纤维织物超高速碰撞热-力学特性数值模拟

针对纤维织物防护结构在空间碎片超高速碰撞下发生的变形、破碎及温升、相变等热-力学问题,引入Johnson-Cook模型及Gruneisen状态方程,结合纤维织物纱线编织几何模型及FEM-SPH耦合算法,建立了纤维织物超高碰撞数值模型,并研究了纤维织物强度对超高速碰撞热-力学特性的影响规律。结果表明:随着纤维织物强度的增加,纤维织物防护结构对弹丸的动能吸收能力增强;纤维织物碰撞区域热效应显著,随着纤维织物强度的增加,碰撞区域中心的热效应先增强后减弱;当纤维织物强度在2000 MPa附近时,碰撞区域中心的热效应较为显著。

能源桩热-力学特性模型试验与数值模拟

能源桩是集地源热泵与建筑桩基于一体的建筑节能技术,具有经济、环保和节省地下空间资源等优点,因热-力耦合作用导致其承载性状不同于普通工程桩。基于室内模型试验和数值模拟研究,针对多次温度循环下饱和黏土地基中能源桩热-力响应展开研究,分析了桩周温度场、桩土沉降、桩侧摩阻力的变化,结果表明:升温时桩身温度沿深度逐渐减小,土体温度沿径向逐渐降低;降温所引起的桩顶沉降量大于升温的膨胀量,多次温度循环导致桩顶产生不可逆的累积沉降,其累积变形可能会对上部结构的安全造成影响。桩周土由于土体的热固结也发生不同程度的沉降,距离桩身越近沉降越大,且土体沉降速率随循环次数的增加呈逐渐减小趋势,三次循环后B_(4)点沉降达到1.42%D(D为桩直径);温度荷载所引起的侧摩阻力随温度的升高和循环次数的增加而逐渐增大;升温时桩体上部产生负的侧摩阻力,下部产生正的侧摩阻力,降温时恰好相反,工作荷载的作用导致桩身产生负摩阻力的区域逐渐变小,位移零点也逐渐上移。运用COMSOL Multiphysics软件建立三维数值模型可较好地模拟热-力耦合作用下能源桩的承载力特性,数值模拟结果与模型试验结果吻合度较高,为试验设计及工程应用给出建议。

冷-热循环下能量桩热-力学特性的数值模拟

能量桩与地基土的热交换取决于建筑物的年能源需求,故能量桩每年受到冷-热循环作用。采用多场耦合有限元数值模拟方法,研究在力学荷载和随时间按正弦函数变化的温度荷载共同作用下悬浮能量桩的热-力学特性。结果表明,随着能量桩冷-热周期性的循环,温度荷载引起的桩身附加轴向应力、桩头附加竖向位移和桩侧附加剪应力也随时间周期性变化,且相位与温度荷载曲线的相位相同。桩升温最大时桩身轴向压应力达到最大值,桩降温最大时桩头沉降达到最大值。地基土的温度改变量随时间周期性地变化,其幅值在桩的中部深度附近最大,在桩二端深度附近较小。地基土温度的变化滞后于温度荷载。离桩越远,地基土的温度达到其最大值的时间越滞后。

冷-热不平衡热荷载下黏土地基中能量桩长期热-力学特性

建立了热-渗流-力(T-H-M)三场耦合能量桩有限元数值分析模型,研究了力学荷载组合不同热聚集度(桩的放热量与吸热量之比)温度荷载下黏土地基中能量桩的长期热-力学特性,包括桩身温度、桩头沉降、桩身轴向应力、地基土温度和超孔隙水压力特性等。计算结果表明:冷-热平衡时桩头沉降随温度荷载循环的增加逐渐增大,桩头发生沉降累积,桩身轴向应力和地基土温度变化的幅值不随温度荷载循环而变化。当桩的放热量大于吸热量时,桩身温度随温度荷载循环的增加而升高,桩头沉降随之减小,但热荷载循环对桩身轴向应力没有影响。桩周土温度随热循环的增加而逐渐增大,产生热聚集现象。温度荷载的热聚集度数值越大,桩身和桩周土的温度越高,桩身最小压应力越大,桩头沉降越小。温度荷载引起的超静孔隙水压力数值很小。

