Search

Bicyclists and pedestrians are two large vulnerable groups of road users. Many cities have allowed cyclists to share space with pedestrians on footpaths and off-road paths to reduce conflict with motor vehicles. The risk of bicyclist-pedestrian accidents is also increasing accordingly. Therefore, there is a need to understand the factors that affect the risk of injury in such accidents, especially to pedestrians who are considered more vulnerable. This paper presents a detailed investigation of bicyclist-pedestrian collisions and possible injury outcomes. The study has considered five levels of collision speed ranging from 10 km/h to 30 km/h, three pedestrian profiles (adult, child, and elderly) differentiated by their weight and height, three bicycles with different masses, and five impact directions. The bicyclist-pedestrian collision simulations have been analyzed based on four metrics: throw distance, peak head velocity on impact with the ground, head injury criterion (HIC) value, and the probability of severe head injury. For each simulation, the throw distance and peak head velocity on impact with the ground are extracted. Following that, the HIC and the probability of severe head injury to pedestrians are computed. The results show a significant effect of collision speed (p

The third rail is a critical piece of railway infrastructure that provides a continuous supply of electricity to power mass rapid transit trains. The vibration of the third rail may excite different resonant modes and affect its structural integrity and reliability by degrading the mechanical properties leading to the damaged or missing structural components. This paper examines vibrational characteristics of the third rail of Singapore Mass Rapid Transit system with damaged and missing structural components. Using the mathematical model, the first five, pin‐to‐pin modes of vibration and natural frequencies were identified and compared with modal and harmonic response obtained from ANSYS finite element models. A good agreement was observed between the analytical and numerical solutions. The study was further extended to study the sagging of the third rail due to structural failure and its impact on collector shoes. It was found that the structural defects could produce resonance modes below 5 Hz. In addition, the sagging and contact force on collector shoes increased by multiple folds when more than 2 claw structures are broken. The methods and the results presented in this article can be used as a tool for predictive maintenance by detecting possi-ble structural failure or defects. Published version This research was funded by Singapore Mass Rapid Transit (SMRT), grant number: EIRRARP5 and research works were carried out at SMRT-NTU Urban Rail Corporate Laboratory, NTU Singapore.

This paper describes the methods underlying the development of an online COVID-19 Epidemic Calculator for tracking COVID-19 growth parameters. From publicly available infection case data, the calculator is used to estimate the effective reproduction number, doubling time, final epidemic size, and death toll. As a case study, we analyzed the results for Singapore during the “Circuit breaker” period from April 7, 2020 to the end of May 2020. The calculator shows that the stringent measures imposed have an immediate effect of rapidly slowing down the spread of the coronavirus. After about two weeks, the effective reproduction number reduced to 1.0. Since then, the number has been fluctuating around 1.0.The COVID-19 Epidemic Calculator is available in the form of an online Google Sheet and the results are presented as Tableau Public dashboards at www.cv19.one. By making the calculator readily accessible online, the public can have a tool to meaningfully assess the effectiveness of measures to control the pandemic.

Oil flowlines, the first &ldquo, pipeline&rdquo, system connected to the wellhead, are pipelines that are 5 to 30.5 cm (two to twelve inches) in diameter, most susceptible to corrosion, and very difficult to inspect. Herein, an external corrosion detection sensor for oil and gas pipelines, consisting of a semicircular plastic strip, a flat dog-bone-shaped sacrificial metal plate made out of the same pipeline material, and an optical fiber with Fiber Bragg Grating (FBG) sensors, is described. In the actual application, multiple FBG optical fibers are attached to an oil and gas pipeline using straps or strips or very large hose clamps, and, every few meters, our proposed corrosion detection sensor will be glued to the FBG sensors. When the plastic parts are attached to the sacrificial metals, the plastic parts will be deformed and stressed, thus, placing the FBG sensors in tension. When corrosion is severe at any given pipeline location, the sacrificial metal at that location will corrode till failure and the tension strain is relieved at that FBG Sensor location, and therefore, a signal is detected at the interrogator. Herein, the external corrosion detection sensor and its design equations are described, and experimental results, verifying our theory, are presented.

