NASA Astrophysics Data System (ADS)
Howland, Michael; Bossuyt, Juliaan; Meyers, Johan; Meneveau, Charles
2015-11-01
Recently, there has been a push towards the optimization in the power output of entire large wind farms through the control of individual turbines, as opposed to operating each turbine in a maximum power point tracking manner. In this vane, the wake deflection by wind turbines in yawed conditions has generated considerable interest in recent years. In order to effectively study the wake deflection according to classical actuator disk momentum theory, a 3D printed drag disk model with a coefficient of thrust of approximately 0.75 - 0.85 and a diameter of 3 cm is used, studied under uniform inflow in a wind tunnel with test section of 1 m by 1.3 m, operating with a negligible inlet turbulence level at an inflow velocity of 10 m/s. Mean velocity profile measurements are performed using Pitot probes. Different yaw angles are considered, including 10, 20, and 30 degrees. We confirm earlier results that (e.g.) a 30 degree yaw angle deflects the center of the wake around 1/2 of a rotor diameter when it impinges on a downstream turbine. Detailed comparisons between the experiments and Large Eddy Simulations using actuator disk model for the wind turbines are carried out in order to help validate the CFD model. Work supported by NSF (grants CBET-113380 and IIA-1243482, the WINDINSPIRE project) and by ERC (ActiveWindFarms, grant no. 306471).
Large eddy simulation of unsteady wind farm behavior using advanced actuator disk models
NASA Astrophysics Data System (ADS)
Moens, Maud; Duponcheel, Matthieu; Winckelmans, Gregoire; Chatelain, Philippe
2014-11-01
The present project aims at improving the level of fidelity of unsteady wind farm scale simulations through an effort on the representation and the modeling of the rotors. The chosen tool for the simulations is a Fourth Order Finite Difference code, developed at Universite catholique de Louvain; this solver implements Large Eddy Simulation (LES) approaches. The wind turbines are modeled as advanced actuator disks: these disks are coupled with the Blade Element Momentum method (BEM method) and also take into account the turbine dynamics and controller. A special effort is made here to reproduce the specific wake behaviors. Wake decay and expansion are indeed initially governed by vortex instabilities. This is an information that cannot be obtained from the BEM calculations. We thus aim at achieving this by matching the large scales of the actuator disk flow to high fidelity wake simulations produced using a Vortex Particle-Mesh method. It is obtained by adding a controlled excitation at the disk. We apply this tool to the investigation of atmospheric turbulence effects on the power production and on the wake behavior at a wind farm level. A turbulent velocity field is then used as inflow boundary condition for the simulations. We gratefully acknowledge the support of GDF Suez for the fellowship of Mrs Maud Moens.
Development of an advanced actuator disk model for Large-Eddy Simulation of wind farms
NASA Astrophysics Data System (ADS)
Moens, Maud; Duponcheel, Matthieu; Winckelmans, Gregoire; Chatelain, Philippe
2015-11-01
This work aims at improving the fidelity of the wind turbine modelling for Large-Eddy Simulation (LES) of wind farms, in order to accurately predict the loads, the production, and the wake dynamics. In those simulations, the wind turbines are accounted for through actuator disks. i.e. a body-force term acting over the regularised disk swept by the rotor. These forces are computed using the Blade Element theory to estimate the normal and tangential components (based on the local simulated flow and the blade characteristics). The local velocities are modified using the Glauert tip-loss factor in order to account for the finite number of blades; the computation of this correction is here improved thanks to a local estimation of the effective upstream velocity at every point of the disk. These advanced actuator disks are implemented in a 4th order finite difference LES solver and are compared to a classical Blade Element Momentum method and to high fidelity wake simulations performed using a Vortex Particle-Mesh method in uniform and turbulent flows.
Numerical Simulation and Wake Modeling of Wind Turbine Rotor as AN Actuator Disk
NASA Astrophysics Data System (ADS)
Shen, Xiang; Wang, Tongguang; Zhong, Wei
Numerical simulations of flow fields around the wind turbine rotor simplified as an actuator disk (AD) with zero thickness have been made to investigate the flow structure and wake development in different operation states. A N-S solver has been used and the energy extracted by the rotor is represented by a discontinuous pressure jump through the actuator disk. Axial pressure and velocity development from far upstream to far downstream is fully described by the simulations, which could never be obtained by the momentum theory. It is showed that there are significant differences in wake development between inviscid and viscous conditions. In inviscid simulations, the axial velocity keeps decreasing along the oncoming flow direction, which is consistent with the momentum theory. In viscous simulations, however, the axial velocity first decreases but then gradually recovers approaching to the undisturbed velocity, due to momentum transport from outer flow to wake flow by viscous shear effect. Based on the numerical analysis, the work of this paper is also focused on wake modeling. A new two-dimensional models based on nonlinear wake development has been developed, which is capable to describe the far wake more accurately.
NASA Astrophysics Data System (ADS)
Marjanovic, N.; Mirocha, J. D.; Chow, F. K.
2013-12-01
In this work, we examine the performance of a generalized actuator disk (GAD) model embedded within the Weather Research and Forecasting (WRF) atmospheric model to study wake effects on successive rows of turbines at a North American wind farm. These wake effects are of interest as they can drastically reduce down-wind energy extraction and increase turbulence intensity. The GAD, which is designed for turbulence-resolving simulations, is used within downscaled large-eddy simulations (LES) forced with mesoscale simulations and WRF's grid nesting capability. The GAD represents the effects of thrust and torque created by a wind turbine on the atmosphere within a disk representing the rotor swept area. The lift and drag forces acting on the turbine blades are parameterized using blade-element theory and the aerodynamic properties of the blades. Our implementation permits simulation of turbine wake effects and turbine/airflow interactions within a realistic atmospheric boundary layer flow field, including resolved turbulence, time-evolving mesoscale forcing, and real topography. The GAD includes real-time yaw and pitch control to respond realistically to changing flow conditions. Simulation results are compared to SODAR data from operating wind turbines and an already existing WRF mesoscale turbine drag parameterization to validate the GAD parameterization.
Three-axis lever actuator with flexure hinges for an optical disk system
NASA Astrophysics Data System (ADS)
Han, Chang-Soo; Kim, Soo-Hyun
2002-10-01
A three-axis lever actuator with a flexure hinge has been designed and fabricated. This actuator is driven by electromagnetic force based on a coil-magnet system and can be used as a high precision actuator and, especially as a pickup head actuator in optical disks. High precision and low sensitivity to external vibration are the major advantages of this lever actuator. An analysis model was found and compared to the finite element method. Dynamic characteristics of the three-axis lever actuator were measured. The results are in very close agreement to those predicted by the model and finite element analysis.
Mirocha, J. D.; Kosovic, B.; Aitken, M. L.; Lundquist, J. K.
2014-01-10
A generalized actuator disk (GAD) wind turbine parameterization designed for large-eddy simulation (LES) applications was implemented into the Weather Research and Forecasting (WRF) model. WRF-LES with the GAD model enables numerical investigation of the effects of an operating wind turbine on and interactions with a broad range of atmospheric boundary layer phenomena. Numerical simulations using WRF-LES with the GAD model were compared with measurements obtained from the Turbine Wake and Inflow Characterization Study (TWICS-2011), the goal of which was to measure both the inflow to and wake from a 2.3-MW wind turbine. Data from a meteorological tower and two light-detection and ranging (lidar) systems, one vertically profiling and another operated over a variety of scanning modes, were utilized to obtain forcing for the simulations, and to evaluate characteristics of the simulated wakes. Simulations produced wakes with physically consistent rotation and velocity deficits. Two surface heat flux values of 20 W m^{–2} and 100 W m^{–2} were used to examine the sensitivity of the simulated wakes to convective instability. Simulations using the smaller heat flux values showed good agreement with wake deficits observed during TWICS-2011, whereas those using the larger value showed enhanced spreading and more-rapid attenuation. This study demonstrates the utility of actuator models implemented within atmospheric LES to address a range of atmospheric science and engineering applications. In conclusion, validated implementation of the GAD in a numerical weather prediction code such as WRF will enable a wide range of studies related to the interaction of wind turbines with the atmosphere and surface.
NASA Astrophysics Data System (ADS)
Garcia Cartagena, Edgardo Javier; Santoni, Christian; Ciri, Umberto; Iungo, Giacomo Valerio; Leonardi, Stefano
2015-11-01
A large-scale wind farm operating under realistic atmospheric conditions is studied by coupling a meso-scale and micro-scale models. For this purpose, the Weather Research and Forecasting model (WRF) is coupled with an in-house LES solver for wind farms. The code is based on a finite difference scheme, with a Runge-Kutta, fractional step and the Actuator Disk Model. The WRF model has been configured using seven one-way nested domains where the child domain has a mesh size one third of its parent domain. A horizontal resolution of 70 m is used in the innermost domain. A section from the smallest and finest nested domain, 7.5 diameters upwind of the wind farm is used as inlet boundary condition for the LES code. The wind farm consists in six-turbines aligned with the mean wind direction and streamwise spacing of 10 rotor diameters, (D), and 2.75D in the spanwise direction. Three simulations were performed by varying the velocity fluctuations at the inlet: random perturbations, precursor simulation, and recycling perturbation method. Results are compared with a simulation on the same wind farm with an ideal uniform wind speed to assess the importance of the time varying incoming wind velocity. Numerical simulations were performed at TACC (Grant CTS070066). This work was supported by NSF, (Grant IIA-1243482 WINDINSPIRE).
Mirocha, Jeffrey D.; Rajewski, Daniel A.; Marjanovic, Nikola; Lundquist, Julie K.; Kosovic, Branko; Draxl, Caroline; Churchfield, Matthew J.
2015-08-27
In this study, wind turbine impacts on the atmospheric flow are investigated using data from the Crop Wind Energy Experiment (CWEX-11) and large-eddy simulations (LESs) utilizing a generalized actuator disk (GAD) wind turbine model. CWEX-11 employed velocity-azimuth display (VAD) data from two Doppler lidar systems to sample vertical profiles of flow parameters across the rotor depth both upstream and in the wake of an operating 1.5 MW wind turbine. Lidar and surface observations obtained during four days of July 2011 are analyzed to characterize the turbine impacts on wind speed and flow variability, and to examine the sensitivity of these changes to atmospheric stability. Significant velocity deficits (VD) are observed at the downstream location during both convective and stable portions of four diurnal cycles, with large, sustained deficits occurring during stable conditions. Variances of the streamwise velocity component, σ_{u}, likewise show large increases downstream during both stable and unstable conditions, with stable conditions supporting sustained small increases of σ_{u} , while convective conditions featured both larger magnitudes and increased variability, due to the large coherent structures in the background flow. Two representative case studies, one stable and one convective, are simulated using LES with a GAD model at 6 m resolution to evaluate the compatibility of the simulation framework with validation using vertically profiling lidar data in the near wake region. Virtual lidars were employed to sample the simulated flow field in a manner consistent with the VAD technique. Simulations reasonably reproduced aggregated wake VD characteristics, albeit with smaller magnitudes than observed, while σu values in the wake are more significantly underestimated. The results illuminate the limitations of using a GAD in combination with coarse model resolution in the simulation of near wake physics, and validation thereof using VAD data.
Mirocha, Jeffrey D.; Rajewski, Daniel A.; Marjanovic, Nikola; Lundquist, Julie K.; Kosovic, Branko; Draxl, Caroline; Churchfield, Matthew J.
2015-08-27
In this study, wind turbine impacts on the atmospheric flow are investigated using data from the Crop Wind Energy Experiment (CWEX-11) and large-eddy simulations (LESs) utilizing a generalized actuator disk (GAD) wind turbine model. CWEX-11 employed velocity-azimuth display (VAD) data from two Doppler lidar systems to sample vertical profiles of flow parameters across the rotor depth both upstream and in the wake of an operating 1.5 MW wind turbine. Lidar and surface observations obtained during four days of July 2011 are analyzed to characterize the turbine impacts on wind speed and flow variability, and to examine the sensitivity of thesemore » changes to atmospheric stability. Significant velocity deficits (VD) are observed at the downstream location during both convective and stable portions of four diurnal cycles, with large, sustained deficits occurring during stable conditions. Variances of the streamwise velocity component, σu, likewise show large increases downstream during both stable and unstable conditions, with stable conditions supporting sustained small increases of σu , while convective conditions featured both larger magnitudes and increased variability, due to the large coherent structures in the background flow. Two representative case studies, one stable and one convective, are simulated using LES with a GAD model at 6 m resolution to evaluate the compatibility of the simulation framework with validation using vertically profiling lidar data in the near wake region. Virtual lidars were employed to sample the simulated flow field in a manner consistent with the VAD technique. Simulations reasonably reproduced aggregated wake VD characteristics, albeit with smaller magnitudes than observed, while σu values in the wake are more significantly underestimated. The results illuminate the limitations of using a GAD in combination with coarse model resolution in the simulation of near wake physics, and validation thereof using VAD data.« less
Euler force actuation mechanism for siphon valving in compact disk-like microfluidic chips.
Deng, Yongbo; Fan, Jianhua; Zhou, Song; Zhou, Teng; Wu, Junfeng; Li, Yin; Liu, Zhenyu; Xuan, Ming; Wu, Yihui
2014-03-01
Based on the Euler force induced by the acceleration of compact disk (CD)-like microfluidic chip, this paper presents a novel actuation mechanism for siphon valving. At the preliminary stage of acceleration, the Euler force in the tangential direction of CD-like chip takes the primary place compared with the centrifugal force to function as the actuation of the flow, which fills the siphon and actuates the siphon valving. The Euler force actuation mechanism is demonstrated by the numerical solution of the phase-field based mathematical model for the flow in siphon valve. In addition, experimental validation is implemented in the polymethylmethacrylate-based CD-like microfluidic chip manufactured using CO2 laser engraving technique. To prove the application of the proposed Euler force actuation mechanism, whole blood separation and plasma extraction has been conducted using the Euler force actuated siphon valving. The newly introduced actuation mechanism overcomes the dependence on hydrophilic capillary filling of siphon by avoiding external manipulation or surface treatments of polymeric material. The sacrifice for highly integrated processing in pneumatic pumping technique is also prevented by excluding the volume-occupied compressed air chamber. PMID:24753736
Euler force actuation mechanism for siphon valving in compact disk-like microfluidic chips
Deng, Yongbo; Fan, Jianhua; Zhou, Song; Zhou, Teng; Wu, Junfeng; Li, Yin; Liu, Zhenyu; Xuan, Ming; Wu, Yihui
2014-01-01
Based on the Euler force induced by the acceleration of compact disk (CD)-like microfluidic chip, this paper presents a novel actuation mechanism for siphon valving. At the preliminary stage of acceleration, the Euler force in the tangential direction of CD-like chip takes the primary place compared with the centrifugal force to function as the actuation of the flow, which fills the siphon and actuates the siphon valving. The Euler force actuation mechanism is demonstrated by the numerical solution of the phase-field based mathematical model for the flow in siphon valve. In addition, experimental validation is implemented in the polymethylmethacrylate-based CD-like microfluidic chip manufactured using CO2 laser engraving technique. To prove the application of the proposed Euler force actuation mechanism, whole blood separation and plasma extraction has been conducted using the Euler force actuated siphon valving. The newly introduced actuation mechanism overcomes the dependence on hydrophilic capillary filling of siphon by avoiding external manipulation or surface treatments of polymeric material. The sacrifice for highly integrated processing in pneumatic pumping technique is also prevented by excluding the volume-occupied compressed air chamber. PMID:24753736
Robust H∞ stabilization of a hard disk drive system with a single-stage actuator
NASA Astrophysics Data System (ADS)
Harno, Hendra G.; Kiin Woon, Raymond Song
2015-04-01
This paper considers a robust H∞ control problem for a hard disk drive system with a single stage actuator. The hard disk drive system is modeled as a linear time-invariant uncertain system where its uncertain parameters and high-order dynamics are considered as uncertainties satisfying integral quadratic constraints. The robust H∞ control problem is transformed into a nonlinear optimization problem with a pair of parameterized algebraic Riccati equations as nonconvex constraints. The nonlinear optimization problem is then solved using a differential evolution algorithm to find stabilizing solutions to the Riccati equations. These solutions are used for synthesizing an output feedback robust H∞ controller to stabilize the hard disk drive system with a specified disturbance attenuation level.
Analysis of supersonic stall bending flutter in axial-flow compressor by actuator disk theory
NASA Technical Reports Server (NTRS)
Adamczyk, J. J.
1978-01-01
An analytical model was developed for predicting the onset of supersonic stall bending flutter in axial-flow compressors. The analysis is based on two-dimensional, compressible, unsteady actuator disk theory. It is applied to a rotor blade row by considering a cascade of airfoils. The effects of shock waves and flow separation are included in the model. Calculations show that the model predicts the onset, in an unshrouded rotor, of a bending flutter mode that exhibits many of the characteristics of supersonic stall bending flutter. The validity of the analysis for predicting this flutter mode is demonstrated.
NASA Astrophysics Data System (ADS)
Olivares-Espinosa, H.; Breton, S.-P.; Masson, C.; Dufresne, L.
2014-12-01
An Actuator Disk (AD) model is implemented in the CFD platform OpenFOAM® with the purpose of studying the characteristics of the turbulent flow in the wake of the rotor of a horizontal-axis wind turbine. This AD model is based on the blade-element theory and it employs airfoil data to calculate the distribution of forces over the disk of a conceptual 5 MW offshore wind turbine. A uniform, non-turbulent flow is used as inflow so the turbulence is only produced in the wake of the AD. Computations are performed using Large-Eddy Simulations (LES) to capture the unsteady fluctuations in the flow. Additionally, a classic Smagorinsky Sub-Grid Scale (SGS) technique is employed to model the unfiltered motions. This new AD implementation makes use of a control system to adjust the rotational velocity of the rotor (below rated power) to the local conditions of the wind flow. The preliminary results show that the wake characteristics are influenced by the force distribution on the disk when compared to the wake produced by a uniformly loaded AD. Also, we observe that the simulated rotor reacts correctly to the introduction of the control system, although operating below the optimal power.
Semi-actuator disk theory for compressor choke flutter
NASA Technical Reports Server (NTRS)
Micklow, J.; Jeffers, J.
1981-01-01
A mathematical anaysis predict the unsteady aerodynamic utilizing semi actuator theory environment for a cascade of airfoils harmonically oscillating in choked flow was developed. A normal shock is located in the blade passage, its position depending on the time dependent geometry, and pressure perturbations of the system. In addition to shock dynamics, the model includes the effect of compressibility, interblade phase lag, and an unsteady flow field upstream and downstream of the cascade. Calculated unsteady aerodynamics were compared with isolated airfoil wind tunnel data, and choke flutter onset boundaries were compared with data from testing of an F100 high pressure compressor stage.
Enhanced actuation of nanocrystalline diamond microelectromechanical disk resonators with AlN layers
NASA Astrophysics Data System (ADS)
Yoshikawa, Taro; Reusch, Markus; Holc, Katarzyna; Iankov, Dimitre; Zuerbig, Verena; Zukauskaite, Agne; Nebel, Christoph E.; Ambacher, Oliver; Lebedev, Vadim
2016-04-01
A great potential of the use of aluminum nitride (AlN) to enhance the actuation of nanocrystalline diamond (NCD) microelectromechanical system disk resonators is revealed. A disk resonator with a unimorph (AlN/NCD) structure is fabricated by depositing a c-axis oriented AlN on a capacitive NCD disk resonator. The unimorph resonator is piezoelectrically actuated with flexural whispering gallery modes with a relatively large electrode gap spacing, i.e., the spacing which is greater than 1 μm, although this is not possible for the capacitive NCD disk resonator. This result is explained by a finite element method simulation where the piezoelectric actuation turns out to be more effective than the capacitive actuation when the electrode gap spacing is >0.8 μm. The simulation also shows that the electrode gap spacing required for the capacitive actuation to be more effective than the piezoelectric actuation exponentially decreases when the resonator dimension is scaled down for higher frequency operations. Our study indicates that the use of AlN is promising to decrease impedance levels of NCD disk resonators especially for their higher frequency operations.
Presas, Alexandre; Egusquiza, Eduard; Valero, Carme; Valentin, David; Seidel, Ulrich
2014-01-01
In this paper, PZT actuators are used to study the dynamic behavior of a rotating disk structure due to rotor-stator interaction excitation. The disk is studied with two different surrounding fluids-air and water. The study has been performed analytically and validated experimentally. For the theoretical analysis, the natural frequencies and the associated mode shapes of the rotating disk in air and water are obtained with the Kirchhoff-Love thin plate theory coupled with the interaction with the surrounding fluid. A model for the Rotor Stator Interaction that occurs in many rotating disk-like parts of turbomachinery such as compressors, hydraulic runners or alternators is presented. The dynamic behavior of the rotating disk due to this excitation is deduced. For the experimental analysis a test rig has been developed. It consists of a stainless steel disk (r = 198 mm and h = 8 mm) connected to a variable speed motor. Excitation and response are measured from the rotating system. For the rotating excitation four piezoelectric patches have been used. Calibrating the piezoelectric patches in amplitude and phase, different rotating excitation patterns are applied on the rotating disk in air and in water. Results show the feasibility of using PZT to control the response of the disk due to a rotor-stator interaction. PMID:25004151
Presas, Alexandre; Egusquiza, Eduard; Valero, Carme; Valentin, David; Seidel, Ulrich
2014-01-01
In this paper, PZT actuators are used to study the dynamic behavior of a rotating disk structure due to rotor-stator interaction excitation. The disk is studied with two different surrounding fluids—air and water. The study has been performed analytically and validated experimentally. For the theoretical analysis, the natural frequencies and the associated mode shapes of the rotating disk in air and water are obtained with the Kirchhoff-Love thin plate theory coupled with the interaction with the surrounding fluid. A model for the Rotor Stator Interaction that occurs in many rotating disk-like parts of turbomachinery such as compressors, hydraulic runners or alternators is presented. The dynamic behavior of the rotating disk due to this excitation is deduced. For the experimental analysis a test rig has been developed. It consists of a stainless steel disk (r = 198 mm and h = 8 mm) connected to a variable speed motor. Excitation and response are measured from the rotating system. For the rotating excitation four piezoelectric patches have been used. Calibrating the piezoelectric patches in amplitude and phase, different rotating excitation patterns are applied on the rotating disk in air and in water. Results show the feasibility of using PZT to control the response of the disk due to a rotor-stator interaction. PMID:25004151
Fabrication of Beam-rotating Actuator for Multiple-beam Disk Drive
NASA Astrophysics Data System (ADS)
Kim, Boung Jun; Kim, Soo Hyun; Kwak, Yoon Keun
2002-05-01
Current trends in computer and communication industries are towards increasingly higher resolution images and video processing techniques. However, such sophisticated processing tasks require massive storage systems such as a compact disk read only memory (CD-ROM) and digital versatile disc (DVD). Current demands in the development of such systems are higher data density storage media and an improved data transfer rate. The latter is discussed in this paper. A multiple-beam optical disk drive is presented as a method for improving the effective data transfer rate by increasing the beam spot number formed on an optical disk. The beam-rotating actuator is necessary for positioning the multiple-beam onto more than one track. Ray tracing was also employed for the real system setup. The beam-rotating actuator is made up of piezoelectric material, a high-stiffness wire hinge and a dove prism. The actuator has an approximately 1 kHz resonance frequency and a suitable operational range. The dynamic equation for the actuator is derived for the control of the real system.
NASA Astrophysics Data System (ADS)
Gu, Bin; Shu, Dong-Wei; Fujii, Yusaku; Shi, Bao-Jun
2008-12-01
In this paper, inertial force of an Actuator Arm of a Hard Disk Drive (HDD) in free oscillation after an impact load is accurately measured by means of a finite element analysis and by carrying out experiments using a modified Levitation Mass Method (LMM). A 3D finite element model of an actuator arm of a HDD is modeled in ANSYS/LS-DYNA using shell elements. An impact load, which is modeled as a half sine force pulse, is applied to a mass, which is attached with the Actuator Arm. The velocity and the inertial force of the mass in free oscillation are obtained from the simulation. In the LMM method, the arm is attached to a mass, i.e. the moving part of an aerostatic linear bearing, and the total force acting on the mass is measured as the inertial force of the mass using an optical interferometer. An impact is applied to the mass with the arm by colliding it to the metal base, and the inertial force of the arm is evaluated during the free oscillation. The velocity and the inertial force of the mass are calculated from the measured time-varying Doppler frequency shift. A good correlation between the experimental and numerical results is achieved. This numerical analysis can be further used to investigate the dynamic response of the actuator arm when it is subjected to different impact load, which is modeled with half sine force pulse with different pulse widths and amplitudes.
Exact actuator disk solutions for non-uniform heavy loading and slipstream contraction
NASA Astrophysics Data System (ADS)
Conway, John T.
1998-06-01
A semi-analytical method has been developed to solve for the inviscid incompressible flow induced by a heavily loaded actuator disk with non-uniform loading. The solution takes the contraction of the slipstream fully into account. The method is an extension of the analytical theory of Conway (1995) for the linearized actuator disk and is exact for an incompressible perfect fluid. The solutions for the velocities and stream function are given as one-dimensional integrals of expressions containing complete elliptic integrals. Any load distribution with bounded radial gradient can be treated. Results are presented here for both contra-rotating and normal propellers. For the special case of a contra-rotating propeller with a parabolic velocity profile in the ultimate wake, the vorticity in the slipstream is shown to be the same as in the analytically tractable spherical vortex of Hill (1894) and the related family of steady vortices explored by Fraenkel (1970, 1972) and Norbury (1973).
NASA Astrophysics Data System (ADS)
Buono, Armand C.
The numerical method presented in this study attempts to predict the mean, non-uniform flow field upstream of a propeller partially immersed in a thick turbulent boundary layer with an actuator disk using CFD based on RANS in ANSYS FLUENT. Three different configurations, involving an infinitely thin actuator disk in the freestream (Configuration 1), an actuator disk near a wall with a turbulent boundary layer (Configuration 2), and an actuator disk with a hub near a wall with a turbulent boundary layer (Configuration 3), were analyzed for a variety of advance ratios ranging from J = 0.48 to J =1.44. CFD results are shown to be in agreement with previous works and validated with experimental data of reverse flow occurring within the boundary layer above the flat plate upstream of a rotor in the Virginia Tech's Stability Wind Tunnel facility. Results from Configuration 3 will be used in future aero-acoustic computations.
Yan, Tianhong; Xu, Xinsheng; Han, Jianqiang; Lin, Rongming; Ju, Bingfeng; Li, Qing
2011-01-01
In this paper, a feedback control mechanism and its optimization for rotating disk vibration/flutter via changes of air-coupled pressure generated using piezoelectric patch actuators are studied. A thin disk rotates in an enclosure, which is equipped with a feedback control loop consisting of a micro-sensor, a signal processor, a power amplifier, and several piezoelectric (PZT) actuator patches distributed on the cover of the enclosure. The actuator patches are mounted on the inner or the outer surfaces of the enclosure to produce necessary control force required through the airflow around the disk. The control mechanism for rotating disk flutter using enclosure surfaces bonded with sensors and piezoelectric actuators is thoroughly studied through analytical simulations. The sensor output is used to determine the amount of input to the actuator for controlling the response of the disk in a closed loop configuration. The dynamic stability of the disk-enclosure system, together with the feedback control loop, is analyzed as a complex eigenvalue problem, which is solved using Galerkin’s discretization procedure. The results show that the disk flutter can be reduced effectively with proper configurations of the control gain and the phase shift through the actuations of PZT patches. The effectiveness of different feedback control methods in altering system characteristics and system response has been investigated. The control capability, in terms of control gain, phase shift, and especially the physical configuration of actuator patches, are also evaluated by calculating the complex eigenvalues and the maximum displacement produced by the actuators. To achieve a optimal control performance, sizes, positions and shapes of PZT patches used need to be optimized and such optimization has been achieved through numerical simulations. PMID:22163788
A Model of the THUNDER Actuator
NASA Technical Reports Server (NTRS)
Curtis, Alan R. D.
1997-01-01
A THUNDER actuator is a composite of three thin layers, a metal base, a piezoelectric wafer and a metal top cover, bonded together under pressure and at high temperature with the LaRC SI polyimid adhesive. When a voltage is applied between the metal layers across the PZT the actuator will bend and can generate a force. This document develops and describes an analytical model the transduction properties of THUNDER actuators. The model development is divided into three sections. First, a static model is described that relates internal stresses and strains and external displacements to the thermal pre-stress and applied voltage. Second, a dynamic energy based model is described that allows calculation of the resonance frequencies, developed force and electrical input impedance. Finally, a fully coupled electro-mechanical transducer model is described. The model development proceeds by assuming that both the thermal pre-stress and the piezoelectric actuation cause the actuator to deform in a pure bend in a single plane. It is useful to think of this as a two step process, the actuator is held flat, differential stresses induce a bending moment, the actuator is released and it bends. The thermal pre-stress is caused by the different amounts that the constituent layers shrink due to their different coefficients of thermal expansion. The adhesive between layers sets at a high temperature and as the actuator cools, the metal layers shrink more than the PZT. The PZT layer is put into compression while the metal layers are in tension. The piezoelectric actuation has a similar effect. An applied voltage causes the PZT layer to strain, which in turn strains the two metal layers. If the PZT layer expands it will put the metal layers into tension and PZT layer into compression. In both cases, if shear force effects are neglected, the actuator assembly will experience a uniform in-plane strain. As the materials each have a different elastic modulus, different stresses will
A magnetorheological actuation system: test and model
NASA Astrophysics Data System (ADS)
John, Shaju; Chaudhuri, Anirban; Wereley, Norman M.
2008-04-01
Self-contained actuation systems, based on frequency rectification of the high frequency motion of an active material, can produce high force and stroke output. Magnetorheological (MR) fluids are active fluids whose rheological properties can be altered by the application of a magnetic field. By using MR fluids as the energy transmission medium in such hybrid devices, a valving system with no moving parts can be implemented and used to control the motion of an output cylinder shaft. The MR fluid based valves are configured in the form of an H-bridge to produce bi-directional motion in an output cylinder by alternately applying magnetic fields in the two opposite arms of the bridge. The rheological properties of the MR fluid are modeled using both Bingham plastic and bi-viscous models. In this study, the primary actuation is performed using a compact terfenol-D rod driven pump and frequency rectification of the rod motion is done using passive reed valves. The pump and reed valve configuration along with MR fluidic valves form a compact hydraulic actuation system. Actuator design, analysis and experimental results are presented in this paper. A time domain model of the actuator is developed and validated using experimental data.
Optimizing a tandem disk model
Healey, J.V.
1983-07-01
A very simple physicomathematical model, in which thin straight blades with zero drag skim across a plane rectangular disk, shows that the maximum power coefficient attains the classical maximum of 0.593 over a range of T and a zero or small negative value of alpha/sub 0/. This maximum appears independent of sigma and there are values of T and alpha/sub 0/ for which the speed through the disk becomes complex and the model breaks down. Extending this model to a tandem disk system leads to a difficulty in defining the power coefficient. Attempts to optimize the system output based on reference areas A/sub 1/, A/sub 2/, and A/sub 4/ prove futile and the sum of the coefficients is chosen for this purpose. For thin blades and zero drag the analytic solution is available and it shows that the maximum value of 2 X 0.593 is attained over a narrow range of slightly negative alpha/sub 0/ (blade nose in) and medium values of T. The maximum is independent of sigma. As T is increased, the model breaks down either after C /SUB psum/ becomes large and negative or after backflow through the downwind disk occurs. There appears to be no requirement on load distribution between the disks. By comparison, modeling a machine with NACA 0012 blades at Re = 1.34 X 10/sup 6/ shows that the maximum value of C /SUB psum/ depends on the solidity. For example, at sigma = 0.4, the maximum value of C /SUB psum/ is 83% of 2 X 0.593. At such high values of sigma, however, the ranges of alpha/sub 0/ and T over which solutions are available become very limited.
NASA Astrophysics Data System (ADS)
Rahman, Md. Arifur; Al Mamun, Abdullah; Yao, Kui
2015-08-01
The head positioning servo system in hard disk drive is implemented nowadays using a dual-stage actuator—the primary stage consisting of a voice coil motor actuator providing long range motion and the secondary stage controlling the position of the read/write head with fine resolution. Piezoelectric micro-actuator made of lead zirconate titanate (PZT) has been a popular choice for the secondary stage. However, PZT micro-actuator exhibits hysteresis—an inherent nonlinear characteristic of piezoelectric material. The advantage expected from using the secondary micro-actuator is somewhat lost by the hysteresis of the micro-actuator that contributes to tracking error. Hysteresis nonlinearity adversely affects the performance and, if not compensated, may cause inaccuracy and oscillation in the response. Compensation of hysteresis is therefore an important aspect for designing head-positioning servo system. This paper presents a new rate dependent model of hysteresis along with rigorous analysis and identification of the model. Parameters of the model are found using particle swarm optimization. Direct inverse of the proposed rate-dependent generalized Prandtl-Ishlinskii model is used as the hysteresis compensator. Effectiveness of the overall solution is underscored through experimental results.
Rahman, Md Arifur; Al Mamun, Abdullah; Yao, Kui
2015-08-01
The head positioning servo system in hard disk drive is implemented nowadays using a dual-stage actuator—the primary stage consisting of a voice coil motor actuator providing long range motion and the secondary stage controlling the position of the read/write head with fine resolution. Piezoelectric micro-actuator made of lead zirconate titanate (PZT) has been a popular choice for the secondary stage. However, PZT micro-actuator exhibits hysteresis—an inherent nonlinear characteristic of piezoelectric material. The advantage expected from using the secondary micro-actuator is somewhat lost by the hysteresis of the micro-actuator that contributes to tracking error. Hysteresis nonlinearity adversely affects the performance and, if not compensated, may cause inaccuracy and oscillation in the response. Compensation of hysteresis is therefore an important aspect for designing head-positioning servo system. This paper presents a new rate dependent model of hysteresis along with rigorous analysis and identification of the model. Parameters of the model are found using particle swarm optimization. Direct inverse of the proposed rate-dependent generalized Prandtl-Ishlinskii model is used as the hysteresis compensator. Effectiveness of the overall solution is underscored through experimental results. PMID:26329224
A Simple Sensor Model for THUNDER Actuators
NASA Technical Reports Server (NTRS)
Campbell, Joel F.; Bryant, Robert G.
2009-01-01
A quasi-static (low frequency) model is developed for THUNDER actuators configured as displacement sensors based on a simple Raleigh-Ritz technique. This model is used to calculate charge as a function of displacement. Using this and the calculated capacitance, voltage vs. displacement and voltage vs. electrical load curves are generated and compared with measurements. It is shown this model gives acceptable results and is useful for determining rough estimates of sensor output for various loads, laminate configurations and thicknesses.
Enhanced laser shutter using a hard disk drive rotary voice-coil actuator
NASA Astrophysics Data System (ADS)
Scholten, R. E.
2007-02-01
Rotary voice-coil motors from computer hard disk drives make excellent mechanical shutters for light beams. However, the complexity of the necessary electronic driving circuit can hinder their application. A new design is presented here, using a single integrated circuit originally intended for controlling dc motors. A digital input signal switches a unipolar power supply bidirectionally through the voice coil. Short high-current pulses are generated on the transitions to ensure rapid shutter action, while a low holding current reduces the power requirement and heating of the actuator. The circuit can reverse the current to brake the shutter and reduce the impact at the end of its travel. With a focused laser beam, the shutter achieves rise times below 500 ns. A method for producing variable length pulses is also described, demonstrating durations as short as 700 ns.
DiskJockey: Protoplanetary disk modeling for dynamical mass derivation
NASA Astrophysics Data System (ADS)
Czekala, Ian
2016-03-01
DiskJockey derives dynamical masses for T Tauri stars using the Keplerian motion of their circumstellar disks, applied to radio interferometric data from the Atacama Large Millimeter Array (ALMA) and the Submillimeter Array (SMA). The package relies on RADMC-3D (ascl:1202.015) to perform the radiative transfer of the disk model. DiskJockey is designed to work in a parallel environment where the calculations for each frequency channel can be distributed to independent processors. Due to the computationally expensive nature of the radiative synthesis, fitting sizable datasets (e.g., SMA and ALMA) will require a substantial amount of CPU cores to explore a posterior distribution in a reasonable timeframe.
Preisach modeling of dielectric elastomer EAP actuator
NASA Astrophysics Data System (ADS)
Hwang, HyunWoo; Kim, Chul-Jin; Kim, Sung Joo; Yang, Hyunseok; Park, No Cheol; Park, Young-Pil
2008-03-01
DE EAP(Dielectric Elastomer ElectroActive Polymer) has advantages in its weight, ease of fabrication and low power consumption. There are many efforts applied to various field in recent ten years. But the present modeling is not enough to appear its characteristics because of its hysteresis. In this paper, we propose modeling of DE EAP with Preisach Model that is used in order to model the hysteretic response arising in PZT and SMA. The modeling of DE EAP with Presach model is verified by experiment with various DE EAP actuators.
Otten, Alexander; van Vuuren, Wieke; Stienen, Arno; van Asseldonk, Edwin; Schouten, Alfred; van der Kooij, Herman
2011-01-01
Robotics used for diagnostic measurements on, e.g. stroke survivors, require actuators that are both stiff and compliant. Stiffness is required for identification purposes, and compliance to compensate for the robots dynamics, so that the subject can move freely while using the robot. A hydraulic actuator can act as a position (stiff) or a torque (compliant) actuator. The drawback of a hydraulic actuator is that it behaves nonlinear. This article examines two methods for controlling a nonlinear hydraulic actuator. The first method that is often applied uses an elastic element (i.e. spring) connected in series with the hydraulic actuator so that the torque can be measured as the deflection of the spring. This torque measurement is used for proportional integral control. The second method of control uses the inverse of the model of the actuator as a linearizing controller. Both methods are compared using simulation results. The controller designed for the series elastic hydraulic actuator is faster to implement, but only shows good performance for the working range for which the controller is designed due to the systems nonlinear behavior. The elastic element is a limiting factor when designing a position controller due to its low torsional stiffness. The model-based controller linearizes the nonlinear system and shows good performance when used for torque and position control. Implementing the model-based controller does require building and validating of the detailed model. PMID:22275654
Pneumatic Artificial Muscle Actuation and Modeling
NASA Astrophysics Data System (ADS)
Leephakpreeda, Thananchai; Wickramatunge, Kanchana C.
2009-10-01
A Pneumatic Artificial Muscle (PAM) yields a natural muscle-like actuator with a high force to weight ratio, a soft and flexible structure, and adaptable compliance for a humanoid robot, rehabilitation and prosthetic appliances to the disabled, etc. To obtain optimum design and usage, the mechanical behavior of the PAM need to be understood. In this study, observations of experimental results reveal an empirical model for relations of physical variables, contraction and air pressure within the PAM, as compared to mechanical characteristics, such as stiffness or/and pulling forces of the PAM available now in market.
Modeling of two-hot-arm horizontal thermal actuator
NASA Astrophysics Data System (ADS)
Yan, Dong; Khajepour, Amir; Mansour, Raafat
2003-03-01
Electrothermal actuators have a very promising future in MEMS applications since they can generate large deflection and force with low actuating voltages and small device areas. In this study, a lumped model of a two-hot-arm horizontal thermal actuator is presented. In order to prove the accuracy of the lumped model, finite element analysis (FEA) and experimental results are provided. The two-hot-arm thermal actuator has been fabricated using the MUMPs process. Both the experimental and FEA results are in good agreement with the results of lumped modeling.
Modeling actuation forces and strains in nastic structures
NASA Astrophysics Data System (ADS)
Matthews, Luke A.; Giurgiutiu, Victor
2006-03-01
Nastic structures are capable of three dimensional shape change using biological principles borrowed from plant motion. The plant motor cells increase or decrease in size through a change in osmotic pressure. When nonuniform cell swelling occurs, it causes the plant tissue to warp and change shape, resulting it net movement, known as nastic motion, which is the same phenomena that causes plants to angle their broad leaf and flower surfaces to face light sources. The nastic structures considered in this paper are composed of a bilayer of microactuator arrays with a fluid reservoir in between the two layers. The actuators are housed in a thin plate and expand when water from the fluid reservoir is pumped into the actuation chamber through a phospholipid bilayer with embedded active transport proteins, which move the water from the low pressure fluid reservoir into a high pressure actuation chamber. Increasing water pressure inside the actuator causes lateral expansion and axial bulging, and the non-uniform net volume change of actuators throughout the nastic structure results in twisting or bending shape change. Modifying the actuation displacement allows controlled volume change. This paper presents an analytical model of the driving and blocking forces involved in actuation, as well as stress and strain that occurs due to the pressure changes. Actuation is driven by increasing osmotic pressure, and blocking forces are taken into consideration to plan actuator response so that outside forces do not counteract the displacement of actuation. Nastic structures are designed with use in unmanned aerial vehicles in mind, so blocking forces are modeled to be similar to in-flight conditions. Stress in the system is modeled so that any residual strain or lasting deformation can be determined, as well as a lifespan before failure from repeated actuation. The long-term aim of our work is to determine the power and energy efficiency of nastic structures actuation mechanism.
Piezoelectric Actuator Modeling Using MSC/NASTRAN and MATLAB
NASA Technical Reports Server (NTRS)
Reaves, Mercedes C.; Horta, Lucas G.
2003-01-01
This paper presents a procedure for modeling structures containing piezoelectric actuators using MSCMASTRAN and MATLAB. The paper describes the utility and functionality of one set of validated modeling tools. The tools described herein use MSCMASTRAN to model the structure with piezoelectric actuators and a thermally induced strain to model straining of the actuators due to an applied voltage field. MATLAB scripts are used to assemble the dynamic equations and to generate frequency response functions. The application of these tools is discussed using a cantilever aluminum beam with a surface mounted piezoelectric actuator as a sample problem. Software in the form of MSCINASTRAN DMAP input commands, MATLAB scripts, and a step-by-step procedure to solve the example problem are provided. Analysis results are generated in terms of frequency response functions from deflection and strain data as a function of input voltage to the actuator.
Numerical modeling of shape memory alloy linear actuator
NASA Astrophysics Data System (ADS)
Jani, Jaronie Mohd; Huang, Sunan; Leary, Martin; Subic, Aleksandar
2015-09-01
The demand for shape memory alloy (SMA) actuators in high-technology applications is increasing; however, there exist technical challenges to the commercial application of SMA actuator technologies, especially associated with actuation duration. Excessive activation duration results in actuator damage due to overheating while excessive deactivation duration is not practical for high-frequency applications. Analytical and finite difference equation models were developed in this work to predict the activation and deactivation durations and associated SMA thermomechanical behavior under variable environmental and design conditions. Relevant factors, including latent heat effect, induced stress and material property variability are accommodated. An existing constitutive model was integrated into the proposed models to generate custom SMA stress-strain curves. Strong agreement was achieved between the proposed numerical models and experimental results; confirming their applicability for predicting the behavior of SMA actuators with variable thermomechanical conditions.
Modeling collisions in circumstellar debris disks
NASA Astrophysics Data System (ADS)
Nesvold, Erika
2015-10-01
Observations of resolved debris disks show a spectacular variety of features and asymmetries, including inner cavities and gaps, inclined secondary disks or warps, and eccentric, sharp-edged rings. Embedded exoplanets could create many of these features via gravitational perturbations, which sculpt the disk directly and by generating planetesimal collisions. In this thesis, I present the Superparticle Model/Algorithm for Collisions in Kuiper belts and debris disks (SMACK), a new method for simultaneously modeling, in 3-D, the collisional and dynamical evolution of planetesimals in a debris disk with planets. SMACK can simulate azimuthal asymmetries and how these asymmetries evolve over time. I show that SMACK is stable to numerical viscosity and numerical heating over 107 yr, and that it can reproduce analytic models of disk evolution. As an example of the algorithm's capabilities, I use SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit and demonstrate that differential precession creates a spiral structure as the ring evolves, but collisions subsequently break up the spiral, leaving a narrower eccentric ring. To demonstrate SMACK's utility in studying debris disk physics, I apply SMACK to simulate a planet on a circular orbit near a ring of planetesimals that are experiencing destructive collisions. Previous simulations of a planet opening a gap in a collisionless debris disk have found that the width of the gap scales as the planet mass to the 2/7th power (alpha = 2/7). I find that gap sizes in a collisional disk still obey a power law scaling with planet mass, but that the index alpha of the power law depends on the age of the system t relative to the collisional timescale t coll of the disk by alpha = 0.32(t/ tcoll)-0.04, with inferred planet masses up to five times smaller than those predicted by the classical gap law. The increased gap sizes likely stem from the interaction between collisions and the mean motion
Modelling Molecular Emission from Young Embedded Disks
NASA Astrophysics Data System (ADS)
Harsono, D.; Visser, R.; van Dishoeck, E. F.; Kristensen, L.; Bruderer, S.; Brinch, C. Hogerheijde, M.
2011-05-01
Circumstellar disks play an important role in the formation of stars and planets. Recent observations and models have placed strong constraints on the later stages of their evolution (the T Tauri or Herbig Ae/Be phase), when an envelope is no longer present. However, little is known of the disk structure and evolution during the embedded phase of star formation. With Herschel and the VLT, and soon ALMA, we will be able to detect and characterize the early stages of disk formation. Sophisticated modeling including both physical and chemical structure of the system would be needed to interpret the high quality of data. We present a two-dimensional, semi-analytical model of disk formation as also used in Visser et al. (2009) and Visser and Dullemond (2010). The dust temperature is determined using a three-dimensional dust continuum radiative transfer code (RADMC-3D). Molecular abundances are calculated by following freeze-out and evaporation from the pre-stellar core up to the formation of the circumstellar disk. Synthetic spectra of CO and H2O within the wavelength ranges observable with Herschel and VLT-CRIRES are then produced at a series of time steps, tracing the different stages of disk formation. We also present simulated ALMA images. We discuss the evolution of the molecular emission and the possibility of identifying the presence of embedded disks.
An MCMC Circumstellar Disks Modeling Tool
NASA Astrophysics Data System (ADS)
Wolff, Schuyler; Perrin, Marshall D.; Mazoyer, Johan; Choquet, Elodie; Soummer, Remi; Ren, Bin; Pueyo, Laurent; Debes, John H.; Duchene, Gaspard; Pinte, Christophe; Menard, Francois
2016-01-01
We present an enhanced software framework for the Monte Carlo Markov Chain modeling of circumstellar disk observations, including spectral energy distributions and multi wavelength images from a variety of instruments (e.g. GPI, NICI, HST, WFIRST). The goal is to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in the derived properties. This modular code is designed to work with a collection of existing modeling tools, ranging from simple scripts to define the geometry for optically thin debris disks, to full radiative transfer modeling of complex grain structures in protoplanetary disks (using the MCFOST radiative transfer modeling code). The MCMC chain relies on direct chi squared comparison of model images/spectra to observations. We will include a discussion of how best to weight different observations in the modeling of a single disk and how to incorporate forward modeling from PCA PSF subtraction techniques. The code is open source, python, and available from github. Results for several disks at various evolutionary stages will be discussed.
Modeling Piezoelectric Stack Actuators for Control of Micromanipulation
NASA Technical Reports Server (NTRS)
Goldfarb, Michael; Celanovic, Nikola
1997-01-01
A nonlinear lumped-parameter model of a piezoelectric stack actuator has been developed to describe actuator behavior for purposes of control system analysis and design, and, in particular, for microrobotic applications requiring accurate position and/or force control. In formulating this model, the authors propose a generalized Maxwell resistive capacitor as a lumped-parameter causal representation of rate-independent hysteresis. Model formulation is validated by comparing results of numerical simulations to experimental data. Validation is followed by a discussion of model implications for purposes of actuator control.
Empirical modeling of dynamic behaviors of pneumatic artificial muscle actuators.
Wickramatunge, Kanchana Crishan; Leephakpreeda, Thananchai
2013-11-01
Pneumatic Artificial Muscle (PAM) actuators yield muscle-like mechanical actuation with high force to weight ratio, soft and flexible structure, and adaptable compliance for rehabilitation and prosthetic appliances to the disabled as well as humanoid robots or machines. The present study is to develop empirical models of the PAM actuators, that is, a PAM coupled with pneumatic control valves, in order to describe their dynamic behaviors for practical control design and usage. Empirical modeling is an efficient approach to computer-based modeling with observations of real behaviors. Different characteristics of dynamic behaviors of each PAM actuator are due not only to the structures of the PAM actuators themselves, but also to the variations of their material properties in manufacturing processes. To overcome the difficulties, the proposed empirical models are experimentally derived from real physical behaviors of the PAM actuators, which are being implemented. In case studies, the simulated results with good agreement to experimental results, show that the proposed methodology can be applied to describe the dynamic behaviors of the real PAM actuators. PMID:23871151
Thrust Production and Wake Structure of an Actuated Lamprey Model
NASA Astrophysics Data System (ADS)
Buchholz, James; Smits, Alexander
2004-11-01
Thrust generation is studied for a flexible lamprey model which is actuated periodically to produce a streamwise traveling wave. Shape memory alloy actuators are used to achieve this deformation. The flow field is investigated using DPIV and flow visualization for a range of Strouhal numbers based on peak-to-peak amplitude of the trailing edge. The vortex kinematics in the spanwise and streamwise planes are examined, and a three-dimensional unsteady vortex model of the wake will be discussed.
Relativistic static thin disks: The counterrotating model
NASA Astrophysics Data System (ADS)
González, Guillermo A.; Espitia, Omar A.
2003-11-01
A detailed study is presented of the counterrotating model (CRM) for generic finite static axially symmetric thin disks with nonzero radial pressure. A general constraint over the counterrotating tangential velocities, needed to cast the surface energy-momentum tensor of the disk as the superposition of two counterrotating perfect fluids, and expressions for the energy density and pressure of the counterrotating fluids are obtained. We show that, in general, it is not possible to take the two counterrotating fluids as circulating along geodesics nor take the two counterrotating tangential velocities as equal and opposite. A simple family of disks is studied that admits some CRMs with well defined counterrotating tangential velocities and stable against radial perturbations.
An Actuator Curve Embedding Method to Model Wind Turbine Wakes
NASA Astrophysics Data System (ADS)
Jha, Pankaj; Schmitz, Sven
2013-11-01
The Actuator Line Method (ALM) is widely used in the wind energy community to model the complex interactions within large wind farms in large-eddy simulation (LES) of the atmospheric boundary layer (ABL) at various stability states. The state-of-the-art in ALM modeling is rooted in the work of Sorensen and Shen (2002). The major weakness of the ALM still remains in having the actuator line discretized as a superposition of individual spherically-spread body forces. The associated overlap of adjacent spherical force fields leads to a large sensitivity of computed blade loads to the way in which the spherical spreading radius is altered along the actuator line (Jha et al. 2013). An Actuator Curve Embedding (ACE) method is developed that considers a general actuator line in 3-D space where the force distribution along the actuator curve is embedded continuously onto the background mesh and without overlap. The ACE method thus is expected to show improved body-force discretization for wind turbine blades, in particular those subject to aeroelastic deformations. Some preliminary results contrasting the ALM and ACE methods are discussed. Support: DOE. Graduate Research Assistant, Aerospace Engineering.
Actuator-valve interface optimization
Burchett, O.L.; Jones, R.L.
1986-01-01
A computer code, Actuator Valve Response (AVR), has been developed to optimize the explosive actuator-valve interface parameters so that the valve plunger velocity is at a maximum when the plunger reaches the valve tubes. The code considers three forces to act on the valve plunger before the plunger reaches the valve tubes. These are the pressure force produced by the actuator, the shear force necessary to shear the seal disks on the actuator and the valve plunger, and the friction force caused by friction between the plunger and the plunger bore. The three forces are modeled by expressions that are explicitly functions of the plunger displacement. A particular actuator-valve combination was analyzed with the computer code AVR with four different combinations of valve plunger seal disk shear strength and initial friction force. (LEW)
Modeling of Radiative Transfer in Protostellar Disks
NASA Technical Reports Server (NTRS)
VonAllmen, Paul; Turner, Neal
2007-01-01
This program implements a spectral line, radiative transfer tool for interpreting Spitzer Space Telescope observations by matching them with models of protostellar disks for improved understanding of planet and star formation. The Spitzer Space Telescope detects gas phase molecules in the infrared spectra of protostellar disks, with spectral lines carrying information on the chemical composition of the material from which planets form. Input to the software includes chemical models developed at JPL. The products are synthetic images and spectra for comparison with Spitzer measurements. Radiative transfer in a protostellar disk is primarily affected by absorption and emission processes in the dust and in molecular gases such as H2, CO, and HCO. The magnitude of the optical absorption and emission is determined by the population of the electronic, vibrational, and rotational energy levels. The population of the molecular level is in turn determined by the intensity of the radiation field. Therefore, the intensity of the radiation field and the population of the molecular levels are inter-dependent quantities. To meet the computational challenges of solving for the coupled radiation field and electronic level populations in disks having wide ranges of optical depths and spatial scales, the tool runs in parallel on the JPL Dell Cluster supercomputer with C++ and Fortran compiler with a Message Passing Interface. Because this software has been developed on a distributed computing platform, the modeling of systems previously beyond the reach of available computational resources is possible.
ON THE TRANSITIONAL DISK CLASS: LINKING OBSERVATIONS OF T TAURI STARS AND PHYSICAL DISK MODELS
Espaillat, C.; Andrews, S.; Qi, C.; Wilner, D.; Ingleby, L.; Calvet, N.; Hernandez, J.; Furlan, E.; D'Alessio, P.; Muzerolle, J. E-mail: sandrews@cfa.harvard.edu E-mail: dwilner@cfa.harvard.edu E-mail: ncalvet@umich.edu E-mail: Elise.Furlan@jpl.nasa.gov E-mail: muzerol@stsci.edu
2012-03-10
Two decades ago 'transitional disks' (TDs) described spectral energy distributions (SEDs) of T Tauri stars with small near-IR excesses, but significant mid- and far-IR excesses. Many inferred this indicated dust-free holes in disks possibly cleared by planets. Recently, this term has been applied disparately to objects whose Spitzer SEDs diverge from the expectations for a typical full disk (FD). Here, we use irradiated accretion disk models to fit the SEDs of 15 such disks in NGC 2068 and IC 348. One group has a 'dip' in infrared emission while the others' continuum emission decreases steadily at all wavelengths. We find that the former have an inner disk hole or gap at intermediate radii in the disk and we call these objects 'transitional disks' and 'pre-transitional disks' (PTDs), respectively. For the latter group, we can fit these SEDs with FD models and find that millimeter data are necessary to break the degeneracy between dust settling and disk mass. We suggest that the term 'transitional' only be applied to objects that display evidence for a radical change in the disk's radial structure. Using this definition, we find that TDs and PTDs tend to have lower mass accretion rates than FDs and that TDs have lower accretion rates than PTDs. These reduced accretion rates onto the star could be linked to forming planets. Future observations of TDs and PTDs will allow us to better quantify the signatures of planet formation in young disks.
Dynamic modeling of brushless dc motors for aerospace actuation
NASA Technical Reports Server (NTRS)
Demerdash, N. A.; Nehl, T. W.
1980-01-01
A discrete time model for simulation of the dynamics of samarium cobalt-type permanent magnet brushless dc machines is presented. The simulation model includes modeling of the interaction between these machines and their attached power conditioners. These are transistorized conditioner units. This model is part of an overall discrete-time analysis of the dynamic performance of electromechanical actuators, which was conducted as part of prototype development of such actuators studied and built for NASA-Johnson Space Center as a prospective alternative to hydraulic actuators presently used in shuttle orbiter applications. The resulting numerical simulations of the various machine and power conditioner current and voltage waveforms gave excellent correlation to the actual waveforms collected from actual hardware experimental testing. These results, numerical and experimental, are presented here for machine motoring, regeneration and dynamic braking modes. Application of the resulting model to the determination of machine current and torque profiles during closed-loop actuator operation were also analyzed and the results are given here. These results are given in light of an overall view of the actuator system components. The applicability of this method of analysis to design optimization and trouble-shooting in such prototype development is also discussed in light of the results at hand.
Dynamic modeling of brushless dc motors for aerospace actuation
NASA Astrophysics Data System (ADS)
Demerdash, N. A.; Nehl, T. W.
1980-11-01
A discrete time model for simulation of the dynamics of samarium cobalt-type permanent magnet brushless dc machines is presented. The simulation model includes modeling of the interaction between these machines and their attached power conditioners. These are transistorized conditioner units. This model is part of an overall discrete-time analysis of the dynamic performance of electromechanical actuators, which was conducted as part of prototype development of such actuators studied and built for NASA-Johnson Space Center as a prospective alternative to hydraulic actuators presently used in shuttle orbiter applications. The resulting numerical simulations of the various machine and power conditioner current and voltage waveforms gave excellent correlation to the actual waveforms collected from actual hardware experimental testing. These results, numerical and experimental, are presented here for machine motoring, regeneration and dynamic braking modes. Application of the resulting model to the determination of machine current and torque profiles during closed-loop actuator operation were also analyzed and the results are given here. These results are given in light of an overall view of the actuator system components. The applicability of this method of analysis to design optimization and trouble-shooting in such prototype development is also discussed in light of the results at hand.
Computational Modeling of Magnetically Actuated Propellant Orientation
NASA Technical Reports Server (NTRS)
Hochstein, John I.
1996-01-01
sufficient performance to support cryogenic propellant management tasks. In late 1992, NASA MSFC began a new investigation in this technology commencing with the design of the Magnetically-Actuated Propellant Orientation (MAPO) experiment. A mixture of ferrofluid and water is used to simulate the paramagnetic properties of LOX and the experiment is being flown on the KC-135 aircraft to provide a reduced gravity environment. The influence of a 0.4 Tesla ring magnet on flow into and out of a subscale Plexiglas tank is being recorded on video tape. The most efficient approach to evaluating the feasibility of MAPO is to compliment the experimental program with development of a computational tool to model the process of interest. The goal of the present research is to develop such a tool. Once confidence in its fidelity is established by comparison to data from the MAPO experiment, it can be used to assist in the design of future experiments and to study the parameter space of the process. Ultimately, it is hoped that the computational model can serve as a design tool for full-scale spacecraft applications.
Nonlinear finite element modeling of THUNDER piezoelectric actuators
NASA Astrophysics Data System (ADS)
Taleghani, Barmac K.; Campbell, Joel F.
1999-06-01
A NASTRAN non-linear finite element model has been developed for predicting the dome heights of THUNDER (Thin Layer Unimorph Ferroelectric Driver) piezoelectric actuators. To analytically validate the finite element model, a comparison was made with a non-linear plate solution using Von Karmen's approximation. A 500 volt input was used to examine the actuator deformation. The NASTRAN finite element model was also compared with experimental results. Four groups of specimens were fabricated and tested. Four different input voltages, which included 120, 160, 200, and 240 Vp-p with a 0 volts offset, were used for this comparison.
Modeling liquid crystal elastomers: actuators, pumps, and robots
NASA Astrophysics Data System (ADS)
Selinger, Robin L. B.; Mbanga, Badel L.; Selinger, Jonathan V.
2008-02-01
We model the dynamics of shape evolution of liquid crystal elastomers (LCE) in three dimensions using finite element elastodynamics. The model predicts the macroscopic mechanical response induced by changes in nematic order, e.g. by heating or cooling through the isotropic/nematic transition or, in azo-doped materials, by exposure to light. We model the performance of LCE actuator devices including multicomponent actuators, peristaltic pumps and self-propelled robots. The goal of this work is to build a bridge between basic soft matter theory and practical materials engineering/device design. Supported by NSF-DMR-0605889.
Non-Linear Finite Element Modeling of THUNDER Piezoelectric Actuators
NASA Technical Reports Server (NTRS)
Taleghani, Barmac K.; Campbell, Joel F.
1999-01-01
A NASTRAN non-linear finite element model has been developed for predicting the dome heights of THUNDER (THin Layer UNimorph Ferroelectric DrivER) piezoelectric actuators. To analytically validate the finite element model, a comparison was made with a non-linear plate solution using Von Karmen's approximation. A 500 volt input was used to examine the actuator deformation. The NASTRAN finite element model was also compared with experimental results. Four groups of specimens were fabricated and tested. Four different input voltages, which included 120, 160, 200, and 240 Vp-p with a 0 volts offset, were used for this comparison.
A comprehensive model for piezoceramic actuators: modelling, validation and application
NASA Astrophysics Data System (ADS)
Quant, Mario; Elizalde, Hugo; Flores, Abiud; Ramírez, Ricardo; Orta, Pedro; Song, Gangbing
2009-12-01
This paper presents a comprehensive model for piezoceramic actuators (PAs), which accounts for hysteresis, non-linear electric field and dynamic effects. The hysteresis model is based on the widely used general Maxwell slip model, while an enhanced electro-mechanical non-linear model replaces the linear constitutive equations commonly used. Further on, a linear second order model compensates the frequency response of the actuator. Each individual model is fully characterized from experimental data yielded by a specific PA, then incorporated into a comprehensive 'direct' model able to determine the output strain based on the applied input voltage, fully compensating the aforementioned effects, where the term 'direct' represents an electrical-to-mechanical operating path. The 'direct' model was implemented in a Matlab/Simulink environment and successfully validated via experimental results, exhibiting higher accuracy and simplicity than many published models. This simplicity would allow a straightforward inclusion of other behaviour such as creep, ageing, material non-linearity, etc, if such parameters are important for a particular application. Based on the same formulation, two other models are also presented: the first is an 'alternate' model intended to operate within a force-controlled scheme (instead of a displacement/position control), thus able to capture the complex mechanical interactions occurring between a PA and its host structure. The second development is an 'inverse' model, able to operate within an open-loop control scheme, that is, yielding a 'linearized' PA behaviour. The performance of the developed models is demonstrated via a numerical sample case simulated in Matlab/Simulink, consisting of a PA coupled to a simple mechanical system, aimed at shifting the natural frequency of the latter.
Computational model of deformable lenses actuated by dielectric elastomers
NASA Astrophysics Data System (ADS)
Lu, Tongqing; Cai, Shengqiang; Wang, Huiming; Suo, Zhigang
2013-09-01
A recent design of deformable lens mimics the human eye, adjusting its focal length in response to muscle-like actuation. The artificial muscle is a membrane of a dielectric elastomer subject to a voltage. Here, we calculate the coupled and inhomogeneous deformation of the lens and the dielectric elastomer actuator by formulating a nonlinear boundary-value problem. We characterize the strain-stiffening elastomer with the Gent model and describe the voltage-induced deformation using the model of ideal dielectric elastomer. The computational predictions agree well with experimental data. We use the model to explore the space of parameters, including the prestretch of the membrane, the volume of the liquid in the lens, and the size of the dielectric elastomer actuator relative to the lens. We examine how various modes of failure limit the minimum radius of curvature.
A voice-actuated wind tunnel model leak checking system
NASA Technical Reports Server (NTRS)
Larson, W. E.
1985-01-01
A voice-actuated wind tunnel model leak checking system was developed. The system uses a voice recognition and response unit to interact with the technician along with a graphics terminal to provide the technician with visual feedback while checking a model for leaks.
Valve, explosive actuated, normally open, pyronetics model 1399
NASA Technical Reports Server (NTRS)
Avalos, E.
1971-01-01
Results of the tests to evaluate open valve, Model 1399 are reported for the the following tests: proof pressure leakage, actuation, disassembly, and burst pressure. It is concluded that the tests demonstrate the soundness of the structural integrity of the valve.
Modelling and control of double-cone dielectric elastomer actuator
NASA Astrophysics Data System (ADS)
Branz, F.; Francesconi, A.
2016-09-01
Among various dielectric elastomer devices, cone actuators are of large interest for their multi-degree-of-freedom design. These objects combine the common advantages of dielectric elastomers (i.e. solid-state actuation, self-sensing capability, high conversion efficiency, light weight and low cost) with the possibility to actuate more than one degree of freedom in a single device. The potential applications of this feature in robotics are huge, making cone actuators very attractive. This work focuses on rotational degrees of freedom to complete existing literature and improve the understanding of such aspect. Simple tools are presented for the performance prediction of the device: finite element method simulations and interpolating relations have been used to assess the actuator steady-state behaviour in terms of torque and rotation as a function of geometric parameters. Results are interpolated by fit relations accounting for all the relevant parameters. The obtained data are validated through comparison with experimental results: steady-state torque and rotation are determined at a given high voltage actuation. In addition, the transient response to step input has been measured and, as a result, the voltage-to-torque and the voltage-to-rotation transfer functions are obtained. Experimental data are collected and used to validate the prediction capability of the transfer function in terms of time response to step input and frequency response. The developed static and dynamic models have been employed to implement a feedback compensator that controls the device motion; the simulated behaviour is compared to experimental data, resulting in a maximum prediction error of 7.5%.
Design, test and model of a hybrid magnetostrictive hydraulic actuator
NASA Astrophysics Data System (ADS)
Chaudhuri, Anirban; Yoo, Jin-Hyeong; Wereley, Norman M.
2009-08-01
The basic operation of hybrid hydraulic actuators involves high frequency bi-directional operation of an active material that is converted to uni-directional motion of hydraulic fluid using valves. A hybrid actuator was developed using magnetostrictive material Terfenol-D as the driving element and hydraulic oil as the working fluid. Two different lengths of Terfenol-D rod, 51 and 102 mm, with the same diameter, 12.7 mm, were used. Tests with no load and with load were carried out to measure the performance for uni-directional motion of the output piston at different pumping frequencies. The maximum no-load flow rates were 24.8 cm3 s-1 and 22.7 cm3 s-1 with the 51 mm and 102 mm long rods respectively, and the peaks were noted around 325 Hz pumping frequency. The blocked force of the actuator was close to 89 N in both cases. A key observation was that, at these high pumping frequencies, the inertial effects of the fluid mass dominate over the viscous effects and the problem becomes unsteady in nature. In this study, we also develop a mathematical model of the hydraulic hybrid actuator in the time domain to show the basic operational principle under varying conditions and to capture phenomena affecting system performance. Governing equations for the pumping piston and output shaft were obtained from force equilibrium considerations, while compressibility of the working fluid was taken into account by incorporating the bulk modulus. Fluid inertia was represented by a lumped parameter approach to the transmission line model, giving rise to strongly coupled ordinary differential equations. The model was then used to calculate the no-load velocities of the actuator at different pumping frequencies and simulation results were compared with experimental data for model validation.
Three Dimensional Modeling of an MRI Actuated Steerable Catheter System
Liu, Taoming; Çavuşoğlu, M. Cenk
2014-01-01
This paper presents the three dimensional kinematic modeling of a novel steerable robotic ablation catheter system. The catheter, embedded with a set of current-carrying micro-coils, is actuated by the magnetic forces generated by the magnetic field of the MRI scanner. This paper develops a 3D model of the MRI actuated steerable catheter system by using finite differences approach. For each finite segment, a quasi-static torque-deflection equilibrium equation is calculated using beam theory. By using the deflection displacements and torsion angles, the kinematic modeling of the catheter system is derived. The proposed models are evaluated by comparing the simulation results of the proposed model with the experimental results of a proof-of-concept prototype. PMID:25328804
Three Dimensional Modeling of an MRI Actuated Steerable Catheter System.
Liu, Taoming; Cavuşoğlu, M Cenk
2014-01-01
This paper presents the three dimensional kinematic modeling of a novel steerable robotic ablation catheter system. The catheter, embedded with a set of current-carrying micro-coils, is actuated by the magnetic forces generated by the magnetic field of the MRI scanner. This paper develops a 3D model of the MRI actuated steerable catheter system by using finite differences approach. For each finite segment, a quasi-static torque-deflection equilibrium equation is calculated using beam theory. By using the deflection displacements and torsion angles, the kinematic modeling of the catheter system is derived. The proposed models are evaluated by comparing the simulation results of the proposed model with the experimental results of a proof-of-concept prototype. PMID:25328804
Model for bending actuators that use electrostrictive graft elastomers
NASA Astrophysics Data System (ADS)
Costen, Robert C.; Su, Ji; Harrison, Joycelyn S.
