James K. Guest

Multiple-Material Topology Optimization of Compliant Mechanisms Created Via PolyJet Three-Dimensional Printing

Compliant mechanisms are able to transfer motion, force, and energy using a monolithic structure without discrete hinge elements. The geometric design freedoms and multimaterial capability offered by the PolyJet 3D printing process enables the fabrication of compliant mechanisms with optimized topology. The inclusion of multiple materials in the topology optimization process has the potential to eliminate the narrow, weak, hingelike sections that are often present in single-material compliant mechanisms and also allow for greater magnitude deflections. In this paper, the authors propose a design and fabrication process for the realization of 3-phase, multiple-material compliant mechanisms. The process is tested on a 2D compliant force inverter. Experimental and numerical performance of the resulting 3-phase inverter is compared against a standard 2-phase design.

Reinforced Concrete Force Visualization and Design Using Bilinear Truss-Continuum Topology Optimization

AbstractA new force visualization and design tool employing hybrid topology optimization is introduced for RC and prestressed concrete structural members. The optimization scheme couples a minimum compliance (maximum stiffness) objective function with a hybrid truss-continuum ground structure that can generate a strut-and-tie model for any general concrete member, loading, and set of boundary conditions. The truss ground structure represents discrete steel reinforcing bars (tensile load paths) that can be sized based on axial forces output directly by the optimization routine, whereas the continuum elements simulate concrete compression struts. This separation of compressive and tensile load-carrying elements is achieved through bilinear elastic models with an orthotropic constitutive relationship for the continuum. Examples are provided demonstrating the potential value of the optimization tool to RC design. Reinforcing layouts that can minimize cracking and reduce steel quantities when compared with tra...

Topology Optimization for Additive Manufacturing: Considering Maximum Overhang Constraint

Additively manufactured components often require temporary support material during the 3D printing process. In the case of polymer material process such as Fuse Deposition Modeling (FDM), the support material can be dissolved away. However in the case of metals in a selective laser melting (SLM) process, the support and component material are one in the same. Since the support structure adds both material cost and post-processing cost to every component printed, it is desired to limit or completely eliminate the need for such material. As such, it is proposed to take advantage of the maximum printable overhang angle (the angle at which the AM process requires no support material) by harnessing topology optimization as the design engine. This is accomplished through a topology optimization projection scheme, in which the angle constraint is imposed through a Heaviside projection and not applied as an explicit constraint. Solutions to two standard topology optimization problems are included and show good agreement with the overhang constraint.

Topology Optimization of Fixed-Geometry Fluid Diodes

This paper proposes using topology optimization to design fixed-geometry fluid diodes that allow easy passage of fluid flowing in one direction while inhibiting flow in the reverse direction. Fixed-geometry diodes do not use movable mechanical parts or deformations, but rather utilize inertial forces of the fluid to achieve this flow behavior. Diode performance is measured by diodicity, defined as the ratio of pressure drop of reverse flow and forward flow, or equivalently the ratio of dissipation of reverse and forward flow. Diodicity can then be maximized by minimizing forward dissipation while maximizing reverse dissipation. While significant research has been conducted in topology optimization of fluids for minimizing dissipation, maximizing dissipation introduces challenges in the form of small, mesh dependent flow channels and that artificial flow in solid region becomes (numerically) desirable. These challenges are circumvented herein using projection methods for controlling the minimum length scale of channels and by introducing an additional penalty term on flow through intermediate porosities. Several solutions are presented, one of which is fabricated by 3D printing and experimentally tested to demonstrate the diodelike behavior.

Optimal design of tunable phononic bandgap plates under equibiaxial stretch

Design and application of phononic crystal (PhCr) acoustic metamaterials has been a topic with tremendous growth of interest in the last decade due to their promising capabilities to manipulate acoustic and elastodynamic waves. Phononic controllability of waves through a particular PhCr is limited only to the spectrums located within its fixed bandgap frequency. Hence the ability to tune a PhCr is desired to add functionality over its variable bandgap frequency or for switchability. Deformation induced bandgap tunability of elastomeric PhCr solids and plates with prescribed topology have been studied by other researchers. Principally the internal stress state and distorted geometry of a deformed phononic crystal plate (PhP) changes its effective stiffness and leads to deformation induced tunability of resultant modal band structure. Thus the microstructural topology of a PhP can be altered so that specific tunability features are met through prescribed deformation. In the present study novel tunable PhPs of this kind with optimized bandgap efficiency-tunability of guided waves are computationally explored and evaluated. Low loss transmission of guided waves throughout thin walled structures makes them ideal for fabrication of low loss ultrasound devices and structural health monitoring purposes. Various tunability targets are defined to enhance or degrade complete bandgaps of plate waves through macroscopic tensile deformation. Elastomeric hyperelastic material is considered which enables recoverable micromechanical deformation under tuning finite stretch. Phononic tunability through stable deformation of phononic lattice is specifically required and so any topology showing buckling instability under assumed deformation is disregarded. Nondominated sorting genetic algorithm (GA) NSGA-II is adopted for evolutionary multiobjective topology optimization of hypothesized tunable PhP with square symmetric unit-cell and relevant topologies are analyzed through finite element method. Following earlier studies by the authors, specialized GA algorithm, topology mapping, assessment and analysis techniques are employed to get feasible porous topologies of assumed thick PhP, efficiently.

