The suppression of low-frequency waves has been a challenging task for acoustic black hole (ABH) because a small truncation of the ABH tip would fail to prevent the transmission of low-frequency waves below the cutoff frequency. Here, we propose a novel approach to achieve perfect ABH to suppress the wave propagation at low frequencies in the range of 3–100[Formula: see text]Hz. Structurally, the perfect ABH consists of two ABHs with rigid materials and a soft material connected between the two ABHs to break the cutoff frequency limit and achieve attenuation of up to 21.3[Formula: see text]dB in the 3–20[Formula: see text]Hz range. The wave energy focusing effect possessed by ABHs, combined with the impedance mutation on the surface where soft and hard materials are connected, can concentrate the wave energy within the soft material, thus achieving a perfect ABH effect. The proposed perfect ABH compensates the defect that ABH cannot suppress low-frequency and sub-low-frequency waves, and provides the possibility of full-band suppression.

In this paper, a ring-slotted spiral local resonant phononic crystal structure is investigated. The energy band characteristics and transmission losses of the structure are calculated using the finite element method. The numerical results show that the structure can generate bandgap in the range of 23.54–102.87 Hz. Combined with the modal coupling theory, the vibrational modes of the ring-slotted spiral local resonant phononic crystal are analyzed to reveal the bandgap formation mechanism of the structure. The effects of the various dimensional parameters and material hardness on the bandgap of the structure are analyzed by varying them. The results show that by varying the filling radius of silicone rubber in the ring-slotted spiral local resonant phononic crystal, the structure can be made to have an onset frequency of 19.42 Hz and generate a bandgap in the range of 19.42–78.16 Hz. A new idea is provided for the application of phononic crystal in low-frequency environment for vibration and noise reduction.

In this paper, the acoustic streaming effects of Sonic Black Hole (SBH) are deeply studied by using the numerical and simulation method. By solving Navier–Stokes equations of compressible fluid, we analyze the flow characteristics of acoustic medium in SBH excited by sound wave, and further discuss the acoustic streaming effects and sound wave capture mechanism of SBH. The phenomenon of simultaneous reduction of medium and high-frequency sound reflection and transmission is analyzed. Under the excitation of medium- and high-frequency sound waves, the interaction between fluid medium flow and SBH structure leads to the uneven internal velocity distribution in the sound propagation direction, which can lead to the phenomenon of sound wave capture and deceleration. For low-frequency sound waves, the velocity distribution of sound medium is uniform, and there is almost no change in velocity gradient, resulting in the uniform distribution of sound pressure without sound absorption. These theoretical and numerical results are in good agreement with the experimental results in the literature, and also verify our results. Finally, by improving the structure, increasing the complexity of sound medium flow and the gradient change in the direction of sound propagation, the sound absorption and insulation ability of the SBH can be further improved. This study reveals the sound transmission mechanism of SBH, which can provide a new idea for the suppression of low-frequency sound waves in SBH.

In acoustic black holes (ABH) at low frequencies, catastrophe sound energy flux behaviour occurs spontaneously if the tip size of the ABHs reaches a critical value. This report demonstrates that this catastrophe behaviour can be quantified by analysing the relative phase transitions using Landau's phase-transition theory. Two catastrophe behaviours corresponding to two stable phases (states) were observed using analytical calculations and a numerical analysis. The sound energy flux was proportional to 3 power laws and square relationships with the tip diameters, respectively. The 3 power law relationships were proved using low-frequency experimental observations. For engineering applications, ABH structures with small tip diameters can isolate more than 11 dB of low-frequency sound waves below 1600 Hz. We associated this cataclysmic phase transition with the geometric structure of the ABHs. (C) 2021 Elsevier Ltd. All rights reserved.

We use numerical and experimental methods to investigate the low frequency sound insulation characteristic of designed thin acoustic black hole (ABH). The numerical results show that the sound energy focusing effect plays a leading role in low frequency sound insulation of designed ABH, and the reflection at the edge of ABH is the main reason of sound insulation in medium and high frequencies. Experimental results display that the Sound Transmission Loss (STL) of the designed ABH is higher than 30 dB below 700 Hz, which shows that the isolated acoustic waves are more than 95%. The low frequency sound insulation performance of proposed ABHs is much better than the traditional acoustic materials, which has great potential applications for low frequency sound insulation.

