Non-dimensional analysis on blast wave propagation in foam concrete:Minimum thickness to avoid stress enhancement

Foam concrete is a prospective material in defense engineering to protect structures due to its high energy absorption capability resulted from the long plateau stage.However,stress enhancement rather than stress mitigation may happen when foam concrete is used as sacrificial claddings placed in the path of an incoming blast load.To investigate this interesting phenomenon,a one-dimensional difference model for blast wave propagation in foam concrete is firstly proposed and numerically solved by improving the second-order Godunov method.The difference model and numerical algorithm are validated against experimental results including both the stress mitigation and the stress enhancement.The difference model is then used to numerically analyze the blast wave propagation and deformation of material in which the effects of blast loads,stress-strain relation and length of foam concrete are considered.In particular,the concept of minimum thickness of foam concrete to avoid stress enhancement is proposed.Finally,non-dimensional analysis on the minimum thickness is conducted and an empirical formula is proposed by curve-fitting the numerical data,which can provide a reference for the application of foam concrete in defense engineering.

Acoustic propagation uncertainty in internal wave environments using an ocean-acoustic joint model

An ocean-acoustic joint model is developed for research of acoustic propagation uncertainty in internal wave environments.The internal waves are numerically produced by tidal forcing over a continental slope using an ocean model.Three parameters(i.e.,internal wave,source depth,and water depth)contribute to the dynamic waveguide environments,and result in stochastic sound fields.The sensitivity of the transmission loss(TL)to environment parameters,statistical characteristics of the TL variation,and the associated physical mechanisms are investigated by the Sobol sensitivity analysis method,the Monte Carlo sampling,and the coupled normal mode theory,respectively.The results show that the TL is most sensitive to the source depth in the near field,resulted from the initial amplitudes of higher-order modes;while in middle and far fields,the internal waves are responsible for more than 80%of the total acoustic propagation contribution.In addition,the standard deviation of the TL in the near field and the shallow layer is smaller than those in the middle and far fields and the deep layer.

EXACT ANALYSIS OF WAVE PROPAGATION IN AN INFINITE RECTANGULAR BEAM

The Fourier series method was extended for the exact analysis of wave propagation in an infinite rectangular beam.Initially,by solving the three-dimensional elastodynamic equations a general analytic solution was derived for wave motion within the beam.And then for the beam with stress-free boundaries,the propagation characteristics of elastic waves were presented.This accurate wave propagation model lays a solid foundation of simultaneous control of coupled waves in the beam.

Vibration and wave propagation analysis of twisted micro-beam using strain gradient theory

In this research, vibration and wave propagation analysis of a twisted micro- beam on Pasternak foundation is investigated. The strain-displacement relations （kine-matic equations） are calculated by the displacement fields of the twisted micro-beam. The strain gradient theory （SGT） is used to implement the size dependent effect at micro-scale. Finally, using an energy method and Hamilton＇s principle, the governing equations of motion for the twisted micro-beam are derived. Natural frequencies and the wave prop- agation speed of the twisted micro-beam are calculated with an analytical method. Also, the natural frequency, the phase speed, the cut-off frequency, and the wave number of the twisted micro-beam are obtained by considering three material length scale parameters, the rate of twist angle, the thickness, the length of twisted micro-beam, and the elastic medium. The results of this work indicate that the phase speed in a twisted micro-beam increases with an increase in the rate of twist angle. Moreover, the wave number is in- versely related with the thickness of micro-beam. Meanwhile, it is directly related to the wave propagation frequency. Increasing the rate of twist angle causes the increase in the natural frequency especially with higher thickness. The effect of the twist angle rate on the group velocity is observed at a lower wave propagation frequency.

High-strain dynamic model of large-diameter pipe piles with soil plug for vertical vibration analysis

A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the soil along pile shaft is divided into slip and nonslip zones and the base soil is modeled as a fictitious-soil pile(FSP)to account for the wave propagation in the soil.True soil properties are adopted and slippage at the pile-soil interface is considered,allowing realistic representation of largediameter OEPP mechanics.The developed model is validated by comparing with conventional models and finite element method(FEM).It is further used to successfully simulate and interpret the behaviors of a steel OEPP during the offshore field test.It is found that the variation in the vertical vibrations of shaft soil along radial direction is significant for large-diameter OEPPs,and the velocity amplitudes of the internal and external soil attenuate following different patterns.The shaft soil motion may not attenuate with depth due to the soil slippage,while the wave attenuation at base soil indicates an influence depth,with a faster attenuation rate than that in the pile.The findings from the current study should aid in simulating the vibration behaviors of large-diameter OEPP-soil system under high-strain dynamic loading.

