Anton H. Basson

Manufacturing cost estimation during design of fabricated parts

Abstract Manufacturing cost estimation models can overcome some of the limitations of relying only on design experience. This paper outlines the role of cost models in design for manufacture (DFM) and the requirements for a design for manufacturing cost estimation models. Cost models for a process typical of batch production of fabricated steel welded assemblies, i.e. tack welding, are presented as examples in this paper, and references are given for cost models of other fabrication processes. The cost models were developed from data collected through time studies and analysed using robust regression statistical methods. The model estimates were compared to production estimates from two companies.

Numerical Simulation of Tip Clearance Effects in Turbomachinery

The numerical formulation developed here includes an efficient grid generation scheme, particularly suited to computational grids for the analysis of turbulent turbomachinery flows and tip clearance flows, and a semi-implicit, pressure-based computational fluid dynamics scheme that directly includes artificial dissipation, and is applicable to both viscous and inviscid flows. The value of this artificial dissipation is optimized to achieve accuracy and convergency in the solution. The numerical model is used to investigate the structure oftip clearance flows in a turbine nozzle. The structure of leakage flow is captured accurately, including blade-to-blade variation of all three velocity components, pitch and yaw angles, losses and blade static pressures in the tip clearance region. The simulation also includes evaluation of such quantities as leakage mass flow, vortex strength, losses, dominant leakage flow regions, and the spanwise extent affected by the leakage flow. It is demonstrated, through optimization of grid size and artificial dissipation, that the tip clearance flow field can be captured accurately.

Investigation of Tip Clearance Phenomena in an Axial Compressor Cascade Using Euler and Navier–Stokes Procedures

Three-dimensional Euler and full Navier-Stokes computational procedures have been utilized to simulate the flow field in an axial compressor cascade with tip clearance. An embedded H-grid topology was utilized to resolve the flow physics in the tip gap region. The numerical procedure employed is a finite difference Runge-Kutta scheme. Available measurements of blade static pressure distributions along the blade span, dynamic pressure and flow angle in the cascade outlet region, and spanwise distributions of blade normal force coefficient and circumferentially averaged flow angle are used for comparison. Several parameters that were varied in the experimental investigations were also varied in the computational studies

Predictive modelling of cervical disc implant wear

This study presents a chain of simulations aimed at estimating the wear in a cervical disc implant and providing insight into the in vivo biomechanical performance of the implant. The simulation chain can start with determining a representative maximum range of motion (ROM) of a persons head. The ROM is used as motion input to a kinematic simulation of the cervical spine containing a disc implant. The cervical spine geometry is obtained from computed tomography (CT) scans and converted to STL format using reverse engineering software. The time histories of the loads imposed by the adjacent vertebrae on the implant, as well as the vertebral relative rotations can be extracted from the kinematic simulation. Alternatively, force and motion profiles prescribed by wear test protocols (e.g. ISO 18192-1 and ASTM F2423-05) can be used. The force and motion profiles are applied as boundary conditions to a non-linear finite element model (FEM) of the implant to determine the time-varying contact stress and slip velocity distributions at the interface between the two halves of the implant. The stresses and slip velocities are used in a linear wear model to estimate the wear rate distribution at the FEMs nodal points where contact occurs. Reverse engineering software is used to triangulate the contact surface so that the total wear volume can be calculated. The simulation chains predicted wear rate shows good agreement with in vitro results in the literature. The simulation chain is thereby demonstrated to be suitable for comparative pre-experimental studies of spinal implant designs.

Dynamic Simulation of Cervical Spine following Single-Level Cervical Disc Replacement

The aim of the present study is to analyze the simulated behavior of the Functional Spinal Unit (FSU) with a disc implant inserted in the C5-C6 segment, compare the results to the literature and use the data for disc design parameters. Intradiscal forces/pressures, bending moments and vertebral body rotations were calculated and compared to in- vitro and simulated results in the literature. This data can also be used to evaluate the prescribed input parameters for the ISO/DIS 18192-1 experimental protocol for evaluating cervical disc implants. LifeMOD was used as simulation software package and the cervical model was set up to closely resemble in-vivo conditions. Maximum range of motion data for ten student volunteers was used as input motion for the model. The results obtained correlated well with literature and it was interesting to see the retained motion at the C5-C6 segment containing the implant, which contradicts clinical and simulation results found for spinal fusion. The presented simulation model is hence deemed proficient to critically evaluate the dynamics of a cervical disc design and to relatively accurately prescribe in-vivo input forces and motions acting on a cervical disc.

