Auto-parametric resonance of a continuous-beam-bridge model under two-point periodic excitation:an experimental investigation and stability analysis

The auto-parametric resonance of a continuous-beam bridge model subjected to a two-point periodic excitation is experimentally and numerically investigated in this study.An auto-parametric resonance experiment of the test model is conducted to observe and measure the auto-parametric resonance of a continuous beam under a two-point excitation on columns.The parametric vibration equation is established for the test model using the finite-element method.The auto-parametric resonance stability of the structure is analyzed by using Newmark's method and the energy-growth exponent method.The effects of the phase difference of the two-point excitation on the stability boundaries of auto-parametric resonance are studied for the test model.Compared with the experiment,the numerical instability predictions of auto-parametric resonance are consistent with the test phenomena,and the numerical stability boundaries of auto-parametric resonance agree with the experimental ones.For a continuous beam bridge,when the ratio of multipoint excitation frequency(applied to the columns)to natural frequency of the continuous girder is approximately equal to 2,the continuous beam may undergo a strong auto-parametric resonance.Combined with the present experiment and analysis,a hypothesis of Volgograd Bridge's serpentine vibration is discussed.

Blast wave characteristics of multi-layer composite charge:Theoretical analysis,numerical simulation,and experimental validation

This article investigates the characteristics of shock wave overpressure generated by multi-layer composite charge under different detonation modes.Combining dimensional analysis and the explosion mechanism of the charge,a peak overpressure prediction model for the composite charge under singlepoint detonation and simultaneous detonation was established.The effects of the charge structure and initiation method on the overpressure field characteristics were investigated in AUTODYN simulation.The accuracy of the prediction model and the reliability of the numerical simulation method were subsequently verified in a series of static explosion experiments.The results reveal that the mass of the inner charge was the key factor determining the peak overpressure of the composite charge under single-point detonation.The peak overpressure in the radial direction improved apparently with an increase in the aspect ratio of the charge.The overpressure curves in the axial direction exhibited a multi-peak phenomenon,and the secondary peak overpressure even exceeded the primary peak at distances of 30D and 40D(where D is the charge diameter).The difference in peak overpressure among azimuth angles of 0-90°gradually decreased with an increase in the propagation distance of the shock wave.The coupled effect of the detonation energy of the inner and outer charge under simultaneous detonation improved the overpressure in both radial and axial directions.The difference in peak overpressure obtained from model prediction and experimental measurements was less than 16.4%.

Analysis of sp Pillar Stability Experiment: Continuous thermo-mechanical model development and calibration

The paper describes an analysis of thermo-mechanical （TM） processes appearing during the Aspo Pillar Stability Experiment （APSE）. This analysis is based on finite elements with elasticity, plasticity and dam- age mechanics models of rock behaviour and some least squares calibration techniques. The main aim is to examine the capability of continuous mechanics models to predict brittle damage behaviour of gran- ite rocks. The performed simulations use an in-house finite element software GEM and self-developed experimental continuum damage MATLAB code. The main contributions are twofold. First, it is an inverse analysis, which is used for （1） verification of an initial stress measurement by back analysis of conver- gence measurement during construction of the access tunnel and （2） identification of heat transfer rock mass properties by an inverse method based on the known heat sources and temperature measurements. Second, three different hierarchically built models are used to estimate the pillar damage zones, i.e. elas- tic model with Drucker-Prager strength criterion, elasto-plastic model with the same yield limit and a combination of elasto-plasticity with continuum damage mechanics. The damage mechanics model is also used to simulate uniaxial and triaxial compressive strength tests on the ,Aspo granite.

