A new solution to estimate the time delay on the topographic site using time domain 3D boundary element method

This study focuses on investigating spatial variation of ground motion that has great influence on the dynamic behavior of the large structures located on the surface topography.One of the most effective parameters on the spatial variation of ground motion is the difference between the arrival time of seismic waves in different points located on the abutments.In this research,a three-dimensional model of the Pacoima Dam site is prepared.The time domain 3 D boundary element method is used to apply non-uniform excitation at the dam supports.This model is subjected to vertically propagating incident SH and P waves.The time delay can be characterized by calculating the value of the time delay for which the cross-correlation between two records is maximized.Finally,to obtain the time delay in a topographic site,a function considering effective parameters such as the height from the canyon base,wave velocity and predominant frequency,is presented.Furthermore,a code was developed for generating the spatially variation of seismic ground motions.The results show that the proposed functions have an acceptable accuracy in estimating the time delay to generate non-uniform ground motion.

Relationship between serum adhesion molecules, trace elements and delayed union of tibial and fibula fractures

Objective:To investigate the relationship between serum adhesion molecules, trace elements and delayed union of tibial and fibula fractures.Methods:A total of 46 patients with delayed union of tibial and fibula fractures in our hospital from May 2014 to June 2016 were selected as the observation group, 46 patients with normal healing of tibial and fibula fractures were selected as the control group, then the serum adhesion molecules and trace elements levels of two groups at forth, eighth and sixteenth week after the surgery were compared.Results:The serum dhesion molecules levels of observation group at forth, eighth and sixteenth week after the surgery were all higher than those of control group, the serum trace elements levels were all lower than those of control group, and the serum adhesion molecules levels of two groups at eighth week after the surgery were all higher than those at other time, the trace elements levels were all lower than those at other time (allP<0.05).Conclusions:The serum adhesion molecules and trace elements of patients with delayed union of tibial and fibula fractures show obviously abnormal state, so those indexes of those patients should be paid to more monitoring and improvement.

Multi-level coarse-grained discrete element method modeling of cylinder particle flow in a rotating drum

The coarse-grained discrete element method(DEM)is probably a feasible option for simulating an actual drum-type biomass boiler,which contains over 10 million cylinder particles.A multi-level study was conducted based on particle and coarse-grained level data to evaluate the adequacy of the coarse-grained approach in terms of geometrical characteristics,kinematic features,and dynamic properties.Two scaling laws for contact parameters were used and compared during the simulations.The results show that the coarse-grained approach can accurately predict the positions of the free surface and active-passive interface,the mixing index,and the orientation properties.Deviations in the velocity fields may occur due to the worse flowability of coarse-grained particles near the free surface.The efficiency is significantly improved by the coarse-grained model compared with the corresponding original case(the same DEM code without a coarse-grained model was used for the original simulations).

Introducing an effective coherence function to generate non-uniform ground motion on topographic site using time-domain boundary element method

In this study,a comprehensive parametric analysis was performed on non-uniform excitation of V-shaped topography using the boundary element method in time domain.For this purpose,wave scattering analysis was carried out on a topography subjected to the SV-wave for different predominant frequencies and shape ratios.Based on the numerical results,new coherence and time delay functions are proposed to generate non-uniform ground motion for topographic irregularities.The efficiency and accuracy of the proposed functions for real engineering problems are indicated by comparison with observations reported in previous literature.

The Finite Volume Element Method for Time-Fractional Nonlinear Fourth-Order Diffusion Equation with Time Delay

In this article, a finite volume element algorithm is presented and discussed for the numerical solutions of a time-fractional nonlinear fourth-order diffusion equation with time delay. By choosing the second-order spatial derivative of the original unknown as an additional variable, the fourth-order problem is transformed into a second-order system. Then the fully discrete finite volume element scheme is formulated by using L1approximation for temporal Caputo derivative and finite volume element method in spatial direction. The unique solvability and stable result of the proposed scheme are proved. A priori estimate of L2-norm with optimal order of convergence O(h2+τ2−α)where τand hare time step length and space mesh parameter, respectively, is obtained. The efficiency of the scheme is supported by some numerical experiments.

A coarse-grained bonded particle model for large-scale rock simulation

For solving the computationally intensive problem encountered by the discrete element method(DEM)in simulating large-scale engineering problems,it is essential to establish a numerical model that can effectively simulate large-scale rocks.In this study,the coarse-graining effect of a linear-Mindlin with bonding model was studied in the unconfined compression strength(UCS)and Brazilian tensile strength(BTS)tests.We found that the main reason for the coarse-graining effect of the BTS tests is that the type I fracture toughness is positively correlated with the size of the particles.Based on the results analysis and fracture mechanics,the coarse-grained(CG)modeling theory was combined with a bonded particle model(BPM)for the first time and a coarse-grained bonded particle model(CG-BPM)was developed,which can be effectively used to model the tensile strength of large-scale rocks with different particle sizes.The excavation damage zone(EDZ)in an underground research laboratory(URL)was selected as an application case,which shows that the coarse-grained bonding model presented in this paper is more accurate and reliable than the traditional one in large-scale rock simulation,at least in the scenario where tensile failure is dominant.

