Numerical modelling of ice ridge keel action on subsea structures

The present paper describes a numerical simulation of the keel-structure interaction where the keel geometry, ice thickness and interaction speed present a scaling ratio of 1:20. The rubble is represented by a Drucker-Prager material with cohesive softening and no dilatation. The partial differential equations are solved with the non-linear Eulerian finite element method of Abaqus Explicit V6.8.2. The results are compared to physical experiments conducted in the ice basin of the Hamburg ship model basin (HSVA). Two identical cubic subsea structures were impacted into the unconsolidated keel portion of two ice ridges with different thermal properties. The results indicate that only slight dilatation occurs, and the models are able to estimate the rubble action and deformed shape. A progressive failure of the rubble occurs. The rubble action is influenced more by the friction angle than it is in punch tests, due to higher confinement at the failure surface.     

碳纳米管力学性能分析的分子结构有限元模型

基于分子结构力学理论,将C—C共价键等效比拟为空间梁单元,利用ANSYS的二次开发工具APDL语言编程创建能够恰当模拟碳纳米管原子间相互作用势的分子结构有限元模型,应用该模型详细研究碳纳米管在简单拉伸和纯扭转时的力学性能及其尺度效应,即手性角和管径变化对碳纳米管杨氏模量、泊松比和剪切模量的定量影响。计算结果表明,杨氏模量和剪切模量与大部分相关文献的结果吻合,但泊松比的数值结果和尺度依赖性规律在国内外文献中尚未获得统一观点,且在弹性模量、泊松比和剪切模量之间未发现明确的定量关系。     

A numerical model of ice crushing using a foam analogue

A numerical model for ice crushing has been constructed that takes into account the physical processes identified in many experimental studies. These include the presence and evolution of high-pressure and low-pressure zones, the rapid removal of ice through melting, and the transformation of relatively intact ice (high-pressure zone material) to low-pressure pulverized ice through the creation and shattering of spalls. The model produces cyclic sawtooth load events and pressure distributions that are roughly characteristic of observed ice behavior. The visual and quantitative results suggest that the physical principles incorporated in the model are correct. While still in the early stages of development, with refinements the model has potential for use in simulations of various ice/structure interaction scenarios.     

双随机分布细观分析模型与复合材料性能预报

发展了一种细观力学有限元分析方法——拟真实的参数化双随机分布模型, 该模型综合考虑了纤维增强树脂基复合材料的真实微结构特点和纤维单丝综合力学性能测试结果的离散性特征, 模拟了复合材料中纤维排列和强度分布的随机性。借助移动窗口法研究了该参数化双随机分布模型的可靠性, 确定了其代表性体积单元的尺寸。基于能量法原理推导了单向复合材料的弹性模量预测公式, 结合能量法和渐进失效分析方法, 利用该细观力学有限元方法分别预测了单向纤维增强树脂基复合材料T300/5228的弹性模量和强度性能。数值模拟结果和大部分试验结果吻合良好, 表明发展的细观力学有限元方法能够较好地预测复合材料的力学性能。      

Ultrasonic determination of the particle concentration in model suspensions and ice slurry

The development of ice slurry for refrigeration systems and the enhancement of its efficiency depend on an accurate control of the ice concentration. We present here an ultrasonic method capable to measure precisely the particle concentration in ice slurry. To calibrate the ultrasonic measurement, we first determine the sound velocity and attenuation in two model suspensions (glass beads/polyethylene glycol and polyethylene beads/vaseline oil) for different particle volume fractions. The experimental results show a good agreement with the predictions of the two-component models in the long-wavelength limit. Additionally, the sound attenuation reveals a clear signature of the aggregate formation in the nearly iso-dense suspension. We next conduct the measurement of the sound velocity in the polypropylene glycol ice slurry where the ice concentration changes with temperature. The ice concentrations extracted from our sound velocity measurements are well consistent with the values determined from the binary phase diagram.     

模型缩聚-模型修正迭代方法的研究

模型修正中通常需要解决自由度匹配问题,模型缩聚是解决这一问题的一种方法。当有限元建模误差较大时,模型缩聚的近似会大大降低模型修正的精度。针对这一问题,提出了模型缩聚-模型修正迭代方法,消除模型缩聚带来的误差。文中应用IRS缩聚和基于频响函数的模型修正方法对提出的迭代方法进行了具体讨论。通过板梁混合结构的数值模拟实验,比较了现有修正方法和迭代修正方法的修正精度。结果表明提出的迭代方法有效提高了修正精度,使修正后的模型频率和物理参数更逼近真实值。同时该方法具有较高的迭代收敛效率,符合实际工程应用的要求。     