Micro Model of Carbon Fiber/Cyanate Ester Composites and Analysis of Machining Damage Mechanism

Machining damage occurs on the surface of carbon fiber reinforced polymer (CFRP) composites during processing. In the current simulation model of CFRP, the initial defects on the carbon fiber and the periodic random distribution of the reinforcement phase in the matrix are not considered in detail, which makes the characteristics of the cutting model significantly different from the actual processing conditions. In this paper, a novel three-phase model of carbon fiber/cyanate ester composites is proposed to simulate the machining damage of the composites. The periodic random distribution of the carbon fiber reinforced phase in the matrix was realized using a double perturbation algorithm. To achieve the stochastic distribution of the strength of a single carbon fiber, a novel method that combines the Weibull intensity distribution theory with the Monte Carlo method is presented. The mechanical properties of the cyanate matrix were characterized by fitting the stress-strain curves, and the cohesive zone model was employed to simulate the interface. Based on the model, the machining damage mechanism of the composites was revealed using finite element simulations and by conducting a theoretical analysis. Furthermore, the milling surfaces of the composites were observed using a scanning electron microscope, to verify the accuracy of the simulation results. In this study, the simulations and theoretical analysis of the carbon fiber/cyanate ester composite processing were carried out based on a novel three-phase model, which revealed the material failure and machining damage mechanism more accurately.

Modeling and Parameter Sensitivity Analysis of Valve‑Controlled Helical Hydraulic Rotary Actuator System

As a type of hydraulic rotary actuator,a helical hydraulic rotary actuator exhibits a large angle,high torque,and compact structure;hence,it has been widely used in various fields.However,its core technology is proprietary to several companies and thus has not been disclosed.Furthermore,the relevant reports are primarily limited to the component level.The dynamic characteristics of the output when a helical rotary actuator is applied to a closed-loop system are investigated from the perspective of driving system design.Two main aspects are considered:one is to establish a reliable mathematical model and the other is to consider the effect of system parameter perturbation on the output.In this study,a detailed mechanical analysis of a helical rotary hydraulic cylinder is first performed,factors such as friction and load are considered,and an accurate dynamic model of the actuator is established.Subsequently,considering the nonlinear characteristics of pressure flow and the dynamic characteristics of the valve,a dynamic model of a valve-controlled helical rotary actuator angle closed-loop system is described based on sixth-order nonlinear state equations,which has never been reported previously.After deriving the system model,a sensitivity analysis of 23 main parameters in the model with a perturbation of 10%is performed under nine operating conditions.Finally,the system dynamics model and sensitivity analysis results are verified via a prototype experiment and co-simulation,which demonstrate the reliability of the theoretical results obtained in this study.The results provide an accurate mathematical model and analysis basis for the structural optimization or control compensation of similar systems.

Modification of B3 Model for Sealed Concrete with Additives Based on Experimental Observations

Thirteen specimens were tested out of which nine were for creep of sealed concrete and four for shrinkage test,for a period of 700 d under controlled temperature condition.The experimental results for creep and shrinkage were compared with creep and shrinkage computation model B3 and distinct discrepancies between observed and calculated creep and shrinkage strains were observed.Based on regression analysis,modification on B3 model has been formulated which will be applicable at least for concrete of characteristics strength of C40 and C50 with additives.Besides,on the basis of observation on identical specimens with varied stress strength ratio,a function is generated which accounts effect of stress strength ratio on creep.Finally,Civil Engineering community is suggested not to follow the creep prediction models without correction at least for modern concrete,as they do not account the effect of additives on its compliance function.

The semi-analytical modeling and vibration reduction analysis of the cylindrical shell with piezoelectric shunt damping patches

By considering electromechanical coupling, a unified dynamic model of the cylindrical shell with the piezoelectric shunt damping patch(PSDP) is created. The model is universal and can simulate the vibration characteristic of the shell under different states including the states in which PSDP cannot be connected, partially connected, and completely connected to the shunt circuit. The equivalent loss factor and elastic modulus with frequency dependence are proposed to consider the electrical damping effect of resistance shunt circuits. Moreover, the semi-analytical dynamic equation of the cylindrical shell with PSDP is derived by the Lagrange equation. An experimental test is carried out on the cylindrical shell with PSDP to verify the vibration suppression ability of PSDP on the cylindrical shell and the correctness of the proposed model. Furthermore, the parameter analysis shows that determining the appropriate resistance value in the shunt circuit can achieve a good vibration suppression effect.

