CALCULATION OF ELASTIC ERROR OF PLANAR MECHANISM—AN EQUIVALENT METHOD

In rigid mechanism dynamic analysis, the equivalence theorem is often used due to its simplicity and perceivability. Based on conjugation and duality between inertia energy storing element and elastic energy storing element, the equivalence theorem is used in elastic error analysis of planar mechanism. A set of calculation formula of elastic error is introduced, and these equations are similar in expression form to the rigid dynamic equation. To demonstrate the method developed, a computation example is given.

Mass‑Spring‑Damping Theory Based Equivalent Mechanical Model for Cylindrical Lithium‑ion Batteries under Mechanical Abuse

An equivalent mechanical model with the equivalent physical meaning of mass-spring-damping is proposed for cylindrical lithium-ion batteries through experiments and theory.The equivalent mechanical model of a cylindrical lithium-ion battery consists of a spring-damping parallel unit.Therefore,a spring-damping parallel unit connecting a damping unit in series is selected to construct the constitutive characteristics of the battery under mechanical abuse.Comparison results show that the equivalent mechanical model can more effectively describe the mechanical properties of the batteries than most cubic fitting models,of which the average relative error of the equivalent mechanical model under different states-of-charge is less than 6.75%.Combined with the proposed equivalent mechanical model,the failure process of the batteries was simulated and analyzed using LS-Dyna and HyperWorks.Under rigid rod tests,failure occurred at the core and bottom of the batteries;under hemispherical punch tests,failure occurred at the core and top,consistent with the experimental results.The average prediction error for the failure displacement under different abuse conditions is less than 4%in the simulations.The equivalent mechanical model requires only a few parameters and can be recognized easily.In the future,the model can be used in safety warning devices based on mechanical penetration.

Dynamic Analysis of Four-Bar Beating-up Mechanism with Joint Clearance

For the four-bar beating-up mechanism of air-jet loom,the plain bearing of linkage is the bearing with dynamic load,and is immersed in the lubricant-box.If the joint clearance is considered,the research on linkage movement could be very complicated.In this paper,the kinematic characteristics of four-bar beating-up mechanism with joint clearance were studied by analyzing the trace of journal center and the balance of radial,tangential forces,and bearing load.The region of principal vibration and its forming causes were discussed.And the results could interpret the measuring curves of four-bar beating-up mechanism completely.

Practical Structural Design Approach of Multiconfiguration Planar Single‑Loop Metamorphic Mechanism with a Single Actuator

As a type of multiconfiguration mechanism that can operate in an under-actuated state,metamorphic mechanisms were proposed more than two decades ago and attracted significant interest.Studies on structural synthesis of metamorphic mechanisms tend to focus more on metamorphic techniques and the structural synthesis of source mechanisms for metamorphic mechanisms.By designing different constraint architectures of metamorphic joints,multistructures can be obtained from the same source metamorphic mechanism.To determine the constraint architectures of metamorphic joints and their different assembly combinations,a kinematic status matrix and a corresponding constraint status matrix are constructed based on the metamorphic cyclogram of a source mechanism.According to the equivalent resistance gradient model and the constraint status matrix,an equivalent resistance matrix for the metamorphic joints is proposed.A structural synthesis matrix of the metamorphic mechanism is then obtained from the equivalent resistance matrix by deducing the constraint form vectors of the metamorphic joints.Furthermore,a kinematic diagram synthesis of the source metamorphic mechanism of a planar single-loop metamorphic mechanism is proposed,which is based on only the 14 one-or zero-degrees-of-freedom linkage groups.The entire structural design method of a metamorphic mechanism is based on the structural synthesis matrix and is presented as a systematic process.Finally,the proposed structural design approach is illustrated by two examples to verify its feasibility and practicality.This study provides an effective method for designing a practical multi-mobility and multiconfiguration planar single-loop metamorphic mechanism with a single actuator.