The maneuverability and compactness of small-wheel and folding bicycles are greatly appreciated. Nonetheless, the performance of these small-wheel bicycles as compared to the big-wheel bicycles has always been questioned. They are often blamed for being less stable, wobbly, or twitchy. It is still unclear how the performance of the small-wheel bicycle designs can be improved. Both small- and big-wheel bicycles are designed with similar ergonomics; therefore, the focus has been on the front steering design. The steering design parameters of 91 big-wheel and 27 small-wheel bicycles were compared, bearing in mind the available front steering design guidelines to understand: (1) the influence of big-wheel bicycle’s frame design on small-wheel bicycles and (2) most common range of design parameters used in current bicycle designs. The analysis showed a strong influence of current big-wheel bicycle design practice on front frame parameter selection of small-wheel bicycles. Furthermore, the self-stability comparison over the most common design range confirmed the lesser stability in the current small-wheel bicycle designs at normal riding speed. However, it was also found that the lesser stability was not the result of small wheels per se, but rather owing to an inadequacy in the current design approach to addressing the complex influence of reducing wheel size and bicycle frame design on its stability and performance. Therefore, an improved design methodology was adopted by incorporating the bicycle dynamics into the current design approach and the front steering design guidelines for small-wheel bicycles have been developed. The guidelines contradict the current small-wheel bicycle design practice, as they recommend steeper headtube angles for small-wheel bicycles. The guidelines were validated with good agreement between the theoretical and experimental results on two prototype 20-inch-wheel bicycles having counter-intuitive steering geometry.

E-scooters are a recent trend and are viewed as a sustainable solution to ease the first and last mile problem in modern transportation. However, an alarming rate of accidents, injuries, and fatalities have caused a significant setback for e-scooters. Many preventive measures and legislation have been put on the e-scooters, but the number of accidents and injuries has not reduced considerably. In this paper, the current design approach of e-scooters has been analyzed, and the most common range of design parameters have been identified. Thereafter, validated mathematical models have been used to quantify the performance of e-scooters and relate them with the safety aspects. Both standing and seated riders on e-scooters have been considered, and their influence on the dynamic performance has been analyzed and compared with the standard 26-in wheel reference safety bicycle. With more than 80% of the accidents and injuries occurring from falling or colliding with obstacles, this paper tries to correlate the dynamics of uncontrolled single-track vehicles with the safety performance of e-scooters. The self-stability, handling, and braking effect have been considered as major performance matrices. The analysis has shown that the current e-scooter designs are not as stable as the reference safety bicycle. Moreover, these e-scooters have been found unstable within the most common range of legislated riding velocity. The results corroborate with the general perception that the current designs of e-scooters are less stable, easy to lose control, twitchy, or wobbly to ride. Furthermore, the standing posture of the rider on the e-scooter has been found dangerous while braking to avoid any disturbances such as potholes or obstacles. Finally, the front steering design guidelines have been proposed to help modify the current design of e-scooters to improve the dynamic performance, hence the safety of the e-scooter riders and the surroundings.

There has been a rapidly growing trend in the use of small-wheeled personal mobility devices (PMDs) such as small-wheeled electric scooters and bicycles for urban mobility in many cities worldwide. However, it is a well-known fact that most of them do not ride as well as conventional big wheel bicycles, and the ride is often described as 'twitchy', 'wobbly' and 'less stable'. A considerable number of casualties involve single-vehicle accidents which can be correlated to their dynamic stability performance. This paper relates the vehicle frame design with safety performance. By using a well-defined mathematical model, the dynamic stability of different personal mobility devices was compared. The research confirms the lesser stability in existing small wheel electric scooters and bicycles. However, the investigation has also found that the reason is not so much the size of the wheel, but the inadequacy of current design practice to properly account for the complex influence of wheel size on stability. Finally, a case study has been presented to illustrate that current designs of small wheel PMDs can be improved for better stability and safety.

