On dissipation coefficients in a rectangular wave tank

Summary An alternative approach to determination of the complex dissipation coefficients at the solid boundaries of a wave tank is suggested. The proposed method is based on the balance between the apparent energy consumption in the wall boundary layer and the full complex energy flux to this layer from the potential core. The present technique allows one to incorporate easily the dissipation in the nonlinear model describing the evolution of standing waves of finite amplitude in a rectangular tank. The relative importance of wavemaker dissipation in this case is discussed.     

Experimental study on the convective heat transfer coefficient of early-age concrete

During the process of setting and hardening in concrete, the temperature profile shows a gradual nonlinear distribution due to the development of heat of hydration in cement. At early ages of concrete structures, this nonlinear distribution can have a large influence on crack evolution. It is thus important to obtain an accurate temperature history, and to do this, it is necessary to examine the thermal properties of the concrete. In this study, the convective heat transfer coefficient, which represents the heat transfer between a concrete surface and ambient air, was experimentally investigated with test variables such as the velocity of wind, the curing conditions, and the ambient temperature.For analyses using the thermal equilibrium boundary condition, it is generally noted that most of the heat release by the evaporation of moisture occurs at an early stage. To consider this phenomenon, the existing thermal equilibrium boundary condition has been modified so as to consider the evaporation quantity due to the evaporation effect. Convective heat transfer coefficients for a specific case were then calculated from the modified thermal equilibrium boundary condition using experimental results.     

Progressive Cross Waves due to the Horizontal Oscillations of a Vertical Cylinder in Water. Evolution Equations

The paper deals with the theoretical analysis of progressive cross waves excited due to the horizontal oscillations of a vertical, surface-piercing circular cylinder in water of constant depth. Although cross waves are a phenomenon well known in laboratory wave tanks, it seems that they have not been observed around horizontally oscillating structures in fluid up to now. Such observations have recently been carried out by the authors on various models of offshore gravity platforms subjected to earthquake-like horizontal excitation in a water tank. The theoretical analysis of the problem is based on a method developed by Becker and Miles (1992) for the radial cross waves due to the motion of an axisymmetric cylindrical wavemaker. Whitham's average-Lagrangian approach is applied. It is shown that the energy transfer to the cross wave is described by the functional which is quadratic, both in the forced basic wave and in the cross wave. Therefore, the solution to second-order problems is necessary for the derivation of the evolution equations. The evolution of the cross wave is found to be described by two complex nonlinear partial differential equations with coefficients depending on a slow radial variable both in linear and nonlinear terms. The evolution equations are coupled through the nonlinear terms and through the boundary conditions as well.     

SMA滑动摩擦阻尼器的数值模拟及参数分析

该文将超弹性形状记忆合金(shape memory alloy,SMA)螺栓和摩擦斜面结合,提出一种SMA滑动摩擦阻尼器(SMA slip friction damper,SMASFD)。介绍了SMASFD的基本构造和工作原理,给出描述滞回行为的理论公式,开展了概念验证试验,建立了三维实体单元有限元模型。试验数据和分析结果均表明,采用合理设计的斜面倾角和摩擦系数,阻尼器可展示出“旗帜形”滞回曲线,拥有良好的耗能能力和优越的自复位能力,并且理论公式和模拟结果均与试验数据吻合良好。基于已经验证的有限元模型,建立了6个额外的有限元模型进行参数分析,关键参数包括斜面倾角、摩擦系数和SMA螺栓的预紧力。参数分析结果表明:阻尼器的非线性变形集中于SMA螺栓内,其他部件保持弹性;增大斜面倾角可提高阻尼器的强度、割线刚度和耗能能力;当接触面间的摩擦系数较大时,阻尼器的耗能能力得到提高,但是超过上限值会导致阻尼器无法自复位;对SMA螺栓施加预紧力可提高阻尼器的初始刚度和割线刚度,但是会降低阻尼器的最大变形能力。     

Radiant Power Exchange in Thermal Radiation Calorimetry

Radiant power exchange for thermal radiation calorimetry was investigated both theoretically and experimentally. The geometrical relation in which a disk-shaped copper specimen and a graphite plate are facing each other was used as the model configuration. Surfaces of the specimen and the plate were blackened with colloidal graphite to achieve a high surface emissivity. The radiant power density absorbed by the specimen was calculated by taking into account the geometrical configuration factors and the total emissivity of the blackened surfaces obtained form spectral reflectivity. A value of 0.56±0.01 was obtained for the radiant power exchange coefficient from the theoretical results in the temperature range from 220 to 430°C. The coefficient obtained experimentally by use of a heat capacity measurement was constant with temperature, with a value of 0.54±0.01 within experimental error. No hysteresis in the coefficient was observed for either heating or cooling processes.     