Development and testing of a detailed kinetic mechanism of natural gas combustion in internal combustion engine

A detailed chemical mechanism to describe the combustion of natural gas in internal combustion （IC） engine has been developed,which is consisting of 233 reversible reactions and 79 species.This mechanism accounts for the oxidation of methane,ethane,propane and nitrogen.It has been tested using IC engine model of CHEMKIN 4.1.1 and experimental measurements.The performance of the proposed mechanism was evaluated at various equivalence ratios （φ=0.6 to φ=1.3）,initial reactor conditions （Tini=500 to 3500 ℃; Pini=1.0 to 10 atm） and engine speed （2000-7000 rpm）.The proposed kinetic mechanism shows good concordances with GRI3.0 mechanism especially in the prediction of temperature,pressure and major product species （H2O,CO2） profiles at stoichiometric conditions （φ=1.0）.The experimental results of measured cylinder pressure,species fractions were also in agreement with simulation results derived from the proposed kinetic mechanism.The proposed mechanism successfully predicts the formation of gaseous pollutants （CO,NO,NO2,NH3） in the engine exhaust.Although there are some discrepancies among each simulation profile,the proposed detailed mechanism is good to represent the combustion of natural gas in IC engine.

Deformation Mechanisms and Safe Drilling Fluids Density in Extremely Thick Salt Formations

Hydrocarbons are very often associated with salt structures. The oil and gas industry is often required to drill along and through long salt sections to reach and recover hydrocarbons. The unique physical properties of salt require special techniques to ensure borehole stability and adequate casing design. This paper assumed that the mechanical behavior of salt is regulated by the magnitude of mean stress and octahedral shear stress and under the influence of different stress conditions the deformation of rock salt can be represented by three domains, i.e. compression domain, volume unchanged domain, and dilatancy domain, which are separated by a stress dependent boundary. In the compression domain, the volume of salt decreases until all microcracks are closed, with only elastic deformation and pure creep; in the volume unchanged domain the deformation is considered steady incompressible flow controlled by pure creep; and in the dilatancy domain the volume of salt increases during deformation due to micro-cracking, causing damage and accelerating ＂creep＂ until failure. This paper presents a hypothesis that the borehole is stable only when the magnitude of octahedral shear stress is below the dilatancy boundary. It gives the design method for determining drilling fluids density, and calculates the closure rate ofborehole with the recommended drilling fluids density. If the closure rate of the borehole is less than 0.1%, the drilling fluids density window can be used during drilling through extremely thick salt formations.

A Precision-Positioning Method for a High-Acceleration Low-Load Mechanism Based on Optimal Spatial and Temporal Distribution of Inertial Energy

High-speed and precision positioning are fundamental requirements for high-acceleration low-load mechanisms in integrated circuit （IC） packaging equipment. In this paper, we derive the transient nonlinear dynamicresponse equations of high-acceleration mechanisms, which reveal that stiffness, frequency, damping, and driving frequency are the primary factors. Therefore, we propose a new structural optimization and velocity-planning method for the precision positioning of a high-acceleration mechanism based on optimal spatial and temporal distribution of inertial energy. For structural optimization, we first reviewed the commonly flexible multibody dynamic optimization using equivalent static loads method （ESLM）, and then we selected the modified ESLM for optimal spatial distribution of inertial energy; hence, not only the stiffness but also the inertia and frequency of the real modal shapes are considered. For velocity planning, we developed a new velocity-planning method based on nonlinear dynamic-response optimization with varying motion conditions. Our method was verified on a high-acceleration die bonder. The amplitude of residual vibration could be decreased by more than 20% via structural optimization and the positioning time could be reduced by more than 40% via asymmetric variable velocity planning. This method provides an effective theoretical support for the precision positioning of high-acceleration low-load mechanisms.