The difficulties in riding small wheel bicycles and their lesser stability have been perceived for a long time. Although small wheel bicycles are designed using the similar approach and guidelines that have worked well for big wheel bicycles, the performance of the big wheelers and the smaller wheelers are markedly different. Since both the big wheelers and small wheelers have same fundamental geometry, most blame the small wheel for this discrepancy in the performance. This paper reviews existing guidelines for bicycle design, especially the front steering geometry for the bicycle, and provides a systematic and quantitative analysis of different wheel sized bicycles. A validated mathematical model has been used as a tool to assess the dynamic performance of the bicycles in term of their self-stability. The results obtained were found to corroborate the subjective perception of cyclists for small wheel bicycles. The current approach for small wheel bicycle design requires higher speed to be self-stable. However, it was found that increasing the headtube angle and selecting a proper trail could improve the dynamic performance of small wheel bicycles. A range of parameters for front steering geometry has been identified for small wheel bicycles that have comparable stability as big wheel bicycles. Interestingly, most of the identified geometries are found to be beyond the ISO recommended range and seem to counter the current approach of small wheel bicycle design. Therefore, it was successfully shown that the guidelines for big wheelers do not translate directly to small wheelers, but careful selection of the front geometry could make small wheel bicycles as stable as big wheel bicycles.

High-powered embedded computing equipment using air transport rack (ATR) form-factors is playing an ever-increasing role in aerospace applications. High power and wattage of the electronics and processors require large heat dissipation. Thus more sophisticated, more efficient, and sometimes exotic thermal cooling systems like loop heat pipes or jet impingement systems are demanded. Despite their better thermal performance, these systems are usually more susceptible to mechanically harsh environment where they are deployed. Random vibration is one of the primary excitation sources in aerospace environments where highly efficient cooling systems are used. In this article, a multiple degree of freedom model of an isolated double-chamber jet impingement cooling system is developed, and its response to random vibration is analyzed and compared to that of a traditional single degree of freedom model. Vibration isolation system properties are optimized to minimize the vibration of the internal components of the cooling system, while the whole system enclosure is confined within an allowed rattle space.

High-powered embedded computing equipment using air transport rack (ATR) form-factors are playing an ever-increasing role in critical military applications in air, land and sea environments. High power and wattage of the electronics and processors require large heat dissipation, and thus more sophisticated and efficient thermal cooling systems such as loop heat pipes or jet impingement systems are demanded. However, these thermal solutions are more susceptible to harsh military environments and thus, for proper performance of thermal and electronic equipment, they need to be protected against shock and vibration inherent in harsh environments like those in military applications. In this paper, an isolated ATR chassis including two jet impingement chambers is modeled as a three-degrees-of-freedom system and its response to random vibration and shock has been studied. Both finite element and experimental modal analysis is utilized to characterize dynamics of the components of the jet impingement system. The response of the model is compared to that of the traditional single-degree-of-freedom model, and the isolation system is optimized in terms of its damping.

The actuator of a hard disk drive (HDD) requires a high bandwidth for fast response to achieve higher recording density. The bandwidth is governed by several factors with the main one being the first in-plane natural frequency of the actuator arm. This paper investigates a new design that can achieve higher actuator bandwidth without sacrificing the out-of-plane stiffness. The design is structurally different from a conventional actuator arm (standard HDD single-stage actuator) and achieves improvement in the first in-plane natural frequency.

Many armies are replacing heavy slow tracked vehicles with their lighter wheeled counterparts for their high mobility and better shoot and scoot capabilities. These features make the vehicle hard to track and target in counter-battery fire. However, when firing high calibre guns, spades are needed to connect the vehicle chassis to the ground, so as to transmit parts of the large firing force directly to the ground. Use of spades hinders the vehicle mobility, while elimination of them paves the way for having quicker and more mobile wheeled vehicles. In this article, vibration response of a spade-less High Mobility Multi-purpose Wheeled Vehicle with a mounted mortar is studied and controlled using stock passive, optimised passive, and optimised semi-active dampers as primary suspensions. The spade-less vehicle with optimised passive and semi-active dampers has a better response in heave, pitch, and fore-aft motions and can fire with better accuracy compared to a spade-less vehicle with stock passive dampers. Simulation results indicate that the spades can be removed from wheeled military vehicles if the precautions are taken for the tyres.

The mechanical robustness of HDDs during operational state has become increasingly more important. In this paper the effect of disk clamping conditions on the operational shock response of a hard disk drive is investigated numerically. A finite element model of the hard disk drive is developed in the commercially available finite element package, ANSYSILSDYNA. The overall model includes the head arm assembly (HAA) and the disk. The shock responses of the drive under half-sine acceleration pulses are simulated when the disk is subjected to various clamping conditions. It is found that the shock response of the drive decreases with the more tightly clamped disk.