Modelling Propagation of Stress Waves through Soil Medium for Ground Response Analysis

buildings located at rock sites. Modelling wave propagation through soil medium helps to derive the primary and secondary wave velocities. Most of the time soil mediums are heterogeneous, layered and undergoes nonlinear strains even under weak excitation. The equivalent linear approximation with one dimensional wave propagation is widely adopted for modeling earthquake excitation for layered soil. In this paper, importance of local soil effects, the process of wave propagation through three dimensional elastic medium, layered medium situated on rigid rock, attenuation of stress waves due to material damping, equivalent linear approximation, the concept of one dimensional wave propagation, and a case study of one dimensional wave propagation as a part of site-specific ground response analyses for Delhi region are included. The case study brings out the importance of carrying out site-specific ground response analyses of buildings considering the scenario earthquakes and actual soil conditions for Delhi region.

Characteristics of Seismic Wave Propagation in the Binchuan Region of Yunnan Using a Dense Seismic Array and Large Volume Airgun Shots

The Binchuan region of Yunnan is a structurally complex region with mountains,basins,and active faults.In this situation,seismic wave propagation exhibits complex characteristics due to strong heterogeneity of underground media instead of following the great-circle path.In order to obtain a high-resolution shallow crustal structure,a dense seismic array was deployed during March 21 to May 30,2017 in this area.To better understand the complexities of seismic wave propagation in this region,we perform array-based frequency-domain beamforming analysis and single-station based polarization analysis to investigate the characteristics of seismic wave propagation,using airgun-generated P-wave signals recorded by dense array stations in this experiment.The results from these two methods both reveal similar but complex characteristics of seismic wave propagation in the Binchuan basin.The azimuth anomalies off the great-circle path are quite large with values up to 30°,which is caused by strong structural heterogeneity in the very shallow crust.Our research provide a better understanding of the complex geologic structures in this area and provide guidance for detecting concealed faults and distribution of velocity anomalies.

Improved quadratic isogeometric element simulation of one-dimensional elastic wave propagation with central difference method

Two improved isogeometric quadratic elements and the central difference scheme are used to formulate the solution procedures of transient wave propagation prob- lems. In the proposed procedures, the lumped matrices corresponding to the isogeomet- ric elements are obtained. The stability conditions of the solution procedures are also acquired. The dispersion analysis is conducted to obtain the optimal Courant-Friedrichs- Lewy （CFL） number or time-step sizes corresponding to the spatial isogeometric elements. The dispersion analysis shows that the isogeometric quadratic element of the fourth-order dispersion error （called the isogeometric analysis （IGA）-f quadratic element） provides far more desirable numerical dissipation/dispersion than the element of the second-order dis- persion error （called the IGA-s quadratic element） when appropriate time-step sizes are selected. The numerical simulations of one-dimensional （1D） transient wave propagation problems demonstrate the effectiveness of the proposed solution procedures.

Influence of the Source Square Size on the Accuracy of Numerical Simulation of Wave Propagation in Half Space

It is well known that the dynamic response of the structure to an earthquake excitation is affected by the interaction with the foundation and the soil.The expansion of informatics and development of the computer capacities has helped the scientists to develop numerical models for approximate solutions of big variety of problems related to SSI(Soil Structure Interaction).Many of those problems involve domain-coupling.In this paper we built numerical model,based on finite differences and we investigate the accuracy of the numerical model depending upon the size of the square domain around the source.We tested eight different square sizes and we analyzed their accuracy regarding to five different wave periods.The results give recommendations for the implementation of the domain-coupling algorithm.

海拔高度对长直坑道内爆炸冲击波传播的影响

为有效表征不同海拔坑道内爆炸冲击波的传播特征,利用非线性显式动力学有限元软件AUTODYN,研究了海拔高度对长直坑道内爆炸冲击波传播的影响规律,探讨了高海拔环境对坑道内冲击波传播的影响,基于量纲分析,建立了适用于不同海拔高度典型坑道内冲击波峰值超压的计算模型,并通过数值计算进行了验证。结果表明:随着海拔高度升高,坑道内爆炸冲击波波阵面传播速度与径向的冲击波参数偏差增大,平面波形成距离增加,冲击波峰值超压降低;在0~4000 m范围内,海拔高度每升高1000 m,冲击波冲量降低约0.91%。结合Sachs无量纲修正方法和量纲分析,推导出不同海拔高度冲击波峰值超压的理论分析模型,模型计算结果与数值计算结果的相对偏差不大于10%,能够为高海拔环境下坑道内爆炸冲击波的传播提供理论依据。