Structural Optimization of Deploying Structures Composed of Linkages

AbstractDetermining the global shape of a deploying structure and the section profiles of its members is a challenging design problem. Geometry, meaning the lengths and relative angles of members, is critical to achieving stable deployment to a desired span, while the design must also satisfy structural capacity demands at each stage of deployment. This paper explores the potential role of formal structural optimization in designing feasible and structurally efficient deploying steel structures composed of linkage elements. Both stochastic search and gradient-based algorithms are used to explore the design space and identify minimum weight solutions that satisfy kinematic and structural constraints. The proposed methodology is tested on the case study of a deploying pantograph. This strategy has the potential to be implemented for a wide range of deploying structures, including retractable roofs, rapidly expandable shelters, deploying space structures, and movable bridges.

Three-Dimensional Force Flow Paths and Reinforcement Design in Concrete via Stress-Dependent Truss-Continuum Topology Optimization

AbstractStrut-and-tie models (STMs) are widely used by RC designers. However, selection of a viable model is a challenging task, especially in complex three-dimensional (3D) design domains with irregular cutouts, which are common in building cores and shear walls. Therefore, topology optimization has been promoted as a means of automating the development of minimum strain energy STMs, which can lead to improved structural behavior. Current drawbacks of such methods are that solutions may be difficult to construct and may fail to properly account for tensile stresses resulting from force spreading. A two-dimensional hybrid truss-continuum topology optimization scheme was recently developed to overcome these challenges with the goal of reconfiguring traditional reinforcement layouts to automatically follow principal tensile stresses, reducing cracking at service loads and increasing strength and ductility at an ultimate limit state. That work is generalized and extended herein to 3D domains and mechanics mo...

3-D phononic crystals with ultra-wide band gaps

In this paper gradient based topology optimization (TO) is used to discover 3-D phononic structures that exhibit ultra-wide normalized all-angle all-mode band gaps. The challenging computational task of repeated 3-D phononic band-structure evaluations is accomplished by a combination of a fast mixed variational eigenvalue solver and distributed Graphic Processing Unit (GPU) parallel computations. The TO algorithm utilizes the material distribution-based approach and a gradient-based optimizer. The design sensitivity for the mixed variational eigenvalue problem is derived using the adjoint method and is implemented through highly efficient vectorization techniques. We present optimized results for two-material simple cubic (SC), body centered cubic (BCC), and face centered cubic (FCC) crystal structures and show that in each of these cases different initial designs converge to single inclusion network topologies within their corresponding primitive cells. The optimized results show that large phononic stop bands for bulk wave propagation can be achieved at lower than close packed spherical configurations leading to lighter unit cells. For tungsten carbide - epoxy crystals we identify all angle all mode normalized stop bands exceeding 100%, which is larger than what is possible with only spherical inclusions.

Agent-Based Simulation of Building Evacuation after an Earthquake: Coupling Human Behavior with Structural Response

AbstractThe safety of building occupants during and immediately after disasters, such as a major earthquake, is highly dependent on the way in which people interact with the damaged physical environment. While there are extensive studies on evacuation from undamaged structures and on structural behavior under seismic and other hazards, research on the influence of building damage on human evacuation behavior is limited. This study presents a framework by which models for buildings and human behavior can be coupled to analyze the dynamic influences of building damage on the evacuation process. The framework combines nonlinear dynamic finite-element modeling of structures, probabilistic modeling of damage, and agent-based modeling of human occupants to investigate the behavior of people as they interact with each other and with their dynamically-deteriorating environment as they attempt to evacuate the building. A case study is presented for a typical three-story commercial office building subjected to the ...

Structural Topology Optimization Considering Correlated Uncertainties in Elastic Modulus

An existing perturbation-based method is extended to consider correlated uncertainties in structural topology optimization problems. The proposed method uses perturbation technique to model uncertainties in the geometry of structures and material properties, and transforms the problem of topology optimization under uncertainty to an augmented deterministic topology optimization problem. This leads to significant computational savings when compared with Monte Carlo-based optimization, which involve multiple formations and inversions of the global stiffness matrix. We study two numerical examples to show the importance of correlation in uncertainty modeling and to verify the proposed method. Numerical examples show that results obtained from the proposed method are in excellent agreement with those obtained when using Monte Carlo-based optimization.