (all P < 0.0000) and felt more confident to perform elliptical excision skills (all P < 0.0000) when compared to the control. There was no significant difference (all P > 0.05) between the groups that trained on bench models. The magnitude of the effect (basic cutaneous surgery skills’ training) was considered large (>0.80) in all measurements. Conclusion: The acquisition of elliptical excision skills after instructor-directed training on low-fidelity bench models was similar to the training on high-fidelity bench models; and there was a more substantial increase in elliptical excision performances of students that trained on all simulators compared to the learning on didactic materials. PMID:24700937

Are there reliable constitutive laws for dynamic friction?

PubMed

Woodhouse, Jim; Putelat, Thibaut; McKay, Andrew

2015-09-28

Structural vibration controlled by interfacial friction is widespread, ranging from friction dampers in gas turbines to the motion of violin strings. To predict, control or prevent such vibration, a constitutive description of frictional interactions is inevitably required. A variety of friction models are discussed to assess their scope and validity, in the light of constraints provided by different experimental observations. Three contrasting case studies are used to illustrate how predicted behaviour can be extremely sensitive to the choice of frictional constitutive model, and to explore possible experimental paths to discriminate between and calibrate dynamic friction models over the full parameter range needed for real applications. © 2015 The Author(s).

Development of a measure of model fidelity for mental health Crisis Resolution Teams.

PubMed

Lloyd-Evans, Brynmor; Bond, Gary R; Ruud, Torleif; Ivanecka, Ada; Gray, Richard; Osborn, David; Nolan, Fiona; Henderson, Claire; Mason, Oliver; Goater, Nicky; Kelly, Kathleen; Ambler, Gareth; Morant, Nicola; Onyett, Steve; Lamb, Danielle; Fahmy, Sarah; Brown, Ellie; Paterson, Beth; Sweeney, Angela; Hindle, David; Fullarton, Kate; Frerichs, Johanna; Johnson, Sonia

2016-12-01

Crisis Resolution Teams (CRTs) provide short-term intensive home treatment to people experiencing mental health crisis. Trial evidence suggests CRTs can be effective at reducing hospital admissions and increasing satisfaction with acute care. When scaled up to national level however, CRT implementation and outcomes have been variable. We aimed to develop and test a fidelity scale to assess adherence to a model of best practice for CRTs, based on best available evidence. A concept mapping process was used to develop a CRT fidelity scale. Participants (n = 68) from a range of stakeholder groups prioritised and grouped statements (n = 72) about important components of the CRT model, generated from a literature review, national survey and qualitative interviews. These data were analysed using Ariadne software and the resultant cluster solution informed item selection for a CRT fidelity scale. Operational criteria and scoring anchor points were developed for each item. The CORE CRT fidelity scale was then piloted in 75 CRTs in the UK to assess the range of scores achieved and feasibility for use in a 1-day fidelity review process. Trained reviewers (n = 16) rated CRT service fidelity in a vignette exercise to test the scale's inter-rater reliability. There were high levels of agreement within and between stakeholder groups regarding the most important components of the CRT model. A 39-item measure of CRT model fidelity was developed. Piloting indicated that the scale was feasible for use to assess CRT model fidelity and had good face validity. The wide range of item scores and total scores across CRT services in the pilot demonstrate the measure can distinguish lower and higher fidelity services. Moderately good inter-rater reliability was found, with an estimated correlation between individual ratings of 0.65 (95% CI: 0.54 to 0.76). The CORE CRT Fidelity Scale has been developed through a rigorous and systematic process. Promising initial testing indicates its value in assessing adherence to a model of CRT best practice and to support service improvement monitoring and planning. Further research is required to establish its psychometric properties and international applicability.

Fidelity to the housing first model and effectiveness of permanent supported housing programs in California.

PubMed

Gilmer, Todd P; Stefancic, Ana; Katz, Marian L; Sklar, Marisa; Tsemberis, Sam; Palinkas, Lawrence A

2014-11-01

Permanent supported housing programs are being implemented throughout the United States. This study examined the relationship between fidelity to the Housing First model and residential outcomes among clients of full service partnerships (FSPs) in California. This study had a mixed-methods design. Quantitative administrative and survey data were used to describe FSP practices and to examine the association between fidelity to Housing First and residential outcomes in the year before and after enrollment of 6,584 FSP clients in 86 programs. Focus groups at 20 FSPs provided qualitative data to enhance the understanding of these findings with actual accounts of housing-related experiences in high- and low-fidelity programs. Prior to enrollment, the mean days of homelessness were greater at high- versus low-fidelity (101 versus 46 days) FSPs. After adjustment for individual characteristics, the analysis found that days spent homeless after enrollment declined by 87 at high-fidelity programs and by 34 at low-fidelity programs. After adjustment for days spent homeless before enrollment, days spent homeless after enrollment declined by 63 at high-fidelity programs and by 53 at low-fidelity programs. After enrollment, clients at high-fidelity programs spent more than 60 additional days in apartments than clients at low-facility programs. Differences were found between high- and low-fidelity FSPs in client choice in housing and how much clients' goals were considered in housing placement. Programs with greater fidelity to the Housing First model enrolled clients with longer histories of homelessness and placed most of them in apartments.

Optimal filtering and Bayesian detection for friction-based diagnostics in machines.

PubMed

Ray, L R; Townsend, J R; Ramasubramanian, A

2001-01-01

Non-model-based diagnostic methods typically rely on measured signals that must be empirically related to process behavior or incipient faults. The difficulty in interpreting a signal that is indirectly related to the fundamental process behavior is significant. This paper presents an integrated non-model and model-based approach to detecting when process behavior varies from a proposed model. The method, which is based on nonlinear filtering combined with maximum likelihood hypothesis testing, is applicable to dynamic systems whose constitutive model is well known, and whose process inputs are poorly known. Here, the method is applied to friction estimation and diagnosis during motion control in a rotating machine. A nonlinear observer estimates friction torque in a machine from shaft angular position measurements and the known input voltage to the motor. The resulting friction torque estimate can be analyzed directly for statistical abnormalities, or it can be directly compared to friction torque outputs of an applicable friction process model in order to diagnose faults or model variations. Nonlinear estimation of friction torque provides a variable on which to apply diagnostic methods that is directly related to model variations or faults. The method is evaluated experimentally by its ability to detect normal load variations in a closed-loop controlled motor driven inertia with bearing friction and an artificially-induced external line contact. Results show an ability to detect statistically significant changes in friction characteristics induced by normal load variations over a wide range of underlying friction behaviors.

The sound of friction: Real-time models, playability and musical applications

NASA Astrophysics Data System (ADS)

Serafin, Stefania

Friction, the tangential force between objects in contact, in most engineering applications needs to be removed as a source of noise and instabilities. In musical applications, friction is a desirable component, being the sound production mechanism of different musical instruments such as bowed strings, musical saws, rubbed bowls and any other sonority produced by interactions between rubbed dry surfaces. The goal of the dissertation is to simulate different instrument whose main excitation mechanism is friction. An efficient yet accurate model of a bowed string instrument, which combines the latest results in violin acoustics with the efficient digital waveguide approach, is provided. In particular, the bowed string physical model proposed uses a thermodynamic friction model in which the finite width of the bow is taken into account; this solution is compared to the recently developed elasto-plastic friction models used in haptics and robotics. Different solutions are also proposed to model the body of the instrument. Other less common instruments driven by friction are also proposed, and the elasto-plastic model is used to provide audio-visual simulations of everyday friction sounds such as squeaking doors and rubbed wine glasses. Finally, playability evaluations and musical applications in which the models have been used are discussed.

Impact of Data Assimilation on Cost-Accuracy Tradeoff in Multi-Fidelity Models at the Example of an Infiltration Problem

NASA Astrophysics Data System (ADS)

Sinsbeck, Michael; Tartakovsky, Daniel

2015-04-01

Infiltration into top soil can be described by alternative models with different degrees of fidelity: Richards equation and the Green-Ampt model. These models typically contain uncertain parameters and forcings, rendering predictions of the state variables uncertain as well. Within the probabilistic framework, solutions of these models are given in terms of their probability density functions (PDFs) that, in the presence of data, can be treated as prior distributions. The assimilation of soil moisture data into model predictions, e.g., via a Bayesian updating of solution PDFs, poses a question of model selection: Given a significant difference in computational cost, is a lower-fidelity model preferable to its higher-fidelity counter-part? We investigate this question in the context of heterogeneous porous media, whose hydraulic properties are uncertain. While low-fidelity (reduced-complexity) models introduce a model error, their moderate computational cost makes it possible to generate more realizations, which reduces the (e.g., Monte Carlo) sampling or stochastic error. The ratio between these two errors determines the model with the smallest total error. We found assimilation of measurements of a quantity of interest (the soil moisture content, in our example) to decrease the model error, increasing the probability that the predictive accuracy of a reduced-complexity model does not fall below that of its higher-fidelity counterpart.

Construction of nested maximin designs based on successive local enumeration and modified novel global harmony search algorithm

NASA Astrophysics Data System (ADS)

Yi, Jin; Li, Xinyu; Xiao, Mi; Xu, Junnan; Zhang, Lin

2017-01-01

Engineering design often involves different types of simulation, which results in expensive computational costs. Variable fidelity approximation-based design optimization approaches can realize effective simulation and efficiency optimization of the design space using approximation models with different levels of fidelity and have been widely used in different fields. As the foundations of variable fidelity approximation models, the selection of sample points of variable-fidelity approximation, called nested designs, is essential. In this article a novel nested maximin Latin hypercube design is constructed based on successive local enumeration and a modified novel global harmony search algorithm. In the proposed nested designs, successive local enumeration is employed to select sample points for a low-fidelity model, whereas the modified novel global harmony search algorithm is employed to select sample points for a high-fidelity model. A comparative study with multiple criteria and an engineering application are employed to verify the efficiency of the proposed nested designs approach.

Exploring load, velocity, and surface disorder dependence of friction with one-dimensional and two-dimensional models.

PubMed

Dagdeviren, Omur E

2018-08-03

The effect of surface disorder, load, and velocity on friction between a single asperity contact and a model surface is explored with one-dimensional and two-dimensional Prandtl-Tomlinson (PT) models. We show that there are fundamental physical differences between the predictions of one-dimensional and two-dimensional models. The one-dimensional model estimates a monotonic increase in friction and energy dissipation with load, velocity, and surface disorder. However, a two-dimensional PT model, which is expected to approximate a tip-sample system more realistically, reveals a non-monotonic trend, i.e. friction is inert to surface disorder and roughness in wearless friction regime. The two-dimensional model discloses that the surface disorder starts to dominate the friction and energy dissipation when the tip and the sample interact predominantly deep into the repulsive regime. Our numerical calculations address that tracking the minimum energy path and the slip-stick motion are two competing effects that determine the load, velocity, and surface disorder dependence of friction. In the two-dimensional model, the single asperity can follow the minimum energy path in wearless regime; however, with increasing load and sliding velocity, the slip-stick movement dominates the dynamic motion and results in an increase in friction by impeding tracing the minimum energy path. Contrary to the two-dimensional model, when the one-dimensional PT model is employed, the single asperity cannot escape to the minimum energy minimum due to constraint motion and reveals only a trivial dependence of friction on load, velocity, and surface disorder. Our computational analyses clarify the physical differences between the predictions of the one-dimensional and two-dimensional models and open new avenues for disordered surfaces for low energy dissipation applications in wearless friction regime.

Recommendations on Model Fidelity for Wind Turbine Gearbox Simulations; NREL (National Renewable Energy Laboratory)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keller, J.; Lacava, W.; Austin, J.

2015-02-01

This work investigates the minimum level of fidelity required to accurately simulate wind turbine gearboxes using state-of-the-art design tools. Excessive model fidelity including drivetrain complexity, gearbox complexity, excitation sources, and imperfections, significantly increases computational time, but may not provide a commensurate increase in the value of the results. Essential designparameters are evaluated, including the planetary load-sharing factor, gear tooth load distribution, and sun orbit motion. Based on the sensitivity study results, recommendations for the minimum model fidelities are provided.

Discontinuous Galerkin methods for modeling Hurricane storm surge

NASA Astrophysics Data System (ADS)

Dawson, Clint; Kubatko, Ethan J.; Westerink, Joannes J.; Trahan, Corey; Mirabito, Christopher; Michoski, Craig; Panda, Nishant

2011-09-01

Storm surge due to hurricanes and tropical storms can result in significant loss of life, property damage, and long-term damage to coastal ecosystems and landscapes. Computer modeling of storm surge can be used for two primary purposes: forecasting of surge as storms approach land for emergency planning and evacuation of coastal populations, and hindcasting of storms for determining risk, development of mitigation strategies, coastal restoration and sustainability. Storm surge is modeled using the shallow water equations, coupled with wind forcing and in some events, models of wave energy. In this paper, we will describe a depth-averaged (2D) model of circulation in spherical coordinates. Tides, riverine forcing, atmospheric pressure, bottom friction, the Coriolis effect and wind stress are all important for characterizing the inundation due to surge. The problem is inherently multi-scale, both in space and time. To model these problems accurately requires significant investments in acquiring high-fidelity input (bathymetry, bottom friction characteristics, land cover data, river flow rates, levees, raised roads and railways, etc.), accurate discretization of the computational domain using unstructured finite element meshes, and numerical methods capable of capturing highly advective flows, wetting and drying, and multi-scale features of the solution. The discontinuous Galerkin (DG) method appears to allow for many of the features necessary to accurately capture storm surge physics. The DG method was developed for modeling shocks and advection-dominated flows on unstructured finite element meshes. It easily allows for adaptivity in both mesh ( h) and polynomial order ( p) for capturing multi-scale spatial events. Mass conservative wetting and drying algorithms can be formulated within the DG method. In this paper, we will describe the application of the DG method to hurricane storm surge. We discuss the general formulation, and new features which have been added to the model to better capture surge in complex coastal environments. These features include modifications to the method to handle spherical coordinates and maintain still flows, improvements in the stability post-processing (i.e. slope-limiting), and the modeling of internal barriers for capturing overtopping of levees and other structures. We will focus on applications of the model to recent events in the Gulf of Mexico, including Hurricane Ike.

Experimental characterization of the effects of pneumatic tubing on unsteady pressure measurements

NASA Technical Reports Server (NTRS)

Whitmore, Stephen A.; Lindsey, William T.; Curry, Robert E.; Gilyard, Glenn B.

1990-01-01

Advances in aircraft control system designs have, with increasing frequency, required that air data be used as flight control feedback. This condition requires that these data be measured with accuracy and high fidelity. Most air data information is provided by pneumatic pressure measuring sensors. Typically unsteady pressure data provided by pneumatic sensing systems are distorted at high frequencies. The distortion is a result of the pressure being transmitted to the pressure sensor through a length of connective tubing. The pressure is distorted by frictional damping and wave reflection. As a result, air data provided all-flush, pneumatically sensed air data systems may not meet the frequency response requirements necessary for flight control augmentation. Both lab and flight test were performed at NASA-Ames to investigate the effects of this high frequency distortion in remotely located pressure measurement systems. Good qualitative agreement between lab and flight data are demonstrated. Results from these tests are used to describe the effects of pneumatic distortion in terms of a simple parametric model.

High Fidelity System Simulation of Multiple Components in Support of the UEET Program

NASA Technical Reports Server (NTRS)

Plybon, Ronald C.; VanDeWall, Allan; Sampath, Rajiv; Balasubramaniam, Mahadevan; Mallina, Ramakrishna; Irani, Rohinton

2006-01-01

The High Fidelity System Simulation effort has addressed various important objectives to enable additional capability within the NPSS framework. The scope emphasized High Pressure Turbine and High Pressure Compressor components. Initial effort was directed at developing and validating intermediate fidelity NPSS model using PD geometry and extended to high-fidelity NPSS model by overlaying detailed geometry to validate CFD against rig data. Both "feedforward" and feedback" approaches of analysis zooming was employed to enable system simulation capability in NPSS. These approaches have certain benefits and applicability in terms of specific applications "feedback" zooming allows the flow-up of information from high-fidelity analysis to be used to update the NPSS model results by forcing the NPSS solver to converge to high-fidelity analysis predictions. This apporach is effective in improving the accuracy of the NPSS model; however, it can only be used in circumstances where there is a clear physics-based strategy to flow up the high-fidelity analysis results to update the NPSS system model. "Feed-forward" zooming approach is more broadly useful in terms of enabling detailed analysis at early stages of design for a specified set of critical operating points and using these analysis results to drive design decisions early in the development process.

First-Order Frameworks for Managing Models in Engineering Optimization

NASA Technical Reports Server (NTRS)

Alexandrov, Natlia M.; Lewis, Robert Michael

2000-01-01

Approximation/model management optimization (AMMO) is a rigorous methodology for attaining solutions of high-fidelity optimization problems with minimal expense in high- fidelity function and derivative evaluation. First-order AMMO frameworks allow for a wide variety of models and underlying optimization algorithms. Recent demonstrations with aerodynamic optimization achieved three-fold savings in terms of high- fidelity function and derivative evaluation in the case of variable-resolution models and five-fold savings in the case of variable-fidelity physics models. The savings are problem dependent but certain trends are beginning to emerge. We give an overview of the first-order frameworks, current computational results, and an idea of the scope of the first-order framework applicability.

How to teach emergency procedural skills in an outdoor environment using low-fidelity simulation.

PubMed

Saxon, Kathleen D; Kapadia, Alison P R; Juneja, Nadia S; Bassin, Benjamin S

2014-03-01

Teaching emergency procedural skills in a wilderness setting can be logistically challenging. To teach these skills as part of a wilderness medicine elective for medical students, we designed an outdoor simulation session with low-fidelity models. The session involved 6 stations in which procedural skills were taught using homemade low-fidelity simulators. At each station, the students encountered a "victim," who required an emergency procedure that was performed using the low-fidelity model. The models are easy and inexpensive to construct, and their design and implementation in the session is described here. Using low-fidelity simulation models in an outdoor setting is an effective teaching tool for emergency wilderness medicine procedures and can easily be reproduced in future wilderness medicine courses. © 2014 Wilderness Medical Society Published by Wilderness Medical Society All rights reserved.

Solvent friction effects propagate over the entire protein molecule through low-frequency collective modes.

PubMed

Moritsugu, Kei; Kidera, Akinori; Smith, Jeremy C

2014-07-24

Protein solvation dynamics has been investigated using atom-dependent Langevin friction coefficients derived directly from molecular dynamics (MD) simulations. To determine the effect of solvation on the atomic friction coefficients, solution and vacuum MD simulations were performed for lysozyme and staphylococcal nuclease and analyzed by Langevin mode analysis. The coefficients thus derived are roughly correlated with the atomic solvent-accessible surface area (ASA), as expected from the fact that friction occurs as the result of collisions with solvent molecules. However, a considerable number of atoms with higher friction coefficients are found inside the core region. Hence, the influence of solvent friction propagates into the protein core. The internal coefficients have large contributions from the low-frequency modes, yielding a simple picture of the surface-to-core long-range damping via solvation governed by collective low-frequency modes. To make use of these findings in implicit-solvent modeling, we compare the all-atom friction results with those obtained using Langevin dynamics (LD) with two empirical representations: the constant-friction and the ASA-dependent (Pastor-Karplus) friction models. The constant-friction model overestimates the core and underestimates the surface damping whereas the ASA-dependent friction model, which damps protein atoms only on the solvent-accessible surface, reproduces well the friction coefficients for both the surface and core regions observed in the explicit-solvent MD simulations. Therefore, in LD simulation, the solvent friction coefficients should be imposed only on the protein surface.

Solvent friction effects propagate over the entire protein molecule through low-frequency collective modes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moritsugu, Kei; Kidera, Akinori; Smith, Jeremy C.

2014-06-25

Protein solvation dynamics has been investigated using atom-dependent Langevin friction coefficients derived directly from molecular dynamics (MD) simulations. To determine the effect of solvation on the atomic friction coefficients, solution and vacuum MD simulations were performed for lysozyme and staphylococcal nuclease and analyzed by Langevin mode analysis. The coefficients thus derived are roughly correlated with the atomic solvent-accessible surface area (ASA), as expected from the fact that friction occurs as the result of collisions with solvent molecules. However, a considerable number of atoms with higher friction coefficients are found inside the core region. Hence, the influence of solvent friction propagatesmore » into the protein core. The internal coefficients have large contributions from the low-frequency modes, yielding a simple picture of the surface-to-core long-range damping via solvation governed by collective low-frequency modes. To make use of these findings in implicit-solvent modeling, we compare the all-atom friction results with those obtained using Langevin dynamics (LD) with two empirical representations: the constant-friction and the ASA-dependent (Pastor Karplus) friction models. The constant-friction model overestimates the core and underestimates the surface damping whereas the ASA-dependent friction model, which damps protein atoms only on the solvent-accessible surface, reproduces well the friction coefficients for both the surface and core regions observed in the explicit-solvent MD simulations. Furthermore, in LD simulation, the solvent friction coefficients should be imposed only on the protein surface.« less

A multivariable model for predicting the frictional behaviour and hydration of the human skin.

PubMed

Veijgen, N K; van der Heide, E; Masen, M A

2013-08-01

The frictional characteristics of skin-object interactions are important when handling objects, in the assessment of perception and comfort of products and materials and in the origins and prevention of skin injuries. In this study, based on statistical methods, a quantitative model is developed that describes the friction behaviour of human skin as a function of the subject characteristics, contact conditions, the properties of the counter material as well as environmental conditions. Although the frictional behaviour of human skin is a multivariable problem, in literature the variables that are associated with skin friction have been studied using univariable methods. In this work, multivariable models for the static and dynamic coefficients of friction as well as for the hydration of the skin are presented. A total of 634 skin-friction measurements were performed using a recently developed tribometer. Using a statistical analysis, previously defined potential influential variables were linked to the static and dynamic coefficient of friction and to the hydration of the skin, resulting in three predictive quantitative models that descibe the friction behaviour and the hydration of human skin respectively. Increased dynamic coefficients of friction were obtained from older subjects, on the index finger, with materials with a higher surface energy at higher room temperatures, whereas lower dynamic coefficients of friction were obtained at lower skin temperatures, on the temple with rougher contact materials. The static coefficient of friction increased with higher skin hydration, increasing age, on the index finger, with materials with a higher surface energy and at higher ambient temperatures. The hydration of the skin was associated with the skin temperature, anatomical location, presence of hair on the skin and the relative air humidity. Predictive models have been derived for the static and dynamic coefficient of friction using a multivariable approach. These two coefficients of friction show a strong correlation. Consequently the two multivariable models resemble, with the static coefficient of friction being on average 18% lower than the dynamic coefficient of friction. The multivariable models in this study can be used to describe the data set that was the basis for this study. Care should be taken when generalising these results. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Demonstration of a Balloon Borne Arc-second Pointer Design

NASA Astrophysics Data System (ADS)

Deweese, K.; Ward, P.

Many designs for utilizing stratospheric balloons as low-cost platforms on which to conduct space science experiments have been proposed throughout the years A major hurdle in extending the range of experiments for which these vehicles are useful has been the imposition of the gondola dynamics on the accuracy with which an instrument can be kept pointed at a celestial target A significant number of scientists have sought the ability to point their instruments with jitter in the arc-second range This paper presents the design and analysis of a stratospheric balloon borne pointing system that is able to meet this requirement The test results of a demonstration prototype of the design with similar ability are also presented Discussion of a high fidelity controller simulation for design analysis is presented The flexibility of the flight train is represented through generalized modal analysis A multiple controller scheme is utilized for coarse and fine pointing Coarse azimuth pointing is accomplished by an established pointing system with extensive flight history residing above the gondola structure A pitch-yaw gimbal mount is used for fine pointing providing orthogonal axes when nominally on target Fine pointing actuation is from direct drive dc motors eliminating backlash problems An analysis of friction nonlinearities and a demonstration of the necessity in eliminating static friction are provided A unique bearing hub design is introduced that eliminates static friction from the system dynamics A control scheme involving linear

Adaptive back-stepping control of the harmonic drive system with LuGre model-based friction compensation

NASA Astrophysics Data System (ADS)

Liu, Sen; Gang, Tieqiang

2018-03-01

Harmonic drives are widely used in aerospace and industrial robots. Flexibility, friction and parameter uncertainty will result in transmission performance degradation. In this paper, an adaptive back-stepping method with friction compensation is proposed to improve the tracking performance of the harmonic drive system. The nonlinear friction is described by LuGre model and compensated with a friction observer, and the uncertainty of model parameters is resolved by adaptive parameter estimation method. By using Lyapunov stability theory, it is proved that all the errors of the closed-loop system are uniformly ultimately bounded. Simulations illustrate the effectiveness of our friction compensation method.

Modeling of Tool-Tissue Interactions for Computer-Based Surgical Simulation: A Literature Review

PubMed Central

Misra, Sarthak; Ramesh, K. T.; Okamura, Allison M.

2009-01-01

Surgical simulators present a safe and potentially effective method for surgical training, and can also be used in robot-assisted surgery for pre- and intra-operative planning. Accurate modeling of the interaction between surgical instruments and organs has been recognized as a key requirement in the development of high-fidelity surgical simulators. Researchers have attempted to model tool-tissue interactions in a wide variety of ways, which can be broadly classified as (1) linear elasticity-based, (2) nonlinear (hyperelastic) elasticity-based finite element (FE) methods, and (3) other techniques that not based on FE methods or continuum mechanics. Realistic modeling of organ deformation requires populating the model with real tissue data (which are difficult to acquire in vivo) and simulating organ response in real time (which is computationally expensive). Further, it is challenging to account for connective tissue supporting the organ, friction, and topological changes resulting from tool-tissue interactions during invasive surgical procedures. Overcoming such obstacles will not only help us to model tool-tissue interactions in real time, but also enable realistic force feedback to the user during surgical simulation. This review paper classifies the existing research on tool-tissue interactions for surgical simulators specifically based on the modeling techniques employed and the kind of surgical operation being simulated, in order to inform and motivate future research on improved tool-tissue interaction models. PMID:20119508

State resolved vibrational relaxation modeling for strongly nonequilibrium flows

NASA Astrophysics Data System (ADS)

Boyd, Iain D.; Josyula, Eswar

2011-05-01

Vibrational relaxation is an important physical process in hypersonic flows. Activation of the vibrational mode affects the fundamental thermodynamic properties and finite rate relaxation can reduce the degree of dissociation of a gas. Low fidelity models of vibrational activation employ a relaxation time to capture the process at a macroscopic level. High fidelity, state-resolved models have been developed for use in continuum gas dynamics simulations based on computational fluid dynamics (CFD). By comparison, such models are not as common for use with the direct simulation Monte Carlo (DSMC) method. In this study, a high fidelity, state-resolved vibrational relaxation model is developed for the DSMC technique. The model is based on the forced harmonic oscillator approach in which multi-quantum transitions may become dominant at high temperature. Results obtained for integrated rate coefficients from the DSMC model are consistent with the corresponding CFD model. Comparison of relaxation results obtained with the high-fidelity DSMC model shows significantly less excitation of upper vibrational levels in comparison to the standard, lower fidelity DSMC vibrational relaxation model. Application of the new DSMC model to a Mach 7 normal shock wave in carbon monoxide provides better agreement with experimental measurements than the standard DSMC relaxation model.

Key variables influencing patterns of lava dome growth and collapse

NASA Astrophysics Data System (ADS)

Husain, T.; Elsworth, D.; Voight, B.; Mattioli, G. S.; Jansma, P. E.

2013-12-01

Lava domes are conical structures that grow by the infusion of viscous silicic or intermediate composition magma from a central volcanic conduit. Dome growth can be characterized by repeated cycles of growth punctuated by collapse, as the structure becomes oversized for its composite strength. Within these cycles, deformation ranges from slow long term deformation to sudden deep-seated collapses. Collapses may range from small raveling failures to voluminous and fast-moving pyroclastic flows with rapid and long-downslope-reach from the edifice. Infusion rate and magma rheology together with crystallization temperature and volatile content govern the spatial distribution of strength in the structure. Solidification, driven by degassing-induced crystallization of magma leads to the formation of a continuously evolving frictional talus as a hard outer shell. This shell encapsulates the cohesion-dominated soft ductile core. Here we explore the mechanics of lava dome growth and failure using a two-dimensional particle-dynamics model. This meshless model follows the natural evolution of a brittle carapace formed by loss of volatiles and rheological stiffening and avoids difficulties of hour-glassing and mesh-entangelment typical in meshed models. We test the fidelity of the model against existing experimental and observational models of lava dome growth. The particle-dynamics model follows the natural development of dome growth and collapse which is infeasible using simple analytical models. The model provides insight into the triggers that lead to the transition in collapse mechasnism from shallow flank collapse to deep seated sector collapse. Increase in material stiffness due to decrease in infusion rate results in the transition of growth pattern from endogenous to exogenous. The material stiffness and strength are strongly controlled by the magma infusion rate. Increase in infusion rate decreases the time available for degassing induced crystallization leading to a transition in the growth pattern, while a decrease in infusion rate results in larger crystals causing the material to stiffen leading to formation of spines. Material stiffness controls the growth direction of the viscous plug in the lava dome interior. Material strength and stiffness controled by rate of infusion influence lava dome growth more significantly than coefficient of frictional of the talus.

Stimulated Brillouin scattering continuous wave phase conjugation in step-index fiber optics.

PubMed

Massey, Steven M; Spring, Justin B; Russell, Timothy H

2008-07-21

Continuous wave (CW) stimulated Brillouin scattering (SBS) phase conjugation in step-index optical fibers was studied experimentally and modeled as a function of fiber length. A phase conjugate fidelity over 80% was measured from SBS in a 40 m fiber using a pinhole technique. Fidelity decreases with fiber length, and a fiber with a numerical aperture (NA) of 0.06 was found to generate good phase conjugation fidelity over longer lengths than a fiber with 0.13 NA. Modeling and experiment support previous work showing the maximum interaction length which yields a high fidelity phase conjugate beam is inversely proportional to the fiber NA(2), but find that fidelity remains high over much longer fiber lengths than previous models calculated. Conditions for SBS beam cleanup in step-index fibers are discussed.

Dynamic and impact contact mechanics of geologic materials: Grain-scale experiments and modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cole, David M.; Hopkins, Mark A.; Ketcham, Stephen A.

2013-06-18

High fidelity treatments of the generation and propagation of seismic waves in naturally occurring granular materials is becoming more practical given recent advancements in our ability to model complex particle shapes and their mechanical interaction. Of particular interest are the grain-scale processes that are activated by impact events and the characteristics of force transmission through grain contacts. To address this issue, we have developed a physics based approach that involves laboratory experiments to quantify the dynamic contact and impact behavior of granular materials and incorporation of the observed behavior indiscrete element models. The dynamic experiments do not involve particle damagemore » and emphasis is placed on measured values of contact stiffness and frictional loss. The normal stiffness observed in dynamic contact experiments at low frequencies (e.g., 10 Hz) are shown to be in good agreement with quasistatic experiments on quartz sand. The results of impact experiments - which involve moderate to extensive levels of particle damage - are presented for several types of naturally occurring granular materials (several quartz sands, magnesite and calcium carbonate ooids). Implementation of the experimental findings in discrete element models is discussed and the results of impact simulations involving up to 5 Multiplication-Sign 105 grains are presented.« less

Theoretical and computational validation of the Kuhn barrier friction mechanism in unfolded proteins.

PubMed

Avdoshenko, Stanislav M; Das, Atanu; Satija, Rohit; Papoian, Garegin A; Makarov, Dmitrii E

2017-03-21

A long time ago, Kuhn predicted that long polymers should approach a limit where their global motion is controlled by solvent friction alone, with ruggedness of their energy landscapes having no consequences for their dynamics. In contrast, internal friction effects are important for polymers of modest length. Internal friction in proteins, in particular, affects how fast they fold or find their binding targets and, as such, has attracted much recent attention. Here we explore the molecular origins of internal friction in unfolded proteins using atomistic simulations, coarse-grained models and analytic theory. We show that the characteristic internal friction timescale is directly proportional to the timescale of hindered dihedral rotations within the polypeptide chain, with a proportionality coefficient b that is independent of the chain length. Such chain length independence of b provides experimentally testable evidence that internal friction arises from concerted, crankshaft-like dihedral rearrangements. In accord with phenomenological models of internal friction, we find the global reconfiguration timescale of a polypeptide to be the sum of solvent friction and internal friction timescales. At the same time, the time evolution of inter-monomer distances within polypeptides deviates both from the predictions of those models and from a simple, one-dimensional diffusion model.

Influence of the pressure dependent coefficient of friction on deep drawing springback predictions

NASA Astrophysics Data System (ADS)

Gil, Imanol; Galdos, Lander; Mendiguren, Joseba; Mugarra, Endika; Sáenz de Argandoña, Eneko

2016-10-01

This research studies the effect of considering an advanced variable friction coefficient on the springback prediction of stamping processes. Traditional constant coefficient of friction considerations are being replaced by more advanced friction coefficient definitions. The aim of this work is to show the influence of defining a pressure dependent friction coefficient on numerical springback predictions of a DX54D mild steel, a HSLA380 and a DP780 high strength steel. The pressure dependent friction model of each material was fitted to the experimental data obtained by Strip Drawing tests. Then, these friction models were implemented in a numerical simulation of a drawing process of an industrial automotive part. The results showed important differences between defining a pressure dependent friction coefficient or a constant friction coefficient.

Measuring trainer fidelity in the transfer of suicide prevention training

PubMed Central

Cross, Wendi F.; Pisani, Anthony R.; Schmeelk-Cone, Karen; Xia, Yinglin; Tu, Xin; McMahon, Marcie; Munfakh, Jimmie Lou; Gould, Madelyn S.

2014-01-01

Background Finding effective and efficient models to train large numbers of suicide prevention interventionists, including ‘hotline’ crisis counselors, is a high priority. Train-the-trainer (TTT) models are widely used but understudied. Aims To assess the extent to which trainers following TTT delivered the Applied Suicide Intervention Skills Training (ASIST) program with fidelity, and to examine fidelity across two trainings and seven training segments. Methods We recorded and reliably rated trainer fidelity, defined as adherence to program content and competence of program delivery, for 34 newly trained ASIST trainers delivering the program to crisis center staff on two separate occasions. A total of 324 observations were coded. Trainer demographics were also collected. Results On average, trainers delivered two-thirds of the program. Previous training was associated with lower levels of trainer adherence to the program. 18% of trainers' observations were rated as solidly competent. Trainers did not improve fidelity from their first to second training. Significantly higher fidelity was found for lectures and lower fidelity was found for interactive training activities including asking about suicide and creating a safe plan. Conclusions We found wide variability in trainer fidelity to the ASIST program following TTT and few trainers had high levels of both adherence and competence. More research is needed to examine the cost-effectiveness of TTT models. PMID:24901061

Proofreading of DNA polymerase: a new kinetic model with higher-order terminal effects

NASA Astrophysics Data System (ADS)

Song, Yong-Shun; Shu, Yao-Gen; Zhou, Xin; Ou-Yang, Zhong-Can; Li, Ming

2017-01-01

The fidelity of DNA replication by DNA polymerase (DNAP) has long been an important issue in biology. While numerous experiments have revealed details of the molecular structure and working mechanism of DNAP which consists of both a polymerase site and an exonuclease (proofreading) site, there were quite a few theoretical studies on the fidelity issue. The first model which explicitly considered both sites was proposed in the 1970s and the basic idea was widely accepted by later models. However, all these models did not systematically investigate the dominant factor on DNAP fidelity, i.e. the higher-order terminal effects through which the polymerization pathway and the proofreading pathway coordinate to achieve high fidelity. In this paper, we propose a new and comprehensive kinetic model of DNAP based on some recent experimental observations, which includes previous models as special cases. We present a rigorous and unified treatment of the corresponding steady-state kinetic equations of any-order terminal effects, and derive analytical expressions for fidelity in terms of kinetic parameters under bio-relevant conditions. These expressions offer new insights on how the higher-order terminal effects contribute substantially to the fidelity in an order-by-order way, and also show that the polymerization-and-proofreading mechanism is dominated only by very few key parameters. We then apply these results to calculate the fidelity of some real DNAPs, which are in good agreements with previous intuitive estimates given by experimentalists.

Physical and Constructive (Limiting) Criterions of Gear Wheels Wear

NASA Astrophysics Data System (ADS)

Fedorov, S. V.

2018-01-01

We suggest using a generalized model of friction - the model of elastic-plastic deformation of the body element, which is located on the surface of the friction pairs. This model is based on our new engineering approach to the problem of friction-triboergodynamics. Friction is examined as transformative and dissipative process. Structural-energetic interpretation of friction as a process of elasto-plastic deformation and fracture contact volumes is proposed. The model of Hertzian (heavy-loaded) friction contact evolution is considered. The least wear particle principle is formulated. It is mechanical (nano) quantum. Mechanical quantum represents the least structural form of solid material body in conditions of friction. It is dynamic oscillator of dissipative friction structure and it can be examined as the elementary nanostructure of metal’s solid body. At friction in state of most complete evolution of elementary tribosystem (tribocontact) all mechanical quanta (subtribosystems) with the exception of one, elasticity and reversibly transform energy of outer impact (mechanic movement). In these terms only one mechanical quantum is the lost - standard of wear. From this position we can consider the physical criterion of wear and the constructive (limiting) criterion of gear teeth and other practical examples of tribosystems efficiency with new tribology notion - mechanical (nano) quantum.

Hybrid surrogate-model-based multi-fidelity efficient global optimization applied to helicopter blade design

NASA Astrophysics Data System (ADS)

Ariyarit, Atthaphon; Sugiura, Masahiko; Tanabe, Yasutada; Kanazaki, Masahiro

2018-06-01

A multi-fidelity optimization technique by an efficient global optimization process using a hybrid surrogate model is investigated for solving real-world design problems. The model constructs the local deviation using the kriging method and the global model using a radial basis function. The expected improvement is computed to decide additional samples that can improve the model. The approach was first investigated by solving mathematical test problems. The results were compared with optimization results from an ordinary kriging method and a co-kriging method, and the proposed method produced the best solution. The proposed method was also applied to aerodynamic design optimization of helicopter blades to obtain the maximum blade efficiency. The optimal shape obtained by the proposed method achieved performance almost equivalent to that obtained using the high-fidelity, evaluation-based single-fidelity optimization. Comparing all three methods, the proposed method required the lowest total number of high-fidelity evaluation runs to obtain a converged solution.

Computational Methods for Nonlinear Dynamic Problems in Solid and Structural Mechanics: Progress in the Theory and Modeling of Friction and in the Control of Dynamical Systems with Frictional Forces

DTIC Science & Technology

1989-03-31

present several numerical studies designed to reveal the effect that some of the governing parameters have on the behavior of the system and, whenever...Friction and in the Control of Dynamical Systems with Frictional Forces FINAL TECHNICAL REPORT March 31, 1989 _ -- I -.7: .-.- - : AFOSR Contract F49620...SOLID AND STRUCTURAL MECHANICS: Progress in the Theory and Modeling of Friction and in the Control of Dynamical Systems with Frictional Forces I I * FINAL

Length scale effects of friction in particle compaction using atomistic simulations and a friction scaling model

NASA Astrophysics Data System (ADS)

Stone, T. W.; Horstemeyer, M. F.

2012-09-01

The objective of this study is to illustrate and quantify the length scale effects related to interparticle friction under compaction. Previous studies have shown as the length scale of a specimen decreases, the strength of a single crystal metal or ceramic increases. The question underlying this research effort continues the thought—If there is a length scale parameter related to the strength of a material, is there a length scale parameter related to friction? To explore the length scale effects of friction, molecular dynamics (MD) simulations using an embedded atom method potential were performed to analyze the compression of two spherical FCC nickel nanoparticles at different contact angles. In the MD model study, we applied a macroscopic plastic contact formulation to determine the normal plastic contact force at the particle interfaces and used the average shear stress from the MD simulations to determine the tangential contact forces. Combining this information with the Coulomb friction law, we quantified the MD interparticle coefficient of friction and showed good agreement with experimental studies and a Discrete Element Method prediction as a function of contact angle. Lastly, we compared our MD simulation friction values to the tribological predictions of Bhushan and Nosonovsky (BN), who developed a friction scaling model based on strain gradient plasticity and dislocation-assisted sliding that included a length scale parameter. The comparison revealed that the BN elastic friction scaling model did a much better job than the BN plastic scaling model of predicting the coefficient of friction values obtained from the MD simulations.

Microphysically Derived Expressions for Rate-and-State Friction Parameters, a, b, and Dc

NASA Astrophysics Data System (ADS)

Chen, Jianye; Niemeijer, A. R.; Spiers, Christopher J.

2017-12-01

Rate-and-state friction (RSF) laws are extensively applied in fault mechanics but have a largely empirical basis reflecting only limited understanding of the underlying physical mechanisms. We recently proposed a microphysical model describing the frictional behavior of a granular fault gouge undergoing deformation in terms of granular flow accompanied by thermally activated creep and intergranular sliding at grain contacts. Numerical solutions reproduced typical experimental results well. Here we extend our model to obtain physically meaningful, analytical expressions for the steady state frictional strength and standard RSF parameters, a, b, and Dc. The frictional strength contains two components, namely, grain boundary friction and friction due to intergranular dilatation. The expressions obtained for a and b linearly reflect the rate dependence of these two terms. Dc scales with slip band thickness and varies only slightly with velocity. The values of a, b, and Dc predicted show quantitative agreement with previous experimental results, and inserting their values into classical RSF laws gives simulated friction behavior that is consistent with the predictions of our numerically implemented model for small departures from steady state. For large velocity steps, the model produces mixed RSF behavior that falls between the Slowness and Slip laws, for example, with an intermediate equivalent slip(-weakening) distance d0. Our model possesses the interesting property not only that a and b are velocity dependent but also that Dc and d0 scale differently from classical RSF models, potentially explaining behaviour seen in many hydrothermal friction experiments and having substantial implications for natural fault friction.

An adaptive sampling method for variable-fidelity surrogate models using improved hierarchical kriging

NASA Astrophysics Data System (ADS)

Hu, Jiexiang; Zhou, Qi; Jiang, Ping; Shao, Xinyu; Xie, Tingli

2018-01-01

Variable-fidelity (VF) modelling methods have been widely used in complex engineering system design to mitigate the computational burden. Building a VF model generally includes two parts: design of experiments and metamodel construction. In this article, an adaptive sampling method based on improved hierarchical kriging (ASM-IHK) is proposed to refine the improved VF model. First, an improved hierarchical kriging model is developed as the metamodel, in which the low-fidelity model is varied through a polynomial response surface function to capture the characteristics of a high-fidelity model. Secondly, to reduce local approximation errors, an active learning strategy based on a sequential sampling method is introduced to make full use of the already required information on the current sampling points and to guide the sampling process of the high-fidelity model. Finally, two numerical examples and the modelling of the aerodynamic coefficient for an aircraft are provided to demonstrate the approximation capability of the proposed approach, as well as three other metamodelling methods and two sequential sampling methods. The results show that ASM-IHK provides a more accurate metamodel at the same simulation cost, which is very important in metamodel-based engineering design problems.

Demonstration of a Balloon Borne Arc-Second Pointer Design

NASA Technical Reports Server (NTRS)

DeWeese, Keith D.; Ward, Philip R.

2006-01-01

Many designs for utilizing stratospheric balloons as low-cost platforms on which to conduct space science experiments have been proposed throughout the years. A major hurdle in extending the range of experiments for which these vehicles are useful has been the imposition of the gondola dynamics on the accuracy with which an instrument can be kept pointed at a celestial target. A significant number of scientists have sought the ability to point their instruments with jitter in the arc-second range. This paper presents the design and analysis of a stratospheric balloon borne pointing system that is able to meet this requirement. The test results of a demonstration prototype of the design with similar ability are also presented. Discussion of a high fidelity controller simulation for design analysis is presented. The flexibility of the flight train is represented through generalized modal analysis. A multiple controller scheme is utilized for coarse and fine pointing. Coarse azimuth pointing is accomplished by an established pointing system, with extensive flight history, residing above the gondola structure. A pitch-yaw gimbal mount is used for fine pointing, providing orthogonal axes when nominally on target. Fine pointing actuation is from direct drive dc motors, eliminating backlash problems. An analysis of friction nonlinearities and a demonstration of the necessity in eliminating static friction are provided. A unique bearing hub design is introduced that eliminates static friction from the system dynamics. A control scheme involving linear accelerometers for enhanced disturbance rejection is also presented. Results from a linear analysis of the total system and the high fidelity simulation are given. Results from a generalized demonstration prototype are presented. Commercial off-the-shelf (COTS) hardware was used to demonstrate the efficacy and performance of the pointer design for a mock instrument. Sub-arcsecond pointing ability from a ground hang test setup is shown from the testing results. This paper establishes that the proposed control strategy can be made robustly stable with significant design margins. Also demonstrated is the efficacy of the proposed system in rejecting disturbances larger than those considered realistic. The system is implemented and demonstrates sub arc second pointing ability using COTS hardware. Finally, we see that sub arc-second pointing stability can be achieved for a large instrument pointing at an inertial target.

High fidelity quasi steady-state aerodynamic model effects on race vehicle performance predictions using multi-body simulation

NASA Astrophysics Data System (ADS)

Mohrfeld-Halterman, J. A.; Uddin, M.

2016-07-01

We described in this paper the development of a high fidelity vehicle aerodynamic model to fit wind tunnel test data over a wide range of vehicle orientations. We also present a comparison between the effects of this proposed model and a conventional quasi steady-state aerodynamic model on race vehicle simulation results. This is done by implementing both of these models independently in multi-body quasi steady-state simulations to determine the effects of the high fidelity aerodynamic model on race vehicle performance metrics. The quasi steady state vehicle simulation is developed with a multi-body NASCAR Truck vehicle model, and simulations are conducted for three different types of NASCAR race tracks, a short track, a one and a half mile intermediate track, and a higher speed, two mile intermediate race track. For each track simulation, the effects of the aerodynamic model on handling, maximum corner speed, and drive force metrics are analysed. The accuracy of the high-fidelity model is shown to reduce the aerodynamic model error relative to the conventional aerodynamic model, and the increased accuracy of the high fidelity aerodynamic model is found to have realisable effects on the performance metric predictions on the intermediate tracks resulting from the quasi steady-state simulation.

Aerodynamic design applying automatic differentiation and using robust variable fidelity optimization

NASA Astrophysics Data System (ADS)

Takemiya, Tetsushi

In modern aerospace engineering, the physics-based computational design method is becoming more important, as it is more efficient than experiments and because it is more suitable in designing new types of aircraft (e.g., unmanned aerial vehicles or supersonic business jets) than the conventional design method, which heavily relies on historical data. To enhance the reliability of the physics-based computational design method, researchers have made tremendous efforts to improve the fidelity of models. However, high-fidelity models require longer computational time, so the advantage of efficiency is partially lost. This problem has been overcome with the development of variable fidelity optimization (VFO). In VFO, different fidelity models are simultaneously employed in order to improve the speed and the accuracy of convergence in an optimization process. Among the various types of VFO methods, one of the most promising methods is the approximation management framework (AMF). In the AMF, objective and constraint functions of a low-fidelity model are scaled at a design point so that the scaled functions, which are referred to as "surrogate functions," match those of a high-fidelity model. Since scaling functions and the low-fidelity model constitutes surrogate functions, evaluating the surrogate functions is faster than evaluating the high-fidelity model. Therefore, in the optimization process, in which gradient-based optimization is implemented and thus many function calls are required, the surrogate functions are used instead of the high-fidelity model to obtain a new design point. The best feature of the AMF is that it may converge to a local optimum of the high-fidelity model in much less computational time than the high-fidelity model. However, through literature surveys and implementations of the AMF, the author xx found that (1) the AMF is very vulnerable when the computational analysis models have numerical noise, which is very common in high-fidelity models, and that (2) the AMF terminates optimization erroneously when the optimization problems have constraints. The first problem is due to inaccuracy in computing derivatives in the AMF, and the second problem is due to erroneous treatment of the trust region ratio, which sets the size of the domain for an optimization in the AMF. In order to solve the first problem of the AMF, automatic differentiation (AD) technique, which reads the codes of analysis models and automatically generates new derivative codes based on some mathematical rules, is applied. If derivatives are computed with the generated derivative code, they are analytical, and the required computational time is independent of the number of design variables, which is very advantageous for realistic aerospace engineering problems. However, if analysis models implement iterative computations such as computational fluid dynamics (CFD), which solves system partial differential equations iteratively, computing derivatives through the AD requires a massive memory size. The author solved this deficiency by modifying the AD approach and developing a more efficient implementation with CFD, and successfully applied the AD to general CFD software. In order to solve the second problem of the AMF, the governing equation of the trust region ratio, which is very strict against the violation of constraints, is modified so that it can accept the violation of constraints within some tolerance. By accepting violations of constraints during the optimization process, the AMF can continue optimization without terminating immaturely and eventually find the true optimum design point. With these modifications, the AMF is referred to as "Robust AMF," and it is applied to airfoil and wing aerodynamic design problems using Euler CFD software. The former problem has 21 design variables, and the latter 64. In both problems, derivatives computed with the proposed AD method are first compared with those computed with the finite differentiation (FD) method, and then, the Robust AMF is implemented along with the sequential quadratic programming (SQP) optimization method with only high-fidelity models. The proposed AD method computes derivatives more accurately and faster than the FD method, and the Robust AMF successfully optimizes shapes of the airfoil and the wing in a much shorter time than SQP with only high-fidelity models. These results clearly show the effectiveness of the Robust AMF. Finally, the feasibility of reducing computational time for calculating derivatives and the necessity of AMF with an optimum design point always in the feasible region are discussed as future work.

An Evaluation of the FLAG Friction Model frictmultiscale2 using the Experiments of Juanicotena and Szarynski

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zocher, Marvin Anthony; Hammerberg, James Edward

The experiments of Juanicotena and Szarynski, namely T101, T102, and T105 are modeled for purposes of gaining a better understanding of the FLAG friction model frictmultiscale2. This exercise has been conducted as a first step toward model validation. It is shown that with inclusion of the friction model in the numerical analysis, the results of Juanicotena and Szarynski are predicted reasonably well. Without the friction model, simulation results do not match the experimental data nearly as well. Suggestions for follow-on work are included.

Friction in Forming of UD Composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sachs, U.; Haanappel, S. P.; Akkerman, R.

2011-05-04

Inter-ply and tool/ply friction play a dominant role in hot stamp forming of UD fiber-reinforced thermoplastic laminates. This research treats friction measurements of a PEEK-AS4 composite system. To this end, an in-house developed friction tester is utilized to pull a laminate through two heat controlled clamping platens. The friction coefficient is determined by relating the clamp force to the pull force. The geometry of the gap between the clamping platens is monitored with micrometer accuracy. A first approach to describe the relation between the geometry and frictional behavior is undertaken by applying a standard thin-film theory for hydrodynamic lubrication. Experimentalmore » measurements showed that the thin-film theory does not entirely cover the underlying physics. Thus a second model is utilized, which employs a Leonov-model to describe the shear deformation of the matrix material, while its viscosity is described with a multi-mode Maxwell model. The combination of both models shows the potential to capture the complete frictional behavior.« less

Uncertainty quantification for PZT bimorph actuators

NASA Astrophysics Data System (ADS)

Bravo, Nikolas; Smith, Ralph C.; Crews, John

2018-03-01

In this paper, we discuss the development of a high fidelity model for a PZT bimorph actuator used for micro-air vehicles, which includes the Robobee. We developed a high-fidelity model for the actuator using the homogenized energy model (HEM) framework, which quantifies the nonlinear, hysteretic, and rate-dependent behavior inherent to PZT in dynamic operating regimes. We then discussed an inverse problem on the model. We included local and global sensitivity analysis of the parameters in the high-fidelity model. Finally, we will discuss the results of Bayesian inference and uncertainty quantification on the HEM.

Stability analysis of a controlled mechanical system with parametric uncertainties in LuGre friction model

NASA Astrophysics Data System (ADS)

Sun, Yun-Hsiang; Sun, Yuming; Wu, Christine Qiong; Sepehri, Nariman

2018-04-01

Parameters of friction model identified for a specific control system development are not constants. They vary over time and have a significant effect on the control system stability. Although much research has been devoted to the stability analysis under parametric uncertainty, less attention has been paid to incorporating a realistic friction model into their analysis. After reviewing the common friction models for controller design, a modified LuGre friction model is selected to carry out the stability analysis in this study. Two parameters of the LuGre model, namely σ0 and σ1, are critical to the demonstration of dynamic friction features, yet the identification of which is difficult to carry out, resulting in a high level of uncertainties in their values. Aiming at uncovering the effect of the σ0 and σ1 variations on the control system stability, a servomechanism with modified LuGre friction model is investigated. Two set-point position controllers are synthesised based on the servomechanism model to form two case studies. Through Lyapunov exponents, it is clear that the variation of σ0 and σ1 has an obvious effect on the stabiltiy of the studied systems and should not be overlooked in the design phase.

Ceramic composites: A review of toughening mechanisms and demonstration of micropillar compression for interface property extraction

DOE PAGES

Kabel, Joey; Hosemann, Peter; Zayachuk, Yevhen; ...

2018-01-24

We present that ceramic fiber–matrix composites (CFMCs) are exciting materials for engineering applications in extreme environments. By integrating ceramic fibers within a ceramic matrix, CFMCs allow an intrinsically brittle material to exhibit sufficient structural toughness for use in gas turbines and nuclear reactors. Chemical stability under high temperature and irradiation coupled with high specific strength make these materials unique and increasingly popular in extreme settings. This paper first offers a review of the importance and growing body of research on fiber–matrix interfaces as they relate to composite toughening mechanisms. Second, micropillar compression is explored experimentally as a high-fidelity method formore » extracting interface properties compared with traditional fiber push-out testing. Three significant interface properties that govern composite toughening were extracted. For a 50-nm-pyrolytic carbon interface, the following were observed: a fracture energy release rate of ~2.5 J/m 2, an internal friction coefficient of 0.25 ± 0.04, and a debond shear strength of 266 ± 24 MPa. Lastly, this research supports micromechanical evaluations as a unique bridge between theoretical physics models for microcrack propagation and empirically driven finite element models for bulk CFMCs.« less

Ceramic composites: A review of toughening mechanisms and demonstration of micropillar compression for interface property extraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kabel, Joey; Hosemann, Peter; Zayachuk, Yevhen

We present that ceramic fiber–matrix composites (CFMCs) are exciting materials for engineering applications in extreme environments. By integrating ceramic fibers within a ceramic matrix, CFMCs allow an intrinsically brittle material to exhibit sufficient structural toughness for use in gas turbines and nuclear reactors. Chemical stability under high temperature and irradiation coupled with high specific strength make these materials unique and increasingly popular in extreme settings. This paper first offers a review of the importance and growing body of research on fiber–matrix interfaces as they relate to composite toughening mechanisms. Second, micropillar compression is explored experimentally as a high-fidelity method formore » extracting interface properties compared with traditional fiber push-out testing. Three significant interface properties that govern composite toughening were extracted. For a 50-nm-pyrolytic carbon interface, the following were observed: a fracture energy release rate of ~2.5 J/m 2, an internal friction coefficient of 0.25 ± 0.04, and a debond shear strength of 266 ± 24 MPa. Lastly, this research supports micromechanical evaluations as a unique bridge between theoretical physics models for microcrack propagation and empirically driven finite element models for bulk CFMCs.« less

Stress-dependent grain size evolution of nanocrystalline Ni-W and its impact on friction behavior

DOE PAGES

Argibay, N.; Furnish, T. A.; Boyce, B. L.; ...

2016-06-07

The friction behavior of ultra-nanocrystalline Ni-W coatings was investigated. A critical stress threshold was identified below which friction remained low, and above which a time-dependent evolution toward higher friction behavior occurred. Founded on established plasticity models we propose a correlation between surface grain size and applied stress that can be used to predict the critical stress separating the two friction regimes. Lastly, this interpretation of plasticity models suggests that macro-scale low and high friction regimes are respectively associated with the nano-scale mechanisms of grain boundary and dislocation-mediated plasticity.

Estimation of internal friction angle of subduction zone in northeast of Japan by using seismic focal mechanisms

NASA Astrophysics Data System (ADS)

Miyakawa, A.; Sato, K.; Otsubo, M.

2017-12-01

Physical properties, such as friction angle of the material, is important to understand the interplate earthquake of a subduction zone. Coulomb wedge model (Davis et al., 1983, JGR) is successfully revealed the relationship between a geometry of an accretionary wedge in a subduction zone and the physical properties of the material composing the accretionary wedge (e.g. Dahlen, 1984, JGR). An internal friction angle of the wedge and the frictional strength of the plate boundary fault control the wedge angle according to the Coulomb wedge model. However, the internal friction angle of the wedge and the frictional strength of the plate boundary fault are hard to estimate. Many previous works assumed the internal friction angle of the wedge on the basis of the laboratory experiments. Then, the frictional strength of the plate boundary fault, which is usually most interested, were evaluated from the observed wedge angle and the assumed internal friction angle of the wedge. Consequently, we should be careful of the selection of the internal friction angle of the wedge, otherwise, the uncertain an inappropriate internal friction angle may mislead the frictional strength of the plate boundary fault. In this study, we employed the newly developed technique to evaluate the internal friction angle of the wedge from the earthquake focal mechanisms occurred in the wedge along Japan Trench, northeast Japan. We used 650 earthquake mechanisms determined by NIED, Japan for the stress and friction coefficient inversion. The stress and friction coefficient inversion method is modified to handle the earthquake focal mechanisms from a computerized method to estimate the friction coefficient from the orientation distribution of faults (Sato, 2016, JSG). Finally, we obtained 25 degrees of internal friction angle of the wedge from the inversion. This value of friction angle is lower than usually assumed internal friction angle (30 degrees) (Byerlee, 1978, PAGEOPH). This lower internal friction angle leads to lower frictional strength of plate boundary fault ( 0.35) according to the Coulomb wedge model. These constrained physical parameters can contribute to understanding the interplate earthquake at each subduction zones.

What Is Essential in Developmental Evaluation? On Integrity, Fidelity, Adultery, Abstinence, Impotence, Long-Term Commitment, Integrity, and Sensitivity in Implementing Evaluation Models

ERIC Educational Resources Information Center

Patton, Michael Quinn

2016-01-01

Fidelity concerns the extent to which a specific evaluation sufficiently incorporates the core characteristics of the overall approach to justify labeling that evaluation by its designated name. Fidelity has traditionally meant implementing a model in exactly the same way each time following the prescribed steps and procedures. The essential…

Modeling of heat transfer in compacted machining chips during friction consolidation process

NASA Astrophysics Data System (ADS)

Abbas, Naseer; Deng, Xiaomin; Li, Xiao; Reynolds, Anthony

2018-04-01

The current study aims to provide an understanding of the heat transfer process in compacted aluminum alloy AA6061 machining chips during the friction consolidation process (FCP) through experimental investigations and mathematical modelling and numerical simulation. Compaction and friction consolidation of machining chips is the first stage of the Friction Extrusion Process (FEP), which is a novel method for recycling machining chips to produce useful products such as wires. In this study, compacted machining chips are modelled as a continuum whose material properties vary with density during friction consolidation. Based on density and temperature dependent thermal properties, the temperature field in the chip material and process chamber caused by frictional heating during the friction consolidation process is predicted. The predicted temperature field is found to compare well with temperature measurements at select points where such measurements can be made using thermocouples.

Is internal friction friction?

USGS Publications Warehouse

Savage, J.C.; Byerlee, J.D.; Lockner, D.A.

1996-01-01

Mogi [1974] proposed a simple model of the incipient rupture surface to explain the Coulomb failure criterion. We show here that this model can plausibly be extended to explain the Mohr failure criterion. In Mogi's model the incipient rupture surface immediately before fracture consists of areas across which material integrity is maintained (intact areas) and areas across which it is not (cracks). The strength of the incipient rupture surface is made up of the inherent strength of the intact areas plus the frictional resistance to sliding offered by the cracked areas. Although the coefficient of internal friction (slope of the strength versus normal stress curve) depends upon both the frictional and inherent strengths, the phenomenon of internal friction can be identified with the frictional part. The curvature of the Mohr failure envelope is interpreted as a consequence of differences in damage (cracking) accumulated in prefailure loading at different confining pressures.

Title: Experimental and analytical study of frictional anisotropy of nanotubes

NASA Astrophysics Data System (ADS)

Riedo, Elisa; Gao, Yang; Li, Tai-De; Chiu, Hsiang-Chih; Kim, Suenne; Klinke, Christian; Tosatti, Erio

The frictional properties of Carbon and Boron Nitride nanotubes (NTs) are very important in a variety of applications, including composite materials, carbon fibers, and micro/nano-electromechanical systems. Atomic force microscopy (AFM) is a powerful tool to investigate with nanoscale resolution the frictional properties of individual NTs. Here, we report on an experimental study of the frictional properties of different types of supported nanotubes by AFM. We also propose a quantitative model to describe and then predict the frictional properties of nanotubes sliding on a substrate along (longitudinal friction) or perpendicular (transverse friction) their axis. This model provides a simple but general analytical relationship that well describes the acquired experimental data. As an example of potential applications, this experimental method combined with the proposed model can guide to design better NTs-ceramic composites, or to self-assemble the nanotubes on a surface in a given direction. M. Lucas et al., Nature Materials 8, 876-881 (2009).

Development and Implementation of CFD-Informed Models for the Advanced Subchannel Code CTF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blyth, Taylor S.; Avramova, Maria

The research described in this PhD thesis contributes to the development of efficient methods for utilization of high-fidelity models and codes to inform low-fidelity models and codes in the area of nuclear reactor core thermal-hydraulics. The objective is to increase the accuracy of predictions of quantities of interests using high-fidelity CFD models while preserving the efficiency of low-fidelity subchannel core calculations. An original methodology named Physics- based Approach for High-to-Low Model Information has been further developed and tested. The overall physical phenomena and corresponding localized effects, which are introduced by the presence of spacer grids in light water reactor (LWR)more » cores, are dissected in corresponding four building basic processes, and corresponding models are informed using high-fidelity CFD codes. These models are a spacer grid-directed cross-flow model, a grid-enhanced turbulent mixing model, a heat transfer enhancement model, and a spacer grid pressure loss model. The localized CFD-models are developed and tested using the CFD code STAR-CCM+, and the corresponding global model development and testing in sub-channel formulation is performed in the thermal- hydraulic subchannel code CTF. The improved CTF simulations utilize data-files derived from CFD STAR-CCM+ simulation results covering the spacer grid design desired for inclusion in the CTF calculation. The current implementation of these models is examined and possibilities for improvement and further development are suggested. The validation experimental database is extended by including the OECD/NRC PSBT benchmark data. The outcome is an enhanced accuracy of CTF predictions while preserving the computational efficiency of a low-fidelity subchannel code.« less

Development and Implementation of CFD-Informed Models for the Advanced Subchannel Code CTF

NASA Astrophysics Data System (ADS)

Blyth, Taylor S.

The research described in this PhD thesis contributes to the development of efficient methods for utilization of high-fidelity models and codes to inform low-fidelity models and codes in the area of nuclear reactor core thermal-hydraulics. The objective is to increase the accuracy of predictions of quantities of interests using high-fidelity CFD models while preserving the efficiency of low-fidelity subchannel core calculations. An original methodology named Physics-based Approach for High-to-Low Model Information has been further developed and tested. The overall physical phenomena and corresponding localized effects, which are introduced by the presence of spacer grids in light water reactor (LWR) cores, are dissected in corresponding four building basic processes, and corresponding models are informed using high-fidelity CFD codes. These models are a spacer grid-directed cross-flow model, a grid-enhanced turbulent mixing model, a heat transfer enhancement model, and a spacer grid pressure loss model. The localized CFD-models are developed and tested using the CFD code STAR-CCM+, and the corresponding global model development and testing in sub-channel formulation is performed in the thermal-hydraulic subchannel code CTF. The improved CTF simulations utilize data-files derived from CFD STAR-CCM+ simulation results covering the spacer grid design desired for inclusion in the CTF calculation. The current implementation of these models is examined and possibilities for improvement and further development are suggested. The validation experimental database is extended by including the OECD/NRC PSBT benchmark data. The outcome is an enhanced accuracy of CTF predictions while preserving the computational efficiency of a low-fidelity subchannel code.

Physically representative atomistic modeling of atomic-scale friction

NASA Astrophysics Data System (ADS)

Dong, Yalin

Nanotribology is a research field to study friction, adhesion, wear and lubrication occurred between two sliding interfaces at nano scale. This study is motivated by the demanding need of miniaturization mechanical components in Micro Electro Mechanical Systems (MEMS), improvement of durability in magnetic storage system, and other industrial applications. Overcoming tribological failure and finding ways to control friction at small scale have become keys to commercialize MEMS with sliding components as well as to stimulate the technological innovation associated with the development of MEMS. In addition to the industrial applications, such research is also scientifically fascinating because it opens a door to understand macroscopic friction from the most bottom atomic level, and therefore serves as a bridge between science and engineering. This thesis focuses on solid/solid atomic friction and its associated energy dissipation through theoretical analysis, atomistic simulation, transition state theory, and close collaboration with experimentalists. Reduced-order models have many advantages for its simplification and capacity to simulating long-time event. We will apply Prandtl-Tomlinson models and their extensions to interpret dry atomic-scale friction. We begin with the fundamental equations and build on them step-by-step from the simple quasistatic one-spring, one-mass model for predicting transitions between friction regimes to the two-dimensional and multi-atom models for describing the effect of contact area. Theoretical analysis, numerical implementation, and predicted physical phenomena are all discussed. In the process, we demonstrate the significant potential for this approach to yield new fundamental understanding of atomic-scale friction. Atomistic modeling can never be overemphasized in the investigation of atomic friction, in which each single atom could play a significant role, but is hard to be captured experimentally. In atomic friction, the interesting physical process is buried between the two contact interfaces, thus makes a direct measurement more difficult. Atomistic simulation is able to simulate the process with the dynamic information of each single atom, and therefore provides valuable interpretations for experiments. In this, we will systematically to apply Molecular Dynamics (MD) simulation to optimally model the Atomic Force Microscopy (AFM) measurement of atomic friction. Furthermore, we also employed molecular dynamics simulation to correlate the atomic dynamics with the friction behavior observed in experiments. For instance, ParRep dynamics (an accelerated molecular dynamic technique) is introduced to investigate velocity dependence of atomic friction; we also employ MD simulation to "see" how the reconstruction of gold surface modulates the friction, and the friction enhancement mechanism at a graphite step edge. Atomic stick-slip friction can be treated as a rate process. Instead of running a direction simulation of the process, we can apply transition state theory to predict its property. We will have a rigorous derivation of velocity and temperature dependence of friction based on the Prandtl-Tomlinson model as well as transition theory. A more accurate relation to prediction velocity and temperature dependence is obtained. Furthermore, we have included instrumental noise inherent in AFM measurement to interpret two discoveries in experiments, suppression of friction at low temperature and the attempt frequency discrepancy between AFM measurement and theoretical prediction. We also discuss the possibility to treat wear as a rate process.