悬浮能量桩-筏基础的热-力学特性数值模拟

针对温度荷载与力学荷载共同作用下砂土地基中的悬浮能量桩-筏基础,建立热-力学响应分析的三维非线性有限元数值模型,研究能量群桩效应、桩间土的温度变化以及能量桩数量和布设方式对桩身附加轴向应力和桩头差异沉降的影响.结果表明,升温荷载作用下,能量群桩内部任意一个桩的桩身附加轴向压应力比单桩作为能量桩时要小得多;在部分能量桩-筏基础中,能量桩的附加压应力沿桩长呈抛物线分布,数值随能量桩数量的增加而减小;非能量桩的附加轴向应力沿桩长呈S形分布,非能量角桩和边桩的上部出现附加拉应力,数值随能量桩数量的增加而增大;能量桩的布设方式对能量桩附加轴向应力有较大影响,但对非能量桩附加轴向应力的影响较小;能量桩非对称布设时桩头间的差异沉降较大,桩周围土的温度取决于其周围能量桩的数量.

预张力纤维织物超高速碰撞热-力学特性分析

高性能纤维织物承力层承担充气舱的内压载荷,并为充气舱提供空间碎片防护。充气舱内压载荷将导致纤维织物承力层产生预张力,并对纤维织物的空间碎片超高速碰撞特性产生显著影响,从而影响其空间碎片防护性能。为分析预张力对纤维织物超高速碰撞过程中热-力学特性的影响,采用Johnson-Cook强度模型和Mie-Grüneisen状态方程建立了纤维材料热-力耦合材料模型,利用有限元法-光滑粒子流体动力学耦合算法对纤维织物的纱线编织结构进行离散建模,并通过施加张力载荷实现纤维织物靶板的预拉伸,进而建立了预张力纤维织物超高速碰撞数值模型,分析并得到了预张力作用下纤维织物超高速碰撞热-力学特性及空间碎片防护性能。结果表明:在弹丸超高速碰撞下,随着预张力的提高,纤维织物穿孔面积增大,碎片云扩散角减小,弹丸动能吸收率降低,碰撞区域温度降低。预张力的存在显著降低了纤维织物的空间碎片防护性能。

温度循环下能量群桩的热-力学特性数值分析

以黏土地基中能量群桩作为研究对象,针对能量桩-筏基础建立了简化的二维热-渗流-力(THM)耦合有限元模型,模拟分析了力学荷载与长期冷-热循环共同作用下能量群桩的热-力学特性。研究结果表明:桩头沉降、桩身轴向应力、地基土的温度和超静孔压均随温度循环呈周期性变化。桩头的沉降累积主要发生在第1个温度循环中,边桩桩头累计沉降最大,内部桩头的累积沉降较小。边桩轴向压应力的幅值远大于中心桩。在温度循环中各相邻桩间土的温度相同,筏板外地基土的温度较之桩间土要小得多。温度循环下地基土产生超静孔隙水压力。桩升温时桩间土中的超静孔压沿深度逐渐减小,而筏板外地基土的超静孔压小于桩间土。能量群桩的群桩效应减小了温度循环引起的桩身轴向应力和筏板的差异沉降。

悬浮能量桩热-力学基本特性的数值模拟

采用多场耦合有限元数值分析方法,研究砂土地基中悬浮能量桩的热-力学特性。结果表明,桩的升温引起附加轴向压应力、上部桩身负摩阻力和桩头隆起。桩的降温引起附加轴向拉应力、上部桩身正摩阻力和桩头沉降。对于给定的温度荷载,能量桩的热-力学响应主要取决于桩头力学荷载的数值,温度荷载引起的桩身附加轴向应力随力学荷载数值的增加而增大,力学荷载超过某一临界值之后保持不变。地基土的温度变化在径向很快衰减,影响范围约为20倍的桩径。能量桩的热-力学特性受桩头约束条件的影响很大。桩头约束越强,温度荷载引起桩身轴向应力数值越大。

Aging Characteristics of Lithium-Ion Battery Under Fast Charging Based on Electrochemical-thermalmechanical Coupling Model

