H. Alicia Kim

Level-Set Topology Optimization with Aeroelastic Constraints

Level-set topology optimization is used to design a wing considering skin buckling under static aeroelastic trim loading, as well as dynamic aeroelastic stability (flutter). The level-set function is defined over the entire 3D volume of a transport aircraft wing box. Therefore, the approach is not limited by any predefined structure and can explore novel configurations. The Sequential Linear Programming (SLP) level-set method is used to solve the constrained optimization problems. The proposed method is demonstrated using three problems with mass, linear buckling and flutter objective and/or constraints. A constraint aggregation method is used to handle multiple buckling constraints in the wing skins. A continuous flutter constraint formulation is used to handle difficulties arising from discontinuities in the design space caused by a switching of the critical flutter mode.

Preliminary Study of Optimum Piezoelectric Cross-Ply Composites for Energy Harvesting

Energy harvesting devices based on a piezoelectric material attached to asymmetric bistable laminate plates have been shown to exhibit high levels of power extraction over a wide range of frequencies. This paper optimizes for the design of bistable composites combined with piezoelectrics for energy harvesting applications. The electrical energy generated during state-change, or “snap-through,” is maximized through variation in ply thicknesses and rectangular laminate edge lengths. The design is constrained by a bistability constraint and limits on both the magnitude of deflection and the force required for the reversible actuation. Optimum solutions are obtained for differing numbers of plies and the numerical investigation results are discussed.

Optimization of piezoelectric bistable composite plates for broadband vibrational energy harvesting

This paper presents a unique arrangement of bistable composite plates with piezoelectric patches bonded to its surface to perform broadband vibration-based energy harvesting from ambient mechanical vibrations. These bistable nonlinear devices have been shown to have improved power generation compared to conventional resonant systems and can be designed to occupy smaller volumes than bistable magnetic cantilever systems. This paper presents the results of an optimization study of bistable composites that are capable of generating greater electrical power from a smaller space by discovering the correct geometric configuration for energy harvesting. Optimum solutions are investigated in a series of design parameter studies intended to reveal the complex interactions of the physical constraints and design requirements. The proposed approach considers the optimal choice of device aspect ratio, thickness, laminate stacking sequence, and piezoelectric surface area. Increased electrical output is found for geometries and piezoelectric configurations which have not been considered previously.

Investigation of bistable piezo-composite plates for broadband energy harvesting

The need to power small electronic components, such as wireless sensor networks, has prompted interest in energy harvesting technologies capable of generating electrical energy from ambient vibrations. There has been a particular focus on piezoelectric materials and devices due to the simplicity of the mechanical to electrical energy conversion and their high strain energy densities compared to electrostatic and electromagnetic equivalents. This paper describes research on an arrangement of piezoelectric elements attached to a bistable asymmetric laminate to understand the dynamic response of the structure and power generation characteristics. The inherent bistability of the underlying structure is exploited for energy harvesting since snap-through from one stable configuration to another is used to strain the piezoelectric materials bonded to the laminate and generate piezoelectric energy. Using high speed digital image correlation, a variety of dynamic modes of oscillation are identified in the bistable harvester. The sensitivity of such vibrational modes to changes in frequency and amplitude are investigated. Electrical power outputs are measured for repeatable snap-through events and are correlated with the modes of oscillation. The typical power generated is approximately 25mW and compares well with the needs of typical wireless senor node applications.

Non-invasive damage detection in composite beams using marker extraction and wavelets

Simple and contactless methods for determining the health of metallic and composite structures are necessary to allow non-invasive Non-Destructive Evaluation (NDE) of damaged structures. Many recognized damage detection techniques, such as frequency shift, generalized fractal dimension and wavelet transform, have been described with the aim to identify, locate damage and determine the severity of damage. These techniques are often tailored for factors such as (i) type of material, (ii) damage patterns (crack, impact damage, delamination), and (iii) nature of input signals (space and time). In this paper, a wavelet-based damage detection framework that locates damage on cantilevered composite beams via NDE using computer vision technologies is presented. Two types of damage have been investigated in this research: (i) defects induced by removing material to reduce stiffness in a metallic beam and (ii) manufactured delaminations in a composite laminate. The novelty in the proposed approach is the use of bespoke computer vision algorithms for the contactless acquisition of modal shapes, a task that is commonly regarded as a barrier to practical damage detection. Using the proposed method, it is demonstrated that modal shapes of cantilever beams can be readily reconstructed by extracting markers using Hough Transform from images captured using conventional slow motion cameras. This avoids the need to use expensive equipment such as laser doppler vibrometers. The extracted modal shapes are then used as input for a wavelet transform damage detection, exploiting both discrete and continuous variants. The experimental results are verified using finite element models (FEM).

