Circuit convergence study using machine learning compact models

Machine learning (ML) compact device models (CM) have emerged as an alternative to physics-based CMs. ML CMs can find a mathematical model close to the device characteristics without much prior knowledge, which saves the time of model formation. Additionally, versatile capabilities such as process-awareness, model merging, and fitting new technologies, promote the usage of ML CMs. While ML CMs draw great attention in CAD, their convergence in SPICE has not been carefully studied. Here different activation functions are used to create ML CMs, and then the circuit convergence is tested. We found that inverse square root unit (ISRU) activation has the best convergence. Besides, gate-to-source and gate-to-drain capacitance is founded to benefit the convergence in transient analysis. The circuit convergence rate is 100% for ISRU, sigmoid, and tanh when the capacitor is present. On the other hand, ISRU significantly outperforms other activation functions in DC sweep, achieving 81% convergence. If quasi-static transient analysis is employed to replace DC sweep, 100% convergence is achieved by ISRU. Due to its superior convergence, ISRU is the most promising for future ML CMs in SPICE.

NUMERICAL PREDICTION OF SLAMMING LOADS DURING WATER ENTRY OF BOW-FLARED SECTIONS

The two-dimensional water entry of bow-flared sections is studied by using a Multi-Material Arbitrary Lagrangian- Eulerian (MMALE) formulation and a penalty-coupling algorithm. A convergence study is carried out, considering the effects of mesh size, the dimension of fluids domain, and fluid leakage phenomenon through the structure. The predicted results on the wetted surface of a bow-flared section are compared with published experimental values in terms of vertical slamming force, pressure distributions at different time instances and the pressure histories at different points. Comparisons between the numerical results and measured values show satisfactory correlation. An approximation method is adopted to estimate the sectional slamming force showing good consistency for the peak forces.

Time Period of the Vibration of the Circular Plate with Circular Variation Both in Thickness and Density

An analysis was carried out to investigate the time period of the thermally induced vibration of clamped and simply supported circular plates with circular variation both in thickness and density. Prior to this study, the variations considered were either linear, quadratic, parabolic, or exponential in nature. To study thermal effect, one-dimensional linear temperature variation on the plates is taken into consideration. Rayleigh–Ritz method is applied to compute the time period of the first three modes of vibration for both plates by varying tapering parameter, thermal gradient, and density. Convergence study of frequency modes for both plates conducted suggests that the convergence rate in case of circular variation is faster than the other studies done. A comparison of time period with the available published results is done. The comparison done concludes that time period obtained in the present study by varying thermal gradient and tapering parameter is found to be less than the other studies done for the same set of parameters. This study helped to establish the fact that, by using circular variation in plate parameters, we can get less time period of frequency modes in comparison to other variations considered till date.

Numerical investigations of 2-D planar magnetic nozzle effects on pulsed plasma plumes

This paper presents a study of a novel type of magnetic nozzle that allows for three-dimensional (3-D) steering of a plasma plume. Numerical simulations were performed using Tech-X’s USim® software to quantify the nozzle’s capabilities. A 2-D planar magnetic nozzle was applied to plumes of a nominal pulsed inductive plasma (PIP) source with discharge parameters similar to those of Missouri S&T’s Missouri Plasmoid Experiment (MPX). Argon and xenon plumes were considered. Simulations were verified and validated through a mesh convergence study as well as comparison with available experimental data. Periodicity was achieved over the simulation run time and phase angle samples were taken to examine plume evolution over pulse cycles. The resulting pressure, velocity, and density fields were analysed for nozzle angles from 0° to 14°. It was found that actual plume divergence was small compared to the nozzle angle. Even with an offset angle of 14° for the magnetic nozzle, the plume vector angle was only about 2° for argon and less than 1° for xenon. The parameters that had the most effect on the vectoring angle were found to be the coil current and inlet velocity.