Combined Visibility and Surrounding Triangles Method for Simulation of Crack Discontinuities in Meshless Methods

In this paper a combined node searching algorithm for simulation of crack discontinuities in meshless methods called combined visibility and surrounding triangles (CVT) is proposed. The element free Galerkin (EFG) method is employed for stress analysis of cracked bodies. The proposed node searching algorithm is based on the combination of surrounding triangles and visibility methods; the surrounding triangles method is used for support domains of nodes and quadrature points generated at the vicinity of crack faces and the visibility method is used for points located on the crack faces. In comparison with the conventional methods, such as the visibility, the transparency, and the diffraction method, this method is simpler with reasonable efficiency. To show the performance of this method, linear elastic fracture mechanics analyses are performed on number of standard test specimens and stress intensity factors are calculated. It is shown that the results are in good agreement with the exact solution and with those generated by the finite element method (FEM)

THREE-DIMENSIONAL BIOMECHANICAL ANALYSIS OF THE TRUNK AND UPPER EXTREMITY DURING WHEELCHAIR PROPULSION WITH CONSIDERING THE EFFECT OF MUSCLE FORCES

INTRODUCTION -The number of wheelchair users continues to increase, but limited research has been conducted with respect to the kinetics of wheelchair propulsion. In many studies I it is mentioned, most paralyzed patients suffer from shoulder pain. This problem is significantly caused by the forces and moments forcing upon the upper extremity and trunk during wheelchair propulsion. Therefore, establishing an investigation leading to optimal wheelchair/ user match to facilitate effective and safe activity is essential. In this research, our aim is obtaining the forces and moments at the joints of the user during wheelchair propulsion. therefore, by using the concepts of biomechanics and robotics, the trunk and upper extremity are modelled as a 3-D Iinkage system with eight degrees of freedom which representing the trunk, arm, forearm and hand. In this model, the most important muscle forces of the trunk and upper extremity in wheelchair propulsion are forcing on the linkage system[Van der Helm, 1991]. The kinetical analysis of the model has been developed, by using the Newton-Euler equations to give the forces and moments at the joints. In parallel the forces and moments which are present at the hand/rim interface during wheelchair propulsion, is collected via a specific wheelchair instrumented with transducers to record them. For kinematical analysis of the wheelchair user, some markers are attached to the joints. The markers provide the possibility of recording the joints' paths in space via videography using two cameras. The images are translated to a computer by using a video blaster board. The user is informed to propel a specific wheelchair at a predefined velocity. Meanwhile, simultaneous output of the experimental set-up for kinematical analysis, and the applied forces and moments to the users hand, is fed in to a computational programs. This program has been written for kinetical analysis of the model. RESULTS -Having mass center of mass and moments of inertia of the users trunk, arm, forearm and hand, the program which has been written for kinetical analysis, yields to give the forces and moments at the joints vS. time. CONCLUSION -To obtain an optimal wheelchair / user match one can change the geometrical dimensions of the chair such as rim diameter, height and placement of the seat, and also propulsion technique and determine their effects on the forces and moments occuring at the joints. Meanwhile, one can use this method in sport for athletes with disabilities. REFRENCES Van der Helm,F.C.T and veenbaas, R(1991): Modelling the mechanical effect of muscles with large attachment sites: Application to the shoulder mechanism. J.Biomechanics. VoI.24,No.12,PP.1151-1163

Finite element modeling of electrospun nanofibre mesh using microstructure architecture analysis

This investigation is aimed at modeling the tensile behavior of electrospun polyurethane (PU) membrane. The PU web is produced with different morphologies and the structural parameters are studied through SEM images. Three-dimensional network is simulated using ABAQUS software. Each fibre is modeled as hyperelastic material and each crosslink is modeled as multi point constrain tie. The stress-strain behavior of PU mat is modeled by finite element method, and the effect of fibre diameter, fibre orientation and thickness of web is investigated. The stress–strain curves of networks at three different morphologies are compared with modeling measurements. The model by using third order reduced polynominal as fibre hyperelastic potential energy function shows good agreement with experimental findings which confirm that the tensile behavior of PU web can be explained entirely by microstructure of the network

