Pathwise Sensitivity Analysis in Transient Regimes

The instantaneous relative entropy (IRE) and the corresponding instanta- neous Fisher information matrix (IFIM) for transient stochastic processes are pre- sented in this paper. These novel tools for sensitivity analysis of stochastic models serve as an extension of the well known relative entropy rate (RER) and the corre- sponding Fisher information matrix (FIM) that apply to stationary processes. Three cases are studied here, discrete-time Markov chains, continuous-time Markov chains and stochastic differential equations. A biological reaction network is presented as a demonstration numerical example

Transient analysis using conical shell elements

The use of the NASTRAN conical shell element in static, eigenvalue, and direct transient analyses is demonstrated. The results of a NASTRAN static solution of an externally pressurized ring-stiffened cylinder agree well with a theoretical discontinuity analysis. Good agreement is also obtained between the NASTRAN direct transient response of a uniform cylinder to a dynamic end load and one-dimensional solutions obtained using a method of characteristics stress wave code and a standing wave solution. Finally, a NASTRAN eigenvalue analysis is performed on a hydroballistic model idealized with conical shell elements

Transient Analysis of a Magnetic Heat Pump

An experimental heat pump that uses a rare earth element as the refrigerant is modeled using NASTRAN. The refrigerant is a ferromagnetic metal whose temperature rises when a magnetic field is applied and falls when the magnetic field is removed. The heat pump is used as a refrigerator to remove heat from a reservoir and discharge it through a heat exchanger. In the NASTRAN model the components modeled are represented by one-dimensional ROD elements. Heat flow in the solids and fluid are analyzed. The problem is mildly nonlinear since the heat capacity of the refrigerant is temperature-dependent. One simulation run consists of a series of transient analyses, each representing one stroke of the heat pump. An auxiliary program was written that uses the results of one NASTRAN analysis to generate data for the next NASTRAN analysis

A preliminary transient-fault experiment on the SIFT computer system

This paper presents the results of a preliminary experiment to study the effectiveness of a fault-tolerant system's ability to handle transient faults. The primary goal of the experiment was to develop the techniques to measure the parameters needed for a reliability analysis of the SIFT computer system which includes th effects of transient faults. A key aspect of such an analysis is the determination of the effectiveness of the operating system's ability to discriminate between transient and permanent faults. A detailed description of the preliminary transient fault experiment along with the results from 297 transient fault injections are given. Although not enough data was obtained to draw statistically significant conclusions, the foundation has been laid for a large-scale transient fault experiment

Transient loads analysis for space flight applications

A significant part of the flight readiness verification process involves transient analysis of the coupled Shuttle-payload system to determine the low frequency transient loads. This paper describes a methodology for transient loads analysis and its implementation for the Spacelab Life Sciences Mission. The analysis is carried out using two major software tools - NASTRAN and an external FORTRAN code called EZTRAN. This approach is adopted to overcome some of the limitations of NASTRAN's standard transient analysis capabilities. The method uses Data Recovery Matrices (DRM) to improve computational efficiency. The mode acceleration method is fully implemented in the DRM formulation to recover accurate displacements, stresses, and forces. The advantages of the method are demonstrated through a numerical example

Gas-core reactor power transient analysis

The gas core reactor is a proposed device which features high temperatures. It has applications in high specific impulse space missions, and possibly in low thermal pollution MHD power plants. The nuclear fuel is a ball of uranium plasma radiating thermal photons as opposed to gamma rays. This thermal energy is picked up before it reaches the solid cavity liner by an inflowing seeded propellant stream and convected out through a rocket nozzle. A wall-burnout condition will exist if there is not enough flow of propellant to convect the energy back into the cavity. A reactor must therefore operate with a certain amount of excess propellant flow. Due to the thermal inertia of the flowing propellant, the reactor can undergo power transients in excess of the steady-state wall burnout power for short periods of time. The objective of this study was to determine how long the wall burnout power could be exceeded without burning out the cavity liner. The model used in the heat-transfer calculation was one-dimensional, and thermal radiation was assumed to be a diffusion process

Transient response analysis for DC-DC boost converter

DC-DC Boost Converter and Hybrid Posicast Controller is developed and simulated using MATLAB Simulink software. DC-DC Boost converter has a very high overshoot and a very high settling time which produce oscillated output response. In order to overcome this weakness, Hybrid Posicast Controller is used in order to regulate the output voltage to a desire value. Hybrid Posicast Controller operated within the feedback loop of the system. Transfer function of DC-DC Boost Converter are derived and Posicast elements of and Td can be calculated directly from the transfer function. Single gain, K is used in order to eliminate the overshoot and minimize the settling time. Simulation results show that Hybrid Posicast Controller effectively regulate the output voltage to a desire value even though load resistance and duty cycle have been changed with a various values. DC-DC Boost Converter using Posicast Controller has an excellent performance to overcome unregulated 377$ input voltage, eliminate overshoot and minimize the settling tim