海南省波浪能开发智能化适宜性分析模型研究

针对目前波浪能开发适宜性分析方法存在的问题及工作量大、成本高的特点,基于地理信息系统(Geographic information system, GIS)、改进的多准则决策方法(Multi-criteria decision making, MCDM)和人工神经网络(Artificial neural network, ANN)提出海南省波浪能开发智能化适宜性分析模型。对于该模型:首先,使用模糊层次分析(Fuzzy analytic hierarchy process, FAHP)法计算评价指标权重,降低专家主观偏差,更好地描述信息的不确定性;其次,提出灰色关联分析-折衷优化(Grey relation analysis-vlse kriterijumska optimizacijaⅠkompromisno resenje, GRA-VIKOR)法计算开发适宜性指数,解决评价过程中部分信息丢失、评价结果不准确的问题;最后依托反向传播(Back propagation, BP)神经网络进行模型训练并进行验证,实现海南省波浪能开发适宜性分析的智能化,不仅提高工作效率,而且降低计算成本。通过模型得到海南省波浪能可开发区域和开发适宜性等级,为海南省波浪能选址决策奠定基础,同时可填补海南省波浪能开发适宜性分析在智能化领域的空白。

隔振(震)沟减隔振(震)技术运用及研究进展

人工振动作为一种新形式的环境污染,被列为世界七大环境公害之一。各种形式的人工振动都涉及弹性波的产生和传播,在振源与保护区之间设立隔振(震)设施来切断弹性波的传播路径,衰减振动能量,降低振动幅度是目前在轨道交通、爆炸、打桩及撞击等常见的工程情况下普遍采用的隔振(震)措施。此外,地震动所产生的振动能量远远高于人工振动,传播的范围和距离更加深远,因此在地震动及人工振动作用下隔振(震)沟的减隔振(震)原理及效果的试验研究、理论研究及数值分析研究具有非常重要的意义。本文对近30年来国内外减隔振(震)技术进行了较为详细的整理,以期为实际工程提供理论支撑。

隧道表面爆破地震波的产生机制及传播特征

为了研究隧道表面爆破地震波的产生机制及传播规律,提出了隧道表面爆破振动平面应变理论模型,得到了隧道表面爆破振动场积分形式解;以龙南隧道爆破工程为背景,建立了有限元数值模型,通过现场测试验证了数值模拟与理论解答的准确性;提出了基于高分辨率Radon变换的隧道爆破地震波波场分离方法,结合理论解析与数值模拟得到了P波、S波、R波的传播特征,最后综合理论结果与波场分离结果提出了隧道爆破地震波作用分区。结果表明:隧道爆破产生P波、S波,R波在自由面迅速发育,3类波呈现指数衰减特征,S波衰减快于P波快于R波。随着爆心距的增大,垂直方向主要成分由S波转变为R波,水平方向主要成分由S波转变为P波,P波转变为R波。Ⅳ级围岩工况下,隧道爆破地震波作用分区为:隧道轴向距掌子面0~6.44 m为爆破近区,主导波型为水平S波;6.44~21.23 m为爆破中区,主导波型为水平P波;21.23 m外为爆破远区,主导波型为垂直R波。爆破分区分界点与单段最大药量呈线性关系,可通过爆破药量得到隧道爆破分区位置,用于隧道安全稳定性分析。

课程-迁移学习物理信息神经网络用于长时间非线性波传播模拟

由于传统物理信息神经网络(PINN)在长时间模拟时存在计算稳定性差甚至无法获得有效解的难题,文章提出了一种基于课程学习和迁移学习的物理信息神经网络(CTL-PINN),用于长时间非线性波传播模拟.该改进的PINN的主要思想是将原长时间历程问题转化成若干个短时间子问题,其求解过程分为3个阶段;在初始阶段,使用传统PINN来获得初始短期子问题的解;在课程学习阶段,使用包含前一步训练信息的传统PINN以时域扩大的方式逐次求解,在迁移学习阶段,使用包含前一步训练信息的传统PINN以时域迁移的方式逐次求解.这种改进的PINN可以避免传统PINN陷入局部最优解的问题.最后通过几个基准算例验证了本文所提出的CTL-PINN方法在模拟长时间非线性波传播过程的有效性和鲁棒性.