Drug diffusion along an intact mammalian cochlea

Intratympanic drug administration depends on the ability of drugs to pass through the round window membrane (RW) at the base of the cochlea and diffuse from this location to the apex. While the RW permeability for many different drugs can be promoted, passive diffusion along the narrowing spiral of the cochlea is limited. Earlier measurements of the distribution of marker ions, corticosteroids and antibiotics demonstrated that the concentration of substances applied to the RW was two to three orders of magnitude higher in the base compared to the apex. The measurements, however, involved perforating the cochlear bony wall and, in some cases, sampling perilymph. These manipulations can change the flow rate of perilymph and lead to intake of perilymph through the cochlear aqueduct, thereby disguising concentration gradients of the delivered substances. In this study, the suppressive effect of salicylate on cochlear amplification via block of the outer hair cell (OHC) somatic motility was utilized to assess salicylate diffusion along an intact guinea pig cochlea in vivo. Salicylate solution was applied to the RW and threshold elevation of auditory nerve responses was measured at different times and frequencies after application. Resultant concentrations of salicylate along the cochlea were calculated by fitting the experimental data using a mathematical model of the diffusion and clearing of salicylate in a tube of variable diameter combined with a model describing salicylate action on cochlear amplification. Concentrations reach a steady-state at different times for different cochlear locations and it takes longer to reach the steady-state at more apical locations. Even at the steady state, the predicted concentration at the apex negligible. Model predictions for the geometry of the longer human cochlea show even higher differences in the steady-state concentrations of the drugs between cochlear base and apex. Our findings confirm conclusions that achieving therapeutic drug concentrations throughout the entire cochlear duct is hardly possible when the drugs are applied to the RW and are distributed via passive diffusion. Assisted methods of drug delivery are needed to reach a more uniform distribution of drugs along the cochlea

Payload Maximization for Mobile Flexible Manipulators in Environment with an Obstacle

A mobile flexible manipulator is developed in order to achieve high performance requirements such as high-speed operation, increased high payload to mass ratio, less weight, and safer operation due to reduced inertia. Hence, this paper presents a method for finding the Maximum Allowable Dynamic Load (MADL) of geometrically nonlinear flexible link mobile manipulators. The full dynamic model of a wheeled mobile base and the mounted flexible manipulator is considered with respect to dynamics of non-holonomic constraint in environment including an obstacle. In dynamical analysis, an efficient model is employed to describe the treatment of a flexible structure in which both the geometric elastic nonlinearity and the foreshortening effects are considered. Then, a path planning algorithm is developed to find the maximum payload that the optimal strategy is based on the indirect solution to the open-loop optimal control problem. In order to verify the effectiveness of the presented algorithm, several simulation studies are carried out for finding the optimal path between two points in the presence of obstacles. The results clearly show the effect of flexibility and the proposed approach on mobile flexible manipulators

Payload Maximization for Mobile Flexible Manipulators in an Environment with Obstacle

A mobile flexible manipulator is developed in order to achieve high performance requirements such as high-speed operation, increased high payload to mass ratio, less weight, and safer operation due to reduced inertia. Hence, this paper presents a method for finding the Maximum Allowable Dynamic Load (MADL) of geometrically nonlinear flexible link mobile manipulators. The full dynamic model of a wheeled mobile base and the mounted flexible manipulator is considered with respect to dynamics of non-holonomic constraint in environment including an obstacle. In dynamical analysis, an efficient model is employed to describe the treatment of a flexible structure in which both the geometric elastic nonlinearity and the foreshortening effects are considered. Then, a path planning algorithm is developed to find the maximum payload that the optimal strategy is based on the indirect solution to the open-loop optimal control problem. In order to verify the effectiveness of the presented algorithm, several simulation studies are carried out for finding the optimal path between two points in the presence of obstacles. The results clearly show the effect of flexibility and the proposed approach on mobile flexible manipulators

Analysis of different material theories used in a FE model of a lumbar segment motion

In this study, a nonlinear poroelastic model of intervertebral disc as an infrastructure was developed. Moreover, a new element was defined consisting a disc (Viscoelastic Euler Beam Element) and a vertebra (Rigid Link) as a unit element. Using the new element, three different viscoelastic finite element models were prepared for lumbar motion segment (L4/L5). Prolonged loading (short-term and longterm creep) and cyclic loading were applied to the models and the results were compared with results of in vivo tests. Simplification of the models by using the new element leads to reduction of the runtime of the models in dynamic analyses to few minutes without losing the accuracy in the results