Search Results

The design of fast machine tools which offer high manufacturing accuracy by employing high performance axis drives requires careful design not only of the individual components of the machine but of the entire machine structure. The overall consideration of the machine tool with its critical components, such as structure, frame and drives, represents a viable approach to achieving a qualitative improvement with regard to increased dynamics and accuracy. During the conceptual design phase of a machine tool for high-speed machining, special attention has to be given to its structure and frame, since very high inertia loads occur as a result of high accelerations caused by the feed drives. In the case of conventional machines these forces play a secondary role.

The theoretical development of a hybrid finite element method is presented. It combines conventional Finite Element Analysis (FEA) with Energy Finite Element Analysis (EFEA) in order to achieve a numerical solution to mid-frequency vibrations. In the mid-frequency range a system is comprised by some members that contain several wavelengths and some members that contain a small number of wavelengths. The former are considered long members and they are modeled by the EFEA. The latter are considered short and they are modeled by the FEA. The new formulation is based on deriving appropriate interface conditions at the joints between sections modeled by the EFEA and the FEA methods. Since the work presented in this paper constitutes a fundamental step in the development of a hybrid method for mid-frequency analysis, the formulation for one flexural degree of freedom in co-linear beams is presented.

A CAE procedure for modeling the aerodynamic excitation of greenhouse surface vibration and its reradiation as noise is described. The procedure begins with a description of the steady flow over the surfaces. This is used as a basis for estimating the spatially varying unsteady pressure loading. The approach is semi-empirical, utilizing normalized pressure data collected through wind tunnel testing of production vehicles. The unsteady pressures are utilized within a normal mode analysis to predict vibration of the greenhouse panels. Interior noise associated with the panel vibration is estimated from a statistical energy analysis model. We show that contributions of multiple surfaces can be significant.

Over the past two decades, significant work has been accomplished in the development and commercial applications of powertrains fueled by alternate fuels like compressed natural gas, hydrogen, liquefied petroleum gas, and alcohol, etc. These fuels have been proven to be very promising in terms of fuel economy and clean emissions. However, almost no work has been done or reported in terms of the noise and vibration aspects of powertrains being powered by these fuels. In this paper, an attempt has been made to elaborate the noise and vibration behavior of powertrains fueled by various alternate fuels. Some distinct powertrain NVH features due to alternate fuel combustion have been portrayed in detail.*

Brake related warranty costs are a major concern to the automotive industry. Large part of these costs are due to noise, more particularly due to the brake squeal complaints. Computer-aided engineering solutions have attracted a lot of attention from the engineering and development community for more effective brake product development. Recently, three brake squeal analysis methods were implemented on disc type brakes in a vehicle program at Ford. This paper summarizes the results and documents the experience obtained during implementation in the vehicle CAE process.

To reduce warranty cost due to brake squeal and provide guidance for brake design, it is important to understand the contributions of key brake design parameters to brake noise. In this paper, a new technique, which employs the nonlinear transient finite element method as well as Taguchi method, is proposed as a design tool for improving the quality of brake systems. This DOE technique has been implemented to a car program. The final results identified the major parameters associated with the brake noise and also led to an optimal design by selecting appropriate levels of those parameters.

Statistical energy analysis is generally used to study the vibroacoustic response of systems with high modal densities. The most accurate predictions are obtained at high frequencies where the modal overlap is high and many modes contribute to the response in each frequency band. Under these conditions, the vibrational response is fairly uniformly distributed over frequency and over the spatial extent of the SEA subsystems. Validation of an SEA model at high frequencies can be accomplished by comparing the predictions of average subsystem response with an average formed from measured data at a relatively small number of locations. At lower frequencies, where the modal overlap is not high, the vibrational response shows significant variability over both frequency and location. Large variability makes validation of the models more difficult.

