H Alicia Kim

University of Bath | UB · Department of Mechanical Engineering

Phase-change materials (PCMs) excel in storing significant thermal energy through the latent heat of fusion during phase changes. However, they often suffer from low thermal conductivity, requiring the incorporation of materials with higher thermal conductivity to overcome this limitation. In this study, we employ the level-set method to topologica...

This study addresses safety concerns within the rapidly evolving Electric Vertical Takeoff and Landing (eVTOL) aircraft domain, focusing on efficient tools to quantify uncertainties in lithium-ion battery behavior-a critical aspect of eVTOL. One major issue with quantifying uncertainty is the prohibitive computational cost associated with many quer...

Electric Vertical TakeOff and Landing (eVTOL) vehicles are considered a promising solution to alleviate traffic congestion and provide an alternative to traditional individual transportation. The design and performance of eVTOL battery packs play a critical role in the development of this mode of transportation. In this paper, we propose a methodol...

Topology optimization is applied to design a lunar rover chassis to reduce thermal losses while maintaining adequate structural strength and stiffness. Space missions in extreme cold environments, such as the permanently shadowed regions (PSR) of the moon, are designed to reduce the power needed to maintain the minimum temperature for items that ca...

This paper presents a CAD-aware plug-and-play framework for topology optimization that results in CAD compatible-optimized geometries. The framework uses two separate kernels: one for defining and updating the geometry, and the other for an unfitted finite element analysis (FEA). The level-set method is used for the handling the geometry, while a m...

This study introduces a novel computational framework for Robust Topology Optimization (RTO) considering imprecise random field parameters. Unlike the worst-case approach, the present method provides upper and lower bounds for the mean and standard deviation of compliance as well as the optimized topological layouts of a structure for various scena...

This study introduces a novel computational framework for Robust Topology Optimization (RTO) considering imprecise random field parameters. Unlike the worst-case approach, the present method provides upper and lower bounds for the mean and standard deviation of compliance as well as the optimized topological layouts of a structure for various scena...

View Video Presentation: https://doi.org/10.2514/6.2022-2548.vid This study is aimed at developing an accessible and non-intrusive level-set topology optimization framework based on the discrete adjoint method and modularized architecture. The physics solver and level-set interface are completely separated and functions independently, and thus its...

View Video Presentation: https://doi.org/10.2514/6.2022-2091.vid In this work a level set topology optimization (LSTO) method is developed in combination with the modified immersed finite element method (mIFEM) and the meshfree reproducing kernel particle method (RKPM) to solve topology optimization problems in fluid-structure interaction (FSI). Wi...

A level set topology optimization (LSTO) using the stabilized nodally integrated reproducing kernel particle method (RKPM) to solve the governing equations is introduced in this paper. This methodology allows for an exact geometry description of a structure at each iteration without remeshing and without any interpolation scheme. Moreover, useful c...

This paper investigates the weight minimization of stiffened panels simultaneously optimizing sizing, layout, and topology under stress and buckling constraints. An effective topology optimization parameterization is presented using multiple level-set functions. Plate elements are employed to model the stiffened panels. The stiffeners are parametri...

In this study, the optimum design of load carrying battery packs that can also exchange heat with a coolant is presented. The level set topology optimization method is used as the design tool. The flow is modeled using the Darcy potential flow, and the heat transfer is modeled using the convection-diffusion equation. The displacement field is compu...

Simultaneous layout and topology optimization of stiffened panels is investigated in this paper using a new level-set-based method. Specifically, plate elements are used to construct a stiffened panel structure. The level set method is then used to manipulate the stiffener layout, with curved members allowed. A free-form mesh deformation method wit...

This paper proposes a new methodology for computing boundary sensitivities in level set topology optimization using the discrete adjoint method. The adjoint equations are constructed using the discretized governing field equations. The objective function is differentiated with respect to the boundary point movement for computing boundary sensitivit...

In this study, we introduce new algorithms for efficient function representation (F-rep) based geometric design using the sparse and dynamic voxel data structure Volumetric Dynamic B+ tree (VDB). The level set method is used as the F-rep method. Specifically, we develop the Fast Sweeping Method for boundary points to level set surfaces velocity ext...

A turbomachinery casing structure provides the necessary support to many crucial systems and components in an aeroengine such as the combustion chamber, compressors, and turbines. A competitive casing structure should be stiff and durable while minimizing weight. This work investigates the possibilities and potential of using topology optimization...

