大型立式玻璃磨边机整机动态特性分析

大型立式玻璃磨边机的动态特性影响玻璃磨边质量和磨边效率。利用Solidworks软件建立某大型立式玻璃磨边机三维实体模型,导入ANSYS软件中,对整机结构有限元动力学分析,得到该磨边机前六阶模态参数,分析了各阶振型对磨边机动态特性的影响,为磨边机结构的改进设计提供了理论依据。     

地铁车辆轴箱吊耳动态分析和优化

针对某型地铁车辆转向架在被吊起时起保护一系悬挂系统作用的轴箱吊耳在车辆运营中多次发生断裂的问题,用HyperWorks建立吊耳的有限元模型,以试验数据作为输入分析模态频率响应,通过仿真结果与试验结果的对比调整模型,保证模型仿真的准确性.综合分析仿真结果和试验结果,找出引起吊耳模态频率响应过大的原因,利用OptiStruct进行结构拓扑优化,根据优化结果提出4种新方案,并分别对比各方案的静强度、模态频率、模态频率响应和体积等,确定最佳设计方案.     

基于CAE的模态综合法误差分析

为研究用模态综合法进行发动机舱前端模型NVH分析时的误差,用整体计算法和模态综合法分别进行截止频率为100,200,300,1 000,2 000和3 000 Hz的模态计算,并基于模态计算结果进行原点传递函数计算.结果表明:考虑静态补偿的模态综合法计算误差小于不考虑静态补偿的计算误差;子系统模态计算截止频率大于2倍原点传递函数频率时,模态综合法计算误差小于10%;当传递函数频率是截止频率的1/3时,误差可以降低到5%。     

巴塘水电站导流洞平面闸门流激振动试验研究

针对巴塘水电站导流洞动水闭门过程中门体出现振动的问题,根据水弹性和重力相似准则建立比尺为1∶25的物理模型。通过模型试验,对平面闸门在闭门阶段的振动加速度、持住力以及门体应变等参量进行试验测定。试验结果表明:闸门在局开挡水时,水平向最大单倍位移幅值为91.974μm,振动危害较小;结构最大Mises应力值为11.32 MPa,闸门整体应力满足强度要求,平面闸门安全可靠。通过ANSYS Workbench平台对闸门进行模态分析。结果表明:干模态基频为40.05 Hz,湿模态基频为35.40 Hz,闸门挡水时脉动主频在10 Hz以内,与湿模态第1阶频率相差较大,闸门产生共振的可能性较低。本文采取的水弹性模型试验技术能够较好地反映平面闸门的动力特性,能够较为准确地预测和分析闸门的流激振动响应特性,可为类似工程的结构优化设计及运行安全监测提供参考。     

Higher-Order and Modal Logic as a Framework for Explanation-Based Generalization

Certain tasks, such as formal program development and theorem proving, fundamentally rely upon the manipulation of higher-order objects such as functions and predicates. Computing tools intended to assist in performing these tasks are at present inadequate in both the amount of knowledge they contain (i.e., the level of support they provide) and in their ability to learn (i.e., their capacity to enhance that support over time). The application of a relevant machine learning technique—explanation-based generalization (EBG)—has thus far been limited to first-order problem representations. We extend EBG to generalize higher-order values, thereby enabling its application to higher-order problem encodings.Logic programming provides a uniform framework in which all aspects of explanation-based generalization and learning may be defined and carried out. First-order Horn logics (e.g., Prolog) are not, however, well suited to higher-order applications. Instead, we employ Prolog, a higher-order logic programming language, as our basic framework for realizing higher-order EBG. In order to capture the distinction between domain theory and training instance upon which EBG relies, we extend Prolog with the necessity operator of modal logic. We develop a meta-interpreter realizing EBG for the extended language, Prolog, and provide examples of higher-order EBG.     