Challenges of Applying a Comprehensive Model of Intervention Fidelity

PubMed Central

Bosak, Kelly; Pozehl, Bunny; Yates, Bernice

2014-01-01

Applying a comprehensive model of fidelity to interventions delivered by Information and Communication Technology (ICT) has multiple challenges. Fidelity must be considered in the design, implementation, evaluation, and reporting of the intervention. The fidelity strategies must address the unique aspects of the technology, including training providers to instruct participants to use the technology and to provide standardized feedback, rather than deliver the intervention in-person. Other challenges include the nonspecific effects resulting from participants accessing unintended content in interventions delivered by the Internet. ICT allows participant receipt and enactment of intervention skills to be assessed by electronic evidence, rather than in-person observation. Interventions using ICT, such as the Internet are unique, and there is less control of participant interaction with various electronic components. Monitoring participant use and providing standardized feedback for receipt and enactment of intervention skills is key to ensuring intervention fidelity. The final challenges involve evaluating and reporting fidelity. PMID:21474676

An Automatic Medium to High Fidelity Low-Thrust Global Trajectory Toolchain; EMTG-GMAT

NASA Technical Reports Server (NTRS)

Beeson, Ryne T.; Englander, Jacob A.; Hughes, Steven P.; Schadegg, Maximillian

2015-01-01

Solving the global optimization, low-thrust, multiple-flyby interplanetary trajectory problem with high-fidelity dynamical models requires an unreasonable amount of computational resources. A better approach, and one that is demonstrated in this paper, is a multi-step process whereby the solution of the aforementioned problem is solved at a lower-fidelity and this solution is used as an initial guess for a higher-fidelity solver. The framework presented in this work uses two tools developed by NASA Goddard Space Flight Center: the Evolutionary Mission Trajectory Generator (EMTG) and the General Mission Analysis Tool (GMAT). EMTG is a medium to medium-high fidelity low-thrust interplanetary global optimization solver, which now has the capability to automatically generate GMAT script files for seeding a high-fidelity solution using GMAT's local optimization capabilities. A discussion of the dynamical models as well as thruster and power modeling for both EMTG and GMAT are given in this paper. Current capabilities are demonstrated with examples that highlight the toolchains ability to efficiently solve the difficult low-thrust global optimization problem with little human intervention.

Analytical model development for the prediction of the frictional resistance of a capsule endoscope inside an intestine.

PubMed

Kim, J S; Sung, I H; Kim, Y T; Kim, D E; Jang, Y H

2007-11-01

For the purpose of optimizing the design of the locomotion mechanism as well as the body shape of a self-propelled capsule endoscope, an analytical model for the prediction of frictional resistance of the capsule moving inside the small intestine was first developed. The model was developed by considering the contact geometry and viscoelasticity of the intestine, based on the experimental investigations on the material properties of the intestine and the friction of the capsule inside the small intestine. In order to verify the model and to investigate the distributions of various stress components applied to the capsule, finite element (FE) analyses were carried out. The comparison of the frictional resistance between the predicted and the experimental values suggested that the proposed model could predict the frictional force of the capsule with reasonable accuracy. Also, the FE analysis results of various stress components revealed the stress relaxation of the intestine and explained that such stress relaxation characteristics of the intestine resulted in lower frictional force as the speed of the capsule decreased. These results suggested that the frontal shape of the capsule was critical to the design of the capsule with desired frictional performance. It was shown that the proposed model can provide quantitative estimation of the frictional resistance of the capsule under various moving conditions inside the intestine. The model is expected to be useful in the design optimization of the capsule locomotion inside the intestine.

Differential-damper topologies for actuators in rehabilitation robotics.

PubMed

Tucker, Michael R; Gassert, Roger

2012-01-01

Differential-damper (DD) elements can provide a high bandwidth means for decoupling a high inertia, high friction, non-backdrivable actuator from its output and can enable high fidelity force control. In this paper, a port-based decomposition is used to analyze the energetic behavior of such actuators in various physical domains. The general concepts are then applied to a prototype DD actuator for illustration and discussion. It is shown that, within physical bounds, the output torque from a DD actuator can be controlled independently from the input speed. This concept holds the potential to be scaled up and integrated in a compact and lightweight package powerful enough for incorporation with a portable lower limb orthotic or prosthetic device.

The effect of friction in the hold down post spherical bearings on hold down post loads

NASA Technical Reports Server (NTRS)

Richardson, James A.

1990-01-01

The effect of friction at the connection of the Solid Rocket Booster (SRB) aft skirt and the mobile launch platform (MLP) hold down posts was analyzed. A simplified model of the shuttle response during the Space Shuttle Main Engine (SSME) buildup was constructed. The model included the effect of stick-slip friction for the rotation of the skirt about the spherical bearing. Current finite element models assume the joint is completely frictionless in rotation and therefore no moment is transferred between the skirt and the hold down posts. The model was partially verified against test data and preliminary parameter studies were performed. The parameter studies indicated that the coefficient of friction strongly influenced the moment on the hold down posts. The coefficient of friction had little effect on hold down post vertical loads, however. Further calibration of the model is necessary before the effect of friction on the hold down post horizontal loads can be analyzed.

Surrogate based wind farm layout optimization using manifold mapping

NASA Astrophysics Data System (ADS)

Kaja Kamaludeen, Shaafi M.; van Zuijle, Alexander; Bijl, Hester

2016-09-01

High computational cost associated with the high fidelity wake models such as RANS or LES serves as a primary bottleneck to perform a direct high fidelity wind farm layout optimization (WFLO) using accurate CFD based wake models. Therefore, a surrogate based multi-fidelity WFLO methodology (SWFLO) is proposed. The surrogate model is built using an SBO method referred as manifold mapping (MM). As a verification, optimization of spacing between two staggered wind turbines was performed using the proposed surrogate based methodology and the performance was compared with that of direct optimization using high fidelity model. Significant reduction in computational cost was achieved using MM: a maximum computational cost reduction of 65%, while arriving at the same optima as that of direct high fidelity optimization. The similarity between the response of models, the number of mapping points and its position, highly influences the computational efficiency of the proposed method. As a proof of concept, realistic WFLO of a small 7-turbine wind farm is performed using the proposed surrogate based methodology. Two variants of Jensen wake model with different decay coefficients were used as the fine and coarse model. The proposed SWFLO method arrived at the same optima as that of the fine model with very less number of fine model simulations.

Translational Dielectric Friction on a Chain of Charged Spheres

PubMed Central

Boughammoura, Sondès; M'halla, Jalel

2014-01-01

We have proved in details that the dielectric friction remains the principal frictional effect for a stretched polyion modeled as a chain of charged spheres, whereas, in the case of Manning's model (infinite thread with a continuous distribution of charge), this friction effect is nonexistent. According to this chain model, it is therefore possible to detect by conductivity measurements any transition from a coiled configuration (ellipsoidal model) to a stretched configuration during dilution process. We have also underlined the important interdependence between the dielectric friction and the ionic condensation of the counterions, in order to distinguish between the Ostwald regime and the Manning regime for which the degree of condensation is practically constant in a large range of concentrations. PMID:24672333

Transient rolling friction model for discrete element simulations of sphere assemblies

NASA Astrophysics Data System (ADS)

Kuhn, Matthew R.

2014-03-01

The rolling resistance between a pair of contacting particles can be modeled with two mechanisms. The first mechanism, already widely addressed in the DEM literature, involves a contact moment between the particles. The second mechanism involves a reduction of the tangential contact force, but without a contact moment. This type of rotational resistance, termed creep-friction, is the subject of the paper. Within the creep-friction literature, the term “creep” does not mean a viscous mechanism, but rather connotes a slight slip that accompanies rolling. Two extremes of particle motions bound the range of creep-friction behaviors: a pure tangential translation is modeled as a Cattaneo-Mindlin interaction, whereas prolonged steady-state rolling corresponds to the traditional wheel-rail problem described by Carter, Poritsky, and others. DEM simulations, however, are dominated by the transient creep-friction rolling conditions that lie between these two extremes. A simplified model is proposed for the three-dimensional transient creep-friction rolling of two spheres. The model is an extension of the work of Dahlberg and Alfredsson, who studied the two-dimensional interactions of disks. The proposed model is applied to two different systems: a pair of spheres and a large dense assembly of spheres. Although creep-friction can reduce the tangential contact force that would otherwise be predicted with Cattaneo-Mindlin theory, a significant force reduction occurs only when the rate of rolling is much greater than the rate of translational sliding and only after a sustained period of rolling. When applied to the deviatoric loading of an assembly of spheres, the proposed creep-friction model has minimal effect on macroscopic strength or stiffness. At the micro-scale of individual contacts, creep-friction does have a modest influence on the incremental contact behavior, although the aggregate effect on the assembly's behavior is minimal.

An analytical elastic plastic contact model with strain hardening and frictional effects for normal and oblique impacts

DOE PAGES

Brake, M. R. W.

2015-02-17

Impact between metallic surfaces is a phenomenon that is ubiquitous in the design and analysis of mechanical systems. We found that to model this phenomenon, a new formulation for frictional elastic–plastic contact between two surfaces is developed. The formulation is developed to consider both frictional, oblique contact (of which normal, frictionless contact is a limiting case) and strain hardening effects. The constitutive model for normal contact is developed as two contiguous loading domains: the elastic regime and a transitionary region in which the plastic response of the materials develops and the elastic response abates. For unloading, the constitutive model ismore » based on an elastic process. Moreover, the normal contact model is assumed to only couple one-way with the frictional/tangential contact model, which results in the normal contact model being independent of the frictional effects. Frictional, tangential contact is modeled using a microslip model that is developed to consider the pressure distribution that develops from the elastic–plastic normal contact. This model is validated through comparisons with experimental results reported in the literature, and is demonstrated to be significantly more accurate than 10 other normal contact models and three other tangential contact models found in the literature.« less

Utilizing Three-Dimensional Printing Technology to Assess the Feasibility of High-Fidelity Synthetic Ventricular Septal Defect Models for Simulation in Medical Education.

PubMed

Costello, John P; Olivieri, Laura J; Krieger, Axel; Thabit, Omar; Marshall, M Blair; Yoo, Shi-Joon; Kim, Peter C; Jonas, Richard A; Nath, Dilip S

2014-07-01

The current educational approach for teaching congenital heart disease (CHD) anatomy to students involves instructional tools and techniques that have significant limitations. This study sought to assess the feasibility of utilizing present-day three-dimensional (3D) printing technology to create high-fidelity synthetic heart models with ventricular septal defect (VSD) lesions and applying these models to a novel, simulation-based educational curriculum for premedical and medical students. Archived, de-identified magnetic resonance images of five common VSD subtypes were obtained. These cardiac images were then segmented and built into 3D computer-aided design models using Mimics Innovation Suite software. An Objet500 Connex 3D printer was subsequently utilized to print a high-fidelity heart model for each VSD subtype. Next, a simulation-based educational curriculum using these heart models was developed and implemented in the instruction of 29 premedical and medical students. Assessment of this curriculum was undertaken with Likert-type questionnaires. High-fidelity VSD models were successfully created utilizing magnetic resonance imaging data and 3D printing. Following instruction with these high-fidelity models, all students reported significant improvement in knowledge acquisition (P < .0001), knowledge reporting (P < .0001), and structural conceptualization (P < .0001) of VSDs. It is feasible to use present-day 3D printing technology to create high-fidelity heart models with complex intracardiac defects. Furthermore, this tool forms the foundation for an innovative, simulation-based educational approach to teach students about CHD and creates a novel opportunity to stimulate their interest in this field. © The Author(s) 2014.

Nonlinear vibration analysis of bladed disks with dry friction dampers

NASA Astrophysics Data System (ADS)

Ciğeroğlu, Ender; Özgüven, H. Nevzat

2006-08-01

In this work, a new model is proposed for the vibration analysis of turbine blades with dry friction dampers. The aim of the study is to develop a multiblade model that is accurate and yet easy to be analyzed so that it can be used efficiently in the design of friction dampers. The suggested nonlinear model for a bladed disk assembly includes all the blades with blade to blade and/or blade to cover plate dry friction dampers. An important feature of the model is that both macro-slip and micro-slip models are used in representing dry friction dampers. The model is simple to be analyzed as it is the case in macro-slip model, and yet it includes the features of more realistic micro-slip model. The nonlinear multidegree-of-freedom (mdof) model of bladed disk system is analyzed in frequency domain by applying a quasi-linearization technique, which transforms the nonlinear differential equations into a set of nonlinear algebraic equations. The solution method employed reduces the computational effort drastically compared to time solution methods for nonlinear systems, which makes it possible to obtain a more realistic model by the inclusion of all blades around the disk, disk itself and all friction dampers since in general system parameters are not identical throughout the geometry. The validation of the method is demonstrated by comparing the results obtained in this study with those given in literature and also with results obtained by time domain analysis. In the case studies presented the effect of friction damper parameters on vibration characteristics of tuned and mistuned bladed disk systems is studied by using a 20 blade system. It is shown that the method presented can be used to find the optimum friction damper values in a bladed disk assembly.

Development and assessment of atomistic models for predicting static friction coefficients

NASA Astrophysics Data System (ADS)

Jahangiri, Soran; Heverly-Coulson, Gavin S.; Mosey, Nicholas J.

2016-08-01

The friction coefficient relates friction forces to normal loads and plays a key role in fundamental and applied areas of science and technology. Despite its importance, the relationship between the friction coefficient and the properties of the materials forming a sliding contact is poorly understood. We illustrate how simple relationships regarding the changes in energy that occur during slip can be used to develop a quantitative model relating the friction coefficient to atomic-level features of the contact. The slip event is considered as an activated process and the load dependence of the slip energy barrier is approximated with a Taylor series expansion of the corresponding energies with respect to load. The resulting expression for the load-dependent slip energy barrier is incorporated in the Prandtl-Tomlinson (PT) model and a shear-based model to obtain expressions for friction coefficient. The results indicate that the shear-based model reproduces the static friction coefficients μs obtained from first-principles molecular dynamics simulations more accurately than the PT model. The ability of the model to provide atomistic explanations for differences in μs amongst different contacts is also illustrated. As a whole, the model is able to account for fundamental atomic-level features of μs, explain the differences in μs for different materials based on their properties, and might be also used in guiding the development of contacts with desired values of μs.

Prediction of Very High Reynolds Number Compressible Skin Friction

NASA Technical Reports Server (NTRS)

Carlson, John R.

1998-01-01

Flat plate skin friction calculations over a range of Mach numbers from 0.4 to 3.5 at Reynolds numbers from 16 million to 492 million using a Navier Stokes method with advanced turbulence modeling are compared with incompressible skin friction coefficient correlations. The semi-empirical correlation theories of van Driest; Cope; Winkler and Cha; and Sommer and Short T' are used to transform the predicted skin friction coefficients of solutions using two algebraic Reynolds stress turbulence models in the Navier-Stokes method PAB3D. In general, the predicted skin friction coefficients scaled well with each reference temperature theory though, overall the theory by Sommer and Short appeared to best collapse the predicted coefficients. At the lower Reynolds number 3 to 30 million, both the Girimaji and Shih, Zhu and Lumley turbulence models predicted skin-friction coefficients within 2% of the semi-empirical correlation skin friction coefficients. At the higher Reynolds numbers of 100 to 500 million, the turbulence models by Shih, Zhu and Lumley and Girimaji predicted coefficients that were 6% less and 10% greater, respectively, than the semi-empirical coefficients.

Rate and State Friction Relation for Nanoscale Contacts: Thermally Activated Prandtl-Tomlinson Model with Chemical Aging

NASA Astrophysics Data System (ADS)

Tian, Kaiwen; Goldsby, David L.; Carpick, Robert W.

2018-05-01

Rate and state friction (RSF) laws are widely used empirical relationships that describe macroscale to microscale frictional behavior. They entail a linear combination of the direct effect (the increase of friction with sliding velocity due to the reduced influence of thermal excitations) and the evolution effect (the change in friction with changes in contact "state," such as the real contact area or the degree of interfacial chemical bonds). Recent atomic force microscope (AFM) experiments and simulations found that nanoscale single-asperity amorphous silica-silica contacts exhibit logarithmic aging (increasing friction with time) over several decades of contact time, due to the formation of interfacial chemical bonds. Here we establish a physically based RSF relation for such contacts by combining the thermally activated Prandtl-Tomlinson (PTT) model with an evolution effect based on the physics of chemical aging. This thermally activated Prandtl-Tomlinson model with chemical aging (PTTCA), like the PTT model, uses the loading point velocity for describing the direct effect, not the tip velocity (as in conventional RSF laws). Also, in the PTTCA model, the combination of the evolution and direct effects may be nonlinear. We present AFM data consistent with the PTTCA model whereby in aging tests, for a given hold time, static friction increases with the logarithm of the loading point velocity. Kinetic friction also increases with the logarithm of the loading point velocity at sufficiently high velocities, but at a different increasing rate. The discrepancy between the rates of increase of static and kinetic friction with velocity arises from the fact that appreciable aging during static contact changes the energy landscape. Our approach extends the PTT model, originally used for crystalline substrates, to amorphous materials. It also establishes how conventional RSF laws can be modified for nanoscale single-asperity contacts to provide a physically based friction relation for nanoscale contacts that exhibit chemical bond-induced aging, as well as other aging mechanisms with similar physical characteristics.

The description of friction of silicon MEMS with surface roughness: virtues and limitations of a stochastic Prandtl-Tomlinson model and the simulation of vibration-induced friction reduction.

PubMed

van Spengen, W Merlijn; Turq, Viviane; Frenken, Joost W M

2010-01-01

We have replaced the periodic Prandtl-Tomlinson model with an atomic-scale friction model with a random roughness term describing the surface roughness of micro-electromechanical systems (MEMS) devices with sliding surfaces. This new model is shown to exhibit the same features as previously reported experimental MEMS friction loop data. The correlation function of the surface roughness is shown to play a critical role in the modelling. It is experimentally obtained by probing the sidewall surfaces of a MEMS device flipped upright in on-chip hinges with an AFM (atomic force microscope). The addition of a modulation term to the model allows us to also simulate the effect of vibration-induced friction reduction (normal-force modulation), as a function of both vibration amplitude and frequency. The results obtained agree very well with measurement data reported previously.

The frequency response of dynamic friction: Enhanced rate-and-state models

NASA Astrophysics Data System (ADS)

Cabboi, A.; Putelat, T.; Woodhouse, J.

2016-07-01

The prediction and control of friction-induced vibration requires a sufficiently accurate constitutive law for dynamic friction at the sliding interface: for linearised stability analysis, this requirement takes the form of a frictional frequency response function. Systematic measurements of this frictional frequency response function are presented for small samples of nylon and polycarbonate sliding against a glass disc. Previous efforts to explain such measurements from a theoretical model have failed, but an enhanced rate-and-state model is presented which is shown to match the measurements remarkably well. The tested parameter space covers a range of normal forces (10-50 N), of sliding speeds (1-10 mm/s) and frequencies (100-2000 Hz). The key new ingredient in the model is the inclusion of contact stiffness to take into account elastic deformations near the interface. A systematic methodology is presented to discriminate among possible variants of the model, and then to identify the model parameter values.

Modelling and tuning for a time-delayed vibration absorber with friction

NASA Astrophysics Data System (ADS)

Zhang, Xiaoxu; Xu, Jian; Ji, Jinchen

2018-06-01

This paper presents an integrated analytical and experimental study to the modelling and tuning of a time-delayed vibration absorber (TDVA) with friction. In system modelling, this paper firstly applies the method of averaging to obtain the frequency response function (FRF), and then uses the derived FRF to evaluate the fitness of different friction models. After the determination of the system model, this paper employs the obtained FRF to evaluate the vibration absorption performance with respect to tunable parameters. A significant feature of the TDVA with friction is that its stability is dependent on the excitation parameters. To ensure the stability of the time-delayed control, this paper defines a sufficient condition for stability estimation. Experimental measurements show that the dynamic response of the TDVA with friction can be accurately predicted and the time-delayed control can be precisely achieved by using the modelling and tuning technique provided in this paper.

Refining Students' Explanations of an Unfamiliar Physical Phenomenon-Microscopic Friction

NASA Astrophysics Data System (ADS)

Corpuz, Edgar De Guzman; Rebello, N. Sanjay

2017-08-01

The first phase of this multiphase study involves modeling of college students' thinking of friction at the microscopic level. Diagnostic interviews were conducted with 11 students with different levels of physics backgrounds. A phenomenographic approach of data analysis was used to generate categories of responses which subsequently were used to generate a model of explanation. Most of the students interviewed consistently used mechanical interactions in explaining microscopic friction. According to these students, friction is due to the interlocking or rubbing of atoms. Our data suggest that students' explanations of microscopic friction are predominantly influenced by their macroscopic experiences. In the second phase of the research, teaching experiment was conducted with 18 college students to investigate how students' explanations of microscopic friction can be refined by a series of model-building activities. Data were analyzed using Redish's two-level transfer framework. Our results show that through sequences of hands-on and minds-on activities, including cognitive dissonance and resolution, it is possible to facilitate the refinement of students' explanations of microscopic friction. The activities seemed to be productive in helping students activate associations that refine their ideas about microscopic friction.

Dynamics of translational friction in needle-tissue interaction during needle insertion.

PubMed

Asadian, Ali; Patel, Rajni V; Kermani, Mehrdad R

2014-01-01

In this study, a distributed approach to account for dynamic friction during needle insertion in soft tissue is presented. As is well known, friction is a complex nonlinear phenomenon. It appears that classical or static models are unable to capture some of the observations made in systems subjected to significant frictional effects. In needle insertion, translational friction would be a matter of importance when the needle is very flexible, or a stop-and-rotate motion profile at low insertion velocities is implemented, and thus, the system is repeatedly transitioned from a pre-sliding to a sliding mode and vice versa. In order to characterize friction components, a distributed version of the LuGre model in the state-space representation is adopted. This method also facilitates estimating cutting force in an intra-operative manner. To evaluate the performance of the proposed family of friction models, experiments were conducted on homogeneous artificial phantoms and animal tissue. The results illustrate that our approach enables us to represent the main features of friction which is a major force component in needle-tissue interaction during needle-based interventions.

Sustaining Fidelity Following the Nationwide PMTO™ Implementation in Norway

PubMed Central

Forgatch, Marion S.; DeGarmo, David S.

2011-01-01

This report describes three studies from the nationwide Norwegian implementation of Parent Management Training – Oregon Model (PMTO™), an empirically supported treatment for families of children with behavior problems (Forgatch and Patterson 2010). Separate stages of the implementation were evaluated using a fidelity measure based on direct observation of intervention sessions. Study 1 assessed growth in fidelity observed early, mid, and late in the training of a group of practitioners. We hypothesized increased fidelity and decreased variability in practice. Study 2 evaluated method fidelity over the course of three generations of practitioners trained in PMTO. Generation 1 (G1) was trained by the PMTO developer/purveyors; Generation 2 (G2) was trained by selected G1 Norwegian trainers; and Generation 3 (G3) was trained by G1 and G2 trainers. We hypothesized decrease in fidelity with each generation. Study 3 tested the predictive validity of fidelity in a cross-cultural replication, hypothesizing that higher fidelity scores would correlate with improved parenting practices observed in parent-child interactions before and after treatment. In Study 1, trainees' performance improved and became more homogeneous as predicted. In Study 2, a small decline in fidelity followed the transfer from the purveyor trainers to Norwegian trainers in G2, but G3 scores were equivalent to those attained by G1. Thus, the hypothesis was not fully supported. Finally, the FIMP validity model replicated; PMTO fidelity significantly contributed to improvements in parenting practices from pre- to post-treatment. The data indicate that PMTO was transferred successfully to Norwegian implementation with sustained fidelity and cross-cultural generalization. PMID:21671090

Regular and reverse nanoscale stick-slip behavior: Modeling and experiments

NASA Astrophysics Data System (ADS)

Landolsi, Fakhreddine; Sun, Yuekai; Lu, Hao; Ghorbel, Fathi H.; Lou, Jun

2010-02-01

We recently proposed a new nanoscale friction model based on the bristle interpretation of single asperity contacts. The model is mathematically continuous and dynamic which makes it suitable for implementation in nanomanipulation and nanorobotic modeling. In the present paper, friction force microscope (FFM) scans of muscovite mica samples and vertically aligned multi-wall carbon nanotubes (VAMWCNTs) arrays are conducted. The choice of these materials is motivated by the fact that they exibit different stick-slip behaviors. The corresponding experimental and simulation results are compared. Our nanoscale friction model is shown to represent both the regular and reverse frictional sawtooth characteristics of the muscovite mica and the VAMWCNTs, respectively.

Hydropower Optimization Using Artificial Neural Network Surrogate Models of a High-Fidelity Hydrodynamics and Water Quality Model

NASA Astrophysics Data System (ADS)

Shaw, Amelia R.; Smith Sawyer, Heather; LeBoeuf, Eugene J.; McDonald, Mark P.; Hadjerioua, Boualem

2017-11-01

Hydropower operations optimization subject to environmental constraints is limited by challenges associated with dimensionality and spatial and temporal resolution. The need for high-fidelity hydrodynamic and water quality models within optimization schemes is driven by improved computational capabilities, increased requirements to meet specific points of compliance with greater resolution, and the need to optimize operations of not just single reservoirs but systems of reservoirs. This study describes an important advancement for computing hourly power generation schemes for a hydropower reservoir using high-fidelity models, surrogate modeling techniques, and optimization methods. The predictive power of the high-fidelity hydrodynamic and water quality model CE-QUAL-W2 is successfully emulated by an artificial neural network, then integrated into a genetic algorithm optimization approach to maximize hydropower generation subject to constraints on dam operations and water quality. This methodology is applied to a multipurpose reservoir near Nashville, Tennessee, USA. The model successfully reproduced high-fidelity reservoir information while enabling 6.8% and 6.6% increases in hydropower production value relative to actual operations for dissolved oxygen (DO) limits of 5 and 6 mg/L, respectively, while witnessing an expected decrease in power generation at more restrictive DO constraints. Exploration of simultaneous temperature and DO constraints revealed capability to address multiple water quality constraints at specified locations. The reduced computational requirements of the new modeling approach demonstrated an ability to provide decision support for reservoir operations scheduling while maintaining high-fidelity hydrodynamic and water quality information as part of the optimization decision support routines.

Hydropower Optimization Using Artificial Neural Network Surrogate Models of a High-Fidelity Hydrodynamics and Water Quality Model

DOE PAGES

Shaw, Amelia R.; Sawyer, Heather Smith; LeBoeuf, Eugene J.; ...

2017-10-24

Hydropower operations optimization subject to environmental constraints is limited by challenges associated with dimensionality and spatial and temporal resolution. The need for high-fidelity hydrodynamic and water quality models within optimization schemes is driven by improved computational capabilities, increased requirements to meet specific points of compliance with greater resolution, and the need to optimize operations of not just single reservoirs but systems of reservoirs. This study describes an important advancement for computing hourly power generation schemes for a hydropower reservoir using high-fidelity models, surrogate modeling techniques, and optimization methods. The predictive power of the high-fidelity hydrodynamic and water quality model CE-QUAL-W2more » is successfully emulated by an artificial neural network, then integrated into a genetic algorithm optimization approach to maximize hydropower generation subject to constraints on dam operations and water quality. This methodology is applied to a multipurpose reservoir near Nashville, Tennessee, USA. The model successfully reproduced high-fidelity reservoir information while enabling 6.8% and 6.6% increases in hydropower production value relative to actual operations for dissolved oxygen (DO) limits of 5 and 6 mg/L, respectively, while witnessing an expected decrease in power generation at more restrictive DO constraints. Exploration of simultaneous temperature and DO constraints revealed capability to address multiple water quality constraints at specified locations. Here, the reduced computational requirements of the new modeling approach demonstrated an ability to provide decision support for reservoir operations scheduling while maintaining high-fidelity hydrodynamic and water quality information as part of the optimization decision support routines.« less

Hydropower Optimization Using Artificial Neural Network Surrogate Models of a High-Fidelity Hydrodynamics and Water Quality Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shaw, Amelia R.; Sawyer, Heather Smith; LeBoeuf, Eugene J.

Hydropower operations optimization subject to environmental constraints is limited by challenges associated with dimensionality and spatial and temporal resolution. The need for high-fidelity hydrodynamic and water quality models within optimization schemes is driven by improved computational capabilities, increased requirements to meet specific points of compliance with greater resolution, and the need to optimize operations of not just single reservoirs but systems of reservoirs. This study describes an important advancement for computing hourly power generation schemes for a hydropower reservoir using high-fidelity models, surrogate modeling techniques, and optimization methods. The predictive power of the high-fidelity hydrodynamic and water quality model CE-QUAL-W2more » is successfully emulated by an artificial neural network, then integrated into a genetic algorithm optimization approach to maximize hydropower generation subject to constraints on dam operations and water quality. This methodology is applied to a multipurpose reservoir near Nashville, Tennessee, USA. The model successfully reproduced high-fidelity reservoir information while enabling 6.8% and 6.6% increases in hydropower production value relative to actual operations for dissolved oxygen (DO) limits of 5 and 6 mg/L, respectively, while witnessing an expected decrease in power generation at more restrictive DO constraints. Exploration of simultaneous temperature and DO constraints revealed capability to address multiple water quality constraints at specified locations. Here, the reduced computational requirements of the new modeling approach demonstrated an ability to provide decision support for reservoir operations scheduling while maintaining high-fidelity hydrodynamic and water quality information as part of the optimization decision support routines.« less

High fidelity quantum gates with vibrational qubits.

PubMed

Berrios, Eduardo; Gruebele, Martin; Shyshlov, Dmytro; Wang, Lei; Babikov, Dmitri

2012-11-26

Physical implementation of quantum gates acting on qubits does not achieve a perfect fidelity of 1. The actual output qubit may not match the targeted output of the desired gate. According to theoretical estimates, intrinsic gate fidelities >99.99% are necessary so that error correction codes can be used to achieve perfect fidelity. Here we test what fidelity can be accomplished for a CNOT gate executed by a shaped ultrafast laser pulse interacting with vibrational states of the molecule SCCl(2). This molecule has been used as a test system for low-fidelity calculations before. To make our test more stringent, we include vibrational levels that do not encode the desired qubits but are close enough in energy to interfere with population transfer by the laser pulse. We use two complementary approaches: optimal control theory determines what the best possible pulse can do; a more constrained physical model calculates what an experiment likely can do. Optimal control theory finds pulses with fidelity >0.9999, in excess of the quantum error correction threshold with 8 × 10(4) iterations. On the other hand, the physical model achieves only 0.9992 after 8 × 10(4) iterations. Both calculations converge as an inverse power law toward unit fidelity after >10(2) iterations/generations. In principle, the fidelities necessary for quantum error correction are reachable with qubits encoded by molecular vibrations. In practice, it will be challenging with current laboratory instrumentation because of slow convergence past fidelities of 0.99.

Rubber friction and tire dynamics.

PubMed

Persson, B N J

2011-01-12

We propose a simple rubber friction law, which can be used, for example, in models of tire (and vehicle) dynamics. The friction law is tested by comparing numerical results to the full rubber friction theory (Persson 2006 J. Phys.: Condens. Matter 18 7789). Good agreement is found between the two theories. We describe a two-dimensional (2D) tire model which combines the rubber friction model with a simple mass-spring description of the tire body. The tire model is very flexible and can be used to accurately calculate μ-slip curves (and the self-aligning torque) for braking and cornering or combined motion (e.g. braking during cornering). We present numerical results which illustrate the theory. Simulations of anti-blocking system (ABS) braking are performed using two simple control algorithms.

Stick-slip friction and ageing in Velcro®

NASA Astrophysics Data System (ADS)

Mariani, Lisa; Angiolillo, Paul

2014-03-01

The mesoscopic hook and loop system of Velcro® provides a model of stick-slip friction that exhibits behavior reminiscent of results seen in nanoscale model systems. The friction is linearly dependent on contact area and independent of driving velocity. Morever, there is a power law dependence of the friction on loading, with exponent between 1/4 and 1/3. Furthermore, the evolution of stick-slip to more smooth sliding, as controlled by contact area, is also noted. These transition predictions follow power law profiles, as well, with respect to increasing contact area. Thus, the hook-and-loop system shows to be a good mesoscale model system of stick-slip friction and provides a link between nanoscale and macroscale friction. Through an investigation into the ageing of the hooks in the system, the data suggests that the hooks age during the shearing regime and take a characteristic time to return to initial attachment strength. Additionally, there does not appear to be a significant affect of ageing on the kinetic friction experienced by the system.

Research on the Mechanism of In-Plane Vibration on Friction Reduction

PubMed Central

Wang, Peng; Ni, Hongjian; Wang, Ruihe; Liu, Weili; Lu, Shuangfang

2017-01-01

A modified model for predicting the friction force between drill-string and borehole wall under in-plane vibrations was developed. It was found that the frictional coefficient in sliding direction decreased significantly after applying in-plane vibration on the bottom specimen. The friction reduction is due to the direction change of friction force, elastic deformation of surface asperities and the change of frictional coefficient. Normal load, surface topography, vibration direction, velocity ratio and interfacial shear factor are the main influence factors of friction force in sliding direction. Lower driving force can be realized for a pair of determinate rubbing surfaces under constant normal load by setting the driving direction along the minimum arithmetic average attack angle direction, and applying intense longitudinal vibration on the rubbing pair. The modified model can significantly improve the accuracy in predicting frictional coefficient under vibrating conditions, especially under the condition of lower velocity ratio. The results provide a theoretical gist for friction reduction technology by vibrating drill-string, and provide a reference for determination of frictional coefficient during petroleum drilling process, which has great significance for realizing digitized and intelligent drilling. PMID:28862679

Testing the Predictive Capability of the High-Fidelity Generalized Method of Cells Using an Efficient Reformulation

NASA Technical Reports Server (NTRS)

Arnold, Steven M. (Technical Monitor); Bansal, Yogesh; Pindera, Marek-Jerzy

2004-01-01

The High-Fidelity Generalized Method of Cells is a new micromechanics model for unidirectionally reinforced periodic multiphase materials that was developed to overcome the original model's shortcomings. The high-fidelity version predicts the local stress and strain fields with dramatically greater accuracy relative to the original model through the use of a better displacement field representation. Herein, we test the high-fidelity model's predictive capability in estimating the elastic moduli of periodic composites characterized by repeating unit cells obtained by rotation of an infinite square fiber array through an angle about the fiber axis. Such repeating unit cells may contain a few or many fibers, depending on the rotation angle. In order to analyze such multi-inclusion repeating unit cells efficiently, the high-fidelity micromechanics model's framework is reformulated using the local/global stiffness matrix approach. The excellent agreement with the corresponding results obtained from the standard transformation equations confirms the new model's predictive capability for periodic composites characterized by multi-inclusion repeating unit cells lacking planes of material symmetry. Comparison of the effective moduli and local stress fields with the corresponding results obtained from the original Generalized Method of Cells dramatically highlights the original model's shortcomings for certain classes of unidirectional composites.

Poroelasticity-driven lubrication in hydrogel interfaces.

PubMed

Reale, Erik R; Dunn, Alison C

2017-01-04

It is widely accepted that hydrogel surfaces are slippery, and have low friction, but dynamic applied stresses alter the hydrogel composition at the interface as water is displaced. The induced osmotic imbalance of compressed hydrogel which cannot swell to equilibrium should drive the resistance to slip against it. This paper demonstrates the driving role of poroelasticity in the friction of hydrogel-glass interfaces, specifically how poroelastic relaxation of hydrogels increases adhesion. We translate the work of adhesion into an effective surface energy density that increases with the duration of applied pressure from 10 to 50 mJ m -2 , as measured by micro-indentation. A model of static friction coefficient is derived from an area-based rules of mixture for the surface energies, and predicts the friction coefficient changes upon initiation of slip. For kinetic friction, the competition between duration of contact and relaxation time is quantified by a contacting Péclet number, Pe C . A single length parameter on the scale of micrometers fits these two models to experimental micro-friction data. These models predict how short durations of applied pressure and faster sliding speeds, do not disrupt interfacial hydration; this prevailing water maintains low friction. At low speeds where interface drainage dominates, the osmotic suction works against slip for higher friction. The prediction of friction coefficients after adhesion characterization by micro-indentation makes use of the interplay between poroelasticity, adhesion, and friction. This approach provides a starting point for prediction of, and design for, hydrogel interfacial friction.

Including Memory Friction in Single- and Two-State Quantum Dynamics Simulations.

PubMed

Brown, Paul A; Messina, Michael

2016-03-03

We present a simple computational algorithm that allows for the inclusion of memory friction in a quantum dynamics simulation of a small, quantum, primary system coupled to many atoms in the surroundings. We show how including a memory friction operator, F̂, in the primary quantum system's Hamiltonian operator builds memory friction into the dynamics of the primary quantum system. We show that, in the harmonic, semi-classical limit, this friction operator causes the classical phase-space centers of a wavepacket to evolve exactly as if it were a classical particle experiencing memory friction. We also show that this friction operator can be used to include memory friction in the quantum dynamics of an anharmonic primary system. We then generalize the algorithm so that it can be used to treat a primary quantum system that is evolving, non-adiabatically on two coupled potential energy surfaces, i.e., a model that can be used to model H atom transfer, for example. We demonstrate this approach's computational ease and flexibility by showing numerical results for both harmonic and anharmonic primary quantum systems in the single surface case. Finally, we present numerical results for a model of non-adiabatic H atom transfer between a reactant and product state that includes memory friction on one or both of the non-adiabatic potential energy surfaces and uncover some interesting dynamical effects of non-memory friction on the H atom transfer process.

Exploring the role of internal friction in the dynamics of unfolded proteins using simple polymer models.

PubMed

Cheng, Ryan R; Hawk, Alexander T; Makarov, Dmitrii E

2013-02-21

Recent experiments showed that the reconfiguration dynamics of unfolded proteins are often adequately described by simple polymer models. In particular, the Rouse model with internal friction (RIF) captures internal friction effects as observed in single-molecule fluorescence correlation spectroscopy (FCS) studies of a number of proteins. Here we use RIF, and its non-free draining analog, Zimm model with internal friction, to explore the effect of internal friction on the rate with which intramolecular contacts can be formed within the unfolded chain. Unlike the reconfiguration times inferred from FCS experiments, which depend linearly on the solvent viscosity, the first passage times to form intramolecular contacts are shown to display a more complex viscosity dependence. We further describe scaling relationships obeyed by contact formation times in the limits of high and low internal friction. Our findings provide experimentally testable predictions that can serve as a framework for the analysis of future studies of contact formation in proteins.

A viscoelastic damage rheology and rate- and state-dependent friction

NASA Astrophysics Data System (ADS)

Lyakhovsky, Vladimir; Ben-Zion, Yehuda; Agnon, Amotz

2005-04-01

We analyse the relations between a viscoelastic damage rheology model and rate- and state-dependent (RS) friction. Both frameworks describe brittle deformation, although the former models localization zones in a deforming volume while the latter is associated with sliding on existing surfaces. The viscoelastic damage model accounts for evolving elastic properties and inelastic strain. The evolving elastic properties are related quantitatively to a damage state variable representing the local density of microcracks. Positive and negative changes of the damage variable lead, respectively, to degradation and recovery of the material in response to loading. A model configuration having an existing narrow zone with localized damage produces for appropriate loading and temperature-pressure conditions an overall cyclic stick-slip motion compatible with a frictional response. Each deformation cycle (limit cycle) can be divided into healing and weakening periods associated with decreasing and increasing damage, respectively. The direct effect of the RS friction and the magnitude of the frictional parameter a are related to material strengthening with increasing rate of loading. The strength and residence time of asperities (model elements) in the weakening stage depend on the rates of damage evolution and accumulation of irreversible strain. The evolutionary effect of the RS friction and overall change in the friction parameters (a-b) are controlled by the duration of the healing period and asperity (element) strengthening during this stage. For a model with spatially variable properties, the damage rheology reproduces the logarithmic dependency of the steady-state friction coefficient on the sliding velocity and the normal stress. The transition from a velocity strengthening regime to a velocity weakening one can be obtained by varying the rate of inelastic strain accumulation and keeping the other damage rheology parameters fixed. The developments unify previous damage rheology results on deformation localization leading to formation of new fault zones with detailed experimental results on frictional sliding. The results provide a route for extending the formulation of RS friction into a non-linear continuum mechanics framework.

Orbit Stability of OSIRIS-REx in the Vicinity of Bennu Using a High-Fidelity Solar Radiation Model

NASA Technical Reports Server (NTRS)

Williams, Trevor; Hughes, Kyle; Mashiku, Alinda; Longuski, James

2015-01-01

The OSIRIS-REx mission (Origins Spectral Interpretation Resource Identification Security Regolith EXPlorer) is an asteroid sample return mission to Bennu (RQ36) that is scheduled to launch in 2016. The planned science operations precluding the small retrieval involve operations in terminator orbits (orbit plane is perpendicular to the sun). Over longer durations the solar radiation pressure (SRP) perturbs the orbit causing it to precess. Our work involves: modeling high fidelity SRP model to capture the perturbations during attitude changes; design a stable orbit from the high fidelity models to analyze the stability over time.

Dynamic rupture modeling with laboratory-derived constitutive relations

USGS Publications Warehouse

Okubo, P.G.

1989-01-01

A laboratory-derived state variable friction constitutive relation is used in the numerical simulation of the dynamic growth of an in-plane or mode II shear crack. According to this formulation, originally presented by J.H. Dieterich, frictional resistance varies with the logarithm of the slip rate and with the logarithm of the frictional state variable as identified by A.L. Ruina. Under conditions of steady sliding, the state variable is proportional to (slip rate)-1. Following suddenly introduced increases in slip rate, the rate and state dependencies combine to produce behavior which resembles slip weakening. When rupture nucleation is artificially forced at fixed rupture velocity, rupture models calculated with the state variable friction in a uniformly distributed initial stress field closely resemble earlier rupture models calculated with a slip weakening fault constitutive relation. Model calculations suggest that dynamic rupture following a state variable friction relation is similar to that following a simpler fault slip weakening law. However, when modeling the full cycle of fault motions, rate-dependent frictional responses included in the state variable formulation are important at low slip rates associated with rupture nucleation. -from Author

Nonlinear friction dynamics on polymer surface under accelerated movement

NASA Astrophysics Data System (ADS)

Aita, Yuuki; Asanuma, Natsumi; Takahashi, Akira; Mayama, Hiroyuki; Nonomura, Yoshimune

2017-04-01

Nonlinear phenomena on the soft material surface are one of the most exciting topics of chemical physics. However, only a few reports exist on the friction phenomena under accelerated movement, because friction between two solid surfaces is considered a linear phenomenon in many cases. We aim to investigate how nonlinear accelerated motion affects friction on solid surfaces. In the present study, we evaluate the frictional forces between two polytetrafluoroethylene (PTFE) resins using an advanced friction evaluation system. On PTFE surfaces, the normalized delay time δ, which is the time lag in the response of the friction force to the accelerated movement, is observed in the pre-sliding friction process. Under high-velocity conditions, kinetic friction increases with velocity. Based on these experimental results, we propose a two-phase nonlinear model including a pre-sliding process (from the beginning of sliding of a contact probe to the establishment of static friction) and a kinetic friction process. The present model consists of several factors including velocity, acceleration, stiffness, viscosity, and vertical force. The findings reflecting the viscoelastic properties of soft material is useful for various fields such as in the fabrication of clothes, cosmetics, automotive materials, and virtual reality systems as well as for understanding friction phenomena on soft material surfaces.

The importance of correct specification of tribological parameters in dynamical systems modelling

NASA Astrophysics Data System (ADS)

Alaci, S.; Ciornei, F. C.; Romanu, I. C.; Ciornei, M. C.

2018-01-01

When modelling the behaviour of dynamical systems, the friction phenomenon cannot be neglected. Dry and fluid friction may occur, but dry friction has more severe effects upon the behaviour of the systems, based on the fact that the introduced discontinuities are more important. In the modelling of dynamical systems, dry friction is the main cause of occurrence of the bifurcation phenomenon. These aspects become more complex if, in the case of dry friction, static and dynamic frictions are put forward. The behaviour of a simple dynamical system is studied, consisting in a prismatic body linked to the ground by a spring, placed on a conveyor belt. The theoretical model is described by a nonlinear differential equation which after numerical integration leads to the conclusion that the steady motion of the prism is an un-damped oscillatory motion. The system was qualitatively modelled using specialised software for dynamical analysis. It was impractical to obtain a steady uniform translational motion of a rigid, therefore the conveyor belt was replaced by a metallic disc in uniform rotation motion. The attempts to compare the CAD model to the theoretical model were unsuccessful because the efforts of selecting the tribological parameters directed to the conclusion that the motion of the prism is a damped oscillation. To decide which of the methods depicts reality, a test-rig was assembled and it indicated a sustained oscillation. The conclusion is that the model employed by the dynamical analysis software cannot describe the actual model and a more complex model is required in the description of the friction phenomenon.

High-Fidelity Simulations of Electromagnetic Propagation and RF Communication Systems

DTIC Science & Technology

2017-05-01

addition to high -fidelity RF propagation modeling, lower-fidelity mod- els, which are less computationally burdensome, are available via a C++ API...expensive to perform, requiring roughly one hour of computer time with 36 available cores and ray tracing per- formed by a single high -end GPU...ER D C TR -1 7- 2 Military Engineering Applied Research High -Fidelity Simulations of Electromagnetic Propagation and RF Communication

DDDAMS-based Urban Surveillance and Crowd Control via UAVs and UGVs

DTIC Science & Technology

2015-12-04

for crowd dynamics modeling by incorporating multi-resolution data, where a grid-based method is used to model crowd motion with UAVs’ low -resolution...information and more computational intensive (and time-consuming). Given that the deployment of fidelity selection results in simulation faces computational... low fidelity information FOV y (A) DR x (A) DR y (A) Not detected high fidelity information Table 1: Parameters for UAV and UGV for their detection

Elastic-plastic cube model for ultrasonic friction reduction via Poisson's effect.

PubMed

Dong, Sheng; Dapino, Marcelo J

2014-01-01

Ultrasonic friction reduction has been studied experimentally and theoretically. This paper presents a new elastic-plastic cube model which can be applied to various ultrasonic lubrication cases. A cube is used to represent all the contacting asperities of two surfaces. Friction force is considered as the product of the tangential contact stiffness and the deformation of the cube. Ultrasonic vibrations are projected onto three orthogonal directions, separately changing contact parameters and deformations. Hence, the overall change of friction forces. Experiments are conducted to examine ultrasonic friction reduction using different materials under normal loads that vary from 40 N to 240 N. Ultrasonic vibrations are generated both in longitudinal and vertical (out-of-plane) directions by way of the Poisson effect. The tests show up to 60% friction reduction; model simulations describe the trends observed experimentally. Copyright © 2013 Elsevier B.V. All rights reserved.

A study on model fidelity for model predictive control-based obstacle avoidance in high-speed autonomous ground vehicles

NASA Astrophysics Data System (ADS)

Liu, Jiechao; Jayakumar, Paramsothy; Stein, Jeffrey L.; Ersal, Tulga

2016-11-01

This paper investigates the level of model fidelity needed in order for a model predictive control (MPC)-based obstacle avoidance algorithm to be able to safely and quickly avoid obstacles even when the vehicle is close to its dynamic limits. The context of this work is large autonomous ground vehicles that manoeuvre at high speed within unknown, unstructured, flat environments and have significant vehicle dynamics-related constraints. Five different representations of vehicle dynamics models are considered: four variations of the two degrees-of-freedom (DoF) representation as lower fidelity models and a fourteen DoF representation with combined-slip Magic Formula tyre model as a higher fidelity model. It is concluded that the two DoF representation that accounts for tyre nonlinearities and longitudinal load transfer is necessary for the MPC-based obstacle avoidance algorithm in order to operate the vehicle at its limits within an environment that includes large obstacles. For less challenging environments, however, the two DoF representation with linear tyre model and constant axle loads is sufficient.

On the role of surface friction in tropical cyclone intensification

NASA Astrophysics Data System (ADS)

Wang, Yuqing

2017-04-01

Recent studies have debated on whether surface friction is positive or negative to tropical cyclone intensification in the view on angular momentum budget. That means whether the frictionally induced inward angular momentum transport can overcome the loss of angular momentum to the surface due to surface friction itself. Although this issue is still under debate, this study investigates another implicit dynamical effect, which modifies the radial location and strength of eyewall convection. We found that moderate surface friction is necessary for rapid intensity of tropical cyclones. This is demonstrated first by a simple coupled dynamical system that couples a multi-level boundary layer model and a shallow water equation model above with mass source parameterized by mass flux from the boundary layer model below, and then by a full physics model. The results show that surface friction leads to the inward penetration of inflow under the eyewall, shift the boundary layer mass convergence slightly inside the radius of maximum wind, and enhance the upward mass flux, and thus diabatic heating in the eyewall and intensification rate of a TC. This intensification process is different from the direct angular momentum budget previously used to explain the role of surface friction in tropical cyclone intensification.

Analytical and numerical analysis of frictional damage in quasi brittle materials

NASA Astrophysics Data System (ADS)

Zhu, Q. Z.; Zhao, L. Y.; Shao, J. F.

2016-07-01

Frictional sliding and crack growth are two main dissipation processes in quasi brittle materials. The frictional sliding along closed cracks is the origin of macroscopic plastic deformation while the crack growth induces a material damage. The main difficulty of modeling is to consider the inherent coupling between these two processes. Various models and associated numerical algorithms have been proposed. But there are so far no analytical solutions even for simple loading paths for the validation of such algorithms. In this paper, we first present a micro-mechanical model taking into account the damage-friction coupling for a large class of quasi brittle materials. The model is formulated by combining a linear homogenization procedure with the Mori-Tanaka scheme and the irreversible thermodynamics framework. As an original contribution, a series of analytical solutions of stress-strain relations are developed for various loading paths. Based on the micro-mechanical model, two numerical integration algorithms are exploited. The first one involves a coupled friction/damage correction scheme, which is consistent with the coupling nature of the constitutive model. The second one contains a friction/damage decoupling scheme with two consecutive steps: the friction correction followed by the damage correction. With the analytical solutions as reference results, the two algorithms are assessed through a series of numerical tests. It is found that the decoupling correction scheme is efficient to guarantee a systematic numerical convergence.

Modeling and simulation of dynamics of a planar-motion rigid body with friction and surface contact

NASA Astrophysics Data System (ADS)

Wang, Xiaojun; Lv, Jing

2017-07-01

The modeling and numerical method for the dynamics of a planar-motion rigid body with frictional contact between plane surfaces were presented based on the theory of contact mechanics and the algorithm of linear complementarity problem (LCP). The Coulomb’s dry friction model is adopted as the friction law, and the normal contact forces are expressed as functions of the local deformations and their speeds in contact bodies. The dynamic equations of the rigid body are obtained by the Lagrange equation. The transition problem of stick-slip motions between contact surfaces is formulated and solved as LCP through establishing the complementary conditions of the friction law. Finally, a numerical example is presented as an example to show the application.

Simulations of a Vibrissa Slipping along a Straight Edge and an Analysis of Frictional Effects during Whisking

PubMed Central

Huet, Lucie A.; Hartmann, Mitra J.Z.

2017-01-01

During tactile exploration, rats sweep their whiskers against objects in a motion called whisking. Here we investigate how a whisker slips along an object’s edge and how friction affects the resulting tactile signals. First, a frictionless model is developed to simulate whisker slip along a straight edge and compared with a previous model that incorporates friction but cannot simulate slip. Results of both models are compared to behavioral data obtained as a rat whisked against a smooth, stainless steel peg. As expected, the frictionless model predicts larger magnitudes of vertical slip than observed experimentally. The frictionless model also predicts forces and moments at the whisker base that are smaller and have a different direction than those predicted by the model with friction. Estimates for the friction coefficient yielded values near 0.48 (whisker/stainless steel). The present work provides the first assessments of the effects of friction on the mechanical signals received by the follicle during active whisking. It also demonstrates a proof-of-principle approach for reducing whisker tracking requirements during experiments and demonstrates the feasibility of simulating a full array of vibrissae whisking against a peg. PMID:26829805

Investigating the feasibility of integrating pavement friction and texture depth data in modeling for INDOT PMS.

DOT National Transportation Integrated Search

2012-11-01

Under INDOTs current friction testing program, the friction is measured annually on interstates but only once every three years on noninterstate : roadways. The states Pavement Management System, however, would require current data if friction ...

Physiological Based Simulator Fidelity Design Guidance

NASA Technical Reports Server (NTRS)

Schnell, Thomas; Hamel, Nancy; Postnikov, Alex; Hoke, Jaclyn; McLean, Angus L. M. Thom, III

2012-01-01

The evolution of the role of flight simulation has reinforced assumptions in aviation that the degree of realism in a simulation system directly correlates to the training benefit, i.e., more fidelity is always better. The construct of fidelity has several dimensions, including physical fidelity, functional fidelity, and cognitive fidelity. Interaction of different fidelity dimensions has an impact on trainee immersion, presence, and transfer of training. This paper discusses research results of a recent study that investigated if physiological-based methods could be used to determine the required level of simulator fidelity. Pilots performed a relatively complex flight task consisting of mission task elements of various levels of difficulty in a fixed base flight simulator and a real fighter jet trainer aircraft. Flight runs were performed using one forward visual channel of 40 deg. field of view for the lowest level of fidelity, 120 deg. field of view for the middle level of fidelity, and unrestricted field of view and full dynamic acceleration in the real airplane. Neuro-cognitive and physiological measures were collected under these conditions using the Cognitive Avionics Tool Set (CATS) and nonlinear closed form models for workload prediction were generated based on these data for the various mission task elements. One finding of the work described herein is that simple heart rate is a relatively good predictor of cognitive workload, even for short tasks with dynamic changes in cognitive loading. Additionally, we found that models that used a wide range of physiological and neuro-cognitive measures can further boost the accuracy of the workload prediction.

Investigating variations in implementation fidelity of an organizational-level occupational health intervention.

PubMed

Augustsson, Hanna; von Thiele Schwarz, Ulrica; Stenfors-Hayes, Terese; Hasson, Henna

2015-06-01

The workplace has been suggested as an important arena for health promotion, but little is known about how the organizational setting influences the implementation of interventions. The aims of this study are to evaluate implementation fidelity in an organizational-level occupational health intervention and to investigate possible explanations for variations in fidelity between intervention units. The intervention consisted of an integration of health promotion, occupational health and safety, and a system for continuous improvements (Kaizen) and was conducted in a quasi-experimental design at a Swedish hospital. Implementation fidelity was evaluated with the Conceptual Framework for Implementation Fidelity and implementation factors used to investigate variations in fidelity with the Framework for Evaluating Organizational-level Interventions. A multi-method approach including interviews, Kaizen notes, and questionnaires was applied. Implementation fidelity differed between units even though the intervention was introduced and supported in the same way. Important differences in all elements proposed in the model for evaluating organizational-level interventions, i.e., context, intervention, and mental models, were found to explain the differences in fidelity. Implementation strategies may need to be adapted depending on the local context. Implementation fidelity, as well as pre-intervention implementation elements, is likely to affect the implementation success and needs to be assessed in intervention research. The high variation in fidelity across the units indicates the need for adjustments to the type of designs used to assess the effects of interventions. Thus, rather than using designs that aim to control variation, it may be necessary to use those that aim at exploring and explaining variation, such as adapted study designs.

Modeling movement and fidelity of American black ducks

USGS Publications Warehouse

Zimpfer, N.L.; Conroy, M.J.

2006-01-01

Spatial relationships among stocks of breeding waterfowl can be an important component of harvest management. Prediction and optimal harvest management under adaptive harvest management (AHM) requires information on the spatial relationships among breeding populations (fidelity and inter-year exchange), as well as rates of movements from breeding to harvest regions. We used band-recovery data to develop a model to estimate probabilities of movement for American black ducks (Anas rubripes) among 3 Canadian breeding strata and 6 harvest regions (3 in Canada, and 3 in the United States) over the period 1965-1998. Model selection criteria suggested that models containing area-, year-, and age-specific recovery rates with area- and sex-specific movement rates were the best for modeling movement. Movement by males to southern harvest areas was variable depending on the originating area. Males from the western breeding area predominantly moved to the Mississippi Flyway or southern Atlantic Flyway (??ij = 0.353, SE = 0.0187 and ??ij = 0.473, SE = 0.037, respectively), whereas males that originated in the eastern and central breeding strata moved to the northern Atlantic flyway (??ij = 0.842, SE = 0.010 and ??ij = 0.578, SE = 0.0222, respectively). We used combined recoveries and recaptures in Program MARK to estimate fidelity to the 3 Canadian breeding strata. Information criteria identified a model containing sex- and age-specific fidelity for black ducks. Estimates of fidelity were 0.9695 (SE = 0.0249) and 0.9554 (SE = 0.0434) for adult males and females, respectively. Estimates of fidelity for juveniles were slightly lower at 0.9210 (SE = 0.0931) and 0.8870 (SE = 0.0475) for males and females, respectively. These models have application to the development of spatially stratified black duck harvest management models for use in AHM.

Entrance and exit region friction factor models for annular seal analysis. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Elrod, David Alan

1988-01-01

The Mach number definition and boundary conditions in Nelson's nominally-centered, annular gas seal analysis are revised. A method is described for determining the wall shear stress characteristics of an annular gas seal experimentally. Two friction factor models are developed for annular seal analysis; one model is based on flat-plate flow theory; the other uses empirical entrance and exit region friction factors. The friction factor predictions of the models are compared to experimental results. Each friction model is used in an annular gas seal analysis. The seal characteristics predicted by the two seal analyses are compared to experimental results and to the predictions of Nelson's analysis. The comparisons are for smooth-rotor seals with smooth and honeycomb stators. The comparisons show that the analysis which uses empirical entrance and exit region shear stress models predicts the static and stability characteristics of annular gas seals better than the other analyses. The analyses predict direct stiffness poorly.

Gravity Modeling for Variable Fidelity Environments

NASA Technical Reports Server (NTRS)

Madden, Michael M.

2006-01-01

Aerospace simulations can model worlds, such as the Earth, with differing levels of fidelity. The simulation may represent the world as a plane, a sphere, an ellipsoid, or a high-order closed surface. The world may or may not rotate. The user may select lower fidelity models based on computational limits, a need for simplified analysis, or comparison to other data. However, the user will also wish to retain a close semblance of behavior to the real world. The effects of gravity on objects are an important component of modeling real-world behavior. Engineers generally equate the term gravity with the observed free-fall acceleration. However, free-fall acceleration is not equal to all observers. To observers on the sur-face of a rotating world, free-fall acceleration is the sum of gravitational attraction and the centrifugal acceleration due to the world's rotation. On the other hand, free-fall acceleration equals gravitational attraction to an observer in inertial space. Surface-observed simulations (e.g. aircraft), which use non-rotating world models, may choose to model observed free fall acceleration as the gravity term; such a model actually combines gravitational at-traction with centrifugal acceleration due to the Earth s rotation. However, this modeling choice invites confusion as one evolves the simulation to higher fidelity world models or adds inertial observers. Care must be taken to model gravity in concert with the world model to avoid denigrating the fidelity of modeling observed free fall. The paper will go into greater depth on gravity modeling and the physical disparities and synergies that arise when coupling specific gravity models with world models.

Epidemics in markets with trade friction and imperfect transactions.

PubMed

Moslonka-Lefebvre, Mathieu; Monod, Hervé; Gilligan, Christopher A; Vergu, Elisabeta; Filipe, João A N

2015-06-07

Market trade-routes can support infectious-disease transmission, impacting biological populations and even disrupting trade that conduces the disease. Epidemiological models increasingly account for reductions in infectious contact, such as risk-aversion behaviour in response to pathogen outbreaks. However, responses in market dynamics clearly differ from simple risk aversion, as are driven by other motivation and conditioned by "friction" constraints (a term we borrow from labour economics). Consequently, the propagation of epidemics in markets of, for example livestock, is frictional due to time and cost limitations in the production and exchange of potentially infectious goods. Here we develop a coupled economic-epidemiological model where transient and long-term market dynamics are determined by trade friction and agent adaptation, and can influence disease transmission. The market model is parameterised from datasets on French cattle and pig exchange networks. We show that, when trade is the dominant route of transmission, market friction can be a significantly stronger determinant of epidemics than risk-aversion behaviour. In particular, there is a critical level of friction above which epidemics do not occur, which suggests some epidemics may not be sustained in highly frictional markets. In addition, friction may allow for greater delay in removal of infected agents that still mitigates the epidemic and its impacts. We suggest that policy for minimising contagion in markets could be adjusted to the level of market friction, by adjusting the urgency of intervention or by increasing friction through incentivisation of larger-volume less-frequent transactions that would have limited effect on overall trade flow. Our results are robust to model specificities and can hold in the presence of non-trade disease-transmission routes. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

History-dependent friction and slow slip from time-dependent microscopic junction laws studied in a statistical framework

NASA Astrophysics Data System (ADS)

Thøgersen, Kjetil; Trømborg, Jørgen Kjoshagen; Sveinsson, Henrik Andersen; Malthe-Sørenssen, Anders; Scheibert, Julien

2014-05-01

To study how macroscopic friction phenomena originate from microscopic junction laws, we introduce a general statistical framework describing the collective behavior of a large number of individual microjunctions forming a macroscopic frictional interface. Each microjunction can switch in time between two states: a pinned state characterized by a displacement-dependent force and a slipping state characterized by a time-dependent force. Instead of tracking each microjunction individually, the state of the interface is described by two coupled distributions for (i) the stretching of pinned junctions and (ii) the time spent in the slipping state. This framework allows for a whole family of microjunction behavior laws, and we show how it represents an overarching structure for many existing models found in the friction literature. We then use this framework to pinpoint the effects of the time scale that controls the duration of the slipping state. First, we show that the model reproduces a series of friction phenomena already observed experimentally. The macroscopic steady-state friction force is velocity dependent, either monotonic (strengthening or weakening) or nonmonotonic (weakening-strengthening), depending on the microscopic behavior of individual junctions. In addition, slow slip, which has been reported in a wide variety of systems, spontaneously occurs in the model if the friction contribution from junctions in the slipping state is time weakening. Next, we show that the model predicts a nontrivial history dependence of the macroscopic static friction force. In particular, the static friction coefficient at the onset of sliding is shown to increase with increasing deceleration during the final phases of the preceding sliding event. We suggest that this form of history dependence of static friction should be investigated in experiments, and we provide the acceleration range in which this effect is expected to be experimentally observable.

History-dependent friction and slow slip from time-dependent microscopic junction laws studied in a statistical framework.

PubMed

Thøgersen, Kjetil; Trømborg, Jørgen Kjoshagen; Sveinsson, Henrik Andersen; Malthe-Sørenssen, Anders; Scheibert, Julien

2014-05-01

To study how macroscopic friction phenomena originate from microscopic junction laws, we introduce a general statistical framework describing the collective behavior of a large number of individual microjunctions forming a macroscopic frictional interface. Each microjunction can switch in time between two states: a pinned state characterized by a displacement-dependent force and a slipping state characterized by a time-dependent force. Instead of tracking each microjunction individually, the state of the interface is described by two coupled distributions for (i) the stretching of pinned junctions and (ii) the time spent in the slipping state. This framework allows for a whole family of microjunction behavior laws, and we show how it represents an overarching structure for many existing models found in the friction literature. We then use this framework to pinpoint the effects of the time scale that controls the duration of the slipping state. First, we show that the model reproduces a series of friction phenomena already observed experimentally. The macroscopic steady-state friction force is velocity dependent, either monotonic (strengthening or weakening) or nonmonotonic (weakening-strengthening), depending on the microscopic behavior of individual junctions. In addition, slow slip, which has been reported in a wide variety of systems, spontaneously occurs in the model if the friction contribution from junctions in the slipping state is time weakening. Next, we show that the model predicts a nontrivial history dependence of the macroscopic static friction force. In particular, the static friction coefficient at the onset of sliding is shown to increase with increasing deceleration during the final phases of the preceding sliding event. We suggest that this form of history dependence of static friction should be investigated in experiments, and we provide the acceleration range in which this effect is expected to be experimentally observable.

Friction Reduction through Ultrasonic Vibration Part 1: Modelling Intermittent Contact.

PubMed

Vezzoli, Eric; Vidrih, Zlatko; Giamundo, Vincenzo; Lemaire-Semail, Betty; Giraud, Frederic; Rodic, Tomaz; Peric, Djordje; Adams, Michael

2017-01-01

Ultrasonic vibration is employed to modify the friction of a finger pad in way that induces haptic sensations. A combination of intermittent contact and squeeze film levitation has been previously proposed as the most probable mechanism. In this paper, in order to understand the underlying principles that govern friction modulation by intermittent contact, numerical models based on finite element (FE) analysis and also a spring-Coulombic slider are developed. The physical input parameters for the FE model are optimized by measuring the contact phase shift between a finger pad and a vibrating plate. The spring-slider model assists in the interpretation of the FE model and leads to the identification of a dimensionless group that allows the calculated coefficient of friction to be approximately superimposed onto an exponential function of the dimensionless group. Thus, it is possible to rationalize the computed relative reduction in friction being (i) dependent on the vibrational amplitude, frequency, and the intrinsic coefficient of friction of the device, and the reciprocal of the exploration velocity, and (ii) independent of the applied normal force, and the shear and extensional elastic moduli of the finger skin provided that intermittent contact is sufficiently well developed. Experimental validation of the modelling using real and artificial fingertips will be reported in part 2 of this work, which supports the current modelling.