2001-07-01
Recently, it was reported that an electrostrictive graft elastomer exhibits large electric field-induced strain (4%). Combined with its high mechanical modulus, the elastomer can offer very promising electromechanical properties, in terms of output mechanical energy density, for an electroactive polymeric material. Therefore, it has been considered as one of the candidates that can be used in high performance, low mass actuation devices in many aerospace applications. Various bi-layer-based bending actuators have been designed and fabricated. An analytic model based on beam theory in the strength of materials has been derived for the transverse deflection, or curvature, and the longitudinal strain of the bi-layer beam. The curvature and strain are functions of the applied voltage and the thickness, width, and Young's modulus of the active and passive layers. The model can be used to optimize the performance of electrostrictive graft elastomer-based actuators to meet the requirements of various applications. In this presentation, optimization and sensitivity studies are applied to the bending performance of such actuators.
Model For Bending Actuators That Use Electrostrictive Graft Elastomers
NASA Technical Reports Server (NTRS)
Costen, Robert C.; Su, Ji; Harrison, Joycelyn S.
2001-01-01
Recently, it was reported that an electrostrictive graft elastomer exhibits large electric field-induced strain (4%). Combined with its high mechanical modulus, the elastomer can offer very promising electromechanical properties, in terms of output mechanical energy density, for an electroactive polymeric material. Therefore, it has been considered as one of the candidates that can be used in high performance, low mass actuation devices in many aerospace applications. Various bilayer- based bending actuators have been designed and fabricated. An analytic model based on beam theory in the strength of materials has been derived for the transverse deflection, or curvature, and the longitudinal strain of the bi-layer beam. The curvature and strain are functions of the applied voltage and the thickness, width, and Young s modulus of the active and passive layers. The model can be used to optimize the performance of electrostrictive graft elastomer-based actuators to meet the requirements of various applications. In this presentation, optimization and sensitivity studies are applied to the bending performance of such actuators.
Towards a Global Evolutionary Model of Protoplanetary Disks
NASA Astrophysics Data System (ADS)
Bai, Xue-Ning
2016-04-01
A global picture of the evolution of protoplanetary disks (PPDs) is key to understanding almost every aspect of planet formation, where standard α-disk models have been continually employed for their simplicity. In the meantime, disk mass loss has been conventionally attributed to photoevaporation, which controls disk dispersal. However, a paradigm shift toward accretion driven by magnetized disk winds has taken place in recent years, thanks to studies of non-ideal magnetohydrodynamic effects in PPDs. I present a framework of global PPD evolution aiming to incorporate these advances, highlighting the role of wind-driven accretion and wind mass loss. Disk evolution is found to be largely dominated by wind-driven processes, and viscous spreading is suppressed. The timescale of disk evolution is controlled primarily by the amount of external magnetic flux threading the disks, and how rapidly the disk loses the flux. Rapid disk dispersal can be achieved if the disk is able to hold most of its magnetic flux during the evolution. In addition, because wind launching requires a sufficient level of ionization at the disk surface (mainly via external far-UV (FUV) radiation), wind kinematics is also affected by the FUV penetration depth and disk geometry. For a typical disk lifetime of a few million years, the disk loses approximately the same amount of mass through the wind as through accretion onto the protostar, and most of the wind mass loss proceeds from the outer disk via a slow wind. Fractional wind mass loss increases with increasing disk lifetime. Significant wind mass loss likely substantially enhances the dust-to-gas mass ratio and promotes planet formation.
NASA Technical Reports Server (NTRS)
Groom, N. J.
1979-01-01
An analytical model of an Annular Momentum Control Device (AMCD) laboratory test model magnetic bearing actuator with permanent magnet fluxbiasing is presented. An AMCD consists of a spinning annular rim which is suspended by a noncontacting linear electromagnetic spin motor. The actuator is treated as a lumped-parameter electromechanical system in the development of the model.
TVC actuator model. [for the space shuttle main engine
NASA Technical Reports Server (NTRS)
Baslock, R. W.
1977-01-01
A prototype Space Shuttle Main Engine (SSME) Thrust Vector Control (TVC) Actuator analog model was successfully completed. The prototype, mounted on five printed circuit (PC) boards, was delivered to NASA, checked out and tested using a modular replacement technique on an analog computer. In all cases, the prototype model performed within the recording techniques of the analog computer which is well within the tolerances of the specifications.
Self-Consistent Models of Accretion Disks
NASA Technical Reports Server (NTRS)
Narayan, Ramesh
1997-01-01
The investigations of advection-dominated accretion flows (ADAFs), with emphasis on applications to X-ray binaries containing black holes and neutron stars is presented. This work is now being recognized as the standard paradigm for understanding the various spectral states of black hole X-ray Binaries (BHXBs). Topics discussed include: (1) Problem in BHXBS, namely that several of these binaries have unusually large concentrations of lithium in their companion stars; (2) A novel test to show that black holes have event horizons; (3) Application of the ADAF model to the puzzling X-ray delay in the recent outburst of the BHXB, GRO J1655-40; (4) Description of the various spectral states in BHXBS; (5) Application of the ADAF model to the famous supermassive black hole at the center of our Galaxy, Sgr A(*); (6) Writing down and solving equations describing steady-state, optically thin, advection-dominated accretion onto a Kerr black hole; (7) The effect of "photon bubble" instability on radiation dominated accretion disks; and (8) Dwarf nova disks in quiescence that have rather low magnetic Reynolds number, of order 10(exp 3).
Models of unsaturated Compton disks around supermassive black holes
NASA Technical Reports Server (NTRS)
Liang, E. P. T.; Thompson, K. A.
1979-01-01
Two inverse-Compton disk models for the hard X-ray spectra of quasi-stellar objects and active galactic nuclei are studied and compared. One is a slightly generalized version of the Shapiro, Lightman and Eardley optically thin disk model, and the other is a conduction-stabilized Corona model. Observational distinctions between the two models are discussed.
Effects of noise variance model on optimal feedback design and actuator placement
NASA Technical Reports Server (NTRS)
Ruan, Mifang; Choudhury, Ajit K.
1994-01-01
In optimal placement of actuators for stochastic systems, it is commonly assumed that the actuator noise variances are not related to the feedback matrix and the actuator locations. In this paper, we will discuss the limitation of that assumption and develop a more practical noise variance model. Various properties associated with optimal actuator placement under the assumption of this noise variance model are discovered through the analytical study of a second order system.
Characterization and modeling of electrostatically actuated polysilicon micromechanical devices
NASA Astrophysics Data System (ADS)
Chan, Edward Keat Leem
Sensors, actuators, transducers, microsystems and MEMS (MicroElertroMechanical Systems) are some of the terms describing technologies that interface information processing systems with the physical world. Electrostatically actuated micromechanical devices are important building blocks in many of these technologies. Arrays of these devices are used in video projection displays, fluid pumping systems, optical communications systems, tunable lasers and microwave circuits. Well-calibrated simulation tools are essential for propelling ideas from the drawing board into production. This work characterizes a fabrication process---the widely-used polysilicon MUMPs process---to facilitate the design of electrostatically actuated micromechanical devices. The operating principles of a representative device---a capacitive microwave switch---are characterized using a wide range of electrical and optical measurements of test structures along with detailed electromechanical simulations. Consistency in the extraction of material properties from measurements of both pull-in voltage and buckling amplitude is demonstrated. Gold is identified as an area-dependent source of nonuniformity in polysilicon thicknesses and stress. Effects of stress gradients, substrate curvature, and film coverage are examined quantitatively. Using well-characterized beams as in-situ surface probes, capacitance-voltage and surface profile measurements reveal that compressible surface residue modifies the effective electrical gap when the movable electrode contacts an underlying silicon nitride layer. A compressible contact surface model used in simulations improves the fit to measurements. In addition, the electric field across the nitride causes charge to build up in the nitride, increasing the measured capacitance over time. The rate of charging corresponds to charge injection through direct tunneling. A novel actuator that can travel stably beyond one-third of the initial gap (a trademark limitation of
Design of high performance piezo composites actuators
NASA Astrophysics Data System (ADS)
Almajid, Abdulhakim A.
Design of high performance piezo composites actuators are developed. Functionally Graded Microstructure (FGM) piezoelectric actuators are designed to reduce the stress concentration at the middle interface existed in the standard bimorph actuators while maintaining high actuation performance. The FGM piezoelectric laminates are composite materials with electroelastic properties varied through the laminate thickness. The elastic behavior of piezo-laminates actuators is developed using a 2D-elasticity model and a modified classical lamination theory (CLT). The stresses and out-of-plane displacements are obtained for standard and FGM piezoelectric bimorph plates under cylindrical bending generated by an electric field throughout the thickness of the laminate. The analytical model is developed for two different actuator geometries, a rectangular plate actuator and a disk shape actuator. The limitations of CLT are investigated against the 2D-elasticity model for the rectangular plate geometry. The analytical models based on CLT (rectangular and circular) and 2D-elasticity are compared with a model based on Finite Element Method (FEM). The experimental study consists of two FGM actuator systems, the PZT/PZT FGM system and the porous FGM system. The electroelastic properties of each layer in the FGM systems were measured and input in the analytical models to predict the FGM actuator performance. The performance of the FGM actuator is optimized by manipulating the thickness of each layer in the FGM system. The thickness of each layer in the FGM system is made to vary in a linear or non-linear manner to achieve the best performance of the FGM piezoelectric actuator. The analytical and FEM results are found to agree well with the experimental measurements for both rectangular and disk actuators. CLT solutions are found to coincide well with the elasticity solutions for high aspect ratios while the CLT solutions gave poor results compared to the 2D elasticity solutions for
Modelling of spring roll actuators based on viscoelastic dielectric elastomers
NASA Astrophysics Data System (ADS)
Zhang, Junshi; Chen, Hualing; Tang, Liling; Li, Bo; Sheng, Junjie; Liu, Lei
2015-06-01
In this article, the effect of viscoelastic deformation is analyzed theoretically to evaluate the performance of spring roll dielectric elastomer (DE) actuators. By patterning the electrodes on the rolls, respectively, two functions are studied: axial elongation and bending. The thermodynamic model of viscoelastic DE spring roll is established, and the governing equation is deduced by the free energy method. It is found that when the applied voltage is static and relatively small, both the axial elongated and bending deformed spring rolls can reach equilibrium after viscoelastic relaxation. The evolutions in different timescales and the final profile are presented. The dynamic response is studied as well, by applying a sinusoidal voltage. For the axial elongated spring roll, viscoelasticity can reduce amplitude and increase mean stretch of the actuator. For the bending deformed spring rolls, the results indicate that the spring stiffness has a more significant impact on dynamic performance compared to the effect of voltage.
Active Flow Control Using Sweeping Jet Actuators on a Semi-Span Wing Model
NASA Technical Reports Server (NTRS)
Melton, LaTunia Pack; Koklu, Mehti
2016-01-01
Wind tunnel experiments were performed using active flow control on an unswept semispan wing model with a 30% chord trailing edge flap to aid in the selection of actuators for a planned high Reynolds number experiment. Two sweeping jet actuator sizes were investigated to determine the influence of actuator size on the active flow control system efficiency. Sweeping jet actuators with orifice sizes of 1 mm x 2 mm and 2 mm x 4 mm were selected because of the differences in actuator jet sweep angle. The parameters that were varied include actuator momentum, freestream velocity, and trailing edge flap deflection angle. Steady and unsteady pressure data, Particle Image Velocimetry data, and force and moment data were acquired to assess the performance of the two actuators. In addition to the wind tunnel experiments, benchtop studies of the actuators were performed to characterize the jets produced by each actuator. Benchtop investigations of the smaller actuator reveal that the jet exiting the actuator has a reduced sweep angle compared to published data for larger versions of this type of actuator. The larger actuator produces an oscillating jet that attaches to the external di?user walls at low supply pressures and produces the expected sweep angles. The AFC results using the smaller actuators show that while the actuators can control flow separation, the selected spacing of 3.3 cm may be too large due to the reduced sweep angle. In comparison, the spacing for the larger actuators, 6.6 cm, appears to be optimal for the Mach numbers investigated. Particle Image Velocimetry results are presented and show how the wall jets produced by the actuators cause the flow to attach to the flap surface.
Test Cases for Modeling and Validation of Structures with Piezoelectric Actuators
NASA Technical Reports Server (NTRS)
Reaves, Mercedes C.; Horta, Lucas G.
2001-01-01
A set of benchmark test articles were developed to validate techniques for modeling structures containing piezoelectric actuators using commercially available finite element analysis packages. The paper presents the development, modeling, and testing of two structures: an aluminum plate with surface mounted patch actuators and a composite box beam with surface mounted actuators. Three approaches for modeling structures containing piezoelectric actuators using the commercially available packages: MSC/NASTRAN and ANSYS are presented. The approaches, applications, and limitations are discussed. Data for both test articles are compared in terms of frequency response functions from deflection and strain data to input voltage to the actuator. Frequency response function results using the three different analysis approaches provided comparable test/analysis results. It is shown that global versus local behavior of the analytical model and test article must be considered when comparing different approaches. Also, improper bonding of actuators greatly reduces the electrical to mechanical effectiveness of the actuators producing anti-resonance errors.
NASA Astrophysics Data System (ADS)
Long, Yongjun; Wei, Xiaohui; Wang, Chunlei; Dai, Xin; Wang, Shigang
2014-05-01
A new rotary normal stress electromagnetic actuator for fast steering mirror (FSM) is presented. The study includes concept design, actuating torque modeling, actuator design, and validation with numerical simulation. To achieve an FSM with compact structure and high bandwidth, the actuator is designed with a cross armature magnetic topology. By introducing bias flux generated by four permanent magnets (PMs), the actuator has high-force density similar to a solenoid but also has essentially linear characteristics similar to a voice coil actuator, leading to a simply control algorithm. The actuating torque output is a linear function of both driving current and rotation angle and is formulated with equivalent magnetic circuit method. To improve modeling accuracy, both the PM flux and coil flux leakages are taken into consideration through finite element simulation. Based on the established actuator model, optimal design of the actuator is presented to meet the requirement of our FSM. Numerical simulation is then presented to validate the concept design, established actuator model, and designed actuator. It is shown that the calculated results are in a good agreement with the simulation results.
Simulation model for analyzing SPUDI with actuated signals
Shafahi, Y.; Haghani, A.; Carter, E.C.; Gupta, K.N.V.
1998-09-01
A time based microsimulation model is developed for analyzing the traffic operation at single point urban diamond interchanges. Features of the model include actuated signal operation, protected and permitted left turn phasing, right turn phasing with and without right turn on red, traffic in shared lanes, traffic in left turn and right turn storage lanes, car following, lane changing, gap acceptance behavior, primary and secondary queue formation and dissipation. The model accepts geometric, traffic, and signal data in an interactive mode. Input files may also be created separately without going through the interactive session. The model outputs include measures of effectiveness such as stopped delay, total delay, average speed, and maximum and average queue length. These measures of effectiveness are given for each turning movement for each approach, and for the intersection as a whole. The model outputs also show the total green time and the total yellow and all red times assigned by the actuated system to each phase during the simulation time. The model results are compared with the actual data collected in the field.
Comprehensive modeling of electrostatically actuated MEMS beams including uncertainty quantification
NASA Astrophysics Data System (ADS)
Snow, Michael G.
MEMS switches have offered dramatic improvements in the performance of RF systems. However, difficulties with reliability has slowed the adoption of MEMS switches in RF systems. These reliability issues are partly due to the poor manufacturing tolerances endemic to MEMS manufacturing processes. These manufacturing tolerances may cause significant variations in performance characteristics. This work focuses on electrostatically actuated MEMS beam capacitive shunt switches. A non-linear dynamic model for these switches was developed. The model accounts for a variety of physical effects including; beam stretching, residual stress, non-rigid boundary conditions, initial curvature, electrostatic fringing field, finite electrodes, squeeze film damping, and distributed contact. The effects of uncertain parameters on the outputs of the model are discovered through response surface based uncertainty quantification techniques. The model accurately predicts the actuation voltages and switching times of these MEMS switches as well as the effects of uncertain parameters. The derived model is widely applicable and accuratly reproduces the results of other models in the literature. Future researchers will be able to rapidly iterate designs and accurately understand the behavior of these switches.
Hysteresis Modeling of Magnetic Shape Memory Alloy Actuator Based on Krasnosel'skii-Pokrovskii Model
Wang, Shoubin; Gao, Wei
2013-01-01
As a new type of intelligent material, magnetically shape memory alloy (MSMA) has a good performance in its applications in the actuator manufacturing. Compared with traditional actuators, MSMA actuator has the advantages as fast response and large deformation; however, the hysteresis nonlinearity of the MSMA actuator restricts its further improving of control precision. In this paper, an improved Krasnosel'skii-Pokrovskii (KP) model is used to establish the hysteresis model of MSMA actuator. To identify the weighting parameters of the KP operators, an improved gradient correction algorithm and a variable step-size recursive least square estimation algorithm are proposed in this paper. In order to demonstrate the validity of the proposed modeling approach, simulation experiments are performed, simulations with improved gradient correction algorithm and variable step-size recursive least square estimation algorithm are studied, respectively. Simulation results of both identification algorithms demonstrate that the proposed modeling approach in this paper can establish an effective and accurate hysteresis model for MSMA actuator, and it provides a foundation for improving the control precision of MSMA actuator. PMID:23737730
Modeling Dust Emission of HL Tau Disk Based on Planet-Disk Interactions
NASA Astrophysics Data System (ADS)
Jin, Sheng; Li, Shengtai; Isella, Andrea; Li, Hui; Ji, Jianghui
2016-02-01
We use extensive global two-dimensional hydrodynamic disk gas+dust simulations with embedded planets, coupled with three-dimensional radiative transfer calculations, to model the dust ring and gap structures in the HL Tau protoplanetary disk observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We include the self-gravity of disk gas and dust components and make reasonable choices of disk parameters, assuming an already settled dust distribution and no planet migration. We can obtain quite adequate fits to the observed dust emission using three planets with masses of 0.35, 0.17, and 0.26 MJup at 13.1, 33.0, and 68.6 AU, respectively. Implications for the planet formation as well as the limitations of this scenario are discussed.
NASA Astrophysics Data System (ADS)
Woitke, P.; Min, M.; Pinte, C.; Thi, W.-F.; Kamp, I.; Rab, C.; Anthonioz, F.; Antonellini, S.; Baldovin-Saavedra, C.; Carmona, A.; Dominik, C.; Dionatos, O.; Greaves, J.; Güdel, M.; Ilee, J. D.; Liebhart, A.; Ménard, F.; Rigon, L.; Waters, L. B. F. M.; Aresu, G.; Meijerink, R.; Spaans, M.
2016-02-01
We propose a set of standard assumptions for the modelling of Class II and III protoplanetary disks, which includes detailed continuum radiative transfer, thermo-chemical modelling of gas and ice, and line radiative transfer from optical to cm wavelengths. The first paper of this series focuses on the assumptions about the shape of the disk, the dust opacities, dust settling, and polycyclic aromatic hydrocarbons (PAHs). In particular, we propose new standard dust opacities for disk models, we present a simplified treatment of PAHs in radiative equilibrium which is sufficient to reproduce the PAH emission features, and we suggest using a simple yet physically justified treatment of dust settling. We roughly adjust parameters to obtain a model that predicts continuum and line observations that resemble typical multi-wavelength continuum and line observations of Class II T Tauri stars. We systematically study the impact of each model parameter (disk mass, disk extension and shape, dust settling, dust size and opacity, gas/dust ratio, etc.) on all mainstream continuum and line observables, in particular on the SED, mm-slope, continuum visibilities, and emission lines including [OI] 63 μm, high-J CO lines, (sub-)mm CO isotopologue lines, and CO fundamental ro-vibrational lines. We find that evolved dust properties, i.e. large grains, often needed to fit the SED, have important consequences for disk chemistry and heating/cooling balance, leading to stronger near- to far-IR emission lines in general. Strong dust settling and missing disk flaring have similar effects on continuum observations, but opposite effects on far-IR gas emission lines. PAH molecules can efficiently shield the gas from stellar UV radiation because of their strong absorption and negligible scattering opacities in comparison to evolved dust. The observable millimetre-slope of the SED can become significantly more gentle in the case of cold disk midplanes, which we find regularly in our T Tauri models
Fabrication, modeling and optimization of an ionic polymer gel actuator
NASA Astrophysics Data System (ADS)
Jo, Choonghee; Naguib, Hani E.; Kwon, Roy H.
2011-04-01
The modeling of the electro-active behavior of ionic polymer gel is studied and the optimum conditions that maximize the deflection of the gel are investigated. The bending deformation of polymer gel under an electric field is formulated by using chemo-electro-mechanical parameters. In the modeling, swelling and shrinking phenomena due to the differences in ion concentration at the boundary between the gel and solution are considered prior to the application of an electric field, and then bending actuation is applied. As the driving force of swelling, shrinking and bending deformation, differential osmotic pressure at the boundary of the gel and solution is considered. From this behavior, the strain or deflection of the gel is calculated. To find the optimum design parameter settings (electric voltage, thickness of gel, concentration of polyion in the gel, ion concentration in the solution, and degree of cross-linking in the gel) for bending deformation, a nonlinear constrained optimization model is formulated. In the optimization model, a bending deflection equation of the gel is used as an objective function, and a range of decision variables and their relationships are used as constraint equations. Also, actuation experiments are conducted using poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) gel and the optimum conditions predicted by the proposed model have been verified by the experiments.
Eccentric-Disk Models for the Nucleus of M31
NASA Astrophysics Data System (ADS)
Peiris, Hiranya V.; Tremaine, Scott
2003-12-01
We construct dynamical models of the ``double'' nucleus of M31 in which the nucleus consists of an eccentric disk of stars orbiting a central black hole. The principal approximation in these models is that the disk stars travel in a Keplerian potential; i.e., we neglect the mass of the disk relative to the black hole. We consider both ``aligned'' models, in which the eccentric disk lies in the plane of the large-scale M31 disk, and ``nonaligned'' models, in which the orientation of the eccentric disk is fitted to the data. Both types of model can reproduce the double structure and overall morphology seen in Hubble Space Telescope photometry. In comparison with the best available ground-based spectroscopy, the models reproduce the asymmetric rotation curve, the peak height of the dispersion profile, and the qualitative behavior of the Gauss-Hermite coefficients h3 and h4. Aligned models fail to reproduce the observation that the surface brightness at P1 is higher than at P2 and yield significantly poorer fits to the kinematics; thus, we favor nonaligned models. Eccentric-disk models fitted to ground-based spectroscopy are used to predict the kinematics observed at much higher resolution by the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, and we find generally satisfactory agreement.
Analytic model and frequency characteristics of plasma synthetic jet actuator
NASA Astrophysics Data System (ADS)
Zong, Hao-hua; Wu, Yun; Li, Ying-hong; Song, Hui-min; Zhang, Zhi-bo; Jia, Min
2015-02-01
This paper reports a novel analytic model of a plasma synthetic jet actuator (PSJA), considering both the heat transfer effect and the inertia of the throat gas. Both the whole cycle characteristics and the repetitive working process of PSJA can be predicted with this model. The frequency characteristics of a PSJA with 87 mm3 volume and different orifice diameters are investigated based on the analytic model combined with experiments. In the repetitive working mode, the actuator works initially in the transitional stage with 20 cycles and then in the dynamic balanced stage. During the transitional stage, major performance parameters of PSJA experience stepped growth, while during the dynamic balanced stage, these parameters are characterized by periodic variation. With a constant discharge energy of 6.9 mJ, there exists a saturated frequency of 4 kHz/6 kHz for an orifice diameter of 1 mm/1.5 mm, at which the time-averaged total pressure of the pulsed jet reaches a maximum. Between 0.5 mm and 1.5 mm, a larger orifice diameter leads to a higher saturated frequency due to the reduced jet duration time. As the actuation frequency increases, both the time-averaged cavity temperature and the peak jet velocity initially increase and then remain almost unchanged at 1600 K and 280 m/s, respectively. Besides, with increasing frequency, the mechanical energy incorporated in single pulsed jet, the expelled mass per pulse, and the time-averaged density in the cavity, decline in a stair stepping way, which is caused by the intermittent decrease of refresh stage duration in one period.
An analytic performance model of disk arrays and its application
NASA Technical Reports Server (NTRS)
Lee, Edward K.; Katz, Randy H.
1991-01-01
As disk arrays become widely used, tools for understanding and analyzing their performance become increasingly important. In particular, performance models can be invaluable in both configuring and designing disk arrays. Accurate analytic performance models are desirable over other types of models because they can be quickly evaluated, are applicable under a wide range of system and workload parameters, and can be manipulated by a range of mathematical techniques. Unfortunately, analytical performance models of disk arrays are difficult to formulate due to the presence of queuing and fork-join synchronization; a disk array request is broken up into independent disk requests which must all complete to satisfy the original request. We develop, validate, and apply an analytic performance model for disk arrays. We derive simple equations for approximating their utilization, response time, and throughput. We then validate the analytic model via simulation and investigate the accuracy of each approximation used in deriving the analytical model. Finally, we apply the analytical model to derive an equation for the optimal unit of data striping in disk arrays.
Sharp Eccentric Rings in Planetless Hydrodynamical Models of Debris Disks
NASA Technical Reports Server (NTRS)
Lyra, W.; Kuchner, M. J.
2013-01-01
Exoplanets are often associated with disks of dust and debris, analogs of the Kuiper Belt in our solar system. These "debris disks" show a variety of non-trivial structures attributed to planetary perturbations and utilized to constrain the properties of the planets. However, analyses of these systems have largely ignored the fact that, increasingly, debris disks are found to contain small quantities of gas, a component all debris disks should contain at some level. Several debris disks have been measured with a dust-to-gas ratio around unity where the effect of hydrodynamics on the structure of the disk cannot be ignored. Here we report that dust-gas interactions can produce some of the key patterns seen in debris disks that were previously attributed to planets. Through linear and nonlinear modeling of the hydrodynamical problem, we find that a robust clumping instability exists in this configuration, organizing the dust into narrow, eccentric rings, similar to the Fomalhaut debris disk. The hypothesis that these disks might contain planets, though thrilling, is not necessarily required to explain these systems.
A Collisional Algorithm for Modeling Circumstellar Debris Disks
NASA Technical Reports Server (NTRS)
Nesvold, Erika; Kuchner, Marc
2011-01-01
Many planetary systems harbor circumstellar disks of dust and planetesimals thought to be debris left over from planet formation. These debris disks exhibit a range of morphological features which can arise from the gravitational perturbations of planets. Accurate models of these features, accounting for the interactions of the particles in a disk with each other and with whatever planets they contain, can act as signposts for planets in debris disks that otherwise could not be detected. Such models can also constrain the planet's mass and orbital parameters. Current models for many disks consider the gravitational and radiative effects of the star and planets on the disk, but neglect the morphological consequences of collisional interactions between the planetesimals. Many observed disk features are not satisfactorily explained by the current generation of models. I am developing a new kind of debris disk model that considers both the gravitational shaping of the disk by planets and the inelastic collisions between particles. I will use a hybrid N-body integrator to numerically solve the equations of motion for the particles and planets in the disk. To include the collisional effects, I begin with an algorithm that tests for collisions at each step of the orbit integration and readjusts the velocities of colliding particles. I am adapting this algorithm to the problem at hand by allowing each particle to represent a "swarm" of planetesimals with a range of masses. When the algorithm detects an encounter between swarms, two or three swarms are produced to approximate the range of possible trajectories of the daughter planetesimals. Here I present preliminary results from my collisional algorithm.
Protoplanetary Disk Structure with Grain Evolution: The ANDES Model
NASA Astrophysics Data System (ADS)
Akimkin, V.; Zhukovska, S.; Wiebe, D.; Semenov, D.; Pavlyuchenkov, Ya.; Vasyunin, A.; Birnstiel, T.; Henning, Th.
2013-03-01
We present a self-consistent model of a protoplanetary disk: "ANDES" ("AccretioN disk with Dust Evolution and Sedimentation"). ANDES is based on a flexible and extendable modular structure that includes (1) a 1+1D frequency-dependent continuum radiative transfer module, (2) a module to calculate the chemical evolution using an extended gas-grain network with UV/X-ray-driven processes and surface reactions, (3) a module to calculate the gas thermal energy balance, and (4) a 1+1D module that simulates dust grain evolution. For the first time, grain evolution and time-dependent molecular chemistry are included in a protoplanetary disk model. We find that grain growth and sedimentation of large grains onto the disk midplane lead to a dust-depleted atmosphere. Consequently, dust and gas temperatures become higher in the inner disk (R <~ 50 AU) and lower in the outer disk (R >~ 50 AU), in comparison with the disk model with pristine dust. The response of disk chemical structure to the dust growth and sedimentation is twofold. First, due to higher transparency a partly UV-shielded molecular layer is shifted closer to the dense midplane. Second, the presence of big grains in the disk midplane delays the freeze-out of volatile gas-phase species such as CO there, while in adjacent upper layers the depletion is still effective. Molecular concentrations and thus column densities of many species are enhanced in the disk model with dust evolution, e.g., CO2, NH2CN, HNO, H2O, HCOOH, HCN, and CO. We also show that time-dependent chemistry is important for a proper description of gas thermal balance.
PROTOPLANETARY DISK STRUCTURE WITH GRAIN EVOLUTION: THE ANDES MODEL
Akimkin, V.; Wiebe, D.; Pavlyuchenkov, Ya.; Zhukovska, S.; Semenov, D.; Henning, Th.; Vasyunin, A.; Birnstiel, T. E-mail: dwiebe@inasan.ru E-mail: zhukovska@mpia.de E-mail: henning@mpia.de E-mail: tbirnstiel@cfa.harvard.edu
2013-03-20
We present a self-consistent model of a protoplanetary disk: 'ANDES' ('AccretioN disk with Dust Evolution and Sedimentation'). ANDES is based on a flexible and extendable modular structure that includes (1) a 1+1D frequency-dependent continuum radiative transfer module, (2) a module to calculate the chemical evolution using an extended gas-grain network with UV/X-ray-driven processes and surface reactions, (3) a module to calculate the gas thermal energy balance, and (4) a 1+1D module that simulates dust grain evolution. For the first time, grain evolution and time-dependent molecular chemistry are included in a protoplanetary disk model. We find that grain growth and sedimentation of large grains onto the disk midplane lead to a dust-depleted atmosphere. Consequently, dust and gas temperatures become higher in the inner disk (R {approx}< 50 AU) and lower in the outer disk (R {approx}> 50 AU), in comparison with the disk model with pristine dust. The response of disk chemical structure to the dust growth and sedimentation is twofold. First, due to higher transparency a partly UV-shielded molecular layer is shifted closer to the dense midplane. Second, the presence of big grains in the disk midplane delays the freeze-out of volatile gas-phase species such as CO there, while in adjacent upper layers the depletion is still effective. Molecular concentrations and thus column densities of many species are enhanced in the disk model with dust evolution, e.g., CO{sub 2}, NH{sub 2}CN, HNO, H{sub 2}O, HCOOH, HCN, and CO. We also show that time-dependent chemistry is important for a proper description of gas thermal balance.
Validation of high displacement piezoelectric actuator finite element models
NASA Astrophysics Data System (ADS)
Taleghani, Barmac K.
2000-08-01
The paper presents the results obtained by using NASTRAN and ANSYS finite element codes to predict doming of the THUNDER piezoelectric actuators during the manufacturing process and subsequent straining due to an applied input voltage. To effectively use such devices in engineering applications, modeling and characterization are essential. Length, width, dome height, and thickness and important parameters for users of such devices. Therefore, finite element models were used to assess the effects of these parameters. NASTRAN and ANSYS used different methods for modeling piezoelectric effects. In NASTRAN, a thermal analogy was used to represent voltage at nodes as equivalent temperatures, while ANSYS processed the voltage directly using piezoelectric finite elements. The results of finite element models were validated by using the experimental results.
Validation of High Displacement Piezoelectric Actuator Finite Element Models
NASA Technical Reports Server (NTRS)
Taleghani, B. K.
2000-01-01
The paper presents the results obtained by using NASTRAN(Registered Trademark) and ANSYS(Regitered Trademark) finite element codes to predict doming of the THUNDER piezoelectric actuators during the manufacturing process and subsequent straining due to an applied input voltage. To effectively use such devices in engineering applications, modeling and characterization are essential. Length, width, dome height, and thickness are important parameters for users of such devices. Therefore, finite element models were used to assess the effects of these parameters. NASTRAN(Registered Trademark) and ANSYS(Registered Trademark) used different methods for modeling piezoelectric effects. In NASTRAN(Registered Trademark), a thermal analogy was used to represent voltage at nodes as equivalent temperatures, while ANSYS(Registered Trademark) processed the voltage directly using piezoelectric finite elements. The results of finite element models were validated by using the experimental results.
Validation of thermal models for a prototypical MEMS thermal actuator.
Gallis, Michail A.; Torczynski, John Robert; Piekos, Edward Stanley; Serrano, Justin Raymond; Gorby, Allen D.; Phinney, Leslie Mary
2008-09-01
This report documents technical work performed to complete the ASC Level 2 Milestone 2841: validation of thermal models for a prototypical MEMS thermal actuator. This effort requires completion of the following task: the comparison between calculated and measured temperature profiles of a heated stationary microbeam in air. Such heated microbeams are prototypical structures in virtually all electrically driven microscale thermal actuators. This task is divided into four major subtasks. (1) Perform validation experiments on prototypical heated stationary microbeams in which material properties such as thermal conductivity and electrical resistivity are measured if not known and temperature profiles along the beams are measured as a function of electrical power and gas pressure. (2) Develop a noncontinuum gas-phase heat-transfer model for typical MEMS situations including effects such as temperature discontinuities at gas-solid interfaces across which heat is flowing, and incorporate this model into the ASC FEM heat-conduction code Calore to enable it to simulate these effects with good accuracy. (3) Develop a noncontinuum solid-phase heat transfer model for typical MEMS situations including an effective thermal conductivity that depends on device geometry and grain size, and incorporate this model into the FEM heat-conduction code Calore to enable it to simulate these effects with good accuracy. (4) Perform combined gas-solid heat-transfer simulations using Calore with these models for the experimentally investigated devices, and compare simulation and experimental temperature profiles to assess model accuracy. These subtasks have been completed successfully, thereby completing the milestone task. Model and experimental temperature profiles are found to be in reasonable agreement for all cases examined. Modest systematic differences appear to be related to uncertainties in the geometric dimensions of the test structures and in the thermal conductivity of the
A mechanical model of a non-uniform ionomeric polymer metal composite actuator
NASA Astrophysics Data System (ADS)
Anton, Mart; Aabloo, Alvo; Punning, Andres; Kruusmaa, Maarja
2008-04-01
This paper describes a mechanical model of an IPMC (ionomeric polymer metal composite) actuator in a cantilever beam configuration. The main contribution of our model is that it gives the most detailed description reported so far of the quasistatic mechanical behaviour of the actuator with non-uniform bending at large deflections. We also investigate a case where part of an IPMC actuator is replaced with a rigid elongation and demonstrate that this configuration would make the actuator behave more linearly. The model is experimentally validated with MuscleSheet™ IPMCs, purchased from BioMimetics Inc.
Model-Based Angular Scan Error Correction of an Electrothermally-Actuated MEMS Mirror
Zhang, Hao; Xu, Dacheng; Zhang, Xiaoyang; Chen, Qiao; Xie, Huikai; Li, Suiqiong
2015-01-01
In this paper, the actuation behavior of a two-axis electrothermal MEMS (Microelectromechanical Systems) mirror typically used in miniature optical scanning probes and optical switches is investigated. The MEMS mirror consists of four thermal bimorph actuators symmetrically located at the four sides of a central mirror plate. Experiments show that an actuation characteristics difference of as much as 4.0% exists among the four actuators due to process variations, which leads to an average angular scan error of 0.03°. A mathematical model between the actuator input voltage and the mirror-plate position has been developed to predict the actuation behavior of the mirror. It is a four-input, four-output model that takes into account the thermal-mechanical coupling and the differences among the four actuators; the vertical positions of the ends of the four actuators are also monitored. Based on this model, an open-loop control method is established to achieve accurate angular scanning. This model-based open loop control has been experimentally verified and is useful for the accurate control of the mirror. With this control method, the precise actuation of the mirror solely depends on the model prediction and does not need the real-time mirror position monitoring and feedback, greatly simplifying the MEMS control system. PMID:26690432
Model-Based Angular Scan Error Correction of an Electrothermally-Actuated MEMS Mirror.
Zhang, Hao; Xu, Dacheng; Zhang, Xiaoyang; Chen, Qiao; Xie, Huikai; Li, Suiqiong
2015-01-01
In this paper, the actuation behavior of a two-axis electrothermal MEMS (Microelectromechanical Systems) mirror typically used in miniature optical scanning probes and optical switches is investigated. The MEMS mirror consists of four thermal bimorph actuators symmetrically located at the four sides of a central mirror plate. Experiments show that an actuation characteristics difference of as much as 4.0% exists among the four actuators due to process variations, which leads to an average angular scan error of 0.03°. A mathematical model between the actuator input voltage and the mirror-plate position has been developed to predict the actuation behavior of the mirror. It is a four-input, four-output model that takes into account the thermal-mechanical coupling and the differences among the four actuators; the vertical positions of the ends of the four actuators are also monitored. Based on this model, an open-loop control method is established to achieve accurate angular scanning. This model-based open loop control has been experimentally verified and is useful for the accurate control of the mirror. With this control method, the precise actuation of the mirror solely depends on the model prediction and does not need the real-time mirror position monitoring and feedback, greatly simplifying the MEMS control system. PMID:26690432
Scott, Erin L.; Mamajek, Eric E.; Pecaut, Mark J.; Quillen, Alice C.; Moolekamp, Fred; Bell, Cameron P. M.
2014-12-10
We investigate the nature of the unusual eclipsing star OGLE LMC-ECL-11893 (OGLE J05172127-6900558) in the Large Magellanic Cloud recently reported by Dong et al. The eclipse period for this star is 468 days, and the eclipses exhibit a minimum of ∼1.4 mag, preceded by a plateau of ∼0.8 mag. Spectra and optical/IR photometry are consistent with the eclipsed star being a lightly reddened B9III star of inferred age ∼150 Myr and mass ∼4 M {sub ☉}. The disk appears to have an outer radius of ∼0.2 AU with predicted temperatures of ∼1100-1400 K. We model the eclipses as being due to either a transiting geometrically thin dust disk or gaseous accretion disk around a secondary object; the debris disk produces a better fit. We speculate on the origin of such a dense circumstellar dust disk structure orbiting a relatively old low-mass companion, and on the similarities of this system to the previously discovered EE Cep.
NASA Astrophysics Data System (ADS)
Scott, Erin L.; Mamajek, Eric E.; Pecaut, Mark J.; Quillen, Alice C.; Moolekamp, Fred; Bell, Cameron P. M.
2014-12-01
We investigate the nature of the unusual eclipsing star OGLE LMC-ECL-11893 (OGLE J05172127-6900558) in the Large Magellanic Cloud recently reported by Dong et al. The eclipse period for this star is 468 days, and the eclipses exhibit a minimum of ~1.4 mag, preceded by a plateau of ~0.8 mag. Spectra and optical/IR photometry are consistent with the eclipsed star being a lightly reddened B9III star of inferred age ~150 Myr and mass ~4 M ⊙. The disk appears to have an outer radius of ~0.2 AU with predicted temperatures of ~1100-1400 K. We model the eclipses as being due to either a transiting geometrically thin dust disk or gaseous accretion disk around a secondary object; the debris disk produces a better fit. We speculate on the origin of such a dense circumstellar dust disk structure orbiting a relatively old low-mass companion, and on the similarities of this system to the previously discovered EE Cep.
Model-Based Optimization for Flapping Foil Actuation
NASA Astrophysics Data System (ADS)
Izraelevitz, Jacob; Triantafyllou, Michael
2014-11-01
Flapping foil actuation in nature, such as wings and flippers, often consist of highly complex joint kinematics which present an impossibly large parameter space for designing bioinspired mechanisms. Designers therefore often build a simplified model to limit the parameter space so an optimum motion trajectory can be experimentally found, or attempt to replicate exactly the joint geometry and kinematics of a suitable organism whose behavior is assumed to be optimal. We present a compromise: using a simple local fluids model to guide the design of optimized trajectories through a succession of experimental trials, even when the parameter space is too large to effectively search. As an example, we illustrate an optimization routine capable of designing asymmetric flapping trajectories for a large aspect-ratio pitching and heaving foil, with the added degree of freedom of allowing the foil to move parallel to flow. We then present PIV flow visualizations of the optimized trajectories.
Multi-scale mechanical modelling of a tubular actuator with compliant metal electrodes
NASA Astrophysics Data System (ADS)
Wang, Peng; Lassen, Benny; Jones, Richard W.
2010-04-01
Rolled tubular dielectric elastomer-based actuators provide larger forces by making multiple thin layers of the dielectric elastomer apply their actuation forces in parallel. Such a rolled actuator is currently being marketed by Danfoss PolyPower A/S. This actuator is core-free has no pre-strain and is free-standing The dielectric elastomer (DE) material used to construct the actuator combines a silicon elastomer with compliant metal electrode technology that provides unidirectional motion. In this contribution the focus is on the three dimensional (3-D) modelling of this core-free tubular actuator. 3-D modelling is achieved by representing the actuator by two two-dimensional (2-D) models thus ensuring that the resulting 2-D models can be handled numerically by finite element simulation and analysis. Initially the Voltagestrain and Strain-blocking force characteristics of the actuators are investigated using only the modelled 'active' area, the electrode covered part of the actuator. The 'passive' area, which reduces the total force provided by the 'active' area, is modelled by approximating the steady-state characteristics of the passive area as a spring with a specified stiffness. The spring stiffness is related directly to the geometry and elastic modulus of the elastomer material in the 'passive' area. Using this simple model in conjunction with the force provided by the 3-D 'active' area model the 'effective force' of the actuator can be found. The use of this 'effective force' expression provides good agreement with the experimental forcestrain data obtained from a Danfoss PolyPower tubular actuator.
Including slot harmonics to mechanical model of two-pole induction machine with a force actuator
NASA Astrophysics Data System (ADS)
Sinervo, Anssi; Arkkio, Antero
2012-10-01
A simple mechanical model is identified for a two-pole induction machine that has a four-pole extra winding as a force actuator. The actuator can be used to suppress rotor vibrations. Forces affecting the rotor of the induction machine are separated into actuator force, purely mechanical force due to mass unbalance, and force caused by unbalanced magnetic pull from higher harmonics and unipolar flux. The force due to higher harmonics is embedded to the mechanical model. Parameters of the modified mechanical model are identified from measurements and the modifications are shown to be necessary. The force produced by the actuator is calculated using the mechanical model, direct flux measurements, and voltage and current of the force actuator. All three methods are shown to give matching results proving that the mechanical model can be used in vibration control. The test machine is shown to have time periodic behavior and discrete Fourier analysis is used to obtain time-invariant model parameters.
Properties of the δ Scorpii Circumstellar Disk from Continuum Modeling
NASA Astrophysics Data System (ADS)
Carciofi, A. C.; Miroshnichenko, A. S.; Kusakin, A. V.; Bjorkman, J. E.; Bjorkman, K. S.; Marang, F.; Kuratov, K. S.; García-Lario, P.; Calderón, J. V. Perea; Fabregat, J.; Magalhães, A. M.
2006-12-01
We present optical WBVR and infrared JHKL photometric observations of the Be binary system δ Sco obtained in 2000-2005, and mid-infrared (10 and 18 μm) photometry and optical (λλ3200-10500) spectropolarimetry obtained in 2001. Our optical photometry confirms the results of a frequent visual monitoring being done by amateurs. The 2001 spectral energy distribution and polarization are successfully modeled with a three-dimensional non-LTE Monte Carlo code that self-consistently calculates the hydrogen level populations, electron temperature, and gas density for hot star disks. Our disk model is hydrostatically supported in the vertical direction and radially controlled by viscosity. Such a disk model has essentially only two free parameters, viz., the equatorial mass-loss rate and the disk outer radius, if one assumes a prescription for the viscosity. We find that the primary companion is surrounded by a small (7R*), geometrically-thin disk, which is highly nonisothermal and fully ionized. Our model requires an average equatorial mass-loss rate of 1.5×10-9 Msolar yr-1 to successfully explain the observations. In 2005, we detected a significant simultaneous decrease in the object's optical and near-infrared brightness, which is associated with a continuous rise in the hydrogen line equivalent widths. We discuss possible causes for this unusual phenomenon, which is difficult to explain in view of current models of Be star disks.
Polyelectrolyte gels as bending actuators: modeling and numerical simulation
NASA Astrophysics Data System (ADS)
Wallmersperger, Thomas; Keller, Karsten; Attaran, Abdolhamid
2013-04-01
Polyelectrolyte gels are ionic electroactivematerials. They have the ability to react as both, sensors and actuators. As actuators they can be used e.g. as artificial muscles or drug delivery control; as sensors they may be used for measuring e.g. pressure, pH or other ion concentrations in the solution. In this research both, anionic and cationic polyelectrolyte gels placed in aqueous solution with mobile anions and cations are investigated. Due to external stimuli the polyelectrolyte gels can swell or shrink enormously by the uptake or delivery of solvent. In the present research a coupled multi-field problem within a continuum mechanics framework is proposed. The modeling approach introduces a set of equations governing multiple fields of the problem, including the chemical field of the ionic species, the electrical field and the mechanical field. The numerical simulation is performed by using the Finite Element Method. Within the study some test cases will be carried out to validate our model. In the works by Gülch et al., the application of combined anionic-cationic gels as grippers was shown. In the present research for an applied electric field, the change of the concentrations and the electric potential in the complete polymer is simulated by the given formulation. These changes lead to variations in the osmotic pressure resulting in a bending of different polyelectrolyte gels. In the present research it is shown that our model is capable of describing the bending behavior of anionic or cationic gels towards the different electrodes (cathode or anode).
Modeling Layered Accretion and the Magnetorotational Instability in Protoplanetary Disks
NASA Astrophysics Data System (ADS)
Lesniak, Michael V., III
2012-05-01
Understanding the temperature structure of protoplanetary disks (PPDs) is paramount to modeling disk evolution and future planet formation. PPDs around T Tauri stars have two primary heating sources, protostellar irradiation, which depends on the flaring of the disk, and accretional heating as viscous coupling between annuli dissipate energy. I have written a "1.5-D" radiative transfer code to calculate disk temperatures assuming hydrostatic and radiative equilibrium. The model solves for the temperature at all locations simultaneously using Rybicki's method, converges rapidly at high optical depth, and retains full frequency dependence. The likely cause of accretional heating in PPDs is the magnetorotational instability (MRI), which acts where gas ionization is sufficiently high for gas to couple to the magnetic field. This will occur in surface layers of the disk, leaving the interior portions of the disk inactive ("dead zone"). I calculate temperatures in PPDs undergoing such "layered accretion." Since the accretional heating is concentrated far from the midplane, temperatures in the disk's interior are lower than in PPDs modeled with vertically uniform accretion. The method is used to study for the first time disks evolving via the magnetorotational instability, which operates primarily in surface layers. I find that temperatures in layered accretion disks do not significantly differ from those of "passive disks," where no accretional heating exists. Emergent spectra are insensitive to active layer thickness, making it difficult to observationally identify disks undergoing layered vs. uniform accretion. I also calculate the ionization chemistry in PPDs, using an ionization network including multiple charge states of dust grains. Combined with a criterion for the onset of the MRI, I calculate where the MRI can be initiated and the extent of dead zones in PPDs. After accounting for feedback between temperature and active layer thickness, I find the surface
On Vertically Global, Horizontally Local Models for Astrophysical Disks
NASA Astrophysics Data System (ADS)
McNally, Colin P.; Pessah, Martin E.
2015-10-01
Disks with a barotropic equilibrium structure, for which the pressure is only a function of the density, rotate on cylinders in the presence of a gravitational potential, so that the angular frequency of such a disk is independent of height. Such disks with barotropic equilibria can be approximately modeled using the shearing box framework, representing a small disk volume with height-independent angular frequency. If the disk is in baroclinic equilibrium, the angular frequency does generally depend on height, and it is thus necessary to go beyond the standard shearing box approach. In this paper, we show that given a global disk model, it is possible to develop approximate models that are local in horizontal planes without an expansion in height with shearing-periodic boundary conditions. We refer to the resulting framework as the vertically global shearing box (VGSB). These models can be non-axisymmetric for globally barotropic equilibria but should be axisymmetric for globally baroclinic equilibria. We provide explicit equations for this VGSB which can be implemented in standard magnetohydrodynamic codes by generalizing the shearing-periodic boundary conditions to allow for a height-dependent angular frequency and shear rate. We also discuss the limitations that result from the radial approximations that are needed in order to impose height-dependent shearing periodic boundary conditions. We illustrate the potential of this framework by studying a vertical shear instability and examining the modes associated with the magnetorotational instability.
Modeling and development of a twisting wing using inductively heated shape memory alloy actuators
NASA Astrophysics Data System (ADS)
Saunders, Robert N.; Hartl, Darren J.; Boyd, James G.; Lagoudas, Dimitris C.
2015-04-01
Wing twisting has been shown to improve aircraft flight performance. The potential benefits of a twisting wing are often outweighed by the mass of the system required to twist the wing. Shape memory alloy (SMA) actuators repeatedly demonstrate abilities and properties that are ideal for aerospace actuation systems. Recent advances have shown an SMA torsional actuator that can be manufactured and trained with the ability to generate large twisting deformations under substantial loading. The primary disadvantage of implementing large SMA actuators has been their slow actuation time compared to conventional actuators. However, inductive heating of an SMA actuator allows it to generate a full actuation cycle in just seconds rather than minutes while still . The aim of this work is to demonstrate an experimental wing being twisted to approximately 10 degrees by using an inductively heated SMA torsional actuator. This study also considers a 3-D electromagnetic thermo-mechanical model of the SMA-wing system and compare these results to experiments to demonstrate modeling capabilities.
Modeling of thermo-mechanical fatigue and damage in shape memory alloy axial actuators
NASA Astrophysics Data System (ADS)
Wheeler, Robert W.; Hartl, Darren J.; Chemisky, Yves; Lagoudas, Dimitris C.
2015-04-01
The aerospace, automotive, and energy industries have seen the potential benefits of using shape memory alloys (SMAs) as solid state actuators. Thus far, however, these actuators are generally limited to non-critical components or over-designed due to a lack of understanding regarding how SMAs undergo thermomechanical or actuation fatigue and the inability to accurately predict failure in an actuator during use. The purpose of this study was to characterize the actuation fatigue response of Nickel-Titanium-Hafnium (NiTiHf) axial actuators and, in turn, use this characterization to predict failure and monitor damage in dogbone actuators undergoing various thermomechanical loading paths. Calibration data was collected from constant load, full cycle tests ranging from 200-600MPa. Subsequently, actuator lifetimes were predicted for four additional loading paths. These loading paths consisted of linearly varying load with full transformation (300-500MPa) and step loads which transition from zero stress to 300-400MPa at various martensitic volume fractions. Thermal cycling was achieved via resistive heating and convective cooling and was controlled via a state machine developed in LabVIEW. A previously developed fatigue damage model, which is formulated such that the damage accumulation rate is general in terms of its dependence on current and local stress and actuation strain states, was utilized. This form allows the model to be utilized for specimens undergoing complex loading paths. Agreement between experiments and simulations is discussed.
A guide to the use of the pressure disk rotor model as implemented in INS3D-UP
NASA Technical Reports Server (NTRS)
Chaffin, Mark S.
1995-01-01
This is a guide for the use of the pressure disk rotor model that has been placed in the incompressible Navier-Stokes code INS3D-UP. The pressure disk rotor model approximates a helicopter rotor or propeller in a time averaged manner and is intended to simulate the effect of a rotor in forward flight on the fuselage or the effect of a propeller on other aerodynamic components. The model uses a modified actuator disk that allows the pressure jump across the disk to vary with radius and azimuth. The cyclic and collective blade pitch angles needed to achieve a specified thrust coefficient and zero moment about the hub are predicted. The method has been validated with experimentally measured mean induced inflow velocities as well as surface pressures on a generic fuselage. Overset grids, sometimes referred to as Chimera grids, are used to simplify the grid generation process. The pressure disk model is applied to a cylindrical grid which is embedded in the grid or grids used for the rest of the configuration. This document will outline the development of the method, and present input and results for a sample case.
Controller modeling and evaluation for PCV electro-mechanical actuator
NASA Astrophysics Data System (ADS)
Parker, Joey K.
1993-11-01
Hydraulic actuators are currently used to operate the propellant control valves (PCV) for the space shuttle main engine (SSME) and other rocket engines. These actuators are characterized by large power to weight ratios, large force capabilities, and rapid accelerations, which favor their use in control valve applications. However, hydraulic systems are also characterized by susceptibility to contamination, which leads to frequent maintenance requirements. The Control Mechanisms Branch (EP34) of the Component Development Division of the Propulsion Laboratory at the Marshall Space Flight Center (MSFC) has been investigating the application of electromechanical actuators as replacements for the hydraulic units in PCV's over the last few years. This report deals with some testing and analysis of a PCV electromechanical actuator (EMA) designed and fabricated by HR Textron, Inc. This prototype actuator has undergone extensive testing by EP34 personnel since early 1993. At this time, the performance of the HR Textron PCV EMA does not meet requirements for position tracking.
Controller modeling and evaluation for PCV electro-mechanical actuator
NASA Technical Reports Server (NTRS)
Parker, Joey K.
1993-01-01
Hydraulic actuators are currently used to operate the propellant control valves (PCV) for the space shuttle main engine (SSME) and other rocket engines. These actuators are characterized by large power to weight ratios, large force capabilities, and rapid accelerations, which favor their use in control valve applications. However, hydraulic systems are also characterized by susceptibility to contamination, which leads to frequent maintenance requirements. The Control Mechanisms Branch (EP34) of the Component Development Division of the Propulsion Laboratory at the Marshall Space Flight Center (MSFC) has been investigating the application of electromechanical actuators as replacements for the hydraulic units in PCV's over the last few years. This report deals with some testing and analysis of a PCV electromechanical actuator (EMA) designed and fabricated by HR Textron, Inc. This prototype actuator has undergone extensive testing by EP34 personnel since early 1993. At this time, the performance of the HR Textron PCV EMA does not meet requirements for position tracking.
NASA Astrophysics Data System (ADS)
Tian, Pengfei; Jones, Richard W.; Yu, Fei
2016-07-01
A dielectric elastomer (DE) tubular actuator, based on compliant metal electrode technology, exhibits hysteresis-like characteristics when driven with a low power rated high voltage power supply (HVPS). This behavior occurs mainly because the DE actuator acts as a capacitive load compromising the ‘slew rate’ of the HVPS during the actuator’s operation. The motivation of this contribution is to investigate the use of elliptical modelling approaches for capturing the hysteresis characteristics exhibited by the DE tubular actuator when it is driven by a low cost low power rated HVPS. The DE tubular actuator considered in this work demonstrates asymmetric hysteresis behaviour due to the nonlinear voltage–strain behaviour of the actuator. A linearization filter placed in series with the actuator (during its operation) ensures a symmetric hysteresis characteristic that can then be modelled using an ellipse-based approach. Elliptical models come in many forms with the two most popular being the constrained general conic form and the general parametric form. Elliptical-based hysteresis model fits are carried out on experimental data obtained from the application of periodic input voltages, at a number of different low-frequencies, to the tubular actuator. The range of frequencies used is related to the possible use of the tubular actuator for attenuating low frequency vibration during DE actuator-based load positioning applications. Constrained conic and general parametric forms of elliptical model are used for modelling the hysteresis characteristics of the DE actuator and rate dependent models developed based on both approaches. The sensitivity of both of these rate dependent models to small inaccuracies in model parameters was then investigated. The general parametric form was found to be more robust in this respect.
A Reduced-Order Model For Zero-Mass Synthetic Jet Actuators
NASA Technical Reports Server (NTRS)
Yamaleev, Nail K.; Carpenter, Mark H.; Vatsa, Veer S.
2007-01-01
Accurate details of the general performance of fluid actuators is desirable over a range of flow conditions, within some predetermined error tolerance. Designers typically model actuators with different levels of fidelity depending on the acceptable level of error in each circumstance. Crude properties of the actuator (e.g., peak mass rate and frequency) may be sufficient for some designs, while detailed information is needed for other applications (e.g., multiple actuator interactions). This work attempts to address two primary objectives. The first objective is to develop a systematic methodology for approximating realistic 3-D fluid actuators, using quasi-1-D reduced-order models. Near full fidelity can be achieved with this approach at a fraction of the cost of full simulation and only a modest increase in cost relative to most actuator models used today. The second objective, which is a direct consequence of the first, is to determine the approximate magnitude of errors committed by actuator model approximations of various fidelities. This objective attempts to identify which model (ranging from simple orifice exit boundary conditions to full numerical simulations of the actuator) is appropriate for a given error tolerance.
Actuator and aerodynamic modeling for high-angle-of-attack aeroservoelasticity
NASA Technical Reports Server (NTRS)
Brenner, Martin J.
1993-01-01
Accurate prediction of airframe/actuation coupling is required by the imposing demands of modern flight control systems. In particular, for agility enhancement at high angle of attack and low dynamic pressure, structural integration characteristics such as hinge moments, effective actuator stiffness, and airframe/control surface damping can have a significant effect on stability predictions. Actuator responses are customarily represented with low-order transfer functions matched to actuator test data, and control surface stiffness is often modeled as a linear spring. The inclusion of the physical properties of actuation and its installation on the airframe is therefore addressed in this paper using detailed actuator models which consider the physical, electrical, and mechanical elements of actuation. The aeroservoelastic analysis procedure is described in which the actuators are modeled as detailed high-order transfer functions and as approximate low-order transfer functions. The impacts of unsteady aerodynamic modeling on aeroservoelastic stability are also investigated in this paper by varying the order of approximation, or number of aerodynamic lag states, in the analysis. Test data from a thrust-vectoring configuration of an F/A-18 aircraft are compared to predictions to determine the effects on accuracy as a function of modeling complexity.
Actuator and aerodynamic modeling for high-angle-of-attack aeroservoelasticity
NASA Technical Reports Server (NTRS)
Brenner, Martin J.
1993-01-01
Accurate prediction of airframe/actuation coupling is required by the imposing demands of modern flight control systems. In particular, for agility enhancement at high angle of attack and low dynamic pressure, structural integration characteristics such as hinge moments, effective actuator stiffness, and airframe/control surface damping can have a significant effect on stability predictions. Actuator responses are customarily represented with low-order transfer functions matched to actuator test data, and control surface stiffness is often modeled as a linear spring. The inclusion of the physical properties of actuation and its installation on the airframe is therefore addressed using detailed actuator models which consider the physical, electrical, and mechanical elements of actuation. The aeroservoelastic analysis procedure is described in which the actuators are modeled as detailed high-order transfer functions and as approximate low-order transfer functions. The impacts of unsteady aerodynamic modeling on aeroservoelastic stability are also investigated by varying the order of approximation, or number of aerodynamic lag states, in the analysis. Test data from a thrust-vectoring configuration of an F/A-l8 aircraft are compared to predictions to determine the effects on accuracy as a function of modeling complexity.
Actuator-valve interface optimization. [Explosive actuators
Burchett, O.L.; Jones, R.L.
1987-02-01
The interface of explosive actuator driven valves can be optimized to maximize the velocity of the valve plunger by using the computer code Actuator-Valve Response. Details of the AVR model of the actuator driven valve plunger and the results of optimizing an actuator-valve interface with AVR are presented. 5 refs., 5 figs., 3 tabs.
A model for neutrino emission from nuclear accretion disks
NASA Astrophysics Data System (ADS)
Deaton, Michael
2015-04-01
Compact object mergers involving at least one neutron star can produce short-lived black hole accretion engines. Over tens to hundreds of milliseconds such an engine consumes a disk of hot, nuclear-density fluid, and drives changes to its surrounding environment through luminous emission of neutrinos. The neutrino emission may drive an ultrarelativistic jet, may peel off the disk's outer layers as a wind, may irradiate those winds or other forms of ejecta and thereby change their composition, may change the composition and thermodynamic state of the disk itself, and may oscillate in its flavor content. We present the full spatial-, angular-, and energy-dependence of the neutrino distribution function around a realistic model of a nuclear accretion disk, to inform future explorations of these types of behaviors. Spectral Einstein Code (SpEC).
Simulations of Accretion Disk Wind Models
NASA Astrophysics Data System (ADS)
Brooks, Craig L.; Yong, Suk Yee; O'Dowd, Matthew; Webster, Rachel L.; Bate, Nicholas
2016-01-01
The kinematics of the broad emission line region (BELR) in quasars is largely unknown, however there is strong evidence that outflows may be a key component. For example, in approximately 15% of quasars we observe broad, blue-shifted absorption features which may be ubiquitous based on line-of-sight arguments. We use a new mathematical description of an outflowing disk-wind with an initial rotational component to predict surface brightness distributions of this wind at different orientations. These surface brightness distributions will allow us to simulate gravitational microlensing of BELR light, with a view to mapping the structure and better understanding the kinematics of these flows.
Modeling and inverse feedforward control for conducting polymer actuators with hysteresis
NASA Astrophysics Data System (ADS)
Wang, Xiangjiang; Alici, Gursel; Tan, Xiaobo
2014-02-01
Conducting polymer actuators are biocompatible with a small footprint, and operate in air or liquid media under low actuation voltages. This makes them excellent actuators for macro- and micro-manipulation devices, however, their positioning ability or accuracy is adversely affected by their hysteresis non-linearity under open-loop control strategies. In this paper, we establish a hysteresis model for conducting polymer actuators, based on a rate-independent hysteresis model known as the Duhem model. The hysteresis model is experimentally identified and integrated with the linear dynamics of the actuator. This combined model is inverted to control the displacement of the tri-layer actuators considered in this study, without using any external feedback. The inversion requires an inverse hysteresis model which was experimentally identified using an inverse neural network model. Experimental results show that the position tracking errors are reduced by more than 50% when the hysteresis inverse model is incorporated into an inversion-based feedforward controller, indicating the potential of the proposed method in enabling wider use of such smart actuators.
Hydrogel core flexible matrix composite (H-FMC) actuators: theory and preliminary modelling
NASA Astrophysics Data System (ADS)
Dicker, M. P. M.; Weaver, P. M.; Rossiter, J. M.; Bond, I. P.
2014-09-01
The underlying theory of a new actuator concept based on hydrogel core flexible matrix composites (H-FMC) is presented. The key principle that underlines the H-FMC actuator operation is that the three-dimensional swelling of a hydrogel is partially constrained in order to improve the amount of useful work done. The partial constraint is applied to the hydrogel by a flexible matrix composite (FMC) that minimizes the hydrogel's volume expansion while swelling. This constraint serves to maximize the fixed charge density and resulting osmotic pressure, the driving force behind actuation. In addition, for certain FMC fibre orientations the Poisson's ratio of the anisotropic FMC laminate converts previously unused hydrogel swelling in the radial and circumferential directions into useful axial strains. The potential benefit of the H-FMC concept to hydrogel actuator performance is shown through comparison of force-stroke curves and evaluation of improvements in useful actuation work. The model used to achieve this couples chemical and electrical components, represented with the Nernst-Plank and Poisson equations, as well as a linear elastic mechanical material model, encompassing limited geometric nonlinearities. It is found that improvements in useful actuation work in the order of 1500% over bare hydrogel performance are achieved by the H-FMC concept. A parametric study is also undertaken to determine the effect of various FMC design parameters on actuator free strain and blocking stress. A comparison to other actuator concepts is also included.
Modeling posture-dependent leg actuation in sagittal plane locomotion.
Schmitt, J; Clark, J
2009-12-01
The spring loaded inverted pendulum template has been shown to accurately model the steady locomotion dynamics of a variety of running animals, and has served as the inspiration for an entire class of dynamic running robots. While the template models the leg dynamics by an energy-conserving spring, insects and animals have structures that dissipate, store and produce energy during a stance phase. Recent investigations into the spring-like properties of limbs, as well as animal response to drop-step perturbations, suggest that animals use their legs to manage energy storage and dissipation, and that this management is important for gait stability. In this paper, we extend our previous analysis of control of the spring loaded inverted pendulum template via changes in the leg touch-down angle to include energy variations during the stance phase. Energy variations are incorporated through leg actuation that varies the force-free leg length during the stance phase, yet maintains qualitatively correct force and velocity profiles. In contrast to the partially asymptotically stable gaits identified in previous analyses, incorporating energy and leg angle variations in this manner produces complete asymptotic stability. Drop-step perturbation simulations reveal that the control strategy is rather robust, with gaits recovering from drops of up to 30% of the nominal hip height. PMID:19946148
Optical actuation of silicon cantilevers: modelling and experimental investigation
NASA Astrophysics Data System (ADS)
Jiang, Fei; Keating, Adrian; Martyuink, Mariusz; Silva, Dilusha; Faraone, Lorenzo; Dell, John M.
2013-05-01
This paper reports on the modeling and experimental investigation of optical excitation of silicon cantilevers. In this work, the silicon cantilevers fabricated have dimensions with width of 15 μm, thickness of 0.26 μm, and variable length from 50 to 120 μm. In order to investigate the effect of the laser modulation frequency and position on the temperature at the anchor edge and displacements at the tip of cantilevers, a transient thermal ANSYS simulation and a steady-state static thermal mechanical ANSYS simulation were undertaken using a structure consisting of silicon device layer, SiO2 sacrificial layer and silicon substrate. The dynamic properties of silicon cantilevers were undertaken by a series of experiments. The period optical driving signal with controlled modulation amplitude was provided by a 405 nm diode laser with a 2.9 μW/μm2 laser power and variable frequencies. The laser spot was located through the longitude direction of silicon cantilevers. In factor, simulation results well matched with experimental observation, including: 1) for untreated silicon cantilevers, the maximum of displacement is observed when the laser beam was located half a diameter way from the anchor on the silicon suspended cantilever side; 2) for the both cantilevers, maximum displacement occurs when the optical actuation frequency is equal to the resonant frequency of cantilevers. Understanding the optical excitation on silicon cantilevers, as waveguides, can potentially increase sensing detection sensitivity (ratio of transmission to cantilever deflection).
Displacement Models for THUNDER Actuators having General Loads and Boundary Conditions
NASA Technical Reports Server (NTRS)
Wieman, Robert; Smith, Ralph C.; Kackley, Tyson; Ounaies, Zoubeida; Bernd, Jeff; Bushnell, Dennis M. (Technical Monitor)
2001-01-01
This paper summarizes techniques for quantifying the displacements generated in THUNDER actuators in response to applied voltages for a variety of boundary conditions and exogenous loads. The PDE (partial differential equations) models for the actuators are constructed in two steps. In the first, previously developed theory quantifying thermal and electrostatic strains is employed to model the actuator shapes which result from the manufacturing process and subsequent repoling. Newtonian principles are then employed to develop PDE models which quantify displacements in the actuator due to voltage inputs to the piezoceramic patch. For this analysis, drive levels are assumed to be moderate so that linear piezoelectric relations can be employed. Finite element methods for discretizing the models are developed and the performance of the discretized models are illustrated through comparison with experimental data.
Crystalline structure of accretion disks: Features of a global model
NASA Astrophysics Data System (ADS)
Montani, Giovanni; Benini, Riccardo
2011-08-01
In this paper, we develop the analysis of a two-dimensional magnetohydrodynamical configuration for an axially symmetric and rotating plasma (embedded in a dipolelike magnetic field), modeling the structure of a thin accretion disk around a compact astrophysical object. Our study investigates the global profile of the disk plasma, in order to fix the conditions for the existence of a crystalline morphology and ring sequence, as outlined by the local analysis pursued in Coppi [Phys. PlasmasPHPAEN1070-664X10.1063/1.1883667 12, 7302 (2005)] and Coppi and Rousseau [Astrophys. J.AJLEEY0004-637X10.1086/500315 641, 458 (2006)]. In the linear regime, when the electromagnetic back-reaction of the plasma is small enough, we show the existence of an oscillating radial behavior for the flux surface function, which very closely resembles the one outlined in the local model, apart from a radial modulation of the amplitude. In the opposite limit, corresponding to a dominant back-reaction in the magnetic structure over the field of central object, we can recognize the existence of a ringlike decomposition of the disk, according to the same modulation of the magnetic flux surface, and a smoother radial decay of the disk density, with respect to the linear case. In this extreme nonlinear regime, the global model seems to predict a configuration very close to that of the local analysis, but here the thermostatic pressure, crucial for the equilibrium setting, is also radially modulated. Among the conditions requested for the validity of such a global model, the confinement of the radial coordinate within a given value sensitive to the disk temperature and to the mass of the central objet, stands; however, this condition corresponds to dealing with a thin disk configuration.