Modal logic as metalogic

The goal of this paper is to show how modal logic may be conceived as recording the derived rules of a logical system in the system itself. This conception of modal logic was propounded by Dana Scott in the early seventies. Here, similar ideas are pursued in a context less classical than Scott's.First a family of propositional logical systems is considered, which is obtained by gradually adding structural rules to a variant of the nonassociative Lambek calculus. In this family one finds systems that correspond to the associative Lambek calculus, linear logic, relevant logics, BCK logic and intuitionistic logic. Above these basic systems, sequent systems parallel to the basic systems are constructed, which formalize various notions of derived rules for the basic systems. The deduction theorem is provable for the basic systems if, and only if, they are at least as strong as systems corresponding to linear logic, or BCK logic, depending on the language, and their deductive metalogic is not stronger than they are.However, though we do not always have the deduction theorem, we may always obtain a modal analogue of the deduction theorem for conservative modal extensions of the basic systems. Modal postulates which are necessary and sufficient for that are postulates of S4 plus modal postulates which mimic structural rules. For example, the modal postulates which Girard has recently considered in linear logic are necessary and sufficient for the modal analogue of the deduction theorem.All this may lead towards results about functional completeness in categories. When functional completeness, which is analogous to the deduction theorem, fails, we may perhaps envisage a modal analogue of functional completeness in a modal category, of which our original category is a full subcategory.     

偏负荷工况混流式水轮机转轮结构稳定性研究

为探究偏负荷运行工况下混流式水轮机转轮结构稳定性,本文基于单向流固耦合方法,对三种典型偏负荷工况下转轮结构进行了静力学分析和模态分析。结果表明：受不稳定水流影响,80%、60%和40%负荷工况下,较大变形分别位于转轮下环、叶片出水边中部以及叶片迎水刃处中部。预应力对转轮结构影响较少,其导致固有频率增加1 Hz左右;而水介质对转轮结构影响较大,导致固有频率降低15% ~ 36%,且得到转轮固有频率更符合工程实际。受导叶出口处水流扰动影响,转轮结构极有可能发生共振,其振型主要表现为径向、弯曲、弯扭及绕轴旋转变形,其中弯扭变形影响最大,极可能导致叶片断裂。该研究成果可为混流式水轮机柔性运行稳定性,提供一定理论参考。     

考虑寄生参数的隔离型双有源桥DC-DC变换器的开关开路故障分析与容错控制策略

双有源桥(DAB)DC-DC变换器开关管的驱动电路故障导致开关开路故障(OCSF),这使得DAB系统拓扑对称性缺失、高频电压和电流发生畸变和直流偏置,进而对系统的可靠性和长期运行稳定性造成不良影响.对此,研究DAB开关管和高频变压器寄生参数对OCSF后系统运行状态的影响,以完善DAB故障分析体系.针对OCSF问题,提出一种基于对称拓扑和对偶原理的故障容错策略,通过闭锁开关使系统运行拓扑恢复对称,并在此基础上提出一种不改变控制器参数、只需改变控制器输出饱和参数的实用控制方法,并在理论上讨论了该方法的可行性.最后,通过实验验证了OCSF模态分析及所提容错控制策略的正确性.     

The Effects of Random Porosities in Resonant Frequencies of Graphene Based on the Monte Carlo Stochastic Finite Element Model

With the distinguished properties in electronics, thermal conductivity, optical transparence and mechanics, graphene has a powerful potential in nanosensors, nano-resonators, supercapacitors, batteries, etc. The resonant frequency of graphene is an important factor in its application and working environment. However, the random dispersed porosities in graphene evidently change the lattice structure and destroy the integrity and geometrical periodicity. This paper focuses on the effects of random porosities in resonant frequencies of graphene. Monte Carlo simulation is applied to propagate the porosities in the finite element model of pristine graphene. The statistical results and probability density distribution of porous graphene with atomic vacancy defects are computed based on the Monte Carlo finite element model. The results of porous graphene with atomic vacancy defects are compared and discussed with the results of graphene with bond vacancy defects. The enhancement effects of atomic vacancy defects are confirmed in porous graphene. The influences of atomic vacancy defects on displacement and rotation vector sums of porous graphene are more concentrated in local places.     

铜基形状记忆合金马氏体相变宏观形状应变特征

利用X射线衍射仪、透射电镜、扫描电镜、原子力显微镜等研究了Cu-18Al-9Mn-3.4Zn(摩尔分数,%)形状记忆合金的马氏体晶体结构、亚结构以及马氏体相变宏观形状应变特征.结果表明:该合金的马氏体晶体结构为18R结构,亚结构为层错;单变体马氏体表面浮凸呈"( ) "型,浮凸高度为400～500nm,浮凸宽度为2 000～2 400 nm;多变体马氏体表面浮凸呈"N"型和"山尖"型,浮凸高度为200～400 nm,浮凸宽度为1 000～1 800nm;浮凸角均为8°～12°;马氏体相变符合G-T模型的双切变特征,惯习面为(113)面.