Analysis of dry friction damping characteristics for short cylindrical shell structures

NASA Astrophysics Data System (ADS)

Wang, Nengmao; Wang, Yanrong

2018-05-01

An efficient mathematical model to describe the friction of short cylindrical shell structures with a dry friction damping sleeve is proposed. The frictional force in the circumference and axial direction is caused by the opposing bending strains at the interface. Slipping will occur at part region of the interface and the mathematic model of the slipping region is established. Ignoring the effect of contact stiffness on the vibration analysis, the friction energy dissipation capability of damping sleeve would be calculated. Structural vibration mode, positive pressure at the interface and vibration stress of the short cylindrical shell structures is analyzed as influence factors to the critical damping ratio. The results show that the circumferential friction energy dissipation is more sensitive to the number of nodal diameter, and the circumferential friction damping ratio increases rapidly with the number of nodal diameter. The slipping frictional force would increase along with the positive pressure, but the slipping region would decrease with it. The peak damping ratio keeps nearly constant. But the vibration stress corresponding to peak damping ratio would increases with the positive pressure. The dry friction damping ratio of damping sleeve contains the effect of frictional force in the circumference and axial direction, and the axial friction plays a major role.

The Fringe-Imaging Skin Friction Technique PC Application User's Manual

NASA Technical Reports Server (NTRS)

Zilliac, Gregory G.

1999-01-01

A personal computer application (CXWIN4G) has been written which greatly simplifies the task of extracting skin friction measurements from interferograms of oil flows on the surface of wind tunnel models. Images are first calibrated, using a novel approach to one-camera photogrammetry, to obtain accurate spatial information on surfaces with curvature. As part of the image calibration process, an auxiliary file containing the wind tunnel model geometry is used in conjunction with a two-dimensional direct linear transformation to relate the image plane to the physical (model) coordinates. The application then applies a nonlinear regression model to accurately determine the fringe spacing from interferometric intensity records as required by the Fringe Imaging Skin Friction (FISF) technique. The skin friction is found through application of a simple expression that makes use of lubrication theory to relate fringe spacing to skin friction.

Investigating students' mental models and knowledge construction of microscopic friction. II. Implications for curriculum design and development

NASA Astrophysics Data System (ADS)

Corpuz, Edgar D.; Rebello, N. Sanjay

2011-12-01

Our previous research showed that students’ mental models of friction at the atomic level are significantly influenced by their macroscopic ideas. For most students, friction is due to the meshing of bumps and valleys and rubbing of atoms. The aforementioned results motivated us to further investigate how students can be helped to improve their present models of microscopic friction. Teaching interviews were conducted to study the dynamics of their model construction as they interacted with the interviewer, the scaffolding activities, and/or with each other. In this paper, we present the different scaffolding activities and the variation in the ideas that students generated as they did the hands-on and minds-on scaffolding activities. Results imply that through a series of carefully designed scaffolding activities, it is possible to facilitate the refinement of students’ ideas of microscopic friction.

Tyre-road friction coefficient estimation based on tyre sensors and lateral tyre deflection: modelling, simulations and experiments

NASA Astrophysics Data System (ADS)

Hong, Sanghyun; Erdogan, Gurkan; Hedrick, Karl; Borrelli, Francesco

2013-05-01

The estimation of the tyre-road friction coefficient is fundamental for vehicle control systems. Tyre sensors enable the friction coefficient estimation based on signals extracted directly from tyres. This paper presents a tyre-road friction coefficient estimation algorithm based on tyre lateral deflection obtained from lateral acceleration. The lateral acceleration is measured by wireless three-dimensional accelerometers embedded inside the tyres. The proposed algorithm first determines the contact patch using a radial acceleration profile. Then, the portion of the lateral acceleration profile, only inside the tyre-road contact patch, is used to estimate the friction coefficient through a tyre brush model and a simple tyre model. The proposed strategy accounts for orientation-variation of accelerometer body frame during tyre rotation. The effectiveness and performance of the algorithm are demonstrated through finite element model simulations and experimental tests with small tyre slip angles on different road surface conditions.

Rheological effects on friction in elastohydrodynamic lubrication

NASA Technical Reports Server (NTRS)

Trachman, E. G.; Cheng, H. S.

1973-01-01

An analytical and experimental investigation is presented of the friction in a rolling and sliding elastohydrodynamic lubricated contact. The rheological behavior of the lubricant is described in terms of two viscoelastic models. These models represent the separate effects of non-Newtonian behavior and the transient response of the fluid. A unified description of the non-Newtonian shear rate dependence of the viscosity is presented as a new hyperbolic liquid model. The transient response of viscosity, following the rapid pressure rise encountered in the contact, is described by a compressional viscoelastic model of the volume response of a liquid to an applied pressure step. The resulting momentum and energy equations are solved by an iterative numerical technique, and a friction coefficient is calculated. The experimental study was performed, with two synthetic paraffinic lubricants, to verify the friction predictions of the analysis. The values of friction coefficient from theory and experiment are in close agreement.

A Comparative Study of High and Low Fidelity Fan Models for Turbofan Engine System Simulation

NASA Technical Reports Server (NTRS)

Reed, John A.; Afjeh, Abdollah A.

1991-01-01

In this paper, a heterogeneous propulsion system simulation method is presented. The method is based on the formulation of a cycle model of a gas turbine engine. The model includes the nonlinear characteristics of the engine components via use of empirical data. The potential to simulate the entire engine operation on a computer without the aid of data is demonstrated by numerically generating "performance maps" for a fan component using two flow models of varying fidelity. The suitability of the fan models were evaluated by comparing the computed performance with experimental data. A discussion of the potential benefits and/or difficulties in connecting simulations solutions of differing fidelity is given.

Linear complementarity formulation for 3D frictional sliding problems

USGS Publications Warehouse

Kaven, Joern; Hickman, Stephen H.; Davatzes, Nicholas C.; Mutlu, Ovunc

2012-01-01

Frictional sliding on quasi-statically deforming faults and fractures can be modeled efficiently using a linear complementarity formulation. We review the formulation in two dimensions and expand the formulation to three-dimensional problems including problems of orthotropic friction. This formulation accurately reproduces analytical solutions to static Coulomb friction sliding problems. The formulation accounts for opening displacements that can occur near regions of non-planarity even under large confining pressures. Such problems are difficult to solve owing to the coupling of relative displacements and tractions; thus, many geomechanical problems tend to neglect these effects. Simple test cases highlight the importance of including friction and allowing for opening when solving quasi-static fault mechanics models. These results also underscore the importance of considering the effects of non-planarity in modeling processes associated with crustal faulting.

Multi-fidelity machine learning models for accurate bandgap predictions of solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pilania, Ghanshyam; Gubernatis, James E.; Lookman, Turab

Here, we present a multi-fidelity co-kriging statistical learning framework that combines variable-fidelity quantum mechanical calculations of bandgaps to generate a machine-learned model that enables low-cost accurate predictions of the bandgaps at the highest fidelity level. Additionally, the adopted Gaussian process regression formulation allows us to predict the underlying uncertainties as a measure of our confidence in the predictions. In using a set of 600 elpasolite compounds as an example dataset and using semi-local and hybrid exchange correlation functionals within density functional theory as two levels of fidelities, we demonstrate the excellent learning performance of the method against actual high fidelitymore » quantum mechanical calculations of the bandgaps. The presented statistical learning method is not restricted to bandgaps or electronic structure methods and extends the utility of high throughput property predictions in a significant way.« less

Multi-fidelity machine learning models for accurate bandgap predictions of solids

DOE PAGES

Pilania, Ghanshyam; Gubernatis, James E.; Lookman, Turab

2016-12-28

Here, we present a multi-fidelity co-kriging statistical learning framework that combines variable-fidelity quantum mechanical calculations of bandgaps to generate a machine-learned model that enables low-cost accurate predictions of the bandgaps at the highest fidelity level. Additionally, the adopted Gaussian process regression formulation allows us to predict the underlying uncertainties as a measure of our confidence in the predictions. In using a set of 600 elpasolite compounds as an example dataset and using semi-local and hybrid exchange correlation functionals within density functional theory as two levels of fidelities, we demonstrate the excellent learning performance of the method against actual high fidelitymore » quantum mechanical calculations of the bandgaps. The presented statistical learning method is not restricted to bandgaps or electronic structure methods and extends the utility of high throughput property predictions in a significant way.« less

Fidelity and outcomes in six integrated dual disorders treatment programs.

PubMed

Chandler, Daniel W

2011-02-01

Fidelity scores and outcomes were measured in six outpatient programs in California which implemented Integrated Dual Disorders Treatment (IDDT). Outcomes were measured for 1 year in four sites and 2 years in two sites; fidelity was assessed at 6 month intervals. Three of the six sites achieved high fidelity (at least a 4 on a 5 point fidelity scale) and three moderate fidelity (at least a 3). Retention in treatment, mental health functioning, stage of substance abuse treatment, abstinence, and psychiatric hospitalization were measured. Outcomes for individual programs were generally positive but not consistent within programs or across programs. Using pooled data in a longitudinal regression model with random effects at person level and adjustment of standard errors for clustering by site, change over time was not statistically significant for the primary outcomes. Fidelity scores had limited association with positive outcomes.

General predictive model of friction behavior regimes for metal contacts based on the formation stability and evolution of nanocrystalline surface films.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Argibay, Nicolas; Cheng, Shengfeng; Sawyer, W. G.

2015-09-01

The prediction of macro-scale friction and wear behavior based on first principles and material properties has remained an elusive but highly desirable target for tribologists and material scientists alike. Stochastic processes (e.g. wear), statistically described parameters (e.g. surface topography) and their evolution tend to defeat attempts to establish practical general correlations between fundamental nanoscale processes and macro-scale behaviors. We present a model based on microstructural stability and evolution for the prediction of metal friction regimes, founded on recently established microstructural deformation mechanisms of nanocrystalline metals, that relies exclusively on material properties and contact stress models. We show through complementary experimentalmore » and simulation results that this model overcomes longstanding practical challenges and successfully makes accurate and consistent predictions of friction transitions for a wide range of contact conditions. This framework not only challenges the assumptions of conventional causal relationships between hardness and friction, and between friction and wear, but also suggests a pathway for the design of higher performance metal alloys.« less

Friction Compensation for Enhancing Transparency of a Teleoperator with Compliant Transmission

PubMed Central

Mahvash, Mohsen; Okamura, Allison

2009-01-01

This article presents a model-based compensator for canceling friction in the tendon-driven joints of a haptic-feedback teleoperator. Unlike position-tracking systems, a teleoperator involves an unknown environment force that prevents the use of tracking position error as a feedback to the compensator. Thus, we use a model-based feedforward friction compensator to cancel the friction forces. We provide conditions for selecting compensator parameters to ensure passivity of the teleoperator and demonstrate performance experimentally. PMID:20514151

Iliotibial band friction syndrome

PubMed Central

2010-01-01

Published articles on iliotibial band friction syndrome have been reviewed. These articles cover the epidemiology, etiology, anatomy, pathology, prevention, and treatment of the condition. This article describes (1) the various etiological models that have been proposed to explain iliotibial band friction syndrome; (2) some of the imaging methods, research studies, and clinical experiences that support or call into question these various models; (3) commonly proposed treatment methods for iliotibial band friction syndrome; and (4) the rationale behind these methods and the clinical outcome studies that support their efficacy. PMID:21063495

Development of a Numerical Model for Orthogonal Cutting. Discussion about the Sensitivity to Friction Problem

NASA Astrophysics Data System (ADS)

San Juan, M.; de la Iglesia, J. M.; Martín, O.; Santos, F. J.

2009-11-01

In despite of the important progresses achieved in the knowledge of cutting processes, the study of certain aspects has undergone the very limitations of the experimental means: temperature gradients, frictions, contact, etc… Therefore, the development of numerical models is a valid tool as a first approach to study of those problems. In the present work, a calculation model under Abaqus Explicit code is developed to represent the orthogonal cutting of AISI 4140 steel. A bidimensional simulation under plane strain conditions, which is considered as adiabatic due to the high speed of the material flow, is chosen. The chip separation is defined by means of a fracture law that allows complex simulations of tool penetration in the workpiece. The strong influence of friction on cutting is proved, therefore a very good definition of materials behaviour laws could be obtained, but an erroneous value of friction coefficient could notably reduce the reliability. Considering the difficulty of checking the friction models used in the simulation, from the tests carried out habitually, the most efficacious way to characterize the friction would be to combine simulation models with cutting tests.

Description of new dry granular materials of variable cohesion and friction coefficient: Implications for laboratory modeling of the brittle crust

NASA Astrophysics Data System (ADS)

Abdelmalak, M. M.; Bulois, C.; Mourgues, R.; Galland, O.; Legland, J.-B.; Gruber, C.

2016-08-01

Cohesion and friction coefficient are fundamental parameters for scaling brittle deformation in laboratory models of geological processes. However, they are commonly not experimental variable, whereas (1) rocks range from cohesion-less to strongly cohesive and from low friction to high friction and (2) strata exhibit substantial cohesion and friction contrasts. This brittle paradox implies that the effects of brittle properties on processes involving brittle deformation cannot be tested in laboratory models. Solving this paradox requires the use of dry granular materials of tunable and controllable brittle properties. In this paper, we describe dry mixtures of fine-grained cohesive, high friction silica powder (SP) and low-cohesion, low friction glass microspheres (GM) that fulfill this requirement. We systematically estimated the cohesions and friction coefficients of mixtures of variable proportions using two independent methods: (1) a classic Hubbert-type shear box to determine the extrapolated cohesion (C) and friction coefficient (μ), and (2) direct measurements of the tensile strength (T0) and the height (H) of open fractures to calculate the true cohesion (C0). The measured values of cohesion increase from 100 Pa for pure GM to 600 Pa for pure SP, with a sub-linear trend of the cohesion with the mixture GM content. The two independent cohesion measurement methods, from shear tests and tension/extensional tests, yield very similar results of extrapolated cohesion (C) and show that both are robust and can be used independently. The measured values of friction coefficients increase from 0.5 for pure GM to 1.05 for pure SP. The use of these granular material mixtures now allows testing (1) the effects of cohesion and friction coefficient in homogeneous laboratory models and (2) testing the effect of brittle layering on brittle deformation, as demonstrated by preliminary experiments. Therefore, the brittle properties become, at last, experimental variables.

Multifunctional Collaborative Modeling and Analysis Methods in Engineering Science

NASA Technical Reports Server (NTRS)

Ransom, Jonathan B.; Broduer, Steve (Technical Monitor)

2001-01-01

Engineers are challenged to produce better designs in less time and for less cost. Hence, to investigate novel and revolutionary design concepts, accurate, high-fidelity results must be assimilated rapidly into the design, analysis, and simulation process. This assimilation should consider diverse mathematical modeling and multi-discipline interactions necessitated by concepts exploiting advanced materials and structures. Integrated high-fidelity methods with diverse engineering applications provide the enabling technologies to assimilate these high-fidelity, multi-disciplinary results rapidly at an early stage in the design. These integrated methods must be multifunctional, collaborative, and applicable to the general field of engineering science and mechanics. Multifunctional methodologies and analysis procedures are formulated for interfacing diverse subdomain idealizations including multi-fidelity modeling methods and multi-discipline analysis methods. These methods, based on the method of weighted residuals, ensure accurate compatibility of primary and secondary variables across the subdomain interfaces. Methods are developed using diverse mathematical modeling (i.e., finite difference and finite element methods) and multi-fidelity modeling among the subdomains. Several benchmark scalar-field and vector-field problems in engineering science are presented with extensions to multidisciplinary problems. Results for all problems presented are in overall good agreement with the exact analytical solution or the reference numerical solution. Based on the results, the integrated modeling approach using the finite element method for multi-fidelity discretization among the subdomains is identified as most robust. The multiple-method approach is advantageous when interfacing diverse disciplines in which each of the method's strengths are utilized. The multifunctional methodology presented provides an effective mechanism by which domains with diverse idealizations are interfaced. This capability rapidly provides the high-fidelity results needed in the early design phase. Moreover, the capability is applicable to the general field of engineering science and mechanics. Hence, it provides a collaborative capability that accounts for interactions among engineering analysis methods.

The tribology of rosin

NASA Astrophysics Data System (ADS)

Smith, J. H.; Woodhouse, J.

2000-08-01

Rosin is well known for its ability to excite stick-slip vibration on a violin string but the precise characteristics of the material which enable it to exhibit this behaviour have not been studied in any detail. A method is described in which the coefficient of friction of rosin is measured during individual cycles of a stick-slip vibration. Friction versus sliding velocity characteristics deduced in this way exhibit hysteresis, similar to that found in other investigations using different materials. No part of the hysteresis loops follow the friction/velocity curve found from steady-sliding experiments. Possible constitutive laws are examined to describe this frictional behaviour. It is suggested by a variety of evidence that contact temperature plays an important role. Friction laws are developed by considering that the friction arises primarily from the shear of a softened or molten layer of rosin, with a temperature-dependent viscosity or shear strength. The temperature of the rosin layer is calculated by modelling the heat flow around the sliding contact. The temperature-based models are shown to reproduce some features of the measurements which are not captured in the traditional model, in which friction depends only on sliding speed. A model based on viscous behaviour of a thin melted layer of rosin gives predictions at variance with observations. However, a model based on plastic yielding at the surface of the rosin gives good agreement with these observations.

Dividing phases in two-phase flow and modeling of interfacial drag

DOE Office of Scientific and Technical Information (OSTI.GOV)

Narumo, T.; Rajamaeki, M.

1997-07-01

Different models intended to describe one-dimensional two-phase flow are considered in this paper. The following models are introduced: conventional six-equation model, conventional model equipped with terms taking into account nonuniform transverse velocity distribution of the phases, several virtual mass models and a model in which the momentum equations have been derived by using the principles of Separation of the Flow According to Velocity (SFAV). The dynamics of the models have been tested by comparing their characteristic velocities to each other and against experimental data. The results show that the SFAV-model makes a hyperbolic system and predicts the propagation velocities ofmore » disturbances with the same order of accuracy as the best tested virtual mass models. Furthermore, the momentum interaction terms for the SFAV-model are considered. These consist of the wall friction terms and the interfacial friction term. The authors model wall friction with two independent terms describing the effect of each fluid on the wall separately. In the steady state, a relationship between the slip velocity and friction coefficients can be derived. Hence, the friction coefficients for the SFAV-model can be calculated from existing correlations, viz. from a drift-flux correlation and a wall friction correlation. The friction model was tested by searching steady-state distributions in a partial BWR fuel channel and comparing the relaxed values with the drift-flux correlation, which agreed very well with each other. In addition, response of the flow to a sine-wave disturbance in the water inlet flux was calculated as function of frequency. The results of the models differed from each other already with frequency of order 5 Hz, while the time constant for the relaxation, obtained from steady-state distribution calculation, would have implied significant differences appear not until with frequency of order 50 Hz.« less

Ultralow nanoscale wear through atom-by-atom attrition in silicon-containing diamond-like carbon

NASA Astrophysics Data System (ADS)

Bhaskaran, Harish; Gotsmann, Bernd; Sebastian, Abu; Drechsler, Ute; Lantz, Mark A.; Despont, Michel; Jaroenapibal, Papot; Carpick, Robert W.; Chen, Yun; Sridharan, Kumar

2010-03-01

Understanding friction and wear at the nanoscale is important for many applications that involve nanoscale components sliding on a surface, such as nanolithography, nanometrology and nanomanufacturing. Defects, cracks and other phenomena that influence material strength and wear at macroscopic scales are less important at the nanoscale, which is why nanowires can, for example, show higher strengths than bulk samples. The contact area between the materials must also be described differently at the nanoscale. Diamond-like carbon is routinely used as a surface coating in applications that require low friction and wear because it is resistant to wear at the macroscale, but there has been considerable debate about the wear mechanisms of diamond-like carbon at the nanoscale because it is difficult to fabricate diamond-like carbon structures with nanoscale fidelity. Here, we demonstrate the batch fabrication of ultrasharp diamond-like carbon tips that contain significant amounts of silicon on silicon microcantilevers for use in atomic force microscopy. This material is known to possess low friction in humid conditions, and we find that, at the nanoscale, it is three orders of magnitude more wear-resistant than silicon under ambient conditions. A wear rate of one atom per micrometre of sliding on SiO2 is demonstrated. We find that the classical wear law of Archard does not hold at the nanoscale; instead, atom-by-atom attrition dominates the wear mechanisms at these length scales. We estimate that the effective energy barrier for the removal of a single atom is ~1 eV, with an effective activation volume of ~1 × 10-28 m.

A comparison of Coulomb and pseudo-Coulomb friction implementations: Application to the table contact phase of gymnastics vaulting.

PubMed

Jackson, M I; Hiley, M J; Yeadon, M R

2011-10-13

In the table contact phase of gymnastics vaulting both dynamic and static friction act. The purpose of this study was to develop a method of simulating Coulomb friction that incorporated both dynamic and static phases and to compare the results with those obtained using a pseudo-Coulomb implementation of friction when applied to the table contact phase of gymnastics vaulting. Kinematic data were obtained from an elite level gymnast performing handspring straight somersault vaults using a Vicon optoelectronic motion capture system. An angle-driven computer model of vaulting that simulated the interaction between a seven segment gymnast and a single segment vaulting table during the table contact phase of the vault was developed. Both dynamic and static friction were incorporated within the model by switching between two implementations of the tangential frictional force. Two vaulting trials were used to determine the model parameters using a genetic algorithm to match simulations to recorded performances. A third independent trial was used to evaluate the model and close agreement was found between the simulation and the recorded performance with an overall difference of 13.5%. The two-state simulation model was found to be capable of replicating performance at take-off and also of replicating key contact phase features such as the normal and tangential motion of the hands. The results of the two-state model were compared to those using a pseudo-Coulomb friction implementation within the simulation model. The two-state model achieved similar overall results to those of the pseudo-Coulomb model but obtained solutions more rapidly. Copyright © 2011 Elsevier Ltd. All rights reserved.

Skin Friction Measurements Using Luminescent Oil Films

NASA Astrophysics Data System (ADS)

Husen, Nicholas M.

As aircraft are designed to a greater extent on computers, the need for accurate and fast CFD algorithms has never been greater. The development of CFD algorithms requires experimental data against which CFD output can be validated and from which insight about flow physics can be acquired. Skin friction, in particular, is an important quantity to predict with CFD, and experimental skin friction data sets aid not only with the validation of the CFD predictions, but also in tuning the CFD models to predict specific flow fields. However, a practical experimental technique for collecting spatially and temporally resolved skin friction data on complex models does not yet exist. This dissertation develops and demonstrates a new luminescent oil film skin friction meter which can produce spatially-resolved quantitative steady and unsteady skin friction data on models with complex curvature. The skin friction acting on the surface of a thin film of oil can be approximated by the expression tauw =mu ouh/h, where mu o is the dynamic viscosity of the oil, uh is the velocity of the surface of the oil film, and h is the thickness of the oil film. The new skin friction meter determines skin friction by measuring h and uh. The oil film thickness h is determined by ratioing the intensity of the fluorescent emissions from the oil film with the intensity of the incident light which is scattered from the surface of the model. When properly calibrated, that ratio provides an absolute oil film thickness value. This oil film thickness meter is therefore referred as the Ratioed-Image Film-Thickness (RIFT) Meter. The oil film velocity uh is determined by monitoring the evolution of tagged molecules within the oil film: Photochromic molecules are dissolved into the fluorescent oil and a pattern is written into the oil film using an ultraviolet laser. The evolution of the pattern is recorded, and standard cross-correlation techniques are applied to the resulting sequence of images. This newly developed skin friction meter is therefore called the Luminescent Oil Film Flow-Tagging skin friction meter, or the LOFFT skin friction meter. The LOFFT skin friction meter is demonstrated by collecting time-averaged skin friction measurements on NASA's FAITH model and by collecting unsteady skin friction measurements with a frequency response of 600Hz. Higher frequency response is possible and is dependent on the experimental setup. This dissertation also contributes to the work done on the Global Luminescent Oil Film Skin Friction Meter (GLOFSFM) by noting that the technique could be influenced by ripples at the oil-air interface. An experiment studying the evolution of ripples at the oil-air interface was conducted to determine under what oil film conditions the GLOFSFM can be appropriately applied. The RIFT meter was crucial for this experiment, as it facilitated quantitative distributed oil film thickness measurements during the wind-tunnel run. The resulting data set is rich in content, permitting the computation of mean wavelengths, peak-to-trough ripple heights, wave speeds, and mean thicknesses. In addition to determining under what oil film conditions the GLOFSFM may be applied, this experiment directly determined the oil film conditions under which the velocity of the ripples may be used to proxy the velocity of the oil film surface. The RIFT meter and the ability to determine oil film surface velocity by monitoring ripple velocities admit yet another time-averaged skin friction meter, the Fluorescent-Oil Ripple-Velocity (FORV) skin friction meter. The FORV skin friction meter recovers skin friction as tau w = muovrip/H, where vrip is the velocity of the ripples, and H is the oil film thickness averaged over the thickness fluctuations due to the ripples. The FORV skin friction meter is demonstrated on NASA's FAITH model.

Economical Unsteady High-Fidelity Aerodynamics for Structural Optimization with a Flutter Constraint

NASA Technical Reports Server (NTRS)

Bartels, Robert E.; Stanford, Bret K.

2017-01-01

Structural optimization with a flutter constraint for a vehicle designed to fly in the transonic regime is a particularly difficult task. In this speed range, the flutter boundary is very sensitive to aerodynamic nonlinearities, typically requiring high-fidelity Navier-Stokes simulations. However, the repeated application of unsteady computational fluid dynamics to guide an aeroelastic optimization process is very computationally expensive. This expense has motivated the development of methods that incorporate aspects of the aerodynamic nonlinearity, classical tools of flutter analysis, and more recent methods of optimization. While it is possible to use doublet lattice method aerodynamics, this paper focuses on the use of an unsteady high-fidelity aerodynamic reduced order model combined with successive transformations that allows for an economical way of utilizing high-fidelity aerodynamics in the optimization process. This approach is applied to the common research model wing structural design. As might be expected, the high-fidelity aerodynamics produces a heavier wing than that optimized with doublet lattice aerodynamics. It is found that the optimized lower skin of the wing using high-fidelity aerodynamics differs significantly from that using doublet lattice aerodynamics.

High Fidelity Virtual Environments: Does Shader Quality or Higher Polygon Count Models Increase Presence and Learning

NASA Astrophysics Data System (ADS)

Horton, Scott

This research study investigated the effects of high fidelity graphics on both learning and presence, or the "sense of being there," inside a Virtual Learning Environment (VLE). Four versions of a VLE on the subject of the element mercury were created, each with a different combination of high and low fidelity polygon models and high and low fidelity shaders. A total of 76 college age (18+ years of age) participants were randomly assigned to one of the four conditions. The participants interacted with the VLE and then completed several posttest measures on learning, presence, and attitudes towards the VLE experience. Demographic information was also collected, including age, computer gameplay experience, number of virtual environments interacted with, gender and time spent in this virtual environment. The data was analyzed as a 2 x 2 between subjects ANOVA. The main effects of shader fidelity and polygon fidelity were both non-significant for both learning and all presence subscales inside the VLE. In addition, there was no significant interaction between shader fidelity and model fidelity. However, there were two significant results on the supplementary variables. First, gender was found to have a significant main effect on all the presence subscales. Females reported higher average levels of presence than their male counterparts. Second, gameplay hours, or the number of hours a participant played computer games per week, also had a significant main effect on participant score on the learning measure. The participants who reported playing 15+ hours of computer games per week, the highest amount of time in the variable, had the highest score as a group on the mercury learning measure while those participants that played 1-5 hours per week had the lowest scores.

Effect of dental arch convexity and type of archwire on frictional forces.

PubMed

Fourie, Zacharias; Ozcan, Mutlu; Sandham, Andrew

2009-07-01

Friction measurements in orthodontics are often derived from models by using brackets placed on flat models with various straight wires. Dental arches are convex in some areas. The objectives of this study were to compare the frictional forces generated in conventional flat and convex dental arch setups, and to evaluate the effect of different archwires on friction in both dental arch models. Two stainless steel models were designed and manufactured simulating flat and convex maxillary right buccal dental arches. Five stainless steel brackets from the maxillary incisor to the second premolar (slot size, 0.22 in, Victory, 3M Unitek, Monrovia, Calif) and a first molar tube were aligned and clamped on the metal model at equal distances of 6 mm. Four kinds of orthodontic wires were tested: (1) A. J. Wilcock Australian wire (0.016 in, G&H Wire, Hannover, Germany); and (2) 0.016 x 0.022 in, (3) 0.018 x 0.022 in, and (4) 0.019 x 0.025 in (3M Unitek GmbH, Seefeld, Germany). Gray elastomeric modules (Power O 110, Ormco, Glendora, Calif) were used for ligation. Friction tests were performed in the wet state with artificial saliva lubrication and by pulling 5 mm of the whole length of the archwire. Six measurements were made from each bracket-wire combination, and each test was performed with new combinations of materials for both arch setups (n = 48, 6 per group) in a universal testing machine (crosshead speed: 20 mm/min). Significant effects of arch model (P = 0.0000) and wire types (P = 0.0000) were found. The interaction term between the tested factors was not significant (P = 0.1581) (2-way ANOVA and Tukey test). Convex models resulted in significantly higher frictional forces (1015-1653 g) than flat models (680-1270 g) (P <0.05). In the flat model, significantly lower frictional forces were obtained with wire types 1 (679 g) and 3 (1010 g) than with types 2 (1146 g) and 4 (1270 g) (P <0.05). In the convex model, the lowest friction was obtained with wire types 1 (1015 g) and 3 (1142 g) (P >0.05). Type 1 wire tended to create the least overall friction in both flat and convex dental arch simulation models.

Friction and lubrication modelling in sheet metal forming: Influence of lubrication amount, tool roughness and sheet coating on product quality

NASA Astrophysics Data System (ADS)

Hol, J.; Wiebenga, J. H.; Carleer, B.

2017-09-01

In the stamping of automotive parts, friction and lubrication play a key role in achieving high quality products. In the development process of new automotive parts, it is therefore crucial to accurately account for these effects in sheet metal forming simulations. This paper presents a selection of results considering friction and lubrication modelling in sheet metal forming simulations of a front fender product. For varying lubrication conditions, the front fender can either show wrinkling or fractures. The front fender is modelled using different lubrication amounts, tool roughness’s and sheet coatings to show the strong influence of friction on both part quality and the overall production stability. For this purpose, the TriboForm software is used in combination with the AutoForm software. The results demonstrate that the TriboForm software enables the simulation of friction behaviour for varying lubrication conditions, i.e. resulting in a generally applicable approach for friction characterization under industrial sheet metal forming process conditions.

Further Validation of the Pathways Housing First Fidelity Scale.

PubMed

Goering, Paula; Veldhuizen, Scott; Nelson, Geoffrey B; Stefancic, Ana; Tsemberis, Sam; Adair, Carol E; Distasio, Jino; Aubry, Tim; Stergiopoulos, Vicky; Streiner, David L

2016-01-01

This study examined whether Housing First fidelity ratings correspond to program operation descriptions from administrative data and predict client outcomes. A multisite, randomized controlled trial (At Home/Chez Soi) in five Canadian cities included two assessments of 12 programs over two years. Outcomes for 1,158 clients were measured every six months. Associations between fidelity ratings and administrative data (Spearman correlations) and participant outcomes (mixed-effects modeling) were examined. Fidelity ratings were generally good (mean ± SD=136.6 ± 10.3 out of a possible range of 38-152; 87% of maximum value). Fidelity was significantly associated with three of four measures of program operation, with correlations between .55 and .60. Greater program fidelity was associated with improvement in housing stability, community functioning, and quality of life. Variation in program fidelity was associated with operations and outcomes, supporting scale validity and intervention effectiveness. These findings reinforced the value of using fidelity monitoring to conduct quality assurance and technical assistance activities.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glascoe, Lee; Gowardhan, Akshay; Lennox, Kristin

In the interest of promoting the international exchange of technical expertise, the US Department of Energy’s Office of Emergency Operations (NA-40) and the French Commissariat à l'Energie Atomique et aux énergies alternatives (CEA) requested that the National Atmospheric Release Advisory Center (NARAC) of Lawrence Livermore National Laboratory (LLNL) in Livermore, California host a joint table top exercise with experts in emergency management and atmospheric transport modeling. In this table top exercise, LLNL and CEA compared each other’s flow and dispersion models. The goal of the comparison is to facilitate the exchange of knowledge, capabilities, and practices, and to demonstrate themore » utility of modeling dispersal at different levels of computational fidelity. Two modeling approaches were examined, a regional scale modeling approach, appropriate for simple terrain and/or very large releases, and an urban scale modeling approach, appropriate for small releases in a city environment. This report is a summary of LLNL and CEA modeling efforts from this exercise. Two different types of LLNL and CEA models were employed in the analysis: urban-scale models (Aeolus CFD at LLNL/NARAC and Parallel- Micro-SWIFT-SPRAY, PMSS, at CEA) for analysis of a 5,000 Ci radiological release and Lagrangian Particle Dispersion Models (LODI at LLNL/NARAC and PSPRAY at CEA) for analysis of a much larger (500,000 Ci) regional radiological release. Two densely-populated urban locations were chosen: Chicago with its high-rise skyline and gridded street network and Paris with its more consistent, lower building height and complex unaligned street network. Each location was considered under early summer daytime and nighttime conditions. Different levels of fidelity were chosen for each scale: (1) lower fidelity mass-consistent diagnostic, intermediate fidelity Navier-Stokes RANS models, and higher fidelity Navier-Stokes LES for urban-scale analysis, and (2) lower-fidelity single-profile meteorology versus higher-fidelity three-dimensional gridded weather forecast for regional-scale analysis. Tradeoffs between computation time and the fidelity of the results are discussed for both scales. LES, for example, requires nearly 100 times more processor time than the mass-consistent diagnostic model or the RANS model, and seems better able to capture flow entrainment behind tall buildings. As anticipated, results obtained by LLNL and CEA at regional scale around Chicago and Paris look very similar in terms of both atmospheric dispersion of the radiological release and total effective dose. Both LLNL and CEA used the same meteorological data, Lagrangian particle dispersion models, and the same dose coefficients. LLNL and CEA urban-scale modeling results show consistent phenomenological behavior and predict similar impacted areas even though the detailed 3D flow patterns differ, particularly for the Chicago cases where differences in vertical entrainment behind tall buildings are particularly notable. Although RANS and LES (LLNL) models incorporate more detailed physics than do mass-consistent diagnostic flow models (CEA), it is not possible to reach definite conclusions about the prediction fidelity of the various models as experimental measurements were not available for comparison. Stronger conclusions about the relative performances of the models involved and evaluation of the tradeoffs involved in model simplification could be made with a systematic benchmarking of urban-scale modeling. This could be the purpose of a future US / French collaborative exercise.« less

Rolling Friction on a Wheeled Laboratory Cart

ERIC Educational Resources Information Center

Mungan, Carl E.

2012-01-01

A simple model is developed that predicts the coefficient of rolling friction for an undriven laboratory cart on a track that is approximately independent of the mass loaded onto the cart and of the angle of inclination of the track. The model includes both deformation of the wheels/track and frictional torque at the axles/bearings. The concept of…

An Analysis of High School Students' Mental Models of Solid Friction in Physics

ERIC Educational Resources Information Center

Kurnaz, Mehmet Altan; Eksi, Cigdem

2015-01-01

Students often have difficulties understanding abstract physics concepts, such as solid friction. This study examines high school students' mental models of solid friction through a case study of 215 high school students in the ninth through twelfth grades. An achievement test with three open-ended questions was created, with questions limited to…

Investigating Students' Mental Models and Knowledge Construction of Microscopic Friction. I. Implications for Curriculum Design and Development

ERIC Educational Resources Information Center

Corpuz, Edgar D.; Rebello, N. Sanjay

2011-01-01

In this paper, we discuss the first phase of a multiphase study aimed at investigating the dynamics of students' knowledge construction in the context of unfamiliar physical phenomenon--microscopic friction. The first phase of this study involved the investigation of the variations in students' mental models of microscopic friction. Clinical…

How to reduce long-term drift in present-day and deep-time simulations?

NASA Astrophysics Data System (ADS)

Brunetti, Maura; Vérard, Christian

2018-06-01

Climate models are often affected by long-term drift that is revealed by the evolution of global variables such as the ocean temperature or the surface air temperature. This spurious trend reduces the fidelity to initial conditions and has a great influence on the equilibrium climate after long simulation times. Useful insight on the nature of the climate drift can be obtained using two global metrics, i.e. the energy imbalance at the top of the atmosphere and at the ocean surface. The former is an indicator of the limitations within a given climate model, at the level of both numerical implementation and physical parameterisations, while the latter is an indicator of the goodness of the tuning procedure. Using the MIT general circulation model, we construct different configurations with various degree of complexity (i.e. different parameterisations for the bulk cloud albedo, inclusion or not of friction heating, different bathymetry configurations) to which we apply the same tuning procedure in order to obtain control runs for fixed external forcing where the climate drift is minimised. We find that the interplay between tuning procedure and different configurations of the same climate model provides crucial information on the stability of the control runs and on the goodness of a given parameterisation. This approach is particularly relevant for constructing good-quality control runs of the geological past where huge uncertainties are found in both initial and boundary conditions. We will focus on robust results that can be generally applied to other climate models.

Friction laws at the nanoscale.

PubMed

Mo, Yifei; Turner, Kevin T; Szlufarska, Izabela

2009-02-26

Macroscopic laws of friction do not generally apply to nanoscale contacts. Although continuum mechanics models have been predicted to break down at the nanoscale, they continue to be applied for lack of a better theory. An understanding of how friction force depends on applied load and contact area at these scales is essential for the design of miniaturized devices with optimal mechanical performance. Here we use large-scale molecular dynamics simulations with realistic force fields to establish friction laws in dry nanoscale contacts. We show that friction force depends linearly on the number of atoms that chemically interact across the contact. By defining the contact area as being proportional to this number of interacting atoms, we show that the macroscopically observed linear relationship between friction force and contact area can be extended to the nanoscale. Our model predicts that as the adhesion between the contacting surfaces is reduced, a transition takes place from nonlinear to linear dependence of friction force on load. This transition is consistent with the results of several nanoscale friction experiments. We demonstrate that the breakdown of continuum mechanics can be understood as a result of the rough (multi-asperity) nature of the contact, and show that roughness theories of friction can be applied at the nanoscale.

Fuzzy control for nonlinear structure with semi-active friction damper

NASA Astrophysics Data System (ADS)

Zhao, Da-Hai; Li, Hong-Nan

2007-04-01

The implementation of semi-active friction damper for vibration mitigation of seismic structure generally requires an efficient control strategy. In this paper, the fuzzy logic based on Takagi-Sugeno model is proposed for controlling a semi-active friction damper that is installed on a nonlinear building subjected to strong earthquakes. The continuous Bouc-Wen hysteretic model for the stiffness is used to describe nonlinear characteristic of the building. The optimal sliding force with friction damper is determined by nonlinear time history analysis under normal earthquakes. The Takagi-Sugeno fuzzy logic model is employed to adjust the clamping force acted on the friction damper according to the semi-active control strategy. Numerical simulation results demonstrate that the proposed method is very efficient in reducing the peak inter-story drift and acceleration of the nonlinear building structure under earthquake excitations.

Modeling Earthquake Rupture and Corresponding Tsunamis Along a Segment of the Alaskan-Aleutian Megathrust

NASA Astrophysics Data System (ADS)

Ryan, K. J.; Geist, E. L.; Oglesby, D. D.; Kyriakopoulos, C.

2016-12-01

Motivated by the 2011 Mw 9 Tohoku-Oki event, we explore the effects of realistic fault dynamics on slip, free surface deformation, and the resulting tsunami generation and local propagation from a hypothetical Mw 9 megathrust earthquake along the Alaskan-Aleutian (A-A) Megathrust. We demonstrate three scenarios: a spatially-homogenous prestress and frictional parameter model and two models with rate-strengthening-like friction (e.g., Dieterich, 1992). We use a dynamic finite element code to model 3-D ruptures, using time-weakening friction (Andrews, 2004) as a proxy for rate-strengthening friction, along a portion of the A-A subduction zone. Given geometric, material, and plate-coupling data along the A-A megathrust assembled from the Science Application for Risk Reduction (SAFRR) team (e.g., Bruns et al., 1987; Hayes et al., 2012; Johnson et al., 2004; Santini et al., 2003; Wells at al., 2003), we are able to dynamically model rupture. Adding frictional-strengthening to a region of the fault reduces both average slip and free surface displacement above the strengthening zone, with the magnitude of the reductions depending on the strengthening zone location. Corresponding tsunami models, which use a finite difference method to solve the long-wave equations (e.g., Liu et al., 1995; Satake, 2002; Shuto, 1991), match sea floor displacement, in time, to the free surface displacement from the rupture models. Tsunami models show changes in local peak amplitudes and beaming patterns for each slip distribution. Given these results, other heterogeneous parameterizations, with respect to prestress and friction, still need to be examined. Additionally, a more realistic fault geometry will likely affect the rupture dynamics. Thus, future work will incorporate stochastic stress and friction distributions as well as a more complex fault geometry based on Slab 1.0 (Hayes et al., 2012).

Ensuring treatment fidelity in a multi-site behavioral intervention study: implementing NIH Behavior Change Consortium recommendations in the SMART trial.

PubMed

Robb, Sheri L; Burns, Debra S; Docherty, Sharron L; Haase, Joan E

2011-11-01

The Stories and Music for Adolescent/Young Adult Resilience during Transplant (SMART) study (R01NR008583; U10CA098543; U10CA095861) is an ongoing multi-site Children's Oncology Group randomized clinical trial testing the efficacy of a therapeutic music video intervention for adolescents/young adults (11-24 years of age) with cancer undergoing stem cell transplant. Treatment fidelity strategies from our trial are consistent with the National Institutes of Health (NIH) Behavior Change Consortium Treatment Fidelity Workgroup (BCC) recommendations and provide a successful working model for treatment fidelity implementation in a large, multi-site behavioral intervention study. In this paper, we summarize 20 specific treatment fidelity strategies used in the SMART trial and how these strategies correspond with NIH BCC recommendations in five specific areas: (1) study design, (2) training providers, (3) delivery of treatment, (4) receipt of treatment, and (5) enactment of treatment skills. Increased use and reporting of treatment fidelity procedures is essential in advancing the reliability and validity of behavioral intervention research. The SMART trial provides a strong model for the application of fidelity strategies to improve scientific findings and addresses the absence of published literature, illustrating the application of BCC recommendations in behavioral intervention studies. Copyright © 2010 John Wiley & Sons, Ltd.

A methodology for the assessment of manned flight simulator fidelity

NASA Technical Reports Server (NTRS)

Hess, Ronald A.; Malsbury, Terry N.

1989-01-01

A relatively simple analytical methodology for assessing the fidelity of manned flight simulators for specific vehicles and tasks is offered. The methodology is based upon an application of a structural model of the human pilot, including motion cue effects. In particular, predicted pilot/vehicle dynamic characteristics are obtained with and without simulator limitations. A procedure for selecting model parameters can be implemented, given a probable pilot control strategy. In analyzing a pair of piloting tasks for which flight and simulation data are available, the methodology correctly predicted the existence of simulator fidelity problems. The methodology permitted the analytical evaluation of a change in simulator characteristics and indicated that a major source of the fidelity problems was a visual time delay in the simulation.

A Planar Quasi-Static Constraint Mode Tire Model

DTIC Science & Technology

2015-07-10

strikes a balance between simple tire models that lack the fidelity to make accurate chassis load predictions and computationally intensive models that...strikes a balance between heuristic tire models (such as a linear point-follower) that lack the fidelity to make accurate chassis load predictions...UNCLASSIFIED: Distribution Statement A. Cleared for public release A PLANAR QUASI-STATIC CONSTRAINT MODE TIRE MODEL Rui Maa John B. Ferris

Identification and compensation of friction for a novel two-axis differential micro-feed system

NASA Astrophysics Data System (ADS)

Du, Fuxin; Zhang, Mingyang; Wang, Zhaoguo; Yu, Chen; Feng, Xianying; Li, Peigang

2018-06-01

Non-linear friction in a conventional drive feed system (CDFS) feeding at low speed is one of the main factors that lead to the complexity of the feed drive. The CDFS will inevitably enter or approach a non-linear creeping work area at extremely low speed. A novel two-axis differential micro-feed system (TDMS) is developed in this paper to overcome the accuracy limitation of CDFS. A dynamic model of TDMS is first established. Then, a novel all-component friction parameter identification method (ACFPIM) using a genetic algorithm (GA) to identify the friction parameters of a TDMS is introduced. The friction parameters of the ball screw and linear motion guides are identified independently using the method, assuring the accurate modelling of friction force at all components. A proportional-derivate feed drive position controller with an observer-based friction compensator is implemented to achieve an accurate trajectory tracking performance. Finally, comparative experiments demonstrate the effectiveness of the TDMS in inhibiting the disadvantageous influence of non-linear friction and the validity of the proposed identification method for TDMS.

Modelling clustering of vertically aligned carbon nanotube arrays.

PubMed

Schaber, Clemens F; Filippov, Alexander E; Heinlein, Thorsten; Schneider, Jörg J; Gorb, Stanislav N

2015-08-06

Previous research demonstrated that arrays of vertically aligned carbon nanotubes (VACNTs) exhibit strong frictional properties. Experiments indicated a strong decrease of the friction coefficient from the first to the second sliding cycle in repetitive measurements on the same VACNT spot, but stable values in consecutive cycles. VACNTs form clusters under shear applied during friction tests, and self-organization stabilizes the mechanical properties of the arrays. With increasing load in the range between 300 µN and 4 mN applied normally to the array surface during friction tests the size of the clusters increases, while the coefficient of friction decreases. To better understand the experimentally obtained results, we formulated and numerically studied a minimalistic model, which reproduces the main features of the system with a minimum of adjustable parameters. We calculate the van der Waals forces between the spherical friction probe and bunches of the arrays using the well-known Morse potential function to predict the number of clusters, their size, instantaneous and mean friction forces and the behaviour of the VACNTs during consecutive sliding cycles and at different normal loads. The data obtained by the model calculations coincide very well with the experimental data and can help in adapting VACNT arrays for biomimetic applications.

An Analysis of the Educational Value of Low-Fidelity Anatomy Models as External Representations

ERIC Educational Resources Information Center

Chan, Lap Ki; Cheng, Maurice M. W.

2011-01-01

Although high-fidelity digital models of human anatomy based on actual cross-sectional images of the human body have been developed, reports on the use of physical models in anatomy teaching continue to appear. This article aims to examine the common features shared by these physical models and analyze their educational value based on the…

Impact of an irregular friction formulation on dynamics of a minimal model for brake squeal

NASA Astrophysics Data System (ADS)

Stender, Merten; Tiedemann, Merten; Hoffmann, Norbert; Oberst, Sebastian

2018-07-01

Friction-induced vibrations are of major concern in the design of reliable, efficient and comfortable technical systems. Well-known examples for systems susceptible to self-excitation can be found in fluid structure interaction, disk brake squeal, rotor dynamics, hip implants noise and many more. While damping elements and amplitude reduction are well-understood in linear systems, nonlinear systems and especially self-excited dynamics still constitute a challenge for damping element design. Additionally, complex dynamical systems exhibit deterministic chaotic cores which add severe sensitivity to initial conditions to the system response. Especially the complex friction interface dynamics remain a challenging task for measurements and modeling. Today, mostly simple and regular friction models are investigated in the field of self-excited brake system vibrations. This work aims at investigating the effect of high-frequency irregular interface dynamics on the nonlinear dynamical response of a self-excited structure. Special focus is put on the characterization of the system response time series. A low-dimensional minimal model is studied which features self-excitation, gyroscopic effects and friction-induced damping. Additionally, the employed friction formulation exhibits temperature as inner variable and superposed chaotic fluctuations governed by a Lorenz attractor. The time scale of the irregular fluctuations is chosen one order smaller than the overall system dynamics. The influence of those fluctuations on the structural response is studied in various ways, i.e. in time domain and by means of recurrence analysis. The separate time scales are studied in detail and regimes of dynamic interactions are identified. The results of the irregular friction formulation indicate dynamic interactions on multiple time scales, which trigger larger vibration amplitudes as compared to regular friction formulations conventionally studied in the field of friction-induced vibrations.

High precision tracking control of a servo gantry with dynamic friction compensation.

PubMed

Zhang, Yangming; Yan, Peng; Zhang, Zhen

2016-05-01

This paper is concerned with the tracking control problem of a voice coil motor (VCM) actuated servo gantry system. By utilizing an adaptive control technique combined with a sliding mode approach, an adaptive sliding mode control (ASMC) law with friction compensation scheme is proposed in presence of both frictions and external disturbances. Based on the LuGre dynamic friction model, a dual-observer structure is used to estimate the unmeasurable friction state, and an adaptive control law is synthesized to effectively handle the unknown friction model parameters as well as the bound of the disturbances. Moreover, the proposed control law is also implemented on a VCM servo gantry system for motion tracking. Simulations and experimental results demonstrate good tracking performance, which outperform traditional control approaches. Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.

Static coefficient of friction between stainless steel and PMMA used in cemented hip and knee implants.

PubMed

Nuño, N; Groppetti, R; Senin, N

2006-11-01

Design of cemented hip and knee implants, oriented to improve the longevity of artificial joints, is largely based on numerical models. The static coefficient of friction between the implant and the bone cement is necessary to characterize the interface conditions in these models and must be accurately provided. The measurement of this coefficient using a repeatable and reproducible methodology for materials used in total hip arthroplasty is missing from the literature. A micro-topographic surface analysis characterized the surfaces of the specimens used in the experiments. The coefficient of friction between stainless steel and bone cement in dry and wet conditions using bovine serum was determined using a prototype computerized sliding friction tester. The effects of surface roughness (polished versus matt) and of contact pressure on the coefficient of friction have also been investigated. The serum influences little the coefficient of friction for the matt steel surface, where the mechanical interactions due to higher roughness are still the most relevant factor. However, for polished steel surfaces, the restraining effect of proteins plays a very relevant role in increasing the coefficient of friction. When the coefficient of friction is used in finite element analysis, it is used for the debonded stem-cement situation. It can thus be assumed that serum will propagate between the stem and the cement mantle. The authors believe that the use of a static coefficient of friction of 0.3-0.4, measured in the present study, is appropriate in finite element models.

Development and validation of a Housing First fidelity survey.

PubMed

Gilmer, Todd P; Stefancic, Ana; Sklar, Marisa; Tsemberis, Sam

2013-09-01

Programs that use the Housing First model are being implemented throughout the United States and internationally. The authors describe the development and validation of a Housing First fidelity survey. A 46-item survey was developed to measure fidelity across five domains: housing process and structure, separation of housing and services, service philosophy, service array, and team structure. The survey was administered to staff and clients of 93 supported-housing programs in California. Exploratory and confirmatory factor analyses were used to identify the items and model structure that best fit the data. Sixteen items were retained in a two-factor model, one related to approach to housing, separation of housing and services, and service philosophy and one related to service array and team structure. Our survey mapped program practices by using a common metric that captured variation in fidelity to Housing First across a large-scale implementation of supported-housing programs.

High-fidelity data embedding for image annotation.

PubMed

He, Shan; Kirovski, Darko; Wu, Min

2009-02-01

High fidelity is a demanding requirement for data hiding, especially for images with artistic or medical value. This correspondence proposes a high-fidelity image watermarking for annotation with robustness to moderate distortion. To achieve the high fidelity of the embedded image, we introduce a visual perception model that aims at quantifying the local tolerance to noise for arbitrary imagery. Based on this model, we embed two kinds of watermarks: a pilot watermark that indicates the existence of the watermark and an information watermark that conveys a payload of several dozen bits. The objective is to embed 32 bits of metadata into a single image in such a way that it is robust to JPEG compression and cropping. We demonstrate the effectiveness of the visual model and the application of the proposed annotation technology using a database of challenging photographic and medical images that contain a large amount of smooth regions.

GIS Data Based Automatic High-Fidelity 3D Road Network Modeling

NASA Technical Reports Server (NTRS)

Wang, Jie; Shen, Yuzhong

2011-01-01

3D road models are widely used in many computer applications such as racing games and driving simulations_ However, almost all high-fidelity 3D road models were generated manually by professional artists at the expense of intensive labor. There are very few existing methods for automatically generating 3D high-fidelity road networks, especially those existing in the real world. This paper presents a novel approach thai can automatically produce 3D high-fidelity road network models from real 2D road GIS data that mainly contain road. centerline in formation. The proposed method first builds parametric representations of the road centerlines through segmentation and fitting . A basic set of civil engineering rules (e.g., cross slope, superelevation, grade) for road design are then selected in order to generate realistic road surfaces in compliance with these rules. While the proposed method applies to any types of roads, this paper mainly addresses automatic generation of complex traffic interchanges and intersections which are the most sophisticated elements in the road networks

Measuring Fidelity of Implementation--Methodological and Conceptual Issues and Challenges. CRESST Report 811

ERIC Educational Resources Information Center

Osmundson, Ellen; Herman, Joan; Ringstaff, Cathy; Dai, Yunyun; Timms, Mike

2012-01-01

A central challenge in efficacy studies centers on the issue of "fidelity of implementation," that is, the extent to which participants use the curriculum specified by curriculum developers. In this study, we describe and discuss a "fidelity of implementation" model using multiple methods and instruments to compare two versions of a science…

Applying the Five-Step Model of Fidelity Assessment to a Randomized Experiment of a High School STEM Intervention

ERIC Educational Resources Information Center

Kopp, Jason P.; Hulleman, Chris S.; Harackiewicz, Judith M.; Rozek, Chris

2012-01-01

Assessing fidelity of implementation is becoming increasingly important in education research, in particular as a tool for understanding variations in treatment effectiveness. Fidelity of implementation is defined as "the determination of how well an intervention is implemented in comparison with the original program design during an efficacy…

Enhancing Therapeutic Gains: Examination of Fidelity to the Model for the Intensive Mental Health Program

ERIC Educational Resources Information Center

Randall, Camille J.; Biggs, Bridget K.

2008-01-01

Given that the development of treatment fidelity assessment protocol is an integral but too frequently ignored aspect of clinical trials for psychological treatments, the Intensive Mental Health Program (IMHP) sought to build fidelity activities into training, program evaluation, and clinical recordkeeping from the outset of a 3 year study period.…

Relationship between Systems Coaching and Problem-Solving Implementation Fidelity in a Response-to-Intervention Model

ERIC Educational Resources Information Center

March, Amanda L.; Castillo, Jose M.; Batsche, George M.; Kincaid, Donald

2016-01-01

The literature on RTI has indicated that professional development and coaching are critical to facilitating problem-solving implementation with fidelity. This study examined the extent to which systems coaching related to the fidelity of problem-solving implementation in 31 schools from six districts. Schools participated in three years of a…

Historical Scientific Models and Theories as Resources for Learning and Teaching: The Case of Friction

NASA Astrophysics Data System (ADS)

Besson, Ugo

2013-05-01

This paper presents a history of research and theories on sliding friction between solids. This history is divided into four phases: from Leonardo da Vinci to Coulomb and the establishment of classical laws of friction; the theories of lubrication and the Tomlinson's theory of friction (1850-1930); the theories of wear, the Bowden and Tabor's synthesis and the birth of Tribology (1930-1980); nanotribology, friction at the atomic scale, and new fields of research (after 1980). Attention is given to recent research, so giving the sense of a topic that is still alive and currently an object of interest, with interpretative controversies. The development of explanatory and visual models is especially stressed, in connection with students' common ideas and with didactic purposes. The history shows that many models proposed in the past have been modified but not abandoned, so that here the scientific evolution has worked more by adding than by eliminating. The last sections discuss problems and proposals on teaching friction and the possible uses in teaching of models, images and theories found in history. Concerning the role of the history in science teaching, the case of friction has particular features, because some recent developments are unknown to most teachers and many results, also not very recent, contrast with the laws usually proposed in textbooks. Here history can supply a number of models, examples and experiments which can constitute useful resources to improve student understanding, joining together objectives of cultural value and of better scientific knowledge.

Bottom friction optimization for a better barotropic tide modelling

NASA Astrophysics Data System (ADS)

Boutet, Martial; Lathuilière, Cyril; Son Hoang, Hong; Baraille, Rémy

2015-04-01

At a regional scale, barotropic tides are the dominant source of variability of currents and water heights. A precise representation of these processes is essential because of their great impacts on human activities (submersion risks, marine renewable energies, ...). Identified sources of error for tide modelling at a regional scale are the followings: bathymetry, boundary forcing and dissipation due to bottom friction. Nevertheless, bathymetric databases are nowadays known with a good accuracy, especially over shelves, and global tide models performances are better than ever. The most promising improvement is thus the bottom friction representation. The method used to estimate bottom friction is the simultaneous perturbation stochastic approximation (SPSA) which consists in the approximation of the gradient based on a fixed number of cost function measurements, regardless of the dimension of the vector to be estimated. Indeed, each cost function measurement is obtained by randomly perturbing every component of the parameter vector. An important feature of SPSA is its relative ease of implementation. In particular, the method does not require the development of tangent linear and adjoint version of the circulation model. Experiments are carried out to estimate bottom friction with the HYbrid Coordinate Ocean Model (HYCOM) in barotropic mode (one isopycnal layer). The study area is the Northeastern Atlantic margin which is characterized by strong currents and an intense dissipation. Bottom friction is parameterized with a quadratic term and friction coefficient is computed with the water height and the bottom roughness. The latter parameter is the one to be estimated. Assimilated data are the available tide gauge observations. First, the bottom roughness is estimated taking into account bottom sediment natures and bathymetric ranges. Then, it is estimated with geographical degrees of freedom. Finally, the impact of the estimation of a mixed quadratic/linear friction is evaluated.

Evaluation of Veterinary Student Surgical Skills Preparation for Ovariohysterectomy Using Simulators: A Pilot Study.

PubMed

Read, Emma K; Vallevand, Andrea; Farrell, Robin M

2016-01-01

This paper describes the development and evaluation of training intended to enhance students' performance on their first live-animal ovariohysterectomy (OVH). Cognitive task analysis informed a seven-page lab manual, 30-minute video, and 46-item OVH checklist (categorized into nine surgery components and three phases of surgery). We compared two spay simulator models (higher-fidelity silicone versus lower-fidelity cloth and foam). Third-year veterinary students were randomly assigned to a training intervention: lab manual and video only; lab manual, video, and $675 silicone-based model; lab manual, video, and $64 cloth and foam model. We then assessed transfer of training to a live-animal OVH. Chi-square analyses determined statistically significant differences between the interventions on four of nine surgery components, all three phases of surgery, and overall score. Odds ratio analyses indicated that training with a spay model improved the odds of attaining an excellent or good rating on 25 of 46 checklist items, six of nine surgery components, all three phases of surgery, and the overall score. Odds ratio analyses comparing the spay models indicated an advantage for the $675 silicon-based model on only 6 of 46 checklist items, three of nine surgery components, and one phase of surgery. Training with a spay model improved performance when compared to training with a manual and video only. Results suggested that training with a lower-fidelity/cost model might be as effective when compared to a higher-fidelity/cost model. Further research is required to investigate simulator fidelity and costs on transfer of training to the operational environment.

Investigating Students' Mental Models and Knowledge Construction of Microscopic Friction. II. Implications for Curriculum Design and Development

ERIC Educational Resources Information Center

Corpuz, Edgar D.; Rebello, N. Sanjay

2011-01-01

Our previous research showed that students' mental models of friction at the atomic level are significantly influenced by their macroscopic ideas. For most students, friction is due to the meshing of bumps and valleys and rubbing of atoms. The aforementioned results motivated us to further investigate how students can be helped to improve their…

Interplay of non-Markov and internal friction effects in the barrier crossing kinetics of biopolymers: insights from an analytically solvable model.

PubMed

Makarov, Dmitrii E

2013-01-07

Conformational rearrangements in biomolecules (such as protein folding or enzyme-ligand binding) are often interpreted in terms of low-dimensional models of barrier crossing such as Kramers' theory. Dimensionality reduction, however, entails memory effects; as a result, the effective frictional drag force along the reaction coordinate nontrivially depends on the time scale of the transition. Moreover, when both solvent and "internal" friction effects are important, their interplay results in a highly nonlinear dependence of the effective friction on solvent viscosity that is not captured by common phenomenological models of barrier crossing. Here, these effects are illustrated using an analytically solvable toy model of an unstructured polymer chain involved in an inter- or intramolecular transition. The transition rate is calculated using the Grote-Hynes and Langer theories, which--unlike Kramers' theory--account for memory. The resulting effective frictional force exerted by the polymer along the reaction coordinate can be rationalized in terms of the effective number of monomers engaged in the transition. Faster transitions (relative to the polymer reconfiguration time scale) involve fewer monomers and, correspondingly, lower friction forces, because the polymer chain does not have enough time to reconfigure in response to the transition.

Diagnosing the impact of alternative calibration strategies on coupled hydrologic models

NASA Astrophysics Data System (ADS)

Smith, T. J.; Perera, C.; Corrigan, C.

2017-12-01

Hydrologic models represent a significant tool for understanding, predicting, and responding to the impacts of water on society and society on water resources and, as such, are used extensively in water resources planning and management. Given this important role, the validity and fidelity of hydrologic models is imperative. While extensive focus has been paid to improving hydrologic models through better process representation, better parameter estimation, and better uncertainty quantification, significant challenges remain. In this study, we explore a number of competing model calibration scenarios for simple, coupled snowmelt-runoff models to better understand the sensitivity / variability of parameterizations and its impact on model performance, robustness, fidelity, and transferability. Our analysis highlights the sensitivity of coupled snowmelt-runoff model parameterizations to alterations in calibration approach, underscores the concept of information content in hydrologic modeling, and provides insight into potential strategies for improving model robustness / fidelity.

Finite-time adaptive sliding mode force control for electro-hydraulic load simulator based on improved GMS friction model

NASA Astrophysics Data System (ADS)

Kang, Shuo; Yan, Hao; Dong, Lijing; Li, Changchun

2018-03-01

This paper addresses the force tracking problem of electro-hydraulic load simulator under the influence of nonlinear friction and uncertain disturbance. A nonlinear system model combined with the improved generalized Maxwell-slip (GMS) friction model is firstly derived to describe the characteristics of load simulator system more accurately. Then, by using particle swarm optimization (PSO) algorithm ​combined with the system hysteresis characteristic analysis, the GMS friction parameters are identified. To compensate for nonlinear friction and uncertain disturbance, a finite-time adaptive sliding mode control method is proposed based on the accurate system model. This controller has the ability to ensure that the system state moves along the nonlinear sliding surface to steady state in a short time as well as good dynamic properties under the influence of parametric uncertainties and disturbance, which further improves the force loading accuracy and rapidity. At the end of this work, simulation and experimental results are employed to demonstrate the effectiveness of the proposed sliding mode control strategy.

Permanent Supportive Housing for Transition-Age Youths: Service Costs and Fidelity to the Housing First Model.

PubMed

Gilmer, Todd P

2016-06-01

Permanent supportive housing (PSH) programs are being implemented nationally and on a large scale. However, little is known about PSH for transition-age youths (ages 18 to 24). This study estimated health services costs associated with participation in PSH among youths and examined the relationship between fidelity to the Housing First model and health service outcomes. Administrative data were used in a quasi-experimental, difference-in-differences design with a propensity score-matched contemporaneous control group to compare health service costs among 2,609 youths in PSH and 2,609 youths with serious mental illness receiving public mental health services in California from January 1, 2004, through June 30, 2010. Data from a survey of PSH program practices were merged with the administrative data to examine changes in service use among 1,299 youths in 63 PSH programs by level of fidelity to the Housing First model. Total service costs increased by $13,337 among youths in PSH compared with youths in the matched control group. Youths in higher-fidelity programs had larger declines in use of inpatient services and larger increases in outpatient visits compared with youths in lower-fidelity programs. PSH for youths was associated with substantial increases in costs. Higher-fidelity PSH programs may be more effective than lower-fidelity programs in reducing use of inpatient services and increasing use of outpatient services. As substantial investments are made in PSH for youths, it is imperative that these programs are designed and implemented to maximize their effectiveness and their impact on youth outcomes.

Numerical Study of Frictional Properties and the Role of Cohesive End-Zones in Large Strike- Slip Earthquakes

NASA Astrophysics Data System (ADS)

Lovely, P. J.; Mutlu, O.; Pollard, D. D.

2007-12-01

Cohesive end-zones (CEZs) are regions of increased frictional strength and/or cohesion near the peripheries of faults that cause slip distributions to taper toward the fault-tip. Laboratory results, field observations, and theoretical models suggest an important role for CEZs in small-scale fractures and faults; however, their role in crustal-scale faulting and associated large earthquakes is less thoroughly understood. We present a numerical study of the potential role of CEZs on slip distributions in large, multi-segmented, strike-slip earthquake ruptures including the 1992 Landers Earthquake (Mw 7.2) and 1999 Hector Mine Earthquake (Mw 7.1). Displacement discontinuity is calculated using a quasi-static, 2D plane-strain boundary element (BEM) code for a homogeneous, isotropic, linear-elastic material. Friction is implemented by enforcing principles of complementarity. Model results with and without CEZs are compared with slip distributions measured by combined inversion of geodetic, strong ground motion, and teleseismic data. Stepwise and linear distributions of increasing frictional strength within CEZs are considered. The incorporation of CEZs in our model enables an improved match to slip distributions measured by inversion, suggesting that CEZs play a role in governing slip in large, strike-slip earthquakes. Additionally, we present a parametric study highlighting the very great sensitivity of modeled slip magnitude to small variations of the coefficient of friction. This result suggests that, provided a sufficiently well-constrained stress tensor and elastic moduli for the surrounding rock, relatively simple models could provide precise estimates of the magnitude of frictional strength. These results are verified by comparison with geometrically comparable finite element (FEM) models using the commercial code ABAQUS. In FEM models, friction is implemented by use of both Lagrange multipliers and penalty methods.

