A sequential element rejection and admission (SERA) topology optimization code written in Matlab

This paper presents the Matlab implementation of the Sequential Element Rejection and Admission (SERA) method for topology optimization of structures and compliant mechanisms. The lines comprising this code include definition of design domain, finite element analysis, sensitivity analysis, mesh-independency filter, optimization algorithm and display of results. Extensions and changes in the algorithm are also included in order to solve multiple load cases, active and passive elements and compliant mechanisms design. The code is intended for educational purposes and introduces an alternative approach to traditional structural topology optimization algorithms. The complete code is provided in the Appendix

Layout optimization of multi-material continuum structures with the isolines topology design method

A heterogeneous or multi-material object is one made from different materials which are distributed continuously or discontinuously. Its properties can be adjusted by controlling the material composition, microstructure and geometry of the object. The development of manufacturing technologies such as rapid prototyping can eliminate the high cost of tooling and offers the possibility to make multi-material structures. However, designing such technologies is not a trivial task and requires the development or modifications of optimization algorithms to take into consideration the different aspects of these problems. This article presents an enhancement to the isolines topology design (ITD) algorithm that allows it to produce multi-material designs. Four examples of the topology design of two-dimensional continuum structures are presented to demonstrate that the ITD algorithm is an efficient and reliable method to achieve the layout optimization of multi-material continuum structures

Rules, precursors and parameterization methodologies for topology optimized structural designs realized through additive manufacturing

Additive manufacturing, more commonly known as 3D printing is a rapidly developing, thoroughly novel means of producing complex, previously difficult to manufacture components. Slowly divorcing itself from previously held preconceptions of rapid prototyping and now capable of producing comparable structures from materials such as titanium and high strength nickel alloys, it is a means of manufacturing structures deemed too complex for existing fabrication techniques. Whilst free of conventional constraints, the unique intricacies of the manufacturing process can lead to the creation of factors, detrimental to production success. The research detailed within this paper demonstrates through example, how the orientation of a part prior to build can be optimized in order to significantly mitigate these effects and to maximize build economics. Furthermore the research details a new method for the combined assessment and tailored structural topology optimization of parts intended for production by specific additive manufacturing technologies

FE Model of Three-Dimensional Steel Beam-to-Column Bolted Extended End-Plate Joint

The rotational behaviour of three-dimensional steel end-plate connections can be studied using the finite element method for the following four reasons: (1) such models are inexpensive and robust; (2) they allow the understanding of local effects; (3) they can be used to generate extensive parametric studies; (4) current version of the component method lacks the appropriate components to predict the behaviour of minor-axis and three-dimensional joints. This work presents a full ANSYS finite element parametric model of a three-dimensional steel beam-to-column bolted extended end-plate joint in both axes for use to obtain their behaviour. The model allows to study four joint configurations (internal, external, corner, and plane) and includes: contact and sliding between different elements; bolt-pretension, and geometric and material non-linearity. This model was calibrated and validated with experimental results found in the literature. The results from the finite element analysis were verified by comparing the obtained moment–rotation curve of the joint. Three parametric studies are presented to show the versatility of the FE model. The results were compared with those obtained with the model proposed by Eurocode 3. The developed ANSYS FE model can be downloaded for free as a single ZIP compressed file from the Technical University of Cartagena (UPCT): http://www.upct.es/goe/publicaciones/FEM_3D_EEP.zip

Estimation of Actuation System Parameters for Lower Limb Prostheses

This paper provides guidelines to estimate the kinematics, energy and torque requirements for lower limb prosthetic actuation systems during daily living activities. These parameters are estimated based on human biomechanical data from different sources to consider the variability due to the assumptions and errors in the analysis and data collection. The results showed that the powered actuation source is important at the ankle joint in the stance phase during level ground walking while it is more important at knee joint during stair ascending. These estimated parameters can be used as guidelines to design and select proper actuation systems

Infill topology optimization of porous structures with discrete variables by the sequential element rejection and admission method

This article presents an infill topology optimization procedure to generate lightweight porous structures. The proposed method is based on discrete variables and builds upon the sequential element rejection and admission method, extending previous work on topology optimization for infill structures. Local volume constraints are introduced in the conventional formulation of the topology optimization problem for maximum stiffness design instead of the global volume constraint. The local constraints are applied, dividing the interior of a given design shape into quadrangular subdomains with variable aspect ratios. The localized material within these subordinate cells is allowed to flow between two discrete material models, ‘real’ and ‘virtual’, where two separate criteria are considered for the rejection and admission of elements. The results demonstrate the effectiveness of the method, showing that detailed porous designs are efficiently achieved with the proposed strategy. Numerical examples demonstrate the effects of the different design parameters

Optimisation of microfluidic polymerase chain reaction devices

The invention and development of Polymerase Chain Reaction (PCR) technology have revolutionised molecular biology and molecular diagnostics. There is an urgent need to optimise the performance of these devices while reducing the total construction and operation costs. This study proposes a CFD-enabled optimisation methodology for continuous flow (CF) PCR devices with serpentine-channel structure, which enables the optimisation of DNA amplification efficiency and pressure drop to be explored while varying the width (W) and height (H) of the microfluidic (μ) channel. This is achieved by using a surrogate-enabled optimisation approach accounting for the geometrical features of a μCFPCR device by performing a series of simulations using COMSOL Multiphysics 5.4®. The values of the objectives are extracted from the CFD solutions, and the response surfaces are created using polyharmonic splines. Genetic algorithms are then used to locate the optimum design parameters. The results indicate that there is the possibility of improving the DNA concentration and the pressure drop in a PCR cycle by ~2.1 % ([W, H] = [400 μm, 50 μm]) and ~95.2 % ([W, H] = [400 μm, 80 μm]) respectively, by modifying its geometry.</jats:p

Effect of Different Prosthetic Knees/feet on the Roll-Over Shape

Roll-over shape (ROS) of knee-ankle-foot (KAF) is a scientific method which has been used to compare performance and design of the different prosthetic foot. In the current study, however, we aimed to understand the influence of the prosthetic components (i.e. knee and foot) on the knee-ankle-foot roll-over shape in a unilateral transfemoral amputee. We performed a case study based on series of experiments with repeated measures on single amputee wearing two different commercially available microprocessor prosthetic knees, during two weeks adaptation period to understand the influence of the prosthetic knee/foot using KAF ROS as an objective measure during level ground walking. The kinematics of the center of pressure (COP), lateral knee and ankle markers were collected and processed to obtain ROS and the results were used to fit a circular shape arc to obtain radius of curvature (ROC). The results indicated that the prosthetic knees have influenced ROC outcomes. The analysis of variance (ANOVA) and post hoc test of the normalized radius of curvature showed the mean of ROC were significantly different between Rheo3 knee, Orion2 and Orion2 with Echelon foot. The amputee reflected his comfort with Rheo3 plus College park foot and Orion with Echelon foot. A conclusion is drawn that multiple comfort zones may exists based on amputee’s ROS metrics. This finding suggests that the design of prosthetic knee should not be considered as a single component but rather as part of a whole system with different comfort zones

Strain-engineering in Germanium membranes towards light sources on Silicon

Bi-axially strained Germanium (Ge) is an ideal material for Silicon (Si) compatible light sources, offering exciting applications in optical interconnect technology. By employing a novel suspended architecture with an optimum design on the curvature, we applied a biaxial tensile strain as large as 0.85% to the central region of the membrane