ERIC Educational Resources Information Center
Goold, Vernell C.
1977-01-01
Numerical control (a technique involving coded, numerical instructions for the automatic control and performance of a machine tool) does not replace fundamental machine tool training. It should be added to the training program to give the student an additional tool to accomplish production rates and accuracy that were not possible before. (HD)
Computerized Numerical Control Curriculum Guide.
ERIC Educational Resources Information Center
Reneau, Fred; And Others
This guide is intended for use in a course in programming and operating a computerized numerical control system. Addressed in the course are various aspects of programming and planning, setting up, and operating machines with computerized numerical control, including selecting manual or computer-assigned programs and matching them with…
A Vocabulary for Numerical Control.
ERIC Educational Resources Information Center
Campbell, Clifton Paul
This glossary presents a standardized nomenclature for numerical control. It defines and describes some 286 technical words, terms, abbreviations, and acronyms which form a specialized vocabulary. The aim of this glossary is to provide a means for arriving at some common understanding of terminology for numerical control technology. Numerous…
Digital numerically controlled oscillator
NASA Technical Reports Server (NTRS)
Cellier, A.; Huey, D. C.; Ma, L. N. (Inventor)
1980-01-01
The frequency and phase of an output signal from an oscillator circuit are controlled with accuracy by a digital input word. Positive and negative alterations in output frequency are both provided for by translating all values of input words so that they are positive. The oscillator reference frequency is corrected only in one direction, by adding phase to the output frequency of the oscillator. The input control word is translated to a single algebraic sign and the digital 1 is added thereto. The translated input control word is then accumulated. A reference clock signal having a frequency at an integer multiple of the desired frequency of the output signal is generated. The accumulated control word is then compared with a threshold level. The output signal is adjusted in a single direction by dividing the frequency of the reference clock signal by a first integer or by an integer different from the first integer.
The Language of Numerical Control: A Glossary.
ERIC Educational Resources Information Center
Campbell, Clifton Paul
Numerical control, a technique for automatically controlling equipment, is a system in which machine actions are determined by symbolic data recorded on a suitable media. This glossary of standardized nomenclature for numerical control defines and describes some 286 technical words and terms. Numerous entries are defined and described as they…
Descriptive Report on Numerically Controlled Equipment.
ERIC Educational Resources Information Center
Campbell, Clifton P.
This report presents descriptive information on numerically controlled operational devises. The information is designed for the education and training community, manufacturers, supervisors, machine operators, and others who do not have an extensive technical background in numerical control. In the first of three chapters, numerical control…
Handbook on Numerically Controlled Operational Devices.
ERIC Educational Resources Information Center
Campbell, Clifton P.
This handbook presents an organized set of descriptive information on numerically controlled operational devices. The information is intended for those involved in industry and technical education and to contribute to the knowledge of numerical control technology. It is also intended for supervisors, manufacturers, machine operators, and others…
An Introduction to Numerical Control. Problems for Numerical Control Part Programming.
ERIC Educational Resources Information Center
Campbell, Clifton P.
This combination text and workbook is intended to introduce industrial arts students to numerical control part programming. Discussed in the first section are the impact of numerical control, training efforts, numerical control in established programs, related information for drafting, and the Cartesian Coordinate System and dimensioning…
Value-Engineering Review for Numerical Control
NASA Technical Reports Server (NTRS)
Warner, J. L.
1984-01-01
Selecting parts for conversion from conventional machining to numerical control, value-engineering review performed for every part to identify potential changes to part design that result in increased production efficiency.
Numerically Controlled Machine Tools and Worker Skills.
ERIC Educational Resources Information Center
Keefe, Jeffrey H.
1991-01-01
Analysis of data from "Industry Wage Surveys of Machinery Manufacturers" on the skill levels of 57 machining jobs found that introduction of numerically controlled machine tools has resulted in a very small reduction in skill levels or no significant change, supporting neither the deskilling argument nor argument that skill levels increase with…
Multiaxis Computer Numerical Control Internship Report
ERIC Educational Resources Information Center
Rouse, Sharon M.
2012-01-01
(Purpose) The purpose of this paper was to examine the issues associated with bringing new technology into the classroom, in particular, the vocational/technical classroom. (Methodology) A new Haas 5 axis vertical Computer Numerical Control machining center was purchased to update the CNC machining curriculum at a community college and the process…
A History of Computer Numerical Control.
ERIC Educational Resources Information Center
Haggen, Gilbert L.
Computer numerical control (CNC) has evolved from the first significant counting method--the abacus. Babbage had perhaps the greatest impact on the development of modern day computers with his analytical engine. Hollerith's functioning machine with punched cards was used in tabulating the 1890 U.S. Census. In order for computers to become a…
Computerized Numerical Control Test Item Bank.
ERIC Educational Resources Information Center
Reneau, Fred; And Others
This guide contains 285 test items for use in teaching a course in computerized numerical control. All test items were reviewed, revised, and validated by incumbent workers and subject matter instructors. Items are provided for assessing student achievement in such aspects of programming and planning, setting up, and operating machines with…
Adapting Inspection Data for Computer Numerical Control
NASA Technical Reports Server (NTRS)
Hutchison, E. E.
1986-01-01
Machining time for repetitive tasks reduced. Program converts measurements of stub post locations by coordinate-measuring machine into form used by numerical-control computer. Work time thus reduced by 10 to 15 minutes for each post. Since there are 600 such posts on each injector, time saved per injector is 100 to 150 hours. With modifications this approach applicable to machining of many precise holes on large machine frames and similar objects.
Research on ARM Numerical Control System
NASA Astrophysics Data System (ADS)
Wei, Xu; JiHong, Chen
Computerized Numerical Control (CNC) machine tools is the foundation of modern manufacturing systems, whose advanced digital technology is the key to solve the problem of sustainable development of machine tool manufacturing industry. The paper is to design CNC system embedded on ARM and indicates the hardware design and the software systems supported. On the hardware side: the driving chip of the motor control unit, as the core of components, is MCX314AL of DSP motion control which is developed by NOVA Electronics Co., Ltd. of Japan. It make convenient to control machine because of its excellent performance, simple interface, easy programming. On the Software side, the uC/OS-2 is selected as the embedded operating system of the open source, which makes a detailed breakdown of the modules of the CNC system. Those priorities are designed according to their actual requirements. The ways of communication between the module and the interrupt response are so different that it guarantees real-time property and reliability of the numerical control system. Therefore, it not only meets the requirements of the current social precision machining, but has good man-machine interface and network support to facilitate a variety of craftsmen use.
Numerically controlled oscillator for the Fermilab booster
Crisp, J.L.; Ducar, R.J.
1989-04-01
In order to improve the stability of the Fermilab Booster low level rf system, a numerically controlled oscillator system is being constructed. Although the system has not been implemented to date, the design is outlined in this paper. The heart of the new system consists of a numerically synthesized frequency generator manufactured by the Sciteq Company. The 3 Ghz/sec rate and 30 to 53 MHz range of the Booster frequency program required the design of a CAMAC based, fast-cycling (1 MHz), 65K X 32 bit, digital function generator. A 1 MHz digital adder and 12 bit analog to digital converter will be used to correct small program errors by phase locking the oscillator to the beam. 6 refs., 1 fig.
Machine Shop. Module 8: CNC (Computerized Numerical Control). Instructor's Guide.
ERIC Educational Resources Information Center
Crosswhite, Dwight
This document consists of materials for a five-unit course on the following topics: (1) safety guidelines; (2) coordinates and dimensions; (3) numerical control math; (4) programming for numerical control machines; and (5) setting and operating the numerical control machine. The instructor's guide begins with a list of competencies covered in the…
Numerical Issues for Circulation Control Calculations
NASA Technical Reports Server (NTRS)
Swanson, Roy C., Jr.; Rumsey, Christopher L.
2006-01-01
Steady-state and time-accurate two-dimensional solutions of the compressible Reynolds-averaged Navier- Stokes equations are obtained for flow over the Lockheed circulation control (CC) airfoil and the General Aviation CC (GACC) airfoil. Numerical issues in computing circulation control flows such as the effects of grid resolution, boundary and initial conditions, and unsteadiness are addressed. For the Lockheed CC airfoil computed solutions are compared with detailed experimental data, which include velocity and Reynolds stress profiles. Three turbulence models, having either one or two transport equations, are considered. Solutions are obtained on a sequence of meshes, with mesh refinement primarily concentrated on the airfoil circular trailing edge. Several effects related to mesh refinement are identified. For example, sometimes sufficient mesh resolution can exclude nonphysical solutions, which can occur in CC airfoil calculations. Also, sensitivities of the turbulence models with mesh refinement are discussed. In the case of the GACC airfoil the focus is on the difference between steady-state and time-accurate solutions. A specific objective is to determine if there is self-excited vortex shedding from the jet slot lip.
Numerically controlled oscillators with hybrid function generators.
Jainiszewski, Ireneusz; Hoppe, Bernhard; Meuth, Hermann
2002-07-01
Numerically controlled oscillators (NCOs), with a hybrid scheme of both look-up tables (LUT) and coordinate transformation digital computer (CORDIC) algorithms for a hardware efficient, high performance sine/cosine function generation are investigated. This scheme combines fast access and power efficiency of reasonably sized LUTs, and arbitrary precision obtainable from a rigorous iteration algorithm. Systematic studies using hardware description language (HDL) models and synthesis lead to optimum LUT/CORDIC ratios, which minimize power consumption and silicon area for a given operating clock frequency. First order error models are presented as guidelines for choosing internal NCO parameters. The NCO accuracy is tested with HDL simulations for all algorithmic states to limit output errors to 1 least significant bit (LSB) and by spectra derived from discrete Fourier transform (DFT) for typical frequency inputs f, resulting in a signal to noise ratio (SNR) of better than 100 dB for an amplitude word length AW of 16 Bit. Two benchmark designs were adopted for the two clock frequencies 200 MHz and 20 MHz, as "high" and "moderate" performance, respectively. The NCO models are synthesized in a 0.35 microm CMOS standard cell target technology and optimized to actually achieve after layout maximum clock frequencies exceeding 310 MHz, i.e., signal frequencies of up to 100 MHz. PMID:12152954
Numerically Controlled Machining Of Wind-Tunnel Models
NASA Technical Reports Server (NTRS)
Kovtun, John B.
1990-01-01
New procedure for dynamic models and parts for wind-tunnel tests or radio-controlled flight tests constructed. Involves use of single-phase numerical control (NC) technique to produce highly-accurate, symmetrical models in less time.
Numerical Control Associated Jobs: State-Wide Survey.
ERIC Educational Resources Information Center
Morton, J. B.; Christensen, Harold
In order to get a better view of the demand for secondary trained numerical control personnel and upgraded adult machinists, a questionnaire was sent to machine shops throughout the State of Oklahoma. The questionnaire was designed to show the present level of employment of numerical control personnel, the anticipated use of retraining facilities,…
Numerical Investigation of Plasma Active Flow Control
NASA Astrophysics Data System (ADS)
Sun, Baigang; Li, Feng; Zhang, Shanshan; Wang, Jingyu; Zhang, Lijuan; Zhao, Erlei
2010-12-01
Based on the theory of EHD (electronhydrodynamic), a simplified volume force model is applied to simulation to analyze the traits of plasma flow control in flow field, in which the cold plasma is generated by a DBD (dielectric-barrier-discharge) actuator. With the para-electric action of volume force in electric field, acceleration characteristics of the plasma flow are investigated for different excitation intensities of RF (radio frequency) power for the actuator. Furthermore, the plasma acceleration leads to an asymmetric distribution of flow field, and hence induces the deflection of jet plume, then results in a significant deflection angle of 6.26° thrust-vectoring effect. It appears that the plasma flow control technology is a new tentative method for the thrust-vectoring control of a space vehicle.
Operating System For Numerically Controlled Milling Machine
NASA Technical Reports Server (NTRS)
Ray, R. B.
1992-01-01
OPMILL program is operating system for Kearney and Trecker milling machine providing fast easy way to program manufacture of machine parts with IBM-compatible personal computer. Gives machinist "equation plotter" feature, which plots equations that define movements and converts equations to milling-machine-controlling program moving cutter along defined path. System includes tool-manager software handling up to 25 tools and automatically adjusts to account for each tool. Developed on IBM PS/2 computer running DOS 3.3 with 1 MB of random-access memory.
SNARC Struggles: Instant Control over Spatial-Numerical Associations
ERIC Educational Resources Information Center
Pfister, Roland; Schroeder, Philipp A.; Kunde, Wilfried
2013-01-01
Numbers and space are tightly linked--a phenomenon that is referred to as the spatial-numerical association of response codes (SNARC) effect (Dehaene, Bossini, & Giraux, 1993). The present study investigates how quickly and flexibly the behavioral impact of such spatial-numerical associations can be controlled. Participants performed a parity…
Numerical evaluation of the performance of active noise control systems
NASA Technical Reports Server (NTRS)
Mollo, C. G.; Bernhard, R. J.
1990-01-01
This paper presents a generalized numerical technique for evaluating the optimal performance of active noise controllers. In this technique, the indirect BEM numerical procedures are used to derive the active noise controllers for optimal control of enclosed harmonic sound fields where the strength of the noise sources or the description of the enclosure boundary may not be known. The performance prediction for a single-input single-output system is presented, together with the analysis of the stability and observability of an active noise-control system employing detectors. The numerical procedures presented can be used for the design of both the physical configuration and the electronic components of the optimal active noise controller.
Differentiated control of web traffic: a numerical analysis
NASA Astrophysics Data System (ADS)
Guo, Liang; Matta, Ibrahim
2002-07-01
Internet measurements show that the size distribution of Web-based transactions is usually very skewed; a few large requests constitute most of the total traffic. Motivated by the advantages of scheduling algorithms which favor short jobs, we propose to perform differentiated control over Web-based transactions to give preferential service to short web requests. The control is realized through service semantics provided by Internet Traffic Managers, a Diffserv-like architecture. To evaluate the performance of such a control system, it is necessary to have a fast but accurate analytical method. To this end, we model the Internet as a time-shared system and propose a numerical approach which utilizes Kleinrock's conservation law to solve the model. The numerical results are shown to match well those obtained by packet-level simulation, which runs orders of magnitude slower than our numerical method.
A Numerical Optimization Approach for Tuning Fuzzy Logic Controllers
NASA Technical Reports Server (NTRS)
Woodard, Stanley E.; Garg, Devendra P.
1998-01-01
This paper develops a method to tune fuzzy controllers using numerical optimization. The main attribute of this approach is that it allows fuzzy logic controllers to be tuned to achieve global performance requirements. Furthermore, this approach allows design constraints to be implemented during the tuning process. The method tunes the controller by parameterizing the membership functions for error, change-in-error and control output. The resulting parameters form a design vector which is iteratively changed to minimize an objective function. The minimal objective function results in an optimal performance of the system. A spacecraft mounted science instrument line-of-sight pointing control is used to demonstrate results.
Computer-Numerical-Control and the EMCO Compact 5 Lathe.
ERIC Educational Resources Information Center
Mullen, Frank M.
This laboratory manual is intended for use in teaching computer-numerical-control (CNC) programming using the Emco Maier Compact 5 Lathe. Developed for use at the postsecondary level, this material contains a short introduction to CNC machine tools. This section covers CNC programs, CNC machine axes, and CNC coordinate systems. The following…
Computer numerical control grinding of spiral bevel gears
NASA Technical Reports Server (NTRS)
Scott, H. Wayne
1991-01-01
The development of Computer Numerical Control (CNC) spiral bevel gear grinding has paved the way for major improvement in the production of precision spiral bevel gears. The object of the program was to decrease the setup, maintenance of setup, and pattern development time by 50 percent of the time required on conventional spiral bevel gear grinders. Details of the process are explained.
Computer used to program numerically controlled milling machine
NASA Technical Reports Server (NTRS)
Harris, T. C.
1967-01-01
Computer program automatically directs a numerically controlled milling machine through a series of cutting and trimming actions. It accepts engineering data points, passes smooth curve segments through the points, breaks the resulting curves into a series of closely spaced points, and transforms these points into the form required by the mechanism.
Integrated product definition representation for agile numerical control applications
Simons, W.R. Jr.; Brooks, S.L.; Kirk, W.J. III; Brown, C.W.
1994-11-01
Realization of agile manufacturing capabilities for a virtual enterprise requires the integration of technology, management, and work force into a coordinated, interdependent system. This paper is focused on technology enabling tools for agile manufacturing within a virtual enterprise specifically relating to Numerical Control (N/C) manufacturing activities and product definition requirements for these activities.
Program Helps Specify Paths For Numerically Controlled Tools
NASA Technical Reports Server (NTRS)
Premack, Timothy; Poland, James, Jr.
1996-01-01
ESDAPT computer program provides graphical programming environment for developing APT (Automatically Programmed Tool) programs for controlling numerically controlled machine tools. Establishes graphical user interface providing user with APT syntax-sensitive text-editing subprogram and windows for displaying geometry and tool paths. APT geometry statements also created by use of menus and screen picks. Written in C language, yacc, lex, and XView for use on Sun4-series computers running SunOS.
Numerical and experimental exploration of phase control of chaos.
Zambrano, Samuel; Allaria, Enrico; Brugioni, Stefano; Leyva, Immaculada; Meucci, Riccardo; Sanjuán, Miguel A F; Arecchi, Fortunato T
2006-03-01
A well-known method to suppress chaos in a periodically forced chaotic system is to add a harmonic perturbation. The phase control of chaos scheme uses the phase difference between a small added harmonic perturbation and the main driving to suppress chaos, leading the system to different periodic orbits. Using the Duffing oscillator as a paradigm, we present here an in-depth study of this technique. A thorough numerical exploration has been made focused in the important role played by the phase, from which new interesting patterns in parameter space have appeared. On the other hand, our novel experimental implementation of phase control in an electronic circuit confirms both the well-known features of this method and the new ones detected numerically. All this may help in future implementations of phase control of chaos, which is globally confirmed here to be robust and easy to implement experimentally. PMID:16599742
Numerical simulation of transition control in boundary layers
NASA Astrophysics Data System (ADS)
Laurien, E.; Kleiser, L.
The transition process from laminar to turbulent boundary layers is simulated by numerical integration of the 3D incompressible Navier-Stokes equations. Spatially periodic wave disturbances in a parallel Blasius flow are assumed. A spectral method with real-space Chebyshev collocation in the normal direction is employed. Both the classical K-type and the subharmonic type of transition are investigated. Good agreement with measurements and flow visualizations of transition experiments is obtained. Control of transition by wave superposition is simulated using periodic wall suction/blowing. It is shown that 2D control works well at an early stage but fails after significant 3D disturbances have developed.
Numerical investigation of closed-loop control for Hall accelerators
Barral, S.; Miedzik, J.
2011-01-01
Low frequency discharge current oscillations in Hall accelerators are conventionally damped with external inductor-capacitor (LC) or resistor-inductor-capacitor (RLC) networks. The role of such network in the stabilization of the plasma discharge is investigated with a numerical model and the potential advantages of proportional-integral-derivative (PID) closed-loop control over RLC networks are subsequently assessed using either discharge voltage or magnetic field modulation. Simulations confirm the reduction of current oscillations in the presence of a RLC network, but suggest that PID control could ensure nearly oscillation-free operation with little sensitivity toward the PID settings.
Teaching Thermal Hydraulics & Numerical Methods: An Introductory Control Volume Primer
Lucas, D.S.
2004-10-03
This paper covers the basics of the implementation of the control volume method in the context of the Homogeneous Equilibrium Model (HEM)(T/H) code using the conservation equations of mass, momentum, and energy. This primer uses the advection equation as a template. The discussion will cover the basic equations of the control volume portion of the course in the primer, which includes the advection equation, numerical methods, along with the implementation of the various equations via FORTRAN into computer programs and the final result for a three equation HEM code and its validation.
Aspects of Numerical Simulation of Circulation Control Airfoils
NASA Technical Reports Server (NTRS)
Swanson, R. C.; Rumsey, C. L.; Anders, S. G.
2005-01-01
The mass-averaged compressible Navier-Stokes equations are solved for circulation control airfoils. Numerical solutions are computed with a multigrid method that uses an implicit approximate factorization smoother. The effects of flow conditions (e.g., free-stream Mach number, angle of attack, momentum coefficient) and mesh on the prediction of circulation control airfoil flows are considered. In addition, the impact of turbulence modeling, including curvature effects and modifications to reduce eddy viscosity levels in the wall jet (i.e., Coanda flow), is discussed. Computed pressure distributions are compared with available experimental data.
Numerical Studies of a Fluidic Diverter for Flow Control
NASA Technical Reports Server (NTRS)
Gokoglu, Suleyman A.; Kuczmarski, Maria A.; Culley, Dennis E.; Raghu, Surya
2009-01-01
The internal flow structure in a specific fluidic diverter is studied over a range from low subsonic to sonic inlet conditions by a time-dependent numerical analysis. The understanding will aid in the development of fluidic diverters with minimum pressure losses and advanced designs of flow control actuators. The velocity, temperature and pressure fields are calculated for subsonic conditions and the self-induced oscillatory behavior of the flow is successfully predicted. The results of our numerical studies have excellent agreement with our experimental measurements of oscillation frequencies. The acoustic speed in the gaseous medium is determined to be a key factor for up to sonic conditions in governing the mechanism of initiating the oscillations as well as determining its frequency. The feasibility of employing plasma actuation with a minimal perturbation level is demonstrated in steady-state calculations to also produce oscillation frequencies of our own choosing instead of being dependent on the fixed-geometry fluidic device.
Numerical Simulations of Plasma Based Flow Control Applications
NASA Technical Reports Server (NTRS)
Suzen, Y. B.; Huang, P. G.; Jacob, J. D.; Ashpis, D. E.
2005-01-01
A mathematical model was developed to simulate flow control applications using plasma actuators. The effects of the plasma actuators on the external flow are incorporated into Navier Stokes computations as a body force vector. In order to compute this body force vector, the model solves two additional equations: one for the electric field due to the applied AC voltage at the electrodes and the other for the charge density representing the ionized air. The model is calibrated against an experiment having plasma-driven flow in a quiescent environment and is then applied to simulate a low pressure turbine flow with large flow separation. The effects of the plasma actuator on control of flow separation are demonstrated numerically.
Numerical optimization of laser fields to control molecular orientation
Ben Haj-Yedder, A.; Auger, A.; Dion, C.M.; Cances, E.; Le Bris, C.; Keller, A.; Atabek, O.
2002-12-01
A thorough numerical illustration of an optimal control scenario dealing with the laser-induced orientation of a diatomic molecule (LiF) is presented. Special emphasis is laid on the definition of the various targets dealing with different orientation characteristics, identified in terms of maximum efficiency (i.e., molecular axis direction closest to the direction of the laser polarization vector), maximum duration (i.e., the time interval during which this orientation is maintained), or of a compromise between efficiency and duration. Excellent postpulse orientation is achieved by sudden, intense pulses. Thermal effects are also studied with an extension of the control scenarios to Boltzmann averaged orientation dynamics at T=5 K.
Interferometric correction system for a numerically controlled machine
Burleson, Robert R.
1978-01-01
An interferometric correction system for a numerically controlled machine is provided to improve the positioning accuracy of a machine tool, for example, for a high-precision numerically controlled machine. A laser interferometer feedback system is used to monitor the positioning of the machine tool which is being moved by command pulses to a positioning system to position the tool. The correction system compares the commanded position as indicated by a command pulse train applied to the positioning system with the actual position of the tool as monitored by the laser interferometer. If the tool position lags the commanded position by a preselected error, additional pulses are added to the pulse train applied to the positioning system to advance the tool closer to the commanded position, thereby reducing the lag error. If the actual tool position is leading in comparison to the commanded position, pulses are deleted from the pulse train where the advance error exceeds the preselected error magnitude to correct the position error of the tool relative to the commanded position.
Teaching Thermal Hydraulics & Numerical Methods: An Introductory Control Volume Primer
D. S. Lucas
2004-10-01
A graduate level course for Thermal Hydraulics (T/H) was taught through Idaho State University in the spring of 2004. A numerical approach was taken for the content of this course since the students were employed at the Idaho National Laboratory and had been users of T/H codes. The majority of the students had expressed an interest in learning about the Courant Limit, mass error, semi-implicit and implicit numerical integration schemes in the context of a computer code. Since no introductory text was found the author developed notes taught from his own research and courses taught for Westinghouse on the subject. The course started with a primer on control volume methods and the construction of a Homogeneous Equilibrium Model (HEM) (T/H) code. The primer was valuable for giving the students the basics behind such codes and their evolution to more complex codes for Thermal Hydraulics and Computational Fluid Dynamics (CFD). The course covered additional material including the Finite Element Method and non-equilibrium (T/H). The control volume primer and the construction of a three-equation (mass, momentum and energy) HEM code are the subject of this paper . The Fortran version of the code covered in this paper is elementary compared to its descendants. The steam tables used are less accurate than the available commercial version written in C Coupled to a Graphical User Interface (GUI). The Fortran version and input files can be downloaded at www.microfusionlab.com.
Direct numerical simulation of vector-controlled free jets
NASA Astrophysics Data System (ADS)
Tsujimoto, K.; Ao, K.; Shakouchi, T.; Ando, T.
2011-12-01
We conduct DNS (direct numerical simulation) of vector controlled free jets. The inflow velocity of jet is periodically oscillated perpendicular to the jet axis. In order to realize the high accurate computation, a discretization in space is performed with hybrid scheme in which Fourier spectral and 6th order compact scheme are adopted. From visualized instantaneous vortex structures, it is found that the flow pattern considerably changes according to the oscillating frequency, i.e., according to the increasing the frequency, wave, bifurcating and flapping modes appear in turn. In order to quantify mixing efficiency under the vector control, as the mixing measure, statistical entropy is investigated. Compared to the uncontrolled jet, the mixing efficiency is improved in order of wavy, flapping and bifurcating modes. Thus the vector control can be expected for the improvement of mixing efficiency. Further to make clear the reason for the mixing enhancement, Snapshot POD and DMD method are applied. The primary flow structures under the vector control are demonstrated.
LQR Control of Thin Shell Dynamics: Formulation and Numerical Implementation
NASA Technical Reports Server (NTRS)
delRosario, R. C. H.; Smith, R. C.
1997-01-01
A PDE-based feedback control method for thin cylindrical shells with surface-mounted piezoceramic actuators is presented. Donnell-Mushtari equations modified to incorporate both passive and active piezoceramic patch contributions are used to model the system dynamics. The well-posedness of this model and the associated LQR problem with an unbounded input operator are established through analytic semigroup theory. The model is discretized using a Galerkin expansion with basis functions constructed from Fourier polynomials tensored with cubic splines, and convergence criteria for the associated approximate LQR problem are established. The effectiveness of the method for attenuating the coupled longitudinal, circumferential and transverse shell displacements is illustrated through a set of numerical examples.
Multiresolution strategies for the numerical solution of optimal control problems
NASA Astrophysics Data System (ADS)
Jain, Sachin
There exist many numerical techniques for solving optimal control problems but less work has been done in the field of making these algorithms run faster and more robustly. The main motivation of this work is to solve optimal control problems accurately in a fast and efficient way. Optimal control problems are often characterized by discontinuities or switchings in the control variables. One way of accurately capturing the irregularities in the solution is to use a high resolution (dense) uniform grid. This requires a large amount of computational resources both in terms of CPU time and memory. Hence, in order to accurately capture any irregularities in the solution using a few computational resources, one can refine the mesh locally in the region close to an irregularity instead of refining the mesh uniformly over the whole domain. Therefore, a novel multiresolution scheme for data compression has been designed which is shown to outperform similar data compression schemes. Specifically, we have shown that the proposed approach results in fewer grid points in the grid compared to a common multiresolution data compression scheme. The validity of the proposed mesh refinement algorithm has been verified by solving several challenging initial-boundary value problems for evolution equations in 1D. The examples have demonstrated the stability and robustness of the proposed algorithm. The algorithm adapted dynamically to any existing or emerging irregularities in the solution by automatically allocating more grid points to the region where the solution exhibited sharp features and fewer points to the region where the solution was smooth. Thereby, the computational time and memory usage has been reduced significantly, while maintaining an accuracy equivalent to the one obtained using a fine uniform mesh. Next, a direct multiresolution-based approach for solving trajectory optimization problems is developed. The original optimal control problem is transcribed into a
Design of a new high precision computer numerical control
Sweeney, D.J.; Weinert, G.F.
1988-06-23
The purpose of this project is to produce a generic high precision computer numerical controller (CNC) for use on microinch- and sub-microinch-resolution machine tools at the Lawrence Livermore National Laboratory. In order to fully utilize the potential of these machine tools, the CNC must include the ability to use multiple feedback sensors on each machine axis, incorporate corrections for quasistatic geometric errors (such as straightness, and squareness), be able to function over a relatively large range of motion (in excess of 60 inches per axis), and be able to produce motion updates at a rate sufficient to take advantage of the high bandwidth of the servo systems. At present, no commercially available CNC can presently meet all of the resolution, feed rate, and length of travel requirements of these machines. In order to minimize the complexity of the system, and thereby increase its reliability and maintainability, the programming was done in a high level language. The number of processors was kept as small as possible while still maintaining the performance requirements. We also used commercially available hardware in preference to building, in order to increase both reliability and maintainability. Special emphasis was given to making the CNC's operator interface as friendly as possible. We have completed a prototype control. We plan to install and test it in 1988. 4 figs.
Controlling Reflections from Mesh Refinement Interfaces in Numerical Relativity
NASA Technical Reports Server (NTRS)
Baker, John G.; Van Meter, James R.
2005-01-01
A leading approach to improving the accuracy on numerical relativity simulations of black hole systems is through fixed or adaptive mesh refinement techniques. We describe a generic numerical error which manifests as slowly converging, artificial reflections from refinement boundaries in a broad class of mesh-refinement implementations, potentially limiting the effectiveness of mesh- refinement techniques for some numerical relativity applications. We elucidate this numerical effect by presenting a model problem which exhibits the phenomenon, but which is simple enough that its numerical error can be understood analytically. Our analysis shows that the effect is caused by variations in finite differencing error generated across low and high resolution regions, and that its slow convergence is caused by the presence of dramatic speed differences among propagation modes typical of 3+1 relativity. Lastly, we resolve the problem, presenting a class of finite-differencing stencil modifications which eliminate this pathology in both our model problem and in numerical relativity examples.
