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Viewing 1 to 30 of 36
2009-06-09
Journal Article
2009-01-2301
Rajeev Penmatsa, Rajankumar Bhatt, Kimberly Farrell, Brent Rochambeau, Carl Fruehan, Uday Verma, Steven Beck, Karim Abdel-Malek
This paper describes an effective integrated method for estimation of subject-specific mass, inertia tensor, and center of mass of individual body segments of a digital avatar for use with physics-based digital human modeling simulation environment. One of the main goals of digital human modeling and simulation environments is that a user should be able to change the avatar (from male to female to a child) at any given time. The user should also be able to change the various link dimensions, like lengths of upper and lower arms, lengths of upper and lower legs, etc. These customizations in digital avatar's geometry change the kinematic and dynamic properties of various segments of its body. Hence, the mass and center of mass/inertia data of the segments must be updated before simulating physics-based realistic motions. Most of the current methods use mass and inertia properties calculated from a set of regression equations based on average of some population.
1998-09-29
Technical Paper
982324
Y. G. Lee, C. S. Yu, P. W. Green, L.-D. Chen, P. B. Butler
One-sixth scale model airbag modules have been used to investigate flow aspiration effects in passenger-side airbag modules. A similarity analysis between flows in the model and the prototype unit assures reasonable approximation of the actual flows. In the controlled flow environment of the model, flow visualization suggests that the underexpanded jet structure follows the universal relationship based on experimental data and shows that aspiration occurs through the aspiration holes. Detailed velocity measurements provide the ratio of the mass added to the discharged gas for a single firing. The same approaches can be applied in the design of full-scale airbag systems.
2005-06-14
Technical Paper
2005-01-2710
Hyung Joo Kim, Emily Horn, Jasbir S. Arora, Karim Abdel- Malek
New methods for fast, adaptive motion prediction of a virtual human are proposed and tested. An optimal locomotion for gait-driven motions like pushing, climbing and pick-up/delivery are sought through gradient-based optimization and inverse-dynamics. Such gait-driven motion can be produced by adapting the normal gait motion to the case when a characteristic force is applied, which is called an applied force. The applied force is a resistance force for pushing case and an object weight for delivery case. The concept of the zero moment point is modified to assess the dynamic equilibrium of the motion in presence of the applied force. For fast calculation, analytical forms of the cost/constraint gradients are provided. Stepping patterns are specified a priori to ensure the continuity of the cost/constraint function gradients. Also, by varying knots for the B-spline curve approximation, the gait stage durations are optimized.
2005-06-14
Technical Paper
2005-01-2717
Joo H. Kim, Karim Abdel-Malek, Jingzhou Yang, Kimberly Farrell, Kyle Nebel
This paper presents an optimization-based algorithm for simulating the dynamic motion of a digital human. We also formulate the metabolic energy expenditure during the motion, which is calculated within our algorithm. This algorithm is implemented and applied to Santos™, an avatar developed at The University of Iowa. Santos™ is a part of a virtual environment for conducting digital human analysis consisting of posture prediction, motion prediction, and physiology studies. This paper demonstrates our dynamic motion algorithm within the Santos™ virtual environment. Mathematical evaluations of human performance are essential to any effort to compare various ergonomic designs. In fact, the human factors design process can be formulated as an optimization problem that maximizes human performance. In particular, an optimal design must be found while taking into consideration the effects of different motions and hand loads corresponding to a number of tasks.
2005-06-14
Technical Paper
2005-01-2691
Q. Wang, Y.-J. Xiang, H.-J. Kim, J. S. Arora, K. Abdel-Malek
Simulating human motion is a complex problem due to redundancy of the human musculoskeletal system. The concept of task-based motion prediction using single- or multi-objective optimization techniques provides a viable approach for predicting intermediate motions of digital humans. It is shown that task-based motion prediction is in fact a numerical optimal control problem. Alternative formulations for simulation of human motion are possible and can be solved by modern nonlinear optimization methods. Three techniques based on state variable elimination, direct collocation and differential inclusion are presented and compared. The basic idea of the formulations is to treat different combinations of the state variables, such as the joint profiles and torques or their parametric representations as independent variables in the optimization process.
