Macroscopic Behavior and Microscopic Structure Evolution of Marine Clay in One-Dimensional Compression Revealed by Discrete Element Simulation

Marine clay has been attracting in-depth research on its mechanical behavior and internal structure evolution, which are crucial to marine infrastructure safety. In the formation process of marine clay, including the sedimentation and consolidation stages, the compression behavior and internal structure evolution are highly dependent on the pore water salinity. Discrete element method (DEM) simulation is a powerful tool to study the microscopic mechanics behind the complicated macroscopic mechanical behavior of marine clay. In this study, a DEM simulation scheme is systematically proposed to numerically study the macroscopic beahvior and microscopic structure evolution of marine clay in one-dimensional compression that mimics the marine clay formation process. First, the proposed calculation scheme for double layer repulsive interaction and van der Waals interaction is introduced. Then, the developed DEM simulation scheme is validated by satisfactorily reproducing the experimentally observed one-dimensional compression curves and internal structure transition from an edge-to-edge/edge-to-face flocculated structure to a face-to-face dispersed structure. Finally, evolutions of coordinate number and fabric anisotropy are quantitatively evaluated in the microscopic view. The noticeable effects of ion concentration on the internal structure evlotion and mechanical behavior of marine clay have been examined and discussed.

Numerical analysis of fatigue crack growth using a plastically dissipated energy factor based model

The investigation of fatigue crack growth (FCG) behavior may contribute to the assessment of damage tolerance of components. To study the FCG behavior considering the elastic–plastic behavior at the crack tip, a numerical simulation scheme based on compact tension (CT) specimen is developed. Also, an effective plastically dissipated energy (PDE) factor composed of maximum PDE ([Formula: see text]) and PDE range ([Formula: see text]) is proposed to establish the expression for evaluating the FCG rate. The simulation results show good agreement with the results of test under same load conditions. Also, the mesh sensitivity analysis and the comparison with test results confirm the validation of proposed model. Based on the proposed numerical simulation scheme, the FCG behavior is studied by analyzing the influence of plastic wake, mean load, load range, overload, underload, load sequence, and cyclic compression load on FCG from the perspective of crack driving force, FCG rate, and crack opening displacement (COD). It is found from the analysis results that the developed numerical simulation scheme can consider the load history effect and crack closure effect. The mechanisms of these factors on the influence of FCG rate are analyzed in detail.

Reliability Design and Simulation of High Density Packaging T/R Module

The requirements, development, packaging characteristics and existing reliability problems of high density packaging T/R modules are introduced, and the importance of reliability design is recognized. Aiming at the reliability problems of Electro Magnetic Compatibility (EMC), heat dissipation and electrostatic discharge, the reliability design and simulation scheme are given, and some cases are provided. Through design analysis and improvement, the reliability of 3D high density packaging T/R modules can be effectively improved.

Bayesian tests of symmetry for the generalized Von Mises distribution

Bayesian tests on the symmetry of the generalized von Mises model for planar directions (Gatto and Jammalamadaka in Stat Methodol 4(3):341–353, 2007) are introduced. The generalized von Mises distribution is a flexible model that can be axially symmetric or asymmetric, unimodal or bimodal. A characterization of axial symmetry is provided and taken as null hypothesis for one of the proposed Bayesian tests. The Bayesian tests are obtained by the technique of probability perturbation. The prior probability measure is perturbed so to give a positive prior probability to the null hypothesis, which would be null otherwise. This allows for the derivation of simple computational formulae for the Bayes factors. Numerical results reveal that, whenever the simulation scheme of the samples supports the null hypothesis, the null posterior probabilities appear systematically larger than their prior counterpart.

Algorithmic Modelling of Advanced Chlorination Procedures for Multimetal Recovery

In the course of developing an innovative process for CO2-optimised valuable metal recovery from precipitation residues accumulating in the zinc industry or nickel industry, the chlorination reactions were investigated. As the basis of small-scale pyrometallurgical experiments, the selected reaction systems were evaluated by means of thermodynamic calculations. With the help of the thermochemical computation software FactSage (Version 8.0), it is possible to simulate the potential valuable metal recovery from residual materials such as jarosite and goethite. In the course of the described investigations, an algorithmically supported simulation scheme was developed by means of Python 3 programming language. The algorithm determines the optimal process parameters for the chlorination of valuable metals, whereby up to 10,000 scenarios can be processed per iteration. This considers the mutual influences and secondary conditions that are neglected in individual calculations.

An Effective Simulation Scheme for Predicting the Aerodynamic Heat of a Scramjet-Propelled Vehicle

Currently, aerothermal research into scramjet-propelled vehicles characterized by a wedge-shaped section is relatively sparse. Based on the Mach number, grid strategy, and numerical method, an effective simulation scheme for predicting the aerodynamic heat of a scramjet-propelled vehicle during flight is proposed in this paper. At different Mach numbers, the appropriate grid strategy and numerical method were determined by validation tests. Two-dimensional external flow field models based on wedge sections were established and, unlike in blunt bodies, the tests showed that at the high supersonic stage, the ideal cell Reynolds number should be no larger than 16. At the hypersonic stage, the ideal cell Reynolds number and aspect ratio of wall cells near the shock should be no larger than 40, and the AUSM+ flux type performs better than Roe’s FDS flux type at the above stages. The aerothermal prediction indicates that during a flight time of about 34 s, the temperature change reaches about 1913.35 °C, and the maximum average temperature change rate reaches 115 °C/s.

Transient Simulation of Distribution System with Converter-Based Distributed Generation for Stability Analysis Using Frequency Response Optimized Integrators

<p>This paper introduces a novel transient simulation scheme and its extension for stability analysis of distribution systems with converter-based distributed generation. Efficiency and accuracy of the simulation scheme with extension are investigated. It is demonstrated that millisecond-level step sizes are applicable to efficient electromagnetic transient simulation for stability analysis of unbalanced power systems while maintaining satisfactory accuracy. The paper also supports the extension of the simulation scheme by showing that the extension has only an insignificant impact on the accuracy but significantly enhances the efficiency.<br></p><p><br></p><p></p><p>This paper has been accepted by the 2021 IEEE IAS Annual Meeting.</p><p></p>

Transient Simulation of Distribution System with Converter-Based Distributed Generation for Stability Analysis Using Frequency Response Optimized Integrators

<p>This paper introduces a novel transient simulation scheme and its extension for stability analysis of distribution systems with converter-based distributed generation. Efficiency and accuracy of the simulation scheme with extension are investigated. It is demonstrated that millisecond-level step sizes are applicable to efficient electromagnetic transient simulation for stability analysis of unbalanced power systems while maintaining satisfactory accuracy. The paper also supports the extension of the simulation scheme by showing that the extension has only an insignificant impact on the accuracy but significantly enhances the efficiency.<br></p><p><br></p><p></p><p>This paper has been accepted by the 2021 IEEE IAS Annual Meeting.</p><p></p>