Stability and accuracy of central difference method for real-time dynamic substructure testing considering mass participation coefficient

For real-time dynamic substructure testing(RTDST),the influence of the inertia force of fluid specimens on the stability and accuracy of the integration algorithms has never been investigated.Therefore,this study proposes to investigate the stability and accuracy of the central difference method(CDM)for RTDST considering the specimen mass participation coefficient.First,the theory of the CDM for RTDST is presented.Next,the stability and accuracy of the CDM for RTDST considering the specimen mass participation coefficient are investigated.Finally,numerical simulations and experimental tests are conducted for verifying the effectiveness of the method.The study indicates that the stability of the algorithm is affected by the mass participation coefficient of the specimen,and the stability limit first increases and then decreases as the mass participation coefficient increases.In most cases,the mass participation coefficient will increase the stability limit of the algorithm,but in specific circumstances,the algorithm may lose its stability.The stability and accuracy of the CDM considering the mass participation coefficient are verified by numerical simulations and experimental tests on a three-story frame structure with a tuned liquid damper.

APPLICATION OF THE MOMENT METHODS TO ANALYSIS OF X-RAY DIFFRACTION LINE PROFILE FOR PA1010-BMI SYSTEM

Pure X-ray diffraction profiles have been analysed for polyamide 1010 and PA1O1O-BMI system by means of multipeak fitting resolution of X-ray diffraction. The methods of variance and fourth moment have been applied to determine the particle size and strain values for the paracrystalline materials. The results indicated that both variance and fourth moment of X-ray diffraction line profile yielded approximately the same values of the particle size and the strain. The particle sizes of (100) reflection have been found to decrease with increasing BMI content, whereas the strain values increased.

Impact of central venous port implantation method and access choice on outcomes

BACKGROUND Although the number of patients who need central venous ports for permanent vascular access is increasing,there is still no“gold standard”for the implantation technique.AIM To identify the implantation technique that should be favored.METHODS Two hundred central venous port-implanted patients in a tertiary hospital were retrospectively evaluated.Patients were assigned into two groups according to the access method.The first group comprised patients whose jugular veins were used,and the second group comprised patients whose subclavian veins were used.Groups were evaluated regarding age,sex,application side,primary diagnosis,active follow-up period in the hospital,chemotherapy agents administered,number of complications,and the Clavien-Dindo severity score.The distribution of the variables was tested with the Kolmogorov-Smirnov test and the Mann-Whitney U test.Theχ^(2) test was used to analyze the variables.RESULTS There was no statistically significant difference between the groups regarding age,sex,side,number of chemotherapy drugs,and duration of port usage(P>0.05).Only 2 patients in group 1 had complications,whereas in group 2 we observed 19 patients with complications(P<0.05).No port occlusion was found in group 1,but the catheters of 4 patients were occluded in group 2.One port was infected in group 1 compared to three infected ports in group 2.Two port ruptures,two pneumothorax,one revision due to a mechanical problem,one tachyarrhythmia during implantation,and four suture line problems were also recorded in group 2 patients.We also showed that it would be sufficient to evaluate and wash ports once every 2 mo.CONCLUSION Our results robustly confirm that the jugular vein route is safer than the subclavian vein approach for central venous port implantation.

Feasibility of central loop TEM method for prospecting multilayer water-fi lled goaf

With deep mining of coal mines, prospecting multilayer water-filled goaf has become a new content that results from geophysical exploration in coalfields. The central loop transient electromagnetic （TEM） method is favorable for prospecting conductive layers because of the coupling relationship between its field structure and formation. However, the shielding effect of conductive overburden would not only require a longer observation time when prospecting the same depth but also weaken the anomalous response of underlying layers. Through direct time domain numerical simulation and horizontal layered earth forward modeling, this paper estimates the length of observation time required to prospect the target, and the distinguishable criterion of multilayer water-filled goal is presented with observation error according to the effect of noise on observation data. The observed emf curves from Dazigou Coal Mine, Shanxi Province can distinguish multilayer water-filled goaf. In quantitative inversion interpretation of observed curves, using electric logging data as initial parameters restrains the equivalence caused by coal formation thin layers. The deduced three-layer and two-layer water-filled goals are confirmed by the drilling hole. The result suggests that when observation time is long enough and with the anomalous situation of underlying layers being greater than the observation error, the use of the central loop TEM method to orosoect a multilaver water-filled goaf is feasible.