The aging characteristics of lithium-ion battery(LIB)under fast charging is investigated based on an electrochemical-thermal-mechanical(ETM)coupling model.Firstly,the ETM coupling model is established by COMSOL Multiphysics.Subsequently,a long cycle test was conducted to explore the aging characteristics of LIB.Specifically,the effects of charging(C)rate and cycle number on battery aging are analyzed in terms of nonuniform distribution of solid electrolyte interface(SEI),SEI formation,thermal stability and stress characteristics.The results indicate that the increases in C rate and cycling led to an increase in the degree of nonuniform distribution of SEI,and thus a consequent increase in the capacity loss due to the SEI formation.Meanwhile,the increases in C rate and cycle number also led to an increase in the heat generation and a decrease in the heat dissipation rate of the battery,respectively,which result in a decrease in the thermal stability of the electrode materials.In addition,the von Mises stress of the positive electrode material is higher than that of the negative electrode material as the cycling proceeds,with the positive electrode material exhibiting tensile deformation and the negative electrode material exhibiting compressive deformation.The available lithium ion concentration of the positive electrode is lower than that of the negative electrode,proving that the tensile-type fracture occurring in the positive material under long cycling dominated the capacity loss process.The aforementioned studies are helpful for researchers to further explore the aging behavior of LIB under fast charging and take corresponding preventive measures.

Elastic Tensor and Thermodynamic Property of Magnesium Silicate Perovskite from First-principles Calculations

The thermodynamic and elastic properties of magnesium silicate （MgSiO3） perovskite at high pressure are investigated with the quasi-harmonic Debye model and the first-principles method based on the density functional theory. The obtained equation of state is consistent with the available experimental data. The heat capacity and the thermal expansion coefficient agree with the observed values and other calculations at high pressures and temperatures. The elastic constants are calculated using the finite strain method. A complete elastic tensor of MgSiO3 perovskite is determined in the wide pressure range. The geologically important quantities： Young＇s modulus, Poisson＇s ratio, Debye temperature, and crystal anisotropy, are derived from the calculated data.

Kinetic and Thermodynamic Studies of Acid Scarlet 3R Adsorption onto Low-cost Adsorbent Developed from Sludge and Straw

A low-cost adsorbent was prepared from sludge and straw by pyrolysis in a dried state with the surface area of the adsorbent of 829.49 ma. g-l, micropore volume of 0.176 cm2·g-1 and average pore radius of 5.0 nm. The kinetic, equilibrium isotherm and thermodynamic characteristics of trisodium 1-（1-naphthylazo）-2-hydroxynaphthalene- 4＇,6,8-trisulphonate （acid scarlet 3R） onto the adsorbent from sludge and straw were investigated. The results indicated that the pseudo second order adsorption was the predominant adsorption mechanism of acid scarlet 3R. Thus, the adsorption phenomenon was suggested as a chemical process. The adsorption data were fitted better with Langmuir model than Freundlich model, indicating that the adsorption of acid scarlet 3R belonged to the monolayer adsorption and mainly occurred in micropores.

Pyrolysis Characteristics and Kinetics of Methyl Oleate Based on TG-FTIR Method

The thermal decomposition characteristics of methyl oleate were preliminarily investigated under nitrogen atmo-sphere by a thermogravimetric analyzer when the ester was heated at a heating rate of 10℃/min from room temperature to 600℃. Furthermore, the pyrolytic and kinetic characteristics of methyl oleate were intensively studied at different heating rates. The gaseous species obtained during thermal decomposition were also identiifed by the TG-FTIR coupling analysis. The results showed that the pyrolysis of methyl oleate proceeded in three stages, viz. the drying stage, the main pyrolysis stage and the residual pyrolysis stage. The initial decomposition temperature, the maximum weight loss temperature, the peak decomposition temperature and the rate of maximum weight loss of methyl oleate increased with the increasing heating rates. Gaseous CO, CO2 and H2O were the typical decomposition products from pyrolysis of methyl oleate. In addition, a kinetic model for thermal decomposition of methyl oleate was built up based on the experimental results using the Coats-Redfern integral method and the multiplelinear regression method. The activation energy, the preexponential factor, the reaction order and the kinetic equation for thermal decomposition of methyl oleate were obtained. Comparison of the experimental data with the calculated ones and analysis of statistical errors of pyrolysis ratios demonstrated that the kinetic model was reliable for studying the pyrolysis of methyl oleate. Finally, the kinetic compensation effect between the preexponential factors and the activation energy in the pyrolysis of methyl oleate was also conifrmed.

