Bruising of apples in four different packages using simulated truck vibration

This paper presents the effects of truck vibration and packaging systems on the bruising of apples. The study investigated four different types of interior packaging, the foam tray, the paper pulp tray, and two different paperboard partition/box combinations. Testing was done on a vibration table using a random controller driven by a power density spectrum simulating truck trailers with leaf-spring and air-cushion suspensions travelling on expressways. The results showed that the foam tray was the best type of interior packaging followed by the paperboard partitions. The paper pulp tray produced the highest levels of damage. The air-cushion truck suspension showed larger damage levels than the leaf-spring suspension for all package types.     

Static Design and Finite Element Analysis of Innovative CFRP Transverse Leaf Spring

This paper describes the design and the numerical modelization of a novel transverse Carbon Fiber Reinforced Plastic (CFRP) leaf-spring prototype for a multilink suspension. The most significant innovation is in the functional integration where the leaf spring has been designed to work as spring, anti-roll bar, lower and longitudinal arms at the same time. In particular, the adopted work flow maintains a very close correlation between virtual simulations and experimental tests. Firstly, several tests have been conducted on the CFRP specimen to characterize the material property. Secondly, a virtual card fitting has been carried out in order to set up the leaf-spring Finite Element (FE) model using CRASURV formulation as material law and RADIOSS as solver. Finally, extensive tests have been done on the manufactured component for validation. The results obtained show a good agreement between virtual simulation and experimental tests. Moreover, this solution enabled the suspension to reduce about 75% of the total mass without losing performance.     

悬索桥纵向和竖向耦合自振研究

悬索桥的振动性状中呈现纵飘振动与竖向反对称低阶振动相互耦合的特点。基于挠度理论和能量原理,研究了耦合自振的频率计算方法。首先把加劲梁的单纯纵飘看作单摆振动,得出其等代摆长和振动频率。再结合主缆的竖向反对称低阶振型下的纵向位移特点,建立考虑主缆纵向位移影响的加劲梁纵飘振动的简化计算模型,获得其势能增量的简单表达式。由哈密顿原理,推演了耦合振动频率的计算方法。通过5 座桥梁实例验证,利用该文公式获得的耦合频率和振型形状判定与有限元计算结果吻合良好,表明该文提出的计算方法实用可靠。     

Natural frequencies and critical loads of beams and columns with damaged boundaries using Chebyshev polynomials

The effects of damaged boundaries on natural frequencies and critical loads of beams and columns of variable cross section with conservative and non-conservative loads are investigated. The shifted Chebyshev polynomials are used to solve the one-dimensional transverse vibration problem, in which the ordinary differential equation is reduced to an algebraic eigenvalue problem. The advantages of this method are that it is easily employed in a symbolic form and that the number of polynomials may be adjusted to attain convergence. In the present study, the damaged boundary is modeled by linear translational and torsional springs, and the effects of the damage severity on the natural frequencies are studied. It is shown that as the amount of damage increases the natural frequencies decrease at rates which vary with the mode number. The method is applied to the instability problems of both uniform and uniformly tapered beams with and without follower forces, and the results for the undamaged cases show agreement when compared with results available in the literature. Convergence studies are carried out to determine the number of Chebyshev polynomials that should be used in the proposed method.     

Measurement and analysis of US truck vibration for leaf spring and air ride suspensions,and development of tests to simulate these conditions

There is a significant amount of goods that are transported using tractor trailers. Most high‐value products, such as electronics, highly perishable goods like fruits and vegetables and most retail consumer products, are shipped using trucks in North America. It is therefore important to measure and quantify the levels of vibration that occur inside this mode of transport as it pertains to damage. Vibration levels inside a tractor‐trailer are a function of the road surface, the speed of the vehicle, the type of suspension and the structure of the trailer. The purpose of this study was to determine the levels of vibration as a function of trailer suspension at normal operating speeds in commercially used truck equipment, over 16000km of road surfaces in North America. Copyright © 2006 John Wiley & Sons, Ltd.     