2005-06-14
Technical Paper
2005-01-2688
S. Rahmatalla, H. J. Kim, M. Shanahan, C. C. Swan
The effect of restrictive clothing on functional reach and on balance and gait during obstacle crossing of five normal subjects is presented in this work using motion capture and stability analyses. The study has shown that restrictive clothing has considerably reduced participants' functional reach. It also forced the participants to change their motion strategy when they cross-higher obstacles. When crossing higher obstacles, the participants averted their stance foot, abducted their arms, flexed their torso, used longer stance time, and increased their hip angle in the medial-lateral (Rolling) and vertical (Yawing) directions. The stability analysis of a virtual human skeletal model with 18 links and 25 degrees of freedom has shown that participants' stability has become critical when they wear restrictive clothing and when they cross higher obstacles.
2005-06-14
Technical Paper
2005-01-2692
Jason C. Olmstead Muhs, Jingzhou Yang
This paper presents a path prediction model for obstacle avoidance. A geodesics model is used to obtain the desired path in Cartesian space. The distance between the start target point (and end target point) and the surface of an obstacle is minimized to determine the boundary points of a geodesic across the surface of the obstacle. The model then numerically solves for a geodesic curve between the two boundary points of the geodesic on the surface of the obstacle. The model offsets the resulting discrete points on the geodesic in the positive normal direction (outside of the obstacle) to form a path of motion around the obstacle.
2005-06-14
Technical Paper
2005-01-2739
Tariq Sinokrot, Jingzhou Yang, Rebecca Fetter, Karim Abdel-Malek
Workspace is an important function for human factors analysis and is widely applied in product design, manufacturing, and ergonomics evaluations. This paper presents the workspace analysis and visualization for Santos™ upper extremity, a new virtual human with over 100 DOFs that is highly realistic in terms of appearance, behavior, and movement. Jacobian Rank deficiency method is implemented to determine the singular surfaces. The joint limits are considered in this formulation; three types of singularities are analyzed. This closed-form formulation can be extended to numerous different scenarios such as different percentiles, age groups, or segments of body. A realtime scheme is used to build the workspace library for Santos™ that will study the boundary surfaces off-line and apply them to Santos™ in the virtual environment (Virtools®). To visualize the workspace, we develop a user interface to generate the cross section of the reach envelope with a plane.
2005-06-14
Technical Paper
2005-01-2727
Esteban Peña Pitarch, Jingzhou Yang, Karim Abdel-Malek
This paper presents a SANTOS™ 25 degree-of-freedom (DOF) hand model and the forward and inverse kinematic analysis. The Denavit-Hartenberg (D-H) method is used to define the position of the end- effector (fingertip). In the SANTOS™ hand model each finger has different constraints and movements (e.g., the middle finger in distal Interphalangeal (DIP) joint can move in Flexion/Extension (F/E) with a range 0–100 degrees, and the thumb in interphalangeal (IP) joint can rotate in F/E with arrange of 15H/80). Including hand model SANTOS™ has over 100 DOFs and the forward and inverse kinematics have been studied. Optimization-based dynamic motion prediction will be used to consider different gestures for hand grasping.
2007-04-16
Technical Paper
2007-01-0551
Kyung K. Choi, Yoojeong Noh, Liu Du
Reliability-based design optimization (RBDO), which includes design optimization in design space and inverse reliability analysis in standard normal space, has been recently developed under the assumption that all input variables are independent because it is difficult to construct a joint probability distribution function (PDF) of input variables with limited data such as the marginal PDF and covariance matrix. However, since in real applications, it is common that some of the input variables are correlated, the RBDO results might contain a significant error if the correlation between input variables for RBDO is not considered. In this paper, Rosenblatt and Nataf transformations, which are the most representative transformation methods and have been widely used in the reliability analysis, have been studied and compared in terms of applicability to RBDO with correlated input variables.