Measurement and correlation of solid-liquid equilibrium data for nitroguanidine in water and organic solvents from 298.15K to 338.15K

Nitroguanidine（NQ） isa high energy and low sensitivity explosive and solid-liquid equilibrium data are significant for study on crystallization of NQ. The solubilities of NQ in water, dimethyl sulfoxide, N, N dimethylformamide, 1,4 butyrolaetone and dimethyl sulfoxide @ water, N, N dimethylformamide ＋ water were measured by dynamic laser monitoring within a temperature range from 298. 15 K to 338. 15 K. The experimental data were correlated by modified Apelblat equation, 2h equation, CNIBS/R K model, andJouyban-Acree model. The results show that the four thermodynamic models can all be used to predict solubility with high accuracy. Accrding to the Akaike＇s information criterion （AIC）, the better models for correlating the solubility of NQ are judged. Additionally, the dissolution enthalpy, entropy and Gibbs free energy were calculated by the van＇t Hoff equation.

Thermogravimetric characteristics and different kinetic models for medical waste composition containing polyvinyl chloride-transfusion tube

Thermogravimetric study of medical transfusion tube （MTT） waste containing polyvinyl chloride （PVC） was carried out using the thermogravimetric analyser （TGA） with N2, at different heating rates of 5, 10, 20, 30, 50 ℃/min. The purpose is to obtain pyrolysis characteristics and kinetic parameters of medical waste. The experimental results indicate that the pyrolysis behavior of the MTT sample is in agreement with its main ingredient of PVC, appearing two stair stepping stages. The influence of the additives in MTT on pyrolysis behavior was also revealed, which could improve MTT pyrolysis at lower temperature in the first stage, and cause obvious unsmoothness and asymmetry of the second DTG peak. Four n-order kinetic models of Coats-Redfern, Ozawa, Kissinger and Freeman-carroll were used to get the kinetic parameters. Furthermore, a novel ＂two-step four-reaction model＂ was established to simulate the whole continuous process. The different methods and the kinetic parameters thus obtained were discussed and compared with each other in literatures. The reasons of deviation among kinetic values were tried to be elucidated. The new established model could more satisfactorily describe the pyrolysis process of MTT, being more mechanistic and conveniently serving for the engineering.

Thermodynamics of Third Order Lovelock Anti-de Sitter Black Holes Revisited

We compute the mass and temperature of third order Lovelock black holes with negative Gauss-Bonnet coefficient a2 〈 0 in anti-de Sitter space and perform the stability analysis of topological black holes. When k = -1, the third order Lovelock black holes are thermodynamically stable for the whole range r＋. When k = 1, we found that the black hole has an intermediate unstable phase for D = 7. In eight dimensional spacetimes, however, a new phase of thermodynamically unstable small black holes appears if the coefficient a is under a critical value. For D ≥ 9, black holes have similar the distributions of thermodynamically stable regions to the case where the coefficient ＆ is under a critical value for D = 8. It is worth to mention that all the thermodynamic and conserved quantities of the black holes with fiat horizon do not depend on the Loveloek coefficients and are the same as those of black holes in general gravity.

Pyrolysis Characteristics and Kinetics of the Preparation Process of Sludge-Based Activated Carbon by ZnCl_2 Activation Method

To obtain the pyrolysis characteristics and kinetics of preparation process of sludge-based activated carbon by ZnCl2 activation method （i.e.the pyrolysis process of the sludge with ZnCl2 activation）,the characteristic of mass loss and gas products generated during pyrolysis of the sludge with ZnCl2 activation were analyzed by thermogravimetric analysis coupled with Fourier Transform Infrared Spectroscopy （TG-FTIR）.The kinetic parameters were calculated by the Coats-Redfem method and the mechanism models were established.The role of ZnCl2 in the pyrolysis process of the sludge with ZnCl2 activation was also illustrated through the comparison of the pyrolysis characteristics and kinetics of the sludge with and without ZnCl2 activation.The results showed that the pyrolysis process of the sludge with ZnCl2 activation can be divided into four stages including the dehydration of sludge and initial depolymerization of a small portion of organics matters,the decomposition of large molecular organic matters into small molecular intermediates,the further degradation of intermediates and volatilization of ZnCl2,and the decomposition of inorganic minerals and undecomposed organic matters.CO2,CO,CH4,H2O,some aldehydes and carboxylic acids are the major pyrolysis gaseous products.The activation energies and pre-exponential factors are in the range of 28.84-206.42 kJ/mol and 9885.16-8.08× 1011 min-1,respectively.During the pyrolysis of sludge,ZnC12 not only can function as a dehydration agent and inhibit the formation of tar,but also can peptize the organic matters in the sludge,making them easier to be decomposed.