A model to predict the shock response of a 1.8-inch hard disk drive (HDD) is developed and validated by experiment. The head-actuator assembly (HAA), spindle disk and flexible base are included in the proposed model. The feasibility of modeling the air bearing as linear springs is investigated for HDD operating shock simulation. Result shows that as far as the vibration of the arm-suspension assembly is concerned, the air bearing between the disk and slider can be modeled by linear springs to speed up the simulation. However, if head/disk interface is concerned, the air bearing should not be modeled as linear springs in the studies of head-disk interface.

Airflow-induced noise from high speed hard disk drive (HDD) is first studied experimentally. Three cases involving the HDD in three different configurations are selected to analyze the contribution of airflow-induced noise in the overall noise level. They are (1) motor without HDD top cover and disks, (2) motor without disks but with top cover, and (3) a complete drive. HDD sound power is measured for the three cases individually. The sound power contribution from airflow force is obtained through sound power change calculation. Finally, a methodology is presented to predict airflow-induced noise through boundary element method (BEM).

We propose a model for a hard disk drive (HDD) based on a flexible multibody dynamics formulation. All the main components in the HDD, i.e., the spindle head actuator, spindle disk, and base are considered flexible components connected by bearing joints. The model takes into account nonlinearity and discontinuity caused by the contact between the dimple and flexure. The air bearing force is obtained by solving the Reynolds equation using the finite volume method and considering Intermolecular force. We found that the intermolecular force will lower the flying height. We investigated the effect of the base stiffness on the shock tolerance of the HDD and found that a stiffer base will benefit the increase of the shock tolerance.

A coupled model for simulating the shock response of operational hard disk drives (HDD) is developed. In this model, flexible multi-body dynamics formulation is used to simulate the structure dynamics of the operating HDD while the finite volume method is used to simulate the air bearing dynamics simultaneously. Nonlinearities and discontinuities between the dimple and flexure are considered. Effect of the contact stiffness between the dimple and the flexure on HDD’s shock tolerance is investigated. Results show that the contact stiffness is of critical importance to the shock tolerance of the HDD.

Shock robustness is an increasingly important design consideration for hard disk drives (HDD), as we move forwards toward consumer applications. For a head actuator assembly (HAA), which is the most important mechanical component of an HDD and consists of a cantilever arm fixed onto a pivot bearing, the maximun relative deflection between the tip of the arm and the pivot can be used as an index for its response to shock. The influence of pulse width/duration and pulse amplitude on the shock response of the relative displacement of the actuator arm is first investigated by the finite element method (FEM). The actuator arm is then simplified as a low-damping single-degree-of-freedom (SDOF) system. The shock response of the finite element model and that of the SDOF system are presented. It is found that, for both the finite element simulation and the theoretical analysis, when subjected to half-sine acceleration shock, the peak relative displacement occurs at a critical frequency ratio ( i . e . β = ω / ω n ≈ 0.6 ) , where ω and ω n are the characteristic frequency of the pulse loading and the first natural frequency of the system. In other words, a pseudo-resonance phenomenon occurs at this critical frequency ratio.

This paper reviews recent advances (mostly after year 2000) in shock and vibration analysis of hard disk drives (HDD) considering the presence of nonlinearities and discontinuities. Components and dynamic phenomena in HDD where effects of mechanical nonlinearity and discontinuities are significant are discussed, e.g., head actuator suspension, dimple and slider, head–disk interface, fluid dynamic bearing, spinning disks, and load/unload dynamics. Ways to model these nonlinearities and discontinuities are reviewed in detail. Our research on modeling an entire HDD in operating mode subject to shock and vibration using a flexible multibody dynamics formulation is also presented. The numerical simulation of the shock response of a 1-in. form factor HDD is presented. A half-sinusoidal acceleration shock is applied at the base of the HDD. Response of the flying height for different shock amplitudes and duration times is simulated.