A hybrid PSO-SVM-based method for predicting the friction coefficient between aircraft tire and coating

NASA Astrophysics Data System (ADS)

Zhan, Liwei; Li, Chengwei

2017-02-01

A hybrid PSO-SVM-based model is proposed to predict the friction coefficient between aircraft tire and coating. The presented hybrid model combines a support vector machine (SVM) with particle swarm optimization (PSO) technique. SVM has been adopted to solve regression problems successfully. Its regression accuracy is greatly related to optimizing parameters such as the regularization constant C , the parameter gamma γ corresponding to RBF kernel and the epsilon parameter \\varepsilon in the SVM training procedure. However, the friction coefficient which is predicted based on SVM has yet to be explored between aircraft tire and coating. The experiment reveals that drop height and tire rotational speed are the factors affecting friction coefficient. Bearing in mind, the friction coefficient can been predicted using the hybrid PSO-SVM-based model by the measured friction coefficient between aircraft tire and coating. To compare regression accuracy, a grid search (GS) method and a genetic algorithm (GA) are used to optimize the relevant parameters (C , γ and \\varepsilon ), respectively. The regression accuracy could be reflected by the coefficient of determination ({{R}2} ). The result shows that the hybrid PSO-RBF-SVM-based model has better accuracy compared with the GS-RBF-SVM- and GA-RBF-SVM-based models. The agreement of this model (PSO-RBF-SVM) with experiment data confirms its good performance.

Understanding and Observing Subglacial Friction Using Seismology

NASA Astrophysics Data System (ADS)

Tsai, V. C.

2017-12-01

Glaciology began with a focus on understanding basic mechanical processes and producing physical models that could explain the principal observations. Recently, however, more attention has been paid to the wealth of recent observations, with many modeling efforts relying on data assimilation and empirical scalings, rather than being based on first-principles physics. Notably, ice sheet models commonly assume that subglacial friction is characterized by a "slipperiness" coefficient that is determined by inverting surface velocity observations. Predictions are usually then made by assuming these slipperiness coefficients are spatially and temporally fixed. However, this is only valid if slipperiness is an unchanging material property of the bed and, despite decades of work on subglacial friction, it has remained unclear how to best account for such subglacial physics in ice sheet models. Here, we describe how basic seismological concepts and observations can be used to improve our understanding and determination of subglacial friction. First, we discuss how standard models of granular friction can and should be used in basal friction laws for marine ice sheets, where very low effective pressures exist. We show that under realistic West Antarctic Ice Sheet conditions, standard Coulomb friction should apply in a relatively narrow zone near the grounding line and that this should transition abruptly as one moves inland to a different, perhaps Weertman-style, dependence of subglacial stress on velocity. We show that this subglacial friction law predicts significantly different ice sheet behavior even as compared with other friction laws that include effective pressure. Secondly, we explain how seismological observations of water flow noise and basal icequakes constrain subglacial physics in important ways. Seismically observed water flow noise can provide constraints on water pressures and channel sizes and geometry, leading to important data on subglacial friction. Basal icequake mechanisms also provide unique constraints on subglacial stress state as well as variations in water pressures. Together, the use of standard seismological concepts and new observations thus promises to provide new constraints on subglacial mechanics and focus attention back on the basic physical processes involved.

A reduced Iwan model that includes pinning for bolted joint mechanics

DOE PAGES

Brake, M. R. W.

2016-10-28

Bolted joints are prevalent in most assembled structures; however, predictive models for their behavior do not exist. Calibrated models, such as the Iwan model, are able to predict the response of a jointed structure over a range of excitations once calibrated at a nominal load. The Iwan model, though, is not widely adopted due to the high computational expense of implementation. To address this, an analytical solution of the Iwan model is derived under the hypothesis that for an arbitrary load reversal, there is a new distribution of dry friction elements, which are now stuck, that approximately resemble a scaledmore » version of the original distribution of dry friction elements. The dry friction elements internal to the Iwan model do not have a uniform set of parameters and are described by a distribution of parameters, i.e., which internal dry friction elements are stuck or slipping at a given load, that ultimately governs the behavior of the joint as it transitions from microslip to macroslip. This hypothesis allows the model to require no information from previous loading cycles. Additionally, the model is extended to include the pinning behavior inherent in a bolted joint. Modifications of the resulting framework are discussed to highlight how the constitutive model for friction can be changed (in the case of an Iwan–Stribeck formulation) or how the distribution of dry friction elements can be changed (as is the case for the Iwan plasticity model). Finally, the reduced Iwan plus pinning model is then applied to the Brake–Reuß beam in order to discuss methods to deduce model parameters from experimental data.« less

An analytical model of dynamic sliding friction during impact

NASA Astrophysics Data System (ADS)

Arakawa, Kazuo

2017-01-01

Dynamic sliding friction was studied based on the angular velocity of a golf ball during an oblique impact. This study used the analytical model proposed for the dynamic sliding friction on lubricated and non-lubricated inclines. The contact area A and sliding velocity u of the ball during impact were used to describe the dynamic friction force Fd = λAu, where λ is a parameter related to the wear of the contact area. A comparison with experimental results revealed that the model agreed well with the observed changes in the angular velocity during impact, and λAu is qualitatively equivalent to the empirical relationship, μN + μη‧dA/dt, given by the product between the frictional coefficient μ and the contact force N, and the additional term related to factor η‧ for the surface condition and the time derivative of A.

Finite element modeling of frictionally restrained composite interfaces

NASA Technical Reports Server (NTRS)

Ballarini, Roberto; Ahmed, Shamim

1989-01-01

The use of special interface finite elements to model frictional restraint in composite interfaces is described. These elements simulate Coulomb friction at the interface, and are incorporated into a standard finite element analysis of a two-dimensional isolated fiber pullout test. Various interfacial characteristics, such as the distribution of stresses at the interface, the extent of slip and delamination, load diffusion from fiber to matrix, and the amount of fiber extraction or depression are studied for different friction coefficients. The results are compared to those obtained analytically using a singular integral equation approach, and those obtained by assuming a constant interface shear strength. The usefulness of these elements in micromechanical modeling of fiber-reinforced composite materials is highlighted.

Bottom friction models for shallow water equations: Manning’s roughness coefficient and small-scale bottom heterogeneity

NASA Astrophysics Data System (ADS)

Dyakonova, Tatyana; Khoperskov, Alexander

2018-03-01

The correct description of the surface water dynamics in the model of shallow water requires accounting for friction. To simulate a channel flow in the Chezy model the constant Manning roughness coefficient is frequently used. The Manning coefficient nM is an integral parameter which accounts for a large number of physical factors determining the flow braking. We used computational simulations in a shallow water model to determine the relationship between the Manning coefficient and the parameters of small-scale perturbations of a bottom in a long channel. Comparing the transverse water velocity profiles in the channel obtained in the models with a perturbed bottom without bottom friction and with bottom friction on a smooth bottom, we constructed the dependence of nM on the amplitude and spatial scale of perturbation of the bottom relief.

Study on longitudinal force simulation of heavy-haul train

NASA Astrophysics Data System (ADS)

Chang, Chongyi; Guo, Gang; Wang, Junbiao; Ma, Yingming

2017-04-01

The longitudinal dynamics model of heavy-haul trains and air brake model used in the longitudinal train dynamics (LTDs) are established. The dry friction damping hysteretic characteristic of steel friction draft gears is simulated by the equation which describes the suspension forces in truck leaf springs. The model of draft gears introduces dynamic loading force, viscous friction of steel friction and the damping force. Consequently, the numerical model of the draft gears is brought forward. The equation of LTDs is strongly non-linear. In order to solve the response of the strongly non-linear system, the high-precision and equilibrium iteration method based on the Newmark-β method is presented and numerical analysis is made. Longitudinal dynamic forces of the 20,000 tonnes heavy-haul train are tested, and models and solution method provided are verified by the test results.

Micromechanics of ice friction

NASA Astrophysics Data System (ADS)

Sammonds, P. R.; Bailey, E.; Lishman, B.; Scourfield, S.

2015-12-01

Frictional mechanics are controlled by the ice micro-structure - surface asperities and flaws - but also the ice fabric and permeability network structure of the contacting blocks. Ice properties are dependent upon the temperature of the bulk ice, on the normal stress and on the sliding velocity and acceleration. This means the shear stress required for sliding is likewise dependent on sliding velocity, acceleration, and temperature. We aim to describe the micro-physics of the contacting surface. We review micro-mechanical models of friction: the elastic and ductile deformation of asperities under normal loads and their shear failure by ductile flow, brittle fracture, or melting and hydrodynamic lubrication. Combinations of these give a total of six rheological models of friction. We present experimental results in ice mechanics and physics from laboratory experiments to understand the mechanical models. We then examine the scaling relations of the slip of ice, to examine how the micro-mechanics of ice friction can be captured simple reduced-parameter models, describing the mechanical state and slip rate of the floes. We aim to capture key elements that they may be incorporated into mid and ocean-basin scale modelling.

Investigation of squeal noise under positive friction characteristics condition provided by friction modifiers

NASA Astrophysics Data System (ADS)

Liu, Xiaogang; Meehan, Paul A.

2016-06-01

Field application of friction modifiers on the top of rail has been shown to effectively curb squeal and reduce lateral forces, but performance can be variable, according to other relevant research. Up to now, most investigations of friction modifiers were conducted in the field, where it is difficult to control or measure important parameters such as angle of attack, rolling speed, adhesion ratio etc. In the present investigation, the effect of different friction modifiers on the occurrence of squeal was investigated on a rolling contact two disk test rig. In particular, friction-creep curves and squeal sound pressure levels were measured under different rolling speeds and friction modifiers. The results show friction modifiers can eliminate or reduce the negative slope of friction-creep curves, but squeal noise still exists. Theoretical modelling of instantaneous creep behaviours reveals a possible reason why wheel squeal still exists after the application of friction modifiers.

Chemical origins of frictional aging.

PubMed

Liu, Yun; Szlufarska, Izabela

2012-11-02

Although the basic laws of friction are simple enough to be taught in elementary physics classes and although friction has been widely studied for centuries, in the current state of knowledge it is still not possible to predict a friction force from fundamental principles. One of the highly debated topics in this field is the origin of static friction. For most macroscopic contacts between two solids, static friction will increase logarithmically with time, a phenomenon that is referred to as aging of the interface. One known reason for the logarithmic growth of static friction is the deformation creep in plastic contacts. However, this mechanism cannot explain frictional aging observed in the absence of roughness and plasticity. Here, we discover molecular mechanisms that can lead to a logarithmic increase of friction based purely on interfacial chemistry. Predictions of our model are consistent with published experimental data on the friction of silica.

Constitutive modelling of lubricants in concentrated contacts at high slide to roll ratios

NASA Technical Reports Server (NTRS)

Tevaarwerk, J. L.

1985-01-01

A constitutive lubricant friction model for rolling/sliding concentrated contacts such as gears and cams was developed, based upon the Johnson and Tevaarwerk fluid rheology model developed earlier. The friction model reported herein differs from the earlier rheological models in that very large slide to roll ratios can now be accommodated by modifying the thermal response of the model. Also the elastic response of the fluid has been omitted from the model, thereby making it much simpler for use in the high slide to roll contacts. The effects of this simplification are very minimal on the outcome of the predicted friction losses (less than 1%). In essence then the lubricant friction model developed for the high slide to roll ratios treats the fluid in the concentrated contact as consisting of a nonlinear viscous element that is pressure, temperature, and strain rate dependent in its shear response. The fluid rheological constants required for the prediction of the friction losses at different contact conditions are obtained by traction measurements on several of the currently used gear lubricants. An example calculation, using this model and the fluid parameters obtained from the experiments, shows that it correctly predicts trends and magnitude of gear mesh losses measured elsewhere for the same fluids tested here.

Three-dimensional friction measurement during hip simulation

PubMed Central

Braun, Steffen; Al-Salehi, Loay; Reinders, Joern; Mueller, Ulrike; Kretzer, J. Philippe

2017-01-01

Objectives Wear of total hip replacements has been the focus of many studies. However, frictional effects, such as high loading on intramodular connections or the interface to the bone, as well as friction associated squeaking have recently increased interest about the amount of friction that is generated during daily activities. The aim of this study was thus to establish and validate a three-dimensional friction setup under standardized conditions. Materials and methods A standard hip simulator was modified to allow for high precision measurements of small frictional effects in the hip during three-dimensional hip articulation. The setup was verified by an ideal hydrostatic bearing and validated with a static-load physical pendulum and an extension-flexion rotation with a dynamic load profile. Additionally, a pendulum model was proposed for screening measurement of frictional effects based on the damping behavior of the angular oscillation without the need for any force/moment transducer. Finally, three-dimensional friction measurements have been realized for ceramic-on-polyethylene bearings of three different sizes (28, 36 and 40 mm). Results A precision of less than 0.2 Nm during three-dimensional friction measurements was reported, while increased frictional torque (resultant as well as taper torque) was measured for larger head diameters. These effects have been confirmed by simple pendulum tests and the theoretical model. A comparison with current literature about friction measurements is presented. Conclusions This investigation of friction is able to provide more information about a field that has been dominated by the reduction of wear. It should be considered in future pre-clinical testing protocols given by international organizations of standardization. PMID:28886102

Three-dimensional friction measurement during hip simulation.

PubMed

Sonntag, Robert; Braun, Steffen; Al-Salehi, Loay; Reinders, Joern; Mueller, Ulrike; Kretzer, J Philippe

2017-01-01

Wear of total hip replacements has been the focus of many studies. However, frictional effects, such as high loading on intramodular connections or the interface to the bone, as well as friction associated squeaking have recently increased interest about the amount of friction that is generated during daily activities. The aim of this study was thus to establish and validate a three-dimensional friction setup under standardized conditions. A standard hip simulator was modified to allow for high precision measurements of small frictional effects in the hip during three-dimensional hip articulation. The setup was verified by an ideal hydrostatic bearing and validated with a static-load physical pendulum and an extension-flexion rotation with a dynamic load profile. Additionally, a pendulum model was proposed for screening measurement of frictional effects based on the damping behavior of the angular oscillation without the need for any force/moment transducer. Finally, three-dimensional friction measurements have been realized for ceramic-on-polyethylene bearings of three different sizes (28, 36 and 40 mm). A precision of less than 0.2 Nm during three-dimensional friction measurements was reported, while increased frictional torque (resultant as well as taper torque) was measured for larger head diameters. These effects have been confirmed by simple pendulum tests and the theoretical model. A comparison with current literature about friction measurements is presented. This investigation of friction is able to provide more information about a field that has been dominated by the reduction of wear. It should be considered in future pre-clinical testing protocols given by international organizations of standardization.

Friction torque in thrust ball bearings grease lubricated

NASA Astrophysics Data System (ADS)

Ianuş, G.; Dumitraşcu, A. C.; Cârlescu, V.; Olaru, D. N.

2016-08-01

The authors investigated experimentally and theoretically the friction torque in a modified thrust ball bearing having only 3 balls operating at low axial load and lubricated with NGLI-00 and NGLI-2 greases. The experiments were made by using spin-down methodology and the results were compared with the theoretical values based on Biboulet&Houpert's rolling friction equations. Also, the results were compared with the theoretical values obtained with SKF friction model adapted for 3 balls. A very good correlation between experiments and Biboulet_&_Houpert's predicted results was obtained for the two greases. Also was observed that the theoretical values for the friction torque calculated with SKF model adapted for a thrust ball bearing having only 3 balls are smaller that the experimental values.

The adhesion and hysteresis effect in friction skin with artificial materials

NASA Astrophysics Data System (ADS)

Subhi, K. A.; Tudor, A.; Hussein, E. K.; Wahad, H. S.

2017-02-01

Human skin is a soft biomaterial with a complex anatomical structure and it has a complex material behavior during the mechanical contact with objects and surfaces. The friction adhesion component is defined by means of the theories of Johnson-Kendall-Roberts (JKR), Derjaguin-Muller-Toporov (DMT) and Maugis - Dugdale (MD). We shall consider the human skin entering into contact with a rigid surface. The deformation (hysteresis) component of the skin friction is evaluated with Voigt rheological model for the spherical contact, with the original model, developed in MATHCAD software. The adhesive component of the skin friction is greater than the hysteresis component for all friction parameters (load, velocity, the strength of interface between skin and the artificial material).

Modelling of the frictional behaviour of the snake skin covered by anisotropic surface nanostructures.

PubMed

Filippov, Alexander E; Gorb, Stanislav N

2016-03-23

Previous experimental data clearly revealed anisotropic friction on the ventral scale surface of snakes. However, it is known that frictional properties of the ventral surface of the snake skin range in a very broad range and the degree of anisotropy ranges as well to a quite strong extent. This might be due to the variety of species studied, diversity of approaches used for the friction characterization, and/or due to the variety of substrates used as a counterpart in the experiments. In order to understand the interactions between the nanostructure arrays of the ventral surface of the snake skin, this study was undertaken, which is aimed at numerical modeling of frictional properties of the structurally anisotropic surfaces in contact with various size of asperities. The model shows that frictional anisotropy appears on the snake skin only on the substrates with a characteristic range of roughness, which is less or comparable with dimensions of the skin microstructure. In other words, scale of the skin relief should reflect an adaptation to the particular range of surfaces asperities of the substrate.

Modelling of the frictional behaviour of the snake skin covered by anisotropic surface nanostructures

PubMed Central

Filippov, Alexander E.; Gorb, Stanislav N.

2016-01-01

Previous experimental data clearly revealed anisotropic friction on the ventral scale surface of snakes. However, it is known that frictional properties of the ventral surface of the snake skin range in a very broad range and the degree of anisotropy ranges as well to a quite strong extent. This might be due to the variety of species studied, diversity of approaches used for the friction characterization, and/or due to the variety of substrates used as a counterpart in the experiments. In order to understand the interactions between the nanostructure arrays of the ventral surface of the snake skin, this study was undertaken, which is aimed at numerical modeling of frictional properties of the structurally anisotropic surfaces in contact with various size of asperities. The model shows that frictional anisotropy appears on the snake skin only on the substrates with a characteristic range of roughness, which is less or comparable with dimensions of the skin microstructure. In other words, scale of the skin relief should reflect an adaptation to the particular range of surfaces asperities of the substrate. PMID:27005001

Modelling of the frictional behaviour of the snake skin covered by anisotropic surface nanostructures

NASA Astrophysics Data System (ADS)

Filippov, Alexander E.; Gorb, Stanislav N.

2016-03-01

Previous experimental data clearly revealed anisotropic friction on the ventral scale surface of snakes. However, it is known that frictional properties of the ventral surface of the snake skin range in a very broad range and the degree of anisotropy ranges as well to a quite strong extent. This might be due to the variety of species studied, diversity of approaches used for the friction characterization, and/or due to the variety of substrates used as a counterpart in the experiments. In order to understand the interactions between the nanostructure arrays of the ventral surface of the snake skin, this study was undertaken, which is aimed at numerical modeling of frictional properties of the structurally anisotropic surfaces in contact with various size of asperities. The model shows that frictional anisotropy appears on the snake skin only on the substrates with a characteristic range of roughness, which is less or comparable with dimensions of the skin microstructure. In other words, scale of the skin relief should reflect an adaptation to the particular range of surfaces asperities of the substrate.

Site fidelity of the declining amphibian Rana sierrae (Sierra Nevada yellow-legged frog)

Treesearch

Kathleen Matthews; Haiganoush Preisler

2010-01-01

From 1997 to 2006, we used mark–recapture models to estimate the site fidelity of 1250 Sierra Nevada yellow-legged frogs (Rana sierrae) in Kings Canyon National Park, California, USA, during their three main activity periods of overwintering, breeding, and feeding. To quantify site fidelity, the tendency to return to and reuse previously occupied...

Influence of the chemical surface structure on the nanoscale friction in plasma nitrided and post-oxidized ferrous alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Freislebem, Márcia; Menezes, Caren M.; Cemin, Felipe

2014-09-15

Friction is a ubiquitous phenomenon in everyday activities spanning from vehicles where efficient brakes are mandatory up to mechanical devices where its minimum effects are pursued for energy efficiency issues. Recently, theoretical models succeed correlating the friction behavior with energy transference via phonons between sliding surfaces. Therefore, considering that the energy losses by friction are prompted through phonons, the chemical surface structure between sliding surfaces is very important to determine the friction phenomenon. In this work, we address the issue of friction between a conical diamond tip sliding on different functionalized flat steel surfaces by focusing the influence of themore » chemical bonds in the outermost layers on the sliding resistance. This geometry allows probing the coupling of the sharp tip with terminator species on the top and underneath material surface at in-depth friction measurements from 20 to 200 nm. Experimentally, the friction coefficient decreases when nitrogen atoms are substituted for oxygen in the iron network. This effect is interpreted as due to energy losses through phonons whilst lower vibrational frequency excitation modes imply lower friction coefficients and a more accurate adjustment is obtained when a theoretical model with longitudinal adsorbate vibration is used.« less

Coefficient of Friction Patterns Can Identify Damage in Native and Engineered Cartilage Subjected to Frictional-Shear Stress

PubMed Central

Whitney, G. A.; Mansour, J. M.; Dennis, J. E.

2015-01-01

The mechanical loading environment encountered by articular cartilage in situ makes frictional-shear testing an invaluable technique for assessing engineered cartilage. Despite the important information that is gained from this testing, it remains under-utilized, especially for determining damage behavior. Currently, extensive visual inspection is required to assess damage; this is cumbersome and subjective. Tools to simplify, automate, and remove subjectivity from the analysis may increase the accessibility and usefulness of frictional-shear testing as an evaluation method. The objective of this study was to determine if the friction signal could be used to detect damage that occurred during the testing. This study proceeded in two phases: first, a simplified model of biphasic lubrication that does not require knowledge of interstitial fluid pressure was developed. In the second phase, frictional-shear tests were performed on 74 cartilage samples, and the simplified model was used to extract characteristic features from the friction signals. Using support vector machine classifiers, the extracted features were able to detect damage with a median accuracy of approximately 90%. The accuracy remained high even in samples with minimal damage. In conclusion, the friction signal acquired during frictional-shear testing can be used to detect resultant damage to a high level of accuracy. PMID:25691395

Finite grid instability and spectral fidelity of the electrostatic Particle-In-Cell algorithm

DOE PAGES

Huang, C. -K.; Zeng, Y.; Wang, Y.; ...

2016-10-01

The origin of the Finite Grid Instability (FGI) is studied by resolving the dynamics in the 1D electrostatic Particle-In-Cell (PIC) model in the spectral domain at the single particle level and at the collective motion level. The spectral fidelity of the PIC model is contrasted with the underlying physical system or the gridless model. The systematic spectral phase and amplitude errors from the charge deposition and field interpolation are quantified for common particle shapes used in the PIC models. Lastly, it is shown through such analysis and in simulations that the lack of spectral fidelity relative to the physical systemmore » due to the existence of aliased spatial modes is the major cause of the FGI in the PIC model.« less

Finite grid instability and spectral fidelity of the electrostatic Particle-In-Cell algorithm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, C. -K.; Zeng, Y.; Wang, Y.

The origin of the Finite Grid Instability (FGI) is studied by resolving the dynamics in the 1D electrostatic Particle-In-Cell (PIC) model in the spectral domain at the single particle level and at the collective motion level. The spectral fidelity of the PIC model is contrasted with the underlying physical system or the gridless model. The systematic spectral phase and amplitude errors from the charge deposition and field interpolation are quantified for common particle shapes used in the PIC models. Lastly, it is shown through such analysis and in simulations that the lack of spectral fidelity relative to the physical systemmore » due to the existence of aliased spatial modes is the major cause of the FGI in the PIC model.« less

Slip-Size Distribution and Self-Organized Criticality in Block-Spring Models with Quenched Randomness

NASA Astrophysics Data System (ADS)

Sakaguchi, Hidetsugu; Kadowaki, Shuntaro

2017-07-01

We study slowly pulling block-spring models in random media. Second-order phase transitions exist in a model pulled by a constant force in the case of velocity-strengthening friction. If external forces are slowly increased, nearly critical states are self-organized. Slips of various sizes occur, and the probability distributions of slip size roughly obey power laws. The exponent is close to that in the quenched Edwards-Wilkinson model. Furthermore, the slip-size distributions are investigated in cases of Coulomb friction, velocity-weakening friction, and two-dimensional block-spring models.

Orbit Stability of OSIRIS-REx in the Vicinity of Bennu Using a High-Fidelity Solar Radiation Model

NASA Technical Reports Server (NTRS)

Williams, Trevor W.; Hughes, Kyle M.; Mashiku, Alinda K.; Longuski, James M.

2015-01-01

Solar radiation pressure is one of the largest perturbing forces on the OSIRISRex trajectory as it orbits the asteroid Bennu. In this work, we investigate how forces due to solar radiation perturb the OSIRIS-REx trajectory in a high-fidelity model. The model accounts for Bennu's non-spherical gravity field, third-body gravity forces from the Sun and Jupiter, as well as solar radiation forces acting on a simplified spacecraft model. Such high-fidelity simulations indicate significant solar radiation pressure perturbations from the nominal orbit. Modifications to the initial design of the nominal orbit are found using a variation of parameters approach that reduce the perturbation in eccentricity by a factor of one-half.

Beyond teacher training: the critical role of professional development in maintaining curriculum fidelity.

PubMed

LaChausse, Robert G; Clark, Kim R; Chapple, Sabrina

2014-03-01

To examine how teacher characteristics affected program fidelity in an impact evaluation study of the Positive Prevention PLUS program, and to propose a comprehensive teacher training and professional development structure to increase program fidelity. Curriculum fidelity logs, lesson observations, and teacher surveys were used to measure teacher characteristics and implementation fidelity including adherence, adaptation, and lesson quality. Compared with non-health credentialed teachers, credential health education teachers had greater comfort and self-efficacy regarding sex-related instruction. Teacher self-efficacy and comfort were significant predictors of adherence. Implementation fidelity may be linked to teacher characteristics that can be enhanced during curriculum training. A 2-day teacher training may not adequately address teacher facilitation skills or the maintenance of institutional supports for implementing a program with fidelity and quality. A new model of comprehensive teacher training and support is offered. This new training infrastructure is intended to contribute to the school district's institutionalization of higher-quality comprehensive sexual health education and increase program fidelity. Copyright © 2014 Society for Adolescent Health and Medicine. All rights reserved.

Experimental evidence for dynamic friction on rock fractures from frequency-dependent nonlinear hysteresis and harmonic generation

NASA Astrophysics Data System (ADS)

Saltiel, Seth; Bonner, Brian P.; Mittal, Tushar; Delbridge, Brent; Ajo-Franklin, Jonathan B.

2017-07-01

Frictional properties affect the propagation of high-amplitude seismic waves across rock fractures and faults. Laboratory evidence suggests that these properties can be measured in active seismic surveys, potentially offering a route to characterizing friction in situ. We present experimental results from a subresonance torsional modulus and attenuation apparatus that utilizes micron-scale sinusoidal oscillations to probe the nonlinear stress-strain relation at a range of strain amplitudes and rates. Nonlinear effects are further quantified using harmonic distortion; however, time series data best illuminate underlying physical processes. The low-frequency stress-strain hysteretic loops show stiffening at the sinusoid's static ends, but stiffening is reduced above a threshold frequency. This shape is determined by harmonic generation in the strain; the stress signal has no harmonics, confirming that the fractured sample is the source of the nonlinearity. These qualitative observations suggest the presence of rate-dependent friction and are consistent between fractures in three different rock types. We propose that static friction at the low strain rate part of the cycle, when given sufficient "healing" time at low oscillation frequencies, causes this stiffening cusp shape in the hysteresis loop. While rate-and-state friction is commonly used to represent dynamic friction, it cannot capture static friction or negative slip velocities. So we implement another dynamic friction model, based on the work of Dahl, which describes this process and produces similar results. Since the two models have a similar form, parameterizations of field data could constraint fault model inputs, such as specific location velocity strengthening or weakening properties.

Adaptive robust motion trajectory tracking control of pneumatic cylinders with LuGre model-based friction compensation

NASA Astrophysics Data System (ADS)

Meng, Deyuan; Tao, Guoliang; Liu, Hao; Zhu, Xiaocong

2014-07-01

Friction compensation is particularly important for motion trajectory tracking control of pneumatic cylinders at low speed movement. However, most of the existing model-based friction compensation schemes use simple classical models, which are not enough to address applications with high-accuracy position requirements. Furthermore, the friction force in the cylinder is time-varying, and there exist rather severe unmodelled dynamics and unknown disturbances in the pneumatic system. To deal with these problems effectively, an adaptive robust controller with LuGre model-based dynamic friction compensation is constructed. The proposed controller employs on-line recursive least squares estimation (RLSE) to reduce the extent of parametric uncertainties, and utilizes the sliding mode control method to attenuate the effects of parameter estimation errors, unmodelled dynamics and disturbances. In addition, in order to realize LuGre model-based friction compensation, the modified dual-observer structure for estimating immeasurable friction internal state is developed. Therefore, a prescribed motion tracking transient performance and final tracking accuracy can be guaranteed. Since the system model uncertainties are unmatched, the recursive backstepping design technology is applied. In order to solve the conflicts between the sliding mode control design and the adaptive control design, the projection mapping is used to condition the RLSE algorithm so that the parameter estimates are kept within a known bounded convex set. Finally, the proposed controller is tested for tracking sinusoidal trajectories and smooth square trajectory under different loads and sudden disturbance. The testing results demonstrate that the achievable performance of the proposed controller is excellent and is much better than most other studies in literature. Especially when a 0.5 Hz sinusoidal trajectory is tracked, the maximum tracking error is 0.96 mm and the average tracking error is 0.45 mm. This paper constructs an adaptive robust controller which can compensate the friction force in the cylinder.

Hands-On and Minds-On Modeling Activities to Improve Students' Conceptions of Microscopic Friction

NASA Astrophysics Data System (ADS)

Corpuz, Edgar G.; Rebello, N. Sanjay

2007-11-01

In this paper we discuss the development and validation of hands-on and minds-on modeling activities geared towards improving students' understanding of microscopic friction. We will also present our investigation on the relative effectiveness of the use of the developed instructional material with two lecture formats—traditional and videotaped lectures. Results imply that through a series of carefully designed hands-on and minds-on modeling activities, it is possible to facilitate the refinement of students' ideas of microscopic friction.

Friction-Stir Welding and Mathematical Modeling

NASA Technical Reports Server (NTRS)

Rostant, Victor D.

1999-01-01

The friction-stir welding process is a remarkable way for making butt and lap joints in aluminum alloys. This process operates by passing a rotating tool between two closely butted plates. Through this process it generates a lot of heat and heated material is stirred from both sides of the plates in which the outcome will one high quality weld. My research has been done to study the FSW through mathematical modeling, and using modeling to better understand what take place during the friction-stir weld.

Linear viscoelasticity of a single semiflexible polymer with internal friction.

PubMed

Hiraiwa, Tetsuya; Ohta, Takao

2010-07-28

The linear viscoelastic behaviors of single semiflexible chains with internal friction are studied based on the wormlike-chain model. It is shown that the frequency dependence of the complex compliance in the high frequency limit is the same as that of the Voigt model. This asymptotic behavior appears also for the Rouse model with internal friction. We derive the characteristic times for both the high frequency limit and the low frequency limit and compare the results with those obtained by Khatri et al.

Fault friction, regional stress, and crust-mantle coupling in southern California from finite element models

NASA Technical Reports Server (NTRS)

Bird, P.; Baumgardner, J.

1984-01-01

To determine the correct fault rheology of the Transverse Ranges area of California, a new finite element to represent faults and a mangle drag element are introduced into a set of 63 simulation models of anelastic crustal strain. It is shown that a slip rate weakening rheology for faults is not valid in California. Assuming that mantle drag effects on the crust's base are minimal, the optimal coefficient of friction in the seismogenic portion of the fault zones is 0.4-0.6 (less than Byerly's law assumed to apply elsewhere). Depending on how the southern California upper mantle seismic velocity anomaly is interpreted, model results are improved or degraded. It is found that the location of the mantle plate boundary is the most important secondary parameter, and that the best model is either a low-stress model (fault friction = 0.3) or a high-stress model (fault friction = 0.85), each of which has strong mantel drag. It is concluded that at least the fastest moving faults in southern California have a low friction coefficient (approximtely 0.3) because they contain low strength hydrated clay gouges throughout the low-temperature seismogenic zone.

Adaptive methods, rolling contact, and nonclassical friction laws

NASA Technical Reports Server (NTRS)

Oden, J. T.

1989-01-01

Results and methods on three different areas of contemporary research are outlined. These include adaptive methods, the rolling contact problem for finite deformation of a hyperelastic or viscoelastic cylinder, and non-classical friction laws for modeling dynamic friction phenomena.

An analysis of the Dahl friction model and its effect on a CMG gimbal rate controller

NASA Technical Reports Server (NTRS)

Nurre, G. S.

1974-01-01

The effects of friction, represented by the Dahl model, on a CMG rate control system was investigated by digital simulation. The conclusion from these simulation results is that gimbal pivot friction can be a significant effect on the gimbal rate control system. The magnitude of the problem this presents depends on the characteristics of the actual pivot. It would appear from this preliminary look that one solution is to insure that the control system natural frequency is higher by some prescribed amount than the natural frequency of the friction loop.

Historical Scientific Models and Theories as Resources for Learning and Teaching: The Case of Friction

ERIC Educational Resources Information Center

Besson, Ugo

2013-01-01

This paper presents a history of research and theories on sliding friction between solids. This history is divided into four phases: from Leonardo da Vinci to Coulomb and the establishment of classical laws of friction; the theories of lubrication and the Tomlinson's theory of friction (1850-1930); the theories of wear, the Bowden and Tabor's…

The experiment research of the friction sliding isolation structure

NASA Astrophysics Data System (ADS)

Zhang, Shirong; Li, Jiangle; Wang, Sheliang

2018-04-01

This paper investigated the theory of the friction sliding isolation structure, The M0S2 solid lubricant was adopted as isolation bearing friction materials, and a new sliding isolation bearing was designed and made. The formula of the friction factor and the compression stress was proposed. The feasibility of the material MoS2 used as the coating material in a friction sliding isolation system was tested on the 5 layers concrete frame model. Two application experiment conditions were presented. The results of the experiment research indicated that the friction sliding isolation technology have a good damping effect.

Peptide chain dynamics in light and heavy water: zooming in on internal friction.

PubMed

Schulz, Julius C F; Schmidt, Lennart; Best, Robert B; Dzubiella, Joachim; Netz, Roland R

2012-04-11

Frictional effects due to the chain itself, rather than the solvent, may have a significant effect on protein dynamics. Experimentally, such "internal friction" has been investigated by studying folding or binding kinetics at varying solvent viscosity; however, the molecular origin of these effects is hard to pinpoint. We consider the kinetics of disordered glycine-serine and α-helix forming alanine peptides and a coarse-grained protein folding model in explicit-solvent molecular dynamics simulations. By varying the solvent mass over more than two orders of magnitude, we alter only the solvent viscosity and not the folding free energy. Folding dynamics at the near-vanishing solvent viscosities accessible by this approach suggests that solvent and internal friction effects are intrinsically entangled. This finding is rationalized by calculation of the polymer end-to-end distance dynamics from a Rouse model that includes internal friction. An analysis of the friction profile along different reaction coordinates, extracted from the simulation data, demonstrates that internal as well as solvent friction varies substantially along the folding pathways and furthermore suggests a connection between friction and the formation of hydrogen bonds upon folding. © 2012 American Chemical Society

Effects of friction reduction of micro-patterned array of rough slider bearing

NASA Astrophysics Data System (ADS)

Kim, M.; Lee, D. W.; Jeong, J. H.; Chung, W. S.; Park, J. K.

2017-08-01

Complex micro-scale patterns have attracted interest because of the functionality that can be created using this type of patterning. This study evaluates the frictional reduction effects of various micro patterns on a slider bearing surface which is operating under mixed lubrication. Due to the rapid growth of contact area under mixed lubrication, it has become important to study the phenomenon of asperity contact in bearings with a heavy load. New analysis using the modified Reynolds equation with both the average flow model and the contact model of asperities is conducted for the rough slider bearing. A numerical analysis is performed to determine the effects of surface roughness on a lubricated bearing. Several dented patterns such as, dot pattern, dashed line patterns are used to evaluate frictional reduction effects. To verify the analytical results, friction test for the micro-patterned samples are performed. From comparing the frictional reduction effects of patterned arrays, the design of them can control the frictional loss of bearings. Our results showed that the design of pattern array on the bearing surface was important to the friction reduction of bearings. To reduce frictional loss, the longitudinal direction of them was better than the transverse direction.

Comparative study of friction between metallic and conventional interactive self-ligating brackets in different alignment conditions.

PubMed

Jakob, Sérgio Ricardo; Matheus, Davison; Jimenez-Pellegrin, Maria Cristina; Turssi, Cecília Pedroso; Amaral, Flávia Lucisano Botelho

2014-01-01

The aim of this study was to compare the friction between three bracket models: conventional stainless steel (Ovation, Dentsply GAC), self-ligating ceramic (In-Ovation, Denstply GAC) and self-ligating stainless steel brackets (In-Ovation R, Dentsply GAC). Five brackets were used for each model. They were bonded to an aluminum prototype that allowed the simulation of four misalignment situations (n = 10). Three of these situations occured at the initial phase (in which a 0.016-in nickel-titanium wire was used): 1. horizontal; 2. vertical; and 3. simultaneous horizontal/vertical. One of the situations occurred at the final treatment phase: 4. no misalignment (in which a 0.019 x 0.025-inch stainless steel rectangular wire was used). The wires slipped through the brackets and friction was measured by a Universal Testing Machine. Analysis of variance followed by Tukey's Test for multiple comparisons (α = 0.05) were applied to assess the results. Significant interaction (p < 0.01) among groups was found. For the tests that simulated initial alignment, Ovation® bracket produced the highest friction. The two self-ligating models resulted in lower and similar values, except for the horizontal situation, in which In-Ovation C® showed lower friction, which was similar to the In-Ovation R® metallic model. For the no misalignment situation, the same results were observed. The self-ligating system was superior to the conventional one due to producing less friction. With regard to the material used for manufacturing the brackets, the In-Ovation C® ceramic model showed less friction than the metallic ones.

Bulk-friction modeling of afterslip and the modified Omori law

USGS Publications Warehouse

Wennerberg, Leif; Sharp, Robert V.

1997-01-01

Afterslip data from the Superstition Hills fault in southern California, a creep event on the same fault, the modified Omori law, and cumulative moments from aftershocks of the 1957 Aleutian Islands earthquake all indicate that the original formulation by Dieterich (1981) [Constitutive properties of faults with simulated gouge. AGU, Geophys. Monogr. 24, 103–120] for friction evolution is more appropriate for systems far from instability than the commonly used approximation developed by Ruina (1983) [Slip instability and state variable friction laws. J. Geophys. Res. 88, 10359–10370] to study instability. The mathematical framework we use to test the friction models is a one-dimensional, massless spring-slider under the simplifying assumption, proposed by Scholz (1990) [The Mechanics of Earthquakes and Faulting. Cambridge University Press] and used by Marone et al. (1991) [On the mechanics of earthquake afterslip. J. Geophys. Res., 96: 8441–8452], that the state variable takes on its velocity-dependent steady-state value throughout motion in response to a step in stress. This assumption removes explicit state-variable dependence from the model, obviating the need to consider state-variable evolution equations. Anti-derivatives of the modified Omori law fit our data very well and are very good approximate solutions to our model equations. A plausible friction model with Omori-law solutions used by Wesson (1988) [Dynamics of fault creep. J. Geophys. Res. 93, 8929–8951] to model fault creep and generalized by Rice (1983) [Constitutive relations for fault slip and earthquake instabilities. Pure Appl. Geophys. 121, 443–475] to a rate-and-state variable friction model yields exactly Omori's law with exponents greater than 1, but yields unstable solutions for Omori exponents less than 1. We estimate from the Dieterich formulation the dimensionless parameter a∗ which is equal to the product of the nominal coefficient of friction and the more commonly reported friction parameter a. We find that a∗ is typically positive, qualitatively consistent with laboratory observations, although our observations are considerably larger than laboratory values. However, we also find good model fits for a∗ < 0 when data correspond to Omori exponents less than 1. A modification of the stability analysis by Rice and Ruina (1983) [Stability of steady frictional slipping. J. Appl. Mech. 50, 343–349] indicates that a∗ < 0 is not a consequence of our assumption regarding state-variable evolution. A consistent interpretation of a∗ < 0 in terms of laboratory models appears to be that the data are from later portions of processes better characterized by two-state-variable friction models. a∗ < 0 is explained by assuming that our data cannot resolve the co-seismic evolution of a short-length-scale state variable to a velocity-weakening state; our parameterization leads to an apparent negative instantaneous viscosity. We estimate the largest critical slip distance associated with afterslip to be ∼1–10 cm, consistent with other estimates for near-surface materials. We assume that our observed large values for a∗ reflect the fact that our model ignores the geometrical complexities of three-dimensional stresses in fractured crustal materials around a fault zone with frictional stresses that vary on a fault surface. Our one-dimensional model parameters reflect spatially averaged, bulk, stress and frictional properties of a fault zone, where we clearly cannot specify the details of the averaging process. Our analysis of Omori's law suggests that bulk-frictional properties of a fault zone are well described by our simple laboratory-based models, but they would need to change during the seismic cycle for a mainshock instability to recur, unless a mainshock-aftershock sequence were characterized by a process similar to the arrested instabilities possible in two-state-variable systems.

Bulk-friction modeling of afterslip and the modified Omori law

NASA Astrophysics Data System (ADS)

Wennerberg, Leif; Sharp, Robert V.

1997-08-01

Afterslip data from the Superstition Hills fault in southern California, a creep event on the same fault, the modified Omori law, and cumulative moments from aftershocks of the 1957 Aleutian Islands earthquake all indicate that the original formulation by Dieterich (1981) [Constitutive properties of faults with simulated gouge. AGU, Geophys. Monogr. 24, 103-120] for friction evolution is more appropriate for systems far from instability than the commonly used approximation developed by Ruina (1983) [Slip instability and state variable friction laws. J. Geophys. Res. 88, 10359-10370] to study instability. The mathematical framework we use to test the friction models is a one-dimensional, massless spring-slider under the simplifying assumption, proposed by Scholz (1990) [The Mechanics of Earthquakes and Faulting. Cambridge University Press] and used by Marone et al. (1991) [On the mechanics of earthquake afterslip. J. Geophys. Res., 96: 8441-8452], that the state variable takes on its velocity-dependent steady-state value throughout motion in response to a step in stress. This assumption removes explicit state-variable dependence from the model, obviating the need to consider state-variable evolution equations. Anti-derivatives of the modified Omori law fit our data very well and are very good approximate solutions to our model equations. A plausible friction model with Omori-law solutions used by Wesson (1988) [Dynamics of fault creep. J. Geophys. Res. 93, 8929-8951] to model fault creep and generalized by Rice (1983) [Constitutive relations for fault slip and earthquake instabilities. Pure Appl. Geophys. 121, 443-475] to a rate-and-state variable friction model yields exactly Omori's law with exponents greater than 1, but yields unstable solutions for Omori exponents less than 1. We estimate from the Dieterich formulation the dimensionless parameter a∗ which is equal to the product of the nominal coefficient of friction and the more commonly reported friction parameter a. We find that a∗ is typically positive, qualitatively consistent with laboratory observations, although our observations are considerably larger than laboratory values. However, we also find good model fits for a∗ < 0 when data correspond to Omori exponents less than 1. A modification of the stability analysis by Rice and Ruina (1983) [Stability of steady frictional slipping. J. Appl. Mech. 50, 343-349] indicates that a∗ < 0 is not a consequence of our assumption regarding state-variable evolution. A consistent interpretation of a∗ < 0 in terms of laboratory models appears to be that the data are from later portions of processes better characterized by two-state-variable friction models. a∗ < 0 is explained by assuming that our data cannot resolve the co-seismic evolution of a short-length-scale state variable to a velocity-weakening state; our parameterization leads to an apparent negative instantaneous viscosity. We estimate the largest critical slip distance associated with afterslip to be ˜1-10 cm, consistent with other estimates for near-surface materials. We assume that our observed large values for a∗ reflect the fact that our model ignores the geometrical complexities of three-dimensional stresses in fractured crustal materials around a fault zone with frictional stresses that vary on a fault surface. Our one-dimensional model parameters reflect spatially averaged, bulk, stress and frictional properties of a fault zone, where we clearly cannot specify the details of the averaging process. Our analysis of Omori's law suggests that bulk-frictional properties of a fault zone are well described by our simple laboratory-based models, but they would need to change during the seismic cycle for a mainshock instability to recur, unless a mainshock-aftershock sequence were characterized by a process similar to the arrested instabilities possible in two-state-variable systems.

Structure of AA5056 after friction drilling

NASA Astrophysics Data System (ADS)

Eliseev, A. A.; Kalashnikova, T. A.; Fortuna, S. V.

2017-12-01

Here we present data on the structure of AA5056 alloy after friction drilling to unveil potentials of the process for use in model experiments on friction stir welding. Our analysis of the average size and volume content of precipitates shows that their content decreases immediately beneath the friction surface and that the structure of this zone is the same as the structure of stirring zones formed in friction stir welding. The data suggest that both processes provide similar metal structures.

Physics-based process model approach for detecting discontinuity during friction stir welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shrivastava, Amber; Pfefferkorn, Frank E.; Duffie, Neil A.

2015-02-12

The goal of this work is to develop a method for detecting the creation of discontinuities during friction stir welding. This in situ weld monitoring method could significantly reduce the need for post-process inspection. A process force model and a discontinuity force model were created based on the state-of-the-art understanding of flow around an friction stir welding (FSW) tool. These models are used to predict the FSW forces and size of discontinuities formed in the weld. Friction stir welds with discontinuities and welds without discontinuities were created, and the differences in force dynamics were observed. In this paper, discontinuities weremore » generated by reducing the tool rotation frequency and increasing the tool traverse speed in order to create "cold" welds. Experimental force data for welds with discontinuities and welds without discontinuities compared favorably with the predicted forces. The model currently overpredicts the discontinuity size.« less

A Supervisor-Targeted Implementation Approach to Promote System Change: The R3 Model.

PubMed

Saldana, Lisa; Chamberlain, Patricia; Chapman, Jason

2016-11-01

Opportunities to evaluate strategies to create system-wide change in the child welfare system (CWS) and the resulting public health impact are rare. Leveraging a real-world, system-initiated effort to infuse the use of evidence-based principles throughout a CWS workforce, a pilot of the R 3 model and supervisor-targeted implementation approach is described. The development of R 3 and its associated fidelity monitoring was a collaboration between the CWS and model developers. Outcomes demonstrate implementation feasibility, strong fidelity scale measurement properties, improved supervisor fidelity over time, and the acceptability and perception of positive change by agency leadership. The value of system-initiated collaborations is discussed.

Value-based payment in implementing evidence-based care: the Mental Health Integration Program in Washington state.

PubMed

Bao, Yuhua; McGuire, Thomas G; Chan, Ya-Fen; Eggman, Ashley A; Ryan, Andrew M; Bruce, Martha L; Pincus, Harold Alan; Hafer, Erin; Unützer, Jürgen

2017-01-01

To assess the role of value-based payment (VBP) in improving fidelity and patient outcomes in community implementation of an evidence-based mental health intervention, the Collaborative Care Model (CCM). Retrospective study based on a natural experiment. We used the clinical tracking data of 1806 adult patients enrolled in a large implementation of the CCM in community health clinics in Washington state. VBP was initiated in year 2 of the program, creating a natural experiment. We compared implementation fidelity (measured by 3 process-of-care elements of the CCM) between patient-months exposed to VBP and patient-months not exposed to VBP. A series of regressions were estimated to check robustness of findings. We estimated a Cox proportional hazard model to assess the effect of VBP on time to achieving clinically significant improvement in depression (measured based on changes in depression symptom scores over time). Estimated marginal effects of VBP on fidelity ranged from 9% to 30% of the level of fidelity had there been no exposure to VBP (P <.05 for every fidelity measure). Improvement in fidelity in response to VBP was greater among providers with a larger patient panel and among providers with a lower level of fidelity at baseline. Exposure to VBP was associated with an adjusted hazard ratio of 1.45 (95% confidence interval, 1.04-2.03) for achieving clinically significant improvement in depression. VBP improved fidelity to key elements of the CCM, both directly incentivized and not explicitly incentivized by the VBP, and improved patient depression outcomes.

Comment on “The reduction of friction in long-runout landslides as an emergent phenomenon” by Brandon C. Johnson et al.

USGS Publications Warehouse

Iverson, Richard M.

2016-01-01

Results from a highly idealized, 2-D computational model indicate that dynamic normal-stress rarefactions might cause friction reduction in long-runout landslides, but the physical relevance of the idealized dynamics has not been confirmed by experimental tests. More importantly, the model results provide no evidence that refutes alternative hypotheses about friction reduction mechanisms. One alternative hypothesis, which is strongly supported by field evidence, experimental data, and the predictions of a well-constrained computational model, involves development of high pore fluid pressures in deforming landslide material or overridden bed material. However, no scientific basis exists for concluding that a universal mechanism is responsible for friction reduction in all long-runout landslides.

Post-seismic and interseismic fault creep I: model description

NASA Astrophysics Data System (ADS)

Hetland, E. A.; Simons, M.; Dunham, E. M.

2010-04-01

We present a model of localized, aseismic fault creep during the full interseismic period, including both transient and steady fault creep, in response to a sequence of imposed coseismic slip events and tectonic loading. We consider the behaviour of models with linear viscous, non-linear viscous, rate-dependent friction, and rate- and state-dependent friction fault rheologies. Both the transient post-seismic creep and the pattern of steady interseismic creep rates surrounding asperities depend on recent coseismic slip and fault rheologies. In these models, post-seismic fault creep is manifest as pulses of elevated creep rates that propagate from the coseismic slip, these pulses feature sharper fronts and are longer lived in models with rate-state friction compared to other models. With small characteristic slip distances in rate-state friction models, interseismic creep is similar to that in models with rate-dependent friction faults, except for the earliest periods of post-seismic creep. Our model can be used to constrain fault rheologies from geodetic observations in cases where the coseismic slip history is relatively well known. When only considering surface deformation over a short period of time, there are strong trade-offs between fault rheology and the details of the imposed coseismic slip. Geodetic observations over longer times following an earthquake will reduce these trade-offs, while simultaneous modelling of interseismic and post-seismic observations provide the strongest constraints on fault rheologies.

Electromechanical imitator of antilock braking modes of wheels with pneumatic tire and its application for the runways friction coefficient measurement

NASA Astrophysics Data System (ADS)

Putov, A. V.; Kopichev, M. M.; Ignatiev, K. V.; Putov, V. V.; Stotckaia, A. D.

2017-01-01

In this paper it is considered a discussion of the technique that realizes a brand new method of runway friction coefficient measurement based upon the proposed principle of measuring wheel braking control for the imitation of antilock braking modes that are close to the real braking modes of the aircraft chassis while landing that are realized by the aircraft anti-skid systems. Also here is the description of the model of towed measuring device that realizes a new technique of runway friction coefficient measuring, based upon the measuring wheel braking control principle. For increasing the repeatability accuracy of electromechanical braking imitation system the sideslip (brake) adaptive control system is proposed. Based upon the Burkhard model and additive random processes several mathematical models were created that describes the friction coefficient arrangement along the airstrip with different qualitative adjectives. Computer models of friction coefficient measuring were designed and first in the world the research of correlation between the friction coefficient measuring results and shape variations, intensity and cycle frequency of the measuring wheel antilock braking modes. The sketch engineering documentation was designed and prototype of the latest generation measuring device is ready to use. The measuring device was tested on the autonomous electromechanical examination laboratory treadmill bench. The experiments approved effectiveness of method of imitation the antilock braking modes for solving the problem of correlation of the runway friction coefficient measuring.

Role of Elasto-Inertial Turbulence in Polymer Drag Reduction

NASA Astrophysics Data System (ADS)

Dubief, Yves; Sid, Samir; Terrapon, Vincent

2017-11-01

Elasto-Inertial Turbulence (EIT) is a peculiar state of turbulence found in dilute polymer solutions flowing in parallel wall flows over a wide range of Reynolds numbers. At subcritical Reynolds numbers, appropriate boundary conditions trigger EIT, a self-sustaining cycle of energy transfers between thin sheets of stretched polymers and velocity perturbations, which translates into an increase of friction drag. For critical and supercritical Reynolds numbers, polymer additives may lead to significant drag reduction, bounded by the asymptotic state known as Maximum Drag Reduction (MDR). The present research investigates the role of EIT in the dynamics of critical and supercritical Reynolds number wall flows. Using high-fidelity direct numerical simulations of channel flows and the FENE-P model, we establish that (i) EIT is two-dimensional, (ii) the scales essential to the existence of EIT are sub-Kolmogorov, and (iii) EIT drives MDR at low and possibly moderate Reynolds number turbulent flows. These findings were validated in two different codes and using unprecedented resolutions for polymer flows. YD is grateful for the support of Binational Science Foundation. SS and VT acknowledges Fonds de la Recherche Scientifique (FNRS), MarieCurie Career Integration Grant and computing allocation from University of Liege and PRACE.

Low cost friction seismic base-isolation of residential new masonry buildings in developing countries: A small masonry house case study

NASA Astrophysics Data System (ADS)

Habieb, A. B.; Milani, G.; Tavio, T.; Milani, F.

2017-07-01

A Finite element model was established to examine performance of a low-cost friction base-isolation system in reducing seismic vulnerability of rural buildings. This study adopts an experimental investigation of the isolation system which was conducted in India. Four friction isolation interfaces, namely, marble-marble, marble-high-density polyethylene, marble-rubber sheet, and marble-geosynthetic were involved. Those interfaces differ in static and dynamic friction coefficient obtained through previous research. The FE model was performed based on a macroscopic approach and the masonry wall is assumed as an isotropic element. In order to observe structural response of the masonry house, elastic and plastic parameters of the brick wall were studied. Concrete damage plasticity (CDP) model was adopted to determine non-linear behavior of the brick wall. The results of FE model shows that involving these friction isolation systems could much decrease response acceleration at roof level. It was found that systems with marble-marble and marble-geosynthetic interfaces reduce the roof acceleration up to 50% comparing to the system without isolation. Another interesting result is there was no damage appearing in systems with friction isolation during the test. Meanwhile a severe failure was clearly visible for a system without isolation.

Comparison of friction produced by two types of orthodontic bracket protectors

PubMed Central

Mendonça, Steyner de Lima; Praxedes Neto, Otávio José; de Oliveira, Patricia Teixeira; dos Santos, Patricia Bittencourt Dutra; Pinheiro, Fábio Henrique de Sá Leitão

2014-01-01

Introduction Fixed orthodontic appliances have been regarded as a common causative factor of oral lesions. To manage soft tissue discomfort, most orthodontists recommend using a small amount of utility wax over the brackets in order to alleviate trauma. This in vitro study aimed at evaluating friction generated by two types of bracket protectors (customized acetate protector [CAP] and temporary resin protector [TRP]) during the initial stages of orthodontic treatment. Methods An experimental model (test unit) was used to assess friction. In order to measure the friction produced in each test, the model was attached to a mechanical testing machine which simulated maxillary canines alignment. Intergroup comparison was carried out by one-way ANOVA with level of significance set at 5%. Results The friction presented by the TRP group was statistically higher than that of the control group at 6 mm. It was also higher than in the control and CAP groups in terms of maximum friction. Conclusion The customized acetate protector (CAP) demonstrated not to interfere in friction between the wire and the orthodontic bracket slot. PMID:24713564

Comparison of friction produced by two types of orthodontic bracket protectors.

PubMed

de Lima Mendonça, Steyner; Praxedes Neto, Otávio José; de Oliveira, Patricia Teixeira; dos Santos, Patricia Bittencourt Dutra; de Sá Leitão Pinheiro, Fábio Henrique

2014-01-01

Fixed orthodontic appliances have been regarded as a common causative factor of oral lesions. To manage soft tissue discomfort, most orthodontists recommend using a small amount of utility wax over the brackets in order to alleviate trauma. This in vitro study aimed at evaluating friction generated by two types of bracket protectors (customized acetate protector [CAP] and temporary resin protector [TRP]) during the initial stages of orthodontic treatment. An experimental model (test unit) was used to assess friction. In order to measure the friction produced in each test, the model was attached to a mechanical testing machine which simulated maxillary canines alignment. Intergroup comparison was carried out by one-way ANOVA with level of significance set at 5%. The friction presented by the TRP group was statistically higher than that of the control group at 6 mm. It was also higher than in the control and CAP groups in terms of maximum friction. The customized acetate protector (CAP) demonstrated not to interfere in friction between the wire and the orthodontic bracket slot.

From Dot to Ring: The Role of Friction in the Deposition Pattern of a Drying Colloidal Suspension Droplet.

PubMed

Xie, Qingguang; Harting, Jens

2018-05-08

The deposition of particles on a substrate by drying a colloidal suspension droplet is at the core of applications ranging from traditional printing on paper to printable electronics or photovoltaic devices. The self-pinning induced by the accumulation of particles at the contact line plays an important role in the formation of a deposit. In this article, we investigate, both numerically and theoretically, the effect of friction between the particles and the substrate on the deposition pattern. Without friction, the contact line shows a stick-slip behavior and a dotlike deposit is left after the droplet is evaporated. By increasing the friction force, we observe a transition from a dotlike to a ringlike deposit. We propose a theoretical model to predict the effective radius of the particle deposit as a function of the friction force. Our theoretical model predicts a critical friction force when self-pinning happens and the effective radius of deposit increases with increasing friction force, confirmed by our simulation results. Our results can find implications for developing active control strategies for the deposition of drying droplets.

Study on the friction of κ-carrageenan hydrogels in air and aqueous environments.

PubMed

Kozbial, Andrew; Li, Lei

2014-03-01

Understanding the friction mechanism of polysaccharide hydrogels, which is the key component of human cartilage that has very low friction coefficient, is critical to develop next generation artificial joint replacement materials. In this study, the friction of the polysaccharide κ-carrageenan hydrogel was investigated to elucidate the effect of external load, cross-linking density, velocity, and environment on friction. Our experimental results show that (1) coefficient of friction (COF) decreases with normal load in air and remains constant in water, (2) increasing cross-linking density concurrently increases friction and is proportional to Young's modulus, (3) COF increases with testing velocity in both air and water, and (4) friction is reduced in aqueous environment due to the lubricating effect of water. The underlying frictional mechanism is discussed on the basis of water transport from bulk to surface and a previously proposed "repulsion-adsorption" model. Copyright © 2013 Elsevier B.V. All rights reserved.

Sensitivities of Tropical Cyclones to Surface Friction and the Coriolis Parameter in a 2-D Cloud-Resolving Model

NASA Technical Reports Server (NTRS)

Chao, Winston C.; Chen, Baode; Tao, Wei-Kuo; Lau, William K. M. (Technical Monitor)

2002-01-01

The sensitivities to surface friction and the Coriolis parameter in tropical cyclogenesis are studied using an axisymmetric version of the Goddard cloud ensemble model. Our experiments demonstrate that tropical cyclogenesis can still occur without surface friction. However, the resulting tropical cyclone has very unrealistic structure. Surface friction plays an important role of giving the tropical cyclones their observed smaller size and diminished intensity. Sensitivity of the cyclogenesis process to surface friction. in terms of kinetic energy growth, has different signs in different phases of the tropical cyclone. Contrary to the notion of Ekman pumping efficiency, which implies a preference for the highest Coriolis parameter in the growth rate if all other parameters are unchanged, our experiments show no such preference.

Microscopic aspects of the effect of friction reducers at the lubrication limit. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Mansot, J. L.

1984-01-01

An attempt is made to analytically model the physicochemical properties of lubricants and their capacity to reduce friction. A technique of frozen fracturing of the lubricants was employed to study the dispersion of additives throughout a lubricant. Adsorption was observed at the liquid-solid interface, which was the region where the solid and lubricant met, and the molecular dispersion of the additive enhanced the effectiveness of the lubricant. The electrically conductive characteristics of the lubricant at the friction interface indicated the presence of tunneling effects. The Bethe model was used to examine the relationship between the coefficient of friction and the variation of interface thickness. The electron transport permitted an inelastic tunnel electron spectroscopic investigation of the molecular transformations undergone by the additive during friction episodes.

Analysing the influence of FSP process parameters on IGC susceptibility of AA5083 using Sugeno - Fuzzy model

NASA Astrophysics Data System (ADS)

Jayakarthick, C.; Povendhan, A. P.; Vaira Vignesh, R.; Padmanaban, R.

2018-02-01

Aluminium alloy AA5083 was friction stir processed to improve the intergranular corrosion (IGC) resistance. FSP trials were performed by varying the process parameters as per Taguchi’s L18 orthogonal array. IGC resistance of the friction stir processed specimens were found by immersing them in concentrated nitric acid and measuring the mass loss per unit area. Results indicate that dispersion and partial dissolution of secondary phase increased IGC resistance of the friction stir processed specimens. A Sugeno fuzzy model was developed to study the effect of FSP process parameters on the IGC susceptibility of friction stir processed specimens. Tool Rotation Speed, Tool Traverse Speed and Shoulder Diameter have a significant effect on the IGC susceptibility of the friction stir processed specimens.

Dynamics of a homogeneous ball on a horizontal plane with sliding, spinning, and rolling friction taken into account

NASA Astrophysics Data System (ADS)

Ishkhanyan, M. V.; Karapetyan, A. V.

2010-04-01

We analyze the dynamics of a homogeneous ball on a horizontal plane with friction of all kinds, namely, sliding, spinning, and rolling friction, taken into account. The qualitative-analytic study of the ball dynamics is supplemented with numerical experiments. The problem on the motion of a homogeneous ball on a horizontal plane with friction was apparently first studied in 1758 by I. Euler (Leonard Euler's son) with sliding friction taken into account in the framework of the Coulomb model. I. Euler showed that the ball sliding ceases in finite time, after which the ball uniformly rolls along a fixed straight line and uniformly spins about the vertical. This result has long become classical and is described in many textbooks on theoretical mechanics. In 1998, V. F. Zhuravlev considered the problem of motion of a homogeneous ball on a horizontal plane with sliding and spinning friction taken into account in the framework of the Contensou-Zhuravlev model [1, 2] and showed that the ball sliding and spinning cease simultaneously, after which the ball uniformly rolls along a fixed straight line. The Contensou-Zhuravlev theory was further developed in [3-7]. In the present paper, we consider themotion of a homogeneous ball on a horizontal plane with friction of all kinds taken into account in the framework of the model proposed in [8]. We show that, in one and the same time, both the sliding velocity and the angular velocity of the ball become zero. Our studies are based on the results obtained in [2], the properties of the friction model proposed in [8], and the method for qualitative analysis of dynamics of dissipative systems [9, 10]. The qualitative-analytic study is supplemented with numerical experiments.

Ground-state fidelity and bipartite entanglement in the Bose-Hubbard model.

PubMed

Buonsante, P; Vezzani, A

2007-03-16

We analyze the quantum phase transition in the Bose-Hubbard model borrowing two tools from quantum-information theory, i.e., the ground-state fidelity and entanglement measures. We consider systems at unitary filling comprising up to 50 sites and show for the first time that a finite-size scaling analysis of these quantities provides excellent estimates for the quantum critical point. We conclude that fidelity is particularly suited for revealing a quantum phase transition and pinning down the critical point thereof, while the success of entanglement measures depends on the mechanisms governing the transition.

Tactile friction of topical formulations.