Design analysis for the control and drive retrofit of a numerically controlled lathe
Cotter, S.L.
1980-01-01
A system approach to the retrofit of a numerically controlled two-axis lathe was taken to identify component function and interrelation. The dynamic system of the motor and machine was modeled and parameter identification experiments were done. This model, in state equation form, was used with the parameters data as the basis of a digital simulation of the system. From this and further analysis of the control characteristics, recommendations for component selection were presented.
Numerical modeling of active separation control by synthetic jets
NASA Astrophysics Data System (ADS)
Aram, Shawn
Zero-Net Mass-Flux (ZNMF) actuators or synthetic jet actuators are versatile micro scale devices with numerous applications in the field of fluid mechanics. The primary focus of the current work is to use time-accurate simulations to study the interaction of these jets with cross flows and to optimize their performance for the control of boundary layer separation. This study consists of four parts. In the first part, a class of phenomenology-based models is proposed to reproduce the flow associated with synthetic jets in grazing flows and simplify the task of ZNMF-based flow control simulations. The proposed models have a non-uniform jet velocity profile with only two spatial degrees of freedom and a uniform slip velocity on the slot-flow boundary. A comparison of key integral quantities associated with the momentum, energy and vorticity fluxes shows that the models with a non-uniform jet velocity during the expulsion phase and uniform jet velocity during the ingestion phase can predict these quantities with good accuracy, whereas a simple plug flow model with a zero slip and uniform jet velocity under-predicts these three quantities during the expulsion phase. Based on our initial analysis, three of the simplest models are selected for further study, including an assessment of their performance for a canonical separated flow at different forcing frequencies. A key finding is that a simple plug-flow type model can predict incorrect trends for separation reduction with the jet frequency. A preliminary attempt is also made to provide empirical closure to these models. The effect of synthetic jets orientation on its interaction with a zero pressure gradient laminar boundary layer is explored in the second part. A rectangular slot is chosen in this study and streamwise and spanwise orientations of this slot are examined. The orientation of the slot is found to have a significant impact on its interaction with the boundary layer. The dominant feature in the streamwise
Numerical controlled polishing, continued force wear and part correction experiments
Hannah, P.R.; Day, R.D.; Hatch, D.J.; McClure, E.R.
1994-09-01
This abstract reports the near completion of the first phase of this program. It is the aim of this program to provide the operator of a N/C diamond turning machine or N/C grinding machine (jig grinder) with the wear characteristics necessary to achieve uniform material removal. The second phase of this program addresses a different problem, although solving this problem is highly dependent on the results of the first phase. Diamond turned, or any lathe turned surface, exhibits regular tool marks due to the tool passing over the surface being cut. Changes in depth of cut, feed rate and work rpm will change the character of these groves, but will not eliminate them. Optical surfaces produced by this process exhibit increased scattering as the light wavelength decreases limiting their use; at least for optical purposes, to IR and some visible applications. Utilizing wear information gathered in the first part of this program we will attempt to reduce these residual tool marks by polishing. The polishing of diamond turned surfaces is not new. Diamond turned metal surfaces, especially in electroless nickel and high phosphorus nickel electroplate have been polished to improve their scatter characteristics. What we believe is unique is the use of a spherical wheel, rotating on axis and being moved over the part in a prescribed manner by numerical control. Over the past year we have made some major changes in our polishing methods and procedures. We have listed below these changes, as a refresher for the reader as to our previous procedures. These changes will be addressed in the body of the text.
A multilevel control system for the large space telescope. [numerical analysis/optimal control
NASA Technical Reports Server (NTRS)
Siljak, D. D.; Sundareshan, S. K.; Vukcevic, M. B.
1975-01-01
A multilevel scheme was proposed for control of Large Space Telescope (LST) modeled by a three-axis-six-order nonlinear equation. Local controllers were used on the subsystem level to stabilize motions corresponding to the three axes. Global controllers were applied to reduce (and sometimes nullify) the interactions among the subsystems. A multilevel optimization method was developed whereby local quadratic optimizations were performed on the subsystem level, and global control was again used to reduce (nullify) the effect of interactions. The multilevel stabilization and optimization methods are presented as general tools for design and then used in the design of the LST Control System. The methods are entirely computerized, so that they can accommodate higher order LST models with both conceptual and numerical advantages over standard straightforward design techniques.
Classical oscillators in the control of quantum tunneling: Numerical experiments
NASA Astrophysics Data System (ADS)
Kar, Susmita; Bhattacharyya, S. P.
2016-06-01
The dynamics of a classical anharmonic oscillator is exploited to control the tunneling dynamics of a quantum particle to which the classical oscillator is coupled. The mixed quantum classical problem is investigated at a mean-field like level. The anharmonic strength (λ) , particle mass (Mc) and harmonic stiffness (ωc) of the classical controller are explored as possible control parameters for the tunneling dynamics. The strength, the type of coupling between the quantum system and classical controller and the effective frequency of the controller emerge as crucial factors in shaping the nature and extent of the control. A whole spectrum of possibilities starting from enhancement, suppression to complete destruction of tunneling emerge depending on values assigned to the control parameters, the type of coupling and the control configuration used. When classical controller is replaced by a quantum controller, the control landscape becomes much simpler.
Numerical research of the optimal control problem in the semi-Markov inventory model
Gorshenin, Andrey K.
2015-03-10
This paper is devoted to the numerical simulation of stochastic system for inventory management products using controlled semi-Markov process. The results of a special software for the system’s research and finding the optimal control are presented.
ERIC Educational Resources Information Center
Sinn, John W.
This instructional manual contains five learning activity packets for use in a workshop on computer numerical control for computer-aided manufacturing. The lessons cover the following topics: introduction to computer-aided manufacturing, understanding the lathe, using the computer, computer numerically controlled part programming, and executing a…
Technical Report on Occupations in Numerically Controlled Metal-Cutting Machining.
ERIC Educational Resources Information Center
Manpower Administration (DOL), Washington, DC. U.S. Employment Service.
At the present time, only 5 percent of the short-run metal-cutting machining in the United States is done by numerically controlled machined tools, but within the next decade it is expected to increase by 50 percent. Numerically controlled machines use taped data which is changed into instructions and directs the machine to do certain steps…
Numerical Modeling of Active Flow Control in a Boundary Layer Ingesting Offset Inlet
NASA Technical Reports Server (NTRS)
Allan, Brian G.; Owens, Lewis R.; Berrier, Bobby L.
2004-01-01
This investigation evaluates the numerical prediction of flow distortion and pressure recovery for a boundary layer ingesting offset inlet with active flow control devices. The numerical simulations are computed using a Reynolds averaged Navier-Stokes code developed at NASA. The numerical results are validated by comparison to experimental wind tunnel tests conducted at NASA Langley Research Center at both low and high Mach numbers. Baseline comparisons showed good agreement between numerical and experimental results. Numerical simulations for the inlet with passive and active flow control also showed good agreement at low Mach numbers where experimental data has already been acquired. Numerical simulations of the inlet at high Mach numbers with flow control jets showed an improvement of the flow distortion. Studies on the location of the jet actuators, for the high Mach number case, were conducted to provide guidance for the design of a future experimental wind tunnel test.
Numerical experiments on the stability of controlled boundary layers
NASA Technical Reports Server (NTRS)
Zang, Thomas A.; Hussaini, M. Y.
1988-01-01
Nonlinear simulations are presented for instability and transition in parallel water boundary layers subjected to pressure gradient, suction, or heating control. In the nonlinear regime, finite amplitude, 2-D Tollmein-Schlichting waves grow faster than is predicted by linear theory. Moreover, this discrepancy is greatest in the case of heating control. Likewise, heating control is found to be the least effective in delaying secondary instabilities of both the fundamental and subharmonic type. Flow field details (including temperature profiles) are presented for both the uncontrolled boundary layer and the heated boundary layer.
A numerical approach to controller design for the ACES facility
NASA Technical Reports Server (NTRS)
Frazier, W. Garth; Irwin, R. Dennis
1993-01-01
In recent years the employment of active control techniques for improving the performance of systems involving highly flexible structures has become a topic of considerable research interest. Most of these systems are quite complicated, using multiple actuators and sensors, and possessing high order models. The majority of analytical controller synthesis procedures capable of handling multivariable systems in a systematic way require considerable insight into the underlying mathematical theory to achieve a successful design. This insight is needed in selecting the proper weighting matrices or weighting functions to cast what is naturally a multiple constraint satisfaction problem into an unconstrained optimization problem. Although designers possessing considerable experience with these techniques have a feel for the proper choice of weights, others may spend a significant amount of time attempting to find an acceptable solution. Another disadvantage of such procedures is that the resulting controller has an order greater than or equal to that of the model used for the design. Of course, the order of these controllers can often be reduced, but again this requires a good understanding of the theory involved.
Numerical Simulation of Fluidic Actuators for Flow Control Applications
NASA Technical Reports Server (NTRS)
Vasta, Veer N.; Koklu, Mehti; Wygnanski, Israel L.; Fares, Ehab
2012-01-01
Active flow control technology is finding increasing use in aerospace applications to control flow separation and improve aerodynamic performance. In this paper we examine the characteristics of a class of fluidic actuators that are being considered for active flow control applications for a variety of practical problems. Based on recent experimental work, such actuators have been found to be more efficient for controlling flow separation in terms of mass flow requirements compared to constant blowing and suction or even synthetic jet actuators. The fluidic actuators produce spanwise oscillating jets, and therefore are also known as sweeping jets. The frequency and spanwise sweeping extent depend on the geometric parameters and mass flow rate entering the actuators through the inlet section. The flow physics associated with these actuators is quite complex and not fully understood at this time. The unsteady flow generated by such actuators is simulated using the lattice Boltzmann based solver PowerFLOW R . Computed mean and standard deviation of velocity profiles generated by a family of fluidic actuators in quiescent air are compared with experimental data. Simulated results replicate the experimentally observed trends with parametric variation of geometry and inflow conditions.
Numerical simulation on inertia controlled steam bubble condensation using MPS
NASA Astrophysics Data System (ADS)
Chong, Daotong; Ishiwatari, Yuki; Oka, Yoshiaki; Yan, Junjie; Liu, Jiping
2013-07-01
Bubble dynamics is quite complicated in the field of two-phase hydrodynamics because the interfacial heat and mass transfer is comprehensively affected by various influencing factors. Bubble condensation can be either thermally controlled or inertia controlled. Inertia controlled bubble condensation indicates that considerable pressure difference exists between the steam bubble and ambient liquid. In this paper, the inertia controlled steam bubble condensation was simulated using moving particle semi-implicit (MPS) method. The spherical bubble is located in the center of the cylindrical pool which makes the possibility of 2-D axisymmetric computation. The lateral and bottom wall are set to be rigid insulated boundaries and the top is free surface boundary. The pool volume must be large enough to eliminate the effects by pool wall. The initial bubble pressure ranges from 0.48 MPa to 3.98 MPa, and the initial bubble diameter ranges from 2 mm to 5 mm, and the ambient water pressure and temperature is 0.1 MPa and 70 °C, respectively. The bubble dynamics during condensation was investigated and the influences of initial bubble pressure and diameter were obtained. The bubble deformation during condensation is shown in figure 1, and the variations of bubble diameters and pressures during condensation are shown in figures 2 and 3, respectively.
Numerical solution of control problems governed by nonlinear differential equations
Heinkenschloss, M.
1994-12-31
In this presentation the author investigates an iterative method for the solution of optimal control problems. These problems are formulated as constrained optimization problems with constraints arising from the state equation and in the form of bound constraints on the control. The method for the solution of these problems uses the special structure of the problem arising from the bound constraint and the state equation. It is derived from SQP methods and projected Newton methods and combines the advantages of both methods. The bound constraint is satisfied by all iterates using a projection, the nonlinear state equation is satisfied in the limit. Only a linearized state equation has to be solved in every iteration. The solution of the linearized problems are done using multilevel methods and GMRES.
Evaluating the Controls on Magma Ascent Rates Through Numerical Modelling
NASA Astrophysics Data System (ADS)
Thomas, M. E.; Neuberg, J. W.
2015-12-01
The estimation of the magma ascent rate is a key factor in predicting styles of volcanic activity and relies on the understanding of how strongly the ascent rate is controlled by different magmatic parameters. The ability to link potential changes in such parameters to monitoring data is an essential step to be able to use these data as a predictive tool. We present the results of a suite of conduit flow models that assess the influence of individual model parameters such as the magmatic water content, temperature or bulk magma composition on the magma flow in the conduit during an extrusive dome eruption. By systematically varying these parameters we assess their relative importance to changes in ascent rate. The results indicate that potential changes to conduit geometry and excess pressure in the magma chamber are amongst the dominant controlling variables that effect ascent rate, but the single most important parameter is the volatile content (assumed in this case as only water). Modelling this parameter across a range of reported values causes changes in the calculated ascent velocities of up to 800%, triggering fluctuations in ascent rates that span the potential threshold between effusive and explosive eruptions.
Professional mathematicians differ from controls in their spatial-numerical associations.
Cipora, Krzysztof; Hohol, Mateusz; Nuerk, Hans-Christoph; Willmes, Klaus; Brożek, Bartosz; Kucharzyk, Bartłomiej; Nęcka, Edward
2016-07-01
While mathematically impaired individuals have been shown to have deficits in all kinds of basic numerical representations, among them spatial-numerical associations, little is known about individuals with exceptionally high math expertise. They might have a more abstract magnitude representation or more flexible spatial associations, so that no automatic left/small and right/large spatial-numerical association is elicited. To pursue this question, we examined the Spatial Numerical Association of Response Codes (SNARC) effect in professional mathematicians which was compared to two control groups: Professionals who use advanced math in their work but are not mathematicians (mostly engineers), and matched controls. Contrarily to both control groups, Mathematicians did not reveal a SNARC effect. The group differences could not be accounted for by differences in mean response speed, response variance or intelligence or a general tendency not to show spatial-numerical associations. We propose that professional mathematicians possess more abstract and/or spatially very flexible numerical representations and therefore do not exhibit or do have a largely reduced default left-to-right spatial-numerical orientation as indexed by the SNARC effect, but we also discuss other possible accounts. We argue that this comparison with professional mathematicians also tells us about the nature of spatial-numerical associations in persons with much less mathematical expertise or knowledge. PMID:26063316
Research on prognostics and health management technology of numerical control equipment
NASA Astrophysics Data System (ADS)
Zheng, Rui; Sun, Hongwei; Zhang, Yingzhi
2014-03-01
Scheduled maintenance and corrective maintenance both construct the tradition l maintenance policy of numerical control equipment, which may bring some problems such as excessive maintenance and inadequate maintenance. Aiming at this phenomena, Prognostics and Health Management (PHM) technology is introduced to improve the reliability and availability of numerical control equipment. Before using this technology, Failure Mode Effects and Criticality Analysis (FMECA)should be firstly made for all the subsystems of numerical control equipment. FMECA is indispensable before PHM, and its purpose is to identify the key subsystems which are suitable for using PHM technology, find out the failure mechanisms of this subsystems, and provide references for building failure mechanism models and defining conditional parameters being monitored. Then a PHM system of numerical control equipment is designed. In this system, every conditional parameter of key subsystems is monitored by various sensors according to its respective failure mechanisms. A method based on multi - sensor data fusion is built to process information from sensors. The method uses the neural network algorithm. Applying the method can analyze the operation condition of numerical control equipment, and then prognoses its performance degradation, life evaluation, machining accuracy, and reliability. All the results can supply helpful evidence for making maintenance policy. Finally, key issues of implementing PHM theology in numerical control equipment are cited with the goal of better practical uses.
Numerical approximation of null controls for the heat equation: Ill-posedness and remedies
NASA Astrophysics Data System (ADS)
Münch, Arnaud; Zuazua, Enrique
2010-08-01
The numerical approximation of exact or trajectory controls for the wave equation is known to be a delicate issue, since the pioneering work of Glowinski-Lions in the nineties, because of the anomalous behavior of the high-frequency spurious numerical waves. Various efficient remedies have been developed and analyzed in the last decade to filter out these high-frequency components: Fourier filtering, Tychonoff's regularization, mixed finite-element methods, multi-grid strategies, etc. Recently convergence rate results have also been obtained. This work is devoted to analyzing this issue for the heat equation, which is the opposite paradigm because of its strong dissipativity and smoothing properties. The existing analytical results guarantee that, at least in some simple situations, as in the finite-difference scheme in 1 - d, the null or trajectory controls for numerical approximation schemes converge. This is due to the intrinsic high-frequency damping of the heat equation that is inherited by its numerical approximation schemes. But when developing numerical simulations the topic appears to be much more subtle and difficult. In fact, efficiently computing the null control for a numerical approximation scheme of the heat equation is a difficult problem in itself. The difficulty is strongly related to the regularizing effect of the heat kernel. The controls of minimal L2-norm are characterized as minima of quadratic functionals on the solutions of the adjoint heat equation, or its numerical versions. These functionals are shown to be coercive in very large spaces of solutions, sufficient to guarantee the L2 character of controls, but very far from being identifiable as energy spaces for the adjoint system. The very weak coercivity of the functionals under consideration makes the approximation problem exponentially ill-posed and the functional framework far from being well adapted to standard techniques in numerical analysis. In practice, the controls of the
Neural computing for numeric-to-symbolic conversion in control systems
NASA Technical Reports Server (NTRS)
Passino, Kevin M.; Sartori, Michael A.; Antsaklis, Panos J.
1989-01-01
A type of neural network, the multilayer perceptron, is used to classify numeric data and assign appropriate symbols to various classes. This numeric-to-symbolic conversion results in a type of information extraction, which is similar to what is called data reduction in pattern recognition. The use of the neural network as a numeric-to-symbolic converter is introduced, its application in autonomous control is discussed, and several applications are studied. The perceptron is used as a numeric-to-symbolic converter for a discrete-event system controller supervising a continuous variable dynamic system. It is also shown how the perceptron can implement fault trees, which provide useful information (alarms) in a biological system and information for failure diagnosis and control purposes in an aircraft example.
Recent advances in numerical simulation and control of asymmetric flows around slender bodies
NASA Technical Reports Server (NTRS)
Kandil, Osama A.; Wong, Tin-Chee; Sharaf, Hazem H.; Liu, C. H.
1992-01-01
The problems of asymmetric flow around slender bodies and its control are formulated using the unsteady, compressible, thin-layer or full Navier-Stokes equations which are solved using an implicit, flux-difference splitting, finite-volume scheme. The problem is numerically simulated for both locally-conical and three-dimensional flows. The numerical applications include studies of the effects of relative incidence, Mach number and Reynolds number on the flow asymmetry. For the control of flow asymmetry, the numerical simulation cover passive and active control methods. For the passive control, the effectiveness of vertical fins placed in the leeward plane of geometric symmetry and side strakes with different orientations is studied. For the active control, the effectiveness of normal and tangential flow injection and surface heating and a combination of these methods is studied.
ERIC Educational Resources Information Center
Biekert, Russell
Accompanying the rapid changes in technology has been a greater dependence on automation and numerical control, which has resulted in the need to find ways of preparing programers for industrial machines using numerical control. To compare the hands-on equipment method and a visual media method of teaching numerical control, an experimental and a…
Force-controlled absorption in a fully-nonlinear numerical wave tank
Spinneken, Johannes Christou, Marios; Swan, Chris
2014-09-01
An active control methodology for the absorption of water waves in a numerical wave tank is introduced. This methodology is based upon a force-feedback technique which has previously been shown to be very effective in physical wave tanks. Unlike other methods, an a-priori knowledge of the wave conditions in the tank is not required; the absorption controller being designed to automatically respond to a wide range of wave conditions. In comparison to numerical sponge layers, effective wave absorption is achieved on the boundary, thereby minimising the spatial extent of the numerical wave tank. In contrast to the imposition of radiation conditions, the scheme is inherently capable of absorbing irregular waves. Most importantly, simultaneous generation and absorption can be achieved. This is an important advance when considering inclusion of reflective bodies within the numerical wave tank. In designing the absorption controller, an infinite impulse response filter is adopted, thereby eliminating the problem of non-causality in the controller optimisation. Two alternative controllers are considered, both implemented in a fully-nonlinear wave tank based on a multiple-flux boundary element scheme. To simplify the problem under consideration, the present analysis is limited to water waves propagating in a two-dimensional domain. The paper presents an extensive numerical validation which demonstrates the success of the method for a wide range of wave conditions including regular, focused and random waves. The numerical investigation also highlights some of the limitations of the method, particularly in simultaneously generating and absorbing large amplitude or highly-nonlinear waves. The findings of the present numerical study are directly applicable to related fields where optimum absorption is sought; these include physical wavemaking, wave power absorption and a wide range of numerical wave tank schemes.
Maier, O.A.
1984-01-01
Some needs addressed concerning computer-aided design and computer-aided manufacture include: data base definition rules and three-dimensional data bases; inclusion of concise dimensional, finishing, and other data in textual or attribute form; usable solid modeling capability; better toolpath control; programmable language section of system capable of addressing the whole system data structure; and broader numerical control macro capability. (LEW)
NASA Astrophysics Data System (ADS)
Sigurdson, J.; Tagerud, J.
1986-05-01
A UNIDO publication about machine tools with automatic control discusses the following: (1) numerical control (NC) machine tool perspectives, definition of NC, flexible manufacturing systems, robots and their industrial application, research and development, and sensors; (2) experience in developing a capability in NC machine tools; (3) policy issues; (4) procedures for retrieval of relevant documentation from data bases. Diagrams, statistics, bibliography are included.
Large scale nonlinear numerical optimal control for finite element models of flexible structures
NASA Technical Reports Server (NTRS)
Shoemaker, Christine A.; Liao, Li-Zhi
1990-01-01
This paper discusses the development of large scale numerical optimal control algorithms for nonlinear systems and their application to finite element models of structures. This work is based on our expansion of the optimal control algorithm (DDP) in the following steps: improvement of convergence for initial policies in non-convex regions, development of a numerically accurate penalty function method approach for constrained DDP problems, and parallel processing on supercomputers. The expanded constrained DDP algorithm was applied to the control of a four-bay, two dimensional truss with 12 soft members, which generates geometric nonlinearities. Using an explicit finite element model to describe the structural system requires 32 state variables and 10,000 time steps. Our numerical results indicate that for constrained or unconstrained structural problems with nonlinear dynamics, the results obtained by our expanded constrained DDP are significantly better than those obtained using linear-quadratic feedback control.
Numerical Simulation of Flow and Determination of Aerodynamic Forces in the Balanced Control Valve
NASA Astrophysics Data System (ADS)
Matas, R.; Straka, F.; Hoznedl, M.
2013-04-01
The contribution subscribes a numerical simulation of a steam flow through a balanced control valve. The influence of some parameters in simulations were tested, analyzed and discussed. As a result of the simulations a graph of aerodynamics forces for a specific turbine characteristic was obtained. The results from numerical simulations were compared with results from experiments. The experiment was performed with an air flow, but the final data were converted with a criterion to steam flow.
Numerical Experiments and Flow Visualization of Drag Reduction using EMHD Control
NASA Astrophysics Data System (ADS)
O'Sullivan, Peter; Biringen, Sedat
1997-11-01
Turbulent channel flow of saltwater is studied numerically with the aim of achieving drag reduction via EMHD control using the Lorentz force of flush-mounted microtiles developed by Bandyopadhyay at NUWC. Previous numerical simulations have indicated significant local spatial deviations on the time-average skin friction (± 10%) in the vicinity of the control actuators. However, there was only negligible net viscous drag reduction (<2%). In an attempt to better understand the physics of the interaction of the controlling Lorentz force with the passage of an advecting incipient burst we have performed numerous short simulations. We scanned a wide variety of archival data from our previous simulations and extracted a good sample of burst ``candidate'' initial conditions. We then advanced these flows forward in time both with and without control. We studied the resulting burst/control dynamics with respect to control strength, duration, temporal frequency, spanwise offset and streamwise spacing of the microtiles. The spatio-temporal response of the burst and sweep structures is crucial to a successful drag reduction strategy. By identifying the key parameters in the control space we aim to narrow the focus of the design problem. We will present our findings of these numerical experiments which are based on data analysis together with flow visualization.
NASA Technical Reports Server (NTRS)
Chen, G.; Zheng, Q.; Coleman, M.; Weerakoon, S.
1983-01-01
This paper briefly reviews convergent finite difference schemes for hyperbolic initial boundary value problems and their applications to boundary control systems of hyperbolic type which arise in the modelling of vibrations. These difference schemes are combined with the primal and the dual approaches to compute the optimal control in the unconstrained case, as well as the case when the control is subject to inequality constraints. Some of the preliminary numerical results are also presented.
NASA Astrophysics Data System (ADS)
Dong, Xing-Jian; Meng, Guang; Peng, Juan-Chun
2006-11-01
The aim of this study is to investigate the efficiency of a system identification technique known as observer/Kalman filter identification (OKID) technique in the numerical simulation and experimental study of active vibration control of piezoelectric smart structures. Based on the structure responses determined by finite element method, an explicit state space model of the equivalent linear system is developed by employing OKID approach. The linear quadratic Gaussian (LQG) algorithm is employed for controller design. The control law is then incorporated into the ANSYS finite element model to perform closed loop simulations. Therefore, the control law performance can be evaluated in the context of a finite element environment. Furthermore, a complete active vibration control system comprising the cantilever plate, the piezoelectric actuators, the accelerometers and the digital signal processor (DSP) board is set up to conduct the experimental investigation. A state space model characterizing the dynamics of the physical system is developed from experimental results using OKID approach for the purpose of control law design. The controller is then implemented by using a floating point TMS320VC33 DSP. Numerical examples by employing the proposed numerical simulation method, together with the experimental results obtained by using the active vibration control system, have demonstrated the validity and efficiency of OKID method in application of active vibration control of piezoelectric smart structures.
NASA Technical Reports Server (NTRS)
Liou, Luen-Woei; Ray, Asok
1991-01-01
A state feedback control law for integrated communication and control systems (ICCS) is formulated by using the dynamic programming and optimality principle on a finite-time horizon. The control law is derived on the basis of a stochastic model of the plant which is augmented in state space to allow for the effects of randomly varying delays in the feedback loop. A numerical procedure for synthesizing the control parameters is then presented, and the performance of the control law is evaluated by simulating the flight dynamics model of an advanced aircraft. Finally, recommendations for future work are made.
NASA Astrophysics Data System (ADS)
Felicetti, Leonard; Palmerini, Giovanni B.
2016-06-01
The paper investigates some analytical and numerical aspects of the formation control exploited by means of inter-spacecraft electrostatic actions. The analysis is based on the evaluation and check of the stability issues by using a sequence of purposely defined Lyapunov functions. The same Lyapunov approach can also define a specific under-actuate control strategy for controlling selected "virtual links" of the formation. Two different selection criteria for these links are then discussed, showing the implications on the control chain. An optimal charge distribution strategy, which assigns univocally the charges to all the spacecraft starting from the charge products computed by the control, is also presented and discussed. Numerical simulations prove the suitability of the proposed approach to a formation of 4 satellites.
Adaptive Numerical Dissipation Control in High Order Schemes for Multi-D Non-Ideal MHD
NASA Technical Reports Server (NTRS)
Yee, H. C.; Sjoegreen, B.
2005-01-01
The required type and amount of numerical dissipation/filter to accurately resolve all relevant multiscales of complex MHD unsteady high-speed shock/shear/turbulence/combustion problems are not only physical problem dependent, but also vary from one flow region to another. In addition, proper and efficient control of the divergence of the magnetic field (Div(B)) numerical error for high order shock-capturing methods poses extra requirements for the considered type of CPU intensive computations. The goal is to extend our adaptive numerical dissipation control in high order filter schemes and our new divergence-free methods for ideal MHD to non-ideal MHD that include viscosity and resistivity. The key idea consists of automatic detection of different flow features as distinct sensors to signal the appropriate type and amount of numerical dissipation/filter where needed and leave the rest of the region free from numerical dissipation contamination. These scheme-independent detectors are capable of distinguishing shocks/shears, flame sheets, turbulent fluctuations and spurious high-frequency oscillations. The detection algorithm is based on an artificial compression method (ACM) (for shocks/shears), and redundant multiresolution wavelets (WAV) (for the above types of flow feature). These filters also provide a natural and efficient way for the minimization of Div(B) numerical error.
Controlled time integration for the numerical simulation of meteor radar reflections
NASA Astrophysics Data System (ADS)
Räbinä, Jukka; Mönkölä, Sanna; Rossi, Tuomo; Markkanen, Johannes; Gritsevich, Maria; Muinonen, Karri
2016-07-01
We model meteoroids entering the Earth's atmosphere as objects surrounded by non-magnetized plasma, and consider efficient numerical simulation of radar reflections from meteors in the time domain. Instead of the widely used finite difference time domain method (FDTD), we use more generalized finite differences by applying the discrete exterior calculus (DEC) and non-uniform leapfrog-style time discretization. The computational domain is presented by convex polyhedral elements. The convergence of the time integration is accelerated by the exact controllability method. The numerical experiments show that our code is efficiently parallelized. The DEC approach is compared to the volume integral equation (VIE) method by numerical experiments. The result is that both methods are competitive in modelling non-magnetized plasma scattering. For demonstrating the simulation capabilities of the DEC approach, we present numerical experiments of radar reflections and vary parameters in a wide range.
NASA Technical Reports Server (NTRS)
Lan, C. Edward; Ge, Fuying
1989-01-01
Control system design for general nonlinear flight dynamic models is considered through numerical simulation. The design is accomplished through a numerical optimizer coupled with analysis of flight dynamic equations. The general flight dynamic equations are numerically integrated and dynamic characteristics are then identified from the dynamic response. The design variables are determined iteratively by the optimizer to optimize a prescribed objective function which is related to desired dynamic characteristics. Generality of the method allows nonlinear effects to aerodynamics and dynamic coupling to be considered in the design process. To demonstrate the method, nonlinear simulation models for an F-5A and an F-16 configurations are used to design dampers to satisfy specifications on flying qualities and control systems to prevent departure. The results indicate that the present method is simple in formulation and effective in satisfying the design objectives.