Temperature dependence of the energy dissipation in dynamic force microscopy

The dissipation of energy in dynamic force microscopy is usually described in terms of an adhesion hysteresis mechanism. This mechanism should become less efficient with increasing temperature. To verify this prediction we have measured topography and dissipation data with dynamic force microscopy in the temperature range from 100?K up to 300?K. We used 3,4,9,10-perylenetetracarboxylic-dianhydride (PTCDA) grown on KBr(001), both materials exhibiting a strong dissipation signal at large frequency shifts. At room temperature, the energy dissipated into the sample (or tip) is 1.9?eV/cycle for PTCDA and 2.7?eV/cycle for KBr, respectively, and is in good agreement with an adhesion hysteresis mechanism. The energy dissipation over the PTCDA surface decreases with increasing temperature, yielding a negative temperature coefficient. For the KBr substrate, we find the opposite behaviour: an increase of dissipated energy with increasing temperature. While the negative temperature coefficient in the case of PTCDA agrees rather well with the adhesion hysteresis model, the positive slope found for KBr points to a hitherto unknown dissipation mechanism.     

Orientational Dynamics and Energy Dissipation in a Liquid Dispersion of Single-Domain Ferroparticles on Exposure to a Linearly Polarized Field

A theoretical investigation of the nonlinear orientational dynamics and energy dissipation in a suspension of noninteracting single-domain ferroparticles with a magnetic hysteresis on exposure to a linearly polarized magnetic field has been performed. The bifurcation properties of the system have been studied; the amplitude and frequency dependences of the powers of total and viscous dissipation have been obtained.__________Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 2, pp. 83–92, March–April, 2005.     

复合材料层板疲劳损伤的有效能耗分析法

通过对纤维增强复合材料层板疲劳过程中能量耗散的不可逆过程的分析,并考虑不同加载次序,建立了一种以有效能耗为基础的非线性疲劳损伤累积法则.并从理论和实验证明了该法则能正确的反映载荷次序效应等疲劳累积损伤规律.     

Boundary conditions for second sound in superfluid 4He

Standing surface waves produced by second sound in superfluid ⁴He have been observed optically. A spectrum of 84 frequencies was obtained. The theoretical spectrum calculated by using the conventional boundary condition of zero heat transfer does not agree with the experimental spectrum. Good agreement is obtained by assuming nonzero heat transfer at the boundary. An empirical heat transfer coefficient is defined and calculated. The amplitudes of the surface waves are discussed and related to the heat transfer.Supported by the Schweizerischer Nationalfonds zur Förderung der Wissenschaftlischen Forschung.     

Effect of Hyperbolic Band Structure on the Energy Loss Rate of Hot Electrons with Non-equilibrium Phonon Distribution in the Extreme Quantum Limit at Low Temperatures in n-Hg0.8Cd0.2Te

The energy loss rate of hot electrons with the non-equilibrium phonons in narrowgap semiconductors with hyperbolic band structures has been investigated in the extreme quantum limit condition in the low temperature region. The calculation is done for n-Hg_0.8Cd_0.2Te sample considering electron scattering by acoustic phonons via piezoelectric coupling to be the dominant loss mechanism. The value of the energy loss rate with hyperbolic band is compared with the results of parabolic and non-parabolic band structures and at the same time all the results are also compared with the experimentally observed data. It is found that with the inclusion of hyperbolic band structure, the value of energy loss rate is found to be close to the experimental values. The dependence of energy loss rate on magnetic field and lattice temperature has been studied. Using the experimental value of the energy loss rate, the phonon life time is evaluated. The value of the phonon life time is found to be of the order of the phonon boundary relaxation time indicating that phonon boundary scattering is the dominant phonon dissipation mechanism. The dependence of the phonon life time on magnetic field, and lattice temperature has also been studied. The phonon life time is also found to decrease with increase in electron temperature.     