PubMed

Skedung, L; Buraczewska-Norin, I; Dawood, N; Rutland, M W; Ringstad, L

2016-02-01

The tactile perception is essential for all types of topical formulations (cosmetic, pharmaceutical, medical device) and the possibility to predict the sensorial response by using instrumental methods instead of sensory testing would save time and cost at an early stage product development. Here, we report on an instrumental evaluation method using tactile friction measurements to estimate perceptual attributes of topical formulations. Friction was measured between an index finger and an artificial skin substrate after application of formulations using a force sensor. Both model formulations of liquid crystalline phase structures with significantly different tactile properties, as well as commercial pharmaceutical moisturizing creams being more tactile-similar, were investigated. Friction coefficients were calculated as the ratio of the friction force to the applied load. The structures of the model formulations and phase transitions as a result of water evaporation were identified using optical microscopy. The friction device could distinguish friction coefficients between the phase structures, as well as the commercial creams after spreading and absorption into the substrate. In addition, phase transitions resulting in alterations in the feel of the formulations could be detected. A correlation was established between skin hydration and friction coefficient, where hydrated skin gave rise to higher friction. Also a link between skin smoothening and finger friction was established for the commercial moisturizing creams, although further investigations are needed to analyse this and correlations with other sensorial attributes in more detail. The present investigation shows that tactile friction measurements have potential as an alternative or complement in the evaluation of perception of topical formulations. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Low fidelity of CORDEX and their driving experiments indicates future climatic uncertainty over Himalayan watersheds of Indus basin

NASA Astrophysics Data System (ADS)

Hasson, Shabeh ul; Böhner, Jürgen; Chishtie, Farrukh

2018-03-01

Assessment of future water availability from the Himalayan watersheds of Indus Basin (Jhelum, Kabul and upper Indus basin—UIB) is a growing concern for safeguarding the sustainable socioeconomic wellbeing downstream. This requires, before all, robust climate change information from the present-day state-of-the-art climate models. However, the robustness of climate change projections highly depends upon the fidelity of climate modeling experiments. Hence, this study assesses the fidelity of seven dynamically refined (0.44° ) experiments, performed under the framework of the coordinated regional climate downscaling experiment for South Asia (CX-SA), and additionally, their six coarse-resolution driving datasets participating in the coupled model intercomparison project phase 5 (CMIP5). We assess fidelity in terms of reproducibility of the observed climatology of temperature and precipitation, and the seasonality of the latter for the historical period (1971-2005). Based on the model fidelity results, we further assess the robustness or uncertainty of the far future climate (2061-2095), as projected under the extreme-end warming scenario of the representative concentration pathway (RCP) 8.5. Our results show that the CX-SA and their driving CMIP5 experiments consistently feature low fidelity in terms of the chosen skill metrics, suggesting substantial cold (6-10 ° C) and wet (up to 80%) biases and underestimation of observed precipitation seasonality. Surprisingly, the CX-SA are unable to outperform their driving datasets. Further, the biases of CX-SA and of their driving CMIP5 datasets are higher in magnitude than their projected changes under RCP8.5—and hence under less extreme RCPs—by the end of 21st century, indicating uncertain future climates for the Indus Basin watersheds. Higher inter-dataset disagreements of both CMIP5 and CX-SA for their simulated historical precipitation and for its projected changes reinforce uncertain future wet/dry conditions whereas the CMIP5 projected warming is less robust owing to higher historical period uncertainty. Interestingly, a better agreement among those CX-SA experiments that have been obtained through downscaling different CMIP5 experiments with the same regional climate model (RCM) indicates the RCMs' ability of modulating the influence of lateral boundary conditions over a large domain. These findings, instead of suggesting the usual skill-based identification of 'reasonable' global or regional low fidelity experiments, rather emphasize on a paradigm shift towards improving their fidelity by exploiting the potential of meso-to-local scale climate models—preferably of those that can solely resolve global-to-local scale climatic processes—in terms of microphysics, resolution and explicitly resolved convections. Additionally, an extensive monitoring of the nival regime within the Himalayan watersheds will reduce the observational uncertainty, allowing for a more robust fidelity assessment of the climate modeling experiments.

Modeling Aftershocks and Foreshocks by Time-Dependent Friction Laws

NASA Astrophysics Data System (ADS)

Lippiello, E.; Landes, F.

2017-12-01

The transition with depth from rate-weakening to rate-strengthening rheology represents a viable mechanism to explain both afterslip and the temporal and spatial organization of aftershocks(Avouac, Annu. Rev. Eart Planet Sci. 2015).On the other hand, elastic models for seismic faults, as the Burridge-Knopoff model, are able to reproduce the Gutenberg-Richter (GR) law (de Arcangelis et al., Phys. Rep. 2016). Here we show that the two approaches can be combined in a minimal model containing only a parameter controlling the heterogeneities of the friction force. The key ingredient is the presence of a time-dependent friction on a temporal scale intermediate between the instantaneous scale of fracture propagation and the very slow one of the driving rate. Several features of aftershocks as the GR law, the productivity law, the spatial clustering and the temporal decay of the aftershock number, appear universal properties independent of details of model parameters and friction law. Quantitative agreement with the Omori law constraints the friction law according to a velocity strengthening rheology. The model also provides agreement with recent experimental results on the statistical properties of foreshock occurrence (Lippiello et al. , Pageoph, 2017). We then obtain insights on the nucleation phase preceding mainshocks which we compare with existing models (Ohnaka, Tectonophysics 1992).

Administrator Strategies that Support High Fidelity Implementation of the Pyramid Model for Promoting Social-Emotional Competence & Addressing Challenging Behavior

ERIC Educational Resources Information Center

Mincic, Melissa; Smith, Barbara J.; Strain, Phil

2009-01-01

Implementing the Pyramid Model with fidelity and achieving positive outcomes for children and their families requires that administrators understand their roles in the implementation process. Every administrative decision impacts program quality and sustainability. This Policy Brief underscores the importance of facilitative administrative…

Multi-fidelity Gaussian process regression for prediction of random fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parussini, L.; Venturi, D., E-mail: venturi@ucsc.edu; Perdikaris, P.

We propose a new multi-fidelity Gaussian process regression (GPR) approach for prediction of random fields based on observations of surrogate models or hierarchies of surrogate models. Our method builds upon recent work on recursive Bayesian techniques, in particular recursive co-kriging, and extends it to vector-valued fields and various types of covariances, including separable and non-separable ones. The framework we propose is general and can be used to perform uncertainty propagation and quantification in model-based simulations, multi-fidelity data fusion, and surrogate-based optimization. We demonstrate the effectiveness of the proposed recursive GPR techniques through various examples. Specifically, we study the stochastic Burgersmore » equation and the stochastic Oberbeck–Boussinesq equations describing natural convection within a square enclosure. In both cases we find that the standard deviation of the Gaussian predictors as well as the absolute errors relative to benchmark stochastic solutions are very small, suggesting that the proposed multi-fidelity GPR approaches can yield highly accurate results.« less

An empirical study of multidimensional fidelity of COMPASS consultation.

PubMed

Wong, Venus; Ruble, Lisa A; McGrew, John H; Yu, Yue

2018-06-01

Consultation is essential to the daily practice of school psychologists (National Association of School Psychologist, 2010). Successful consultation requires fidelity at both the consultant (implementation) and consultee (intervention) levels. We applied a multidimensional, multilevel conception of fidelity (Dunst, Trivette, & Raab, 2013) to a consultative intervention called the Collaborative Model for Promoting Competence and Success (COMPASS) for students with autism. The study provided 3 main findings. First, multidimensional, multilevel fidelity is a stable construct and increases over time with consultation support. Second, mediation analyses revealed that implementation-level fidelity components had distant, indirect effects on student Individualized Education Program (IEP) outcomes. Third, 3 fidelity components correlated with IEP outcomes: teacher coaching responsiveness at the implementation level, and teacher quality of delivery and student responsiveness at the intervention levels. Implications and future directions are discussed. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Improving the prediction of the final part geometry in high strength steels U drawing by means of advanced material and friction models

NASA Astrophysics Data System (ADS)

de Argandoña, Eneko Saenz; Mendiguren, Joseba; Otero, Irune; Mugarra, Endika; Otegi, Nagore; Galdos, Lander

2018-05-01

Steel has been used in vehicles from the automotive industry's inception. Different steel grades are continually being developed in order to satisfy new fuel economy requirements. For example, advanced high strength steel grades (AHSS) are widely used due to their good strength/weight ratio. Because each steel grade has a different microstructure composition and hardness, they show different behaviors when they are subjected to different strain paths. Similarly, the friction behavior when using different contact pressures is considerably altered. In the present paper, four different steel grades, ZSt380, DP600, DP780 and Fortiform 1050 materials are deeply characterized using uniaxial and cyclic tension-compression tests. Coefficient of friction (COF) is also obtained using strip drawing tests. These results have been used to calibrate mixed kinematic-hardening material models as well as pressure dependent friction models. Finally, the geometrical accuracy of the different material and friction models has been evaluated by comparing the numerical predictions with experimental demonstrators obtained using a U-Drawing tester.

Effects of rail dynamics and friction characteristics on curve squeal

NASA Astrophysics Data System (ADS)

Ding, B.; Squicciarini, G.; Thompson, D. J.

2016-09-01

Curve squeal in railway vehicles is an instability mechanism that arises in tight curves under certain running and environmental conditions. In developing a model the most important elements are the characterisation of friction coupled with an accurate representation of the structural dynamics of the wheel. However, the role played by the dynamics of the rail is not fully understood and it is unclear whether this should be included in a model or whether it can be safely neglected. This paper makes use of previously developed time domain and frequency domain curve squeal models to assess whether the presence of the rail and the falling characteristics of the friction force can modify the instability mechanisms and the final response. For this purpose, the time-domain model has been updated to include the rail dynamics in terms of its state space representation in various directions. Frequency domain and time domain analyses results show that falling friction is not the only reason for squeal and rail dynamics can play an important role, especially under constant friction conditions.

Modeling SMAP Spacecraft Attitude Control Estimation Error Using Signal Generation Model

NASA Technical Reports Server (NTRS)

Rizvi, Farheen

2016-01-01

Two ground simulation software are used to model the SMAP spacecraft dynamics. The CAST software uses a higher fidelity model than the ADAMS software. The ADAMS software models the spacecraft plant, controller and actuator models, and assumes a perfect sensor and estimator model. In this simulation study, the spacecraft dynamics results from the ADAMS software are used as CAST software is unavailable. The main source of spacecraft dynamics error in the higher fidelity CAST software is due to the estimation error. A signal generation model is developed to capture the effect of this estimation error in the overall spacecraft dynamics. Then, this signal generation model is included in the ADAMS software spacecraft dynamics estimate such that the results are similar to CAST. This signal generation model has similar characteristics mean, variance and power spectral density as the true CAST estimation error. In this way, ADAMS software can still be used while capturing the higher fidelity spacecraft dynamics modeling from CAST software.

Numerical Simulation of Tension Properties for Al-Cu Alloy Friction Stir-Welded Joints with GTN Damage Model

NASA Astrophysics Data System (ADS)

Sun, Guo-Qin; Sun, Feng-Yang; Cao, Fang-Li; Chen, Shu-Jun; Barkey, Mark E.

2015-11-01

The numerical simulation of tensile fracture behavior on Al-Cu alloy friction stir-welded joint was performed with the Gurson-Tvergaard-Needleman (GTN) damage model. The parameters of the GTN model were studied in each region of the friction stir-welded joint by means of inverse identification. Based on the obtained parameters, the finite element model of the welded joint was built to predict the fracture behavior and tension properties. Good agreement can be found between the numerical and experimental results in the location of the tensile fracture and the mechanical properties.

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Moore, John A.; Barton, Nathan R.; Florando, Jeff; Mulay, Rupalee; Kumar, Mukul

2017-10-01

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material’s structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V’s mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments or lower fidelity models. The results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.

Improving Mixed Variable Optimization of Computational and Model Parameters Using Multiple Surrogate Functions

DTIC Science & Technology

2008-03-01

multiplicative corrections as well as space mapping transformations for models defined over a lower dimensional space. A corrected surrogate model for the...correction functions used in [72]. If the low fidelity model g(x̃) is defined over a lower dimensional space then a space mapping transformation is...required. As defined in [21, 72], space mapping is a method of mapping between models of different dimensionality or fidelity. Let P denote the space

A New Design for Airway Management Training with Mixed Reality and High Fidelity Modeling.

PubMed

Shen, Yunhe; Hananel, David; Zhao, Zichen; Burke, Daniel; Ballas, Crist; Norfleet, Jack; Reihsen, Troy; Sweet, Robert

2016-01-01

Restoring airway function is a vital task in many medical scenarios. Although various simulation tools have been available for learning such skills, recent research indicated that fidelity in simulating airway management deserves further improvements. In this study, we designed and implemented a new prototype for practicing relevant tasks including laryngoscopy, intubation and cricothyrotomy. A large amount of anatomical details or landmarks were meticulously selected and reconstructed from medical scans, and 3D-printed or molded to the airway intervention model. This training model was augmented by virtually and physically presented interactive modules, which are interoperable with motion tracking and sensor data feedback. Implementation results showed that this design is a feasible approach to develop higher fidelity airway models that can be integrated with mixed reality interfaces.

Sources of variation in breeding-ground fidelity of mallards (Anas platyrhynchos)

USGS Publications Warehouse

Doherty, P.F.; Nichols, J.D.; Tautin, J.; Voelzer, J.E.; Smith, G.W.; Benning, D.S.; Bentley, V.R.; Bidwell, J.K.; Bollinger, K.S.; Brazda, A.R.; Buelna, E.K.; Goldsberry, J.R.; King, R.J.; Roetker, F.H.; Solberg, J.W.; Thorpe, P.P.; Wortham, J.S.

2002-01-01

Generalizations used to support hypotheses about the evolution of fidelity to breeding areas in birds include the tendency for fidelity to be greater in adult birds than in yearlings. In ducks, in contrast to most bird species, fidelity is thought to be greater among females than males. Researchers have suggested that fidelity in ducks is positively correlated with pond availability. However, most estimates of fidelity on which these inferences have been based represent functions of survival and recapture-resighting probabilities in addition to fidelity. We applied the modeling approach developed by Burnham to recapture and band recovery data of mallard ducks to test the above hypotheses about fidelity. We found little evidence of sex differences in adult philopatry, with females being slightly more philopatric than males in one study area, but not in a second study area. However, yearling females were more philopatric than yearling males in both study areas. We found that adults were generally more philopatric than yearlings. We could find no relationship between fidelity and pond availability. Our results, while partially supporting current theory concerning sex and age differences in philopatry, suggest that adult male mallards are more philopatric than once thought, and we recommend that other generalizations about philopatry be revisited with proper estimation techniques.

Experimental and theoretical study of friction torque from radial ball bearings

NASA Astrophysics Data System (ADS)

Geonea, Ionut; Dumitru, Nicolae; Dumitru, Ilie

2017-10-01

In this paper it is presented a numerical simulation and an experimental study of total friction torque from radial ball bearings. For this purpose it is conceived a virtual CAD model of the experimental test bench for bearing friction torque measurement. The virtual model it is used for numerical simulation in Adams software, that allows dynamic study of multi-body systems and in particularly with facility Adams Machinery of dynamic behavior of machine parts. It is manufactured an experimental prototype of the test bench for radial ball bearings friction torque measurement. In order to measure the friction torque of the tested bearings it is used an equal resistance elastic beam element, with strain gauge transducer to measure bending deformations. The actuation electric motor of the bench has the shaft mounted on two bearings and the motor housing is fixed to the free side of the elastic beam, which is bended by a force proportional with the total friction torque. The beam elastic element with strain gauge transducer is calibrated in order to measure the force occurred. Experimental determination of the friction torque is made for several progressive radial loads. It is established the correlation from the friction torque and bearing radial load. The bench allows testing of several types and dimensions of radial bearings, in order to establish the bearing durability and of total friction torque.

Simulation on friction taper plug welding of AA6063-20Gr metal matrix composite

NASA Astrophysics Data System (ADS)

Hynes, N. Rajesh Jesudoss; Nithin, Abeyram M.

2016-05-01

Friction taper plug welding a variant of friction welding is useful in welding of similar and dissimilar materials. It could be used for joining of composites to metals in sophisticated aerospace applications. In the present work numerical simulation of friction taper plug welding process is carried out using finite element based software. Graphite reinforced AA6063 is modelled using the software ANSYS 15.0 and temperature distribution is predicted. Effect of friction time on temperature distribution is numerically investigated. When the friction time is increased to 30 seconds, the tapered part of plug gets detached and fills the hole in the AA6063 plate perfectly.

Modeling of Passive Acoustic Liners from High Fidelity Numerical Simulations

NASA Astrophysics Data System (ADS)

Ferrari, Marcello do Areal Souto

Noise reduction in aviation has been an important focus of study in the last few decades. One common solution is setting up acoustic liners in the internal walls of the engines. However, measurements in the laboratory with liners are expensive and time consuming. The present work proposes a nonlinear physics-based time domain model to predict the acoustic behavior of a given liner in a defined flow condition. The parameters of the model are defined by analysis of accurate numerical solutions of the flow obtained from a high-fidelity numerical code. The length of the cavity is taken into account by using an analytical procedure to account for internal reflections in the interior of the cavity. Vortices and jets originated from internal flow separations are confirmed to be important mechanisms of sound absorption, which defines the overall efficiency of the liner. Numerical simulations at different frequency, geometry and sound pressure level are studied in detail to define the model parameters. Comparisons with high-fidelity numerical simulations show that the proposed model is accurate, robust, and can be used to define a boundary condition simulating a liner in a high-fidelity code.

Estimation of Dynamic Friction Process of the Akatani Landslide Based on the Waveform Inversion and Numerical Simulation

NASA Astrophysics Data System (ADS)

Yamada, M.; Mangeney, A.; Moretti, L.; Matsushi, Y.

2014-12-01

Understanding physical parameters, such as frictional coefficients, velocity change, and dynamic history, is important issue for assessing and managing the risks posed by deep-seated catastrophic landslides. Previously, landslide motion has been inferred qualitatively from topographic changes caused by the event, and occasionally from eyewitness reports. However, these conventional approaches are unable to evaluate source processes and dynamic parameters. In this study, we use broadband seismic recordings to trace the dynamic process of the deep-seated Akatani landslide that occurred on the Kii Peninsula, Japan, which is one of the best recorded large slope failures. Based on the previous results of waveform inversions and precise topographic surveys done before and after the event, we applied numerical simulations using the SHALTOP numerical model (Mangeney et al., 2007). This model describes homogeneous continuous granular flows on a 3D topography based on a depth averaged thin layer approximation. We assume a Coulomb's friction law with a constant friction coefficient, i. e. the friction is independent of the sliding velocity. We varied the friction coefficients in the simulation so that the resulting force acting on the surface agrees with the single force estimated from the seismic waveform inversion. Figure shows the force history of the east-west components after the band-pass filtering between 10-100 seconds. The force history of the simulation with frictional coefficient 0.27 (thin red line) the best agrees with the result of seismic waveform inversion (thick gray line). Although the amplitude is slightly different, phases are coherent for the main three pulses. This is an evidence that the point-source approximation works reasonably well for this particular event. The friction coefficient during the sliding was estimated to be 0.38 based on the seismic waveform inversion performed by the previous study and on the sliding block model (Yamada et al., 2013), whereas the frictional coefficient estimated from the numerical simulation was about 0.27. This discrepancy may be due to the digital elevation model, to the other forces such as pressure gradients and centrifugal acceleration included in the model. However, quantitative interpretation of this difference requires further investigation.

Adaptive integral backstepping sliding mode control for opto-electronic tracking system based on modified LuGre friction model

NASA Astrophysics Data System (ADS)

Yue, Fengfa; Li, Xingfei; Chen, Cheng; Tan, Wenbin

2017-12-01

In order to improve the control accuracy and stability of opto-electronic tracking system fixed on reef or airport under friction and external disturbance conditions, adaptive integral backstepping sliding mode control approach with friction compensation is developed to achieve accurate and stable tracking for fast moving target. The nonlinear observer and slide mode controller based on modified LuGre model with friction compensation can effectively reduce the influence of nonlinear friction and disturbance of this servo system. The stability of the closed-loop system is guaranteed by Lyapunov theory. The steady-state error of the system is eliminated by integral action. The adaptive integral backstepping sliding mode controller and its performance are validated by a nonlinear modified LuGre dynamic model of the opto-electronic tracking system in simulation and practical experiments. The experiment results demonstrate that the proposed controller can effectively realise the accuracy and stability control of opto-electronic tracking system.

On the Link Between Kolmogorov Microscales and Friction in Wall-Bounded Flow of Viscoplastic Fluids

NASA Astrophysics Data System (ADS)

Ramos, Fabio; Anbarlooei, Hamid; Cruz, Daniel; Silva Freire, Atila; Santos, Cecilia M.

2017-11-01

Most discussions in literature on the friction coefficient of turbulent flows of fluids with complex rheology are empirical. As a rule, theoretical frameworks are not available even for some relatively simple constitutive models. In this work, we present a new family of formulas for the evaluation of the friction coefficient of turbulent flows of a large family of viscoplastic fluids. The developments combine an unified analysis for the description of the Kolmogorov's micro-scales and the phenomenological turbulence model of Gioia and Chakraborty. The resulting Blasius-type friction equation has only Blasius' constant as a parameter, and tests against experimental data show excellent agreement over a significant range of Hedstrom and Reynolds numbers. The limits of the proposed model are also discussed. We also comment on the role of the new formula as a possible benchmark test for the convergence of DNS simulations of viscoplastic flows. The friction formula also provides limits for the Maximum Drag Reduction (MDR) for viscoplastic flows, which resembles MDR asymptote for viscoelastic flows.

Depth variations of friction rate parameter derived from dynamic modeling of GPS afterslip associated with the 2003 Mw 6.5 Chengkung earthquake in eastern Taiwan

NASA Astrophysics Data System (ADS)

Lee, J. C.; Liu, Z. Y. C.; Shirzaei, M.

2016-12-01

The Chihshang fault lies at the plate suture between the Eurasian and the Philippine Sea plates along the Longitudinal Valley in eastern Taiwan. Here we investigate depth variation of fault frictional parameters derived from the post-seismic slip model of the 2003 Mw 6.5 Chengkung earthquake. Assuming a rate-strengthening friction, we implement an inverse dynamic modeling scheme to estimate the frictional parameter (a-b) and reference friction coefficient (μ*) in depths by taking into account: pre-seismic stress as well as co-seismic and post-seismic coulomb stress changes associated with the 2003 Chengkung earthquake. We investigate two coseismic models by Hsu et al. (2009) and Thomas et al. (2014). Model parameters, including stress gradient, depth dependent a-b and μ*, are determined from fitting the transient post-seismic geodetic signal measured at 12 continuous GPS stations. In our inversion scheme, we apply a non-linear optimization algorithm, Genetic Algorithm (GA), to search for the optimum frictional parameters. Considering the zone with velocity-strengthening frictional properties along Chihshang fault, the optimum a-b is 7-8 × 10-3 along the shallow part of the fault (0-10 km depth) and 1-2 × 10-2 in 22-28 km depth. Optimum solution for μ* is 0.3-0.4 in 0-10 km depth and reaches 0.8 in 22-28 km depth. The optimized stress gradient is 54 MPa/ km. The inferred frictional parameters are consistent with the laboratory measurements on clay-rich fault zone gouges comparable to the Lichi Melange, which is thrust over Holocene alluvial deposits across the Chihshang fault, considering the main rock composition of the Chihshang fault, at least at the upper kilometers level of the fault. Our results can facilitate further studies in particular on seismic cycle and hazard assessment of active faults.

A phase-plane analysis of localized frictional waves

NASA Astrophysics Data System (ADS)

Putelat, T.; Dawes, J. H. P.; Champneys, A. R.

2017-07-01

Sliding frictional interfaces at a range of length scales are observed to generate travelling waves; these are considered relevant, for example, to both earthquake ground surface movements and the performance of mechanical brakes and dampers. We propose an explanation of the origins of these waves through the study of an idealized mechanical model: a thin elastic plate subject to uniform shear stress held in frictional contact with a rigid flat surface. We construct a nonlinear wave equation for the deformation of the plate, and couple it to a spinodal rate-and-state friction law which leads to a mathematically well-posed problem that is capable of capturing many effects not accessible in a Coulomb friction model. Our model sustains a rich variety of solutions, including periodic stick-slip wave trains, isolated slip and stick pulses, and detachment and attachment fronts. Analytical and numerical bifurcation analysis is used to show how these states are organized in a two-parameter state diagram. We discuss briefly the possible physical interpretation of each of these states, and remark also that our spinodal friction law, though more complicated than other classical rate-and-state laws, is required in order to capture the full richness of wave types.

A phase-plane analysis of localized frictional waves

PubMed Central

Dawes, J. H. P.; Champneys, A. R.

2017-01-01

Sliding frictional interfaces at a range of length scales are observed to generate travelling waves; these are considered relevant, for example, to both earthquake ground surface movements and the performance of mechanical brakes and dampers. We propose an explanation of the origins of these waves through the study of an idealized mechanical model: a thin elastic plate subject to uniform shear stress held in frictional contact with a rigid flat surface. We construct a nonlinear wave equation for the deformation of the plate, and couple it to a spinodal rate-and-state friction law which leads to a mathematically well-posed problem that is capable of capturing many effects not accessible in a Coulomb friction model. Our model sustains a rich variety of solutions, including periodic stick–slip wave trains, isolated slip and stick pulses, and detachment and attachment fronts. Analytical and numerical bifurcation analysis is used to show how these states are organized in a two-parameter state diagram. We discuss briefly the possible physical interpretation of each of these states, and remark also that our spinodal friction law, though more complicated than other classical rate-and-state laws, is required in order to capture the full richness of wave types. PMID:28804255

A phase-plane analysis of localized frictional waves.

PubMed

Putelat, T; Dawes, J H P; Champneys, A R

2017-07-01

Sliding frictional interfaces at a range of length scales are observed to generate travelling waves; these are considered relevant, for example, to both earthquake ground surface movements and the performance of mechanical brakes and dampers. We propose an explanation of the origins of these waves through the study of an idealized mechanical model: a thin elastic plate subject to uniform shear stress held in frictional contact with a rigid flat surface. We construct a nonlinear wave equation for the deformation of the plate, and couple it to a spinodal rate-and-state friction law which leads to a mathematically well-posed problem that is capable of capturing many effects not accessible in a Coulomb friction model. Our model sustains a rich variety of solutions, including periodic stick-slip wave trains, isolated slip and stick pulses, and detachment and attachment fronts. Analytical and numerical bifurcation analysis is used to show how these states are organized in a two-parameter state diagram. We discuss briefly the possible physical interpretation of each of these states, and remark also that our spinodal friction law, though more complicated than other classical rate-and-state laws, is required in order to capture the full richness of wave types.

A reduced-order model from high-dimensional frictional hysteresis

PubMed Central

Biswas, Saurabh; Chatterjee, Anindya

2014-01-01

Hysteresis in material behaviour includes both signum nonlinearities as well as high dimensionality. Available models for component-level hysteretic behaviour are empirical. Here, we derive a low-order model for rate-independent hysteresis from a high-dimensional massless frictional system. The original system, being given in terms of signs of velocities, is first solved incrementally using a linear complementarity problem formulation. From this numerical solution, to develop a reduced-order model, basis vectors are chosen using the singular value decomposition. The slip direction in generalized coordinates is identified as the minimizer of a dissipation-related function. That function includes terms for frictional dissipation through signum nonlinearities at many friction sites. Luckily, it allows a convenient analytical approximation. Upon solution of the approximated minimization problem, the slip direction is found. A final evolution equation for a few states is then obtained that gives a good match with the full solution. The model obtained here may lead to new insights into hysteresis as well as better empirical modelling thereof. PMID:24910522

CTF (Subchannel) Calculations and Validation L3:VVI.H2L.P15.01

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gordon, Natalie

The goal of the Verification and Validation Implementation (VVI) High to Low (Hi2Lo) process is utilizing a validated model in a high resolution code to generate synthetic data for improvement of the same model in a lower resolution code. This process is useful in circumstances where experimental data does not exist or it is not sufficient in quantity or resolution. Data from the high-fidelity code is treated as calibration data (with appropriate uncertainties and error bounds) which can be used to train parameters that affect solution accuracy in the lower-fidelity code model, thereby reducing uncertainty. This milestone presents a demonstrationmore » of the Hi2Lo process derived in the VVI focus area. The majority of the work performed herein describes the steps of the low-fidelity code used in the process with references to the work detailed in the companion high-fidelity code milestone (Reference 1). The CASL low-fidelity code used to perform this work was Cobra Thermal Fluid (CTF) and the high-fidelity code was STAR-CCM+ (STAR). The master branch version of CTF (pulled May 5, 2017 – Reference 2) was utilized for all CTF analyses performed as part of this milestone. The statistical and VVUQ components of the Hi2Lo framework were performed using Dakota version 6.6 (release date May 15, 2017 – Reference 3). Experimental data from Westinghouse Electric Company (WEC – Reference 4) was used throughout the demonstrated process to compare with the high-fidelity STAR results. A CTF parameter called Beta was chosen as the calibration parameter for this work. By default, Beta is defined as a constant mixing coefficient in CTF and is essentially a tuning parameter for mixing between subchannels. Since CTF does not have turbulence models like STAR, Beta is the parameter that performs the most similar function to the turbulence models in STAR. The purpose of the work performed in this milestone is to tune Beta to an optimal value that brings the CTF results closer to those measured in the WEC experiments.« less

Design of tyre force excitation for tyre-road friction estimation

NASA Astrophysics Data System (ADS)

Albinsson, Anton; Bruzelius, Fredrik; Jacobson, Bengt; Fredriksson, Jonas

2017-02-01

Knowledge of the current tyre-road friction coefficient is essential for future autonomous vehicles. The environmental conditions, and the tyre-road friction in particular, determine both the braking distance and the maximum cornering velocity and thus set the boundaries for the vehicle. Tyre-road friction is difficult to estimate during normal driving due to low levels of tyre force excitation. This problem can be solved by using active tyre force excitation. A torque is added to one or several wheels in the purpose of estimating the tyre-road friction coefficient. Active tyre force excitation provides the opportunity to design the tyre force excitation freely. This study investigates how the tyre force should be applied to minimise the error of the tyre-road friction estimate. The performance of different excitation strategies was found to be dependent on both tyre model choice and noise level. Furthermore, the advantage with using tyre models with more parameters decreased when noise was added to the force and slip ratio.

Comparative study of friction between metallic and conventional interactive self-ligating brackets in different alignment conditions

PubMed Central

Jakob, Sérgio Ricardo; Matheus, Davison; Jimenez-Pellegrin, Maria Cristina; Turssi, Cecília Pedroso; do Amaral, Flávia Lucisano Botelho

2014-01-01

Objective The aim of this study was to compare the friction between three bracket models: conventional stainless steel (Ovation, Dentsply GAC), self-ligating ceramic (In-Ovation, Denstply GAC) and self-ligating stainless steel brackets (In-Ovation R, Dentsply GAC). Methods Five brackets were used for each model. They were bonded to an aluminum prototype that allowed the simulation of four misalignment situations (n = 10). Three of these situations occurred at the initial phase (in which a 0.016-in nickel-titanium wire was used): 1. horizontal; 2. vertical; and 3. simultaneous horizontal/vertical. One of the situations occurred at the final treatment phase: 4. no misalignment (in which a 0.019 x 0.025-inch stainless steel rectangular wire was used). The wires slipped through the brackets and friction was measured by a Universal Testing Machine. Results Analysis of variance followed by Tukey's Test for multiple comparisons (α = 0.05) were applied to assess the results. Significant interaction (p < 0.01) among groups was found. For the tests that simulated initial alignment, Ovation® bracket produced the highest friction. The two self-ligating models resulted in lower and similar values, except for the horizontal situation, in which In-Ovation C® showed lower friction, which was similar to the In-Ovation R® metallic model. For the no misalignment situation, the same results were observed. Conclusion The self-ligating system was superior to the conventional one due to producing less friction. With regard to the material used for manufacturing the brackets, the In-Ovation C® ceramic model showed less friction than the metallic ones. PMID:25162570

FAST TRACK COMMUNICATION: Ground-state fidelity and entanglement entropy for the quantum three-state Potts model in one spatial dimension

NASA Astrophysics Data System (ADS)

Dai, Yan-Wei; Hu, Bing-Quan; Zhao, Jian-Hui; Zhou, Huan-Qiang

2010-09-01

The ground-state fidelity per lattice site is computed for the quantum three-state Potts model in a transverse magnetic field on an infinite-size lattice in one spatial dimension in terms of the infinite matrix product state algorithm. It is found that, on the one hand, a pinch point is identified on the fidelity surface around the critical point, and on the other hand, the ground-state fidelity per lattice site exhibits bifurcations at pseudo critical points for different values of the truncation dimension, which in turn approach the critical point as the truncation dimension becomes large. This implies that the ground-state fidelity per lattice site enables us to capture spontaneous symmetry breaking when the control parameter crosses the critical value. In addition, a finite-entanglement scaling of the von Neumann entropy is performed with respect to the truncation dimension, resulting in a precise determination of the central charge at the critical point. Finally, we compute the transverse magnetization, from which the critical exponent β is extracted from the numerical data.

A new algorithm for modeling friction in dynamic mechanical systems

NASA Technical Reports Server (NTRS)

Hill, R. E.

1988-01-01

A method of modeling friction forces that impede the motion of parts of dynamic mechanical systems is described. Conventional methods in which the friction effect is assumed a constant force, or torque, in a direction opposite to the relative motion, are applicable only to those cases where applied forces are large in comparison to the friction, and where there is little interest in system behavior close to the times of transitions through zero velocity. An algorithm is described that provides accurate determination of friction forces over a wide range of applied force and velocity conditions. The method avoids the simulation errors resulting from a finite integration interval used in connection with a conventional friction model, as is the case in many digital computer-based simulations. The algorithm incorporates a predictive calculation based on initial conditions of motion, externally applied forces, inertia, and integration step size. The predictive calculation in connection with an external integration process provides an accurate determination of both static and Coulomb friction forces and resulting motions in dynamic simulations. Accuracy of the results is improved over that obtained with conventional methods and a relatively large integration step size is permitted. A function block for incorporation in a specific simulation program is described. The general form of the algorithm facilitates implementation with various programming languages such as FORTRAN or C, as well as with other simulation programs.

First-passage time of Brownian motion with dry friction.

PubMed

Chen, Yaming; Just, Wolfram

2014-02-01

We provide an analytic solution to the first-passage time (FPT) problem of a piecewise-smooth stochastic model, namely Brownian motion with dry friction, using two different but closely related approaches which are based on eigenfunction decompositions on the one hand and on the backward Kolmogorov equation on the other. For the simple case containing only dry friction, a phase-transition phenomenon in the spectrum is found which relates to the position of the exit point, and which affects the tail of the FPT distribution. For the model containing as well a driving force and viscous friction the impact of the corresponding stick-slip transition and of the transition to ballistic exit is evaluated quantitatively. The proposed model is one of the very few cases where FPT properties are accessible by analytical means.

Analysis of tablet compaction. I. Characterization of mechanical behavior of powder and powder/tooling friction.

PubMed

Cunningham, J C; Sinka, I C; Zavaliangos, A

2004-08-01

In this first of two articles on the modeling of tablet compaction, the experimental inputs related to the constitutive model of the powder and the powder/tooling friction are determined. The continuum-based analysis of tableting makes use of an elasto-plastic model, which incorporates the elements of yield, plastic flow potential, and hardening, to describe the mechanical behavior of microcrystalline cellulose over the range of densities experienced during tableting. Specifically, a modified Drucker-Prager/cap plasticity model, which includes material parameters such as cohesion, internal friction, and hydrostatic yield pressure that evolve with the internal state variable relative density, was applied. Linear elasticity is assumed with the elastic parameters, Young's modulus, and Poisson's ratio dependent on the relative density. The calibration techniques were developed based on a series of simple mechanical tests including diametrical compression, simple compression, and die compaction using an instrumented die. The friction behavior is measured using an instrumented die and the experimental data are analyzed using the method of differential slices. The constitutive model and frictional properties are essential experimental inputs to the finite element-based model described in the companion article. Copyright 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2022-2039, 2004

Skin friction under pressure. The role of micromechanics

NASA Astrophysics Data System (ADS)

Leyva-Mendivil, Maria F.; Lengiewicz, Jakub; Limbert, Georges

2018-03-01

The role of contact pressure on skin friction has been documented in multiple experimental studies. Skin friction significantly raises in the low-pressure regime as load increases while, after a critical pressure value is reached, the coefficient of friction of skin against an external surface becomes mostly insensitive to contact pressure. However, up to now, no study has elucidated the qualitative and quantitative nature of the interplay between contact pressure, the material and microstructural properties of the skin, the size of an indenting slider and the resulting measured macroscopic coefficient of friction. A mechanistic understanding of these aspects is essential for guiding the rational design of products intended to interact with the skin through optimally-tuned surface and/or microstructural properties. Here, an anatomically-realistic 2D multi-layer finite element model of the skin was embedded within a computational contact homogenisation procedure. The main objective was to investigate the sensitivity of macroscopic skin friction to the parameters discussed above, in addition to the local (i.e. microscopic) coefficient of friction defined at skin asperity level. This was accomplished via the design of a large-scale computational experiment featuring 312 analyses. Results confirmed the potentially major role of finite deformations of skin asperities on the resulting macroscopic friction. This effect was shown to be modulated by the level of contact pressure and relative size of skin surface asperities compared to those of a rigid slider. The numerical study also corroborated experimental observations concerning the existence of two contact pressure regimes where macroscopic friction steeply and non-linearly increases up to a critical value, and then remains approximately constant as pressure increases further. The proposed computational modelling platform offers attractive features which are beyond the reach of current analytical models of skin friction, namely, the ability to accommodate arbitrary kinematics, non-linear constitutive properties and the complex skin microstructure.

Reaction wheel low-speed compensation using a dither signal

NASA Astrophysics Data System (ADS)

Stetson, John B., Jr.

1993-08-01

A method for improving low-speed reaction wheel performance on a three-axis controlled spacecraft is presented. The method combines a constant amplitude offset with an unbiased, oscillating dither to harmonically linearize rolling solid friction dynamics. The complete, nonlinear rolling solid friction dynamics using an analytic modification to the experimentally verified Dahl solid friction model were analyzed using the dual-input describing function method to assess the benefits of dither compensation. The modified analytic solid friction model was experimentally verified with a small dc servomotor actuated reaction wheel assembly. Using dither compensation abrupt static friction disturbances are eliminated and near linear behavior through zero rate can be achieved. Simulated vehicle response to a wheel rate reversal shows that when the dither and offset compensation is used, elastic modes are not significantly excited, and the uncompensated attitude error reduces by 34:1.

Physical processes in wheel-rail contact and its implications on vehicle-track interaction

NASA Astrophysics Data System (ADS)

Six, K.; Meierhofer, A.; Müller, G.; Dietmaier, P.

2015-05-01

Friction within the wheel-rail contact highly influences all aspects of vehicle-track interaction. Models describing this frictional behaviour are of high relevance, for example, for reliable predictions on drive train dynamics. It has been shown by experiments, that the friction at a certain position on rail is not describable by only one number for the coefficient of friction. Beside the contact conditions (existence of liquids, solid third bodies, etc.) the vehicle speed, normal loading and contact geometry are further influencing factors. State-of-the-art models are not able to account for this sufficiently. Thus, an Extended-Creep-Force-Model was developed taking into account effects from third body layers. This model is able to describe all considered effects. In this way, a significant improvement of the prediction quality with respect to all aspects of vehicle-track interaction is expected.

Teacher Fidelity to a Physical Education Curricular Model and Physical Activity Outcomes

ERIC Educational Resources Information Center

Stylianou, Michalis; Kloeppel, Tiffany; Kulinna, Pamela; van der Mars, Han

2016-01-01

Background: This study was informed by the bodies of literature emphasizing the role of physical education in promoting physical activity (PA) and addressing teacher fidelity to curricular models. Purpose: The purpose of this study was to compare student PA levels, lesson context, and teacher PA promotion behavior among classes where teachers were…

Injury representation against ballistic threats using three novel numerical models.

PubMed

Breeze, Johno; Fryer, R; Pope, D; Clasper, J

2017-06-01

Injury modelling of ballistic threats is a valuable tool for informing policy on personal protective equipment and other injury mitigation methods. Currently, the Ministry of Defence (MoD) and Centre for Protection of National Infrastructure (CPNI) are focusing on the development of three interlinking numerical models, each of a different fidelity, to answer specific questions on current threats. High-fidelity models simulate the physical events most realistically, and will be used in the future to test the medical effectiveness of personal armour systems. They are however generally computationally intensive, slow running and much of the experimental data to base their algorithms on do not yet exist. Medium fidelity models, such as the personnel vulnerability simulation (PVS), generally use algorithms based on physical or engineering estimations of interaction. This enables a reasonable representation of reality and greatly speeds up runtime allowing full assessments of the entire body area to be undertaken. Low-fidelity models such as the human injury predictor (HIP) tool generally use simplistic algorithms to make injury predictions. Individual scenarios can be run very quickly and hence enable statistical casualty assessments of large groups, where significant uncertainty concerning the threat and affected population exist. HIP is used to simulate the blast and penetrative fragmentation effects of a terrorist detonation of an improvised explosive device within crowds of people in metropolitan environments. This paper describes the collaboration between MoD and CPNI using an example of all three fidelities of injury model and to highlight future areas of research that are required. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

Assessing Degree of Susceptibility to Landslide Hazard

NASA Astrophysics Data System (ADS)

Sheridan, M. F.; Cordoba, G. A.; Delgado, H.; Stefanescu, R.

2013-05-01

The modeling of hazardous mass flows, both dry and water saturated, is currently an area of active research and several stable models have now emerged that have differing degrees of physical and mathematical fidelity. Models based on the early work of Savage and Hutter (1989) assume that very large dense granular flows could be modeled as incompressible continua governed by a Coulomb failure criterion. Based on this concept, Patra et al. (2005) developed a code for dry avalanches, which proposes a thin layer mathematical model similar to shallow-water equations. This concept was implemented in the widely-used TITAN2D program, which integrates the shock-capturing Godunov solution methodology for the equation system. We propose a method to assess the susceptibility of specific locations susceptible to landslides following heavy tephra fall using the TIATN2D code. Successful application requires that the range of several uncertainties must be framed in the selection of model input data: 1) initial conditions, like volume and location of origin of the landslide, 2) bed and internal friction parameters and 3) digital elevation model (DEM) uncertainties. Among the possible ways of coping with these uncertainties, we chose to use Latin Hypercube Sampling (LHS). This statistical technique reduces a computationally intractable problem to such an extent that is it possible to apply it, even with current personal computers. LHS requires that there is only one sample in each row and each column of the sampling matrix, where each row (multi-dimensional) corresponds to each uncertainty. LHS requires less than 10% of the sample runs needed by Monte Carlo approaches to achieve a stable solution. In our application LHS output provides model sampling for 4 input parameters: initial random volumes, UTM location (x and y), and bed friction. We developed a simple Octave script to link the output of LHS with TITAN2D. In this way, TITAN2D can run several times with successively different initial conditions provided by the LHC routine. Finally the set of results from TITAN2D are computed to obtain the distribution of maximum exceedance probability given that a landslide occurs at a place of interest. We apply this method to find sectors least prone to be affected by landslides, in a region along the Panamerican Highway in the southern part of Colombia. The goal of such a study is to provide decision makers to improve their assessments regarding permissions for development along the highway.

Implementation fidelity trajectories of a health promotion program in multidisciplinary settings: managing tensions in rehabilitation care.

PubMed

Hoekstra, Femke; van Offenbeek, Marjolein A G; Dekker, Rienk; Hettinga, Florentina J; Hoekstra, Trynke; van der Woude, Lucas H V; van der Schans, Cees P

2017-12-01

Although the importance of evaluating implementation fidelity is acknowledged, little is known about heterogeneity in fidelity over time. This study aims to generate insight into the heterogeneity in implementation fidelity trajectories of a health promotion program in multidisciplinary settings and the relationship with changes in patients' health behavior. This study used longitudinal data from the nationwide implementation of an evidence-informed physical activity promotion program in Dutch rehabilitation care. Fidelity scores were calculated based on annual surveys filled in by involved professionals (n = ± 70). Higher fidelity scores indicate a more complete implementation of the program's core components. A hierarchical cluster analysis was conducted on the implementation fidelity scores of 17 organizations at three different time points. Quantitative and qualitative data were used to explore organizational and professional differences between identified trajectories. Regression analyses were conducted to determine differences in patient outcomes. Three trajectories were identified as the following: 'stable high fidelity' (n = 9), 'moderate and improving fidelity' (n = 6), and 'unstable fidelity' (n = 2). The stable high fidelity organizations were generally smaller, started earlier, and implemented the program in a more structured way compared to moderate and improving fidelity organizations. At the implementation period's start and end, support from physicians and physiotherapists, professionals' appreciation, and program compatibility were rated more positively by professionals working in stable high fidelity organizations as compared to the moderate and improving fidelity organizations (p < .05). Qualitative data showed that the stable high fidelity organizations had often an explicit vision and strategy about the implementation of the program. Intriguingly, the trajectories were not associated with patients' self-reported physical activity outcomes (adjusted model β = - 651.6, t(613) = - 1032, p = .303). Differences in organizational-level implementation fidelity trajectories did not result in outcome differences at patient-level. This suggests that an effective implementation fidelity trajectory is contingent on the local organization's conditions. More specifically, achieving stable high implementation fidelity required the management of tensions: realizing a localized change vision, while safeguarding the program's standardized core components and engaging the scarce physicians throughout the process. When scaling up evidence-informed health promotion programs, we propose to tailor the management of implementation tensions to local organizations' starting position, size, and circumstances. The Netherlands National Trial Register NTR3961 . Registered 18 April 2013.

Two dimensional modeling of elastic wave propagation in solids containing cracks with rough surfaces and friction - Part II: Numerical implementation.

PubMed

Delrue, Steven; Aleshin, Vladislav; Truyaert, Kevin; Bou Matar, Olivier; Van Den Abeele, Koen

2018-01-01

Our study aims at the creation of a numerical toolbox that describes wave propagation in samples containing internal contacts (e.g. cracks, delaminations, debondings, imperfect intergranular joints) of known geometry with postulated contact interaction laws including friction. The code consists of two entities: the contact model and the solid mechanics module. Part I of the paper concerns an in-depth description of a constitutive model for realistic contacts or cracks that takes into account the roughness of the contact faces and the associated effects of friction and hysteresis. In the crack model, three different contact states can be recognized: contact loss, total sliding and partial slip. Normal (clapping) interactions between the crack faces are implemented using a quadratic stress-displacement relation, whereas tangential (friction) interactions were introduced using the Coulomb friction law for the total sliding case, and the Method of Memory Diagrams (MMD) in case of partial slip. In the present part of the paper, we integrate the developed crack model into finite element software in order to simulate elastic wave propagation in a solid material containing internal contacts or cracks. We therefore implemented the comprehensive crack model in MATLAB® and introduced it in the Structural Mechanics Module of COMSOL Multiphysics®. The potential of the approach for ultrasound based inspection of solids with cracks showing acoustic nonlinearity is demonstrated by means of an example of shear wave propagation in an aluminum sample containing a single crack with rough surfaces and friction. Copyright © 2017 Elsevier B.V. All rights reserved.

Effect of friction on the rheology of dense suspensions

NASA Astrophysics Data System (ADS)

Gallier, Stany; Lemaire, Elisabeth; Peters, François; Lobry, Laurent

2014-11-01

This work reports three-dimensional numerical simulations of sheared non-Brownian concentrated suspensions using a fictitious domain method. Contacts between particles are modeled using a DEM-like approach (Discrete Element Method), which allows for a more physical description, including roughness and friction. This study emphasizes the effect of friction between particles and its role on rheological properties, especially on normal stress differences. Friction is shown to notably increase viscosity and second normal stress difference | N2 | and decrease | N1 | , in better agreement with experiments. The hydrodynamic and contact contributions to the overall particle stress are particularly investigated and this shows that the effect of friction is mostly due to the additional contact stress since the hydrodynamic stress remains unaffected by friction. Simulation results are also compared with experiments and the agreement is improved when friction is accounted for: this suggests that friction is operative in actual suspensions.

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, John A.; Barton, Nathan R.; Florando, Jeff

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material's structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V's mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments ormore » lower fidelity models. Lastly, the results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.« less

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

DOE PAGES

Moore, John A.; Barton, Nathan R.; Florando, Jeff; ...

2017-08-24

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material's structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V's mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments ormore » lower fidelity models. Lastly, the results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.« less

Linking microstructural evolution and macro-scale friction behavior in metals [Predicting the friction behavior of metals using a microstructural evolution model

DOE PAGES

Argibay, N.; Chandross, M.; Cheng, S.; ...

2016-11-21

A correlation is established between the macro-scale friction regimes of metals and a transition between two dominant atomistic mechanisms of deformation. Metals tend to exhibit bi-stable friction behavior—low and converging or high and diverging. These general trends in behavior are shown to be largely explained using a simplified model based on grain size evolution, as a function of contact stress and temperature, and are demonstrated for self-mated pure copper and gold sliding contacts. Specifically, the low-friction regime (where µ < 0.5) is linked to the formation of ultra-nanocrystalline surface films (10–20 nm), driving toward shear accommodation by grain boundary sliding.more » Above a critical combination of stress and temperature—demonstrated to be a material property—shear accommodation transitions to dislocation dominated plasticity and high friction, with µ > 0.5. We utilize a combination of experimental and computational methods to develop and validate the proposed structure–property relationship. As a result, this quantitative framework provides a shift from phenomenological to mechanistic and predictive fundamental understanding of friction for crystalline materials, including engineering alloys.« less

The molecular dynamic simulation on impact and friction characters of nanofluids with many nanoparticles system

PubMed Central

2011-01-01

Impact and friction model of nanofluid for molecular dynamics simulation was built which consists of two Cu plates and Cu-Ar nanofluid. The Cu-Ar nanofluid model consisted of eight spherical copper nanoparticles with each particle diameter of 4 nm and argon atoms as base liquid. The Lennard-Jones potential function was adopted to deal with the interactions between atoms. Thus motion states and interaction of nanoparticles at different time through impact and friction process could be obtained and friction mechanism of nanofluids could be analyzed. In the friction process, nanoparticles showed motions of rotation and translation, but effected by the interactions of nanoparticles, the rotation of nanoparticles was trapped during the compression process. In this process, agglomeration of nanoparticles was very apparent, with the pressure increasing, the phenomenon became more prominent. The reunited nanoparticles would provide supporting efforts for the whole channel, and in the meantime reduced the contact between two friction surfaces, therefore, strengthened lubrication and decreased friction. In the condition of overlarge positive pressure, the nanoparticles would be crashed and formed particles on atomic level and strayed in base liquid. PMID:21711753

Understanding dynamic friction through spontaneously evolving laboratory earthquakes

PubMed Central

Rubino, V.; Rosakis, A. J.; Lapusta, N.

2017-01-01

Friction plays a key role in how ruptures unzip faults in the Earth’s crust and release waves that cause destructive shaking. Yet dynamic friction evolution is one of the biggest uncertainties in earthquake science. Here we report on novel measurements of evolving local friction during spontaneously developing mini-earthquakes in the laboratory, enabled by our ultrahigh speed full-field imaging technique. The technique captures the evolution of displacements, velocities and stresses of dynamic ruptures, whose rupture speed range from sub-Rayleigh to supershear. The observed friction has complex evolution, featuring initial velocity strengthening followed by substantial velocity weakening. Our measurements are consistent with rate-and-state friction formulations supplemented with flash heating but not with widely used slip-weakening friction laws. This study develops a new approach for measuring local evolution of dynamic friction and has important implications for understanding earthquake hazard since laws governing frictional resistance of faults are vital ingredients in physically-based predictive models of the earthquake source. PMID:28660876

Friction factor data for flat plate tests of smooth and honeycomb surfaces. M.S. Thesis

NASA Technical Reports Server (NTRS)

Ha, Tae Woong

1989-01-01

Friction factors for honeycomb surfaces were measured with a flat plate tester. The flat plate test apparatus was described and a method was discussed for determining the friction factor experimentally. The friction factor model was developed for the flat plate test based on the Fanno Line Flow. The comparisons of the friction factor were plotted for smooth surfaces and six-honeycomb surfaces with three-clearances, 6.9 bar to 17.9 bar range of inlet pressures, and 5,000 to 100,000 range of the Reynolds number. The optimum geometries for the maximum friction factor were found as a function of cell width to cell depth and cell width to clearance ratios.

Quantum friction on monoatomic layers and its classical analog

NASA Astrophysics Data System (ADS)

Maslovski, Stanislav I.; Silveirinha, Mário G.

2013-07-01

We consider the effect of quantum friction at zero absolute temperature resulting from polaritonic interactions in closely positioned two-dimensional arrays of polarizable atoms (e.g., graphene sheets) or thin dielectric sheets modeled as such arrays. The arrays move one with respect to another with a nonrelativistic velocity v≪c. We confirm that quantum friction is inevitably related to material dispersion, and that such friction vanishes in nondispersive media. In addition, we consider a classical analog of the quantum friction which allows us to establish a link between the phenomena of quantum friction and classical parametric generation. In particular, we demonstrate how the quasiparticle generation rate typically obtained from the quantum Fermi golden rule can be calculated classically.

Computer simulation of earthquakes

NASA Technical Reports Server (NTRS)

Cohen, S. C.

1976-01-01

Two computer simulation models of earthquakes were studied for the dependence of the pattern of events on the model assumptions and input parameters. Both models represent the seismically active region by mechanical blocks which are connected to one another and to a driving plate. The blocks slide on a friction surface. In the first model elastic forces were employed and time independent friction to simulate main shock events. The size, length, and time and place of event occurrence were influenced strongly by the magnitude and degree of homogeniety in the elastic and friction parameters of the fault region. Periodically reoccurring similar events were frequently observed in simulations with near homogeneous parameters along the fault, whereas, seismic gaps were a common feature of simulations employing large variations in the fault parameters. The second model incorporated viscoelastic forces and time-dependent friction to account for aftershock sequences. The periods between aftershock events increased with time and the aftershock region was confined to that which moved in the main event.

Calibration of 3D ALE finite element model from experiments on friction stir welding of lap joints

NASA Astrophysics Data System (ADS)

Fourment, Lionel; Gastebois, Sabrina; Dubourg, Laurent

2016-10-01

In order to support the design of such a complex process like Friction Stir Welding (FSW) for the aeronautic industry, numerical simulation software requires (1) developing an efficient and accurate Finite Element (F.E.) formulation that allows predicting welding defects, (2) properly modeling the thermo-mechanical complexity of the FSW process and (3) calibrating the F.E. model from accurate measurements from FSW experiments. This work uses a parallel ALE formulation developed in the Forge® F.E. code to model the different possible defects (flashes and worm holes), while pin and shoulder threads are modeled by a new friction law at the tool / material interface. FSW experiments require using a complex tool with scroll on shoulder, which is instrumented for providing sensitive thermal data close to the joint. Calibration of unknown material thermal coefficients, constitutive equations parameters and friction model from measured forces, torques and temperatures is carried out using two F.E. models, Eulerian and ALE, to reach a satisfactory agreement assessed by the proper sensitivity of the simulation to process parameters.

Numerical investigation of fluid mud motion using a three-dimensional hydrodynamic and two-dimensional fluid mud coupling model

NASA Astrophysics Data System (ADS)

Yang, Xiaochen; Zhang, Qinghe; Hao, Linnan

2015-03-01

A water-fluid mud coupling model is developed based on the unstructured grid finite volume coastal ocean model (FVCOM) to investigate the fluid mud motion. The hydrodynamics and sediment transport of the overlying water column are solved using the original three-dimensional ocean model. A horizontal two-dimensional fluid mud model is integrated into the FVCOM model to simulate the underlying fluid mud flow. The fluid mud interacts with the water column through the sediment flux, current, and shear stress. The friction factor between the fluid mud and the bed, which is traditionally determined empirically, is derived with the assumption that the vertical distribution of shear stress below the yield surface of fluid mud is identical to that of uniform laminar flow of Newtonian fluid in the open channel. The model is validated by experimental data and reasonable agreement is found. Compared with numerical cases with fixed friction factors, the results simulated with the derived friction factor exhibit the best agreement with the experiment, which demonstrates the necessity of the derivation of the friction factor.

Basal friction evolution and crevasse distribution during the surge of Basin 3, Austfonna ice-cap - offline coupling between a continuum ice dynamic model and a discrete element model

NASA Astrophysics Data System (ADS)

Gong, Yongmei; Zwinger, Thomas; Åström, Jan; Gladstone, Rupert; Schellenberger, Thomas; Altena, Bas; Moore, John

2017-04-01

The outlet glacier at Basin 3, Austfonna ice-cap entered its active surge phase in autumn 2012. We assess the evolution of the basal friction during the surge through inverse modelling of basal friction coefficients using recent velocity observation from 2012 to 2014 in a continuum ice dynamic model Elmer/ice. The obtained basal friction coefficient distributions at different time instances are further used as a boundary condition in a discrete element model (HiDEM) that is capable of computing fracturing of ice. The inverted basal friction coefficient evolution shows a gradual 'unplugging' of the stagnant frontal area and northwards and inland expansion of the fast flowing region in the southern basin. The validation between the modeled crevasses distribution and the satellite observation in August 2013 shows a good agreement in shear zones inland and at the frontal area. Crevasse distributions of the summer before and after the glacier reached its maximum velocity in January 2013 (August 2012 and August 2014, respectively) are also evaluated. Previous studies suggest the triggering and development of the surge are linked to surface melt water penetrating through ice to form an efficient basal hydrology system thereby triggering a hydro- thermodynamic feedback. This preliminary offline coupling between a continuum ice dynamic model and a discrete element model will give a hint on future model development of linking supra-glacial to sub-glacial hydrology system.

Synergy and Self-organization in Tribosystem’s evolution. Energy Model of Friction

NASA Astrophysics Data System (ADS)

Fedorov, S. V.; Assenova, E.

2018-01-01

Different approaches are known to treat self-organization in tribosystems, related to the structural adaptation in the formation of dissipative surface structures and of frictional or tribo-films, using of synergistic modifying of layers and coatings, e.g. of the selective material transfer during friction, etc. Regarding tribological processes in contact systems, self-organization is observed as spontaneous creation of higher ordered structures during the contact interaction. The proposed paper considers friction as process of transformation and dissipation of energy and process of elasto-plastic deformation localized in thin surface layers of the interacting bodies. Еnergetic interpretation of friction is proposed. Based on the energy balance equations of friction, the evolution of tribosystems is followed in its adaptive-dissipative character. It reflects the variable friction surfaces compatibility and the nonlinear dynamics of friction evolution. Structural-energy relationships in the contacting surfaces evolution are obtained. Maximum of tribosystem’s efficiency during the evolution is the stage of self-organzation of the friction surface layers, which is a state of abnormal low friction and wear.

Friction behavior of a microstructured polymer surface inspired by snake skin.

PubMed

Baum, Martina J; Heepe, Lars; Gorb, Stanislav N

2014-01-01

The aim of this study was to understand the influence of microstructures found on ventral scales of the biological model, Lampropeltis getula californiae, the California King Snake, on the friction behavior. For this purpose, we compared snake-inspired anisotropic microstructured surfaces to other microstructured surfaces with isotropic and anisotropic geometry. To exclude that the friction measurements were influenced by physico-chemical variations, all friction measurements were performed on the same epoxy polymer. For frictional measurements a microtribometer was used. Original data were processed by fast Fourier transformation (FFT) with a zero frequency related to the average friction and other peaks resulting from periodic stick-slip behavior. The data showed that the specific ventral surface ornamentation of snakes does not only reduce the frictional coefficient and generate anisotropic frictional properties, but also reduces stick-slip vibrations during sliding, which might be an adaptation to reduce wear. Based on this extensive comparative study of different microstructured polymer samples, it was experimentally demonstrated that the friction-induced stick-slip behavior does not solely depend on the frictional coefficient of the contact pair.

Multifamily Group Psychoeducation in New York State: Implementation and Fidelity Outcomes.

PubMed

Kealey, Edith M; Leckman-Westin, Emily; Jewell, Thomas C; Finnerty, Molly T

2015-11-01

The study examined implementation outcomes from a large state initiative to support dissemination of multifamily group (MFG) psychoeducation in outpatient mental health settings. Thirty-one sites participated in the project. Baseline training in the MFG model was followed by monthly expert consultation delivered in either a group (16 sites) or individual format (15 sites). Research staff assessed fidelity to the MFG model by telephone at baseline and 12, 18, and 24 months and documented time to completion of three key milestones: holding a family joining session, a family educational workshop, and an MFG meeting. Intent-to-train analyses found that 12 sites (39%) achieved high fidelity to the MFG model, and 20 (65%) achieved moderate or high fidelity. Mean scores on the Family Psychoeducation Fidelity Assessment Scale increased over time. Twenty-five sites (81%) conducted at least one joining session, and 20 (65%) conducted at least one MFG. Mean±SD time from baseline to the first group was 11.75±4.78 months. Programs that held the first joining session within four to 12 months after training were significantly more likely than programs that did not to conduct a group (p<.05). No significant differences were found by consultation format. Implementation of moderate- to high-fidelity MFG programs in routine outpatient mental health settings is feasible. Sites that moved very quickly or very slowly in early implementation stages were less likely to be successful in conducting an MFG. More research on the efficiency and effectiveness of consultation formats is needed to guide future implementation efforts.

Monte Carlo calibration of avalanches described as Coulomb fluid flows.

PubMed

Ancey, Christophe

2005-07-15

The idea that snow avalanches might behave as granular flows, and thus be described as Coulomb fluid flows, came up very early in the scientific study of avalanches, but it is not until recently that field evidence has been provided that demonstrates the reliability of this idea. This paper aims to specify the bulk frictional behaviour of snow avalanches by seeking a universal friction law. Since the bulk friction coefficient cannot be measured directly in the field, the friction coefficient must be calibrated by adjusting the model outputs to closely match the recorded data. Field data are readily available but are of poor quality and accuracy. We used Bayesian inference techniques to specify the model uncertainty relative to data uncertainty and to robustly and efficiently solve the inverse problem. A sample of 173 events taken from seven paths in the French Alps was used. The first analysis showed that the friction coefficient behaved as a random variable with a smooth and bell-shaped empirical distribution function. Evidence was provided that the friction coefficient varied with the avalanche volume, but any attempt to adjust a one-to-one relationship relating friction to volume produced residual errors that could be as large as three times the maximum uncertainty of field data. A tentative universal friction law is proposed: the friction coefficient is a random variable, the distribution of which can be approximated by a normal distribution with a volume-dependent mean.

Debris-bed friction of hard-bedded glaciers

USGS Publications Warehouse

Cohen, D.; Iverson, N.R.; Hooyer, T.S.; Fischer, U.H.; Jackson, M.; Moore, P.L.

2005-01-01

[1] Field measurements of debris-bed friction on a smooth rock tablet at the bed of Engabreen, a hard-bedded, temperate glacier in northern Norway, indicated that basal ice containing 10% debris by volume exerted local shear traction of up to 500 kPa. The corresponding bulk friction coefficient between the dirty basal ice and the tablet was between 0.05 and 0.08. A model of friction in which nonrotating spherical rock particles are held in frictional contact with the bed by bed-normal ice flow can account for these measurements if the power law exponent for ice flowing past large clasts is 1. A small exponent (n < 2) is likely because stresses in ice are small and flow is transient. Numerical calculations of the bed-normal drag force on a sphere in contact with a flat bed using n = 1 show that this force can reach values several hundred times that on a sphere isolated from the bed, thus drastically increasing frictional resistance. Various estimates of basal friction are obtained from this model. For example, the shear traction at the bed of a glacier sliding at 20 m a-1 with a geothermally induced melt rate of 0.006 m a-1 and an effective pressure of 300 kPa can exceed 100 kPa. Debris-bed friction can therefore be a major component of sliding resistance, contradicting the common assumption that debris-bed friction is negligible. Copyright 2005 by the American Geophysical Union.

Periodic Forced Response of Structures Having Three-Dimensional Frictional Constraints

NASA Astrophysics Data System (ADS)

CHEN, J. J.; YANG, B. D.; MENQ, C. H.

2000-01-01

Many mechanical systems have moving components that are mutually constrained through frictional contacts. When subjected to cyclic excitations, a contact interface may undergo constant changes among sticks, slips and separations, which leads to very complex contact kinematics. In this paper, a 3-D friction contact model is employed to predict the periodic forced response of structures having 3-D frictional constraints. Analytical criteria based on this friction contact model are used to determine the transitions among sticks, slips and separations of the friction contact, and subsequently the constrained force which consists of the induced stick-slip friction force on the contact plane and the contact normal load. The resulting constrained force is often a periodic function and can be considered as a feedback force that influences the response of the constrained structures. By using the Multi-Harmonic Balance Method along with Fast Fourier Transform, the constrained force can be integrated with the receptance of the structures so as to calculate the forced response of the constrained structures. It results in a set of non-linear algebraic equations that can be solved iteratively to yield the relative motion as well as the constrained force at the friction contact. This method is used to predict the periodic response of a frictionally constrained 3-d.o.f. oscillator. The predicted results are compared with those of the direct time integration method so as to validate the proposed method. In addition, the effect of super-harmonic components on the resonant response and jump phenomenon is examined.

EBT Fidelity Trajectories Across Training Cohorts Using the Interagency Collaborative Team Strategy

PubMed Central

Hecht, Debra; Aarons, Greg; Fettes, Danielle; Hurlburt, Michael; Ledesma, Karla

2015-01-01

The Interdisciplinary Collaborative Team (ICT) strategy uses front-line providers as adaptation, training and quality control agents for multi-agency EBT implementation. This study tests whether an ICT transmits fidelity to subsequent provider cohorts. SafeCare was implemented by home visitors from multiple community-based agencies contracting with child welfare. Client-reported fidelity trajectories for 5,769 visits, 957 clients and 45 providers were compared using three-level growth models. Provider cohorts trained and live-coached by the ICT attained benchmark fidelity after 12 weeks, and this was sustained. Hispanic clients reported high cultural competency, supporting a cultural adaptation crafted by the ICT. PMID:25586878

EBT Fidelity Trajectories Across Training Cohorts Using the Interagency Collaborative Team Strategy.

PubMed

Chaffin, Mark; Hecht, Debra; Aarons, Greg; Fettes, Danielle; Hurlburt, Michael; Ledesma, Karla

2016-03-01

The Interdisciplinary Collaborative Team (ICT) strategy uses front-line providers as adaptation, training and quality control agents for multi-agency EBT implementation. This study tests whether an ICT transmits fidelity to subsequent provider cohorts. SafeCare was implemented by home visitors from multiple community-based agencies contracting with child welfare. Client-reported fidelity trajectories for 5,769 visits, 957 clients and 45 providers were compared using three-level growth models. Provider cohorts trained and live-coached by the ICT attained benchmark fidelity after 12 weeks, and this was sustained. Hispanic clients reported high cultural competency, supporting a cultural adaptation crafted by the ICT.

Internal friction and dislocation collective pinning in disordered quenched solid solutions

NASA Astrophysics Data System (ADS)

D'Anna, G.; Benoit, W.; Vinokur, V. M.