A numerical study of transition control by periodic suction-blowing
NASA Technical Reports Server (NTRS)
Biringen, Sedat
1987-01-01
The applicability of active control of transition by periodic suction-blowing is investigated via direct numerical simulations of the Navier-Stokes equations. The time-evolution of finite-amplitude disturbances in plane channel flow is compared in detail with and without control. The analysis indicates that, for relatively small three dimensional amplitudes, a two dimensional control effectively reduces disturbance growth rates even for linearly unstable Reynolds numbers. After the flow goes through secondary instability, three dimensional control seems necessary to stabilize the flow. An investigation of the temperature field suggests that passive temperature contamination is operative to reflect the flow dynamics during transition.
ERIC Educational Resources Information Center
Stanton, Michael; And Others
1985-01-01
Three reports on the effects of high technology on the nature of work include (1) Stanton on applications and implications of computer-aided design for engineers, drafters, and architects; (2) Nardone on the outlook and training of numerical-control machine tool operators; and (3) Austin and Drake on the future of clerical occupations in automated…
CNC Turning Center Advanced Operations. Computer Numerical Control Operator/Programmer. 444-332.
ERIC Educational Resources Information Center
Skowronski, Steven D.; Tatum, Kenneth
This student guide provides materials for a course designed to introduce the student to the operations and functions of a two-axis computer numerical control (CNC) turning center. The course consists of seven units. Unit 1 presents course expectations and syllabus, covers safety precautions, and describes the CNC turning center components, CNC…
Numerical Control Machining and the Issue of Deskilling. An Empirical View.
ERIC Educational Resources Information Center
Zicklin, Gilbert
1987-01-01
Research on the effects of numerical control (NC) machining on the skills of machinists presents mixed results. Interviews with a small group of machinists experienced in both conventional and NC matching suggest seven major factors that affect whether NC automation changes the overall skill level. The deskilling hypothesis is not supported by…
ERIC Educational Resources Information Center
Skowronski, Steven D.
This student guide provides materials for a course designed to instruct the student in the recommended procedures used when setting up tooling and verifying part programs for a two-axis computer numerical control (CNC) turning center. The course consists of seven units. Unit 1 discusses course content and reviews and demonstrates set-up procedures…
Plans and resources required for a computer numerically controlled machine tool tester
Newton, L.E.; Burleson, R.R.; McCue, H.K.; Pomernacki, C.L.; Mansfield, A.R.; Childs, J.J.
1982-07-19
Precision computer numerically controlled (CNC) machine tools present unique and especially difficult problems in the areas of qualification and fault isolation. In this report, we examine and classify these problems, discuss methods to resolve them effectively, and present estimates of the resources needed to design and build a CNC/machine tool tester.
An efficient step-size control method in numerical integration for astrodynamical equations
NASA Astrophysics Data System (ADS)
Liu, C. Z.; Cui, D. X.
2002-11-01
Using the curvature of the integral curve, a step-size control method is introduced in this paper. This method will prove to be the efficient scheme in the sense that it saves computation time and improve accuracy of numerical integration.
A numerical approach to controller design with an application to a space structure test facility
NASA Technical Reports Server (NTRS)
Frazier, W. G.; Irwin, R. D.
1992-01-01
An iterative numerical algorithm that improves feasible closed loop design criteria by updating the parameters of a linear controller is developed. The algorithm allows the use of experimentally derived data collected from the open loop plant. It eliminates the need for an accurate parametric model of the open loop system. Experimental results from the application of a controller designed for a large space structure ground test facility using the algorithm are presented.
Numerical Experiments and Flow Visualization of Drag Reduction using EMHD Control
NASA Astrophysics Data System (ADS)
O'Sullivan, Peter; Biringen, Sedat
1998-11-01
Turbulent channel flow of saltwater is studied numerically with the aim of achieving drag reduction via EMHD control using the Lorentz force of flush-mounted microtiles similar to those developed by Bandyopadhyay at NUWC. Our prior numerical simulations indicated significant local spatial deviations on the time-average skin friction (± 10%) in the vicinity of the control actuators. However, there was negligible net viscous drag reduction (<1%). To better understand the physics of the interaction of the controlling Lorentz force with the passage of advecting burst events we have performed short-duration simulations. We implement a burst detection scheme based on that of Alfredsson and Johansson (1984) in order to locate and track the strongest Q2 events in the flow. Subsequently, we compare the evolution of these structures, both with and without EMHD control. We find that the specific designs we have studied do not succeed in reducing the primary Reynolds stress as a burst advects above an actuator. Via flow visualization of large-scale coherent structures we find that the classic hairpin vortices which populate the boundary layer are not significantly affected by the applied control - apart from a temporary spatial phase shift. We will present our findings of these numerical experiments and discuss the prospects for a more successful design and control strategy.
NASA Astrophysics Data System (ADS)
Wu, Zhen
Active sound filed control techniques have received growing attention since they provide alternative solutions to low-frequency sound control, where the conventional passive methods have not been very successful. They have wide industrial and military applications such as noise reduction, room acoustics design, acoustic measurements, underwater acoustic camouflage, etc. An appropriate model of an acoustical system serves as the basis of control law synthesis and active control system design. A classical system model describes the dynamics of an acoustic system in a view of input/output relation through transfer functions. On the other hand, a time-domain based state-space model equivalently describes the system dynamics in terms of internal system variables and provides a direct physical insight of active control of sound. Furthermore, based on a state-space model, one can take advantage of modern control analysis and synthesis tools to design an optimal control system for broadband, global sound absorption. This thesis explores state-space feedback control in unbounded acoustic systems. State-space models are developed for unbounded one-dimensional acoustic systems using a finite-difference method with special boundary treatments. State feedback control algorithms including state estimations are developed using optimal control theory (LQG). Numerical simulation results of the closed-loop system responses demonstrate the optimal performance of active control systems considering the trade-off between the high reflection reduction and limited sensing/actuating power. Two numerical examples, an active underwater sound absorbing coating system, and an active noise control system in a duct, are studied. For the active underwater sound absorbing system, a feedback control system involving two sensors and one actuator is designed. Numerical simulation of the closed-loop response indicates a substantial and broadband reflection (echo) reduction for this design. A variety
NASA Technical Reports Server (NTRS)
Korte, John J.
1990-01-01
A numerical simulation of the actuation system for the propulsion control valve (PCV) of the NASA Langley Aircraft Landing Dynamics Facility was developed during the preliminary design of the PCV and used throughout the entire project. The simulation is based on a predictive model of the PCV which is used to evaluate and design the actuation system. The PCV controls a 1.7 million-pound thrust water jet used in propelling a 108,000-pound test carriage. The PCV can open and close in 0.300 second and deliver over 9,000 gallons of water per sec at pressures up to 3150 psi. The numerical simulation results are used to predict transient performance and valve opening characteristics, specify the hydraulic control system, define transient loadings on components, and evaluate failure modes. The mathematical model used for numerically simulating the mechanical fluid power system is described, and numerical results are demonstrated for a typical opening and closing cycle of the PCV. A summary is then given on how the model is used in the design process.
Control of Flow Structure in Square Cross-Sectioned U Bend using Numerical Modeling
NASA Astrophysics Data System (ADS)
Yavuz, Mehmet Metin; Guden, Yigitcan
2014-11-01
Due to the curvature in U-bends, the flow development involves complex flow structures including Dean vortices and high levels of turbulence that are quite critical in considering noise problems and structural failure of the ducts. Computational fluid dynamic (CFD) models are developed using ANSYS Fluent to analyze and to control the flow structure in a square cross-sectioned U-bend with a radius of curvature Rc/D = 0.65. The predictions of velocity profiles on different angular positions of the U-bend are compared against the experimental results available in the literature and the previous numerical studies. The performances of different turbulence models are evaluated to propose the best numerical approach that has high accuracy with reduced computation time. The numerical results of the present study indicate improvements with respect to the previous numerical predictions and very good agreement with the available experimental results. In addition, a flow control technique is utilized to regulate the flow inside the bend. The elimination of Dean vortices along with significant reduction in turbulence levels in different cross flow planes are successfully achieved when the flow control technique is applied. The project is supported by Meteksan Defense Industries, Inc.
Shaking table test and numerical analysis of offshore wind turbine tower systems controlled by TLCD
NASA Astrophysics Data System (ADS)
Chen, Jianbing; Liu, Youkun; Bai, Xueyuan
2015-03-01
A wind turbine system equipped with a tuned liquid column damper (TLCD) is comprehensively studied via shaking table tests using a 1/13-scaled model. The effects of wind and wave actions are considered by inputting response-equivalent accelerations on the shaking table. The test results show that the control effect of the TLCD system is significant in reducing the responses under both wind-wave equivalent loads and ground motions, but obviously varies for different inputs. Further, a blade-hub-tower integrated numerical model for the wind turbine system is established. The model is capable of considering the rotational effect of blades by combining Kane's equation with the finite element method. The responses of the wind tower equipped with TLCD devices are numerically obtained and compared to the test results, showing that under both controlled and uncontrolled conditions with and without blades' rotation, the corresponding responses exhibit good agreement. This demonstrates that the proposed numerical model performs well in capturing the wind-wave coupled response of the offshore wind turbine systems under control. Both numerical and experimental results show that the TLCD system can significantly reduce the structural response and thus improve the safety and serviceability of the offshore wind turbine tower systems. Additional issues that require further study are discussed.
Numerical Investigation of Rotorcraft Fuselage Drag Reduction Using Active Flow Control
NASA Technical Reports Server (NTRS)
Allan, Brian G.; Schaeffler, Norman W.
2011-01-01
The effectiveness of unsteady zero-net-mass-flux jets for fuselage drag reduction was evaluated numerically on a generic rotorcraft fuselage in forward flight with a rotor. Previous efforts have shown significant fuselage drag reduction using flow control for an isolated fuselage by experiment and numerical simulation. This work will evaluate a flow control strategy, that was originally developed on an isolated fuselage, in a more relevant environment that includes the effects of a rotor. Evaluation of different slot heights and jet velocity ratios were performed. Direct comparisons between an isolated fuselage and rotor/fuselage simulations were made showing similar flow control performance at a -3deg fuselage angle-of-attack condition. However, this was not the case for a -5deg angle-of-attack condition where the performance between the isolated fuselage and rotor/fuselage were different. The fuselage flow control resulted in a 17% drag reduction for a peak C(sub mu) of 0.0069 in a forward flight simulation where mu = 0:35 and CT/sigma = 0:08. The CFD flow control results also predicted a favorable 22% reduction of the fuselage download at this same condition, which can have beneficial compounding effects on the overall performance of the vehicle. This numerical investigation was performed in order to provide guidance for a future 1/3 scale wind tunnel experiment to be performed at the NASA 14-by 22-Foot Subsonic Tunnel.
Numerical Modeling of Cavitating Venturi: A Flow Control Element of Propulsion System
NASA Technical Reports Server (NTRS)
Majumdar, Alok; Saxon, Jeff (Technical Monitor)
2002-01-01
In a propulsion system, the propellant flow and mixture ratio could be controlled either by variable area flow control valves or by passive flow control elements such as cavitating venturies. Cavitating venturies maintain constant propellant flowrate for fixed inlet conditions (pressure and temperature) and wide range of outlet pressures, thereby maintain constant, engine thrust and mixture ratio. The flowrate through the venturi reaches a constant value and becomes independent of outlet pressure when the pressure at throat becomes equal to vapor pressure. In order to develop a numerical model of propulsion system, it is necessary to model cavitating venturies in propellant feed systems. This paper presents a finite volume model of flow network of a cavitating venturi. The venturi was discretized into a number of control volumes and mass, momentum and energy conservation equations in each control volume are simultaneously solved to calculate one-dimensional pressure, density, and flowrate and temperature distribution. The numerical model predicts cavitations at the throat when outlet pressure was gradually reduced. Once cavitation starts, with further reduction of downstream pressure, no change in flowrate is found. The numerical predictions have been compared with test data and empirical equation based on Bernoulli's equation.
A numerical study for design of depth, pitch and roll control system of a towed vehicle
Koterayama, W.; Yamaguchi, S.; Nakamura, M.; Moriyama, A.; Akamatsu, T.
1994-12-31
A towed vehicle system, FLYING FISH, is under development for use in making chemical and physical measurements which enable the authors to obtain spacially continuous and real time data in an ocean mixed layer. The heave, pitch and roll of FLYING FISH are controlled by a main wing and horizontal tail wings which permit its stable attitudes and assure accurate measurements. The numerical simulation of motions was carried out to design the optimal control system of this towed vehicle system and the results gave the data for the design of the mechanical parts of the control system.
Hadjitheodorou, Amalia; Kalosakas, George
2014-09-01
We investigate, both analytically and numerically, diffusion-controlled drug release from composite spherical formulations consisting of an inner core and an outer shell of different drug diffusion coefficients. Theoretically derived analytical results are based on the exact solution of Fick's second law of diffusion for a composite sphere, while numerical data are obtained using Monte Carlo simulations. In both cases, and for the range of matrix parameter values considered in this work, fractional drug release profiles are described accurately by a stretched exponential function. The release kinetics obtained is quantified through a detailed investigation of the dependence of the two stretched exponential release parameters on the device characteristics, namely the geometrical radii of the inner core and outer shell and the corresponding drug diffusion coefficients. Similar behaviors are revealed by both the theoretical results and the numerical simulations, and approximate analytical expressions are presented for the dependencies. PMID:25063169
NASA Astrophysics Data System (ADS)
Diniş, C. M.; Popa, G. N.; Iagăr, A.
2016-02-01
The paper is an analysis of two-positions (hysteresis) regulators, self-tuned PID controller and PID controller for temperature control used for indirect heat resistance furnaces. For PID controller was used three methods of tuning: Ziegler-Nichols step response model, Cohen-Coon tuning rules and Ziegler-Nichols tuning rules. In experiments it used an electric furnace with indirect heating with active power of resistance of 1 kW/230V AC and a numerical temperature regulator AT-503 type (ANLY). It got a much better temperature control when using the Cohen-Coon tuning rules method than those of Ziegler-Nichols step response method and Ziegler-Nichols tuning rules method.
Numerical analysis of a variable camber rotor blade as a lift control device
NASA Technical Reports Server (NTRS)
Awani, A. O.; Stroub, R. H.
1984-01-01
A new rotor configuration called the variable camber rotor was numerically investigated as a lift control device. This rotor differs from a conventional (baseline) rotor only in the blade aft section. In this configuration, the aft section or flap is attached to the forward section by pin joint arrangement, and also connected to the rotor control system for the control of rotor thrust level and vectoring. Pilot action to the flap deflection controls rotor lift and tip path plane tilt. The drag due to flaps is presented and the theoretical result correlated with test data. The assessment of payoff for the variable camber rotor in comparison with conventional (baseline) rotor was examined in hover. The variable camber rotor is shown to increase hover power required by 1.35%, but such a minimal power penalty is not significant enough to be considered a negative result. In forward flight, the control needs of the variable camber rotor were evaluated.
3D Numerical Analysis of Flow Control on Wind Turbine Blades
NASA Astrophysics Data System (ADS)
Sahni, Onkar; Karaismail, Ertan
2011-11-01
Wind turbine blades are exposed to unsteady and spatially-varying loadings in a real field. These loadings result in fluctuating structural forces which in turn lead to failure of blades as well as gearbox. In this study, we perform numerical analysis of flow over a wind turbine blade placed in a wind tunnel; where dynamic motions are imposed to the blade in order to emulate scenarios observed in a real field. Furthermore, we also study the effect of active flow control (via synthetic-jets) on unsteady aerodynamic characteristics of the blade under dynamic motions; the idea is to be able to control aerodynamic loads and mitigate failures. Numerical analysis is based on massively parallel simulations using hybrid turbulence models. Comparisons with experimental data will also be included.
Coherent control in quantum dot gain media using shaped pulses: a numerical study.
Mishra, Akhilesh Kumar; Karni, Ouri; Eisenstein, Gadi
2015-11-16
We present a numerical study of coherent control in a room temperature InAs/InP quantum dot (QD) semiconductor optical amplifier (SOA) using shaped ultra-short pulses. Both the gain and absorption regimes were analyzed for pulses with central wavelengths lying on either side of the inhomogeneously broadened gain spectrum. The numerical experiments predict that in the gain regime the coherent interactions between a QD SOA and a pulse can be controlled by incorporating a quadratic spectral phase (QSP) in the pulse profile. The sequential interaction with the gain medium of different spectral components of the pulse results in either suppression or enhancement of the coherent signatures on the pulse profile depending upon their proximity to the gain spectrum peak. In the absorption regime, positive QSP induces a negative chirp that adds up to that of a two photon absorption induced Kerr-like effect resulting in pulse compression while negative QSP enhances dispersive broadening of the pulse. PMID:26698476
NASA Astrophysics Data System (ADS)
Zacharos, Athanasios; Kontis, Konstantinos
Four different circulation controlled airfoils have been numerically simulated. The baseline airfoil was a 17% thick supercritical airfoil. Different blowing rates have been examined by adjusting the slot height and blowing velocity. A number of turbulence models were employed, these were: Spalart-Allmaras, standard κ ɛ, realizable κ ɛ, SST κ ω and Reynolds stress model. The results from the numerical simulations were compared with experimental data at zero angle of attack. The solutions indicated that at momentum coefficients, Cμ=0.1 or greater, all isotropic turbulence models failed to capture the physics of the circulation control problem. The Reynolds stress model captured successfully the physics at Cμ=0.1. At greater values of momentum coefficient, the Reynolds stress model also failed to predict the experimentally measured lift coefficients because the jet remained attached to the surface of the airfoil. The Spalart-Allmaras model consistently predicted the right trend for lift variation with Cμ in all cases tested.
Feedback control of a pitching and plunging airfoil via direct numerical simulation
NASA Astrophysics Data System (ADS)
Dawson, Scott; Brunton, Steven; Rowley, Clarence
2012-11-01
Feedback control is implemented in direct numerical simulations at a Reynolds number of 100 to allow a two-dimensional flat plate airfoil to track desired lift profiles using pitching and plunging motions. Robust controllers are designed using both classical models (Theodorsen) and empirical reduced-order models identified from direct numerical simulations. We investigate the capabilities of a variety of controllers for plunging motion and for pitching about different pitch axis locations. Effective control is achieved across a wide range of angles of attack, despite strongly nonlinear flow physics. The forces caused by rapid airfoil motion may be utilized to achieve high lift coefficients for short periods of time. It is also possible to track periodic lift profiles with average lift coefficients that are significantly greater than those achieved by a steady airfoil. The enhanced lift that arises at certain frequencies appears to be caused by favorable interaction of wake vortices. The ability of the controllers to reject gust disturbances and attenuate sensor noise is also investigated, which is relevant for the implementation of such controllers in an experimental setting. This work is supported by AFOSR grant FA9550-12-1-0075.
Numerical simulation of diffusion-controlled droplet growth Dynamical correlation effects
NASA Technical Reports Server (NTRS)
Beenakker, C. W. J.
1986-01-01
Diffusion-controlled coarsening (Ostwald ripening) of precipitated solutions is studied by numerical simulation. An algorithm is devised which exploits the screening of solute concentration fields, thereby removing the restriction to small systems of previous work. Simulation of the coarsening of 5000 droplets at 10-percent volume fraction reveals long-ranged dynamical correlations which broaden the droplet size-distribution function and increase the coarsening-rate coefficient.
NASA Technical Reports Server (NTRS)
Grosveld, Ferdinand W.
1996-01-01
The active acoustic and structural noise control characteristics of a double wall cylinder with and without ring stiffeners were numerically evaluated. An exterior monopole was assumed to acoustically excite the outside of the double wall cylinder at an acoustic cavity resonance frequency. Structural modal vibration properties of the inner and outer shells were analyzed by post-processing the results from a finite element analysis. A boundary element approach was used to calculate the acoustic cavity response and the coupled structural-acoustic interaction. In the frequency region of interest, below 500 Hz, all structural resonant modes were found to be acoustically slow and the nonresonant modal response to be dominant. Active sound transmission control was achieved by control forces applied to the inner or outer shell, or acoustic control monopoles placed just outside the inner or outer shell. A least mean square technique was used to minimize the interior sound pressures at the nodes of a data recovery mesh. Results showed that single acoustic control monopoles placed just outside the inner or outer shells resulted in better sound transmission control than six distributed point forces applied to either one of the shells. Adding stiffeners to the double wall structure constrained the modal vibrations of the shells, making the double wall stiffer with associated higher modal frequencies. Active noise control obtained for the stiffened double wall configurations was less than for the unstiffened cylinder. In all cases, the acoustic control monopoles controlled the sound transmission into the interior better than the structural control forces.
Numerical investigations of passive flow control elements for vertical axis wind turbine
NASA Astrophysics Data System (ADS)
Frunzulica, Florin; Dumitrache, Alexandru; Suatean, Bogdan
2014-12-01
In this paper we numerically investigate the possibilities to control the dynamic stall phenomenon, with application to vertical axis wind turbines. The dynamic stall appears at low tip speed ratio (TSR<4) and it has a great impact on structural integrity of the wind turbine and power performances. For this reason we performed a CFD 2D analysis of the dynamic stall phenomenon around NACA 0012 airfoil equipped with a passive flow control device, in pitching motion at relative low Reynolds number (˜105). Three passive flow control devices are numerically investigated: a turbulence promoter mounted on the leading edge, a thin channel and a step on the upper surface of the airfoil. For the present studies, the unsteady Reynolds averaged Navier-Stokes (RANS) model is the suitable approach to perform the dynamic stall simulations with an acceptable computational cost and reasonable accuracy. The results are compared to those of an existing experimental case test for unmodified NACA 0012 airfoil. The capability of this device was investigated numerically on a vertical axis wind turbine (2D model), where blades are generated with NACA 0018 airfoil.
Geometric versus numerical optimal control of a dissipative spin-(1/2) particle
Lapert, M.; Sugny, D.; Zhang, Y.; Braun, M.; Glaser, S. J.
2010-12-15
We analyze the saturation of a nuclear magnetic resonance (NMR) signal using optimal magnetic fields. We consider both the problems of minimizing the duration of the control and its energy for a fixed duration. We solve the optimal control problems by using geometric methods and a purely numerical approach, the grape algorithm, the two methods being based on the application of the Pontryagin maximum principle. A very good agreement is obtained between the two results. The optimal solutions for the energy-minimization problem are finally implemented experimentally with available NMR techniques.
NASA Astrophysics Data System (ADS)
Tang, Xiaojun
2016-04-01
The main purpose of this work is to provide multiple-interval integral Gegenbauer pseudospectral methods for solving optimal control problems. The latest developed single-interval integral Gauss/(flipped Radau) pseudospectral methods can be viewed as special cases of the proposed methods. We present an exact and efficient approach to compute the mesh pseudospectral integration matrices for the Gegenbauer-Gauss and flipped Gegenbauer-Gauss-Radau points. Numerical results on benchmark optimal control problems confirm the ability of the proposed methods to obtain highly accurate solutions.
Numerical solution of the controlled Duffing oscillator by semi-orthogonal spline wavelets
NASA Astrophysics Data System (ADS)
Lakestani, M.; Razzaghi, M.; Dehghan, M.
2006-09-01
This paper presents a numerical method for solving the controlled Duffing oscillator. The method can be extended to nonlinear calculus of variations and optimal control problems. The method is based upon compactly supported linear semi-orthogonal B-spline wavelets. The differential and integral expressions which arise in the system dynamics, the performance index and the boundary conditions are converted into some algebraic equations which can be solved for the unknown coefficients. Illustrative examples are included to demonstrate the validity and applicability of the technique.
NASA Technical Reports Server (NTRS)
Sjoegreen, B.; Yee, H. C.
2001-01-01
The recently developed essentially fourth-order or higher low dissipative shock-capturing scheme of Yee, Sandham and Djomehri (1999) aimed at minimizing nu- merical dissipations for high speed compressible viscous flows containing shocks, shears and turbulence. To detect non smooth behavior and control the amount of numerical dissipation to be added, Yee et al. employed an artificial compression method (ACM) of Harten (1978) but utilize it in an entirely different context than Harten originally intended. The ACM sensor consists of two tuning parameters and is highly physical problem dependent. To minimize the tuning of parameters and physical problem dependence, new sensors with improved detection properties are proposed. The new sensors are derived from utilizing appropriate non-orthogonal wavelet basis functions and they can be used to completely switch to the extra numerical dissipation outside shock layers. The non-dissipative spatial base scheme of arbitrarily high order of accuracy can be maintained without compromising its stability at all parts of the domain where the solution is smooth. Two types of redundant non-orthogonal wavelet basis functions are considered. One is the B-spline wavelet (Mallat & Zhong 1992) used by Gerritsen and Olsson (1996) in an adaptive mesh refinement method, to determine regions where re nement should be done. The other is the modification of the multiresolution method of Harten (1995) by converting it to a new, redundant, non-orthogonal wavelet. The wavelet sensor is then obtained by computing the estimated Lipschitz exponent of a chosen physical quantity (or vector) to be sensed on a chosen wavelet basis function. Both wavelet sensors can be viewed as dual purpose adaptive methods leading to dynamic numerical dissipation control and improved grid adaptation indicators. Consequently, they are useful not only for shock-turbulence computations but also for computational aeroacoustics and numerical combustion. In addition, these
Numerical solution of a conspicuous consumption model with constant control delay☆
Huschto, Tony; Feichtinger, Gustav; Hartl, Richard F.; Kort, Peter M.; Sager, Sebastian; Seidl, Andrea
2011-01-01
We derive optimal pricing strategies for conspicuous consumption products in periods of recession. To that end, we formulate and investigate a two-stage economic optimal control problem that takes uncertainty of the recession period length and delay effects of the pricing strategy into account. This non-standard optimal control problem is difficult to solve analytically, and solutions depend on the variable model parameters. Therefore, we use a numerical result-driven approach. We propose a structure-exploiting direct method for optimal control to solve this challenging optimization problem. In particular, we discretize the uncertainties in the model formulation by using scenario trees and target the control delays by introduction of slack control functions. Numerical results illustrate the validity of our approach and show the impact of uncertainties and delay effects on optimal economic strategies. During the recession, delayed optimal prices are higher than the non-delayed ones. In the normal economic period, however, this effect is reversed and optimal prices with a delayed impact are smaller compared to the non-delayed case. PMID:22267871
A numerical study of active structural acoustic control in a stiffened, double wall cylinder
NASA Technical Reports Server (NTRS)
Grosveld, Ferdinand W.; Coats, T. J.; Lester, H. C.; Silcox, R. J.
1994-01-01
It is demonstrated that active structural acoustic control of complex structural/acoustic coupling can be numerically modeled using finite element and boundary element techniques in conjunction with an optimization procedure to calculate control force amplitudes. Appreciable noise reduction is obtained when the structure is excited at a structural resonance of the outer shell or an acoustic resonance of the inner cavity. Adding ring stiffeners as a connection between the inner and outer shells provides an additional structural transmission path to the interior cavity and coupled the modal behavior of the inner and outer shells. For the case of excitation at the structural resonance of the unstiffened outer shell, adding the stiffeners raises the structural resonance frequencies. The effectiveness of the control forces is reduced due to the off resonance structural response. For excitation at an acoustic cavity resonance, the controller effectiveness is enhanced.
Numerical investigation on the temperature control of a NIF cryogenic target
NASA Astrophysics Data System (ADS)
Sun, Y.; Zhou, G.; Li, Q.; Li, L. F.
2015-12-01
Numerical investigation was performed on the temperature control of NIF cryogenic target in order to get a temperature uniformity of 0.1mK on the surface of the capsule. Heat transfer process was discussed to find out major factors in the temperature control, tamping gas heat transfer and free convection of the tamping gas was calculated. Spherically symmetric temperature field is required due to energy released from the tritium decay within the capsule, auxiliary heating is set on the hohlraum to compensate the higher heat loss caused by the lower tamping gas thermal resistance on the mid plane. Free convection effect of the tamping gas is reduced by separating the tamping gas with plastic films and independent temperature control of the cooling arm. This research may provide theoretical foundation and reference for temperature control on the cryogenic target.
Numerical dissipation control in high order shock-capturing schemes for LES of low speed flows
NASA Astrophysics Data System (ADS)
Kotov, D. V.; Yee, H. C.; Wray, A. A.; Sjögreen, B.; Kritsuk, A. G.
2016-02-01
The Yee & Sjögreen adaptive numerical dissipation control in high order scheme (High Order Filter Methods for Wide Range of Compressible Flow Speeds, ICOSAHOM 09, 2009) is further improved for DNS and LES of shock-free turbulence and low speed turbulence with shocklets. There are vastly different requirements in the minimization of numerical dissipation for accurate turbulence simulations of different compressible flow types and flow speeds. Traditionally, the method of choice for shock-free turbulence and low speed turbulence are by spectral, high order central or high order compact schemes with high order linear filters. With a proper control of a local flow sensor, appropriate amount of numerical dissipation in high order shock-capturing schemes can have spectral-like accuracy for compressible low speed turbulent flows. The development of the method includes an adaptive flow sensor with automatic selection on the amount of numerical dissipation needed at each flow location for more accurate DNS and LES simulations with less tuning of parameters for flows with a wide range of flow speed regime during the time-accurate evolution, e.g., time varying random forcing. An automatic selection of the different flow sensors catered to the different flow types is constructed. A Mach curve and high-frequency oscillation indicators are used to reduce the tuning of parameters in controlling the amount of shock-capturing numerical dissipation to be employed for shock-free turbulence, low speed turbulence and turbulence with strong shocks. In Kotov et al. (High Order Numerical Methods for LES of Turbulent Flows with Shocks, ICCFD8, Chengdu, Sichuan, China, July 14-18, 2014) the LES of a turbulent flow with a strong shock by the Yee & Sjögreen scheme indicated a good agreement with the filtered DNS data. A work in progress for the application of the adaptive flow sensor for compressible turbulence with time-varying random forcing is forthcoming. The present study examines the
Wang Lei; Babikov, Dmitri
2011-02-15
Anharmonicity of the quantized motional states of ions in a Paul trap can be utilized to address the state-to-state transitions selectively and control the motional modes of trapped ions coherently and adiabatically [Zhao and Babikov, Phys. Rev. A 77, 012338 (2008)]. In this paper we study two sources of the vibrational anharmonicity in the ion traps: the intrinsic Coulomb anharmonicity due to ion-ion interactions and the external anharmonicity of the trapping potential. An accurate numerical approach is used to compute energies and wave functions of vibrational eigenstates. The magnitude of the Coulomb anharmonicity is determined and shown to be insufficient for successful control. In contrast, anharmonicity of the trapping potential allows one to control the motion of ions very efficiently using the time-varying electric fields. Optimal control theory is used to derive the control pulses. One ion in a slightly anharmonic trap can be easily controlled. In the two- and three-ion systems the symmetric stretching mode is dark and cannot be controlled at all. The other two normal modes of the three-ion system can be controlled and used, for example, to encode a two-qubit system into the motional states of ions. A trap architecture that allows the necessary amount of vibrational anharmonicity to be achieved is proposed.
