基于相对密度机床立柱结构的动力学拓扑优化

构造了基于相对密度法的连续体结构动力学拓扑优化设计数学模型,以结构的相对密度为设计变量,结构基频最大化为目标函数,满足结构工况和相对体积比为约束条件,采用启发式优化准则法进行迭代求解;基于该方法和等效质量块对机床立柱结构进行了动力学拓扑优化设计,再对优化后整机进行了动力学仿真。仿真结果表明,该优化设计模型可大大提高机床整机的动、静态特性,同时也验证了所提出的设计模型及优化准则的合理性和有效性。

考虑滑移的螺栓连接动力学建模方法

螺栓连接结构受载时经常会出现滑移,这种滑移会影响结构的动力学性能,继而对结构的性能和寿命造成影响。本文以双螺栓连接结构为对象,通过实验和数值仿真手段研究滑移对结构模态特性的影响。实验结果表明,预紧力的增大会导致共振频率上升,而随着激励幅值增大,共振频率下降且每个周期能量耗散量对模态力的梯度增大。基于实验结果,结合考虑滑移的Iwan模型理论,建立非线性动力学模型,应用四阶龙格库塔法进行求解。根据计算结果对宏观滑移情况下的结构模态进行分析,发现此时二阶弹性模态中的共振频率下降量增大,能量耗散量对模态力的梯度降低。该数值计算模型可以很好地表征螺栓连接结构的模态特性,且计算效率高。

钛酸锶熔化和淬火过程的分子动力学模拟

对钛酸锶(STO)快速升温熔化和快速冷却过程进行分子动力学模拟。通过快速升温熔化过程中体系内能和体积的变化,分析了非晶态钛酸锶的结构特征和动力学特征;将熔化的STO快速冷却后,瞬时原子构型图表明获得的非晶态STO基本保持了液态的结构特征。分析了晶态、液态和非晶态时的对关联函数和原子配位数,确定出Ti-O截断半径的分布,进一步观察了STO非晶过程的微观结构特性和动力学特征。

环境激励振动模态分析在桥梁结构检测与健康监测中的应用

文中对试验模态分析(EMA),特别是基于环境激励的振动模态分析(AMA)的进展,及其在桥梁结构检测和健康监测的应用进行了综合评述.主要内容包括:结构动力学特性在桥梁结构检测和健康监测中的作用,传统试验模态分析和环境激励模态分析的进展,以及环境激励模态分析在桥梁结构检测与健康监测应用实例.

辽西地区地基基础和建筑物的地震反应特性的研究

为了对中国辽西地区的地基基础和建筑物的地震反应特性进行研究,首先,对微动观测在辽西地区的时间侧面的安定性和微动观测在辽西地区的区域方面的适用性进行了试验和确认,并且得到了肯定的结果;然后,应用常时微动观测对辽西地区进行观测,并且对观测结果的准确性进行讨论;最后,根据观测结果作出卓越振动频率分布图和地基表层层厚图,再对辽西地区代表性建筑物(辽宁工学院国际交流中心)进行常时微动观测并和建筑物模型化的一次元和二次元分析结果进行比较,得到了比较一致的结果,证明了二次元模型化的正确性。根据以上结果在辽西地区选出地质条件不同的3点,设想国际交流中心建设在辽西地区3个地基构造不同的地基基础上,通过输入神户地震波进行地震反应分析。得到了由于地基反应特性不同,在相同的地震作用下,相同建筑物的反应特性、建筑物的轴力、剪应力都有很大的差异的规律。

自动化集装箱码头低架桥横梁振动与小车行走速度的关系

根据结构动力学原理,分析了小车行走速度与低架桥弯曲振动之间的关系,得到了在现有的参数条件下,小车行走不会激发起低架桥强列振动的结论。

Microscopic damage and dynamic mechanical properties of rock under freeze-thaw environment