2004-06-15
Technical Paper
2004-01-2172
Zan Mi, Kim Farrell, Karim Abdel-Malek
A general methodology and associated computational algorithm for predicting realistic postures of digital humans (mannequins) in a virtual environment is presented. The basic plot for this effort is a task-based approach, where we believe that humans assume different postures for different tasks. The underlying problem is characterized by the calculation (or prediction) of the joint displacements of the human body in such a way to accomplish a specified task. In this work, we have not limited the number of degrees of freedom associated with the model. Each task has been defined by a number of human performance measures that are mathematically represented by cost functions that evaluate to a real number. Cost functions are then optimized, i.e., minimized or maximized subject to a number of constraints. The problem is formulated as a multi-objective optimization algorithm where one or more cost functions are considered as objective functions that drive the model to a solution.
2008-04-14
Technical Paper
2008-01-0603
Jie Zhang, Yunqing Zhang, Liping Chen, Jingzhou Yang
Active steering systems can help the driver to master critical driving situations. This paper presents a fuzzy logic control strategy on active steering vehicle based on a multi-body vehicle dynamic model. The multi-body vehicle dynamic model using ADAMS can accurately predict the dynamic performance of the vehicle. A new hybrid steering scheme including both active front steering (applying an additional front steering angle besides the driver input) and rear steering is presented to control both yaw velocity and sideslip angle. A set of fuzzy logic rules is designed for the active steering controller, and the fuzzy controller can adjust both sideslip angle and yaw velocity through the co-simulation between ADAMS and the Matlab fuzzy control unit with the optimized membership function. To ensure the design of high-quality fuzzy control rules, a rule optimization strategy is introduced.
2008-04-14
Journal Article
2008-01-0600
Yunqing Zhang, Chaoyong Tang, Wei Chen, Liping Chen, Jingzhou Yang
A robust design procedure is applied to achieve improved vehicle handling performance as an integral part of simulation-based vehicle design. This paper presents a hybrid robust design method, the robust design process strategy (RDPS), which makes full use of the intense complementary action of characteristics between the Response Surface Methodology (RSM) and the Taguchi method, to get the robust design of the vehicle handling performance. The vehicle multi-body dynamic model is built in the platform that is constructed by the software of iSIGHT, ADAMS/CAR, and MATLAB. The design-of-experiment method of the Latin Hypercube (LHC) is used to obtain the approximate area values, and then the RDPS is utilized to achieve improved vehicle handling performance results. The validation is made by the Monte Carlo Simulation Technique (MCST) in terms of the effectiveness of the RDPS in solving robust design problems.
2006-04-03
Technical Paper
2006-01-0696
Jingzhou Yang, Tariq Sinokrot, Karim Abdel-Malek, Kyle Nebel
Human performance measures such as discomfort and joint displacement play an important role in product design. The virtual human Santos™, a new generation of virtual humans developed at the University of Iowa, goes directly to the CAD model to evaluate a design, saving time and money. This paper presents an optimization-based workspace zone differentiation and visualization. Around the workspace of virtual humans, a volume is discretized to small zones and the posture prediction on each central point of the zone will determine whether the points are outside the workspace as well as the values of different objective functions. Visualization of zone differentiation is accomplished by showing different colors based on values of human performance measures on points that are located inside the workspace. The proposed method can subsequently help ergonomic design.
2006-04-03
Technical Paper
2006-01-0697
J. Yang, T. Marler, S. Beck, J. Kim, Q. Wang, X. Zhou, E. Pena Pitarch, K. Farrell, A. Patrick, J. Potratz, K. Abdel-Malek, J. Arora, Kyle Nebel
This paper presents new capabilities of the virtual-human Santos™ introduced last year. Santos™ is an avatar that has extensive modeling and simulation features. It is a digital human model with over 100 degrees-of-freedom (DOF), where the hand model has 25 DOF, direct optimization-based method, and real-human like appearance. The newly developed analysis includes (1) a 25-DOF hand model that is the first step to study hand grasping; (2) posture prediction advances such as multiple end-effectors (two arms, two arms + head + legs), real-time inverse kinematics for posture prediction for any points, vision functionality; (3) dynamic motion prediction with external loads; and (4) musculosteletal modeling that includes determining muscle forces, and muscle stress.