In this paper, we introduce a level set topology optimization formulation considering coupled mechanical and thermal loads. Examples considering stress and compliance minimization under temperature and volume constraints, and mass minimization under stress and temperature constraints, are presented. The p-norm of the stress field and temperature fi...

This paper presents a level set topology optimization method in combination with the reproducing kernel particle method (RKPM) for the design of structures subjected to design-dependent pressure loads. RKPM allows for arbitrary particle placement in discretization and approximation of unknowns. This attractive property in combination with the impli...

In this paper, the wing box of an aircraft is optimized using a level set topology optimization method and considering aerostructural coupling. A new level set method is developed where the design domain and the finite element analysis domain are represented by two separate meshes, and coordinates and sensitivities are transformed from one mesh to...

Shell structures are some of the most widely used in engineering applications. Flat plates, stiffened panels, and wing ribs are each examples of components for which the design features may be dictated by the critical buckling load. Despite this practical significance, there exists only a handful of studies in the literature documenting application...

A few level-set topology optimization (LSTO) methods have been proposed to address complex fluid-structure interaction. Most of them did not explore benchmark fluid pressure loading problems and some of their solutions are inconsistent with those obtained via density-based and binary topology optimization methods. This paper presents a LSTO strateg...

This paper presents a level set topology optimization method for manipulation of stress and strain integral functions in a prescribed region (herein called sub-structure) of a linear elastic domain. The method is able to deviate or concentrate the flux of stress in the sub-structure by optimizing the shape and topologies of the boundaries outside o...

This paper introduces a new approach to multiscale optimization, where design optimization is applied at two scales: the macroscale, where the structure is optimized, and the microscale, where the material is optimized. Thus, structure and material are optimized simultaneously. We approach multiscale design optimization by linearizing and formulati...

Linear buckling constraints are important in structural topology optimization for obtaining designs that can support the required loads without failure. During the optimization process, the critical buckling eigenmode can change; this poses a challenge to gradient-based optimization and can require the computation of a large number of linear buckli...

The use of bistable laminates is a potential approach to realize broadband piezoelectric based energy harvesting by introducing elastic non-linearities to the system. In this paper the dynamic response of a piezoelectric material attached to a bistable laminate beam is examined based on the experimental measurement of the generated voltage-time se...

In this paper we examine the modal response of a bistable electro-mechanical energy harvesting device based on characterisation of the experimental time-series. A piezoelectric element attached to a vibrating bistable carbon-fibre reinforced polymer laminate plate was used for the conversion of mechanical vibrations to electrical energy under harmo...

The use of bistable laminates is a potential approach to realize broadband piezoelectric based energy harvesting systems. In this paper the dynamic response of a piezoelectric material attached to a bistable laminate plate is examined based on the experimental generated voltage time series. The system was subjected to harmonic excitations and exhib...

Reliable machining monitoring systems are essential for lowering production time and manufacturing costs. Existing expensive monitoring systems focus on prevention/detection of tool malfunctions and provide information for process optimisation by force measurement. An alternative and cost-effective approach is monitoring acoustic emissions (AEs) fr...

Advanced fiber placement (AFP) composite manufacturing technology offers a means to tailor composite fibers for complex loading environments and significantly improve the overall structural efficiency. This paper introduces a new method to optimize the continuously varying fiber paths for AFP using a level set method. The paths of the fibers are de...

The present paper introduces a new technique for simultaneously optimising the topology and continuous material distribution of a structure. Topology optimisation offers great potential for novel, improved structural designs and is an ideal design tool for additive manufacturing (AM) techniques. Level set based topology optimisation produces soluti...

This chapter presents a unifying theoretical model for describing fluid-solid coupling in porous materials. It proceeds by forming a variety of cellular solid systems without fluid and subjects these systems to numerical testing to determine their elastic response. From these numerical tests, the elastic tensor of the cellular solid can be determin...

This paper introduces a unifying theory for describing complex behavior for porous materials. The key ingredients are the stored energy in solid-fluid interaction as well as the solid-solid and fluid-fluid interactions. A finite element formulation is employed which naturally accounts for the pore-pore network effects and is easily applicable to mo...

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...

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 re...

This paper presents a level set based method for optimising the design of fibre angles in composite structures where the angles vary continuously. Advanced fibre placement (AFP) composite manufacturing technology can lay fibres at continuously varying angle offering an opportunity to significantly improve the overall structural efficiency from the...

