压力对冰水固流转化速率影响的实验研究

本文对圆柱形冰块融化过程进行了数学分析,得到了冰水固流转化的数学关系及冰的温度与压力的关系,通过冰块融化实验,研究了压力对融冰速率的影响,通过Matlab曲线拟合与数据分析,得出了圆柱形冰块融化速率与时间随压力变化的经验公式,最后用Ansys进行了数值仿真验证.     

温度增量对冰水固流转化速率影响的实验研究

通过RPH-80型可程序恒温恒湿试验箱研究了温度增量对圆柱体冰块融化速率的影响。研究结果表明:试验箱的温度在0℃~50℃区间内,随着温度增量的增大,圆柱体冰块的融化速率逐渐加快。通过数据分析,得出了圆柱体冰块的温度增量与融化时间、融化速率都呈多项式函数规律变化。选取温度增量为20℃的冰块融化过程进行ANSYS数值仿真验证,得出:圆柱体冰块棱边部分最先开始融化;随着时间的增长,冰块的侧面比上表面开始融化的时间早,这亦与实际的融化状况相符。     

马铃薯晚疫病传播的数学建模与仿真模拟

运用数学建模和仿真模拟方法研究不同品种马铃薯混种方式对晚疫病的防治效果.首先,针对马铃薯晚疫病病原菌在植物上繁殖和在空间中传播的特点建立偏微分方程的传染病模型.模型的数值结果反映了晚疫病形成与传染的空间分布和时间变化规律,与田间一些观测现象相吻合.然后通过灵敏度分析,探讨了叶片大小、孢子囊感染效率和病斑半径最大增长速率等诸多参数对疫情发展的影响.最后,构造了具有不同参数值的四类马铃薯品种的各种混种方式,通过计算仿真模拟,比较了晚疫病在的不同混种方式下的传染过程.实验结果表明随机混种方式具有较好的抗病效果.     

凝聚态物质振动-平动能量弛豫过程的分子动力学模拟

本文利用分子动力学计算机模拟方法,研究了稠密态双原子分子振动-平动弛豫速率与分子离解能、密度和温度的关系。发现振动弛豫速率随着分子离解能的增高而下降。这一现象与由光谱数据得到的结果是一致的。它可以用振动频率的下降来解释;分子振动弛豫速率随密度增大而加快,在我们所作的范围内,似乎看不到弛豫速率与温度有关。     

金属材料中低加载速率下的动态韧脆转变及断裂韧性测量

金属材料在冲击下的韧脆转变现象和动态断裂韧性的测量是金属材料冲击力学性能研究的重要组成部分.针对金属材料在冲击下的韧脆转变现象认识不足和韧性材料在较低加载率下动态$J$-$R$阻力曲线难以测量的现状,提出了采用高速材料试验机, 设计专用试验夹具,测量15MnTi钢和11MnNiMo钢在不同加载速率下的韧脆转变过程,以及裂尖约束对其动态韧脆转变速率变化的影响.在高速材料试验机上采用上夹具辊刹车,通过调节压缩杆长度改变试验中裂纹扩展量的试验方法,测量了15MnTi钢三点弯曲试样件在较低加载率下的动态断裂韧性.试验发现15MnTi钢CT试验件加载速率低于0.025 m/s时呈现出韧性断裂的特点,加载速率在0.1,$\sim$,0.5 m/s时为韧脆结合型断裂,加载速率高于0.5 m/s后进入脆性断裂区; 11MnNiMo钢CT试验件加载速率大于1.5 m/s后,分层断裂过程中出现先脆断后韧段的现象;发现15MnTi钢和11MnNiMo的动态韧脆转变速率受裂尖约束的影响非常明显,面内约束和面外约束的升高都会导致材料动态脆断速率出现明显降低;还发现三点弯曲试验中, 15MnTi钢在8788 MPa$\cdot$mm/s加载率内断裂韧性随加载率的提升呈现出缓慢下降的趋势.      