For understanding the rock microscopic damage and dynamic mechanical properties subjected to recurrent freeze-thaw cycles, experiments for five groups of homogeneous sandstone under different freeze-thaw cycles were conducted. After freezethaw, nuclear magnetic resonance(NMR) tests and impact loading tests were carried out, from which microscopic damage characteristics of sandstone and dynamic mechanical parameters were obtained. The results indicate that the porosity increases with the increase of cycle number, the rate of porosity growth descends at the beginning of freeze-thaw, yet accelerates after a certain number of cycles. The proportion of pores with different sizes changes dynamically and the multi-scale distribution of pores tends to develop on pore structure with the continuing impact of freeze-thaw and thawing. Dynamic compressive stress-strain curve of sandstone undergoing freeze-thaw can be divided into four phases, and the phase of compaction is inconspicuous compared with the static curve. Elastic modulus and dynamic peak intensity of sandstone gradually decrease with freeze-thaw cycles, while peak strain increases. The higher the porosity is, the more serious the degradation of dynamic intensity is. The porosity is of a polynomial relationship with the dynamic peak intensity.

GPCR A2AAR Agonist Binding and Induced Conformation Changes of Functional Switches

Agonist binding of A2A adenosine receptor （A2AAR） shows protective effects against inflammatory and immune. Efforts are exerted in understanding the general mechanism and developing A2AAR selectively binding agonists. Using molecular dynamics （MD） simula- tions, we have studied the interactions between A2AAR and its agonist （adenosine）, and analyzed the induced dynamic behaviors of the receptor. Key residues interacting with adenosine are identified： A63^2.61,I66^2.64,V84^3.32,L85^3.33,T88^3.36,F168^5.29,M177^5.38,L249^6.51,H250^6.52 and N253^6.55 interacting with adenosine with affinities larger than 0.5 kcal/mol. Moreover, no interaction between adenosine and L167^5.28 is observed, which supports our previous findings that L1675^5.28 is an antagonist specific binding reside. The dynamic be- haviors of agonist bound A2AAR are found to be different from apo-A2AAR in three typical functional switches： （i） tight ＂ionic lock＂ forms in adenosine-A2AAR, but it is in equilibrium between formation and breakage in apo-A2AAR; （ii） the ＂rotamer toggle switch＂, T88^3.36/F242^6.44/W246^6.48, adopted different rotameric conformations in adenosin-A2AAR and apo-A2AAR; （iii） adenosine-A2AAR has a flexible intracellular loop 2 （IC2） and s-helical IC3, while apo-A2AAR preferred s-helical IC2 and flexible IC3. Our results indicate that agonist binding induced different conformational rearrangements of these characteristic functional switches in adenosine-A2AAR and apo-A2AAR.

Design and evaluation of cab seat suspension system based on negative stiffness structure

To improve the vibration-isolation performance of cab seats,the optimization model of the seat suspension system of construction machinery cabs is proposed based on the negative stiffness structure.The negative stiffness nonlinear kinetic equation is established by designing the seat negative stiffness suspension structure(NSS).Using MATLAB,the different parameters of the suspension system and their influences on the dynamic stiffness are analyzed.The ideal configuration parameter range of the suspension system is obtained.Meanwhile,the optimization model of NSS is proposed,and the vibration transmissibility characteristics are simulated and analyzed by different methods.The results show that the displacement and acceleration amplitudes of the optimized seat suspension system are evidently reduced,and the four-time power vibration dose value and root mean square calculation values in the vertical vibration direction of the seat decrease by 86%and 87%,respectively.Seat effective amplitude transmissibility(SEAT)and the vibration transmissibility ratio values also decrease.Moreover,the peak frequencies of the vibration transmitted to the driver deviate from the key frequency values,which easily cause human discomfort.Thus,the design of the seat suspension system has no effect on the health condition of the driver after being vibrated.The findings also illustrate that the NSS suspension system has good vibration-isolation performance,and the driver's ride comfort is improved.

