基于LMS Virtual.lab水稻插秧机变速箱的动力学特性仿真

【目的】研究并改善水稻插秧机变速箱动力总成结构.【方法】结合虚拟样机与动态仿真技术,借助UG和LMS Virtual.lab软件,根据水稻插秧机变速器的拓扑结构及运动关系,建立关于变速箱的多体动力学仿真模型.通过对变速箱齿轮轴系及变速箱壳体的局部柔性化处理,分析了关于变速箱刚柔耦合的多体动力学特性;利用BDF算法获取了虚拟样机在各挡位下参与扭矩传递的仿真速度与理论值的拟合情况,齿轮系统啮合力的频谱特性以及各轴在各阶振动频率下的应力应变分布情况.【结果】在箱体结构设计时要注意,在壳体与壳体的连接部位和壳体与轴承的连接部位适当加强结构强度,同时在固定点位置以及壳体非连接部位可以适当降低结构强度以节省材料.【结论】成功实现水稻插秧机变速箱的动力学建模与仿真.     

EQ 6105 DTAA柴油机连杆的有限元分析

以EQ6105DTAA柴油机连杆为研究对象,对该连杆进行了有限元分析和强度研究。文中详细介绍了连杆载荷和约束条件的处理,并应用了I-DEAS软件对连杆计算模型进行了计算,得出了连杆应力分布图,找出了薄弱环节,为连杆的设计提供了支持。     

EQ 6105 DTAA柴油机连杆的有限元分析

以EQ 6105 DTAA柴油机连杆为研究对象,对该连杆进行了有限元分析和强度研究.文中详细介绍了连杆载荷和约束条件的处理,并应用了I-DEAS软件对连杆计算模型进行了计算,得出了连杆应力分布图,找出了薄弱环节,为连杆的设计提供了支持.     

挖坑机执行机构的动力学分析及仿真研究

采用多体建模的方法简洁地表达了该多体系统方程。运用拉格朗日方程和多体动力学建立了挖坑机动臂、斗杆及钻头的刚性运动微分方程。通过对运动微分方程的推导与求解,对动臂、斗杆及钻头的角速度和角加速度进行了分析。以6T小型挖坑机执行机构为研究对象,在三维建模软件Pro/E中建立了挖坑机几何模型,并导入动力学仿真软件ADAMS,进行了动力学仿真。采用角速度传感器测出了挖坑机空载状态下动臂与斗杆的角速度,仿真结果与试验误差在5%内,验证了模型的准确性。证明了采用多体动力学方法建立的挖坑机的运动方程可以描述挖坑机的各项动力学特性,提供了一种逆方式仿真验证模型的方法,可广泛应用于挖掘机执行机构。     

基于联合仿真技术的整车主动悬架建模及平顺性仿真分析

本文以车辆动力学为理论依据,以多软件联合仿真技术为手段,结合某型轿车的参数,在ADAMS/Car环境中建立了整车多刚体系统动力学模型,并通过ADAMS/Control模块将整车的多刚体动力学模型导入到EASY5环境中,与EASY5环境下建立的主动悬架的液压系统构成了整车主动悬架的系统的动力学模型;在MATLAB/Sirnulink环境下建立了整车的分散模糊控制模型,应用三个软件的联合仿真实现了整车虚拟样机的平顺性仿真.多软件联合仿真技术为主动悬架的建模和仿真提高了新的解决思路.     

汽车麦克弗森滑柱式悬架多刚体模型的建立及仿真

以多刚体系统动力学的拉格朗日方法时汽车麦克弗森滑柱式悬架进行研究,根据结构特点建立其多刚体模型,进行了理论分析和计算机仿真。分析及算例结果表明．所建立的多刚体模型精确,采用的拉格朗日方法易行,仿真精度较高,是汽车悬架精确分析的理想方法。     

顶驱钻井装置吊卡动力学仿真研究

结合对比分析几种顶部驱动钻井装置吊卡结构,提出采用多体系统动力学理论研究顶驱吊卡的动力学特性,利用SolidWorks软件建立液压驱动吊卡三维实体模型,结合COSMOSMotion软件对其进行动力学仿真,为后续的有限元分析奠定基础。     

基于有限元法的农用车辆发动机连杆动静态特性分析

连杆是农业车辆发动机的重要组成部分。由于农业车辆作业强度大,连杆作业过程中其结构、位移及应力变化严重影响作业性能。针对以上问题,本文以某厂生产的内燃机连杆为研究对象,利用三维建模软件NX10.0建立连杆组模型,采用有限元法对连杆杆身、大头轴瓦、小头衬套进行受力分析,并对连杆在自由模态和预应力模态下的动态特性进行了分析。结果表明：连杆受拉伸载荷时最大应力为199 MPa,受压缩载荷时最大应力为230 MPa,且杆身两侧会发生翘曲变形,最大变形量为0.03 mm;在相同的接触条件和约束条件下,自由模态下前10阶振型和预应力下前6阶振型的变形总是在大（小）头处、杆身与两端的过渡处、杆身的中间部位。     