Numerical study on the influence of boss cap fins on efficiency of controllable-pitch propeller
NASA Astrophysics Data System (ADS)
Xiong, Ying; Wang, Zhanzhi; Qi, Wanjiang
2013-03-01
Numerical simulation is investigated to disclose how propeller boss cap fins (PBCF) operate utilizing Reynolds-averaged Navier-Stokes (RANS) method. In addition, exploration of the influencing mechanism of PBCF on the open water efficiency of one controllable-pitch propeller is analyzed through the open water characteristic curves, blade surface pressure distribution and hub streamline distribution. On this basis, the influence of parameters including airfoil profile, diameter, axial position of installation and circumferential installation angle on the open water efficiency of the controllable-pitch propeller is investigated. Numerical results show: for the controllable-pitch propeller, the thrust generated is at the optimum when the radius of boss cap fins is 1.5 times of propeller hub with an optimal installation position in the axial direction, and its optimal circumferential installation position is the midpoint of the extension line of the front and back ends of two adjacent propeller roots in the front of fin root. Under these optimal parameters, the gain of open water efficiency of the controllable-pitch propeller with different advance velocity coefficients is greater than 0.01, which accounts for approximately an increase of 1%-5% of open water efficiency.
Research on numerical control system based on S3C2410 and MCX314AL
NASA Astrophysics Data System (ADS)
Ren, Qiang; Jiang, Tingbiao
2008-10-01
With the rapid development of micro-computer technology, embedded system, CNC technology and integrated circuits, numerical control system with powerful functions can be realized by several high-speed CPU chips and RISC (Reduced Instruction Set Computing) chips which have small size and strong stability. In addition, the real-time operating system also makes the attainment of embedded system possible. Developing the NC system based on embedded technology can overcome some shortcomings of common PC-based CNC system, such as the waste of resources, low control precision, low frequency and low integration. This paper discusses a hardware platform of ENC (Embedded Numerical Control) system based on embedded processor chip ARM (Advanced RISC Machines)-S3C2410 and DSP (Digital Signal Processor)-MCX314AL and introduces the process of developing ENC system software. Finally write the MCX314AL's driver under the embedded Linux operating system. The embedded Linux operating system can deal with multitask well moreover satisfy the real-time and reliability of movement control. NC system has the advantages of best using resources and compact system with embedded technology. It provides a wealth of functions and superior performance with a lower cost. It can be sure that ENC is the direction of the future development.
Real time control and numerical simulation of pipeline subjected to landslide
Cuscuna, S.; Giusti, G.; Gramola, C.
1984-06-01
This paper describes SNAM research activity in the study of behaviour and real-time control of pipelines in landslide areas. The subject can be delt considering three different aspects: 1. Geotechnical characterization of unstable soils. The mechanical parameters of soil and the landslide types are defined; 2. Structural analysis of pipe-soil system. By means of a finite element program it's possible to study the pipe-soil interaction; in this numerical code the soil parameters attend by the non-linear elastic behaviour of pipe restraints. The results of this analysis are the location of the expected most stressed sections of pipe and the global behaviour of pipe inside the soil. 3. Instrumental control. The adoption of a suitable appliance of vibrating wire strain gauges allows the strain control of pipe in time. The aim is to make possible timely interventions in order to guarantee the installation safety.
NASA Technical Reports Server (NTRS)
Reed, John A.; Afjeh, Abdollah A.; Lewandowski, Henry; Homer, Patrick T.; Schlichting, Richard D.
1996-01-01
The NASA Numerical Propulsion System Simulation (NPSS) project is exploring the use of computer simulation to facilitate the design of new jet engines. Several key issues raised in this research are being examined in an NPSS-related research project: zooming, monitoring and control, and support for heterogeneity. The design of a simulation executive that addresses each of these issues is described. In this work, the strategy of zooming, which allows codes that model at different levels of fidelity to be integrated within a single simulation, is applied to the fan component of a turbofan propulsion system. A prototype monitoring and control system has been designed for this simulation to support experimentation with expert system techniques for active control of the simulation. An interconnection system provides a transparent means of connecting the heterogeneous systems that comprise the prototype.
Numerical Simulation of Non-Equilibrium Plasma Discharge for High Speed Flow Control
NASA Astrophysics Data System (ADS)
Balasubramanian, Ramakrishnan; Anandhanarayanan, Karupannasamy; Krishnamurthy, Rajah; Chakraborty, Debasis
2016-06-01
Numerical simulation of hypersonic flow control using plasma discharge technique is carried out using an in-house developed code CERANS-TCNEQ. The study is aimed at demonstrating a proof of concept futuristic aerodynamic flow control device. The Kashiwa Hypersonic and High Temperature wind tunnel study of plasma discharge over a flat plate had been considered for numerical investigation. The 7-species, 18-reaction thermo-chemical non-equilibrium, two-temperature air-chemistry model due Park is used to model the weakly ionized flow. Plasma discharge is modeled as Joule heating source terms in both the translation-rotational and vibrational energy equations. Comparison of results for plasma discharge at Mach 7 over a flat plate with the reference data reveals that the present study is able to mimic the exact physics of complex flow such as formation of oblique shock wave ahead of the plasma discharge region with a resultant rise in surface pressure and vibrational temperature up to 7000 K demonstrating the use of non-equilibrium plasma discharge for flow control at hypersonic speeds.
Numerical prediction of energy consumption in buildings with controlled interior temperature
Jarošová, P.; Št’astník, S.
2015-03-10
New European directives bring strong requirement to the energy consumption of building objects, supporting the renewable energy sources. Whereas in the case of family and similar houses this can lead up to absurd consequences, for building objects with controlled interior temperature the optimization of energy demand is really needed. The paper demonstrates the system approach to the modelling of thermal insulation and accumulation abilities of such objetcs, incorporating the significant influence of additional physical processes, as surface heat radiation and moisture-driven deterioration of insulation layers. An illustrative example shows the numerical prediction of energy consumption of a freezing plant in one Central European climatic year.
A numerical model including PID control of a multizone crystal growth furnace
NASA Technical Reports Server (NTRS)
Panzarella, Charles H.; Kassemi, Mohammad
1992-01-01
This paper presents a 2D axisymmetric combined conduction and radiation model of a multizone crystal growth furnace. The model is based on a programmable multizone furnace (PMZF) designed and built at NASA Lewis Research Center for growing high quality semiconductor crystals. A novel feature of this model is a control algorithm which automatically adjusts the power in any number of independently controlled heaters to establish the desired crystal temperatures in the furnace model. The control algorithm eliminates the need for numerous trial and error runs previously required to obtain the same results. The finite element code, FIDAP, used to develop the furnace model, was modified to directly incorporate the control algorithm. This algorithm, which presently uses PID control, and the associated heat transfer model are briefly discussed. Together, they have been used to predict the heater power distributions for a variety of furnace configurations and desired temperature profiles. Examples are included to demonstrate the effectiveness of the PID controlled model in establishing isothermal, Bridgman, and other complicated temperature profies in the sample. Finally, an example is given to show how the algorithm can be used to change the desired profile with time according to a prescribed temperature-time evolution.
NASA Astrophysics Data System (ADS)
Xia, Qian-Jin; Huang, Wei-Xi; Xu, Chun-Xiao; Cui, Gui-Xiang
2015-04-01
Opposition control of spatially developing turbulent boundary layers for skin friction drag reduction is studied by direct numerical simulations. The boundary layer extends 800θ0 in the streamwise (x) direction, with θ0 denoting the momentum thickness at the flow inlet. The Reynolds number, based on the external flow velocity and the momentum thickness, ranges from 300 to 860. Opposition control applied in different streamwise ranges, i.e. 200\\lt x/{{θ }0}\\lt 350 and 200\\lt x/{{θ }0}\\lt 550, as well as the uncontrolled case, are simulated. Statistical results and instantaneous flow fields are presented, with special attention paid to the spatial evolution properties of the boundary layer flow with control and the underlying mechanism. It is observed that a long spatial transient region after the control start and a long recovery region after the control end are present in the streamwise direction. A maximum drag reduction rate of about 22% is obtained as the transient region is passed, and an overshoot in the local skin friction coefficient (Cf) occurs in the recovery region. A new identity is derived for dynamical decomposition of Cf. Reduction of Cf by opposition control and overshoot of Cf in the recovery region are explained by quantifying the contributions from the viscous shear stress term, the Reynolds shear stress term, the mean convection term and other terms.
A numerical model of controlled bioinduced mineralization in a porous medium to prevent corrosion
NASA Astrophysics Data System (ADS)
Afanasyev, Michael; van Paassen, Leon; Heimovaara, Timo
2013-04-01
This paper presents a numerical model of controlled bioinduced mineralization in a porous medium as a possible corrosion protection mechanism. Corrosion is a significant economic problem - recent reports evaluate the annual cost of metal corrosion as 3-4% of the gross domestic product (GDP), in both developed and developing countries. Corrosion control methods currently used are costly and unsustainable as they require the use of larger volumes of materials, hazardous chemicals and regular inspections. As an alternative corrosion control method, bioinduced deposition of protective mineral layers has been proposed. Bioinduced precipitation of calcite has already been investigated for CO2 geological sequestration and soil improvement. To our knowledge, though, no numerical study of biomineralization for corrosion protection has been described yet. Our model includes three phases - solid, biofilm and mobile water. In the latter the reactive elements are dissolved, which are involved in the precipitation and the biofilm growth. The equations that describe the pore water flow, chemical reactions in the mobile water, consumption of substrate and expulsion of metabolic products by the biofilm are briefly presented. Also, the changes in porosity and permeability of the porous medium through biofilm growth and solids precipitation are included. Our main assumptions are that the biofilm is uniform, has a constant density and composition, that all chemical reactions except for substrate consumption occur in the mobile water, and that the precipitates are uniformly distributed on the surface of the solids. We validate the model with simple analytical solutions and against experimental data. The metabolism of the micro-organisms introduces changes in the physical and chemical characteristics of the environment, such as concentrations of chemicals and pH levels. As an extension to the model, we couple these changes to the rates of biofilm growth and precipitation rates. The
Numerical study of three-dimensional separation and flow control at a wing/body junction
NASA Technical Reports Server (NTRS)
Ash, Robert L.; Lakshmanan, Balakrishnan
1989-01-01
The problem of three-dimensional separation and flow control at a wing/body junction has been investigated numerically using a three-dimensional Navier-Stokes code. The numerical code employs an algebraic grid generation technique for generating the grid for unmodified junction and an elliptic grid generation technique for filleted fin junction. The results for laminar flow past a blunt fin/flat plate junction demonstrate that after grid refinement, the computations agree with experiment and reveal a strong dependency of the number of vortices at the junction on Mach number and Reynolds number. The numerical results for pressure distribution, particle paths and limiting streamlines for turbulent flow past a swept fin show a decrease in the peak pressure and in the extent of the separated flow region compared to the laminar case. The results for a filleted juncture indicate that the streamline patterns lose much of their vortical character with proper filleting. Fillets with a radius of three and one-half times the fin leading edge diameter or two times the incoming boundary layer thickness, significantly weaken the usual necklace interaction vortex for the Mach number and Reynolds number considered in the present study.
Adaptive Numerical Dissipative Control in High Order Schemes for Multi-D Non-Ideal MHD
NASA Technical Reports Server (NTRS)
Yee, H. C.; Sjoegreen, B.
2004-01-01
The goal is to extend our adaptive numerical dissipation control in high order filter schemes and our new divergence-free methods for ideal MHD to non-ideal MHD that include viscosity and resistivity. The key idea consists of automatic detection of different flow features as distinct sensors to signal the appropriate type and amount of numerical dissipation/filter where needed and leave the rest of the region free of numerical dissipation contamination. These scheme-independent detectors are capable of distinguishing shocks/shears, flame sheets, turbulent fluctuations and spurious high-frequency oscillations. The detection algorithm is based on an artificial compression method (ACM) (for shocks/shears), and redundant multi-resolution wavelets (WAV) (for the above types of flow feature). These filter approaches also provide a natural and efficient way for the minimization of Div(B) numerical error. The filter scheme consists of spatially sixth order or higher non-dissipative spatial difference operators as the base scheme for the inviscid flux derivatives. If necessary, a small amount of high order linear dissipation is used to remove spurious high frequency oscillations. For example, an eighth-order centered linear dissipation (AD8) might be included in conjunction with a spatially sixth-order base scheme. The inviscid difference operator is applied twice for the viscous flux derivatives. After the completion of a full time step of the base scheme step, the solution is adaptively filtered by the product of a 'flow detector' and the 'nonlinear dissipative portion' of a high-resolution shock-capturing scheme. In addition, the scheme independent wavelet flow detector can be used in conjunction with spatially compact, spectral or spectral element type of base schemes. The ACM and wavelet filter schemes using the dissipative portion of a second-order shock-capturing scheme with sixth-order spatial central base scheme for both the inviscid and viscous MHD flux
Numerical Study of Control of Flow Separation Over a Ramp with Nanosecond Plasma Actuator
NASA Astrophysics Data System (ADS)
Zheng, J. G.; Khoo, B. C.; Cui, Y. D.; Zhao, Z. J.; Li, J.
2016-06-01
The nanosecond plasma discharge actuator driven by high voltage pulse with typical rise and decay time of several to tens of nanoseconds is emerging as a promising active flow control means in recent years and is being studied intensively. The characterization study reveals that the discharge induced shock wave propagates through ambient air and introduces highly transient perturbation to the flow. On the other hand, the residual heat remaining in the discharge volume may trigger the instability of external flow. In this study, this type of actuator is used to suppress flow separation over a ramp model. Numerical simulation is carried out to investigate the interaction of the discharge induced disturbance with the external flow. It is found that the flow separation region over the ramp can be reduced significantly. Our work may provide some insights into the understanding of the control mechanism of nanosecond pulse actuator.
Numerical Studies of an Array of Fluidic Diverter Actuators for Flow Control
NASA Technical Reports Server (NTRS)
Gokoglu, Suleyman A.; Kuczmarski, Maria A.; Culley, Dennis E.; Raghu, Surya
2011-01-01
In this paper, we study the effect of boundary conditions on the behavior of an array of uniformly-spaced fluidic diverters with an ultimate goal to passively control their output phase. This understanding will aid in the development of advanced designs of actuators for flow control applications in turbomachinery. Computations show that a potential design is capable of generating synchronous outputs for various inlet boundary conditions if the flow inside the array is initiated from quiescence. However, when the array operation is originally asynchronous, several approaches investigated numerically demonstrate that re-synchronization of the actuators in the array is not practical since it is very sensitive to asymmetric perturbations and imperfections. Experimental verification of the insights obtained from the present study is currently being pursued.
Numerical study of linear feedback control for form-drag reduction
NASA Astrophysics Data System (ADS)
Dahan, Jeremy; Morgans, Aimee
2012-11-01
The present work is a numerical investigation of linear system identification and model-based feedback control methods for form-drag reduction. Large-Eddy Simulation (LES) is used to represent the flow over a simple bluff body with a sharp trailing edge, with a turbulent separation. For actuation, two types of perturbations are considered: a model of zero-net-mass-flux slot jets and momentum sources. Pressure measurements distributed over the base of the body provide the sensor information. The first part of the study will focus on the open-loop characterization of the flow. The base pressure field will be studied in relation to the wake dynamics. The effect of key actuation and flow parameters, such as actuation type, actuation location and Reynolds number, will be investigated. A black-box model of the flow response, obtained via system identification, will be examined. The second part will look at the design of robust controllers. It will be shown that uncertainties in the model and inflow conditions can be partially mitigated by the robustness of the controller. The behaviour of the feedback-controlled flow will be compared with the results achievable using open-loop forcing to draw conclusions about the success of the flow response model and the controller synthesis. PhD student in Department of Aeronautics.
Numerical simulations of interactions among aerodynamics, structural dynamics, and control systems
NASA Astrophysics Data System (ADS)
Preidikman, Sergio
A robust technique for performing numerical simulations of nonlinear unsteady aeroelastic behavior is developed. The technique is applied to long-span bridges and the wing of a modern business jet. The heart of the procedure is combining the aerodynamic and structural models. The aerodynamic model is a general unsteady vortex-lattice method. The structural model for the bridges is a rigid roadbed supported by linear and torsional springs. For the aircraft wing, the structural model is a cantilever beam with rigid masses attached at various positions along the span; it was generated with the NASTRAN program. The structure, flowing air, and control devices are considered to be the elements of a single dynamic system. All the governing equations are integrated simultaneously and interactively in the time domain; a predictor-corrector method was adapted to perform this integration. For long-span bridges, the simulation predicts the onset of flutter accurately, and the numerical results strongly suggest that an actively controlled wing attached below the roadbed can easily suppress the wind-excited oscillations. The governing equations for a proposed passive system were developed. The wing structure is modelled with finite elements. The deflections are expressed as an expansion in terms of the free-vibration modes. The time-dependent coefficients are the generalized coordinates of the entire dynamic system. The concept of virtual work was extended to develop a method to transfer the aerodynamic loads to the structural nodes. Depending on the speed of the aircraft, the numerical results show damped responses to initial disturbances (although there are no viscous terms in either the aerodynamic or structural model), merging of modal frequencies, the development of limit-cycle oscillations, and the occurrence of a supercritical Hopf bifurcation leading to motion on a torus.
Numerical algorithms for computations of feedback laws arising in control of flexible systems
NASA Technical Reports Server (NTRS)
Lasiecka, Irena
1989-01-01
Several continuous models will be examined, which describe flexible structures with boundary or point control/observation. Issues related to the computation of feedback laws are examined (particularly stabilizing feedbacks) with sensors and actuators located either on the boundary or at specific point locations of the structure. One of the main difficulties is due to the great sensitivity of the system (hyperbolic systems with unbounded control actions), with respect to perturbations caused either by uncertainty of the model or by the errors introduced in implementing numerical algorithms. Thus, special care must be taken in the choice of the appropriate numerical schemes which eventually lead to implementable finite dimensional solutions. Finite dimensional algorithms are constructed on a basis of a priority analysis of the properties of the original, continuous (infinite diversional) systems with the following criteria in mind: (1) convergence and stability of the algorithms and (2) robustness (reasonable insensitivity with respect to the unknown parameters of the systems). Examples with mixed finite element methods and spectral methods are provided.
Aradag, Selin
2013-01-01
In this study, the impact of laser energy deposition on pressure oscillations and relative sound pressure levels (SPL) in an open supersonic cavity flow is investigated. Laser energy with a magnitude of 100 mJ is deposited on the flow just above the cavity leading edge and up to 7 dB of reduction is obtained in the SPL values along the cavity back wall. Additionally, proper orthogonal decomposition (POD) method is applied to the x-velocity data obtained as a result of computational fluid dynamics simulations of the flow with laser energy deposition. Laser is numerically modeled using a spherically symmetric temperature distribution. By using the POD results, the effects of laser energy on the flow mechanism are presented. A one-dimensional POD methodology is applied to the surface pressure data to obtain critical locations for the placement of sensors for real time flow control applications. PMID:24363612
Numerical and Experimental Investigation of Plasma Actuator Control of Modified Flat-back Airfoil
NASA Astrophysics Data System (ADS)
Mertz, Benjamin; Corke, Thomas
2010-11-01
Flat-back airfoil designs have been proposed for use on the inboard portion of large wind turbine blades because of their good structural characteristics. These structural characteristics are achieved by adding material to the aft portion of the airfoil while maintaining the camber of the origional airfoil shape. The result is a flat vertical trailing edge which increases the drag and noise produced by these airfoils. In order to improve the aerodynamic efficiency of these airfoils, the use of single dielectric barrier discharge (SDBD) plasma actuators was investigated experimentally and numerically. To accomplish this, a rounded trailing edge was added to traditional flat-back airfoil and plasma actuators were used symmetrically to control the flow separation casued by the blunt trailing edge. The actuators were used asymmetrically in order to vector the wake and increase the lift produced by the airfoil similar to adding camber.
Numerical Studies of a Supersonic Fluidic Diverter Actuator for Flow Control
NASA Technical Reports Server (NTRS)
Gokoglu, Suleyman A.; Kuczmarski, Maria A.; Culley, Dennis e.; Raghu, Surya
2010-01-01
The analysis of the internal flow structure and performance of a specific fluidic diverter actuator, previously studied by time-dependent numerical computations for subsonic flow, is extended to include operation with supersonic actuator exit velocities. The understanding will aid in the development of fluidic diverters with minimum pressure losses and advanced designs of flow control actuators. The self-induced oscillatory behavior of the flow is successfully predicted and the calculated oscillation frequencies with respect to flow rate have excellent agreement with our experimental measurements. The oscillation frequency increases with Mach number, but its dependence on flow rate changes from subsonic to transonic to supersonic regimes. The delay time for the initiation of oscillations depends on the flow rate and the acoustic speed in the gaseous medium for subsonic flow, but is unaffected by the flow rate for supersonic conditions
Yilmaz, Ibrahim; Aradag, Selin
2013-01-01
In this study, the impact of laser energy deposition on pressure oscillations and relative sound pressure levels (SPL) in an open supersonic cavity flow is investigated. Laser energy with a magnitude of 100 mJ is deposited on the flow just above the cavity leading edge and up to 7 dB of reduction is obtained in the SPL values along the cavity back wall. Additionally, proper orthogonal decomposition (POD) method is applied to the x-velocity data obtained as a result of computational fluid dynamics simulations of the flow with laser energy deposition. Laser is numerically modeled using a spherically symmetric temperature distribution. By using the POD results, the effects of laser energy on the flow mechanism are presented. A one-dimensional POD methodology is applied to the surface pressure data to obtain critical locations for the placement of sensors for real time flow control applications. PMID:24363612
NASA Astrophysics Data System (ADS)
Coats, T. J.; Silcox, R. J.; Lester, H. C.
Market pressure for more fuel efficient air travel has led to increased use of turboprop and higher bypass turbofan engines. The low frequency components of propeller, jet and boundary layer noise are difficult to attenuate with conventional passive techniques. Weight and geometric restrictions for sound absorbing meterials limit the amount and type of treatment that may be applied. An active noise control (ANC) method is providing to be an attractive alternative. The approach taken in this paper uses a numerical finite/boundary element method (FEM/BEM) that may be easilty adapted to arbitrary geometries. A double walled cylinder is modeled using commercially available software. The outer shell is modeled as an aluminum cylinder, similar to that of aircraft skins. The inner shell is modeled as a composite material representative of a lightweight, stiff trim panel. Two different inner shell materials are used. The first is representative of current trim structure, the second a much stiffer composite. The primary source is generated by an exterior acoustic monopole. Control fields are generated using normal force inputs to the inner cylindrical shell. A linear least mean square (LMS) algorithm is used to determine amplitudes of control forces that minimize the interior acoustic field. Coupling of acoustic and structural modes and noise reductions are discussed for each of the inner shell materials.
NASA Technical Reports Server (NTRS)
Coats, T. J.; Silcox, R. J.; Lester, H. C.
1993-01-01
Market pressure for more fuel efficient air travel has led to increased use of turboprop and higher bypass turbofan engines. The low frequency components of propeller, jet and boundary layer noise are difficult to attenuate with conventional passive techniques. Weight and geometric restrictions for sound absorbing meterials limit the amount and type of treatment that may be applied. An active noise control (ANC) method is providing to be an attractive alternative. The approach taken in this paper uses a numerical finite/boundary element method (FEM/BEM) that may be easilty adapted to arbitrary geometries. A double walled cylinder is modeled using commercially available software. The outer shell is modeled as an aluminum cylinder, similar to that of aircraft skins. The inner shell is modeled as a composite material representative of a lightweight, stiff trim panel. Two different inner shell materials are used. The first is representative of current trim structure, the second a much stiffer composite. The primary source is generated by an exterior acoustic monopole. Control fields are generated using normal force inputs to the inner cylindrical shell. A linear least mean square (LMS) algorithm is used to determine amplitudes of control forces that minimize the interior acoustic field. Coupling of acoustic and structural modes and noise reductions are discussed for each of the inner shell materials.
NASA Astrophysics Data System (ADS)
Eltaweel, Ahmed
Prediction and reduction of airframe noise are critically important to the development of quieter civil transport aircraft. The key to noise reduction is a full understanding of the underlying noise source mechanisms. In this study, tandem cylinders in cross-flow as an idealization of a complex aircraft landing gear configuration are considered to investigate the noise generation and its reduction by flow control using single dielectric barrier discharge plasma actuators. The flow over tandem cylinders at ReD = 22, 000 with and without plasma actuation is computed using large-eddy simulation. The plasma effect is modeled as a body force obtained from a semi-empirical model. The flow statistics and surface pressure frequency spectra show excellent agreement with previous experimental measurements. For acoustic calculations, a boundary-element method is implemented to solve the convected Lighthill equation. The solution method is validated in a number of benchmark problems including flows over a cylinder, a rod-airfoil configuration, and a sphere. With validated flow field and acoustic solver, acoustic analysis is performed for the tandem-cylinder configuration to extend the experimental results and understand the mechanisms of noise generation and its control. Without flow control, the acoustic field is dominated by the interaction between the downstream cylinder and the upstream wake. Through suppression of vortex shedding from the upstream cylinder, the interaction noise is reduced drastically by the plasma flow control, and the vortex-shedding noise from the downstream cylinder becomes equally important. At a free-stream Mach number of 0.2, the peak sound pressure level is reduced by approximately 16 dB. This suggests the viability of plasma actuation for active control of airframe noise. The numerical investigation is extended to the noise from a realistic landing gear experimental model. Coarse-mesh computations are performed, and preliminary results are
Numerical Investigation of Active Flow Control on Wind Turbines under Yaw Misalignment
NASA Astrophysics Data System (ADS)
Tran, Steven; Corson, David; Sahni, Onkar
2012-11-01
Yaw misalignment dramatically increases unsteady aerodynamic loading on wind turbine blades over each revolution. The resulting fluctuating loads on each blade cause fatigue in the system and subsequently, failure leading to increased maintenance costs and unnecessary downtime. In this study we numerically analyze the effects of yaw misalignment on complete rotating wind turbines with blades of O(5m) in length. We consider two wind speeds at rated and above-rated regimes, where the effect of yaw misalignment is more pronounced. For the baseline configuration comparisons are made with the existing experimental data. To mitigate the resulting unsteady aerodynamic loading, we apply synthetic-jet based fluidic actuation in order to achieve fast-time response (in contrast to traditional yaw control strategies). O(5-10) jets are placed along the outer half of blade span. Along the chord two jet locations (x/c = 0.05 and 0.40) are considered. Actuation strategies for jets are based on partial loop control with pulse modulation. All simulations are based on unsteady Reynolds-averaged Navier-Stokes (URANS) equations. NYSERDA.
Numerical simulations of a vertical tail of a commercial aircraft with active flow control
NASA Astrophysics Data System (ADS)
Rasquin, Michel; Martin, Jeffrey; Jansen, Kenneth
2012-11-01
A series of numerical simulations of a realistic vertical tail of a commercial aircraft, with a tapered swept stabilizer and a rudder, is considered in this work with application of flow control. Flow control is known to have the capacity to augment the streamwise momentum near the rudder suction peak where separation is typically observed to limit rudder effectiveness for high deflection angles. Specifically, we use Delayed Detached Eddy Simulations (DDES) to study the interaction of a cross flow with an array of 24 synthetic jets for a 0° angle of attack, a 30° deflection angle and a Reynolds number of 7×105. We concentrate our analysis on the influence of the spacing between successive active jets in the spanwise direction. Indeed, our current simulations suggest that doubling the number of active jets at a lower Reynolds number improves the lateral force while opposite effect is observed at the considered Reynolds number when using the same size jets. These simulations offer insight into the fundamental physics of the flow structures in the vicinity of the synthetic jets by accurately resolving the complete synthetic jet pathway and the vorticity plume where the jet structures interact with each other and with the primary flow. The Boeing Company and the Argonne Leadership Computing Facility are acknowledged for their support and resources through the INCITE program.
NASA Astrophysics Data System (ADS)
Beneda, Károly
2012-11-01
The utilization of turbomachines requires up-to-date technologies to ensure safe operation throughout the widest possible range that makes novel ideas necessary to cope with classic problems. One of the most dangerous instability in compression systems is surge that has to be suppressed before its onset to avoid structural damages as well as other adverse consequences in the system. As surge occurs at low delivered mass flow rates the conventional widely spread surge control is based on bypassing the unnecessary airflow back to the atmosphere. This method has been implemented on a large number of aircraft and provides a robust control on suppressing compressor surge while creating a significant efficiency loss. This paper deals with an idea that has been originally designed as a fixed geometry that could be realized using up-to-date MEMS technology resulting in moderate losses but comparable stability enhancement. Previously the author has established the one-dimensional mathematical model of the concept, but it is indispensable - before the real instrument can be developed - to carry out detailed numerical simulation of the device. The aim of the paper is to acquaint the efforts of this CFD simulation.
NASA Technical Reports Server (NTRS)
Conner, M. D.; Tang, D. M.; Dowell, E. H.; Virgin, L. N.
1997-01-01
A three degree-of-freedom aeroelastic typical section with control surface freeplay is modeled theoretically as a system of piecewise linear state-space models. The system response is determined by time marching of the governing equations using a standard Runge-Kutta algorithm in conjunction with Henon's method for integrating a system of equations to a prescribed surface of phase space section. Henon's method is used to locate the "switching points" accurately and efficiently as the system moves from one linear region into another. An experimental model which closely approximates the three degree-of-freedom, typical section in two-dimensional, incompressible flow has been created to validate the theoretical model. Consideration is given to modeling realistically the structural damping present in the experimental system. The effect of the freeplay on the system response is examined numerically and experimentally. The development of the state-space model offers a low-order, computationally efficient means of modeling fully the freeplay nonlinearity and may offer advantages in future research which will investigate the effects of freeplay on the control of flutter in the typical section.