Mathematical modelling of the human body is widely used for automotive crash-safety research and design. Simulations have contributed to a reduction of injury numbers by optimisation of vehicle structures and restraint systems. Currently such simulations are largely performed using occupant models based on crash-dummies. These models inherit the apparent differences between dummies and the real human body. Furthermore, crash-dummies are only available for a limited set of body sizes. In order to assess passive safety for different body sizes, a method has been developed to generate models representing subjects of varying anthropometry. This method has been applied to “scale” crash-dummy models towards different body sizes and proportions. As a next step, models of the real human body for impact loading have been developed. A combination of modelling techniques is applied using rigid bodies for most body segments, but describing the thorax as a flexible structure.

In pushing and pulling wheeled objects, the effect of the exerted force on local musculo-skeletal loads depends on the direction of force exertion. Several questions about the direction of force exertion in pushing and pulling, the effects of handle height and force level on force direction, and the quantitative implications for musculoskeletal load, were addressed in the present study. Eight subjects pushed against or pulled on a stationary bar at various handle heights and horizontal force levels, while they were walking on a treadmill. Generally, a significant change towards a more horizontal force direction was observed at increasing handle heights and force levels. From the observed net joint torque values in the shoulder and lumbo-sacral joint it was deduced that local musculoskeletal loads can not be deduced unequivocally from the magnitude of the force required to perform a task.

Overexertion injuries comprise the largest category of nonfatal injuries among construction workers. These injuries typically occur when the biomechanical stresses associated with tasks such as lifting, carrying, pushing, etc., exceed the worker’s strength capacity. Two studies were conducted to measure the whole-body isometric strength capability of 56 construction workers. The first study examined the effect of four typical postures (2 symmetric lifts and 2 asymmetric lifts) associated with scaffold end frame disassembly. The effect of posture on isometric strength capability was significant; the strength capability ranged from 366 N to 676 N. The second study evaluated the effect of hand separation distance (46 cm, 86.4 cm, and 116.8 cm) and vertical hand placement (knuckle, elbow, and acromial heights) on isometric force during symmetric lifting postures. The interaction effect of hand separation distance - vertical hand placement on isometric strength capability was significant.

Owing to the lack of biofidelity in mechanical dummy, the current trend is to utilize anatomic dummy models as a human surrogate in computer simulations involving automobile crash. The lack of biofidelity implies that mechanical dummies cannot adequately express crash injuries, which mainly consist of bone fracture and soft tissue damage. Accordingly, there is a pressing demand for an anatomic human model that can replace mechanical dummies in order to gain insight into the damage mechanisms and help establish tolerance limits for crash injuries.

An electronic measurement system called PCMAN has been developed by the Institute of Ergonomics of the Technische Universität München to carry out body and posture measurements. PCMAN can produce model-like, three-dimensional images of a body quickly, reliably and precisely. The resulting data can be computer-processed using the CAD human model RAMSIS. PCMAN works with several images taken from different directions. From these, three-dimensional coordinates can be calculated by measuring corresponding points on the frames. The RAMSIS grid model can also be fitted into the subject's body measurements and posture. This is done by over-laying RAMSIS on the bitmaps of the subject and adjusting it to the subject's exact shape by changing the body surface and the location of the joints. PCMAN works with standard cameras operating at 25 frames per second.

This study quantitatively analyzed the movement of a driver's upper body in relationship to vehicle motion using Peak Motus, the three-dimensional image processing system. Consequently, this analysis method proved useful and effective in introducing the correlation between driver behavior and vehicle motion with numerical values. It was found that while cornering, the drivers tended to incline their upper bodies to one side against centrifugal force and turn their heads in advance in the direction the vehicle was heading.

For human motion studies, which are to be used for either dynamic biomechanical analyses or development of human motion simulation models, it is important to establish an empirical motion database derived from efficient measurement and well-standardized data processing methodologies. This paper describes the motion recording and data processing system developed for modeling seated reach motions at the University of Michigan's HUMOSIM Laboratory. Both electromagnetic (Flock of Birds) and optical (Qualysis) motion capture systems are being used simultaneously to record the motion data. Using both types of devices provides a robust means to record human motion, but each has different limitations and advantages. The amount of kinematic information (DOFs), external sources of noise, shadowing, off-line marker identification/tracking time, and setup cost are key differences.