加载速率对40Cr钢Ⅱ型动态断裂特性的影响

采用新型Ⅱ型动态断裂测试技术,对高强钢40Cr在高加载速率下的Ⅱ型动态断裂特性进行了测试研究。基于新设计的Ⅱ型动态断裂试样和分离式霍普金森压杆（split Hopkinson pressure bar, SHPB）技术,通过实验-数值方法确定了裂尖在加载过程中的应力强度因子曲线。采用应变片法确定了试样的起裂时间,最终得到40Cr的Ⅱ型动态断裂韧性值,并对其加载速率相关性和材料的失效机理进行了研究。结果表明,在1.08～5.53 TPa·m1/2/s的加载速率范围内,40Cr的Ⅱ型动态断裂韧性基本表现为与加载速率成正相关的变化趋势。通过对试样断口形貌的分析,确定了材料的失效模式及机理,发现随着加载速率的增加,存在拉伸型失效向绝热剪切型失效模式转变的现象。     

考虑应变率效应的混凝土随机损伤本构模型研究

混凝土材料组分复杂且具有随机分布的特点, 其受力力学行为不可避免地存在非线性和随机性. 同时, 在动力荷载作用下, 混凝土材料具有不可忽视的率敏感性. 为了综合反映混凝土受力力学行为中的非线性、随机性与率敏感性, 本文从对材料的纳-微观裂纹扩展分析入手, 引入速率过程理论描述纳观裂纹的扩展速率, 并研究了对应的能量耗散过程. 在此基础上通过裂纹层级模型将纳观分析推演到微观尺度, 建立了微观能量耗散的基本表达式. 进而与微-细观随机断裂模型相结合, 形成了混凝土纳-微-细观随机损伤本构模型. 同时, 基于速率相关势垒的分析, 揭示了动力强度的提高源自加载速率和原子键断裂速率的竞争机制. 据此, 假定微裂纹间相互作用与应变率比值的相关关系以建立微弹簧能量耗散速率与应变率的联系, 实现了从静力本构模型向动力本构模型的扩展. 数值算例表明, 建议模型能够同时反映混凝土材料力学行为中的非线性、随机性和率敏感性. 最后通过与相关试验结果的对比, 验证了建议模型的正确性.      

大载荷下线振动微机械陀螺谐振频率漂移特性

线振动 MEMS 陀螺在大载荷条件下,驱动轴与检测轴的谐振频率会发生漂移,频差随载荷变大.这类型振动陀螺为了提高灵敏度往往将两个振动轴的谐振频率设计得尽量靠近,但当角速率载荷较大时,两个振动轴的谐振频率将发生分裂漂移,彼此互相远离.漂移量与向心加速度无关,近似与角速率载荷的平方成正比,且两轴的谐振频率越靠近漂移越剧烈.考虑到 Coriolis 效应的弹簧质量块二维振动数学模型可定量描述该现象,表明此现象为线振动陀螺 Coriolis 效应的一部分.理论分析、仿真研究和实验数据的不同角度对这种频率漂移特性的分析结果吻合良好,为进一步结构优化奠定了理论基础.     

凝聚态物质振动-平动能量弛豫过程的分子动力学模拟

本文利用分子动力学计算机模拟方法,研究了稠密态双原子分子振动-平动弛豫速率与分子离解能、密度和温度的关系。发现振动弛豫速率随着分子离解能的增高而下降。这一现象与由光谱数据得到的结果是一致的。它可以用振动频率的下降来解释;分子振动弛豫速率随密度增大而加快,在我们所作的范围内,似乎看不到弛豫速率与温度有关。     

融化巧克力浆料流变特性的实验研究

对融化巧克力浆料进行了实验研究，揭示了其假塑性和触变性．并根据实验结果得到了融化巧克力浆料的全流变本构方程．     

相变材料接触熔化的研究

对有关相变材料接触熔化的研究成果进行了全面的综述, 内容包括:封闭空间的接 触熔化、围绕热源的接触熔化、滑动接触熔化、滚动接触熔化、冰的压力熔化、接 触熔化的量级分析与修正、由液体边界层内的热扩散引起的熔化、不连续接触点上 熔化与润滑、固体内部传热的影响、玻璃的软化与接触熔化.     