1997-12-01

We introduce the collective pinning of dislocations in disordered quenched solid solutions and calculate the macroscopic mechanical response to a small dc or ac applied stress. This work is a generalization of the Granato-Lücke string model, able to describe self-consistently short and long range dislocation motion. Under dc applied stress the long distance dislocation creep has at the microscopic level avalanche features, which result in a macroscopic nonlinear "glassy" velocity-stress characteristic. Under ac conditions the model predicts, in addition to the anelastic internal friction relaxation in the high frequency regime, a linear internal friction background which remains amplitude-independent down to a crossover frequency to a strongly nonlinear internal friction regime.

Fault detection in mechanical systems with friction phenomena: an online neural approximation approach.

PubMed

Papadimitropoulos, Adam; Rovithakis, George A; Parisini, Thomas

2007-07-01

In this paper, the problem of fault detection in mechanical systems performing linear motion, under the action of friction phenomena is addressed. The friction effects are modeled through the dynamic LuGre model. The proposed architecture is built upon an online neural network (NN) approximator, which requires only system's position and velocity. The friction internal state is not assumed to be available for measurement. The neural fault detection methodology is analyzed with respect to its robustness and sensitivity properties. Rigorous fault detectability conditions and upper bounds for the detection time are also derived. Extensive simulation results showing the effectiveness of the proposed methodology are provided, including a real case study on an industrial actuator.

Mechatronic design of haptic forceps for robotic surgery.

PubMed

Rizun, P; Gunn, D; Cox, B; Sutherland, G

2006-12-01

Haptic feedback increases operator performance and comfort during telerobotic manipulation. Feedback of grasping pressure is critical in many microsurgical tasks, yet no haptic interface for surgical tools is commercially available. Literature on the psychophysics of touch was reviewed to define the spectrum of human touch perception and the fidelity requirements of an ideal haptic interface. Mechanical design and control literature was reviewed to translate the psychophysical requirements to engineering specification. High-fidelity haptic forceps were then developed through an iterative process between engineering and surgery. The forceps are a modular device that integrate with a haptic hand controller to add force feedback for tool actuation in telerobotic or virtual surgery. Their overall length is 153 mm and their mass is 125 g. A contact-free voice coil actuator generates force feedback at frequencies up to 800 Hz. Maximum force output is 6 N (2N continuous) and the force resolution is 4 mN. The forceps employ a contact-free magnetic position sensor as well as micro-machined accelerometers to measure opening/closing acceleration. Position resolution is 0.6 microm with 1.3 microm RMS noise. The forceps can simulate stiffness greater than 20N/mm or impedances smaller than 15 g with no noticeable haptic artifacts or friction. As telerobotic surgery evolves, haptics will play an increasingly important role. Copyright 2006 John Wiley & Sons, Ltd.

Some aerodynamic considerations related to wind tunnel model surface definition

NASA Technical Reports Server (NTRS)

Gloss, B. B.

1980-01-01

The aerodynamic considerations related to model surface definition are examined with particular emphasis in areas of fabrication tolerances, model surface finish, and orifice induced pressure errors. The effect of model surface roughness texture on skin friction is also discussed. It is shown that at a given Reynolds number, any roughness will produce no skin friction penalty.

Gravity-Off-loading System for Large-Displacement Ground Testing of Spacecraft Mechanisms

NASA Technical Reports Server (NTRS)

Han, Olyvia; Kienholz, David; Janzen, Paul; Kidney, Scott

2010-01-01

Gravity-off-loading of deployable spacecraft mechanisms during ground testing is a long-standing problem. Deployable structures which are usually too weak to support their own weight under gravity require a means of gravity-off-loading as they unfurl. Conventional solutions to this problem have been helium-filled balloons or mechanical pulley/counterweight systems. These approaches, however, suffer from the deleterious effects of added inertia or friction forces. The changing form factor of the deployable structure itself and the need to track the trajectory of the center of gravity also pose a challenge to these conventional technologies. This paper presents a novel testing apparatus for high-fidelity zero-gravity simulation for special application to deployable space structures such as solar arrays, magnetometer booms, and robotic arms in class 100,000 clean room environments

Torsional Tribological Behavior and Torsional Friction Model of Polytetrafluoroethylene against 1045 Steel

PubMed Central

Wang, Shibo; Niu, Chengchao

2016-01-01

In this work, the plane-on-plane torsional fretting tribological behavior of polytetrafluoroethylene (PTFE) was studied. A model of a rigid, flat-ended punch acting on an elastic half-space was built according to the experimental conditions. The results indicate that the shape of T–θ curves was influenced by both the torsional angle and the normal load. The torsion friction torque and wear rate of PTFE exponentially decreased when the torsion angle rose. The torsional torque increased from 0.025 N·m under a normal load of 43 N to 0.082 N·m under a normal load of 123 N. With sequentially increasing normal load, the value of torque was maintained. With rising normal load, the wear mass loss of PTFE disks was increased and the wear rate was decreased. Good agreement was found with the calculated torque according to the model and the experimental torque except for that under a normal load of 163 N. The difference under a normal load of 163 N was caused by the coefficient of friction. Usually the coefficient of friction of a polymer decreases with increasing normal load, whereas a constant coefficient of friction was applied in the model. PMID:26799324

The Indeterminate Case of Classical Static Friction When Coupled with Tension

NASA Astrophysics Data System (ADS)

Hahn, Kenneth D.; Russell, Jacob M.

2018-02-01

It has been noted that the static friction force poses challenges for students and, at times, even their instructors. Unlike the gravitational force, which has a precise and unambiguous magnitude (FG = mg), the magnitude and direction of the static friction force depend on other forces at play. Friction can be understood rather well in terms of complicated atomic-scale interactions between surfaces. Ringlein and Robbins survey aspects of the atomic origins of friction, and Folkerts explores factors that affect the value of static friction. However, what students typically encounter in an introductory course ignores the atomic origins of friction (beyond perhaps a brief overview of the atomic model). The rules of dry friction (i.e., non-lubricated surfaces in contact) taught in introductory physics were originally published in 1699 by Guillaume Amontons. Amontons's first law states that the force of friction is directly proportional to the applied load, i.e., f = μFN, where FN is the normal force and μ is the coefficient of friction. His second law states that the force of friction is independent of the macroscopic area of contact. These laws were verified by Coulomb in 1781.

Utilizing Adjoint-Based Error Estimates for Surrogate Models to Accurately Predict Probabilities of Events

DOE PAGES

Butler, Troy; Wildey, Timothy

2018-01-01

In thist study, we develop a procedure to utilize error estimates for samples of a surrogate model to compute robust upper and lower bounds on estimates of probabilities of events. We show that these error estimates can also be used in an adaptive algorithm to simultaneously reduce the computational cost and increase the accuracy in estimating probabilities of events using computationally expensive high-fidelity models. Specifically, we introduce the notion of reliability of a sample of a surrogate model, and we prove that utilizing the surrogate model for the reliable samples and the high-fidelity model for the unreliable samples gives preciselymore » the same estimate of the probability of the output event as would be obtained by evaluation of the original model for each sample. The adaptive algorithm uses the additional evaluations of the high-fidelity model for the unreliable samples to locally improve the surrogate model near the limit state, which significantly reduces the number of high-fidelity model evaluations as the limit state is resolved. Numerical results based on a recently developed adjoint-based approach for estimating the error in samples of a surrogate are provided to demonstrate (1) the robustness of the bounds on the probability of an event, and (2) that the adaptive enhancement algorithm provides a more accurate estimate of the probability of the QoI event than standard response surface approximation methods at a lower computational cost.« less

Utilizing Adjoint-Based Error Estimates for Surrogate Models to Accurately Predict Probabilities of Events

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butler, Troy; Wildey, Timothy

In thist study, we develop a procedure to utilize error estimates for samples of a surrogate model to compute robust upper and lower bounds on estimates of probabilities of events. We show that these error estimates can also be used in an adaptive algorithm to simultaneously reduce the computational cost and increase the accuracy in estimating probabilities of events using computationally expensive high-fidelity models. Specifically, we introduce the notion of reliability of a sample of a surrogate model, and we prove that utilizing the surrogate model for the reliable samples and the high-fidelity model for the unreliable samples gives preciselymore » the same estimate of the probability of the output event as would be obtained by evaluation of the original model for each sample. The adaptive algorithm uses the additional evaluations of the high-fidelity model for the unreliable samples to locally improve the surrogate model near the limit state, which significantly reduces the number of high-fidelity model evaluations as the limit state is resolved. Numerical results based on a recently developed adjoint-based approach for estimating the error in samples of a surrogate are provided to demonstrate (1) the robustness of the bounds on the probability of an event, and (2) that the adaptive enhancement algorithm provides a more accurate estimate of the probability of the QoI event than standard response surface approximation methods at a lower computational cost.« less

Microphysically derived expressions for rate-and-state friction and fault stability parameters

NASA Astrophysics Data System (ADS)

Chen, Jianye; Niemeijer, Andre; Spiers, Christopher

2017-04-01

Rate-and-state friction (RSF) laws and associated parameters are extensively applied to fault mechanics, mainly on an empirical basis with a limited understanding of the underlying physical mechanisms. We recently established a general microphysical model [Chen and Spiers, 2016], for describing both steady-state and transient frictional behavior of any granular fault gouge material undergoing deformation by granular flow plus an arbitrary creep mechanism at grain contacts, such as pressure solution. We further showed that the model is able to reproduce typical experimental frictional results, namely "velocity stepping" and "slide-hold-slide" sequences, in satisfactory agreement with the main features and trends observed. Here, we extend our model, which we explored only numerically thus far, to obtain analytical solutions for the classical rate and state friction parameters from a purely microphysical modelling basis. By analytically solving the constitutive equations of the model under various boundary conditions, physically meaningful, theoretical expressions for the RSF parameters, i.e. a, b and Dc, are obtained. We also apply linear stability analysis to a spring-slider system, describing interface friction using our model, to yield analytical expressions of the critical stiffness (Kc) and critical recurrence wavelength (Wc) of the system. The values of a , b and Dc, as well as Kc and Wc, predicted by these expressions agree well with the numerical modeling results and acceptably with values obtained from experiments, on calcite for instance. Inserting the parameters obtained into classical RSF laws (slowness and slip laws) and conducting forward modelling gives simulated friction behavior that is fully consistent with the direct predictions of our numerically implemented model. Numerical tests with friction obeying our model show that the slip stability of fault motion exhibits a transition from stable sliding, via self-sustained oscillations, to stick slips with decreasing elastic stiffness, decreasing loading rate, and increasing normal stress, which is fully consistent with our linear stability analysis and also with previous RSF models that employed constant values of the RSF parameters. Importantly, our analytical expressions for. a, b, Dc, Kc and Wc, are functions of the internal microstructure of the fault (porosity, grain size and shear zone thickness), the material properties of the fault gouge (e.g. creep law parameters like activation energy, stress sensitivity, grain size sensitivity), and the ambient conditions the fault is subjected to (temperature and normal stress). The expressions obtained thus have clear physical meaning allowing a more meaningful extrapolation to natural conditions. On the basis of these physics-based expressions, seismological implications for slip on natural faults (e.g. subduction zone interfaces, faults in carbonate terrains) are discussed. Reference Chen, J., and C. J. Spiers (2016), Rate and state frictional and healing behavior of carbonate fault gouge explained using microphysical model, J. Geophys. Res., 121, doi:10.1002/2016JB013470.

Internal friction in enzyme reactions.

PubMed

Rauscher, Anna; Derényi, Imre; Gráf, László; Málnási-Csizmadia, András

2013-01-01

The empirical concept of internal friction was introduced 20 years ago. This review summarizes the results of experimental and theoretical studies that help to uncover the nature of internal friction. After the history of the concept, we describe the experimental challenges in measuring and interpreting internal friction based on the viscosity dependence of enzyme reactions. We also present speculations about the structural background of this viscosity dependence. Finally, some models about the relationship between the energy landscape and internal friction are outlined. Alternative concepts regarding the viscosity dependence of enzyme reactions are also discussed. Copyright © 2012 International Union of Biochemistry and Molecular Biology, Inc.

Friction damping of two-dimensional motion and its application in vibration control

NASA Technical Reports Server (NTRS)

Menq, C.-H.; Chidamparam, P.; Griffin, J. H.

1991-01-01

This paper presents an approximate method for analyzing the two-dimensional friction contact problem so as to compute the dynamic response of a structure constrained by friction interfaces. The friction force at the joint is formulated based on the Coulomb model. The single-term harmonic balance scheme, together with the receptance approach of decoupling the effect of the friction force on the structure from those of the external forces has been utilized to obtain the steady state response. The computational efficiency and accuracy of the method are demonstrated by comparing the results with long-term time solutions.

A Model for Couples. How Two Can Grow Together

ERIC Educational Resources Information Center

Sherwood, John J.; Scherer, John J.

1975-01-01

The authors present a model which follows the development of a male-female relationship through dating, marriage and divorce. They discuss the factors that cause friction between a husband and wife and offer procedures for coping with such friction. (SE)

Dynamic mortar finite element method for modeling of shear rupture on frictional rough surfaces

NASA Astrophysics Data System (ADS)

Tal, Yuval; Hager, Bradford H.

2017-09-01

This paper presents a mortar-based finite element formulation for modeling the dynamics of shear rupture on rough interfaces governed by slip-weakening and rate and state (RS) friction laws, focusing on the dynamics of earthquakes. The method utilizes the dual Lagrange multipliers and the primal-dual active set strategy concepts, together with a consistent discretization and linearization of the contact forces and constraints, and the friction laws to obtain a semi-smooth Newton method. The discretization of the RS friction law involves a procedure to condense out the state variables, thus eliminating the addition of another set of unknowns into the system. Several numerical examples of shear rupture on frictional rough interfaces demonstrate the efficiency of the method and examine the effects of the different time discretization schemes on the convergence, energy conservation, and the time evolution of shear traction and slip rate.

Brittle and ductile friction modeling of triggered tremor in Guerrero, Mexico

NASA Astrophysics Data System (ADS)

Zhang, Y.; Daub, E. G.; Wu, C.

2017-12-01

Low frequency earthquakes (LFEs), which make up the highest amplitude portions of non-volcanic tremor, are mostly found along subduction zones at a depth of 30-40km which is typically within the brittle-ductile transition zone. Previous studies in Guerrero, Mexico demonstrated a relationship between the bursts of LFEs and the contact states of fault interfaces, and LFEs that triggered by different mechanisms were observed along different parts of the subduction zone. To better understand the physics of fault interfaces at depth, especially the influence of contact states of these asperities, we use a brittle-ductile friction model to simulate the occurrence of LFE families from a model of frictional failure and slip. This model takes the stress state, slip rate, perturbation force, fault area, and brittle-ductile frictional contact characteristics and simulates the times and amplitudes of LFE occurrence for a single family. We examine both spontaneous and triggered tremor occurrence by including stresses due to external seismic waves, such as the 2010 Maule Earthquake, which triggered tremor and slow slip on the Guerrero section of the subduction zone. By comparing our model output with detailed observations of LFE occurrence, we can determine valuable constraints on the frictional properties of subduction zones at depth.

High fidelity simulations of infrared imagery with animated characters

NASA Astrophysics Data System (ADS)

Näsström, F.; Persson, A.; Bergström, D.; Berggren, J.; Hedström, J.; Allvar, J.; Karlsson, M.

2012-06-01

High fidelity simulations of IR signatures and imagery tend to be slow and do not have effective support for animation of characters. Simplified rendering methods based on computer graphics methods can be used to overcome these limitations. This paper presents a method to combine these tools and produce simulated high fidelity thermal IR data of animated people in terrain. Infrared signatures for human characters have been calculated using RadThermIR. To handle multiple character models, these calculations use a simplified material model for the anatomy and clothing. Weather and temperature conditions match the IR-texture used in the terrain model. The calculated signatures are applied to the animated 3D characters that, together with the terrain model, are used to produce high fidelity IR imagery of people or crowds. For high level animation control and crowd simulations, HLAS (High Level Animation System) has been developed. There are tools available to create and visualize skeleton based animations, but tools that allow control of the animated characters on a higher level, e.g. for crowd simulation, are usually expensive and closed source. We need the flexibility of HLAS to add animation into an HLA enabled sensor system simulation framework.

Steady and transient sliding under rate-and-state friction

NASA Astrophysics Data System (ADS)

Putelat, Thibaut; Dawes, Jonathan H. P.

2015-05-01

The physics of dry friction is often modelled by assuming that static and kinetic frictional forces can be represented by a pair of coefficients usually referred to as μs and μk, respectively. In this paper we re-examine this discontinuous dichotomy and relate it quantitatively to the more general, and smooth, framework of rate-and-state friction. This is important because it enables us to link the ideas behind the widely used static and dynamic coefficients to the more complex concepts that lie behind the rate-and-state framework. Further, we introduce a generic framework for rate-and-state friction that unifies different approaches found in the literature. We consider specific dynamical models for the motion of a rigid block sliding on an inclined surface. In the Coulomb model with constant dynamic friction coefficient, sliding at constant velocity is not possible. In the rate-and-state formalism steady sliding states exist, and analysing their existence and stability enables us to show that the static friction coefficient μs should be interpreted as the local maximum at very small slip rates of the steady state rate-and-state friction law. Next, we revisit the often-cited experiments of Rabinowicz (J. Appl. Phys., 22:1373-1379, 1951). Rabinowicz further developed the idea of static and kinetic friction by proposing that the friction coefficient maintains its higher and static value μs over a persistence length before dropping to the value μk. We show that there is a natural identification of the persistence length with the distance that the block slips as measured along the stable manifold of the saddle point equilibrium in the phase space of the rate-and-state dynamics. This enables us explicitly to define μs in terms of the rate-and-state variables and hence link Rabinowicz's ideas to rate-and-state friction laws. This stable manifold naturally separates two basins of attraction in the phase space: initial conditions in the first one lead to the block eventually stopping, while in the second basin of attraction the sliding motion continues indefinitely. We show that a second definition of μs is possible, compatible with the first one, as the weighted average of the rate-and-state friction coefficient over the time the block is in motion.

Intermediate Fidelity Closed Brayton Cycle Power Conversion Model

NASA Technical Reports Server (NTRS)

Lavelle, Thomas M.; Khandelwal, Suresh; Owen, Albert K.

2006-01-01

This paper describes the implementation of an intermediate fidelity model of a closed Brayton Cycle power conversion system (Closed Cycle System Simulation). The simulation is developed within the Numerical Propulsion Simulation System architecture using component elements from earlier models. Of particular interest, and power, is the ability of this new simulation system to initiate a more detailed analysis of compressor and turbine components automatically and to incorporate the overall results into the general system simulation.

Initial Integration of Noise Prediction Tools for Acoustic Scattering Effects

NASA Technical Reports Server (NTRS)

Nark, Douglas M.; Burley, Casey L.; Tinetti, Ana; Rawls, John W.

2008-01-01

This effort provides an initial glimpse at NASA capabilities available in predicting the scattering of fan noise from a non-conventional aircraft configuration. The Aircraft NOise Prediction Program, Fast Scattering Code, and the Rotorcraft Noise Model were coupled to provide increased fidelity models of scattering effects on engine fan noise sources. The integration of these codes led to the identification of several keys issues entailed in applying such multi-fidelity approaches. In particular, for prediction at noise certification points, the inclusion of distributed sources leads to complications with the source semi-sphere approach. Computational resource requirements limit the use of the higher fidelity scattering code to predict radiated sound pressure levels for full scale configurations at relevant frequencies. And, the ability to more accurately represent complex shielding surfaces in current lower fidelity models is necessary for general application to scattering predictions. This initial step in determining the potential benefits/costs of these new methods over the existing capabilities illustrates a number of the issues that must be addressed in the development of next generation aircraft system noise prediction tools.

The influence of bed friction variability due to land cover on storm-driven barrier island morphodynamics

USGS Publications Warehouse

Passeri, Davina L.; Long, Joseph W.; Plant, Nathaniel G.; Bilskie, Matthew V.; Hagen, Scott C.

2018-01-01

Variations in bed friction due to land cover type have the potential to influence morphologic change during storm events; the importance of these variations can be studied through numerical simulation and experimentation at locations with sufficient observational data to initialize realistic scenarios, evaluate model accuracy and guide interpretations. Two-dimensional in the horizontal plane (2DH) morphodynamic (XBeach) simulations were conducted to assess morphodynamic sensitivity to spatially varying bed friction at Dauphin Island, AL using hurricanes Ivan (2004) and Katrina (2005) as experimental test cases. For each storm, three bed friction scenarios were simulated: (1) a constant Chezy coefficient across land and water, (2) a constant Chezy coefficient across land and depth-dependent Chezy coefficients across water, and (3) spatially varying Chezy coefficients across land based on land use/land cover (LULC) data and depth-dependent Chezy coefficients across water. Modeled post-storm bed elevations were compared qualitatively and quantitatively with post-storm lidar data. Results showed that implementing spatially varying bed friction influenced the ability of XBeach to accurately simulate morphologic change during both storms. Accounting for frictional effects due to large-scale variations in vegetation and development reduced cross-barrier sediment transport and captured overwash and breaching more accurately. Model output from the spatially varying friction scenarios was used to examine the need for an existing sediment transport limiter, the influence of pre-storm topography and the effects of water level gradients on storm-driven morphodynamics.

STICK-SLIP-SEPARATION Analysis and Non-Linear Stiffness and Damping Characterization of Friction Contacts Having Variable Normal Load

NASA Astrophysics Data System (ADS)

Yang, B. D.; Chu, M. L.; Menq, C. H.

1998-03-01

Mechanical systems in which moving components are mutually constrained through contacts often lead to complex contact kinematics involving tangential and normal relative motions. A friction contact model is proposed to characterize this type of contact kinematics that imposes both friction non-linearity and intermittent separation non-linearity on the system. The stick-slip friction phenomenon is analyzed by establishing analytical criteria that predict the transition between stick, slip, and separation of the interface. The established analytical transition criteria are particularly important to the proposed friction contact model for the transition conditions of the contact kinematics are complicated by the effect of normal load variation and possible interface separation. With these transition criteria, the induced friction force on the contact plane and the variable normal load perpendicular to the contact plane, can be predicted for any given cyclic relative motions at the contact interface and hysteresis loops can be produced so as to characterize the equivalent damping and stiffness of the friction contact. These-non-linear damping and stiffness methods along with the harmonic balance method are then used to predict the resonant response of a frictionally constrained two-degree-of-freedom oscillator. The predicted results are compared with those of the time integration method and the damping effect, the resonant frequency shift, and the jump phenomenon are examined.

Systematic evaluation of implementation fidelity of complex interventions in health and social care

PubMed Central

2010-01-01

Background Evaluation of an implementation process and its fidelity can give insight into the 'black box' of interventions. However, a lack of standardized methods for studying fidelity and implementation process have been reported, which might be one reason for the fact that few prior studies in the field of health service research have systematically evaluated interventions' implementation processes. The aim of this project is to systematically evaluate implementation fidelity and possible factors influencing fidelity of complex interventions in health and social care. Methods A modified version of The Conceptual Framework for Implementation Fidelity will be used as a conceptual model for the evaluation. The modification implies two additional moderating factors: context and recruitment. A systematic evaluation process was developed. Multiple case study method is used to investigate implementation of three complex health service interventions. Each case will be investigated in depth and longitudinally, using both quantitative and qualitative methods. Discussion This study is the first attempt to empirically test The Conceptual Framework for Implementation Fidelity. The study can highlight mechanism and factors of importance when implementing complex interventions. Especially the role of the moderating factors on implementation fidelity can be clarified. Trial Registration Supported Employment, SE, among people with severe mental illness -- a randomized controlled trial: NCT00960024. PMID:20815872

Variable friction device for structural control based on duo-servo vehicle brake: Modeling and experimental validation

NASA Astrophysics Data System (ADS)

Cao, Liang; Downey, Austin; Laflamme, Simon; Taylor, Douglas; Ricles, James

2015-07-01

Supplemental damping can be used as a cost-effective method to reduce structural vibrations. In particular, passive systems are now widely accepted and have numerous applications in the field. However, they are typically tuned to specific excitations and their performances are bandwidth-limited. A solution is to use semi-active devices, which have shown to be capable of substantially enhanced mitigation performance. The authors have recently proposed a new type of semi-active device, which consists of a variable friction mechanism based on a vehicle duo-servo drum brake, a mechanically robust and reliable technology. The theoretical performance of the proposed device has been previously demonstrated via numerical simulations. In this paper, we further the understanding of the device, termed Modified Friction Device (MFD) by fabricating a small scale prototype and characterizing its dynamic behavior. While the dynamics of friction is well understood for automotive braking technology, we investigate for the first time the dynamic behavior of this friction mechanism at low displacements and velocities, in both forward and backward directions, under various hydraulic pressures. A modified 3-stage dynamic model is introduced. A LuGre friction model is used to characterize the friction zone (Stage 1), and two pure stiffness regions to characterize the dynamics of the MFD once the rotation is reversed and the braking shoes are sticking to the drum (Stage 2) and the rapid build up of forces once the shoes are held by the anchor pin (Stage 3). The proposed model is identified experimentally by subjecting the prototype to harmonic excitations. It is found that the proposed model can be used to characterize the dynamics of the MFD, and that the largest fitting error arises at low velocity under low pressure input. The model is then verified by subjecting the MFD to two different earthquake excitations under different pressure inputs. The model is capable of tracking the device's response, despite a lower fitting performance under low pressure and small force output, as it was found in the harmonic tests due to the possible nonlinearity in Stage 2 of the model.

Multiple spatially localized dynamical states in friction-excited oscillator chains

NASA Astrophysics Data System (ADS)

Papangelo, A.; Hoffmann, N.; Grolet, A.; Stender, M.; Ciavarella, M.

2018-03-01

Friction-induced vibrations are known to affect many engineering applications. Here, we study a chain of friction-excited oscillators with nearest neighbor elastic coupling. The excitation is provided by a moving belt which moves at a certain velocity vd while friction is modelled with an exponentially decaying friction law. It is shown that in a certain range of driving velocities, multiple stable spatially localized solutions exist whose dynamical behavior (i.e. regular or irregular) depends on the number of oscillators involved in the vibration. The classical non-repeatability of friction-induced vibration problems can be interpreted in light of those multiple stable dynamical states. These states are found within a "snaking-like" bifurcation pattern. Contrary to the classical Anderson localization phenomenon, here the underlying linear system is perfectly homogeneous and localization is solely triggered by the friction nonlinearity.

Contact Dependence and Velocity Crossover in Friction between Microscopic Solid/Solid Contacts.

PubMed

McGraw, Joshua D; Niguès, Antoine; Chennevière, Alexis; Siria, Alessandro

2017-10-11

Friction at the nanoscale differs markedly from that between surfaces of macroscopic extent. Characteristically, the velocity dependence of friction between apparent solid/solid contacts can strongly deviate from the classically assumed velocity independence. Here, we show that a nondestructive friction between solid tips with radius on the scale of hundreds of nanometers and solid hydrophobic self-assembled monolayers has a strong velocity dependence. Specifically, using laterally oscillating quartz tuning forks, we observe a linear scaling in the velocity at the lowest accessed velocities, typically hundreds of micrometers per second, crossing over into a logarithmic velocity dependence. This crossover is consistent with a general multicontact friction model that includes thermally activated breaking of the contacts at subnanometric elongation. We find as well a strong dependence of the friction on the dimensions of the frictional probe.

Thermal Protection System Mass Estimating Relationships for Blunt-Body, Earth Entry Spacecraft

NASA Technical Reports Server (NTRS)

Sepka, Steven A.; Samareh, Jamshid A.

2015-01-01

System analysis and design of any entry system must balance the level fidelity for each discipline against the project timeline. One way to inject high fidelity analysis earlier in the design effort is to develop surrogate models for the high-fidelity disciplines. Surrogate models for the Thermal Protection System (TPS) are formulated as Mass Estimating Relationships (MERs). The TPS MERs are presented that predict the amount of TPS necessary for safe Earth entry for blunt-body spacecraft using simple correlations that closely match estimates from NASA's high-fidelity ablation modeling tool, the Fully Implicit Ablation and Thermal Analysis Program (FIAT). These MERs provide a first order estimate for rapid feasibility studies. There are 840 different trajectories considered in this study, and each TPS MER has a peak heating limit. MERs for the vehicle forebody include the ablators Phenolic Impregnated Carbon Ablator (PICA) and Carbon Phenolic atop Advanced Carbon-Carbon. For the aftbody, the materials are Silicone Impregnated Reusable Ceramic Ablator (SIRCA), Acusil II, SLA-561V, and LI-900. The MERs are accurate to within 14% (at one standard deviation) of FIAT prediction, and the most any MER under predicts FIAT TPS thickness is 18.7%. This work focuses on the development of these MERs, the resulting equations, model limitations, and model accuracy.

Rupture models with dynamically determined breakdown displacement

USGS Publications Warehouse

Andrews, D.J.

2004-01-01

The critical breakdown displacement, Dc, in which friction drops to its sliding value, can be made dependent on event size by specifying friction to be a function of variables other than slip. Two such friction laws are examined here. The first is designed to achieve accuracy and smoothness in discrete numerical calculations. Consistent resolution throughout an evolving rupture is achieved by specifying friction as a function of elapsed time after peak stress is reached. Such a time-weakening model produces Dc and fracture energy proportional to the square root of distance rupture has propagated in the case of uniform stress drop. The second friction law is more physically motivated. Energy loss in a damage zone outside the slip zone has the effect of increasing Dc and limiting peak slip velocity (Andrews, 1976). This article demonstrates a converse effect, that artificially limiting slip velocity on a fault in an elastic medium has a toughening effect, increasing fracture energy and Dc proportionally to rupture propagation distance in the case of uniform stress drop. Both the time-weakening and the velocity-toughening models can be used in calculations with heterogeneous stress drop.

Three dimensional modelling of earthquake rupture cycles on frictional faults

NASA Astrophysics Data System (ADS)

Simpson, Guy; May, Dave

2017-04-01

We are developing an efficient MPI-parallel numerical method to simulate earthquake sequences on preexisting faults embedding within a three dimensional viscoelastic half-space. We solve the velocity form of the elasto(visco)dynamic equations using a continuous Galerkin Finite Element Method on an unstructured pentahedral mesh, which thus permits local spatial refinement in the vicinity of the fault. Friction sliding is coupled to the viscoelastic solid via rate- and state-dependent friction laws using the split-node technique. Our coupled formulation employs a picard-type non-linear solver with a fully implicit, first order accurate time integrator that utilises an adaptive time step that efficiently evolves the system through multiple seismic cycles. The implementation leverages advanced parallel solvers, preconditioners and linear algebra from the Portable Extensible Toolkit for Scientific Computing (PETSc) library. The model can treat heterogeneous frictional properties and stress states on the fault and surrounding solid as well as non-planar fault geometries. Preliminary tests show that the model successfully reproduces dynamic rupture on a vertical strike-slip fault in a half-space governed by rate-state friction with the ageing law.

Effects of Structural Deformations of the Crank-Slider Mechanism on the Estimation of the Instantaneous Engine Friction Torque

NASA Astrophysics Data System (ADS)

CHALHOUB, N. G.; NEHME, H.; HENEIN, N. A.; BRYZIK, W.

1999-07-01

The focus on the current study is to assess the effects of structural deformations of the crankshaft/connecting-rod/piston mechanism on the computation of the instantaneous engine friction torque. This study is performed in a fully controlled environment in order to isolate the effects of structural deformations from those of measurement errors or noise interference. Therefore, a detailed model, accounting for the rigid and flexible motions of the crank-slider mechanism and including engine component friction formulations, is considered in this study. The model is used as a test bed to generate the engine friction torque,Tfa, and to predict the rigid and flexible motions of the system in response to the cylinder gas pressure. The torsional vibrations and the rigid body angular velocity of the crankshaft, as predicted by the detailed model of the crank-slider mechanism, are used along with the engine load torque and the cylinder gas pressure in the (P-ω) method to estimate the engine friction torque,Tfe. This method is well suited for the purpose of this study because its formulation is based on the rigid body model of the crank-slider mechanism. The digital simulation results demonstrate that the exclusion of the structural deformations of the crank-slider mechanism from the formulation of the (P-ω) method leads to an overestimation of the engine friction torque near the top-dead-center (TDC) position of the piston under firing conditions. Moreover, for the remainder of the engine cycle, the estimated friction torque exhibits large oscillations and takes on positive numerical values as if it is inducing energy into the system. Thus, the adverse effects of structural deformations of the crank-slider mechanism on the estimation of the engine friction torque greatly differ in their nature from one phase of the engine cycle to another.

An Application of Calculus: Optimum Parabolic Path Problem

ERIC Educational Resources Information Center

Atasever, Merve; Pakdemirli, Mehmet; Yurtsever, Hasan Ali

2009-01-01

A practical and technological application of calculus problem is posed to motivate freshman students or junior high school students. A variable coefficient of friction is used in modelling air friction. The case in which the coefficient of friction is a decreasing function of altitude is considered. The optimum parabolic path for a flying object…

75 FR 32863 - Airworthiness Directives; PILATUS AIRCRAFT LTD. Model PC-12/47E Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2010-06-10

... describes the unsafe condition as: Reports have been received indicating that, if the power control friction...: Reports have been received indicating that, if the power control friction wheel is tightened, the reverse... indicating that, if the power control friction wheel is tightened, the reverse thrust latch may stick and...

Wiping Metal Transfer in Friction Stir Welding

NASA Technical Reports Server (NTRS)

Nunes, Arthur C., Jr.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

Much evidence suggests that as the friction stir pin-tool moves along a weld seam the displacement of metal takes place by a wiping action at the surface of a plug of metal that rotates with the tool. The wiping model is explained and some consequences for the friction stir welding process are drawn.

Influence of damage and basal friction on the grounding line dynamics

NASA Astrophysics Data System (ADS)

Brondex, Julien; Gagliardini, Olivier; Gillet-Chaulet, Fabien; Durand, Gael

2016-04-01

The understanding of grounding line dynamics is a major issue in the prediction of future sea level rise due to ice released from polar ice sheets into the ocean. This dynamics is complex and significantly affected by several physical processes not always adequately accounted for in current ice flow models. Among those processes, our study focuses on ice damage and evolving basal friction conditions. Softening of the ice due to damaging processes is known to have a strong impact on its rheology by reducing its viscosity and therefore promoting flow acceleration. Damage creates where shear stresses are high enough which is usually the case at shear margins and in the vicinity of pinning points in contact with ice-shelves. Those areas are known to have a buttressing effect on ice shelves contributing to stabilize the grounding line. We aim at evaluating the extent to which this stabilizing effect is hampered by damaging processes. Several friction laws have been proposed by various author to model the contact between grounded-ice and bedrock. Among them, Coulomb-type friction laws enable to account for reduced friction related to low effective pressure (the ice pressure minus the water pressure). Combining such a friction law to a parametrization of the effective pressure accounting for the fact that the area upstream the grounded line is connected to the ocean, is expected to have a significant impact on the grounding line dynamics. Using the finite-element code Elmer/Ice within which both the Coulomb-type friction law, the effective pressure parametrization and the damage model have been implemented, the goal of this study is to investigate the sensitivity of the grounding line dynamics to damage and to an evolving basal friction. The relative importance between those two processes on the grounding line dynamics is addressed as well.

United Formula for the Friction Factor in the Turbulent Region of Pipe Flow.

PubMed

Li, Shuolin; Huai, Wenxin

2016-01-01

Friction factor is an important element in both flow simulations and river engineering. In hydraulics, studies on the friction factor in turbulent regions have been based on the concept of three flow regimes, namely, the fully smooth regime, the fully rough regime, and the transitional regime, since the establishment of the Nikuradze's chart. However, this study further demonstrates that combining the friction factor with Reynolds number yields a united formula that can scale the entire turbulent region. This formula is derived by investigating the correlation between friction in turbulent pipe flow and its influencing factors, i.e., Reynolds number and relative roughness. In the present study, the formulae of Blasius and Stricklerare modified to rearrange the implicit model of Tao. In addition, we derive a united explicit formula that can compute the friction factor in the entire turbulent regimes based on the asymptotic behavior of the improved Tao's model. Compared with the reported formulae of Nikuradze, the present formula exhibits higher computational accuracy for the original pipe experiment data of Nikuradze.

Fidelity and moderating factors in complex interventions: a case study of a continuum of care program for frail elderly people in health and social care

PubMed Central

2012-01-01

Background Prior studies measuring fidelity of complex interventions have mainly evaluated adherence, and not taken factors affecting adherence into consideration. A need for studies that clarify the concept of fidelity and the function of factors moderating fidelity has been emphasized. The aim of the study was to systematically evaluate implementation fidelity and possible factors influencing fidelity of a complex care continuum intervention for frail elderly people. Methods The intervention was a systematization of the collaboration between a nurse with geriatric expertise situated at the emergency department, the hospital ward staff, and a multi-professional team with a case manager in the municipal care services for older people. Implementation was evaluated between September 2008 and May 2010 with observations of work practices, stakeholder interviews, and document analysis according to a modified version of The Conceptual Framework for Implementation Fidelity. Results A total of 16 of the 18 intervention components were to a great extent delivered as planned, while some new components were added to the model. No changes in the frequency or duration of the 18 components were observed, but the dose of the added components varied over time. Changes in fidelity were caused in a complex, interrelated fashion by all the moderating factors in the framework, i.e., context, staff and participant responsiveness, facilitation, recruitment, and complexity. Discussion The Conceptual Framework for Implementation Fidelity was empirically useful and included comprehensive measures of factors affecting fidelity. Future studies should focus on developing the framework with regard to how to investigate relationships between the moderating factors and fidelity over time. Trial registration ClinicalTrials.gov, NCT01260493. PMID:22436121

The influence of fault geometry and frictional contact properties on slip surface behavior and off-fault damage: insights from quasi-static modeling of small strike-slip faults from the Sierra Nevada, CA

NASA Astrophysics Data System (ADS)

Ritz, E.; Pollard, D. D.

2011-12-01

Geological and geophysical investigations demonstrate that faults are geometrically complex structures, and that the nature and intensity of off-fault damage is spatially correlated with geometric irregularities of the slip surfaces. Geologic observations of exhumed meter-scale strike-slip faults in the Bear Creek drainage, central Sierra Nevada, CA, provide insight into the relationship between non-planar fault geometry and frictional slip at depth. We investigate natural fault geometries in an otherwise homogeneous and isotropic elastic material with a two-dimensional displacement discontinuity method (DDM). Although the DDM is a powerful tool, frictional contact problems are beyond the scope of the elementary implementation because it allows interpenetration of the crack surfaces. By incorporating a complementarity algorithm, we are able to enforce appropriate contact boundary conditions along the model faults and include variable friction and frictional strength. This tool allows us to model quasi-static slip on non-planar faults and the resulting deformation of the surrounding rock. Both field observations and numerical investigations indicate that sliding along geometrically discontinuous or irregular faults may lead to opening of the fault and the formation of new fractures, affecting permeability in the nearby rock mass and consequently impacting pore fluid pressure. Numerical simulations of natural fault geometries provide local stress fields that are correlated to the style and spatial distribution of off-fault damage. We also show how varying the friction and frictional strength along the model faults affects slip surface behavior and consequently influences the stress distributions in the adjacent material.

The Friction Factor in the Forchheimer Equation for Rock Fractures

NASA Astrophysics Data System (ADS)

Zhou, Jia-Qing; Hu, Shao-Hua; Chen, Yi-Feng; Wang, Min; Zhou, Chuang-Bing

2016-08-01

The friction factor is an important dimensionless parameter for fluid flow through rock fractures that relates pressure head loss to average flow velocity; it can be affected by both fracture geometry and flow regime. In this study, a theoretical formula form of the friction factor containing both viscous and inertial terms is formulated by incorporating the Forchheimer equation, and a new friction factor model is proposed based on a recent phenomenological relation for the Forchheimer coefficient. The viscous term in the proposed formula is inversely proportional to Reynolds number and represents the limiting case in Darcy flow regime when the inertial effects diminish, whereas the inertial term is a power function of the relative roughness and represents a limiting case in fully turbulent flow regime when the fracture roughness plays a dominant role. The proposed model is compared with existing friction factor models for fractures through parametric sensitivity analyses and using experimental data on granite fractures, showing that the proposed model has not only clearer physical significance, but also better predictive performance. By accepting proper percentages of nonlinear pressure drop to quantify the onset of Forchheimer flow and fully turbulent flow, a Moody-type diagram with explicitly defined flow regimes is created for rock fractures of varying roughness, indicating that rougher fractures have a large friction factor and are more prone to the Forchheimer flow and fully turbulent flow. These findings may prove useful in better understanding of the flow behaviors in rock fractures and improving the numerical modeling of non-Darcy flow in fractured aquifers.

The Cascading Effects of Multiple Dimensions of Implementation on Program Outcomes: a Test of a Theoretical Model.

PubMed

Berkel, Cady; Mauricio, Anne M; Sandler, Irwin N; Wolchik, Sharlene A; Gallo, Carlos G; Brown, C Hendricks

2017-12-14

This study tests a theoretical cascade model in which multiple dimensions of facilitator delivery predict indicators of participant responsiveness, which in turn lead to improvements in targeted program outcomes. An effectiveness trial of the 10-session New Beginnings Program for divorcing families was implemented in partnership with four county-level family courts. This study included 366 families assigned to the intervention condition who attended at least one session. Independent observers provided ratings of program delivery (i.e., fidelity to the curriculum and process quality). Facilitators reported on parent attendance and parents' competence in home practice of program skills. At pretest and posttest, children reported on parenting and parents reported child mental health. We hypothesized effects of quality on attendance, fidelity and attendance on home practice, and home practice on improvements in parenting and child mental health. Structural Equation Modeling with mediation and moderation analyses were used to test these associations. Results indicated quality was significantly associated with attendance, and attendance moderated the effect of fidelity on home practice. Home practice was a significant mediator of the links between fidelity and improvements in parent-child relationship quality and child externalizing and internalizing problems. Findings provide support for fidelity to the curriculum, process quality, attendance, and home practice as valid predictors of program outcomes for mothers and fathers. Future directions for assessing implementation in community settings are discussed.

Modeling of rock friction 2. Simulation of preseismic slip

USGS Publications Warehouse

Dieterich, J.H.

1979-01-01

The constitutive relations developed in the companion paper are used to model detailed observations of preseismic slip and the onset of unstable slip in biaxial laboratory experiments. The simulations employ a deterministic plane strain finite element model to represent the interactions both within the sliding blocks and between the blocks and the loading apparatus. Both experiments and simulations show that preseismic slip is controlled by initial inhomogeneity of shear stress along the sliding surface relative to the frictional strength. As a consequence of the inhomogeneity, stable slip begins at a point on the surface and the area of slip slowly expands as the external loading increases. A previously proposed correlation between accelerating rates of stable slip and growth of the area of slip is supported by the simulations. In the simulations and in the experiments, unstable slip occurs shortly after a propagating slip event traverses the sliding surface and breaks out at the ends of the sample. In the model the breakout of stable slip causes a sudden acceleration of slip rates. Because of velocity dependency of the constitutive relationship for friction, the rapid acceleration of slip causes a decrease in frictional strength. Instability occurs when the frictional strength decreases with displacement at a rate that exceeds the intrinsic unloading characteristics of the sample and test machine. A simple slider-spring model that does not consider preseismic slip appears to approximate the transition adequately from stable sliding to unstable slip as a function of normal stress, machine stiffness, and surface roughness for small samples. However, for large samples and for natural faults the simulations suggest that the simple model may be inaccurate because it does not take into account potentially large preseismic displacements that will alter the friction parameters prior to instability. Copyright ?? 1979 by the American Geophysical Union.

The Langley Stability and Transition Analysis Code (LASTRAC) : LST, Linear and Nonlinear PSE for 2-D, Axisymmetric, and Infinite Swept Wing Boundary Layers

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan

2003-01-01

During the past two decades, our understanding of laminar-turbulent transition flow physics has advanced significantly owing to, in a large part, the NASA program support such as the National Aerospace Plane (NASP), High-speed Civil Transport (HSCT), and Advanced Subsonic Technology (AST). Experimental, theoretical, as well as computational efforts on various issues such as receptivity and linear and nonlinear evolution of instability waves take part in broadening our knowledge base for this intricate flow phenomenon. Despite all these advances, transition prediction remains a nontrivial task for engineers due to the lack of a widely available, robust, and efficient prediction tool. The design and development of the LASTRAC code is aimed at providing one such engineering tool that is easy to use and yet capable of dealing with a broad range of transition related issues. LASTRAC was written from scratch based on the state-of-the-art numerical methods for stability analysis and modem software technologies. At low fidelity, it allows users to perform linear stability analysis and N-factor transition correlation for a broad range of flow regimes and configurations by using either the linear stability theory (LST) or linear parabolized stability equations (LPSE) method. At high fidelity, users may use nonlinear PSE to track finite-amplitude disturbances until the skin friction rise. Coupled with the built-in receptivity model that is currently under development, the nonlinear PSE method offers a synergistic approach to predict transition onset for a given disturbance environment based on first principles. This paper describes the governing equations, numerical methods, code development, and case studies for the current release of LASTRAC. Practical applications of LASTRAC are demonstrated for linear stability calculations, N-factor transition correlation, non-linear breakdown simulations, and controls of stationary crossflow instability in supersonic swept wing boundary layers.

Ice Friction in the Sport of Bobsleigh

NASA Astrophysics Data System (ADS)

Poirier, Louis

The primary objective of this work is to examine the effect of the bobsleigh runner profile on ice / runner friction. The work is centered on a computational model (F.A.S.T. 3.2b) which calculates the coefficient of friction between a steel blade and ice. The first step was to analyze runners used in the sport of bobsleigh. This analysis was performed using a handheld rocker gauge, a device used in speed skating. The size of the device was optimized for hockey, short and long track speed skating, and bobsleigh. A number of runners were measured using the gauge and it was found that the portion of the runner contacting the ice generally has a rocker value of (20--50) m. Next, the hardness of athletic ice surfaces was analyzed. The ice hardness was determined by dropping steel balls varying in mass from (8--540) g onto the ice surface, from a height of (0.3--1.2) m, and measuring the diameter of the indentation craters. The ice hardness was found to be P¯(T) = ((--0.6 +/- 0.4) T + 14.7 +/- 2.1) MPa and the elastic recovery of the ice surface was found to be negligible. The F.A.S.T. model was adapted from a speed skate model to calculate the coefficient of friction between a bobsleigh runner and a flat ice surface. The model predicts that maximum velocities are obtained for temperatures between --10 and --20°C, in agreement with observations on the Calgary bobsleigh track. The model for flat ice suggests that the flattest runners produce the lowest coefficient of friction and that the rocker affects friction more than the cross-sectional radius. The coefficient of friction between runners and ice and the drag performance of 2-men bobsleighs were determined from radar speed measurements taken at the Calgary Olympic Oval and at Canada Olympic Park: at the Ice House and on the bobsleigh track during a World Cup competition. The mean coefficient of friction was found to be mu = (5.3 +/- 2.0) x 10--3 and the mean drag performance was CdA = (0.18 +/- 0.02) m2.

On Multifunctional Collaborative Methods in Engineering Science

NASA Technical Reports Server (NTRS)

Ransom, Jonathan B.

2001-01-01

Multifunctional methodologies and analysis procedures are formulated for interfacing diverse subdomain idealizations including multi-fidelity modeling methods and multi-discipline analysis methods. These methods, based on the method of weighted residuals, ensure accurate compatibility of primary and secondary variables across the subdomain interfaces. Methods are developed using diverse mathematical modeling (i.e., finite difference and finite element methods) and multi-fidelity modeling among the subdomains. Several benchmark scalar-field and vector-field problems in engineering science are presented with extensions to multidisciplinary problems. Results for all problems presented are in overall good agreement with the exact analytical solution or the reference numerical solution. Based on the results, the integrated modeling approach using the finite element method for multi-fidelity discretization among the subdomains is identified as most robust. The multiple method approach is advantageous when interfacing diverse disciplines in which each of the method's strengths are utilized.

Friction Reduction through Ultrasonic Vibration Part 2: Experimental Evaluation of Intermittent Contact and Squeeze Film Levitation.

PubMed

Sednaoui, Thomas; Vezzoli, Eric; Dzidek, Brygida; Lemaire-Semail, Betty; Chappaz, Cedrick; Adams, Michael

2017-01-01

In part 1 of the current study of haptic displays, a finite element (FE) model of a finger exploring a plate vibrating out-of-plane at ultrasonic frequencies was developed as well as a spring-frictional slider model. It was concluded that the reduction in friction induced by the vibrations could be ascribed to ratchet mechanism as a result of intermittent contact. The relative reduction in friction calculated using the FE model could be superimposed onto an exponential function of a dimensionless group defined from relevant parameters. The current paper presents measurements of the reduction in friction, involving real and artificial fingertips, as a function of the vibrational amplitude and frequency, the applied normal force and the exploration velocity. The results are reasonably similar to the calculated FE values and also could be superimposed using the exponential function provided that the intermittent contact was sufficiently well developed, which for the frequencies examined correspond to a minimum vibrational amplitude of  ∼ 1 µm P-P. It was observed that the reduction in friction depends on the exploration velocity and is independent of the applied normal force and ambient air pressure, which is not consistent with the squeeze film mechanism. However, the modelling did not incorporate the influence of air and the effect of ambient pressure was measured under a limited range of conditions, Thus squeeze film levitation may be synergistic with the mechanical interaction.

Study on Abrasive Wear of Brake Pad in the Large-megawatt Wind Turbine Brake Based on Deform Software

NASA Astrophysics Data System (ADS)

Zhang, Shengfang; Hao, Qiang; Sha, Zhihua; Yin, Jian; Ma, Fujian; Liu, Yu

2017-12-01

For the friction and wear issues of brake pads in the large-megawatt wind turbine brake during braking, this paper established the micro finite element model of abrasive wear by using Deform-2D software. Based on abrasive wear theory and considered the variation of the velocity and load in the micro friction and wear process, the Archard wear calculation model is developed. The influence rules of relative sliding velocity and friction coefficient in the brake pad and disc is analysed. The simulation results showed that as the relative sliding velocity increases, the wear will be more serious, while the larger friction coefficient lowered the contact pressure which released the wear of the brake pad.

Tidal Energy Resource Assessment for McMurdo Station, Antarctica

DTIC Science & Technology

2016-12-01

highest power coefficient possible, only to provide a high- fidelity data set for a simple geometry turbine model at reasonably high blade chord Reynolds...highest power coefficient possible, only to provide a high-fidelity data set for a simple geometry turbine model at reasonably high blade chord...Reynolds numbers. Tip speed ratio, , is defined as = where is the anglular velocity of the blade and is the

Fidelity assessment of a UH-60A simulation on the NASA Ames vertical motion simulator

NASA Technical Reports Server (NTRS)

Atencio, Adolph, Jr.

1993-01-01

Helicopter handling qualities research requires that a ground-based simulation be a high-fidelity representation of the actual helicopter, especially over the frequency range of the investigation. This experiment was performed to assess the current capability to simulate the UH-60A Black Hawk helicopter on the Vertical Motion Simulator (VMS) at NASA Ames, to develop a methodology for assessing the fidelity of a simulation, and to find the causes for lack of fidelity. The approach used was to compare the simulation to the flight vehicle for a series of tasks performed in flight and in the simulator. The results show that subjective handling qualities ratings from flight to simulator overlap, and the mathematical model matches the UH-60A helicopter very well over the range of frequencies critical to handling qualities evaluation. Pilot comments, however, indicate a need for improvement in the perceptual fidelity of the simulation in the areas of motion and visual cuing. The methodology used to make the fidelity assessment proved useful in showing differences in pilot work load and strategy, but additional work is needed to refine objective methods for determining causes of lack of fidelity.

Solar Sail Spaceflight Simulation

NASA Technical Reports Server (NTRS)

Lisano, Michael; Evans, James; Ellis, Jordan; Schimmels, John; Roberts, Timothy; Rios-Reyes, Leonel; Scheeres, Daniel; Bladt, Jeff; Lawrence, Dale; Piggott, Scott

2007-01-01

The Solar Sail Spaceflight Simulation Software (S5) toolkit provides solar-sail designers with an integrated environment for designing optimal solar-sail trajectories, and then studying the attitude dynamics/control, navigation, and trajectory control/correction of sails during realistic mission simulations. Unique features include a high-fidelity solar radiation pressure model suitable for arbitrarily-shaped solar sails, a solar-sail trajectory optimizer, capability to develop solar-sail navigation filter simulations, solar-sail attitude control models, and solar-sail high-fidelity force models.

Temperature and circulation in the stratospheres of the outer planets

NASA Technical Reports Server (NTRS)

Conrath, Barney J.; Gierasch, Peter J.; Leroy, Stephen S.

1989-01-01

A zonally symmetric, linear radiative-dynamical model is compared with observations of the upper tropospheres and stratospheres of the outer planets. Seasonal variation is included in the model. Friction is parameterized by linear drag (Rayleigh friction). Gas opacities are accounted for but aerosols are omitted. Horizontal temperature gradients are small on all the planets. Seasonal effects are strongest on Saturn and Neptune but are weak even in these cases, because the latitudinal gradient of radiative heating is weak. Seasonal effects on Uranus are extremely weak because the radiative time constant is longer that the orbital period. One free parameter in the model is the frictional time constant. Comparison with observed temperature perturbations over zonal currents in the troposphere shows that the frictional time constant is on the same order as the radiative time constant for all these objects. Vertical motions predicted by the model are extremely weak. They are much smaller than one scale height per orbital period, except in the immediate neighborhood of tropospheric and zonal currents.

Parameters Identification of Interface Friction Model for Ceramic Matrix Composites Based on Stress-Strain Response

NASA Astrophysics Data System (ADS)

Han, Xiao; Gao, Xiguang; Song, Yingdong

2017-10-01

An approach to identify parameters of interface friction model for Ceramic Matrix composites based on stress-strain response was developed. The stress distribution of fibers in the interface slip region and intact region of the damaged composite was determined by adopting the interface friction model. The relation between maximum strain, secant moduli of hysteresis loop and interface shear stress, interface de-bonding stress was established respectively with the method of symbolic-graphic combination. By comparing the experimental strain, secant moduli of hysteresis loop with computation values, the interface shear stress and interface de-bonding stress corresponding to first cycle were identified. Substituting the identification of parameters into interface friction model, the stress-strain curves were predicted and the predicted results fit experiments well. Besides, the influence of number of data points on identifying the value of interface parameters was discussed. And the approach was compared with the method based on the area of hysteresis loop.

Cyriax's deep friction massage application parameters: Evidence from a cross-sectional study with physiotherapists.

PubMed

Chaves, Paula; Simões, Daniela; Paço, Maria; Pinho, Francisco; Duarte, José Alberto; Ribeiro, Fernando

2017-12-01

Deep friction massage is one of several physiotherapy interventions suggested for the management of tendinopathy. To determine the prevalence of deep friction massage use in clinical practice, to characterize the application parameters used by physiotherapists, and to identify empirical model-based patterns of deep friction massage application in degenerative tendinopathy. observational, analytical, cross-sectional and national web-based survey. 478 physiotherapists were selected through snow-ball sampling method. The participants completed an online questionnaire about personal and professional characteristics as well as specific questions regarding the use of deep friction massage. Characterization of deep friction massage parameters used by physiotherapists were presented as counts and proportions. Latent class analysis was used to identify the empirical model-based patterns. Crude and adjusted odds ratios and 95% confidence intervals were computed. The use of deep friction massage was reported by 88.1% of the participants; tendinopathy was the clinical condition where it was most frequently used (84.9%) and, from these, 55.9% reported its use in degenerative tendinopathy. The "duration of application" parameters in chronic phase and "frequency of application" in acute and chronic phases are those that diverge most from those recommended by the author of deep friction massage. We found a high prevalence of deep friction massage use, namely in degenerative tendinopathy. Our results have shown that the application parameters are heterogeneous and diverse. This is reflected by the identification of two application patterns, although none is in complete agreement with Cyriax's description. Copyright © 2017 Elsevier Ltd. All rights reserved.

Effect of laser surface texturing (LST) on tribochemical films dynamics and friction and wear performance

DOE PAGES

Olofinjana, Bolutife; Lorenzo-Martin, Cinta; Ajayi, Oyelayo O.; ...

2015-06-06

Surface texturing or topographical design is one of the primary techniques to control friction and wear performance of surfaces in tribological contact. Laser surface texturing (LST), whereby a laser beam is used to produce regular arrays of dimples on a surface, has been demonstrated to reduce friction in conformal lubricated contacts. Friction and wear behavior under boundary lubrication is also known to be dependent on the formation and durability of the tribochemical film formed from lubricant additives. In this paper, the effects of LST on the formation and durability of tribochemical films and its consequent impacts on friction and wearmore » behavior in various lubrication regimes were evaluated. Friction and wear tests that cycled through different lubrication regimes were conducted with both polished and LST treated surfaces using a synthetic lubricant with and without model additives of ZDDP and MoDTC mixture. In the base oil without additives, LST produced noticeable reduction in friction in all lubrication regimes. However, with low-friction model additives, friction was higher in tests with LST due to significant differences in the tribochemical film formation in the polished and LST surfaces, as well as the sliding counterface. Continuous tribo-films were formed on ball conterface rubbed against polished surfaces while the films were streaky and discontinuous in ball rubbed against LST surfaces. LST produced more wear on the ball counterface in both base and additized oils. Lastly, no measurable wear was observed in both the polished and LST flat specimens.« less

A finite element study on rail corrugation based on saturated creep force-induced self-excited vibration of a wheelset-track system

NASA Astrophysics Data System (ADS)

Chen, G. X.; Zhou, Z. R.; Ouyang, H.; Jin, X. S.; Zhu, M. H.; Liu, Q. Y.

2010-10-01

The present work proposes friction coupling at the wheel-rail interface as the mechanism for formation of rail corrugation. Stability of a wheelset-track system is studied using the finite element complex eigenvalue method. Two models for a wheelset-track system on a tight curved track and on a straight track are established. In these two models, motion of the wheelset is coupled with that of the rail by friction. Creep force at the interface is assumed to become saturated and approximately equal to friction force, which is equal to the normal contact force multiplied by dynamic coefficient of friction. The rail is supported by vertical and lateral springs and dampers at the positions of sleepers. Numerical results show that there is a strong propensity of self-excited vibration of the wheelset-track system when the friction coefficient is larger than 0.21. Some unstable frequencies fall in the range 60-1200 Hz, which correspond to frequencies of rail corrugation. Parameter sensitivity analysis shows that the dynamic coefficient of friction, spring stiffness and damping of the sleeper supports all have important influences on the rail corrugation formation. Bringing the friction coefficient below a certain level can suppress or eliminate rail corrugation.

Effect of friction on vibrotactile sensation of normal and dehydrated skin.

PubMed

Chen, S; Ge, S; Tang, W; Zhang, J

2016-02-01

Vibrotactile sensation mediated is highly dependent on surface mechanical and frictional properties. Dehydration of skin could change these properties. To investigate the relationship between friction and vibrotactile sensation of normal and dehydrated skin. Vibrations were firstly measured during surface exploration using a biomimetic sensor. Piglet skin was used as human skin model to study frictional properties for both normal and dehydrated skin using an atomic force microscope on nanoscale and a pin-on-disk tribometer on macroscale. Effect of vibrational frequency on friction and vibrotactile perception was also observed on nano and macro scale for normal and dehydrated skin. The result indicated that dehydrated skin was less sensitive than normal skin. The coefficient of friction of dehydrated skin is smaller than that of normal skin on both nano and macro scale. The coefficient of friction increases as increasing scanning frequencies. There is a positive correlation between coefficient of friction and vibrotactile sensation on nanoscale and macroscale. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Velocity-strengthening friction significantly affects interfacial dynamics, strength and dissipation

PubMed Central

Bar-Sinai, Yohai; Spatschek, Robert; Brener, Efim A.; Bouchbinder, Eran

2015-01-01

Frictional interfaces abound in natural and man-made systems, yet their dynamics are not well-understood. Recent extensive experimental data have revealed that velocity-strengthening friction, where the steady-state frictional resistance increases with sliding velocity over some range, is a generic feature of such interfaces. This physical behavior has very recently been linked to slow stick-slip motion. Here we elucidate the importance of velocity-strengthening friction by theoretically studying three variants of a realistic friction model, all featuring identical logarithmic velocity-weakening friction at small sliding velocities, but differ in their higher velocity behaviors. By quantifying energy partition (e.g. radiation and dissipation), the selection of interfacial rupture fronts and rupture arrest, we show that the presence or absence of strengthening significantly affects the global interfacial resistance and the energy release during frictional instabilities. Furthermore, we show that different forms of strengthening may result in events of similar magnitude, yet with dramatically different dissipation and radiation rates. This happens because the events are mediated by rupture fronts with vastly different propagation velocities, where stronger velocity-strengthening friction promotes slower rupture. These theoretical results may have significant implications on our understanding of frictional dynamics. PMID:25598161

Nonlinear shear wave interaction at a frictional interface: energy dissipation and generation of harmonics.

PubMed

Meziane, A; Norris, A N; Shuvalov, A L

2011-10-01

Analytical and numerical modeling of the nonlinear interaction of shear wave with a frictional interface is presented. The system studied is composed of two homogeneous and isotropic elastic solids, brought into frictional contact by remote normal compression. A shear wave, either time harmonic or a narrow band pulse, is incident normal to the interface and propagates through the contact. Two friction laws are considered and the influence on interface behavior is investigated: Coulomb's law with a constant friction coefficient and a slip-weakening friction law which involves static and dynamic friction coefficients. The relationship between the nonlinear harmonics and the dissipated energy, and the dependence on the contact dynamics (friction law, sliding, and tangential stress) and on the normal contact stress are examined in detail. The analytical and numerical results indicate universal type laws for the amplitude of the higher harmonics and for the dissipated energy, properly non-dimensionalized in terms of the pre-stress, the friction coefficient and the incident amplitude. The results suggest that measurements of higher harmonics can be used to quantify friction and dissipation effects of a sliding interface. © 2011 Acoustical Society of America

Controlling the transmitted information of a multi-photon interacting with a single-Cooper pair box

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kadry, Heba, E-mail: hkadry1@yahoo.com; Abdel-Aty, Abdel-Haleem, E-mail: hkadry1@yahoo.com; Zakaria, Nordin, E-mail: hkadry1@yahoo.com

2014-10-24

We study a model of a multi-photon interaction of a single Cooper pair box with a cavity field. The exchange of the information using this system is studied. We quantify the fidelity of the transmitted information. The effect of the system parameters (detuning parameter, field photons, state density and mean photon number) in the fidelity of the transmitted information is investigated. We found that the fidelity of the transmitted information can be controlled using the system parameters.

Skin-Friction Measurements in a 3-D, Supersonic Shock-Wave/Boundary-Layer Interaction

NASA Technical Reports Server (NTRS)

Wideman, J. K.; Brown, J. L.; Miles, J. B.; Ozcan, O.

1994-01-01

The experimental documentation of a three-dimensional shock-wave/boundary-layer interaction in a nominal Mach 3 cylinder, aligned with the free-stream flow, and 20 deg. half-angle conical flare offset 1.27 cm from the cylinder centerline. Surface oil flow, laser light sheet illumination, and schlieren were used to document the flow topology. The data includes surface-pressure and skin-friction measurements. A laser interferometric skin friction data. Included in the skin-friction data are measurements within separated regions and three-dimensional measurements in highly-swept regions. The skin-friction data will be particularly valuable in turbulence modeling and computational fluid dynamics validation.

Boundary-layer transition and global skin friction measurement with an oil-fringe imaging technique

NASA Technical Reports Server (NTRS)

Monson, Daryl J.; Mateer, George G.; Menter, Florian R.

1993-01-01

A new oil-fringe imaging system skin friction (FISF) technique to measure skin friction on wind tunnel models is presented. In the method used to demonstrate the technique, lines of oil are applied on surfaces that connect the intended sets of measurement points, and then a wind tunnel is run so that the oil thins and forms interference fringes that are spaced in proportion to local skin friction. After a run the fringe spacings are imaged with a CCD-array digital camera and measured on a computer. Skin friction and transition measurements on a two-dimensional wing are presented and compared with computational predictions.

Generalized contact and improved frictional heating in the material point method

NASA Astrophysics Data System (ADS)

Nairn, J. A.; Bardenhagen, S. G.; Smith, G. D.

2017-09-01

The material point method (MPM) has proved to be an effective particle method for computational mechanics modeling of problems involving contact, but all prior applications have been limited to Coulomb friction. This paper generalizes the MPM approach for contact to handle any friction law with examples given for friction with adhesion or with a velocity-dependent coefficient of friction. Accounting for adhesion requires an extra calculation to evaluate contact area. Implementation of velocity-dependent laws usually needs numerical methods to find contacting forces. The friction process involves work which can be converted into heat. This paper provides a new method for calculating frictional heating that accounts for interfacial acceleration during the time step. The acceleration terms is small for many problems, but temporal convergence of heating effects for problems involving vibrations and high contact forces is improved by the new method. Fortunately, the new method needs few extra calculations and therefore is recommended for all simulations.

Generalized contact and improved frictional heating in the material point method

NASA Astrophysics Data System (ADS)

Nairn, J. A.; Bardenhagen, S. G.; Smith, G. D.

2018-07-01

The material point method (MPM) has proved to be an effective particle method for computational mechanics modeling of problems involving contact, but all prior applications have been limited to Coulomb friction. This paper generalizes the MPM approach for contact to handle any friction law with examples given for friction with adhesion or with a velocity-dependent coefficient of friction. Accounting for adhesion requires an extra calculation to evaluate contact area. Implementation of velocity-dependent laws usually needs numerical methods to find contacting forces. The friction process involves work which can be converted into heat. This paper provides a new method for calculating frictional heating that accounts for interfacial acceleration during the time step. The acceleration terms is small for many problems, but temporal convergence of heating effects for problems involving vibrations and high contact forces is improved by the new method. Fortunately, the new method needs few extra calculations and therefore is recommended for all simulations.

An extended supersonic combustion model for the dynamic analysis of hypersonic vehicles

NASA Technical Reports Server (NTRS)

Bossard, J. A.; Peck, R. E.; Schmidt, D. K.