Semi-empirical modeling of hysteresis compensation in magnetostrictive actuator
NASA Astrophysics Data System (ADS)
Ji, Ki-Hyun; Park, Hae-Jung; Park, Young-Woo; Wereley, Norman M.
2013-04-01
Hysteresis causes a delayed response to a given input in a magnetostrictive actuator (MA). It becomes critical when the MA has to be controlled in precise and real-time mode. An efficient way to compensate hysteresis must be considered. The Jiles-Atherton and Preisach models have been applied mostly in the literature, but these models need complex mathematics that makes them difficult to be applied in precise and real-time mode. Thus, this paper presents a semi-empirical model to compensate hysteresis in the MA. The idea comes from the similarity of the shapes between the hysteresis-compensated input voltage to the MA, and the output voltage of R-C circuit. The respective hysteresis-compensated input voltage and R-C circuit are expressed as polynomial and exponential equations, resulting in two closed-form equations about capacitance. One set of capacitance values for each frequency is selected by simulating the derived equations. Experiments are performed to choose one capacitance value among a set of capacitance values from simulation, based on trial-and-error. The concept of the hysteresis loss is introduced and defined as the ratio of areas between the hysteretic and reference curves. It is observed that the percent change of hysteresis loss increases as the frequency increases up to 400 Hz, but decreases with further increase of the frequency up to 800 Hz. It can be concluded that the proposed approach is effective to compensate hysteresis in the MA, and that hysteresis loss definition introduced by us can be used as a helpful measure of hysteresis compensation.
Computational modeling and parametric study of a rotary actuator driven by piezoelectric composites
NASA Astrophysics Data System (ADS)
Li, Hing L.; Lee, ShiWei R.
1998-07-01
An innovative actuation principle was introduced in a previous study to drive a rotary actuator by piezoelectric composite laminate. The driving element is a three layer laminated beam with piezoceramics sandwiched between two antisymmetric composite laminae. By taking advantage of the structural coupling, a rotary actuator similar to ultrasonic motors can be implemented. A prototype of the mentioned actuator has been fabricated. The objective of this study is to model this device by finite element method. A commercial finite element code, ANSYS, was employed to simulate the rotary actuator. The piezoelectric laminate and the rotor were modeled by solid brick elements and special constraint element was used to account for the contact between two separate bodies. Static and transient dynamic analyses were conducted to simulate the deformation and the angular motion of the rotary actuator, respectively. Parametric study was performed by modal and harmonic analyses to investigate the dynamic response of the driving laminate. The results of this study confirmed the proposed actuation principle and the developed computational model may be used for the optimization of future design.
NASA Astrophysics Data System (ADS)
Stuebner, Michael; Smith, Ralph C.
2010-04-01
Macro Fiber Composite (MFC) actuators utilize PZT fibers embedded in an epoxy matrix for structural actuation. Due to their construction, they are lightweight and provide broadband inputs. Significant advantages of MFC actuators are their high performance, durability, and flexibility when compared to traditional piezoceramic actuators. They are presently being considered for a range of applications including positioning of membrane mirrors and structural control in the aerospace and automotive industry. However, they exhibit varying degrees of hysteresis and constitutive nonlinearities throughout their operating range that must be incorporated in models to achieve the full capabilities of the materials. In this paper, hysteresis is modeled using the homogenized energy model. The inverse model is then used to construct an inverse compensator framework suitable for subsequent control design. The performance of the inverse compensator is illustrated through a numerical example.
APPLICATION OF THE DISK EVAPORATION MODEL TO ACTIVE GALACTIC NUCLEI
Liu, B. F.
2009-12-10
The disk corona evaporation model extensively developed for the interpretation of observational features of black hole X-ray binaries (BHXRBs) is applied to active galactic nuclei (AGNs). Since the evaporation of gas in the disk can lead to its truncation for accretion rates less than a maximal evaporation rate, the model can naturally account for the soft spectrum in high-luminosity AGNs and the hard spectrum in low-luminosity AGNs. The existence of two different luminosity levels describing transitions from the soft to hard state and from the hard to soft state in BHXRBs, when applied to AGNs, suggests that AGNs can be in either spectral state within a range of luminosities. For example, at a viscosity parameter, alpha, equal to 0.3, the Eddington ratio from the hard-to-soft transition and from the soft-to-hard transition occurs at 0.027 and 0.005, respectively. The differing Eddington ratios result from the importance of Compton cooling in the latter transition, in which the cooling associated with soft photons emitted by the optically thick inner disk in the soft spectral state inhibits evaporation. When the Eddington ratio of the AGN lies below the critical value corresponding to its evolutionary state, the disk is truncated. With decreasing Eddington ratios, the inner edge of the disk increases to greater distances from the black hole with a concomitant increase in the inner radius of the broad-line region, R {sub BLR}. The absence of an optically thick inner disk at low luminosities (L) gives rise to region in the R {sub BLR}-L plane for which the relation R {sub BLR} propor to L {sup 1/2} inferred at high luminosities is excluded. As a result, a lower limit to the accretion rate is predicted for the observability of broad emission lines, if the broad-line region is associated with an optically thick accretion disk. Thus, true Seyfert 2 galaxies may exist at very low accretion rates/luminosities. The differences between BHXRBs and AGNs in the framework of
The effect of plasma actuator on the depreciation of the aerodynamic drag on box model
NASA Astrophysics Data System (ADS)
Harinaldi, Budiarso, Julian, James; Rabbani M., N.
2016-06-01
Recent active control research advances have provided many benefits some of which in the field of transportation by land, sea as well as by air. Flow engineering by using active control has proven advantages in energy saving significantly. One of the active control equipment that is being developed, especially in the 21st century, is a plasma actuator, with the ability to modify the flow of fluid by the approach of ion particles makes these actuators a very powerful and promising tool. This actuator can be said to be better to the previously active control such as suction, blowing and synthetic jets because it is easier to control, more flexible because it has no moving parts, easy to be manufactured and installed, and consumes a small amount of energy with maximum capability. Plasma actuator itself is the composition of a material composed of copper and a dielectric sheet, where the copper sheets act as an electricity conductor and the dielectric sheet as electricity insulator. Products from the plasma actuators are ion wind which is the result of the suction of free air around the actuator to the plasma zone. This study investigates the ability of plasma actuators in lowering aerodynamic drag which is commonly formed in the models of vehicles by varying the shape of geometry models and the flow speed.
Modeling and control of a hydraulically actuated flexible-prismatic link robot
Love, L.; Kress, R.; Jansen, J.
1996-12-01
Most of the research related to flexible link manipulators to date has focused on single link, fixed length, single plane of vibration test beds. In addition, actuation has been predominantly based upon electromagnetic motors. Ironically, these elements are rarely found in the existing industrial long reach systems. This manuscript describes a new hydraulically actuated, long reach manipulator with a flexible prismatic link at Oak Ridge National Laboratory (ORNL). Focus is directed towards both modeling and control of hydraulic actuators as well as flexible links that have variable natural frequencies.
NASA Technical Reports Server (NTRS)
Duyar, A.; Guo, T.-H.; Merrill, W.; Musgrave, J.
1991-01-01
In a previous study, Guo, Merrill and Duyar, 1990, reported a conceptual development of a fault detection and diagnosis system for actuation faults of the Space Shuttle main engine. This study, which is a continuation of the previous work, implements the developed fault detection and diagnosis scheme for the real time actuation fault diagnosis of the Space Shuttle Main Engine. The scheme will be used as an integral part of an intelligent control system demonstration experiment at NASA Lewis. The diagnosis system utilizes a model based method with real time identification and hypothesis testing for actuation, sensor, and performance degradation faults.
Orthotropic deflection model for corner-supported plates with segmented in-plane actuators.
Sumali, Hartono; Washington, Gregory N.; Massad, Jordan Elias
2005-02-01
The shape control of thin, flexible structures has been studied primarily for edge-supported thin plates. For applications involving reconfigurable apertures such as membrane optics and active RF surfaces, corner-supported configurations may prove more applicable. Corner-supported adaptive structures allow for parabolic geometries, greater flexibility, and larger achievable deflections when compared to edge-supported geometries under similar actuation conditions. Preliminary models have been developed for corner-supported thin plates actuated by isotropic piezoelectric actuators. However, typical piezoelectric materials are known to be orthotropic. This paper extends a previously-developed isotropic model for a corner-supported, thin, rectangular bimorph to a more general orthotropic model for a bimorph actuated by a two-dimensional array of segmented PVDF laminates. First, a model determining the deflected shape of an orthotropic laminate for a given distribution of voltages over the actuator array is derived. Second, symmetric actuation of a bimorph consisting of orthotropic material is simulated using orthogonally-oriented laminae. Finally, the results of the model are shown to agree well with layered-shell finite element simulations for simple and complex voltage distributions.
Planet formation in transition disks: Modeling, spectroscopy, and theory
NASA Astrophysics Data System (ADS)
Liskowsky, Joseph Paul
due to either a massive planet accreting the material onto it or via a photoevaporation process whereby the central star's radiation field ejects material from the inner disk out of the bound system in the the interstellar medium. It is presumed that this phase is the last gasp of the planetary disk's evolution before the debris disk stage and before a fully formed solar system evolves. Our work specifically focuses on one object of this transition disk class: HD100546. We add to the understanding of transition disks by showing that a model where ro-vibrational OH emission in the NIR is preferentially emitted along the 'wall' of the disk is consistent with observations, and furthermore that adding an eccentricity to this `wall' component is required to generate the necessary observed line shape. In conjunction with this observation we present supporting material which motivates the usage of such an eccentric wall component in light of predictions of the influence of giant planet formation occurring within the disk.
Effects of source vs. interactive actuator assumptions on modelling of a smart structure
NASA Technical Reports Server (NTRS)
Robertshaw, Harry H.; Wynn, Robert H., Jr.; Kimiavi, Babak
1990-01-01
Embedded or internal actuators in a structure are being utilized to perform vibration attenuation, pointing maneuvers, damage control, and other adaptive tasks. The controls-structures-interaction (CSI) design process depends strongly on the coupled dynamic response of the structure and the actuators. A bond graph approach is used to guide this analytical study to uncover the effects of certain generic actuator types on the closed-loop, initial condition control of a single-mode structural model and an eighteen-state model of an active truss. So-called 'flow' and 'effort' source actuator types were studied and were shown to have significant differences in closed-loop response for ranges of initial conditions and system open-loop natural frequencies.
Structure of relativistic accretion disk with non-standard model
NASA Astrophysics Data System (ADS)
Khesali, A. R.; Salahshoor, K.
2016-07-01
The structure of stationary, axisymmetric advection-dominated accretion disk (ADAF) around rotating black hole, using non-standard model, was examined. In this model, the transport efficiency of the angular momentum α was dependent on the magnetic Prandtl number α ∝ Pm^{δ } . The full relativistic shear stress recently obtained by a new manner, was used. By considering black hole spin and Prandtl number instantaneously, the structure of ADAFs was changed in inner and outer region of the disk. It was discovered that the accretion flow was denser and hotter in the inner region, due to the black hole spin, and in the outer region, due to the presence of Prandtl parameter. Inasmuch as the rotation of the black hole affected the transport efficiency of angular momentum in parts of the disk very close to the even horizon, then in these regions, the viscosity depended on the rotation of black hole. Also, it was discovered that the effect of the black hole spin on the structure of the disk was related to the presence of Prandtl parameter.
Modeling Disk Cracks in Rotors by Utilizing Speed Dependent Eccentricity
NASA Astrophysics Data System (ADS)
Gyekenyesi, Andrew L.; Sawicki, Jerzy T.; Haase, Wayne C.
2010-03-01
This paper discusses the feasibility of vibration-based structural health monitoring for detecting disk cracks in rotor systems. The approach of interest assumes that a crack located on a rotating disk causes a minute change in the system’s center of mass due to the centrifugal force induced opening of the crack. The center of mass shift is expected to reveal itself in the vibration vector (i.e., whirl response; plotted as amplitude and phase versus speed) gathered during a spin-up and/or spin-down test. Here, analysis is accomplished by modeling a Jeffcott rotor that is characterized by analytical, numerical, and experimental data. The model, which has speed dependent eccentricity, is employed in order to better understand the sensitivity of the approach. For the experimental set-up emulated here (i.e., a single disk located mid-span on a flexible shaft), it appears that a rather sizable flaw in the form of a through-thickness notch could be detected by monitoring the damage-induced shift in center of mass. Although, identifying actual disk cracks in complex “real world” environments, where noncritical crack lengths are small and excessive mechanical and/or electrical noise are present, would prove to be rather challenging. Further research is needed in this regard.
An Analytic Model for Buoyancy Resonances in Protoplanetary Disks
NASA Astrophysics Data System (ADS)
Lubow, Stephen H.; Zhu, Zhaohuan
2014-04-01
Zhu et al. found in three-dimensional shearing box simulations a new form of planet-disk interaction that they attributed to a vertical buoyancy resonance in the disk. We describe an analytic linear model for this interaction. We adopt a simplified model involving azimuthal forcing that produces the resonance and permits an analytic description of its structure. We derive an analytic expression for the buoyancy torque and show that the vertical torque distribution agrees well with the results of the Athena simulations and a Fourier method for linear numerical calculations carried out with the same forcing. The buoyancy resonance differs from the classic Lindblad and corotation resonances in that the resonance lies along tilted planes. Its width depends on damping effects and is independent of the gas sound speed. The resonance does not excite propagating waves. At a given large azimuthal wavenumber ky > h -1 (for disk thickness h), the buoyancy resonance exerts a torque over a region that lies radially closer to the corotation radius than the Lindblad resonance. Because the torque is localized to the region of excitation, it is potentially subject to the effects of nonlinear saturation. In addition, the torque can be reduced by the effects of radiative heat transfer between the resonant region and its surroundings. For each azimuthal wavenumber, the resonance establishes a large scale density wave pattern in a plane within the disk.
Constraining Collisional Models of Planetesimals in Debris Disks
NASA Astrophysics Data System (ADS)
MacGregor, Meredith A.; Wilner, David J.; Hughes, A. Meredith; Steele, Amy; Ricci, Luca; Andrews, Sean M.; Chandler, Claire J.; Tahli Maddison, Sarah
2016-01-01
Debris disks around main-sequence stars are produced by the ongoing collisional erosion of planetesimals, analogous to Kuiper Belt Objects (KBOs) or comets in our own Solar System. Observations of these dusty belts offer a window into the physical and dynamical properties of planetesimals in extrasolar systems through the size distribution of dust grains. In particular, the millimeter/radio spectral index of thermal dust emission encodes information on the grain size distribution that can be used to test proposed collisional models of planetesimals. We have made sensitive Jansky Very Large Array (JVLA) observations of a sample of 7 nearby debris disks at 9 mm and combine these with archival Australia Telescope Compact Array (ATCA) observations of 8 additional debris disks at 7 mm. Using measurements at (sub)millimeter wavelengths from the literature, we place tight constraints on the millimeter spectral indices and thus grain size distributions of this sample of debris disks. Our analysis gives a weighted mean for the slope of the power-law grain distribution that is close to the classical prediction for a steady-state collisional cascade (q=3.5), but not consistent with the steeper distributions predicted by recent models that include more complex fragmentation processes. To interpret this result, we explore the effects of material strengths, velocity distributions, and small-size cutoffs on the steady-state grain size distribution.
An analytic model for buoyancy resonances in protoplanetary disks
Lubow, Stephen H.; Zhu, Zhaohuan E-mail: zhzhu@astro.princeton.edu
2014-04-10
Zhu et al. found in three-dimensional shearing box simulations a new form of planet-disk interaction that they attributed to a vertical buoyancy resonance in the disk. We describe an analytic linear model for this interaction. We adopt a simplified model involving azimuthal forcing that produces the resonance and permits an analytic description of its structure. We derive an analytic expression for the buoyancy torque and show that the vertical torque distribution agrees well with the results of the Athena simulations and a Fourier method for linear numerical calculations carried out with the same forcing. The buoyancy resonance differs from the classic Lindblad and corotation resonances in that the resonance lies along tilted planes. Its width depends on damping effects and is independent of the gas sound speed. The resonance does not excite propagating waves. At a given large azimuthal wavenumber k{sub y} > h {sup –1} (for disk thickness h), the buoyancy resonance exerts a torque over a region that lies radially closer to the corotation radius than the Lindblad resonance. Because the torque is localized to the region of excitation, it is potentially subject to the effects of nonlinear saturation. In addition, the torque can be reduced by the effects of radiative heat transfer between the resonant region and its surroundings. For each azimuthal wavenumber, the resonance establishes a large scale density wave pattern in a plane within the disk.
Design Optimization Tool for Synthetic Jet Actuators Using Lumped Element Modeling
NASA Technical Reports Server (NTRS)
Gallas, Quentin; Sheplak, Mark; Cattafesta, Louis N., III; Gorton, Susan A. (Technical Monitor)
2005-01-01
The performance specifications of any actuator are quantified in terms of an exhaustive list of parameters such as bandwidth, output control authority, etc. Flow-control applications benefit from a known actuator frequency response function that relates the input voltage to the output property of interest (e.g., maximum velocity, volumetric flow rate, momentum flux, etc.). Clearly, the required performance metrics are application specific, and methods are needed to achieve the optimal design of these devices. Design and optimization studies have been conducted for piezoelectric cantilever-type flow control actuators, but the modeling issues are simpler compared to synthetic jets. Here, lumped element modeling (LEM) is combined with equivalent circuit representations to estimate the nonlinear dynamic response of a synthetic jet as a function of device dimensions, material properties, and external flow conditions. These models provide reasonable agreement between predicted and measured frequency response functions and thus are suitable for use as design tools. In this work, we have developed a Matlab-based design optimization tool for piezoelectric synthetic jet actuators based on the lumped element models mentioned above. Significant improvements were achieved by optimizing the piezoceramic diaphragm dimensions. Synthetic-jet actuators were fabricated and benchtop tested to fully document their behavior and validate a companion optimization effort. It is hoped that the tool developed from this investigation will assist in the design and deployment of these actuators.
NASA Astrophysics Data System (ADS)
Aljanaideh, Omar; Habineza, Didace; Rakotondrabe, Micky; Al Janaideh, Mohammad
2016-04-01
An experimental study has been carried out to characterize rate-dependent hysteresis of a piezoelectric tube actuator at different excitation frequencies. The experimental measurements were followed by modeling and compensation of the hysteresis nonlinearities of the piezoelectric tube actuator using both the inverse rate-dependent Prandtl-Ishlinskii model (RDPI) and inverse rate-independent Prandtl-Ishlinskii model (RIPI) coupled with a controller. The comparison of hysteresis modeling and compensation of the actuator with both models is presented.
Research on Hysteresis of Piezoceramic Actuator Based on the Duhem Model
Wang, Jingyuan
2013-01-01
To improve the modeling accuracy of piezoceramic actuator in the precision positioning system, the Duhem hysteretic model of the piezoceramic actuator was proposed. The paper used the polynomial function to approach the piecewise continuous function and f(v) and g(v) in the Duhem model, adopted recursive least squares algorithm and gradient correction algorithm to identify parameter α, polynomial coefficients of f and g in the Duhem model, and established the nonlinear parametric model of the piezoceramic actuator. Contrasting the simulation results of recursive least squares algorithm and gradient correction algorithm, the modeling accuracy is 0.24% when adopting the recursive least squares algorithm, and the modeling accuracy is 0.11% when adopting the gradient correction method. The result showed that the gradient correction algorithm could meet the modeling accuracy better, and the structure of the algorithm is simple, adaptable, and easy to implement. PMID:23861658
Osmotic actuation modelling for innovative biorobotic solutions inspired by the plant kingdom.
Sinibaldi, E; Puleo, G L; Mattioli, F; Mattoli, V; Di Michele, F; Beccai, L; Tramacere, F; Mancuso, S; Mazzolai, B
2013-06-01
Osmotic-driven plant movements are widely recognized as impressive examples of energy efficiency and low power consumption. These aspects motivate the interest in developing an original biomimetic concept of new actuators based on the osmotic principle exploited by plants. This study takes a preliminary step in this direction, by modelling the dynamic behaviour of two exemplificative yet relevant implementations of an osmotic actuator concept. In more detail, the considered implementations differ from each other in the way actuation energy storage is achieved (through a piston displacement in the former case, through membrane bulging in the latter). The dynamic problem is analytically solved for both cases; scaling laws for the actuation figures of merit (namely characteristic time, maximum force, maximum power, power density, cumulated work and energy density) as a function of model parameters are obtained for the bulging implementation. Starting from such performance indicators, a preliminary dimensioning of the envisaged osmotic actuator is exemplified, based on design targets/constraints (such as characteristic time and/or maximum force). Moreover, model assumptions and limitations are discussed towards effective prototypical development and experimental testing. Nonetheless, this study takes the first step towards the design of new actuators based on the natural osmotic principle, which holds potential for disruptive innovation in many fields, including biorobotics and ICT solutions. PMID:23648821
Microstructure Modeling of Third Generation Disk Alloys
NASA Technical Reports Server (NTRS)
Jou, Herng-Jeng
2010-01-01
The objective of this program was to model, validate, and predict the precipitation microstructure evolution, using PrecipiCalc (QuesTek Innovations LLC) software, for 3rd generation Ni-based gas turbine disc superalloys during processing and service, with a set of logical and consistent experiments and characterizations. Furthermore, within this program, the originally research-oriented microstructure simulation tool was to be further improved and implemented to be a useful and user-friendly engineering tool. In this report, the key accomplishments achieved during the third year (2009) of the program are summarized. The activities of this year included: Further development of multistep precipitation simulation framework for gamma prime microstructure evolution during heat treatment; Calibration and validation of gamma prime microstructure modeling with supersolvus heat treated LSHR; Modeling of the microstructure evolution of the minor phases, particularly carbides, during isothermal aging, representing the long term microstructure stability during thermal exposure; and the implementation of software tools. During the research and development efforts to extend the precipitation microstructure modeling and prediction capability in this 3-year program, we identified a hurdle, related to slow gamma prime coarsening rate, with no satisfactory scientific explanation currently available. It is desirable to raise this issue to the Ni-based superalloys research community, with hope that in future there will be a mechanistic understanding and physics-based treatment to overcome the hurdle. In the mean time, an empirical correction factor was developed in this modeling effort to capture the experimental observations.
A Reduced-Order Model for Efficient Simulation of Synthetic Jet Actuators
NASA Technical Reports Server (NTRS)
Yamaleev, Nail K.; Carpenter, Mark H.
2003-01-01
A new reduced-order model of multidimensional synthetic jet actuators that combines the accuracy and conservation properties of full numerical simulation methods with the efficiency of simplified zero-order models is proposed. The multidimensional actuator is simulated by solving the time-dependent compressible quasi-1-D Euler equations, while the diaphragm is modeled as a moving boundary. The governing equations are approximated with a fourth-order finite difference scheme on a moving mesh such that one of the mesh boundaries coincides with the diaphragm. The reduced-order model of the actuator has several advantages. In contrast to the 3-D models, this approach provides conservation of mass, momentum, and energy. Furthermore, the new method is computationally much more efficient than the multidimensional Navier-Stokes simulation of the actuator cavity flow, while providing practically the same accuracy in the exterior flowfield. The most distinctive feature of the present model is its ability to predict the resonance characteristics of synthetic jet actuators; this is not practical when using the 3-D models because of the computational cost involved. Numerical results demonstrating the accuracy of the new reduced-order model and its limitations are presented.
Radiation Hydrodynamical Models of the Inner Rim in Protoplanetary Disks
NASA Astrophysics Data System (ADS)
Flock, Mario
2016-06-01
Many stars host planets orbiting within one astronomical unit (AU). These close planets’ origins are a mystery that motivates investigating protoplanetary disks’ central regions. A key factor governing the conditions near the star is the silicate sublimation front, which largely determines where the starlight is absorbed, and which is often called the inner rim. We present the first radiation hydrodynamical modeling of the sublimation front in the disks around the young intermediate-mass stars called Herbig Ae stars. The models are axisymmetric, and include starlight heating, silicate grains sublimating and condensing to equilibrium at the local, timedependent temperature and density, and accretion stresses parametrizing the results of MHD magneto-rotational turbulence models. The results compare well with radiation hydrostatic solutions, and prove to be dynamically stable. Passing the model disks into Monte Carlo radiative transfer calculations, we show that the models satisfy observational constraints on the inner rims’s location. A small optically-thin halo of hot dust naturally arises between the inner rim and the star. The inner rim has a substantial radial extent, corresponding to several disk scale heights. While the front’s overall position varies with the stellar luminosity, its radial extent depends on the mass accretion rate. A pressure maximum develops at the position of thermal ionization at temperatures about 1000 K. The pressure maximum is capable of halting solid pebbles’ radial drift and concentrating them in a zone where temperatures are su ciently high for annealing to form crystalline silicates.
Finite element modeling of electromechanical behavior of a dielectric electroactive polymer actuator
NASA Astrophysics Data System (ADS)
Deodhar, Aseem; York, Alexander; Hodgins, Micah; Seelecke, Stefan
2011-04-01
Dielectric Electroactive Polymers (DEAP) will undergo large deformations when subject to an electric field making them an attractive material for use in novel actuator systems. There are many challenges with successful application and design of DEAP actuators resulting from their inherent electromechanical coupling and non-linear material behavior. FE modeling of the material behavior is a useful tool to better understand such systems and aid in the optimal design of prototypes. These modeling efforts must account for the electromechanical coupling in order to accurately predict their response to multiple loading conditions expected during real operating conditions. This paper presents a Finite Element model of a dielectric elastomer undergoing out-of-plane, axisymmetric deformation. The response of the elastomer was investigated while it was subjected to mechanical and electric fields and combined electro-mechanical actuation. The compliant electrodes have a large effect on the mechanical behavior of the EAP which needs to be taken into consideration while modeling the EAP as a system. The model is adapted to include the effect of electrode stiffness on the mechanical response of the actuator. The model was developed using the commercial Finite Element Modeling software, COMSOL. The results from the mechanical simulations are presented in the form of forcedisplacement curves and are validated with comparisons to experimental results. Electromechanical simulations are carried out and the stroke of the actuator for different electrode stiffness values is compared with experimental values when the EAP is biased with a constant force.
Constraints on Planetesimal Collision Models in Debris Disks
NASA Astrophysics Data System (ADS)
MacGregor, Meredith A.; Wilner, David J.; Chandler, Claire; Ricci, Luca; Maddison, Sarah T.; Cranmer, Steven R.; Andrews, Sean M.; Hughes, A. Meredith; Steele, Amy
2016-06-01
Observations of debris disks offer a window into the physical and dynamical properties of planetesimals in extrasolar systems through the size distribution of dust grains. In particular, the millimeter spectral index of thermal dust emission encodes information on the grain size distribution. We have made new VLA observations of a sample of seven nearby debris disks at 9 mm, with 3\\prime\\prime resolution and ∼5 μJy beam‑1rms. We combine these with archival ATCA observations of eight additional debris disks observed at 7 mm, together with up-to-date observations of all disks at (sub)millimeter wavelengths from the literature, to place tight constraints on the millimeter spectral indices and thus grain size distributions. The analysis gives a weighted mean for the slope of the power-law grain size distribution, n(a)\\propto {a}-q, of < q> =3.36+/- 0.02, with a possible trend of decreasing q for later spectral type stars. We compare our results to a range of theoretical models of collisional cascades, from the standard self-similar, steady-state size distribution (q = 3.5) to solutions that incorporate more realistic physics such as alternative velocity distributions and material strengths, the possibility of a cutoff at small dust sizes from radiation pressure, and results from detailed dynamical calculations of specific disks. Such effects can lead to size distributions consistent with the data, and plausibly the observed scatter in spectral indices. For the AU Mic system, the VLA observations show clear evidence of a highly variable stellar emission component; this stellar activity obviates the need to invoke the presence of an asteroid belt to explain the previously reported compact millimeter source in this system.
Tests and Techniques for Characterizing and Modeling X-43A Electromechanical Actuators
NASA Technical Reports Server (NTRS)
Lin, Yohan; Baumann, Ethan; Bose, David M.; Beck, Roger; Jenney, Gavin
2008-01-01
A series of tests were conducted on the electromechanical actuators of the X-43A research vehicle in preparation for the Mach 7 and 10 hypersonic flights. The tests were required to help validate the actuator models in the simulation and acquire a better understanding of the installed system characteristics. Static and dynamic threshold, multichannel crosstalk, command-to-surface timing, free play, voltage regeneration, calibration, frequency response, compliance, hysteretic damping, and aircraft-in-the-loop tests were performed as part of this effort. This report describes the objectives, configurations, and methods for those tests, as well as the techniques used for developing second-order actuator models from the test results. When the first flight attempt failed because of actuator problems with the launch vehicle, further analysis and model enhancements were performed as part of the return-to-flight activities. High-fidelity models are described, along with the modifications that were required to match measurements taken from the research vehicle. Problems involving the implementation of these models into the X-43A simulation are also discussed. This report emphasizes lessons learned from the actuator testing, simulation modeling, and integration efforts for the X-43A hypersonic research vehicle.
NASA Astrophysics Data System (ADS)
Han, Chulhee; Kim, Wan Ho; Choi, Seung-Bok
2016-04-01
This paper proposes a new type of a direct-drive valve (DDV) suspension system for vehicle controlled by the piezostack actuator associated with displacement amplifier. In order to achieve this goal, a new type of controllable piezostack DDV damper is designed and its performance evaluation of damping force is undertaken. Next, a full vehicle suspension system consisting of sprung mass, spring, tire and the piezostack DDV damper is constructed. After deriving the governing equations of the motion for the proposed the piezostack DDV suspension system, the skyhook controller is implemented for the realization of the full vehicle. Analytical model of the whole suspension system is then derived and performance characteristics are analyzed through numerical simulation. Finally, vibration control responses of the vehicle suspension system such as vertical acceleration are evaluated under both bump and sine road conditions.
Microstructure Modeling of 3rd Generation Disk Alloy
NASA Technical Reports Server (NTRS)
Jou, Herng-Jeng
2008-01-01
The objective of this initiative, funded by NASA's Aviation Safety Program, is to model, validate, and predict, with high fidelity, the microstructural evolution of third-generation high-refractory Ni-based disc superalloys during heat treating and service conditions. This initiative is a natural extension of the DARPA-AIM (Accelerated Insertion of Materials) initiative with GE/Pratt-Whitney and with other process simulation tools. Strong collaboration with the NASA Glenn Research Center (GRC) is a key component of this initiative and the focus of this program is on industrially relevant disk alloys and heat treatment processes identified by GRC. Employing QuesTek s Computational Materials Dynamics technology and PrecipiCalc precipitation simulator, physics-based models are being used to achieve high predictive accuracy and precision. Combining these models with experimental data and probabilistic analysis, "virtual alloy design" can be performed. The predicted microstructures can be optimized to promote desirable features and concurrently eliminate nondesirable phases that can limit the reliability and durability of the alloys. The well-calibrated and well-integrated software tools that are being applied under the proposed program will help gas turbine disk alloy manufacturers, processing facilities, and NASA, to efficiently and effectively improve the performance of current and future disk materials.
One-dimensional analytical model development of a plasma-based actuator
NASA Astrophysics Data System (ADS)
Popkin, Sarah Haack
This dissertation provides a method for modeling the complex, multi-physics, multi-dimensional processes associated with a plasma-based flow control actuator, also known as the SparkJet, by using a one-dimensional analytical model derived from the Euler and thermodynamic equations, under varying assumptions. This model is compared to CFD simulations and experimental data to verify and/or modify the model where simplifying assumptions poorly represent the real actuator. The model was exercised to explore high-frequency actuation and methods of improving actuator performance. Using peak jet momentum as a performance metric, the model shows that a typical SparkJet design (1 mm orifice diameter, 84.8 mm3 cavity volume, and 0.5 J energy input) operated over a range of frequencies from 1 Hz to 10 kHz shows a decrease in peak momentum corresponding to an actuation cutoff frequency of 800 Hz. The model results show that the cutoff frequency is primarily a function of orifice diameter and cavity volume. To further verify model accuracy, experimental testing was performed involving time-dependent, cavity pressure and arc power measurements as a function of orifice diameter, cavity volume, input energy, and electrode gap. The cavity pressure measurements showed that pressure-based efficiency ranges from 20% to 40%. The arc power measurements exposed the deficiency in assuming instantaneous energy deposition and a calorically perfect gas and also showed that arc efficiency was approximately 80%. Additional comparisons between the pressure-based modeling and experimental results show that the model captures the actuator dependence on orifice diameter, cavity volume, and input energy but over-estimates the duration of the jet flow during Stage 2. The likely cause of the disagreement is an inaccurate representation of thermal heat transfer related to convective heat transfer or heat loss to the electrodes.
Asymmetric mass models of disk galaxies. I. Messier 99
NASA Astrophysics Data System (ADS)
Chemin, Laurent; Huré, Jean-Marc; Soubiran, Caroline; Zibetti, Stefano; Charlot, Stéphane; Kawata, Daisuke
2016-04-01
Mass models of galactic disks traditionally rely on axisymmetric density and rotation curves, paradoxically acting as if their most remarkable asymmetric features, such as lopsidedness or spiral arms, were not important. In this article, we relax the axisymmetry approximation and introduce a methodology that derives 3D gravitational potentials of disk-like objects and robustly estimates the impacts of asymmetries on circular velocities in the disk midplane. Mass distribution models can then be directly fitted to asymmetric line-of-sight velocity fields. Applied to the grand-design spiral M 99, the new strategy shows that circular velocities are highly nonuniform, particularly in the inner disk of the galaxy, as a natural response to the perturbed gravitational potential of luminous matter. A cuspy inner density profile of dark matter is found in M 99, in the usual case where luminous and dark matter share the same center. The impact of the velocity nonuniformity is to make the inner profile less steep, although the density remains cuspy. On another hand, a model where the halo is core dominated and shifted by 2.2-2.5 kpc from the luminous mass center is more appropriate to explain most of the kinematical lopsidedness evidenced in the velocity field of M 99. However, the gravitational potential of luminous baryons is not asymmetric enough to explain the kinematical lopsidedness of the innermost regions, irrespective of the density shape of dark matter. This discrepancy points out the necessity of an additional dynamical process in these regions: possibly a lopsided distribution of dark matter.
Validated model of arc-filament plasma actuators for control of wall-bounded flows
NASA Astrophysics Data System (ADS)
Bodony, Daniel; Natarajan, Mahesh
2011-11-01
Plasma actuators based on the electrical arcs between two electrodes have shown promise in controlling high-subsonic and low-supersonic flows. Simulation-based predictions of these flows have often used heuristic models for the effect the plasma has on the flow to be controlled. In this talk we present a two-parameter model of the actuator which combines the unsteady Joule heating induced by the plasma with a thermally perfect model of air. PIV and spectroscopy data are used, in conjunction with simulations, to understand the two parameters and demonstrate how their values are to be determined. The importance of the cavity in which the electrodes are mounted is discussed, as is the role of diffusion. We demonstrate the use of the actuator model by controlling a high-subsonic, separating boundary layer in an S-duct geometry. Supported by the Rolls-Royce Corporation.
Piezoelectric actuator models for active sound and vibration control of cylinders
NASA Technical Reports Server (NTRS)
Lester, Harold C.; Lefebvre, Sylvie
1993-01-01
Analytical models for piezoelectric actuators, adapted from flat plate concepts, are developed for noise and vibration control applications associated with vibrating circular cylinders. The loadings applied to the cylinder by the piezoelectric actuators for the bending and in-plane force models are approximated by line moment and line force distributions, respectively, acting on the perimeter of the actuator patch area. Coupling between the cylinder and interior acoustic cavity is examined by studying the modal spectra, particularly for the low-order cylinder modes that couple efficiently with the cavity at low frequencies. Within the scope of this study, the in-plane force model produced a more favorable distribution of low-order modes, necessary for efficient interior noise control, than did the bending model.
One-dimensional disk model simulation for klystron design
Yonezawa, H.; Okazaki, Y.
1984-05-01
In 1982, one of the authors (Okazaki), of Toshiba Corporation, wrote a one-dimensional, rigid-disk model computer program <1> to serve as a reliable design tool for the 150 MW klystron development project. This is an introductory note for the users of this program. While reviewing the so-called disk programs presently available, hypotheses such as gridded interaction gaps, a linear relation between phase and position, and so on, were found. These hypotheses bring serious limitations and uncertainties into the computational results. JPNDISK was developed to eliminate these defects, to follow the equations of motion as rigorously as possible, and to obtain self-consistent solutions for the gap voltages and the electron motion. Although some inaccuracy may be present in the relativistic region, JPNDISK, in its present form, seems a most suitable tool for klystron design; it is both easy and inexpensive to use.
Modeling and optimization of IPMC actuator for autonomous jellyfish vehicle (AJV)
NASA Astrophysics Data System (ADS)
Joshi, Keyur B.; Akle, Barbar J.; Leo, Donald J.; Priya, Shashank
2011-04-01
Ionomeric Polymer Metal Composite (IPMC) actuators generate high flexural strains at small voltage amplitudes of 2-5V. IPMCs bend toward the anode when a potential drop is applied across its thickness. The actuation mechanism is due to the motion of ions inside it; which requires a form of hydration to dissociate and mobilize the charges. In our group IPMCs are developed either water based or Ionic Liquid based which is also known as the dry IPMCs. This combination of small voltage requirement with operation in both dry and underwater conditions makes the IPMCs a viable alternative for an Autonomous Jellyfish Vehicle (AJV). In this study, we estimate the mechanical properties of IPMC actuator having curved geometry using FEM model to match the experimental deformation. We combine the results from an electric model to estimate charge accumulated on electrode surface with piezoelectric model to estimate stress due to this charge accumulation. In the last step, the results are integrated with a structural model to simulate the actuator deformation. We have designed an AJV with embedded IPMC actuators using these properties to achieve the curvature of relaxed and contracted Jellyfish (Aurelia Aurita). Bio-mimetic deformation profile was achieved by using structural mechanics of beams with large deformation with only application of +/- 0.8V to optimized beam within 8.1% error norm in relaxed state and 21.3% in contracted state, with only -0.24% to 0.26% maximum flexural strain at maximum curvature point in contracted state.
Drag-o-llision Models of Extrasolar Planets in Debris Disks
NASA Technical Reports Server (NTRS)
Kuchner, Marc
2009-01-01
An extrasolar planet sculpts the famous debris disk around Fomalhaut; probably many other debris disks contain planets that we could locate if only we could better recognize their signatures in the dust that surrounds them. But the interaction between planets and debris disks involves both orbital resonances and collisions among grains and rocks in the disks---difficult processes to model simultaneously. The author describes new 3-D models of debris disk dynamics, Drag-o-llision models, that incorporate both collisions and resonant trapping of dust for the first time. The author also discusses the implications of these models for coronagraphic imaging with Gemini and other telescopes.
Development of a dc Motor Model and an Actuator Efficiency Model
Watkins, John Clifford; Mc Kellar, Michael George; DeWall, Kevin George
2001-07-01
For the past several years, researchers at the Idaho National Engineering and Environmental Laboratory, under the sponsorship of the U.S. Nuclear Regulatory Commission, have been investigating the ability of motor-operated valves (MOVs) used in Nuclear Power Plants to close or open when subjected to design basis flow and pressure loads. Part of this research addresses the response of a dcpowered motor-operated gate valve to assess whether it will achieve flow isolation and to evaluate whether it will slow down excessively under design-basis conditions and thus fail to achieve the required stroke time. As part of this research, we have developed a model of a dc motor operating under load and a model of actuator efficiency under load based on a first principle evaluation of the equipment. These models include the effect that reduced voltage at the Motor Control Center and elevated containment temperatures have on the performance of a dc powered MOV. The model also accounts for motor torque and speed changes that result from the heatup of the motor during the stroke. These models are part of the Motor- Operated Valve In Site Test Assessment (MISTA) software which is capable of independently evaluating the ability of dc-powered motoroperated gate valves to achieve flow isolation and to meet required stroke times under design-basis conditions. This paper presents an overview of the dc motor model and the actuator efficiency under load model. The paper then compares the analytical results from the models with the results of actual dc motor and actuator testing, including comparisons of the effect reduced voltage, elevated containment temperature, and motor heating during the stroke have on an MOV.
The Behavior of Accretion Disks in Low Mass X-ray Binaries: Disk Winds and Alpha Model
NASA Astrophysics Data System (ADS)
Bayless, Amanda J.
2010-01-01
This dissertation presents research on two low mass X-ray binaries. The eclipsing low-mass X-ray binary 4U 1822-371 is the prototypical accretion disk corona (ADC) system. We have obtained new time-resolved UV spectroscopy with the ACS/SBC on the Hubble Space Telescope and new V- and J-band photometry with the 1.3-m SMARTS telescope at CTIO. We show that the accretion disk in the system has a strong wind with projected velocities up to 4000 km/s as determined from the Doppler width of the C IV emission line. The broad and shallow eclipse indicates that the disk has a vertically-extended, optically-thick component at optical wavelengths. This component extends almost to the edge of the disk and has a height equal to 50% of the disk radius. As it has a low brightness temperature, we identify it as the optically-thick base of the disk wind. V1408 Aql (=4U 1957+115) is a low mass X-ray binary which continues to be a black hole candidate. We have new photometric data of this system from the Otto Struve 2.1-m telescope's high speed CCD photometer at McDonald Observatory. The light curve is largely sinusoidal which we model with two components: a constant light source from the disk and a sinusoidal modulation at the orbital period from the irradiated face of the companion star. This is a radical re-interpretation of the orbital light curve. We do not require a large or asymmetric disk rim to account for the modulation in the light curve. Thus, the orbital inclination is unconstrained in our new model, removing the foundation for any claims of the compact object being a black hole.
NASA Astrophysics Data System (ADS)
Kikuchi, Kunitomo; Sakamoto, Takumi; Tsuchitani, Shigeki; Asaka, Kinji
2011-04-01
Ionic polymer metal composites (IPMCs) that can operate in air have recently been developed by incorporating an ionic liquid in ionic polymers. To understand transduction in these composites, it is important to determine the role of the ionic liquid in the ionic polymer (Nafion®), to identify the counter cation, and to investigate the interaction of IPMCs with water vapor in the air. We used Fourier-transform infrared spectroscopy to analyze three Nafion® membranes, which were soaked in mixtures of water and an ionic liquid (1-ethyl-3-methyl-imidazolium tetrafluoroborate (EMIBF4), 1-buthyl-3-methyl-imidazolium tetrafluoroborate (BMIBF4), and 1-buthyl-3-methyl-imidazolium hexafluorophosphate (BMIPF6)). The results demonstrate that only cations (EMI+ and BMI+) in the ionic liquids are taken into the Nafion® membranes as counter ions and that the water content of the membranes in air is less than ˜4% that of Nafion® swollen with water. Based on the experimental results, a transduction model is proposed for an IPMC with an ionic liquid. In this model, bending is caused by local swelling due to the volume effect of the bulky counter cations. This model can explain 30-50% of the experimentally observed bending curvature.
NASA Astrophysics Data System (ADS)
Shen, Qi; Palmre, Viljar; Stalbaum, Tyler; Kim, Kwang J.
2015-09-01
The ionic polymer-metal composite (IPMC) is an emerging smart material in actuation and sensing applications, such as artificial muscles, underwater actuators, and advanced medical devices. However, the effect of the change in surface electrode properties on the actuating of IPMC has not been well studied. To address this problem, we theoretically predict and experimentally investigate the dynamic electro-mechanical response of the IPMC thin-strip actuator. A model of the IPMC actuator is proposed based on the Poisson-Nernst-Planck equations for ion transport and charge dynamics in the polymer membrane, while a physical model for the change of surface resistance of the electrodes of the IPMC due to deformation is also incorporated. By incorporating these two models, a complete, dynamic, physics-based model for IPMC actuators is presented. To verify the model, IPMC samples were prepared and experiments were conducted. The results show that the theoretical model can accurately predict the actuating performance of IPMC actuators over a range of dynamic conditions. Additionally, the charge dynamics inside the polymer during the oscillation of the IPMC is presented. It is also shown that the charge at the boundary mainly affects the induced stress of the IPMC. The current study is beneficial for the comprehensive understanding of the surface electrode effect on the performance of IPMC actuators.
Shape memory alloy micro-actuator performance prediction using a hybrid constitutive model
NASA Astrophysics Data System (ADS)
Wong, Franklin C.; Boissonneault, Olivier
2006-03-01
The volume and weight budgets in missiles and gun-launched munitions have decreased with the military forces' emphasis on soldier-centric systems and rapid deployability. Reduction in the size of control actuation systems employed in today's aerospace vehicles would enhance overall vehicle performance as long as there is no detrimental impact on flight performance. Functional materials such as shape memory alloys (SMA's) offer the opportunity to create compact, solid-state actuation systems for flight applications. A hybrid SMA model was developed for designing micro-actuated flow effectors. It was based on a combination of concepts originally presented by Likhatchev for microstructural modelling and Brinson for modelling of transformation kinetics. The phase diagram for a 0.1mm SMA wire was created by carrying out tensile tests in a Rheometrics RSA-II solids analyser over a range of temperatures from 30°C to 130°C. The characterization parameters were used in the hybrid model to predict the displacement-time trajectories for the wire. Experimental measurements were made for a SMA wire that was subjected to a constant 150g load and short, intense 4.5 to 10V pulses. Actuation frequency was limited by the cooling rate rather than the heating rate. A second set of experiments studied the performance of SMA wires in an antagonistic micro-actuator set-up. A series of 2 or 3V step inputs were alternately injected into each wire to characterize the peak to peak displacement and the motion time constant. A maximum frequency of 0.25Hz was observed. An antagonistic actuator model based on the hybrid SMA model predicted reasonably well the displacement-time results.
MODELING MAGNETOROTATIONAL TURBULENCE IN PROTOPLANETARY DISKS WITH DEAD ZONES
Okuzumi, Satoshi; Hirose, Shigenobu
2011-12-01
Turbulence driven by magnetorotational instability (MRI) crucially affects the evolution of solid bodies in protoplanetary disks. On the other hand, small dust particles stabilize MRI by capturing ionized gas particles needed for the coupling of the gas and magnetic fields. To provide an empirical basis for modeling the coevolution of dust and MRI, we perform three-dimensional, ohmic-resistive MHD simulations of a vertically stratified shearing box with an MRI-inactive 'dead zone' of various sizes and with a net vertical magnetic flux of various strengths. We find that the vertical structure of turbulence is well characterized by the vertical magnetic flux and three critical heights derived from the linear analysis of MRI in a stratified disk. In particular, the turbulent structure depends on the resistivity profile only through the critical heights and is insensitive to the details of the resistivity profile. We discover scaling relations between the amplitudes of various turbulent quantities (velocity dispersion, density fluctuation, vertical diffusion coefficient, and outflow mass flux) and vertically integrated accretion stresses. We also obtain empirical formulae for the integrated accretion stresses as a function of the vertical magnetic flux and the critical heights. These empirical relations allow us to predict the vertical turbulent structure of a protoplanetary disk for a given strength of the magnetic flux and a given resistivity profile.
Radiation Hydrodynamics Models of the Inner Rim in Protoplanetary Disks
NASA Astrophysics Data System (ADS)
Flock, M.; Fromang, S.; Turner, N. J.; Benisty, M.
2016-08-01
Many stars host planets orbiting within a few astronomical units (AU). The occurrence rate and distributions of masses and orbits vary greatly with the host star’s mass. These close planets’ origins are a mystery that motivates investigating protoplanetary disks’ central regions. A key factor governing the conditions near the star is the silicate sublimation front, which largely determines where the starlight is absorbed, and which is often called the inner rim. We present the first radiation hydrodynamical modeling of the sublimation front in the disks around the young intermediate-mass stars called Herbig Ae stars. The models are axisymmetric and include starlight heating silicate grains sublimating and condensing to equilibrium at the local, time-dependent temperature and density and accretion stresses parameterizing the results of MHD magnetorotational turbulence models. The results compare well with radiation hydrostatic solutions and prove to be dynamically stable. Passing the model disks into Monte Carlo radiative transfer calculations, we show that the models satisfy observational constraints on the inner rim’s location. A small optically thin halo of hot dust naturally arises between the inner rim and the star. The inner rim has a substantial radial extent, corresponding to several disk scale heights. While the front’s overall position varies with the stellar luminosity, its radial extent depends on the mass accretion rate. A pressure maximum develops near the location of thermal ionization at temperatures of about 1000 K. The pressure maximum is capable of halting solid pebbles’ radial drift and concentrating them in a zone where temperatures are sufficiently high for annealing to form crystalline silicates.
Continuum damage model for ferroelectric materials and its application to multilayer actuators
NASA Astrophysics Data System (ADS)
Gellmann, Roman; Ricoeur, Andreas
2016-05-01
In this paper a micromechanical continuum damage model for ferroelectric materials is presented. As a constitutive law it is implemented into a finite element (FE) code. The model is based on micromechanical considerations of domain switching and its interaction with microcrack growth and coalescence. A FE analysis of a multilayer actuator is performed, showing the initiation of damage zones at the electrode tips during the poling process. Further, the influence of mechanical pre-stressing on damage evolution and actuating properties is investigated. The results provided in this work give useful information on the damage of advanced piezoelectric devices and their optimization.
Modeling and analysis of bio-syncretic micro-swimmers for cardiomyocyte-based actuation.
Zhang, Chuang; Wang, Jingyi; Wang, Wenxue; Xi, Ning; Wang, Yuechao; Liu, Lianqing
2016-01-01
Along with sensation and intelligence, actuation is one of the most important factors in the development of conventional robots. Many novel achievements have been made regarding bio-based actuators to solve the challenges of conventional actuation. However, few studies have focused on methods for controlling the movement performance of bio-syncretic robots by designing robotic structures and programming actuation bio-entities. In this paper, a theoretical model was derived considering kinematics and hydromechanics to describe the dynamics of a dolphin-shaped microstructure and to control the bio-syncretic swimmer movement by establishing the relationships between the swimming velocity of the bio-swimmer, the cell seeding concentration and the cell contractility. The proposed theoretical model was then verified with the fabricated biomimetic swimmer prototype actuated by equivalent external magnetism replacing the bio-entity force based on the study of living, beating cardiomyocyte contractility. This work can improve the development of bio-syncretic robots with an approach to preplanning the seeding concentration of cells for controlling the movement velocity of microstructures, and is also meaningful for biomimetic robots, medical treatments and interventional therapy applications. PMID:27545346
Modeling and Simulation of Aerodynamic Single Dielectric Barrier Discharge Plasma Actuators
NASA Astrophysics Data System (ADS)
Orlov, Dmitri; Font, Gabriel
2008-11-01
This work presents different approaches to modeling of the plasma actuator, an electrical flow control device, which is now widely used in aerodynamics for separation control, lift enhancement, drag reduction and flight control without moving surfaces. Study of the physics of the discharge in air at atmospheric pressure was performed using particle (PIC-DSMC) and fluid plasma simulations. Based on the experimentally obtained data electro-static and lumped-element circuit models were developed for engineering purposes. Numerical flow simulations were performed to study the effect of the plasma body force on the neutral fluid. The results agreed well with the experiments. An application of the plasma actuators to the leading-edge separation control on the NACA 0021 airfoil was studied numerically. The results were obtained for a range of angles of attack. Improvement in the airfoil characteristics was observed in numerical simulations at high angles of attack in cases with plasma actuation.
NASA Astrophysics Data System (ADS)
Gu, Guo-Ying; Gupta, Ujjaval; Zhu, Jian; Zhu, Li-Min; Zhu, Xiang-Yang
2015-07-01
In the practical applications of actuators, the control of their deformation or driving force is a key issue. Most of recent studies on dielectric elastomer actuators (DEAs) focus on issues of mechanics, physics, and material science, whereas less importance is given to the control of these soft actuators. In this paper, we underline the importance of a nonlinear dynamic model as the basis for a feedforward deformation control approach of a rubber-based DEA. Experimental evidence shows the effectiveness of the feedforward controller. The present study confirms that a DEA's trajectory can be finely controlled with a solid nonlinear dynamic model despite the presence of material nonlinearities and electromechanical coupling. The effective control of DEAs may pave the way for extensive emerging applications to soft robots.
Modeling Planet-Building Stellar Disks with Radiative Transfer Code
NASA Astrophysics Data System (ADS)
Swearingen, Jeremy R.; Sitko, Michael L.; Whitney, Barbara; Grady, Carol A.; Wagner, Kevin Robert; Champney, Elizabeth H.; Johnson, Alexa N.; Warren, Chelsea C.; Russell, Ray W.; Hammel, Heidi B.; Lisse, Casey M.; Cure, Michel; Kraus, Stefan; Fukagawa, Misato; Calvet, Nuria; Espaillat, Catherine; Monnier, John D.; Millan-Gabet, Rafael; Wilner, David J.
2015-01-01
Understanding the nature of the many planetary systems found outside of our own solar system cannot be completed without knowledge of the beginnings these systems. By detecting planets in very young systems and modeling the disks of material around stars from which they form, we can gain a better understanding of planetary origin and evolution. The efforts presented here have been in modeling two pre-transitional disk systems using a radiative transfer code. With the first of these systems, V1247 Ori, a model that fits the spectral energy distribution (SED) well and whose parameters are consistent with existing interferometry data (Kraus et al 2013) has been achieved. The second of these two systems, SAO 206462, has presented a different set of challenges but encouraging SED agreement between the model and known data gives hope that the model can produce images that can be used in future interferometry work. This work was supported by NASA ADAP grant NNX09AC73G, and the IR&D program at The Aerospace Corporation.
Design and Modeling of a 3-D Magnetic Actuator for Magnetic Microbead Manipulation.
Zhang, Zhipeng; Menq, Chia-Hsiang
2011-06-01
This paper presents the design, implementation, modeling, and analyses of a hexapole magnetic actuator that is capable of 3-D manipulation of a magnetic microbead. The magnetic actuator employs six sharp-tipped magnetic poles placed in hexapole configuration, six actuating coils, and a magnetic yoke. The magnetic poles concentrate the magnetic flux generated by the coils to the workspace, resulting in a high magnetic field with a large field gradient for magnetic force generation on the magnetic microbead. A lumped-parameter magnetic force model is then established to characterize nonlinearity of the magnetic force exerting on the magnetic microbead with respect to the applied currents to the coils and the position dependence of the magnetic force in the workspace. The force generation capability of the designed system is then explored using the force model. Moreover, an inverse force model is derived and its effect on the magnetic actuation capability is investigated. The inverse force model facilitates the implementation of a feedback control law to stabilize and control the motion of a magnetic microbead. Experimental results in terms of the magnetic force in relation to stable motion control of a magnetic microbead are used to validate the force model. PMID:24382943
Parameterized reduced order modeling of misaligned stacked disks rotor assemblies
NASA Astrophysics Data System (ADS)
Ganine, Vladislav; Laxalde, Denis; Michalska, Hannah; Pierre, Christophe
2011-01-01
Light and flexible rotating parts of modern turbine engines operating at supercritical speeds necessitate application of more accurate but rather computationally expensive 3D FE modeling techniques. Stacked disks misalignment due to manufacturing variability in the geometry of individual components constitutes a particularly important aspect to be included in the analysis because of its impact on system dynamics. A new parametric model order reduction algorithm is presented to achieve this goal at affordable computational costs. It is shown that the disks misalignment leads to significant changes in nominal system properties that manifest themselves as additional blocks coupling neighboring spatial harmonics in Fourier space. Consequently, the misalignment effects can no longer be accurately modeled as equivalent forces applied to a nominal unperturbed system. The fact that the mode shapes become heavily distorted by extra harmonic content renders the nominal modal projection-based methods inaccurate and thus numerically ineffective in the context of repeated analysis of multiple misalignment realizations. The significant numerical bottleneck is removed by employing an orthogonal projection onto the subspace spanned by first few Fourier harmonic basis vectors. The projected highly sparse systems are shown to accurately approximate the specific misalignment effects, to be inexpensive to solve using direct sparse methods and easy to parameterize with a small set of measurable eccentricity and tilt angle parameters. Selected numerical examples on an industrial scale model are presented to illustrate the accuracy and efficiency of the algorithm implementation.
The Vertical Structure of Nuclear Starburst Disks: Testing a Model of AGN Obscuration
NASA Astrophysics Data System (ADS)
Ballantyne, David R.; Gohil, Raj
2016-04-01
Nuclear starburst disks are Eddington-limited, radiation pressure supported disks that may be active in the nuclear environment of active galaxies (ULIRGS and AGNs). Earlier analytical models suggested that, under certain conditions, these disks may be geometrically thick on pc-scales, and thus could be a viable source for AGN obscuration, partcularly at z≤1, when gas factions in galaxies are still significant. Here, we present early results from numerical 2D models of nuclear starburst disks where the vertical structure is calculated explicitly from solving the hydrostatic balance and radiative transfer equations. We quantitatively assess under which conditions the starburst disk may present substantial obscuring columns for AGN observations.
Modelling Cosmic-Ray Effects in the Protosolar Disk
NASA Technical Reports Server (NTRS)
Wilson, Thomas L.
2010-01-01
The role that Galactic cosmic rays (GCRs) and solar energetic particles (SEPs) play in the dynamic evolution of protosolar disks and the origin of our Solar System is a fundamental one. The GCRs are an important component of the interstellar medium (ISM), and even play a role in correcting the age determinations of some irons versus CAIs (calcium-aluminum inclusions) in meteoroids . Because CRs also are one of the energy transport mechanisms in a planetary nebula, the question of modelling their effect upon this broad subject is a serious topic for planetary science. The problem is addressed here.
Resonance-based low-frequency synthetic jet actuator modeling, design, and testing
NASA Astrophysics Data System (ADS)
Gravatt, Lynn; Flatau, Alison
2006-03-01
Synthetic Jet Actuators have been the topic of extensive study in the aerospace industry because of their ability to actively control flow over aerodynamic surfaces without discrete control surfaces such as a flap. One challenge has been to develop a low frequency, lightweight actuator that can provide large displacements. This study will discuss the modeling, design, manufacture, and testing of a bimorph piezo-composite actuator that will provide such displacements at low frequencies. The design employs two opposing benders that provide a piston-type motion. The initial goals of this study were to achieve 30 m/s out of the slot while maintaining the mechanical resonant frequency of the system at about 100 Hz.
Eversion of bistable shells under magnetic actuation: a model of nonlinear shapes
NASA Astrophysics Data System (ADS)
Seffen, Keith A.; Vidoli, Stefano
2016-06-01
We model in closed form a proven bistable shell made from a magnetic rubber composite material. In particular, we incorporate a non-axisymmetrical displacement field, and we capture the nonlinear coupling between the actuated shape and the magnetic flux distribution around the shell. We are able to verify the bistable nature of the shell and we explore its eversion during magnetic actuation. We show that axisymmetrical eversion is natural for a perfect shell but that non-axisymmetrical eversion rapidly emerges under very small initial imperfections, as observed in experiments and in a computational analysis. We confirm the non-uniform shapes of shell and we study the stability of eversion by considering how the landscape of total potential and magnetic energies of the system changes during actuation.
Disk-Corona Model of Active Galactic Nuclei with Nonthermal Pairs
NASA Technical Reports Server (NTRS)
Tsuruta, Sachiko; Kellen, Michael
1995-01-01
As a promising model for the X-ray emission from radio-quiet quasars and Seyfert 1 nuclei, we present a nonthermal disk-corona model, where soft photons from a disk are Comptonized by the nonthermal electron-positron pairs in a coronal region above the disk. Various characteristics of our model are qualitatively similar to the homogeneous, spherical, nonthermal pair models previously studied, but the important difference is that in our disk-corona model gamma-ray depletion is far more efficient, and, moreover, the gamma-ray annihilation line is much less prominent. Consequently, this model naturally satisfies the observed constraints on active galactic nuclei.
Burst-Disk Device Simulates Effect Of Pyrotechnic Device
NASA Technical Reports Server (NTRS)
Rogers, James P.; Sexton, James H.
1995-01-01
Expendable disks substituted for costly pyrotechnic devices for testing actuators. Burst-disk device produces rush of pressurized gas similar to pyrotechnic device. Designed to reduce cost of testing pyrotechnically driven emergency actuators (parachute-deploying mechanisms in original application).
NASA Technical Reports Server (NTRS)
Joshi, Suresh M.
2012-01-01
This paper explores a class of multiple-model-based fault detection and identification (FDI) methods for bias-type faults in actuators and sensors. These methods employ banks of Kalman-Bucy filters to detect the faults, determine the fault pattern, and estimate the fault values, wherein each Kalman-Bucy filter is tuned to a different failure pattern. Necessary and sufficient conditions are presented for identifiability of actuator faults, sensor faults, and simultaneous actuator and sensor faults. It is shown that FDI of simultaneous actuator and sensor faults is not possible using these methods when all sensors have biases.
Zhu, Guangzhi; Zhu, Xiao; Zhu, Changhong; Shang, Jianli
2012-09-10
This article presents the fundamental principles of operational performance of a continuous wave (cw) thin-disk laser with multiple disks in one resonator. Based on the model of an end-pumped Yb:YAG thin-disk laser with nonuniform temperature distribution, the effect of the multiple disks in one resonator is considered. The analytic expressions are derived to analyze the laser output intensity, laser intensity in the resonator, threshold intensity, and the optical efficiency of a thin-disk laser with multiple disks arranged in series. The dependence of output coupler reflectivity and the number of thin disks on various parameters are investigated, which are useful to determine the optimal output coupler reflectivity of the thin-disk lasers and control the laser intensity in the resonator. PMID:22968282
Design, modelling and control of a micro-positioning actuator based on magnetic shape memory alloys
NASA Astrophysics Data System (ADS)
Minorowicz, Bartosz; Leonetti, Giuseppe; Stefanski, Frederik; Binetti, Giulio; Naso, David
2016-07-01
This paper presents an actuator based on magnetic shape memory alloys (MSMAs) suitable for precise positioning in a wide range (up to 1 mm). The actuator is based on the spring returned operating mode and uses a Smalley wave spring to maintain the same operating parameters of a classical coil spring, while being characterized by a smaller dimension. The MSMA element inside the actuator provides a deformation when excited by an external magnetic field, but its behavior is characterized by an asymmetric and saturated hysteresis. Thus, two models are exploited in this work to represent such a non-linear behavior, i.e., the modified and generalized Prandtl–Ishlinskii models. These models are particularly suitable for control purposes due to the existence of their analytical inversion that can be easily exploited in real time control systems. To this aim, this paper investigates three closed-loop control strategies, namely a classical PID regulator, a PID regulator with direct hysteresis compensation, and a combined PID and feedforward compensation strategy. The effectiveness of both modelling and control strategies applied to the designed MSMA-based actuator is illustrated by means of experimental results.
A validated model for induction heating of shape memory alloy actuators
NASA Astrophysics Data System (ADS)
Saunders, Robert N.; Boyd, James G.; Hartl, Darren J.; Brown, Jonathan K.; Calkins, Frederick T.; Lagoudas, Dimitris C.
2016-04-01
Shape memory alloy (SMA) actuators deliver high forces while being compact and reliable, making them ideal for consideration in aerospace applications. One disadvantage of these thermally driven actuators is their slow cyclic time response compared to conventional actuators. Induction heating has recently been proposed to quickly heat SMA components. However efforts to date have been purely empirical. The present work approachs this problem in a computational manner by developing a finite element model of induction heating in which the time-harmonic electromagnetic equations are solved for the Joule heat power field, the energy equation is solved for the temperature field, and the linear momentum equations are solved to find the stress, displacement, and internal state variable fields. The combined model was implemented in Abaqus using a Python script approach and applied to SMA torque tube and beam actuators. The model has also been used to examine magnetic flux concentrators to improve the induction systems performance. Induction heating experiments were performed using the SMA torque tube, and the model agreed well with the experiments.
Subminiature hydraulic actuator
NASA Technical Reports Server (NTRS)
Sevart, F. D.
1978-01-01
Subminiature, single-vane rotary actuator for wind-tunnel test-model control-surface actuation systems presents severe torque and system band-pass requirements with stringent space and weight limitations. Actuator has very low leakage of fluid from one side to other, permitting use in precision position servo-systems.
Automated optic disk boundary detection by modified active contour model.
Xu, Juan; Chutatape, Opas; Chew, Paul
2007-03-01
This paper presents a novel deformable-model-based algorithm for fully automated detection of optic disk boundary in fundus images. The proposed method improves and extends the original snake (deforming-only technique) in two aspects: clustering and smoothing update. The contour points are first self-separated into edge-point group or uncertain-point group by clustering after each deformation, and these contour points are then updated by different criteria based on different groups. The updating process combines both the local and global information of the contour to achieve the balance of contour stability and accuracy. The modifications make the proposed algorithm more accurate and robust to blood vessel occlusions, noises, ill-defined edges and fuzzy contour shapes. The comparative results show that the proposed method can estimate the disk boundaries of 100 test images closer to the groundtruth, as measured by mean distance to closest point (MDCP) <3 pixels, with the better success rate when compared to those obtained by gradient vector flow snake (GVF-snake) and modified active shape models (ASM). PMID:17355059
Three-dimensional modelling of film flows over spinning disks
NASA Astrophysics Data System (ADS)
Zhao, Kun; Wray, Alex; Yang, Junfeng; Matar, Omar
2014-11-01
Film flows over spinning disks are of central importance to a wide array of industrial processes, such as the augmentation of heat and mass transfer in chemical reactors, or power production in metallurgy. As a result they have been extensively investigated experimentally. Theoretically they constitute an interesting problem due to the interplay of inertial, capillary, centrifugal and Coriolis forces. However, modelling efforts have typically been restricted to the consideration of the one-dimensional axisymmetric situation. We extend the existing models to incorporate azimuthal variations. The resultant system is solved via the use of an operator-splitting method. In addition, we have performed Direct Numerical Simulations of the system. We compare the low order model, the direct simulations and the results of experiments, to reveal a wide variety of different flow regimes in accordance with existing literature. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.
NASA Astrophysics Data System (ADS)
Yan, Su
2007-12-01
To improve the fuel consumption of a satellite, maintain the position and orientation and eliminate the unwanted thruster vibration, intelligent composite structure technology was proposed in the ADPICAS (Adaptive Damping and Positioning using Intelligent Composite Active Structures) project funded by the ONR (Office of Naval Research) in collaboration with the NRL (Naval Research Laboratory) in 2000. This dissertation introduces the author's research achievements in developing smart composite panels for the ADPICAS project, including modeling, actuator optimization, and vibration control. The method of separation of variables is presented to derive the analytical shape functions for complex composite structures with asymmetric constraints, i.e., the 2-D Adaptive Composite Circular Plate (ACCP) in cylindrical coordinates and the 3-D Adaptive Composite Satellite Dish (ACSD) in spherical coordinates. Following these solutions, two modeling approaches are developed to obtain the models of adaptive composite panels including an adaptive composite beam, the ACCP, and the ACSD. One model approach is to employ the Lagrange-Rayleigh-Ritz method based on the developed analytical shape functions. Meanwhile, the transfer function estimation technique, combining the finite element analyses, is applied to obtain the numerical model of the composite panels. Aiming at improving the actuation efficiency, a Genetic Algorithm is presented to optimize the piezoelectric actuator placement on the composite panels. Taking the inertia and stiffness characteristics of the piezoelectric actuators into account, this algorithm defines the performance index as a weighted summation of control error and control energy consumption, and obtained the optimal solution that minimizes the performance index. Furthermore, an adaptive disturbance observer/feed-forward (ADOB/FF) controller is proposed to achieve simultaneous precision positioning and vibration suppression of the adaptive composite panels
Lin, Jhih-Hong; Chiang, Mao-Hsiung
2016-01-01
Magnetic shape memory (MSM) alloys are a new class of smart materials with extraordinary strains up to 12% and frequencies in the range of 1 to 2 kHz. The MSM actuator is a potential device which can achieve high performance electromagnetic actuation by using the properties of MSM alloys. However, significant non-linear hysteresis behavior is a significant barrier to control the MSM actuator. In this paper, the Preisach model was used, by capturing experiments from different input signals and output responses, to model the hysteresis of MSM actuator, and the inverse Preisach model, as a feedforward control, provided compensational signals to the MSM actuator to linearize the hysteresis non-linearity. The control strategy for path tracking combined the hysteresis compensator and the modified fuzzy sliding mode control (MFSMC) which served as a path controller. Based on the experimental results, it was verified that a tracking error in the order of micrometers was achieved. PMID:27571081
NASA Astrophysics Data System (ADS)
Hodgins, M.; Rizzello, G.; Naso, D.; York, A.; Seelecke, S.