Analyzing Parabolic Profile Path for Underwater Towed-Cable

This article discusses the dynamic state analysis of underwater towed-cable when tow-ship changes its speed in a direction making parabolic profile path. A three-dimensional model of underwater towed system is studied. The established governing equations for the system have been solved using the central implicit finite-difference method. The obtained difference non-linear coupled equations are solved by Newton＇s method and satisfactory results were achieved. The solution of this problem has practical importance in the estimation of dynamic loading and motion, and hence it is directly applicable to the enhancement of safety and the effectiveness of the offshore activities.

Simulation on venting process and valve opening control method for gas trunk pipelines

Determining the venting time of a gas trunk pipeline segment provides an important basis for formulating an emergency plan in the advent of unexpected accidents.As the natural gas venting process corresponds to the transient flow,it is necessary to establish a transient hydraulic-thermal simulation model in order to determine the venting time.In this paper,based on two kinds of venting scenarios in which there is only one venting point in the venting system of a gas trunk pipeline segment—namely,where the venting point is either at one of the two ends or at the junction of two gas trunk pipeline segments—transient hydraulic-thermal simulation models are established.The models consist of gas flow governing equations,the gas state equation,gas physical property equations,initial conditions,and appropriate boundary conditions.The implicit central difference method is used to discretize the gas flow partial differential equations,and the trust-region-dogleg algorithm is used to solve the equations corresponding to each time step,in order to dynamically simulate the whole venting process.The judgment condition for the end of the venting process is that the average pressure of gas trunk pipeline segment is less than 0.11 MPa(actual pressure).Comparing the simulation results of the proposed model with those of the OLGA software and real operational data,we find that the venting time error is less than 10%.On this basis,a venting valve opening control principle is proposed,which prevents the venting noise from exceeded the specified noise value(85 d B)in the venting design of domestic gas pipeline projects.The established calculation model for venting time(dynamic simulation model)for a gas trunk pipeline segment and the proposed opening control principle of venting valve provide reference for the optimal operation of gas pipeline venting systems.

Calibration of Discrete Element Heat Transfer Parameters by Central Composite Design

The efficiency and precision of parameter calibration in discrete element method （DEM） are not satisfactory, and parameter calibration for granular heat transfer is rarely involved. Accordingly, parameter calibration for granular heat transfer with the DEM is studied. The heat transfer in granular assemblies is simulated with DEM, and the effective thermal conductivity （ETC） of these granular assemblies is measured with the transient method in simulations. The measurement testbed is designed to test the ETC of the granular assemblies under normal pressure and a vacuum based on the steady method. Central composite design （CCD） is used to simulate the impact of the DEM parameters on the ETC of granular assemblies, and the heat transfer parameters are calibrated and compared with experimental data. The results show that, within the scope of the considered parameters, the ETC of the granular assemblies increases with an increasing particle thermal conductivity and decreases with an increasing particle shear modulus and particle diameter. The particle thermal conductivity has the greatest impact on the ETC of granular assemblies followed by the particle shear modulus and then the particle diameter. The calibration results show good agreement with the experimental results. The error is less than 4%, which is within a reasonable range for the scope of the CCD parameters. The proposed research provides high efficiency and high accuracy parameter calibration for granular heat transfer in DEM.