Numerical and experimental direct shear tests for coarse-grained soils

The presence of particles larger than the permissible dimensions of conventional laboratory specimens causes difficulty in the determination of shear strength of coarse-grained soils. In this research, the influence of particle size on shear strength of coarse-grained soils was investigated by resorting to experimental tests in different scale and numerical simulations based on discrete element method （DEM）. Experimental tests on such soil specimens were based on using the techniques designated as ＂parallel＂ and ＂scalping＂ to prepare gradation of samples in view of the limitation of laboratory specimen size. As a second approach, the direct shear test was numerically simulated on assemblies of elliptical particles. The behaviors of samples under experimental and numerical tests are presented and compared, indicating that the modification of sample gradation has a significant influence on the mechanical properties of coarse-grained soils. It is noted that the shear strengths of samples produced by the scalping method are higher than samples by the parallel method. The scalping method for preparing specimens for direct shear test is therefore recommended. The micromechanical behavior of assemblies under direct shear test is also discussed and the effects of stress level on sample behavior are investigated.

Analysis of Pulverized Coal by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy （LIBS） has been used to detect atomic species in various enviromnents. The quantitative analysis （C, H, O, N and S） of representative coal samples are being carried out with LIBS, and the effects of particle size are analyzed. A powerful pulse Nd：YAG laser is focused on the coal sample at atmosphere pressure, and the emission spectra from laser-induced plasmas are measured by time-resolved spectroscopy, and the intensity of analyzed spectral lines is obtained through observing the laser plasma with a delay time of 0.4 #s. The experimental results show that the slope of calibration curve is nearly 1 when the concentration of the analyzed element is relatively low, and the slope of curve is nearly 0.5 when the concentration of C is higher than other elements. In addition, using the calibration-free model without self-absorption effect, the results show that the decreasing of particle size leads to an increase of the plasma temperature.

Ultrasonic beam steering using Neumann boundary condition in multiplysics

The traditional one-dimensional ultrasonic beam steering has time delay and is thus a complicated problem. A numerical model of ultrasonic beam steering using Neumann boundary condition in multiplysics is presented in the present paper. This model is based on the discrete wave number method that has been proved theoretically to satisfy the continuous conditions. The propagating angle of novel model is a function of the distance instead of the time domain. The propagating wave fronts at desired angles are simulated with the single line sources for plane wave. The result indicates that any beam angle can be steered by discrete line elements resources without any time delay.

Evaluation of coarse-grained CFD-DEM models with the validation of PEPT measurements

Computational Fluid Dynamics coupled with Discrete Element Method (CFD-DEM) is a commonly used numerical method to model gas-solid flow in fluidised beds and other multiphase systems. A significant limitation of CFD-DEM is the feasibility of the realistic simulation of large numbers of particles. Coarse-graining (CG) approaches, through which groups of multiple individual particles are represented by single, larger particles, can substantially reduce the total number of particles while maintaining similar system dynamics. As these three CG models have not previously been compared, there remains some debate, however, about the best practice in the application of CG in CFD-DEM simulations. In this paper, we evaluate the performance of three typical CG methods based on simulations of a bubbling fluidised bed. This is achieved through the use of a numerical validation framework, which makes full use of the high-resolution 3D positron emission particle tracking (PEPT) measurements to rigorously validate the outputs of CFD-DEM simulations conducted using various different coarse-graining models, and various different degrees of coarse-graining. The particle flow behaviours in terms of the particle occupancy field, velocity field, circulation time, and bubble size and velocity, are comprehensively analysed. It is shown that the CG simulation starts to fail when the size ratio between the bed chamber and the particles decreases to approximately 20. It is also observed, somewhat surprisingly, that the specific CG approach applied to interparticle contact parameters does not have a substantial effect on the simulation results for the bubbling bed simulations across a wide range of CG factors.

