Sandro L. Vatanabe

Topology optimization with manufacturing constraints

Manufacturing constraint techniques based on a unified projection-based approach are addressed.A projection technique combined with mapping technique is implemented to apply different kinds of manufacturing constraints in the topology optimization.A domain of design variables is projected in a pseudo-density domain to obtain a solution to the optimization problem.The minimum member size, minimum hole size, symmetry, extrusion, pattern repetition, turning, casting, forging and rolling constraints are implemented.The goal is to achieve feasible engineering solutions, which can be fabricated by means of well-known manufacturing processes. Despite being an effective and a general method to obtain optimal solutions, topology optimization generates solutions with complex geometries, which are neither cost-effective nor practical from a manufacturing (industrial) perspective. Manufacturing constraint techniques based on a unified projection-based approach are presented herein to properly restrict the range of solutions to the optimization problem. The traditional stiffness maximization problem is considered in conjunction with a novel projection scheme for implementing constraints. Essentially, the present technique considers a domain of design variables projected in a pseudo-density domain to find the solution. The relation between both domains is defined by the projection function and variable mappings according to each constraint of interest. The following constraints have been implemented: minimum member size, minimum hole size, symmetry, pattern repetition, extrusion, turning, casting, forging and rolling. These constraints illustrate the ability of the projection scheme to efficiently control the optimization solution (i.e. without adding a large computational cost). Illustrative examples are provided in order to explore the manufacturing constraints in conjunction with the unified projection-based approach.

Maximizing phononic band gaps in piezocomposite materials by means of topology optimization

Phononic crystals (PCs) can exhibit phononic band gaps within which sound and vibrations at certain frequencies do not propagate. In fact, PCs with large band gaps are of great interest for many applications, such as transducers, elastic/acoustic filters, noise control, and vibration shields. Previous work in the field concentrated on PCs made of elastic isotropic materials; however, band gaps can be enlarged by using non-isotropic materials, such as piezoelectric materials. Because the main property of PCs is the presence of band gaps, one possible way to design microstructures that have a desired band gap is through topology optimization. Thus in this work, the main objective is to maximize the width of absolute elastic wave band gaps in piezocomposite materials designed by means of topology optimization. For band gap calculation, the finite element analysis is implemented with Bloch-Floquet theory to solve the dynamic behavior of two-dimensional piezocomposite unit cells. Higher order frequency branches are investigated. The results demonstrate that tunable phononic band gaps in piezocomposite materials can be designed by means of the present methodology.

Design and Characterization of a Biomimetic Piezoelectric Pump Inspired on Group Fish Swimming Effect

Flow pumps are important tools in several engineering areas, such as in the fields of bioengineering and thermal management solutions for electronic devices. Nowadays, many of the new flow pump principles are based on the use of piezoelectric actuators, which present some advantages such as miniaturization potential and lower noise generation. In previous work, authors presented a study of a novel pump configuration based on placing an oscillating bimorph piezoelectric actuator in water to generate flow. It was concluded that this oscillatory behavior (such as fish swimming) yields vortex interaction, generating flow rate due to the action and reaction principle. Thus, following this idea the objective of this work is to explore this oscillatory principle by studying the interaction among generated vortex from two bimorph piezoelectric actuators oscillating inside the same pump channel, which is similar to the interaction of vortex generated by frontal fish and posterior ones when they swim together in a group formation. It is shown that parallel−series configurations of bimorph piezoelectric actuators inside the same pump channel provide higher flow rates and pressure for liquid pumping than simple parallel−series arrangements of corresponding single piezoelectric pumps, respectively. The scope of this work includes structural simulations of bimorph piezoelectric actuators, fluid flow simulations, and prototype construction for result validation.

Water cooling system using a piezoelectrically actuated flow pump for a medical headlight system

The microchips inside modern electronic equipment generate heat and demand, each day, the use of more advanced cooling techniques as water cooling systems, for instance. These systems combined with piezoelectric flow pumps present some advantages such as higher thermal capacity, lower noise generation and miniaturization potential. The present work aims at the development of a water cooling system based on a piezoelectric flow pump for a head light system based on LEDs. The cooling system development consists in design, manufacturing and experimental characterization steps. In the design step, computational models of the pump, as well as the heat exchanger were built to perform sensitivity studies using ANSYS finite element software. This allowed us to achieve desired flow and heat exchange rates by varying the frequency and amplitude of the applied voltage. Other activities included the design of the heat exchanger and the dissipation module. The experimental tests of the cooling system consisted in measuring the temperature difference between the heat exchanger inlet and outlet to evaluate its thermal cooling capacity for different values of the flow rate. Comparisons between numerical and experimental results were also made.

Computational and experimental characterization of a low-cost piezoelectric valveless diaphragm pump

Flow pumps act as important devices in areas such as Bioengineering, Medicine, and Pharmacy, among other areas of Engineering, mainly for delivering liquids or gases at small-scale and precision flow rate quantities. Principles for pumping fluids based on piezoelectric actuators have been widely studied, since they allow the construction of pump systems for displacement of small fluid volumes with low power consumption. This work studies valveless piezoelectric diaphragm pumps for flow generation, which uses a piezoelectric ceramic (PZT) as actuator to move a membrane (diaphragm) up and down as a piston. The direction of the flow is guaranteed by valveless configuration based on a nozzle–diffuser system that privileges the flow in just one pumping direction. Most research efforts on development of valveless flow pump deal either with computational simulations based on simplified models or with simplified physical approaches based on analytical models. The main objective of this work is the study of a methodology to develop a low-cost valveless piezoelectric diaphragm flow pump using computational simulations, parametric study, prototype manufacturing, and experimental characterization. The parametric study has shown that the eccentricity of PZT layer and metal layer plays a key role in the performance of the pump.