Measurement of the fracture energy using three-point bend tests: Part 1—Influence of experimental procedures

Available measures of the fracture energy G_F obtained with the procedure proposed by RILEM TC-50 provide values that appear to change with sample size, calling into question the possibility of considering G_F as a material parameter. In this paper some possible sources of experimental errors, when the RILEM proposal is applied, are ascertained, namely the apparent energy dissipation from hysteresis in the testing equipment and energy dissipation in the lateral supports. It is concluded that either some other sources of energy dissipation are operative or that G_F cannot be considered a material property.     

Solution of an Inverse Problem of Heat Conduction of 45 Steel with Martensite Phase Transformation in High Pressure during Gas Quenching

In order to simulate thermal strains,thermal stresses,residual stresses and microstructure of the steel during gas quenching by means of the numerical method,it is necessary to obtain an accurate boundary condition of temperature field.The surface heat transfer coefficient is a key parameter.The explicit finite difference method,nonlinear estimation method and the experimental relation between temperature and time during gas quenching have been used to solve the inverse problem of heat conduction.The relationship between surface temperature and surface heat transfer coefficient of a cylinder has been given.The nonlinear surface heat transfer coefficients include the coupled effects between martensitic phase transformation and temperature.     

Modeling of uncertainty for flood wave propagation induced by variations in initial and boundary conditions using expectation operator on explicit numerical solutions

This study proposes a framework for uncertainty analysis by incorporating explicit numerical solutions of governing equations for flood wave propagation with the expectation operator. It aims at effectively evaluating the effect of variations in initial and boundary conditions on the estimation of flood waves. Spatiotemporal semivariogram models are employed to quantify the correlation of the variables in time and space. The 1D nonlinear kinematic wave equation for the overland flow (named EVO_NS_KWE) is applied in the model development. Model validation is made by comparison with the Monte Carlo simulation model in the calculation of statistical properties of model outputs (ie, flow depths), that is, the mean, standard deviation, and coefficient of variation. The results from the model validation show that the EVO_NS_KWE model can produce excellent approximations of the mean and less satisfactory approximations of the standard deviation and coefficient of variation compared with those obtained by using the Monte Carlo simulation model. It concludes that the uncertainties of flow depths in the domain are significantly affected by variations in the boundary condition. Future application of the EVO_NS_KWE model enables the evaluation of uncertainty in model outputs induced by the initial and boundary condition subject to uncertainty and will also provide corresponding probabilistic information for risk quantification method.     

组合式双圆锥耗能器的设计与性能模拟分析

设计了组合式双圆锥耗能器,阐述了其构造和耗能原理,采用有限元软件对18个不同尺寸的双圆锥耗能元件和3个不同组装方式的双圆锥耗能器进行了数值仿真分析,研究了不同设计参数对双圆锥耗能器的滞回性能和应力分布的影响。研究结果表明：对于双圆锥耗能元件,当其总高H一定时,其初始刚度和屈服位移取决于两个锥体中较大锥体的高度大小;屈服位移可设置在1mm以内,耗能系数值可达2.5。双圆锥耗能元件通过不同的方式组合成双圆锥耗能器时,双圆锥耗能器的滞回性能取决于所选用的双圆锥耗能元件和其上、下连接板的刚度,当连接板刚度较大时,双圆锥耗能元件的滞回性能与其组装后的双圆锥耗能器的相关滞回性能满足叠加关系,双圆锥耗能器的相关滞回性能可由所选用的双圆锥耗能元件的相关参数(初始刚度、屈服位移和耗能系数等)来确定。     

Fatigue Hysteresis Behavior of Unidirectional SiC/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> Composite at Elevated Temperature under Tension-Tension Loading

In this paper, the fatigue hysteresis behavior of unidirectional SiC/Si₃N₄ ceramic-matrix composite at elevated temperature has been investigated. The hysteresis loops models considering interface friction between fibers and the matrix have been developed to establish the relationships between the fatigue hysteresis loops, fatigue hysteresis dissipated energy and the interface frictional coefficient. Using the experimental fatigue hysteresis dissipated energy, the interface frictional coefficient of SiC/Si₃N₄ composite at 1000 °C were obtained for different cycle numbers and fatigue peak stresses. The effects of fatigue peak stress, test temperature and cycle number on the evolution of fatigue hysteresis dissipated energy and interface frictional coefficient have been analyzed. It was found that the fatigue hysteresis dissipated energy can be used to monitor the interface debonding and damage evolution inside of the composite.     

