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The purpose of this paper is design a stable walking gait for robot UXA-90. We applied Zero Moment Point (ZMP) based preview control to generate Center of Mass (CoM) trajectory. The ankle trajectories were created by spline interpolation method. Experiment results show that our method can make robot walking stable.

A novel technique to evaluate fracture mechanics parameters is investigated employing the equivalent domain integral (EDI) method and nodal integration (NI) techniques. Galerkin-based meshfree method is adopted. Reproducing kernel (RK) is chosen for the meshfree interpolant. Stabilized conforming nodal integration (SCNI) and sub-domain stabilized conforming integration (SSCI) are adopted for numerically integrating the stiffness matrix. Voronoi diagram is employed to compute volume of each NI domain. The EDI method is addressed to evaluate the fracture mechanics parameters, i.e., energy release rate and stress intensity factors (SIFs). Because the displacement and its derivatives are computed based on SCNI/SSCI, the EDI can be discretized by summing up the physical quantities and volume of each cell/sub-cell. No special quadrature rule is required. To separate the energy release rate into the mixed-mode SIFs, interaction integral method is chosen. Efficient and accurate fracture parameter computation is achieved. Some numerical examples are demonstrated for mixed-mode fracture parameter evaluation and crack propagation analysis. Accuracy and effectiveness of the presented approach are studied.

Herein we report a strain sensor with SiC/Si heterostructure exhibiting performance enhanced toward ultra-sensitivity using a bonded pico-light-emitting-diode. First, a cantilever with SiC/Si heterostructure is fabricated, followed by bonding a pico-LED on the top of the cantilever. The lateral photovoltage and photocurrent, then, are investigated under different LED supply voltages. The lateral photovoltage and photocurrent are as high as 7.9 mV and 19.06 µA, respectively, as the bonded LED is powered by a supply voltage of 6V. Finally, the performance of the strain sensor was investigated. When the bonded LED is OFF, the gauge factor (GF) of the strain sensor is 20.5. This GF significantly increases to 18,000 when the bonded LED is ON, which is thousand-time modulation. In other word, the strain sensor with bonded LED has ultra-high sensitivity.

We discuss the relevance of the lattice Boltzmann method (LBM) for soft matter alongside other simulation methods. We set up a popular problem of self-assembly of Janus spheres by combining native fluid and particle models in LBM with a simple amphiphilic pair potential. Thermal fluctuations and close contact corrections are also incorporated along with a novel periodic boundary condition for finite-sized 3D particles. Preliminary results of Janus sphere self-assembly are presented and compared with similar works in the literature. We also comment on the difficulties that LBM faces tackling such problems.

This paper is devoted to the micro-mechanical origins of the high compressibility of brittle tubular particle assemblies. The material is extremely porous due to the presence of a large hole within the tube-shaped particle. The release of the inner void, protected by a fragile shell, gives the material a very strong ability to compress. The compressive response is investigated by means of the discrete element method, DEM, using crushable elements. To address the complexity of the model, a step-by-step breakdown is developed. The paper comprises the comparison of the numerical results with both results obtained by the authors and existing experiments. With the insights provided by the DEM, we have sought to better understand the phenomena that originate at the grain scale and that govern macroscopic behaviour. Grain breakage was proven to control the compressive behaviour, and thus, the importance of internal pores dominates the inter-particle voids. Then, a novel concept of compressibility analysis has been proposed using the separation of the double porosity and the quantification of the pore collapse through primary grain breakage. Finally, a general, geometrical development of a semi-analytical model has been proposed aiming the prediction of the evolution of double porosity vs axial strain.

The Particle Flow Code is a typical DEM numerical software; however, the microparameters of DEM models need to be calibrated before numerical simulation. In most cases, the trial-and-error method is used; however, it takes a great deal of time and the results depend on the researchers’ experience. To address this issue, the cross-entropy method (CEM), differential evolution (DE), electromagnetic field optimization (EFO), moth–flame optimization (MFO) and salp swarm optimization (SSO) algorithm have been used for microparameters calibration. We provide a numerical simulation example to verify the validity of these microparameter calibration methods; it turns out that the number of iterations was large. To reduce the computational effort of obtaining suitable microparameters of the DEM model, we determine the optimal hyperparameters of the CEM, DE, EFO, MFO and SSO microparameter calibrating techniques. Through the analysis of the results, the number of iterations of these algorithms was markedly reduced. Considering the number of iterations, the number of hyperparameters and the results of numerical simulation, we suggest SSO algorithm for microparameter calibration. We also give another numerical simulation example to verify the validity of the proposed method. We found that the number of iterations for obtaining suitable microparameters was less than 100, and only 1 hyperparameter needed to be determined. Compared with previous studies, the number of iterations decreased remarkably.

The mechanically over-excavated cavity along the borehole represents an innovative technology designed to enhance permeability in soft coal seams. This study aims to elucidate the complex mechanisms that influence the mechanical properties and crack evolution of over-excavated cavities. Uniaxial compression tests were performed on coal specimens with double over-excavated cavities, and the impact of cavity length–height ratio and shape on mechanical properties and crack evolution was investigated using digital image correlation techniques and acoustic emission (AE) measurements. Discrete element method simulations provided deeper insights into stress evolution and crack behavior around the cavities. The presence of an over-excavated cavity significantly affected the specimen’s mechanical properties, with the effect’s magnitude closely linked to the length–height ratio. As this ratio decreased, the peak stress and elastic modulus of the specimen increased. Specimens containing elliptical cavities demonstrated higher elastic modulus and peak stress compared to those with rectangular cavities of the same length. Crack initiation and propagation displayed distinct features, such as a sudden surge in AE counts and the appearance of strain concentration regions. The failure mode of the specimen was dominated by shear failure combined with tensile failure, and spalling of the specimen appeared as the length–height ratio decreased, indicating stronger damage. Numerical simulations aligned well with experimental findings, revealing tensile and shear cracks as predominant, with failure resulting from crack coalescence. Specimens containing rectangular cavities were more prone to failure than those with elliptical cavities due to stress concentration in corners. The maximum compressive principal stress was concentrated at the tips of the left and right flaws. The release and transfer of stress concentration zones played a pivotal role in influencing the evolution and behavior of cracks, ultimately impacting the overall mechanical response and failure characteristics of the specimen. The research findings provide valuable insights for optimizing the parameters of mechanically over-excavated cavities in coal mines, enhancing performance and safety.