NASA Astrophysics Data System (ADS)
Temirbekov, Nurlan M.; Baigereyev, Dossan R.
2016-08-01
The paper focuses on the numerical implementation of a model optimal control problem governed by equations of three-phase non-isothermal flow in porous media. The objective is to achieve preassigned temperature distribution along the reservoir at a given time of development by controlling mass flow rate of heat transfer agent on the injection well. The problem of optimal control is formulated, the adjoint problem is presented, and an algorithm for the numerical solution is proposed. Results of computational experiments are presented for a test problem.
Direct numerical simulations of low Reynolds number turbulent channel flow with EMHD control
NASA Astrophysics Data System (ADS)
O'Sullivan, Peter L.; Biringen, Sedat
1998-05-01
We present results of numerical simulations of turbulence control in saltwater channel flows using electromagnetic (EM) forces. The control actuators are millimeter-sized micro-tiles flush mounted in the lower channel wall. This arrangement closely models one of the experimental designs proposed and developed by Bandyopadhyay at NUWC. We have studied two main secondary flow patterns which we denote by UV and WV (i.e., predominantly streamwise/normal and spanwise/normal) induced by both static and pulsed EM forcing. We have observed low net drag reduction, with a maximum of approximately 1%. This may be within the uncertainty of our computations. However, we have also found regions of localized reduction/increase in wall shear stress as high as ±11% versus the uncontrolled flow. Also, in every simulation with control we have observed a consistent (albeit small) reduction in skin friction which increases confidence in the results. The method of pulsing the EM force did not result in any observable resonance effects, at the low Reynolds numbers of this study. The mean turbulence intensities appear to be only weakly correlated with the reduction in viscous drag. The change in net drag does not appear to scale linearly on the magnitude of the EM forcing in the cases we have considered. Flow visualizations in the both the UV and WV cases indicate that the mean secondary flow above the actuators consists of a pair of near-wall oppositely oriented streamwise vortices which induce a flow where the normal velocity is wall-ward and is accompanied by strong spanwise wall jets.
NASA Astrophysics Data System (ADS)
Pelletier, Jon D.
2009-04-01
Ripples and transverse dunes in areas of abundant sand supply increase in height and spacing as a function of time, grain size, and excess shear velocity. How and why each of these factors influence ripple and transverse dune size, however, is not precisely known. In this paper, the controls on the height and spacing of ripples and transverse dunes in areas of abundant sand supply are investigated using a numerical model for the formation of eolian bedforms from an initially flat surface. This bedform evolution model combines the basic elements of Werner's [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107-1110.] cellular automaton model of dune formation with a model for boundary layer flow over complex topography. Particular attention is paid to the relationship between bed shear stress and slope on the windward (stoss) side of evolving bedforms. Nonlinear boundary layer model results indicate that bed shear stresses on stoss slopes increase with increasing slope angle up to approximately 20°, then decrease with increasing slope angle as backpressure effects become limiting. In the bedform evolution model, the linear boundary layer flow model of Jackson and Hunt [Jackson, P.S., Hunt, J.C.R., 1975. Turbulent wind flow over a low hill. Quarterly Journal of the Royal Meteorological Society 101, 929-955.], generalized to 3D, is modified to include the nonlinear relationship between bed shear stress and slope. Bed shear stresses predicted by the modified Jackson and Hunt flow model are then used to predict rates of erosion and deposition iteratively through time within a mass-conservative framework similar to Werner [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107-1110.]. Beginning with a flat bed, the model forms ripples that grow in height and spacing until a dynamic steady-state condition is achieved in which bedforms migrate downwind without further growth
NASA Astrophysics Data System (ADS)
Bhagatwala, Ankit; Sankaran, Ramanan; Kokjohn, Sage; Chen, Jacqueline
2014-11-01
Results from one and two-dimensional direct numerical simulations under dual-fuel Reactivity Controlled Compression Ignition (RCCI) conditions will be presented. These simulations employ an improved model of compression heating through mass source/sink terms developed in a previous work, which incorporates feedback from the flow to follow a predetermined experimental pressure trace. One-dimensional simulations explored the effect of temperature and fuel concentration gradients on the combustion mode. Two-dimensional simulations explored parametric variation in temperature stratification, pressure profiles and n-heptane concentration. Statistics derived from analysis of local diffusion/reaction balances were used to elucidate combustion characteristics for the different cases. Both deflagration and spontaneous ignition modes were observed to co-exist. Higher n-heptane concentration and higher level of thermal stratification resulted in a greater degree of flame propagation, whereas lower n-heptane concentration (higher fraction of iso-octane) and higher pressure resulted in more prevalent autoignition. Starting with a uniform initial temperature and a stratified n-heptane concentration also resulted in a large fraction of combustion occurring through flame propagation.
Numerical Prediction of Surface Heat Flux During Multiple Jets Firing for Missile Control
NASA Astrophysics Data System (ADS)
Saha, S.; Sinha, P. K.; Chakraborty, D.
2013-01-01
Numerical simulations are carried out to obtain the flowfield and heat flux arising out of the flow interactions of different control thrusters viz. vernier, pitch, yaw, roll and divert thruster among themselves as well as with free stream at different altitudes of operation. Three critical points on a typical trajectory of a missile are chosen and combinations of the thrusters operating at those conditions are considered. Simulations have also been performed to simulate DT motor interaction with free stream at different altitude. The interaction of different motor flowfield with the free stream presents a very complex flowfield. Flow gradients are very high close to the nozzle exit because of high altitude operation of motors. 3-Dimensional RANS equations are solved along with k-ɛ turbulence model on unstructured tetrahedral grid using commercial CFD software. The flow properties along with the surface heat flux distribution for four isothermal wall temperatures 350, 450, 550, 650 K are computed and provided for surface temperature prediction. It is observed that with increase in altitude, the high heat flux region reduces and heat transfer coefficient is independent of wall temperature.
Numerical approach of collision avoidance and optimal control on robotic manipulators
NASA Technical Reports Server (NTRS)
Wang, Jyhshing Jack
1990-01-01
Collision-free optimal motion and trajectory planning for robotic manipulators are solved by a method of sequential gradient restoration algorithm. Numerical examples of a two degree-of-freedom (DOF) robotic manipulator are demonstrated to show the excellence of the optimization technique and obstacle avoidance scheme. The obstacle is put on the midway, or even further inward on purpose, of the previous no-obstacle optimal trajectory. For the minimum-time purpose, the trajectory grazes by the obstacle and the minimum-time motion successfully avoids the obstacle. The minimum-time is longer for the obstacle avoidance cases than the one without obstacle. The obstacle avoidance scheme can deal with multiple obstacles in any ellipsoid forms by using artificial potential fields as penalty functions via distance functions. The method is promising in solving collision-free optimal control problems for robotics and can be applied to any DOF robotic manipulators with any performance indices and mobile robots as well. Since this method generates optimum solution based on Pontryagin Extremum Principle, rather than based on assumptions, the results provide a benchmark against which any optimization techniques can be measured.
NASA Technical Reports Server (NTRS)
Liu, Yi; Sankar, Lakshmi N.; Englar, Robert J.; Ahuja, Krishan K.
2003-01-01
The aerodynamic characteristics of a Circulation Control Wing (CCW) airfoil have been numerically investigated, and comparisons with experimental data have been made. The configuration chosen was a supercritical airfoil with a 30 degree dual-radius CCW flap. Steady and pulsed jet calculations were performed. It was found that the use of steady jets, even at very small mass flow rates, yielded a lift coefficient that is comparable or superior to conventional high-lift systems. The attached flow over the flap also gave rise to lower drag coefficients, and high L/D ratios. Pulsed jets with a 50% duty cycle were also studied. It was found that they were effective in generating lift at lower reduced mass flow rates compared to a steady jet, provided the pulse frequency was sufficiently high. This benefit was attributable to the fact that the momentum coefficient of the pulsed jet, during the portions of the cycle when the jet was on, was typically twice as much as that of a steady jet.
Numerical Study Comparing RANS and LES Approaches on a Circulation Control Airfoil
NASA Technical Reports Server (NTRS)
Rumsey, Christopher L.; Nishino, Takafumi
2011-01-01
A numerical study over a nominally two-dimensional circulation control airfoil is performed using a large-eddy simulation code and two Reynolds-averaged Navier-Stokes codes. Different Coanda jet blowing conditions are investigated. In addition to investigating the influence of grid density, a comparison is made between incompressible and compressible flow solvers. The incompressible equations are found to yield negligible differences from the compressible equations up to at least a jet exit Mach number of 0.64. The effects of different turbulence models are also studied. Models that do not account for streamline curvature effects tend to predict jet separation from the Coanda surface too late, and can produce non-physical solutions at high blowing rates. Three different turbulence models that account for streamline curvature are compared with each other and with large eddy simulation solutions. All three models are found to predict the Coanda jet separation location reasonably well, but one of the models predicts specific flow field details near the Coanda surface prior to separation much better than the other two. All Reynolds-averaged Navier-Stokes computations produce higher circulation than large eddy simulation computations, with different stagnation point location and greater flow acceleration around the nose onto the upper surface. The precise reasons for the higher circulation are not clear, although it is not solely a function of predicting the jet separation location correctly.
Improvement in thickness uniformity of thick SOI by numerically controlled local wet etching.
Yamamura, Kazuya; Ueda, Kazuaki; Hosoda, Mao; Zettsu, Nobuyuki
2011-04-01
Silicon-on-insulator (SOI) wafers are promising semiconductor materials for high-speed LSIs, low-power-consumption electric devices and micro electro mechanical systems (MEMS). The thickness distribution of an SOI causes the variation of threshold voltage in electronic devices manufactured on the SOI wafer. The thickness distribution of a thin SOI, which is manufactured by applying a smart cut technique, is comparatively uniform. On the other hand, a thick SOI has a large thickness distribution because a bonded wafer is thinned by conventional grinding and polishing. For a thick SOI wafer with a thickness of 1 microm, it is required that the tolerance of thickness variation is less than 50 nm. However, improving the thickness uniformity of a thick SOI layer to a tolerance of +/- 5% is difficult by conventional machining because of the fundamental limitations of these techniques. We have developed numerically controlled local wet etching (NC-LWE) technique as a novel deterministic subaperture figuring and finishing technique, which utilizes a localized chemical reaction between the etchant and the surface of the workpiece. We demonstrated an improvement in the thickness distribution of a thick SOI by NC-LWE using an HF/HNO3 mixture, and thickness variation improved from 480 nm to 200 nm within a diameter of 170 mm. PMID:21776652
Numerical Simulation of a Nanosecond-Pulse Discharge for High-Speed Flow Control
NASA Astrophysics Data System (ADS)
Poggie, Jonathan; Adamovich, Igor
2012-10-01
Numerical calculations were carried out to examine the physics of the operation of a nanosecond-pulse, single dielectric barrier discharge in a configuration with planar symmetry. This simplified configuration was chosen as a vehicle to develop a physics based nanosecond discharge model, including realistic air plasma chemistry and compressible bulk gas flow. First, a reduced plasma kinetic model was developed by carrying out a sensitivity analysis of zero-dimensional plasma computations with an extended chemical kinetic model. Transient, one- dimensional discharge computations were then carried out using the reduced kinetic model, incorporating a drift-diffusion formulation for each species, a self-consistent computation of the electric potential using the Poisson equation, and a mass-averaged gas dynamic formulation for the bulk gas motion. Discharge parameters (temperature, pressure, and input waveform) were selected to be representative of recent experiments on bow shock control with a nanosecond discharge in a Mach 5 cylinder flow. The computational results qualitatively reproduce many of the features observed in the experiments, including the rapid thermalization of the input electrical energy and the consequent formation of a weak shock wave. At breakdown, input electrical energy is rapidly transformed (over roughly 1 ns) into ionization products, dissociation products, and electronically excited particles, with subsequent thermalization over a relatively longer time-scale (roughly 10 μs).
NASA Astrophysics Data System (ADS)
Mathew, Reuble; Shi Yang, Hong Yi; Hall, Kimberley
2015-03-01
Optimal quantum control (OQC), which iteratively optimizes the control Hamiltonian to achieve a target quantum state, is a versatile approach for manipulating quantum systems. For optically-active transitions, OQC can be implemented using femtosecond pulse shaping which provides control over the amplitude and/or phase of the electric field. Optical pulse shaping has been employed to optimize physical processes such as nonlinear optical signals, photosynthesis, and has recently been applied to optimizing single-qubit gates in multiple semiconductor quantum dots. In this work, we examine the use of numerical pulse shape optimization for optimal quantum control of multiple qubits confined to quantum dots as a function of their electronic structure parameters. The numerically optimized pulse shapes were found to produce high fidelity quantum gates for a range of transition frequencies, dipole moments, and arbitrary initial and final states. This work enhances the potential for scalability by reducing the laser resources required to control multiple qubits.
Kreuzer, O.P.; Blenkinsop, T.G.; Morrison, R.J.; Peters, S.G.
2007-01-01
The approach taken in this paper, namely synthesising a wealth of previous information with new data and a genetic model, in combination with integrated numerical analyses, led to new insights into the geological controls on the localisation of auriferous veins and residual prospectivity of the Charters Towers goldfield, NE Australia. The method also has implications for the assessment of other "mature" goldfields worldwide. Despite a number of different ore controls having operated within the Charters Towers goldfield, the controlling factors can be linked to a single genetic model for orogenic, granitoid-hosted lode-gold mineralisation in a brittle deformation regime (D4) of NE-SW to NNE-SSW shortening, under conditions of supralithostatic fluid pressure and low stress difference. Spatial autocorrelation results suggest district-scale alignment of the auriferous veins parallel to and overlapping with the ESE-WNW- to E-W-striking Charters Towers-Ravenswood lineament, a major crustal boundary in the basement to the Ravenswood batholith. At the camp-scale, auriferous veins have abundance and proximity relationships with NW-SE-, NNW-SSE-, NE-SW- and ENE-WSW-oriented lineaments, suggesting that structures that controlled gold deposition in one camp did not necessarily control mineralisation in other camps. Fractal dimensions obtained with the box-counting method range from 1.02 to 1.10, whereas veins in the Charters Towers City camp are characterised by a significantly higher fractal dimension of 1.28. This discrepancy may be taken to imply that most or all outcropping and near-surface deposits within the Charters Towers City camp have been found and that new discoveries are more likely to occur at greater levels of depth, or outside the boundaries of this camp. The new understanding has implications for the assessment of the residual prospectivity of the Charters Towers goldfield, where large areas of prospective rock types and structures (e.g., approximately 40% of
ERIC Educational Resources Information Center
Rummell, Winfield Raymond
This study was designed to investigate the effectiveness of low cost instructional simulation, with numerical control (N/C) used as the subject vehicle. A unit of study was developed that included a detailed list of the behavioral changes which were desired for the students and the instructional materials and procedures deemed necessary for aiding…
ERIC Educational Resources Information Center
El Paso Community Coll., TX.
Curriculum guides are provided for plastics technology, industrial maintenance, and computer numerical control. Each curriculum is divided into a number of courses. For each course these instructor materials are presented in the official course outline: course description, course objectives, unit titles, texts and materials, instructor resources,…
CO2 migration in the vadose zone: experimental and numerical modelling of controlled gas injection
NASA Astrophysics Data System (ADS)
gasparini, andrea; credoz, anthony; grandia, fidel; garcia, david angel; bruno, jordi
2014-05-01
The mobility of CO2 in the vadose zone and its subsequent transfer to the atmosphere is a matter of concern in the risk assessment of the geological storage of CO2. In this study the experimental and modelling results of controlled CO2 injection are reported to better understanding of the physical processes affecting CO2 and transport in the vadose zone. CO2 was injected through 16 micro-injectors during 49 days of experiments in a 35 m3 experimental unit filled with sandy material, in the PISCO2 facilities at the ES.CO2 centre in Ponferrada (North Spain). Surface CO2 flux were monitored and mapped periodically to assess the evolution of CO2 migration through the soil and to the atmosphere. Numerical simulations were run to reproduce the experimental results, using TOUGH2 code with EOS7CA research module considering two phases (gas and liquid) and three components (H2O, CO2, air). Five numerical models were developed following step by step the injection procedure done at PISCO2. The reference case (Model A) simulates the injection into a homogeneous soil(homogeneous distribution of permeability and porosity in the near-surface area, 0.8 to 0.3 m deep from the atmosphere). In another model (Model B), four additional soil layers with four specific permeabilities and porosities were included to predict the effect of differential compaction on soil. To account for the effect of higher soil temperature, an isothermal simulation called Model C was also performed. Finally, the assessment of the rainfall effects (soil water saturation) on CO2 emission on surface was performed in models called Model D and E. The combined experimental and modelling approach shows that CO2 leakage in the vadose zone quickly comes out through preferential migration pathways and spots with the ranges of fluxes in the ground/surface interface from 2.5 to 600 g·m-2·day-1. This gas channelling is mainly related to soil compaction and climatic perturbation. This has significant implications to
Numerical simulation of rifting controlled by magmatic underplating in the South China Sea
NASA Astrophysics Data System (ADS)
Xu, Hehua
2016-04-01
the approach that it suggests re-meshing at every time time step, which can be easily done with marker-in-cell algorithm. Based on the numerical model behaviour in this study, the role of underplated magmatic bodies in localization is linked with an anomalously high temperature and rock melting. The most important factor in controlling localization of deformation is the strength contrast between the weakened and non-weakened regions. Studies show that the deformation can be redistributed into a different region if the underplated magmatic bodies emplacement in multiple multiple regions during the extensional process. we have discussed the microcontinent formations observed in the South China Sea.
Décollement controls on strain distribution in mountain belts: insights from numerical models.
NASA Astrophysics Data System (ADS)
Grool, Arjan R.; Huismans, Ritske S.; Ford, Mary
2016-04-01
Doubly vergent orogens have a pro-wedge (lower plate) and a retro-wedge (upper plate). Most shortening is accommodated in the pro-wedge while retro-wedge shortening is typically limited. For example, the Eastern Pyrenees have experienced about 145 km of convergence, of which about 125 km (86%) was accommodated in the pro-wedge and about 20 km (14%) in the retro-wedge. Strain partitioning between pro- and retro-wedge is influenced by several factors, some of which have been identified in past work: Extensional inheritance and syn-orogenic sedimentation can help to increase the percentage of total shortening accommodated in the retro-wedge while erosion promotes pro-wedge shortening. We use high-resolution 2D numerical models to investigate factors that control pro- versus retro-wedge shortening. For a total convergence similar to the Eastern Pyrenees, our models predict that variations in extensional inheritance and syn-orogenic sedimentation will result in a maximum of 10% of total shortening being accommodated in the retro-wedge. Here, we investigate the role of 1) the rheology and 2) distribution of a décollement layer. Our models show that: 1) Décollement rheology has a first order control on strain distribution between the pro- and the retro-wedge. After 145 km of total convergence, a model with a weak frictional (ϕ=2, shale-like) décollement will only accommodate 10% of total shortening in the retro-wedge. In contrast, in models with a weak viscous (μ=1018, salt-like) décollement retro-wedge shortening amounts to 18% and a stronger, but still weak, viscous décollement (μ=1019) leads to 21%. 2) Décollement distribution influences the timing of the first outward propagation of thick-skinned deformation in the retro-wedge. In the Eastern Pyrenees, thick-skinned deformation propagated out into the retro-wedge within 145 km of total convergence. In models with a décollement on both sides of the orogen this only occurred after 240 km. If, as in the Eastern
NASA Astrophysics Data System (ADS)
Pervin, Mollika; Ghergut, Iulia; Graf, Thomas; Peche, Aaron
2016-04-01
work, we explore some mechanisms and geologic controls that can lead to the formation of extensive vapor-dominated zones within a two-phase system. In particular, we investigate the effect of vertical heterogeneity of permeability (stratified reservoir, containing a permeability barrier) on the liquid water saturation profile within a modified HP model. Though in field observations liquid water has been directly encountered only within the condensation zone at reservoir top, it was speculated that large amounts of liquid water might also exist below the condensation zone. This is of great practical significance to the exploitation of vapor-dominated reservoirs, as their longevity depends on the fluid reserves in place. Within this work, we demonstrate by numerical simulations of a modified HP model that high values of liquid water saturation (>0.8) can prevail even far below the condensation zone. Such findings are useful as a baseline for future calculations regarding the economic exploitation of vapor-dominated systems, where premature productivity drop (or dry-out) is the main issue of concern. References: Eastman, G. Y:, 1968: The heat pipe. Scientific American, 218(5):38-46. Preuss, K. A., 1985: A quantitative model of vapor-dominated geothermal reservoirs as heat pipes in fractured porous rock, Transactions, Geothermal Resources. Council, 9(2), 353-361. Truesdell, A. H., and White, D.E. 1973: Production of superheated Steam from Vapor- dominated geothermal reservoirs. Geothermics, 2(3-4), 154-173
Numerical model of boundary-layer control using air-jet generated vortices
NASA Astrophysics Data System (ADS)
Henry, F. S.; Pearcey, H. H.
1994-12-01
Numerical calculations of the three-dimensional flowfield generated by pitched and skewed air jets issuing into an otherwise undisturbed turbulent boundary layer are presented. It is demonstrated that each such jet produces a single strong longitudinal vortex. The strength of the vortex, as inferred from its effect on the development of skin friction, is shown to be influenced by pitch and skew angles, exit velocity, and downstream distance in ways which accord with published experimental results. The calculated beneficial effect that the longitudinal vortices have on the development of skin friction in an adverse pressure gradient demonstrates the mechanism by which vortex generators delay boundary-layer separation. It follows that the numerical model could be used to optimize arrays of air-jet vortex generators. Furthermore, the facility to quantify the interaction between the vortex and the boundary layer should also be valuable in the application of vane vortex generators, and possible even more generally.
NASA Astrophysics Data System (ADS)
Bouallegue, Kais; Chaari, Abdessattar
In this study, one propose to study a numeric type strategy permitting the generation of any shape of path in view of the scheduling of the trajectories for a car-like mobile robot where the planned motions considered are continuous sequences in the space of the robot. These paths are programmed in order to have some types of closed or open trajectories. One is interested in the motion control of the robot from an initial position to a final position while optimizing the consumed energy in its alternated circular motion on both sides of the segment joining these two points. In this study, one presents a new method based on a numeric approach conceived from the kinematics equations of the robot. This new technique of numeric, adaptive and dynamic control of the robot is implemented on DSP21065L of the SHARC family. This algorithm assures the robot control of an initial position of departure to a final position of arrival without the existence of obstacles.
NASA Astrophysics Data System (ADS)
Ireland, Laralee Gordon
A numerical model was developed to investigate the possibility of implementing active control (ANC) to minimize noise radiation from high-bypass turbofan engines. Previous experimental work on the NASA Glenn Research Center active noise control fan (ANCF) was encouraging, but the question remained whether the modal approach investigated could be effective on real engines. The engine model developed for this research project uses an indirect boundary element method, implemented with Sysnoise, and a multi-mode Newton's algorithm, implemented with MATLAB(TM), to simulate the active control. Noise from the inlet was targeted. Both the experimental and numerical results based on the NASA ANCF simplified cylindrical engine geometry indicate overall reductions in the m = 2 component of the noise. Reductions obtained at the numerical sensor rings range from 17 dB to 63 dB and at a plane in the duct inlet, -8 dB to 33 dB. Rings mounted on the inlet duct are unable to accurately predict the total reduction of the inlet field, but the controller is still able to effectively reduce the total acoustic field. Generally, one sensor ring and one actuator ring per propagating mode were necessary to control the inlet field. At frequencies close to the cut-off frequency of a mode, an additional sensor and actuator ring were needed to adequately control the inlet field due to the evanescent mode. A more realistic, but still axisymmetric, engine geometry based on the GE CF6-80C engine was developed and the same algorithm used. Reductions obtained at the sensor rings range from 4 dB to 56 dB and at the duct inlet plane, from 12 dB to 26 dB. The overall far field noise radiation from the engine remained unchanged (0.4 dB) or decreased slightly (3.6 dB). The inlet noise was controlled at all frequencies but the noise from the exhaust was increased. The effect of inlet control on the exhaust radiation suggests the need for a controller that targets both the inlet and exhaust noise
NASA Technical Reports Server (NTRS)
Allan Brian G.; Owens, Lewis, R.
2006-01-01
This paper will investigate the validation of a NASA developed, Reynolds-averaged Navier-Stokes (RANS) flow solver, OVERFLOW, for a boundary-layer-ingesting (BLI) offset (S-shaped) inlet in transonic flow with passive and active flow control devices as well as the baseline case. Numerical simulations are compared to wind tunnel results of a BLI inlet conducted at the NASA Langley 0.3-Meter Transonic Cryogenic Tunnel. Comparisons of inlet flow distortion, pressure recovery, and inlet wall pressures are performed. The numerical simulations are compared to the BLI inlet data at a freestream Mach number of 0.85 and a Reynolds number of approximately 2 million based on the length of the fan-face diameter. The numerical simulations with and without wind tunnel walls are performed, quantifying effects of the tunnel walls on the BLI inlet flow measurements. The wind tunnel test evaluated several different combinations of jet locations and mass flow rates as well as a vortex generator (VG) vane case. The numerical simulations will be performed on a single jet configuration for varying actuator mass flow rates at a fix inlet mass flow condition. Validation of the numerical simulations for the VG vane case will also be performed for varying inlet mass flow rates. Overall, the numerical simulations were able to predict the baseline circumferential flow distortion, DPCPavg, very well for comparisons made within the designed operating range of the BLI inlet. However the CFD simulations did predict a total pressure recovery that was 0.01 lower than the experiment. Numerical simulations of the baseline inlet flow also showed good agreement with the experimental inlet centerline surface pressures. The vane case showed that the CFD predicted the correct trends in the circumferential distortion for varying inlet mass flow but had a distortion level that was nearly twice as large as the experiment. Comparison to circumferential distortion measurements for a 15 deg clocked 40 probe
Steckelberg, Anke; Albrecht, Martina; Kezle, Anna; Kasper, Jürgen; Mühlhauser, Ingrid
2013-01-01
Introduction: In Germany the implementation of human papillomavirus (HPV) vaccination for women aged 12–17 years was accompanied by various campaigns. Evidence-based information including numerical data was not provided. However, standard information leads to overestimation of cancer risk and effects of HPV vaccination. Confidence in children’s ability to deal with numerical data is low, especially in disadvantaged pupils. The aim of the present study was to compare the effects of a standard leaflet with an information leaflet supplemented with numerical data on ‘risk knowledge’ regarding HPV vaccination among schoolgirls. Methods: Randomised-controlled short-term trial. All 108 schoolgirls of seven school classes were asked to participate and 105 agreed. Participants were vocational schoolgirls who were preparing for grade 10 graduation and who were members of the target group for HPV vaccination. The control group was asked to read a standard leaflet on HPV vaccination of the German Women’s Health Network. The intervention group received the same leaflet, but it was supplemented with numerical information on cancer risk and assumed effects of the HPV vaccination on cancer prevention. As baseline characteristics we surveyed: age, vaccination status, attitude towards HPV vaccination and aspects regarding migration background. The primary end point was ‘risk knowledge’. Questionnaire surveys were performed under experimental conditions. Individual randomisation, participants, and intention-to-treat data analyses were blinded. The study was approved by the Ministry of Education and Culture of Schleswig-Holstein and the ethics committee of the Hamburg Chamber of Physicians. Results: We analysed ‘risk knowledge’ for all 105 randomised participants. Baseline characteristics of the two groups were comparable. Numerical risk information recipients were more likely to give correct answers compared to standard information recipients: Mean value of risk
Ponderomotive stabilization of flute modes in mirrors Feedback control and numerical results
NASA Technical Reports Server (NTRS)
Similon, P. L.
1987-01-01
Ponderomotive stabilization of rigid plasma flute modes is numerically investigated by use of a variational principle, for a simple geometry, without eikonal approximation. While the near field of the studied antenna can be stabilizing, the far field has a small contribution only, because of large cancellation by quasi mode-coupling terms. The field energy for stabilization is evaluated and is a nonnegligible fraction of the plasma thermal energy. A new antenna design is proposed, and feedback stabilization is investigated. Their use drastically reduces power requirements.
NASA Astrophysics Data System (ADS)
Kiuchi, Kenta; Shinkai, Hisa-Aki
2008-02-01
We present our numerical comparisons between the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) formulation widely used in numerical relativity today and its adjusted versions using constraints. We performed three test beds: gauge-wave, linear wave, and Gowdy-wave tests, proposed by the Mexico workshop on the formulation problem of the Einstein equations. We tried three kinds of adjustments, which were previously proposed from the analysis of the constraint propagation equations, and investigated how they improve the accuracy and stability of evolutions. We observed that the signature of the proposed Lagrange multipliers are always right and the adjustments improve the convergence and stability of the simulations. When the original BSSN system already shows satisfactory good evolutions (e.g., linear wave test), the adjusted versions also coincide with those evolutions, while in some cases (e.g., gauge-wave or Gowdy-wave tests) the simulations using the adjusted systems last 10 times as long as those using the original BSSN equations. Our demonstrations imply a potential to construct a robust evolution system against constraint violations even in highly dynamical situations.
NASA Astrophysics Data System (ADS)
Bosioc, A. I.; Tanasa, C.; Muntean, S.; Susan-Resiga, R. F.
2010-08-01
The paper presents our numerical results and experimental measurements for swirling flow with precessing vortex rope into a conical diffuser with water jet control. A test rig was designed and developed at Politehnica University of Timisoara in order to investigate different flow control techniques. Consequently, a vortex rope like in Francis turbine cone at 70% partial discharge is generated into the test rig section. The jet control method is experimentally investigated in order to mitigate the vortex rope and its associated pressure fluctuations. The unsteady pressure is recorded in 8 transducers flush mounted on the wall of the test section at different values of the jet discharge. The amplitude and frequency of the vortex rope is obtained based on unsteady pressure measurements using Fourier analysis. The 3D computational domain corresponds to the test rig section. The three-dimensional full unsteady turbulent computation is performed with jet control for different values of discharge. In numerical simulation, the unsteady pressures are obtained on the cone wall at the same positions as those in experimental investigation. Consequently, the amplitude and frequency of the vortex rope are computed and validated with experimental data. As a result, the amplitude and frequency are diminished if the water jet discharge is increased.