A thermodynamic theory of localized deformation based on the operator principle

The dissipation field of a continuum is studied here by a new operator theory of irreversible thermodynamics; the evolution equations of the dissipation field can be obtained in the condition of knowing the phenomenological nonlinear constitutive relation of materials. In this theory, the basic state equation, which is the state of minimum dissipation, is utilized for solving the distribution of the dissipation field of quasi-statics, and the higher order state equations are corresponding to the dissipation fields of dynamics. The paper also gives a method to get the dissipation force operator by using Helmholtz’s free energy function. In the final part of this paper, several important phenomena of the localized deformation, such as the plastic instability of necking and shear band, are predicted in the form of an analytical formula.     

Estimation of magnetohydrodynamic radiative nanofluid flow over a porous non‐linear stretching surface: application in biomedical research

The present study investigates the effects of thermal radiation and chemical reaction on magnetohydrodynamic flow, heat, and mass transfer characteristics of nanofluids such as Cu–water and Ag–water over a non‐linear porous stretching surface in the presence of viscous dissipation and heat generation. Using similarity transformation, the governing boundary layer equations of the problem are transformed into non‐linear ordinary differential equations and solved numerically by the shooting method along with the Runge–Kutta–Fehlberg fourth–fifth‐order integration scheme. The influences of various parameters on velocity, temperature, and concentration profiles of the flow field are analysed and the results are plotted graphically. A backpropagation neural network is applied to predict the skin friction coefficient, Nusselt number, and Sherwood number and these results are presented through graphs. The present numerical results are compared with the existing results and are found to be in good agreement. The results of artificial neural network and the obtained numerical values agree well with an error <5%.Inspec keywords: silver, copper, transforms, nanofluidics, friction, backpropagation, heat radiation, water, external flows, partial differential equations, nonlinear differential equations, boundary layers, Runge‐Kutta methods, mass transfer, flow through porous media, magnetohydrodynamicsOther keywords: magnetohydrodynamic radiative nanofluid flow, nonlinear stretching surface, biomedical research, thermal radiation, chemical reaction, magnetohydrodynamic flow, nonlinear porous stretching surface, viscous dissipation, similarity transformation, governing boundary layer equations, nonlinear ordinary differential equations, shooting method, Runge–Kutta–Fehlberg fourth–fifth‐order integration scheme, flow field, backpropagation neural network, Cu–water nanofluid, Ag–water nanofluid, skin friction coefficient, Nusselt number, Sherwood number, artificial neural network, Ag‐H₂ O, Cu‐H₂ O     

Hysteresis of the current-voltage characteristic of a continuous electron-beam-controlled discharge in a nitrogen flow

A hysteresis in the current-voltage characteristic of continuous electric discharge controlled by an electron beam in a nitrogen flow has been experimentally observed. It is suggested that the transition from a self-sustained glow discharge regime (typical of ionization chamber) to the electron-beam-controlled discharge is accompanied by the transition from the laminar to turbulent boundary layer at the cathode surface.     

Nonlinear resonant characteristics of shallow fluid layers

Results are presented from an experimental investigation of the motion of a shallow layer of water in a square tank that was oscillated horizontally with small amplitude at frequencies close to the natural frequency of the layer. The aim was to assess the validity of certain theoretical predictions relating to nonlinear resonance in shallow layers based on asymptotic analysis. These concern the hysteretic nature of the resonance profile and the existence of non-trivial oscillatory components associated with shock-like discontinuities in the derived solution for the free surface configuration. The experimental results support the theoretical predictions and show a coincidence in parameter space between the regions of hysteresis and oscillatory transition.     

电流变阻尼器的设计及模型参数识别

因为电/磁流变阻尼器能够将主动控制和被动设备的优点有效结合起来,所以使用这种阻尼器的结构振动半主动控制方法在近年来吸引了更多人的目光.本文描述了关于电流变阻尼器的设计和动态特性试验.已建立的电流变阻尼器的动力特性将在不同的电场强度和变化的位移幅度下进行测试.通过一系列激振频率下的周期振动测试,我们可以得到在不同位移和速度下恢复力的滞回曲线,建立hysteretic biviscous模型.通过把根据试验得到的滞回曲线和使用hysteretic biviscous模型预测得到的滞回曲线进行比较可知,这种模型可以十分准确地获得阻尼器的非线性的阻尼特性.