2014-10-01
Dielectric electro-active polymer (DEAP) technology holds promise for enabling lightweight, energy efficient, and scalable actuators. The circular DEAP actuator configuration (also known as cone or diaphragm actuator) in particular shows potential in applications such as pumps, valves, micro-positioners and loudspeakers. For a quantitative prediction of the actuator behavior as well as for design optimization tasks, material models which can reproduce the coupled electromechanical behavior inherent to these actuators are necessary. This paper presents a non-linear viscoelastic model based on an electro-mechanical Ogden free energy expression for the DEAP. The DEAP model is coupled with a spring/mass system to study the dynamic performance of such a representative system from static behavior to 50 Hz. The system is identified and validated by several different experiments.
Pseudo-Rigid-Body Model and Kinematic Analysis of MRI-Actuated Catheters
Greigarn, Tipakorn; Çavuşoğlu, M. Cenk
2015-01-01
This paper presents a kinematic study of a pseudorigid-body model (PRBM) of MRI-compatible, magnetically actuated, steerable catheters. It includes a derivation of a mathematical model of the PRBM of the catheter, singularity studies of the model, and a new manipulability measure. While the forward kinematics of the model presented here is applicable to PRBMs for other applications, actuation method is unique to the particular design. Hence, a careful study of singularities and manipulability of the model is required. The singularities are studied from the underlying equations of motion with intuitive interpretations. The proposed manipulability measure is a generalization of the inverse condition number manipulability measure of robotic manipulators. While the PRBM is an approximation of the flexible catheter, kinematic studies of the PRBM still provide some insight into feasibility and limitations of the catheter, which is beneficial to the design and motion planning of the catheter. PMID:26413380
NASA Astrophysics Data System (ADS)
Rosenblatt, F.; Morrison, J. F.; Iannucci, L.
2008-03-01
Controlling turbulence is a major aim for many engineering disciplines. Decades of research, have shown that the large frictional drag in turbulent flows is attributed to the existence of near-wall coherent structures. Turbulence control is therefore likely to be achieved by manipulating these coherent structures. The challenge this presents is to find actuators that are functional at the spatial scales of those coherent structures (10 μm to 0.1 mm) and their temporal scale (100 kHz). Recent advances in MEMS technology have made possible the construction of such actuators. Electroactive polymers (EAP) provide excellent performance, are lightweight, flexible, and inexpensive. Therefore EAPs, and in particular dielectric elastomers (DEAs), provide many potential applications as micro-actuators. The modelling and simulating of EAP actuators are a cost-effective way of providing a better understanding of the material itself in order to optimise designs. A technique to accurately model DEA materials, taking into account its non-linearities as well as its large deformations, is being developed in this study.
Nonlinear dynamic modeling for smart material electro-hydraulic actuator development
NASA Astrophysics Data System (ADS)
Larson, John P.; Dapino, Marcelo J.
2013-03-01
Smart material electro-hydraulic actuators use hydraulic rectification by one-way check valves to amplify the motion of smart materials, such as magnetostrictives and piezoelectrics, in order to create compact, lightweight actuators. A piston pump driven by a smart material is combined with a hydraulic cylinder to form a self-contained, power-by-wire actuator that can be used in place of a conventional hydraulic system without the need for hydraulic lines and a centralized pump. The performance of an experimental actuator driven by a 12.7 mm diameter, 114 mm length Terfenol-D rod is evaluated over a range of applied input frequencies, loads, and currents. The peak performance achieved is 37 W, moving a 220 N load at a rate of 17 cm/s and producing a blocked pressure of 12.5 MPa. Additional tests are conducted to quantify the dynamic behavior of the one-way reed valves using a scanning laser vibrometer to identify the frequency response of the reeds and the effect of the valve seat and fluid mass loading. A lumped-parameter model is developed for the system that includes valve inertia and fluid response nonlinearities, and the model results are compared with the experimental data.
NASA Astrophysics Data System (ADS)
Hunt, A.; Chen, Z.; Tan, X.; Kruusmaa, M.
2016-03-01
Ionic electroactive polymers (IEAPs), particularly ionic polymer-metal composites (IPMCs) and carbon-polymer composites (CPCs), bend when a voltage is applied on their electrodes, and conversely, they generate an electrical signal when subjected to a mechanical bending. In this work we study and compare the capabilities of IPMC and CPC actuators and sensors in closed-loop control applications. We propose and realize an integrated IEAP sensor-actuator design, characterize its performance using three different materials, and compare the results. The design consists of two short IEAP actuators and one sensor mechanically coupled together in a parallel configuration, and an attached rigid extension significantly longer than the IEAPs. This allows the device to be compliant, simple to construct, lightweight, easy to miniaturize, and functionally similar to a one-degree-of-freedom rotational joint. For control design and accurate position sensing in feedback experiments, we adapt physics-based and control-oriented models of actuation and sensing dynamics, and perform experiments to identify their parameters. In performance characterization, both model-based {H}∞ control and proportional-integral control are explored. System responses to step inputs, sinusoids, and random references are measured, and long-duration sinusoidal tracking experiments are performed. The results show that, while IEAP position sensing is stable for only a limited time-span, H ∞ control significantly improves the performance of the device.
Tilted Accretion Disk Models of Sgr A* Flares
NASA Astrophysics Data System (ADS)
Dexter, Jason; Fragile, P. C.
2013-01-01
Sagittarius A* (Sgr A*), the Galactic center massive black hole candidate, is an unparalleled laboratory for low-luminosity accretion theory. First discovered as a compact radio source, Sgr A* has since been observed to undergo rapid, large amplitude NIR/X-ray flares. The many proposed phenomenological models cannot simultaneously explain both the flaring emission and the peak of the SED in the submillimeter. I will describe flares seen in numerical simulations of black hole accretion flows where the disk angular momentum is misaligned from that of the black hole. Eccentric fluid orbits driven by gravitational torques converge and form strong shocks, which can lead to significant particle heating. The resulting NIR emission can reproduce the observations, and is completely unrelated to the submillimeter emission, which is included in these models and is also in excellent agreement with observations. I will describe the prospects for testing accretion theory and constraining the properties of Sgr A* with exciting ongoing multi-wavelength observations.
Numerical modeling of the interstellar medium in galactic disks
NASA Technical Reports Server (NTRS)
Rosen, A.; Bregman, J. N.; Norman, Michael L.
1993-01-01
We have been developing detailed hydrodynamic models of the global interstellar medium in the hope of understanding the mass and volume occupied by various phases, as well as their structure and kinematics. In our model, the gas is modeled by one fluid while representative Pop 1 stars are modeled by a second fluid. The two fluids are coupled in that the gas forms into stars at a rate given by a Schmidt law while stellar mass loss returns matter into the gas phase (on a time scale of 100 Myr). Also, the stars heat the gas through stellar winds and the gas cools through optically thin radiation. The time behavior of these two fluids is studied in two spatial dimensions with the Eulerian finite difference numerical hydrodynamic code Zen. The two spatial dimensions are along the plane of a disk (x, total length of 2 kpc) and perpendicular to the disk (z, total height of +/- 15 kpc) and a galactic gravitational field in the z direction, typical of that at the solar circle, is imposed upon the simulation; self-gravity and rotation are absent. For the boundary conditions, outflow is permitted at the top and bottom of the grid (z = +/- 15 kpc) while periodic boundary conditions are imposed upon left and right sides of the grid. As initial conditions, we assumed a gaseous distribution like that seen for the H1 by earlier researchers, although the results are insensitive to the initial conditions. We have run simulations in which the heating due to stars, parameterized as a stellar wind velocity, a, is varied from low (a = 150 km/s), to intermediate (a = 300 km/s), to high (a = 600 km/s). Since the intermediate case is roughly equivalent to the Galactic energy injection rate from supernovae, this summary will concentrate on results from this simulation.
A finite element approach to model and analyze photostrictive optical actuators
NASA Astrophysics Data System (ADS)
Rahman, Mosfequr
Photostrictive materials, called PLZT, exhibit large photostriction under uniform illumination of high-energy light. These materials are of interest for future generation wireless remote control photo-actuators, micro-actuators, and micro-sensors applications. The photostrictive effect is a superposition phenomenon of bulk photovoltaic effect and converse piezoelectric effect. In this present research photostrictive thin films are analyzed to evaluate their use as actuators in a future MEMS gyroscope. The finite element method is used for accurate analysis of photostrictive thin films. Four-node isoparametric quadrilateral plane stress elements are used to model photostrictive thin film and eight-node nonconforming brick elements are used to model a silicon wafer under the photostrictive thin film. A numerical finite element code, BAMAFEM, has been modified by introducing photostrictive material modeling capability. For generation of program code the FORTRAN90 language is used. Established analytical solutions have been used to verify the BAMAFEM finite element results. Comparison of BAMAFEM results and MATLAB results of 2-D displacements indicate that BAMAFEM results almost match with the theoretical results. For the verification of the finite element formulation of the photostrictive element and the BAMAFEM program code, a steel simply supported beam with one PLZT actuator bonded on top of the beam is studied. The BAMAFEM result for transverse deflection matches the analytical result within a small difference (1.7%). Using the valid and verified modified BAMAFEM finite element program code, static analysis has been done to calculate transverse deflection for a silicon cantilever beam with a PLZT actuator bonded on the whole top surface of the beam. BAMAFEM output of transverse deflection matched the analytical result of the same with a percent error of 1%.
NASA Technical Reports Server (NTRS)
Yam, Yeung; Johnson, Timothy L.; Lang, Jeffrey H.
1987-01-01
A model reduction technique based on aggregation with respect to sensor and actuator influence functions rather than modes is presented for large systems of coupled second-order differential equations. Perturbation expressions which can predict the effects of spillover on both the reduced-order plant model and the neglected plant model are derived. For the special case of collocated actuators and sensors, these expressions lead to the derivation of constraints on the controller gains that are, given the validity of the perturbation technique, sufficient to guarantee the stability of the closed-loop system. A case study demonstrates the derivation of stabilizing controllers based on the present technique. The use of control and observation synthesis in modifying the dimension of the reduced-order plant model is also discussed. A numerical example is provided for illustration.
Non-linear time variant model intended for polypyrrole-based actuators
NASA Astrophysics Data System (ADS)
Farajollahi, Meisam; Madden, John D. W.; Sassani, Farrokh
2014-03-01
Polypyrrole-based actuators are of interest due to their biocompatibility, low operation voltage and relatively high strain and force. Modeling and simulation are very important to predict the behaviour of each actuator. To develop an accurate model, we need to know the electro-chemo-mechanical specifications of the Polypyrrole. In this paper, the non-linear time-variant model of Polypyrrole film is derived and proposed using a combination of an RC transmission line model and a state space representation. The model incorporates the potential dependent ionic conductivity. A function of ionic conductivity of Polypyrrole vs. local charge is proposed and implemented in the non-linear model. Matching of the measured and simulated electrical response suggests that ionic conductivity of Polypyrrole decreases significantly at negative potential vs. silver/silver chloride and leads to reduced current in the cyclic voltammetry (CV) tests. The next stage is to relate the distributed charging of the polymer to actuation via the strain to charge ratio. Further work is also needed to identify ionic and electronic conductivities as well as capacitance as a function of oxidation state so that a fully predictive model can be created.
NASA Astrophysics Data System (ADS)
Suzuki, Y.
2016-05-01
This article demonstrates the practical applicability of a method of modelling shape memory alloys (SMAs) as actuators. For this study, a pair of SMA wires was installed in an antagonistic manner to form an actuator, and a linear differential equation that describes the behaviour of the actuator’s generated force relative to its input voltage was derived for the limited range below the austenite onset temperature. In this range, hysteresis need not be considered, and the proposed SMA actuator can therefore be practically applied in linear control systems, which is significant because large deformations accompanied by hysteresis do not necessarily occur in most vibration control cases. When specific values of the parameters used in the differential equation were identified experimentally, it became clear that one of the parameters was dependent on ambient airflow velocity. The values of this dependent parameter were obtained using an additional SMA wire as a sensor. In these experiments, while the airflow distribution around the SMA wires was varied by changing the rotational speed of the fans in the wind tunnels, an input voltage was conveyed to the SMA actuator circuit, and the generated force was measured. In this way, the parameter dependent on airflow velocity was estimated in real time, and it was validated that the calculated force was consistent with the measured one.
Flow Separation Control on A Full-Scale Vertical Tail Model Using Sweeping Jet Actuators
NASA Technical Reports Server (NTRS)
Andino, Marlyn Y.; Lin, John C.; Washburn, Anthony E.; Whalen, Edward A.; Graff, Emilio C.; Wygnanski, Israel J.
2015-01-01
This paper describes test results of a joint NASA/Boeing research effort to advance Active Flow Control (AFC) technology to enhance aerodynamic efficiency. A full-scale Boeing 757 vertical tail model equipped with sweeping jets AFC was tested at the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel at NASA Ames Research Center. The flow separation control optimization was performed at 100 knots, a maximum rudder deflection of 30deg, and sideslip angles of 0deg and -7.5deg. Greater than 20% increments in side force were achieved at the two sideslip angles with a 31-actuator AFC configuration. Flow physics and flow separation control associated with the AFC are presented in detail. AFC caused significant increases in suction pressure on the actuator side and associated side force enhancement. The momentum coefficient (C sub mu) is shown to be a useful parameter to use for scaling-up sweeping jet AFC from sub-scale tests to full-scale applications. Reducing the number of actuators at a constant total C(sub mu) of approximately 0.5% and tripling the actuator spacing did not significantly affect the flow separation control effectiveness.
MODELING COLLISIONAL CASCADES IN DEBRIS DISKS: THE NUMERICAL METHOD
Gaspar, Andras; Psaltis, Dimitrios; Oezel, Feryal; Rieke, George H.; Cooney, Alan E-mail: dpsaltis@as.arizona.edu E-mail: grieke@as.arizona.edu
2012-04-10
We develop a new numerical algorithm to model collisional cascades in debris disks. Because of the large dynamical range in particle masses, we solve the integro-differential equations describing erosive and catastrophic collisions in a particle-in-a-box approach, while treating the orbital dynamics of the particles in an approximate fashion. We employ a new scheme for describing erosive (cratering) collisions that yields a continuous set of outcomes as a function of colliding masses. We demonstrate the stability and convergence characteristics of our algorithm and compare it with other treatments. We show that incorporating the effects of erosive collisions results in a decay of the particle distribution that is significantly faster than with purely catastrophic collisions.
Tests and consequences of disk plus halo models of gamma-ray burst sources
NASA Technical Reports Server (NTRS)
Smith, I. A.
1995-01-01
The gamma-ray burst observations made by the Burst and Transient Source Experiment (BATSE) and by previous experiments are still consistent with a combined Galactic disk (or Galactic spiral arm) plus extended Galactic halo model. Testable predictions and consequences of the disk plus halo model are discussed here; tests performed on the expanded BATSE database in the future will constrain the allowed model parameters and may eventually rule out the disk plus halo model. Using examples, it is shown that if the halo has an appropriate edge, BATSE will never detect an anisotropic signal from the halo of the Andromeda galaxy. A prediction of the disk plus halo model is that the fraction of the bursts observed to be in the 'disk' population rises as the detector sensitivity improves. A careful reexamination of the numbers of bursts in the two populations for the pre-BATSE databases could rule out this class of models. Similarly, it is predicted that different satellites will observe different relative numbers of bursts in the two classes for any model in which there are two different spatial distribiutions of the sources, or for models in which there is one spatial distribution of the sources that is sampled to different depths for the two classes. An important consequence of the disk plus halo model is that for the birthrate of the halo sources to be small compared to the birthrate of the disk sources, it is necessary for the halo sources to release many orders of magnitude more energy over their bursting lifetime than the disk sources. The halo bursts must also be much more luminous than the disk bursts; if this disk-halo model is correct, it is necessary to explain why the disk sources do not produce halo-type bursts.
NASA Technical Reports Server (NTRS)
Demerdash, N. A.; Nehl, T. W.
1979-01-01
A comprehensive digital model for the analysis of the dynamic-instantaneous performance of a power conditioner fed samarium-cobalt permanent magnet brushless DC motor is presented. The particular power conditioner-machine system at hand, for which this model was developed, is a component of an actual prototype electromechanical actuator built for NASA-JSC as a possible alternative to hydraulic actuators as part of feasibility studies for the shuttle orbiter applications. Excellent correlation between digital simulated and experimentally obtained performance data was achieved for this specific prototype. This is reported on in this paper. Details of one component of the model, its applications and the corresponding results are given in this paper.
A dynamic model for generating actuator specifications for small arms barrel active stabilization
NASA Astrophysics Data System (ADS)
Pathak, Anupam; Brei, Diann; Luntz, Jonathan; Lavigna, Chris
2006-03-01
Due to stresses encountered in combat, it is known that soldier marksmanship noticeably decreases regardless of prior training. Active stabilization systems in small arms have potential to address this problem to increase soldier survivability and mission effectiveness. The key to success is proper actuator design, but this is highly dependent on proper specification which is challenging due to the human/weapon interaction. This paper presents a generic analytical dynamic model which is capable of defining the necessary actuation specifications for a wide range of small arms platforms. The model is unique because it captures the human interface--shoulder and arm--that introduces the jitter disturbance in addition to the geometry, inertial properties and active stabilization stiffness of the small arms platform. Because no data to date is available for actual shooter-induced disturbance in field conditions, a method is given using the model to back-solve from measured shooting range variability data the disturbance amplitude information relative to the input source (arm or shoulder). As examples of the applicability of the model to various small arms systems, two different weapon systems were investigated: the M24 sniper weapon and the M16 assault rifle. In both cases, model based simulations provided valuable insight into impact on the actuation specifications (force, displacement, phase, frequency) due to the interplay of the human-weapon-active stabilization interface including the effect of shooter-disturbance frequency, disturbance location (shoulder vs. arm), and system parameters (stiffness, barrel rotation).
Dong, R.; Rafikov, R.; Zhu, Z.; Brandt, T.; Janson, M.; Hartmann, L.; Whitney, B.; Muto, T.; Hashimoto, J.; Kuzuhara, M.; Grady, C.; Follette, K.; Tanii, R.; Itoh, Y.; Thalmann, C.; Wisniewski, J.; Mayama, S.; Abe, L.; Brandner, W.; Carson, J.; and others
2012-05-10
Transitional circumstellar disks around young stellar objects have a distinctive infrared deficit around 10 {mu}m in their spectral energy distributions, recently measured by the Spitzer Infrared Spectrograph (IRS), suggesting dust depletion in the inner regions. These disks have been confirmed to have giant central cavities by imaging of the submillimeter continuum emission using the Submillimeter Array (SMA). However, the polarized near-infrared scattered light images for most objects in a systematic IRS/SMA cross sample, obtained by HiCIAO on the Subaru telescope, show no evidence for the cavity, in clear contrast with SMA and Spitzer observations. Radiative transfer modeling indicates that many of these scattered light images are consistent with a smooth spatial distribution for {mu}m-sized grains, with little discontinuity in the surface density of the {mu}m-sized grains at the cavity edge. Here we present a generic disk model that can simultaneously account for the general features in IRS, SMA, and Subaru observations. Particularly, the scattered light images for this model are computed, which agree with the general trend seen in Subaru data. Decoupling between the spatial distributions of the {mu}m-sized dust and mm-sized dust inside the cavity is suggested by the model, which, if confirmed, necessitates a mechanism, such as dust filtration, for differentiating the small and big dust in the cavity clearing process. Our model also suggests an inwardly increasing gas-to-dust ratio in the inner disk, and different spatial distributions for the small dust inside and outside the cavity, echoing the predictions in grain coagulation and growth models.
The Thermodynamic Model of a Moon Forming Disk Based on SPH Simulations
NASA Astrophysics Data System (ADS)
Nakajima, M.; Stevenson, D. J.
2011-12-01
According to the giant impact hypothesis, a Mars size body hits the proto-Earth in the late stage of Earth forming event (e.g. Benz et al., 1986, Thompson and Stevenson 1988). The impact generates a debris disk around the proto-Earth, from which the Moon is accreted. SPH simulations suggest that the silicate disk has high temperature (~ a few thousands K) and partially vaporized (~10-30% by mass) (Canup 2004). However, SPH does not determine the state of the resulting hydrostatic disk. To do this, we have taken the output of SPH, applied conservation of entropy, mass and angular momentum and corrected for the additional energy released upon quick relaxation to the hydrostatic Keplerian state. We find that the disk is remarkably uniform in entropy but is of lower entropy than the adjacent outer shell of Earth. Constant entropy implies a temperature variation, typically from 4500K (inner disk) to 2500K (outer disk) at the midplane. For grazing impact cases (impact angles: 40 - 60 degrees, impact velocity: escape velocity, mantle material: forsterite), 90% of the disk mass is within 10 Earth radius. The disk vapor mass fractions are about 10-20%, which are consistent with Canup (2004) results. This may be an underestimate because iron is more volatile than magnesium. Mass loss from this disk will be small. The effects of initial condition differences will be discussed in the presentation. This is the first attempt to create a bridge between SPH results and a thermodynamic disk model.
Component based modelling of piezoelectric ultrasonic actuators for machining applications
NASA Astrophysics Data System (ADS)
Saleem, A.; Salah, M.; Ahmed, N.; Silberschmidt, V. V.
2013-07-01
Ultrasonically Assisted Machining (UAM) is an emerging technology that has been utilized to improve the surface finishing in machining processes such as turning, milling, and drilling. In this context, piezoelectric ultrasonic transducers are being used to vibrate the cutting tip while machining at predetermined amplitude and frequency. However, modelling and simulation of these transducers is a tedious and difficult task. This is due to the inherent nonlinearities associated with smart materials. Therefore, this paper presents a component-based model of ultrasonic transducers that mimics the nonlinear behaviour of such a system. The system is decomposed into components, a mathematical model of each component is created, and the whole system model is accomplished by aggregating the basic components' model. System parameters are identified using Finite Element technique which then has been used to simulate the system in Matlab/SIMULINK. Various operation conditions are tested and performed to demonstrate the system performance.
Modeling fluid structure interaction with shape memory alloy actuated morphing aerostructures
NASA Astrophysics Data System (ADS)
Oehler, Stephen D.; Hartl, Darren J.; Turner, Travis L.; Lagoudas, Dimitris C.
2012-04-01
The development of efficient and accurate analysis techniques for morphing aerostructures incorporating shape memory alloys (SMAs) continues to garner attention. These active materials have a high actuation energy density, making them an ideal replacement for conventional actuation mechanisms in morphing structures. However, SMA components are often exposed to the same highly variable environments experienced by the aeroelastic assemblies into which they are incorporated. This is motivating design engineers to consider modeling fluidstructure interaction for prescribing dynamic, solution-dependent boundary conditions. This work presents a computational study of a particular morphing aerostructure with embedded, thermally actuating SMA ribbons and demonstrates the effective use of fluid-structure interaction modeling. A cosimulation analysis is utilized to determine the surface deflections and stress distributions of an example aerostructure with embedded SMA ribbons using the Abaqus Finite Element Analysis (FEA) software suite, combined with an Abaqus Computational Fluid Dynamics (CFD) processor. The global FEA solver utilizes a robust user-defined material subroutine which contains an accurate three-dimensional SMA constitutive model. Variations in the ambient fluid environment are computed using the CFD solver, and fluid pressure is mapped into surface distributed loads. Results from the analysis are qualitatively validated with independently obtained data from representative flow tests previously conducted on a physical prototype of the same aerostructure.
A top-down multi-scale modeling for actuation response of polymeric artificial muscles
NASA Astrophysics Data System (ADS)
Yang, Qianxi; Li, Guoqiang
2016-07-01
A class of innovative artificial muscles made of high-strength polymeric fibers such as fishing lines or sewing threads have been discovered recently. These muscles are fabricated by a simple "twist-insertion" procedure, which have attracted increasing attention due to their low cost and readily availability, giant tensile stroke, record energy density, and easy controllability. In the present paper, we established a multi-scale modeling framework for the thermomechanical actuation responses by a top-down strategy, spanning from macro-scale helical spring analysis down to molecular level chain interaction study. Comparison between modeling results and experimental results exhibited excellent agreement. The effect of the micro-, meso- and macro-scale parameters on the actuation responses of the artificial muscle was further discussed through a parametric study per the validated model. This work helps understand the physical origin behind the remarkable tensile actuation behavior of the twisted-then-coiled polymeric artificial muscles and also provides inspirations for optimal design of advanced artificial muscles made by twist-insertion procedure.
Circumstellar disks in binary star systems. Models for γ Cephei and α Centauri
NASA Astrophysics Data System (ADS)
Müller, T. W. A.; Kley, W.
2012-03-01
Context. As of today, over 50 planetary systems have been discovered in binary star systems, some of which have binary separations that are smaller than 20 AU. In these systems the gravitational forces from the binary have a strong influence on the evolution of the protoplanetary disk and hence the planet formation process. Aims: We study the evolution of viscous and radiative circumstellar disks under the influence of a companion star. We focus on the eccentric γ Cephei and α Centauri system as examples and compare disk quantities such as disk eccentricity and precession rate to previous isothermal simulations. Methods: We performed two-dimensional hydrodynamical simulations of the binary star systems under the assumption of coplanarity of the disk, host star and binary companion. We used the grid-based, staggered mesh code FARGO with an additional energy equation to which we added radiative cooling based on opacity tables. Results: The eccentric binary companion perturbs the disk around the primary star periodically. Upon passing periastron, spirals arms are induced that wind from the outer disk towards the star. In isothermal simulations this results in disk eccentricities up to edisk ≈ 0.2, but in more realistic radiative models we obtain much smaller eccentricities of about edisk ≈ 0.04-0.06 with no real precession. Models with varying viscosity and disk mass indicate that disks with less mass have lower temperatures and higher disk eccentricity. Conclusions: The fairly high disk eccentricities, as indicated in previous isothermal disk simulations, implied a more difficult planet formation in the γ Cephei system caused by the enhanced collision velocities of planetesimals. We have shown that under more realistic conditions with radiative cooling the disk becomes less eccentric and thus planet formation may be made easier. However, we estimate that the viscosity in the disk has to very low, with α ≲ 0.001, because otherwise the disk's lifetime will be
NASA Technical Reports Server (NTRS)
Leigh, Timothy D.; Zimmerman, David C.
1991-01-01
Experiments have shown that piezoceramic materials display a nonlinear relationship between the applied electric field and the actuation strain. This relationship also displays a substantial hysteresis upon reversal of the applied field. In this paper, piezoceramic actuator models are incorporated into the structural equations of motion to arrive at a set of nonlinear actively controlled structural equations of motion. A new implicit algorithm for determining the time history of the actively controlled structure is presented. The algorithm employs the trapezoidal rule for stepping the equations forward in time. The algorithm is compared to an explicit algorithm and is shown to provide greater numerical accuracy. In addition, the numerical stability and convergence characteristics are presented via example. The new algorithm displays convergence and stability properties that are comparable to the standard trapezoidal rule used for dynamic systems without hysteresis.
Protoplanetary disk formation and evolution models: DM Tau and GM Aur
NASA Astrophysics Data System (ADS)
Hueso, R.; Guillot, T.
2002-09-01
We study the formation and evolution of protoplanetary disks using an axisymmetric turbulent disk model. We compare model results with observational parameters derived for the DM Tau and GM Aur systems. These are relatively old T Tauri stars with large and massive protoplanetary disks. Early disk formation is studied in the standard scenario of slowly rotating isothermal collapsing spheres and is strongly dependent on the initial angular momentum and the collapse accretion rate. The viscous evolution of the disk is integrated in time using the classical Alpha prescription of turbulence. We follow the temporal evolution of the disks until their characteristics fit the observed characteristics of DM Tau and GM Aur. We therefore obtain the set of model parameters that are able to explain the present state of these disks. We also study the disk evolution under the Beta parameterization of turbulence, recently proposed for sheared flows on protoplanetary disks. Both parameterizations allow explaining the present state of both DM Tau and GM Aur. We infer a value of Alpha between 5x10-3 to 0.02 for DM Tau and one order of magnitude smaller for GM Aur. Values of the Beta parameter are in accordance with theoretical predictions of Beta around 2x10-5 but with a larger dispersion on other model parameters, which make us favor the Alpha parameterization of turbulence. Implications for planetary system development in these systems are presented. In particular, GM Aur is a massive and slowly evolving disk where conditions are very favorable for planetesimal growth. The large value of present disk mass and the relatively small observed accretion rate of this system may also be indicative of the presence of an inner gas giant planet. Acknowledgements: This work has been supported by Programme Nationale de Planetologie. R. Hueso acknowledges a post-doctoral fellowship from Gobierno Vasco.
Modelling of piezoelectric actuator dynamics for active structural control
NASA Technical Reports Server (NTRS)
Hagood, Nesbitt W.; Chung, Walter H.; Von Flotow, Andreas
1990-01-01
The paper models the effects of dynamic coupling between a structure and an electrical network through the piezoelectric effect. The coupled equations of motion of an arbitrary elastic structure with piezoelectric elements and passive electronics are derived. State space models are developed for three important cases: direct voltage driven electrodes, direct charge driven electrodes, and an indirect drive case where the piezoelectric electrodes are connected to an arbitrary electrical circuit with embedded voltage and current sources. The equations are applied to the case of a cantilevered beam with surface mounted piezoceramics and indirect voltage and current drive. The theoretical derivations are validated experimentally on an actively controlled cantilevered beam test article with indirect voltage drive.
A voice-actuated wind tunnel model leak checking system
NASA Technical Reports Server (NTRS)
Larson, William E.
1989-01-01
A computer program has been developed that improves the efficiency of wind tunnel model leak checking. The program uses a voice recognition unit to relay a technician's commands to the computer. The computer, after receiving a command, can respond to the technician via a voice response unit. Information about the model pressure orifice being checked is displayed on a gas-plasma terminal. On command, the program records up to 30 seconds of pressure data. After the recording is complete, the raw data and a straight line fit of the data are plotted on the terminal. This allows the technician to make a decision on the integrity of the orifice being checked. All results of the leak check program are stored in a database file that can be listed on the line printer for record keeping purposes or displayed on the terminal to help the technician find unchecked orifices. This program allows one technician to check a model for leaks instead of the two or three previously required.
MODELING MID-INFRARED VARIABILITY OF CIRCUMSTELLAR DISKS WITH NON-AXISYMMETRIC STRUCTURE
Flaherty, K. M.; Muzerolle, J.
2010-08-20
Recent mid-infrared observations of young stellar objects have found significant variations possibly indicative of changes in the structure of the circumstellar disk. Previous models of this variability have been restricted to axisymmetric perturbations in the disk. We consider simple models of a non-axisymmetric variation in the inner disk, such as a warp or a spiral wave. We find that the precession of these non-axisymmetric structures produces negligible flux variations but a change in the height of these structures can lead to significant changes in the mid-infrared flux. Applying these models to observations of the young stellar object LRLL 31 suggests that the observed variability could be explained by a warped inner disk with variable scale height. This suggests that some of the variability observed in young stellar objects could be explained by non-axisymmetric disturbances in the inner disk and this variability would be easily observable in future studies.
NASA Astrophysics Data System (ADS)
Cai, Zhen-Yi; Wang, Jun-Xian; Gu, Wei-Min; Sun, Yu-Han; Wu, Mao-Chun; Huang, Xing-Xing; Chen, Xiao-Yang
2016-07-01
The UV–optical variability of active galactic nuclei and quasars is useful for understanding the physics of the accretion disk and is gradually being attributed to stochastic fluctuations over the accretion disk. Quasars generally appear bluer when they brighten in the UV–optical bands; the nature of this phenomenon remains controversial. Recently, Sun et al. discovered that the color variation of quasars is timescale-dependent, in the way that faster variations are even bluer than longer term ones. While this discovery can directly rule out models that simply attribute the color variation to contamination from the host galaxies, or to changes in the global accretion rates, it favors the stochastic disk fluctuation model as fluctuations in the inner-most hotter disk could dominate the short-term variations. In this work, we show that a revised inhomogeneous disk model, where the characteristic timescales of thermal fluctuations in the disk are radius-dependent (i.e., τ ˜ r; based on that originally proposed by Dexter & Agol), can reproduce well a timescale-dependent color variation pattern, similar to the observed one and unaffected by the uneven sampling and photometric error. This demonstrates that one may statistically use variation emission at different timescales to spatially resolve the accretion disk in quasars, thus opening a new window with which to probe and test the accretion disk physics in the era of time domain astronomy. Caveats of the current model, which ought to be addressed in future simulations, are discussed.
NASA Technical Reports Server (NTRS)
Duyar, A.; Guo, T.-H.; Merrill, W.; Musgrave, J.
1992-01-01
In a previous study, Guo, Merrill and Duyar, 1990, reported a conceptual development of a fault detection and diagnosis system for actuation faults of the space shuttle main engine. This study, which is a continuation of the previous work, implements the developed fault detection and diagnosis scheme for the real time actuation fault diagnosis of the space shuttle main engine. The scheme will be used as an integral part of an intelligent control system demonstration experiment at NASA Lewis. The diagnosis system utilizes a model based method with real time identification and hypothesis testing for actuation, sensor, and performance degradation faults.
NASA Technical Reports Server (NTRS)
Patre, Parag; Joshi, Suresh M.
2011-01-01
Decentralized adaptive control is considered for systems consisting of multiple interconnected subsystems. It is assumed that each subsystem s parameters are uncertain and the interconnection parameters are not known. In addition, mismatch can exist between each subsystem and its reference model. A strictly decentralized adaptive control scheme is developed, wherein each subsystem has access only to its own state but has the knowledge of all reference model states. The mismatch is estimated online for each subsystem and the mismatch estimates are used to adaptively modify the corresponding reference models. The adaptive control scheme is extended to the case with actuator failures in addition to mismatch.
Computer Model Shows a Disk Galaxy's Life History
This cosmological simulation follows the development of a single disk galaxy over about 13.5 billion years, from shortly after the Big Bang to the present time. Colors indicate old stars (red), you...
Comparing different CFD wind turbine modelling approaches with wind tunnel measurements
NASA Astrophysics Data System (ADS)
Kalvig, Siri; Manger, Eirik; Hjertager, Bjørn
2014-12-01
The performance of a model wind turbine is simulated with three different CFD methods: actuator disk, actuator line and a fully resolved rotor. The simulations are compared with each other and with measurements from a wind tunnel experiment. The actuator disk is the least accurate and most cost-efficient, and the fully resolved rotor is the most accurate and least cost-efficient. The actuator line method is believed to lie in between the two ends of the scale. The fully resolved rotor produces superior wake velocity results compared to the actuator models. On average it also produces better results for the force predictions, although the actuator line method had a slightly better match for the design tip speed. The open source CFD tool box, OpenFOAM, was used for the actuator disk and actuator line calculations, whereas the market leading commercial CFD code, ANSYS/FLUENT, was used for the fully resolved rotor approach.
NASA Technical Reports Server (NTRS)
Whitney, Barbara A.; Hartmann, Lee
1992-01-01
We describe a Monte Carlo code that accurately treats multiple scattering, absorption, and polarization by dust, and use this code to calculate images of dusty disks around young stellar objects. We present some approximate analytic results that describe the behavior of the Monte Carlo calculations. A geometrically thin disk illuminated by a central T Tauri star scatters very little light at distances of many AU from the star. Viewed at any inclination, the flux scattered by such a disk at the distance to the nearest star-forming region will be overwhelmed by the stellar image. An optically thick disk that has a flaring surface may be observable, especially if viewed nearly edge-on so that the stellar source becomes occulted. An optically thin disk with a finite opening angle, similar to the one surrounding beta Pictoris, is about as observable as the typical flared optically thick disk at a similar distance from the earth. The polarization position angle is perpendicular to the disk plane in all of the models, in contrast to observations of many young stellar objects which have the position angle oriented parallel to the presumed disk plane. We suggest that the scattered light structures observed around many premain-sequence objects are dusty envelopes rather than disks.
NASA Astrophysics Data System (ADS)
Walton, John P.; Coutu, Ronald A.; Starman, LaVern
2015-02-01
There are numerous applications for micromirror arrays seen in our everyday lives. From flat screen televisions and computer monitors, found in nearly every home and office, to advanced military weapon systems and space vehicles, each application bringing with it a unique set of requirements. The microelectromechanical systems (MEMS) industry has researched many ways micromirror actuation can be accomplished and the different constraints on performance each design brings with it. This paper investigates a new "zipper" approach to electrostatically driven micromirrors with the intent of improving duel plane beam steering by coupling large deflection angles, over 30°, and a fast switching speed. To accomplish this, an extreme initial deflection is needed which can be reached using high stress bimorph beams. Currently this requires long beams and high voltage for the electrostatic pull in or slower electrothermal switching. The idea for this "zipper" approach is to stack multiple beams of a much shorter length and allow for the deflection of each beam to be added together in order to reach the required initial deflection height. This design requires much less pull-in voltage because the pull-in of one short beam will in turn reduce the height of the all subsequent beams, making it much easier to actuate. Using modeling and simulation software to characterize operations characteristics, different bimorph cantilever beam configurations are explored in order to optimize the design. These simulations show that this new "zipper" approach increases initial deflection as additional beams are added to the assembly without increasing the actuation voltage.
NASA Technical Reports Server (NTRS)
Schwartz, Robert W.; Ballato, J.; Northwang, W. D.; Laoratanakul, P.
2000-01-01
Dome formation in Rainbow and Thunder actuators occurs to relieve thermal expansion mismatch stress between the metallic and piezoelectric layers during cooling from device fabrication temperatures. Accompanying this process is the generation of an internal stress profile within the devices and the development of significant tensile stresses within the surface region of the piezoelectric. These tensile stresses affect the domain configuration (ratio of c-to-a domains), and improve the 90 deg. domain wall movement response of the device in this region of the piezoelectric. This results in improved electromechanical performance compared to standard direct extensional and flextensional devices, presumably because of the contributions of stress to the non-linearity of the piezoelectric d-coefficients. 1 Interestingly, this improvement in response seems counterintuitive; a stress perpendicular to the direction of the applied electric field should impede, not contribute to 90' domain switching. Further consideration of the lower region of the piezoelectric that is under compressive stress thus appears warranted. The specified objectives of the research were to: 1. Conduct finite element and equivalent circuit simulation-based investigations to understand the effects of actuator geometry on internal stress distribution and actuator performance (displacement and load-bearing capabilities). 2. Use the results of the modeling studies to predict the processing conditions (geometry and thickness ratio) required for the fabrication of Rainbow ceramics with optimized performance.
NASA Astrophysics Data System (ADS)
Zhu, Zicai; Wang, Yanjie; Liu, Yanfa; Asaka, Kinji; Sun, Xiaofei; Chang, Longfei; Lu, Pin
2016-07-01
Water containing ionic polymer-metal composites (IPMCs) show complex deformation properties with water content. In order to develop a simple application-oriented model for engineering application, actuation mechanisms and model equations should be simplified as necessary. Beginning from our previous comprehensive multi-physical model of IPMC actuator, numerical analysis was performed to obtain the main factors influencing the bending deformation and the corresponding simplified model. In this paper, three aspects are mainly concerned. (1) Regarding mass transport process, the diffusion caused by concentration gradient mainly influences the concentrations of cation and water at the two electrode boundaries. (2) By specifying the transport components as hydrated cation and free water in the model, at the cathode, the hydrated cation concentration profile is more flat, whereas the concentrations of both free water and the total water show drastic changes. In general, the two influence the redistribution of cation and water but have little impact on deformation prediction. Thus, they can be ignored in the simplification. (3) An extended osmotic pressure is proposed to cover all eigen stresses simply with an effective osmotic coefficient. Combining with a few other linearized methods, a simplified model has been obtained by sacrificing the prediction precision on the transport process. Furthermore, the improved model has been verified by fitting with IPMC deformation evolved with water content. It shows that the simplified model has the ability to predict the complex deformations of IPMCs.
Muniraj, Murali; Arulmozhiyal, Ramaswamy
2015-01-01
A control actuation system has been used extensively in automotive, aerospace, and defense applications. The major challenges in modeling control actuation system are rise time, maximum peak to peak overshoot, and response to nonlinear system with percentage error. This paper addresses the challenges in modeling and real time implementation of control actuation system for missiles glider applications. As an alternative fuzzy-PID controller is proposed in BLDC motor drive followed by linkage mechanism to actuate fins in missiles and gliders. The proposed system will realize better rise time and less overshoot while operating in extreme nonlinear dynamic system conditions. A mathematical model of BLDC motor is derived in state space form. The complete control actuation system is modeled in MATLAB/Simulink environment and verified by performing simulation studies. A real time prototype of the control actuation is developed with dSPACE-1104 hardware controller and a detailed analysis is carried out to confirm the viability of the proposed system. PMID:26613102
Muniraj, Murali; Arulmozhiyal, Ramaswamy
2015-01-01
A control actuation system has been used extensively in automotive, aerospace, and defense applications. The major challenges in modeling control actuation system are rise time, maximum peak to peak overshoot, and response to nonlinear system with percentage error. This paper addresses the challenges in modeling and real time implementation of control actuation system for missiles glider applications. As an alternative fuzzy-PID controller is proposed in BLDC motor drive followed by linkage mechanism to actuate fins in missiles and gliders. The proposed system will realize better rise time and less overshoot while operating in extreme nonlinear dynamic system conditions. A mathematical model of BLDC motor is derived in state space form. The complete control actuation system is modeled in MATLAB/Simulink environment and verified by performing simulation studies. A real time prototype of the control actuation is developed with dSPACE-1104 hardware controller and a detailed analysis is carried out to confirm the viability of the proposed system. PMID:26613102
NASA Astrophysics Data System (ADS)
Abel, Julianna; Luntz, Jonathan; Brei, Diann
2012-08-01
Active knits are a unique architectural approach to meeting emerging smart structure needs for distributed high strain actuation with simultaneous force generation. This paper presents an analytical state-based model for predicting the actuation response of a shape memory alloy (SMA) garter knit textile. Garter knits generate significant contraction against moderate to large loads when heated, due to the continuous interlocked network of loops of SMA wire. For this knit architecture, the states of operation are defined on the basis of the thermal and mechanical loading of the textile, the resulting phase change of the SMA, and the load path followed to that state. Transitions between these operational states induce either stick or slip frictional forces depending upon the state and path, which affect the actuation response. A load-extension model of the textile is derived for each operational state using elastica theory and Euler-Bernoulli beam bending for the large deformations within a loop of wire based on the stress-strain behavior of the SMA material. This provides kinematic and kinetic relations which scale to form analytical transcendental expressions for the net actuation motion against an external load. This model was validated experimentally for an SMA garter knit textile over a range of applied forces with good correlation for both the load-extension behavior in each state as well as the net motion produced during the actuation cycle (250% recoverable strain and over 50% actuation). The two-dimensional analytical model of the garter stitch active knit provides the ability to predict the kinetic actuation performance, providing the basis for the design and synthesis of large stroke, large force distributed actuators that employ this novel architecture.
NASA Astrophysics Data System (ADS)
Kruusamäe, Karl; Brunetto, Paola; Punning, Andres; Kodu, Margus; Jaaniso, Raivo; Graziani, Salvatore; Fortuna, Luigi; Aabloo, Alvo
2011-12-01
This paper further discusses a concept of creating a self-sensing ionic polymer-metal composite (IPMC) actuating device with patterned surface electrodes where the actuator and sensor elements are separated by a grounded shielding electrode. Different patterning methods are discussed and compared in detail; the presented experimental data give an understanding of the qualitative properties of the patterns created. Finally, an electromechanical model of the device is proposed and validated.
Modeling Eclipses in the Classical Nova V Persei: The Role of the Accretion Disk Rim
NASA Astrophysics Data System (ADS)
Shafter, A. W.; Misselt, K. A.
2006-06-01
Multicolor (BVRI) light curves of the eclipsing classical nova V Per are presented, and a total of 12 new eclipse timings are measured for the system. When combined with previous eclipse timings from the literature, these timings yield a revised ephemeris for the times of mideclipse given by HJD=2,447,442.8260(1)+0.107123474(3)E. The eclipse profiles are analyzed with a parameter-fitting model that assumes four sources of luminosity: a white dwarf primary star, a main-sequence secondary star, a flared accretion disk with a rim, and a bright spot at the intersection of the mass transfer stream and the disk periphery. Model parameters include the temperatures of the white dwarf (T1) and the secondary star (T2), the radius (Rd) and temperature (Td), of the disk periphery, the inner disk radius (Rin), the disk power-law temperature exponent (α) and thickness (hr), and a bright spot temperature enhancement factor (χs). A matrix of model solutions are computed, covering an extensive range of plausible parameter values. The solution matrix is then explored to determine the optimum values for the fitting parameters and their associated errors. For models that treat the accretion disk as a flat structure without a rim, optimum fits require that the disk have a flat temperature profile. Although models with a truncated inner disk (Rin>>R1) result in a steeper temperature profile, steady state models with a temperature profile characterized by T(r)~r-3/4 are found only for models with a significant disk rim. A comparison of the observed brightness and color at mideclipse with the photometric properties of the best-fitting model suggests that V Per lies at a distance of ~1 kpc.
Reduced-order modeling of high-speed jets controlled by arc filament plasma actuators
NASA Astrophysics Data System (ADS)
Sinha, Aniruddha; Serrani, Andrea; Samimy, Mo
2013-02-01
Arc filament plasma actuators applied to high-speed and high Reynolds number jets have demonstrated significant mixing enhancement when operated near the jet column mode (JCM) frequency. A feedback-oriented reduced-order model is developed for this flow from experimental data. The existent toolkit of stochastic estimation, proper orthogonal decomposition, and Galerkin projection is adapted to yield a 35-dimensional model for the unforced jet. Explicit inclusion of a "shift mode" stabilizes the model. The short-term predictive capability of instantaneous flow fields is found to degrade beyond a single flow time step, but this horizon may be adequate for feedback control. Statistical results from long-term simulations agree well with experimental observations. The model of the unforced jet is augmented to incorporate the effects of plasma actuation. Periodic forcing is modeled as a deterministic pressure wave specified on the inflow boundary of the modeling domain. Simulations of the forced model capture the nonlinear response that leads to optimal mixing enhancement in a small range of frequencies near the JCM.
Torsional fatigue model for limitorque type SMB/SB/SBD actuators for motor-operated valves
Somogyi, D.; Alvarez, P.D.; Kalsi, M.S.
1996-12-01
Kalsi Engineering, Inc. has recently developed a computer program to predict the torsional fatigue life of Limitorque Type SMB/SB/SBD actuators for motor-operated valves under given loading levels, including those that exceed the ratings. The development effort was an outgrowth of the {open_quote}Thrust Rating Increase{close_quote} test program. The fatigue model computes all pertinent stress components and their variations as a function of the loading ramp. The cumulative damage and fatigue life due to stress cycling is computed by use of a modification of Miner`s rule. Model predictions were validated against actual cyclic loading test results.
NASA Technical Reports Server (NTRS)
Yam, Y.; Lang, J. H.; Johnson, T. L.; Shih, S.; Staelin, D. H.
1983-01-01
A model reduction procedure based on aggregation with respect to sensor and actuator influences rather than modes is presented for large systems of coupled second-order differential equations. Perturbation expressions which can predict the effects of spillover on both the aggregated and residual states are derived. These expressions lead to the development of control system design constraints which are sufficient to guarantee, to within the validity of the perturbations, that the residual states are not destabilized by control systems designed from the reduced model. A numerical example is provided to illustrate the application of the aggregation and control system design method.
Modeling self-subtraction in angular differential imaging: Application to the HD 32297 debris disk
Esposito, Thomas M.; Fitzgerald, Michael P.; Graham, James R.; Kalas, Paul
2014-01-01
We present a new technique for forward-modeling self-subtraction of spatially extended emission in observations processed with angular differential imaging (ADI) algorithms. High-contrast direct imaging of circumstellar disks is limited by quasi-static speckle noise, and ADI is commonly used to suppress those speckles. However, the application of ADI can result in self-subtraction of the disk signal due to the disk's finite spatial extent. This signal attenuation varies with radial separation and biases measurements of the disk's surface brightness, thereby compromising inferences regarding the physical processes responsible for the dust distribution. To compensate for this attenuation, we forward model the disk structure and compute the form of the self-subtraction function at each separation. As a proof of concept, we apply our method to 1.6 and 2.2 μm Keck adaptive optics NIRC2 scattered-light observations of the HD 32297 debris disk reduced using a variant of the 'locally optimized combination of images' algorithm. We are able to recover disk surface brightness that was otherwise lost to self-subtraction and produce simplified models of the brightness distribution as it appears with and without self-subtraction. From the latter models, we extract radial profiles for the disk's brightness, width, midplane position, and color that are unbiased by self-subtraction. Our analysis of these measurements indicates a break in the brightness profile power law at r ≈ 110 AU and a disk width that increases with separation from the star. We also verify disk curvature that displaces the midplane by up to 30 AU toward the northwest relative to a straight fiducial midplane.
Modeling Self-subtraction in Angular Differential Imaging: Application to the HD 32297 Debris Disk
NASA Astrophysics Data System (ADS)
Esposito, Thomas M.; Fitzgerald, Michael P.; Graham, James R.; Kalas, Paul
2014-01-01
We present a new technique for forward-modeling self-subtraction of spatially extended emission in observations processed with angular differential imaging (ADI) algorithms. High-contrast direct imaging of circumstellar disks is limited by quasi-static speckle noise, and ADI is commonly used to suppress those speckles. However, the application of ADI can result in self-subtraction of the disk signal due to the disk's finite spatial extent. This signal attenuation varies with radial separation and biases measurements of the disk's surface brightness, thereby compromising inferences regarding the physical processes responsible for the dust distribution. To compensate for this attenuation, we forward model the disk structure and compute the form of the self-subtraction function at each separation. As a proof of concept, we apply our method to 1.6 and 2.2 μm Keck adaptive optics NIRC2 scattered-light observations of the HD 32297 debris disk reduced using a variant of the "locally optimized combination of images" algorithm. We are able to recover disk surface brightness that was otherwise lost to self-subtraction and produce simplified models of the brightness distribution as it appears with and without self-subtraction. From the latter models, we extract radial profiles for the disk's brightness, width, midplane position, and color that are unbiased by self-subtraction. Our analysis of these measurements indicates a break in the brightness profile power law at r ≈ 110 AU and a disk width that increases with separation from the star. We also verify disk curvature that displaces the midplane by up to 30 AU toward the northwest relative to a straight fiducial midplane.
Tracking control of piezoelectric actuators using a polynomial-based hysteresis model
NASA Astrophysics Data System (ADS)
Gan, Jinqiang; Zhang, Xianmin; Wu, Heng
2016-06-01
A polynomial-based hysteresis model that describes hysteresis behavior in piezoelectric actuators is presented. The polynomial-based model is validated by comparing with the classic Prandtl-Ishlinskii model. Taking the advantages of the proposed model into consideration, inverse control using the polynomial-based model is proposed. To achieve better tracking performance, a hybrid control combining the developed inverse control and a proportional-integral-differential feedback loop is then proposed. To demonstrate the effectiveness of the proposed tracking controls, several comparative experiments of the polynomial-based model and Prandtl-Ishlinskii model are conducted. The experimental results show that inverse control and hybrid control using the polynomial-based model in trajectory-tracking applications are effective and meaningful.
Two-Dimensional Scramjet Inlet Unstart Model: Wind-Tunnel Blockage and Actuation Systems Test
NASA Technical Reports Server (NTRS)
Holland, Scott D.
1994-01-01
This supplement to NASA TM 109152 shows the Schlieren video (10 min. 52 sec., color, Beta and VHS) of the external flow field and a portion of the internal flow field of a two-dimensional scramjet inlet model in the NASA Langley 20-Inch Mach 6 Tunnel. The intent of the overall test program is to study (both experimentally and computationally) the dynamics of the inlet unstart; this (phase I) effort examines potential wind-tunnel blockage issues related to model sizing and the adequacy of the actuation systems in accomplishing the start and unstart. The model is equipped with both a moveable cowl and aft plug. Windows in the inlet sidewalls allow limited optical access to the internal shock structure. In the video, flow is from right to left, and the inlet is oriented inverted with respect to flight, i.e., with the cowl on top. The plug motion is obvious because the plug is visible in the aft window. The cowl motion, however, is not as obvious because the cowl is hidden from view by the inlet sidewall. The end of the cowl actuator arm, however, becomes visible above the inlet sidewalls between the windows when the cowl is up (see figure 1b of the primary document). The model is injected into the tunnel and observed though several actuation sequences with two plug configurations over a range of unit freestream Reynolds number at a nominal freestream Mach number of 6. The framing rate and shutter speed of the camera were too slow to fully capture the dynamics of the unstart but did prove sufficient to identify inlet start and unstart. This series of tests indicated that the model was appropriately sized for this facility and identified operability limits required first to allow the inlet to start and second to force the unstart.
Integrated modeling for determining launch survival and limitations of actuated lightweight mirrors
NASA Astrophysics Data System (ADS)
Cohan, Lucy E.; Miller, David W.
2008-07-01
The future of space telescopes lies in large, lightweight, segmented aperture systems. Segmented apertures eliminate manufacturability and launch vehicle fairing diameter as apertures size constraints. Low areal density, actuated segments allow the systems to meet both launch mass restrictions and on-orbit wavefront error requirements. These systems, with silicon carbide as a leading material, have great potential for increasing the productivity, affordability, and manufacturability of future space-based optical systems. Thus far, progress has been made on the manufacturing, sensing, actuation, and on-orbit control of such systems. However, relatively little attention has been paid to the harsh environment of launch. The launch environment may dominate aspects of the design of the mirror segments, with survivability requirements eliminating many potentially good designs. Integrated modeling of a mirror segment can help identify trends in mirror geometries that maximize launch performance, ensuring survivability without drastically over designing the mirror. A finite element model of a single, ribbed, actuated, silicon carbide mirror segment is created, and is used to develop a dynamic, state-space model, with launch load spectra as disturbance inputs, and mirror stresses as performance outputs. The parametric nature of this model allows analysis of many geometrically different mirror segments, helping to identify key parameters for launch survival. The modeling method described herein will enable identification of the design decisions that are dominated by launch, and will allow for development of launch-load alleviation techniques to further push the areal density boundaries in support of the creation of larger and lighter mirrors than previously possible.
Constraints on black hole spins with a general relativistic accretion disk corona model
NASA Astrophysics Data System (ADS)
You, Bei; Cao, Xin-Wu; Yuan, Ye-Fei
2016-04-01
The peaks in the spectra of the accretion disks surrounding massive black holes in quasars are in the far-UV or soft X-ray band, which are usually not observed. However, in the disk corona model, soft photons from the disk are Comptonized to high energy in the hot corona, and the hard X-ray spectra (luminosity and spectral shape) contain information on the incident spectra from the disk. The values of black hole spin parameter a* are inferred from the spectral fitting, which are spread over a large range, ∼ ‑0.94 to 0.998. We find that the inclination angles and mass accretion rates are well determined by the spectral fitting, but the results are sensitive to the accuracy of black hole mass estimates. No tight constraints on the black hole spins are achieved, if the uncertainties in black hole mass measurements are a factor of four, which are typical for the single-epoch reverberation mapping method. Recently, the accuracy of black hole mass measurement has been significantly improved to 0.2 – 0.4 dex with the velocity resolved reverberation mapping method. The black hole spin can be well constrained if the mass measurement accuracy is ≲ 50%. In the accretion disk corona scenario, a fraction of power dissipated in the disk is transported into the corona, and therefore the accretion disk is thinner than a bare disk for the same mass accretion rate, because the radiation pressure in the disk is reduced. We find that the thin disk approximation, H/R ≲ 0.1, is still valid if 0.3 < ṁ < 0.5, provided half of the dissipated power is radiated in the corona above the disk.
Modeling and control of actuators for high performance structural dynamic testing
NASA Astrophysics Data System (ADS)
Gao, X.; Dyke, S. J.
2014-05-01
Most research in the structural engineering field uses either a simplified data-based model or a physics-based model to describe the dynamic behavior of servo-hydraulic actuators. In either way, the nominal model is typically used for modeling, analysis and control design. However, little effort has been directed to model uncertainties that are inherently associated with any physical system. A robust modeling approach is proposed in this study that can characterize both parametric and non-parametric uncertainties. The combination of this uncertainty with the nominal model provides a powerful tool to analyze the system performance and stability properties. Several control techniques are evaluated experimentally, and an H∞ robust control design is demonstrated to achieve the best performance as well as good robustness.
Models that Teach about the Computer: AppleWorks and ProDOS, the Computer's Memory and Disk Storage.
ERIC Educational Resources Information Center
Niess, Margaret L.
1989-01-01
This final article in a series on creating models for teaching about computer memory and disk storage and retrieval focuses on AppleWorks software and the Professional Disk Operating System (ProDOS). Instructions for creating a paper model of the AppleWorks menu system and the ProDOS disk file are given. (LRW)
A SMACK Model of Colliding Planetesimals in the β Pictoris Debris Disk
NASA Astrophysics Data System (ADS)
Nesvold, Erika R.; Kuchner, Marc J.
2015-12-01
We present a new model of the β Pictoris disk-and-planet system that simulates both the planetesimal collisions and the dynamics of the resulting dust grains, allowing us to model features and asymmetries in both thermal and scattered light images of the disk. Our two-part model first simulates the collisional and dynamical evolution of the planetesimals with the Superparticle-Method Algorithm for Collisions in Kuiper belts and then simulates the dynamical evolution of the resulting dust grains with a standard Bulirsch-Stoer N-body integrator. Given the observed inclination and eccentricity of the β Pictoris b planet, the model neatly ties together several features of the disk: the central hole in the submillimeter images, the two-disk “x”-pattern seen in scattered light, and possibly even the clumpy gas seen by ALMA. We also find that most of the dust in the β Pictoris system is likely produced outside the ring at 60-100 AU. Instead of a birth ring, this disk has a “stirring ring” at 60-100 AU where the high-velocity collisions produced by the secular wave launched by the planet are concentrated. The two-disk x-pattern arises because collisions occur more frequently at the peaks and troughs of the secular wave. The perturbations of the disk in this region create an azimuthally and vertically asymmetric spatial distribution of collisions, which could yield an azimuthal clump of gas without invoking resonances or an additional planet.
Accretion disk dynamics. α-viscosity in self-similar self-gravitating models
NASA Astrophysics Data System (ADS)
Kubsch, Marcus; Illenseer, Tobias F.; Duschl, Wolfgang J.
2016-04-01
Aims: We investigate the suitability of α-viscosity in self-similar models for self-gravitating disks with a focus on active galactic nuclei (AGN) disks. Methods: We use a self-similar approach to simplify the partial differential equations arising from the evolution equation, which are then solved using numerical standard procedures. Results: We find a self-similar solution for the dynamical evolution of self-gravitating α-disks and derive the significant quantities. In the Keplerian part of the disk our model is consistent with standard stationary α-disk theory, and self-consistent throughout the self-gravitating regime. Positive accretion rates throughout the disk demand a high degree of self-gravitation. Combined with the temporal decline of the accretion rate and its low amount, the model prohibits the growth of large central masses. Conclusions: α-viscosity cannot account for the evolution of the whole mass spectrum of super-massive black holes (SMBH) in AGN. However, considering the involved scales it seems suitable for modelling protoplanetary disks.
NASA Astrophysics Data System (ADS)
Snow, Michael G.; Bajaj, Anil K.
2015-08-01
This work presents an uncertainty quantification (UQ) analysis of a comprehensive model for an electrostatically actuated microelectromechanical system (MEMS) switch. The goal is to elucidate the effects of parameter variations on certain key performance characteristics of the switch. A sufficiently detailed model of the electrostatically actuated switch in the basic configuration of a clamped-clamped beam is developed. This multi-physics model accounts for various physical effects, including the electrostatic fringing field, finite length of electrodes, squeeze film damping, and contact between the beam and the dielectric layer. The performance characteristics of immediate interest are the static and dynamic pull-in voltages for the switch. Numerical approaches for evaluating these characteristics are developed and described. Using Latin Hypercube Sampling and other sampling methods, the model is evaluated to find these performance characteristics when variability in the model's geometric and physical parameters is specified. Response surfaces of these results are constructed via a Multivariate Adaptive Regression Splines (MARS) technique. Using a Direct Simulation Monte Carlo (DSMC) technique on these response surfaces gives smooth probability density functions (PDFs) of the outputs characteristics when input probability characteristics are specified. The relative variation in the two pull-in voltages due to each of the input parameters is used to determine the critical parameters.
Shahmohammadi, Mehrdad; Asgharzadeh Shirazi, Hadi; Karimi, Alireza; Navidbakhsh, Mahdi
2014-10-01
Degeneration of intervertebral disk (IVD) has been increased in recent years. The lumbar herniation can be cured using conservative and surgical procedures. Surgery is considered after failure of conservative treatment. Partial discectomy, fusion, and total disk replacement (TDR) are also common surgical treatments for degenerative disk disease. However, due to limitations and disadvantages of the current treatments, many studies have been carried out to approach the best design of mimicking natural disk. Recently, a new method of TDRs has been introduced using nature deformation of IVD by reinforced fibers of annulus fibrosis. Nonetheless, owing to limitations of experimental works on the human body, numerical studies of IVD may help to understand load transfer and biomechanical properties within the disks with reinforced fibers. In this study, a three-dimensional (3D) finite element model of the L2-L3 disk vertebrae unit with 12 vertical fibers embedded into annulus fibrosis was constructed. The IVD was subjected to compressive force, bending moment, and axial torsion. The most important parameters of disk failures were compared to that of experimental data. The results showed that the addition of reinforced fibers into the disk invokes a significant decrease of stress in the nucleus and annulus. The findings of this study may have implications not only for developing IVDs with reinforced fibers but also for the application of fiber reinforced IVD in orthopedics surgeries as a suitable implant. PMID:24981720
Modeling dust growth in protoplanetary disks: The breakthrough case
NASA Astrophysics Data System (ADS)
Drążkowska, J.; Windmark, F.; Dullemond, C. P.
2014-07-01
Context. Dust coagulation in protoplanetary disks is one of the initial steps toward planet formation. Simple toy models are often not sufficient to cover the complexity of the coagulation process, and a number of numerical approaches are therefore used, among which integration of the Smoluchowski equation and various versions of the Monte Carlo algorithm are the most popular. Aims: Recent progress in understanding the processes involved in dust coagulation have caused a need for benchmarking and comparison of various physical aspects of the coagulation process. In this paper, we directly compare the Smoluchowski and Monte Carlo approaches to show their advantages and disadvantages. Methods: We focus on the mechanism of planetesimal formation via sweep-up growth, which is a new and important aspect of the current planet formation theory. We use realistic test cases that implement a distribution in dust collision velocities. This allows a single collision between two grains to have a wide range of possible outcomes but also requires a very high numerical accuracy. Results: For most coagulation problems, we find a general agreement between the two approaches. However, for the sweep-up growth driven by the "lucky" breakthrough mechanism, the methods exhibit very different resolution dependencies. With too few mass bins, the Smoluchowski algorithm tends to overestimate the growth rate and the probability of breakthrough. The Monte Carlo method is less dependent on the number of particles in the growth timescale aspect but tends to underestimate the breakthrough chance due to its limited dynamic mass range. Conclusions: We find that the Smoluchowski approach, which is generally better for the breakthrough studies, is sensitive to low mass resolutions in the high-mass, low-number tail that is important in this scenario. To study the low number density features, a new modulation function has to be introduced to the interaction probabilities. As the minimum resolution
Stroke maximizing and high efficient hysteresis hybrid modeling for a rhombic piezoelectric actuator
NASA Astrophysics Data System (ADS)
Shao, Shubao; Xu, Minglong; Zhang, Shuwen; Xie, Shilin
2016-06-01
Rhombic piezoelectric actuator (RPA), which employs a rhombic mechanism to amplify the small stroke of PZT stack, has been widely used in many micro-positioning machineries due to its remarkable properties such as high displacement resolution and compact structure. In order to achieve large actuation range along with high accuracy, the stroke maximizing and compensation for the hysteresis are two concerns in the use of RPA. However, existing maximization methods based on theoretical model can hardly accurately predict the maximum stroke of RPA because of approximation errors that are caused by the simplifications that must be made in the analysis. Moreover, despite the high hysteresis modeling accuracy of Preisach model, its modeling procedure is trivial and time-consuming since a large set of experimental data is required to determine the model parameters. In our research, to improve the accuracy of theoretical model of RPA, the approximation theory is employed in which the approximation errors can be compensated by two dimensionless coefficients. To simplify the hysteresis modeling procedure, a hybrid modeling method is proposed in which the parameters of Preisach model can be identified from only a small set of experimental data by using the combination of discrete Preisach model (DPM) with particle swarm optimization (PSO) algorithm. The proposed novel hybrid modeling method can not only model the hysteresis with considerable accuracy but also significantly simplified the modeling procedure. Finally, the inversion of hysteresis is introduced to compensate for the hysteresis non-linearity of RPA, and consequently a pseudo-linear system can be obtained.
NASA Technical Reports Server (NTRS)
Webb, J. A., Jr.
1974-01-01
The multipurpose ventricular actuating system is a pneumatic signal generating device that provides controlled driving pressures for actuating pulsatile blood pumps. Overall system capabilities, the timing circuitry, and calibration instruction are included.
NASA Astrophysics Data System (ADS)
Camp, Elizabeth H.; Cal, Raúl Bayoán
2016-08-01
An array of model rotating wind turbines is compared experimentally to an array of static porous disks in order to quantify the similarities and differences in the mean kinetic energy transport within the wakes produced in these two cases. Stereo particle image velocimetry measurements are done in a wind tunnel bracketing the center turbine in the fourth row of a 4 ×3 array of model turbines. Equivalent sets of rotors and porous disks are created by matching their respective induction factors. The primary difference in the mean velocity components is found in the spanwise mean velocity component, which is as much as 190% different between the rotor and disk case. Horizontal averages of mean kinetic energy transport terms in the region where rotation is most important show percent differences in the range 3%-41%, which decrease to 1%-6% at streamwise coordinates where rotation is less important. Octant analysis is performed on the most significant term related to vertical mean kinetic energy flux u'v' ¯U . The average percent difference between corresponding octants is as much as 68% different in the near wake and as much as 17% different in the far wake. Furthermore, octant analysis elucidates the three-dimensional nature of sweeps and ejections in the near wake of the rotor case. Together, these results imply that a stationary porous disk adequately represents the mean kinetic energy transport of a rotor in the far wake where rotation is less important, while significant discrepancies exist at streamwise locations where rotation is a key phenomenon. This comparison has implications in the use of an actuator disk to model the wind turbine rotor in computational simulations specifically for studies where Reynolds stresses, turbulence intensity, or interactions with the atmosphere are of interest.
NASA Technical Reports Server (NTRS)
Grzenia, B. J.; Tycner, C.; Jones, C. E.; Rinehart, S. A.; vanBelle, G. T.; Sigut, T. A. A.
2013-01-01
Geometrical (uniform disk) and numerical models were calculated for a set of B-emission (Be) stars observed with the Palomar Testbed Interferometer (PTI). Physical extents have been estimated for the disks of a total of15 stars via uniform disk models. Our numerical non-LTE models used parameters for the B0, B2, B5, and B8spectral classes and following the framework laid by previous studies, we have compared them to infrared K-band interferometric observations taken at PTI. This is the first time such an extensive set of Be stars observed with long-baseline interferometry has been analyzed with self-consistent non-LTE numerical disk models.