Motion Characteristics Analysis of a Novel Spherical Two-degree-of-freedom Parallel Mechanism

Current research on spherical parallel mechanisms(SPMs)mainly focus on surgical robots,exoskeleton robots,entertainment equipment,and other fields.However,compared with the SPM,the structure types and research contents of the SPM are not abundant enough.In this paper,a novel two-degree-of-freedom(2DOF)SPM with symmetrical structure is proposed and analyzed.First,the models of forward kinematics and inverse kinematics are established based on D-H parameters,and the Jacobian matrix of the mechanism is obtained and verified.Second,the workspace of the mechanism is obtained according to inverse kinematics and link interference conditions.Next,rotational characteristics analysis shows that the end effector can achieve continuous rotation about an axis located in the mid-plane and passing through the rotation center of the mechanism.Moreover,the rotational characteristics of the mechanism are proved,and motion planning is carried out.A numerical example is given to verify the kinematics analysis and motion planning.Finally,some variant mechanisms can be synthesized.This work lays the foundation for the motion control and practical application of this 2DOF SPM.

Simulation and Analysis of Spatial Weft Insertion Mechanism Considering Flexibility and Clearance

A 3D model of the spatial four-bar weft insertion mechanism was built with unigraphics NX(UG) according to the actual requirement,and dynamics simulation was carried out by importing the model into ADAMS.Without considering the clearance,the motion characteristic curve of the sword belt was generated through ADAMS combined with MATLAB.In this paper the hinge between the rod and the sector gear was selected as an example with different values of clearance,outputting the motion characteristic curve of the sword belt.Finite element analysis(FEA)was conducted,the flexible body was generated by importing the forked frame into ANSYS,and flexible dynamics simulation was carried out by importing the flexible body into ADAMS to replace the rigid rod.A comprehensive comparison of the output characteristics of the sword belt was conducted in the consideration of the clearance or flexible.Analysis of the force on the left hinge of the rod was carried out with the ADAMS post processing module.With the same clearance,considering the flexibility,amplitude of fluctuation of the force on the hinge increased obviously.

A new method of characterizing equivalent strain for equal channel angular processing

In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new approach to characterize the equivalent strain was proposed. The results show that there exists better accordance between mechanical property （such as hardness or strength） and equivalent strain after rolling and ECAP in a certain range of deformation amount, and Gauss equation can be satisfied among the equivalent strain and the mechanical properties for ECAP. Through regression analysis on the data of hardness and strength after the deformation, a more generalized expression of equivalent strain for ECAP is proposed as：ε=k0exp[-（k1M-k2）^2], where M is the strength or hardness of the material, k1 is the modified coefficient （k1∈ （0, 1））, ko and k2 are two parameters dependent on the critical strain and mechanical property that reaches saturation state for the material, respectively. In this expression the equivalent strain for ECAP is characterized novelly through the mechanical parameter relating to material property rather than the classical geometry equation.

Distributed Energy Saving Mechanism Based on CoMP in LTE-A System

To reduce the energy consumption of the LTE-A system,a distributed energy-saving mechanism based on Co MP(Co MPDESM) is proposed to solve the inadequate coverage problem under the dormant cells.First,the network is divided into clusters based on the equivalent cell principle.Then,we transfer global optimization into a group of subproblems.Second,a joint processing-based cooperative cell selection model is constructed to determine cooperative cells and dormant cells.Third,the compensative cells with a determined threshold are selected to control users' access.Finally,a simulation is implemented in Matlab.Results show that the energy-saving rate can reach 36.4% and that the mechanism meets the network coverage requirement.Thus,joint processing can be effectively applied in an energy saving mechanism and used to improve the network performance of edge users without increasing transmission power.

COMPRESSIVE COMMINUTION MECHANISM OF PARTICLE BEDS

Granular material mechanics,finite element analysis and crushing theory are applied to study the compressive comminution mechanism of particle beds in this paper.This is a new method by which we have established an equivalent model of granular material,determined the values and distributions of contact forces and discovered a crushing law.The model has been tested on the newly designed equipment and proved to be correct.Some new characteristics and laws of compressive comminution of particle beds have been found.