行星齿轮轮系的类型综合对行星齿轮机构的选型和创新设计有着重要作用,该文采用枚举法得到了全部 7 种含 V结构的单级行星齿轮轮系,对于不含 V 结构的单级行星齿轮轮系,借鉴图论中的拓扑图与邻接矩阵,定义了新的结构不变量——特征向量来表达行星齿轮轮系,提出了改正规则与归一化规则对特征向量进行修正与类型同构识别,得到了不含 V结构单级行星齿轮轮系的 10 种结构类型,并通过实例验证了运用归一化规则进行同构识别的可行性.

行星齿轮轮系的类型综合对行星齿轮机构的选型和创新设计有着重要作用,采用枚举法得到了全部7种含V结构的单级行星齿轮轮系,对于不含V结构的单级行星齿轮轮系,借鉴图论中的拓扑图与邻接矩阵,定义了新的结构不变量——特征向量来表达行星齿轮轮系,提出了利用改正规则与归一化规则对特征向量进行修正与类型同构识别,得到了不含V结构单级行星齿轮轮系的10种结构类型,并通过实例验证了运用归一化规则进行同构识别的可行性.

已知压电振子只有处于共振状态才能保证电能的输出水平,但环境中的振源频率远低于普通压电振子的固有频率.对于两种周期结构悬臂梁,建立其理论模型,分别通过数值仿真软件与有限元软件求解其固有频率.结果 表明,折叠梁的固有频率对梁段数的增加更为敏感,在梁段数较高的情况下折叠梁的固有频率较低,低频俘能性能优于螺旋梁,但是其各阶模态固有频率之间的跨度较大且不平均,能够与环境中振源频率匹配的模态阶数较少,其宽频俘能能力不如螺旋梁.

随着九杆二自由度机构在轻工、包装机械等设备中的广泛应用,研究其预定轨迹的寻迹算法显得尤其重要.以药品包装盒开内盒九杆二自由度机构为研究对象,将其转化为两种八杆单自由度机构,建立相应的运动分析数学模型;通过运动学仿真分析,获得两种八杆单自由度机构的运动区域,得到九杆二自由度机构的运动轨迹与运动范围;再在将机构与工艺轨迹参数化基础上,建立其约束条件,提出了九杆二自由度机构实现预定轨迹的寻迹算法,并通过寻迹算法获得开内盒九杆二自由度机构开内盒运动轨迹的原动件控制参数;最后,对寻迹算法进行完善,并应用获得的控制参数进行运动仿真,验证了寻迹算法的正确性.

为分析出各单元在其他某些单元或分系统失效情况下的可靠度,并建立精确的可靠度模型.应用应力-强度分布干涉理论,并基于马尔可夫链和纯灭模型对行星传动中各重要零件单元的可靠度计算进行了分析,再建立行星轮系统的可靠度模型,推导了系统可靠度计算公式,得出风电机组变桨减速器的纯灭模型可靠度计算结果.实例计算分析表明:运用纯灭模型得到的可靠度,比传统方法更接近实际情况,并能从失效概率直观分析薄弱环节零件及其原因.

Taking the RV reducer as the research object,and considering the influences of the sys-tem stiffness and the eccentric angle of cycloid gear on torsional vibration characteristics,a 13 DOF modified torsional dynamics model was established by lumped-parameter method.The impacts of cy-cloid gear eccentric angle on the natural frequency were analyzed by calculating the natural frequency and corresponding modal shapes of the system.Using the partial derivative method,the sensitivity of natural frequency to moment of inertia and stiffness was calculated.The results show that the key fac-tor influencing the natural frequency is the bearing stiffness.

双级摆线钢球减速器存在偏心质量,在其工作时因其引起的受迫振动是影响该减速器传动性能的主要因素.针对双级摆线铜球减速器,在分析其结构特性与传动原理基础上,推导了其传动比计算公式,分析了不平衡质量对其振动的影响,并构建了双级摆线铜球减速器动力学分析模型,对其弯曲与扭转受迫振动进行了研究.分析结果表明,双级摆线钢球减速器的振动主要是横向弯曲振动,输入轴组件两反相偏心质量旋转时产生的离心惯性力,是造成其横向弯曲受迫振动的主要因素,振动的强弱主要由输入转速和两偏心质量的质径积决定.

We establish 16 DOF nonlinear dynamic equations about helical bevel gear systems, which are used in car axle, and consider time varied meshing stiffness, meshing damping, gear backlash and transmission error. Making the equations dimensionless, Runge-Kutta method is used to solve the dimensionless equations to obtain the time histories. We investigate the influence of gear backlash on the dynamic characteristics of the system. The results provide a theoretical basis for optimization design of the gear system.