Grzenia, B. J.; Tycner, C.; Jones, C. E.; Sigut, T. A. A.; Rinehart, S. A.; Van Belle, G. T.
2013-05-15
Geometrical (uniform disk) and numerical models were calculated for a set of B-emission (Be) stars observed with the Palomar Testbed Interferometer (PTI). Physical extents have been estimated for the disks of a total of 15 stars via uniform disk models. Our numerical non-LTE models used parameters for the B0, B2, B5, and B8 spectral classes and following the framework laid by previous studies, we have compared them to infrared K-band interferometric observations taken at PTI. This is the first time such an extensive set of Be stars observed with long-baseline interferometry has been analyzed with self-consistent non-LTE numerical disk models.
NASA Astrophysics Data System (ADS)
Shu, Liang; Wu, Guichu; Chen, Dingfang; Dapino, Marcelo J.
2016-03-01
On active bending structures, the actuation direction and the excitation field direction are not the same. Simple lumped parameter models are inadequate to describe the relationship between output displacement and input field. In this paper, a dynamic distributed parameter model is presented to describe the system dynamics of a galfenol bending actuator. To consider nonlinearities and hysteresis in bending, a nonlinear magnetomechanical model is developed to characterize the hysteretic magnetostriction generated by the galfenol layer. A dynamic real-time control strategy is proposed to compensate for hysteresis. A nonlinear inverse filter is constructed to linearize the hysteresis based on the proposed distributed parameter model. In order to increase the calculation efficiency, a new iteration method is proposed to calculate the filter. The iteration stepsize of the input field can be adaptively updated according to the inverting error. Simulation results show that significant enhancement of convergence efficiency can be achieved by using the proposed method compared with the existing fixed step size method. Experiments have been conducted to verify the real-time control strategy.
NASA Astrophysics Data System (ADS)
Pusey, Jason L.; Yoo, Jin-Hyeong
2014-06-01
We document the design and preliminary numerical simulation study of a high fidelity model of Canid, a recently introduced bounding robot. Canid is a free-standing, power-autonomous quadrupedal machine constructed from standard commercially available electromechanical and structural elements, incorporating compliant C-shaped legs like those of the decade old RHex design, but departing from that standard (and, to the best of our knowledge, from any prior) robot platform in its parallel actuated elastic spine. We have used a commercial modeling package to develop a finite-element model of the actuated, cable-driven, rigid-plate-reinforced harness for the carbon-fiber spring that joins the robot's fore- and hind-quarters. We compare a numerical model of this parallel actuated elastic spine with empirical data from preliminary physical experiments with the most important component of the spine assembly: the composite leaf spring. Specifically, we report our progress in tuning the mechanical properties of a standard modal approximation to a conventional compliant beam model whose boundary conditions represent constraints imposed by the actuated cable driven vertebral plates that comprise the active control affordance over the spine. We conclude with a brief look ahead at near-term future experiments that will compare predictions of this fitted composite spring model with data taken from the physical spine flexed in isolation from the actuated harness.
NASA Technical Reports Server (NTRS)
Kim, Y. W.; Metzger, D. E.
1992-01-01
The test facility, test methods and results are presented for an experimental study modeling the cooling of turbine disks in the blade attachment regions with multiple impinging jets, in a configuration simulating the disk cooling method employed on the Space Shuttle Main Engine oxygen turbopump. The study's objective was to provide a comparison of detailed local convection heat transfer rates obtained for a single center-supply of disk coolant with those obtained with the present flight configuration where disk coolant is supplied through an array of 19 jets located near the disk outer radius. Specially constructed disk models were used in a program designed to evaluate possible benefits and identify any possible detrimental effects involved in employing an alternate disk cooling scheme. The study involved the design, construction and testing of two full scale rotating model disks, one plane and smooth for baseline testing and the second contoured to the present flight configuration, together with the corresponding plane and contoured stator disks. Local heat transfer rates are determined from the color display of encapsulated liquid crystals coated on the disk in conjunction with use of a computer vision system. The test program was composed of a wide variety of disk speeds, flowrates, and geometrical configurations, including testing for the effects of disk boltheads and gas ingestion from the gas path region radially outboard of the disk-cavity.
Scour around a perforated disk modeling a marine hydrokinetic device
NASA Astrophysics Data System (ADS)
Beninati, M. L.; Soliani, G.; Zhou, C. C.; Krane, M.; Fontaine, A.
2013-12-01
A study was conducted to investigate the behavior of scour hole dimensions and scour rates around a bottom-mounted cylindrical support structure of a perforated disk. The experiments focus on collecting temporal variations of scour depth around the support structure of the perforated disk for two scour regimes: transitional (ReD = 8500 and 9400) and live-bed (ReD = 10200). A perforated disk is used to approximate the drag of a submerged, horizontal axis, marine hydrokinetic (MHK) turbine. The goal is to compare the scour behavior around a perforated disk to that of a marine hydrokinetic (MHK) device. This study is motivated by the need to predict the environmental effect of MHK devices on an erodible bed. Testing is conducted in the small-scale hydraulic flume facility (1.2 m wide, 0.38 m deep, and 9.75 m long) at Bucknell University. The base of the support structure is marked incrementally to allow for time based observations of changes in scour depth. Bed form topologies are then acquired after a three hour time interval using a 2D sediment bed profiler. Experimental results show that scour rate is dependent on flow speed. Additionally, an increase in scour hole size occurs as the scour conditions are varied from transitional to live-bed.
Rhombic micro-displacement amplifier for piezoelectric actuator and its linear and hybrid model
NASA Astrophysics Data System (ADS)
Chen, Jinglong; Zhang, Chunlin; Xu, Minglong; Zi, Yanyang; Zhang, Xinong
2015-01-01
This paper proposes rhombic micro-displacement amplifier (RMDA) for piezoelectric actuator (PA). First, the geometric amplification relations are analyzed and linear model is built to analyze the mechanical and electrical properties of this amplifier. Next, the accurate modeling method of amplifier is studied for important application of precise servo control. The classical Preisach model (CPM) is generally implemented using a numerical technique based on the first-order reversal curves (FORCs). The accuracy of CPM mainly depends on the number of FORCs. However, it is generally difficult to achieve enough number of FORCs in practice. So, Support Vector Machine (SVM) is employed in the work to circumvent the deficiency of the CPM. Then the hybrid model, which is based on discrete CPM and SVM is developed to account for hysteresis and dynamic effects. Finally, experimental validation is carried out. The analyzed result shows that this amplifier with the hybrid model is suitable for control application.
Zhou, Miaolei; Zhang, Qi; Wang, Jingyuan
2014-01-01
As a new type of smart material, magnetic shape memory alloy has the advantages of a fast response frequency and outstanding strain capability in the field of microdrive and microposition actuators. The hysteresis nonlinearity in magnetic shape memory alloy actuators, however, limits system performance and further application. Here we propose a feedforward-feedback hybrid control method to improve control precision and mitigate the effects of the hysteresis nonlinearity of magnetic shape memory alloy actuators. First, hysteresis nonlinearity compensation for the magnetic shape memory alloy actuator is implemented by establishing a feedforward controller which is an inverse hysteresis model based on Krasnosel'skii-Pokrovskii operator. Secondly, the paper employs the classical Proportion Integration Differentiation feedback control with feedforward control to comprise the hybrid control system, and for further enhancing the adaptive performance of the system and improving the control accuracy, the Radial Basis Function neural network self-tuning Proportion Integration Differentiation feedback control replaces the classical Proportion Integration Differentiation feedback control. Utilizing self-learning ability of the Radial Basis Function neural network obtains Jacobian information of magnetic shape memory alloy actuator for the on-line adjustment of parameters in Proportion Integration Differentiation controller. Finally, simulation results show that the hybrid control method proposed in this paper can greatly improve the control precision of magnetic shape memory alloy actuator and the maximum tracking error is reduced from 1.1% in the open-loop system to 0.43% in the hybrid control system. PMID:24828010
Magnetocentrifugally driven flows from young stars and disks. 1: A generalized model
NASA Astrophysics Data System (ADS)
Shu, Frank; Najita, Joan; Ostriker, Eve; Wilkin, Frank; Ruden, Steven; Lizano, Susana
1994-07-01
We propose a generalized model for stellar spin-down, disk accretion, and truncation, and the origin of winds, jets, and bipolar outflows from young stellar objects. We consider the steady state dynamics of accretion of matter from a viscous and imperfectly conducting disk onto a young star with a strong magnetic field. For an aligned stellar magnetosphere, shielding currents in the surface layers of the disk prevent stellar field lines from penetrating the disk everywhere except for a range of radii about pi = Rx, where the Keplerian angular speed of rotation Omegax equals the angular speed of the star Omega*. For the low disk accretion rates and high magnetic fields associated with typical T Tauri stars, Rx exceeds the radius of the star R* by a factor of a few, and the inner disk is effectively truncated at a radius Rt somewhat smaller than Rx. Where the closed field lines between Rt and Rx bow sufficiently inward, the accreting gas attaches itself to the field and is funneled dynamically down the effective potential (gravitational plus centrifugal) onto the star. Contrary to common belief, the accompanying magnetic torques associated with this accreting gas may transfer angular momentum mostly to the disk rather than to the star. Thus, the star can spin slowly as long as Rx remains significantly greater than R*. Exterior to Rx field lines threading the disk bow outward, which makes the gas off the mid-plane rotate at super-Keplerian velocities. This combination drives a magnetocentrifugal wind with a mass-loss rate Mw equal to a definite fraction f of the disk accretion rate MD. For high disk accretion rates, Rx is forced down to the stellar surface, the star is spun to breakup, and the wind is generated in a manner identical to that proposed by Shu, Lizano, Ruden, & Najita in a previous communication to this journal. In two companion papers (II and III), we develop a detailed but idealized theory of the magnetocentrifugal acceleration process.
An alternative model for the origin of gaps in circumstellar disks
NASA Astrophysics Data System (ADS)
Vorobyov, Eduard I.; Regaly, Zsolt; Guedel, Manuel; Lin, Doug N. C.
2016-03-01
Aims: Motivated by recent observational and numerical studies suggesting that collapsing protostellar cores may be replenished from the local environment, we explore the evolution of protostellar cores submerged in the external counter-rotating environment. These models predict the formation of counter-rotating disks with a deep gap in the gas surface density separating the inner disk (corotating with the star) and the outer counter-rotating disk. The properties of these gaps are compared to those of planet-bearing gaps that form in disks hosting giant planets. Methods: We employ numerical hydrodynamics simulations of collapsing cores that are replenished from the local counter-rotating environment and numerical hydrodynamics simulations of isolated disks hosting giant planets to derive the properties of the gaps that form in both cases. Results: Our numerical simulations demonstrate that counter-rotating disks can form for a wide range of mass and angular momentum available in the local environment. The gap that separates both disks has a substantial depletion factor, can be located at a distance from ten to over a hundred AU from the star, and can propagate inward with velocity ranging from 1 AU Myr-1 to >100 AU Myr-1. Unlike our previous conclusion, the gap can therefore be a long-lived phenomenon that is, in some case, comparable to the lifetime of the disk itself. For a proper choice of the planetary mass, the viscous α-parameter and disk mass, the planet-bearing gaps and gaps in counter-rotating disks may show a remarkable similarity in the gas density profile and depletion factor, which may complicate their observational differentiation.
Discrete sensing and actuation in a simulation model of frequency responsive loads
Nutaro, James J; Protopopescu, Vladimir A
2012-01-01
Loads acting autonomously on a local frequency signal can improve the response of a power system to sudden changes in supply, demand, or both. In this paper we address the use of load for regulating frequency by using feedback control. We extend prior research that focused on continuous proportional control, whereby one assumes that the load responds instantaneously, continuously, and in direct proportion to the changing frequency. However, sensors employed in any practical system have a finite sensitivity which introduces quantization effects into the control. As a result, a critical factor in the design of such a control is the relationship between the sensitivity of the sensor and the gain of the actuator. To study this issue, our model is constructed in two parts. The continuous dynamics of the power system is coupled to discrete event models of the sensors by state events that describe the detection points available to them. The quantized signals from the sensors are transformed by the actuators into discrete changes of load which, in turn, change the frequency and thereby complete the control loop. We illustrate the model with a scenario that involves a sudden, unanticipated change in load and the combined response of the control and power system to recover from the event.
An Analytic Model for the Success Rate of a Robotic Actuator System in Hitting Random Targets
Bradley, Stuart
2015-01-01
Autonomous robotic systems are increasingly being used in a wide range of applications such as precision agriculture, medicine, and the military. These systems have common features which often includes an action by an “actuator” interacting with a target. While simulations and measurements exist for the success rate of hitting targets by some systems, there is a dearth of analytic models which can give insight into, and guidance on optimization, of new robotic systems. The present paper develops a simple model for estimation of the success rate for hitting random targets from a moving platform. The model has two main dimensionless parameters: the ratio of actuator spacing to target diameter; and the ratio of platform distance moved (between actuator “firings”) to the target diameter. It is found that regions of parameter space having specified high success are described by simple equations, providing guidance on design. The role of a “cost function” is introduced which, when minimized, provides optimization of design, operating, and risk mitigation costs. PMID:26610500
Models of Be Star Disks Constrained by Long-baseline Interferometry
NASA Astrophysics Data System (ADS)
Tycner, Christopher; Jones, C. E.; Sigut, T. A.; Thomson, L.; Molak, A.
2006-12-01
We demonstrate how theoretical models of the circumstellar disks surrounding Be stars are constrained by interferometric observations that spatially resolve the circumstellar regions. The disk models are constructed using a non-LTE radiative transfer code developed by Sigut & Jones, which incorporates a number of improvements over previous treatments of the thermal structure, including a realistic chemical composition. We show that the disk models of three Be stars, κ Dra, υ Cyg, and β Psc agree with the interferometric observations only for particular ranges of the disk parameters, which results in specific density structure and temperature distribution constraints. C.T. acknowledges that this work was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Michelson Fellowship Program. JPL is managed for NASA by the California Institute of Technology. C. E. J. and T. A. A. S. acknowledge financial support from NSERC.
Using FU Orionis outbursts to constrain self-regulated protostellar disk models
NASA Technical Reports Server (NTRS)
Bell, K. R.; Lin, D. N. C.
1994-01-01
One-dimensional, convective, vertical structure models and one dimensional time-dependent, radial diffusion models are combined to create a self-consistent picture in which FU Orionis outbursts occur in young stellar objects (YSOs) as the result of a large-scale, self-regulated, thermal ionization instability in the surrounding protostellar accretion disk. Although active accretion disks have long been postulated to be ubiqitous among low-mass YSOs, few constraints have until now been imposed on physical conditions in these disks. By fitting the results of time-dependent disk models to observed timescales of FU Orionis events, we estimate the magnitude of the effective viscous stress in the inner disk (r approximately less than 1 AU) to be, in accordance with an ad hoc 'alpha' prescription, the product of the local sound speed, pressure scale height, and an efficiency factor alpha of 10(exp -4) where hydrogen is neutral and 10(exp 3) where hydrogen is ionized. We hypothesize that all YSOs receive infall onto their outer disks which is steady (or slowly declining with time) and that FU Orionis outbursts are self-regulated, disk outbursts which occur only in systems which transport matter inward at a rate sufficiently high to cause hydrogen to be ionized in the inner disk. We estimate a critical mass flux of dm(sub crit)/dt = 5 x 10(exp 7) solar mass/yr independent of the magnitude of alpha for systems with one solar mass, three solar radius central objects. Infall accretion rates in the range of dm(sub in)/dt = 1-10) x 10(exp -6) solar mass/yr produce observed FU Orionis timescales consistent with estimates of spherical molecular cloud core collapse rates. Modeled ionization fronts are typically initiated near the inner edge of the disk and propogate out to a distance of several tens of stellar radii. Beyond this region, the disk transports mass steadily inward at the supplied constant infall rate. Mass flowing through the innermost disk annulus is equal to dm
Theoretical modeling of pulse discharge cycle in dielectric barrier discharge plasma actuator
NASA Astrophysics Data System (ADS)
Sato, Shintaro; Ohnishi, Naofumi
2016-07-01
Simple models based on two-dimensional simulations are proposed to estimate intervals of periodically observed current pulses with a positive-going voltage in a dielectric barrier discharge plasma actuator. There are two distinct peaks in one streamer discharge; one is related to the formation of an ion cloud and the other is related to a filamentary discharge that is identified as a streamer. Simulation results show that the intervals of the current pulses depend on the slope of the applied voltage. For the ion-cloud formation phase, we model the time evolution of electron number density at the exposed electrode with ionization frequency. For the ion-cloud expansion phase, a positive ion cylinder model is proposed to estimate the electric field generated by surface charge on the dielectric. These models well reproduce the discharge intervals obtained in the numerical simulations.
Numerical investigation of airflow inside a 1-in hard disk drive
NASA Astrophysics Data System (ADS)
Suriadi, M. A.; Tan, C. S.; Zhang, Q. D.; Yip, T. H.; Sundaravadivelu, K.
2006-08-01
The increasing application of the hard disk drive in consumer electronic devices has pushed the usage of the small form factor hard drives. At the same time, the data storage industry continues to enhance the capacity and performance of computer hard disk drive. The concerns of track mis-registration caused by various runout still remain with the form factor change. The objective of the current study is to numerically investigate the airflow characteristic inside a 1 in hard disk drive. The simulation model is constructed based on the currently available 1-in micro-drive in the market, with 3600 rpm disk rotation speed, thus the flow Reynolds number based on the disk tip radius is around 4.8×10 3. Two models with different actuator arm positions (outside and middle-disk) were studied. The simulation results show that the standard k-epsilon model used allows us to extract similar information and understanding as that from more developed numerical model. Good agreement in normalized velocity magnitude and flow pattern is observed between the numerical and experimental results. At different actuator arm positions, streamlines and velocity vectors plots show the effect of the actuator arm position to the flow pattern, especially around the arm. This arm position also affects the radial and tangential shear stress values over the disk, which may help to estimate the wind loss and power consumption.
NASA Technical Reports Server (NTRS)
Allan, Brian G.
2000-01-01
A reduced order modeling approach of the Navier-Stokes equations is presented for the design of a distributed optimal feedback kernel. This approach is based oil a Krylov subspace method where significant modes of the flow are captured in the model This model is then used in all optimal feedback control design where sensing and actuation is performed oil tile entire flow field. This control design approach yields all optimal feedback kernel which provides insight into the placement of sensors and actuators in the flow field. As all evaluation of this approach, a two-dimensional shear layer and driven cavity flow are investigated.
Samadi, B; Achiche, S; Parent, A; Ballaz, L; Chouinard, U; Raison, M
2016-11-01
The use of exoskeletons as an aid for people with musculoskeletal disorder is the subject to an increasing interest in the research community. These devices are expected to meet the specific needs of users, such as children with cerebral palsy (CP) who are considered a significant population in pediatric rehabilitation. Although these exoskeletons should be designed to ease the movement of people with physical shortcoming, their design is generally based on data obtained from healthy adults, which leads to oversized components that are inadequate to the targeted users. Consequently, the objective of this study is to custom-size the lower limb exoskeleton actuators based on dynamic modeling of the human body for children with CP on the basis of hip, knee, and ankle joint kinematics and dynamics of human body during gait. For this purpose, a multibody modeling of the human body of 3 typically developed children (TD) and 3 children with CP is used. The results show significant differences in gait patterns especially in knee and ankle with respectively 0.39 and -0.33 (Nm/kg) maximum torque differences between TD children and children with CP. This study provides the recommendations to support the design of actuators to normalize the movement of children with CP. PMID:26980164
MODELING THE RESOLVED DISK AROUND THE CLASS 0 PROTOSTAR L1527
Tobin, John J.; Hartmann, Lee; Calvet, Nuria; Chiang, Hsin-Fang; Looney, Leslie W.; Wilner, David J.; Loinard, Laurent; D'Alessio, Paola
2013-07-01
We present high-resolution sub/millimeter interferometric imaging of the Class 0 protostar L1527 IRS (IRAS 04368+2557) at {lambda} = 870 {mu}m and 3.4 mm from the Submillimeter Array and Combined Array for Research in Millimeter Astronomy. We detect the signature of an edge-on disk surrounding the protostar with an observed diameter of 180 AU in the sub/millimeter images. The mass of the disk is estimated to be 0.007 M{sub Sun }, assuming optically thin, isothermal dust emission. The millimeter spectral index is observed to be quite shallow at all the spatial scales probed: {alpha} {approx} 2, implying a dust opacity spectral index {beta} {approx} 0. We model the emission from the disk and surrounding envelope using Monte Carlo radiative transfer codes, simultaneously fitting the sub/millimeter visibility amplitudes, sub/millimeter images, resolved L' image, spectral energy distribution, and mid-infrared spectrum. The best-fitting model has a disk radius of R = 125 AU, is highly flared (H{proportional_to}R {sup 1.3}), has a radial density profile {rho}{proportional_to}R {sup -2.5}, and has a mass of 0.0075 M{sub Sun }. The scale height at 100 AU is 48 AU, about a factor of two greater than vertical hydrostatic equilibrium. The resolved millimeter observations indicate that disks may grow rapidly throughout the Class 0 phase. The mass and radius of the young disk around L1527 are comparable to disks around pre-main-sequence stars; however, the disk is considerably more vertically extended, possibly due to a combination of lower protostellar mass, infall onto the disk upper layers, and little settling of {approx}1 {mu}m-sized dust grains.
1/f Fluctuation and a Many-Body Disk Model of Slip Phenomena
NASA Astrophysics Data System (ADS)
Hirata, Takayuki
1999-10-01
A many-body disk system was investigated as a model of slip phenomena. A two-dimensional many-body disk system was used as a model of the boundary layer between slip surfaces. Frustrated states occurred in this system depending on the disk configuration. Experiments with this were carried out using a random packing configuration (packing fraction: 0.74 ˜0.76). Acrylic resin disks were packed between a co-axial outer rotating cylinder and an inner fixed cylinder. The outer cylinder was rotated by a motor and the torque at the fixed inner cylinder was measured in a time series. Stick-slip and 1/f fluctuation were observed in the time series.
Hydrodynamic Models of Line-Driven Accretion Disk Winds III: Local Ionization Equilibrium
NASA Technical Reports Server (NTRS)
Pereyra, Nicolas Antonio; Kallman, Timothy R.; White, Nicholas E. (Technical Monitor)
2002-01-01
We present time-dependent numerical hydrodynamic models of line-driven accretion disk winds in cataclysmic variable systems and calculate wind mass-loss rates and terminal velocities. The models are 2.5-dimensional, include an energy balance condition with radiative heating and cooling processes, and includes local ionization equilibrium introducing time dependence and spatial dependence on the line radiation force parameters. The radiation field is assumed to originate in an optically thick accretion disk. Wind ion populations are calculated under the assumption that local ionization equilibrium is determined by photoionization and radiative recombination, similar to a photoionized nebula. We find a steady wind flowing from the accretion disk. Radiative heating tends to maintain the temperature in the higher density wind regions near the disk surface, rather than cooling adiabatically. For a disk luminosity L (sub disk) = solar luminosity, white dwarf mass M(sub wd) = 0.6 solar mass, and white dwarf radii R(sub wd) = 0.01 solar radius, we obtain a wind mass-loss rate of M(sub wind) = 4 x 10(exp -12) solar mass yr(exp -1) and a terminal velocity of approximately 3000 km per second. These results confirm the general velocity and density structures found in our earlier constant ionization equilibrium adiabatic CV wind models. Further we establish here 2.5D numerical models that can be extended to QSO/AGN winds where the local ionization equilibrium will play a crucial role in the overall dynamics.
Observations and models of deuterated H3+ in proto-planetary disks.
Ceccarelli, Cecilia; Dominik, Carsten
2006-11-15
Young, gas-rich proto-planetary disks orbiting around solar-type young stars represent a crucial phase in disk evolution and planetary formation. Of particular relevance is to observationally track the evolution of the gas, which governs the overall evolution of the disk and is eventually dispersed. However, the bulk of the mass resides in the plane, which is so cold and dense that virtually all heavy-element-bearing molecules freeze out onto the dust grains and disappear from the gas phase. In this paper, we show that the ground-state ortho-H2D+ transition is the best, if not the only, tracer of the disk-plane gas. We report the theoretical models of the chemical structure of the plane of the disk, where the deuterated forms of H3+, including H2D+, play a major role. We also compare the theoretical predictions with the observations obtained towards the disk of the young star DM Tau and show that the ionization rate is probably enhanced there, perhaps owing to the penetration of X-rays from the central object through the disk plane. We conclude by remarking that the ground-state ortho-H2D+ transition is such a powerful diagnostic that it may also reveal the matter in the dark halos of external galaxies, if it is hidden in cold, dense and small clouds, as several theories predict. PMID:17015395
NASA Astrophysics Data System (ADS)
Bouda, Vaclav; Boudova, Lea; Haluzikova, Denisa
2005-05-01
The aim of the presentation is to propose an alternative model of mammalian skeletal muscle function, which reflects the simplicity of nature and can be applied in engineering. Van der Waals attractive and repulsive electrostatic forces are assumed to control the design of internal structures and functions of contractile units of the muscles - sarcomere. The role of myosin heads is crucial for the higher order formation. The model of the myosin head lattice is the working model for the sarcomere contraction interpretation. The contraction is interpreted as a calcium induced phase transition of the lattice, which results in relative actin-myosin sliding and/or force generation. The model should provide the engineering science with a simple analogy to technical actuators of high performance.
A Flight Dynamics Model for a Multi-Actuated Flexible Rocket Vehicle
NASA Technical Reports Server (NTRS)
Orr, Jeb S.
2011-01-01
A comprehensive set of motion equations for a multi-actuated flight vehicle is presented. The dynamics are derived from a vector approach that generalizes the classical linear perturbation equations for flexible launch vehicles into a coupled three-dimensional model. The effects of nozzle and aerosurface inertial coupling, sloshing propellant, and elasticity are incorporated without restrictions on the position, orientation, or number of model elements. The present formulation is well suited to matrix implementation for large-scale linear stability and sensitivity analysis and is also shown to be extensible to nonlinear time-domain simulation through the application of a special form of Lagrange s equations in quasi-coordinates. The model is validated through frequency-domain response comparison with a high-fidelity planar implementation.
MODELING THE HD 32297 DEBRIS DISK WITH FAR-INFRARED HERSCHEL DATA
Donaldson, J. K.; Lebreton, J.; Augereau, J.-C.; Krivov, A. V.
2013-07-20
HD 32297 is a young A-star ({approx}30 Myr) 112 pc away with a bright edge-on debris disk that has been resolved in scattered light. We observed the HD 32297 debris disk in the far-infrared and sub-millimeter with the Herschel Space Observatory PACS and SPIRE instruments, populating the spectral energy distribution (SED) from 63 to 500 {mu}m. We aimed to determine the composition of dust grains in the HD 32297 disk through SED modeling, using geometrical constraints from the resolved imaging to break the degeneracies inherent in SED modeling. We found the best fitting SED model has two components: an outer ring centered around 110 AU, seen in the scattered light images, and an inner disk near the habitable zone of the star. The outer disk appears to be composed of grains >2 {mu}m consisting of silicates, carbonaceous material, and water ice with an abundance ratio of 1:2:3 respectively and 90% porosity. These grains appear consistent with cometary grains, implying the underlying planetesimal population is dominated by comet-like bodies. We also discuss the 3.7{sigma} detection of [C II] emission at 158 {mu}m with the Herschel PACS instrument, making HD 32297 one of only a handful of debris disks with circumstellar gas detected.
Modeling the HD 32297 Debris Disk With Far-Infrared Herschel Data
NASA Technical Reports Server (NTRS)
Donaldson, J.K.; Lebreton, J.; Roberge, A.; Augereau, J.-C.; Krivov, A. V.
2013-01-01
HD 32297 is a young A-star (approx. 30 Myr) 112 pc away with a bright edge-on debris disk that has been resolved in scattered light. We observed the HD 32297 debris disk in the far-infrared and sub-millimeter with the Herschel Space Observatory PACS and SPIRE instruments, populating the spectral energy distribution (SED) from 63 to 500 micron..We aimed to determine the composition of dust grains in the HD 32297 disk through SED modeling, using geometrical constraints from the resolved imaging to break the degeneracies inherent in SED modeling. We found the best fitting SED model has two components: an outer ring centered around 110 AU, seen in the scattered light images, and an inner disk near the habitable zone of the star. The outer disk appears to be composed of grains>2 micron consisting of silicates, carbonaceous material, and water ice with an abundance ratio of 1:2:3 respectively and 90% porosity. These grains appear consistent with cometary grains, implying the underlying planetesimal population is dominated by comet-like bodies. We also discuss the 3.7 sigma detection of [C ii] emission at 158 micron with the Herschel PACS instrument, making HD 32297 one of only a handful of debris disks with circumstellar gas detected
HERSCHEL PACS OBSERVATIONS AND MODELING OF DEBRIS DISKS IN THE TUCANA-HOROLOGIUM ASSOCIATION
Donaldson, J. K.; Roberge, A.; Chen, C. H.; Augereau, J.-C.; Menard, F.; Eiroa, C.; Meeus, G.; Krivov, A. V.; Mathews, G. S.; Riviere-Marichalar, P.; Sandell, G.
2012-07-10
We present Herschel PACS photometry of 17 B- to M-type stars in the 30 Myr old Tucana-Horologium Association. This work is part of the Herschel Open Time Key Programme 'Gas in Protoplanetary Systems'. 6 of the 17 targets were found to have infrared excesses significantly greater than the expected stellar IR fluxes, including a previously unknown disk around HD30051. These six debris disks were fitted with single-temperature blackbody models to estimate the temperatures and abundances of the dust in the systems. For the five stars that show excess emission in the Herschel PACS photometry and also have Spitzer IRS spectra, we fit the data with models of optically thin debris disks with realistic grain properties in order to better estimate the disk parameters. The model is determined by a set of six parameters: surface density index, grain size distribution index, minimum and maximum grain sizes, and the inner and outer radii of the disk. The best-fitting parameters give us constraints on the geometry of the dust in these systems, as well as lower limits to the total dust masses. The HD105 disk was further constrained by fitting marginally resolved PACS 70 {mu}m imaging.
Determining the optimal smoothing length scale for actuator line models of wind turbine blades
NASA Astrophysics Data System (ADS)
Martinez, Luis; Meneveau, Charles
2015-11-01
The actuator line model (ALM) is a widely used tool for simulating wind turbines when performing Large-Eddy Simulations. The ALM uses a smearing kernel ηɛ = 1 /ɛ3π 3 / 2 exp (-r2 /ɛ2) , where r is the distance to an actuator point, and ɛ is the smoothing length scale which establishes the kernel width, to project the lift and drag forces onto the grid. In this work, we develop formulations to establish the optimum value of the smoothing length scale ɛ, based on physical arguments, instead of purely numerical constraints. This parameter has a very important role in the ALM, to provide a length scale, which may, for example, be related to the chord of the airfoil being studied. In the proposed approach, we compare features (such as vertical pressure gradient) of a potential flow solution for flow over a lifting surface with features of the solution of the Euler equations with a body force term. The potential flow solution over a lifting surface is used as a general representation of an airfoil. The method presented aims to minimize the difference between these features of the flow fields as a function of the smearing length scale (ɛ), in order to obtain the optimum value. This work is supported by NSF (IGERT and IIA-1243482) and computations use XSEDE resources.
Two-spring model for active compression textiles with integrated NiTi coil actuators
NASA Astrophysics Data System (ADS)
Holschuh, B.; Newman, D.
2015-03-01
This paper describes the development and implementation of a two-spring model to predict the performance of hybrid compression textiles combining passive elastic fabrics and integrated NiTi shape memory alloy (SMA) coil actuators. An analytic model that treats passive fabric-SMA coil systems as conjoined linear springs is presented to predict garment passive and active counter-pressure as a function of 11 design variables. For a fixed SMA coil design (encompassing five design variables), the model predicts that passive fabric material modulus, initial length, width and thickness determine both passive counter-pressure magnitude and activation stroke length, and that passive and active pressures are highly dependent on the relative unstretched lengths of the conjoined SMA-fabric system compared to the total limb circumference. Several passive fabrics were tested to determine their moduli and to generally assess the fabric linearity model assumption: two fabrics (spandex and neoprene) were found to behave linearly up to 200% strain, while two other fabrics (flat polyester elastic and a tri-laminate Lycra) were found to be nonlinear in the same strain envelope. Five hypothetical compression tourniquet designs are presented using experimentally determined fabric characteristics and previously studied SMA actuators developed at MIT. The performance of each tourniquet design is discussed with a specific focus on mechanical counter-pressure (MCP) space suit design requirements, with designs presented that achieve the full MCP design specification (\\gt 29.6 kPa) while minimizing (\\lt 5 mm) garment thickness. The modeling framework developed in this effort enables compression garment designers to tailor counter-pressure and activation stroke properties of active compression garments based on a variety of design parameters to meet a wide range of performance specifications.
Modeling of end-pumped Yb:YAG thin-disk lasers with nonuniform temperature distribution.
Zhu, Guangzhi; Zhu, Xiao; Zhu, Changhong; Shang, Jianli; Wan, Hailin; Guo, Fei; Qi, Lijun
2012-05-10
A plane wave model with nonuniform temperature distribution in the thin-disk crystal is developed to describe the dynamic behavior of an end-pumped Yb:YAG thin-disk laser. A set of couple-rate equations and 2D stationary heat-conduction equations are derived. The stable temperature distribution in the disk crystal is calculated using a numerical iterative method. The analytic expression is capable of dealing with more practical laser systems than previous works on this subject as it allows for nonuniform temperature distribution in the disk crystal. Based on these results, we examined laser output intensity as a function of pump intensity, dopant concentration, resonator coupler reflectivity, crystal thickness and temperature of cooling liquid. PMID:22614469
Dong Ruobing; Rafikov, Roman; Zhu Zhaohuan; Brandt, Timothy; Hashimoto, Jun; Whitney, Barbara; Kudo, Tomoyuki; Egner, S.; Guyon, O.; Hayano, Y.; Muto, Takayuki; McClure, Melissa K.; Wisniewski, John; Abe, L.; Brandner, W.; Feldt, M.; Goto, M.; Carson, J.; Grady, C.; Hayashi, M.; and others
2012-12-01
Through detailed radiative transfer modeling, we present a disk+cavity model to simultaneously explain both the spectral energy distribution (SED) and Subaru H-band polarized light imaging for the pre-transitional protoplanetary disk PDS 70. In particular, we are able to match not only the radial dependence but also the absolute scale of the surface brightness of the scattered light. Our disk model has a cavity 65 AU in radius, which is heavily depleted of sub-micron-sized dust grains, and a small residual inner disk that produces a weak but still optically thick near-IR excess in the SED. To explain the contrast of the cavity's edge in the Subaru image, a factor of {approx}1000 depletion for the sub-micron-sized dust inside the cavity is required. The total dust mass of the disk may be on the order of 10{sup -4} M {sub Sun }, only weakly constrained due to the lack of long-wavelength observations and the uncertainties in the dust model. The scale height of the sub-micron-sized dust is {approx}6 AU at the cavity edge, and the cavity wall is optically thick in the vertical direction at H-band. PDS 70 is not a member of the class of (pre-)transitional disks identified by Dong et al., whose members only show evidence of the cavity in the millimeter-size dust but not the sub-micron-sized dust in resolved images. The two classes of (pre-)transitional disks may form through different mechanisms, or they may simply be at different evolution stages in the disk-clearing process.
Computational design and multiscale modeling of a nanoactuator using DNA actuation.
Hamdi, Mustapha
2009-12-01
Developments in the field of nanobiodevices coupling nanostructures and biological components are of great interest in medical nanorobotics. As the fundamentals of bio/non-bio interaction processes are still poorly understood in the design of these devices, design tools and multiscale dynamics modeling approaches are necessary at the fabrication pre-project stage. This paper proposes a new concept of optimized carbon nanotube based servomotor design for drug delivery and biomolecular transport applications. The design of an encapsulated DNA-multi-walled carbon nanotube actuator is prototyped using multiscale modeling. The system is parametrized by using a quantum level approach and characterized by using a molecular dynamics simulation. Based on the analysis of the simulation results, a servo nanoactuator using ionic current feedback is simulated and analyzed for application as a drug delivery carrier. PMID:19880974
A model of an X-ray-illuminated accretion disk and corona
NASA Technical Reports Server (NTRS)
Raymond, John C.
1993-01-01
The X-ray-illuminated surface of the accretion disk in a low-mass X-ray Binary (LMXRB) and the X-ray-heated corona above the disk produce optical, UV, and soft X-ray emission lines. This paper presents 1D models of the emission line spectra and the vertical temperature and density structures at different radii. The models include a detailed treatment of the important atomic processes and an escape probability treatment of radiative transfer. Soker and Raymond (1993) use the density structure predicted by these models for a 2D Monte Carlo simulation of the photon scattering in the accretion disk corona (ADC) to examine the effects of the ADC on the angular distribution of X-rays and the flux of X-rays incident on the outer disk. This paper concentrates on the emission line fluxes for various elemental abundances and disk parameters. The UV lines of the classic LMXRBs are consistent with the model predictions. Some CNO processing is necessary to account for the nitrogen and helium abundances in Sco X-1 and other LMXRBs. Comparison of the models with observed spectra also points to a soft X-ray component with luminosity comparable to the hard X-rays. The models predict a substantial luminosity in the group of highly ionized iron lines near 100 A.
The Disk Wind Model and the Effect on the Virial Black Hole Mass Estimation
NASA Astrophysics Data System (ADS)
Yong, Suk Yee
2015-09-01
The current 'standard quasar model' consists of a central engine, accretion disk, and jet. However, these components cannot entirely explain some quasar spectral features, specifically, the presence of broad emission lines (BELs), which are assumed to originate from high velocity gas in the broad line region (BLR). The addition of a wind to the standard model provides a mechanism to drive the outflowing gas emanated from the accretion disk. The shape of the emission line profiles in the BLR, in particular, the velocity offsets and skewness for different viewing angles, are explored. The impact on the virial black hole mass calculation due to the quasar's orientation to the observer is also tested. The geometry of the BLR is modelled by implementing the wind component or the disk wind model. While the models are dependent on the specified parameters, they are able to qualitatively reproduce the predicted features of the emission lines.
GLOBAL SIMULATIONS OF ACCRETION DISKS. I. CONVERGENCE AND COMPARISONS WITH LOCAL MODELS
Sorathia, Kareem A.; Reynolds, Christopher S.; Stone, James M.; Beckwith, Kris
2012-04-20
Grid-based magnetohydrodynamic (MHD) simulations have proven invaluable for the study of astrophysical accretion disks. However, the fact that angular momentum transport in disks is mediated by MHD turbulence (with structure down to very small scales) raises the concern that the properties of the modeled accretion disks are affected by the finite numerical resolution of the simulation. By implementing an orbital advection algorithm into the Athena code in cylindrical geometry, we have performed a set of global (but unstratified) Newtonian disk simulations extending up to resolutions previously unattained. We study the convergence of these models as a function of spatial resolution and initial magnetic field geometry. The usual viscosity parameter ({alpha}) or the ratio of thermal-to-magnetic pressure ({beta}) is found to be a poor diagnostic of convergence, whereas the average tilt angle of the magnetic field in the (r, {phi})-plane is a very good diagnostic of convergence. We suggest that this is related to the saturation of the MHD turbulence via parasitic modes of the magnetorotational instability. Even in the case of zero-net magnetic flux, we conclude that our highest resolution simulations (with 32 zones and 64 zones per vertical scale height) have achieved convergence. Our global simulations reach resolutions comparable to those used in local, shearing-box models of MHD disk turbulence. We find that the saturation predictors derived from local simulations correspond well to the instantaneous correlations between local flux and stress found in our global simulations. However, the conservation of magnetic flux implicit in local models is not realized in our global disks. Thus, the magnetic connectivity of an accretion disk represents physics that is truly global and cannot be captured in any ab initio local model.
SMACK: A New Algorithm for Modeling Collisions and Dynamics of Planetesimals in Debris Disks
NASA Technical Reports Server (NTRS)
Nesvold, Erika Rose; Kuchner, Marc J.; Rein, Hanno; Pan, Margaret
2013-01-01
We present the Superparticle Model/Algorithm for Collisions in Kuiper belts and debris disks (SMACK), a new method for simultaneously modeling, in 3-D, the collisional and dynamical evolution of planetesimals in a debris disk with planets. SMACK can simulate azimuthal asymmetries and how these asymmetries evolve over time. We show that SMACK is stable to numerical viscosity and numerical heating over 10(exp 7) yr, and that it can reproduce analytic models of disk evolution. We use SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit. Differential precession creates a spiral structure as the ring evolves, but collisions subsequently break up the spiral, leaving a narrower eccentric ring.
NASA Astrophysics Data System (ADS)
Lebreton, J.; van Lieshout, R.; Augereau, J.-C.; Absil, O.; Mennesson, B.; Kama, M.; Dominik, C.; Bonsor, A.; Vandeportal, J.; Beust, H.; Defrère, D.; Ertel, S.; Faramaz, V.; Hinz, P.; Kral, Q.; Lagrange, A.-M.; Liu, W.; Thébault, P.
2013-07-01
Context. Debris disks are thought to be extrasolar analogs to the solar system planetesimal belts. The star Fomalhaut harbors a cold debris belt at 140 AU comparable to the Edgeworth-Kuiper belt, as well as evidence of a warm dust component, unresolved by single-dish telescopes, which is suspected of being a bright analog to the solar system's zodiacal dust. Aims: Interferometric observations obtained with the VLTI/VINCI instrument and the Keck Interferometer Nuller have identified near- and mid-infrared excesses attributed respectively to hot and warm exozodiacal dust residing in the inner few AU of the Fomalhaut environment. We aim to characterize the properties of this double inner dust belt and to unveil its origin. Methods: We performed parametric modeling of the exozodiacal disk ("exozodi") using the GRaTeR radiative transfer code to reproduce the interferometric data, complemented by mid- to far-infrared photometric measurements from Spitzer and Herschel. A detailed treatment of sublimation temperatures was introduced to explore the hot population at the size-dependent sublimation rim. We then used an analytical approach to successively testing several source mechanisms for the dust and suspected parent bodies. Results: A good fit to the multiwavelength data is found by two distinct dust populations: (1) a population of very small (0.01 to 0.5 μm), hence unbound, hot dust grains confined in a narrow region (~0.1-0.3 AU) at the sublimation rim of carbonaceous material; (2) a population of bound grains at ~2 AU that is protected from sublimation and has a higher mass despite its fainter flux level. We propose that the hot dust is produced by the release of small carbon grains following the disruption of dust aggregates that originate in the warm component. A mechanism, such as gas braking, is required to further confine the small grains for a long enough time. In situ dust production could hardly be ensured for the age of the star, so we conclude that the
NASA Technical Reports Server (NTRS)
Holland, Scott D.
1994-01-01
The present study examines the wind-tunnel blockage and actuation systems effectiveness in starting and forcibly unstarting a two-dimensional scramjet inlet in the NASA Langley 20-Inch Mach 6 Tunnel. The intent of the overall test program is to study (both experimentally and computationally) the dynamics of the inlet unstart; however, prior to the design and fabrication of an expensive, instrumented wind-tunnel model, it was deemed necessary first to examine potential wind-tunnel blockage issues related to model sizing and to examine the adequacy of the actuation systems in accomplishing the start and unstart. The model is equipped with both a moveable cowl and aft plug. Windows in the inlet sidewalls allow limited optical access to the internal shock structure; schlieren video was used to identify inlet start and unstart. A chronology of each actuation sequence is provided in tabular form along with still frames from the schlieren video. A pitot probe monitored the freestream conditions throughout the start/unstart process to determine if there was a blockage effect due to the model start or unstart. Because the purpose of this report is to make the phase I (blockage and actuation systems) data rapidly available to the community, the data is presented largely without analysis of the internal shock interactions or the unstart process. This series of tests indicated that the model was appropriately sized for this facility and identified operability limits required first to allow the inlet to start and second to force the unstart.
Quasi-static model of collimated jets and radio lobes. I. Accretion disk and jets
Colgate, Stirling A.; Li, Hui; Fowler, T. Kenneth; Pino, Jesse
2014-07-10
This is the first of a series of papers showing that when an efficient dynamo can be maintained by accretion disks around supermassive black holes in active galactic nuclei, it can lead to the formation of a powerful, magnetic helix that could explain both the observed radio jet/lobe structures on very large scales and ultimately the enormous power inferred from the observed ultra-high-energy cosmic rays. In this work, we solve a set of one-dimensional equations similar to the steady-state standard accretion disk model, but now including the large-scale magnetic fields giving rises to jets. We find that the frequently made assumption that large-scale fields are frozen into the disk is fundamentally incorrect, due to the necessity for current and the accreting mass to flow perpendicular to magnetic flux surfaces. A correct treatment greatly simplifies the calculations, yielding fields that leave the disk nearly vertically with magnetic profiles uniquely determined by disk angular momentum conservation. Representative solutions of the magnetic fields in different radial regions of the disk surface are given, and they determine the overall key features in the jet structure and its dissipation, which will be the subjects of later papers.
Model predictive driving simulator motion cueing algorithm with actuator-based constraints
NASA Astrophysics Data System (ADS)
Garrett, Nikhil J. I.; Best, Matthew C.
2013-08-01
The simulator motion cueing problem has been considered extensively in the literature; approaches based on linear filtering and optimal control have been presented and shown to perform reasonably well. More recently, model predictive control (MPC) has been considered as a variant of the optimal control approach; MPC is perhaps an obvious candidate for motion cueing due to its ability to deal with constraints, in this case the platform workspace boundary. This paper presents an MPC-based cueing algorithm that, unlike other algorithms, uses the actuator positions and velocities as the constraints. The result is a cueing algorithm that can make better use of the platform workspace whilst ensuring that its bounds are never exceeded. The algorithm is shown to perform well against the classical cueing algorithm and an algorithm previously proposed by the authors, both in simulation and in tests with human drivers.
Kang, Rongjie; Branson, David T; Zheng, Tianjiang; Guglielmino, Emanuele; Caldwell, Darwin G
2013-09-01
Biological tentacles, such as octopus arms, have entirely flexible structures and virtually infinite degrees of freedom (DOF) that allow for elongation, shortening and bending at any point along the arm length. The amazing dexterity of biological tentacles has driven the growing implementation of continuum manipulators in robotic systems. This paper presents a pneumatic manipulator inspired by biological continuum structures in some of their key features and functions, such as continuum morphology, intrinsic compliance and stereotyped motions with hyper redundant DOF. The kinematics and dynamics of the manipulator are formulated and identified, and a hierarchical controller taking inspiration from the structure of an octopus nervous system is used to relate desired stereotyped motions to individual actuator inputs. Simulations and experiments are carried out to validate the model and prototype where good agreement was found between the two. PMID:23851387
Formulation, predictions, and sensitivity analysis of a pyrotechnically actuated pin puller model
Gonthier, K.A.; Powers, J.M.
1994-07-01
This article presents an analysis for pyrotechnic combustion and pin motion in the NASA Standard Initiator (NSI) actuated pin puller. The conservation principles and constitutive relations for a multiphase system are posed and reduced to a set of five ordinary differential equations which are solved to predict the system`s performance. The model tracks the interactions of the unreacted, incompressible solid pyrotechnic, incompressible condensed phase combustion products, and gas phase combustion products. Predicted pressure histories for the firing of an NSI into (1) the pin puller device, (2) a 10 cm(sup 3) closed vessel, and (3) an apparatus known as the Dynamic Test Device compare well with experimental results. A sensitivity analysis reveals large regions in parameter space where system performance is insensitive to particular parametric values; smaller regions of high sensitivity are also found. 15 refs.
NASA Astrophysics Data System (ADS)
Chaterjee, S.; Pohit, G.
2009-05-01
A comprehensive model of an electrostatically actuated microcantilever beam separated from the ground plane by relatively larger gap is formulated accounting for the nonlinearities of the system arising out of electric forces, geometry of the deflected beam and the inertial terms. Since the gap is relatively large, the electrostatic model is formulated incorporating higher order correction of electrostatic forces. First static analysis is carried out to match the results obtained from the proposed model with the results provided by other researchers. It is observed that reduced order model exhibits good convergence when five or more number of modes is considered for the analysis. Dynamic analysis of the model is performed with five modes. The study indicates that although electrostatic forces cause softening characteristics whereas geometric nonlinearity produces stiffening effect on the microstructure, the nonlinearities play a significant role when pull-in occurs. The consideration of slope and curvature of deformable electrode for modelling the electrostatic forces for large gap separations predicts more accurate results. For applications in and around pull-in zone, the large deflection model needs to be considered for effective design.
García, J.; Steiner, J. F.; McClintock, J. E.; Brenneman, L. E-mail: jsteiner@head.cfa.harvard.edu E-mail: lbrenneman@cfa.harvard.edu; and others
2014-02-20
X-ray reflection models are used to constrain the properties of the accretion disk, such as the degree of ionization of the gas and the elemental abundances. In combination with general relativistic ray tracing codes, additional parameters like the spin of the black hole and the inclination to the system can be determined. However, current reflection models used for such studies only provide angle-averaged solutions for the flux reflected at the surface of the disk. Moreover, the emission angle of the photons changes over the disk due to relativistic light bending. To overcome this simplification, we have constructed an angle-dependent reflection model with the XILLVER code and self-consistently connected it with the relativistic blurring code RELLINE. The new model, relxill, calculates the proper emission angle of the radiation at each point on the accretion disk and then takes the corresponding reflection spectrum into account. We show that the reflected spectra from illuminated disks follow a limb-brightening law highly dependent on the ionization of disk and yet different from the commonly assumed form I∝ln (1 + 1/μ). A detailed comparison with the angle-averaged model is carried out in order to determine the bias in the parameters obtained by fitting a typical relativistic reflection spectrum. These simulations reveal that although the spin and inclination are mildly affected, the Fe abundance can be overestimated by up to a factor of two when derived from angle-averaged models. The fit of the new model to the Suzaku observation of the Seyfert galaxy Ark 120 clearly shows a significant improvement in the constraint of the physical parameters, in particular by enhancing the accuracy in the inclination angle and the spin determinations.
SMACK: A NEW ALGORITHM FOR MODELING COLLISIONS AND DYNAMICS OF PLANETESIMALS IN DEBRIS DISKS
Nesvold, Erika R.; Kuchner, Marc J.; Pan, Margaret; Rein, Hanno E-mail: Marc.Kuchner@nasa.gov E-mail: rein@ias.edu
2013-11-10
We present the Superparticle-Method/Algorithm for Collisions in Kuiper belts and debris disks (SMACK), a new method for simultaneously modeling, in three dimensions, the collisional and dynamical evolution of planetesimals in a debris disk with planets. SMACK can simulate azimuthal asymmetries and how these asymmetries evolve over time. We show that SMACK is stable to numerical viscosity and numerical heating over 10{sup 7} yr and that it can reproduce analytic models of disk evolution. We use SMACK to model the evolution of a debris ring containing a planet on an eccentric orbit. Differential precession creates a spiral structure as the ring evolves, but collisions subsequently break up the spiral, leaving a narrower eccentric ring.
An Efficient Monte Carlo Method for Modeling Radiative Transfer in Protoplanetary Disks
NASA Technical Reports Server (NTRS)
Kim, Stacy
2011-01-01
Monte Carlo methods have been shown to be effective and versatile in modeling radiative transfer processes to calculate model temperature profiles for protoplanetary disks. Temperatures profiles are important for connecting physical structure to observation and for understanding the conditions for planet formation and migration. However, certain areas of the disk such as the optically thick disk interior are under-sampled, or are of particular interest such as the snow line (where water vapor condenses into ice) and the area surrounding a protoplanet. To improve the sampling, photon packets can be preferentially scattered and reemitted toward the preferred locations at the cost of weighting packet energies to conserve the average energy flux. Here I report on the weighting schemes developed, how they can be applied to various models, and how they affect simulation mechanics and results. We find that improvements in sampling do not always imply similar improvements in temperature accuracies and calculation speeds.
Effect of Synthetic Jet Actuator Spacing on the Performance Enhancement of a Vertical Tail Model
NASA Astrophysics Data System (ADS)
Monastero, Marianne; Rathay, Nicholas; Whalen, Edward; Amitay, Michael
2014-11-01
The use of synthetic-jet-based active flow control to augment the side force produced by vertical tail models through rudder separation control was experimentally investigated in the Rensselaer Polytechnic Institute Subsonic Wind Tunnel. Increasing the side force generated by the vertical tail may lead to a reduction in tail size and, therefore, less drag and fuel consumption. Stereo particle image velocimetry and aerodynamic load data were acquired with a focus on the effect of non-dimensional spacing between jets on the resulting flowfield and forces for a 1/19th scale model based on a Boeing 767 commercial airplane. For some rudder deflections, differing results with active flow control were found when force data for the 1/19th scale model were compared to force data obtained on a larger, 1/9th scale model. Actuator spacing was varied and individual jet momentum coefficient was held constant for these experiments. These results show the need for more fundamental testing to understand why jets are beneficial or detrimental to the augmented side force and how those effects scale-up. A new model was designed to enable a fundamental study of the effect on the flowfield of various jet and model parameters such as sweep angle, jets spacing, rudder chord extent, and rudder deflection.
Static and transient modeling of fast moving ball actuator as a display device
NASA Astrophysics Data System (ADS)
Lee, Jongmo; Yoon, Ho Won; Hong, MunPyo; Jhun, Chul Gyu; Bae, Byung Seong; Han, Seungoh
2016-04-01
FMBA(Fast Moving Ball Actuator), developed as novel electronic-paper display, has already proven its operability and functionality. However, optimization issues related with low operating voltage, high refresh rate, fine pixel and higher display resolution, etc. are still remaining to be improved for a successful commercialization. In order to optimize such issues effectively, static and transient model were developed and verified by comparing the calculated results to the measured. The static model is based on the force balancing equation between the driving and the holding forces while the transient model is developed from Newton's 2nd law by adding the inertia as well as the resistive damping forces caused by the surroundings. With the simplified static model, driving voltage of 30.71 V was obtained, which is reasonably matched to the measured voltage of 40 V. Based on the transient model, also, the transient response of the device can be estimated within reasonable margin. Considering the absence of reliable key parameters of surface roughness, static and dynamic frictional coefficient, and refractive indices, the developed static and transient models account well the experimental results and thus they are expected to contribute further improvements in FMBA.
MEMS Actuated Deformable Mirror
Papavasiliou, A; Olivier, S; Barbee, T; Walton, C; Cohn, M
2005-11-10
This ongoing work concerns the creation of a deformable mirror by the integration of MEMS actuators with Nanolaminate foils through metal compression boning. These mirrors will use the advantages of these disparate technologies to achieve dense actuation of a high-quality, continuous mirror surface. They will enable advanced adaptive optics systems in large terrestrial telescopes. While MEMS actuators provide very dense actuation with high precision they can not provide large forces typically necessary to deform conventional mirror surfaces. Nanolaminate foils can be fabricated with very high surface quality while their extraordinary mechanical properties enable very thin, flexible foils to survive the rigors of fabrication. Precise metal compression bonding allows the attachment of the fragile MEMS actuators to the thin nanolaminate foils without creating distortions at the bond sites. This paper will describe work in four major areas: (1) modeling and design, (2) bonding development, (3) nanolaminate foil development, (4) producing a prototype. A first-principles analytical model was created and used to determine the design parameters. A method of bonding was determined that is both strong, and minimizes the localized deformation or print through. Work has also been done to produce nanolaminate foils that are sufficiently thin, flexible and flat to be deformed by the MEMS actuators. Finally a prototype was produced by bonding thin, flexible nanolaminate foils to commercially available MEMS actuators.
NASA Astrophysics Data System (ADS)
Buoso, Stefano; Palacios, Rafael
2016-04-01
This work presents a numerical framework for the simulation and design of integrally actuated membrane wings with feedback control. The performance of the aeroelastic system are evaluated using a high-fidelity model. It consists in a fluid solver based on the direct numerical integration of the unsteady Navier-Stokes equations implicitly coupled with a geometrically non-linear dynamic structural model which has been calibrated using experimental data. The rate-dependent constitutive law for the dielectric elastomer considered for the integral wing actuation is based on a non-linear formulation. The framework also includes a methodology for the model reduction of the fully-coupled system. The resulting low-order description showed to retain the main system dynamics, and can therefore be used for the design of the control scheme for the wing. Results highlights the potential to achieve on-demand aerodynamics using the actuation concept proposed. In particular, it is shown that the wing aerodynamic performance is noticeably enhanced through the actuation and the disturbances on the lift in case of gusts can be reduced up to 60%.
Multi-scale/multi-physical modeling in head/disk interface of magnetic data storage
NASA Astrophysics Data System (ADS)
Chung, Pil Seung; Smith, Robert; Vemuri, Sesha Hari; Jhon, Young In; Tak, Kyungjae; Moon, Il; Biegler, Lorenz T.; Jhon, Myung S.
2012-04-01
The model integration of the head-disk interface (HDI) in the hard disk drive system, which includes the hierarchy of highly interactive layers (magnetic layer, carbon overcoat (COC), lubricant, and air bearing system (ABS)), has recently been focused upon to resolve technical barriers and enhance reliability. Heat-assisted magnetic recording especially demands that the model simultaneously incorporates thermal and mechanical phenomena by considering the enormous combinatorial cases of materials and multi-scale/multi-physical phenomena. In this paper, we explore multi-scale/multi-physical simulation methods for HDI, which will holistically integrate magnetic layers, COC, lubricants, and ABS in non-isothermal conditions.
RADIATIVE TRANSFER MODELS OF A POSSIBLE PLANET IN THE AB AURIGAE DISK
Jang-Condell, Hannah; Kuchner, Marc J.
2010-05-01
Recent coronagraphic imaging of the AB Aurigae disk has revealed a region of low polarized scattered light suggestive of perturbations from a planet at a radius of {approx}100 AU. We model this darkened region using our fully non-plane-parallel radiative-transfer code combined with a simple hydrostatic equilibrium approximation to self-consistently solve for the structure of the disk surface as seen in scattered light. By comparing the observations to our models, we find that the observations are consistent with the absence of a planet, with an upper limit of 1 M {sub J}.
Non-linear modelling and optimal control of a hydraulically actuated seismic isolator test rig
NASA Astrophysics Data System (ADS)
Pagano, Stefano; Russo, Riccardo; Strano, Salvatore; Terzo, Mario
2013-02-01
This paper investigates the modelling, parameter identification and control of an unidirectional hydraulically actuated seismic isolator test rig. The plant is characterized by non-linearities such as the valve dead zone and frictions. A non-linear model is derived and then employed for parameter identification. The results concerning the model validation are illustrated and they fully confirm the effectiveness of the proposed model. The testing procedure of the isolation systems is based on the definition of a target displacement time history of the sliding table and, consequently, the precision of the table positioning is of primary importance. In order to minimize the test rig tracking error, a suitable control system has to be adopted. The system non-linearities highly limit the performances of the classical linear control and a non-linear one is therefore adopted. The test rig mathematical model is employed for a non-linear control design that minimizes the error between the target table position and the current one. The controller synthesis is made by taking no specimen into account. The proposed approach consists of a non-linear optimal control based on the state-dependent Riccati equation (SDRE). Numerical simulations have been performed in order to evaluate the soundness of the designed control with and without the specimen under test. The results confirm that the performances of the proposed non-linear controller are not invalidated because of the presence of the specimen.
NASA Astrophysics Data System (ADS)
Martin, Robert David, Jr.
C-band scatterometer measurements were made of a tallgrass prairie in an attempt to determine the degree of correlation between (1) the backscattering coefficient (sigma_sp{rm tr}{ circ}) and different expressions of soil moisture and (2) the backscattering coefficient and various canopy parameters. The findings of this study support those made in previous studies in terms of the optimum polarization and view angle selection for soil moisture work (i.e., near-nadir view angles and HH and VV polarizations). In contrast to previous studies, view angles of 30 ^circ and 45^circ also produced strong correlations with soil moisture. A moderately strong correlation and partial correlation was found between sigma_sp{rm tr}{circ} and leaf water potential, indicating some capability of C-band measurements to detect extremes in the water status of prairie vegetation under shallow soil conditions. Also, site differences due to burn treatments appeared to cause significant differences in the sensitivity of sigma_sp{ rm tr}{circ} to soil moisture. In a second study, the disk model developed by Drs. Eom and Fung was tested against a set of field measurements of sigma_sp{rm tr} {circ} from a crop of sunflowers. The model overestimated sigma_sp{ rm tr}{circ} at early growth stages, but decreased the overestimate as the crop matured. The author modified the model to accommodate canopies with non-uniform, continuous leaf angle distributions. The modification altered the shape of the response curve for predicted sigma_sp{rm tr }{circ} versus view angle, but failed to reduce the overestimate in the early growth states. Additional modifications (e.g., incorporating row structure information) may be necessary. A new model, called the Projected Disk Component Model (PDCM), was developed to help explain the behavior of the modified disk model (MDM). By reducing several types of theoretical disk canopies to a simple, quantitative measure of their constituent horizontal and vertical
A semi-analytical model for exploring Galilean satellites formation from a massive disk
NASA Astrophysics Data System (ADS)
Miguel, Yamila; Ida, Shigeru
2016-03-01
A better knowledge of jovian satellites' origins will bring light on the environment that surrounded Jupiter during its formation and can help us to understand the characteristics of this unique satellite system. We developed a semi-analytical model to investigate Jupiter's regular satellite formation and present the results of our population synthesis calculations. We performed simulations adopting a massive, static, low-viscosity circumplanetary disk model, in agreement with a current study of magnetorotational instability in a circum-planetary disk. We find that the high gas density leads to very rapid migration of satellitesimals due to gas drag and type II migration of satellites in a faster disk-dominated mode. A large concentration of solids, large building blocks and longer type II migration time-scales favor formation and survival of large satellites. However, bodies as massive as Ganymede and those located far away from Jupiter, such as Callisto, are difficult to form with this scenario.
High-Contrast Near-Infrared Imaging and Modeling of Planets and Debris Disks
NASA Astrophysics Data System (ADS)
Rodigas, Timothy; Hinz, P.; Weinberger, A. J.; Close, L. M.; Debes, J. H.
2014-01-01
wavelength range. These images reveal the disk at unprecedented detail, allowing detailed compositional and morphological modeling of the dust.
Magnetocentrifugally driven flows from young stars and disks. 1: A generalized model
NASA Technical Reports Server (NTRS)
Shu, Frank; Najita, Joan; Ostriker, Eve; Wilkin, Frank; Ruden, Steven; Lizano, Susana
1994-01-01
We propose a generalized model for stellar spin-down, disk accretion, and truncation, and the origin of winds, jets, and bipolar outflows from young stellar objects. We consider the steady state dynamics of accretion of matter from a viscous and imperfectly conducting disk onto a young star with a strong magnetic field. For an aligned stellar magnetosphere, shielding currents in the surface layers of the disk prevent stellar field lines from penetrating the disk everywhere except for a range of radii about pi = R(sub x), where the Keplerian angular speed of rotation Omega(sub x) equals the angular speed of the star Omega(sub *). For the low disk accretion rates and high magnetic fields associated with typical T Tauri stars, R(sub x) exceeds the radius of the star R(sub *) by a factor of a few, and the inner disk is effectively truncated at a radius R(sub t) somewhat smaller than R(sub x). Where the closed field lines between R(sub t) and R(sub x) bow sufficiently inward, the accreting gas attaches itself to the field and is funneled dynamically down the effective potential (gravitational plus centrifugal) onto the star. Contrary to common belief, the accompanying magnetic torques associated with this accreting gas may transfer angular momentum mostly to the disk rather than to the star. Thus, the star can spin slowly as long as R(sub x) remains significantly greater than R(sub *). Exterior to R(sub x) field lines threading the disk bow outward, which makes the gas off the mid-plane rotate at super-Keplerian velocities. This combination drives a magnetocentrifugal wind with a mass-loss rate M(sub w) equal to a definite fraction f of the disk accretion rate M(sub D). For high disk accretion rates, R(sub x) is forced down to the stellar surface, the star is spun to breakup, and the wind is generated in a manner identical to that proposed by Shu, Lizano, Ruden, & Najita in a previous communication to this journal. In two companion papers (II and III), we develop a
... the disk. This may place pressure on nearby nerves or the spinal cord. ... Lumbar radiculopathy; Cervical radiculopathy; Herniated intervertebral disk; Prolapsed intervertebral disk; Slipped disk; Ruptured disk; Herniated nucleus pulposus
NASA Technical Reports Server (NTRS)
Narasimhan, Sriram; Roychoudhury, Indranil; Balaban, Edward; Saxena, Abhinav
2010-01-01
Model-based diagnosis typically uses analytical redundancy to compare predictions from a model against observations from the system being diagnosed. However this approach does not work very well when it is not feasible to create analytic relations describing all the observed data, e.g., for vibration data which is usually sampled at very high rates and requires very detailed finite element models to describe its behavior. In such cases, features (in time and frequency domains) that contain diagnostic information are extracted from the data. Since this is a computationally intensive process, it is not efficient to extract all the features all the time. In this paper we present an approach that combines the analytic model-based and feature-driven diagnosis approaches. The analytic approach is used to reduce the set of possible faults and then features are chosen to best distinguish among the remaining faults. We describe an implementation of this approach on the Flyable Electro-mechanical Actuator (FLEA) test bed.
NASA Astrophysics Data System (ADS)
Boz, Utku; Basdogan, Ipek
2015-12-01
Structural vibrations is a major cause for noise problems, discomfort and mechanical failures in aerospace, automotive and marine systems, which are mainly composed of plate-like structures. In order to reduce structural vibrations on these structures, active vibration control (AVC) is an effective approach. Adaptive filtering methodologies are preferred in AVC due to their ability to adjust themselves for varying dynamics of the structure during the operation. The filtered-X LMS (FXLMS) algorithm is a simple adaptive filtering algorithm widely implemented in active control applications. Proper implementation of FXLMS requires availability of a reference signal to mimic the disturbance and model of the dynamics between the control actuator and the error sensor, namely the secondary path. However, the controller output could interfere with the reference signal and the secondary path dynamics may change during the operation. This interference problem can be resolved by using an infinite impulse response (IIR) filter which considers feedback of the one or more previous control signals to the controller output and the changing secondary path dynamics can be updated using an online modeling technique. In this paper, IIR filtering based filtered-U LMS (FULMS) controller is combined with online secondary path modeling algorithm to suppress the vibrations of a plate-like structure. The results are validated through numerical and experimental studies. The results show that the FULMS with online secondary path modeling approach has more vibration rejection capabilities with higher convergence rate than the FXLMS counterpart.
Complete modeling of rotary ultrasonic motors actuated by traveling flexural waves
NASA Astrophysics Data System (ADS)
Bao, Xiaoqi; Bar-Cohen, Yoseph
2000-06-01
Ultrasonic rotary motors have the potential to meet this NASA need and they are developed as actuators for miniature telerobotic applications. These motors are being adapted for operation at the harsh space environments that include cryogenic temperatures and vacuum and analytical tools for the design of efficient motors are being developed. A hybrid analytical model was developed to address a complete ultrasonic motor as a system. Included in this model is the influence of the rotor dynamics, which was determined experimentally to be important to the motor performance. The analysis employs a 3D finite element model to express the dynamic characteristics of the stator with piezoelectric elements and the rotor. The details of the stator including the teeth, piezoelectric ceramic, geometry, bonding layer, etc. are included to support practical USM designs. A brush model is used for the interface layer and Coulomb's law for the friction between the stator and the rotor. The theoretical predictions were corroborated experimentally for the motor. In parallel, efforts have been made to determine the thermal and vacuum performance of these motors. To explore telerobotic applications for USMs a robotic arm was constructed with such motors.