南海夏季沿岸内波与定点声起伏特征分析

利用2020年6月海南岛沿岸试验数据,分析内波及声能量起伏特征。试验海域以全日潮内波为主,并伴随有高频内波活动。内波活动引起360 Hz单频信号20 km定点声起伏峰峰值超过30 dB,320~400 Hz线性调频信号起伏峰峰值超过15 dB。利用测量数据结合数值仿真,讨论了内波引起单频信号和线性调频信号呈现不同起伏特征的原因。结果表明:试验海域内波活动导致单频声场模态间干涉条纹出现移动,进而导致接收位置处特定频率的声能量出现大幅度的快速起伏;由于带宽内的平均作用,宽带信号的能量起伏远小于单频信号的能量起伏。当内波传播速度变化时,各内波成分在声传播路径上出现的时间和位置发生了变化,使得声场出现剧烈起伏的时间也随之变化。

Ti-Pt周期调制梯度材料的制备及准等熵加载特性

基于波阻抗梯度材料的准等熵加载技术是掌握材料动态响应特性的重要技术手段,对于提升材料服役性能至关重要。采用电子束蒸发镀膜技术成功制备出Ti-Pt周期调制梯度材料,通过对周期层内双组分(Ti和Pt单层)厚度的调控,实现了波阻抗的宏观梯度变化。梯度材料实测总厚度与理论设计总厚度的误差仅为1.67%,并且实测平均硬度及弹性模量分别为2.8和99.8 GPa。材料内部层界面清晰,物相分析未发现金属合金相。利用一级轻气炮驱动TiPt周期调制梯度材料加载5μm厚Al靶,在Al靶内产生冲击-准等熵加载波形。数值模拟结果与实验曲线在上升趋势上吻合良好,5μm厚Al靶处的粒子速度、应力和应变率曲线的准等熵段存在较大起伏,应变率曲线在正负值间持续振荡,并且振幅较大。应力云图显示周期调制梯度材料在加载过程中会形成多个波系的追赶、叠加、整合。数值模拟结果显示,当靶材厚度为60μm时,波系完成整合,转变为连续的压缩波。结合数值模拟结果开展了60μm厚Al靶的轻气炮加载实验,粒子速度曲线和应力曲线的准等熵段转变为平滑的加载波形,应变率曲线准等熵段振幅显著减小,实现了良好的准等熵加载效果。研究结果表明,周期调制梯度材料与靶材厚度需进行匹配设计,研究结果可为新型周期调制梯度结构的应用提供指导。

结构噪声核心价值与理论逻辑解读 第三部分:WPA法与机理分析

[目的]波传播分析法也称WPA法,在分析混合动力系统(如浮筏)中弹性波的抵消机制方面具有独特的优点。[方法]基于WPA法,从振动微分方程和弹性波的传播、反射视角解析结构噪声。[结果]分析表明:WPA法使研究者能够从表观参数(如振动加速度)进入内核参数(弹性波),深层剖析振动能量的注入、传导以及波与声辐射之间的因果关系。WPA法可嵌入谐力相位表达,能够研究多源抵消机制;由于采用指数型函数,方程的推导具有规律性和规整性,适合工程技术人员开展深入的机理分析。[结论]从"复杂系统"到"简单系统"抽象,WPA法更容易发现共同性和关键性的一般科学规律,从而实现系统动力学性能的极致设计。

用WPA法解算分布力激励下梁结构的响应特性

利用WPA法 ,亦称波传递法 ,对任意支承形式的梁在分布力激励下的动响应和动特性进行分析 ,并对均布力作用下的悬臂梁进行了理论推导 ,证实这种计算方式是正确的。

Disturbances Propagation in Supersonic Boundary Layers

Disturbances propagation processes are investigated in two-dimensional boundary layers for the case of strong viscous-inviscid interaction. The speed of upstream disturbances propagation as a function of specific heat ratio and Prandtl number is determined. Formula for speed propagation is developed on the basis of characteristics and subcharacteristics analysis corresponding to the gasdynamic wave processes and processes of convection and diffusion.

Universality Class of the Nonequilibrium Phase Transition in Two-Dimensional Ising Ferromagnet Driven by Propagating Magnetic Field Wave

The purpose of this work is to identify the universality class of the nonequilibrium phase transition in the two-dimensional kinetic Ising ferromagnet driven by propagating magnetic field wave. To address this issue, the finite size analysis of the nonequilibrium phase transition, in two-dimensional Ising ferromagnet driven by plane propagating magnetic wave, is studied by Monte Carlo simulation. It is observed that the system undergoes a nonequilibrium dynamic phase transition from a high temperature dynamically symmetric (propagating) phase to a low temperature dynamically symmetry-broken (pinned) phase as the system is cooled below the transition temperature. This transition temperature is determined precisely by studying the fourth-order Binder Cumulant of the dynamic order parameter as a function of temperature for different system sizes (L). From the finite size analysis of dynamic order parameter ?and the dynamic susceptibility , we have estimated the critical exponents and ?(measured from the data read at the critical temperature obtained from Binder cumulant), and (measured from the peak positions of dynamic susceptibility). Our results indicate that such driven Ising ferromagnet belongs to the same universality class of the two-dimensional equilibrium Ising ferromagnet (where and ), within the limits of statistical errors.