Chern, I-Liang
1994-08-01
Two versions of a control volume method on a symmetrized icosahedral grid are proposed for solving the shallow-water equations on a sphere. One version expresses of the equations in the 3-D Cartersian coordinate system, while the other expresses the equations in the northern/southern polar sterographic coordinate systems. The pole problem is avoided because of these expressions in both versions and the quasi-homogenity of the icosahedral grid. Truncation errors and convergence tests of the numerical gradient and divergent operators associated with this method are studied. A convergence tests of the numerical gradient and divergent operators associated with this method are studied. A convergence test for a steady zonal flow is demonstrated. Several simulations of Rossby-Haurwitz waves with various numbers are also performed.
Numerical simulations of flow fields through conventionally controlled wind turbines & wind farms
NASA Astrophysics Data System (ADS)
Emre Yilmaz, Ali; Meyers, Johan
2014-06-01
In the current study, an Actuator-Line Model (ALM) is implemented in our in-house pseudo-spectral LES solver SP-WIND, including a turbine controller. Below rated wind speed, turbines are controlled by a standard-torque-controller aiming at maximum power extraction from the wind. Above rated wind speed, the extracted power is limited by a blade pitch controller which is based on a proportional-integral type control algorithm. This model is used to perform a series of single turbine and wind farm simulations using the NREL 5MW turbine. First of all, we focus on below-rated wind speed, and investigate the effect of the farm layout on the controller calibration curves. These calibration curves are expressed in terms of nondimensional torque and rotational speed, using the mean turbine-disk velocity as reference. We show that this normalization leads to calibration curves that are independent of wind speed, but the calibration curves do depend on the farm layout, in particular for tightly spaced farms. Compared to turbines in a lone-standing set-up, turbines in a farm experience a different wind distribution over the rotor due to the farm boundary-layer interaction. We demonstrate this for fully developed wind-farm boundary layers with aligned turbine arrangements at different spacings (5D, 7D, 9D). Further we also compare calibration curves obtained from full farm simulations with calibration curves that can be obtained at a much lower cost using a minimal flow unit.
NASA Technical Reports Server (NTRS)
Allan, Brian G.; Owens, Lewis R.
2006-01-01
This paper will investigate the validation of the NASA developed, Reynolds-averaged Navier-Stokes (RANS) flow solver, OVERFLOW, for a boundary-layer-ingesting (BLI) offset (S-shaped) inlet in transonic flow with passive and active flow control devices as well as a baseline case. Numerical simulations are compared to wind tunnel results of a BLI inlet experiment conducted at the NASA Langley 0.3-Meter Transonic Cryogenic Tunnel. Comparisons of inlet flow distortion, pressure recovery, and inlet wall pressures are performed. The numerical simulations are compared to the BLI inlet data at a free-stream Mach number of 0.85 and a Reynolds number of approximately 2 million based on the fanface diameter. The numerical simulations with and without tunnel walls are performed, quantifying tunnel wall effects on the BLI inlet flow. A comparison is made between the numerical simulations and the BLI inlet experiment for the baseline and VG vane cases at various inlet mass flow rates. A comparison is also made to a BLI inlet jet configuration for varying actuator mass flow rates at a fixed inlet mass flow rate. Overall, the numerical simulations were able to predict the baseline circumferential flow distortion, DPCP avg, very well within the designed operating range of the BLI inlet. A comparison of the average total pressure recovery showed that the simulations were able to predict the trends but had a negative 0.01 offset when compared to the experimental levels. Numerical simulations of the baseline inlet flow also showed good agreement with the experimental inlet centerline surface pressures. The vane case showed that the CFD predicted the correct trends in the circumferential distortion levels for varying inlet mass flow but had a distortion level that was nearly twice as large as the experiment. Comparison to circumferential distortion measurements for a 15 deg clocked 40 probe rake indicated that the circumferential distortion levels are very sensitive to the symmetry of
NASA Astrophysics Data System (ADS)
Takei, Hiroyasu; Yoshinaga, Keinosuke; Matsuyama, Satoshi; Yamauchi, Kazuto; Sano, Yasuhisa
2015-01-01
Silicon-on-insulator (SOI) wafers are important semiconductor substrates in high-performance devices. In accordance with device miniaturization requirements, ultrathin and highly uniform top silicon layers (SOI layers) are required. A novel method involving numerically controlled (NC) atmospheric-pressure plasma sacrificial oxidation using an electrode array system was developed for the effective fabrication of an ultrathin SOI layer with extremely high uniformity. Spatial resolution and oxidation properties are the key factors controlling ultraprecision machining. The controllability of plasma oxidation and the oxidation properties of the resulting experimental electrode array system were examined. The results demonstrated that the method improved the thickness uniformity of the SOI layer over one-sixth of the area of an 8-in. wafer area.
Numerical simulation of tip clearance flow passive control in axial turbine
NASA Astrophysics Data System (ADS)
Li, Wei; Qiao, Wei-Yang; Xu, Kai-Fu; Luo, Hua-Ling
2008-06-01
This paper focuses on the effects of five different passive turbine tip clearance flow control methods on the tip clearance flow physics, which consists of a partial suction side squealer tip, a double squealer tip, a pressure side tip shelf with inclined squealer tip on a double squealer tip, a tip platform extension edge in pressure side and in suction side respectively. A pressure-correction based, 3D Reynolds-averaged Navier-Stokes equations CFD code with Reynolds Stress Model was adopted. The variable specific heat was considered. The detailed tip clearance flow field with different squealer rims was described with the streamline and the velocity vector. Accordingly, the mechanisms of five passive controls were elucidated; the effects of the passive controls on turbine efficiency and tip clearance flow field were illuminated. The results showed that the secondary flow loss near the outer casing including the tip leakage losses and the passage vortex losses could be reduced in all the five passive control methods. The turbine efficiency could be increased via the rational passive turbine tip clearance flow control. The Improved PS Squealer had the best effect on turbine efficiency, and the efficiency increased by 0.215%.
NASA Astrophysics Data System (ADS)
Bovy, Benoît; Braun, Jean; Demoulin, Alain
2016-06-01
We present a new numerical framework for simulating short to long-term hillslope evolution. This modeling framework, to which we have given the name CLICHE (CLImate Control on Hillslope Evolution), aims to better capture the control of climate on soil dynamics. It allows the use of realistic forcing that involves, through a specific time discretization scheme, the variability of both the temperature and precipitation at time scales ranging from the daily rainfall events to the climatic oscillations of the Quaternary, also including seasonal variability. Two simple models of soil temperature and soil water balance permit the link between the climatic inputs and derived quantities that take part in the computation of the soil flux, such as the surface water discharge and the depth of the non-frozen soil layer. Using this framework together with a multi-process parameterization of soil transport, we apply an original method to calculate hillslope effective diffusivity as a function of climate. This allows us to demonstrate the ability of the model to simulate observed rates of hillslope erosion under different climates (cold and temperate) with a single set of parameter values. Numerical experiments furthermore suggest a potential high peak of sediment transport on hillslopes during the glacial-interglacial transitions of the Quaternary. We finally discuss the need to improve the parameterization of the soil production and transport processes in order to explicitly account for other key controlling factors that are also climate-sensitive, such as biological activity.
Schuster, Eugenio
2014-05-02
The strong coupling between the different physical variables involved in the plasma transport phenomenon and the high complexity of its dynamics call for a model-based, multivariable approach to profile control where those predictive models could be exploited. The overall objective of this project has been to extend the existing body of work by investigating numerically and experimentally active control of unstable fluctuations, including fully developed turbulence and the associated cross-field particle transport, via manipulation of flow profiles in a magnetized laboratory plasma device. Fluctuations and particle transport can be monitored by an array of electrostatic probes, and Ex B flow profiles can be controlled via a set of biased concentric ring electrodes that terminate the plasma column. The goals of the proposed research have been threefold: i- to develop a predictive code to simulate plasma transport in the linear HELCAT (HELicon-CAThode) plasma device at the University of New Mexico (UNM), where the experimental component of the proposed research has been carried out; ii- to establish the feasibility of using advanced model-based control algorithms to control cross-field turbulence-driven particle transport through appropriate manipulation of radial plasma flow profiles, iii- to investigate the fundamental nonlinear dynamics of turbulence and transport physics. Lehigh University (LU), including Prof. Eugenio Schuster and one full-time graduate student, has been primarily responsible for control-oriented modeling and model-based control design. Undergraduate students have also participated in this project through the National Science Foundation Research Experience for Undergraduate (REU) program. The main goal of the LU Plasma Control Group has been to study the feasibility of controlling turbulence-driven transport by shaping the radial poloidal flow profile (i.e., by controlling flow shear) via biased concentric ring electrodes.
NASA Technical Reports Server (NTRS)
Buck, Gregory A.; Li, Weiming; Tong, Timothy W.
1993-01-01
Consideration is given to three generic families of luminaries with lamp power ranging from 11 to 150 watts. A concept of an equivalent radiation node boundary temperature was used to impose worst hot and cold environments, and transient finite difference models were developed to study the effects of geometry and optical properties of thermal control coatings. Minimum and maximum transient temperatures were computed at the critical location during 90 minute orbit and were compared with allowable limits. Results show that with the proper choice of optical properties, the luminaries can be passively controlled to within acceptable limits.
NASA Astrophysics Data System (ADS)
Vadillo, Jose L.
2005-07-01
Active control of flow over airfoils is currently an area of heightened interest in the aerospace community because of its potential in reducing drag, eliminating separation at high angles of attack, and modulating the aerodynamic forces and moments. We study these possibilities by performing several numerical simulations. Numerical simulations are performed by employing an Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations solver in conjunction with a two-equation Shear-Stress-Transport (SST) turbulence model. In particular, the computations are performed for the following three classes of flows: (1) Subsonic flow past a 24% thick Clark-Y airfoil with a triangular bump on the upper surface with and without a synthetic jet actuator. The goal is to perform numerical simulations of this experimentally observed fluidic modification of airfoil pressure distributions leading to reduced pressure drag. The computations are compared with experiments performed at Georgia Tech. (2) Transonic flow past a NACA64A010 airfoil with a synthetic jet actuator. The goal is to control the shock/boundary layer interaction on the airfoil using a synthetic jet actuator to reduce drag as well to achieve desired modulation of aerodynamic forces and moments. (3) Subsonic flow past a commercial supercritical airfoil leveraging the presence of a Gurney flap with a synthetic jet actuator. The goal is again to improve the aerodynamic performance (increase or maintain lift and reduce drag) by using a synthetic jet actuator integrated in a bump on the pressure surface of the airfoil near the trailing edge. The computations are compared with the experiments performed at Georgia Tech. The computations as well as the experiments show the feasibility of active flow control in reducing the drag of airfoils and in achieving the desired modulation of aerodynamic forces and moments.
ERIC Educational Resources Information Center
Laski, Elida V.; Dulaney, Alana
2015-01-01
The present study tested the "interference hypothesis"-that learning and using more advanced representations and strategies requires the inhibition of prior, less advanced ones. Specifically, it examined the relation between inhibitory control and number line estimation performance. Experiment 1 compared the accuracy of adults' (N = 53)…
Factors Controlling Slab Retreat and the Formation of Back-Arcs: Insights from Numerical Models
NASA Astrophysics Data System (ADS)
Huismans, R. S.; Grool, A.
2014-12-01
Although subduction is a first order plate tectonic process, the factors controlling the dynamics of slab roll-back and back-arc formation are still not very well understood. We present self-consistent thermo-mechanical models to study oceanic subduction, slab retreat, and back arc formation. We focus on two aspects of the subduction process: 1) factors that control retreat of the subduction zone, and 2) those that control the opening of the back arc. The model evolution is calculated using 2D plane strain thermo-mechanical finite element techniques for the finite element solution of incompressible viscous-plastic creeping flows (Fullsack, 1995). The models extend from the surface to 660 km depth. The upper surface of the model is free to move. We investigate interaction of the subducting slab with the overlying plate and focus on factors that may control the opening of a back-arc basin. The down going plate is driven by a kinematic boundary condition, far from the subduction zone. After an initial stage of far-field driven contraction, negative buoyant down welling of the oceanic lithosphere may drive continued subduction zone leading to mature subduction and the formation of an extensional back arc. The models suggest that two primary factors are required for slab retreat and the formation of an extensional back-arc system: 1) Convective destabilization and weakening of the overlying continental back arc region, and 2) sufficient negative buoyancy of the subducting plate.
On the numerical simulation of flutter and its suppression by active control
Dong, B.; Mook, D.T.
1994-12-31
The classic problem of predicting the motion (flutter) of a rigid airfoil mounted on an elastic support in a steady freestream is revisited. In the classic approach, the equations of motion were linearized, the supports were linear springs, the motion was assumed to be periodic, the aerodynamic loads were predicted by Wagner`s function, and the solution was obtained in the so-called frequency domain. In the present approach, the equations of motion are in their fully nonlinear form, the supports may be nonlinear springs, the motion is not assumed to be periodic, the loads are predicted by a general unsteady vorticity-panel method, and the solution is obtained in the so-called time domain. After it is demonstrated that the present approach predicts the onset of flutter and the post-flutter behavior for flat-plate as well as thick airfoils, the airfoil -is modified by the addition of a flap at the trailing edge. The flap is part of an actively controlled servomechanism, and it is demonstrated that flutter can be readily controlled with very little effort by a variety of feedback-control laws. In the present approach, emphasis is placed on considering the airfoil, its supports, the flowing air and the control/servo mechanism collectively to be a single dynamic system. All the equations of motion and control laws are solved simultaneously and interactively; thus, complete interactions among the various subsystems are captured. The present simulation of an oscillating airfoil provides some characteristics of the flutter phenomenon that were missed in previous studies: for example, it is shown that, in the absence of flaps, the motion in heave (the translational part of the motion) is responsible for adding energy to (exciting) the structural subsystem while the motion in pitch is responsible for extracting energy from (damping) the structural subsystem. Below the critical speed, there is more dissipation than excitation and hence all initial disturbances decay.
Numerical Investigation of Synthetic-jet based Flow Control on Vertical-axis Wind Turbine Blades
NASA Astrophysics Data System (ADS)
Menon, Ashwin; Tran, Steven; Sahni, Onkar
2013-11-01
Vertical-axis wind turbines encounter large unsteady aerodynamic loads in a sustained fashion due to the continuously varying angle of attack that is experienced by turbine blades during each revolution. Moreover, the detachment of the leading edge vortex at high angles of attack leads to sudden change in aerodynamic loads that result in structural vibrations and fatigue, and possibly failure. This numerical study focuses on using synthetic-jet based fluidic actuation to reduce the unsteady loading on VAWT blades. In the simulations, the jets are placed at the dominant separation location that is observed in the baseline case. We consider different tip-speed ratios, O(2-5), and we also study the effect of blowing ratio (to be in O(0.5-1.5)) and reduced frequency, i.e., ratio of jet frequency to flow frequency (to be in O(5-15)). For all cases, unsteady Reynolds-averaged Navier-Stokes simulations are carried out by using the Spallart-Allamaras turbulence model, where stabilized finite element method is employed for spatial discretization along with an implicit time-integration scheme.
NASA Astrophysics Data System (ADS)
Dong, Wen-Chao; Lu, Shan-Ping; Lu, Hao; Li, Dian-Zhong; Rong, Li-Jian; Li, Yi-Yi
2014-12-01
The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elastic-plastic FEM analysis based on SYSWELD code. Then, the welding distortion of floor structure was predicted using a linear elastic FEM and shrinkage method based on Weld Planner software. The effects of welding sequence, clamping configuration and reverse deformation on welding distortion of floor structure were examined numerically. The results indicate that the established elastic FEM model for floor structure is reliable for predicting the distribution of welding distortion in view of the good agreement between the calculated results and the measured distortion for real double floor structure. Compared with the welding sequence, the clamping configuration and the reverse deformation have a significant influence on the welding distortion of floor structure. In the case of 30 mm reverse deformation, the maximum deformation can be reduced about 70% in comparison to an actual welding process.
Numerical study of near-wall coherent structures and their control in turbulent boundary layers
NASA Astrophysics Data System (ADS)
Schoppa, Wade; Hussain, Fazle
Using direct numerical simulations of turbulent channel flow, we present a new method for skin friction reduction by prevention of streamwise vortex formation near the wall. Instability of lifted, vortex-free low-speed streaks (above a critical strength ωyc) is shown to generate new streamwise vortices, which dominate near-wall turbulence phenomena. This new vortex formation mechanism consists of: (i) instability-initiated streak waviness in the horizontal plane, (ii) generation of thin horizontal sheets of streamwise vorticity and induction of positive stretching ∂u/ϖx (i.e. positive VISA), inherent to streak waviness, and finally (iii) vorticity sheet collapse via stretching (rather than roll-up) into streamwise vortices. The instability mechanism is explained and its evolutionary dynamics are documented. Significantly, the 3D features of the (instantaneous) instability-generated vortices agree well with the coherent structures educed (i.e. ensemble-averaged) from fully turbulent flow, suggesting the prevalence of this mechanism.
NASA Astrophysics Data System (ADS)
Fiorentini, Marcello; Orlandini, Stefano; Paniconi, Claudio
2015-07-01
A process-based numerical model of integrated surface-subsurface flow is analyzed in order to identify, track, and reduce the mass balance errors affiliated with the model's coupling scheme. The sources of coupling error include a surface-subsurface grid interface that requires node-to-cell and cell-to-node interpolation of exchange fluxes and ponding heads, and a sequential iterative time matching procedure that includes a time lag in these same exchange terms. Based on numerical experiments carried out for two synthetic test cases and for a complex drainage basin in northern Italy, it is shown that the coupling mass balance error increases during the flood recession limb when the rate of change in the fluxes exchanged between the surface and subsurface is highest. A dimensionless index that quantifies the degree of coupling and a saturated area index are introduced to monitor the sensitivity of the model to coupling error. Error reduction is achieved through improvements to the heuristic procedure used to control and adapt the time step interval and to the interpolation algorithm used to pass exchange variables from nodes to cells. The analysis presented illustrates the trade-offs between a flexible description of surface and subsurface flow processes and the numerical errors inherent in sequential iterative coupling with staggered nodal points at the land surface interface, and it reveals mitigation strategies that are applicable to all integrated models sharing this coupling and discretization approach.
NASA Astrophysics Data System (ADS)
Domański, Zbigniew; Ciesielski, Mariusz; Mochnacki, Bohdan
2010-03-01
The paper presents the method to analyse the thermal processes occurring in the cast composite solidification. The cast is formed by a bundle of parallel fibres randomly immersed in a host metal matrix. The heat is transferred from the metal matrix and absorbed by the fibres. The objective of this paper is to evaluate the volumetric fraction of the fibres for which the solidification of the metal matrix occurs only due to the presence of fibres playing a role of internal chills. Our method is to compute Voronoi diagrams with Voronoi regions representing the geometric location of the fibres in the metal matrix and to use these regions as control volumes within a variant of the Control Volume Method.
Numerical investigation of engine-to-slip dynamics for motorcycle traction control applications
NASA Astrophysics Data System (ADS)
Massaro, M.; Sartori, R.; Lot, R.
2011-03-01
This work discusses the motorcycle engine-to-slip dynamics which are strictly related to the traction control design. A street motorcycle is analysed by means of an advanced mathematical model which also includes the tyre flexibility and the transmission compliance. The effects of the following parameters on engine-to-slip dynamics are investigated: vehicle speed, engaged gear ratio, sprocket absorber flexibility and road properties. Guidelines for increasing the maximum achievable closed-loop bandwidth are given.
NASA Astrophysics Data System (ADS)
Krasheninnikov, S. Yu.; Pudovikov, D. E.; Torohov, S. A.
2012-01-01
Solving the problem of creating an environmentally friendly "green plane" implies development and implementation of several actions aimed at increasing airplane performance and reducing environmental contamination. One possible way to solve this problem is to reduce the powerplant weight, in particular, by decreasing its length. The airplane engine flowpath comprises transition ducts: those between the low- and high-pressure compressors, between the compressor and combustor, and between the high- and low-pressure turbines. In a modern high-bypass turbofan, the flowpath varies in the streamwise direction. Shorter transition ducts have greater curvature. Because of this, intensive separation may occur, which leads to increased losses in the flowpath and to significant growth of nonuniformity of flow parameters. Vast experience of numerical and experimental studies of unsteady separated flows has been accumulated by now. In many cases, however, these investigations are performed in a two-dimensional (2D) formulation, which is primarily caused by the high cost of three-dimensional (3D) unsteady calculations. The numerical and experimental work [1] shows that flows in diffuser ducts can have an essentially unsteady 3D structure. This is valid even for ducts modeling 2D configurations. This paper describes the results of a numerical study of the flow structure and its features in model S-shaped transition ducts, as well as the results of using a synthetic jet generator for flow control and for reduction of total pressure losses. Three-dimensional flows are numerically modeled by the unsteady Reynolds-averaged Navier-Stokes (URANS) / RANS methods. The calculations show that the use of the synthetic jet generator can lead to duct loss reduction by 45%.
Numerical Investigation of Bending-Body Projectile Aerodynamics for Maneuver Control
NASA Astrophysics Data System (ADS)
Youn, Eric; Silton, Sidra
2015-11-01
Precision munitions are an active area of research for the U.S. Army. Canard-control actuators have historically been the primary mechanism used to maneuver fin-stabilized, gun-launched munitions. Canards are small, fin-like control surfaces mounted at the forward section of the munition to provide the pitching moment necessary to rotate the body in the freestream flow. The additional lift force due to the rotated body and the canards then alters the flight path toward the intended target. As velocity and maneuverability requirements continue to increase, investigation of other maneuver mechanisms becomes necessary. One option for a projectile with a large length-to-diameter ratio (L/D) is a bending-body design, which imparts a curvature to the projectile body along its axis. This investigation uses full Navier-Stokes computational fluid dynamics simulations to evaluate the effectiveness of an 8-degree bent nose tip on an 8-degree bent forward section of an L/D =10 projectile. The aerodynamic control effectiveness of the bending-body concept is compared to that of a standard L/D =10 straight-body projectile as well as that of the same projectile with traditional canards. All simulations were performed at supersonic velocities between Mach 2-4.
Liu, Chuan-shun; Zhao, Hui; Luo, Ji-wu
2009-01-01
An Evapotranspirative Landfill Cover (ET Landfill Cover) is a simple and economical percolation control system that involves a monolithic soil layer with a vegetative cover.Percolation control in an ET cover system relies on the storage of moisture within the cover soils during precipitation events and subsequently returns it to the atmosphere by evapotranspiration. Percolation control experiments of a bare soil cover and 5 different ET covers were implemented in comprehensive experimental station of water environment of Wuhan University and the water balance calculation of each cover system was conducted, the results shown that the ET cover of 60 cm loamy soil layer with shrub was the most effective among the 6 experimental disposals. However, the experiments demonstrated 60 cm thick of soil layer was not enough to prevent percolation during rainy season and keep the shrub alive during drought season without irrigation. So the Hydrus 2D was selected to simulate the soil water movement in ET covers with different cover thicknesses, the simulations shown that the optimal ET cover in Wuhan area should be 120-140 cm loamy soil layer with shrub. PMID:19353895
Analytical and numerical aspects in solving the controlled 3D Gross-Pitaevskii equation
Fedele, R.; Jovanovic, D.; De Nicola, S.; Eliasson, B.; Shukla, P. K.
2009-11-10
The results of recently developed investigations, that have been carried out within the framework of the controlling potential method (CPM), are reviewed. This method allows one to decompose a three dimensional (3D) Gross-Pitaevskii equation (GPE) into the pair of coupled Schroedinger-type equations. Under suitable mathematical conditions, the solutions of the 3D controlled GPE can be constructed from the solutions of a 2D linear Schroedinger equation (the transverse component of the GPE) coupled with a 1D nonlinear Schroedinger equation (the longitudinal component of the GPE). Such decomposition allows one to cast the solutions in the form of the product of the solutions of the transverse and the longitudinal components of the GPE. The coupling between these two equations is the functional of both the transverse and the longitudinal profiles. It is shown that the CPM can be used to obtain a new class of three-dimensional solitary waves solutions of the GPE, which governs the dynamics of Bose-Einstein condensates. By imposing an external controlling potential, the desired time-dependent shape of the localized BECs is obtained. The stability of the exact solutions was checked with direct simulations of the time -dependent, three-dimensional GPE. Our simulations show that the localized condensates are stable with respect to perturbed initial conditions.
NASA Astrophysics Data System (ADS)
Biffi, Carlo Alberto; Bassani, P.; Tuissi, A.; Carnevale, M.; Lecis, N.; LoConte, A.; Previtali, B.
2012-12-01
Shape memory alloys (SMAs) are very interesting smart materials not only for their shape memory and superelastic effects but also because of their significant intrinsic damping capacity. The latter is exhibited upon martensitic transformations and especially in martensitic state. The combination of these SMA properties with the mechanical and the lightweight of fiberglass-reinforced polymer (FGRP) is a promising solution for manufacturing of innovative composites for vibration suppression in structural applications. CuZnAl sheets, after laser patterning, were embedded in a laminated composite between a thick FGRP core and two thin outer layers with the aim of maximizing the damping capacity of the beam for passive vibration suppression. The selected SMA Cu66Zn24Al10 at.% was prepared by vacuum induction melting; the ingot was subsequently hot-and-cold rolled down to 0.2 mm thickness tape. The choice of a copper alloy is related to some advantages in comparison with NiTiCu SMA alloys, which was tested for the similar presented application in a previous study: lower cost, higher storage modulus and consequently higher damping properties in martensitic state. The patterning of the SMA sheets was performed by means of a pulsed fiber laser. After the laser processing, the SMA sheets were heat treated to obtain the desired martensitic state at room temperature. The transformation temperatures were measured by differential scanning calorimetry (DSC). The damping properties were determined, at room temperature, on full-scale sheet, using a universal testing machine (MTS), with cyclic tensile tests at different deformation amplitudes. Damping properties were also determined as a function of the temperature on miniature samples with a dynamical mechanical analyzer (DMA). Numerical modeling of the laminated composite, done with finite element method analysis and modal strain energy approaches, was performed to estimate the corresponding total damping capacity and then
NASA Astrophysics Data System (ADS)
Gao, Xin; Narteau, Clément; Rozier, Olivier
2016-03-01
Unlike ripples, there are only few numerical studies on grain size segregation at the scale of dunes in aeolian environments. Here we use a cellular automaton model to analyze vertical sorting in granular mixtures under steady unidirectional flow conditions. We investigate the feedbacks between dune growth and the segregation mechanisms by varying the size of coarse grains and their proportion within the bed. We systematically observe the development of a horizontal layer of coarse grains at the top of which sorted bed forms may grow by amalgamation. The formation of such an armor layer controls the overall sediment transport and availability. The emergence of dunes and the transition from barchan to transverse dune fields depend only on the grain size distribution of the initial sediment layer. As confirmed by observation, this result indicates that armor layers should be present in most arid deserts, where they are likely to control dune morphodynamics.
NASA Astrophysics Data System (ADS)
Mazhul, I. I.; Volkov, V. F.; Zvegintsev, V. I.; Ivanov, I. V.
2016-01-01
A possible influence of the deflection of control surfaces on the aerodynamics of an axisymmetric slender configuration at supersonic flow speeds is considered. A classical configuration consisting from the fuselage in the form of a body of revolution and having cross frontal fins and six-blade trailing stabilizers is considered as the investigation object. The physical flow pattern at the deflection of horizontal fin consoles is investigated and the estimates are obtained for the influence of this deflection on both the characteristics of elements (the body and stabilizers) as well as on the integral aerodynamic characteristics of the entire configuration. Numerical computations of the flow have been done at the freestream Mach number M = 3 in the range of attack angles α = 0-10° and the angles of the control surfaces deflection δ cs = ±5° on the basis of the averaged Navier-Stokes equations and the SST k-ω turbulence model.
Suárez-Pellicioni, Macarena; Núñez-Peña, María Isabel; Colomé, Àngels
2014-01-01
This study uses event-related brain potentials (ERPs) to investigate the electrophysiological correlates of numeric conflict monitoring in math-anxious individuals, by analyzing whether math anxiety is related to abnormal processing in early conflict detection (as shown by the N450 component) and/or in a later, response-related stage of processing (as shown by the conflict sustained potential; Conflict-SP). Conflict adaptation effects were also studied by analyzing the effect of the previous trial’s congruence in current interference. To this end, 17 low math-anxious (LMA) and 17 high math-anxious (HMA) individuals were presented with a numerical Stroop task. Groups were extreme in math anxiety but did not differ in trait or state anxiety or in simple math ability. The interference effect of the current trial (incongruent-congruent) and the interference effect preceded by congruence and by incongruity were analyzed both for behavioral measures and for ERPs. A greater interference effect was found for response times in the HMA group than in the LMA one. Regarding ERPs, the LMA group showed a greater N450 component for the interference effect preceded by congruence than when preceded by incongruity, while the HMA group showed greater Conflict-SP amplitude for the interference effect preceded by congruence than when preceded by incongruity. Our study showed that the electrophysiological correlates of numeric interference in HMA individuals comprise the absence of a conflict adaptation effect in the first stage of conflict processing (N450) and an abnormal subsequent up-regulation of cognitive control in order to overcome the conflict (Conflict-SP). More concretely, our study shows that math anxiety is related to a reactive and compensatory recruitment of control resources that is implemented only when previously exposed to a stimuli presenting conflicting information. PMID:24918584
NASA Astrophysics Data System (ADS)
Russo, David
2016-05-01
The aim of the present numerical study was to extend the data-driven protocol for the control of soil salinity, to control chloride and nitrate concentrations and mass fluxes below agricultural fields irrigated with treated waste water (TWW). The protocol is based on alternating irrigation water quality between TWW and desalinized water (DSW), guided by solute concentrations at soil depth, zs. Two different schemes, the first requires measurements of soil solution concentrations of chloride and nitrate at zs, while, the second scheme requires only measurements of soil solution EC at zs, were investigated. For this purpose, 3-D numerical simulations of flow and transport were performed for variably saturated, spatially heterogeneous, flow domains located at two different field sites. The sites differ in crop type, irrigation method, and in their lithology; these differences, in turn, considerably affect the performance of the proposed schemes, expressed in terms of their ability to reduce solute concentrations that drained below the root zone. Results of the analyses suggest that the proposed data-driven schemes allow the use of low-quality water for irrigation, while minimizing the consumption of high-quality water to a level, which, for given climate, soil, crop, irrigation method, and water quality, may be determined by the allowable nitrate and chloride concentrations in the groundwater. The results of the present study indicate that with respect to the diminution of groundwater contamination by chloride and nitrate, the more data demanding, first scheme is superior the second scheme.