Micro sliding friction model considering periodic variation stress distribution of contact surface and experimental verification

Micro sliding phenomenon widely exists in the operation process of mechanical systems,and the micro sliding friction mechanism is always a research hotspot.In this work,based on the total reflection method,a measuring device for interface contact behavior under two-dimensional(2D)vibration is built.The stress distribution is characterized by the light intensity distribution of the contact image,and the interface contact behavior in the 2D vibration process is studied.It is found that the vibration angle of the normal direction of the contact surface and its fluctuation affect the interface friction coefficient,the tangential stiffness,and the fluctuation amplitude of the stress distribution.Then they will affect the change of friction state and energy dissipation in the process of micro sliding.Further,an improved micro sliding friction model is proposed based on the experimental analysis,with the nonlinear change of contact parameters caused by the normal contact stress distribution fluctuation taken into account.This model considers the interface tangential stiffness fluctuation,friction coefficient hysteresis,and stress distribution fluctuation,whose simulation results are consistent well with the experimental results.It is found that considering the nonlinear effect of a certain contact parameter alone may bring a greater error to the prediction of friction behavior.Only by integrating multiple contact parameters can the accuracy of friction prediction is improved.

Experimental Study of Churning Losses in Swash Plate Axial Piston Pump

The problem of the churning loss in swash plate axial piston machines is investigated through experimental measurement and theoretical analysis. Several works surrounding churning loss in hydraulic components have been proposed in the past, but few have conducted experimental studies and accounted for both dry and wet housing conditions. In this study,a specialized experimental setup is established, which includes a transparent test pump diligently designed for performing various functions of tests. The test pump can work as a real pump without losing any actual features of pump operation. The torque loss in both the dry housing pump and wet housing pump is measured in terms of the shaft speed and its predictive model is also developed analytically. The comparisons between measured and calculated torque loss are presented, showing how speed influences torque loss in both conditions. The advantage/disadvantages of the two cases are summarized. The significance of the test setup is highlighted by verifying the proposed model, which can advance the understanding of energy losses of high speed pumps in future.

Experimental Study on Free Spanning Submarine Pipeline Under Dynamic Excitation

Seismic load has a significant effect on the response of a free spanning submarine pipeline when the pipeline is constructed in a seismically active region. The model experiment is performed on an underwater shaking table to simulate the response of submarine pipelines under dynamic input. In consideration of the effects of the terrestrial and submarine pipeline, water depth, support condition, distance from seabed, empty and full pipeline, and span on dynamic response, 120 groups of experiments are conducted. Affecting factors are analyzed and conclusions are drawn for reference. For the control of dynamic response, the span of a submarine pipeline is by far more important than the other factors. Meanwhile, the rosponse difference between a submarine pipeline under sine excitation and that under random excitation exists in experiments.

Sensitivity Analysis,Determination and Optimization of Granite RHT Parameters

The RHT model has 34 parameters,among which 19 parameters can be obtained by experiments or theoretical calculations and the remaining 15 parameters are difficult to acquire.In this study,firstly,10 Hopkinson impact tests were conducted to acquire the typical stress-strain curves of granite under dynamic loads.Through the sensitivity analysis,it is found that 13 of the 15 difficult-acquired parameters are effective to affect the shape of the stress-strain curve,and the other two parameters have no effect.Following the initial determination of model parameters with reference to the concrete RHT model,a new approach is proposed to optimize the 13 influential parameters through the LS-DYNA numerical simulation and orthogonal experiments.Finally,the determined granite RHT model parameters are verified by the results of Hopkinson impact tests conducted in this study and the bullet penetration test by Wang et al.Both results of the numerical simulations are in a good agreement with the tested results,which validates the suitability of the proposed method to acquire RHT model parameters for granite and the other rocks.

STRAIN-GRADIENT STRESS ANALYSIS IN SAINT-VENANT BENDING

Light beam deflections caused by stress or strain gradients are inves- tigated analytically and experimentally in homogeneous beam specimens which are subjected to a particular case of flexure with shear. This study is a generalization of the prior an alytical-experimental examination of strain-gradient light deflections produced in stressed plates, which had concentrated on the simplest case where in- formation of interest is collected along a line of symmetry of the stress field. Main purpose of the present investigation is to document the efficacy of the strain-gradient method in analysis of the general case of stress state. The most interesting stress state is that in a beam subjected to the Saint-Venant bending, where the transversal and the longitudinal axes of the beam are in pure shear. The obtained results are compared with the predictions of the developed analytical models and with the pre- dictions of Filon's stress function. The procedures of evaluating the photoelastic and material coefficients using strain-gradient techniques were tested positively.