2006-04-03
Technical Paper
2006-01-1488
Yong-Sheng Zhao, Li-Ping Chen, Yun-Qing Zhang, Jingzhou Yang
Due to the influence of non-linear dynamic characteristic of clutch, time-delays, external disturbance and parameter uncertainty, it is difficult to control the automated clutch precisely during the engaging process of the automated clutch for automatic mechanical transmission (AMT) vehicles. Here, an enhanced fuzzy sliding mode controller (EFSMC) has been proposed to control the automated clutch. To meet the real-time requirement of the automated clutch, the region-wise linear technology is adapted to reduce the fuzzy rules of the EFSMC. The simulation results have shown that the proposed controller can achieve a higher performance with minimum reaching time and smooth control actions. In addition, it shows that the controller is effective and robust to the parametric variation and external disturbance.
2008-06-17
Journal Article
2008-01-1932
Joo H. Kim, Yujiang Xiang, Rajan Bhatt, Jingzhou Yang, Hyun-Joon Chung, Amos Patrick, Anith J. Mathai, Jasbir S. Arora, Karim Abdel-Malek, John P. Obusek
We propose an algorithm of predicting dynamic biped motions of Santos™ human model. An alternative and efficient formulation of the Zero-Moment Point (ZMP) for dynamic balance and the approximated ground reaction forces/moments are derived from the resultant reaction loads, which includes the gravity, the externally applied loads, and the inertia. The optimization problem is formulated to address the redundancy of the human task, where the general biped and the task-specific constraints are imposed depending on the task requirements. The proposed method is fully predictive and generates physically feasible human-like motions from scratch without any input reference from motion capture or animation. The resulting generated motions demonstrate how a human reacts effectively to different external load conditions in performing a given task by showing realistic features of cause and effect.
2008-06-17
Technical Paper
2008-01-1930
Yujiang Xiang, Salam Rahmatalla, Hyun-Joon Chung, Joo Kim, Rajankumar Bhatt, Anith Mathai, Steve Beck, Timothy Marler, Jingzhou Yang, Jasbir S. Arora, Karim Abdel-Malek, John P. Obusek
In this study, an optimization-based approach for simulating the lifting motion of a three dimensional digital human model is presented. Lifting motion is generated by minimizing a performance measure subjected to basic physical and kinematical constraints. Two performance measures are investigated: one is the dynamic effort; the other is the compression and shear forces on the lumbar joint. The lifting strategies are predicted with different performance measures. The joint strength (torque limit) and the compression and shear force on lumbar joint are also addressed in this study to avoid injury during lifting motion.
2008-06-17
Technical Paper
2008-01-1931
Rajankumar Bhatt, Yujiang Xiang, Joo Kim, Anith Mathai, Rajeev Penmatsa, Hyun-Joon Chung, Hyun-Jung Kwon, Amos Patrick, Salam Rahmatalla, Timothy Marler, Steve Beck, Jingzhou Yang, Jasbir Arora, Karim Abdel-Malek, John P. Obusek
The objective of this paper is to present our method of predicting and simulating visually realistic and dynamically consistent human stair-climbing motion. The digital human is modeled as a 55-degrees of freedom branched mechanical system with associated human anthropometry-based link lengths, mass moments of inertia, and centers of gravity. The joint angle profiles are determined using a B-spline-based parametric optimization technique subject to different physics-based, task-based, and environment-based constraints. The formulation offers the ability to study effects of the magnitude and location of external forces on the resulting joint angle profiles and joint torque profiles. Several virtual experiments are conducted using this optimization-based approach and results are presented.