NASA Astrophysics Data System (ADS)
Al-Taie, Fatimah; Werner, Herbert
2016-06-01
A technique for model reduction of exponentially stable spatially interconnected systems is presented, where the order of the reduced model is determined by the number of truncated small generalised singular values of the structured solutions to a pair of Lyapunov inequalities. For parameter-invariant spatially interconnected systems, the technique is based on solving a pair of Lyapunov inequalities in continuous-time and -space domain with a rank constraint. Using log-det and cone complementarity methods, an improved error bound can be obtained. The approach is extended to spatially parameter-varying systems, and a balanced truncation approach using parameter-dependent Gramians is proposed to reduce the conservatism caused by the use of constant Gramians. This is done by considering two important operators, which can be used to represent multidimensional systems (temporal- and spatial-linear parameter varying interconnected systems). The results are illustrated with their application to an experimentally identified spatially interconnected model of an actuated beam; the experimentally obtained response to an excitation signal is compared with the response predicted by a reduced model.
Accretion disk models for QSOs and active galactic nuclei - The role of magnetic viscosity
NASA Technical Reports Server (NTRS)
Sakimoto, P. J.; Coroniti, F. V.
1981-01-01
The inner regions of standard accretion disk models are known to be thermally unstable, and when scaled to quasar black hole masses, optically thin. Alternative accretion disk models are constructed under the assumption of a purely magnetic viscosity in the limiting cases of equipartition of gas and magnetic pressures and global flux conservation. The inner regions of these models are considerably denser than the standard model and therefore remain optically thick in all regions. The equipartition model is thermally stable throughout, while flux conservation leads to a localized thermal instability at the gas pressure/radiation pressure boundary and marginal stability as the radial distance approaches zero. The outer regions of quasar scaled accretion disks are strongly self-gravitating, leading to a vertical scale height which is smaller than that found in the inner region. Most of the outer region is gravitationally unstable, implying that the outer parts of galactic nuclei accretion disks are populated by dense self-gravitating gas clouds or possibly by stars.
NASA Astrophysics Data System (ADS)
Liang, Binbin; Zhang, Long; Wang, Binglei; Zhou, Shenjie
2015-07-01
A size-dependent model for the electrostatically actuated Nano-Electro-Mechanical Systems (NEMS) incorporating nonlinearities and Casimir force is presented by using a variational method. The governing equation and boundary conditions are derived with the help of strain gradient elasticity theory and Hamilton principle. Generalized differential quadrature (GDQ) method is employed to solve the problem numerically. The pull-in instability with Casimir force included is then studied. The results reveal that Casimir force, which is a spontaneous force between the two electrodes, can reduce the external applied voltage. With Casimir force incorporated, the pull-in instability occurs without voltage applied when the beam size is in nanoscale. The minimum gap and detachment length can be calculated from the present model for different beam size, which is important for NEMS design. Finally, discussions of size effect induced by the strain gradient terms reveal that the present model is more accurate since size effect play an important role when beam in nanoscale.
Thickness effects in electroactive polymers actuators: a simple explanation and modeling
NASA Astrophysics Data System (ADS)
Yuse, K.; Guyomar, D.; Kanda, M.
2011-04-01
For practical use, the electrical field requirements of Electro Active Polymer (EAP) actuators have to be lowered down. Recently, we developed nano carbon filled polymeric films which can generate a large strain (30-50%) at moderate electrical field (less than 20 MV/m). Herein, the electrostrictive strain saturates versus electrical field and that the maximum strain depends strongly on the sample thickness. Combining polarization saturation effect and heterogeneities in the polymer thickness lead to a model that describes correctly the strain behavior versus electrical field, polymer thickness and frequency. A three-layer model was established which assumes that the polymer is not homogeneous along the thickness. Two outer and one inner layers exist, which must be formed during the polymer curing. It is considered that these layers have slightly different characteristics, such as permittivity. When the electrical field is input parallel to the polymer thickness, a different strain would take place in each layer according to the field distribution. Since the layers are attached together, the strain must be the same in each layer. Consequently stresses appear in the different layers. Introducing in this model a saturation of the polarization for high field leads to simulation results that fit well the experimental data.
An explicit physics-based model of ionic polymer-metal composite actuators
NASA Astrophysics Data System (ADS)
Pugal, David; Kim, Kwang J.; Aabloo, Alvo
2011-10-01
The Poisson-Nernst-Planck system of equations is used to simulate the charge dynamics due to ionic current and resulting time-dependent displacement of ionic polymer-metal composite (IPMC) materials. Measured data show that currents through the polymer of IPMC cause potential gradients on the electrodes. Existing physics based models of IPMC do not explicitly consider how this affects the charge formation near the electrodes and resulting actuation of IPMC. We have developed an explicit physics based model that couples the currents in the polymer to the electric current in the continuous electrodes of IPMC. The coupling is based on the Ramo-Shockley theorem. The circular dependency concept is used to explain how the dependency between the ionic current and the potential drop in the electrodes is calculated and how they affect each other. Simulations were carried out using the finite element method. Calculated potential gradients, electric currents, and tip displacement of IPMC were validated against experimental data. We also show how the model is general in respect to the different types of currents in the polymer and how it can be used in more complicated cases such as 3D simulations.
Analysis of VAWT aerodynamics and design using the Actuator Cylinder flow model
NASA Astrophysics Data System (ADS)
Madsen, H. Aa; Paulsen, U. S.; Vitae, L.
2014-12-01
The actuator cylinder (AC) flow model is defined as the ideal VAWT rotor. Radial directed volume forces are applied on the circular path of the VAWT rotor airfoil and constitute an energy conversion in the flow. The power coefficient for the ideal as well as the real energy conversion is defined. The describing equations for the two-dimensional AC model are presented and a solution method splitting the final solution in a linear and non-linear part is briefly described. A family of loadforms approaching the uniform loading is used to study the ideal energy conversion indicating that the maximum power coefficient for the ideal energy conversion of a VAWT could exceed the Betz limit. The real energy conversion of the 5MW DeepWind rotor is simulated with the AC flow model in combination with the blade element analysis. Aerodynamic design aspects are discussed on this basis revealing that the maximum obtainable power coefficient for a fixed pitch VAWT is constrained by the fundamental cyclic variation of inflow angle and relative velocity leading to a loading that deviates considerably from the uniform loading.
An Accretion Disk-outflow Model for Hysteretic State Transition in X-Ray Binaries
NASA Astrophysics Data System (ADS)
Cao, Xinwu
2016-01-01
We suggest a model of the advection-dominated accretion flow (ADAF) with magnetically driven outflows to explain the hysteretic state transition observed in X-ray binaries (XRBs). The transition from a thin disk to an ADAF occurs when the mass accretion rate is below a critical value. The critical mass accretion rate for the ADAF can be estimated by equating the equilibration timescale to the accretion timescale of the ADAF, which is sensitive to its radial velocity. The radial velocity of thin disks is very small, which leads to the advection of the external field in thin disks becoming very inefficient. ADAFs are present in the low/hard states of XRBs, and their radial velocity is large compared with the thin disk. The external field can be dragged inward efficiently by the ADAF, so a strong large-scale magnetic field threading the ADAF can be formed, which may accelerate a fraction of gas in the ADAF into the outflows. Such outflows may carry away a large amount of angular momentum from the ADAF, which significantly increases the radial velocity of the ADAF. This leads to a high critical mass accretion rate, below which an ADAF with magnetic outflows can survive. Our calculations show that the critical luminosity of the ADAF with magnetic outflows can be one order of magnitude higher than that for a conventional ADAF, if the ratio of gas to magnetic pressure β ∼ 4 in the disk. This can naturally explain the hysteretic state transition observed in XRBs.
NASA Technical Reports Server (NTRS)
Chen, Kaiyou; Halpern, Jules P.
1990-01-01
Previously, it was claimed that the broad emission lines of the radio galaxy Arp 102B can be fitted by the line profile from a simple relativistic Keplerian thin disk. It was argued that the lines originating from the relativistic accretion disk could be polarized due to electron scattering, which is likely to be the dominant opacity in the line-emitting region of Arp 102B. In the present work, the expected polarization properties of these broad emission lines are calculated. The percentage of polarization depends strongly on the inclination angle. For some angles, the red peak of the polarized, double-peaked line profile can be higher than the blue peak. This is in contrast to the total line profile, in which the blue peak is always higher than the red one. Spectropolarimetric observations could, therefore, provide an independent test of the relativistic disk model for the broad emission lines of Arp 102B and other active galactic nuclei.
Ceramic Inclusions In Powder Metallurgy Disk Alloys: Characterization and Modeling
NASA Technical Reports Server (NTRS)
Bonacuse, Pete; Kantzos, Pete; Telesman, Jack
2002-01-01
Powder metallurgy alloys are increasingly used in gas turbine engines, especially as the material chosen for turbine disks. Although powder metallurgy materials have many advantages over conventionally cast and wrought alloys (higher strength, higher temperature capability, etc.), they suffer from the rare occurrence of ceramic defects (inclusions) that arise from the powder atomization process. These inclusions can have potentially large detrimental effect on the durability of individual components. An inclusion in a high stress location can act as a site for premature crack initiation and thereby considerably reduce the fatigue life. Because these inclusions are exceedingly rare, they usually don't reveal themselves in the process of characterizing the material for a particular application (the cumulative volume of the test bars in a fatigue life characterization is typically on the order of a single actual component). Ceramic inclusions have, however, been found to be the root cause of a number of catastrophic engine failures. To investigate the effect of these inclusions in detail, we have undertaken a study where a known population of ceramic particles, whose composition and morphology are designed to mimic the 'natural' inclusions, are added to the precursor powder. Surface connected inclusions have been found to have a particularly large detrimental effect on fatigue life, therefore the volume of ceramic 'seeds' added is calculated to ensure that a minimum number will occur on the surface of the fatigue test bars. Because the ceramic inclusions are irregularly shaped and have a tendency to break up in the process of extrusion and forging, a method of calculating the probability of occurrence and expected intercepted surface and embedded cross-sectional areas were needed. We have developed a Monte Carlo simulation to determine the distributions of these parameters and have verified the simulated results with observations of ceramic inclusions found in macro
Multi-Color Model for the Protoplanetary Disks HL Tau and HD142527
NASA Astrophysics Data System (ADS)
Hanawa, Tomoyuki; Mochida, Kazuki
2016-05-01
Protoplanetary disks are circumstellar disks of gas and dust, from which planets may eventually form or be in the process of forming. Recent direct imaging of them has enabled us to derive the density and temperature distributions. Interestingly they often show quite different features depending on the wavelength observed. The near-infrared emission is dominated by scattering of stellar light while the mm- and submm- wave emissions are dominated by thermal dust emission. Thus, the near-infrared emission traces a low density surface layer where stellar light is scattered toward us. The mm- and submm- wave emission trace the high density part of the disk near the mid plane. In order to explain the wavelength- dependent images, we have constructed a passive disk model for HL Tau and HD142527. The former shows concentric rings in the ALMA image while the latter shows a highly asymmetric arc. Our models are based on the multi-color radiation transfer calculation. It takes account of radiation ranging from 100 nm to 3.16 mm. We used the M1 model to solve the radiative equilibrium. Our model gives some constraints on the optical properties of the dust.
Self-Gravitating Eccentric Disk Models for the Double Nucleus of M31
NASA Astrophysics Data System (ADS)
Salow, Robert M.; Statler, Thomas S.
2004-08-01
We present new dynamical models of weakly self-gravitating, finite dispersion eccentric stellar disks around central black holes for the double nucleus of M31. The disk is fixed in a frame rotating at constant precession speed and is populated by stars on quasi-periodic orbits whose parents are numerically integrated periodic orbits in the total potential. A distribution of quasi-periodic orbits about a given parent is approximated by a distribution of Kepler orbits dispersed in eccentricity and orientation, using an approximate phase-space distribution function written in terms of the integrals of motion in the Kepler problem. We use these models, along with an optimization routine, to fit available published kinematics and photometry in the inner 2" of the nucleus. A grid of 24 best-fit models is computed to accurately constrain the mass of the central black hole and nuclear disk parameters. We find that the supermassive black hole in M31 has mass MBH=5.62+/-0.66×107 Msolar, which is consistent with the observed correlation between the central black hole mass and the velocity dispersion of its host spheroid. Our models precess rapidly, at Ω=36.5+/-4.2 km s-1 pc-1, and possess a characteristic radial eccentricity distribution, which gives rise to multimodal line-of-sight velocity distributions along lines of sight near the black hole. These features can be used as sensitive discriminants of disk structure.
NASA Astrophysics Data System (ADS)
Rojas-Arriagada, A.; Recio-Blanco, A.; de Laverny, P.; Schultheis, M.; Guiglion, G.; Mikolaitis, Š.; Kordopatis, G.; Hill, V.; Gilmore, G.; Randich, S.; Alfaro, E. J.; Bensby, T.; Koposov, S. E.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Zaggia, S.; Chiappini, C.
2016-02-01
Context. Recent spectroscopic surveys have begun to explore the Galactic disk system on the basis of large data samples, with spatial distributions sampling regions well outside the solar neighborhood. In this way, they provide valuable information for testing spatial and temporal variations of disk structure kinematics and chemical evolution. Aims: The main purposes of this study are to demonstrate the usefulness of a rigorous mathematical approach to separate substructures of a stellar sample in the abundance-metallicity plane, and provide new evidence with which to characterize the nature of the metal-poor end of the thin disk sequence. Methods: We used a Gaussian mixture model algorithm to separate in the [Mg/Fe] vs. [Fe/H] plane a clean disk star subsample (essentially at RGC< 10 kpc) from the Gaia-ESO survey (GES) internal data release 2 (iDR2). We aim at decomposing it into data groups highlighting number density and/or slope variations in the abundance-metallicity plane. An independent sample of disk red clump stars from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) was used to cross-check the identified features. Results: We find that the sample is separated into five groups associated with major Galactic components; the metal-rich end of the halo, the thick disk, and three subgroups for the thin disk sequence. This is confirmed with the sample of red clump stars from APOGEE. The three thin disk groups served to explore this sequence in more detail. The two metal-intermediate and metal-rich groups of the thin disk decomposition ([Fe/H] > -0.25 dex) highlight a change in the slope at solar metallicity. This holds true at different radial regions of the Milky Way. The distribution of Galactocentric radial distances of the metal-poor part of the thin disk ([Fe/H] < -0.25 dex) is shifted to larger distances than those of the more metal-rich parts. Moreover, the metal-poor part of the thin disk presents indications of a scale height
Modeling MHD accretion-ejection: episodic ejections of jets triggered by a mean-field disk dynamo
Stepanovs, Deniss; Fendt, Christian; Sheikhnezami, Somayeh E-mail: fendt@mpia.de
2014-11-20
We present MHD simulations exploring the launching, acceleration, and collimation of jets and disk winds. The evolution of the disk structure is consistently taken into account. Extending our earlier studies, we now consider the self-generation of the magnetic field by an α{sup 2}Ω mean-field dynamo. The disk magnetization remains on a rather low level, which helps to evolve the simulations for T > 10, 000 dynamical time steps on a domain extending 1500 inner disk radii. We find the magnetic field of the inner disk to be similar to the commonly found open field structure, favoring magneto-centrifugal launching. The outer disk field is highly inclined and predominantly radial. Here, differential rotation induces a strong toroidal component, which plays a key role in outflow launching. These outflows from the outer disk are slower, denser, and less collimated. If the dynamo action is not quenched, magnetic flux is continuously generated, diffuses outward through the disk, and fills the entire disk. We have invented a toy model triggering a time-dependent mean-field dynamo. The duty cycles of this dynamo lead to episodic ejections on similar timescales. When the dynamo is suppressed as the magnetization falls below a critical value, the generation of the outflows and also accretion is inhibited. The general result is that we can steer episodic ejection and large-scale jet knots by a disk-intrinsic dynamo that is time-dependent and regenerates the jet-launching magnetic field.
NASA Astrophysics Data System (ADS)
Jacobs, William R.; Wilson, Emma D.; Assaf, Tareq; Rossiter, Jonathan; Dodd, Tony J.; Porrill, John; Anderson, Sean R.
2015-05-01
Current models of dielectric elastomer actuators (DEAs) are mostly constrained to first principal descriptions that are not well suited to the application of control design due to their computational complexity. In this work we describe an integrated framework for the identification of control focused, data driven and time-varying DEA models that allow advanced analysis of nonlinear system dynamics in the frequency-domain. Experimentally generated input-output data (voltage-displacement) was used to identify control-focused, nonlinear and time-varying dynamic models of a set of film-type DEAs. The model description used was the nonlinear autoregressive with exogenous input structure. Frequency response analysis of the DEA dynamics was performed using generalized frequency response functions, providing insight and a comparison into the time-varying dynamics across a set of DEA actuators. The results demonstrated that models identified within the presented framework provide a compact and accurate description of the system dynamics. The frequency response analysis revealed variation in the time-varying dynamic behaviour of DEAs fabricated to the same specifications. These results suggest that the modelling and analysis framework presented here is a potentially useful tool for future work in guiding DEA actuator design and fabrication for application domains such as soft robotics.
Single actuator wave-like robot (SAW): design, modeling, and experiments.
Zarrouk, David; Mann, Moshe; Degani, Nir; Yehuda, Tal; Jarbi, Nissan; Hess, Amotz
2016-01-01
In this paper, we present a single actuator wave-like robot, a novel bioinspired robot which can move forward or backward by producing a continuously advancing wave. The robot has a unique minimalistic mechanical design and produces an advancing sine wave, with a large amplitude, using only a single motor but with no internal straight spine. Over horizontal surfaces, the robot does not slide relative to the surface and its direction of locomotion is determined by the direction of rotation of the motor. We developed a kinematic model of the robot that accounts for the two-dimensional mechanics of motion and yields the speed of the links relative to the motor. Based on the optimization of the kinematic model, and accounting for the mechanical constraints, we have designed and built multiple versions of the robot with different sizes and experimentally tested them (see movie). The experimental results were within a few percentages of the expectations. The larger version attained a top speed of 57 cm s(-1) over a horizontal surface and is capable of climbing vertically when placed between two walls. By optimizing the parameters, we succeeded in making the robot travel by 13% faster than its own wave speed. PMID:27367548
Slotted-wall research with disk and parachute models in a low-speed wind tunnel
Macha, J.M.; Buffington, R.J.; Henfling, J.L. ); Every, D. Van; Harris, J.L. )
1990-01-01
An experimental investigation of slotted-wall blockage interference has been conducted using disk and parachute models in a low speed wind tunnel. Test section open area ratio, model geometric blockage ratio, and model location along the length of the test section were systematically varied. Resulting drag coefficients were compared to each other and to interference-free measurements obtained in a much larger wind tunnel where the geometric blockage ratio was less than 0.0025. 9 refs., 10 figs.
Modeling and experiment of three-degree-of-freedom actuators using piezoelectric buzzers
NASA Astrophysics Data System (ADS)
Chen, W. M.; Liu, T. S.
2013-10-01
This study presents innovative three-degree-of-freedom piezoelectric actuators. Under the piezoelectric force and dry friction, the piezoelectric actuators not only can move in the Z-axis direction, but also rotate around the Y-axis and Z-axis. The Z-axis displacement can reach 62 mm and the rotation angle around the Y-axis and Z-axis can reach 270° and 360°, respectively. Compared with the literature, this innovative actuator design achieves one-degree-of-freedom translation and two-degree-of-freedom rotation. Equations of motion are derived based on the piezoelectric properties and Newton’s law. Two types of actuators are created in this study. In the first type, the centers of four piezoelectric buzzers are attached to an arm while in the other type each rim of the four piezoelectric buzzers is attached to the arm. Experimental results are compared with theoretical results. According to the experimental results, the present actuator can accomplish a translational velocity of 11 mm s-1, a Y-axis angular velocity of 8.96 rad s-1, a Z-axis angular velocity of 2.63 rad s-1, and a force of 2.49 mN. By using four piezoelectric buzzers, this study creates piezoelectric actuators capable of both translational and rotational motions.
Modelling and characterization of inflated dielectric elastomer actuators with tubular configuration
NASA Astrophysics Data System (ADS)
Zhang, Chi; Chen, Hualing; Liu, Lei; Li, Dichen
2015-06-01
A dielectric elastomer undergoes large and fast deformation subject to external electric stimuli, making it a promising artificial muscle for various kinds of actuators, sensors and energy generators. This paper presents an actuator fabricated by (1) rolling a dielectric elastomer membrane, (2) pre-stretching the membrane along the radial direction and fixing the edges with rigid cylindrical plastic ends, and (3) applying a force to the end along the longitudinal direction and pumping air into the tube for inflation. Subject to a voltage, the structure works as an actuator with a large linear stroke. Governing equations of this actuator are established and simulation results are found to agree well with experimental results. We examine four modes of failure, namely loss of tension, electrical breakdown, snap-through instability and tensile rupture, with a variation in applied pressure. The actuating voltage is greatly reduced by applying pressure, providing the possibility of low-voltage driving. By regulating the applied pressure, large actuation strain and displacement are obtained simultaneously and the distributions of stretch, true stress and the true electric field become more homogeneous.
NASA Technical Reports Server (NTRS)
Holloway, Sidney E., III
1994-01-01
This paper describes the mechanical design, analysis, fabrication, testing, and lessons learned by developing a uniquely designed spaceflight-like actuator. The linear proof mass actuator (LPMA) was designed to attach to both a large space structure and a ground test model without modification. Previous designs lacked the power to perform in a terrestrial environment while other designs failed to produce the desired accelerations or frequency range for spaceflight applications. Thus, the design for a unique actuator was conceived and developed at NASA Langley Research Center. The basic design consists of four large mechanical parts (mass, upper housing, lower housing, and center support) and numerous smaller supporting components including an accelerometer, encoder, and four drive motors. Fabrication personnel were included early in the design phase of the LPMA as part of an integrated manufacturing process to alleviate potential difficulties in machining an already challenging design. Operating testing of the LPMA demonstrated that the actuator is capable of various types of load functions.
NASA Technical Reports Server (NTRS)
Holloway, S. E., III
1995-01-01
This paper describes the mechanical design, analysis, fabrication, testing, and lessons learned by developing a uniquely designed spaceflight-like actuator. The Linear Proof Mass Actuator (LPMA) was designed to attach to both a large space structure and a ground test model without modification. Previous designs lacked the power to perform in a terrestrial environment while other designs failed to produce the desired accelerations or frequency range for spaceflight applications. Thus, the design for a unique actuator was conceived and developed at NASA Langley Research Center. The basic design consists of four large mechanical parts (Mass, Upper Housing, Lower Housing, and Center Support) and numerous smaller supporting components including an accelerometer, encoder, and four drive motors. Fabrication personnel were included early in the design phase of the LPMA as part of an integrated manufacturing process to alleviate potential difficulties in machining an already challenging design. Operational testing of the LPMA demonstrated that the actuator is capable of various types of load functions.
Thermal modeling of head disk interface system in heat assisted magnetic recording
Vemuri, Sesha Hari; Seung Chung, Pil; Jhon, Myung S.; Min Kim, Hyung
2014-05-07
A thorough understanding of the temperature profiles introduced by the heat assisted magnetic recording is required to maintain the hotspot at the desired location on the disk with minimal heat damage to other components. Here, we implement a transient mesoscale modeling methodology termed lattice Boltzmann method (LBM) for phonons (which are primary carriers of energy) in the thermal modeling of the head disk interface (HDI) components, namely, carbon overcoat (COC). The LBM can provide more accurate results compared to conventional Fourier methodology by capturing the nanoscale phenomena due to ballistic heat transfer. We examine the in-plane and out-of-plane heat transfer in the COC via analyzing the temperature profiles with a continuously focused and pulsed laser beam on a moving disk. Larger in-plane hotspot widening is observed in continuously focused laser beam compared to a pulsed laser. A pulsed laser surface develops steeper temperature gradients compared to continuous hotspot. Furthermore, out-of-plane heat transfer from the COC to the media is enhanced with a continuous laser beam then a pulsed laser, while the temperature takes around 140 fs to reach the bottom surface of the COC. Our study can lead to a realistic thermal model describing novel HDI material design criteria for the next generation of hard disk drives with ultra high recording densities.
Evolution of spiral galaxies. 3: Application of the multiphase model to the galactic disk
NASA Astrophysics Data System (ADS)
Ferrini, Federico; Molla, Mercedes; Pardi, Maria Chiara; Diaz, Angeles I.
1994-06-01
We present an application of the multiphase model of Ferrini and coworkers, developed for the solar neighborhood, to other regions of the disk of the Galaxy in order to reproduce the observed element abundance gradients. The model describes the Galaxy as a two-zone system (halo and disk) sliced into nine cylindrical concentric regions and studies the time evolution of the five populations which inhabit the Milky Way: diffuse gas, molecular clouds, low-mass (m less than 4 M solar masses) and high-mass stars, and stellar remnants. Our final aim is to reproduce the metallicity gradients that are observed in the Milky Way and in other external galaxies. We analyze the evolution of these gradients in time in order to relate their behavior to other galactic quantities such as the star formation rate and the infall rate. The model describes the Galaxy by fitting a large number of observational constraints: abundance gradients, age-metallicity relations for disk and halo, both gas and mass distributions (including radial differences in the characteristic shapes of atomic and molecular gas), and radial distribution and history of star formation rate. The time evolution of abundance gradients is computed, revealing a flattening of gradients with time. In particular, the oxygen abundance was steeper at early times as a consequence of a larger infall. Since the disk is evolving and the gas is consumed, a saturation level is reached in every ring and the gradient will decrease to a minimum value.
Ceramic Inclusions in Powder Metallurgy Disk Alloys: Characterization and Modeling
NASA Technical Reports Server (NTRS)
Bonacuse, Peter J.
2001-01-01
Powder metallurgy alloys are increasingly used in gas turbine engines, especially in turbine disk applications. Although powder metallurgy materials have many advantages over conventionally cast and wrought alloys (higher strength, higher temperature capability, etc.), they suffer from the rare occurrence of ceramic defects (inclusions) that are inherent to the powder atomization process. These inclusions can have a potentially large detrimental effect on the durability of individual components. An inclusion in a high stress location can act as a site for premature crack initiation and thereby considerably reduce the fatigue life. Because these inclusions are exceedingly rare, they typically do not reveal themselves in the process of characterizing the material for a particular application (the cumulative volume of the test bars in a fatigue life characterization is typically on the order of a single actual component). Ceramic inclusions have, however, been found to be the root cause of a number of catastrophic engine failures. To investigate the effect of these inclusions in detail, we have undertaken a study where known populations of ceramic particles, whose composition and morphology are designed to mimic the "natural" inclusions, are added to the precursor powder. Surface-connected inclusions have been found to have a particularly large detrimental effect on fatigue life; therefore, the quantity of ceramic "seeds" added is calculated to ensure that a minimum number will intersect the surface of the fatigue test bars. Because the ceramic inclusions are irregularly shaped and have a tendency to break up in the process of extrusion and forging, a method of calculating the probability of occurrence and expected intercepted surface area was needed. We have developed a Monte Carlo simulation to determine the distributions of these parameters and have verified the simulated results with observations of ceramic inclusions found in macroscopic slices from extrusions
NASA Astrophysics Data System (ADS)
Klement, R.; Carciofi, A. C.; Rivinius, Th.; Panoglou, D.; Vieira, R. G.; Bjorkman, J. E.; Štefl, S.; Tycner, C.; Faes, D. M.; Korčáková, D.; Müller, A.; Zavala, R. T.; Curé, M.
2015-12-01
Context. The viscous decretion disk (VDD) model is able to explain most of the currently observable properties of the circumstellar disks of Be stars. However, more stringent tests, focusing on reproducing multitechnique observations of individual targets via physical modeling, are needed to study the predictions of the VDD model under specific circumstances. In the case of nearby, bright Be star β CMi, these circumstances are a very stable low-density disk and a late-type (B8Ve) central star. Aims: The aim is to test the VDD model thoroughly, exploiting the full diagnostic potential of individual types of observations, in particular, to constrain the poorly known structure of the outer disk if possible, and to test truncation effects caused by a possible binary companion using radio observations. Methods: We use the Monte Carlo radiative transfer code HDUST to produce model observables, which we compare with a very large set of multitechnique and multiwavelength observations that include ultraviolet and optical spectra, photometry covering the interval between optical and radio wavelengths, optical polarimetry, and optical and near-IR (spectro)interferometry. Results: A parametric VDD model with radial density exponent of n = 3.5, which is the canonical value for isothermal flaring disks, is found to explain observables typically formed in the inner disk, while observables originating in the more extended parts favor a shallower, n = 3.0, density falloff. Theoretical consequences of this finding are discussed and the outcomes are compared with the predictions of a fully self-consistent VDD model. Modeling of radio observations allowed for the first determination of the physical extent of a Be disk (35+10-5 stellar radii), which might be caused by a binary companion. Finally, polarization data allowed for an indirect measurement of the rotation rate of the star, which was found to be W ≳ 0.98, i.e., very close to critical. Based partly on observations from Ond
Non-LTE spectral models for the gaseous debris-disk component of Ton 345
NASA Astrophysics Data System (ADS)
Hartmann, S.; Nagel, T.; Rauch, T.; Werner, K.
2014-11-01
Context. For a fraction of single white dwarfs with debris disks, an additional gaseous disk was discovered. Both dust and gas are thought to be created by the disruption of planetary bodies. Aims: The composition of the extrasolar planetary material can directly be analyzed in the gaseous disk component, and the disk dynamics might be accessible by investigating the temporal behavior of the Ca ii infrared emission triplet, hallmark of the gas disk. Methods: We obtained new optical spectra for the first helium-dominated white dwarf for which a gas disk was discovered (Ton 345) and modeled the non-LTE spectra of viscous gas disks composed of carbon, oxygen, magnesium, silicon, sulfur, and calcium with chemical abundances typical for solar system asteroids. Iron and its possible line-blanketing effects on the model structure and spectral energy distribution was still neglected. A set of models with different radii, effective temperatures, and surface densities as well as chondritic and bulk-Earth abundances was computed and compared with the observed line profiles of the Ca ii infrared triplet. Results: Our models suggest that the Ca ii emission stems from a rather narrow gas ring with a radial extent of R = 0.44-0.94 R⊙, a uniform surface density Σ = 0.3 g cm-2, and an effective temperature of Teff ≈ 6000 K. The often assumed chemical mixtures derived from photospheric abundances in polluted white dwarfs - similar to a chondritic or bulk-Earth composition - produce unobserved emission lines in the model and therefore have to be altered. We do not detect any line-profile variability on timescales of hours, but we confirm the long-term trend over the past decade for the red-blue asymmetry of the double-peaked lines. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).
A Statistical Study of Accretion Disk Model Spectra for Cataclysmic Variables
NASA Astrophysics Data System (ADS)
Puebla, Raúl E.; Diaz, Marcos P.; Hubeny, Ivan
2007-11-01
We have performed a statistical test of the currently used accretion disk models for cataclysmic variables (CVs) using a set of 33 CVs with steady disks (10 old novae and 23 nova-like systems). The mass transfer rate () for each system was also calculated. Ultraviolet (UV) data were fitted by model spectra using a multiparametric optimization method, aiming to constrain the values. It was verified that these accretion disk models fail to fit both color and flux simultaneously, as previously noted when composite stellar atmosphere models were fitted to the UV spectra of CVs by Wade. By applying such models to a sample of novae and nova-like CVs, we confirm that the limb-darkening effect must be taken into account when estimating mass transfer rates, especially for high-inclination systems. Important fitting degeneracies of the basic disk parameters are analyzed. Our simulations suggest that to reproduce the observations a revision of the temperature profile, at least in the innermost parts of the disk, seems to be required, and possibly the vertical distribution of the viscosity should be revised. In addition, an optically thin layer or an extended disk component should be considered. This component may be physically represented by a disk wind and/or a chromosphere. A physical description of the emission-line profiles may help to break the degeneracies that appear when only the continuum is analyzed. The average value of found for nova-like systems is ~9.3 × 10-9 Modot yr-1, while ~1.3 × 10-8 Modot yr-1 is found for old classical novae. No clear evidence is found for either the presence or absence of a correlation between and the orbital period. Such correlation analysis was performed for high accretion rate systems (15 nova-like systems and 10 old novae), but we were not able to find a well-defined correlation as found by Patterson. By measuring the equivalent width of the emission lines (C IV λ1550 and He II λ1640) we found a lack of systems with low and
Huang, Guoliang; Song, Fei; Wang, Xiaodong
2010-01-01
Elastic waves, especially guided waves, generated by a piezoelectric actuator/sensor network, have shown great potential for on-line health monitoring of advanced aerospace, nuclear, and automotive structures in recent decades. Piezoelectric materials can function as both actuators and sensors in these applications due to wide bandwidth, quick response and low costs. One of the most fundamental issues surrounding the effective use of piezoelectric actuators is the quantitative evaluation of the resulting elastic wave propagation by considering the coupled piezo-elastodynamic behavior between the actuator and the host medium. Accurate characterization of the local interfacial stress distribution between the actuator and the host medium is the key issue for the problem. This paper presents a review of the development of analytical, numerical and hybrid approaches for modeling of the coupled piezo-elastodynamic behavior. The resulting elastic wave propagation for structural health monitoring is also summarized. PMID:22319319
Modeling the Formation and Evolution of Wind-Capture Disks In Binary Systems
NASA Astrophysics Data System (ADS)
Huarte-Espinosa, M.; Carroll-Nellenback, J.; Nordhaus, J.; Frank, A.; Blackman, E.
2014-04-01
In this talk I will present results of recent models of the formation, evolution and physical properties of accretion disks formed via wind capture in binary systems. Using the AMR code AstroBEAR, we have carried out high resolution 3D simulations that follow a stellar mass secondary in the co-rotating frame as it orbits a wind producing AGB primary. A resolution criteria, based on considerations of Bondi-Hoyle flows, must be met in order to properly resolve the formation of accretion disks around the secondary. We then compare simulations of binaries with three different orbital radii (10, 15, 20 AU). Disks are formed in all three cases, however the size of the disk and, most importantly, its accretion rate decreases with orbital radii. In addition, the shape of the orbital motions of material within the disk becomes increasingly elliptical with increasing binary separation. The flow is mildly unsteady with "fluttering" around the bow shock observed. The disks are generally well aligned with the orbital plane after a few binary orbits. We do not observe the presence of any large scale, violent instabilities (such as the flip-flop mode). For the first time it is observed that the wind component that is accreted towards the secondary has a vortex tube-like structure. In the context of AGB binary systems that might be precursors to Pre-Planetary and Planetary Nebula, we find that the wind accretion rates at the chosen orbital separations are generally too small to produce the most powerful outflows observed in these systems if the companions are main sequence stars but marginally capable if the companions are white dwarfs. It is likely that many of the more powerful PPN and PN involve closer binaries than the ones considered here.
Model identification of terfenol-D magnetostrictive actuator for precise positioning control
NASA Astrophysics Data System (ADS)
Saleem, Ashraf; Ghodsi, Mojtaba; Mesbah, Mostefa; Ozer, Abdullah
2016-04-01
Feedback control strategies are desirable for disturbance rejection of human-induced vibrations in civil engineering structures as human walking forces cannot easily be measured. In relation to human-induced vibration control studies, most past researches have focused on floors and footbridges and the widely used linear controller implemented in the trials has been the direct velocity feedback (DVF) scheme. With appropriate compensation to enhance its robustness, it has been shown to be effective at damping out the problematic modes of vibration of the structures in which the active vibration control systems have been implemented. The work presented here introduces a disturbance observer (DOB) that is used with an outer-loop DVF controller. Results of analytical studies presented in this work based on the dynamic properties of a walkway bridge structure demonstrate the potential of this approach for enhancing the vibration mitigation performance offered by a purely DVF controller. For example, estimates of controlled frequency response functions indicate improved attenuation of vibration around the dominant frequency of the walkway bridge structure as well as at higher resonant frequencies. Controlled responses from three synthesized walking excitation forces on a walkway bridge structure model show that the inclusion of the disturbance observer with an outer loop DVF has potential to improve on the vibration mitigation performance by about 3.5% at resonance and 6-10% off-resonance. These are realised with hard constraints being imposed on the low frequency actuator displacements.
THE STABILITY OF LOW SURFACE BRIGHTNESS DISKS BASED ON MULTI-WAVELENGTH MODELING
MacLachlan, J. M.; Wood, K.; Matthews, L. D.; Gallagher, J. S.
2011-11-01
To investigate the structure and composition of the dusty interstellar medium (ISM) of low surface brightness (LSB) disk galaxies, we have used multi-wavelength photometry to construct spectral energy distributions for three low-mass, edge-on LSB galaxies (V{sub rot} = 88-105 km s{sup -1}). We use Monte Carlo radiation transfer codes that include the effects of transiently heated small grains and polycyclic aromatic hydrocarbon molecules to model and interpret the data. We find that, unlike the high surface brightness galaxies previously modeled, the dust disks appear to have scale heights equal to or exceeding their stellar scale heights. This result supports the findings of previous studies that low-mass disk galaxies have dust scale heights comparable to their stellar scale heights and suggests that the cold ISM of low-mass, LSB disk galaxies may be stable against fragmentation and gravitational collapse. This may help to explain the lack of observed dust lanes in edge-on LSB galaxies and their low current star formation rates. Dust masses are found in the range (1.16-2.38) x 10{sup 6} M{sub sun}, corresponding to face-on (edge-on), V-band, optical depths 0.034 {approx}< {tau}{sub face} {approx}< 0.106 (0.69 {approx}< {tau}{sub eq} {approx}< 1.99).
Identification of a nonlinear black-box model for a self-sensing polymer metal composite actuator
NASA Astrophysics Data System (ADS)
Quang Truong, Dinh; Ahn, Kyoung Kwan; Nam, Doan Ngoc Chi; Yoon, Jong Il
2010-08-01
An ion polymer metal composite (IPMC) is an electro-active polymer that bends in response to a small applied electrical field as a result of the mobility of cations in the polymer network and vice versa. The aim of this paper is the identification of a novel accurate nonlinear black-box model (NBBM) for IPMC actuators with self-sensing behavior based on a recurrent multi-layer perceptron neural network (RMLPNN) and a self-adjustable learning mechanism (SALM). Firstly, an IPMC actuator is investigated. Driving voltage signals are applied to the IPMC in order to identify the IPMC characteristics. Secondly, the advanced NBBM for the IPMC is built with suitable inputs and output to estimate the IPMC tip displacement. Finally, the model parameters are optimized by the collected input/output training data. Modeling results show that the proposed self-sensing methodology based on the optimized NBBM model can well describe the bending behavior of the IPMC actuator corresponding to its applied power without using any measuring sensor.
Contact graphs of disk packings as a model of spatial planar networks
NASA Astrophysics Data System (ADS)
Zhang, Zhongzhi; Guan, Jihong; Ding, Bailu; Chen, Lichao; Zhou, Shuigeng
2009-08-01
Spatially constrained planar networks are frequently encountered in real-life systems. In this paper, based on a space-filling disk packing we propose a minimal model for spatial maximal planar networks, which is similar to but different from the model for Apollonian networks (Andrade et al 2005 Phys. Rev. Lett. 94 018702). We present an exhaustive analysis of various properties of our model, and obtain the analytic solutions for most of the features, including degree distribution, clustering coefficient, average path length and degree correlations. The model recovers some striking generic characteristics observed in most real networks. To address the robustness of the relevant network properties, we compare the structural features between the investigated network and the Apollonian networks. We show that topological properties of the two networks are encoded in the way of disk packing. We argue that spatial constraints of nodes are relevant to the structure of the networks.
Anisotropic Multishell Analytical Modeling of an Intervertebral Disk Subjected to Axial Compression.
Demers, Sébastien; Nadeau, Sylvie; Bouzid, Abdel-Hakim
2016-04-01
Studies on intervertebral disk (IVD) response to various loads and postures are essential to understand disk's mechanical functions and to suggest preventive and corrective actions in the workplace. The experimental and finite-element (FE) approaches are well-suited for these studies, but validating their findings is difficult, partly due to the lack of alternative methods. Analytical modeling could allow methodological triangulation and help validation of FE models. This paper presents an analytical method based on thin-shell, beam-on-elastic-foundation and composite materials theories to evaluate the stresses in the anulus fibrosus (AF) of an axisymmetric disk composed of multiple thin lamellae. Large deformations of the soft tissues are accounted for using an iterative method and the anisotropic material properties are derived from a published biaxial experiment. The results are compared to those obtained by FE modeling. The results demonstrate the capability of the analytical model to evaluate the stresses at any location of the simplified AF. It also demonstrates that anisotropy reduces stresses in the lamellae. This novel model is a preliminary step in developing valuable analytical models of IVDs, and represents a distinctive groundwork that is able to sustain future refinements. This paper suggests important features that may be included to improve model realism. PMID:26833355
FROM DUST TO PLANETESIMALS: AN IMPROVED MODEL FOR COLLISIONAL GROWTH IN PROTOPLANETARY DISKS
Garaud, Pascale; Meru, Farzana; Galvagni, Marina; Olczak, Christoph
2013-02-20
Planet formation occurs within the gas- and dust-rich environments of protoplanetary disks. Observations of these objects show that the growth of primordial submicron-sized particles into larger aggregates occurs at the earliest evolutionary stages of the disks. However, theoretical models of particle growth that use the Smoluchowski equation to describe collisional coagulation and fragmentation have so far failed to produce large particles while maintaining a significant population of small grains. This has generally been attributed to the existence of two barriers impeding growth due to bouncing and fragmentation of colliding particles. In this paper, we demonstrate that the importance of these barriers has been artificially inflated through the use of simplified models that do not take into account the stochastic nature of the particle motions within the gas disk. We present a new approach in which the relative velocities between two particles are described by a probability distribution function that models both deterministic motion (from the vertical settling, radial drift, and azimuthal drift) and stochastic motion (from Brownian motion and turbulence). Taking both into account can give quite different results to what has been considered recently in other studies. We demonstrate the vital effect of two 'ingredients' for particle growth: the proper implementation of a velocity distribution function that overcomes the bouncing barrier and, in combination with mass transfer in high-mass-ratio collisions, boosts the growth of larger particles beyond the fragmentation barrier. A robust result of our simulations is the emergence of two particle populations (small and large), potentially explaining simultaneously a number of longstanding problems in protoplanetary disks, including planetesimal formation close to the central star, the presence of millimeter- to centimeter-sized particles far out in the disk, and the persistence of {mu}m-sized grains for millions of
NASA Technical Reports Server (NTRS)
Powell, W. W., Sr.
1979-01-01
Two theories emerged as the cause of undesired oscillations at frequencies between 40 and 60 Hz in the Orbiter Vehicle inboard and outboard elevon actuation subsystems during hardware testing. Both the "hardover feedback" and "deadspace" theories were examined using continuous system modeling program simulation. Results did not support the "hardover feedback" theory but showed that deadspace in the torque feedback spring connections to the servospools must be considered to be a possible cause of the oscillations. Further investigation is recommended.
NASA Astrophysics Data System (ADS)
Datta, Supratik
2009-12-01
Iron-gallium alloys (Galfenol) are structural magnetostrictive materials that exhibit high free-strain at low magnetic fields, high stress-sensitivity and useful thermo-mechanical properties. Galfenol, like smart materials in general, is attractive for use as a dynamic actuator and/or sensor material and can hence find use in active shape and vibration control, real-time structural health monitoring and energy harvesting applications. Galfenol possesses significantly higher yield strength and greater ductility than most smart materials, which are generally limited to use under compressive loads. The unique structural attributes of Galfenol introduce opportunities for use of a smart material in applications that involve tension, bending, shear or torsion. A principal motivation for the research presented in this dissertation is that bending and shear loads lead to development of non-uniform stress and magnetic fields in Galfenol which introduce significantly more complexity to the considerations to be modeled, compared to modeling of purely axial loads. This dissertation investigates the magnetostrictive response of Galfenol under different stress and magnetic field conditions which is essential for understanding and modeling Galfenol's behavior under bending, shear or torsion. Experimental data are used to calculate actuator and sensor figures of merit which can aid in design of adaptive structures. The research focuses on the bending behavior of Galfenol alloys as well as of laminated composites having Galfenol attached to other structural materials. A four-point bending test under magnetic field is designed, built and conducted on a Galfenol beam to understand its performance as a bending sensor. An extensive experimental study is conducted on Galfenol-Aluminum laminated composites to evaluate the effect of magnetic field, bending moment and Galfenol-Aluminum thickness ratio on actuation and sensing performance. A generalized recursive algorithm is presented for
NASA Technical Reports Server (NTRS)
Waszak, Martin R.; Fung, Jimmy
1998-01-01
This report describes the development of transfer function models for the trailing-edge and upper and lower spoiler actuators of the Benchmark Active Control Technology (BACT) wind tunnel model for application to control system analysis and design. A simple nonlinear least-squares parameter estimation approach is applied to determine transfer function parameters from frequency response data. Unconstrained quasi-Newton minimization of weighted frequency response error was employed to estimate the transfer function parameters. An analysis of the behavior of the actuators over time to assess the effects of wear and aerodynamic load by using the transfer function models is also presented. The frequency responses indicate consistent actuator behavior throughout the wind tunnel test and only slight degradation in effectiveness due to aerodynamic hinge loading. The resulting actuator models have been used in design, analysis, and simulation of controllers for the BACT to successfully suppress flutter over a wide range of conditions.
The LDCM actuator for vibration suppression
NASA Technical Reports Server (NTRS)
Ide, Eric N.; Lindner, Douglas K.
1988-01-01
A linear dc motor (LDCM) has been proposed as an actuator for the COFS I mast and the COFS program ground test Mini-Mast. The basic principles of operation of the LDCM as an actuator for vibration suppression in large flexible structures are reviewed. Because of force and stroke limitations, control loops are required to stabilize the actuator, which results in a non-standard actuator-plant configuration. A simulation model that includes LDCM actuator control loops and a finite element model of the Mast is described, with simulation results showing the excitation capability of the actuator.
Modelling Dusty Circumbinary Disk around B[e] Supergiant RY Sct
NASA Astrophysics Data System (ADS)
Men'shchikov, Alexander; Miroshnichenko, Anatoly
2005-08-01
The supergiant RY Sct is an eclipsing binary system with a fairly large infrared (IR) excess caused by the presence of circumbinary dust. Many strong forbidden lines ([O i], [N ii], [S iii], [Fe ii]), in combination with the near-IR excess, put it in the list of peculiar Be or B[e] stars. Although RY Sct is one of the best-studied systems, even its basic physical parameters remain unreliable. Recent IR images of the system, obtained with a 0.3 arcsec resolution at the 10-m Keck telescope, showed the dusty disk at the wavelengths 3-20 μm and stimulated us to perform its detailed modelling using our 2-D radiative transfer code. Our model reproduces all available observations of RY Sct obtained during the last few decades. The modelling demonstrated that the observations cannot be described by a single model at one moment in time, implying rapid changes in the dusty disk during the last 20 years. Assuming that a temperature of 27,000 K describes both components of the binary and that its distance is 1.8 kpc, its total luminosity is 4.2 - 105 solar luminosity. The model disk has the optical depth of 0.04 and the opening angle of 26° (between the boundaries). Dust in the disk exists between 60 AU and 105 AU, where it blends into the interstellar medium. We observe the disk almost edge-on, at an angle of 14° to its midplane. The total mass of the disk is 0.017 solar mass. There is a strong density enhancement at 1800 AU from the binary, which emits most of the IR radiation and is prominent in the Keck telescope images. Presumably, the dense ring has been created by a fast wind that swept out and compressed the previously lost material in the older and slower stellar wind. Our model predicts that presently there is a large amount of small, hot dust grains in the dust formation zone, whose emission changed the shape of the SED of RY Sct in the near IR. The dust density must now be significantly greater in the dust formation zone, suggesting a much higher massloss rate
Simple wideband models for disks and wires in the eddy current approximation
NASA Astrophysics Data System (ADS)
Scott, Waymond R.; McFadden, Michael
2013-05-01
Wideband electromagnetic induction systems have shown improved false alarm rates when compared with traditional metal detectors. Calibration of these sensors and the development of algorithms for target discrimination could be assisted by a set of models for common targets. In this paper, simple wideband models of the eddy current response for a wire and disk are provided. These are provided in the form of a singularity expansion of the polarizability dyadic. In an effort to make this form more concrete, a major focus of the paper is on relating the terms of the expansion to graphs of the currents present on the disk. The models provided in the paper are based on limiting forms of a cylinder as computed using the body-of-revolutions finite element method. Measured polarizability dyadics are also shown to fit the forms provided reasonably well.
NASA Astrophysics Data System (ADS)
Zhu, Wei; Bian, Leixiang; An, Yi; Chen, Gangli; Rui, Xiaoting
2015-07-01
This paper outlines an optical beam steering system built using a two-axis fast steering mirror (FSM) with piezoelectric stack actuators to maintain precise pointing control. A novel mathematical model of the FSM is put forward by using a transfer matrix method of a multibody system to describe the dynamics characteristics and a hysteresis model to represent the hysteresis. Based on the proposed model, a model-based hybrid control is applied to force the output angle of the FSM to track the laser beam accurately thereafter. The experimental results are in accordance with the theoretical analysis. The results highlight significantly improved accuracy in the beam tracking control of the FSM.
A Resonantly Excited Disk-Oscillation Model of High-Frequency QPOs of Microquasars
NASA Astrophysics Data System (ADS)
Kato, Shoji
2012-12-01
A possible model of twin high-frequency QPOs (HF QPOs) of microquasars is examined. The disk is assumed to have global magnetic fields and to be deformed with a two-armed pattern. In this deformed disk, a set of a two-armed (m = 2) vertical p-mode oscillation and an axisymmetric (m = 0) g-mode oscillation is considered. They resonantly interact through the disk deformation when their frequencies are the same. This resonant interaction amplifies the set of the above oscillations in the case where these two oscillations have wave energies of opposite signs. These oscillations are assumed to be excited most efficiently in the case where the radial group velocities of these two waves vanish at the same place. The above set of oscillations is not unique, depending on the node number n, of oscillations in the vertical direction. We consider that the basic two sets of oscillations correspond to the twin QPOs. The frequencies of these oscillations depend on the disk parameters, such as the strength of the magnetic fields. For observational mass ranges of GRS 1915+ 105, GRO J1655-40, XTE J1550-564, and HEAO H1743-322, the spins of these sources are estimated. High spins of these sources can be described if the disks have weak poloidal magnetic fields as well as toroidal magnetic fields of moderate strength. In this model the 3:2 frequency ratio of high-frequency QPOs is not related to their excitation, but occurs by chance.
The structure and appearance of winds from supercritical accretion disks. I - Numerical models
NASA Technical Reports Server (NTRS)
Meier, D. L.
1979-01-01
Equations for the structure and appearance of supercritical accretion disks and the radiation-driven winds which emanate from them are derived and solved by a steady-state hydrodynamic computer code with a relaxation technique used in stellar structure problems. The present model takes into account the mass of the accreting star, the total accretion rate, a generalization of the disk alpha parameter which accounts for heating by processes in addition to viscosity, and the ratio of the total luminosity to the Eddington luminosity. Solutions indicate that for accretion onto a hard-surfaced star, steady, optically thick winds result for even slightly supercritical accretion, and the object will appear as a supergiant star with a high mass loss rate and a nonblackbody spectrum. Winds from black hole accretion disks are expected to depend on the form of the accretion interior to the critical radius, possibly consisting of no ejection at all, a wind similar to that of a hard-surfaced star, or a column of material ejected from a hole in the accretion disk.
A model for the magnetic field in the molecular disk at the Galactic center
Wardle, M.; Konigl, A. )
1990-10-01
A model for the magnetic field configuration in the Galactic center disk is presented. The field has an open geometry and represents the poloidal field detected at larger distances from the Galactic center, stretched and twisted by the effects of advection and shear in a magnetized accretion disk. It is concluded that the 100 micron polarization measurements of Hildebrand et al. (1990) imply that the radial and azimuthal components of the magnetic field in the disk are comparable and have opposite signs, consistent with the generation of B(phi) from B(r) by differential rotation. The polarization measurements indicate that the z-component of the field is smaller than both /B(phi)/ and /B(r)/; thus, they do not by themselves require that the field lines thread the disk. The field strengths of order 1 mG inferred from the Zeeman measurements and the fact that /B(phi)/ and /B(r)/ exceed B(z) imply that the field could remove the excess angular momentum of the accreted matter in the form of a centrifugally driven outflow. 31 refs.
THE DISK EVAPORATION MODEL FOR THE SPECTRAL FEATURES OF LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI
Qiao, Erlin; Liu, B. F.; Panessa, Francesca; Liu, J. Y.
2013-11-10
Observations show that the accretion flows in low-luminosity active galactic nuclei probably have a two-component structure with an inner, hot, optically thin, advection-dominated accretion flow (ADAF) and an outer, truncated, cool, optically thick accretion disk. As shown by Taam et al., the truncation radius as a function of mass accretion rate is strongly affected by including the magnetic field within the framework of disk evaporation model, i.e., an increase in the magnetic field results in a smaller truncation radius of the accretion disk. In this work, we calculate the emergent spectrum of an inner ADAF + an outer truncated accretion disk around a supermassive black hole based on the prediction by Taam et al.. It is found that an increase in the magnetic field from β = 0.8 to β = 0.5 (with magnetic pressure p{sub m} = B {sup 2}/8π = (1 – β)p{sub tot}, p{sub tot} = p{sub gas} + p{sub m}) results in a factor of ∼8.7 increase in the luminosity from the truncated accretion disk. Meanwhile, results of the peak emission of the truncated accretion disk shift toward a a factor of ∼5 higher frequency. We found that the equipartition of gas pressure to magnetic pressure, i.e., β = 0.5, failed to explain the observed anti-correlation between L{sub 2-10{sub keV}}/L{sub Edd} and the bolometric correction κ{sub 2-10{sub keV}} (with κ{sub 2-10{sub keV}} = L{sub bol}/L{sub 2-10{sub keV}}). The emergent spectra for larger values of β = 0.8 or β = 0.95 can explain the observed L{sub 2-10{sub keV}}/L{sub Edd}-κ{sub 2-10{sub keV}} correlation. We argue that in the disk evaporation model, the electrons in the corona are assumed to be heated only by a transfer of energy from the ions to electrons via Coulomb collisions, which is reasonable for accretion with a lower mass accretion rate. Coulomb heating is the dominated heating mechanism for the electrons only if the magnetic field is strongly sub-equipartition, which is roughly consistent with observations.
NASA Astrophysics Data System (ADS)
Gan, Jinqiang; Zhang, Xianmin; Wu, Heng
2016-03-01
In this paper, a generalized hysteresis model is developed to describe both rate-independent and rate-dependent hysteresis in piezoelectric actuators. Based on the classical Prandtl-Ishlinskii (P-I) model, the developed model adds a quadratic polynomial and makes other small changes. When it is used to describe rate-independent hysteresis, the parameters of the model are constants, which can be identified by self-adaptive particle swarm optimization. The effectiveness of this rate-independent modified P-I model is demonstrated by comparing simulation results of the developed model and the classic Prandtl-Ishlinskii model. Simulation results suggest that the rate-independent modified P-I model can describe hysteresis more precisely. Compared with the classical P-I model, the rate-independent modified P-I model reduces modeling error by more than 50%. When it is used to describe rate-independent hysteresis, a one-side operator is adopted and the parameters are functions with input frequency. The results of the experiments and simulations have shown that the proposed models can accurately describe both rate-independent and rate-dependent hysteresis in piezoelectric actuators.
Gan, Jinqiang; Zhang, Xianmin; Wu, Heng
2016-03-01
In this paper, a generalized hysteresis model is developed to describe both rate-independent and rate-dependent hysteresis in piezoelectric actuators. Based on the classical Prandtl-Ishlinskii (P-I) model, the developed model adds a quadratic polynomial and makes other small changes. When it is used to describe rate-independent hysteresis, the parameters of the model are constants, which can be identified by self-adaptive particle swarm optimization. The effectiveness of this rate-independent modified P-I model is demonstrated by comparing simulation results of the developed model and the classic Prandtl-Ishlinskii model. Simulation results suggest that the rate-independent modified P-I model can describe hysteresis more precisely. Compared with the classical P-I model, the rate-independent modified P-I model reduces modeling error by more than 50%. When it is used to describe rate-independent hysteresis, a one-side operator is adopted and the parameters are functions with input frequency. The results of the experiments and simulations have shown that the proposed models can accurately describe both rate-independent and rate-dependent hysteresis in piezoelectric actuators. PMID:27036808
Modelling the effect of actuator-like behavior in dielectric elastomer generators
NASA Astrophysics Data System (ADS)
Zanini, P.; Rossiter, J.; Homer, M.
2015-10-01
Dielectric Elastomer Generators (DEGs) have been claimed as one promising technology for renewable mechanical to electrical energy harvesting, due to their lightweight, low cost, and high energy density. Dielectric elastomers have a dual behavior, able to convert electrical energy into mechanical if charged electrostatically and to convert mechanical to electrical energy if stretched and relaxed in a cycle that exploits its capacitance change. During such energy harvesting cycles, the material needs an electrical energy bias to be able to convert mechanical work into electrical energy, which produces an actuator behavior on the DEG that results in losses and decreases its performance. In this paper, we investigate this actuation behavior and its effect on energy harvesting in the DEGs. We compare two different charging methods and show that a constant voltage method can increase the net energy harvested by 5 times, despite the unwanted actuation effect.
NASA Astrophysics Data System (ADS)
Song, Yan; Fang, Xiaosheng; Diao, Qingda
2016-03-01
In this paper, we discuss the mixed H2/H∞ distributed robust model predictive control problem for polytopic uncertain systems subject to randomly occurring actuator saturation and packet loss. The global system is decomposed into several subsystems, and all the subsystems are connected by a fixed topology network, which is the definition for the packet loss among the subsystems. To better use the successfully transmitted information via Internet, both the phenomena of actuator saturation and packet loss resulting from the limitation of the communication bandwidth are taken into consideration. A novel distributed controller model is established to account for the actuator saturation and packet loss in a unified representation by using two sets of Bernoulli distributed white sequences with known conditional probabilities. With the nonlinear feedback control law represented by the convex hull of a group of linear feedback laws, the distributed controllers for subsystems are obtained by solving an linear matrix inequality (LMI) optimisation problem. Finally, numerical studies demonstrate the effectiveness of the proposed techniques.
NASA Astrophysics Data System (ADS)
Quang Truong, Dinh; Ahn, Kyoung Kwan
2014-07-01
An ion polymer metal composite (IPMC) is an electroactive polymer that bends in response to a small applied electric field as a result of mobility of cations in the polymer network and vice versa. This paper presents an innovative and accurate nonlinear black-box model (NBBM) for estimating the bending behavior of IPMC actuators. The model is constructed via a general multilayer perceptron neural network (GMLPNN) integrated with a smart learning mechanism (SLM) that is based on an extended Kalman filter with self-decoupling ability (SDEKF). Here the GMLPNN is built with an ability to autoadjust its structure based on its characteristic vector. Furthermore, by using the SLM based on the SDEKF, the GMLPNN parameters are optimized with small computational effort, and the modeling accuracy is improved. An apparatus employing an IPMC actuator is first set up to investigate the IPMC characteristics and to generate the data for training and validating the model. The advanced NBBM model for the IPMC system is then created with the proper inputs to estimate IPMC tip displacement. Next, the model is optimized using the SLM mechanism with the training data. Finally, the optimized NBBM model is verified with the validating data. A comparison between this model and the previously developed model is also carried out to prove the effectiveness of the proposed modeling technique.
A GENERAL RELATIVISTIC MODEL OF ACCRETION DISKS WITH CORONAE SURROUNDING KERR BLACK HOLES
You Bei; Cao Xinwu; Yuan Yefei E-mail: cxw@shao.ac.cn
2012-12-20
We calculate the structure of a standard accretion disk with a corona surrounding a massive Kerr black hole in the general relativistic frame, in which the corona is assumed to be heated by the reconnection of the strongly buoyant magnetic fields generated in the cold accretion disk. The emergent spectra of accretion disk-corona systems are calculated by using the relativistic ray-tracing method. We propose a new method to calculate the emergent Comptonized spectra from the coronae. The spectra of disk-corona systems with a modified {alpha}-magnetic stress show that both the hard X-ray spectral index and the hard X-ray bolometric correction factor L{sub bol}/L{sub X,2-10keV} increase with the dimensionless mass accretion rate, which is qualitatively consistent with the observations of active galactic nuclei. The fraction of the power dissipated in the corona decreases with increasing black hole spin parameter a, which leads to lower electron temperatures of the coronae for rapidly spinning black holes. The X-ray emission from the coronae surrounding rapidly spinning black holes becomes weak and soft. The ratio of the X-ray luminosity to the optical/UV luminosity increases with the viewing angle, while the spectral shape in the X-ray band is insensitive to the viewing angle. We find that the spectral index in the infrared waveband depends on the mass accretion rate and the black hole spin a, which deviates from the f{sub {nu}}{proportional_to}{nu}{sup 1/3} relation expected by the standard thin disk model.
X-RAY REFLECTED SPECTRA FROM ACCRETION DISK MODELS. I. CONSTANT DENSITY ATMOSPHERES
Garcia, J.; Kallman, T. R. E-mail: timothy.r.kallman@nasa.go
2010-08-01
We present new models for illuminated accretion disks, their structure, and reprocessed emission. We consider the effects of incident X-rays on the surface of an accretion disk by simultaneously solving the equations of radiative transfer, energy balance, and ionization equilibrium over a large range of column densities. We assume plane-parallel geometry and azimuthal symmetry, such that each calculation corresponds to a ring at a given distance from the central object. Our models include recent and complete atomic data for K-shell processes of the iron and oxygen isonuclear sequences. We examine the effect on the spectrum of fluorescent K{alpha} line emission and absorption in the emitted spectrum. We also explore the dependence of the spectrum on the strength of the incident X-rays and other input parameters, and discuss the importance of Comptonization on the emitted spectrum.
Numerical Modeling of Dusty Disk System Morphologies With Deep Impact Derived Opacities
NASA Astrophysics Data System (ADS)
Fraine, Jonathan; Lisse, C. M.; Kuchner, M.; Stark, C.
2008-09-01
We have taken existing dust morphology modeling software, ZODIPIC (Kuchner et al. 2007) and modified the opacity data to reflect the species detected in comets from the Deep Impact mission, the Spitzer survey of comets, STARDUST, and bright exo-planetary dust spectra. Opacities from multiple chemical species were adapted to the ZODIPIC code and now contain spectra that can match the existing spectra from the debris disk systems. User supplied coefficients can now modify pre-programmed spectral species to match morphological outputs with desired empirical expectations. This tool can aid in generating expectations for direct or indirect observations of exoplanetary debris disks. We show example morphological models of silicate rich (e.g., HD69830, Beichman et al. 2005) and carbon-rich (Beta Pic like, Roberge et al. 2007) systems.
X-ray Reflected Spectra from Accretion Disk Models. I. Constant Density Atmospheres
NASA Technical Reports Server (NTRS)
Garcia, Javier; Kallman, Timothy R.
2009-01-01
We present new models for illuminated accretion disks, their structure and reprocessed emission. We consider the effects of incident X-rays on the surface of an accretion disk by solving simultaneously the equations of radiative transfer, energy balance and ionization equilibrium over a large range of column densities. We assume plane-parallel geometry and azimuthal symmetry, such that each calculation corresponds to a ring at a given distance from the central object. Our models include recent and complete atomic data for K-shell of the iron and oxygen isonuclear sequences. We examine the effect on the spectrum of fluorescent Ka line emission and absorption in the emitted spectrum. We also explore the dependence of the spectrum on the strength of the incident X-rays and other input parameters, and discuss the importance of Comptonization on the emitted spectrum.
Microstructure Modeling of 3rd Generation Disk Alloys
NASA Technical Reports Server (NTRS)
Jou, Herng-Jeng
2010-01-01
The objective of this program is to model, validate, and predict the precipitation microstructure evolution, using PrecipiCalc (QuesTek Innovations LLC) software, for 3rd generation Ni-based gas turbine disc superalloys during processing and service, with a set of logical and consistent experiments and characterizations. Furthermore, within this program, the originally research-oriented microstructure simulation tool will be further improved and implemented to be a useful and user-friendly engineering tool. In this report, the key accomplishment achieved during the second year (2008) of the program is summarized. The activities of this year include final selection of multicomponent thermodynamics and mobility databases, precipitate surface energy determination from nucleation experiment, multiscale comparison of predicted versus measured intragrain precipitation microstructure in quench samples showing good agreement, isothermal coarsening experiment and interaction of grain boundary and intergrain precipitates, primary microstructure of subsolvus treatment, and finally the software implementation plan for the third year of the project. In the following year, the calibrated models and simulation tools will be validated against an independently developed experimental data set, with actual disc heat treatment process conditions. Furthermore, software integration and implementation will be developed to provide material engineers valuable information in order to optimize the processing of the 3rd generation gas turbine disc alloys.
Lower Bound on the Mean Square Displacement of Particles in the Hard Disk Model
NASA Astrophysics Data System (ADS)
Richthammer, Thomas
2016-08-01
The hard disk model is a 2D Gibbsian process of particles interacting via pure hard core repulsion. At high particle density the model is believed to show orientational order, however, it is known not to exhibit positional order. Here we investigate to what extent particle positions may fluctuate. We consider a finite volume version of the model in a box of dimensions 2 n × 2 n with arbitrary boundary configuration, and we show that the mean square displacement of particles near the center of the box is bounded from below by c log n. The result generalizes to a large class of models with fairly arbitrary interaction.
A METHOD FOR THE STUDY OF ACCRETION DISK EMISSION IN CATACLYSMIC VARIABLES. I. THE MODEL
Puebla, Raul E.; Diaz, Marcos P.; John Hillier, D.; Hubeny, Ivan E-mail: marcos@astro.iag.usp.br E-mail: hubeny@as.arizona.edu
2011-07-20
We have developed a spectrum synthesis method for modeling the ultraviolet (UV) emission from the accretion disk from cataclysmic variables (CVs). The disk is separated into concentric rings, with an internal structure from the Wade and Hubeny disk-atmosphere models. For each ring, a wind atmosphere is calculated in the comoving frame with a vertical velocity structure obtained from a solution of the Euler equation. Using simple assumptions, regarding rotation and the wind streamlines, these one-dimensional models are combined into a single 2.5-dimensional model for which we compute synthetic spectra. We find that the resulting line and continuum behavior as a function of the orbital inclination is consistent with the observations, and verify that the accretion rate affects the wind temperature, leading to corresponding trends in the intensity of UV lines. In general, we also find that the primary mass has a strong effect on the P Cygni absorption profiles, the synthetic emission line profiles are strongly sensitive to the wind temperature structure, and an increase in the mass-loss rate enhances the resonance line intensities. Synthetic spectra were compared with UV data for two high orbital inclination nova-like CVs-RW Tri and V347 Pup. We needed to include disk regions with arbitrary enhanced mass loss to reproduce reasonably well widths and line profiles. This fact and a lack of flux in some high ionization lines may be the signature of the presence of density-enhanced regions in the wind, or alternatively, may result from inadequacies in some of our simplifying assumptions.
METALLICITY GRADIENTS THROUGH DISK INSTABILITY: A SIMPLE MODEL FOR THE MILKY WAY'S BOXY BULGE
Martinez-Valpuesta, Inma; Gerhard, Ortwin E-mail: gerhard@mpe.mpg.de
2013-03-20
Observations show a clear vertical metallicity gradient in the Galactic bulge, which is often taken as a signature of dissipative processes in the formation of a classical bulge. Various evidence shows, however, that the Milky Way is a barred galaxy with a boxy bulge representing the inner three-dimensional part of the bar. Here we show with a secular evolution N-body model that a boxy bulge formed through bar and buckling instabilities can show vertical metallicity gradients similar to the observed gradient if the initial axisymmetric disk had a comparable radial metallicity gradient. In this framework, the range of metallicities in bulge fields constrains the chemical structure of the Galactic disk at early times before bar formation. Our secular evolution model was previously shown to reproduce inner Galaxy star counts and we show here that it also has cylindrical rotation. We use it to predict a full mean metallicity map across the Galactic bulge from a simple metallicity model for the initial disk. This map shows a general outward gradient on the sky as well as longitudinal perspective asymmetries. We also briefly comment on interpreting metallicity gradient observations in external boxy bulges.
Modeling X-ray Absorbers in AGNs with MHD-Driven Accretion-Disk Winds
NASA Astrophysics Data System (ADS)
Fukumura, Keigo; Kazanas, D.; Shrader, C. R.; Tombesi, F.; Contopoulos, J.; Behar, E.