RANDOM RESPONSES OF A TWO-DEGREE-OF-FREEDOM STRUCTURE WITH STRONGLY NONLINEAR COUPLING AND PARAMETRIC INTERACTION

This paper investigates the random responses of a TDOF structure with strongly nonlinear coupling and parametric vibration. With the nonlinear cou- pling of inertia in the equations of motion of the system being removed by successive elimination, the non-Gaussian moment equation method (NGM) is applied and 69 moment equations are integrated with central cumulative truncation technique. The stochastic central difference-cum-statistical linearization method(SCD-SL) and the digital simulation method(DSM) are also used. A comparison of results by different methods are given and the SCD-SL method is the most efficient method.

A Spectral Method for Convection-Diffusion Equations

In the practical problems such as nuclear waste pollution and seawater intrusion etc., many problems are reduced to solving the convection-diffusion equation, so the research of convection-diffusion equation is of great value. In this work, a spectral method is presented for solving one and two dimensional convection-diffusion equation with source term. The finite difference method is also used to solve the convection diffusion equation. The numerical experiments show that the spectral method is more efficient than other methods for solving the convection-diffusion equation.

Central Discontinuous Galerkin Method for the Navier-Stokes Equations

Central discontinuous Galerkin（CDG）method is used to solve the Navier-Stokes equations for viscous flow in this paper.The CDG method involves two pieces of approximate solutions defined on overlapping meshes.Taking advantages of the redundant representation of the solution on the overlapping meshes,the cell interface of one computational mesh is right inside the staggered mesh,hence approximate Riemann solvers are not needed at cell interfaces.Third order total variation diminishing（TVD）Runge-Kutta（RK）methods are applied in time discretization.Numerical examples for 1D and2 D viscous flow simulations are presented to validate the accuracy and robustness of the CDG method.

A New Method for Identifying Influential Nodes and Important Edges in Complex Networks

The identification of the influential nodes in a network is of great significance for understanding the features of the network and controlling the complexity of networks in society and in biology. In this paper, we propose a novel centrality measure for a node by considering the importance of edges and compare the performance of this method with existing seven topological-based ranking methods on the Susceptible-Infected-Recovered （SIR） model. The simulation results for four different types of real networks show that the proposed method is robust and exhibits excellent performance in identifying the most influential nodes when spreading starting from both single origin and multipleorigins simultaneously.

Contact Behavior of Worn Bearings with Elastoplastic Functionally Graded Coating Based on Mixed Elastohydrodynamic Lubrication

The dynamic contact behavior of worn bearings with elastoplastic functionally graded coating is studied,and the interacting effect between worn band and functionally graded surface is analyzed.The surface deformation and roughness are included in the film thickness.The mixed elastohydrodynamic lubrication combined with point contact model is introduced to analyze the oil pressure in the contact zone.By using the Fourier transform method and Papkovich-Neuber potential function,the displacements and stress fields in the elastoplastic functionally graded coating are obtained.The second-order central difference method is used to solve the Reynolds equation.It is found that the repeated surface interaction can result in the sharp increase in pressure in bearings,and the oil pressure increases with increasing graded index.The entrainment of oil in the inlet and outlet zones becomes more evident if a large graded index is selected.

Multiquadric Finite Difference (MQ-FD) Method and its Application

The conventional finite difference(FD)schemes are based on the low order polynomial approximation in a local region.This paper shows that when the polynomial approximation is replaced by the multiquadric(MQ)function approximation in the same region,a new FD method,which is termed as MQ-FD method in this work,can be developed.The paper gives analytical formulas of the MQ-FD method and carries out a performance study for its derivative approximation and solution of Poisson equation and the incompressible Navier-Stokes equations.In addition,the effect of the shape parameter c in MQ on the formulas of the MQFD method is analyzed.Derivative approximation in one-dimensional space and Poisson equation in two-dimensional space are taken as model problems to study the accuracy of the MQ-FD method.Furthermore,a lid-driven flow problem in a square cavity is simulated by the MQ-FD method.The obtained results indicate that this method may solve the engineering problem very accurately with a proper choice of the shape parameter c.