Experiments on melting of a vertical ice layer immersed in immiscible liquid

Experiments on the melting of a vertical ice layer immersed in immiscible liquid yielded quantitative results both for the timewise evolution of the melting front and the heat transfer. Vegetable oil, which was contained in a rectangular vessel, was adopted as a testing liquid. A bubble-free ice block stuck on a cooled wall was installed vertically in the vessel. The experiments were carried out for the immiscible liquid temperatures from 7.6 to 30.0 ^°C, while for the cooled wall temperatures from 0 to ?11.5 ^°C. The flow structure of the liquid and the melting front were extensively observed and recorded photographically. It was found that the heat transfer and the rate of melting are significantly affected by a couple of fluid motions of both the water melt induced by melting of ice and the immiscible liquid based on free convection.     

Effects of the heat transfer fluid velocity on the storage characteristics of a cylindrical latent heat energy storage system: a numerical study

A numerical study of the effects of the thermal fluid velocity on the storage characteristics of a cylindrical latent heat energy storage system (LHESS) was conducted. Due to the low thermal conductivity of phase change materials (PCMs) used in LHESS, fins were added to the system to increase the rate of heat transfer and charging. Finite elements were used to implement the developed numerical method needed to study and solve for the phase change heat transfer (melting of PCM) encountered in a LHESS during charging. The effective heat capacity method was applied in order to account for the large amount of latent energy stored during melting of the PCM and the moving interface between the solid and liquid phases. The effects of the heat transfer fluid (HTF) velocity on the melting rate of the PCM were studied for configurations having between 0 and 18 fins. Results show that the overall heat transfer rate to the PCM increases with an increase in the HTF velocity. However, the effect of the HTF velocity was observed to be small in configurations having very few fins, owing to the large residual thermal resistance offered by the PCM. However, the effect of the HTF velocity becomes more pronounced with addition of fins; since the thermal resistance on the PCM side of the LHESS is significantly reduce by the large number of fins in the system.     

Problem of a solid half-space melted by a hot rotating disk or ring

The sliding friction of solids at high speed and under heavy load may be accompanied by a transition to the plastic or fluid state in the friction contact zone [1]. The stage corresponding to a developed fluid layer is investigated without taking into account the plastic deformation of the rubbing bodies; it is assumed that all the heat released is expended exclusively on melting the solid. Previous attempts to investigate this stage theoretically have been based on the approximation of a fluid layer of constant thickness and the use of the heat balance equation [1, 2]. Here, the velocity and temperature profiles are approximated by relations quadratic in the transverse coordinate with coefficients that depend on the longitudinal coordinate. These are determined from the boundary conditions and the integral relations of boundary layer theory. The relations obtained are used to determine the rate at which a hot rotating ring melts through a block of ice.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 30–34, May–June, 1990.     

Effects of the number and distribution of fins on the storage characteristics of a cylindrical latent heat energy storage system: a numerical study

A numerical study of the effects of the number and distribution of fins on the storage characteristics of a cylindrical latent heat energy storage system (LHESS) was conducted. Due to the low thermal conductivity of phase change materials (PCMs) used in LHESS, fins were added to the system to increase the rate of heat transfer and charging. Finite elements were used to implement the developed numerical method needed to study and solve for the phase change heat transfer (melting of PCM) encountered in a LHESS during charging. The effective heat capacity method was applied in order to account for the large amount of latent energy stored during melting of the PCM and the moving interface between the solid and liquid phases. The effects of increasing the number and distribution of fins on the melting rate of the PCM were studied for configurations having between 0 and 27 fins for heat transfer fluid (HTF) velocities of 0.05 and 0.5?m/s. Results show that the overall heat transfer rate to the PCM increases with an increase in the number of fins irrespective of the HTF velocity. It was also observed that the total amount of energy stored after 12?h increases nearly linearly with the addition of fins up to 12 fins; further addition of fins increasing the total energy stored by ever smaller amounts.     