Dynamic analysis and nonlinear identification of space deployable structure

The dynamic equivalent continuum modeling method of the mast which is based on energy equivalency principle was investigated. And three kinds of mast dynamic model were established, which were equivalent continuum model, finite element model and simulation model, respectively. The mast frequencies and mode shapes were calculated by these models and compared with each other. The error between the equivalent continuum model and the finite element model is less than 5% when the mast length is longer. Dynamic responses of the mast with different lengths are tested, the mode frequencies and mode shapes are compared with finite element model. The mode shapes match well with each other, while the frequencies tested by experiments are lower than the results of the finite element model, which reflects the joints lower the mast stiffness. The nonlinear dynamic characteristics are presented in the dynamic responses of the mast under different excitation force levels. The joint nonlinearities in the deployable mast are identified as nonlinear hysteresis contributed by the coulomb friction which soften the mast stiffness and lower the mast frequencies.

基于FLUENT软件基础上的水力切割煤层工艺设计

为了提高水力割缝工艺喷嘴切割效果,基于FLUENT软件模拟高压水在喷嘴内部的流动过程,建立计算机模拟的喷嘴网格模型,研究评价喷嘴几何参数的效果,结果表明切割效果显著,可以提高煤层透气性,缩短抽采达标时间。

Relationship between local damage and structural dynamic behavior

Damage in the structures alters the structural dynamic behavior. Damage generally occurs locally in the components of structures, and its effect often exhibits in the changes of both local and global characteristics of structures. Better understanding of this relationship helps to monitor and assess the condition of structures and develop dynamics-based structural health monitoring techniques. In this study, the relationship between the local damage and structural dynamic behavior is investigated. To validate the concept, an experiment of a three-dimensional (3-D) steel frame structure with different magnitudes of local damage is illustrated. The experimental results indicate that the change of global resonant response between the intact and damage structure is not obvious. The change of local resonant responses measured near the location of saw-cut crack damage is quite significant. The experimental study conducted indicates that the local resonant responses at the low order resonance can be used as an effective damage identification method to detect and quantify the local damage in the 3D frame structures.

Molecular simulation study of dynamical properties of room temperature ionic liquids with carbon pieces

Room temperature ionic liquids(RTILs) with dispersed carbon pieces exhibit distinctive physiochemical properties. To explore the molecular mechanism, RTILs/carbon pieces mixture was investigated by molecular dynamics(MD) simulation in this work. Rigid and flexible carbon pieces in the form of graphene with different thicknesses and carbon nanotubes in different sizes were dispersed in a representative RTIL 1-butyl-3-methyl-imidazolium dicyanamide([Bmim][DCA]). This study demonstrated that the diffusion coefficients of RTILs in the presence of flexible carbons are similar to those of bulk RTILs at varying temperatures, which is in contrast to the decreased diffusion of RTILs in the presence of rigid carbons. In addition, interfacial ion number density at rigid carbon surfaces was higher than that at flexible ones, which is correlated with the accessible external surface area of carbon pieces. The life time of cation-anion pair in the presence of carbon pieces also exhibited a dependence on carbon flexibility. RTILs with dispersed rigid carbon pieces showed longer ion pair life time than those with flexible ones, in consistence with the observation in diffusion coefficients. This work highlights the necessity of including the carbon flexibility when performing MD simulation of RTILs in the presence of dispersed carbon pieces in order to obtain the reliable dynamical and interfacial structural properties.

Structure and Dynamics of Ethanol Adsorbed on a Mica Surface

The structural and dynamic properties of nanoscale ethanol film on a mica surface are investigated via molecular dynamics simulations. We observe a dense, almost fiat ethanol bilayer formed in the vicinity of the mica surface, with the hydrophobic alkyl groups pointing outward from the surface. Remarkably, such ethanol bilayer is laterally well-ordered with patterned adsorption sites. Each ethanol molecule in the first layer donates one hydrogen bond to the surface basal oxygen atoms and accepts one hydrogen bond from that in the second layer. The ethanol molecules within the bilayer exhibit constrained lateral mobility and delayed dynamics as compared with bulk ethanol, whereas those on top of the bilayer have bulk-like characteristics.