This paper emphasizes the importance of a fast and reliable tool for design parametric studies. Three methods that have been used in studying the shock phenomena in hard disk drives (HDD) are discussed briefly. A more efficient (i.e. faster and reasonably accurate) method is proposed. This new method uses state-space formulation to model the structural components of the HDD and quasi-static concept to model the non-linearity of the air bearing. The structural and the air bearing response, and their coupled interaction are evaluated simultaneously. The computation time and the accuracy of the proposed method are compared against two existing methods: the full finite element model and CML’s HDD dynamics event simulator. The proposed method is found to be much faster with reasonably good accuracy. Experimental shock tests also show that the method is reliable in predicting the shock tolerance of the HDD. A procedure on how to do parametric study with this method is proposed and the effect of overmold and voice coil stiffness on the shock tolerance is studied.

Recent development of the shock analysis on the HDD is briefly reviewed. A flexible multi-body dynamics formulation is developed to simulate the shock response of the HDD. If one component in the HDD is changed, only mode shapes and frequencies of that component should be re-calculated and then used to obtain the system’s response. Steady state Reynolds equation is solved to obtain the air pressure on the slider and disk for various slider positions. An air pressure table is formed and used to model the non-linear air bearing during the simulation. Responses of flying height for different direction and shock duration time are analyzed. Results show that the flying state of the slider is more sensitive to the shock with shorter duration time.

Hard disk drives (HDD) are increasingly being used in mobile applications and consumer electronic devices in potentially harsh dynamic environments. In mission-critical applications such as in computers on board trains and military vehicles, the vibration experienced by the operating HDD can be very severe. An effective suspension system is necessary to isolate the HDD from the strong vibration transmitted from the ground, vehicle engine, etc. This paper gives details on how to design, test and evaluate vibration isolation systems for operating HDD subjected to very severe random vibrations based on military specifications MIL-STD-810E. One design is presented and evaluated based on well-defined criteria. Design principles on how to achieve the required degree of vibration isolation is described. A computer simulation model of an example design is formulated and correlated with experiments. It is shown that a low-cost, vibration isolation system can indeed be made that will allow an HDD to operate well when subjected to strong input vibration.

For a head actuator assembly, its shock dynamic response and damage may be studied and assessed using vertical drop test simulation. The maximum relative deflection between the tip of the arm and the pivot can be used as an index of its response to shock. The pulse width effect on the peak response of the relative displacement of an actuator arm during a drop test was investigated by finite element method. The actuator arm was simplified as a single-degree-of-freedom (SDOF) system. It was found that for both the finite element analysis of the actuator arm, and the theoretical analysis of its simplified model as an SDOF system, when subjected to single half-sine acceleration pulses, the peak values of the maximum relative displacement occured at a certain frequency ratio, i.e., a pseudo-resonance phenomenon.

This paper presents the mathematical models of the spindle/disks–shaft–housing system for vibro-acoustic analysis of hard disk drives operating in idle mode. A complete model of a spindle/disks assembly–shaft–housing system is developed using a multi-body system Lagrangian formulation. The transfer functions between source excitations and induced vibration on the housing are derived. The effect of adding flexibility to the non-spinning components (i.e. housing and shaft) is examined and the model capabilities are demonstrated through parameter studies.

Dropping, striking, or bouncing a hard disk drive (HDD) against a hard surface can damage it internally without external evidence of damage. Contact with a hard ground will lift the slider off the disk surface and then slap back on the surface. A drive that is subjected to this type of shock may fail on initial use or the reliability of the drive may degrade over time. Therefore, industry has a lot of interest on the shock conditions that cause a slider to lift off the disk surface. Finite element software such as ANSYS/LS-DYNA is often used to analyze this shock problem. However, this method consumes a great amount of time. It is also difficult to perform design parameter studies because it requires re-analysis of the model of the entire HDD system when certain design variables are changed. This paper presents a flexible multi-body dynamics formulation to analyze the shock problem of non-operating HDDs. Governing equations of motion of the voice coil motor (VCM)–actuators assembly and the disks–spindle system are derived using a Lagrangian formulation. By introducing constraint equations between the slider and the disk surface, the shock response of the whole HDD system has been obtained. Numerical results show that the method is reasonable and the acceleration amplitude which makes the slider lift off can be determined in a significantly shorter time than by the conventional approach. Finally, the effect of drive parameters on shock resistance, such as shock duration and slider resting location are analyzed.