2008-06-17
Technical Paper
2008-01-1855
Salam Rahmatalla, Yujiang Xiang, Rosalind Smith, Jinzheng Li, John Muesch, Rajan Bhatt, Colby Swan, Jasbir S. Arora, Karim Abdel-Malek
A framework to validate the predicted motion of a computer human model (Santos) is presented in this work. The proposed validation framework is a task-based methodology. It depends on the comparison of selected motion determinants and joint angles that play major roles in the task, using qualitative and quantitative statistical techniques. In the present work, the validation of Santos walking will be presented. Fortunately, the determinants for normal walking are well defined in the literature and can be represented by (i) hip flexion/extension, (ii) knee flexion/extension, (iii) ankle plantar/dorsiflexion, (iv) pelvic tilt, (v) pelvic rotation, and (vi) lateral pelvic displacement. While Santos is an ongoing research project, the results have shown significant qualitative agreements between the walking determinants of Santos and the walking determinants of four normal subjects.
2008-06-17
Technical Paper
2008-01-1871
Xuemei Feng, Jingzhou Yang, Karim Abdel-Malek
The human shoulder plays an important role in human posture and motion, especially in scenarios in which humans need achieve tasks with external loads. The shoulder complex model is critical in digital human modeling and simulation because a fidelity model is the basis for realistic posture and motion predictions for digital humans. The complexity of the shoulder mechanism makes it difficult to model a shoulder complex realistically. Although many researchers have attempted to model the human shoulder complex, there has not been a survey of these models and their benefits and limitations. This paper attempts to review various biomechanical models proposed and summarize the pros and cons. It focuses mainly on the human modeling domain, although some of these models were originally from the robotics field. The models are divided into two major categories: open-loop chain models and closed-loop chain models.
2008-06-17
Technical Paper
2008-01-1870
Xuemei Feng, Jingzhou Yang, Karim Abdel-Malek
This paper presents a novel approach to determining the joint motion coupling relationship for the human shoulder complex. The human shoulder complex is the most sophisticated part in terms of degrees of freedom and motion. In the literature, different human shoulder biomechanical models have been developed for various purposes. Also, researchers have realized that there are constant movement relationships among the shoulder bones: the clavicle, scapula, and humerus. This is due to muscles and tendons that are involved in skeletal motions. These relationships, which are also called shoulder rhythm, entail joint motion coupling and joint limit coupling. However, the scope of this work is to determine the joint motion coupling relationship. This relationship is available in the literature, but it is an Euler-angle-based relationship. In the virtual human modeling environment, we cannot directly use this Euler-angle-based relationship.
2008-06-17
Technical Paper
2008-01-1909
Anith Mathai, Jinzengh Li, Karim Abdel-Malek, Lindsey Knake, Julie Wisch, Christina Godin, Jim Chiang
The Snook tables (Liberty Mutual Tables) are a collection of data sets compiled from studies based on a psychophysical approach to material-handling tasks. These tables are used to determine safe loads for lifting, lowering, carrying pulling, and pushing. The tables take into account different population percentiles, gender, and frequency of activity. However, while using these tables to analyze a work place, Ergonomists often have to select from discrete data points closest to the actual work place parameters thereby reducing accuracy of results. To compound the problem further, multiple interrelated variables are involved, making it difficult to analyze parameters intuitively. For example, it can be difficult to answer questions such as, does reducing the lifting height lower the recommended lifting weight, if the lifting distance is increased? To resolve such issues, this paper presents a new methodology for implementing the Snook tables using multi variable regression.
2007-06-12
Technical Paper
2007-01-2491
Joo H. Kim, Karim Abdel-Malek, Jingzhou Yang, Kyle J. Nebel
Our previous formulation for optimization-based dynamic motion simulation of a serial-link human upper body (from waist to right hand) is extended to predict the motion of a tree-structured human model that includes the torso, right arm, and left arm, with various applied external loads. The dynamics of tree-structured systems is formulated and implemented. The equations of motion for the tree structures must be derived carefully when dealing with the connection link. The optimum solution results show realistic dual-arm human motions and the required joint actuator torques. In the second part of this paper, a new method is introduced in which the constraint forces and moments at the joints are calculated along with the motion and muscle-induced actuator torques. A set of fictitious joints are modeled in addition to the real joints.