Experimental analysis of human motion has been based on optical, magnetic, or electronic tracking techniques to determine body segment locations and orientations. The Average Coordinate Reference System (ACRS) method was developed to reduce experimental errors in human locomotion analysis. Experimentally measured kinematic data is used to conduct analysis in human modeling, and the model accuracy is directly related to the accuracy of the data. However, the accuracy is questionable due to skin movement, deformation of skeletal structure while in motion and limitations of commercial motion analysis systems. In this study, the ACRS method is applied to an optically-tracked segment marker system, although it can be applied to many of the others as well. Many previous studies adopted redundant marker systems, using four or five optical markers, instead of the basic three marker system to provide statistically better results of body segment position and orientation.

The ergonomic design of automobiles has changed over in the last years. It is increasingly being transferred from the usage of two-dimensional templates of the human shape to computer-aided manmodels. So far these models were mainly used for static anthropometric investigations on the drivers workplace. Dynamic questions can be answered only very insufficiently. In the context of this work a methodology was developed to precalculate target directed human movements in a motor vehicle environment with the CAD-manmodel RAMSIS. A new two-piece model was developed. In this model dynamic boundary conditions, so called dynamic restrictions, for any movement in a car are determined, concerning outside parameters. In the following, the entire bodyposture is determined by a statistical posture probability model, considering these dynamic restrictions. A control theory of human movements was derived from the field of neurophysiology.

This paper describes a method for interactive manipulation of digital human models using the Lagrange multiplier method to simulate their motion under the approximation of first order dynamics, where F = mν. This method provides a natural framework for mixing rigid constraints with flexible goals in both Cartesian and joint space. Features like gravity and contact can thus be incorporated according to strict mathematical principles. We have implemented such a system for the specific task of positioning vehicle occupant models. Although the Lagrange multiplier method for solving constrained dynamics is well documented, its utility in this context has not been widely recognised.

Modeling normal human reach behavior is dependent on many factors. Anthropometry, age, gender, joint mobility and muscle strength are a few such factors related to the individual being modeled. Reach locations, seat configurations, and tool weights are a few other task factors that can affect dynamic reach postures. This paper describes how two different modeling approaches are being used in the University of Michigan Human Motion Simulation Laboratory to predict normal seated reaching motions. One type of model uses an inverse kinematic structure with an optimization procedure that minimizes the weighted sum of the instantaneous velocity of each body segment. The second model employs a new functional regression technique to fit polynomial equations to the angular displacements of each body segment. To develop and validate these models, 38 subjects of widely varying age and anthropometry were asked to perform reaching motions while seated in simulated vehicle or industrial workplace.

Data of human body form and shape (static anthropometry) and human motion (dynamic anthropometry) of future operators are important ergonomic factors for workplace design. Although a large amount of static anthropometric data has been collected from different groups by several investigators, relating motion data of the same subjects were not collected. For this reason human form, shape and motion data were collected from 50 subjects performing tasks at two seated console workplaces. In this way new knowledge about movement strategies and the dependence of human motion on human form and shape was obtained. The goal was to make possible the prediction of individual movement behavior based on individual body form and shape while performing specific manual tasks at console workplaces.

In this work a methodological approach for the analysis of the car driver's posture and of the seat performance and functionality is presented. It has been designed to integrate the information from the measurement of the driver's posture and anthropometry with the seat characteristics as described by shape and pressure map. The experimental protocol was applied on eight subjects. The data analysis allows for the definition of some new interesting parameters. An important result is the estimation of the relationship between pressure and interpenetration that represents a predictive model for pressure distribution from the anthropometrical data of the anatomical surface of the back. This should be confirmed by a wider analysis and it could lead to new instruments for the evaluation of seat prototypes.