2013-04-01
We have proposed a systematic view of the observed X-ray absorbers, namely warm absorbers (WAs) in soft X-ray and highly-ionized ultra-fast outflows (UFOs), in the context of magnetically-driven accretion-disk wind models. While potentially complicated by variability and thermal instability in these energetic outflows, in this simplistic model we have calculated 2D kinematic field as well as density and ionization structure of the wind with density profile of 1/r corresponding to a constant column distribution per decade of ionization parameter. In particular we show semi-analytically that the inner layer of the disk-wind manifests itself as the strongly-ionized fast outflows while the outer layer is identified as the moderately-ionized absorbers. The computed characteristics of these two apparently distinct absorbers are consistent with X-ray data (i.e. a factor of ~100 difference in column and ionization parameters as well as low wind velocity vs. near-relativistic flow). With the predicted contour curves for these wind parameters one can constrain allowed regions for the presence of WAs and UFOs.The model further implies that the UFO's gas pressure is comparable to that of the observed radio jet in 3C111 suggesting that the magnetized disk-wind with density profile of 1/r is a viable agent to help sustain such a self-collimated jet at small radii.
Miniature linear-to-rotary motion actuator
NASA Technical Reports Server (NTRS)
Sorokach, Michael R., Jr.
1993-01-01
A miniature hydraulic actuation system capable of converting linear actuator motion to control surface rotary motion has been designed for application to active controls on dynamic wind tunnel models. Due to space constraints and the torque requirements of an oscillating control surface at frequencies up to 50 Hertz, a new actuation system was developed to meet research objectives. This new actuation system was designed and developed to overcome the output torque limitations and fluid loss/sealing difficulties associated with an existing vane type actuator. Static control surface deflections and dynamic control surface oscillations through a given angle are provided by the actuation system. The actuator design has been incorporated into a transonic flutter model with an active trailing edge flap and two active spoilers. The model is scheduled for testing in the LaRC 16 Foot Transonic Dynamics Tunnel during Summer 1993. This paper will discuss the actuation system, its design, development difficulties, test results, and application to aerospace vehicles.
NASA Technical Reports Server (NTRS)
Tilton, Charles (Inventor); Weiler, Jeff (Inventor); Palmer, Randall (Inventor); Appel, Philip (Inventor)
2008-01-01
An actuated atomizer is adapted for spray cooling or other applications wherein a well-developed, homogeneous and generally conical spray mist is required. The actuated atomizer includes an outer shell formed by an inner ring; an outer ring; an actuator insert and a cap. A nozzle framework is positioned within the actuator insert. A base of the nozzle framework defines swirl inlets, a swirl chamber and a swirl chamber. A nozzle insert defines a center inlet and feed ports. A spool is positioned within the coil housing, and carries the coil windings having a number of turns calculated to result in a magnetic field of sufficient strength to overcome the bias of the spring. A plunger moves in response to the magnetic field of the windings. A stop prevents the pintle from being withdrawn excessively. A pintle, positioned by the plunger, moves between first and second positions. In the first position, the head of the pintle blocks the discharge passage of the nozzle framework, thereby preventing the atomizer from discharging fluid. In the second position, the pintle is withdrawn from the swirl chamber, allowing the atomizer to release atomized fluid. A spring biases the pintle to block the discharge passage. The strength of the spring is overcome, however, by the magnetic field created by the windings positioned on the spool, which withdraws the plunger into the spool and further compresses the spring.
AdS Black Disk Model for Small-x Deep Inelastic Scattering
Cornalba, Lorenzo; Costa, Miguel S.; Penedones, Joao
2010-08-13
Using the approximate conformal invariance of QCD at high energies we consider a simple anti-de Sitter black disk model to describe saturation in deep inelastic scattering. Deep inside saturation the structure functions have the same power law scaling, F{sub T}{approx}F{sub L}{approx}x{sup -{omega}}, where {omega} is related to the expansion rate of the black disk with energy. Furthermore, the ratio F{sub L}/F{sub T} is given by the universal value (1+{omega}/3+{omega}), independently of the target. For {gamma}*-{gamma}* scattering at high energies we obtain explicit expressions and ratios for the total cross sections of transverse and longitudinal photons in terms of the single parameter {omega}.
A Disk-Corona Model for Optical-to-Hard X-ray spectrum of AGN
NASA Astrophysics Data System (ADS)
Kawaguchi, T.; Shimura, T.; Mineshige, S.
We construct a disk-corona model to account for the optical-to-X-ray spectral energy distributions of Seyfert nuclei and QSOs. We study the emission spectrum emerging from a vertical disk-corona structure composed of two-temperature plasma by solving hydrostatic equilibrium and radiative transfer self-consistently. A fraction f of viscous heating is assumed to be dissipated in a corona where advective cooling is also included, and the remaining fraction, 1-f, within the main body of the disk. The model exhibits different photon indices in X-ray (Γ ~ 2.5 below 2 keV and ~ 1.5 above, where Fν ∝ ν(1 - Γ)) as the result of different emission mechanisms and different sites; the former slope is due to unsaturated Comptonization from the innermost zone and the latter is due to a combination of Comptonization and bremsstrahlung from the entire corona (<= 300 RSch). Because of the shorter dynamical time-scale at inner region than that at outer region, the emission from the inner radii is likely to be more variable than radiation from the outer parts. Then, the X-ray spectrum is expected to be softer in brighter phase, as observed in many Broad-Line Seyfert 1 nuclei.
Titius-Bode laws in the solar system. 2: Build your own law from disk models
NASA Astrophysics Data System (ADS)
Dubrulle, B.; Graner, F.
1994-02-01
Simply respecting both scale and rotational invariance, it is easy to construct an endless collection of theoretical models predicting a Titius-Bode law, irrespective to their physical content. Due to the numerous ways to get the law and its intrinsic arbitrariness, it is not a useful constraint on theories of solar system formation. To illustrate the simple elegance of scale-invariant methods, we explicitly cook up one of the simplest examples, an infinitely thin cold gaseous disk rotating around a central object. In that academic case, the Titius-Bode law holds during the linear stage of the gravitational instability. The time scale of the instability is of the order of a self-gravitating time scale, (G rhod)-1/2, where rhod is the disk density. This model links the separation between different density maxima with the ratio MD/MC of the masses of the disk and the central object; for instance, MD/MC of the order of 0.18 roughly leads to the observed separation between the planets. We discuss the boundary conditions and the limit of the Wentzel-Kramer-Brillouin (WKB) approximation.
Two-dimensional modeling of an aircraft engine structural bladed disk-casing modal interaction
NASA Astrophysics Data System (ADS)
Legrand, Mathias; Pierre, Christophe; Cartraud, Patrice; Lombard, Jean-Pierre
2009-01-01
In modern turbo machines such as aircraft jet engines, structural contacts between the casing and bladed disk may occur through a variety of mechanisms: coincidence of vibration modes, thermal deformation of the casing, rotor imbalance due to design uncertainties to name a few. These nonlinear interactions may result in severe damage to both structures and it is important to understand the physical circumstances under which they occur. In this study, we focus on a modal coincidence during which the vibrations of each structure take the form of a k-nodal diameter traveling wave characteristic of axi-symmetric geometries. A realistic two-dimensional model of the casing and bladed disk is introduced in order to predict the occurrence of this very specific interaction phenomenon versus the rotation speed of the engine. The equations of motion are solved using an explicit time integration scheme in conjunction with the Lagrange multiplier method where friction is accounted for. This model is validated from the comparison with an analytical solution. The numerical results show that the structures may experience different kinds of behaviors (namely damped, sustained and divergent motions) mainly depending on the rotational velocity of the bladed disk.
Chemistry in disks. IX. Observations and modelling of HCO+ and DCO+ in DM Tauri
NASA Astrophysics Data System (ADS)
Teague, R.; Semenov, D.; Guilloteau, S.; Henning, Th.; Dutrey, A.; Wakelam, V.; Chapillon, E.; Pietu, V.
2015-02-01
Aims: We study the deuteration and ionization structure of the DM Tau disk via interferometric observations and modelling of the key molecular ions, HCO+ and DCO+. Methods: The Plateau de Bure Array is used to observe DM Tau in lines of HCO+ (1-0), (3-2) and DCO+ (3-2) with a ~ 1.5'' angular and ~0.2 km s-1 spectral resolution. Using a power-law fitting approach the observed column densities profiles are derived and thus the isotopic ratio RD = DCO+/HCO+. Chemical modelling allowed an exploration of the sensitivity of HCO+ and DCO+ abundances to physical parameters out with temperature. A steady state approximation was employed to observationally constrain the ionization fraction x(e-). Results: Fitting of radiative transfer models suggests that there is a chemical hole in HCO+ and DCO+, extending up to 50 AU from the star. More work is required to discern the cause of this. The observed column densities of HCO+ and DCO+ at 100 AU were (9.8+0.3-0.7) × 1012 and (1.2 ± 0.7) × 1012 cm-2 respectively. Where both HCO+ and DCO+ were present, RD was found to increase radially from 0.1 at 50 AU to 0.2 at 450 AU. This behaviour was well reproduced by the chemical model. The X-ray luminosity of the central star, the interstellar UV and CO depletion were found to be the most important physical parameters controlling the abundances of HCO+ and DCO+. Differences in the vertical extent of HCO+ and DCO+ molecular layers resulted in different responses to changing physical parameters, manifesting as radial gradients in RD. The ionization fraction was found to be x(e-) ~ 10-7 in the molecular layer, comparable to the disk averaged value. Modelling shows that while HCO+ is the most dominant charged molecular ion in our disk model, atomic ions, such as C+, S+, H+, Na+ and Mg+, dominate the charge in both the molecular layer and disk atmosphere. Conclusions: A high value of RD is indicative of continued deuterium fractionation in a protoplanetary disk after pre/protostellar phases
NASA Astrophysics Data System (ADS)
Wu, Yongxian
IPMCs can also be tailored through the applied DC or AC functions. It is found that the Nafion-based IPMC's initial motion towards the anode can be controlled and ultimately eliminated by applying a potential ramp at a suitably slow rate. These results have significant bearing on verifying various IPMC actuation models.
Development of a Higher Order Laminate Theory for Modeling Composites with Induced Strain Actuators
NASA Technical Reports Server (NTRS)
Chattopadhyay, Aditi; Seeley, Charles E.
1996-01-01
A refined higher order plate theory is developed to investigate the actuation mechanism of piezoelectric materials surface bonded or embedded in composite laminates. The current analysis uses a displacement field which accurately accounts for transverse shear stresses. Some higher order terms are identified by using the conditions that shear stresses vanish at all free surfaces. Therefore, all boundary conditions for displacements and stresses are satisfied in the present theory. The analysis is implemented using the finite element method which provides a convenient means to construct a numerical solution due to the discrete nature of the actuators. The higher order theory is computationally less expensive than a full three dimensional analysis. The theory is also shown to agree well with published experimental results. Numerical examples are presented for composite plates with thicknesses ranging from thin to very thick.
Numerical modelling of Mars supersonic disk-gap-band parachute inflation
NASA Astrophysics Data System (ADS)
Gao, Xinglong; Zhang, Qingbin; Tang, Qiangang
2016-06-01
The transient dynamic behaviour of supersonic disk-gap-band parachutes in a Mars entry environment involving fluid structure interactions is studied. Based on the multi-material Arbitrary Lagrange-Euler method, the coupling dynamic model between a viscous compressible fluid and a flexible large deformation structure of the parachute is solved. The inflation performance of a parachute with a fixed forebody under different flow conditions is analysed. The decelerating parameters of the parachute, including drag area, opening loads, and coefficients, are obtained from the supersonic wind tunnel test data from NASA. Meanwhile, the evolution of the three-dimensional shape of the disk-gap-band parachute during supersonic inflation is presented, and the structural dynamic behaviour of the parachute is predicted. Then, the influence of the presence of the capsule on the flow field of the parachute is investigated, and the wake of unsteady fluid and the distribution of shock wave around the supersonic parachute are presented. Finally, the structural dynamic response of the canopy fabric under high-pressure conditions is comparatively analysed. The results show that the disk-gap-band parachute is well inflated without serious collapse. As the Mach numbers increase from 2.0 to 2.5, the drag coefficients gradually decrease, along with a small decrease in inflation time, which corresponds with test results, and proves the validity of the method proposed in this paper.
Distributed structural control using multilayered piezoelectric actuators
NASA Technical Reports Server (NTRS)
Cudney, Harley H.; Inman, Daniel J.; Oshman, Yaakov
1990-01-01
A method of segmenting piezoelectric sensors and actuators is proposed which can preclude the currently experienced cancelation of sensor signals, or the reduction of actuator effectiveness, due to the integration of the property undergoing measurement or control. The segmentation method is demonstrated by a model developed for beam structures, to which multiple layers of piezoelectric materials are attached. A numerical study is undertaken of increasing active and passive damping of a beam using the segmented sensors and actuators over unsegmented sensors and actuators.
MODELING COLLISIONAL CASCADES IN DEBRIS DISKS: STEEP DUST-SIZE DISTRIBUTIONS
Gaspar, Andras; Psaltis, Dimitrios; Rieke, George H.; Oezel, Feryal E-mail: dpsaltis@as.arizona.edu E-mail: fozel@as.arizona.edu
2012-07-20
We explore the evolution of the mass distribution of dust in collision-dominated debris disks, using the collisional code introduced in our previous paper. We analyze the equilibrium distribution and its dependence on model parameters by evolving over 100 models to 10 Gyr. With our numerical models, we confirm that systems reach collisional equilibrium with a mass distribution that is steeper than the traditional solution by Dohnanyi. Our model yields a quasi-steady-state slope of n(m) {approx} m{sup -1.88} [n(a) {approx} a{sup -3.65}] as a robust solution for a wide range of possible model parameters. We also show that a simple power-law function can be an appropriate approximation for the mass distribution of particles in certain regimes. The steeper solution has observable effects in the submillimeter and millimeter wavelength regimes of the electromagnetic spectrum. We assemble data for nine debris disks that have been observed at these wavelengths and, using a simplified absorption efficiency model, show that the predicted slope of the particle-mass distribution generates spectral energy distributions that are in agreement with the observed ones.
Bills, K.C.; Kress, R.L.; Kwon, D.S.; Baker, C.P.
1994-12-31
This paper describes ORNL`s development of an environment for the simulation of robotic manipulators. Simulation includes the modeling of kinematics, dynamics, sensors, actuators, control systems, operators, and environments. Models will be used for manipulator design, proposal evaluation, control system design and analysis, graphical preview of proposed motions, safety system development, and training. Of particular interest is the development of models for robotic manipulators having at least one flexible link. As a first application, models have been developed for the Pacific Northwest Laboratory`s Flexible Beam Test Bed (PNL FBTB), which is a 1-Degree-of-Freedom, flexible arm with a hydraulic base actuator. ORNL transferred control algorithms developed for the PNL FBTB to controlling IGRIP models. A robust notch filter is running in IGRIP controlling a full dynamics model of the PNL test bed. Model results provide a reasonable match to the experimental results (quantitative results are being determined) and can run on ORNL`s Onyx machine in approximately realtime. The flexible beam is modeled as six rigid sections with torsional springs between each segment. The spring constants were adjusted to match the physical response of the flexible beam model to the experimental results. The controller is able to improve performance on the model similar to the improvement seen on the experimental system. Some differences are apparent, most notably because the IGRIP model presently uses a different trajectory planner than the one used by ORNL on the PNL test bed. In the future, the trajectory planner will be modified so that the experiments and models are the same. The successful completion of this work provides the ability to link C code with IGRIP, thus allowing controllers to be developed, tested, and tuned in simulation and then ported directly to hardware systems using the C language.
NASA Technical Reports Server (NTRS)
Brudnicki, Myron (Inventor)
1995-01-01
Rotary actuators and other mechanical devices incorporating shape memory alloys are provided herein. Shape memory alloys are a group of metals which when deformed at temperatures below their martensite temperatures, resume the shapes which they had prior to the deformation if they are heated to temperatures above their austensite temperatures. Actuators in which shape memory alloys are employed include bias spring types, in which springs deform the shape memory alloy (SMA), and differential actuators, which use two SMA members mechanically connected in series. Another type uses concentric cylindrical members. One member is in the form of a sleeve surrounding a cylinder, both being constructed of shape memory alloys. Herein two capstans are mounted on a shaft which is supported in a framework. Each capstan is capable of rotating the shaft. Shape memory wire, as two separate lengths of wire, is wrapped around each capstan to form a winding around that capstan. The winding on one capstan is so wrapped that the wire is in a prestretched state. The winding on the other capstan is so wrapped that the wire is in a taut, but not a prestretched, state. Heating one performs work in one direction, thus deforming the other one. When the other SMA is heated the action is reversed.
NASA Technical Reports Server (NTRS)
Kumar, Parikshith K.; Desai, Uri; Chatzigeorgiou, George; Lagoudas, Dimitris C.; Monroe, James; Karaman, Ibrahim; Noebe, Ron; Bigelow, Glen
2010-01-01
The present work is focused on studying the cycling actuation behavior of HTSMAs undergoing simultaneous creep and transformation. For the thermomechanical testing, a high temperature test setup was assembled on a MTS frame with the capability to test up to temperatures of 600 C. Constant stress thermal cycling tests were conducted to establish the actuation characteristics and the phase diagram for the chosen HTSMA. Additionally, creep tests were conducted at constant stress levels at different test temperatures to characterize the creep behavior of the alloy over the operational range. A thermodynamic constitutive model is developed and extended to take into account a) the effect of multiple thermal cycling on the generation of plastic strains due to transformation (TRIP strains) and b) both primary and secondary creep effects. The model calibration is based on the test results. The creep tests and the uniaxial tests are used to identify the viscoplastic behavior of the material. The parameters for the SMA properties, regarding the transformation and transformation induced plastic strain evolutions, are obtained from the material phase diagram and the thermomechanical tests. The model is validated by predicting the material behavior at different thermomechanical test conditions.
NASA Astrophysics Data System (ADS)
Lavaroni, Luca; Watson, Simon J.; Cook, Malcolm J.; Dubal, Mark R.
2014-06-01
In this paper computational fluid dynamics (CFD) simulations are performed using ANSYS CFX to compare wake interaction results obtained from two rotor modelling methodologies: the standard actuator disc and the blade element momentum model (BEM). The unsteady simulations embed Coriolis forces and neutral stability conditions in the surface layer and stable conditions in the free stream. The BEM method is implemented in the CFD code through a pre-processing set of files that employs look-up tables. The control system for the wind turbines is considered through look-up tables that are constructed based on operational wind farm data. Simulations using the actuator disc and BEM methodologies have been performed using a number of different turbulence models in order to compare the wind turbine wake structure results. The use of URANS and LES numerical methods, coupled with the two different methodologies of representing the turbine, enables an assessment to be made of the details required for varying degrees of accuracy in computing the wake structures. The findings stress the importance of including the rotation of the wake and the non-uniform load on the rotor in LES simulations to account for more accurate turbulence intensity levels in the near wake.
An X-Ray Reprocessing Model of Disk Thermal Emission in Type 1 Seyfert Galaxies
NASA Astrophysics Data System (ADS)
Chiang, James
2002-06-01
Using a geometry consisting of a hot central Comptonizing plasma surrounded by a thin accretion disk, we model the optical through hard X-ray spectral energy distributions of the type 1 Seyfert galaxies NGC 3516 and NGC 7469. As in the model proposed by Poutanen, Krolik, & Ryde for the X-ray binary Cyg X-1 and later applied to Seyfert galaxies by Zdziarski, Lubiński, & Smith, feedback between the radiation reprocessed by the disk and the thermal Comptonization emission from the hot central plasma plays a pivotal role in determining the X-ray spectrum and, as we show, the optical and ultraviolet spectra as well. Seemingly uncorrelated optical/UV and X-ray light curves, similar to those that have been observed from these objects can, in principle, be explained by variations in the size, shape, and temperature of the Comptonizing plasma. Furthermore, by positing a disk mass accretion rate that satisfies a condition for global energy balance between the thermal Comptonization luminosity and the power available from accretion, one can predict the spectral properties of the heretofore poorly measured hard X-ray continuum above ~50 keV in type 1 Seyfert galaxies. Conversely, forthcoming measurements of the hard X-ray continuum by more sensitive hard X-ray and soft γ-ray telescopes, such as those aboard the International Gamma-Ray Astrophysics Laboratory, in conjunction with simultaneous optical, UV, and soft X-ray monitoring, will allow the mass accretion rates to be directly constrained for these sources in the context of this model.
An X-Ray Reprocessing Model of Disk Thermal Emission in Type 1 Seyfert Galaxies
NASA Technical Reports Server (NTRS)
Chiang, James; White, Nicholas E. (Technical Monitor)
2002-01-01
Using a geometry consisting of a hot central Comptonizing plasma surrounded by a thin accretion disk, we model the optical through hard X-ray spectral energy distributions of the type 1 Seyfert. galaxies NGC 3516 and NGC 7469. As in the model proposed by Poutanen, Krolik, and Ryde for the X-ray binary Cygnus X-1 and later applied to Seyfert galaxies by Zdziarski, Lubifiski, and Smith, feedback between the radiation reprocessed by the disk and the thermal Comptonization emission from the hot central plasma plays a pivotal role in determining the X-ray spectrum, and as we show, the optical and ultraviolet spectra as well. Seemingly uncorrelated optical/UV and X-ray light curves, similar to those which have been observed from these objects can, in principle, be explained by variations in the size, shape, and temperature of the Comptonizing plasma. Furthermore, by positing a disk mass accretion rate which satisfies a condition for global energy balance between the thermal Comptonization luminosity and the power available from accretion, one can predict the spectral properties of the heretofore poorly measured hard X-ray continuum above approximately 50 keV in type 1 Seyfert galaxies. Conversely, forthcoming measurements of the hard X-ray continuum by more sensitive hard X-ray and soft gamma-ray telescopes, such as those aboard the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) in conjunction with simultaneous optical, UV, and soft X-ray monitoring, will allow the mass accretion rates to be directly constrained for these sources in the context of this model.
The Disk Wind Model of the Broad Line Regions in Active Galactic Nuclei and Cataclysmic Variables
NASA Technical Reports Server (NTRS)
Begelman, Mitchell
2002-01-01
This is the final progress report for our Astrophysics Theory Program (NRA 97-OSS12) grant NAG5-7723. We have made considerable progress on incorporating photoionization calculations with a 2.5D hydrodynamical code to model disk winds in AGNs. Following up on our simultaneous broad band monitoring campaign of the type I Seyfert galaxy NGC 5548, we have investigated the constraints imposed on models of accretion in Seyfert galaxies by their optical, UV, and X-ray spectral energy distributions (SEDs). Using results from thermal Comptonization models that relate the physical properties of the hot inner accretion flow to the thermal reprocessing that occurs in the surrounding colder thin disk, we find that we can constrain the central black hole mass, accretion rate and size scale of the hot central flow. We have applied our model to observations of Seyfert galaxies NGC 3516, NGC 7469 and NGC 5548. Our mass and accretion rate estimates for these objects roughly agree with those found using other methods.
V3885 Sagittarius: A Comparison With a Range of Standard Model Accretion Disks
NASA Technical Reports Server (NTRS)
Linnell, Albert P.; Godon, Patrick; Hubeny, Ivan; Sion, Edward M; Szkody, Paula; Barrett, Paul E.
2009-01-01
A chi-squared analysis of standard model accretion disk synthetic spectrum fits to combined Far Ultraviolet Spectroscopic Explorer and Space Telescope Imaging Spectrograph spectra of V3885 Sagittarius, on an absolute flux basis, selects a model that accurately represents the observed spectral energy distribution. Calculation of the synthetic spectrum requires the following system parameters. The cataclysmic variable secondary star period-mass relation calibrated by Knigge in 2006 and 2007 sets the secondary component mass. A mean white dwarf (WD) mass from the same study, which is consistent with an observationally determined mass ratio, sets the adopted WD mass of 0.7M(solar mass), and the WD radius follows from standard theoretical models. The adopted inclination, i = 65 deg, is a literature consensus, and is subsequently supported by chi-squared analysis. The mass transfer rate is the remaining parameter to set the accretion disk T(sub eff) profile, and the Hipparcos parallax constrains that parameter to mas transfer = (5.0 +/- 2.0) x 10(exp -9) M(solar mass)/yr by a comparison with observed spectra. The fit to the observed spectra adopts the contribution of a 57,000 +/- 5000 K WD. The model thus provides realistic constraints on mass transfer and T(sub eff) for a large mass transfer system above the period gap.
Modular droplet actuator drive
NASA Technical Reports Server (NTRS)
Pollack, Michael G. (Inventor); Paik, Philip (Inventor)
2011-01-01
A droplet actuator drive including a detection apparatus for sensing a property of a droplet on a droplet actuator; circuitry for controlling the detection apparatus electronically coupled to the detection apparatus; a droplet actuator cartridge connector arranged so that when a droplet actuator cartridge electronically is coupled thereto: the droplet actuator cartridge is aligned with the detection apparatus; and the detection apparatus can sense the property of the droplet on a droplet actuator; circuitry for controlling a droplet actuator coupled to the droplet actuator connector; and the droplet actuator circuitry may be coupled to a processor.
Modeling and analysis of the thermal effects of a circular bimorph piezoelectric actuator.
Wang, Hairen; Yang, Shengfeng
2016-02-01
A theoretical analysis of the thermal effects of a circular bimorph piezoelectric actuator (CBPA) was performed. The circular bimorph structure consists of two flexible piezoelectric ceramic layers and one metallic layer in the middle, and is powered to produce flexural deformation. The CBPA, which may be a good match for large adaptive optics telescopes, has a large stroke and a high resonance frequency. We have derived analytical solutions (both the static solution and the dynamic solution) of the thermal effects of introducing (and increasing the thickness of) a metallic layer into the bimorph. Numerical results are presented to illustrate the dependence of the CBPA's performance upon the physical parameters. PMID:26836094
Linear stability analysis for an optimum Glauert rotor modelled by an actuator disc
NASA Astrophysics Data System (ADS)
Smith, D. M.; Blackburn, H. M.; Sheridan, J.
2014-06-01
We approximate a wind turbine using the Actuator Disc methodology with loading for an optimum Glauert rotor, and vary blade length and tip speed ratio, to determine base flows for linear stability computations at a Reynolds number of 100. Results from such computations suggest that the least stable mode is axisymmetric and insensitive to changes in tip speed operation, suggesting that the stability properties in the farfield wake for an optimised rotor are independent of the chosen tip speed optimization point. Higher azimuthal modes promote greater variation in velocities and may be relevant to cases at higher Reynolds numbers.
Models of the η Corvi Debris Disk from the Keck Interferometer, Spitzer, and Herschel
NASA Astrophysics Data System (ADS)
Lebreton, J.; Beichman, C.; Bryden, G.; Defrère, D.; Mennesson, B.; Millan-Gabet, R.; Boccaletti, A.
2016-02-01
Debris disks are signposts of analogs to small-body populations of the solar system, often, however, with much higher masses and dust production rates. The disk associated with the nearby star η Crv is especially striking, as it shows strong mid- and far-infrared excesses despite an age of ∼1.4 Gyr. We undertake constructing a consistent model of the system that can explain a diverse collection of spatial and spectral data. We analyze Keck Interferometer Nuller measurements and revisit Spitzer and additional spectrophotometric data, as well as resolved Herschel images, to determine the dust spatial distribution in the inner exozodi and in the outer belt. We model in detail the two-component disk and the dust properties from the sub-AU scale to the outermost regions by fitting simultaneously all measurements against a large parameter space. The properties of the cold belt are consistent with a collisional cascade in a reservoir of ice-free planetesimals at 133 AU. It shows marginal evidence for asymmetries along the major axis. KIN enables us to establish that the warm dust consists of a ring that peaks between 0.2 and 0.8 AU. To reconcile this location with the ∼400 K dust temperature, very high albedo dust must be invoked, and a distribution of forsterite grains starting from micron sizes satisfies this criterion, while providing an excellent fit to the spectrum. We discuss additional constraints from the LBTI and near-infrared spectra, and we present predictions of what James Webb Space Telescope can unveil about this unusual object and whether it can detect unseen planets.
Rheological properties of the soft-disk model of two-dimensional foams.
Langlois, Vincent J; Hutzler, Stefan; Weaire, Denis
2008-08-01
The soft-disk model previously developed and applied by Durian [D. J. Durian, Phys. Rev. Lett. 75, 4780 (1995)] is brought to bear on problems of foam rheology of longstanding and current interest, using two-dimensional systems. The questions at issue include the origin of the Herschel-Bulkley relation, normal stress effects (dilatancy), and localization in the presence of wall drag. We show that even a model that incorporates only linear viscous effects at the local level gives rise to nonlinear (power-law) dependence of the limit stress on strain rate. With wall drag, shear localization is found. Its nonexponential form and the variation of localization length with boundary velocity are well described by a continuum model in the spirit of Janiaud etal [Phys. Rev. Lett. 97, 038302 (2006)]. Other results satisfactorily link localization to model parameters, and hence tie together continuum and local descriptions. PMID:18850830
Electromechanical characteristic analysis of a dielectric electroactive polymer (DEAP) actuator
NASA Astrophysics Data System (ADS)
Zhu, Yinlong; Zhou, Hongpin; Wang, Huaming
2015-10-01
To assist in the design and optimization of dielectric electroactive polymer (DEAP) actuators, an analytical model for the electromechanical response of cone DEAP actuators is developed. Using the Yeoh form strain energy potential and the Maxwell stress tensor, the constitutive relationship of the DEAP that accounts for the electromechanical coupling behavior is deduced. The equilibrium equations of DEAP actuators with a cone configuration are derived and an analytical model is then proposed. With this model, the actuation characteristics of the DEAP actuator, including actuation displacement, force output and efficiency can be calculated. Additionally, the principal stresses and principal stretch ratio of the membrane under different actuation voltages can be determined, along with the wrinkling failure mode of DEAP actuators. The experimental results for the DEAP actuator matched the numerical results determined using the proposed model. As such, the proposed work is beneficial as a guide for the design optimization of DEAP actuators.
Modeling the X-ray Irradiation of the LkCa 15 Protoplanetary Disk Using XMM-Newton Archival Data
NASA Astrophysics Data System (ADS)
Skinner, Stephen
A giant protoplanet has been detected orbiting the nearby T Tauri star LkCa 15 using IR masked aperture techniques. The protoplanet (LkCa 15b) orbits within the dust-depleted inner region of a circumstellar disk at a projected separation of ~16 AU from the central star. The star itself is quite young (age ~2 Myr) making this system an excellent laboratory for studying the earliest stages of exoplanet formation. We detected LkCa 15 as a bright X-ray source in a short 9.8 ks Chandra observation during 2009. More recently, we obtained a deeper follow-up X-ray observation of LkCa 15 in 2014 with XMM-Newton providing a higher quality spectrum. We propose here to analyze the XMM-Newton data and use the derived spectral parameters along with known disk properties to model the X-ray heating and ionization of the LkCa 15 disk and to determine the gas-to-dust ratio (G/D) along the line-of-sight through the disk. X-ray heating and ionization affect the thermal and chemical structure in the disk and, along with the G/D ratio, are crucial parameters needed to determine physical conditions in the inner disk and construct realistic planet formation models. We are requesting ADAP funding to support the analysis and publication of this valuable XMM-Newton data set, which is now in the public archive.
Modelling circumbinary protoplanetary disks. I. Fluid simulations of the Kepler-16 and 34 systems
NASA Astrophysics Data System (ADS)
Lines, S.; Leinhardt, Z. M.; Baruteau, C.; Paardekooper, S.-J.; Carter, P. J.
2015-10-01
Context. The Kepler mission's discovery of a number of circumbinary planets orbiting close (ap< 1.1 au) to the stellar binary raises questions as to how these planets could have formed given the intense gravitational perturbations the dual stars impart on the disk. The gas component of circumbinary protoplanetary disks is perturbed in a similar manner to the solid, planetesimal dominated counterpart, although the mechanism by which disk eccentricity originates differs. Aims: This is the first work of a series that aims to investigate the conditions for planet formation in circumbinary protoplanetary disks. Methods: We present a number of hydrodynamical simulations that explore the response of gas disks around two observed binary systems: Kepler-16 and Kepler-34. We probe the importance of disk viscosity, aspect-ratio, inner boundary condition, initial surface density gradient, and self-gravity on the dynamical evolution of the disk, as well as its quasi-steady-state profile. Results: We find there is a strong influence of binary type on the mean disk eccentricity, e̅d, leading to e̅d = 0.02 - 0.08 for Kepler-16 and e̅d = 0.10 - 0.15 in Kepler-34. The value of α-viscosity has little influence on the disk, but we find a strong increase in mean disk eccentricity with increasing aspect-ratio due to wave propagation effects. The choice of inner boundary condition only has a small effect on the surface density and eccentricity of the disk. Our primary finding is that including disk self-gravity has little impact on the evolution or final state of the disk for disks with masses less than 12.5 times that of the minimum-mass solar nebula. This finding contrasts with the results of self-gravity relevance in circumprimary disks, where its inclusion is found to be an important factor in describing the disk evolution.
THE MASS-DEPENDENT STAR FORMATION HISTORIES OF DISK GALAXIES: INFALL MODEL VERSUS OBSERVATIONS
Chang, R. X.; Hou, J. L.; Shen, S. Y.; Shu, C. G.
2010-10-10
We introduce a simple model to explore the star formation histories of disk galaxies. We assume that the disk originate and grows by continuous gas infall. The gas infall rate is parameterized by the Gaussian formula with one free parameter: the infall-peak time t{sub p} . The Kennicutt star formation law is adopted to describe how much cold gas turns into stars. The gas outflow process is also considered in our model. We find that, at a given galactic stellar mass M{sub *}, the model adopting a late infall-peak time t{sub p} results in blue colors, low-metallicity, high specific star formation rate (SFR), and high gas fraction, while the gas outflow rate mainly influences the gas-phase metallicity and star formation efficiency mainly influences the gas fraction. Motivated by the local observed scaling relations, we 'construct' a mass-dependent model by assuming that the low-mass galaxy has a later infall-peak time t{sub p} and a larger gas outflow rate than massive systems. It is shown that this model can be in agreement with not only the local observations, but also with the observed correlations between specific SFR and galactic stellar mass SFR/M{sub *} {approx} M{sub *} at intermediate redshifts z < 1. Comparison between the Gaussian-infall model and the exponential-infall model is also presented. It shows that the exponential-infall model predicts a higher SFR at early stage and a lower SFR later than that of Gaussian infall. Our results suggest that the Gaussian infall rate may be more reasonable in describing the gas cooling process than the exponential infall rate, especially for low-mass systems.
NASA Technical Reports Server (NTRS)
Nelson, D. P.
1983-01-01
Wind tunnel model tests were conducted to demonstrate the aerodynamic performance improvements of a refined actuated inlet ejector nozzle. Models of approximately one-tenth scale were configured to simulate nozzle operation at takeoff, subsonic cruise, transonic cruise and supersonic cruise. Variations of model components provided a performance evaluation of ejector inlet and exit area, forebody boattail angle and ejector inlet operation in the open and closed mode. Approximately 700 data points were acquired at Mach numbers of 0, 0.36, 0.9, 1.2, and 2.0 for a wide range of nozzle flow conditions. Results show that relative to two ejector nozzles previously tested performance was improved significantly at takeoff and subsonic cruise performance, a C sub f of 0.982, was attained equal to the high performance of the previous tests. The established advanced supersonic transport propulsion study performance goals were met or closely approached at takeoff and supersonic cruise.
NASA Astrophysics Data System (ADS)
Cotroneo, Vincenzo; Davis, William N.; Reid, Paul B.; Schwartz, Daniel A.; Trolier-McKinstry, Susan; Wilke, Rudeger H. T.
2011-09-01
The present generation of X-ray telescopes emphasizes either high image quality (e.g. Chandra with sub-arc second resolution) or large effective area (e.g. XMM-Newton), while future observatories under consideration (e.g. Athena, AXSIO) aim to greatly enhance the effective area, while maintaining moderate (~10 arc-seconds) image quality. To go beyond the limits of present and planned missions, the use of thin adjustable optics for the control of low-order figure error is needed to obtain the high image quality of precisely figured mirrors along with the large effective area of thin mirrors. The adjustable mirror prototypes under study at Smithsonian Astrophysical Observatory are based on two different principles and designs: 1) thin film lead-zirconate-titanate (PZT) piezoelectric actuators directly deposited on the mirror back surface, with the strain direction parallel to the glass surface (for sub-arc-second angular resolution and large effective area), and 2) conventional leadmagnesium- niobate (PMN) electrostrictive actuators with their strain direction perpendicular to the mirror surface (for 3-5 arc second resolution and moderate effective area). We have built and operated flat test mirrors of these adjustable optics. We present the comparison between theoretical influence functions as obtained by finite element analysis and the measured influence functions obtained from the two test configurations.
Vollmer, Bernd; Leroy, Adam K.
2011-01-15
Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps contains free parameters, which can be constrained by observations of molecular gas, atomic gas, and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproduced by the model. In the framework of this model, the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in the star formation regime is realized by replacing the free-fall time in the prescription of the star formation rate with the molecule formation timescale. Depending on the star formation prescription, the break radius is located near the transition region between the molecular-gas-dominated and atomic-gas-dominated parts of the galactic disk or closer to the optical radius. It is found that only less massive galaxies (log M(M{sub sun}) {approx}< 10) can balance gas loss via star formation by radial gas accretion within the disk. These galaxies can thus access their gas reservoirs with large angular momentum. On the other hand, the star formation of massive galaxies is determined by the external gas mass accretion rate from a putative spherical halo of ionized gas or from satellite accretion. In the absence of this external accretion, star formation slowly exhausts the gas within the optical disk within the star formation timescale.
A DISK-WIND MODEL FOR THE NEAR-INFRARED EXCESS EMISSION IN PROTOSTARS
Bans, Alissa; Koenigl, Arieh E-mail: akonigl@uchicago.edu
2012-10-20
Protostellar systems, ranging from low-luminosity classical T Tauri and Herbig Ae stars to high-luminosity Herbig Be stars, exhibit a near-infrared (NIR) excess in their spectra that is dominated by a bump in the monochromatic luminosity with a peak near 3 {mu}m. The bump can be approximated by a thermal emission component of temperature {approx}1500 K that is of the order of the sublimation temperature of interstellar dust grains. In the currently popular 'puffed-up rim' scenario, the bump represents stellar radiation that propagates through the optically thin inner region of the surrounding accretion disk and is absorbed and reemitted by the dust that resides just beyond the dust sublimation radius r {sub sub}. However, this model cannot account for the strongest bumps measured in these sources, and it predicts a pronounced secondary bounce in the interferometric visibility curve that is not observed. In this paper we present an alternative interpretation, which attributes the bump to reemission of stellar radiation by dust that is uplifted from the disk by a centrifugally driven wind. Winds of this type are a leading candidate for the origin of the strong outflows associated with protostars, and there is observational evidence for disk winds originating on scales {approx}r {sub sub}. Using a newly constructed Monte Carlo radiative transfer code and focusing on low-luminosity sources, we show that this model can account for the NIR excess emission even in bright Herbig Ae stars such as AB Auriga and MWC 275, and that it successfully reproduces the basic features of the visibilities measured in these protostars. We argue that a robust dusty outflow in these sources could be self-limiting-through shielding of the stellar FUV photons-to a relatively narrow launching region between r {sub sub} and {approx}2 r {sub sub}. We also suggest that the NIR and scattered-light variability exhibited by a source like MWC 275 can be attributed in this picture to the uplifting of
Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback
NASA Astrophysics Data System (ADS)
Tombesi, F.
2016-05-01
Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this ``quasar mode'' feedback came from the recent X-ray observation of a mildly relativistic accretion disk wind in a ultraluminous infrared galaxy (ULIRG) and its connection with a large-scale molecular outflow, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and the dynamics of these winds. Some of these models have been directly compared to X-ray spectra, providing important insights into the wind physics. However, fundamental improvements on these studies will come only from the unprecedented energy resolution and sensitivity of the upcoming X-ray observatories, namely ASTRO-H (launch date early 2016) and Athena (2028).
NASA Astrophysics Data System (ADS)
Mangina, R. S.; Enloe, C. L.; Font, G. I.
2015-11-01
We present an experimental case study of time-resolved force production by an aerodynamic plasma actuator immersed in various mixtures of electropositive (N2) and electronegative gases (O2 and SF6) at atmospheric pressure using a fixed AC high-voltage input of 16 kV peak amplitude at 200 Hz frequency. We have observed distinct changes in the discharge structures during both negative- and positive-going voltage half-cycles, with corresponding variations in the actuator's force production: a ratio of 4:1 in the impulse produced by the negative-going half-cycle of the discharge among the various gas mixtures we explored, 2:1 in the impulse produced by the positive-going half-cycle, and cases in which the negative-going half-cycle dominates force production (by a ratio of 1.5:1), where the half-cycles produce identical force levels, and where the positive-going half cycle dominates (by a ratio of 1:5). We also present time-resolved experimental evidence for the first time that shows electrons do play a significant role in the momentum coupling to surrounding neutrals during the negative going voltage half-cycle of the N2 discharge. We show that there is sufficient macroscopic variation in the plasma that the predictions of numerical models at the microscopic level can be validated even though the plasma itself cannot be measured directly on those spatial and temporal scales.
A NEW RAYTRACER FOR MODELING AU-SCALE IMAGING OF LINES FROM PROTOPLANETARY DISKS
Pontoppidan, Klaus M.; Meijerink, Rowin; Blake, Geoffrey A.; Dullemond, Cornelis P.
2009-10-20
The material that formed the present-day solar system originated in feeding zones in the inner solar nebula located at distances within approx20 AU from the Sun, known as the planet-forming zone. Meteoritic and cometary material contain abundant evidence for the presence of a rich and active chemistry in the planet-forming zone during the gas-rich phase of solar system formation. It is a natural conjecture that analogs can be found among the zoo of protoplanetary disks around nearby young stars. The study of the chemistry and dynamics of planet formation requires: (1) tracers of dense gas at 100-1000 K and (2) imaging capabilities of such tracers with 5-100 mas (0.5-20 AU) resolution, corresponding to the planet-forming zone at the distance of the closest star-forming regions. Recognizing that the rich infrared (2-200 mum) molecular spectrum recently discovered to be common in protoplanetary disks represents such a tracer, we present a new general ray-tracing code, RADLite, that is optimized for producing infrared line spectra and images from axisymmetric structures. RADLite can consistently deal with a wide range of velocity gradients, such as those typical for the inner regions of protoplanetary disks. The code is intended as a back-end for chemical and excitation codes, and can rapidly produce spectra of thousands of lines for grids of models for comparison with observations. Such radiative transfer tools will be crucial for constraining both the structure and chemistry of planet-forming regions, including data from current infrared imaging spectrometers and extending to the Atacama Large Millimeter Array and the next generation of Extremely Large Telescopes, the James Webb Space Telescope and beyond.
An Eccentric-Disk Model for the Nucleus of M31
NASA Astrophysics Data System (ADS)
Tremaine, Scott
1995-08-01
The nucleus of M31 may be a thick eccentric disk, composed of stars traveling on nearly Keplerian orbits around a black hole or other dark compact object. This hypothesis reproduces most of the features seen in HST photometry of the center of M31; in particular the bright off-center source P1 is the apoapsis region of the disk. An eccentric disk can also explain the rotation curve and asymmetric dispersion profile revealed by ground-based observations. The central object must be smaller than ~1 pc so that the potential felt by the disk is nearly Keplerian. The disk eccentricity may be excited by dynamical friction from the bulge.
NASA Technical Reports Server (NTRS)
Ruoff, C. F. (Inventor)
1985-01-01
A mechanical actuator can be constructed by employing a plurality of memory metal actuator elements in parallel to control the amount of actuating force. In order to facilitate direct control by digital control signals provided by a computer or the like, the actuating elements may vary in stiffness according to a binary relationship. The cooling or reset time of the actuator elements can be reduced by employing Peltier junction cooling assemblies in the actuator.
NASA Astrophysics Data System (ADS)
Millan-Gabet, Rafael; Che, Xiao; Monnier, John D.; Sitko, Michael L.; Russell, Ray W.; Grady, Carol A.; Day, Amanda N.; Perry, R. B.; Harries, Tim J.; Aarnio, Alicia N.; Colavita, Mark M.; Wizinowich, Peter L.; Ragland, Sam; Woillez, Julien
2016-08-01
We present near- and mid-infrared (MIR) interferometric observations made with the Keck Interferometer Nuller and near-contemporaneous spectro-photometry from the infrared telescope facilities (IRTFs) of 11 well-known young stellar objects, several of which were observed for the first time in these spectral and spatial resolution regimes. With au-level spatial resolution, we first establish characteristic sizes of the infrared emission using a simple geometrical model consisting of a hot inner rim and MIR disk emission. We find a high degree of correlation between the stellar luminosity and the MIR disk sizes after using near-infrared data to remove the contribution from the inner rim. We then use a semi-analytical physical model to also find that the very widely used “star + inner dust rim + flared disk” class of models strongly fails to reproduce the spectral energy distribution (SED) and spatially resolved MIR data simultaneously; specifically a more compact source of MIR emission is required than results from the standard flared disk model. We explore the viability of a modification to the model whereby a second dust rim containing smaller dust grains is added, and find that the 2-rim model leads to significantly improved fits in most cases. This complexity is largely missed when carrying out SED modeling alone, although detailed silicate feature fitting by McClure et al. recently came to a similar conclusion. As has been suggested recently by Menu et al., the difficulty in predicting MIR sizes from the SED alone might hint at “transition disk”-like gaps in the inner au; however, the relatively high correlation found in our MIR disk size versus stellar luminosity relation favors layered disk morphologies and points to missing disk model ingredients instead.
NASA Astrophysics Data System (ADS)
Esposito, Thomas; Fitzgerald, M. P.; Kalas, P.; Graham, J. R.
2012-01-01
We have spatially resolved the debris disk around the A star HD 32297 in scattered light using Keck NIRC2 coronagraphic imaging with adaptive optics in the H and K bands. We used angular differential imaging and the LOCI algorithm to suppress the stellar PSF and reveal the nearly edge-on disk. Although LOCI is effective in subtracting quasistatic speckles in the stellar PSF, its application can result in self-subtraction of the disk signal due to its finite spatial extent. The degree of self-subtraction varies with radius, which would preclude accurate measurement of the surface brightness profile and compromise our inferences regarding the physical processes responsible for the dust distribution. We have developed a new technique to model the effects of self-subtraction on spatially extended emission introduced by the LOCI-processed angular differential imaging. Our method accounts for both the self-subtraction kernel's dependence on LOCI parameters and spatial location. We forward model the structure of the disk and compute the form of the self-subtraction at each radius, and then use this to jointly extract the disk surface brightness, scale height, and midplane location as functions of radius. Our investigation into the inner structure of the disk recovers a previously reported brightness asymmetry. This may be indicative of a perturbed density distribution or a change in average grain properties due to a recent stochastic event. A comparison of the surface brightness and morphology of the disk between two wavelengths can provide insight into the size and distribution of dust grains as well as the grains’ interaction with the surrounding environment. In addition, we can apply our self-subtraction modeling technique to future high-contrast imaging of this system and others like it. This work was supported in part by University of California Lab Research Program 09-LR-01-118057-GRAJ and NSF grant AST-0909188.
Mars Science Laboratory Rover Actuator Thermal Design
NASA Technical Reports Server (NTRS)
Novak, Keith S.; Liu, Yuanming; Lee, Chern-Jiin; Hendricks, Steven
2010-01-01
NASA will launch a 900 kg rover, part of the Mars Science Laboratory (MSL) mission, to Mars in October of 2011. The MSL rover is scheduled to land on Mars in August of 2012. The rover employs 31, electric-motor driven actuators to perform a variety of engineering and science functions including: mobility, camera pointing, telecommunications antenna steering, soil and rock sample acquisition and sample processing. This paper describes the MSL rover actuator thermal design. The actuators have stainless steel housings and planetary gearboxes that are lubricated with a "wet" lubricant. The lubricant viscosity increases with decreasing temperature. Warm-up heaters are required to bring the actuators up to temperature (above -55 C) prior to use in the cold wintertime environment of Mars (when ambient atmosphere temperatures are as cold as -113 C). Analytical thermal models of all 31 MSL actuators have been developed. The actuators have been analyzed and warm-up heaters have been designed to improve actuator performance in cold environments. Thermal hardware for the actuators has been specified, procured and installed. This paper presents actuator thermal analysis predicts, and describes the actuator thermal hardware and its operation. In addition, warm-up heater testing and thermal model correlation efforts for the Remote Sensing Mast (RSM) elevation actuator are discussed.
NASA Technical Reports Server (NTRS)
Dove, James B.; Wilms, Joern; Maisack, Michael; Begelman, Mitchell C.
1997-01-01
We apply our self-consistent accretion disk corona (ADC) model, with two different geometries, to the broadband X-ray spectrum of the black hole candidate Cygnus X-1. As shown in a companion paper, models in which the Comptonizing medium is a slab surrounding the cold accretion disk cannot have a temperature higher than about 140 keV for optical depths greater than 0.2, resulting in spectra that are much softer than the observed 10-30 keV spectrum of Cyg X-1. In addition, the slab-geometry models predict a substantial "soft excess" at low energies, a feature not observed for Cyg X-1, and Fe K-alpha fluorescence lines that are stronger than observed. Previous Comptonization models in the literature have invoked a slab geometry with optical depth tau(sub T) approx. greater than 0.3 and coronal temperature T(sub c) approx. 150 keV, but they are not self-consistent. Therefore, ADC models with a slab geometry are not appropriate for explaining the X-ray spectrum of Cyg X-1. Models with a spherical corona and an exterior disk, however, predict much higher self-consistent coronal temperatures than the slab-geometry models. The higher coronal temperatures are due to the lower amount of reprocessing of coronal radiation in the accretion disk, giving rise to a lower Compton cooling rate. Therefore, for the sphere-plus-disk geometry, the predicted spectrum can be hard enough to describe the observed X-ray continuum of Cyg X-1 while predicting Fe fluorescence lines having an equivalent width of approx. 40 eV. Our best-fit parameter values for the sphere-plus-disk geometry are tau(sub T) approx. equal to 1.5 and T(sub c) approx. equal to 90 keV.
NASA Astrophysics Data System (ADS)
May, Andrew A.; Ashman, Paul; Huang, Jiaoyan; Dhaniyala, Suresh; Holsen, Thomas M.
2011-08-01
Computational fluid dynamics (CFD) simulations coupled with wind tunnel-experiments were used to determine the sampling rate (SR) of the widely used polyurethane foam (PUF) disk passive sampler. In the wind-tunnel experiments, water evaporation rates from a water saturated PUF disk installed in the sampler housing were determined by measuring weight loss over time. In addition, a modified passive sampler designed to collect elemental mercury (Hg 0) with gold-coated filters was used. Experiments were carried out at different wind speeds and various sampler angles. The SRs obtained from wind-tunnel experiments were compared to those obtained from the field by scaling the values by the ratios of air diffusivities. Three-dimensional (3D) CFD simulations were also used to generate SRs for both polychlorinated biphenyls (PCBs) and Hg 0. Overall, the modeled and measured SRs agree well and are consistent with the values obtained from field studies. As previously observed, the SRs increased linearly with increasing wind speed. In addition, it was determined that the SR was strongly dependent on the angle of the ambient wind. The SRs increased when the base was tilted up pointing into the wind and when the base was tilted down (i.e., such that the top of the sampler was facing the wind) the SR decreased initially and then increased. The results suggest that there may be significant uncertainty in concentrations obtained from passive sampler measurements without knowledge of wind speed and wind angle relative to the sampler.
How does the mass transport in disk galaxy models influence the character of orbits?
NASA Astrophysics Data System (ADS)
Zotos, Euaggelos E.
We explore the regular or chaotic nature of orbits of stars moving in the meridional (R,z) plane of an axially symmetric time-dependent disk galaxy model with a central, spherically symmetric nucleus. In particular, mass is linearly transported from the disk to the galactic nucleus, in order to mimic, in a way, the case of self-consistent interactions of an actual N-body simulation. We thus try to unveil the influence of this mass transportation on the different families of orbits of stars by monitoring how the percentage of chaotic orbits, as well as the percentages of orbits of the main regular resonant families, evolve as the galaxy develops a dense and massive nucleus in its core. The SALI method is applied to samples of orbits in order to distinguish safely between ordered and chaotic motion. In addition, a method based on the concept of spectral dynamics is used for identifying the various families of regular orbits and also for recognizing the secondary resonances that bifurcate from them. Our computations strongly suggest that the amount of the observed chaos is substantially increased as the nucleus becomes more massive. Furthermore, extensive numerical calculations indicate that there are orbits which change their nature from regular to chaotic and vice versa and also orbits which maintain their orbital character during the galactic evolution. The present outcomes are compared to earlier related work.
NASA Astrophysics Data System (ADS)
Liu, Yanfang; Shan, Jinjun; Gabbert, Ulrich; Qi, Naiming
2013-11-01
A physics-based fractional-order Maxwell resistive capacitor (FOMRC) model is proposed to characterize nonlinear hysteresis and creep behaviors of a piezoelectric actuator (PEA). The Maxwell resistive capacitor (MRC) model is interpreted physically in the electric domain for PEAs. Based on this interpretation, the MRC model is modified to directly describe the relationship between the input voltage and the output displacement of a PEA. Then a procedure is developed to identify the parameters of the MRC model. This procedure is capable of being carried out using the measured input and output of a PEA only. A fractional-order dynamics is integrated into the MRC model to describe the effect of creep, as well as the detachment of hysteresis loops caused by creep. Moreover, the inverse FOMRC model is constructed to compensate for hysteresis and creep in an open-loop positioning application of PEAs. Simulation and experiments are carried out to validate the proposed model. The PEA compensated by the inverse FOMRC model shows an excellent linear behavior.
NASA Astrophysics Data System (ADS)
Lynch, Brian
Shape memory alloys have become increasingly popular for use in many engineering fields, including aerospace, robotics, and biomechanics. A major research focus is the application of Nitinol shape memory alloy wire as an actuator. While position and force control of shape memory alloy actuator wires has been successfully demonstrated in the past, most control algorithms have been developed using position feedback. Recently, it has been shown that there exists a significant correlation between the electrical resistance and strain of the material. This correlation has been used to model the strain as a function of the electrical resistance for use in predicting the actuator position for control purposes. However, the influence of applied stress as well as the presence of a third microstructure phase (R-phase) make modeling of the resistance-strain correlation difficult since hysteretic effects become more substantial. This thesis presents new models of the resistance-stress-strain behaviour of shape memory alloy for use in actuator position control. Characterization of the material behaviour was performed through experimental analysis, and used to develop the models based on empirical curve fitting. The models were then validated through simulation as well as application in a simple PID position control algorithm. Furthermore, two different alloys were investigated: a Ni-Ti alloy called Flexinol which exhibits significant hysteresis due to the presence of R-phase, as well as a Ni-Ti-Cu alloy which shows negligible hysteresis.
Chemistry in disks. IV. Benchmarking gas-grain chemical models with surface reactions
NASA Astrophysics Data System (ADS)
Semenov, D.; Hersant, F.; Wakelam, V.; Dutrey, A.; Chapillon, E.; Guilloteau, St.; Henning, Th.; Launhardt, R.; Piétu, V.; Schreyer, K.
2010-11-01
Context. We describe and benchmark two sophisticated chemical models developed by the Heidelberg and Bordeaux astrochemistry groups. Aims: The main goal of this study is to elaborate on a few well-described tests for state-of-the-art astrochemical codes covering a range of physical conditions and chemical processes, in particular those aimed at constraining current and future interferometric observations of protoplanetary disks. Methods: We considered three physical models: a cold molecular cloud core, a hot core, and an outer region of a T Tauri disk. Our chemical network (for both models) is based on the original gas-phase osu_03_2008 ratefile and includes gas-grain interactions and a set of surface reactions for the H-, O-, C-, S-, and N-bearing molecules. The benchmarking was performed with the increasing complexity of the considered processes: (1) the pure gas-phase chemistry, (2) the gas-phase chemistry with accretion and desorption, and (3) the full gas-grain model with surface reactions. The chemical evolution is modeled within 109 years using atomic initial abundances with heavily depleted metals and hydrogen in its molecular form. Results: The time-dependent abundances calculated with the two chemical models are essentially the same for all considered physical cases and for all species, including the most complex polyatomic ions and organic molecules. This result, however, required a lot of effort to make all necessary details consistent through the model runs, e.g., definition of the gas particle density, density of grain surface sites, or the strength and shape of the UV radiation field. Conclusions: The reference models and the benchmark setup, along with the two chemical codes and resulting time-dependent abundances are made publicly available on the internet. This will facilitate and ease the development of other astrochemical models and provide nonspecialists with a detailed description of the model ingredients and requirements to analyze the cosmic
NASA Astrophysics Data System (ADS)
Hoadley, Keri; France, Kevin
2015-01-01
Probing the surviving molecular gas within the inner regions of protoplanetary disks (PPDs) around T Tauri stars (1 - 10 Myr) provides insight into the conditions in which planet formation and migration occurs while the gas disk is still present. We model observed far ultraviolet (FUV) molecular hydrogen (H₂) fluorescent emission lines that originate within the inner regions (< 10 AU) of 9 well-studied Classic T Tauri stars, using the Hubble Space Telescope Cosmic Origins Spectrograph (COS), to explore the physical structure of the molecular disk at different PPD dust evolutionary stages. We created a 2D radiative transfer model that estimates the density and temperature distributions of warm, inner radial H₂ (T > 1500 K) with a set of 6 free parameters and produces a data cube of expected emission line profiles that describe the physical structure of the inner molecular disk atmosphere. By comparing the modeled emission lines with COS H₂ fluorescence emission features, we estimate the physical structure of the molecular disk atmosphere for each target with the set of free parameters that best replicate the observed lines. First results suggest that, for all dust evolutionary stages of disks considered, ground-state H₂ populations are described by a roughly constant temperature T(H₂) = 2500 +/- 1000 K. Possible evolution of the density structure of the H₂ atmosphere between intact and depleting dust disks may be distinguishable, but large errors in the inferred best-fit parameter sets prevent us from making this conclusion. Further improvements to the modeling framework and statistical comparison in determining the best-fit model-to-data parameter sets are ongoing, beginning with improvements to the radiative transfer model and use of up-to-date HI Lyman α absorption optical depths (see McJunkin in posters) to better estimate disk structural parameters. Once improvements are implemented, we will investigate the possible presence of a molecular wind
Analytical model of thermal effect and optical path difference in end-pumped Yb:YAG thin disk laser.
Zhu, Guangzhi; Zhu, Xiao; Wang, Mu; Feng, Yufan; Zhu, Changhong
2014-10-10
An analytical model of the thermal effect and optical path difference (OPD) of a thin disk laser is developed with the combination of the analytical method and commercial finite element analysis software. The distributions of temperature, stress, strain, and OPD caused by temperature gradient, axial thermal strain (bulging), thermal strain-induced birefringence, and deformation are obtained. Based on the analytical model, the production mechanisms, features, and influence of OPD in an end-pumped thin disk laser are discussed, which make the causes of spherical and aspherical parts of the OPD more obvious. Furthermore, the OPD including the spherical and aspherical parts of the thin disk crystal is discussed for various pumping intensities. PMID:25322379
Thermodynamic model of MHD turbulence and some of its applications to accretion disks
NASA Astrophysics Data System (ADS)
Kolesnichenko, A. V.; Marov, M. Ya.
2008-06-01
Within the framework of the main problem of cosmogony related to the reconstruction of the evolution of the protoplanetary gas-dust cloud that surrounded the proto-Sun at an early stage of its existence, we have derived a closed system of magnetohydrodynamic equations for the scale of mean motion in the approximation of single-fluid magnetohydrodynamics designed to model the shear and convective turbulent flows of electrically conducting media in the presence of a magnetic field. These equations are designed for schematized formulations and the numerical solution of special problems to interconsistently model intense turbulent flows of cosmic plasma in accretion disks and associated coronas, in which the magnetic field noticeably affects the dynamics of astrophysical processes. In developing the model of a conducting turbulized medium, apart from the conventional probability-theoretical averaging of the MHD equations, we systematically use the weighted Favre averaging. The latter allows us to considerably simplify the writing of the averaged equations of motion for a compressible fluid and the analysis of the mechanisms of macroscopic field amplification by turbulent flows. To clearly interpret the individual components of the plasma and field-energy balance, we derive various energy equations that allow us to trace the possible energy conversions from one form into another, in particular, to understand the transfer mechanisms of the gravitational and kinetic energies of the mean motion into magnetic energy. Special emphasis is placed on the method for obtaining the closure relations for the total (with allowance made for the magnetic field) kinetic turbulent stress tensor in an electrically conducting medium and the turbulent electromotive force (or the so-called magnetic Reynolds tensor). This method also makes it possible to analyze the constraints imposed on the turbulent transport coefficients by the entropy growth condition. As applied to the problem of
NASA Astrophysics Data System (ADS)
Ghanbari, Mina; Hossainpour, Siamak; Rezazadeh, Ghader
2015-11-01
This paper deals with the analysis of a novel micro-electromechanical sensor for measurement of microscale fluid physical properties. The proposed sensor is made up of a micro-beam with one end fixed and a micro-plate as a sensing element at its free end, which is immersed in a microscale fluid media. As fluids show different behavior in microscale than in macroscale, the microscale fluid media have been modeled based on micro-polar theory. So non-classical properties of fluid that are absent in macroscale flows need to be measured. In order to actuate the sensor longitudinally, an AC voltage is applied to the piezoelectric layers on the upper and lower surfaces of the micro-beam. Coupled governing partial differential equations of motion of the fluid field and longitudinal vibration of the micro-beam have been derived based on micro-polar theory. The obtained governing differential equations with time-varying boundary conditions have been simplified and transformed to an enhanced form with homogenous boundary conditions. Then, they have been discretized over the beam and fluid domain using Galerkin-based reduced-order model. The dynamic response of the sensing element for different piezoelectric actuation voltages and different exciting frequencies has been studied. It has been shown that by investigating damping and inertial effect fluid loading on response of the micro-beam, properties of a microscale fluid can be measured. At the end, effects of geometrical parameters of the sensor on the response of sensing element have been studied.
Powerful Electromechanical Linear Actuator
NASA Technical Reports Server (NTRS)
Cowan, John R.; Myers, William N.
1994-01-01
Powerful electromechanical linear actuator designed to replace hydraulic actuator that provides incremental linear movements to large object and holds its position against heavy loads. Electromechanical actuator cleaner and simpler, and needs less maintenance. Two principal innovative features that distinguish new actuator are use of shaft-angle resolver as source of position feedback to electronic control subsystem and antibacklash gearing arrangement.
NASA Astrophysics Data System (ADS)
Caponetto, R.; De Luca, V.; Graziani, S.; Sapuppo, F.
2013-12-01
IPMCs are electroactive polymers which can be used both as sensors and as actuators. The modeling of IPMC transducers is an open issue relevant to the development of effective applications. A multiphysics model of IPMC actuators is here implemented. It integrates the description of the electrical, mechanical, chemical and thermal coupled physics domains in a unique solution and, as a novelty, it allows the study in the frequency domain and the comparison with experimental response of the IPMC device. The IPMC white box modeling requires several macro- and microscopic parameters, not always accessible via theoretical approaches or experimentation. This work presents a new model optimization procedure which integrates the Nelder-Mead simplex method with the COMSOL Multiphysics®models. The proposed procedure uses experimental data and fits model simulations to IPMC real behavior for microscopic parameters’ identification. The model is developed for IPMCs with ethylene glycol as the solvent.
Your backbone, or spine, is made up of 26 bones called vertebrae. In between them are soft disks filled with a jelly-like substance. These disks cushion the vertebrae and keep them in place. As you age, ...
NASA Astrophysics Data System (ADS)
Najafi Sohi, Ali; Nieva, Patricia M.; Khajepour, Amir
2015-03-01
An analytical model for the electrothermomechanical analysis of out-of-plane deformation in resistively heated single-stepped beams is presented. The model takes into account the conductive heat transfer from the beam to the substrate in which it is anchored. It also considers the temperature dependence of the beam material properties and accounts for the locally enhanced resistive heating effect around the release holes in the beam to predict temperature distribution along the beam. Energy method and Euler-Bernoulli beam theory are used for the prediction of out-of-plane deformation and stress distribution of the beam, as well as the out-of-plane rotation at the middle of the beam. The model considers the nonuniformity of the air gap between the beam and the substrate and captures the resultant asymmetric temperature distribution along the beam. The out-of-plane rotations in the middle of the single-stepped beam predicted by the analytical model and measured experimentally agree within 10%. The analytical model is then used to predict the maximum actuation current, which results in high temperature plastic deformation and agrees with the experiments within 5%. The proposed analytical model provides a good approach for systematic design and analysis of out-of-plane electrothermal microactuators based on single-stepped beam design.
NASA Astrophysics Data System (ADS)
Oh, Sang Hoon; Kim, Woong-Tae; Lee, Hyung Mok
2015-07-01
Using self-consistent three-dimensional (3D) N-body simulations, we investigate the physical properties of nonaxisymmetric features in a disk galaxy created by a tidal interaction with its companion. The primary galaxy consists of a stellar disk, a bulge, and a live halo, corresponding to Milky-Way-type galaxies, while the companion is represented by a halo alone. We vary the companion mass and the pericenter distance to explore situations with differing tidal strength parameterized by either the relative tidal force P or the relative imparted momentum S. We find that the formation of a tidal tail in the outer parts requires P≳ 0.05 or S≳ 0.07. A stronger interaction results in a stronger, less wound tail that forms earlier. Similarly, a stronger tidal forcing produces stronger, more loosely wound spiral arms in the inner parts. The arms are approximately logarithmic in shape, with both amplitude and pitch angle decaying with time. The derived pattern speed decreases with radius and is close to the {{Ω }}-κ /2 curve at late time, with Ω and κ denoting the angular and epicycle frequencies, respectively. This suggests that the tidally induced spiral arms are most likely kinematic density waves weakly modified by self-gravity. Compared to the razor-thin counterparts, arms in the 3D models are weaker, have a smaller pitch angle, and wind and decay more rapidly. The 3D density structure of the arms is well described by the concentrated and sinusoidal models when the arms are in the nonlinear and linear regimes, respectively. We demonstrate that dynamical friction between interacting galaxies transfers the orbital angular momentum of one galaxy to the spin angular momentum of the companion halo.
Zhuravlev, Viacheslav V.; Ivanov, Pavel B.; Teixeira, Danilo Morales
2014-12-01
In this paper, we introduce the first results that use data extracted directly from numerical simulations as inputs to the analytic twisted disk model of Zhuravlev and Ivanov. In both numerical and analytic approaches, fully relativistic models of tilted and twisted disks having a moderate effective viscosity around a slowly rotating Kerr black hole are considered. Qualitatively, the analytic model demonstrates the same dynamics as the simulations, although with some quantitative offset. Namely, the general relativistic magnetohydrodynamic simulations typically give smaller variations of tilt and twist across the disk. When the black hole and the disk rotate in the same direction, the simulated tilted disk and analytic model show no sign of Bardeen-Petterson alignment, even in the innermost parts of the disk where the characteristic time for relaxation to a quasi-stationary configuration is of the same order as the computation time. In the opposite case, when the direction of the disk's rotation is opposite to that of the black hole, a partial alignment is observed, in agreement with previous theoretical estimates. Thus, both fully numerical and analytic schemes demonstrate that the Bardeen-Petterson effect may not be possible for the case of prograde rotation provided that disk's effective viscosity is sufficiently small. This may have implications in modeling of different astrophysical phenomena such as disk spectra and jet orientation.
Flight control actuation system
NASA Technical Reports Server (NTRS)
Wingett, Paul T. (Inventor); Gaines, Louie T. (Inventor); Evans, Paul S. (Inventor); Kern, James I. (Inventor)
2004-01-01
A flight control actuation system comprises a controller, electromechanical actuator and a pneumatic actuator. During normal operation, only the electromechanical actuator is needed to operate a flight control surface. When the electromechanical actuator load level exceeds 40 amps positive, the controller activates the pneumatic actuator to offset electromechanical actuator loads to assist the manipulation of flight control surfaces. The assistance from the pneumatic load assist actuator enables the use of an electromechanical actuator that is smaller in size and mass, requires less power, needs less cooling processes, achieves high output forces and adapts to electrical current variations. The flight control actuation system is adapted for aircraft, spacecraft, missiles, and other flight vehicles, especially flight vehicles that are large in size and travel at high velocities.