AN ARTIFICIAL DISSIPATION FORMULATION FOR A SEMI-IMPLICIT, PRESSURE BASED SOLUTION SCHEME FOR VISCOUS AND INVISCID FLOWS

SUMMARY The formulation of artificial dissipation terms for a semi-implicit, pressure based flow solver, similar to SIMPLE type formulations, is presented and is applied to both the Euler and the Navier-Stokes equations. The formulation uses generalized coordinates and a non-staggered grid. This formulation is compared to some SIMPLE and time marching formulations. The relationship between SIMPLE and time marching formulations is discussed briefly. The artificial dissipation inherent in some commonly used semi-implicit formulations, e.g. upwind differencing, powerlaw, QUICK and pressure weighting, is investigated. The scheme used here includes these dissipation terms directly, but retains the ability to mimic previous schemes. The potential for errors introduced by the simultaneous use of artificial dissipation in the continuity equation and central differencing of convective terms, is revealed. The effect of the amount of dissipation on the accuracy of the solution and the convergence rate is quantitativ...

Development and testing of a prototype reflex measurement system employing artificial neural networks

This paper presents the development, testing and performance evaluation of a patellar tendon reflex measurement system to provide a quantitative reflex evaluation for use by medical practitioners and in a telemedicine or E-medicine environment. A prototype was developed that makes use of XSens MTx orientation sensors, force-sensitive resistors and an electromyogram to measure the reflex response. Suitable parameters from the sensors were identified for analysis, and clinical testing was performed on 20 subjects to collect data to evaluate the systems performance. Subjective reflex evaluations were conducted by three medical doctors according to a standard reflex grading scale using video recordings of the tests. Multi-layer feed-forward (MLFF) artificial neural networks (ANNs) were used to analyze the collected data with the aim of pattern identification and reflex grading prediction. It was found that the MLFF network delivered the corresponding reflex grading with an accuracy of 85%, which was of the same order as the rate of differences between the subjective reflex evaluations performed by the doctors (80%). The use of ANNs to analyze a reflex measurement offers a repeatable and concise representation of the reflex that is familiar to doctors and can be developed for use in a general clinical setting or for telemedicine purposes.

Grid generation for three-dimensional turbomachinery geometries including tip clearance

An efficient technique for the generation of structured grids for viscous flow computations in turbomachinery blade rows (two- and three-dimensional), and a specialized embedded //-grid for application, particularly to tip clearance flows, are presented. The grid generation technique uses a combination of algebraic and elliptic methods to obtain smooth grids while maintaining strict control over grid spacing and orthogonality at domain boundaries. A geometric series scheme is used to distribute boundary points. Algebraically generated layers next to boundaries are used, thus excluding highly clustered regions from the elliptic generation procedures domain. The computational efficiency of the elliptic generation procedure is greatly enhanced by the application of the minimal residual method. The embedded //-grid topology provides good resolution of tip clearance effects. This topology requires only minor modifications to flow solvers developed for conventional //-grids. The results obtained with an embedded //-grid are compared to those obtained using a thin-tip approximation. A linear compressor cascade with tip clearance was used as a test case. Both grid topologies capture the dominant flow structures associated with the leakage flow. The embedded //-grid provided better quantitative agreement with the experimental results.

Erlang-based control implementation for a holonic manufacturing cell

Holonic control is generally used in reconfigurable manufacturing systems since the modularity of holonic control holds the promise of easier reconfiguration, reduction in complexity and cost, along with increased maintainability and reliability. As an alternative to the commonly used agent-based approach, this paper presents an Erlang-based holon internal architecture and implementation methodology that exploits Erlang’s capabilities. The paper shows that Erlang is well suited to the requirements of holonic and reconfigurable systems – due to strong modularity, scalability, customisability, maintainability and robustness characteristics.

Towards Alternatives for Agent Based Control in Reconfigurable Manufacturing Systems

Most researchers in reconfigurable manufacturing systems (RMSs) have used the agent based control (ABC) approach, because the capabilities of agent based software and their development platforms make it easier and quicker to test their research. Due to the reluctance of industries to adopt ABC, this paper considers the factors that would affect the choice of alternatives for ABC, with an emphasis on cell-level control rather than on factory-level control or production planning related aspects. The paper shows that design considerations include reconfiguration level, self-reconfiguration intelligence and controller platform splitting. Some design choices will lead to ABC having significant advantages, while others will allow the use of software approaches more often used in industry.