2007-06-12
Technical Paper
2007-01-2490
Hyun-Joon Chung, Yujiang Xiang, Anith Mathai, Salam Rahmatalla, Joo Kim, Timothy Marler, Steve Beck, Jingzhou Yang, Jasbir Arora, Karim Abdel-Malek, John Obusek
A method to simulate digital human running using an optimization-based approach is presented. The digital human is considered as a mechanical system that includes link lengths, mass moments of inertia, joint torques, and external forces. The problem is formulated as an optimization problem to determine the joint angle profiles. The kinematics analysis of the model is carried out using the Denavit-Hartenberg method. The B-spline approximation is used for discretization of the joint angle profiles, and the recursive formulation is used for the dynamic equilibrium analysis. The equations of motion thus obtained are treated as equality constraints in the optimization process. With this formulation, a method for the integration of constrained equations of motion is not required. This is a unique feature of the present formulation and has advantages for the numerical solution process.
2007-06-12
Technical Paper
2007-01-2489
Y. Xiang, H.J. Chung, A. Mathai, S. Rahmatalla, J. Kim, T. Marler, S. Beck, J. Yang, J.S. Arora, K. Abdel-Malek, J. Obusek
In this study, an optimization-based approach for simulating the walking motion of a digital human model is presented. A spatial skeletal model having 55 degrees of freedom is used to demonstrate the approach. Design variables are the joint angle profiles. Walking motion is generated by minimizing the mechanical energy subjected to basic physical and kinematical constraints. A formulation for symmetric and periodic normal walking is developed and results are presented. Backpack and ground reaction forces are taken into account in the current formulation, and the effects of the backpack on normal walking are discussed.
2005-04-11
Technical Paper
2005-01-0530
Kyung K. Choi, Jun Tang, Edwin Hardee, Byeng D. Youn
In the Army mechanical fatigue subject to external and inertia transient loads in the service life of mechanical systems often leads to a structural failure due to accumulated damage. Structural durability analysis that predicts the fatigue life of mechanical components subject to dynamic stresses and strains is a compute intensive multidisciplinary simulation process, since it requires the integration of several computer-aided engineering tools and considerable data communication and computation. Uncertainties in geometric dimensions due to manufacturing tolerances cause the indeterministic nature of the fatigue life of a mechanical component.
1999-05-18
Technical Paper
1999-01-1910
Joung H. Mun, Jeffrey S. Freeman, Kwan Rim
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.
1999-03-01
Technical Paper
1999-01-0539
P.-C. Sui, L.-D. Chen, James P. Seaba, Yoshinori Wariishi
Two mathematical models for the catalyst layer of a PEMFC, i.e. the macro-homogenous model and the agglomerate model are evaluated in this paper. The characteristics of both models and the application of both models to optimal design of catalyst layer are discussed. The one-dimensional governing equations of both models are solved analytically or numerically using the finite difference method. A simplified, analytic solution of the macro-homogenous model under ideal conditions is derived. Parametric study and sensitivity analyses are performed for the agglomerate model to identify the parameters that have significant influences on the performance of a PEMFC. Several parameters including the electrolyte thickness, porosity, oxygen permeability, and layer thickness are found to affect the limiting current significantly. A solid model is developed to visualize the structure of a catalyst layer. This solid model is used to estimate effective transport properties.
1999-03-01
Technical Paper
1999-01-0436
P. W. Green, C. S. Yu, P. B. Butler, L. D. Chen, Y. G. Lee, J. T. Wang
Aspirating airbag modules are unique from other designs in that the gas entering the airbag is a mixture of inflator-delivered gas and ambient-temperature air entrained from the atmosphere surrounding the module. Today's sophisticated computer simulations of an airbag deployment typically require as input the mass-flow rate, chemical composition and thermal history of the gas exiting the canister and entering the airbag. While the mass-flow rate and temperature of the inflator-delivered gas can be obtained from a standard tank test, information on air entrainment into an aspirated canister is limited. The purpose of this study is to provide quantitative information about the aspirated mass-flow rate during airbag deployment. Pressure and velocity measurements are combined with high-speed photography in order to gain further insight into the relationship between the canister pressure, the rate of cabin-air entrainment and the airbag deployment.
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