Maltsev, Victor A.; Vinogradova, Tatiana M.; Bogdanov, Konstantin Y.; Lakatta, Edward G.; Stern, Michael D.
2004-01-01
Recent studies employing Ca2+ indicators and confocal microscopy demonstrate substantial local Ca2+ release beneath the cell plasma membrane (subspace) of sinoatrial node cells (SANCs) occurring during diastolic depolarization. Pharmacological and biophysical experiments have suggested that the released Ca2+ interacts with the plasma membrane via the ion current (INaCa) produced by the Na+/Ca2+ exchanger and constitutes an important determinant of the pacemaker rate. This study provides a numerical validation of the functional importance of diastolic Ca2+ release for rate control. The subspace Ca2+ signals in rabbit SANCs were measured by laser confocal microscopy, averaged, and calibrated. The time course of the subspace [Ca2+] displayed both diastolic and systolic components. The diastolic component was mainly due to the local Ca2+ releases; it was numerically approximated and incorporated into a SANC cellular electrophysiology model. The model predicts that the diastolic Ca2+ release strongly interacts with plasma membrane via INaCa and thus controls the phase of the action potential upstroke and ultimately the final action potential rate. PMID:15041695
Numerical assessment of efficiency and control stability of an HTS synchronous motor
NASA Astrophysics Data System (ADS)
Xian, Wei; Yuan, Weijia; Coombs, T. A.
2010-06-01
A high temperature superconducting (HTS) permanent magnet synchronous motor (PMSM) is designed and developed in Cambridge University. It is expected to become cost competitive with the conventional PMSM owing to its high efficiency, high power density, high torque density, etc. The structure and parameters of HTS PMSM are detailed. Both AC losses by transport current and applied filed in stator armature winding of HTS PMSM are also analyzed. Computed and simulated results of the characteristics of the HTS PMSM and conventional PMSM are compared. The improvement on stability of direct torque control (DTC) on the HTS PMSM is estimated, and proved by simulation on Matlab/Simulink.
Hun Yeon, Ju; Chan, Karen Y. T.; Wong, Ting-Chia; Chan, Kelvin; Sutherland, Michael R.; Ismagilov, Rustem F.; Pryzdial, Edward L. G.; Kastrup, Christian J.
2015-01-01
Developing bio-compatible smart materials that assemble in response to environmental cues requires strategies that can discriminate multiple specific stimuli in a complex milieu. Synthetic materials have yet to achieve this level of sensitivity, which would emulate the highly evolved and tailored reaction networks of complex biological systems. Here we show that the output of a naturally occurring network can be replaced with a synthetic material. Exploiting the blood coagulation system as an exquisite biological sensor, the fibrin clot end-product was replaced with a synthetic material under the biological control of a precisely regulated cross-linking enzyme. The functions of the coagulation network remained intact when the material was incorporated. Clot-like polymerization was induced in indirect response to distinct small molecules, phospholipids, enzymes, cells, viruses, an inorganic solid, a polyphenol, a polysaccharide, and a membrane protein. This strategy demonstrates for the first time that an existing stimulus-responsive biological network can be used to control the formation of a synthetic material by diverse classes of physiological triggers. PMID:25975772
NASA Astrophysics Data System (ADS)
Hun Yeon, Ju; Chan, Karen Y. T.; Wong, Ting-Chia; Chan, Kelvin; Sutherland, Michael R.; Ismagilov, Rustem F.; Pryzdial, Edward L. G.; Kastrup, Christian J.
2015-05-01
Developing bio-compatible smart materials that assemble in response to environmental cues requires strategies that can discriminate multiple specific stimuli in a complex milieu. Synthetic materials have yet to achieve this level of sensitivity, which would emulate the highly evolved and tailored reaction networks of complex biological systems. Here we show that the output of a naturally occurring network can be replaced with a synthetic material. Exploiting the blood coagulation system as an exquisite biological sensor, the fibrin clot end-product was replaced with a synthetic material under the biological control of a precisely regulated cross-linking enzyme. The functions of the coagulation network remained intact when the material was incorporated. Clot-like polymerization was induced in indirect response to distinct small molecules, phospholipids, enzymes, cells, viruses, an inorganic solid, a polyphenol, a polysaccharide, and a membrane protein. This strategy demonstrates for the first time that an existing stimulus-responsive biological network can be used to control the formation of a synthetic material by diverse classes of physiological triggers.
Numerical investigations of turbulent flow past a rectangular cylinder with active flow control
NASA Astrophysics Data System (ADS)
Luong, Sanh B.
The objective of the present research was to investigate the effects of rotating circular cylinders to control high intensity wind load. This research used computational fluid dynamics (CFD) to simulate high Reynolds number gust-like wind load condition for a transient duration of 12 seconds across a three-dimensional rectangular cylinder with dimension of 240x15x7 meters and aspect ratio (Breadth/Height) of 2.3. An array of 20 circular cylinders was positioned along the leading edges of the rectangular bridge cylinder. The research analyzed turbulent flow characteristics across the top and bottom deck surfaces and the development of wake region during two cases: 1) stationary cylinders and 2) rotated cylinders at 400 RPM or velocity ratio of lambda = 1.33. The Strouhal number flow characteristics of 0.08 and 0.17 for aspect ratio of 2 to 3 analyzed in this study were found to be in agreements with published literature.
Numerical simulation of the magnetoresistance effect controlled by electric field in p–n junction
NASA Astrophysics Data System (ADS)
Pan, Yang; Wen-Jie, Chen; Jiao, Wang; Zhao-Wen, Yan; Jian-Li, Qiao; Tong, Xiao; Xin, Wang; Zheng-Peng, Pang; Jian-Hong, Yang
2016-04-01
The magnetoresistance effect of a p–n junction under an electric field which is introduced by the gate voltage at room temperature is investigated by simulation. As auxiliary models, the Lombardi CVT model and carrier generation-recombination model are introduced into a drift-diffusion transport model and carrier continuity equations. All the equations are discretized by the finite-difference method and the box integration method and then solved by Newton iteration. Taking advantage of those models and methods, an abrupt junction with uniform doping is studied systematically, and the magnetoresistance as a function of doping concentration, SiO2 thickness and geometrical size is also investigated. The simulation results show that the magnetoresistance (MR) can be controlled substantially by the gate and is dependent on the polarity of the magnetic field.
Numerical study of plasma-assisted aerodynamic control for hypersonic vehicles
NASA Astrophysics Data System (ADS)
Bisek, Nicholas J.
Plasma actuators and various forms of volumetric energy deposition have received a good deal of research attention recently as a means of hypersonic flight control. Ground-based and flight experiments are extremely expensive and potentially dangerous, thus creating a need for computational tools capable of quickly and accurately modeling these devices and their effects on the flow-field. This thesis addresses these limitations by developing and incorporating several new features into an existing parallelized three-dimensional flow solver to accurately account for electromagnetic effects. A phenomenological heating model is developed and coupled to the fluid solver to investigate whether a practical level of pitch moment control can be achieved from volumetric energy deposition for a representative hypersonic vehicle. The results imply that the shape of the deposition volume does not have a significant effect on the flow structure, whereas the amount of energy deposited greatly influences the flow-field. The results suggest that these systems could be potential replacements for traditional mechanical flaps. While the phenomenological heating model sufficiently characterizes the downstream flow properties, it is a highly simplified physical model. To improve the physical fidelity and accuracy in the near-field, a three-dimensional magnetohydrodynamics (MHD) solver is developed and coupled to the fluid solver. This solver accurately computes the current density and electric field, and accounts for their effects on the flow-field. A particularly important parameter in the MHD solver is the electrical conductivity. Although several semi-empirical models exist in the literature, none provide generality across different flight regimes and gas compositions. Boltzmann's equation provides the necessary generality, but directly coupling a Boltzmann solver to a fluid solver is computationally prohibitive, even for a modern, multi-processor computing facility. A surrogate model
NASA Technical Reports Server (NTRS)
Thompson, J. F.; Mcwhorter, J. C.; Siddiqi, S. A.; Shanks, S. P.
1973-01-01
Numerical methods of integration of the equations of motion of a controlled satellite under the influence of gravity-gradient torque are considered. The results of computer experimentation using a number of Runge-Kutta, multi-step, and extrapolation methods for the numerical integration of this differential system are presented, and particularly efficient methods are noted. A large bibliography of numerical methods for initial value problems for ordinary differential equations is presented, and a compilation of Runge-Kutta and multistep formulas is given. Less common numerical integration techniques from the literature are noted for further consideration.
NASA Astrophysics Data System (ADS)
Ballan, Michele; Manzolaro, Mattia; Meneghetti, Giovanni; Andrighetto, Alberto; Monetti, Alberto; Bisoffi, Giovanni; Prete, Gianfranco
2016-06-01
The SPES project at INFN-LNL aims at the production of neutron-rich Radioactive Ion Beams (RIBs) using the ISOL (Isotope Separation On Line) technique. A 40 MeV 200 μA proton beam will directly impinge a uranium carbide target, generating approximately 1013 fissions per second. The target system is installed under vacuum inside a water-cooled chamber, and have to maintain high working temperatures, close to 2000 °C. During operation the proton beam provides the heating power required to keep the target at the desired temperature level. As a consequence, its characteristics have to be strictly controlled in order to avoid undesired overheating. According to the original design of the control system, the proton beam can be suddenly interrupted in case of out of range vacuum or cooling water flow levels. With the aim to improve the reliability of the control system a set of temperature sensors has been installed close to the target. Their types and installation positions were defined taking into consideration the detailed information coming from a dedicated thermal-electric model that allowed to investigate the most critical and inaccessible target hot-spots. This work is focused on the definition and experimental validation of the aforementioned numerical model. Its results were used to appropriately install two type C thermocouples, a PT100 thermo-resistance and a residual primary beam current detector. In addition the numerical model will be used for the definition of appropriate thresholds for each installed temperature sensor, since it allows to define a relationship between the locally measured values with the overall calculated temperature field. In case of over temperatures the monitoring system will send warning signals or in case interrupt the proton beam.
NASA Astrophysics Data System (ADS)
Gallego, E.; Soriano, C.; Roca, F. X.; Perales, J. F.; Alarcón, M.; Guardino, X.
Odour episodes and environmental air quality are topics of worldwide concern, mainly due to the fact that industrial facilities are often located very close to inhabited areas. Several atmospheric pollutants, mainly volatile organic compounds (VOCs), are responsible for odour episodes of varying degrees of annoyance. A methodology based on the simultaneous application of social participation (by building databases of odour episodes and acquiring air samples), chemical control and the computation of back trajectories allows us to identify the origin of odour episodes. A validated analytical method, based on thermal desorption (TD) coupled with gas chromatography (GC) and mass spectrometry (MS), is used to identify and determine a wide range of VOCs that cause odour nuisance and affect air quality in outdoor air. Back-trajectory modelling is used to track the origin of the air mass responsible for the discomfort backwards in time, mainly to find possible VOC sources outside the urban area. The procedure combines, on one hand, an analytical approach based on the acquisition of samples, which requires the participation of the affected population (which means that social participation is used as a scientific tool), and on the other hand, a modelling approach. Three examples are described to illustrate the methodology.
Numerical Simulations of Flow Separation Control in Low-Pressure Turbines using Plasma Actuators
NASA Technical Reports Server (NTRS)
Suzen, Y. B.; Huang, P. G.; Ashpis, D. E.
2007-01-01
A recently introduced phenomenological model to simulate flow control applications using plasma actuators has been further developed and improved in order to expand its use to complicated actuator geometries. The new modeling approach eliminates the requirement of an empirical charge density distribution shape by using the embedded electrode as a source for the charge density. The resulting model is validated against a flat plate experiment with quiescent environment. The modeling approach incorporates the effect of the plasma actuators on the external flow into Navier Stokes computations as a body force vector which is obtained as a product of the net charge density and the electric field. The model solves the Maxwell equation to obtain the electric field due to the applied AC voltage at the electrodes and an additional equation for the charge density distribution representing the plasma density. The new modeling approach solves the charge density equation in the computational domain assuming the embedded electrode as a source therefore automatically generating a charge density distribution on the surface exposed to the flow similar to that observed in the experiments without explicitly specifying an empirical distribution. The model is validated against a flat plate experiment with quiescent environment.
Numerical constraints and feedback control of double-strand breaks in mouse meiosis
Kauppi, Liisa; Barchi, Marco; Lange, Julian; Baudat, Frédéric; Jasin, Maria; Keeney, Scott
2013-01-01
Different organisms display widely different numbers of the programmed double-strand breaks (DSBs) that initiate meiotic recombination (e.g., hundreds per meiocyte in mice and humans vs. dozens in nematodes), but little is known about what drives these species-specific DSB set points or the regulatory pathways that control them. Here we examine male mice with a lowered dosage of SPO11, the meiotic DSB catalyst, to gain insight into the effect of reduced DSB numbers on mammalian chromosome dynamics. An approximately twofold DSB reduction was associated with the reduced ability of homologs to synapse along their lengths, provoking prophase arrest and, ultimately, sterility. In many spermatocytes, chromosome subsets displayed a mix of synaptic failure and synapsis with both homologous and nonhomologous partners (“chromosome tangles”). The X chromosome was nearly always involved in tangles, and small autosomes were involved more often than large ones. We conclude that homolog pairing requirements dictate DSB set points during meiosis. Importantly, our results reveal that karyotype is a key factor: Smaller autosomes and heteromorphic sex chromosomes become weak links when DSBs are reduced below a critical threshold. Unexpectedly, unsynapsed chromosome segments trapped in tangles displayed an elevated density of DSB markers later in meiotic prophase. The unsynapsed portion of the X chromosome in wild-type males also showed evidence that DSB numbers increased as prophase progressed. These findings point to the existence of a feedback mechanism that links DSB number and distribution with interhomolog interactions. PMID:23599345
Numerical analysis of the primary processes controlling oxygen dynamics on the Louisiana shelf
NASA Astrophysics Data System (ADS)
Yu, L.; Fennel, K.; Laurent, A.; Murrell, M. C.; Lehrter, J. C.
2015-04-01
The Louisiana shelf, in the northern Gulf of Mexico, receives large amounts of freshwater and nutrients from the Mississippi-Atchafalaya river system. These river inputs contribute to widespread bottom-water hypoxia every summer. In this study, we use a physical-biogeochemical model that explicitly simulates oxygen sources and sinks on the Louisiana shelf to identify the key mechanisms controlling hypoxia development. First, we validate the model simulation against observed dissolved oxygen concentrations, primary production, water column respiration, and sediment oxygen consumption. In the model simulation, heterotrophy is prevalent in shelf waters throughout the year, except near the mouths of the Mississippi and Atchafalaya rivers, where primary production exceeds respiratory oxygen consumption during June and July. During this time, efflux of oxygen to the atmosphere, driven by photosynthesis and surface warming, becomes a significant oxygen sink. A substantial fraction of primary production occurs below the pycnocline in summer. We investigate whether this primary production below the pycnocline is mitigating the development of hypoxic conditions with the help of a sensitivity experiment where we disable biological processes in the water column (i.e., primary production and water column respiration). With this experiment we show that below-pycnocline primary production reduces the spatial extent of hypoxic bottom waters only slightly. Our results suggest that the combination of physical processes (advection and vertical diffusion) and sediment oxygen consumption largely determine the spatial extent and dynamics of hypoxia on the Louisiana shelf.
Numerical Analysis of Synthetic Jet Flow Control on a Vertical Tail
NASA Astrophysics Data System (ADS)
Martin, Jeff
Airflow over a stabilizer-rudder assembly is simulated on an unstructured grid using a stream-line upwind Petrov-Galerkin (SUPG) weighted residual finite element formulation of the incompressible Navier-Stokes equations. These studies seek to determine the effectiveness of synthetic jet flow control in increasing side force over the vertical tail. The two models under investigation are the Beta model, with 12 jets aligned along the span of the stabilizer, and a Beta model scaled up by a factor of 1.969, with 24 jets aligned along the span of the stabilizer. These two models have Reynolds numbers of 3.6x10 5 and 7.1x105, respectively, where both are based on the mean aerodynamic chord. The flow solver, Phasta, is used to run these simulations. URANS simulations on the Beta model with a 5° sideslip angle and 20° rudder deflection angle show that unsteady blowing with a blowing ratio of 1.0 increases the total side force coefficient by 14% with respect to the baseline. The Cp data obtained as a function of percent chord showed improvement in Cp from unsteady blowing in the outboard region, but negligible change in the inboard region. This data is in agreement with experimental values. Speed isosurface data was obtained for the Beta model with a 0° sideslip angle and 30° rudder deflection angle, with steady blowing. It was found that these isosurfaces create ridges and valleys along the span, suggesting interference between the jets. The same result was found for the scaled-up Beta model with a 0° sideslip angle and 30° rudder deflection angle, with steady blowing.
NASA Astrophysics Data System (ADS)
Oki, Delwyn S.; Souza, William R.; Bolke, Edward L.; Bauer, Glenn R.
The coastal aquifer system of southern Oahu, Hawaii, USA, consists of highly permeable volcanic aquifers overlain by weathered volcanic rocks and interbedded marine and terrestrial sediments of both high and low permeability. The weathered volcanic rocks and sediments are collectively known as caprock, because they impede the free discharge of groundwater from the underlying volcanic aquifers. A cross-sectional groundwater flow and transport model was used to evaluate the hydrogeologic controls on the regional flow system in southwestern Oahu. Controls considered were: (a) overall caprock hydraulic conductivity; and (b) stratigraphic variations of hydraulic conductivity in the caprock. Within the caprock, variations in hydraulic conductivity, caused by stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of groundwater flow and the distribution of water levels and salinity. Results of cross-sectional modeling confirm the general groundwater flow pattern that would be expected in a layered coastal system. Groundwater flow is: (a) predominantly upward in the low-permeability sedimentary units; and (b) predominantly horizontal in the high-permeability sedimentary units. Résumé Le système aquifère littoral du sud d'Oahu (Hawaii, États-Unis) est constitué par des aquifères de terrains volcaniques très perméables, recouverts par des roches volcaniques altérées, et interstratifiés avec des sédiments marins et continentaux de perméabilité aussi bien forte que faible. Les roches volcaniques altérées et les sédiments sont globalement considérés comme une couverture, parce qu'ils s'opposent à l'écoulement de l'eau souterraine provenant des aquifères volcaniques sous-jacents. Les contrôles hydrogéologiques sur le système aquifère régional du sud-ouest d'Oahu ont étéévaluées au moyen d'un modèle d'écoulement et de transport sur une section transversale. Ces contrôles prennent en compte la conductivit
NASA Astrophysics Data System (ADS)
Oki, Delwyn S.; Souza, William R.; Bolke, Edward L.; Bauer, Glenn R.
The coastal aquifer system of southern Oahu, Hawaii, USA, consists of highly permeable volcanic aquifers overlain by weathered volcanic rocks and interbedded marine and terrestrial sediments of both high and low permeability. The weathered volcanic rocks and sediments are collectively known as caprock, because they impede the free discharge of groundwater from the underlying volcanic aquifers. A cross-sectional groundwater flow and transport model was used to evaluate the hydrogeologic controls on the regional flow system in southwestern Oahu. Controls considered were: (a) overall caprock hydraulic conductivity; and (b) stratigraphic variations of hydraulic conductivity in the caprock. Within the caprock, variations in hydraulic conductivity, caused by stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of groundwater flow and the distribution of water levels and salinity. Results of cross-sectional modeling confirm the general groundwater flow pattern that would be expected in a layered coastal system. Groundwater flow is: (a) predominantly upward in the low-permeability sedimentary units; and (b) predominantly horizontal in the high-permeability sedimentary units. Résumé Le système aquifère littoral du sud d'Oahu (Hawaii, États-Unis) est constitué par des aquifères de terrains volcaniques très perméables, recouverts par des roches volcaniques altérées, et interstratifiés avec des sédiments marins et continentaux de perméabilité aussi bien forte que faible. Les roches volcaniques altérées et les sédiments sont globalement considérés comme une couverture, parce qu'ils s'opposent à l'écoulement de l'eau souterraine provenant des aquifères volcaniques sous-jacents. Les contrôles hydrogéologiques sur le système aquifère régional du sud-ouest d'Oahu ont étéévaluées au moyen d'un modèle d'écoulement et de transport sur une section transversale. Ces contrôles prennent en compte la conductivit
NASA Astrophysics Data System (ADS)
Hemmings, B.; Whitaker, F.; Gottsmann, J.; Hughes, A.
2013-12-01
A quantitative understanding of hydrology is important for resource management in all island settings. In some volcanic island terrains, like the Lesser Antilles island of Montserrat, where high permeability surface geology generates limited and ephemeral drainage systems, water supplies rely entirely on the productivity of springs and groundwater aquifers. In active volcanic island settings the interaction of groundwater with volcanic processes can contribute to the hazard, triggering phreatic explosions and lahars. Hydrological systems have also been observed to respond to volcanic and tectonic perturbations. Understanding the fundamental hydrology in regions of active volcanism is essential for development of a truly multi-parameter hazard monitoring dataset, as well as effective exploitation of geothermal resources. Montserrat hosts a number of productive springs, six of which are trapped (yielding ~ 50 L/sec) to meet the islands entire freshwater demand. Most springs flow from elevations of 200-400 m into loosing streams on the flanks of the extinct volcanic complex of Centre Hills (CH), active 0.5 -1 Ma. The lack of surface water on Montserrat, despite deep incision into the volcaniclastic deposits, indicates the water table is at a relatively low elevation, suggesting springs are sourced from perched aquifers. Records from 1988 to present demonstrate that spring yields experience significant fluctuation. This clearly reflects variation in precipitation, but sensitivity of discharge to the magnitude, duration and frequency of recharge fluctuations is poorly understood. There is also circumstantial evidence that spring yields respond to volcanic and tectonic perturbations associated with the active Soufriere Hills Volcano to the south. We explore the potential geological and hydrological controls on spring distribution and behaviour using the integral finite element code TOUGH2. Initial simulations help develop a new conceptual hydrogeological model for CH
Liu, Jie; Haddad, Elias K.; Marceau, Joshua; Morabito, Kaitlyn M.; Rao, Srinivas S.; Filali-Mouhim, Ali; Sekaly, Rafick-Pierre; Graham, Barney S.
2016-01-01
CD8 T cells are involved in pathogen clearance and infection-induced pathology in respiratory syncytial virus (RSV) infection. Studying bulk responses masks the contribution of individual CD8 T cell subsets to protective immunity and immunopathology. In particular, the roles of subdominant responses that are potentially beneficial to the host are rarely appreciated when the focus is on magnitude instead of quality of response. Here, by evaluating CD8 T cell responses in CB6F1 hybrid mice, in which multiple epitopes are recognized, we found that a numerically subdominant CD8 T cell response against DbM187 epitope of the virus matrix protein expressed high avidity TCR and enhanced signaling pathways associated with CD8 T cell effector functions. Each DbM187 T effector cell lysed more infected targets on a per cell basis than the numerically dominant KdM282 T cells, and controlled virus replication more efficiently with less pulmonary inflammation and illness than the previously well-characterized KdM282 T cell response. Our data suggest that the clinical outcome of viral infections is determined by the integrated functional properties of a variety of responding CD8 T cells, and that the highest magnitude response may not necessarily be the best in terms of benefit to the host. Understanding how to induce highly efficient and functional T cells would inform strategies for designing vaccines intended to provide T cell-mediated immunity. PMID:26943673
Misumi, Kazuhiro; Tsumune, Daisuke; Tsubono, Takaki; Tateda, Yutaka; Aoyama, Michio; Kobayashi, Takuya; Hirose, Katsumi
2014-10-01
We used numerical simulations to investigate major controls on spatiotemporal variations of (137)Cs activities in seabed sediments off the Fukushima coast during the first year after the Fukushima Daiichi Nuclear Power Plant accident. The numerical model we used includes (137)Cs transfer between bottom water and sediment by adsorption and desorption, and radioactive decay. The model successfully reproduced major features of the observed spatiotemporal variations of (137)Cs activities in sediments. The spatial pattern of (137)Cs in sediments, which mainly reflected the history of (137)Cs activities in bottom water overlying the sediments and the sediment particle size distribution, became established during the first several months after the accident. The simulated temporal persistence of the (137)Cs activity in the sediments was due to adsorption of (137)Cs onto the sediment mineral fraction having a long desorption timescale of (137)Cs. The simulated total (137)Cs inventory in sediments integrated over the offshore area, where most of the monitoring stations were located, was on the order of 10(13) Bq; this value is consistent with a previous estimate based on observed data. Taking into account (137)Cs activities in sediments in both the coastal area and in the vicinity of the power plant, the simulated total inventory of (137)Cs in sediments off the Fukushima coast increased to a value on the order of 10(14) Bq. PMID:24980438
NASA Astrophysics Data System (ADS)
Fan, Juli; Tian, Lu; Jia, Xudong
2016-06-01
Transmission of airborne bacteria is the main factor causing surgical site infection (SSI). Horizontal laminar flow screen is a kind of new clean equipment, which can prevent SSI effectively. Numerical simulation is conducted on the pollution control effect of operating table protected by horizontal laminar flow screen. A three-dimensional model is established, discrete phase model (DPM) is used for calculation. Numerical simulation is carried out to evaluate the particle trajectories with the Lagrange approach, and the dynamic mesh is used. Air movement in the case with and without people’s walking is analyzed. As a result, people’s walking would not affect the distribution of pollutants at the key area of the operating table, the vertex caused by the walking person does little influence on flow field of the whole operating room and the influence area is about 0.24m to 0.75m around the walking person. The protective effect of pollutants with horizontal laminar flow screen for the key areas of operating table is excellent. This work provides references for the study on the depuration of operating room or other occasion.
Kawabata, Hirokazu; Funazaki, Ken-Ichi; Nakata, Ryota; Takahashi, Daichi
2014-06-01
This study deals with the experimental and numerical studies of the effect of flow control devices (FCDs) on the film cooling performance of a circular cooling hole on a flat plate. Two types of FCDs with different heights are examined in this study, where each of them is mounted to the flat plate upstream of the cooling hole by changing its lateral position with respect to the hole centerline. In order to measure the film effectiveness as well as heat transfer downstream of the cooling hole with upstream FCD, a transient method using a high-resolution infrared camera is adopted. The velocity field downstream of the cooling hole is captured by 3D laser Doppler velocimeter (LDV). Furthermore, the aerodynamic loss associated with the cooling hole with/without FCD is measured by a total pressure probe rake. The experiments are carried out at blowing ratios ranging from 0.5 to 1.0. In addition, numerical simulations are also made to have a better understanding of the flow field. LES approach is employed to solve the flow field and visualize the vortex structure around the cooling hole with FCD. When a taller FCD is mounted to the plate, the film effectiveness tends to increase due to the vortex structure generated by the FCD. As FCD is laterally shifted from the centerline, the film effectiveness increases, while the lift-off of cooling air is also promoted when FCD is put on the center line. PMID:25278646
Numerical study of wingtip shed vorticity reduction by wing Boundary Layer Control
NASA Astrophysics Data System (ADS)
Posada, Jose Alejandro
Wingtip vortex reductions have been obtained by Boundary Layer Control application to an AR=1.5 rectangular wing using a NACA 0012 airfoil. If wingtip shed vorticity could be reduced significantly, then so would induced drag resulting in improved cruise fuel economy. Power savings would be even more impressive at low flight speed or in climb. A two dimensional wing produces lift without wingtip vorticity. Its bound vorticity, Gamma, equals the contour integral of the boundary layer vorticity gamma or Gamma = ∮gamma · dl. Where the upper and lower boundary layers meet at the cusped TE, their local static pressure pu=pl then the boundary layer outer edge inviscid velocity Vupper=Vlower and gammalower=-gamma upper. This explains the 2-D wing self cancellation of the upper and lower surface boundary layer vorticity when they meet upon shedding at the trailing edge. In finite wings, the presence of spanwise pressure gradients near the wing tips misaligns gammalower and gammaupper at the wingtip TE preventing the upper and lower surface boundary layers from completely canceling each other. To prevent them from generating wing tip vortices, the local boundary layers need to be captured in suction slots. Once vorticity is captured, it can be eliminated by viscous mixing prior to venting over board. The objective of this dissertation was to use a commercial Computational Fluid Dynamics code (Fluent) to search for the best configuration to locate BLC suction slots to capture non-parallel boundary layer vorticity prior to shedding near the wingtips. The configuration selected for running the simulations was tested by trying to duplicate a 3D wing for which sufficient experimental and computational models by others are available. The practical case selected was done by Chow et al in the 32 x 48 in. low speed wind tunnel at the Fluid Mechanics Laboratory of NASA Ames Research Center, and computationally analyzed by Dacles-Mariani et al, and Khim and Rhee. The present
Shibahara, Masafumi; Yamamura, Kazuya; Sano, Yasuhisa; Sugiyama, Tsuyoshi; Endo, Katsuyoshi; Mori, Yuzo
2005-09-15
To improve the thickness uniformity of thin quartz crystal wafer, a new machining process that utilizes an atmospheric pressure plasma was developed. In an atmospheric pressure plasma process, since the kinetic energy of ions that impinge to the wafer surface is small and the density of the reactive species is large, high-efficiency machining without damage is realized, and the thickness distribution is corrected by numerically controlled scanning of the quartz wafer to the localized high-density plasma. By using our developed machining process, the thickness distribution of an AT cut wafer was improved from 174 nm [peak to valley (p-v)] to 67 nm (p-v) within 94 s. Since there are no unwanted spurious modes in the machined quartz wafer, it was proved that the developed machining method has a high machining efficiency without any damage.