This paper presents a level set topology optimisation method for stress. The formulation for shape derivatives is derived and used to establish the level set optimisation method. A new hole insertion method is developed and implemented in the level set method. The method is applied to optimise two numerical problems: One is the well-known L-beam pr...

This paper describes the manufacture, characterisation and actuation of functional composites using asymmetric bistable composites. Such laminate structures are finding interest in applications such shape changing applications, energy harvesting and de-icing. In this paper results are presented for bistable structures that are actuated by a variety...

A functionally graded material (FGM) provides a spatial blend of material properties throughout a structure. This paper studies the efficacy of FGM for the aeroelastic tailoring of a metallic cantilever plate-like wing, wherein a genetic algorithm provides Pareto trade-off curves between static and dynamic aeroelastic metrics. A key comparison is b...

The use of bistable laminates is a potential approach to realize more broadband piezoelectric based energy harvesting systems. Based on the experimental time series of a bistable laminate plate we have examined its dynamic response. The system was subjected to harmonic excitations showing the existence of single well and snap-through vibrations of...

Wireless sensor networks are being increasingly accepted as an effective tool for structural health monitoring. The ability to deploy a wireless array of sensors efficiently and effectively is a key factor in structural health monitoring. Sensor installation and management can be difficult in practice for a variety of reasons: a hostile environment...

This paper describes the manufacture of structural composites incorporating piezoelectric fibres which are finding interest in applications such as shape-changing applications, sensors to detect mechanical strain or vibration and energy harvesting. In this paper preliminary results are presented for a simple cantilever structure consisting of piezo...

The purpose of this work is to develop a level set topology optimization method for an unstructured three-dimensional mesh and apply it to wing box design for coupled aerostructural considerations. The paper develops fast marching and upwind schemes suitable for unstructured meshes, which make the level set method robust and efficient. The method i...

In this paper we explore the effect of the orientation of the main crystallographic axes in relaxor-ferroelectric single crystals (SCs) on the piezoelectric anisotropy and squared figures of merit of 2–2 parallel-connected SC/auxetic polymer composites. The single-crystal component for the composite is chosen from the perovskite-type solid solution...

The need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted interest in recent years for energy harvesting technologies capable of capturing energy from broadband ambient vibrations. Encouraging results have been reported for an arrangement of piezoelectric layers attached to carbon fiber...

This paper introduces an approach to level-set topology optimization that can handle multiple constraints and simultaneously optimize non-level-set design variables. The key features of the new method are discretized boundary integrals to estimate function changes and the formulation of an optimization sub-problem to attain the velocity function. T...

The purpose of this work is to use level set topology optimization to improve the design of a representative wing box structure for the NASA common research model. The objective is to minimize the total compliance of the structure under aerodynamic and body force loading, where the aerodynamic loading is coupled to the structural deformation. A tax...

This paper presents analytical modelling and experimental characterisation of an arrangement of bistable composite plates with bonded piezoelectric elements to perform broadband vibration-based energy harvesting from ambient mechanical vibrations. These bistable devices have the potential to exhibit improved power generation compared to conventiona...

This paper considers a novel electro-thermal system combining aligned carbon nanotubes (A-CNT) as a resistive heater and bistable laminates. The use of A-CNT heaters to actuate bistable laminates is characterized in terms of steady-state shape as a function of applied voltage to the heating element and the transient response of the laminate to heat...

This review provides a detailed overview of the energy harvesting technologies associated with piezoelectric materials along with the closely related sub-classes of pyroelectrics and ferroelectrics. These properties are, in many cases, present in the same material, providing the intriguing prospect of a material that can harvest energy from multipl...

In this paper a bistable asymmetric laminate is manufactured and coupled to a ferroelectric material for potential energy harvesting applications. A cantilever configuration is explored and the harvester response as a function of vibration frequency, vibration level and electrical load resistance examined. The harvester is characterised at low and...

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...

Robust topology optimization has long been considered computationally intractable as it combines two highly expensive computational strategies. This paper considers simultaneous minimization of expectancy and variance of compliance in the presence of uncertainties in loading magnitude, using exact formulations and analytically derived sensitivities...

The continuing need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted renewed interest in recent years for energy harvesting technologies capable of capturing energy from ambient vibrations. A particular focus has been placed on piezoelectric materials and devices due to the simplicity of...

Under certain conditions asymmetric composite laminates can have a bistable response to mechanical loading. A transition between the two stable states provides opportunities to produce large deflections or shape changes from relatively low energy inputs that do not need to be maintained to sustain a specific shape. Such laminates are attracting int...