Kinematic Characteristics and Thermophoretic Deposition of Inhalable Particles in Turbulent Duct Flow

The kinematical characteristics and thermophoretic deposition of inhalable particles with the diameters of 0-2.5μm （hereafter referred to as PM2.5） suspended in turbulent air flow in a rectangular duct with temperature distribution were experimentally studied. Particle dynamics analyzer （PDA） was used for the on-line measurement of particle motion and particle concentration distribution in the cross-sections of the duct. The influences of the parameters such as the ratio of the bulk air temperature to the cold wall temperature and the air flow rate in the duct on the kinematical characteristics and the deposition efficiencies of PM2.5 were investigated. The experimental re- sults show that the deposition efficiencies of PM2.5 mainly depend on the temperature difference between the air and the cold wail, wffile the air flow rate and the particlecon^centration almost affect hardly tile clep0si-tion-effi ciency. The radial force thermophoresis to push PM2.5 to the cold wail is found the key factor for PM2.5 deposition.Based on the experimental results, an empirical modified Romay correlation for the calculation of thermophoretic deposition efficiency of PM2.5 is presenlext. The empirical correlation agrees reasonably well with the experimental data.

Physicochemical Parameters for Biological and Synthetic Surfactants Used as Detergents

Biological and synthetic surfactants were compared in terms of their ability to reduce interfacial tension, change the thermodynamic characteristics of a pre-conditioned surface, and to modify the rheological properties of their respective formulations at two different temperatures. Both classes of suffactants were able to reduce the inteffacial tension of their formulations to a similar level. However, the biosurfactants were more effective than the synthetics surfactants. Biosurfactants also altered the surface properties of stainless steel, rendering it hydrophilic. Microbial adhesion to stainless steel conditioned with biosurfactants was found to be thermodynamically unfavorable for all microbial strains tested. A linear relationship between shear stress and shear rate was obtained across a range of experimental conditions for all surfactant mixtures, indicating that all formulations behaved as Newtonian fluids.

Effect of heat treatment on mechanical and wear properties of Zn−40Al−2Cu−2Si alloy

In order to determine the effect of heat treatment on the mechanical and wear properties of Zn−40Al−2Cu−2Si alloy,different heat treatments including homogenization followed by air-cooling(H1),homogenization followed by furnace-cooling(H2),stabilization(T5)and quench−aging(T6 and T7)were applied.The effects of these heat treatments on the mechanical and tribological properties of the alloy were studied by metallography and,mechanical and wear tests in comparison with SAE 65 bronze.The wear tests were performed using a block on cylinder type test apparatus.The hardness,tensile strength and compressive strength of the alloy increase by the application of H1 and T6 heat treatments,and all the heat treatments except T6,increase its elongation to fracture.H1,T5 and T6 heat treatments cause a reduction in friction coefficient and wear volume of the alloy.However,this alloy exhibits the lowest friction coefficient and wear volume after T6 heat treatment.Therefore,T6 heat treatment appears to be the best process for the lubricated tribological applications of this alloy at a pressure of 14 MPa.However,Zn−40Al−2Cu−2Si alloy in the as-cast and heat-treated conditions shows lower wear loss or higher wear resistance than the bronze.

Theoretical Calculations for Structural, Elastic and Thermodynamic Properties of MgB2 under High Pressure

We have investigated the structural and elastic properties of MgB2 under high pressures using the full- potential linearized muffin-tin orbital （FP-LMTO） scheme within the generalized gradient approximation correction （GGA） in the frame of density functional theory. The calculated pressure dependence of the normalized volume is in excellent agreement with the experimental results. At the same time the elastic constants and acoustic anisotropy as a function of applied pressure are presented. Through the quasi-harmonic Debye model, we also investigate the thermodynamic properties of MgB2.