NASA Astrophysics Data System (ADS)
Majumdar, Alok; Valenzuela, Juan; LeClair, Andre; Moder, Jeff
2016-03-01
This paper presents a numerical model of a system-level test bed-the multipurpose hydrogen test bed (MHTB) using the Generalized Fluid System Simulation Program (GFSSP). MHTB is representative in size and shape of a space transportation vehicle liquid hydrogen propellant tank, and ground-based testing was performed at NASA Marshall Space Flight Center (MSFC) to generate data for cryogenic storage. GFSSP is a finite volume-based network flow analysis software developed at MSFC and used for thermofluid analysis of propulsion systems. GFSSP has been used to model the self-pressurization and ullage pressure control by the Thermodynamic Vent System (TVS). A TVS typically includes a Joule-Thompson (J-T) expansion device, a two-phase heat exchanger (HEX), and a mixing pump and liquid injector to extract thermal energy from the tank without significant loss of liquid propellant. For the MHTB tank, the HEX and liquid injector are combined into a vertical spray bar assembly. Two GFSSP models (Self-Pressurization and TVS) were separately developed and tested and then integrated to simulate the entire system. The Self-Pressurization model consists of multiple ullage nodes, a propellant node, and solid nodes; it computes the heat transfer through multilayer insulation blankets and calculates heat and mass transfer between the ullage and liquid propellant and the ullage and tank wall. A TVS model calculates the flow through a J-T valve, HEX, and spray and vent systems. Two models are integrated by exchanging data through User Subroutines of both models. Results of the integrated models have been compared with MHTB test data at a 50% fill level. Satisfactory comparison was observed between tests and numerical predictions.
NASA Astrophysics Data System (ADS)
Gada, Komal Kantilal
Numerical investigations of an optimized thin airfoil with a passive and an active flow control device (riblets and rotary cylinder) have been performed. The objectives of the thesis were to investigate the tip vortices reduction using riblets and decrease in flow separation, using a rotary cylinder for improved lift-to-drag ratio. The investigations has application potentials in improving performances of Micro Air Vehicles (MAVs). The airfoil has a chord length of 19.66 cm and a span of 25 cm. with the free stream mean velocity was set at 20 m/s. The Reynolds number was calculated as 3 x 10 4. Investigations with base model of the airfoil have shown flow separation at approximately 85% chord length at an angle of attack of 17 degrees. For investigation using passive flow control device, i.e. riblets, investigations were performed for different radial sizes but at a fixed location. It was found that with 1 mm radial size riblet, the tip vortices were reduced by approximately 95%, as compared to the baseline model. Although negligible lift-to-drag improvement was seen, a faster dissipation rate in turbulent kinetic energy was observed. Furthermore, investigations were carried out using the active flow control device. The rotary cylinder with a 0.51 cm in diameter was placed slightly downstream of the location of flow separation, i.e. at x/c = 0.848. Investigations were performed at different cylinder's rotations, corresponding to different tangential velocities of being higher than, equal to and less than the free stream mean velocity. Results have shown approximately 10% improvement in lift to drag ratio when the tangential velocity is near the free stream mean velocity. Further investigation may include usage of the riblets and the rotary cylinder combined, to increase the stability as well as the lift-to-drag ratio of the MAVs.
NASA Technical Reports Server (NTRS)
Nixon, Douglas D.
2009-01-01
Discrete/Continuous (D/C) control theory is a new generalized theory of discrete-time control that expands the concept of conventional (exact) discrete-time control to create a framework for design and implementation of discretetime control systems that include a continuous-time command function generator so that actuator commands need not be constant between control decisions, but can be more generally defined and implemented as functions that vary with time across sample period. Because the plant/control system construct contains two linear subsystems arranged in tandem, a novel dual-kernel counter-flow convolution integral appears in the formulation. As part of the D/C system design and implementation process, numerical evaluation of that integral over the sample period is required. Three fundamentally different evaluation methods and associated algorithms are derived for the constant-coefficient case. Numerical results are matched against three available examples that have closed-form solutions.
NASA Astrophysics Data System (ADS)
Petrov, G. M.; Boris, D. R.; Petrova, Tz B.; Lock, E. H.; Fernsler, R. F.; Walton, S. G.
2013-12-01
In this work, the second in a series of two, a spatially averaged model of an electron beam generated Ar-N2 plasma is developed to identify the processes behind the measured influence of trace amounts of N2 on the development of the electron energy distribution function. The model is based on the numerical solution of the electron Boltzmann equation self-consistently coupled to a set of rate balance equations for electrons, argon and nitrogen species. Like the experiments, the calculations cover only the low-energy portion (<50 eV) of the electron energy distribution, and therefore a source term is added to the Boltzmann equation to represent ionization by the beam. Similarly, terms representing ambipolar diffusion along and across the magnetic field are added to allow for particle loss and electrostatic cooling from the ambipolar electric field. This work focuses on the changes introduced by adding a small admixture of nitrogen to an argon background. The model predictions for the electron energy distribution function, electron density and temperature are in good agreement with the experimentally measured data reported in part I, where it was found that the electron and ion energy distributions can be controlled by adjusting the fraction of nitrogen in the gas composition.
NASA Astrophysics Data System (ADS)
Troch, Peter A.; Pangle, Luke; Niu, Guo-Yue; Dontsova, Katerina; Barron-Gafford, Greg; van Haren, Joost; Pavao-Zuckerman, Mitch
2014-05-01
The Landscape Evolution Observatory (LEO) at Biosphere 2-The University of Arizona consists of three identical, sloping, 333 m2 convergent landscapes inside a 5,000 m2 environmentally controlled facility. These engineered landscapes contain 1-meter depth of basaltic tephra, ground to homogenous loamy sand that will undergo physical, chemical, and mineralogical changes over many years. Each landscape contains a spatially dense sensor and sampler network capable of resolving meter-scale lateral heterogeneity and sub-meter scale vertical heterogeneity in moisture, energy and carbon states and fluxes. The density of sensors and frequency at which they can be polled allows for data collection at spatial and temporal scales that are impossible in natural field settings. Embedded solution and gas samplers allow for quantification of biogeochemical processes, and facilitate the use of chemical tracers to study water movement at very high spatial resolutions. Each ~600 metric ton landscape has load cells embedded into the structure to measure changes in total system mass with 0.05% full-scale repeatability (equivalent to less than 1 cm of precipitation). This facilitates the real time accounting of hydrological partitioning at the hillslope scale. Each hillslope is equipped with an engineered rain system capable of raining at rates between 3 and 45 mm/hr in a range of spatial patterns. The rain systems are capable of creating long-term steady state conditions or running complex simulations. The precipitation water supply storage system is flexibly designed to facilitate addition of tracers at constant or time-varying rates for any of the three hillslopes. This presentation will discuss detection of early landscape evolution in terms of hydrological, geochemical and microbial processes through controlled experimentation, data analysis, and numerical modeling during the commissioning phase of the first hillslope at LEO.
NASA Astrophysics Data System (ADS)
Kim, Jungkwun; Yoon, Yong-Kyu; Allen, Mark G.
2016-03-01
This paper presents a computer-numerical-controlled ultraviolet light-emitting diode (CNC UV-LED) lithography scheme for three-dimensional (3D) microfabrication. The CNC lithography scheme utilizes sequential multi-angled UV light exposures along with a synchronized switchable UV light source to create arbitrary 3D light traces, which are transferred into the photosensitive resist. The system comprises a switchable, movable UV-LED array as a light source, a motorized tilt-rotational sample holder, and a computer-control unit. System operation is such that the tilt-rotational sample holder moves in a pre-programmed routine, and the UV-LED is illuminated only at desired positions of the sample holder during the desired time period, enabling the formation of complex 3D microstructures. This facilitates easy fabrication of complex 3D structures, which otherwise would have required multiple manual exposure steps as in the previous multidirectional 3D UV lithography approach. Since it is batch processed, processing time is far less than that of the 3D printing approach at the expense of some reduction in the degree of achievable 3D structure complexity. In order to produce uniform light intensity from the arrayed LED light source, the UV-LED array stage has been kept rotating during exposure. UV-LED 3D fabrication capability was demonstrated through a plurality of complex structures such as V-shaped micropillars, micropanels, a micro-‘hi’ structure, a micro-‘cat’s claw,’ a micro-‘horn,’ a micro-‘calla lily,’ a micro-‘cowboy’s hat,’ and a micro-‘table napkin’ array.
NASA Technical Reports Server (NTRS)
Gilchrist, Alan R.; Kooi, Henk; Beaumont, Christopher
1994-01-01
The relationship between morphology and surficial geology is used to quantify the denudation that has occurred across southwestern Africa sicne the fragmentation of Gondwana during the Early Mesozoic. Two main points emerge. Signficant denudation, of the order of kilometers, is widespread except in the Kalahari region of the continental interior. The denudation is systematically distributed so that the continental exterior catchment, draining directly to the Cape basin, is denuded to a greater depth than the interior catchment inland of the Great Escarpment. The analysis also implies tha the majority of the denudation occurred before the beginning of the Cenozoic for both teh exerior and interior catchments. Existing models of landscape development are reviewed, and implications of the denudation chronology are incorporated into a revised conceptual model. This revision implies tha thte primary effect of rifting on the subsequent landscape evolution is that it generates two distinct drainage regimes. A marginal upwarp, or rift flank uplift, separates rejuvenated rivers that drain into the subsiding rift from rivers in the continetal interior that are deflected but not rejuvenated. The two catchments evolve independently unless they are integrated by breaching of hte marginal upwarp. If this occurs, the exterior baselevel is communicated to the interior catchment that is denuded accordingly. Denudation rates generally decrease as the margin evolves, and this decrease is reinforced by the exposure of substrate that is resistant to denudation and/or a change to a more arid climate. The observations do not reveal a particular style of smaller-scale landscape evolution, sucha s escarpment retreat, that is responsible for the differential denudation across the region. It is proposed that numerical model experiments, which reflect the observational insights at the large scale, may identify the smaller-scale controls on escarpment development if the model and natural
ERIC Educational Resources Information Center
BOLDT, MILTON; POKORNY, HARRY
THIRTY-THREE MACHINE SHOP INSTRUCTORS FROM 17 STATES PARTICIPATED IN AN 8-WEEK SEMINAR TO DEVELOP THE SKILLS AND KNOWLEDGE ESSENTIAL FOR TEACHING THE OPERATION OF NUMERICALLY CONTROLLED MACHINE TOOLS. THE SEMINAR WAS GIVEN FROM JUNE 20 TO AUGUST 12, 1966, WITH COLLEGE CREDIT AVAILABLE THROUGH STOUT STATE UNIVERSITY. THE PARTICIPANTS COMPLETED AN…
ERIC Educational Resources Information Center
Bauch, Klaus Dieter
The study was designed to investigate the effects of Numerical Control Technology and Computer-Aided Manufacturing (NC/CAM) in American industry on industrial education and engineering technology education. The specific purpose was to identify a data base and rationale for curriculum development in NC/CAM through a comparison of views by…
NASA Astrophysics Data System (ADS)
Aghababa, Mohammad Pourmahmood
2012-03-01
The aim of this note is to point out some comments to the article [Delavari H, Ghaderi R, Ranjbar A, Momani S. Fuzzy fractional order sliding mode controller for nonlinear systems, Commun Nonlinear Sci Numer Simulat 15 (2010) 963-978].
ERIC Educational Resources Information Center
Pine, Douglas Taylor
This study utilized 120 metalworking students and six teachers from Columbus, Ohio area high schools to ascertain the effects of teaching numerical control to industrial arts students by means of simulator-aided activities versus nonsimulator aided activities. Scores obtained from an achievement test, attitude inventory, and word address…
Lippke, F.
1996-02-01
Direct steam generation (DSG) in parabolic troughs was first studied in the early 1980s by Murphy (1982) and Pederson (1982). Intensive research on DSG then started in 1988, when Luz identified this technology as the desired system for a future generation of its power plants. These R and D activities were not terminated by Luz`s demise in 1991, but have been continued by several institutes and companies in Europe as well as in Israel (Dagan et al., 1991, Mueller et al., 1992a, b, 1993, 1994). This paper concerns the dynamic reaction of the water-steam flow. In order to investigate this, a numerical simulation program of the water-steam flow. In order to investigate this, a numerical simulation program was developed at the ZSW. The numerical approach, its verification, and results of an extended study concerning the reaction and the control (ability) of a once-through DSG system at different weather conditions are presented.
Lippke, F.
1995-11-01
Direct steam generation (DSG) in parabolic troughs was first studied in the early eighties by Murphy (1982) and Pederson (1982). Intensive research on DSG then started in 1988, when Luz identified this technology as the desired system for a future generation of its power plants. These R and D activities were not terminated on Luz`s demise in 1991, but have been continued by several institutes and companies in Europe as well as in Israel (Dagan et al., 1991, Mueller et al., 1992a,b, 1993, 1994). This paper concerns the dynamic reaction of the water-steam flow. In order to investigate this, a numerical simulation program was developed at the ZSW. The numerical approach, its verification, and results of an extended study concerning the reaction and the control(ability) of a once-through DSG system at different weather conditions are presented.
Burd, W.; Culler, D.; Eskridge, T.; Cox, L.; Slater, T.
1993-08-01
The Milling Assistant (MA) programming system demonstrates the automated development of tool paths for Numerical Control (NC) machine tools. By integrating a Case-Based Reasoning decision processor with a commercial CAD/CAM software, intelligent tool path files for milled and point-to-point features can be created. The operational system is capable of reducing the time required to program a variety of parts and improving product quality by collecting and utilizing ``best of practice`` machining strategies.
NASA Astrophysics Data System (ADS)
Burd, William; Culler, David; Eskridge, Tom; Cox, Leon; Slater, Ted
1993-08-01
The Milling Assistant (MA) programming system demonstrates the automated development of tool paths for Numerical Control (NC) machine tools. By integrating a Case-Based Reasoning decision processor with a commercial CAD/CAM software, intelligent tool path files for milled and point-to-point features can be created. The operational system is capable of reducing the time required to program a variety of parts and improving product quality by collecting and utilizing 'best of practice' machining strategies.
ERIC Educational Resources Information Center
Siegler, Robert S.; Braithwaite, David W.
2016-01-01
In this review, we attempt to integrate two crucial aspects of numerical development: learning the magnitudes of individual numbers and learning arithmetic. Numerical magnitude development involves gaining increasingly precise knowledge of increasing ranges and types of numbers: from non-symbolic to small symbolic numbers, from smaller to larger…
NASA Astrophysics Data System (ADS)
Xu, Z.; Hu, B. X.; Davis, H.
2014-12-01
A groundwater flow cycling process between a submarine spring and an inland fresh water spring has been simulated using the latest research version of MODFLOW-CFP (Conduit Flow Process). Spring Creek Springs and Wakulla Spring, which are located in a marine estuary and 18 km inland, respectively, are two major groundwater discharge spots of Woodville Karst Plain (WKP), North Florida, USA. The two springs are found to be connected with karst conduits networks. Rising sea level may put seawater into the Spring Creek Springs and block groundwater discharge, which, in turn, increases freshwater discharge at Wakulla Spring. Three repeating phases in a karst spring flow cycle were proposed from low rainfall period to heavy rainfall period, and back to low rainfall period. During low rainfall periods, seawater flowed back into the conduits at Spring Creek Spring and freshwater was diverted to Wakulla Spring. After heavy rainfall, seawater was pushed back from Spring Creek Spring conduits. A MODFLOW model for WKP was modified to numerically study the groundwater flow cycling and seawater intrusion for three years. Conduit network distribution, high speed groundwater flow and exchange between conduits and matrix domain were simulated through the MODFLOW-CFP model. Rainfall, springs and creeks discharge data were used to calibrate the model. Simulation results catch very well with measurements, and numerically presented the three-phase groundwater cycling. In additional, simulation results were also supported by temperature data measured in conduits, which reflect precipitation recharge to groundwater, and indicate conduit flow direction. Key Words: Karst, Seawater Instrusion, MODFLOW-CFP, Groundwater Cycling
Using PASCAL for numerical analysis
NASA Technical Reports Server (NTRS)
Volper, D.; Miller, T. C.
1978-01-01
The data structures and control structures of PASCAL enhance the coding ability of the programmer. Proposed extensions to the language further increase its usefulness in writing numeric programs and support packages for numeric programs.
NASA Astrophysics Data System (ADS)
Van Der Beek, P.; Mercier, J.; Braun, J.
2015-12-01
Although the Himalayan range is traditionally presented as cylindrical, its geological structure, topography, precipitation, and exhumation patterns all vary significantly along-strike. The potential climatic or tectonic controls on these spatially variable topographic, precipitation and exhumation patterns have been widely discussed in recent years. A growing body of data suggests that variations in the geometry of the main Himalayan detachment (in particular the presence or absence of a major mid-crustal ramp) strongly control the kinematics, exhumation and topography of the orogen. However, what controls these variations in detachment geometry and their possible temporal evolution remains unclear. Here we report new thermo-mechanical modeling results to address these issues. We model the evolution of the Himalayan fold-and-thrust belt over the last ~30 Myr, focusing on the role of rheology and pre-existing structures in controlling this evolution. Our model results lead us to propose a scenario for the formation of Greater Himalayan klippen within the Lesser Himalayan fold-and-thrust belt and suggest a transient temporal evolution of the structure and topography of the fold-and-thrust belt in response to ramp formation at the orogenic front and subsequent migration toward the orogen interior. These results suggest that asynchronous ramp underthrusting in different segments of the range could control along-strike variations in topography, structure and exhumation of the mountain belt.
Strakova, Eva; Zikova, Alice; Vohradsky, Jiri
2014-01-01
A computational model of gene expression was applied to a novel test set of microarray time series measurements to reveal regulatory interactions between transcriptional regulators represented by 45 sigma factors and the genes expressed during germination of a prokaryote Streptomyces coelicolor. Using microarrays, the first 5.5 h of the process was recorded in 13 time points, which provided a database of gene expression time series on genome-wide scale. The computational modeling of the kinetic relations between the sigma factors, individual genes and genes clustered according to the similarity of their expression kinetics identified kinetically plausible sigma factor-controlled networks. Using genome sequence annotations, functional groups of genes that were predominantly controlled by specific sigma factors were identified. Using external binding data complementing the modeling approach, specific genes involved in the control of the studied process were identified and their function suggested. PMID:24157841
NASA Astrophysics Data System (ADS)
Corbi, Fabio; Herrendorfer, Robert; Funiciello, Francesca; van Dinther, Ylona
2016-04-01
Subduction megathrust earthquakes are one of the most destructive phenomena on Earth. Unraveling the role of parameters governing this process is difficult, mainly due to the short historical and instrumental observation period. To overcome this we run previously validated analogue and numerical seismic cycle models to study two of the most significant parameters; the width of the seismogenic zone W and subduction velocity Vs. Both simplified, essentially 2D, models have a comparable setup representing a rigid, straight slab with a seismogenic zone subducting beneath a viscoelastic forearc. We create thousands of years long time series of stress build up and sudden release via frictional instabilities (i.e., analog earthquakes) to study the resulting statistics of these events. In particular, we analyze seismic rate τ, maximum magnitude Mmax and moment release rate MRR. We show that: a) τ is directly correlated with Vs and inversely correlated with W; b) Mmax is directly correlated with W and insensitive to Vs; and c) MRR is directly correlated both with W and Vs. Wider seismogenic zones are associated to larger fault strength, which causes a longer recurrence time (due to the larger stress that must be reached for the rupture initiation) and larger seismic potential in terms of maximum size and release moment. Vs tunes the recurrence time and MMR. Similarly, in nature wider seismogenic zones are associated with the largest events and Vs tunes τ. Correlations in nature are however generally weaker than in our models, suggesting that other parameters (e.g., sediment thickness and trench parallel extent of the megathrust) may play a relevant role for the seismic behavior of subduction interfaces.
Tietze-Jaensch, Holger; Schneider, Stephan; Aksyutina, Yuliya; Bosbach, Dirk; Gauthier, Rene; Eissler, Alexander
2012-07-01
The German product quality control is inter alia responsible for control of two radioactive waste forms of heat generating waste: a) homogeneous vitrified HLW and b) heterogeneous compacted hulls, end-pieces and technological metallic waste. In either case, significantly different metrology is employed at the site of the conditioning plant for the obligatory nuclide inventory declaration. To facilitate an independent evaluation and checking of the accompanying documentation numerical simulations are carried out. The physical and chemical properties of radioactive waste residues are used to assess the data consistency and uncertainty margins, as well as to predict the long-term behavior of the radioactive waste. This is relevant for repository acceptance and safety considerations. Our new numerical approach follows a bottom-up simulation starting from the burn-up behavior of the fuel elements in the reactor core. The output of these burn-up calculations is then coupled with a program that simulates the material separation in the subsequent dissolution and extraction processes normalized to the mass balance. Follow-up simulations of the separated reprocessing lines of a) the vitrification of highly-active liquid and b) the compaction of residual intermediate-active metallic hulls remaining after fuel pellets dissolution, end-pieces and technological waste, allows calculating expectation values for the various repository relevant properties of either waste stream. The principles of the German product quality control of radioactive waste residues from the spent fuel reprocessing have been introduced and explained. Namely, heat generating homogeneous vitrified HLW and heterogeneous compacted metallic MLW have been discussed. The advantages of a complementary numerical property simulation have been made clear and examples of benefits are presented. We have compiled a new program suite to calculate the physical and radio-chemical properties of common nuclear waste
NASA Astrophysics Data System (ADS)
Torabmostaedi, Hosein; Zhang, Tao
2014-12-01
The development of a new quenching design combining rapid cooling with an expansion for controlling the size of nanoparticles synthesized at industrial scale by flame spray pyrolysis was investigated. The design of the quenching device was supported by simulations using a coupled computational fluid dynamics-monodisperse aerosol model to reduce the size of the primary particles and their agglomerate diameters while conserving the production yield at the filter above the burner. The results showed that quenching the spray flame in an open environment led to lower production yield due to the negative velocity of quenching gas which diverted the particles to the bottom of reactor. An additional upstream air flow could help to increase the particle production yield at high air flow rates, while it had a negative effect on the penetration depth of quenching gas inside the main flame which resulted in higher flame heights. The new design showed that adding an enclosure around the burner and quenching ring can significantly increase the quenching efficiency and reduce the particle size. The technique to control the particle size was also studied in this paper.
NASA Astrophysics Data System (ADS)
Torabmostaedi, Hosein; Zhang, Tao
2014-09-01
The development of a new quenching design combining rapid cooling with an expansion for controlling the size of nanoparticles synthesized at industrial scale by flame spray pyrolysis was investigated. The design of the quenching device was supported by simulations using a coupled computational fluid dynamics-monodisperse aerosol model to reduce the size of the primary particles and their agglomerate diameters while conserving the production yield at the filter above the burner. The results showed that quenching the spray flame in an open environment led to lower production yield due to the negative velocity of quenching gas which diverted the particles to the bottom of reactor. An additional upstream air flow could help to increase the particle production yield at high air flow rates, while it had a negative effect on the penetration depth of quenching gas inside the main flame which resulted in higher flame heights. The new design showed that adding an enclosure around the burner and quenching ring can significantly increase the quenching efficiency and reduce the particle size. The technique to control the particle size was also studied in this paper.
Heckman, B.K.; Chinn, V.K.
1981-01-01
The development and use of computer programs written to produce the paper tape needed for the automation, or numeric control, of drill presses employed to fabricate computed-designed printed circuit boards are described. (LCL)
NASA Astrophysics Data System (ADS)
DeSpirito, James; Vaughn, Milton E., Jr.; Washington, W. D.
2002-09-01
Viscous computational fluid dynamic simulations were used to predict the aerodynamic coefficients and flowfield around a generic canard-controlled missile configuration in supersonic flow. Computations were performed for Mach 1.5 and 3.0, at six angles of attack between 0 and 10, with 0 and 10 canard deflection, and with planar and grid tail fins, for a total of 48 cases. Validation of the computed results was demonstrated by the very good agreement between the computed aerodynamic coefficients and those obtained from wind tunnel measurements. Visualizations of the flowfield showed that the canard trailing vortices and downwash produced a low-pressure region on the starboard side of the missile that in turn produced an adverse side force. The pressure differential on the leeward fin produced by the interaction with the canard trailing vortices is primarily responsible for the adverse roll effect observed when planar fins are used. Grid tail fins improved the roll effectiveness of the canards at low supersonic speed. No adverse rolling moment was observed with no canard deflection, or at the higher supersonic speed for either tail fin type due to the lower intensity of the canard trailing vortices in these cases. Flow visualizations from the simulations performed in this study help in the understanding of the flow physics and can lead to improved canard and tail fin designs for missiles and rockets.
NASA Astrophysics Data System (ADS)
Yang, Jubiao; Krane, Michael; Zhang, Lucy
2013-11-01
Vocal fold vibrations and the glottal jet are successfully simulated using the modified Immersed Finite Element method (mIFEM), a fully coupled dynamics approach to model fluid-structure interactions. A self-sustained and steady vocal fold vibration is captured given a constant pressure input at the glottal entrance. The flow rates at different axial locations in the glottis are calculated, showing small variations among them due to the vocal fold motion and deformation. To further facilitate the understanding of the phonation process, two control volume analyses, specifically with Bernoulli's equation and Newton's 2nd law, are carried out for the glottal flow based on the simulation results. A generalized Bernoulli's equation is derived to interpret the correlations between the velocity and pressure temporally and spatially along the center line which is a streamline using a half-space model with symmetry boundary condition. A specialized Newton's 2nd law equation is developed and divided into terms to help understand the driving mechanism of the glottal flow.
NASA Astrophysics Data System (ADS)
Fasel, Hermann F.
2002-07-01
Wall jets over a curved wall geometry (Coanda flows) are investigated using DNS and turbulence modeling. In experiments large coherent structures have enhanced the effectiveness of wall jets in delaying or preventing flow separation on airfoils. Understanding the behavior of these structures is essential for utilizing wall jets for separation control. The research objective is to investigate curvature effects on large coherent structures, in particular the development of longitudinal (Goertler-type) vortices and their interaction with 2D vortices. The focus is on Coanda cylinders using two computational approaches. With the Flow Simulation Methodology (FSM), a turbulent wall jet is computed over a cylinder segment on a body-fitted grid. In FSM, the contribution of the turbulence model depends on the grid resolution relative to a local turbulent length scale. For a flat-plate reference case, FSM is employed as DNS, LES, and URANS. In all cases the large 2D vortices are captured. For the curved-wall geometry, FSM is employed as a DNS. Goertler-type vortices emerge in the simulation but remain weak due to the narrow computational domain. In the second approach, Coanda flows including nozzle and separated region are computed using immersed boundary techniques (IBT). The feasibility of IBT for Coanda Flows is established.
Numerical study of micro-ramp vortex generator for supersonic ramp flow control at Mach 2.5
NASA Astrophysics Data System (ADS)
Yan, Y.; Chen, L.; Li, Q.; Liu, C.
2016-03-01
An implicit large eddy simulation, implemented using a fifth-order, bandwidth-optimized weighted essentially non-oscillatory scheme, was used to study the flow past a compression ramp at Mach 2.5 and Re_{θ } = 5760 with and without a micro-ramp vortex generator (MVG) upstream. The MVG serves as a passive flow control device. The results suggested that MVGs may distinctly reduce the separation zone at the ramp corner and lower the boundary layer shape factor. New findings regarding the MVG-ramp interacting flow included the surface pressure distribution, three-dimensional structures of the re-compression shock waves, surface separation topology, and a new secondary vortex system. The formation of the momentum deficit was studied in depth. A new mechanism was observed wherein a series of vortex rings originated from the MVG-generated high shear at the boundary of the momentum deficit zone. Vortex rings strongly interact with the shock-separated flow and play an important role in the separation zone reduction.
Alizadeh, A; Wang, J K; Pooyan, S; Mirbozorgi, S A; Wang, M
2013-10-01
In this paper, the effect of temperature difference between inlet flow and walls on the electro-osmotic flow through a two-dimensional microchannel is investigated. The main objective is to study the effect of temperature variations on the distribution of ions and consequently internal electric potential field, electric body force, and velocity fields in an electro-osmotic flow. We assume constant temperature and zeta potential on walls and use the mean temperature of each cross section to characterize the Boltzmann ion distribution across the channel. Based on these assumptions, the multiphysical transports are still able to be described by the classical Poisson-Boltzmann model. In this work, the Navier-Stokes equation for fluid flow, the Poisson-Boltzmann equation for ion distribution, and the energy equation for heat transfer are solved by a couple lattice Boltzmann method. The modeling results indicate that the temperature difference between walls and the inlet solution may lead to two symmetrical vortices at the entrance region of the microchannel which is appropriate for mixing enhancements. The advantage of this phenomenon for active control of mixing in electro-osmotic flow is the manageability of the vortex scale without extra efforts. For instance, the effective domain of this pattern could broaden by the following modulations: decreasing the external electric potential field, decreasing the electric double layer thickness, or increasing the temperature difference between inlet flow and walls. This work may provide a novel strategy for design or optimization of microsystems. PMID:23859813
NASA Astrophysics Data System (ADS)
Troch, P. A.; Gevaert, A.; Smit, Y.; Niu, G.; Nakolan, L.; Kyzivat, E.
2013-12-01
The Landscape Evolution Observatory (LEO) at Biosphere 2-The University of Arizona consists of three identical, sloping, 333 m2 convergent landscapes inside a 5,000 m2 environmentally controlled facility. These engineered landscapes contain 1-meter depth of basaltic tephra, ground to homogenous loamy sand that will undergo physical, chemical, and mineralogical changes over many years. Each landscape contains a spatially dense sensor and sampler network capable of resolving meter-scale lateral heterogeneity and sub-meter scale vertical heterogeneity in moisture, energy and carbon states and fluxes. The density of sensors and frequency at which they can be polled allows for data collection at spatial and temporal scales that are impossible in natural field settings. Embedded solution and gas samplers allow for quantification of biogeochemical processes, and facilitate the use of chemical tracers to study water movement at very high spatial resolutions. Each ~600 metric ton landscape has load cells embedded into the structure to measure changes in total system mass with 0.05% full-scale repeatability (equivalent to less than 1 cm of precipitation). This facilitates the real time accounting of hydrological partitioning at the hillslope scale. Each hillslope is equipped with an engineered rain system capable of raining at rates between 3 and 45 mm/hr in a range of spatial patterns. The rain systems are capable of creating long-term steady state conditions or running complex simulations. The precipitation water supply storage system is flexibly designed to facilitate addition of tracers at constant or time-varying rates for any of the three hillslopes. Six trenches measure subsurface flow via tipping bucket gauges and electromagnetic flowmeters. This presentation will give an overview of lessons learned during the commissioning phase of the first hillslope of LEO, and will indicate several opportunities for collaborative research at Biosphere 2.