With the increasing use of electromechanical systems, such as hard disk drives (HDD), CD-Rom drives, and DVD drives in the consumer electronics industry, there is a growing demand for quieter products. The noise emitted from these devices may originate from the vibration of mechanical components in operation, such as bearings, gears, and actuators, etc. The vibration is then transmitted to other parts of the devices, such as cover and basement, etc., and the noise emitted may then be amplified. This paper aims to present an approach to study idle noise, which is an important type of noise in HDD due to spinning. The dynamic characteristics of ball-bearing disks/spindle systems of HDD including flexible stationary structures, such as top cover, shaft, and basement, etc., are analyzed based on a multibody dynamic formulation. The discrete governing equations of motion for the system are derived through the use of Lagrangian equation while elastic deformations of the stationary structures are descri...

This paper presents a flexible multibody dynamics formulation to analyze the vibration of hard disk drives. The formulation is applied in analyzing the vibration of the voice coil motor (VCM)-actuators assembly and the disks-spindle system. There are flexible components as well as rigid bodies in the system. Governing equations of motion of the VCM-actuators assembly and disks-spindle system are derived by using a Lagrangian formulation. Elastic deformations of flexible bodies are described by modal coordinates from a finite-element (FE) formulation. After obtaining the formulations, modal analysis and nonoperating shock response are analyzed. The numerical analyses are significantly faster compared to a full FE approach and is potentially useful when the system requires repeated analysis of the model of the entire system when certain design variables are changed.

This paper presents a feedback control technique applied to flutter of a rotating disk in an enclosure. Rotating disk flutter is an aeroelastic instability induced by the coupling of the disk and the air around the disk. The flutter may occur at high rotation speed and the disk will then vibrate with large amplitude. The control system consists of a sensor to pick up the disk vibrations, and the signals are processed to generate a pressure disturbance in the air inside the enclosure. The instability of the rotating disk is initially analyzed and the disk flutter is observed by calculating the eigenvalues of the disk-enclosure system. The feedback control mechanism is then introduced and the control performance is evaluated based on the control effect on the imaginary parts of the eigenvalues. It is demonstrated that, with a proper combination of the control gain and the phase shift, the feedback control can suppress the disk flutter. The stability map shows that the controller has a large operation region and is therefore robust.

With the increasing use of electro-mechanical systems such as hard disk drives, CD-Rom drives, and DVD drives in the consumer electronics industry, there is a growing demand for quieter products. The noise emitted from these devices may originate from the vibration of mechanical components in operation, such as bearings, gears and actuators. The vibration is then transmitted to other parts of the devices, such as the cover, and the noise emitted may then be amplified. This paper aims to develop a method for identify the acoustic noise emitted from hard disk drive seek process. In order to determine effective noise and vibration control of seek noise during the seek process, we first investigate the dynamic characteristic of the head actuator assembly under the different electrical drive signal using finite element method. In this paper, a bearing stiffness matrix (6 × 6) is adopted and performed using ANSYS element (Matrix 27). Using this method, we can understand the vibro-acoustic characteristics of hard disk drives and their components, and the mechanisms of vibration and sound transmission. Experiments are being conducted to demonstrate its validity through experiments. The method will also enable design optimisation for noise to be carried out at the design stage, before a new product is built, or help guide design changes on an existing device.

With the increasing use of electromechanical microsystems, such as hard disk drives, CD-ROM drives, and DVD drives in the consumer electronics industry, there is a growing demand for quieter products. The noise emitted from these devices may originate from the vibration of mechanical components in operation, such as bearings, gears, and actuators. The vibration is then transmitted to other parts of the device, such as the covers, and the noise emitted may then be amplified. The objective of this article is to find a way to control seek noise in hard disk drives. Piezoelectric actuators are attached to the cover, which are used to excite the cover and suppress noise transmission of the cover of hard disk drives. A controller feedback of vibration observes through piezoelectric sensors and adjusts the voltage inputs to the actuators to minimize the radiated sound level. To get the optimal piezoelectric actuator location, genetic algorithms with immune diversity are adopted. Numerical results show t...