Loading Magnitude Uncertainty in Level-Set Based Topology Optimization

Engineering environments are often complex, which introduces uncertainty into the design process. Thus, uncertainties should be considered during design and optimization of structures to produce robust and reliable solutions. This paper presents topology optimization with uncertainty by minimizing expected compliance. A simple and efficient formulation is developed to solve this problem under uncertainty in loading magnitude. The formulation is applied to the level set method and illustrative examples demonstrate that more robust structures can be obtained compared to the deterministic solutions.

Investigation of aligned conductive polymer nanocomposites for actuation of bistable laminates

In this paper the coupled electro-thermo-mechanical actuation of bistable laminates using aligned carbon nanotubes is investigated. Applications for such actuators include ice protection systems (IPS) for aerosurfaces that can dislodge ice accretion via a combination of thermal and mechanical mechanisms. This study presents both new experimental results and multi-physics finite element modelling of the actuation and the resulting large deformation, focusing on both static and transient performance characterization.

A Light-Weight Framework for Bridge-Building from Desktop to Cloud

A significant trend in science research for at least the past decade has been the increasing uptake of computational techniques (modelling) for insilico experimentation, which is trickling down from the grand challenges that require capability computing to smaller-scale problems suited to capacity computing. Such virtual experiments also establish an opportunity for collaboration at a distance. At the same time, the development of web service and cloud technology, is providing a potential platform to support these activities. The problem on which we focus is the technical hurdles for users without detailed knowledge of such mechanisms – in a word, ‘accessibility’ – specifically: (i) the heavy weight and diversity of infrastructures that inhibits shareability and collaboration between services, (ii) the relatively complicated processes associated with deployment and management of web services for non-disciplinary specialists, and (iii) the relative technical difficulty in packaging the legacy software that encapsulates key discipline knowledge for web-service environments. In this paper, we describe a light-weight framework based on cloud and REST to address the above issues. The framework provides a model that allows users to deploy REST services from the desktop on to computing infrastructure without modification or recompilation, utilizing legacy applications developed for the command-line. A behind-the-scenes facility provides asynchronous distributed staging of data (built directly on HTTP and REST). We describe the framework, comprising the service factory, data staging services and the desktop file manager overlay for service deployment, and present experimental results regarding: (i) the improvement in turnaround time from the data staging service, and (ii) the evaluation of usefulness and usability of the framework through case studies in image processing and in multi-disciplinary optimization.

Two-Dimensional Fixed Grid Based Finite Element Structural Analysis

This paper introduces a new fixed mesh structural analysis technique based on isoparametric formulations from classic finite element analysis. Fixed mesh methods are popular in boundary based optimisation as they avoid mesh distortion problems and reanalysis is simple and efficient. The area ratio based fixed grid method is often employed due to its favourable simplicity in implementation. However, maximum errors occur along the boundary due to homogenization of stiffness. Also errors are area ratio dependant, producing an undesirable variation of errors along the boundary. The aim of the isoparametric fixed grid method was to reduce the error dependency on area ratio without significantly reducing the efficiency of the area ratio formulation. The two dimensional isoparametric method divides boundary elements into three types depending on their inside area shape. Quadrilateral elements were formulated using a bilinear isoparametric formulation and an algebraic expression for the stiffness matrix was derived using a priori information about the element shape. Triangular elements were formulated as constant strain triangles and pentagonal element stiffness matrices were approximated by linear interpolation of quadrilateral and inside element matrices. Numerical examples were used to compare the isoparametric to the area ratio fixed grid method using a fitted mesh as a baseline for displacement error calculation. The examples showed some promising benefits in accuracy of the isoparametric fixed grid method, but also revealed areas for improvement.