Application of molybdenum target X-ray photography in imaging analysis of caudal intervertebral disc degeneration in rats

BACKGROUND Conventional plain X-ray images of rats,the most common animals used as degeneration models,exhibit unclear vertebral structure and blurry intervertebral disc spaces due to their small size,slender vertebral bodies.AIM To apply molybdenum target X-ray photography in the evaluation of caudal intervertebral disc(IVD)degeneration in rat models.METHODS Two types of rat caudal IVD degeneration models(needle-punctured model and endplate-destructed model)were established,and their effectiveness was verified using nuclear magnetic resonance imaging.Molybdenum target inspection and routine plain X-ray were then performed on these models.Additionally,four observers were assigned to measure the intervertebral height of degenerated segments on molybdenum target plain X-ray images and routine plain X-ray images,respectively.The degeneration was evaluated and statistical analysis was subsequently conducted.RESULTS Nine rats in the needle-punctured model and 10 rats in the endplate-destructed model were effective.Compared with routine plain X-ray images,molybdenum target plain X-ray images showed higher clarity,stronger contrast,as well as clearer and more accurate structural development.The McNemar test confirmed that the difference was statistically significant(P=0.031).In the two models,the reliability of the intervertebral height measured by the four observers on routine plain X-ray images was poor(ICC<0.4),while the data obtained from the molybdenum target plain X-ray images were more reliable.CONCLUSIONMolybdenum target inspection can obtain clearer images and display fine calcification in the imaging evaluation of caudal IVD degeneration in rats,thus ensuring a more accurate evaluation of degeneration.

基于DEMATEL-ISM的高校实验教师队伍发展影响因素关联测度

为识别高校实验教师队伍发展影响因素及其关联关系,从个人层面、组织层面以及社会层面3个维度建立了高校实验教师发展影响因素集,应用决策实验室分析法(DEMATEL)测算出实验教师发展影响因素的中心度、原因度、影响度以及被影响度,通过解释结构模型(ISM)方法构建了实验教师发展影响因素的4级层次递阶结构,进而揭示了实验教师发展影响因素之间的深层次逻辑关联及其作用机理。研究结果表明,人事政策与管理体制、行业与产业需求、教研资源投入、科技创新环境以及技术更新与迭代是影响实验教师队伍发展的原因类因素,而实践创新能力、实验室建设与管理水平、实验教学经验、学术水平以及职称等级是影响实验教师队伍发展的结果类因素。本研究可为高校实验教师队伍发展改革提供决策支持。

Modelling and Simulation of Hydro-gel Growth Mechanism by Analysis of Experimental Data

We have experimentally studied the growth process of a water-absorbing polymer commonly known as hydro-gel. We took a number of spherical beads, immersed them in pure water, measured their diameters at regular intervals of time and plotted graphs showing the change in volume with the time of immersion, to analyze their swelling properties. We have formulated a dynamical model on the basis of curve-fitting to our experimental data. Our mathematical modelling is devoted solely towards the explanation of the swelling of spherical hydro-gels and we have interpreted our observations on these basis. And finally evaluating the constants of the process, we have shown that the results obtained from our modelling and numerical simulation exactly match the experimental data. The justification of this new approach lies in its successful application for the complete explanation of our observations through numerical and analytical ways.

EMA与OMA模态参数辨识统一性方法

现代模态测试的对象正从系统部件转向整体结构,系统的动力学特征正变得越来越复杂,表现在结构组件众多导致系统模态密集化、局部化;在实际的工程结构中,甚至无法对大型结构施加有效的激励或激励的成本很高,使得EMA方法不能进行,只能使用OMA方法。在系统动力学特征越加复杂与参数辨识难度增加的同时,对参数辨识的要求越来越高;对算法的模态辨识能力要求越来越高;EMA与OMA都面临着整体频段的拟合困难、模型阶次与模态参数选择困难以及测点数的迅速增大带来的计算量剧增等困难;并且,EMA与OMA之间还存在着辨识方法不能统一的问题;简要回顾了VF算法原理,并进一步将VF算法拓展到OMA问题中,将频域内的EMA与OMA建立一个统一辨识流程,实现了整个频段上的整体拟合;简化了模态参数辨识流程,减少人工介入工以及由于频段划分不当造成的识别质量的下降。利用公开数据进一步验证了EMA问题中,VF算法在低信噪比和大规模曲线数目时的辨识效果,以及在OMA问题中的良好适用性。