In this paper effect of the orientation of the main crystallographic axes on the piezoelectric anisotropy and hydrostatic parameters of 2–2 parallel-connected single crystal (SC) / auxetic polymer composites is analysed. SCs are chosen among the perovskite-type relaxor-ferroelectric solid solutions of (1 – x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 and xPb(In1/2Nb...

The structural performance of two advanced composite tow-steered shells, manufactured using a fiber placement system, is assessed using both experimental and analytical methods. The fiber orientation angles vary continuously around the shell circumference from ±10 degrees on the shell crown and keel, to ±45 degrees on the shell sides. The two shell...

This paper presents an objective function formulation of robust topology optimisation. Noting that the most common objective for topology optimisation is minimisation of compliance, the robust objective in this paper considers minimisation of a weighted sum of expected and variance of compliance. The uncertainties considered are in the magnitude an...

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...

SUMMARY Structural shape and topology optimization using level set functions is becoming increasingly popular. However, traditional methods do not naturally allow for new hole creation and solutions can be dependent on the initial design. Various methods have been proposed that enable new hole insertion; however, the link between hole insertion and...

We present a method for finding solutions of large‐scale binary programming problems where the calculation of derivatives is very expensive. We then apply this method to a topology optimization problem of weight minimization subject to compliance and buckling constraints. We derive an analytic expression for the derivative of the stress stiffness m...

Asymmetric composite laminates can have a bistable response to mechanical loading. The large deflections that can be achieved by snap-through from one stable state to another, along with a need for small and removable energy input, make them of interest for a wide range of engineering applications. After 30 years of research efforts the shapes and...

Topology optimisation is the most general form of structural optimisation, capable of calculating the optimal arrangement of material in a loaded structure. Low weight efficient structures are vital to aircraft performance making aerospace structures an ideal field for the application of topology optimisation. In this investigation 3D level set top...

Level set topology optimization defines the solution using the level set function values stored at the nodes of a regular finite element grid. These values represent a signed distance function which indicates the distance from each node to the structural boundaries. During optimization, nodal sensitivities are used to update the level set function...

A minimum-weight optimization strategy for Variable Angle Tow (VAT) panels subject to buckling and manufacture constraints is presented. The optimization is performed using a fast-running optimization package which employs exact strip analysis for buckling and a gradient-based optimization method. A new VAT panel manufacturing method providing good...

Modern engineering is demanding a greater integration of multidisciplinary approaches. The framework for multidisciplinary optimization design turns to adopt web-based technology to construct a diversified and distributed environment for engineering computation. With the development of Internet technology, new technology can be applied and new arch...

This paper introduces variance into the robust compliance topology optimization problem where there is uncertainty in loading magnitude. An analytical formulation for compliance variance is derived and shape sensitivities for the level set optimization method are obtained using the adjoint method. Variance is combined with expected compliance to po...

This paper presents an arrangement of bistable composite plates with bonded piezoelectric patches to perform broadband vibration-based energy harvesting from ambient mechanical vibrations. These bistable nonlinear devices have the potential to exhibit improved power generation compared to conventional resonant systems and can be designed to occupy...

The problem of staging data in workflows has received much attention over the last decade, with a variety of user-directed and automatic solutions. The latter are the focus of the first contribution in this paper, where we propose a simple peer-to-peer solution adapted to the needs of RESTful services. The second contribution, is the combination of...

This paper presents an arrangement of bistable composites combined with piezoelectrics for broadband energy harvesting of ambient vibrations. These non-linear devices have improved power generation over conventional resonant systems and can be designed to occupy smaller volumes than magnetic cantilever systems. This paper presents results based on...

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 desi...

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 gen...

Adaptive structures that allow large deformations under the application of a low and noncontinuous energy input are gaining increasing interest in the aerospace industry. One potential mechanism of realizing shape control is piezoelectric actuation of asymmetric composite laminates. This article presents an optimization study for the design of bist...

This paper develops and validates a finite-element model to predict both the cured shape and snap-through of asymmetric bistable laminates actuated by piezoelectric macro fiber composites attached to the laminate. To fully describe piezoelectric actuation, the three-dimensional compliance [s_ij], piezoelectric [d_ij], and relati...

Boundary based structural optimization methods often employ a fixed grid FEM to compute sensitivities for efficiency and simplicity. A simple and popular fixed grid approach is to modify the stiffness of elements intersected by the boundary by an area-fraction weighting. However, poor sensitivities and numerical instabilities can occur when using t...