Solidification and melting heat transfer to an unfixed phase change material (PCM) encapsulated in a horizontal concentric annulus

The solidification and melting process of an unfixed PCM between two isothermal concentric horizontal cylinders was investigated by experimental techniques and by a combined analytical and numerical method. During the solidification process concentric solid PCM layers form at both tube walls, growing slowly into the annulus. Assuming quasi-steady heat conduction, this process is described by a simple analysis. The melting PCM reveals a different behaviour. Due to gravitational forces the solid phase moves downwards. Experiments prove that the solid retains contact with the lower part of the outer tube as well as with the upper part of the inner tube. In this process thin liquid films form between the solid body and the heated walls and heat transfer by conduction is the dominating mechanism during melting. Heat transfer by natural convection causes the melting at the upper interface. There, the melting rates, however, are comparatively small. The theoretical approach and the numerical analysis are based on a balance of the pressure forces in the thin liquid films and of the gravitational force acting on the solid material. As a result melting rates and heat fluxes may be predicted. For practical application a Nusselt correlation is derived.     

Heat transfer enhancement of PCM melting in 2D horizontal elliptical tube using metallic porous matrix

In this study, the melting process of ice as a phase-change material (PCM) saturated with a nickel–steel porous matrix inside a horizontal elliptical tube is investigated. Due to the low thermal conductivity of the PCM, it is motivated to augment the heat transfer performance of the system simultaneously by finding an optimum value of the aspect ratio and impregnating a metallic porous matrix into the base PCM. The lattice Boltzmann method with a double distribution function formulated based on the enthalpy method, is applied at the representative elementary volume scale under the local thermal equilibrium assumption between the PCM and porous matrix in the composite. While reducing or increasing the aspect ratio of the circular tubes leads to the expedited melting, the 90\(^{\circ }\) inclination of each elliptical tube in the case of the pure PCM melting does not affect the melting rate. With the reduction in the porosity, the effective thermal conductivity and melting rate in all tubes promoted. Although the natural convection is fully suppressed due to the significant flow blockage in the porous structure, the melting rates are generally increased in all cases.     

Effect of cavity inclination on a temperature and concentration controlled double diffusive convection at ice plate melting

This paper is concerned with the double diffusive convection due to the melting of an ice plate into a calcium chloride aqueous solution inside a rectangular cavity. It is mainly considered the effect of the cavity inclination on the melting rate and the mean melting Nusselt- and Sherwood-numbers, experimentally as well as numerically. The ice plate melts spontaneously with decreasing temperature at the melting front even if initially there does not exist a temperature difference between the ice and the liquid. The concentration- and temperature-gradients near the melting front induce double diffusive convection in the liquid, which will affect the melting rate. Experiments reveal that the mean melting mass increases monotonically with increasing cavity inclination. The numerical analysis based on the laminar assumption predicts well the melting mass in the range of =0–90°, however, under-predicts the melting mass in the range of =90–180° as compared with the experimental results.     

基于S-ALE方法的圆柱体垂直出水破冰研究

以往针对结构物垂直贯穿冰层破裂的研究多不考虑水的作用, 与实际应用场景不符. 本文应用 LS-DYNA 有限元软件建立了基于结构化-任意拉格朗日欧拉(S-ALE)流固耦合方法及罚函数接触算法的冰?水?结构物耦合作用数值模拟方法. 采用欧拉算法描述空气域和水域, 采用拉格朗日算法描述圆柱体结构和冰层结构, 使用弹塑性应变率模型表征冰材料力学性质. 自主搭建了圆柱体垂直贯穿冰层试验台架, 验证了有限元方法计算结构物?冰层相互作用问题的可行性. 通过模拟圆柱体垂直出水破冰过程, 并与无水环境下圆柱体垂直贯穿冰层破裂过程进行对比. 结果表明: 有水环境下结构物?冰层间作用存在“水垫效应”; 冰层突破载荷极值大小与有、无水环境无显著变化; 有水环境下的结构物突破冰层冰载荷持续时间明显长于无水环境下持续时间; 有水环境冰层弹性变形阶段更长, 且有水环境冰层挠度变化大于无水环境下的挠度变化. 本文研究成果为极地冰区环境下结构物垂直出水破冰的结构强度计算及优化设计提供了研究基础.      

NUMERICAL STUDY OF THE THERMAL STATE OF AN ICE LAYER CONTAINING AIR BUBBLES

Journal of Applied Mechanics and Technical Physics - The melting of an ice layer with air bubbles on exposure to an artificial thermal radiation source is studied by mathematical modeling within...