1993-01-01

The development of an advanced dynamic model for aeroelastic hypersonic vehicles powered by air breathing engines requires an adequate engine model. This report provides a discussion of some of the more important features of supersonic combustion and their relevance to the analysis and design of supersonic ramjet engines. Of particular interest are those aspects of combustion that impact the control of the process. Furthermore, the report summarizes efforts to enhance the aeropropulsive/aeroelastic dynamic model developed at the Aerospace Research Center of Arizona State University by focusing on combustion and improved modeling of this flow. The expanded supersonic combustor model described here has the capability to model the effects of friction, area change, and mass addition, in addition to the heat addition process. A comparison is made of the results from four cases: (1) heat addition only; (2) heat addition plus friction; (3) heat addition, friction, and area reduction, and (4) heat addition, friction, area reduction, and mass addition. The relative impact of these effects on the Mach number, static temperature, and static pressure distributions within the combustor are then shown. Finally, the effects of frozen versus equilibrium flow conditions within the exhaust plume is discussed.

LOW-ENGINE-FRICTION TECHNOLOGY FOR ADVANCED NATURAL-GAS RECIPROCATING ENGINES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Victor Wong; Tian Tian; Luke Moughon

This program aims at improving the efficiency of advanced natural-gas reciprocating engines (ANGRE) by reducing piston and piston ring assembly friction without major adverse effects on engine performance, such as increased oil consumption and wear. An iterative process of simulation, experimentation and analysis is being followed towards achieving the goal of demonstrating a complete optimized low-friction engine system. To date, a detailed set of piston and piston-ring dynamic and friction models have been developed and applied that illustrate the fundamental relationships among mechanical, surface/material and lubricant design parameters and friction losses. Demonstration of low-friction ring-pack designs in the Waukesha VGFmore » 18GL engine confirmed total engine FEMP (friction mean effective pressure) reduction of 7-10% from the baseline configuration without significantly increasing oil consumption or blow-by flow. This represents a substantial (30-40%) reduction of the ringpack friction alone. The measured FMEP reductions were in good agreement with the model predictions. Further improvements via piston, lubricant, and surface designs offer additional opportunities. Tests of low-friction lubricants are in progress and preliminary results are very promising. The combined analysis of lubricant and surface design indicates that low-viscosity lubricants can be very effective in reducing friction, subject to component wear for extremely thin oils, which can be mitigated with further lubricant formulation and/or engineered surfaces. Hence a combined approach of lubricant design and appropriate wear reduction offers improved potential for minimum engine friction loss. Piston friction studies indicate that a flatter piston with a more flexible skirt, together with optimizing the waviness and film thickness on the piston skirt offer significant friction reduction. Combined with low-friction ring-pack, material and lubricant parameters, a total power cylinder friction reduction of 30-50% is expected, translating to an engine efficiency increase of two percentage points from its current baseline towards the goal of 50% ARES engine efficiency. The design strategies developed in this study have promising potential for application in all modern reciprocating engines as they represent simple, low-cost methods to extract significant fuel savings. The current program has possible spinoffs and applications in other industries as well, including transportation, CHP, and diesel power generation. The progress made in this program has wide engine efficiency implications, and potential deployment of low-friction engine components or lubricants in the near term is possible as current investigations continue.« less

Implementation of a Smeared Crack Band Model in a Micromechanics Framework

NASA Technical Reports Server (NTRS)

Pineda, Evan J.; Bednarcyk, Brett A.; Waas, Anthony M.; Arnold, Steven M.

2012-01-01

The smeared crack band theory is implemented within the generalized method of cells and high-fidelity generalized method of cells micromechanics models to capture progressive failure within the constituents of a composite material while retaining objectivity with respect to the size of the discretization elements used in the model. An repeating unit cell containing 13 randomly arranged fibers is modeled and subjected to a combination of transverse tension/compression and transverse shear loading. The implementation is verified against experimental data (where available), and an equivalent finite element model utilizing the same implementation of the crack band theory. To evaluate the performance of the crack band theory within a repeating unit cell that is more amenable to a multiscale implementation, a single fiber is modeled with generalized method of cells and high-fidelity generalized method of cells using a relatively coarse subcell mesh which is subjected to the same loading scenarios as the multiple fiber repeating unit cell. The generalized method of cells and high-fidelity generalized method of cells models are validated against a very refined finite element model.

The attenuation of Love waves and toroidal oscillations of the earth.

NASA Technical Reports Server (NTRS)

Jackson, D. D.

1971-01-01

An attempt has been made to invert a large set of attenuation data for Love waves and toroidal oscillations in the earth, using a recent method by Backus and Gilbert. The difficulty in finding an acceptable model of internal friction which explains the data, under the assumption that the internal friction is independent of frequency, casts doubt on the validity of this assumption. A frequency-dependent model of internal friction is presented which is in good agreement with the seismic data and with recent experimental measurements of attenuation in rocks.

An asymptotic preserving multidimensional ALE method for a system of two compressible flows coupled with friction

NASA Astrophysics Data System (ADS)

Del Pino, S.; Labourasse, E.; Morel, G.

2018-06-01

We present a multidimensional asymptotic preserving scheme for the approximation of a mixture of compressible flows. Fluids are modelled by two Euler systems of equations coupled with a friction term. The asymptotic preserving property is mandatory for this kind of model, to derive a scheme that behaves well in all regimes (i.e. whatever the friction parameter value is). The method we propose is defined in ALE coordinates, using a Lagrange plus remap approach. This imposes a multidimensional definition and analysis of the scheme.

Onset of frictional sliding of rubber–glass contact under dry and lubricated conditions

PubMed Central

Tuononen, Ari J.

2016-01-01

Rubber friction is critical in many applications ranging from automotive tyres to cylinder seals. The process where a static rubber sample transitions to frictional sliding is particularly poorly understood. The experimental and simulation results in this paper show a completely different detachment process from the static situation to sliding motion under dry and lubricated conditions. The results underline the contribution of the rubber bulk properties to the static friction force. In fact, simple Amontons’ law is sufficient as a local friction law to produce the correct detachment pattern when the rubber material and loading conditions are modelled properly. Simulations show that micro-sliding due to vertical loading can release initial shear stresses and lead to a high static/dynamic friction coefficient ratio, as observed in the measurements. PMID:27291939

Finite element based simulation on friction stud welding of metal matrix composites to steel

NASA Astrophysics Data System (ADS)

Hynes, N. Rajesh Jesudoss; Tharmaraj, R.; Velu, P. Shenbaga; Kumar, R.

2016-05-01

Friction welding is a solid state joining technique used for joining similar and dissimilar materials with high integrity. This new technique is being successfully applied to the aerospace, automobile, and ship building industries, and is attracting more and more research interest. The quality of Friction Stud Welded joints depends on the frictional heat generated at the interface. Hence, thermal analysis on friction stud welding of stainless steel (AISI 304) and aluminium silicon carbide (AlSiC) combination is carried out in the present work. In this study, numerical simulation is carried out using ANSYS software and the temperature profiles are predicted at various increments of time. The developed numerical model is found to be adequate to predict temperature distribution of friction stud weld aluminium silicon carbide/stainless steel joints.

Autonomous Aerobraking: Thermal Analysis and Response Surface Development

NASA Technical Reports Server (NTRS)

Dec, John A.; Thornblom, Mark N.

2011-01-01

A high-fidelity thermal model of the Mars Reconnaissance Orbiter was developed for use in an autonomous aerobraking simulation study. Response surface equations were derived from the high-fidelity thermal model and integrated into the autonomous aerobraking simulation software. The high-fidelity thermal model was developed using the Thermal Desktop software and used in all phases of the analysis. The use of Thermal Desktop exclusively, represented a change from previously developed aerobraking thermal analysis methodologies. Comparisons were made between the Thermal Desktop solutions and those developed for the previous aerobraking thermal analyses performed on the Mars Reconnaissance Orbiter during aerobraking operations. A variable sensitivity screening study was performed to reduce the number of variables carried in the response surface equations. Thermal analysis and response surface equation development were performed for autonomous aerobraking missions at Mars and Venus.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olofinjana, Bolutife; Lorenzo-Martin, Cinta; Ajayi, Oyelayo O.

Surface texturing or topographical design is one of the primary techniques to control friction and wear performance of surfaces in tribological contact. Laser surface texturing (LST), whereby a laser beam is used to produce regular arrays of dimples on a surface, has been demonstrated to reduce friction in conformal lubricated contacts. Friction and wear behavior under boundary lubrication is also known to be dependent on the formation and durability of the tribochemical film formed from lubricant additives. In this paper, the effects of LST on the formation and durability of tribochemical films and its consequent impacts on friction and wearmore » behavior in various lubrication regimes were evaluated. Friction and wear tests that cycled through different lubrication regimes were conducted with both polished and LST treated surfaces using a synthetic lubricant with and without model additives of ZDDP and MoDTC mixture. In the base oil without additives, LST produced noticeable reduction in friction in all lubrication regimes. However, with low-friction model additives, friction was higher in tests with LST due to significant differences in the tribochemical film formation in the polished and LST surfaces, as well as the sliding counterface. Continuous tribo-films were formed on ball conterface rubbed against polished surfaces while the films were streaky and discontinuous in ball rubbed against LST surfaces. LST produced more wear on the ball counterface in both base and additized oils. Lastly, no measurable wear was observed in both the polished and LST flat specimens.« less

Nonlinear friction modelling and compensation control of hysteresis phenomena for a pair of tendon-sheath actuated surgical robots

NASA Astrophysics Data System (ADS)

Do, T. N.; Tjahjowidodo, T.; Lau, M. W. S.; Phee, S. J.

2015-08-01

Natural Orifice Transluminal Endoscopic Surgery (NOTES) is a special method that allows surgical operations via natural orifices like mouth, anus, and vagina, without leaving visible scars. The use of flexible tendon-sheath mechanism (TSM) is common in these systems because of its light weight in structure, flexibility, and easy transmission of power. However, nonlinear friction and backlash hysteresis pose many challenges to control of such systems; in addition, they do not provide haptic feedback to assist the surgeon in the operation of the systems. In this paper, we propose a new dynamic friction model and backlash hysteresis nonlinearity for a pair of TSM to deal with these problems. The proposed friction model, unlike current approaches in the literature, is smooth and able to capture the force at near zero velocity when the system is stationary or operates at small motion. This model can be used to estimate the friction force for haptic feedback purpose. To improve the system tracking performances, a backlash hysteresis model will be introduced, which can be used in a feedforward controller scheme. The controller involves a simple computation of the inverse hysteresis model. The proposed models are configuration independent and able to capture the nonlinearities for arbitrary tendon-sheath shapes. A representative experimental setup is used to validate the proposed models and to demonstrate the improvement in position tracking accuracy and the possibility of providing desired force information at the distal end of a pair of TSM slave manipulator for haptic feedback to the surgeons.

F-14 modeling study

NASA Technical Reports Server (NTRS)

Levison, William H.

1988-01-01

This study explored application of a closed loop pilot/simulator model to the analysis of some simulator fidelity issues. The model was applied to two data bases: (1) a NASA ground based simulation of an air-to-air tracking task in which nonvisual cueing devices were explored, and (2) a ground based and inflight study performed by the Calspan Corporation to explore the effects of simulator delay on attitude tracking performance. The model predicted the major performance trends obtained in both studies. A combined analytical and experimental procedure for exploring simulator fidelity issues is outlined.

Development of Ku-band rendezvous radar tracking and acquisition simulation programs

NASA Technical Reports Server (NTRS)

1986-01-01

The fidelity of the Space Shuttle Radar tracking simulation model was improved. The data from the Shuttle Orbiter Radar Test and Evaluation (SORTE) program experiments performed at the White Sands Missile Range (WSMR) were reviewed and analyzed. The selected flight rendezvous radar data was evaluated. Problems with the Inertial Line-of-Sight (ILOS) angle rate tracker were evaluated using the improved fidelity angle rate tracker simulation model.

Aerodynamic Simulation of Ice Accretion on Airfoils

NASA Technical Reports Server (NTRS)

Broeren, Andy P.; Addy, Harold E., Jr.; Bragg, Michael B.; Busch, Greg T.; Montreuil, Emmanuel

2011-01-01

This report describes recent improvements in aerodynamic scaling and simulation of ice accretion on airfoils. Ice accretions were classified into four types on the basis of aerodynamic effects: roughness, horn, streamwise, and spanwise ridge. The NASA Icing Research Tunnel (IRT) was used to generate ice accretions within these four types using both subscale and full-scale models. Large-scale, pressurized windtunnel testing was performed using a 72-in.- (1.83-m-) chord, NACA 23012 airfoil model with high-fidelity, three-dimensional castings of the IRT ice accretions. Performance data were recorded over Reynolds numbers from 4.5 x 10(exp 6) to 15.9 x 10(exp 6) and Mach numbers from 0.10 to 0.28. Lower fidelity ice-accretion simulation methods were developed and tested on an 18-in.- (0.46-m-) chord NACA 23012 airfoil model in a small-scale wind tunnel at a lower Reynolds number. The aerodynamic accuracy of the lower fidelity, subscale ice simulations was validated against the full-scale results for a factor of 4 reduction in model scale and a factor of 8 reduction in Reynolds number. This research has defined the level of geometric fidelity required for artificial ice shapes to yield aerodynamic performance results to within a known level of uncertainty and has culminated in a proposed methodology for subscale iced-airfoil aerodynamic simulation.

Impact and Crashworthiness Characteristics of Venera Type Landers for Future Venus Missions

NASA Technical Reports Server (NTRS)

Schroeder, Kevin; Bayandor, Javid; Samareh, Jamshid

2016-01-01

In this paper an in-depth investigation of the structural design of the Venera 9-14 landers is explored. A complete reverse engineering of the Venera lander was required. The lander was broken down into its fundamental components and analyzed. This provided in-sights into the hidden features of the design. A trade study was performed to find the sensitivity of the lander's overall mass to the variation of several key parameters. For the lander's legs, the location, length, configuration, and number are all parameterized. The size of the impact ring, the radius of the drag plate, and other design features are also parameterized, and all of these features were correlated to the change of mass of the lander. A multi-fidelity design tool used for further investigation of the parameterized lander was developed. As a design was passed down from one level to the next, the fidelity, complexity, accuracy, and run time of the model increased. The low-fidelity model was a highly nonlinear analytical model developed to rapidly predict the mass of each design. The medium and high fidelity models utilized an explicit finite element framework to investigate the performance of various landers upon impact with the surface under a range of landing conditions. This methodology allowed for a large variety of designs to be investigated by the analytical model, which identified designs with the optimum structural mass to payload ratio. As promising designs emerged, investigations in the following higher fidelity models were focused on establishing their reliability and crashworthiness. The developed design tool efficiently modelled and tested the best concepts for any scenario based on critical Venusian mission requirements and constraints. Through this program, the strengths and weaknesses inherent in the Venera-Type landers were thoroughly investigated. Key features identified for the design of robust landers will be used as foundations for the development of the next generation of landers for future exploration missions to Venus.

Locomotive and reptation motion induced by internal force and friction.

PubMed

Sakaguchi, Hidetsugu; Ishihara, Taisuke

2011-06-01

We propose a simple mechanical model of locomotion induced by internal force and friction. We first construct a system of two elements as an analog of the bipedal motion. The internal force does not induce a directional motion by itself because of the action-reaction law, but a directional motion becomes possible by the control of the frictional force. The efficiency of these model systems is studied using an analogy to the heat engine. As a modified version of the two-element model, we construct a model that exhibits a bipedal motion similar to kinesin's motion of molecular motor. Next, we propose a linear chain model and a ladder model as an extension of the original two-element model. We find a transition from a straight to a snake-like motion in a ladder model by changing the strength of the internal force.

Rate-dependent frictional adhesion in natural and synthetic gecko setae

PubMed Central

Gravish, Nick; Wilkinson, Matt; Sponberg, Simon; Parness, Aaron; Esparza, Noe; Soto, Daniel; Yamaguchi, Tetsuo; Broide, Michael; Cutkosky, Mark; Creton, Costantino; Autumn, Kellar

2010-01-01

Geckos owe their remarkable stickiness to millions of dry, hard setae on their toes. In this study, we discovered that gecko setae stick more strongly the faster they slide, and do not wear out after 30 000 cycles. This is surprising because friction between dry, hard, macroscopic materials typically decreases at the onset of sliding, and as velocity increases, friction continues to decrease because of a reduction in the number of interfacial contacts, due in part to wear. Gecko setae did not exhibit the decrease in adhesion or friction characteristic of a transition from static to kinetic contact mechanics. Instead, friction and adhesion forces increased at the onset of sliding and continued to increase with shear speed from 500 nm s−1 to 158 mm s−1. To explain how apparently fluid-like, wear-free dynamic friction and adhesion occur macroscopically in a dry, hard solid, we proposed a model based on a population of nanoscopic stick–slip events. In the model, contact elements are either in static contact or in the process of slipping to a new static contact. If stick–slip events are uncorrelated, the model further predicted that contact forces should increase to a critical velocity (V*) and then decrease at velocities greater than V*. We hypothesized that, like natural gecko setae, but unlike any conventional adhesive, gecko-like synthetic adhesives (GSAs) could adhere while sliding. To test the generality of our results and the validity of our model, we fabricated a GSA using a hard silicone polymer. While sliding, the GSA exhibited steady-state adhesion and velocity dependence similar to that of gecko setae. Observations at the interface indicated that macroscopically smooth sliding of the GSA emerged from randomly occurring stick–slip events in the population of flexible fibrils, confirming our model predictions. PMID:19493896

Comparison of Two Methods for Calculating the Frictional Properties of Articular Cartilage Using a Simple Pendulum and Intact Mouse Knee Joints

PubMed Central

Drewniak, Elizabeth I.; Jay, Gregory D.; Fleming, Braden C.; Crisco, Joseph J.

2009-01-01

In attempts to better understand the etiology of osteoarthritis, a debilitating joint disease that results in the degeneration of articular cartilage in synovial joints, researchers have focused on joint tribology, the study of joint friction, lubrication, and wear. Several different approaches have been used to investigate the frictional properties of articular cartilage. In this study, we examined two analysis methods for calculating the coefficient of friction (μ) using a simple pendulum system and BL6 murine knee joints (n=10) as the fulcrum. A Stanton linear decay model (Lin μ) and an exponential model that accounts for viscous damping (Exp μ) were fit to the decaying pendulum oscillations. Root mean square error (RMSE), asymptotic standard error (ASE), and coefficient of variation (CV) were calculated to evaluate the fit and measurement precision of each model. This investigation demonstrated that while Lin μ was more repeatable, based on CV (5.0% for Lin μ; 18% for Exp μ), Exp μ provided a better fitting model, based on RMSE (0.165° for Exp μ; 0.391° for Lin μ) and ASE (0.033 for Exp μ; 0.185 for Lin μ), and had a significantly lower coefficient of friction value (0.022±0.007 for Exp μ; 0.042±0.016 for Lin μ) (p=0.001). This study details the use of a simple pendulum for examining cartilage properties in situ that will have applications investigating cartilage mechanics in a variety of species. The Exp μ model provided a more accurate fit to the experimental data for predicting the frictional properties of intact joints in pendulum systems. PMID:19632680

Dynamic Stability of the Rate, State, Temperature, and Pore Pressure Friction Model at a Rock Interface

NASA Astrophysics Data System (ADS)

Sinha, Nitish; Singh, Arun K.; Singh, Trilok N.

2018-05-01

In this article, we study numerically the dynamic stability of the rate, state, temperature, and pore pressure friction (RSTPF) model at a rock interface using standard spring-mass sliding system. This particular friction model is a basically modified form of the previously studied friction model namely the rate, state, and temperature friction (RSTF). The RSTPF takes into account the role of thermal pressurization including dilatancy and permeability of the pore fluid due to shear heating at the slip interface. The linear stability analysis shows that the critical stiffness, at which the sliding becomes stable to unstable or vice versa, increases with the coefficient of thermal pressurization. Critical stiffness, on the other hand, remains constant for small values of either dilatancy factor or hydraulic diffusivity, but the same decreases as their values are increased further from dilatancy factor (˜ 10^{ - 4} ) and hydraulic diffusivity (˜ 10^{ - 9} {m}2 {s}^{ - 1} ) . Moreover, steady-state friction is independent of the coefficient of thermal pressurization, hydraulic diffusivity, and dilatancy factor. The proposed model is also used for predicting time of failure of a creeping interface of a rock slope under the constant gravitational force. It is observed that time of failure decreases with increase in coefficient of thermal pressurization and hydraulic diffusivity, but the dilatancy factor delays the failure of the rock fault under the condition of heat accumulation at the creeping interface. Moreover, stiffness of the rock-mass also stabilizes the failure process of the interface as the strain energy due to the gravitational force accumulates in the rock-mass before it transfers to the sliding interface. Practical implications of the present study are also discussed.

Analysis Method of Friction Torque and Weld Interface Temperature during Friction Process of Steel Friction Welding

NASA Astrophysics Data System (ADS)

Kimura, Masaaki; Inoue, Haruo; Kusaka, Masahiro; Kaizu, Koichi; Fuji, Akiyoshi

This paper describes an analysis method of the friction torque and weld interface temperature during the friction process for steel friction welding. The joining mechanism model of the friction welding for the wear and seizure stages was constructed from the actual joining phenomena that were obtained by the experiment. The non-steady two-dimensional heat transfer analysis for the friction process was carried out by calculation with FEM code ANSYS. The contact pressure, heat generation quantity, and friction torque during the wear stage were calculated using the coefficient of friction, which was considered as the constant value. The thermal stress was included in the contact pressure. On the other hand, those values during the seizure stage were calculated by introducing the coefficient of seizure, which depended on the seizure temperature. The relationship between the seizure temperature and the relative speed at the weld interface in the seizure stage was determined using the experimental results. In addition, the contact pressure and heat generation quantity, which depended on the relative speed of the weld interface, were solved by taking the friction pressure, the relative speed and the yield strength of the base material into the computational conditions. The calculated friction torque and weld interface temperatures of a low carbon steel joint were equal to the experimental results when friction pressures were 30 and 90 MPa, friction speed was 27.5 s-1, and weld interface diameter was 12 mm. The calculation results of the initial peak torque and the elapsed time for initial peak torque were also equal to the experimental results under the same conditions. Furthermore, the calculation results of the initial peak torque and the elapsed time for initial peak torque at various friction pressures were equal to the experimental results.

Measuring Implementation Fidelity in a Community-Based Parenting Intervention

PubMed Central

Breitenstein, Susan M.; Fogg, Louis; Garvey, Christine; Hill, Carri; Resnick, Barbara; Gross, Deborah

2012-01-01

Background Establishing the feasibility and validity of implementation fidelity monitoring strategies is an important methodological step in implementing evidence-based interventions on a large scale. Objectives The objective of the study was to examine the reliability and validity of the Fidelity Checklist, a measure designed to assess group leader adherence and competence delivering a parent training intervention (the Chicago Parent Program) in child care centers serving low-income families. Method The sample included 9 parent groups (12 group sessions each), 12 group leaders, and 103 parents. Independent raters reviewed 106 audiotaped parent group sessions and coded group leaders’ fidelity on the Adherence and Competence Scales of the Fidelity Checklist. Group leaders completed self-report adherence checklists and a measure of parent engagement in the intervention. Parents completed measures of consumer satisfaction and child behavior. Results High interrater agreement (Adherence Scale = 94%, Competence Scale = 85%) and adequate intraclass correlation coefficients (Adherence Scale = .69, Competence Scale = .91) were achieved for the Fidelity Checklist. Group leader adherence changed over time, but competence remained stable. Agreement between group leader self-report and independent ratings on the Adherence Scale was 85%; disagreements were more frequently due to positive bias in group leader self-report. Positive correlations were found between group leader adherence and parent attendance and engagement in the intervention and between group leader competence and parent satisfaction. Although child behavior problems improved, improvements were not related to fidelity. Discussion The results suggest that the Fidelity Checklist is a feasible, reliable, and valid measure of group leader implementation fidelity in a group-based parenting intervention. Future research will be focused on testing the Fidelity Checklist with diverse and larger samples and generalizing to other group-based interventions using a similar intervention model. PMID:20404777

Intelligent Flow Friction Estimation.

PubMed

Brkić, Dejan; Ćojbašić, Žarko

2016-01-01

Nowadays, the Colebrook equation is used as a mostly accepted relation for the calculation of fluid flow friction factor. However, the Colebrook equation is implicit with respect to the friction factor (λ). In the present study, a noniterative approach using Artificial Neural Network (ANN) was developed to calculate the friction factor. To configure the ANN model, the input parameters of the Reynolds Number (Re) and the relative roughness of pipe (ε/D) were transformed to logarithmic scales. The 90,000 sets of data were fed to the ANN model involving three layers: input, hidden, and output layers with, 2, 50, and 1 neurons, respectively. This configuration was capable of predicting the values of friction factor in the Colebrook equation for any given values of the Reynolds number (Re) and the relative roughness (ε/D) ranging between 5000 and 10(8) and between 10(-7) and 0.1, respectively. The proposed ANN demonstrates the relative error up to 0.07% which had the high accuracy compared with the vast majority of the precise explicit approximations of the Colebrook equation.

Piezoelectric power generation using friction-induced vibration

NASA Astrophysics Data System (ADS)

Tadokoro, Chiharu; Matsumoto, Aya; Nagamine, Takuo; Sasaki, Shinya

2017-06-01

In order to examine the feasibility of power generation by using friction-induced vibration with a piezoelectric element, we performed experiments and numerical analysis. In the experiments, the generated power in the piezoelectric element and the displacement of an oscillator were measured by a newly developed apparatus that embodied a single-degree-of-freedom (1-DOF) system with friction. In the numerical analysis, an analytical model of a 1-DOF system with friction and piezoelectric element was proposed to simulate the experiments. The experimental results demonstrated that the power of a few microwatts was generated by sliding between a steel ball and a steel plate lubricated with glycerol. In this study, a maximum power of approximately 10 μW was generated at a driving velocity of 40 mm s-1 and a normal load of 15 N. The numerical results demonstrated good qualitative agreement with the experimental results. This implies that this analytical model can be applied to optimize the oscillator design in piezoelectric power generation using friction-induced vibration.

Experiments and numerical simulations of nonlinear vibration responses of an assembly with friction joints - Application on a test structure named "Harmony"

NASA Astrophysics Data System (ADS)

Claeys, M.; Sinou, J.-J.; Lambelin, J.-P.; Todeschini, R.

2016-03-01

In presence of friction, the frequency response function of a metallic assembly is strongly dependent on the excitation level. The local stick-slip behavior at the friction interfaces induces energy dissipation and local stiffness softening. These phenomena are studied both experimentally and numerically on a test structure named "Harmony". Concerning the numerical part, a classical complete methodology from the finite element and friction modeling to the prediction of the nonlinear vibrational response is implemented. The well-known Harmonic Balance Method with a specific condensation process on the nonlinear frictional elements is achieved. Also, vibration experiments are performed to validate not only the finite element model of the test structure named "Harmony" at low excitation levels but also to investigate the nonlinear behavior of the system on several excitation levels. A scanning laser vibrometer is used to measure the nonlinear behavior and the local stick-slip movement near the contacts.

Assessing intervention fidelity in a multi-level, multi-component, multi-site program: the Children's Healthy Living (CHL) program.

PubMed

Butel, Jean; Braun, Kathryn L; Novotny, Rachel; Acosta, Mark; Castro, Rose; Fleming, Travis; Powers, Julianne; Nigg, Claudio R

2015-12-01

Addressing complex chronic disease prevention, like childhood obesity, requires a multi-level, multi-component culturally relevant approach with broad reach. Models are lacking to guide fidelity monitoring across multiple levels, components, and sites engaged in such interventions. The aim of this study is to describe the fidelity-monitoring approach of The Children's Healthy Living (CHL) Program, a multi-level multi-component intervention in five Pacific jurisdictions. A fidelity-monitoring rubric was developed. About halfway during the intervention, community partners were randomly selected and interviewed independently by local CHL staff and by Coordinating Center representatives to assess treatment fidelity. Ratings were compared and discussed by local and Coordinating Center staff. There was good agreement between the teams (Kappa = 0.50, p < 0.001), and intervention improvement opportunities were identified through data review and group discussion. Fidelity for the multi-level, multi-component, multi-site CHL intervention was successfully assessed, identifying adaptations as well as ways to improve intervention delivery prior to the end of the intervention.

CAM/LIFTER forces and friction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gabbey, D.J.; Lee, J.; Patterson, D.J.

1992-02-01

This report details the procedures used to measure the cam/lifter forces and friction. The present effort employed a Cummins LTA-10, and focuses on measurements and dynamic modeling of the injector train. The program was sponsored by the US Department of Energy in support of advanced diesel engine technology. The injector train was instrumented to record the instantaneous roller speed, roller pin friction torque, pushrod force, injector link force and cam speed. These measurements, together with lift profiles for pushrod and injector link displacement, enabled the friction work loss in the injector train to be determined. Other significant design criteria suchmore » as camshaft roller follower slippage and maximum loads on components were also determined. Future efforts will concentrate on the dynamic model, with tests run as required for correlation.« less

Progressive Failure of a Unidirectional Fiber-Reinforced Composite Using the Method of Cells: Discretization Objective Computational Results

NASA Technical Reports Server (NTRS)

Pineda, Evan J.; Bednarcyk, Brett A.; Waas, Anthony M.; Arnold, Steven M.

2012-01-01

The smeared crack band theory is implemented within the generalized method of cells and high-fidelity generalized method of cells micromechanics models to capture progressive failure within the constituents of a composite material while retaining objectivity with respect to the size of the discretization elements used in the model. An repeating unit cell containing 13 randomly arranged fibers is modeled and subjected to a combination of transverse tension/compression and transverse shear loading. The implementation is verified against experimental data (where available), and an equivalent finite element model utilizing the same implementation of the crack band theory. To evaluate the performance of the crack band theory within a repeating unit cell that is more amenable to a multiscale implementation, a single fiber is modeled with generalized method of cells and high-fidelity generalized method of cells using a relatively coarse subcell mesh which is subjected to the same loading scenarios as the multiple fiber repeating unit cell. The generalized method of cells and high-fidelity generalized method of cells models are validated against a very refined finite element model.

Rendering edge enhancement tactile phenomenon by friction variation in dynamic touch.

PubMed

Abdolvahab, Mohammad

2011-01-04

Variable friction tactile displays have been recently used to render virtual textures and gratings. Neural basis of perceptual mechanism of detection of edge-like features resulting in discrimination of virtual gratings during active touching these tactile actuators is studied using a finite-element biomechanical model of human fingertip. The predicted neural response of the mechanoreceptors, i.e. the computed strain energy density at the location of selected mechanoreceptors as a measure of neural discharge rate of the corresponding receptors, to local reduction of friction between fingerpad and surface are shown to exhibit a similar shape as the edge enhancement phenomenon, particularly in a sudden burst at the boundary of variable friction regions. This phenomenon is supposed to account for the illusion of virtual edges rendered through the modification of contact forces. The presence of this sudden burst under varied model parameters was investigated. It was shown that while the appearance of this phenomenon in simulation results was invariant to model parameters, associated alteration of the edge enhancement ratio might be considered for the purpose of the tuning of the variable friction tactile display. Copyright © 2010 Elsevier Ltd. All rights reserved.

Stick–slip friction of gecko-mimetic flaps on smooth and rough surfaces

PubMed Central

Das, Saurabh; Cadirov, Nicholas; Chary, Sathya; Kaufman, Yair; Hogan, Jack; Turner, Kimberly L.; Israelachvili, Jacob N.

2015-01-01

The discovery and understanding of gecko ‘frictional-adhesion’ adhering and climbing mechanism has allowed researchers to mimic and create gecko-inspired adhesives. A few experimental and theoretical approaches have been taken to understand the effect of surface roughness on synthetic adhesive performance, and the implications of stick–slip friction during shearing. This work extends previous studies by using a modified surface forces apparatus to quantitatively measure and model frictional forces between arrays of polydimethylsiloxane gecko footpad-mimetic tilted microflaps against smooth and rough glass surfaces. Constant attachments and detachments occur between the surfaces during shearing, as described by an avalanche model. These detachments ultimately result in failure of the adhesion interface and have been characterized in this study. Stick–slip friction disappears with increasing velocity when the flaps are sheared against a smooth silica surface; however, stick–slip was always present at all velocities and loads tested when shearing the flaps against rough glass surfaces. These results demonstrate the significance of pre-load, shearing velocity, shearing distances, commensurability and shearing direction of gecko-mimetic adhesives and provide us a simple model for analysing and/or designing such systems. PMID:25589569

Consideration of Wear Rates at High Velocities

DTIC Science & Technology

2010-03-01

Strain vs. Three-dimensional Model . . . . . . . . . . . . 57 3.11 Example Single Asperity Wear Rate Integral . . . . . . . . . . 58 4.1 Third Stage...Slipper Accumulated Frictional Heating . . . . . . 67 4.2 Surface Temperature Third Stage Slipper, ave=0.5 . . . . . . . 67 4.3 Melt Depth Example...64 A3S Coefficient for Frictional Heat Curve Fit, Third Stage Slipper 66 B3S Coefficient for Frictional Heat Curve Fit, Third

Internal friction in an intrinsically disordered protein—Comparing Rouse-like models with experiments

NASA Astrophysics Data System (ADS)

Soranno, Andrea; Zosel, Franziska; Hofmann, Hagen

2018-03-01

Internal friction is frequently found in protein dynamics. Its molecular origin however is difficult to conceptualize. Even unfolded and intrinsically disordered polypeptide chains exhibit signs of internal friction despite their enormous solvent accessibility. Here, we compare four polymer theories of internal friction with experimental results on the intrinsically disordered protein ACTR (activator of thyroid hormone receptor). Using nanosecond fluorescence correlation spectroscopy combined with single-molecule Förster resonance energy transfer (smFRET), we determine the time scales of the diffusive chain dynamics of ACTR at different solvent viscosities and varying degrees of compaction. Despite pronounced differences between the theories, we find that all models can capture the experimental viscosity-dependence of the chain relaxation time. In contrast, the observed slowdown upon chain collapse of ACTR is not captured by any of the theories and a mechanistic link between chain dimension and internal friction is still missing, implying that the current theories are incomplete. In addition, a discrepancy between early results on homopolymer solutions and recent single-molecule experiments on unfolded and disordered proteins suggests that internal friction is likely to be a composite phenomenon caused by a variety of processes.

Inferring Fault Frictional and Reservoir Hydraulic Properties From Injection-Induced Seismicity

NASA Astrophysics Data System (ADS)

Jagalur-Mohan, Jayanth; Jha, Birendra; Wang, Zheng; Juanes, Ruben; Marzouk, Youssef

2018-02-01

Characterizing the rheological properties of faults and the evolution of fault friction during seismic slip are fundamental problems in geology and seismology. Recent increases in the frequency of induced earthquakes have intensified the need for robust methods to estimate fault properties. Here we present a novel approach for estimation of aquifer and fault properties, which combines coupled multiphysics simulation of injection-induced seismicity with adaptive surrogate-based Bayesian inversion. In a synthetic 2-D model, we use aquifer pressure, ground displacements, and fault slip measurements during fluid injection to estimate the dynamic fault friction, the critical slip distance, and the aquifer permeability. Our forward model allows us to observe nonmonotonic evolutions of shear traction and slip on the fault resulting from the interplay of several physical mechanisms, including injection-induced aquifer expansion, stress transfer along the fault, and slip-induced stress relaxation. This interplay provides the basis for a successful joint inversion of induced seismicity, yielding well-informed Bayesian posterior distributions of dynamic friction and critical slip. We uncover an inverse relationship between dynamic friction and critical slip distance, which is in agreement with the small dynamic friction and large critical slip reported during seismicity on mature faults.

An algorithm for simulating fracture of cohesive-frictional materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nukala, Phani K; Sampath, Rahul S; Barai, Pallab

Fracture of disordered frictional granular materials is dominated by interfacial failure response that is characterized by de-cohesion followed by frictional sliding response. To capture such an interfacial failure response, we introduce a cohesive-friction random fuse model (CFRFM), wherein the cohesive response of the interface is represented by a linear stress-strain response until a failure threshold, which is then followed by a constant response at a threshold lower than the initial failure threshold to represent the interfacial frictional sliding mechanism. This paper presents an efficient algorithm for simulating fracture of such disordered frictional granular materials using the CFRFM. We note that,more » when applied to perfectly plastic disordered materials, our algorithm is both theoretically and numerically equivalent to the traditional tangent algorithm (Roux and Hansen 1992 J. Physique II 2 1007) used for such simulations. However, the algorithm is general and is capable of modeling discontinuous interfacial response. Our numerical simulations using the algorithm indicate that the local and global roughness exponents ({zeta}{sub loc} and {zeta}, respectively) of the fracture surface are equal to each other, and the two-dimensional crack roughness exponent is estimated to be {zeta}{sub loc} = {zeta} = 0.69 {+-} 0.03.« less

Internal friction in an intrinsically disordered protein-Comparing Rouse-like models with experiments.

PubMed

Soranno, Andrea; Zosel, Franziska; Hofmann, Hagen

2018-03-28

Internal friction is frequently found in protein dynamics. Its molecular origin however is difficult to conceptualize. Even unfolded and intrinsically disordered polypeptide chains exhibit signs of internal friction despite their enormous solvent accessibility. Here, we compare four polymer theories of internal friction with experimental results on the intrinsically disordered protein ACTR (activator of thyroid hormone receptor). Using nanosecond fluorescence correlation spectroscopy combined with single-molecule Förster resonance energy transfer (smFRET), we determine the time scales of the diffusive chain dynamics of ACTR at different solvent viscosities and varying degrees of compaction. Despite pronounced differences between the theories, we find that all models can capture the experimental viscosity-dependence of the chain relaxation time. In contrast, the observed slowdown upon chain collapse of ACTR is not captured by any of the theories and a mechanistic link between chain dimension and internal friction is still missing, implying that the current theories are incomplete. In addition, a discrepancy between early results on homopolymer solutions and recent single-molecule experiments on unfolded and disordered proteins suggests that internal friction is likely to be a composite phenomenon caused by a variety of processes.

Low-Engine-Friction Technology for Advanced Natural-Gas Reciprocating Engines

DOE Office of Scientific and Technical Information (OSTI.GOV)

Victor Wong; Tian Tian; G. Smedley

This program aims at improving the efficiency of advanced natural-gas reciprocating engines (ANGRE) by reducing piston and piston ring assembly friction without major adverse effects on engine performance, such as increased oil consumption and wear. An iterative process of simulation, experimentation and analysis has been followed towards achieving the goal of demonstrating a complete optimized low-friction engine system. In this program, a detailed set of piston and piston-ring dynamic and friction models have been adapted and applied that illustrate the fundamental relationships among mechanical, surface/material and lubricant design parameters and friction losses. Demonstration of low-friction ring-pack designs in the Waukeshamore » VGF 18GL engine confirmed ring-pack friction reduction of 30-40%, which translates to total engine FEMP (friction mean effective pressure) reduction of 7-10% from the baseline configuration without significantly increasing oil consumption or blow-by flow. The study on surface textures, including roughness characteristics, cross hatch patterns, dimples and grooves have shown that even relatively small-scale changes can have a large effect on ring/liner friction, in some cases reducing FMEP by as much as 30% from a smooth surface case. The measured FMEP reductions were in good agreement with the model predictions. The combined analysis of lubricant and surface design indicates that low-viscosity lubricants can be very effective in reducing friction, subject to component wear for extremely thin oils, which can be mitigated with further lubricant formulation and/or engineered surfaces. Hence a combined approach of lubricant design and appropriate wear reduction offers improved potential for minimum engine friction loss. Testing of low-friction lubricants showed that total engine FMEP reduced by up to {approx}16.5% from the commercial reference oil without significantly increasing oil consumption or blow-by flow. Piston friction studies indicate that a flatter piston with a more flexible skirt, together with optimizing the waviness and film thickness on the piston skirt offer significant friction reduction. Combined with low-friction ring-pack, material and lubricant parameters, a total power cylinder friction reduction of 30-50% is expected, translating to an engine efficiency increase of two percentage points from its current baseline towards the goal of 50% ARES engine efficiency. The design strategies developed in this study have promising potential for application in all modern reciprocating engines as they represent simple, low-cost methods to extract significant fuel savings. The current program has possible spinoffs and applications in other industries as well, including transportation, CHP, and diesel power generation. The progress made in this program has wide engine efficiency implications, and potential deployment of low-friction engine components or lubricants in the near term is quite possible.« less

Quasi-dynamic earthquake fault systems with rheological heterogeneity

NASA Astrophysics Data System (ADS)

Brietzke, G. B.; Hainzl, S.; Zoeller, G.; Holschneider, M.

2009-12-01

Seismic risk and hazard estimates mostly use pure empirical, stochastic models of earthquake fault systems tuned specifically to the vulnerable areas of interest. Although such models allow for reasonable risk estimates, such models cannot allow for physical statements of the described seismicity. In contrary such empirical stochastic models, physics based earthquake fault systems models allow for a physical reasoning and interpretation of the produced seismicity and system dynamics. Recently different fault system earthquake simulators based on frictional stick-slip behavior have been used to study effects of stress heterogeneity, rheological heterogeneity, or geometrical complexity on earthquake occurrence, spatial and temporal clustering of earthquakes, and system dynamics. Here we present a comparison of characteristics of synthetic earthquake catalogs produced by two different formulations of quasi-dynamic fault system earthquake simulators. Both models are based on discretized frictional faults embedded in an elastic half-space. While one (1) is governed by rate- and state-dependent friction with allowing three evolutionary stages of independent fault patches, the other (2) is governed by instantaneous frictional weakening with scheduled (and therefore causal) stress transfer. We analyze spatial and temporal clustering of events and characteristics of system dynamics by means of physical parameters of the two approaches.

Probabilistic Fatigue Damage Prognosis Using a Surrogate Model Trained Via 3D Finite Element Analysis

NASA Technical Reports Server (NTRS)

Leser, Patrick E.; Hochhalter, Jacob D.; Newman, John A.; Leser, William P.; Warner, James E.; Wawrzynek, Paul A.; Yuan, Fuh-Gwo

2015-01-01

Utilizing inverse uncertainty quantification techniques, structural health monitoring can be integrated with damage progression models to form probabilistic predictions of a structure's remaining useful life. However, damage evolution in realistic structures is physically complex. Accurately representing this behavior requires high-fidelity models which are typically computationally prohibitive. In the present work, a high-fidelity finite element model is represented by a surrogate model, reducing computation times. The new approach is used with damage diagnosis data to form a probabilistic prediction of remaining useful life for a test specimen under mixed-mode conditions.

A high-fidelity airbus benchmark for system fault detection and isolation and flight control law clearance

NASA Astrophysics Data System (ADS)

Goupil, Ph.; Puyou, G.

2013-12-01

This paper presents a high-fidelity generic twin engine civil aircraft model developed by Airbus for advanced flight control system research. The main features of this benchmark are described to make the reader aware of the model complexity and representativeness. It is a complete representation including the nonlinear rigid-body aircraft model with a full set of control surfaces, actuator models, sensor models, flight control laws (FCL), and pilot inputs. Two applications of this benchmark in the framework of European projects are presented: FCL clearance using optimization and advanced fault detection and diagnosis (FDD).

On the origin of why static or breakloose friction is larger than kinetic friction, and how to reduce it: the role of aging, elasticity and sequential interfacial slip.

PubMed

Lorenz, B; Persson, B N J

2012-06-06

We discuss the origin of static friction and show how it can be reduced towards kinetic friction by the appropriate design of the sliding system. The basic idea is to use elastically soft solids and apply the external forces in such a way that different parts of the contacting interface start to slip at different times during the (tangential) loading process. In addition, the local slip must be large enough in order to result in a strong drop in the static friction force. We illustrate the theoretical predictions with the results of a simple model experiment.

Internal Friction And Instabilities Of Rotors

NASA Technical Reports Server (NTRS)

Walton, J.; Artiles, A.; Lund, J.; Dill, J.; Zorzi, E.

1992-01-01

Report describes study of effects of internal friction on dynamics of rotors prompted by concern over instabilities in rotors of turbomachines. Theoretical and experimental studies described. Theoretical involved development of nonlinear mathematical models of internal friction in three joints found in turbomachinery - axial splines, Curvic(TM) splines, and interference fits between smooth cylindrical surfaces. Experimental included traction tests to determine the coefficients of friction of rotor alloys at various temperatures, bending-mode-vibration tests of shafts equipped with various joints and rotordynamic tests of shafts with axial-spline and interference-fit joints.

Modelling Ocean Dissipation in Icy Satellites: A Comparison of Linear and Quadratic Friction

NASA Astrophysics Data System (ADS)

Hay, H.; Matsuyama, I.

2015-12-01

Although subsurface oceans are confirmed in Europa, Ganymede, Callisto, and strongly suspected in Enceladus and Titan, the exact mechanism required to heat and maintain these liquid reservoirs over Solar System history remains a mystery. Radiogenic heating can supply enough energy for large satellites whereas tidal dissipation provides the best explanation for the presence of oceans in small icy satellites. The amount of thermal energy actually contributed to the interiors of these icy satellites through oceanic tidal dissipation is largely unquantified. Presented here is a numerical model that builds upon previous work for quantifying tidally dissipated energy in the subsurface oceans of the icy satellites. Recent semi-analytical models (Tyler, 2008 and Matsuyama, 2014) have solved the Laplace Tidal Equations to estimate the time averaged energy flux over an orbital period in icy satellite oceans, neglecting the presence of a solid icy shell. These models are only able to consider linear Rayleigh friction. The numerical model presented here is compared to one of these semi-analytical models, finding excellent agreement between velocity and displacement solutions for all three terms to the tidal potential. Time averaged energy flux is within 2-6% of the analytical values. Quadratic (bottom) friction is then incorporated into the model, replacing linear friction. This approach is commonly applied to terrestrial ocean dissipation studies where dissipation scales nonlinearly with velocity. A suite of simulations are also run for the quadratic friction case which are then compared to and analysed against recent scaling laws developed by Chen and Nimmo (2013).

LOW-ENGINE-FRICTION TECHNOLOGY FOR ADVANCED NATURAL-GAS RECIPROCATING ENGINES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Victor W. Wong; Tian Tian; Grant Smedley

2003-08-28

This program aims at improving the efficiency of advanced natural-gas reciprocating engines (ANGRE) by reducing piston/ring assembly friction without major adverse effects on engine performance, such as increased oil consumption and emissions. A detailed set of piston/ring dynamic and friction models have been developed and applied that illustrated the fundamental relationships between design parameters and friction losses. Various low-friction strategies and concepts have been explored, and engine experiments will validate these concepts. An iterative process of experimentation, simulation and analysis, will be followed with the goal of demonstrating a complete optimized low-friction engine system. As planned, MIT has developed guidelinesmore » for an initial set of low-friction piston-ring-pack designs. Current recommendations focus on subtle top-piston-ring and oil-control-ring characteristics. A full-scale Waukesha F18 engine has been installed at Colorado State University and testing of the baseline configuration is in progress. Components for the first design iteration are being procured. Subsequent work includes examining the friction and engine performance data and extending the analyses to other areas to evaluate opportunities for further friction improvement and the impact on oil consumption/emission and wear, towards demonstrating an optimized reduced-friction engine system.« less

Implementation into earthquake sequence simulations of a rate- and state-dependent friction law incorporating pressure solution creep

NASA Astrophysics Data System (ADS)

Noda, H.

2016-05-01

Pressure solution creep (PSC) is an important elementary process in rock friction at high temperatures where solubilities of rock-forming minerals are significantly large. It significantly changes the frictional resistance and enhances time-dependent strengthening. A recent microphysical model for PSC-involved friction of clay-quartz mixtures, which can explain a transition between dilatant and non-dilatant deformation (d-nd transition), was modified here and implemented in dynamic earthquake sequence simulations. The original model resulted in essentially a kind of rate- and state-dependent friction (RSF) law, but assumed a constant friction coefficient for clay resulting in zero instantaneous rate dependency in the dilatant regime. In this study, an instantaneous rate dependency for the clay friction coefficient was introduced, consistent with experiments, resulting in a friction law suitable for earthquake sequence simulations. In addition, a term for time-dependent strengthening due to PSC was added which makes the friction law logarithmically rate-weakening in the dilatant regime. The width of the zone in which clasts overlap or, equivalently, the interface porosity involved in PSC plays a role as the state variable. Such a concrete physical meaning of the state variable is a great advantage in future modelling studies incorporating other physical processes such as hydraulic effects. Earthquake sequence simulations with different pore pressure distributions demonstrated that excess pore pressure at depth causes deeper rupture propagation with smaller slip per event and a shorter recurrence interval. The simulated ruptures were arrested a few kilometres below the point of pre-seismic peak stress at the d-nd transition and did not propagate spontaneously into the region of pre-seismic non-dilatant deformation. PSC weakens the fault against slow deformation and thus such a region cannot produce a dynamic stress drop. Dynamic rupture propagation further down to brittle-plastic transition, evidenced by geological observations, would require even smaller frictional resistance at coseismic slip rate, suggesting the importance of implementation of dynamic weakening activated at coseismic slip rates for more realistic simulation of earthquake sequences. The present models produced much smaller afterslip at deeper parts of arrested ruptures than those with logarithmic RSF laws because of a more significant rate-strengthening effect due to linearly viscous PSC. Detailed investigation of afterslip would give a clue to understand the deformation mechanism which controls shear resistance of the fault in a region of arrest of earthquake ruptures.

Temporal variation in fault friction and its effects on the slip evolution of a thrust fault over several earthquake cycles

NASA Astrophysics Data System (ADS)

Hampel, Andrea; Hetzel, Ralf

2013-04-01

The friction coefficient is a key parameter for the slip evolution of faults, but how temporal changes in friction affect fault slip is still poorly known. By using three-dimensional numerical models with a thrust fault that is alternately locked and released, we show that variations in the friction coefficient affect both coseismic and long-term fault slip (Hampel and Hetzel, 2012). Decreasing the friction coefficient by 5% while keeping the duration of the interseismic phase constant leads to a four-fold increase in coseismic slip, whereas a 5% increase nearly suppresses slip. A gradual decrease or increase of friction over several earthquake cycles (1-5% per earthquake) considerably alters the cumulative fault slip. In nature, the slip deficit (surplus) resulting from variations in the friction coefficient would presumably be compensated by a longer (shorter) interseismic phase, but the magnitude of the changes required for compensation render variations of the friction coefficient of >5% unlikely. Reference Hampel, A., R. Hetzel (2012) Temporal variation in fault friction and its effects on the slip evolution of a thrust fault over several earthquake cycles. Terra Nova, 24, 357-362, doi: 10.1111/j.1365-3121.2012.01073.x.

Study on the CO2 electric driven fixed swash plate type compressor for eco-friendly vehicles

NASA Astrophysics Data System (ADS)

Nam, Donglim; Kim, Kitae; Lee, Jehie; Kwon, Yunki; Lee, Geonho

2017-08-01

The purpose of this study is to experiment and to performance analysis about the electric-driven fixed swash plate compressor using alternate refrigerant(R744). Comprehensive simulation model for an electric driven compressor using CO2 for eco-friendly vehicle is presented. This model consists of compression model and dynamic model. The compression model included valve dynamics, leakage, and heat transfer models. And the dynamic model included frictional loss between piston ring and cylinder wall, frictional loss between shoe and swash plate, frictional loss of bearings, and electric efficiency. Especially, because the efficiency of an electric parts(motor and inverter) in the compressor affects the loss of the compressor, the dynamo test was performed. We made the designed compressor, and tested the performance of the compressor about the variety pressure conditions. Also we compared the performance analysis result and performance test result.

Steady-state propagation speed of rupture fronts along one-dimensional frictional interfaces.

PubMed

Amundsen, David Skålid; Trømborg, Jørgen Kjoshagen; Thøgersen, Kjetil; Katzav, Eytan; Malthe-Sørenssen, Anders; Scheibert, Julien

2015-09-01

The rupture of dry frictional interfaces occurs through the propagation of fronts breaking the contacts at the interface. Recent experiments have shown that the velocities of these rupture fronts range from quasistatic velocities proportional to the external loading rate to velocities larger than the shear wave speed. The way system parameters influence front speed is still poorly understood. Here we study steady-state rupture propagation in a one-dimensional (1D) spring-block model of an extended frictional interface for various friction laws. With the classical Amontons-Coulomb friction law, we derive a closed-form expression for the steady-state rupture velocity as a function of the interfacial shear stress just prior to rupture. We then consider an additional shear stiffness of the interface and show that the softer the interface, the slower the rupture fronts. We provide an approximate closed form expression for this effect. We finally show that adding a bulk viscosity on the relative motion of blocks accelerates steady-state rupture fronts and we give an approximate expression for this effect. We demonstrate that the 1D results are qualitatively valid in 2D. Our results provide insights into the qualitative role of various key parameters of a frictional interface on its rupture dynamics. They will be useful to better understand the many systems in which spring-block models have proved adequate, from friction to granular matter and earthquake dynamics.

Spine growth mechanisms: friction and seismicity at Mt. Unzen, Japan

NASA Astrophysics Data System (ADS)

Hornby, Adrian; Kendrick, Jackie; Hirose, Takehiro; Henton De Angelis, Sarah; De Angelis, Silvio; Umakoshi, Kodo; Miwa, Takahiro; Wadsworth, Fabian; Dingwell, Don; Lavallee, Yan

2014-05-01

The final episode of dome growth during the 1991-1995 eruption of Mt. Unzen was characterised by spine extrusion accompanied by repetitive seismicity. This type of cyclic activity has been observed at several dome-building volcanoes and recent work suggests a source mechanism of brittle failure of magma in the conduit. Spine growth may proceed by densification and closure of permeable pathways within the uppermost conduit magma, leading to sealing of the dome and inflation of the edifice. Amplified stresses on the wall rock and plug cause brittle failure near the conduit wall once static friction forces are overcome, and during spine growth these fractures may propagate to the dome surface. The preservation of these features is rare, and the conduit is typically inaccessible; therefore spines, the extruded manifestation of upper conduit material, provide the opportunity to study direct evidence of brittle processes in the conduit. At Mt. Unzen the spine retains evidence for brittle deformation and slip, however mechanical constraints on the formation of these features and their potential impact on eruption dynamics have not been well constrained. Here, we conduct an investigation into the process of episodic spine growth using high velocity friction apparatus at variable shear slip rate (0.4-1.5 m.s-1) and normal stress (0.4-3.5 MPa) on dome rock from Mt. Unzen, generating frictional melt at velocity >0.4 m.s-1 and normal stress >0.7 MPa. Our results show that the presence of frictional melt causes a deviation from Byerlee's frictional rule for rock friction. Melt generation is a disequilibrium process: initial amphibole breakdown leads to melt formation, followed by chemical homogenization of the melt layer. Ultimately, the experimentally generated frictional melts have a similar final chemistry, thickness and comminuted clast size distribution, thereby facilitating the extrapolation of a single viscoelastic model to describe melt-lubricated slip events at Mt. Unzen. To that end we apply state of the art 2-phase rheological models to estimate the dynamic apparent viscosities acting on the slip plane during a given slip event. Physical parameters of individual slip events in the conduit are constrained through calculation of seismic moments from earthquake swarms recorded during spine growth at Unzen. The combination of experimental data and viscosity modelling for frictional melt with seismic analysis provides a model for material response during slip in the upper conduit at Unzen. This model may have applicability to other eruption modes and volcanoes and further our understanding of cyclic eruptive activity during lava dome formation.

Analogue modeling of 3-D structural segmentation in fold-and-thrust belts: interactions between frictional and viscous provinces in foreland basins

NASA Astrophysics Data System (ADS)

Borderie, Sandra; Graveleau, Fabien; Witt, César; Vendeville, Bruno C.

2016-04-01

Accretionary wedges are generally segmented both across and along strike because of diverse factors including tectonic and stratigraphic inheritance. In fold-and-thrust belts, along-strike stratigraphic changes in the foreland sequence are classically observed and cause a curvature of the deformation front. Although the parameters controlling this curvature are well documented, the structural interactions and mutual influences between adjacent provinces are much less analyzed. To investigate this question, we deformed analogue models in a compressional box equipped with digital cameras and a topographic measurement apparatus. Models where shortened above a basal frictional detachment (glass microbeads) and segmentation was tested by having a region in which we added an interbedded viscous level (silicone polymer) within the sedimentary cover (dry sand). By changing the number (2 or 3) and the relative width of the purely frictional and viscous provinces, our goal was to characterize geometrically and kinematically the interactions between the viscous and the purely frictional provinces. We used a commercial geomodeller to generate 3-D geometrical models. The results indicate that regardless of the relative width of the purely frictional vs. viscous provinces, the deformation style in the frictional province is not influenced by the presence of the adjacent viscous province. On the contrary, the structural style and the deformation kinematics in the viscous province is significantly impacted by the presence or absence of an adjacent purely frictional province. At first order, the deformation style in the viscous province depends on its width, and three structural styles can be defined along strike. Far from the frictional area, structures are primarily of salt-massif type, and they do not seem to be influenced by the frictional wedge province. Towards the frictional province, deformation changes gradually to a zone of purely forethrusts (foreland verging), and finally to a highly faulted zone with both fore- and backthrusts (hinterland verging). In addition, a kinematic analysis indicates that narrow viscous provinces are strongly influenced by the presence of an adjacent frictional province. Indeed, propagation of shallow thrusts occurs in sequence and the deformation front reaches lately the external décollement pinchout. On the contrary, the deformation front of the wide viscous provinces propagates rapidly to the external décollement pinchout, then younger thrusts form out of sequence. Along-strike segmentation also affects the deep structures (thrusts detaching on the basal frictional décollement). In the viscous province, the presence of an upper viscous décollement opposes the advance of the basal deformation front. There, the rear of the wedge is characterized by imbrications of thrusts sheets (antiformal stacks), and the deep deformation front is convex towards the hinterland. Our experiments allow to better understand the dynamics of salt-controlled fold-and-thrust belts such as in the Huallaga (Peru) and Kuqa (China) basins or the Franklin Mountains (NW Canada).

Alternative methods to model frictional contact surfaces using NASTRAN

NASA Technical Reports Server (NTRS)

Hoang, Joseph

1992-01-01

Elongated (slotted) holes have been used extensively for the integration of equipment into Spacelab racks. In the past, this type of interface has been modeled assuming that there is not slippage between contact surfaces, or that there is no load transfer in the direction of the slot. Since the contact surfaces are bolted together, the contact friction provides a load path determined by the normal applied force (bolt preload) and the coefficient of friction. Three alternate methods that utilize spring elements, externally applied couples, and stress dependent elements are examined to model the contacted surfaces. Results of these methods are compared with results obtained from methods that use GAP elements and rigid elements.

High-Fidelity Roadway Modeling and Simulation

NASA Technical Reports Server (NTRS)

Wang, Jie; Papelis, Yiannis; Shen, Yuzhong; Unal, Ozhan; Cetin, Mecit

2010-01-01

Roads are an essential feature in our daily lives. With the advances in computing technologies, 2D and 3D road models are employed in many applications, such as computer games and virtual environments. Traditional road models were generated by professional artists manually using modeling software tools such as Maya and 3ds Max. This approach requires both highly specialized and sophisticated skills and massive manual labor. Automatic road generation based on procedural modeling can create road models using specially designed computer algorithms or procedures, reducing the tedious manual editing needed for road modeling dramatically. But most existing procedural modeling methods for road generation put emphasis on the visual effects of the generated roads, not the geometrical and architectural fidelity. This limitation seriously restricts the applicability of the generated road models. To address this problem, this paper proposes a high-fidelity roadway generation method that takes into account road design principles practiced by civil engineering professionals, and as a result, the generated roads can support not only general applications such as games and simulations in which roads are used as 3D assets, but also demanding civil engineering applications, which requires accurate geometrical models of roads. The inputs to the proposed method include road specifications, civil engineering road design rules, terrain information, and surrounding environment. Then the proposed method generates in real time 3D roads that have both high visual and geometrical fidelities. This paper discusses in details the procedures that convert 2D roads specified in shape files into 3D roads and civil engineering road design principles. The proposed method can be used in many applications that have stringent requirements on high precision 3D models, such as driving simulations and road design prototyping. Preliminary results demonstrate the effectiveness of the proposed method.

Intervention Fidelity in Family-Based Prevention Counseling for Adolescent Problem Behaviors

ERIC Educational Resources Information Center

Hogue, Aaron; Liddle, Howard A.; Singer, Alisa; Leckrone, Jodi

2005-01-01

This study examined fidelity in multidimensional family prevention (MDFP), a family-based prevention counseling model for adolescents at high risk for substance abuse and related behavior problems, in comparison to two empirically based treatments for adolescent drug abuse: multidimensional family therapy (MDFT) and cognitive-behavioral therapy…

A "Common Factors" Approach to Developing Culturally Tailored HIV Prevention Interventions

ERIC Educational Resources Information Center

Owczarzak, Jill; Phillips, Sarah D.; Filippova, Olga; Alpatova, Polina; Mazhnaya, Alyona; Zub, Tatyana; Aleksanyan, Ruzanna

2016-01-01

The current dominant model of HIV prevention intervention dissemination involves packaging interventions developed in one context, training providers to implement that specific intervention, and evaluating the extent to which providers implement it with fidelity. Research shows that providers rarely implement these programs with fidelity due to…

Characterization of friction in the 3.6m Devasthal optical telescope

NASA Astrophysics Data System (ADS)

Kumar, T. S.; Bastin, Christian; Kumar, Brijesh

2016-07-01

In this paper, we present the work on characterization of friction in the 3.6 m Devasthal optical telescope axes. The telescope azimuth axis is supported on a hydrostatic bearing while the altitude and rotator axes are supported on hydrodynamic bearings. Both altitude and azimuth axes are driven directly by high power BLDC motors and the rotator is driven by BLDC motor via a gearbox. This system is designed by AMOS, Belgium and tuned to achieve a tracking accuracy better than 0.1 arcsec RMS. Friction poses control related problems at such low speeds hence it is important to periodically characterize the behaviour at each axes. Compensation is necessary if the friction behaviour changes over the time and starts dominating the overall system response. For identifying friction each axis of telescope is rotated at different constant speeds and speed versus torque maps are generated. The LuGre model for friction is employed and nonlinear optimization is performed to identify the four static parameters of friction. The behaviour of friction for each axis is presented and the results are discussed.

Dependence of internal friction on folding mechanism.

PubMed

Zheng, Wenwei; De Sancho, David; Hoppe, Travis; Best, Robert B

2015-03-11

An outstanding challenge in protein folding is understanding the origin of "internal friction" in folding dynamics, experimentally identified from the dependence of folding rates on solvent viscosity. A possible origin suggested by simulation is the crossing of local torsion barriers. However, it was unclear why internal friction varied from protein to protein or for different folding barriers of the same protein. Using all-atom simulations with variable solvent viscosity, in conjunction with transition-path sampling to obtain reaction rates and analysis via Markov state models, we are able to determine the internal friction in the folding of several peptides and miniproteins. In agreement with experiment, we find that the folding events with greatest internal friction are those that mainly involve helix formation, while hairpin formation exhibits little or no evidence of friction. Via a careful analysis of folding transition paths, we show that internal friction arises when torsion angle changes are an important part of the folding mechanism near the folding free energy barrier. These results suggest an explanation for the variation of internal friction effects from protein to protein and across the energy landscape of the same protein.

ARC integration into the NEAMS Workbench

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stauff, N.; Gaughan, N.; Kim, T.

2017-01-01

One of the objectives of the Nuclear Energy Advanced Modeling and Simulation (NEAMS) Integration Product Line (IPL) is to facilitate the deployment of the high-fidelity codes developed within the program. The Workbench initiative was launched in FY-2017 by the IPL to facilitate the transition from conventional tools to high fidelity tools. The Workbench provides a common user interface for model creation, real-time validation, execution, output processing, and visualization for integrated codes.

Adolescent and parent motivation for change affects psychotherapy outcomes among youth with poorly controlled diabetes.

PubMed

Ellis, Deborah A; Berio, Heidi; Carcone, April Idalski; Naar-King, Sylvie

2012-01-01

Investigate effect of baseline motivation for change on treatment fidelity, therapeutic alliance, treatment dose, and treatment outcome in a randomized controlled trial of family therapy for youth with poorly controlled diabetes. Seventy-four adolescents and caregivers completed measures of motivation for change. Measures of fidelity, alliance, dose, and youth health status were collected. Structural equation modeling was used to test the direct and indirect effects of motivation on treatment outcomes. Parent motivation was significantly related to alliance and fidelity. Only alliance was significantly related to posttreatment metabolic control. In adolescent models, only motivation was significantly related to alliance. In both models, motivation had a significant indirect effect on metabolic control through alliance. Findings demonstrate the importance of parent and youth initial motivational status and treatment alliance to treatment outcome among youth with poorly controlled diabetes. Additional research on treatment techniques that promote motivation for change is needed.

Effect of the coefficient of friction and tightening speed on the preload induced at the dental implant complex with the finite element method.

PubMed

Bulaqi, Haddad Arabi; Mousavi Mashhadi, Mahmoud; Geramipanah, Farideh; Safari, Hamed; Paknejad, Mojgan

2015-05-01

To prevent screw loosening, a clear understanding of the factors influencing secure preload is necessary. The purpose of this study was to investigate the effect of coefficient of friction and tightening speed on screw tightening based on energy distribution method with exact geometric modeling and finite element analysis. To simulate the proper boundary conditions of the screw tightening process, the supporting bone of an implant was considered. The exact geometry of the implant complex, including the Straumann dental implant, direct crown attachment, and abutment screw were modeled with Solidworks software. Abutment screw/implant and implant/bone interfaces were designed as spiral thread helixes. The screw-tightening process was simulated with Abaqus software, and to achieve the target torque, an angular displacement was applied to the abutment screw head at different coefficients of friction and tightening speeds. The values of torque, preload, energy distribution, elastic energy, and efficiency were obtained at the target torque of 35 Ncm. Additionally, the torque distribution ratio and preload simulated values were compared to theoretically predicted values. Upon reducing the coefficient of friction and enhancing the tightening speed, the angle of turn increased at the target torque. As the angle of turn increased, the elastic energy and preload also increased. Additionally, by increasing the coefficient of friction, the frictional dissipation energy increased but the efficiency decreased, whereas the increase in tightening speed insignificantly affected efficiency. The results of this study indicate that the coefficient of friction is the most influential factor on efficiency. Increasing the tightening speed lowered the response rate to the frictional resistance, thus diminishing the coefficient of friction and slightly increasing the preload. Increasing the tightening speed has the same result as reducing the coefficient of friction. Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Dynamic analysis of the mechanical seals of the rotor of the labyrinth screw pump

NASA Astrophysics Data System (ADS)

Lebedev, A. Y.; Andrenko, P. M.; Grigoriev, A. L.