Mangina, R. S.; Enloe, C. L.; Font, G. I.
2015-11-15
We present an experimental case study of time-resolved force production by an aerodynamic plasma actuator immersed in various mixtures of electropositive (N{sub 2}) and electronegative gases (O{sub 2} and SF{sub 6}) at atmospheric pressure using a fixed AC high-voltage input of 16 kV peak amplitude at 200 Hz frequency. We have observed distinct changes in the discharge structures during both negative- and positive-going voltage half-cycles, with corresponding variations in the actuator's force production: a ratio of 4:1 in the impulse produced by the negative-going half-cycle of the discharge among the various gas mixtures we explored, 2:1 in the impulse produced by the positive-going half-cycle, and cases in which the negative-going half-cycle dominates force production (by a ratio of 1.5:1), where the half-cycles produce identical force levels, and where the positive-going half cycle dominates (by a ratio of 1:5). We also present time-resolved experimental evidence for the first time that shows electrons do play a significant role in the momentum coupling to surrounding neutrals during the negative going voltage half-cycle of the N{sub 2} discharge. We show that there is sufficient macroscopic variation in the plasma that the predictions of numerical models at the microscopic level can be validated even though the plasma itself cannot be measured directly on those spatial and temporal scales.
Kuang, Y; Hilgers, A; Sadiq, M; Cochran, S; Corner, G; Huang, Z
2016-07-01
Clear needle visualisation is recognised as an unmet need for ultrasound guided percutaneous needle procedures including regional anaesthesia and tissue biopsy. With inadequate needle visibility, these procedures may result in serious complications or a failed operation. This paper reports analysis of the modal behaviour of a previously proposed ultrasound-actuated needle configuration, which may overcome this problem by improving needle visibility in colour Doppler imaging. It uses a piezoelectric transducer to actuate longitudinal resonant modes in needles (outer diameter 0.8-1.2mm, length>65mm). The factors that affect the needle's vibration mode are identified, including the needle length, the transducer's resonance frequency and the gripping position. Their effects are investigated using finite element modelling, with the conclusions validated experimentally. The actuated needle was inserted into porcine tissue up to 30mm depth and its visibility was observed under colour Doppler imaging. The piezoelectric transducer is able to generate longitudinal vibration with peak-to-peak amplitude up to 4μm at the needle tip with an actuating voltage of 20Vpp. Actuated in longitudinal vibration modes (distal mode at 27.6kHz and transducer mode at 42.2kHz) with a drive amplitude of 12-14Vpp, a 120mm needle is delineated as a coloured line in colour Doppler images, with both needle tip and shaft visualised. The improved needle visibility is maintained while the needle is advanced into the tissue, thus allowing tracking of the needle position in real time. Moreover, the needle tip is highlighted by strong coloured artefacts around the actuated needle generated by its flexural vibration. A limitation of the technique is that the transducer mode requires needles of specific lengths so that the needle's resonance frequency matches the transducer. This may restrict the choice of needle lengths in clinical applications. PMID:27022669
NASA Astrophysics Data System (ADS)
Zhu, Guangzhi; Qiu, Yuli; Wang, Zexiong; Zhu, Xiao; Zhu, Changhong
2016-08-01
An analytical model is developed to analyze the optical field distribution of thin disk laser with a thermal-optical aberration gain medium. The fundamental mode field distribution is calculated by using the eigenvector method of the resonator transit matrix for different pumping parameters. The analytical results show that the uniformity of the pumping spot is an important factor that impacts the beam quality of thin disk laser. The uniform pumping spot is beneficial to decrease thermal aberration and Optical Path Difference (OPD) of thin disk crystal, and to improve the beam quality. However, the beam quality still decreases slightly with the increasing of pumping intensity under the uniform pumping condition. The main reason for degradation of beam quality is the aspherical part of OPD which leads to diffraction losses of the resonator and wavefront deformation.
GIANT PLANET FORMATION BY DISK INSTABILITY IN LOW MASS DISKS?
Boss, Alan P.
2010-12-20
Forming giant planets by disk instability requires a gaseous disk that is massive enough to become gravitationally unstable and able to cool fast enough for self-gravitating clumps to form and survive. Models with simplified disk cooling have shown the critical importance of the ratio of the cooling to the orbital timescales. Uncertainties about the proper value of this ratio can be sidestepped by including radiative transfer. Three-dimensional radiative hydrodynamics models of a disk with a mass of 0.043 M{sub sun} from 4 to 20 AU in orbit around a 1 M{sub sun} protostar show that disk instabilities are considerably less successful in producing self-gravitating clumps than in a disk with twice this mass. The results are sensitive to the assumed initial outer disk (T{sub o}) temperatures. Models with T{sub o} = 20 K are able to form a single self-gravitating clump, whereas models with T{sub o} = 25 K form clumps that are not quite self-gravitating. These models imply that disk instability requires a disk with a mass of at least {approx}0.043 M{sub sun} inside 20 AU in order to form giant planets around solar-mass protostars with realistic disk cooling rates and outer-disk temperatures. Lower mass disks around solar-mass protostars must rely upon core accretion to form inner giant planets.
High Performance Piezoelectric Actuated Gimbal (HIERAX)
Charles Tschaggeny; Warren Jones; Eberhard Bamberg
2007-04-01
This paper presents a 3-axis gimbal whose three rotational axes are actuated by a novel drive system: linear piezoelectric motors whose linear output is converted to rotation by using drive disks. Advantages of this technology are: fast response, high accelerations, dither-free actuation and backlash-free positioning. The gimbal was developed to house a laser range finder for the purpose of tracking and guiding unmanned aerial vehicles during landing maneuvers. The tilt axis was built and the test results indicate excellent performance that meets design specifications.
NASA Astrophysics Data System (ADS)
Ballering, Nicholas P.; Su, Kate Y. L.; Rieke, George H.; Gáspár, András
2016-06-01
We investigate whether varying the dust composition (described by the optical constants) can solve a persistent problem in debris disk modeling—the inability to fit the thermal emission without overpredicting the scattered light. We model five images of the β Pictoris disk: two in scattered light from the Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph at 0.58 μm and HST/Wide Field Camera 3 (WFC 3) at 1.16 μm, and three in thermal emission from Spitzer/Multiband Imaging Photometer for Spitzer (MIPS) at 24 μm, Herschel/PACS at 70 μm, and Atacama Large Millimeter/submillimeter Array at 870 μm. The WFC3 and MIPS data are published here for the first time. We focus our modeling on the outer part of this disk, consisting of a parent body ring and a halo of small grains. First, we confirm that a model using astronomical silicates cannot simultaneously fit the thermal and scattered light data. Next, we use a simple generic function for the optical constants to show that varying the dust composition can improve the fit substantially. Finally, we model the dust as a mixture of the most plausible debris constituents: astronomical silicates, water ice, organic refractory material, and vacuum. We achieve a good fit to all data sets with grains composed predominantly of silicates and organics, while ice and vacuum are, at most, present in small amounts. This composition is similar to one derived from previous work on the HR 4796A disk. Our model also fits the thermal spectral energy distribution, scattered light colors, and high-resolution mid-IR data from T-ReCS for this disk. Additionally, we show that sub-blowout grains are a necessary component of the halo.
Nikkhoo, Mohammad; Khalaf, Kinda; Kuo, Ya-Wen; Hsu, Yu-Chun; Haghpanahi, Mohammad; Parnianpour, Mohamad; Wang, Jaw-Lin
2015-01-01
The risk of low back pain resulted from cyclic loadings is greater than that resulted from prolonged static postures. Disk degeneration results in degradation of disk solid structures and decrease of water contents, which is caused by activation of matrix digestive enzymes. The mechanical responses resulted from internal solid–fluid interactions of degenerative disks to cyclic loadings are not well studied yet. The fluid–solid interactions in disks can be evaluated by mathematical models, especially the poroelastic finite element (FE) models. We developed a robust disk poroelastic FE model to analyze the effect of degeneration on solid–fluid interactions within disk subjected to cyclic loadings at different loading frequencies. A backward analysis combined with in vitro experiments was used to find the elastic modulus and hydraulic permeability of intact and enzyme-induced degenerated porcine disks. The results showed that the averaged peak-to-peak disk deformations during the in vitro cyclic tests were well fitted with limited FE simulations and a quadratic response surface regression for both disk groups. The results showed that higher loading frequency increased the intradiscal pressure, decreased the total fluid loss, and slightly increased the maximum axial stress within solid matrix. Enzyme-induced degeneration decreased the intradiscal pressure and total fluid loss, and barely changed the maximum axial stress within solid matrix. The increase of intradiscal pressure and total fluid loss with loading frequency was less sensitive after the frequency elevated to 0.1 Hz for the enzyme-induced degenerated disk. Based on this study, it is found that enzyme-induced degeneration decreases energy attenuation capability of disk, but less change the strength of disk. PMID:25674562
A Modification of the Levich Model to Flux at a Rotating Disk in the presence of Planktonic Bacteria
NASA Astrophysics Data System (ADS)
Jones, Akhenaton-Andrew; Buie, Cullen
2015-11-01
The Levich model of flow at a rotating disk describes convective mass transport to a disk when edge effects and wall effects can be neglected. It is used to interpret electrochemical reaction kinetics and electrochemical impedance of flow systems. The solution has been shown to be invalid for high densities (~ 1 % v/v) of inert, non-motile nano-sized particles (<0.1 μm) and macro-particles (>1.5 μm), yet little work has been done for motile bacteria and bacterial sized particles. The influence of planktonic bacteria on rotating disk experiments is crucial for the evaluation of electrochemically active biofilms. In this work, we show that the presence of bacteria creates significant deviation from the ideal Levich model not shared by inert particles. We also study the impact of dead (fixed) bacteria on deviation form the Levich model. This work has implications for studies of microbial induced corrosion, microbial adhesion, and antibiotic transport to adhered biofilms preformed in rotating disk systems.
Structure of Disk-dominated Galaxies. II. Color Gradients and Stellar Population Models
NASA Astrophysics Data System (ADS)
MacArthur, Lauren A.; Courteau, Stéphane; Bell, Eric; Holtzman, Jon A.
2004-06-01
We investigate optical and near-IR color gradients in a sample of 172 low-inclination galaxies spanning Hubble types S0-Irr. The colors are compared with stellar population synthesis models from which luminosity-weighted average ages and metallicities are determined. We explore the effects of different underlying star formation histories and additional bursts of star formation. Our results are robust in a relative sense under the assumption that our galaxies shared a similar underlying star formation history and that no bursts involving more than ~10% of the galaxy mass have occurred in the past 1-2 Gyr. Because the observed gradients show radial structure, we measure ``inner'' and ``outer'' disk age and metallicity gradients. Trends in age and metallicity and their gradients are explored as a function of Hubble type, rotational velocity, total near-IR galaxy magnitude, central surface brightness, and scale length. We find strong correlations in age and metallicity with Hubble type, rotational velocity, total magnitude, and central surface brightness in the sense that earlier-type, faster rotating, more luminous, and higher surface brightness galaxies are older and more metal-rich, suggesting an early and more rapid star formation history for these galaxies. The increasing trends with rotational velocity and total magnitude level off for Vrot>~120kms-1 and MK<~-23 mag, respectively. This effect is stronger for metallicity (than age), which could reflect a threshold potential above which all metals are retained and thus metallicity saturates at the yield. Outer disk gradients are found to be weaker than the inner gradients as expected for a slower variation of the potential and surface brightness in the outer parts. We find that stronger age gradients are associated with weaker metallicity gradients. Trends in gradients with galaxy parameters are compared with model predictions: these trends do not agree with predictions of semianalytic models of hierarchical galaxy
A numerical model for the formation and long-term evolution of protostars and protostellar disks
NASA Astrophysics Data System (ADS)
Fateeva, A. M.; Zhilkin, A. G.; Pavlyuchenkov, Ya. N.; Vorobyov, E. I.
2016-02-01
We present a physical and numerical model for studying the formation and evolution of protostellar objects with solar and sub-solar masses. The model covers several evolutionary phases of these objects starting from the gravitational collapse of an initially unstable pre-stellar cloud, proceeding through the formation and collapse of the first hydrostatic core, and ending with the complete dissipation of the initial cloud and formation of a protostar and protostellar disk. The model is described by a system of MHD equations that includes Ohmic dissipation and ambipolar diffusion, and also a scheme for calculating the thermal and ionization structure of the cloud. We employ the multicomponent approach for computing the thermal structure of collapsing protostellar cloud, in which the dust and gas temperatures are treated separately, allowing us to accurately describe the initial stages of the cloud's gravitational contraction and collapse. We present the first results showing the structure of an initially quasi-equilibrium protostellar cloud during the first stages of gravitational collapse and subsequent evolution.
Superconducting linear actuator
NASA Technical Reports Server (NTRS)
Johnson, Bruce; Hockney, Richard
1993-01-01
Special actuators are needed to control the orientation of large structures in space-based precision pointing systems. Electromagnetic actuators that presently exist are too large in size and their bandwidth is too low. Hydraulic fluid actuation also presents problems for many space-based applications. Hydraulic oil can escape in space and contaminate the environment around the spacecraft. A research study was performed that selected an electrically-powered linear actuator that can be used to control the orientation of a large pointed structure. This research surveyed available products, analyzed the capabilities of conventional linear actuators, and designed a first-cut candidate superconducting linear actuator. The study first examined theoretical capabilities of electrical actuators and determined their problems with respect to the application and then determined if any presently available actuators or any modifications to available actuator designs would meet the required performance. The best actuator was then selected based on available design, modified design, or new design for this application. The last task was to proceed with a conceptual design. No commercially-available linear actuator or modification capable of meeting the specifications was found. A conventional moving-coil dc linear actuator would meet the specification, but the back-iron for this actuator would weigh approximately 12,000 lbs. A superconducting field coil, however, eliminates the need for back iron, resulting in an actuator weight of approximately 1000 lbs.
Single-crystal disk drive miniactuators
NASA Astrophysics Data System (ADS)
Giovanardi, Marco; McKenney, Kevin B.; Rule, John A.; Yoshikawa, Shoko
2001-08-01
As hard disk drive areal densities increase at a compound annual growth rate (CAGR) of 60%, disk drives must position the head over increasingly small areas while moving more rapidly to reach the desired position. This results in an increase in vibration disturbance. To meet this demand, many hard disk drive manufactures have created prototype dual-stage actuators employing piezoelectric ceramics for the second stage. These are an attractive means of obtaining higher-bandwidth control due to the low inertia and size of the actuator element. As the technology improves, the next limiting factor will be the amount of displacement obtainable with traditional piezoceramic elements. Under the AXIS (Advanced Crystal Integrated System) Consortium program funded by DARPA, the application of PZN-PT single crystal piezoceramic as a second stage disk drive actuator was studied, based on the fact that the single crystal material provides larger stroke than its traditional PZT counterparts. The transverse (d31) strain of PZN-PT single crystal was measured to be about two times larger than that of PZT-5H ceramic. Both materials were integrated into a disk drive system and compared as second stage actuators. The methodologies used and the servo control techniques applied are also discussed in the paper.
NASA Astrophysics Data System (ADS)
Dutrey, A.; Semenov, D.; Chapillon, E.; Gorti, U.; Guilloteau, S.; Hersant, F.; Hogerheijde, M.; Hughes, M.; Meeus, G.; Nomura, H.; Piétu, V.; Qi, C.; Wakelam, V.
Protoplanetary disks composed of dust and gas are ubiquitous around young stars and are commonly recognized as nurseries of planetary systems. Their lifetime, appearance, and structure are determined by an interplay between stellar radiation, gravity, thermal pressure, magnetic field, gas viscosity, turbulence, and rotation. Molecules and dust serve as major heating and cooling agents in disks. Dust grains dominate the disk opacities, reprocess most of the stellar radiation, and shield molecules from ionizing ultraviolet (UV)/X-ray photons. Disks also dynamically evolve by building up planetary systems, which drastically change their gas and dust density structures. Over the past decade, significant progress has been achieved in our understanding of disk chemical composition thanks to the upgrade or advent of new millimeter/infrared (IR) facilities [Submillimeter Array (SMA), Plateau de Bure Interferometer (PdBI), Combined Array for Research in Millimeter-wave Astronomy (CARMA), Herschel, Expanded Very Large Array (e-VLA), Atacama Large Millimeter/submillimeter Array (ALMA)]. Some major breakthroughs in our comprehension of the disk physics and chemistry have been done since Protostars and Planets V (Reipurth et al., 2007). This review will present and discuss the impact of such improvements on our understanding of the disk physical structure and chemical composition.
Photometric models of disk-integrated observations of the OSIRIS-REx target Asteroid (101955) Bennu
NASA Astrophysics Data System (ADS)
Takir, Driss; Clark, Beth Ellen; Drouet d'Aubigny, Christian; Hergenrother, Carl W.; Li, Jian-Yang; Lauretta, Dante S.; Binzel, Richard P.
2015-05-01
We used ground-based photometric phase curve data of the OSIRIS-REx target Asteroid (101955) Bennu and low phase angle data from Asteroid (253) Mathilde as a proxy to fit Bennu data with Minnaert, Lommel-Seeliger, (RObotic Lunar Orbiter) ROLO, Hapke, and McEwen photometric models, which capture the global light scattering properties of the surface and subsequently allow us to calculate the geometric albedo, phase integral, spherical Bond albedo, and the average surface normal albedo for Bennu. We find that Bennu has low reflectance and geometric albedo values, such that multiple scattering is expected to be insignificant. Our photometric models relate the reflectance from Bennu's surface to viewing geometry as functions of the incidence, emission, and phase angles. Radiance Factor functions (RADFs) are used to model the disk-resolved brightness of Bennu. The Minnaert, Lommel-Seeliger, ROLO, and Hapke photometric models work equally well in fitting the best ground-based photometric phase curve data of Bennu. The McEwen model works reasonably well at phase angles from 20° to 70°. Our calculated geometric albedo values of 0.047-0.014+0.012,0.047-0.014+0.005 , and 0.048-0.022+0.012 for the Minnaert, the Lommel-Seeliger, and the ROLO models respectively are consistent with the geometric albedo of 0.045 ± 0.015 computed by Emery et al. (Emery, J.P. et al. [2014]. Icarus 234, 17-35) and Hergenrother et al. (Hergenrother, C.W. et al. [2014].
How The Inner Disk Communicates to the Outer Disk
NASA Astrophysics Data System (ADS)
Goto, Miwa
2009-08-01
We investigated how evolution in the outer disk has an influence on the inner disk of a protoplanetary disk system. Thanks to two-layer models that give the theoretical platform of disk geometry, we now have a good handle on how dust evolves in outer protoplanetary disks (>10 AU). It has long been thought that the outer and inner disks dissipate on roughly the same time scale as sub-mm observations of nearby T Tauri systems has suggested. However, new high spatial resolution observations point toward the dissipation of an inner disk as not being a simple extension of the outer disk. We performed preliminary tests of the differential disk evolution in gas and dust in the inner disks of Herbig Ae/Be stars using the CO vibrational band as the gas probe. The line luminosity of CO v = 1-0 P(30) has a reasonable correlation with the near-infrared excess over the stellar photosphere. It guarantees that the CO vibration band is a secure probe of the inner disk, as is expected from its high critical density, high excitation temperature, and kinematics. On the other hand, the line luminosity of P(30) does not show a clear trend either with far-infrared color, near-infrared/far-infrared-color, or the type of the spectral energy distribution (SED) (I/II). The inner disks (<1 AU) of Herbig Ae/Be stars of our sample are influenced little by the geometry of the outer disks.
Thin-disk models in an integrable Weyl-Dirac theory
NASA Astrophysics Data System (ADS)
Vieira, Ronaldo S. S.; Letelier, Patricio S.
2014-01-01
We construct a class of static, axially symmetric solutions representing razor-thin disks of matter in the Integrable Weyl-Dirac theory proposed in Israelit (Found Phys 29:1303,
Wai, Rong-Jong; Yang, Zhi-Wei
2008-10-01
This paper focuses on the development of adaptive fuzzy neural network control (AFNNC), including indirect and direct frameworks for an n-link robot manipulator, to achieve high-precision position tracking. In general, it is difficult to adopt a model-based design to achieve this control objective due to the uncertainties in practical applications, such as friction forces, external disturbances, and parameter variations. In order to cope with this problem, an indirect AFNNC (IAFNNC) scheme and a direct AFNNC (DAFNNC) strategy are investigated without the requirement of prior system information. In these model-free control topologies, a continuous-time Takagi-Sugeno (T-S) dynamic fuzzy model with online learning ability is constructed to represent the system dynamics of an n-link robot manipulator. In the IAFNNC, an FNN estimator is designed to tune the nonlinear dynamic function vector in fuzzy local models, and then, the estimative vector is used to indirectly develop a stable IAFNNC law. In the DAFNNC, an FNN controller is directly designed to imitate a predetermined model-based stabilizing control law, and then, the stable control performance can be achieved by only using joint position information. All the IAFNNC and DAFNNC laws and the corresponding adaptive tuning algorithms for FNN weights are established in the sense of Lyapunov stability analyses to ensure the stable control performance. Numerical simulations and experimental results of a two-link robot manipulator actuated by dc servomotors are given to verify the effectiveness and robustness of the proposed methodologies. In addition, the superiority of the proposed control schemes is indicated in comparison with proportional-differential control, fuzzy-model-based control, T-S-type FNN control, and robust neural fuzzy network control systems. PMID:18784015
Malandrino, Andrea; Pozo, José M.; Castro-Mateos, Isaac; Frangi, Alejandro F.; van Rijsbergen, Marc M.; Ito, Keita; Wilke, Hans-Joachim; Dao, Tien Tuan; Ho Ba Tho, Marie-Christine; Noailly, Jérôme
2015-01-01
Capturing patient- or condition-specific intervertebral disk (IVD) properties in finite element models is outmost important in order to explore how biomechanical and biophysical processes may interact in spine diseases. However, disk degenerative changes are often modeled through equations similar to those employed for healthy organs, which might not be valid. As for the simulated effects of degenerative changes, they likely depend on specific disk geometries. Accordingly, we explored the ability of continuum tissue models to simulate disk degenerative changes. We further used the results in order to assess the interplay between these simulated changes and particular IVD morphologies, in relation to disk cell nutrition, a potentially important factor in disk tissue regulation. A protocol to derive patient-specific computational models from clinical images was applied to different spine specimens. In vitro, IVD creep tests were used to optimize poro-hyperelastic input material parameters in these models, in function of the IVD degeneration grade. The use of condition-specific tissue model parameters in the specimen-specific geometrical models was validated against independent kinematic measurements in vitro. Then, models were coupled to a transport-cell viability model in order to assess the respective effects of tissue degeneration and disk geometry on cell viability. While classic disk poro-mechanical models failed in representing known degenerative changes, additional simulation of tissue damage allowed model validation and gave degeneration-dependent material properties related to osmotic pressure and water loss, and to increased fibrosis. Surprisingly, nutrition-induced cell death was independent of the grade-dependent material properties, but was favored by increased diffusion distances in large IVDs. Our results suggest that in situ geometrical screening of IVD morphology might help to anticipate particular mechanisms of disk degeneration. PMID:25717471
Malandrino, Andrea; Pozo, José M; Castro-Mateos, Isaac; Frangi, Alejandro F; van Rijsbergen, Marc M; Ito, Keita; Wilke, Hans-Joachim; Dao, Tien Tuan; Ho Ba Tho, Marie-Christine; Noailly, Jérôme
2015-01-01
Capturing patient- or condition-specific intervertebral disk (IVD) properties in finite element models is outmost important in order to explore how biomechanical and biophysical processes may interact in spine diseases. However, disk degenerative changes are often modeled through equations similar to those employed for healthy organs, which might not be valid. As for the simulated effects of degenerative changes, they likely depend on specific disk geometries. Accordingly, we explored the ability of continuum tissue models to simulate disk degenerative changes. We further used the results in order to assess the interplay between these simulated changes and particular IVD morphologies, in relation to disk cell nutrition, a potentially important factor in disk tissue regulation. A protocol to derive patient-specific computational models from clinical images was applied to different spine specimens. In vitro, IVD creep tests were used to optimize poro-hyperelastic input material parameters in these models, in function of the IVD degeneration grade. The use of condition-specific tissue model parameters in the specimen-specific geometrical models was validated against independent kinematic measurements in vitro. Then, models were coupled to a transport-cell viability model in order to assess the respective effects of tissue degeneration and disk geometry on cell viability. While classic disk poro-mechanical models failed in representing known degenerative changes, additional simulation of tissue damage allowed model validation and gave degeneration-dependent material properties related to osmotic pressure and water loss, and to increased fibrosis. Surprisingly, nutrition-induced cell death was independent of the grade-dependent material properties, but was favored by increased diffusion distances in large IVDs. Our results suggest that in situ geometrical screening of IVD morphology might help to anticipate particular mechanisms of disk degeneration. PMID:25717471
NASA Astrophysics Data System (ADS)
Carraro, G.
2015-08-01
This review summarises the invited presentation I gave on the Milky Way disc. The idea underneath was to touch those topics that can be considered hot nowadays in the Galactic disk research: the reality of the thick disk, the spiral structure of the Milky Way, and the properties of the outer Galactic disk. A lot of work has been done in recent years on these topics, but a coherent and clear picture is still missing. Detailed studies with high quality spectroscopic data seem to support a dual Galactic disk, with a clear separation into a thin and a thick component. Much confusion and very discrepant ideas still exist concerning the spiral structure of the Milky Way. Our location in the disk makes it impossible to observe it, and we can only infer it. This process of inference is still far from being mature, and depends a lot on the selected tracers, the adopted models and their limitations, which in many cases are neither properly accounted for, nor pondered enough. Finally, there are very different opinions on the size (scale length, truncation radius) of the Galactic disk, and on the interpretation of the observed outer disk stellar populations in terms either of external entities (Monoceros, Triangulus-Andromeda, Canis Major), or as manifestations of genuine disk properties (e.g., warp and flare).
NASA Astrophysics Data System (ADS)
Goel, Amit; Montgomery, Michele; Wiegand, Paul
2016-01-01
Accretion disks are ubiquitous in Active Galactic Nuclei, in protostellar systems forming protoplanets, and in close binary star systems such as X-ray binaries, Cataclysmic Variables, and Algols, for example. Observations such as disk tilt are found in all of these different accreting system types, suggesting a common physics must be present. To understand the common connections between these different system types, which can help us understand their unique evolutions, we need to better understand the physics of accretion. For example, viscosity is typically a constant value in the disk of a system that is in a specific state such as a quiescent state. However, viscosity can't be constant throughout the disk, especially at the boundaries. To learn more about viscosity and other common parameters in these disk, we use Bayesian Inference and Markov Chain Monte Carlo techniques to make predictions of events to come in the numerical simulations of these accreting disks. In this work, we present our techniques and initial findings.
Design, testing and two-dimensional flow modeling of a multiple-disk fan
Engin, Tahsin; Oezdemir, Mustafa; Cesmeci, Sevki
2009-11-15
A multiple-disk Tesla type fan has been designed, tested and analyzed two-dimensionally using the conservation of angular momentum principle. Experimental results showed that such multiple-disk fans exhibited exceptionally low performance characteristics, which could be attributed to the low viscosity, tangential nature of the flow, and large mechanical energy losses at both suction and discharge sections that are comparable to the total input power. By means of theoretical analysis, local and overall shearing stresses on the disk surfaces have been determined based on tangential and radial velocity distributions of the air flow of different volume flow rates at prescribed disk spaces and rotational speeds. Then the total power transmitted by rotating disks to air flow, and the power acquired by the air flow in the gap due to transfer of angular momentum have been obtained by numerically integrating shearing stresses over the disk surfaces. Using the measured shaft and hydraulic powers, these quantities were utilized to evaluate mechanical energy losses associated with the suction and discharge sections of the fan. (author)
Magnetic bearings for a spaceflight optical disk recorder
NASA Technical Reports Server (NTRS)
Hockney, Richard; Gondhalekar, Vijay; Hawkey, Timothy
1991-01-01
The development and testing of a magnetic bearing system for the translator of the read/write head in a magneto-optic disk drive are discussed. The asymmetrical three-pole actuators with permanent magnet bias support the optical head, and its tracking and focusing servos, through their radial excursion above the disk. The specifications for the magnetic bearing are presented, along with the configuration of the magnetic hardware. Development of a five degree of freedom collision model is examined which allowed assessment of the system response during large scale transients. Experimental findings and the results of performance testing are presented, including the roll-off of current-to-force due to eddy current loss in the magnetic materials.
Micromachined electrostatic vertical actuator
Lee, Abraham P.; Sommargren, Gary E.; McConaghy, Charles F.; Krulevitch, Peter A.
1999-10-19
A micromachined vertical actuator utilizing a levitational force, such as in electrostatic comb drives, provides vertical actuation that is relatively linear in actuation for control, and can be readily combined with parallel plate capacitive position sensing for position control. The micromachined electrostatic vertical actuator provides accurate movement in the sub-micron to micron ranges which is desirable in the phase modulation instrument, such as optical phase shifting. For example, compact, inexpensive, and position controllable micromirrors utilizing an electrostatic vertical actuator can replace the large, expensive, and difficult-to-maintain piezoelectric actuators. A thirty pound piezoelectric actuator with corner cube reflectors, as utilized in a phase shifting diffraction interferometer can be replaced with a micromirror and a lens. For any very precise and small amplitudes of motion` micromachined electrostatic actuation may be used because it is the most compact in size, with low power consumption and has more straightforward sensing and control options.
Experimental investigation of resonant MEMS switch with ac actuation
NASA Astrophysics Data System (ADS)
Pal, Jitendra; Zhu, Yong; Wang, Boyi; Lu, Junwei; Khan, Fahimullah; Viet Dao, Dzung; Wang, Yifan
2016-06-01
In this letter, modeling, analysis, and experimental investigation for a resonant MEMS switch are presented. The resonant switch harnesses its mechanical resonance to lower the required actuation voltage by a substantial factor over the switch with static actuation. With alternating actuation voltage at its mechanical resonance frequency of 6.6 kHz, the average capacitance is tuned by changing the gap between fixed and movable electrodes. Based on the proposed actuation method, the device offers 57.44% lower actuation voltage compared with the switch with static actuation.
Towards a comprehensive model of Earth's disk-integrated Stokes vector
NASA Astrophysics Data System (ADS)
García Muñoz, A.
2015-07-01
at three wavelengths (0.48, 0.56 and 0.63 μm) during a flyby in 2005. The light curves show distinct structure associated with the varying aspect of the Earth's visible disk (phases of 98-107°) as the planet undergoes a full 24 h rotation; the structure is reasonably well reproduced with model simulations.
Constraining the Physics of AM Canum Venaticorum Systems with the Accretion Disk Instability Model
NASA Astrophysics Data System (ADS)
Cannizzo, John K.; Nelemans, Gijs
2015-04-01
Recent work by Levitan et al. has expanded the long-term photometric database for AM CVn stars. In particular, their outburst properties are well correlated with orbital period and allow constraints to be placed on the secular mass transfer rate between secondary and primary if one adopts the disk instability model for the outbursts. We use the observed range of outbursting behavior for AM CVn systems as a function of orbital period to place a constraint on mass transfer rate versus orbital period. We infer a rate ˜5× {{10}-9}{{M}⊙ } y{{r}-1}{{({{P}orb}/1000 s)}-5.2}. We show that the functional form so obtained is consistent with the recurrence time-orbital period relation found by Levitan et al. using a simple theory for the recurrence time. Also, we predict that their steep dependence of outburst duration on orbital period will flatten considerably once the longer orbital period systems have more complete observations.
Strain actuated aeroelastic control
NASA Technical Reports Server (NTRS)
Lazarus, Kenneth B.
1992-01-01
Viewgraphs on strain actuated aeroelastic control are presented. Topics covered include: structural and aerodynamic modeling; control law design methodology; system block diagram; adaptive wing test article; bench-top experiments; bench-top disturbance rejection: open and closed loop response; bench-top disturbance rejection: state cost versus control cost; wind tunnel experiments; wind tunnel gust alleviation: open and closed loop response at 60 mph; wind tunnel gust alleviation: state cost versus control cost at 60 mph; wind tunnel command following: open and closed loop error at 60 mph; wind tunnel flutter suppression: open loop flutter speed; and wind tunnel flutter suppression: closed loop state cost curves.
Electromagnetic rotational actuation.
Hogan, Alexander Lee
2010-08-01
There are many applications that need a meso-scale rotational actuator. These applications have been left by the wayside because of the lack of actuation at this scale. Sandia National Laboratories has many unique fabrication technologies that could be used to create an electromagnetic actuator at this scale. There are also many designs to be explored. In this internship exploration of the designs and fabrications technologies to find an inexpensive design that can be used for prototyping the electromagnetic rotational actuator.
NASA Astrophysics Data System (ADS)
Johnson, Andrew R.; Stanway, Roger
2005-05-01
Flexibility and speed of response are two key requirements in the design of machinery for high-speed manufacturing operations. These two requirements are often conflicting and their resolution requires considerable ingenuity on the part of the designer. A novel actuator based upon the use of twin electro-rheological (ER) clutches is described together with its modification to control the motion (angular displacement, angular velocity) of a robot manipulator arm. The development of a new experimental facility involving the robot manipulator arm is described. In the basic twin ER clutch facility, the motion of a toothed belt is controlled by manipulating the electric field applied to each ER clutch. The belt, in turn, controls the angular position and velocity of the robot arm. The use of twin clutches allows motion to be imparted in opposite directions without the need for return springs or similar mechanisms. To improve the positional performance an ER brake is added to the robot arm mechanism. The extension to the dynamic model for the ER clutch mechanism to incorporate the robot arm and ER brake is outlined and is validated experimentally. The displacement response of the robot arm is then examined as a trend study using different motor driving speeds. The positional accuracy of the robot arm and its repeatability is then demonstrated.
NASA Astrophysics Data System (ADS)
Oishi, Ryutaro; Yoshida, Hitoshi; Nagai, Hideki; Xu, Ya; Jang, Byung-Koog
2002-07-01
A smart composite material system which has three smart functions of sensor, actuator and processor has been developed intend to apply to structure of house for controlling ambient temperature and humidity, hands of robot for holding and feeling an object, and so on. A carbon fiber reinforced plastics (CFRP) is used as matrix in the smart composite. The size of the matrix is 120mm x 24mm x 0.45mm. The CFRP plate is combined two Ni-Ti shape memory alloy (SMA) wires with an elastic rubber to construct a composite material. The composite material has a characteristic of reversible response with respect to temperature. A photo-sensor and temperature sensor are embedded in the composite material. The composite material has a processor function to combine with a simple CPU (processor) unit. For demonstrating the capability of the composite material system, a model is built up for controlling certain behaviors such as gripping and releasing a spherical object. The amplitude of gripping force is (3.0 plus/minus 0.3) N in the measurement, which is consistent with our calculation of 2.7 N. Out of a variety of functions to be executed by the CPU, it is shown to exert calculation and decision making in regard to object selection, object holding, and ON-OFF control of action by external commands.
Final report : compliant thermo-mechanical MEMS actuators, LDRD #52553.
Walraven, Jeremy Allen; Baker, Michael Sean; Headley, Thomas Jeffrey; Plass, Richard Anton
2004-12-01
Thermal actuators have proven to be a robust actuation method in surface-micromachined MEMS processes. Their higher output force and lower input voltage make them an attractive alternative to more traditional electrostatic actuation methods. A predictive model of thermal actuator behavior has been developed and validated that can be used as a design tool to customize the performance of an actuator to a specific application. This tool has also been used to better understand thermal actuator reliability by comparing the maximum actuator temperature to the measured lifetime. Modeling thermal actuator behavior requires the use of two sequentially coupled models, the first to predict the temperature increase of the actuator due to the applied current and the second to model the mechanical response of the structure due to the increase in temperature. These two models have been developed using Matlab for the thermal response and ANSYS for the structural response. Both models have been shown to agree well with experimental data. In a parallel effort, the reliability and failure mechanisms of thermal actuators have been studied. Their response to electrical overstress and electrostatic discharge has been measured and a study has been performed to determine actuator lifetime at various temperatures and operating conditions. The results from this study have been used to determine a maximum reliable operating temperature that, when used in conjunction with the predictive model, enables us to design in reliability and customize the performance of an actuator at the design stage.
NASA Astrophysics Data System (ADS)
Palacin, J.; Salleras, M.; Puig, M.; Samitier, J.; Marco, S.
2004-07-01
In this work, we approach the problem of extracting a dynamic multiport thermal compact model from thermal impedance transients of microsystems using genetic algorithms. The model takes the form of a unique RC network, using a thermal-electrical analogy. The model topology is codified in a binary chromosoma and nonlinear least squares is used for sizing their components. The compact model topology evolution is genetically controlled to obtain the RC network that minimizes the reconstruction error of the thermal impedance transients. As an example, the proposed methodology is applied to an innovative silicon microthruster and compared with random search and sequential forward selection.
NASA Technical Reports Server (NTRS)
Mullette, Mark; Matthews, Gary; Russell, Kevin (Technical Monitor)
2002-01-01
The actuator technology required for AMSD and subsequently NGST are critical in the successful development for future cryogenic systems. Kodak has undertaken an extensive test plan to determine the performance of the force actuators developed under the AMSD program. These actuators are currently in testing at MSFC and are expected to finish this test cycle in early June 2002.
NASA Technical Reports Server (NTRS)
Packard, D. T.
1982-01-01
A new class of electromechanical actuators is described. These dual drive actuators were developed for the NASA-JPL Galileo Spacecraft. The dual drive actuators are fully redundant and therefore have high inherent reliability. They can be used for a variety of tasks, and they can be fabricated quickly and economically.
NASA Astrophysics Data System (ADS)
Gorti, U.; Hollenbach, D.
2004-09-01
We model gas and dust emission from regions 0.3-20 AU from a central low-mass star in intermediate-aged (~107 yr) disks whose dust is fairly optically thin to stellar radiation. The models treat thermal balance and chemistry self-consistently and calculate the vertical density and temperature structure of the gas in a disk. The gas and dust temperatures are calculated separately. The models cover gas masses 10-3 to 1 MJ and dust masses 10-7 to 10-4 MJ and treat solar-type (G and K) stars. We focus on mid-infrared and far-infrared emission lines from various gas species such as the rotational lines of H2, OH, H2O, and CO molecules and the fine-structure lines of carbon, oxygen, sulfur, iron, and silicon atoms and ions. These lines and the dust continuum are observable by the Spitzer Space Telescope and future missions including SOFIA and the Herschel Space Observatory. We find that the [S I] 25.23 μm line is the strongest emission line for a wide range of disk and stellar parameters, followed by emission from [Si II] 34.8 μm, [Fe II] 26 μm, and [O I] 63 μm. [Fe I] 24 μm and rotational lines of OH and H2O are strong when gas masses are high (>~0.1 MJ). Emission from the rotational lines of H2 is more difficult to detect unless disk gas masses are substantial (>~0.1 MJ). For emission from H2 lines to be observable and yet for the dust to be optically thin in stellar light, the ratio of gas to small submillimeter-sized dust particle mass in the disk needs to be >~1000, or at least an order of magnitude higher than that in the interstellar medium. This may be possible at intermediate stages in disk evolution, such as in the gas-gathering stage of the core accretion scenario for giant planet formation, in which most of the dust has coagulated into larger objects (>>1 mm) but the gas has not yet fully dispersed. Whereas the absolute fluxes observed in some lines such as [Fe I] 24 μm and H2 S(0) 28 μm primarily measure the gas mass in the disks, various line ratios
NASA Astrophysics Data System (ADS)
Landin, N. R.; Mendes, L. T. S.; Vaz, L. P. R.; Alencar, S. H. P.
2016-02-01
Context. Rotational evolution in young stars is described by pre-main sequence evolutionary tracks including non-gray boundary conditions, rotation, conservation of angular momentum, and simulations of disk-locking. Aims: By assuming that disk-locking is the regulation mechanism for the stellar angular velocity during the early stages of pre-main sequence evolution, we use our rotating models and observational data to constrain disk lifetimes (Tdisk) of a representative sample of low-mass stars in two young clusters, the Orion Nebula cluster (ONC) and NGC 2264, and to better understand their rotational evolution. Methods: The period distributions of the ONC and NGC 2264 are known to be bimodal and to depend on the stellar mass. To follow the rotational evolution of these two clusters' stars, we generated sets of evolutionary tracks from a fully convective configuration with low central temperatures (before D- and Li-burning). We assumed that the evolution of fast rotators can be represented by models considering conservation of angular momentum during all stages and of moderate rotators by models considering conservation of angular velocity during the first stages of evolution. With these models we estimate a mass and an age for all stars. Results: The resulting mass distribution for the bulk of the cluster population is in the ranges of 0.2-0.4 M⊙ and 0.1-0.6 M⊙ for the ONC and NGC 2264, respectively. For the ONC, we assume that the secondary peak in the period distribution is due to high-mass objects still locked in their disks, with a locking period (Plock) of ~8 days. For NGC 2264 we make two hypotheses: (1) the stars in the secondary peak are still locked with Plock = 5 days, and (2) NGC 2264 is in a later stage in the rotational evolution. Hypothesis 2 implies in a disk-locking scenario with Plock = 8 days, a disk lifetime of 1 Myr and, after that, constant angular momentum evolution. We then simulated the period distribution of NGC 2264 when the mean age
Plasma actuators for bluff body flow control
NASA Astrophysics Data System (ADS)
Kozlov, Alexey V.
The aerodynamic plasma actuators have shown to be efficient flow control devices in various applications. In this study the results of flow control experiments utilizing single dielectric barrier discharge plasma actuators to control flow separation and unsteady vortex shedding from a circular cylinder in cross-flow are reported. This work is motivated by the need to reduce landing gear noise for commercial transport aircraft via an effective streamlining created by the actuators. The experiments are performed at Re D = 20,000...164,000. Circular cylinders in cross-flow are chosen for study since they represent a generic flow geometry that is similar in all essential aspects to a landing gear oleo or strut. The minimization of the unsteady flow separation from the models and associated large-scale wake vorticity by using actuators reduces the radiated aerodynamic noise. Using either steady or unsteady actuation at ReD = 25,000, Karman shedding is totally eliminated, turbulence levels in the wake decrease significantly and near-field sound pressure levels are reduced by 13.3 dB. Unsteady actuation at an excitation frequency of St D = 1 is found to be most effective. The unsteady actuation also has the advantage that total suppression of shedding is achieved for a duty cycle of only 25%. However, since unsteady actuation is associated with an unsteady body force and produces a tone at the actuation frequency, steady actuation is more suitable for noise control applications. Two actuation strategies are used at ReD = 82,000: spanwise and streamwise oriented actuators. Near field microphone measurements in an anechoic wind tunnel and detailed study of the near wake using LDA are presented in the study. Both spanwise and streamwise actuators give nearly the same noise reduction level of 11.2 dB and 14.2 dB, respectively, and similar changes in the wake velocity profiles. The contribution of the actuator induced noise is found to be small compared to the natural shedding
Attitude-control model identification of on-orbit satellites actuated by reaction wheels
NASA Astrophysics Data System (ADS)
Geng, Li-Hui; Xiao, De-Yun; Wang, Qian; Zhang, Tao; Song, Jing-Yan
2010-03-01
With the long-term running of an on-orbit satellite, parameters in its attitude model are naturally altered due to the wastage of on-board components and the consumption of propellants or pay loads. In order to obtain high-accuracy attitude-control models and improve the on-orbit adaptation of an attitude controller, identification of an on-orbit satellite becomes another available approach. Due to the effect of exogenous disturbing torques and the measurement noises, estimation of the attitude-control models is eventually converted into that of an errors-in-variables model (EIVM). Since any a priori information on disturbing noises is not known in the on-orbit environment, an L2-optimal identification algorithm is proposed to estimate a generalized attitude model (GAM) for the satellite and then the corresponding noise model (NM) can be readily given by a model transformation to the GAM. During the parameter optimization for GAM, v-gap metric is employed as a minimization criterion to reduce the conservativeness of the resulting model and the optimization problem can be solved by linear matrix inequalities (LMIs). Finally, the testbed of a micro-satellite simulator is utilized to demonstrate the effectiveness of the proposed identification algorithm.
NASA Astrophysics Data System (ADS)
Lines, S.; Leinhardt, Z. M.; Baruteau, C.; Paardekooper, S.-J.; Carter, P. J.
2016-05-01
Aims: We investigate the feasibility of planetesimal growth in circumbinary protoplanetary disks around the observed systems Kepler-16 and Kepler-34 under the gravitational influence of a precessing eccentric gas disk. Methods: We embed the results of our previous hydrodynamical simulations of protoplanetary disks around binaries into an N-body code to perform 3D, high-resolution, inter-particle gravity-enabled simulations of planetesimal growth and dynamics that include the gravitational force imparted by the gas. Results: Including the full, precessing asymmetric gas disk generates high eccentricity orbits for planetesimals orbiting at the edge of the circumbinary cavity, where the gas surface density and eccentricity have their largest values. The gas disk is able to efficiently align planetesimal pericenters in some regions leading to phased, non-interacting orbits. Outside of these areas eccentric planetesimal orbits become misaligned and overlap leading to crossing orbits and high relative velocities during planetesimal collisions. This can lead to an increase in the number of erosive collisions that far outweighs the number of collisions that result in growth. Gravitational focusing from the static axisymmetric gas disk is weak and does not significantly alter collision outcomes from the gas free case. Conclusions: Due to asymmetries in the gas disk, planetesimals are strongly perturbed onto highly eccentric orbits. Where planetesimals orbits are not well aligned, orbit crossings lead to an increase in the number of erosive collisions. This makes it difficult for sustained planetesimal accretion to occur at the location of Kepler-16b and Kepler-34b and we therefore rule out in situ growth. This adds further support to our initial suggestions that most circumbinary planets should form further out in the disk and migrate inwards.
ERIC Educational Resources Information Center
Gale, John C.; And Others
1985-01-01
This four-article section focuses on information storage capacity of the optical disk covering the information workstation (uses microcomputer, optical disk, compact disc to provide reference information, information content, work product support); use of laser videodisc technology for dissemination of agricultural information; encoding databases…
From Collapsing Cloud Core to Protoplanetary Disk - A radiation transfer model for L1489 IRS
NASA Astrophysics Data System (ADS)
Brinch, Christian; Hogerheijde, Michiel R.; Jørgensen, Jes K.
We present a new molecular line radiation transfer model of the low-mass Young Stellar Object L1489 IRS (d ~ 140 pc) which may represent a short-lived transitional stage from collapsing cloud core to a star with a protoplanetary disk in Keplarian rotation (Hogerheijde 2001). The model includes a detailed description of the velocity field, the abundance of several molecular species and the shape and orientation of the object. L1489 IRS is seen to be surrounded by a flattened structure, in which both Keplarian rotation and inward motion are detected over size scales ranging from an outer radius of 2000 AU to within 0.1 AU from the central star (Boogert et al. 2002). With the observed inward motions, it would only take a few times 104 years for material at 2000 AU to spiral into the star, suggesting that this object may be very short lived. We use a flattened density distribution in our model to accommodate the non-spherical structure of L1489 IRS. In this study we aim to provide a better description of the physical and chemical characteristics of L1489 IRS through comparison between a detailed model and existing observations. Our model is described by a flattened Plummer-like density distribution (Stamatellos et al. 2004) given by, n(r, θ) = n0 ( 1 + [r/r0]2 )p/2 sinf ( θ ), where the parameter f determines the flatness. We adopt the value p = -1.8 for the radial density slope, based on the fit to the SCUBA submillimeter emission by Jørgensen et al. (2002). Integrating this profile results in a total disk mass of 0.03 M*. We use a radial temperature distribution given by a power-law with an index of -0.35 and T0 = 19.4 K at r0 = 1000 AU. The velocity field is parameterised by the mass of the central star M* and the angle α between the resulting velocity vector and the azimuthal direction. A value of α = 0 thus correspond to pure Keplarian rotation around a star of mass M*. Our free parameters are: M*, α, f, Xmol, and the inclination angle, i. The molecular
MODELING HIGH-VELOCITY QSO ABSORBERS WITH PHOTOIONIZED MAGNETOHYDRODYNAMIC DISK WINDS
Fukumura, Keigo; Kazanas, Demosthenes; Behar, Ehud
2010-11-10
We extend our modeling of the ionization structure of magnetohydrodynamic (MHD) accretion-disk winds, previously applied to Seyfert galaxies, to a population of quasi-stellar objects (QSOs) of much lower X-ray-to-UV flux ratios, i.e., smaller {alpha}{sub ox} index, motivated by UV/X-ray ionized absorbers with extremely high outflow velocities in UV-luminous QSOs. We demonstrate that magnetically driven winds ionized by a spectrum with {alpha}{sub ox} {approx_equal} -2 can produce the charge states responsible for C IV and Fe XXV/Fe XXVI absorption in wind regions with corresponding maximum velocities of v(C IV) {approx_lt}0.1c and v(Fe XXV) {approx_lt} 0.6c (where c is the speed of light) and column densities N {sub H} {approx} 10{sup 23}-10{sup 24} cm{sup -2}, in general agreement with observations. In contrast to the conventional radiation-driven wind models, high-velocity flows are always present in our MHD-driven winds but manifest in the absorption spectra only for {alpha}{sub ox} {approx_lt} -2, as larger {alpha}{sub ox} values ionize the wind completely out to radii too large to demonstrate the presence of these high velocities. We thus predict increasing velocities of these ionized absorbers with decreasing (steeper) {alpha}{sub ox}, a quantity that emerges as the defining parameter in the kinematics of the active galactic nucleus UV/X-ray absorbers.
NASA Technical Reports Server (NTRS)
Cuzzi, J. N.; Petaev, M.; Scott, E. R. D.; Weidenschilling, S.; Ciesla, F. J.
2004-01-01
In this talk we assess theoretical models of the radial, temporal, and thermal evolution of nebula solids, and their ultimate accretion into planetesimals such as we see today, using meteorite evidence as a guide. Each class of chondrites contains a characteristic suite of chondrules and CAIs that may have formed over a period of several Myr during which planetesimals were accreting in the disk. Details of the various models for transient melting of chondrules and igneous CAIs will be left to others. However, high-temperature processes of different kinds evaporation, alteration, etc did affect these constituents and their environment over this time span. Here we describe evolutionary scenarios consistent with a large time gap between CAI and chondrule formation and the presence of distinctive suites of chondrules and CAIs in each chondrite class. Particle-gas dynamical processes transport particles of all relevant sizes (microns to many meters) within the nebula and affect their evolution in a variety of important ways. Turbulent radial diffusion spreads particles radially down their concentration gradients - as one example, it can prevent CAIs from being lost into the sun on several Myr timescales [1]. Vertical diffusion spreads the dense midplane particle layer, determining its volume density, which in turn affects the particle growth rate and even the dominant growth process [2-4]. Turbulent concentration selects aerodynamically sorted particles for orders-of-magnitude density enhancement, and is applicable to porous, fluffy particles of appropriate size as well as to solid chondrules [5]. Inward radial drift under gas drag brings a surprisingly large amount of material to regions where it evaporates; these evaporation fronts cause significant chemical modification of the nebula gas over a wide range of radii [6]. Radial transport by stellar winds can be important for small particles [7].
Lyra, Wladimir; Mac Low, Mordecai-Mark E-mail: mordecai@amnh.org
2012-09-01
It has been suggested that the transition between magnetorotationally active and dead zones in protoplanetary disks should be prone to the excitation of vortices via Rossby wave instability (RWI). However, the only numerical evidence for this has come from alpha disk models, where the magnetic field evolution is not followed, and the effect of turbulence is parameterized by Laplacian viscosity. We aim to establish the phenomenology of the flow in the transition in three-dimensional resistive-magnetohydrodynamical models. We model the transition by a sharp jump in resistivity, as expected in the inner dead zone boundary, using the PENCIL CODE to simulate the flow. We find that vortices are readily excited in the dead side of the transition. We measure the mass accretion rate finding similar levels of Reynolds stress at the dead and active zones, at the {alpha} Almost-Equal-To 10{sup -2} level. The vortex sits in a pressure maximum and does not migrate, surviving until the end of the simulation. A pressure maximum in the active zone also triggers the RWI. The magnetized vortex that results should be disrupted by parasitical magneto-elliptic instabilities, yet it subsists in high resolution. This suggests that either the parasitic modes are still numerically damped or that the RWI supplies vorticity faster than they can destroy it. We conclude that the resistive transition between the active and dead zones in the inner regions of protoplanetary disks, if sharp enough, can indeed excite vortices via RWI. Our results lend credence to previous works that relied on the alpha-disk approximation, and caution against the use of overly reduced azimuthal coverage on modeling this transition.
Cryogenic actuator for subnanometer positioning
NASA Astrophysics Data System (ADS)
Bree, B. v.; Janssen, H.; Paalvast, S.; Albers, R.
2012-09-01
This paper discusses the development, realization, and qualification of a positioning actuator concept specifically for cryogenic environments. Originally developed for quantum physics research, the actuator also has many applications in astronomic cryogenic instruments to position optical elements with nanometer level accuracy and stability. Typical applications include the correction of thermally induced position errors of optical components after cooling down from ambient to cryogenic temperatures or sample positioning in microscopes. The actuator is nicknamed the ‘PiezoKnob’ because it is piezo based and it is compatible with the typical manipulator knob often found in standard systems for optical benches, such as linear stages or tip/tilt lens holders. Actuation with high stiffness piezo elements enables the Piezoknob to deliver forces up to 50 Newton which allows relatively stiff guiding mechanisms or large pre-loads. The PiezoKnob has been qualified at 77 Kelvin and was shown to work down to 2 Kelvin. As part of the qualification program, the custom developed driving electronics and set point profile have been fine-tuned, by combing measurements with predictions from a dynamic model, thus maximizing efficiency and minimizing power dissipation. Furthermore, the actuator holds its position without power and thanks to its mechanical layout it is absolutely insensitive to drift of the piezo elements or the driving electronics.
Simulations of Ice Nucleation by Model AgI Disks and Plates.
Zielke, Stephen A; Bertram, Allan K; Patey, G N
2016-03-10
Silver iodide is one of the most effective ice nuclei known. We use molecular dynamics simulations to investigate ice nucleation by AgI disks and plates with radii ranging from 1.15 to 2.99 nm. It is shown that disks and plates in this size range are effective ice nuclei, nucleating bulk ice at temperatures as warm as 14 K below the equilibrium freezing temperature, on simulation time scales (up to a few hundred nanoseconds). Ice nucleated on the Ag exposed surface of AgI disks and plates. Shortly after supercooling an ice cluster forms on the AgI surface. The AgI-stabilized ice cluster fluctuates in size as time progresses, but, once formed, it is constantly present. Eventually, depending on the disk or plate size and the degree of supercooling, a cluster fluctuation achieves critical size, and ice nucleates and rapidly grows to fill the simulation cell. Larger AgI disks and plates support larger ice clusters and hence can nucleate ice at warmer temperatures. This work may be useful for understanding the mechanism of ice nucleation on nanoparticles and active sites of larger atmospheric particles. PMID:26878341
Omnidirectional Actuator Handle
NASA Technical Reports Server (NTRS)
Moetteli, John B.
1995-01-01
Proposed actuator handle comprises two normally concentric rings, cables, and pulleys arranged such that relative displacement of rings from concentricity results in pulling of cable and consequent actuation of associated mechanism. Unlike conventional actuator handles like levers on farm implements, actuated from one or two directions only, proposed handle reached from almost any direction and actuated by pulling or pushing inner ring in any direction with respect to outer ring. Flanges installed on inner ring to cover gap between inner ring and housing to prevent clothing from being caught.
Bimorphic polymeric photomechanical actuator
NASA Technical Reports Server (NTRS)
Sarkisov, Sergey S. (Inventor); Curley, Michael J. (Inventor); Adamovsky, Grigory (Inventor); Sarkisov, Jr., Sergey S. (Inventor); Fields, Aisha B. (Inventor)
2006-01-01
A bimorphic polymeric photomechanical actuator, in one embodiment using polyvinylidene fluoride (PVDF) as a photosensitive body, transmitting light over fiber optic cables, and controlling the shape and pulse duration of the light pulse to control movement of the actuator. Multiple light beams are utilized to generate different ranges of motion for the actuator from a single photomechanical body and alternative designs use multiple light beams and multiple photomechanical bodies to provide controlled movement. Actuator movement using one or more ranges of motion is utilized to control motion to position an actuating element in three dimensional space.
NASA Astrophysics Data System (ADS)
Coltrin, M. E.; Kee, R. J.; Evans, G. H.; Meeks, E.; Rupley, F. M.; Grcar, J. F.
1991-08-01
In a rotating-disk reactor, a heated substrate spins (at typical speeds of 1000 rpm or more) in an enclosure through which the reactants flow. The rotating disk geometry has the important property that in certain operating regimes the species and temperature gradients normal to the disk are equal everywhere on the disk. Thus, such a configuration has great potential for highly uniform chemical vapor deposition (CVD), and indeed commercial rotating-disk CVD reactors are now available. In certain operating regimes, the equations describing the complex three-dimensional spiral fluid motion can be solved by a separation-of-variables transformation that reduces the equations to a system of ordinary differential equations. Strictly speaking, the transformation is only valid for an unconfined infinite-radius disk and buoyancy-free flow. Furthermore, only some boundary conditions are consistent with the transformation (e.g., temperature, gas-phase composition, and approach velocity all specified to be independent of radius at some distances above the disk). Fortunately, however, the transformed equations will provide a very good practical approximation to the flow in a finite-radius reactor over a large fraction of the disk (up to approximately 90 percent of the disk radius) when the reactor operating parameters are properly chosen, i.e., high rotation rates. In the limit of zero rotation rate, the rotating disk flow reduces to a stagnation-point flow, for which a similar separation-of-variables transformation is also available. Such flow configurations ('pedestal reactors') also find use in CVD reactors. In this report we describe a model formulation and mathematical analysis of rotating-disk and stagnation-point CVD reactors. Then we apply the analysis to a compute code called SPIN and describe its implementation and use.
Coltrin, M.E. ); Kee, R.J.; Evans, G.H.; Meeks, E.; Rupley, F.M.; Grcar, J.F. )
1991-08-01
In rotating-disk reactor a heated substrate spins (at typical speeds of 1000 rpm or more) in an enclosure through which the reactants flow. The rotating disk geometry has the important property that in certain operating regimes{sup 1} the species and temperature gradients normal to the disk are equal everywhere on the disk. Thus, such a configuration has great potential for highly uniform chemical vapor deposition (CVD),{sup 2--5} and indeed commercial rotating-disk CVD reactors are now available. In certain operating regimes, the equations describing the complex three-dimensional spiral fluid motion can be solved by a separation-of-variables transformation{sup 5,6} that reduces the equations to a system of ordinary differential equations. Strictly speaking, the transformation is only valid for an unconfined infinite-radius disk and buoyancy-free flow. Furthermore, only some boundary conditions are consistent with the transformation (e.g., temperature, gas-phase composition, and approach velocity all specified to be independent of radius at some distances above the disk). Fortunately, however, the transformed equations will provide a very good practical approximation to the flow in a finite-radius reactor over a large fraction of the disk (up to {approximately}90% of the disk radius) when the reactor operating parameters are properly chosen, i.e, high rotation rates. In the limit of zero rotation rate, the rotating disk flow reduces to a stagnation-point flow, for which a similar separation-of-variables transformation is also available. Such flow configurations ( pedestal reactors'') also find use in CVD reactors. In this report we describe a model formulation and mathematical analysis of rotating-disk and stagnation-point CVD reactors. Then we apply the analysis to a compute code called SPIN and describe its implementation and use. 31 refs., 4 figs.
Studies of Circumstellar Disk Evolution
NASA Technical Reports Server (NTRS)
Hartmann, Lee W.
2005-01-01
The aim of this project is to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we are developing much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; measuring disk accretion rates in these systems; and constructing detailed model disk structures consistent with observations to infer physical conditions such as grain growth in protoplanetary disks.
Actuator forces in CFD: RANS and LES modeling in OpenFOAM
NASA Astrophysics Data System (ADS)
Schito, P.; Zasso, A.
2014-06-01
Wind turbine wakes are a very challenging topic for scientific computations, but modern CFD frameworks and latest HPC centers allow setting up numerical computations on the wake induced by the wind turbine. The main issues is that the correct modeling of the wake is related to the correct modeling of the interaction between the blade and the incoming flow. The aim of the proposed work is to estimate the aerodynamic forces acting on the blades in order to correctly generate the rotor wake applying equivalent aerodynamic force source on the flow. The definition of a blade forces is done developing a model able to correctly estimate this aerodynamic forces as a function of the local flow seen by the blade during its revolution.
Modeling of dielectric barrier discharge plasma actuators driven by repetitive nanosecond pulses
Likhanskii, Alexandre V.; Shneider, Mikhail N.; Macheret, Sergey O.; Miles, Richard B.
2007-07-15
A detailed physical model for an asymmetric dielectric barrier discharge (DBD) in air driven by repetitive nanosecond voltage pulses is developed. In particular, modeling of DBD with high voltage repetitive negative and positive nanosecond pulses combined with positive dc bias is carried out. Operation at high voltage is compared with operation at low voltage, highlighting the advantage of high voltages, however the effect of backward-directed breakdown in the case of negative pulses results in a decrease of the integral momentum transferred to the gas. The use of positive repetitive pulses with dc bias is demonstrated to be promising for DBD performance improvement. The effects of the voltage waveform not only on force magnitude, but also on the spatial profile of the force, are shown. The crucial role of background photoionization in numerical modeling of ionization waves (streamers) in DBD plasmas is demonstrated.
THE GAS/DUST RATIO OF CIRCUMSTELLAR DISKS: TESTING MODELS OF PLANETESIMAL FORMATION
Horne, David; Gibb, Erika; Rettig, Terrence W.; Tilley, David; Balsara, Dinshaw; Brittain, Sean
2012-07-20
We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6-5b. {sup 12}CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust column density ratio and disk inclination similar to that found by Rettig et al.
The Gas/Dust Ratio of Circumstellar Disks: Testing Models of Planetesimal Formation
NASA Astrophysics Data System (ADS)
Horne, David; Gibb, Erika; Rettig, Terrence W.; Brittain, Sean; Tilley, David; Balsara, Dinshaw
2012-07-01
We present high-resolution, near-infrared NIRSPEC observations of CO absorption toward six class II T Tauri stars: AA Tau, DG Tau, IQ Tau, RY Tau, CW Tau, and Haro 6-5b. 12CO overtone absorption lines originating from the circumstellar disk of each object were used to calculate line-of-sight gas column densities toward each source. We measured the gas/dust ratio as a function of disk inclination, utilizing measured visual extinctions and inclinations for each star. The majority of our sources show further evidence for a correlation between the gas/dust column density ratio and disk inclination similar to that found by Rettig et al.
35 Hz shape memory alloy actuator with bending-twisting mode
NASA Astrophysics Data System (ADS)
Song, Sung-Hyuk; Lee, Jang-Yeob; Rodrigue, Hugo; Choi, Ik-Seong; Kang, Yeon June; Ahn, Sung-Hoon
2016-02-01
Shape Memory Alloy (SMA) materials are widely used as an actuating source for bending actuators due to their high power density. However, due to the slow actuation speed of SMAs, there are limitations in their range of possible applications. This paper proposes a smart soft composite (SSC) actuator capable of fast bending actuation with large deformations. To increase the actuation speed of SMA actuator, multiple thin SMA wires are used to increase the heat dissipation for faster cooling. The actuation characteristics of the actuator at different frequencies are measured with different actuator lengths and results show that resonance can be used to realize large deformations up to 35 Hz. The actuation characteristics of the actuator can be modified by changing the design of the layered reinforcement structure embedded in the actuator, thus the natural frequency and length of an actuator can be optimized for a specific actuation speed. A model is used to compare with the experimental results of actuators with different layered reinforcement structure designs. Also, a bend-twist coupled motion using an anisotropic layered reinforcement structure at a speed of 10 Hz is also realized. By increasing their range of actuation characteristics, the proposed actuator extends the range of application of SMA bending actuators.
35 Hz shape memory alloy actuator with bending-twisting mode
Song, Sung-Hyuk; Lee, Jang-Yeob; Rodrigue, Hugo; Choi, Ik-Seong; Kang, Yeon June; Ahn, Sung-Hoon
2016-01-01
Shape Memory Alloy (SMA) materials are widely used as an actuating source for bending actuators due to their high power density. However, due to the slow actuation speed of SMAs, there are limitations in their range of possible applications. This paper proposes a smart soft composite (SSC) actuator capable of fast bending actuation with large deformations. To increase the actuation speed of SMA actuator, multiple thin SMA wires are used to increase the heat dissipation for faster cooling. The actuation characteristics of the actuator at different frequencies are measured with different actuator lengths and results show that resonance can be used to realize large deformations up to 35 Hz. The actuation characteristics of the actuator can be modified by changing the design of the layered reinforcement structure embedded in the actuator, thus the natural frequency and length of an actuator can be optimized for a specific actuation speed. A model is used to compare with the experimental results of actuators with different layered reinforcement structure designs. Also, a bend-twist coupled motion using an anisotropic layered reinforcement structure at a speed of 10 Hz is also realized. By increasing their range of actuation characteristics, the proposed actuator extends the range of application of SMA bending actuators. PMID:26892438
Active noise control - Piezoceramic actuators in fluid/structure interaction models
NASA Technical Reports Server (NTRS)
Banks, H. T.; Fang, W.; Smith, R. C.
1991-01-01
A model for a 2-D acoustic cavity with a flexible boundary (a beam) controlled via piezoceramic patches producing bending moments in the beam is considered. The associated control problem for this fluid/structure interaction system to reduce the acoustic pressure in the cavity involves unbounded control inputs. Approximation methods in the context of an LQR state space formulation are discussed, and numerical results are presented to demonstrate the effectiveness of this approach in computing feedback controls for noise reduction.
Ostriker, Eve C.; McKee, Christopher F.; Leroy, Adam K. E-mail: cmckee@astro.berkeley.ed
2010-10-01
We develop a model for the regulation of galactic star formation rates {Sigma}{sub SFR} in disk galaxies, in which interstellar medium (ISM) heating by stellar UV plays a key role. By requiring that thermal and (vertical) dynamical equilibrium are simultaneously satisfied within the diffuse gas, and that stars form at a rate proportional to the mass of the self-gravitating component, we obtain a prediction for {Sigma}{sub SFR} as a function of the total gaseous surface density {Sigma} and the midplane density of stars+dark matter {rho}{sub sd}. The physical basis of this relationship is that the thermal pressure in the diffuse ISM, which is proportional to the UV heating rate and therefore to {Sigma}{sub SFR}, must adjust until it matches the midplane pressure value set by the vertical gravitational field. Our model applies to regions where {Sigma} {approx}< 100 M{sub sun} pc{sup -2}. In low-{Sigma}{sub SFR} (outer-galaxy) regions where diffuse gas dominates, the theory predicts that {Sigma}{sub SFR{proportional_to}{Sigma}{radical}}({rho}{sub sd}). The decrease of thermal equilibrium pressure when {Sigma}{sub SFR} is low implies, consistent with observations, that star formation can extend (with declining efficiency) to large radii in galaxies, rather than having a sharp cutoff at a fixed value of {Sigma}. The main parameters entering our model are the ratio of thermal pressure to total pressure in the diffuse ISM, the fraction of diffuse gas that is in the warm phase, and the star formation timescale in self-gravitating clouds; all of these are (at least in principle) direct observables. At low surface density, our model depends on the ratio of the mean midplane FUV intensity (or thermal pressure in the diffuse gas) to the star formation rate, which we set based on solar-neighborhood values. We compare our results to recent observations, showing good agreement overall for azimuthally averaged data in a set of spiral galaxies. For the large flocculent spiral