基于实测数据的弦支穹顶计算模型修正

 为了使有限元计算模型给出的分析结果与相应的实测结果有良好的相关性,确保计算结果能切实有效地预测结构实测结果,并指导实际结构建造的顺利进行,对一弦支穹顶结构的试验模型实测结果与有限元模型计算结果进行对比分析,发现了理论模型与实际结构之间的差异,识别出导致差异的主要原因,并提出了基于测试结果对计算模型进行修正的算法与理论．通过对一实际试验模型进行的修正计算表明,修正算法能够基于实测数据便捷地对模型进行修正．最后对修正计算模型和原始模型的计算结果与实际模型结构的测试结果进行了对比分析,结果表明,修正后的计算模型较原始模型计算结果与实际模型的实测结果更加吻合,修正模型能够更加准确地描述实际结构．     

Model test study of the nonsimultaneous failure of ice before wide conical structures

From 2007 to 2008, a series of model tests were performed to observe the ice failure before wide conical structures. The variable testing parameters include the water line diameter of the model cone and ice speed. When D/h > 25, the failures of ice wedges around the cone start to behave nonsimultaneously in these tests. The rubble piece size and the ride-up height were found to have linear relationships with the ratio of D/h in the tests. Several independent zones of bending were found in the nonsimultaneous failure process of ice. With the increasing of the ratio of D/h and the number of independent zones, the total ice force was found being reduced by degrees.     

Mechanical properties of three-dimensional braided composites

Recently developed digital element approach, which treats textile composite manufacturing process as a nonlinear solid mechanics problem, was successfully used to investigate the complicated microstructure of 3D braided rectangular preform. The yarns interaction and cross-sectional deformation, which were neglected in traditional topological model, could be analyzed exactly. Results showed that yarns inside 3D braided preform were curvy, which was opposite to the straight-yarns assumption of topological model and, yarns curvature inside the preform, which was very difficult to be explored before both experimentally and theoretically, was investigated numerically. After that, the mechanical properties of 3D rectangular braided composites, such as tensile stiffness, shear stiffness and Poisson ratio were calculated through the volume-average-compliance method. Comparison was conducted for those from the topological model and digital element approach, and topological model was found to underestimate greatly both the tensile stiffness and shear stiffness.     

Mechanical analysis of 3D braided composites: a finite element model

The analysis of 3D braided composites is more difficult due to its complex microstructure. A new type of finite element method is developed to predict the effective moduli and the local stress within 3D braided composites under the 3D mechanical loading. To verify the present method, the material properties of undamaged 3D braided composites predicted in this paper are compared with the previous work. To demonstrate this method, some examples are analyzed.     

超弹性SMA复合阻尼器的计算模型及参数分析

介绍了超弹性SMA复合阻尼器的构造及工作原理,并根据它的受力特性,建立了该阻尼器的力学计算模型,针对模型中的关键参数:阻尼器内滑条槽深与接触面摩擦系数、SMA丝的预应变及缠绕量、环境温度及位移幅值等对阻尼器力学性能的影响规律进行了分析。分析结果表明:阻尼器的初始刚度、输出力和滞回面积随内滑条槽深、SMA丝缠绕量、接触面的摩擦系数的增加而增加;在不同的位移幅值下,阻尼器的荷载-位移曲线形状分别呈三角形、四边形和五边形等多边形形式,表现为变刚度的特性;阻尼器的屈服位移和输出力随环境温度的升高而线性增加;当对SMA丝施加一定的初始预应变,SMA复合阻尼器表现为摩擦型阻尼器。最后,将模型结果与实验结果进行了对比,两者基本吻合。     

Mechanical properties of silkworm cocoon pelades

The pelade, the innermost layer of silkworm cocoon next to the chrysalis, has special microstructures, mechanical properties and protective functions distinctly different from those of all the other layers. In the present paper, a series of static tensile tests and dynamic mechanical thermal analysis were performed for the first time to measure the mechanical properties of pelades, including Young’s modulus, tensile strength and thermomechanical parameters. The fracture process of precracked pelade specimens was observed by in-situ scanning electron microscopy under tension. It is found that the Young’s modulus, tensile strength, storage modulus and loss modulus of cocoon pelades are superior to the corresponding thickness-averaged values of a complete silkworm cocoon. The damage and fracture process of pelades involve delamination, silk breaking and damage localization band. The results indicate that silkworm caterpillars can be appreciated as sophisticated sewers to make anisotropic and optimized structures of cocoons with both protective functions and mechanical properties varying in their thickness direction. The present study might be helpful to guide biomimetic design of novel safe-guarding materials and structures from both the viewpoints of microstructures and spatial functional gradients.     