Vibration analysis of laminated composite plates with damage using the perturbation method

The present work focuses on vibration characteristics of damaged laminated composite plates. Damage is considered as a local reduction of anisotropic plate stiffness, and three damage factors (representing the damage severity, damage anisotropy, and damage location/area, respectively) are defined to describe damage status in the laminated composite plates. The analytical solutions are obtained by the perturbation method. A numerical analysis is conducted on the vibration of damaged laminated composited plates, and the effect of damage factors on the vibration characteristics is discussed. Results indicate that three damage factors have different influences on the vibration characteristics. Also, the modal curvatures and strain energy show higher damage sensitivity than the natural frequencies and displacement mode shapes. The perturbation-based vibration analysis developed in this study can be used to effectively evaluate the effect of damage on the vibration behavior of anisotropic plates and potentially identify the damage in the laminated plates.     

一系螺旋弹簧动刚度对车辆-轨道耦合振动影响分析

建立准确表征一系悬挂轴箱螺旋弹簧波动特性的力学模型,运用动刚度矩阵法求解,研究其对悬挂系统隔振性能影响。结合基于格林函数法的车辆-轨道耦合动力学模型,引入弹簧刚度频变特性,对比分析考虑一系螺旋弹簧频变刚度前后车辆动力学性能之间的差异。结果表明,动刚度矩阵法可以精确求解螺旋弹簧随频率变化的动刚度特性,在一阶模态振动频率后弹簧刚度值呈现103等级的剧烈变化,该结果与有限元模型结果一致;一系螺旋弹簧的动态频率特性导致轮轨激励由车轮至构架的振动位移传递率提高到接近于1,而对车体的振动传递率提高到了10-3左右;在整车车辆-轨道动力学计算中,其对轮轨振动影响较小,但车体与构架出现了较高的高频振动能量峰值。包含一系悬挂动刚度的车辆模型更接近实际,为了降低车辆振动,应尽量提高一系螺旋弹簧自振频率并降低动刚度变化幅值。       

Effect of impact failure on the damping characteristics of beam-like composite structures

This study deals with the free vibration response and damping characteristic of a cantilever composite beam having a single impact failure on it. The fundamental vibration frequency of the beam is measured experimentally using a non-contact technique for different failure locations and the damping ratio is calculated from the envelope of the free vibration response. A failure model based on the delamination formation is used in the finite element model of the damaged composite beam to determine the fundamental vibration frequencies. In the finite element modeling, ANSYS APDL language is used to create the composite beam model with different failure sizes and locations automatically. Experimental results show that damping ratio is more sensitive to a failure on the beam than the natural frequency and severity and location of the failure have considerable effects on the damping ratio.     

Effect of impact failure on the damping characteristics of beam-like composite structures

This study deals with the free vibration response and damping characteristic of a cantilever composite beam having a single impact failure on it. The fundamental vibration frequency of the beam is measured experimentally using a non-contact technique for different failure locations and the damping ratio is calculated from the envelope of the free vibration response. A failure model based on the delamination formation is used in the finite element model of the damaged composite beam to determine the fundamental vibration frequencies. In the finite element modeling, ANSYS APDL language is used to create the composite beam model with different failure sizes and locations automatically. Experimental results show that damping ratio is more sensitive to a failure on the beam than the natural frequency and severity and location of the failure have considerable effects on the damping ratio.     

Effects of local damage on vibration characteristics of composite pyramidal truss core sandwich structure

The effects of local damage on the natural frequencies and the corresponding vibration modes of composite pyramidal truss core sandwich structures are studied in the present paper. Hot press molding method is used to fabricate intact and damaged pyramidal truss core sandwich structures, and modal testing is carried out to obtain their natural frequencies. A FEM model is also constructed to investigate their vibration characteristics numerically. It is found that the calculated natural frequencies are in relatively good agreement with the measured results. By using the experimentally validated FEM model, a series of numerical analyses are conducted to further explore the effects of damage extent, damage location, damage form on the vibration characteristics of composite pyramidal truss core sandwich structures as well as the influence of boundary conditions. The conclusion derived from this study is expected to be useful for analyzing practical problems related to structural health monitoring of composite lattice sandwich structures.     