A Hand Prosthesis with an Under-Actuated and Self-Adaptive Finger Mechanism

One of the major problems faced by hand amputees is the unavailability of a lightweight and powered multi-functional hand prosthesis. Under-actuated finger designs play a key role to make the hand prosthesis lightweight. In this paper, a hand prosthesis with an under-actuated and self-adaptive finger mechanism is proposed. The proposed finger is capable to generate passively different flexion/extension angles for a proximal interphalangeal (PIP) joint and a distal interphalangeal (DIP) joint for each flexion angle of metacarpophalangeal (MCP) joint. In addition, DIP joint is capable to generate different angles for the same angle of PIP joint. Hand prosthesis is built on the proposed finger mechanism. The hand prosthesis enables user to grasp objects with various geometries by performing five grasping patterns. Thumb of the hand prosthesis includes opposition/apposition in addition to flexion/extension of MCP and interphalangeal (IP) joint. Kinematic analysis of the proposed finger has been carried out to verify the movable range of the joints. Simulations and experiments are carried out to verify the effectiveness of the proposed finger mechanism and the hand prosthesis.

Design and Kinematics Analysis of a Parallel Mechanism to be Utilized as a Luggage Door by an Analogy to a Four – Bar Mechanism

In this study, a luggage door mechanism to be used in commercial vehicles such as midibuses and buses is designed and analyzed. The mechanism is designed as a parallel hinged system. Velocities, rotational veloci- ties and rotational accelerations of selected points on the design are calculated. Furthermore, the experiment- tal model of the design is established and it is seen that the data taken from the model are compatible with the calculated results. The aim of this study is to design a mechanism with the minimal workspace so that the door can be utilized in narrow areas and the ergonomics of the luggage door is improved. Considering both commercial and passenger vehicle sales, vehicle interior and exterior trim features have an exceptionally important role in automotive industry, in addition to vehicle performance characteristics. In today’s compete- tive environment, parts used in a vehicle’s internal and external trim have to meet user demands in terms of ergonomics as well as aesthetics. Due to its similarity to a four-bar mechanism, kinematics analysis of the design was carried out based on a four-bar mechanism, which is used extensively in industry.

The Analysis of Link Mechanism and Its Programming Realization

This paper introduces realization method of kinematics analysis for the planar four bar mechanism based on the MFC. A mathematicat model is established by a simple and effective method, using the computer simulation technology can the dynamic demonstration mechanism taotion and automatic drawing trajectory curve of arbitrary point on the connecting rod, and can output various motion displacement, speed and acceleration diagram. The paper provides a simple way for motion analysis of planar four link.

The Kinematics Analysis of Heald Selecting Mechanism of Rotary Electronic Dobby

In order to improve the reliability of the mechanical movement of the rotary electronic dobby, the kinematics analysis of the heald selection mechanism is carried out and the simulation is carried out with Matlab. Firstly, the operation mechanism of the heald selection mechanism is analyzed in detail. The conjugate cam is mapped. The cam profile curve is fitted with cubic spline interpolation. Secondly, based on the overall analysis method and the complex vector method, the kinematics analysis of the key components after the high pair low generation is performed, and the angular displacement and angular velocity of each component are calculated with the rotation of the active cam. Finally, the movement curve diagram is drawn with Matlab, which lays the foundation for the dynamic analysis and in-depth study of the selection mechanism in the future.

城乡等值化视角下旅游驱动乡村治理的理论逻辑与作用机制

乡村旅游是乡村振兴的重要路径,而乡村治理又是乡村振兴的核心内容.通过旅游驱动乡村治理已在实践层面和理论研究中受到持续关注,但是对其理论逻辑和作用机制的探究还有待深化.该文基于城乡等值化视角,分析旅游驱动城乡要素流动改善乡村治理的理论逻辑和作用机制.研究发现:1)乡村旅游能够打破乡村治理的边界,桥接城乡要素的流动,通过促进城乡要素的双向循环流动来推动乡村治理;2)在城乡等值化背景下,乡村旅游通过调整土地、人才、资本、文化、生态、技术等城乡要素的流动状态,在乡村治理层面形成响应,进而助推达成乡村经济、社会、文化、生态、政治等多元治理目标;3)应根据乡村旅游发展实际,将其置于城乡协调发展的整体框架下,旅游驱动乡村治理的积极贡献才能最大地发挥出来.