空心微珠填充聚氨酯泡沫塑料的力学性能

对不同密度和不同填充质量比的空心玻璃微珠填充聚氨酯泡沫塑料进行拉、压实验,研究了微珠对复合泡沫塑料力学性能的影响。实验结果表明:复合泡沫塑料拉伸曲线特征与普通泡沫塑料类似,但具有不同于普通泡沫塑料的压缩应力-应变特性;材料密度越大,微珠对胞体壁的增强效果越好;微珠团聚和界面粘结不良将可能导致材料力学性能的下降。根据有限元模拟结果和试件破坏形貌的观察探讨了材料的变形和破坏机制。      

预制空心板桥梁格模型的荷载试验验证

以某预应力空心板桥为例,采用梁格法建立有限元模型,用荷载试验实测数据对其挠度计算值及其挠度横向分布进行对比验证。可为空心板桥建模精细化提供参考。     

Mechanical properties and microstructure of polyetheretherketone-hydroxyapatite nanocomposite materials

For the first time the polyetheretherketone (PEEK)-hydroxyapatite (HA) nanocomposite materials were successfully prepared, and their microstructure and mechanical properties, such as tensile strength, load-displacement and Young's modulus, were examined. The specimens laminated by the PEEK-HA composite layers with 5 vol.% and 15 vol.% HA were also successfully made, which gave a promising mechanical strength and a high HA content on the specimen surface. This novel approach should be of significance in manufacturing PEEK-HA biomaterials with both satisfactory mechanical properties and high bioactivity.     

Mechanical properties of additive laser-welded NiTi alloy

Laser welding would be a suitable joining technique for NiTi shape memory alloy if the mechanical properties of laser weld were improved. With this purpose, effects of additive on mechanical properties of laser-welded NiTi alloy have been experimentally studied. Welding specimens used in this study were 2 mm thick hot-rolled plates with a chemical composition of Ni50.9Ti49.1. (Ni50.9Ti49.1)-Ce2 (at.%) alloy foil or Ni47Ti44Nb9 plate was used as filler metal to add Ce or Nb element into NiTi laser weld metal. Both tensile strength and the toughness of additive-welding specimens were improved significantly compared with non-additive-welding specimen. The mechanical property improvement was attributed to the fine solidification NiTi grains and good grain-linking in weld center. The microstructure control mechanisms of these two additive welds were discussed.     

Mechanical properties of cork: Effect of hydration

Cork is known to exhibit low permeability to liquids and gases, imputrescibility and good mechanical properties, with a remarkable elasticity. These properties make this material particularly interesting for sealing wine. We focused in this study on the compression properties of cork along the radial and tangential direction at 25 °C under atmospheric pressure when cork is stored in various relative humidity environments, from 0% to 100%.The direction of compression significantly affected the Young’s modulus, with a higher value for the radial direction. This corresponds to the orientation of the lenticels which reinforce the rigidity of the material when the strain is applied along their growth direction. More surprising is the effect of water sorption in cork on its mechanical property. Both radial and tangential directions exhibit the same behavior when the relative humidity is increasing. First the Young’s modulus is constant up to 50% relative humidity (RH) with mean values around 37 MPa and 22 MPa for radial and tangential directions, respectively. Then, above this point, the increase in water content leads to a decrease in material rigidity which is attributed to water clusters formations. For high moisture contents, the anisotropy of cork is reduced: Young’s moduli are of 10.5 MPa and 6.6 MPa for radial and tangential orientations, respectively.Differential scanning calorimetry and dynamic mechanical thermal analysis (DMTA) allowed to identify a glass transition temperature (T_g) in cork over a broad range of temperatures, depending on the moisture content and giving a T_g-midpoint from −8 °C to 3 °C. Moreover, a secondary transition was observed by DMTA at approximately −80 °C, for 50% RH.     

斜拉桥有限元建模与模型修正

以圆弧桥面、单偏置斜塔的Safti斜拉桥为对象，研究了斜拉桥的有限元建模技术和基于敏感度分析的有限元模型修正技术及其对该桥的应用。基于该桥现场测量的模态数据，修正后的有限元模型获得了较好的改善。     

Mechanical and transport properties of IBAD/EDDC–SmBCO coated conductor tapes during fatigue loading

In electrical devices like superconducting motor, generator and SMES, HTS coated conductor (CC) tapes will be subjected to alternating stress or strain during manufacturing and operation. The repeated loading will affect the mechanical integrity and eventually the electrical transport property of CC tapes. Therefore in such applications, electro-mechanical property of CC tapes should be evaluated. In this study, the endurance of an IBAD/EDDC–SmBCO CC tape under high-cycle fatigue loading has been evaluated. Applied maximum stress and fatigue life (S–N) relation was obtained at 77 K. The mechanical properties and the critical current, I_c, of the sample under fatigue loading were investigated at 77 K. Considering the practical operating environment, the effect of the stress ratio R, on the degradation behavior of I_c under fatigue loading was also examined.     

神经网络在建筑物有限元模型修正中的应用

建立了多层建筑结构间刚度与自振频率之间的神经网络模型,阐述了将人工神经网络应用于建筑的有限元模型修正的思想以及具体实施步骤和关键性问题,着重介绍了ＢＰ网络的拓扑结构及其改进的学习算法。数值例证说明：将人工神经网络和结构模态参数识别方法结合对结构有限元模型修正是可行的。