高速列车车下设备模态匹配研究

建立了整备状态车体有限元模型及包含车体弹性的高速列车车辆刚柔耦合动力学模型,分析了车下设备吊挂方式对车体整备状态模态参数的影响,提出车下设备隔振橡胶件参数设计方法,并研究了整备状态下车体与车下设备悬挂模态参数的匹配关系。结果表明,车下设备采用弹性吊挂时,车体整备状态下的模态频率显著提升;合理设置车下设备隔振悬挂参数可有效降低车体弹性振动,算例中,当橡胶件的静挠度设置为8~9 mm时,设备浮沉频率可与车体垂向一阶弯曲频率避开,侧滚频率可与车体菱形变形模态频率避开,有源设备高频振动减振效果理想,车辆可以获得优良的运行平稳性,同时车下设备自身振动亦不剧烈。     

核筒悬挂结构体系自振特性研究

对高层建筑核筒式悬挂结构的动力特性进行了理论与振动台试验研究。推导了相应公式,编制了计算程序Hangsys;在模拟地震振动台上通过正弦波扫描和激振器激励对结构的自振特性进行了试验研究。理论计算和试验结果符合较好。结果表明,核筒悬挂结构具有较低的自振频率,具有良好的抗震性能。     

某型电视机壳体结构动力学分析及改进

利用有限元软件ANSYS,建立长虹SF21366型电视机结构的参数化模型;对该结构的谐响应计算分析发现：电视机壳体结构的频率大多数落在道路能量最集中的080Hz频段,运输中易产生共振损坏。实现对该型电视机壳体结构的局部改进;并对比分析改进前后壳体动态特性参数,证实改进后的壳体结构动态特性优良。为该型电视机降噪设计和控制振动破坏提供理论依据。     

Vibration-dependent morphology and crystal structure of isotactic polypropylene

A small homemade device was used to study the influence of mechanical vibration on the crystal structure and morphology of isotactic polypropylene (iPP) under different melting temperatures, vibration times, vibration frequencies, and cooling rates. The crystallite size, crystal structure, and crystallinity of iPP under or without vibration treatment were investigated by means of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and polarized microscopy observation (PLM). The crystallization of iPP varied with the length of vibration time, vibration frequency, cooling rate, and melt temperature. Compared with the data of conventional samples measured by DSC, vibration could increase the crystallinity of iPP, make melting peak of α-crystal move toward higher temperature and make that of β-crystal shift to lower temperature. Meanwhile, WAXD measurements showed that the vibration could reduce the content of β-crystal evidently, particularly at the lower vibration frequency, lower cooling rate, and higher melting temperature. Furthermore, PLM measurements showed that the vibration made the spherulite size smaller.     

Comparison between lateral,longitudinal, and vertical vibration levels in commercial truck shipments

The widespread use of tractor trailers for the shipment of packaged products has brought about the need to be able to quantify accurately the nature of the shipping environment as it pertains to damage. The purpose of this study was to compare the levels of lateral and longitudinal vibration to vertical levels measured in the same truck trailer travelling over the average USA highway. Four truck-trailer shipments, two with light loads and two with heavy loads, were instrumented with accelerometers and recording equipment. From the data acquired, power spectral density plots were developed. The results showed that below 20 Hz, lateral and longitudinal vibration levels were generally much lower than vertical levels, but at frequencies above 20 Hz, all three were similar. The more heavily loaded trucks showed higher lateral and longitudinal levels of vibration than the lightly loaded ones.     