基于STFT-AOK的星箭力学环境等效频谱分析

星箭力学环境的频谱特性研究对于力学试验环境条件设计非常重要。工程上通常基于冲击响应谱变换获得力学环境参数等效频谱,然而该方法受稳态放大系数Q取值的影响较大。为此,文章提出一种基于短时傅里叶变换–自适应优化核函数(STFT-AOK)融合技术的星箭力学环境等效频谱分析方法。研究结果表明:STFT-AOK方法可在AOK准确定位频率成分和瞬态特征时频区域的基础上,结合STFT的准确幅值,构造出频率分辨率高且幅值准确的时频分布,实现力学环境等效频谱的有效获取,适用于各种复杂瞬态星箭力学环境参数的频谱分析。

“双曲线”型煤样承载力学特性试验研究

煤炭地下气化结束后,两气化炉间形成类“双曲线”形煤柱,支撑覆岩,保障气化区域安全稳定。为研究类“双曲线”形煤柱承载力学特性,基于声发射监测系统和XTDIC三维全场应变测量系统,开展了不同侧向拱高(h=0,3,7,10,13,17 mm)的6组“双曲线”形煤样单轴压缩试验,分析了h对煤样峰值载荷、变形破坏及声发射特征的影响,揭示了其承载破坏机制。结果表明:①“双曲线”形煤样可分为矩形结构(主要承载体)和侧向拱结构,其承载破坏机制与其受力形式、侧向拱结构有关;随着h增大,煤样承载能力降低,与h=0煤样相比,峰值载荷分别降低了7.66%,13.56%,26.83%,35.28%,62.75%。②随着h增大,煤样整体受力形式由以受压为主向受压–受弯曲转变,中部区域产生应力集中而形成薄弱区,对应的水平位移场向中部迁移,最终汇集于中部边缘处;而垂直位移场由水平条带状向倾斜条带状转变,最终集中于煤样侧向拱结构上端。③在轴向载荷作用下,煤样侧向拱结构对其矩形结构中部区域产生等效作用力,加之煤样非均质性影响,加剧了薄弱区损伤程度,该作用随着h增大而增强,煤样承受载荷未超过其抗拉强度即产生剪切破坏,其破坏模式由拉–剪混合破坏向剪切破坏转变,均伴随着不同程度的剥落和局部弹射破坏。④煤样声发射累计计数–时间曲线演化可分为3种类型,当h为0和3 mm时,分为“上凸”式增长、相对快速增长、快速增长、“突变”式增长4个阶段,其演化特征与常规煤岩试样一致;当h为7 mm和10 mm时,分为相对快速增长、快速增长、“突变”式增长3个阶段;当h为13 mm和17 mm时,分为快速增长和“突变”式增长2个阶段;峰后阶段均呈“突变”式增长,而峰前阶段增长形式不一致是由煤样裂纹稳定扩展和中部区域持续损伤共同导致的。

底部双排配筋单孔空心预制梁力学性能试验研究

为了研究新型装配式单孔空心预制梁的抗弯承载力和变形性能,并提高其工作性能。试验共设计并制作了3根单孔空心预制梁和1根实心预制梁,通过试验和理论计算相结合的分析手段,重点研究单孔空心预制梁和实心预制梁的破坏机理、裂缝发展、荷载-挠度曲线、变形性能及抗弯承载力等。结果表明:单孔空心预制梁与普通实心预制梁的破坏特征相似,且其裂缝分布较均匀、间距小,延性好;在相同荷载作用下,单孔空心预制梁挠度大于实心预制梁,其整体受力变形性能相对优越。提出了截面有效面积等效法和混凝土轴心抗压强度等效法2种计算方法,通过对比分析发现,混凝土轴心抗压强度等效法计算值误差仅为0.82%,满足工程要求,而且单孔空心预制梁与实心梁相比还可节约材料8.72%。因此,单孔空心预制梁具有良好的应用前景。