直升机模式下倾转旋翼机多体气弹动力稳定性分析

通过多体动力学方法建立了倾转旋翼机动力学分析模型。结合动力入流，研究了直升机模式下倾转旋翼机非线性非定常气弹耦合动力学特性。集成了非定常动态入流方程与倾转过渡状态的多体动力学方程，建立了倾转旋翼机时域非定常气弹耦合分析模型。以半展长弹性机翼全铰接式倾转旋翼机模型为例，在直升机模式下分析了桨叶摆振刚度及飞行速度对倾转旋翼机气弹稳定性的影响。数值计算表明：建立的多体动力学模型能够快速分析直升机模式下倾转旋翼机复杂的旋翼／机翼气弹耦合动力学特性。     

基于有限元法的农用车辆发动机连杆动静态态特性分析

连杆是农业车辆发动机的重要组成部分,由于农业车辆作业强度大,连杆作业过程中其结构、位移及应力变化严重影响作业性能。针对以上问题,本文以某厂生产的内燃机连杆为研究对象,利用三维建模软件NX10.0建立连杆组模型。采用有限元法对连杆杆身,大头轴瓦,小头衬套进行受力分析。研究表明:连杆受拉伸载荷时最大应力为199Mpa,受压缩载荷时最大应力为230Mpa,且在杆身两侧会发生翘曲变形,最大变形量为0.03mm。对连杆在自由模态和预应力模态下进行了动态特性分析,在设置了相同的接触条件和约束条件下,得到自由模态下前10阶的振型和预应力下前6阶的振型,发现变形总是在大、小头处,杆身与两端的过渡处,杆身的中间部位。本文研究结果为指导连杆组及发动机设计提供理论依据。     

Transformation of a star into a planet in a millisecond pulsar binary

Millisecond pulsars are thought to be neutron stars that have been spun-up by accretion of matter from a binary companion. Although most are in binary systems, some 30% are solitary, and their origin is therefore mysterious. PSR J1719-1438, a 5.7-millisecond pulsar, was detected in a recent survey with the Parkes 64-meter radio telescope. We show that this pulsar is in a binary system with an orbital period of 2.2 hours. The mass of its companion is near that of Jupiter, but its minimum density of 23 grams per cubic centimeter suggests that it may be an ultralow-mass carbon white dwarf. This system may thus have once been an ultracompact low-mass x-ray binary, where the companion narrowly avoided complete destruction.     

Action at a distance along a DNA

A number of ways are known by which an event at one location on a DNA molecule can affect an event at a distant location on the same molecule. Three classes of mechanisms are described for such distal actions: tracking or translocation of a protein along a DNA, the association of two proteins bound at separate sites to form a DNA loop in between, and distal interactions that are affected by the topology of the DNA. The basic characteristics of each type of mechanism are discussed in terms of the known physicochemical properties of DNA. The various modes of action at a distance are often interrelated. Examples include the formation of positively and negatively supercoiled DNA loops by tracking and the strong effects of DNA topology on looping.     

Conversion of a peroxiredoxin into a disulfide reductase by a triplet repeat expansion

Pathways for the reduction of protein disulfide bonds are found in all organisms and are required for the reductive recycling of certain enzymes including the essential protein ribonucleotide reductase. An Escherichia coli strain that lacks both thioredoxin reductase and glutathione reductase grows extremely poorly. Here, we show that a mutation occurring at high frequencies in the gene ahpC, encoding a peroxiredoxin, restores normal growth to this strain. This mutation is the result of a reversible expansion of a triplet nucleotide repeat sequence, leading to the addition of one amino acid that converts the AhpC protein from a peroxidase to a disulfide reductase. The ready mutational interconversion between the two activities could provide an evolutionary advantage to E. coli.     

Development of a receptor on a foreign nerve fiber in a Pacinian corpuscle

When the sensory fiber of a Pacinian corpuscle (in cat mesentery) is transected (at the inferior mesenteric nerve) transduction fails within 30 hours: the nerve ending produces no generator potentials in response to mechanical stimulation. Electrically elicited nerve impulse conduction continues for at least another 18 hours. A transducer mechanism develops on a regenerating nerve fiber when this fiber enters the denervated corpuscle. Such transducer development takes place on myelinated fibers from the inferior mesenteric nerve, which normally supplies corpuscles, as well as on myelinated hypogastric nerve fibers, which normally do not go to corpuscles, including fibers larger than the original corpuscle afferents.     

离散型三维竞争系统中某群体竞争获胜的条件

研究了离散型三维竞争系统的模型结构与稳定性,得到了这类竞争系统中各类平衡点的坐标及其性质,获得了系统在某些边界上的平衡点渐近稳定的充分条件和不稳定的充分条件,并由此得到了系统中的某群体在竞争过程中竞争获胜淘汰所有对手的条件和参与竞争的各个群体永不和谐的充分条件.