Bayesian inference and Markov chain Monte Carlo based estimation of a geoscience model parameter

The critical slip distance in rate and state model for fault friction in the study of potential earthquakes can vary wildly from micrometers to few meters depending on the length scale of the critically stressed fault. This makes it incredibly important to construct an inversion framework that provides good estimates of the critical slip distance purely based on the observed acceleration at the seismogram. The framework is based on Bayesian inference and Markov chain Monte Carlo. The synthetic data is generated by adding noise to the acceleration output of spring-slider-damper idealization of the rate and state model as the forward model.

Aliasing Effects on Nodal Acceleration Output From Nonlinear Finite Element Simulations

Nodal acceleration output from nonlinear finite element crash simulations often contains high frequency components. If this output is not sampled frequently enough the high frequency components will be aliased and the resulting acceleration output will be inaccurate. It is recommended in this paper that a low-pass filter be installed in the crashworthiness finite element codes which would remove the high frequency components of the nodal accelerations before they are sampled for output. This would completely eliminate aliasing error in acceleration output. Prior to this installation, there are several options for reducing the effects of aliasing on acceleration output. One option is to request very high sampling rates for acceleration output; however this will result in very large output files. Another option is to calculate the accelerations by differentiating the output velocities. This option, which effectively is an averaging filter acting on the accelerations, is available in the finite element code DYNA3D. The properties of this filter are examined in this paper and it is shown that this filter is very effective in reducing the effects of aliasing on acceleration output, although it should not be expected to completely eliminate potential aliasing problems. Finally, guidelines are presented for selecting nodes and sampling rates based on local natural frequencies that will reduce the effect of aliasing of the acceleration output.

Validation of a Hand/Wrist Electromechanical Goniometer

This paper describes a new hand/wrist electromechanical goniometer that measures wrist angle, velocity, and acceleration in the radial/ulnar and flexion/extension planes. The research objectives of this paper were to validate the angle and motion measures from this goniometer. The results of this research show that the coefficient of variation of the angle measured by the goniometer and the angle measured by a video-based Motion Analysis system was 3%. By smoothing the voltage data three times in software, the goniometer estimated well the velocity and acceleration measures under controlled dynamic conditions. Three smoothing repetitions appear to be the best smoothing regimen for the goniometer because it reduced signal noise while still maintaining the sensitivity of the velocity and acceleration output. Overall, the goniometer is an easy-to-use, accurate system of measuring wrist angle and motion. This goniometer will be used to build a database of wrist motion in industrial tasks.