Browsing by Subject "Finite element analysis (FEA)"
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Item A finite element test bed for development of feedback control laws for electrostatic MEMS(2005-12) Kawade, Balasaheb D.; Berg, Jordan M.; Dallas, Timothy E. J.; Idesman, Alexander V.This project presents the ANSYS simulation techniques for an electrostatically-actuated MEMS device incorporating feedback control laws. The electrostatic MEMS device consists of a movable electrode, suspended on flexible, elastic structures, and one or more fixed drive electrodes. Nonlinear feedback control laws are simulated in ANSYS multi-physics solver and a transducer element. ANSYS multi-physics solver is limited for these types of simulations. ANSYS doesn’t support multiframe restart and the combined circuit and electrostatic analysis are incompatible. This work presents simulation techniques based on numerical methods to circumvent these limitations. The proposed technique eliminates the circuit elements from the model, and instead propagates the associated states in an APDL macro. ANSYS auto time stepping method is not applicable for closed-loop feedback control systems because loads are calculated at each step based on simulation output at the previous step. An adaptive step size Runge-Kutta integration routine is incorporated within APDL macro to develop an efficient simulation technique. The simulation efficiency of the static closed loop feedback control systems is increased by a factor more than 100. However, a dynamic closed loop feedback control systems exhibits only a brief initial transient, and then does not permit further step size increases. To increase the simulation efficiency of such systems, the adaptation logic is turned off once the step size stabilizes. Simulation results for representative MEMS devices including a one-DOF piston microactuator and a two-DOF rotating/translating microactuator demonstrate the efficiency of these simulation techniques.Item A finite element test bed for development of feedback control laws for electrostatic MEMS(Texas Tech University, 2005-12) Kawade, Balasaheb D.; Berg, Jordan M.; Dallas, Timothy E. J.; Idesman, Alexander V.This project presents the ANSYS simulation techniques for an electrostatically-actuated MEMS device incorporating feedback control laws. The electrostatic MEMS device consists of a movable electrode, suspended on flexible, elastic structures, and one or more fixed drive electrodes. Nonlinear feedback control laws are simulated in ANSYS multi-physics solver and a transducer element. ANSYS multi-physics solver is limited for these types of simulations. ANSYS doesn’t support multiframe restart and the combined circuit and electrostatic analysis are incompatible. This work presents simulation techniques based on numerical methods to circumvent these limitations. The proposed technique eliminates the circuit elements from the model, and instead propagates the associated states in an APDL macro. ANSYS auto time stepping method is not applicable for closed-loop feedback control systems because loads are calculated at each step based on simulation output at the previous step. An adaptive step size Runge-Kutta integration routine is incorporated within APDL macro to develop an efficient simulation technique. The simulation efficiency of the static closed loop feedback control systems is increased by a factor more than 100. However, a dynamic closed loop feedback control systems exhibits only a brief initial transient, and then does not permit further step size increases. To increase the simulation efficiency of such systems, the adaptation logic is turned off once the step size stabilizes. Simulation results for representative MEMS devices including a one-DOF piston microactuator and a two-DOF rotating/translating microactuator demonstrate the efficiency of these simulation techniques.Item Finite element design procedures for hybrid MSE/Soil-nail retaining wall systems(Texas Tech University, 2006-12) Alhabshi, Abdulrahman; Jayawickrama, Priyantha W.; Budek, Andrew; Newhouse, Charles D.; Senadheera, SanjayaIn recent years, many departments of transportation are working to keep pace with population growth by considering major infrastructure improvements to their highways. The successive expansion of the highway system to meet increasing demand has made extension of the right-of-way economically prohibitive. The use of earth retaining walls has allowed highway upgrades to be constructed within existing right-of-ways, consequently lowering the additional cost of acquiring separate lands. Texas Department of Transportation and other DOTs construct Hybrid MSE/Soil-nail retaining wall systems to replace existing highway embankments that separate two sections of a roadway. These systems are typically used to allow for widening both sides of the road by constructing a new lane to each roadway while excluding the need to acquire additional right-of-way. The design of such systems, in particular for the soil nail wall, is done using computer programs such Goldnail and Snail. These computer codes are based on limit-equilibrium methods and are typically used as design tools for conventional wall systems in which some degree of wall deflection is tolerated. They do not however, address large deflection due to significant surcharge caused by the use of excessive height of MSE wall. Moreover, these methods do not account for the additional outward thrust expected to occur at the soil nail/MSE wall interface. As a result, the requirements for designing hybrid walls systems should not only be based on stability but should also be based on wall deformation. The focus of this research study is to examine the adequacy of the current method recommended by TxDOT and to develop a design procedure for the hybrid wall systems which will address the shortcomings in the currently used methods in practice. The new performance method is based on extensive finite element analysis that will address not only the stability of the structure but also the wall deformations as well as the force transfer in the reinforcements.