基于饱和约束LMS算法的磁悬浮隔振器控制研究

研究磁悬浮隔振器的抗饱和减振控制,针对限幅抗饱和法容易激起磁悬浮隔振器共振和Boaz Rafaely抗饱和算法的阈值很难确定,如果阈值选择过大容易激起磁悬浮隔振器共振,如果选择过小则损失减振效果这些问题,提出一种饱和约束处理方法,即加入连续惩罚函数方法。推导相应的改进LMS算法并设计出抗饱和自适应前馈控制律。通过仿真和在磁悬浮隔振器系统上进行实验对比,验证这种方法相对于限幅抗饱和算法和Boaz Rafaely抗饱和算法具有一定的优越性。     

基于Rayleigh法的独塔非对称悬索桥基频简化算法

为了便于计算独塔非对称悬索桥振动基频,采用Rayleigh法分别推导了一阶正、反对称竖弯及扭转振动基频估算公式,考虑了不对称跨径布置对振动基频的影响,并提出了非对称独塔悬索桥合理的跨径比例。将表征跨径关系的参数k取1即可得到独塔双跨对称悬索桥的基频估算公式,最后通过有限元法验证估算公式的有效性和可靠性。研究结果表明:独塔非对称悬索桥一阶正、反对称竖弯、扭转频率的有限元解和文中解的误差都在10%以内,表明推导的估算公式解与有限元解误差能满足设计阶段的要求,最后讨论了跨径相关系数变化对竖弯和扭转基频的影响并给出了合理边中跨比的建议,该公式可以方便指导独塔悬索桥方案设计和动力计算。     

Vibration analysis of size-dependent flexoelectric nanoplates incorporating surface and thermal effects

This article is concerned with the thermo-mechanical vibration behavior of flexoelectric nanoplates under uniform and linear temperature distributions. Flexoelectric nanoplates have higher natural frequencies than conventional piezoelectric nanoplates, especially at lower thicknesses. Both nonlocal and surface effects are considered in the analysis of flexoelectric nanoplates for the first time. Hamilton's principle is employed to derive the governing equations and the related boundary conditions, which are solved applying the Galerkin-based solution. A comparison study is also performed to verify the present formulation with those of previous data. Numerical results are presented to investigate the influences of the flexoelectricity, nonlocal parameters, surface elasticity, temperature rise, plate thickness, and various boundary conditions on the vibration frequencies of thermally affected flexoelectric nanoplate.     

客车异常振动噪声的分析和控制

某款轻型客车样车在90 km/h左右速度行驶时,车厢地板出现剧烈振动并伴随共鸣噪声,严重影响汽车NVH性能。通过试验手段,在五档加速工况对振动频率进行时间跟踪,找到可能的激励源。从三维频谱图识别出车内主要振动和噪声频率与传动轴的1阶和2阶转动频率相同。对此进行加强传动轴支架,支架加橡胶垫和改换悬置为进口悬置的改进。由此可使整车振动噪声水平大幅度降低。     

Vibration characteristics of composite piezoceramic plates at resonant frequencies: experiments and numerical calculations

The experimental measurement of the resonant frequencies for the piezoceramic material is generally performed by impedance analysis. In this paper, we employ an optical interferometry method called the amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) to investigate the vibration characteristics of piezoceramic/aluminum laminated plates. The AF-ESPI is a powerful tool for the full-field, noncontact, and real-time measurement method of surface displacement for vibrating bodies. As compared with the conventional film recording and optical reconstruction procedures used for holographic interferometry, the interferometric fringes of AF-ESPI are produced instantly by a video recording system. Because the clear fringe patterns measured by the AF-ESPI method will be shown only at resonant frequencies, both the resonant frequencies and corresponding vibration mode shapes are obtained experimentally at the same time. Excellent quality of the interferometric fringe patterns for both the in-plane and out-of-plane vibration mode shapes are demonstrated. Two different configurations of piezoceramic/aluminum laminated plates, which exhibit different vibration characteristics because of the polarization direction, are investigated in detail. From experimental results, we find that some of the out-of-plane vibration modes (Type A) with lower resonant frequencies cannot be measured by the impedance analysis; however, all of the vibration modes of piezoceramic/aluminum laminated plates can be obtained by the AF-ESPI method. Finally, the numerical finite element calculations are also performed, and the results are compared with the experimental measurements. Excellent agreements of the resonant frequencies and mode shapes are obtained for both results.