COARSE-GRAINED ATOMISTIC MODELING AND SIMULATION OF INELASTIC MATERIAL BEHAVIOR

This paper presents a new methodology for coarse-grained atomistic simulation of inelastic material behavior including phase transformations in ceramics and dislocation mediated plasticity in metals. The methodology combines an atomistic formulation of balance equations and a modified finite element method. With significantly fewer degrees of freedom than those of a fully atomistic model and without additional constitutive rules but the interatomic force field, the new coarse-grained （CG） method is shown to be feasible in predicting the nonlinear constitutive re- sponses of materials and also reproducing atomic-scale phenomena such as phase transformations （diamond --, 13-Sn） in silicon and dislocation nucleation and migration, formation of dislocation loops and stacking faults ribbons in single crystal nickel. Direct comparisons between CG and the corresponding full molecular dynamics （MD） simulations show that the present methodology is efficient and promising in modeling and simulation of inelastic material behavior without losing the essential atomistic features. The potential applications and the limitations of the CG method are also discussed.

Clock generator and OOK modulator for RFID application

The clock generator and OOK modulator for RFID (Radio Frequency Identification) presented in this paper consist of a current source and delay elements. The simple constant-gm structure is adopted in the current source design and the current consumption of the current source is only about 2 μA. The delay elements, the clock generator and OOK modulator are introduced in detail in the paper. The designed circuits are fabricated by 0.6 μm CMOS process. The area of the core circuit is only about 400 μm×80 μm. The delay time of all three samples is in the range of 9 μs to 21 μs when the supply voltage varies from 2 V to 4 V. As the measured results satisfy the system requirements, these circuit structures are suitable for RFID application.

Discrete particle methods for engineering simulation:Reproducing mesoscale structures in multiphase systems

Most natural resources are processed as particle-fluid multiphase systems in chemical,mineral and material indus-tries,therefore,discrete particles methods(DPM)are reasonable choices of simulation method for engineering the relevant processes and equipments.However,direct application of these methods is challenged by the complex multiscale behavior of such systems,which leads to enormous computational cost or otherwise qualitatively inac-curate description of the mesoscale structures.The coarse-grained DPM based on the energy-minimization multi-scale(EMMS)model,or EMMS-DPM,was proposed to reduce the computational cost by several orders while main-taining an accurate description of the mesoscale structures,which paves the way for its engineering applications.Further empowered by the high-efficiency multi-scale DEM software DEMms and the corresponding customized heterogeneous supercomputing facilities with graphics processing units(GPUs),it may even approach realtime simulation of industrial reactors.This short review will introduce the principle of DPM,in particular,EMMS-DPM,and the recent developments in modeling,numerical implementation and application of large-scale DPM which aims to reach industrial scale on one hand and resolves mesoscale structures critical to reaction-transport coupling on the other hand.This review finally prospects on the future developments of DPM in this direction.

An experimental and numerical approach-characterisation of power cartridge for water-jet application

Power Cartridges are pyrotechnic devices where hot combustion gases utilized to do mechanical work for disruption of suspected Improvised Explosive Devices(IEDs). It plays a vital role either in destroying the suspicious object or making them non-functional by generating the gas pressure on burning of propellant against the water column inside the barrel, Present work is focused on characterisation,numerical solution such as deformation; strain; stress using FEM(Finite Element Method), design qualification, performance and evaluation of power cartridge for disruptor application. Experimental trials for pressure-time(P-t) measurement in closed vessel(CV), various electrical parameters like all fire current(AFC), no fire current(NFC) and ignition delay have been measured. Further, mechanical properties for brass material have been determined. An attempt has been made to characterise the power cartridge by FEM and carrying out the experiments for water-jet application.

A novel power-on-reset circuit for passive UHF RFID tag chip

A novel power-on-reset(POR) circuit with simple architecture, small values of capacitances, ultralower power consumption, and self-adjustable delay time of reset pulse for passive UHF RFID tags is presented in this paper. A proposed delay element was adopted for the features of small capacitances and wide power supply rise time range. An inverter was used as a two-inputs logic device to simplify the architecture of the circuit. The technology used for design and simulation is SMIC 0.18 μm RF. Simulation results show that the circuit functions well under different process corners with different power supply rise time, and is able to generate a POR signal after the power supply is briefly powered off. The static power consumption is less than 30 pA. Moreover, the circuit operates properly along with other modules of analog front-end.

On Approximation and Computation of Navier-Stokes Flow

We present an approximation method for the non-stationary nonlinear in- compressible Navier-Stokes equations in a cylindrical domain （0, T） x G, where G C ]R3 is a smoothly bounded domain. Our method is applicable to general three-dimensional flow without any symmetry restrictions and relies on existence, uniqueness and rep- resentation results from mathematical fluid dynamics. After a suitable time delay in the nonlinear convective term v. ~7v we obtain globally （in time） uniquely solvable equations, which - by using semi-implicit time differences - can be transformed into a finite number of Stokes-type boundary value problems. For the latter a boundary element method based on a corresponding hydrodynamical potential theory is carried out. The method is reported in short outlines ranging from approximation theory up to numerical test calculations.