In order to improve the precision of the Fluid-Structure Interaction (FSI) calculation results of the torque converter, aiming at the distortion of the grid cell that emerged in the simulation process, a regional meshing method for improving mesh quality of the flow field around the blade is proposed. Based on the FSI, the flow field analysis and structure analysis of the Hydraulic Torque Converter (HTC) are combined by using the fluid-structure interaction platform of ANASYS Workbench. The analysis method and process of fluid-structure interaction are presented. Then, the deformation and stress distribution of blades are determined by combining computational fluid dynamics analysis and structural static analysis. Finally, according to the specific distribution of stress, the blade structure of the HTC is improved. The rationality of the optimization is verified.

基于SIMPLE算法,采用RNG k-ε湍流模型,结合有限体积法对流场的控制方程进行离散,运用ANSYS Workbench软件中的CFX模块和Static Structure模块进行流固耦合模拟,在考虑风力机机舱与塔架的影响下对风力机整机在4种不同风速下的流场特性和风力机运行过程中结构的应力应变进行模拟仿真,与无机舱和塔架情况下的流场特性进行了对比.结果表明:机舱和塔架的存在对流场的特性有明显的影响;叶片的风压分布在叶尖部位比较明显;风力机整机最大应力集中在叶片上距叶根2/3处;在风速增加的情况下,叶根与轮毂连接处的应力有比较明显的增加.

According to the new indexing cam mechanism, the essay intends to study its transmission principle. Based on the analytical method, the essay also constructs a body coordinate system, establishes the profile equation and completes the 3D modeling. A method of calculating the nonlinear assembly modal analysis under critical state has been put forward, and by taking the new indexing cam mechanism as an example, the essay completes the modal analysis to get the linear modal result under two critical states. Therefore, the frequency range and vibration mode of the system can be obtained, which lays a foundation for the dynamics of a novel mechanism.

针对目前国内涂装生产线上存在的工作效率低、油漆利用率不高、工作环境恶劣等问题,从结构设计方面对铝型材喷涂设备进行了分析研究,设计出多喷头漆料真空雾化喷涂室.分析了喷涂室抽风系统中的通风方式并计算了其通风量,探讨了沿程摩擦阻力、局部阻力对风量风压的影响,研究了喷头的位置对喷涂的影响.采用螺旋传动与曲柄滑块机构组合对喷头架传动机构进行设计,来调节喷头的径向移动和角度摆动,实现最佳喷涂效果.最后通过对喷头架结构进行三维建模,运用ADAMS对其进行了运动学仿真分析,结果表明设计方法与结果可信.

A kind of the pressurization device with symmetric two-step orthogonal toggle force amplifier and the disk spring is designed,toggle force amplifier’s form and its working principle are introduced,and the mathematical model is formed by the combination of symmetric two-step orthogonal toggle force amplifier and the disk spring.The self-locking system,using of the application of orthogonal toggle force moving over the critical point of self-locking and force amplifying function,combination of the disk spring without energy consumption condition,can safely keep force in long time,and has obvious energy saving effect.

In view of low efficiency,bad resistance on cavitation property,the curve hump and overload of centrifugal pumps,an objective optimization mathematical model is established. This model sets performance curve without humps and the centrifugal pump without overload as constraint conditions,and is aimed at maximum efficiency and minimum cavitation property allowance. The genetic algorithm is adopted to solve the parameters to avoid the local optimization. And the global optimal result is obtained. Compared with the centrifugal pump of the traditional method,the results show that the efficiency,resistance of cavitation performance and the curve hump all are well improved. And the problem of overload is also solved to provide an important reference to the centrifugal pump's design.

An approach,based on bounded-error estimation via interval analysis,was presented to identify dynamic parameters of LuGre friction model herein.The approach assumed the error of measurement output data of dynamic system with LuGre friction force was bounded.Hence,the problem of parameter idelification can be transformed into that of set inversion,which will be effec-tively solved via interval analysis.The four static parameters of LuGre friction model were estimated using least-square method in sliding regime,which deceased sharply the amounts of parameters iden-tified using interval analysis.In comparison with the traditional estimation methods the main advanta-ges of the proposed method are that,as it is global,it bypasses the problem of initialization.Moreo-ver,the method avoids amount error due to transformation of measurement output data.An identifi-cation example was given to show the correctness and efficiency of the proposed method.