The spring-force factor is a multiple scalar that amplifies (or reduces) the spring force of a road-wheel suspension. The setting of spring-force factors for individual suspensions can change the s...

In this paper, a semi-active control of vehicle suspension system with magnetorheological (MR) damper is presented. At first a MR damper working in flow mode is designed. Performance testing is done for this damper with INSTRON machine. Then a mathematical model, Bouc–Wen model, is adopted to characterize the performance of the MR damper. With optimization method in MATLAB® and experimental results of MR damper, the coefficients of the model are determined. Finally, a scaled quarter car model is set up including the model of the MR damper and a semi-active control strategy is adopted to control the vibration of suspension system. Simulation results show that with the semi-active control the vibration of suspension system is well controlled.

Vibration testing of plastic ball grid array (PBGA) assemblies to assess the reliability of the solder joints under external vibration excitations was reported in this paper. The test vehicle was an assembly with four 256 I/Os PBGA modules assembled on a printed circuit board (PCB). During the test, the assembly was clamped at two opposite sides to a vibration shaker. It was found that the dynamic displacement of the assembly under external out-of-plane sinusoidal vibration excitations was highly nonlinear. In order to determine the reliability of the solder joints, the resistance of each module was continuously monitored during the test. Under an out-of-plane sweep sinusoidal excitation with a constant acceleration amplitude of 2.5 G within a narrow frequency band around the fundamental resonant frequency of the assembly, the first-time-to-failure and mean-time-to-failure of the solder joints were found to be 0.46 and 6.19 million vibration cycles respectively. The failed solder joints were at the corners of the PBGA module. Most failures were due to cracks near the copper pad on the PCB side.

A technique is proposed to inversely determine the material constants of laminated cylindrical shells from transient dynamic displacement responses obtained at only one receiving point on the outer surface of shells. An analytical-numerical method is used for forward calculation that relates the material constants to the displacement responses. A uniform crossover micro-genetic algorithm (uniform µGA) is employed as the inverse operator to determine the material constants of the laminated cylindrical shells. Examples are presented to demonstrate this inverse technique for material characterization of laminated shells. The robustness of the technique to the effect of measurement noise is also investigated. Satisfactory identification results have shown the effectiveness of the present inverse technique as well as its robustness to the given noise added to the input displacement responses.

This paper proposes a feature-based approach for the virtual prototyping of hydraulic systems. It presents a framework which allows the designer to develop a virtual hydraulic system prototype in a more intuitive manner, i.e. through assembly of virtual components with engineering data. The approach is based on identifying the data required for the development of the virtual prototypes, and separating the information into behaviour, structural, and product attributes. Suitable representations of these attributes are presented, and the framework for the feature-based virtual prototyping approach is established, based on the hierarchical structure of components in a hydraulic system. The proposed framework not only provides a precise model of the hydraulic prototype but also offers the possibility of designing variation classes of prototypes whose members are derived by changing certain virtual components with different features.

Generally, the low-cycle fatigue induced by thermal cycling is the major concern in the reliability of surface mount technology for electronic packaging, but the high-cycle fatigue induced by vibration can also contribute significant effect, especially for applications in automobile, military, and avionic industries. To assess vibration induced fatigue failures, the dynamic properties of printed circuit board (PCB) assemblies play a very important role. In this paper, the dynamic properties of a plastic ball grid array (PBGA) assembly were characterized by using experimental modal testing and finite element analysis. The bare PCB and PCB assembly with PBGA modules mounted were tested and analyzed separately, so that the influence of PBGA modules on the PCB’s dynamic properties could be identified. It was found that mounting PBGA modules to PCB increased the stiffness of the PCB. Results of constant-amplitude vibration reliability testing of the PBGA assembly are also reported. It was found that the PBGA assembly was vulnerable to vibration, and fatigue failure always occurred at the corner solder balls of the PBGA module.

A linear magnetorheological (MR) damper, supplied by Lord Corporation, was tested and modeled. Under dynamic conditions, the effects of displacement amplitude, frequency, and magnetic fields on the mechanical properties of MR damper, such as damping force, equivalent-damping capability, were experimentally studied with an INSTRON test machine. A viscoelastic-plastic model is proposed to model the MR behavior. It is shown that the damper response can be satisfactorily predicted with this model.