Design of phononic band gaps in functionally graded piezocomposite materials by using topology optimization

One of the properties of composite materials is the possibility of having phononic band gaps, within which sound and vibrations at certain frequencies do not propagate. These materials are called Phononic Crystals (PCs). PCs with large band gaps are of great interest for many applications, such as transducers, elastic/ acoustic filters, noise control, and vibration shields. Most of previous works concentrates on PCs made of elastic isotropic materials; however, band gaps can be enlarged by using non-isotropic materials, such as piezoelectric materials. Since the main property of PCs is the presence of band gaps, one possible way to design structures which have a desired band gap is through Topology Optimization Method (TOM). TOM is a computational technique that determines the layout of a material such that a prescribed objective is maximized. Functionally Graded Materials (FGM) are composite materials whose properties vary gradually and continuously along a specific direction within the domain of the material. One of the advantages of applying the FGM concept to TOM is that it is not necessary a discrete 0-1 result, once the material gradation is part of the solution. Therefore, the interpretation step becomes easier and the dispersion diagram obtained from the optimization is not significantly modified. In this work, the main objective is to optimize the position and width of piezocomposite materials band gaps. Finite element analysis is implemented with Bloch-Floquet theory to solve the dynamic behavior of two-dimensional functionally graded unit cells. The results demonstrate that phononic band gaps can be designed by using this methodology.

Modeling of Functionally Graded Materials

Functionally graded material (FGM) represents a new class of composites that consists of a graded pattern of material composition and/or microstructures. Because the properties of FGM-constituent materials change gradually in the unit cell domain, its modeling is complex and can be achieved by using graded finite elements (GFE), which incorporate the material property gradient at the size scale of the element and reduce the discontinuity of the material distribution. This chapter presents the verification of FGM modeling using GFE for dynamic applications and examples of numerical modeling of FGMs for energy harvesting, piezoelectric sensors, and phononic material applications.

Automatic Creation of Blending Surfaces in Hydropower Generators Turbine Blades

Abstract Hydropower generators turbine blade is a one of kind product that requires specific maintenance. They are designed in very specific software tools based on features, which allow good CAD/CAE automation by simply tweaking parameters. However, such CAD/CAE automation has brought an undesired side effect: its hard to add new features that are not considered in the original CAD. Specially in simulation-optimization applications, where parameters that are not considered in the design must be modified. This is the case in this work, where fluid-structure analysis is performed and a geometric feature that transcend the design activity (blending surface between the crown and the blade) is modified. This paper describes an ongoing project which involves the implementation of a module able to intercept the geometry generated by a CAD program using the IGES format, create/modify a new geometric feature and update the fluid volume and blade geometries. The surface boundary curves are extracted, and the adjacency relationship between the surfaces is determined by coordinate numerical comparison. The surfaces are coherently oriented and the solid models are completely determined. Using the de Boors algorithm and the surface orientation a model with exclusive triangular faces coherently oriented is created, and then the blending surface is automatically created. The refined mesh for the models are created and fluid-structure analysis is performed for the simulation-optimization.

Design of Phononic Materials Using Multiresolution Topology Optimization

In this work the Multiresolution Topology Optimization (MTOP) scheme is investigated to obtain high resolution designs of phononic (elastic) materials, focusing primarily on acoustic waveguides. We demonstrate via numerical examples that the resolution of the design can be significantly improved without refining the finite element mesh. The first one is the simplest case where one might be interested in maximizing the energy reaching certain parts of the domain. The second and more interesting example is the creation of different propagation patterns for different frequencies, thus creating smart filters. The results demonstrate the power and potential of our computational framework to design sophisticated acoustic wave devices.Copyright

Design of Functionally Graded Piezocomposite Materials Using Topology Optimization

Piezocomposite materials provides effective properties (elastic, piezoelectric, and dielectric) that produce a better performance than pure piezoelectric materials. In the optimization of a piezocomposite the objective is to obtain an improvement in its performance characteristics, usually by changing the volume fractions of constituent materials, its properties, shape of inclusions, and the mechanical properties of the polymer matrix in the composite unit cell. An interesting application for piezoelectric materials are energy harvesting devices which stores energy from the environment. This work presents designs of functionally graded piezocomposite materials using topology optimization and homogenization method in order to maximize the electromechanical coupling coefficientk and the mechanical-to-electrical energy conversion, aiming at energy harvesting applications. The Functionally Graded Material (FGM) concept is applied to reduce the stress concentration between the constitutive materials and to investigate the influence of material gradation. The homogenization method is implemented using the graded finite element concept which takes into account the continuous gradation inside the finite elements. The material model used is based on the SIMP (Solid Isotropic Material With Penalization) and the optimization problem is solved by using the MMA (Method of Moving Asymptotes) algorithm.