2017-08-01

A mathematical model of the work of the mechanical seal with smooth rings made from cast tungsten carbide in the condition of liquid friction is drawn up. A special feature of this model is the allowance for the thermal expansion of a liquid in the gap between the rings; this effect acting in the conjunction with the frictional forces creates additional pressure and lift which in its turn depends on the width of the gap and the speed of sliding. The developed model displays the processes of separation, transportation and heat removal in the compaction elements and also the resistance to axial movement of the ring arising in the gap caused by the pumping effect and the friction in the flowing liquid; the inertia of this fluid is taken into account by the mass reduction method. The linearization of the model is performed and the dynamic characteristics of the transient processes and the forced oscillations of the device are obtained. The conditions imposed on the parameters of the mechanical seal are formulated to provide a regime of the liquid friction, which minimizes the wear.

Role of friction in vertically oscillated granular materials

NASA Astrophysics Data System (ADS)

Moon, Sung Joon; Swift, J. B.; Swinney, Harry L.

2002-11-01

We use a previously validated molecular dynamics simulation of vertically oscillated granular layers to study how the contact friction affects standing wave patterns. Our collision model follows Walton(O. R. Walton, in Particulate Two-Phase Flow), edited by M. C. Roco (Butterworth-Heinemann, Boston, 1993), p. 884.: Dissipation in the normal component of colliding velocity is characterized by the normal coefficient of restitution e (0<= e < 1), and interaction in the tangential component by the tangential coefficient of restitution β = β(μ,e,Φ), where -1<= β <= β_0, μ is the static coefficient of friction on the surface of grains, Φ is the collision angle, and β0 corresponds to the crossover between static and sliding friction. We varied the above parameters independently for the grain-grain collisions and for the grain-wall collisions. The grain-grain friction changes the phase diagram of patterns significantly, and the patterns become fuzzy as the friction is decreased. The grain-wall friction is necessary to stabilize the patterns.

Fully Coupled Thermomechanical Finite Element Analysis of Material Evolution During Friction-Stir Welding of AA5083

DTIC Science & Technology

2009-09-03

coefficients are set to a value of 0.3. The stick/slip critical shear stress level is defined using a modified Coulomb friction law. Within this law, there...Modified Johnson Cook Model Equivalent Plastic Strain a P M,htgnert S d lei Y 1 2 3 4 5 6 7 420 440 460 480 500 520 540 560 Original Johnson Cook Model...Lett., 2005, 59, 3315–3318. 7 Thomas, W. M. and Nicholas, E. D. Friction stir welding for the transportation industries. Mater. Des ., 1997, 18, 269

Real data assimilation for optimization of frictional parameters and prediction of afterslip in the 2003 Tokachi-oki earthquake inferred from slip velocity by an adjoint method

NASA Astrophysics Data System (ADS)

Kano, Masayuki; Miyazaki, Shin'ichi; Ishikawa, Yoichi; Hiyoshi, Yoshihisa; Ito, Kosuke; Hirahara, Kazuro

2015-10-01

Data assimilation is a technique that optimizes the parameters used in a numerical model with a constraint of model dynamics achieving the better fit to observations. Optimized parameters can be utilized for the subsequent prediction with a numerical model and predicted physical variables are presumably closer to observations that will be available in the future, at least, comparing to those obtained without the optimization through data assimilation. In this work, an adjoint data assimilation system is developed for optimizing a relatively large number of spatially inhomogeneous frictional parameters during the afterslip period in which the physical constraints are a quasi-dynamic equation of motion and a laboratory derived rate and state dependent friction law that describe the temporal evolution of slip velocity at subduction zones. The observed variable is estimated slip velocity on the plate interface. Before applying this method to the real data assimilation for the afterslip of the 2003 Tokachi-oki earthquake, a synthetic data assimilation experiment is conducted to examine the feasibility of optimizing the frictional parameters in the afterslip area. It is confirmed that the current system is capable of optimizing the frictional parameters A-B, A and L by adopting the physical constraint based on a numerical model if observations capture the acceleration and decaying phases of slip on the plate interface. On the other hand, it is unlikely to constrain the frictional parameters in the region where the amplitude of afterslip is less than 1.0 cm d-1. Next, real data assimilation for the 2003 Tokachi-oki earthquake is conducted to incorporate slip velocity data inferred from time dependent inversion of Global Navigation Satellite System time-series. The optimized values of A-B, A and L are O(10 kPa), O(102 kPa) and O(10 mm), respectively. The optimized frictional parameters yield the better fit to the observations and the better prediction skill of slip velocity afterwards. Also, further experiment shows the importance of employing a fine-mesh model. It will contribute to the further understanding of the frictional properties on plate interfaces and lead to the forecasting system that provides useful information on the possibility of consequent earthquakes.

Tire/runway friction interface

NASA Technical Reports Server (NTRS)

Yager, Thomas J.

1990-01-01

An overview is given of NASA Langley's tire/runway pavement interface studies. The National Tire Modeling Program, evaluation of new tire and landing gear designs, tire wear and friction tests, and tire hydroplaning studies are examined. The Aircraft Landing Dynamics Facility is described along with some ground friction measuring vehicles. The major goals and scope of several joint FAA/NASA programs are identified together with current status and plans.

Integrated view of internal friction in unfolded proteins from single-molecule FRET, contact quenching, theory, and simulations

PubMed Central

Soranno, Andrea; Holla, Andrea; Dingfelder, Fabian; Nettels, Daniel; Makarov, Dmitrii E.; Schuler, Benjamin

2017-01-01

Internal friction is an important contribution to protein dynamics at all stages along the folding reaction. Even in unfolded and intrinsically disordered proteins, internal friction has a large influence, as demonstrated with several experimental techniques and in simulations. However, these methods probe different facets of internal friction and have been applied to disparate molecular systems, raising questions regarding the compatibility of the results. To obtain an integrated view, we apply here the combination of two complementary experimental techniques, simulations, and theory to the same system: unfolded protein L. We use single-molecule Förster resonance energy transfer (FRET) to measure the global reconfiguration dynamics of the chain, and photoinduced electron transfer (PET), a contact-based method, to quantify the rate of loop formation between two residues. This combination enables us to probe unfolded-state dynamics on different length scales, corresponding to different parts of the intramolecular distance distribution. Both FRET and PET measurements show that internal friction dominates unfolded-state dynamics at low denaturant concentration, and the results are in remarkable agreement with recent large-scale molecular dynamics simulations using a new water model. The simulations indicate that intrachain interactions and dihedral angle rotation correlate with the presence of internal friction, and theoretical models of polymer dynamics provide a framework for interrelating the contribution of internal friction observed in the two types of experiments and in the simulations. The combined results thus provide a coherent and quantitative picture of internal friction in unfolded proteins that could not be attained from the individual techniques. PMID:28223518

Integrated view of internal friction in unfolded proteins from single-molecule FRET, contact quenching, theory, and simulations.

PubMed

Soranno, Andrea; Holla, Andrea; Dingfelder, Fabian; Nettels, Daniel; Makarov, Dmitrii E; Schuler, Benjamin

2017-03-07

Internal friction is an important contribution to protein dynamics at all stages along the folding reaction. Even in unfolded and intrinsically disordered proteins, internal friction has a large influence, as demonstrated with several experimental techniques and in simulations. However, these methods probe different facets of internal friction and have been applied to disparate molecular systems, raising questions regarding the compatibility of the results. To obtain an integrated view, we apply here the combination of two complementary experimental techniques, simulations, and theory to the same system: unfolded protein L. We use single-molecule Förster resonance energy transfer (FRET) to measure the global reconfiguration dynamics of the chain, and photoinduced electron transfer (PET), a contact-based method, to quantify the rate of loop formation between two residues. This combination enables us to probe unfolded-state dynamics on different length scales, corresponding to different parts of the intramolecular distance distribution. Both FRET and PET measurements show that internal friction dominates unfolded-state dynamics at low denaturant concentration, and the results are in remarkable agreement with recent large-scale molecular dynamics simulations using a new water model. The simulations indicate that intrachain interactions and dihedral angle rotation correlate with the presence of internal friction, and theoretical models of polymer dynamics provide a framework for interrelating the contribution of internal friction observed in the two types of experiments and in the simulations. The combined results thus provide a coherent and quantitative picture of internal friction in unfolded proteins that could not be attained from the individual techniques.

Vertical structure and physical processes of the Madden-Julian oscillation: Linking hindcast fidelity to simulated diabatic heating and moistening

DOE PAGES

Klingaman, Nicholas P.; Woolnough, Steven J.; Jiang, Xianan; ...

2015-04-10

Here, many theories for the Madden-Julian oscillation (MJO) focus on diabatic processes, particularly the evolution of vertical heating and moistening. Poor MJO performance in weather and climate models is often blamed on biases in these processes and their interactions with the large-scale circulation. We introduce one of the three components of a model evaluation project, which aims to connect MJO fidelity in models to their representations of several physical processes, focusing on diabatic heating and moistening. This component consists of 20 day hindcasts, initialized daily during two MJO events in winter 2009–2010. The 13 models exhibit a range of skill:more » several have accurate forecasts to 20 days lead, while others perform similarly to statistical models (8–11 days). Models that maintain the observed MJO amplitude accurately predict propagation, but not vice versa. We find no link between hindcast fidelity and the precipitation-moisture relationship, in contrast to other recent studies. There is also no relationship between models' performance and the evolution of their diabatic heating profiles with rain rate. A more robust association emerges between models' fidelity and net moistening: the highest-skill models show a clear transition from low-level moistening for light rainfall to midlevel moistening at moderate rainfall and upper level moistening for heavy rainfall. The midlevel moistening, arising from both dynamics and physics, may be most important. Accurately representing many processes may be necessary but not sufficient for capturing the MJO, which suggests that models fail to predict the MJO for a broad range of reasons and limits the possibility of finding a panacea.« less

Micro-mechanical modeling of the cement-bone interface: the effect of friction, morphology and material properties on the micromechanical response.

PubMed

Janssen, Dennis; Mann, Kenneth A; Verdonschot, Nico

2008-11-14

In order to gain insight into the micro-mechanical behavior of the cement-bone interface, the effect of parametric variations of frictional, morphological and material properties on the mechanical response of the cement-bone interface were analyzed using a finite element approach. Finite element models of a cement-bone interface specimen were created from micro-computed tomography data of a physical specimen that was sectioned from an in vitro cemented total hip arthroplasty. In five models the friction coefficient was varied (mu=0.0; 0.3; 0.7; 1.0 and 3.0), while in one model an ideally bonded interface was assumed. In two models cement interface gaps and an optimal cement penetration were simulated. Finally, the effect of bone cement stiffness variations was simulated (2.0 and 2.5 GPa, relative to the default 3.0 GPa). All models were loaded for a cycle of fully reversible tension-compression. From the simulated stress-displacement curves the interface deformation, stiffness and hysteresis were calculated. The results indicate that in the current model the mechanical properties of the cement-bone interface were caused by frictional phenomena at the shape-closed interlock rather than by adhesive properties of the cement. Our findings furthermore show that in our model maximizing cement penetration improved the micromechanical response of the cement-bone interface stiffness, while interface gaps had a detrimental effect. Relative to the frictional and morphological variations, variations in the cement stiffness had only a modest effect on the micro-mechanical behavior of the cement-bone interface. The current study provides information that may help to better understand the load-transfer mechanisms taking place at the cement-bone interface.

Rotary Engine Friction Test Rig Development Report

DTIC Science & Technology

2011-12-01

fundamental research is needed to understand the friction characteristics of the rotary engine that lead to accelerated wear and tear on the seals...that includes a turbocharger . Once the original GT-Suite model is validated, the turbocharger model will be more accurate. This validation will...prepare for turbocharger and fuel-injector testing, which will lead to further development and calibration of the model. Further details are beyond the

Friction weakening in granular flows deduced from seismic records at the Soufrière Hills Volcano, Montserrat

NASA Astrophysics Data System (ADS)

Levy, Clara; Mangeney, Anne; Bonilla, Fabian; Hibert, Clément; Calder, Eliza S.; Smith, Patrick J.

2015-11-01

Accurate modeling of rockfalls and pyroclastic flows is still an open issue, partly due to a lack of measurements related to their dynamics. Using seismic data from the Soufrière Hills Volcano, Montserrat, and granular flow modeling, we show that the power laws relating the seismic energy Es to the seismic duration ts and relating the loss of potential energy ΔEp to the flow duration tf are very similar, like the power laws observed at Piton de la Fournaise, Reunion Island. Observations showing that tf≃ts suggest a constant ratio Es/ΔEp≃10-5. This similarity in these two power laws can be obtained only when the granular flow model uses a friction coefficient that decreases with the volume transported. Furthermore, with this volume-dependent friction coefficient, the simulated force applied by the flow to the ground correlates well with the seismic energy, highlighting the signature of this friction weakening effect in seismic data.

Friction weakening in granular flows deduced from seismic records at the Soufrière Hills Volcano, Montserrat

NASA Astrophysics Data System (ADS)

Levy, Clara; Mangeney, Anne; Bonilla, Fabian; Hibert, Clément; Calder, Eliza; Smith, Paddy

2015-04-01

Accurate modelling of rockfalls and pyroclastic flows is still an open issue, partly due the lack of measurements related to the dynamics of such events. Using seismic data from the Soufrière Hills Volcano and granular flow modelling, we show that the power laws relating the seismic energy Es to the seismic duration ts and relating the loss of potential energy ΔEp to the flow duration tf are very similar (Ei ≈ tiβ with i = s,p), as observed previously at Piton de la Fournaise, Reunion Island. Observations showing that tf ≃ ts suggest a constant ratio Es/ΔEp ≃ 10-5. This similarity in the power laws can be obtained only when the granular flow model uses a friction coefficient that decreases with the volume involved. Furthermore, with this volume-dependent friction coefficient, the simulated force applied by the flow to the ground correlates well with the seismic energy, highlighting the signature of this friction weakening effect in seismic data.

Fuzzy logic inference-based Pavement Friction Management and real-time slippery warning systems: A proof of concept study.

PubMed

Najafi, Shahriar; Flintsch, Gerardo W; Khaleghian, Seyedmeysam

2016-05-01

Minimizing roadway crashes and fatalities is one of the primary objectives of highway engineers, and can be achieved in part through appropriate maintenance practices. Maintaining an appropriate level of friction is a crucial maintenance practice, due to the effect it has on roadway safety. This paper presents a fuzzy logic inference system that predicts the rate of vehicle crashes based on traffic level, speed limit, and surface friction. Mamdani and Sugeno fuzzy controllers were used to develop the model. The application of the proposed fuzzy control system in a real-time slippery road warning system is demonstrated as a proof of concept. The results of this study provide a decision support model for highway agencies to monitor their network's friction and make appropriate judgments to correct deficiencies based on crash risk. Furthermore, this model can be implemented in the connected vehicle environment to warn drivers of potentially slippery locations. Published by Elsevier Ltd.

Vehicle States Observer Using Adaptive Tire-Road Friction Estimator

NASA Astrophysics Data System (ADS)

Kwak, Byunghak; Park, Youngjin

Vehicle stability control system is a new idea which can enhance the vehicle stability and handling in the emergency situation. This system requires the information of the yaw rate, sideslip angle and road friction in order to control the traction and braking forces at the individual wheels. This paper proposes an observer for the vehicle stability control system. This observer consisted of the state observer for vehicle motion estimation and the road condition estimator for the identification of the coefficient of the road friction. The state observer uses 2 degrees-of-freedom bicycle model and estimates the system variables based on the Kalman filter. The road condition estimator uses the same vehicle model and identifies the coefficient of the tire-road friction based on the recursive least square method. Both estimators make use of each other information. We show the effectiveness and feasibility of the proposed scheme under various road conditions through computer simulations of a fifteen degree-of-freedom non-linear vehicle model.

Sobriety Treatment and Recovery Teams: Implementation Fidelity and Related Outcomes.

PubMed

Huebner, Ruth A; Posze, Lynn; Willauer, Tina M; Hall, Martin T

2015-01-01

Although integrated programs between child welfare and substance abuse treatment are recommended for families with co-occurring child maltreatment and substance use disorders, implementing integrated service delivery strategies with fidelity is a challenging process. This study of the first five years of the Sobriety Treatment and Recovery Team (START) program examines implementation fidelity using a model proposed by Carroll et al. (2007). The study describes the process of strengthening moderators of implementation fidelity, trends in adherence to START service delivery standards, and trends in parent and child outcomes. Qualitative and quantitative measures were used to prospectively study three START sites serving 341 families with 550 parents and 717 children. To achieve implementation fidelity to service delivery standards required a pre-service year and two full years of operation, persistent leadership, and facilitative actions that challenged the existing paradigm. Over four years of service delivery, the time from the child protective services report to completion of five drug treatment sessions was reduced by an average of 75 days. This trend was associated with an increase in parent retention, parental sobriety, and parent retention of child custody. Conclusions/Importance: Understanding the implementation processes necessary to establish complex integrated programs may support realistic allocation of resources. Although implementation fidelity is a moderator of program outcome, complex inter-agency interventions may benefit from innovative measures of fidelity that promote improvement without extensive cost and data collection burden. The implementation framework applied in this study was useful in examining implementation processes, fidelity, and related outcomes.

A model to describe the surface gradient-nanograin formation and property of friction stir processed laser Co-Cr-Ni-Mo alloy

NASA Astrophysics Data System (ADS)

Li, Ruidi; Yuan, Tiechui; Qiu, Zili

2014-07-01

A gradient-nanograin surface layer of Co-base alloy was prepared by friction stir processing (FSP) of laser-clad coating in this work. However, it is lack of a quantitatively function relationship between grain refinement and FSP conditions. Based on this, an analytic model is derived for the correlations between carbide size, hardness and rotary speed, layer depth during in-situ FSP of laser-clad Co-Cr-Ni-Mo alloy. The model is based on the principle of typical plastic flow in friction welding and dynamic recrystallization. The FSP experiment for modification of laser-clad Co-based alloy was conducted and its gradient nanograin and hardness were characterized. It shows that the model is consistent with experimental results.

Modeling and analysis of wet friction clutch engagement dynamics

NASA Astrophysics Data System (ADS)

Iqbal, Shoaib; Al-Bender, Farid; Ompusunggu, Agusmian P.; Pluymers, Bert; Desmet, Wim

2015-08-01

In recent years, there has been a significant increase in the usage of wet-friction clutches. Presently researchers across the globe are involved in improving the performance and lifetime of clutches through testing and simulation. To understand the clutch vibrational and dynamical behavior, an SAE#2 test setup mathematical model based on extended reset-integrator friction model is developed in this paper. In order to take into account the different phases of fluid lubrication during engagement cycle, the model includes the experimentally determined Stribeck function. In addition the model considers the viscous effect and the delay in the actuation pressure signal. The model is validated with the experiments performed on the SAE#2 test setup in both time and frequency domains. By analyzing the set of experimental results, we confirmed that the amplitude of shudder vibration is independent of the amplitude of applied contact pressure fluctuation.

CAM/LIFTER forces and friction. Final report, September 15, 1988--November 30, 1991

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gabbey, D.J.; Lee, J.; Patterson, D.J.

1992-02-01

This report details the procedures used to measure the cam/lifter forces and friction. The present effort employed a Cummins LTA-10, and focuses on measurements and dynamic modeling of the injector train. The program was sponsored by the US Department of Energy in support of advanced diesel engine technology. The injector train was instrumented to record the instantaneous roller speed, roller pin friction torque, pushrod force, injector link force and cam speed. These measurements, together with lift profiles for pushrod and injector link displacement, enabled the friction work loss in the injector train to be determined. Other significant design criteria suchmore » as camshaft roller follower slippage and maximum loads on components were also determined. Future efforts will concentrate on the dynamic model, with tests run as required for correlation.« less

Numerical study of centrifugal compressor stage vaneless diffusers

NASA Astrophysics Data System (ADS)

Galerkin, Y.; Soldatova, K.; Solovieva, O.

2015-08-01

The authors analyzed CFD calculations of flow in vaneless diffusers with relative width in range from 0.014 to 0.100 at inlet flow angles in range from 100 to 450 with different inlet velocity coefficients, Reynolds numbers and surface roughness. The aim is to simulate calculated performances by simple algebraic equations. The friction coefficient that represents head losses as friction losses is proposed for simulation. The friction coefficient and loss coefficient are directly connected by simple equation. The advantage is that friction coefficient changes comparatively little in range of studied parameters. Simple equations for this coefficient are proposed by the authors. The simulation accuracy is sufficient for practical calculations. To create the complete algebraic model of the vaneless diffuser the authors plan to widen this method of modeling to diffusers with different relative length and for wider range of Reynolds numbers.

Fluid-structure interaction in straight pipelines with different anchoring conditions

NASA Astrophysics Data System (ADS)

Ferras, David; Manso, Pedro A.; Schleiss, Anton J.; Covas, Dídia I. C.

2017-04-01

This investigation aims at assessing the fluid-structure interaction (FSI) occurring during hydraulic transients in straight pipeline systems fixed to anchor blocks. A two mode 4-equation model is implemented incorporating the main interacting mechanisms: Poisson, friction and junction coupling. The resistance to movement due to inertia and dry friction of the anchor blocks is treated as junction coupling. Unsteady skin friction is taken into account in friction coupling. Experimental waterhammer tests collected from a straight copper pipe-rig are used for model validation in terms of wave shape, timing and damping. Numerical results successfully reproduce laboratory measurements for realistic values of calibration parameters. The novelty of this paper is the presentation of a 1D FSI solver capable of describing the resistance to movement of anchor blocks and its effect on the transient pressure wave propagation in straight pipelines.

Numerical modelling in friction lap joining of aluminium alloy and carbon-fiber-reinforced-plastic sheets

NASA Astrophysics Data System (ADS)

Das, A.; Bang, H. S.; Bang, H. S.

2018-05-01

Multi-material combinations of aluminium alloy and carbon-fiber-reinforced-plastics (CFRP) have gained attention in automotive and aerospace industries to enhance fuel efficiency and strength-to-weight ratio of components. Various limitations of laser beam welding, adhesive bonding and mechanical fasteners make these processes inefficient to join metal and CFRP sheets. Friction lap joining is an alternative choice for the same. Comprehensive studies in friction lap joining of aluminium to CFRP sheets are essential and scare in the literature. The present work reports a combined theoretical and experimental study in joining of AA5052 and CFRP sheets using friction lap joining process. A three-dimensional finite element based heat transfer model is developed to compute the temperature fields and thermal cycles. The computed results are validated extensively with the corresponding experimentally measured results.

Interpretation of the human skin biotribological behaviour after tape stripping

PubMed Central

Pailler-Mattei, C.; Guerret-Piécourt, C.; Zahouani, H.; Nicoli, S.

2011-01-01

The present study deals with the modification of the human skin biotribological behaviour after tape stripping. The tape-stripping procedure consists in the sequential application and removal of adhesive tapes on the skin surface in order to remove stratum corneum (SC) layers, which electrically charges the skin surface. The skin electric charges generated by tape stripping highly change the skin friction behaviour by increasing the adhesion component of the skin friction coefficient. It has been proposed to rewrite the friction adhesion component as the sum of two terms: the first classical adhesion term depending on the intrinsic shear strength, τ0, and the second term depending on the electric shear strength, τelec. The experimental results allowed to estimate a numerical value of the electric shear strength τelec. Moreover, a plan capacitor model with a dielectric material inside was used to modelize the experimental system. This physical model permitted to evaluate the friction electric force and the electric shear strength values to calculate the skin friction coefficient after the tape stripping. The comparison between the experimental and the theoretical value of the skin friction coefficient after the tape stripping has shown the importance of the electric charges on skin biotribological behaviour. The static electric charges produced by tape stripping on the skin surface are probably able to highly modify the interaction of formulations with the skin surface and their spreading properties. This phenomenon, generally overlooked, should be taken into consideration as it could be involved in alteration of drug absorption. PMID:21227961

Internal rotor friction instability

NASA Technical Reports Server (NTRS)

Walton, J.; Artiles, A.; Lund, J.; Dill, J.; Zorzi, E.

1990-01-01

The analytical developments and experimental investigations performed in assessing the effect of internal friction on rotor systems dynamic performance are documented. Analytical component models for axial splines, Curvic splines, and interference fit joints commonly found in modern high speed turbomachinery were developed. Rotor systems operating above a bending critical speed were shown to exhibit unstable subsynchronous vibrations at the first natural frequency. The effect of speed, bearing stiffness, joint stiffness, external damping, torque, and coefficient of friction, was evaluated. Testing included material coefficient of friction evaluations, component joint quantity and form of damping determinations, and rotordynamic stability assessments. Under conditions similar to those in the SSME turbopumps, material interfaces experienced a coefficient of friction of approx. 0.2 for lubricated and 0.8 for unlubricated conditions. The damping observed in the component joints displayed nearly linear behavior with increasing amplitude. Thus, the measured damping, as a function of amplitude, is not represented by either linear or Coulomb friction damper models. Rotordynamic testing of an axial spline joint under 5000 in.-lb of static torque, demonstrated the presence of an extremely severe instability when the rotor was operated above its first flexible natural frequency. The presence of this instability was predicted by nonlinear rotordynamic time-transient analysis using the nonlinear component model developed under this program. Corresponding rotordynamic testing of a shaft with an interference fit joint demonstrated the presence of subsynchronous vibrations at the first natural frequency. While subsynchronous vibrations were observed, they were bounded and significantly lower in amplitude than the synchronous vibrations.

Interpretation of the human skin biotribological behaviour after tape stripping.

PubMed

Pailler-Mattei, C; Guerret-Piécourt, C; Zahouani, H; Nicoli, S

2011-07-06

The present study deals with the modification of the human skin biotribological behaviour after tape stripping. The tape-stripping procedure consists in the sequential application and removal of adhesive tapes on the skin surface in order to remove stratum corneum (SC) layers, which electrically charges the skin surface. The skin electric charges generated by tape stripping highly change the skin friction behaviour by increasing the adhesion component of the skin friction coefficient. It has been proposed to rewrite the friction adhesion component as the sum of two terms: the first classical adhesion term depending on the intrinsic shear strength, τ(0), and the second term depending on the electric shear strength, τ(elec). The experimental results allowed to estimate a numerical value of the electric shear strength τ(elec). Moreover, a plan capacitor model with a dielectric material inside was used to modelize the experimental system. This physical model permitted to evaluate the friction electric force and the electric shear strength values to calculate the skin friction coefficient after the tape stripping. The comparison between the experimental and the theoretical value of the skin friction coefficient after the tape stripping has shown the importance of the electric charges on skin biotribological behaviour. The static electric charges produced by tape stripping on the skin surface are probably able to highly modify the interaction of formulations with the skin surface and their spreading properties. This phenomenon, generally overlooked, should be taken into consideration as it could be involved in alteration of drug absorption.

Stochastic estimation of human arm impedance under nonlinear friction in robot joints: a model study.

PubMed

Chang, Pyung Hun; Kang, Sang Hoon

2010-05-30

The basic assumption of stochastic human arm impedance estimation methods is that the human arm and robot behave linearly for small perturbations. In the present work, we have identified the degree of influence of nonlinear friction in robot joints to the stochastic human arm impedance estimation. Internal model based impedance control (IMBIC) is then proposed as a means to make the estimation accurate by compensating for the nonlinear friction. From simulations with a nonlinear Lugre friction model, it is observed that the reliability and accuracy of the estimation are severely degraded with nonlinear friction: below 2 Hz, multiple and partial coherence functions are far less than unity; estimated magnitudes and phases are severely deviated from that of a real human arm throughout the frequency range of interest; and the accuracy is not enhanced with an increase of magnitude of the force perturbations. In contrast, the combined use of stochastic estimation and IMBIC provides with accurate estimation results even with large friction: the multiple coherence functions are larger than 0.9 throughout the frequency range of interest and the estimated magnitudes and phases are well matched with that of a real human arm. Furthermore, the performance of suggested method is independent of human arm and robot posture, and human arm impedance. Therefore, the IMBIC will be useful in measuring human arm impedance with conventional robot, as well as in designing a spatial impedance measuring robot, which requires gearing. (c) 2010 Elsevier B.V. All rights reserved.

Enforcing elemental mass and energy balances for reduced order models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, J.; Agarwal, K.; Sharma, P.

2012-01-01

Development of economically feasible gasification and carbon capture, utilization and storage (CCUS) technologies requires a variety of software tools to optimize the designs of not only the key devices involved (e., g., gasifier, CO{sub 2} adsorber) but also the entire power generation system. High-fidelity models such as Computational Fluid Dynamics (CFD) models are capable of accurately simulating the detailed flow dynamics, heat transfer, and chemistry inside the key devices. However, the integration of CFD models within steady-state process simulators, and subsequent optimization of the integrated system, still presents significant challenges due to the scale differences in both time and length,more » as well the high computational cost. A reduced order model (ROM) generated from a high-fidelity model can serve as a bridge between the models of different scales. While high-fidelity models are built upon the principles of mass, momentum, and energy conservations, ROMs are usually developed based on regression-type equations and hence their predictions may violate the mass and energy conservation laws. A high-fidelity model may also have the mass and energy balance problem if it is not tightly converged. Conservations of mass and energy are important when a ROM is integrated to a flowsheet for the process simulation of the entire chemical or power generation system, especially when recycle streams are connected to the modeled device. As a part of the Carbon Capture Simulation Initiative (CCSI) project supported by the U.S. Department of Energy, we developed a software framework for generating ROMs from CFD simulations and integrating them with Process Modeling Environments (PMEs) for system-wide optimization. This paper presents a method to correct the results of a high-fidelity model or a ROM such that the elemental mass and energy are conserved perfectly. Correction factors for the flow rates of individual species in the product streams are solved using a minimization algorithm based on Lagrangian multiplier method. Enthalpies of product streams are also modified to enforce the energy balance. The approach is illustrated for two ROMs, one based on a CFD model of an entrained-flow gasifier and the other based on the CFD model of a multiphase CO{sub 2} adsorber.« less

New developments in tribomechanical modeling of automotive sheet steel forming

NASA Astrophysics Data System (ADS)

Khandeparkar, Tushar; Chezan, Toni; van Beeck, Jeroen

2018-05-01

Forming of automotive sheet metal body panels is a complex process influenced by both the material properties and contact conditions in the forming tooling. Material properties are described by the material constitutive behavior and the material flow into the forming die can be described by the tribological system. This paper investigates the prediction accuracy of the forming process using the Tata Steel state of the art description of the material constitutive behavior in combination with different friction models. A cross-die experiment is used to investigate the accuracy of local deformation modes typically seen in automotive sheet metal forming operations. Results of advanced friction models as well as the classical Coulomb friction description are compared to the experimentally measured strain distribution and material draw-in. Two hot-dip galvanized coated steel forming grades were used for the investigations. The results show that the accuracy of the simulation is not guaranteed by the advanced friction models for the entire investigated blank holder force range, both globally and locally. A measurable difference between the calculated and measured local strains is seen for both studied models even in the case where the global indicator, i.e. the draw-in, is well predicted.

Modeling, design, and testing of a proof-of-concept prototype damper with friction and eddy current damping effects

NASA Astrophysics Data System (ADS)

Amjadian, Mohsen; Agrawal, Anil K.

2018-01-01

Friction is considered as one of the most reliable mechanisms of energy dissipation that has been utilized extensively in passive damping devices to mitigate vibration of civil engineering structures subjected to extreme natural hazards such as earthquakes and windstorms. However, passive friction dampers are well-known for having a highly nonlinear hysteretic behavior caused by stick-slip motion at low velocities, a phenomenon that is inherent in friction and increases the acceleration response of the structure under control unfavorably. The authors have recently proposed the theoretical concept of a new type of damping device termed as "Passive Electromagnetic Eddy Current Friction Damper" (PEMECFD) in which an eddy current damping mechanism was utilized not only to decrease the undesirable effects of stick-slip motion, but also to increase the energy dissipation capacity of the damping device as a whole. That study was focused on demonstration of the theoretical performance of the proposed damping device through numerical simulations. This paper further investigates the influence of eddy current damping on energy dissipation due to friction through modeling, design, and testing of a proof-of-concept prototype damper. The design of this damper has been improved over the design in the previous study. The normal force in this damper is produced by the repulsive magnetic force between two cuboidal permanent magnets (PMs) magnetized in the direction normal to the direction of the motion. The eddy current damping force is generated because of the motion of the two PMs and two additional PMs relative to a copper plate in their vicinity. The dynamic models for the force-displacement relationship of the prototype damper are based on LuGre friction model, electromagnetic theory, and inertial effects of the prototype damper. The parameters of the dynamic models have been identified through a series of characterization tests on the prototype damper under harmonic excitations of different frequencies in the laboratory. Finally, the identified dynamic models have been validated by subjecting the prototype damper to two different random excitations. The results indicate that the proposed dynamic models are capable of representing force-displacement behavior of the new type of passive damping device for a wide range of operating conditions.

Modeling of Instabilities and Self-organization at the Frictional Interface

NASA Astrophysics Data System (ADS)

Mortazavi, Vahid

The field of friction-induced self-organization and its practical importance remains unknown territory to many tribologists. Friction is usually thought of as irreversible dissipation of energy and deterioration; however, under certain conditions, friction can lead to the formation of new structures at the interface, including in-situ tribofilms and various patterns at the interface. This thesis studies self-organization and instabilities at the frictional interface, including the instability due to the temperature-dependency of the coefficient of friction, the transient process of frictional running-in, frictional Turing systems, the stick-and-slip phenomenon, and, finally, contact angle (CA) hysteresis as an example of solid-liquid friction and dissipation. All these problems are chosen to bridge the gap between fundamental interest in understanding the conditions leading to self-organization and practical motivation. We study the relationship between friction-induced instabilities and friction-induced self-organization. Friction is usually thought of as a stabilizing factor; however, sometimes it leads to the instability of sliding, in particular when friction is coupled with another process. Instabilities constitute the main mechanism for pattern formation. At first, a stationary structure loses its stability; after that, vibrations with increasing amplitude occur, leading to a limit cycle corresponding to a periodic pattern. The self-organization is usually beneficial for friction and wear reduction because the tribological systems tend to enter a state with the lowest energy dissipation. The introductory chapter starts with basic definitions related to self-organization, instabilities and friction, literature review, and objectives. We discuss fundamental concepts that provide a methodological tool to investigate, understand and enhance beneficial processes in tribosystems which might lead to self-organization. These processes could result in the ability of a frictional surface to exhibit "self-protection" and "self-healing" properties. Hence, this research is dealing with the fundamental concepts that allow the possibility of the development of a new generation of tribosystem and materials that reinforce such properties. In chapter 2, we investigate instabilities due to the temperature-dependency of the coefficient of friction. The temperature-dependency of the coefficient of friction can have a significant effect on the frictional sliding stability, by leading to the formation of "hot" and "cold" spots on the contacting surfaces. We formulate a stability criterion and perform a case study of a brake disk. In chapter 3, we study frictional running-in. Running-in is a transient period on the onset of the frictional sliding, in which friction and wear decrease to their stationary values. In this research, running-in is interpreted as friction-induced self-organization process. We introduce a theoretical model of running-in and investigate rough profile evolution assuming that its kinetics is driven by two opposite processes or events, i.e., smoothening which is typical for the deformation-driven friction and wear, and roughening which is typical for the adhesion-driven friction and wear. In chapter 4, we investigate the possibility of the so-called Turing-type pattern formation during friction. Turing or reaction-diffusion systems describe variations of spatial concentrations of chemical components with time due to local chemical reactions coupled with diffusion. During friction, the patterns can form at the sliding interface due to the mass transfer (diffusion), heat transfer, various tribochemical reactions, and wear. In chapter 5, we investigate how interfacial patterns including propagating trains of stick and slip zones form due to dynamic sliding instabilities. These can be categorized as self-organized patterns. We treat stick and slip as two phases at the interface, and study the effects related to phase transitions. Our results show how interfacial patterns form, how the transition between stick and slip zones occurs, and which parameters affect them. In chapter 6, we use Cellular Potts Model to study contact angle (CA) hysteresis as a measure of solid-liquid energy dissipation. We simulate CA hysteresis for a droplet over the tilted patterned surface, and a bubble placed under the surface immersed in liquid. We discuss the dependency of CA hysteresis on the surface structure and other parameters. This analysis allows decoupling of the 1D (pinning of the triple line) and 2D effects (adhesion hysteresis in the contact area) and obtain new insights on the nature of CA hysteresis. To summarize, we examine different cases in frictional interface and observe similar trends. We investigate and discus how these trends could be beneficial in design, synthesis and characterization of different materials and tribosystems. Furthermore, we describe how to utilize fundamental concepts for specific engineering applications. Finally, the main theme of this research is to find new applications of concept of self-organization to tribology and the role played by different physical and chemical interactions in modifying and controlling friction and wear. (Abstract shortened by UMI.)

Synthetic Air Data Estimation: A case study of model-aided estimation

NASA Astrophysics Data System (ADS)

Lie, F. Adhika Pradipta

A method for estimating airspeed, angle of attack, and sideslip without using conventional, pitot-static airdata system is presented. The method relies on measurements from GPS, an inertial measurement unit (IMU) and a low-fidelity model of the aircraft's dynamics which are fused using two, cascaded Extended Kalman Filters. In the cascaded architecture, the first filter uses information from the IMU and GPS to estimate the aircraft's absolute velocity and attitude. These estimates are used as the measurement updates for the second filter where they are fused with the aircraft dynamics model to generate estimates of airspeed, angle of attack and sideslip. Methods for dealing with the time and inter-state correlation in the measurements coming from the first filter are discussed. Simulation and flight test results of the method are presented. Simulation results using high fidelity nonlinear model show that airspeed, angle of attack, and sideslip angle estimation errors are less than 0.5 m/s, 0.1 deg, and 0.2 deg RMS, respectively. Factors that affect the accuracy including the implication and impact of using a low fidelity aircraft model are discussed. It is shown using flight tests that a single linearized aircraft model can be used in lieu of a high-fidelity, non-linear model to provide reasonably accurate estimates of airspeed (less than 2 m/s error), angle of attack (less than 3 deg error), and sideslip angle (less than 5 deg error). This performance is shown to be relatively insensitive to off-trim attitudes but very sensitive to off-trim velocity.

A comparison of the lubrication behavior of whey protein model foods using tribology in linear and elliptical movement.

PubMed

Campbell, Caroline L; Foegeding, E Allen; van de Velde, Fred

2017-08-01

Lubrication is an important factor in the sensory evaluation of food products. Tribology provides a theoretical framework and instrumental methods for evaluating frictional properties between two moving surfaces and the lubrication behavior of products between these surfaces. Relating frictional measurements to sensory properties detected during oral processing requires careful and pertinent choices in surface materials and testing conditions. The aims of this study were to investigate: (a) differences in lubrication behavior of a range of food textures and (b) the differences between linear and elliptical movement and added saliva to understand the contribution of food structure to friction. Six whey protein model food samples, ranging in texture from fluid to semisolid to soft solid, were analyzed using a pin on disk tribometer to determine the coefficient of friction (COF) across a range of sliding speeds. The samples were analyzed in their initial form and post-oral processing (n = 4) in both linear and elliptical movements. Elliptical movement slightly decreased coefficients of friction and extended the shape of the friction curve. Increases in test food viscosity decreased the COF but differences in viscosity were not apparent when test foods were mixed with saliva. Data correction for viscosity shifted the friction curves horizontally, indicating that lubrication had a greater impact upon friction than viscosity. This study provides initial insights for further comparison of linear and elliptical movement with a variety of sample compositions. Sensory perception of smoothness and creaminess are often major contributors to overall hedonic food liking and are a major reason why products high in fat and sugar are more highly preferred over other foods. These parameters are influenced by friction and lubrication between the tongue, palate, teeth, food products, and saliva during oral processing. Tribology provides an instrumental method to evaluate friction between moving surfaces that mimic oral surfaces and the lubrication behavior of foods. Trends in frictional measurements can be correlated with sensory ratings of the same foods to better understand why preferences exist for certain foods or food compositions and how to effectively improve the acceptability and enjoyment of healthier foods. © 2017 Wiley Periodicals, Inc.

Expectations in the Wall Region of a Large-Eddy Simulation

NASA Astrophysics Data System (ADS)

Spalart, Philippe R.; Strelets, Mikhail Kh.; Travin, Andrey

The expectations fall into two categories. The first relates to the method and how general it should be, how applicable to unstructured grids in complex three-dimensional geometries and very high Reynolds numbers, even if the exercise uses a structured grid in a two-dimensional flow at moderate Reynolds number. The view-point is that there should be a known path from the research activity to the creation of a machine or the prediction of weather. If not, the gap in this path takes on a high priority and the work is labeled as preliminary. An example of such a litmus test is whether the grid design requires knowledge of the direction of the skin friction. The second category relates to the fidelity of the description of the turbulence which can be assembled. As an example, the shear stress in a wall-bounded LES is calculated quite well as the sum of a viscous stress, a "modeled" Reynolds stress, and a "resolved" Reynolds stress. However, the same has not been achieved for the other Reynolds stresses, unless the grid is such that Quasi-Direct Numerical Simulation is taking place. Higher-order quantities are even more troublesome. We also discuss a remedy to Log-Layer Mismatch called "Energized Wall-Modeled LES" which is most simple, cost-free, and compatible with grids that are useable in practice. The added term provides visible extra activity, and improves all the Reynolds stresses in addition to the mean velocity.

The influence of suspension components friction on race car vertical dynamics

NASA Astrophysics Data System (ADS)

Benini, Claudio; Gadola, Marco; Chindamo, Daniel; Uberti, Stefano; Marchesin, Felipe P.; Barbosa, Roberto S.

2017-03-01

This work analyses the effect of friction in suspension components on a race car vertical dynamics. It is a matter of fact that race cars aim at maximising their performance, focusing the attention mostly on aerodynamics and suspension tuning: suspension vertical and rolling stiffness and damping are parameters to be taken into account for an optimal setup. Furthermore, friction in suspension components must not be ignored. After a test session carried out with a F4 on a Four Poster rig, friction was detected on the front suspension. The real data gathered allow the validation of an analytical model with friction, confirming that its influence is relevant for low frequency values closed to the car pitch natural frequency. Finally, some setup proposals are presented to describe what should be done on actual race cars in order to correct vehicle behaviour when friction occurs.

Quantum phase transitions in a two-dimensional quantum XYX model: ground-state fidelity and entanglement.

PubMed

Li, Bo; Li, Sheng-Hao; Zhou, Huan-Qiang

2009-06-01

A systematic analysis is performed for quantum phase transitions in a two-dimensional anisotropic spin-1/2 antiferromagnetic XYX model in an external magnetic field. With the help of an innovative tensor network algorithm, we compute the fidelity per lattice site to demonstrate that the field-induced quantum phase transition is unambiguously characterized by a pinch point on the fidelity surface, marking a continuous phase transition. We also compute an entanglement estimator, defined as a ratio between the one-tangle and the sum of squared concurrences, to identify both the factorizing field and the critical point, resulting in a quantitative agreement with quantum Monte Carlo simulation. In addition, the local order parameter is "derived" from the tensor network representation of the system's ground-state wave functions.

Strengthening organizations to implement evidence-based clinical practices.

PubMed

VanDeusen Lukas, Carol; Engle, Ryann L; Holmes, Sally K; Parker, Victoria A; Petzel, Robert A; Nealon Seibert, Marjorie; Shwartz, Michael; Sullivan, Jennifer L

2010-01-01

Despite recognition that implementation of evidence-based clinical practices (EBPs) usually depends on the structure and processes of the larger health care organizational context, the dynamics of implementation are not well understood. This project's aim was to deepen that understanding by implementing and evaluating an organizational model hypothesized to strengthen the ability of health care organizations to facilitate EBPs. CONCEPTUAL MODEL: The model posits that implementation of EBPs will be enhanced through the presence of three interacting components: active leadership commitment to quality, robust clinical process redesign incorporating EBPs into routine operations, and use of management structures and processes to support and align redesign. In a mixed-methods longitudinal comparative case study design, seven medical centers in one network in the Department of Veterans Affairs participated in an intervention to implement the organizational model over 3 years. The network was selected randomly from three interested in using the model. The target EBP was hand-hygiene compliance. Measures included ratings of implementation fidelity, observed hand-hygiene compliance, and factors affecting model implementation drawn from interviews. Analyses support the hypothesis that greater fidelity to the organizational model was associated with higher compliance with hand-hygiene guidelines. High-fidelity sites showed larger effect sizes for improvement in hand-hygiene compliance than lower-fidelity sites. Adherence to the organizational model was in turn affected by factors in three categories: urgency to improve, organizational environment, and improvement climate. Implementation of EBPs, particularly those that cut across multiple processes of care, is a complex process with many possibilities for failure. The results provide the basis for a refined understanding of relationships among components of the organizational model and factors in the organizational context affecting them. This understanding suggests practical lessons for future implementation efforts and contributes to theoretical understanding of the dynamics of the implementation of EBPs.

Reconnection Dynamics and Mutual Friction in Quantum Turbulence

NASA Astrophysics Data System (ADS)

Laurie, Jason; Baggaley, Andrew W.

2015-07-01

We investigate the behaviour of the mutual friction force in finite temperature quantum turbulence in He, paying particular attention to the role of quantized vortex reconnections. Through the use of the vortex filament model, we produce three experimentally relevant types of vortex tangles in steady-state conditions, and examine through statistical analysis, how local properties of the tangle influence the mutual friction force. Finally, by monitoring reconnection events, we present evidence to indicate that vortex reconnections are the dominant mechanism for producing areas of high curvature and velocity leading to regions of high mutual friction, particularly for homogeneous and isotropic vortex tangles.

Making molehills out of mountains: landscape genetics of the Mojave desert tortoise

USGS Publications Warehouse

Hagerty, Bridgette E.; Nussear, Kenneth E.; Esque, Todd C.; Tracy, C. Richard

2010-01-01

Heterogeneity in habitat often influences how organisms traverse the landscape matrix that connects populations. Understanding landscape connectivity is important to determine the ecological processes that influence those movements, which lead to evolutionary change due to gene flow. Here, we used landscape genetics and statistical models to evaluate hypotheses that could explain isolation among locations of the threatened Mojave desert tortoise (Gopherus agassizii). Within a causal modeling framework, we investigated three factors that can influence landscape connectivity: geographic distance, barriers to dispersal, and landscape friction. A statistical model of habitat suitability for the Mojave desert tortoise, based on topography, vegetation, and climate variables, was used as a proxy for landscape friction and barriers to dispersal. We quantified landscape friction with least-cost distances and with resistance distances among sampling locations. A set of diagnostic partial Mantel tests statistically separated the hypotheses of potential causes of genetic isolation. The best-supported model varied depending upon how landscape friction was quantified. Patterns of genetic structure were related to a combination of geographic distance and barriers as defined by least-cost distances, suggesting that mountain ranges and extremely low-elevation valleys influence connectivity at the regional scale beyond the tortoises' ability to disperse. However, geographic distance was the only influence detected using resistance distances, which we attributed to fundamental differences between the two ways of quantifying friction. Landscape friction, as we measured it, did not influence the observed patterns of genetic distances using either quantification. Barriers and distance may be more valuable predictors of observed population structure for species like the desert tortoise, which has high dispersal capability and a long generation time.

Evaluating the Implementation Fidelity of Technology Immersion and Its Relationship with Student Achievement

ERIC Educational Resources Information Center

Shapley, Kelly S.; Sheehan, Daniel; Maloney, Catherine; Caranikas-Walker, Fanny

2010-01-01

In a pilot study of the Technology Immersion model, high-need middle schools were "immersed" in technology by providing a laptop for each student and teacher, wireless Internet access, curricular and assessment resources, professional development, and technical and pedagogical support. This article examines the fidelity of model…

Nursing Simulation: A Review of the Past 40 Years

ERIC Educational Resources Information Center

Nehring, Wendy M.; Lashley, Felissa R.

2009-01-01

Simulation, in its many forms, has been a part of nursing education and practice for many years. The use of games, computer-assisted instruction, standardized patients, virtual reality, and low-fidelity to high-fidelity mannequins have appeared in the past 40 years, whereas anatomical models, partial task trainers, and role playing were used…

Prehension Synergies in the Grasps With Complex Friction Patterns: Local Versus Synergic Effects and the Template Control

PubMed Central

Niu, Xun; Latash, Mark L.; Zatsiorsky, Vladimir M.

2010-01-01

We studied adjustments of digit forces to changes in the friction. The subjects held a handle statically in a three-digit grasp. The friction under each digit was either high or low, resulting in eight three-element friction sets (such grasps were coined the grasps with complex friction pattern). The total load was also manipulated. It was found that digit forces were adjusted not only to the supported load and local friction, but also to friction at other digits (synergic effects). When friction under a digit was low, its tangential force decreased and the normal force increased (local effects). The synergic effects were directed to maintain the equilibrium of the handle. The relation between the individual digit forces and loads agreed with the triple-product model: fin=ki(2)ki(1)L, where fin is normal force of digit i, L is the load (newtons), ki(1) is a dimensionless coefficient representing sharing the total tangential force among the digits (Σki(1)=1.0), and ki(2) is a coefficient representing the relation between the tangential and normal forces of digit i (the overall friction equivalent, OFE). At each friction set, the central controller selected the grasping template—a three-element array of ki(2)ki(1) products—and then scaled the template with the load magnitude. PMID:17493928

Advances in Measurement of Skin Friction in Airflow

NASA Technical Reports Server (NTRS)

Brown, James L.; Naughton, Jonathan W.

2006-01-01

The surface interferometric skin-friction (SISF) measurement system is an instrument for determining the distribution of surface shear stress (skin friction) on a wind-tunnel model. The SISF system utilizes the established oil-film interference method, along with advanced image-data-processing techniques and mathematical models that express the relationship between interferograms and skin friction, to determine the distribution of skin friction over an observed region of the surface of a model during a single wind-tunnel test. In the oil-film interference method, a wind-tunnel model is coated with a thin film of oil of known viscosity and is illuminated with quasi-monochromatic, collimated light, typically from a mercury lamp. The light reflected from the outer surface of the oil film interferes with the light reflected from the oil-covered surface of the model. In the present version of the oil-film interference method, a camera captures an image of the illuminated model and the image in the camera is modulated by the interference pattern. The interference pattern depends on the oil-thickness distribution on the observed surface, and this distribution can be extracted through analysis of the image acquired by the camera. The oil-film technique is augmented by a tracer technique for observing the streamline pattern. To make the streamlines visible, small dots of fluorescentchalk/oil mixture are placed on the model just before a test. During the test, the chalk particles are embedded in the oil flow and produce chalk streaks that mark the streamlines. The instantaneous rate of thinning of the oil film at a given position on the surface of the model can be expressed as a function of the instantaneous thickness, the skin-friction distribution on the surface, and the streamline pattern on the surface; the functional relationship is expressed by a mathematical model that is nonlinear in the oil-film thickness and is known simply as the thin-oil-film equation. From the image data acquired as described, the time-dependent oil-thickness distribution and streamline pattern are extracted and by inversion of the thin-oil-film equation it is then possible to determine the skin-friction distribution. In addition to a quasi-monochromatic light source, the SISF system includes a beam splitter and two video cameras equipped with filters for observing the same area on a model in different wavelength ranges, plus a frame grabber and a computer for digitizing the video images and processing the image data. One video camera acquires the interference pattern in a narrow wavelength range of the quasi-monochromatic source. The other video camera acquires the streamline image of fluorescence from the chalk in a nearby but wider wavelength range. The interference- pattern and fluorescence images are digitized, and the resulting data are processed by an algorithm that inverts the thin-oil-film equation to find the skin-friction distribution.

Features that contribute to the usefulness of low-fidelity models for surgical skills training.

PubMed

Langebæk, R; Berendt, M; Pedersen, L T; Jensen, A L; Eika, B

2012-04-07

For practical, ethical and economic reasons, veterinary surgical education is becoming increasingly dependent on models for training. The limited availability and high cost of commercially produced surgical models has increased the need for useful, low-cost alternatives. For this reason, a number of models were developed to be used in a basic surgical skills course for veterinary students. The models were low fidelity, having limited resemblance to real animals. The aim of the present study was to describe the students' learning experience with the models and to report their perception of the usefulness of the models in applying the trained skills to live animal surgery. One hundred and forty-six veterinary fourth-year students evaluated the models on a four-point Likert scale. Of these, 26 additionally participated in individual semistructured interviews. The survey results showed that 75 per cent of the students rated the models 'useful'/'very useful'. Interviews revealed that tactile, dimensional, visual, situational and emotional features are important to students' perception of a successful translation of skills from models to live animal. In conclusion, low-fidelity models are useful educational tools in preparation for live animal surgery. However, there are specific features to take into account when developing models in order for students to perceive them as useful.

Spawning site fidelity of wild and hatchery lake trout (Salvelinus namaycush) in northern Lake Huron

USGS Publications Warehouse

Binder, Thomas; Riley, Stephen C.; Holbrook, Christopher; Hansen, Michael J.; Bergstedt, Roger A.; Bronte, Charles R.; He, Ji; Krueger, Charles C.

2016-01-01

Fidelity to high-quality spawning sites helps ensure that adults repeatedly spawn at sites that maximize reproductive success. Fidelity is also an important behavioural characteristic to consider when hatchery-reared individuals are stocked for species restoration, because artificial rearing environments may interfere with cues that guide appropriate spawning site selection. Acoustic telemetry was used in conjunction with Cormack–Jolly–Seber capture–recapture models to compare degree of spawning site fidelity of wild and hatchery-reared lake trout (Salvelinus namaycush) in northern Lake Huron. Annual survival was estimated to be between 77% and 81% and did not differ among wild and hatchery males and females. Site fidelity estimates were high in both wild and hatchery-reared lake trout (ranging from 0.78 to 0.94, depending on group and time filter), but were slightly lower in hatchery-reared fish than in wild fish. The ecological implication of the small difference in site fidelity between wild and hatchery-reared lake trout is unclear, but similarities in estimates suggest that many hatchery-reared fish use similar spawning sites to wild fish and that most return to those sites annually for spawning.

Nonmonotonic velocity dependence of atomic friction.

PubMed

Reimann, Peter; Evstigneev, Mykhaylo

2004-12-03

We propose a theoretical model for friction force microscopy experiments with special emphasis on the realistic description of dissipation and inertia effects. Its main prediction is a nonmonotonic dependence of the friction force upon the sliding velocity of the atomic force microscope tip relative to an atomically flat surface. The region around the force maximum can be approximately described by a universal scaling law and should be observable under experimentally realistic conditions.

Effect of bone-soft tissue friction on ultrasound axial shear strain elastography

NASA Astrophysics Data System (ADS)

Tang, Songyuan; Chaudhry, Anuj; Kim, Namhee; Reddy, J. N.; Righetti, Raffaella

2017-08-01

Bone-soft tissue friction is an important factor affecting several musculoskeletal disorders, frictional syndromes and the ability of a bone fracture to heal. However, this parameter is difficult to determine using non-invasive imaging modalities, especially in clinical settings. Ultrasound axial shear strain elastography is a non-invasive imaging modality that has been used in the recent past to estimate the bonding between different tissue layers. As most elastography methods, axial shear strain elastography is primarily used in soft tissues. More recently, this technique has been proposed to assess the bone-soft tissue interface. In this paper, we investigate the effect of a variation in bone-soft tissue friction coefficient in the resulting axial shear strain elastograms. Finite element poroelastic models of bone specimens exhibiting different bone-soft tissue friction coefficients were created and mechanically analyzed. These models were then imported to an ultrasound elastography simulation module to assess the presence of axial shear strain patterns. In vitro experiments were performed to corroborate selected simulation results. The results of this study show that the normalized axial shear strain estimated at the bone-soft tissue interface is statistically correlated to the bone-soft tissue coefficient of friction. This information may prove useful to better interpret ultrasound elastography results obtained in bone-related applications and, possibly, monitor bone healing.

An Alternative Frictional Boundary Condition for Computational Fluid Dynamics Simulation of Friction Stir Welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Gaoqiang; Feng, Zhili; Zhu, Yucan

For better application of numerical simulation in optimization and design of friction stir welding (FSW), this paper presents a new frictional boundary condition at the tool/workpiece interface for computational fluid dynamics (CFD) modeling of FSW. The proposed boundary condition is based on an implementation of the Coulomb friction model. Using the new boundary condition, the CFD simulation yields non-uniform distribution of contact state over the tool/workpiece interface, as validated by the experimental weld macrostructure. It is found that interfacial sticking state is present over large area at the tool-workpiece interface, while significant interfacial sliding occurs at the shoulder periphery, themore » lower part of pin side, and the periphery of pin bottom. Due to the interfacial sticking, a rotating flow zone is found under the shoulder, in which fast circular motion occurs. The diameter of the rotating flow zone is smaller than the shoulder diameter, which is attributed to the presence of the interfacial sliding at the shoulder periphery. For the simulated welding condition, the heat generation due to friction and plastic deformation makes up 54.4 and 45.6% of the total heat generation rate, respectively. In conclusion, the simulated temperature field is validated by the good agreement to the experimental measurements.« less

Effect of bone-soft tissue friction on ultrasound axial shear strain elastography.

PubMed

Tang, Songyuan; Chaudhry, Anuj; Kim, Namhee; Reddy, J N; Righetti, Raffaella

2017-07-12

Bone-soft tissue friction is an important factor affecting several musculoskeletal disorders, frictional syndromes and the ability of a bone fracture to heal. However, this parameter is difficult to determine using non-invasive imaging modalities, especially in clinical settings. Ultrasound axial shear strain elastography is a non-invasive imaging modality that has been used in the recent past to estimate the bonding between different tissue layers. As most elastography methods, axial shear strain elastography is primarily used in soft tissues. More recently, this technique has been proposed to assess the bone-soft tissue interface. In this paper, we investigate the effect of a variation in bone-soft tissue friction coefficient in the resulting axial shear strain elastograms. Finite element poroelastic models of bone specimens exhibiting different bone-soft tissue friction coefficients were created and mechanically analyzed. These models were then imported to an ultrasound elastography simulation module to assess the presence of axial shear strain patterns. In vitro experiments were performed to corroborate selected simulation results. The results of this study show that the normalized axial shear strain estimated at the bone-soft tissue interface is statistically correlated to the bone-soft tissue coefficient of friction. This information may prove useful to better interpret ultrasound elastography results obtained in bone-related applications and, possibly, monitor bone healing.

An empirically based steady state friction law and implications for fault stability

NASA Astrophysics Data System (ADS)

Spagnuolo, E.; Nielsen, S.; Violay, M.; Di Toro, G.

2016-04-01

Empirically based rate-and-state friction laws (RSFLs) have been proposed to model the dependence of friction forces with slip and time. The relevance of the RSFL for earthquake mechanics is that few constitutive parameters define critical conditions for fault stability (i.e., critical stiffness and frictional fault behavior). However, the RSFLs were determined from experiments conducted at subseismic slip rates (V < 1 cm/s), and their extrapolation to earthquake deformation conditions (V > 0.1 m/s) remains questionable on the basis of the experimental evidence of (1) large dynamic weakening and (2) activation of particular fault lubrication processes at seismic slip rates. Here we propose a modified RSFL (MFL) based on the review of a large published and unpublished data set of rock friction experiments performed with different testing machines. The MFL, valid at steady state conditions from subseismic to seismic slip rates (0.1 µm/s < V < 3 m/s), describes the initiation of a substantial velocity weakening in the 1-20 cm/s range resulting in a critical stiffness increase that creates a peak of potential instability in that velocity regime. The MFL leads to a new definition of fault frictional stability with implications for slip event styles and relevance for models of seismic rupture nucleation, propagation, and arrest.

A Micro-Force Sensor with Slotted-Quad-Beam Structure for Measuring the Friction in MEMS Bearings

PubMed Central

Liu, Huan; Yang, Shuming; Zhao, Yulong; Jiang, Zhuangde; Liu, Yan; Tian, Bian

2013-01-01

Presented here is a slotted-quad-beam structure sensor for the measurement of friction in micro bearings. Stress concentration slots are incorporated into a conventional quad-beam structure to improve the sensitivity of force measurements. The performance comparison between the quad-beam structure sensor and the slotted-quad-beam structure sensor are performed by theoretical modeling and finite element (FE) analysis. A hollow stainless steel probe is attached to the mesa of the sensor chip by a tailor-made organic glass fixture. Concerning the overload protection of the fragile beams, a glass wafer is bonded onto the bottom of sensor chip to limit the displacement of the mesa. The calibration of the packaged device is experimentally performed by a tri-dimensional positioning stage, a precision piezoelectric ceramic and an electronic analytical balance, which indicates its favorable sensitivity and overload protection. To verify the potential of the proposed sensor being applied in micro friction measurement, a measurement platform is established. The output of the sensor reflects the friction of bearing resulting from dry friction and solid lubrication. The results accord with the theoretical modeling and demonstrate that the sensor has the potential application in measuring the micro friction force under stable stage in MEMS machines. PMID:24084112

An Alternative Frictional Boundary Condition for Computational Fluid Dynamics Simulation of Friction Stir Welding

DOE PAGES

Chen, Gaoqiang; Feng, Zhili; Zhu, Yucan; ...

2016-07-11

For better application of numerical simulation in optimization and design of friction stir welding (FSW), this paper presents a new frictional boundary condition at the tool/workpiece interface for computational fluid dynamics (CFD) modeling of FSW. The proposed boundary condition is based on an implementation of the Coulomb friction model. Using the new boundary condition, the CFD simulation yields non-uniform distribution of contact state over the tool/workpiece interface, as validated by the experimental weld macrostructure. It is found that interfacial sticking state is present over large area at the tool-workpiece interface, while significant interfacial sliding occurs at the shoulder periphery, themore » lower part of pin side, and the periphery of pin bottom. Due to the interfacial sticking, a rotating flow zone is found under the shoulder, in which fast circular motion occurs. The diameter of the rotating flow zone is smaller than the shoulder diameter, which is attributed to the presence of the interfacial sliding at the shoulder periphery. For the simulated welding condition, the heat generation due to friction and plastic deformation makes up 54.4 and 45.6% of the total heat generation rate, respectively. In conclusion, the simulated temperature field is validated by the good agreement to the experimental measurements.« less

SPH calculations of asteroid disruptions: The role of pressure dependent failure models

NASA Astrophysics Data System (ADS)

Jutzi, Martin

2015-03-01

We present recent improvements of the modeling of the disruption of strength dominated bodies using the Smooth Particle Hydrodynamics (SPH) technique. The improvements include an updated strength model and a friction model, which are successfully tested by a comparison with laboratory experiments. In the modeling of catastrophic disruptions of asteroids, a comparison between old and new strength models shows no significant deviation in the case of targets which are initially non-porous, fully intact and have a homogeneous structure (such as the targets used in the study by Benz and Asphaug, 1999). However, for many cases (e.g. initially partly or fully damaged targets and rubble-pile structures) we find that it is crucial that friction is taken into account and the material has a pressure dependent shear strength. Our investigations of the catastrophic disruption threshold Q D * as a function of target properties and target sizes up to a few 100 km show that a fully damaged target modeled without friction has a Q D * which is significantly (5-10 times) smaller than in the case where friction is included. When the effect of the energy dissipation due to compaction (pore crushing) is taken into account as well, the targets become even stronger ( Q D * is increased by a factor of 2-3). On the other hand, cohesion is found to have an negligible effect at large scales and is only important at scales ≲ 1 km. Our results show the relative effects of strength, friction and porosity on the outcome of collisions among small (≲ 1000 km) bodies. These results will be used in a future study to improve existing scaling laws for the outcome of collisions (e.g. Leinhardt and Stewart, 2012).

Distinct Element Method modelling of fold-related fractures in a multilayer sequence

NASA Astrophysics Data System (ADS)

Kaserer, Klemens; Schöpfer, Martin P. J.; Grasemann, Bernhard

2017-04-01

Natural fractures have a significant impact on the performance of hydrocarbon systems/reservoirs. In a multilayer sequence, both the fracture density within the individual layers and the type of fracture intersection with bedding contacts are key parameters controlling fluid pathways. In the present study the influence of layer stacking and interlayer friction on fracture density and connectivity within a folded sequence is systematically investigated using 2D Distinct Element Method modelling. Our numerical approach permits forward modelling of both fracture nucleation/propagation/arrest and (contemporaneous) frictional slip along bedding planes in a robust and mechanically sound manner. Folding of the multilayer sequence is achieved by enforcing constant curvature folding by means of a velocity boundary condition at the model base, while a constant overburden pressure is maintained at the model top. The modelling reveals that with high bedding plane friction the multilayer stack behaves mechanically as a single layer so that the neutral surface develops in centre of the sequence and fracture spacing is controlled by the total thickness of the folded sequence. In contrast, low bedding plane friction leads to decoupling of the individual layers (flexural slip folding) so that a neutral surface develops in the centre of each layer and fracture spacing is controlled by the thickness of the individual layers. The low interfacial friction models illustrate that stepping of fractures across bedding planes is a common process, which can however have two contrasting origins: The mechanical properties of the interface cause fracture stepping during fracture propagation. Originally through-going fractures are later offset by interfacial slip during folding. A combination of these two different origins may lead to (apparently) inconsistent fracture offsets across bedding planes within a flexural slip fold.