  Asymmetric laminates are known to exhibit two stable cylindrical states and one unstable saddle state. Such bistability has attracted attention in aerospace applications because of the potential low energy requirement to achieve a large deflection or change in shape. This paper presents experimental observations of a generic asymmetric [−30/60] l...

The behavior of hysteretic, coupled elastic and fluid systems is modeled. The emphasis is on quasistatic equilibrium in response to prescribed chemical potential (μ) protocols and prescribed stress (σ) protocols. Hysteresis arises in these models either from the presence of hysterons or from the presence of self-trapping internal fields. This latte...

Bistable asymmetric composites with piezoelectric actuators that induce ‘snap-through’ from one stable state to another are candidate smart materials for shape-change (morphing) applications. This paper combines a homogenised piezoelectric model of a Macro Fibre Composite with a bistable asymmetric laminate model. Both predicted shape and snap-thro...

Adaptive structures offering large deformations with small and removable energy input are gaining increasing interest in the aerospace industry. One such mechanism is actuated asymmetric composite laminates. This paper presents an optimization formulation for the design of bistable laminates for reversible snap-through enabled by two orthogonal pie...

Uncertainty is an important consideration in structural design and optimization to produce robust and reliable solutions. This paper introduces an efficient and accurate approach to robust structural topology optimization. The objective is to minimize expected compliance with uncertainty in loading magnitude and applied direction, where uncertainti...

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 iden...

The macroscopic behavior of a system of elastic elements that can be in one of two states, depending on the relationship between the stress they carry to a critical stress (different for each elastic element), is studied. There are two extreme cases: (1) in which the critical stress is hysteretic (there is microscopic hysteresis) and (2) in which t...

This paper presents a novel metamodel formulation for efficient function emulation based on Radial Basis Function (RBF) interpolation. Lattice sampling plans and the geometry of the Voronoi tessellation are exploited to localise the RBF interpolation with the aim of increasing efficiency for large scale modelling with minimum loss of global accurac...

This paper develops a finite element (FE) approach using commercial ANSYS V11.0 software to accurately predict the cured shape of bistable composites by including the influence of manufacturing imperfections, such as resin rich areas and ply-thickness variations. Laminate composition was characterised by optical microscopy and their cured shapes me...

A study was conducted to introduce an actuation mechanism, called shape memory alloy-piezoelectric active structures (SMAPAS) that combined the advantages of the piezoelectric shape memory alloy (SMA) materials to achieve self-resetting bistable composites. The approach used piezoelectric actuation to provide a rapid snap-through with significant d...

Uncertainty is an important consideration in structural design and optimization to produce robust and reliable solutions. Existing methods that include loading direction uncertainty in structural topology optimization may not represent realistic uncertainties or employ a discrete sampling approach that approximates the effect of the uncertainty. Th...

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 formula...

Asymmetric laminates can have a bistable response to loading, making them of particular interest for applications requiring a large deflection with relatively small and removable energy input. After nearly 30 years of research effort the effects of ply orientation and laminate geometry on the room-temperature shapes of such laminates are well under...

Granular media, from unconsolidated to consolidated, are supported by a complex contact set. In their quasi-static response granular media exhibit stress-strain hysteresis with end-point memory. They often show slow dynamics in transient response (release of an applied stress) and in dynamic response (under AC drive). To model granular media succes...

Multi-disciplinary design optimization (MDO) is the process whereby the often conflicting requirements of the different disciplines to the engineering design process attempts to converge upon a description that represents an acceptable compromise in the design space. We present a simple demonstrator of a flexible workflow framework for engineering...

This paper presents a numerical investigation in the influence of loading on the trabecular architecture of a femoral head using structural optimization. Previous literature has shown that structural optimization can be used to simulate the response of bone to external loading conditions, in the cases of os-calcis and vertebrae of which the loading...

This paper presents the development and validation of a coupled-field finite element model to predict the response of a piezoelectrically actuated bistable laminate for structural morphing applications. Derivation of materials properties and validation of piezoelectric actuator model against experimental data are described. The model shows qualitat...

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 it...

This paper characterises the properties of unsymmetric bistable carbon fibre composites actuated using a single piezoelectric macro fibre actuator. A piezoelectric–laminate combination under two-axis constraint was evaluated in terms of its load–deflection characteristics, snap-through force and stiffness. The load–deflection characteristics indica...