飞机道面EMAS阻滞性能建模分析

结合实际情况,对机轮作用下EMAS的破坏作用做了静力学分析.在此基础上,对系统作了适当的假设和简化,建立了含有耗散函数的Lagrange动力学方程.此外,运用MATLAB软件对该动力学模型进行了仿真,得到了飞机在X、Y方向上位移和速度随时间变化的曲线,较好地描述了真机在EMAS阻滞状态下的实际情况,验证了该系统模型的有效性,为飞机道面EMAS的进一步研究提供了有效的理论支持.

Metal-soil interface adhesion in clay clogging during shield tunneling:Theoretical model and experimental validation

Clogging is a major geohazards risk in mechanized tunnelling through cohesive soils.Clay clogging results from the high adhesion between the clay and metal.Based on the water film theory and Reynolds fluid equation,the interfacial adhesion between metal and soil is simplified in this study as viscous hydrodynamic behavior between planes.Considering the influence of capillary force and the viscous force of water film at the interface between metal and soil,a theoretical calculation model of interfacial adhesion between metal and soil is established.The influence of water film thickness and separation rate on the interfacial adhesion between metal and soil is qualitatively analyzed.Then,the adhesion stress between the clay and the metal surface was tested with a pullout test and the influence of moisture content,pullout rates and types of clay minerals on the adhesion stress was analyzed.Finally,the calculation model of adhesion force was compared with the experimental results.The calculation model of soil adhesion stress established in this paper can quantitatively describe the relationship between soil adhesion force and moisture content and can also qualitatively reveal the influence mechanism of soil moisture content on adhesion stress.

DYNAMIC FINITE ELEMENT MODEL UPDATING BASED ON GLOBAL INFORMATION OF STRUCTURES

Finite element model updating method based on global information is proposed.Prior investigation upon design space of structural parameters is performed before updating usingstatistic analysis, including parameter screening using variance analysis and response surfacefitting using regression analysis. The parameter screening method selects the design parametersconsidering the result of hypothesis testing, which is a kind of global information. Meanwhile, thetraditional updating method considers local sensitivity which only gives the information at solepoint in the design space. Response surface fitting constructs a close-form multinomial whichdescribes the relationship between concerned structural feature and selected updating parameters. Itis an approximation to finite element models(FEM) and used as a substitution in the updatingiterations. The presented updating method can be applied without the restriction of linearassumption. In addition, there is no data exchange between the updating program and the finite-element analysis program in the updating iterations. This makes the method practical inengineering. An aircraft test structure, GARTEUR, is employed to verify the effectiveness of themethod. After updating, the error of modal frequencies is less than 3 percent.

Analysis with binaural auditory model and experiment on the timbre of Ambisonics recording and reproduction

A scheme for analyzing the timbre in spatial sound with binaural auditory model is proposed and the Ambisonics is taken as an example for analysis. Ambisonics is a spatial sound system based on physical sound field reconstruction. The errors and timbre colorations in the final reconstructed sound field depend on the spatial aliasing errors on both the recording and reproducing stages of Ambisonics. The binaural loudness level spectra in Ambisonics recon- struction is calculated by using Moore＇s revised loudness model and then compared with the result of real sound source, so as to evaluate the timbre coloration in Ambisonics quantitatively. The results indicate that, in the case of ideal ＇independent signals, the high-frequency limit and radius of region without perceived timbre coloration increase with the order of Ambisonics. On the other hand, in the case of recording by microphone array, once the high-frequency limit of microphone array exceeds that of sound field reconstruction, array recording influences little on the binaural loudness level spectra and thus timbre in final reconstruction up to the high- frequency limit of reproduction. Based on the binaural auditory model analysis, a scheme for optimizing design of Ambisonics recording and reproduction is also suggested. The subjective experiment yields consistent results with those of binaural model, thus verifies the effectiveness of the model analysis.