121 research outputs found
Fast multipole accelerated unsteady vortex lattice method based computations
No full textThe authors present an accelerated aerodynamic computational model derived from the integration of the fast multipole method (FMM) with the unsteady vortex lattice method (UVLM) based aerodynamic model. It is determined that the performance of this computational model depends on the tuning of some FMM parameters and that there is a tradeoff between the computational speed and the accuracy of the computed loads. This tradeoff is examined by varying the truncation number, the order of the Gauss-Legendre quadrature, and the clustering parameter for the wake velocity calculations. Results of the computational cost reduction study achieved through the accelerated aerodynamic simulator are reported for a planar, rectangular lifting surface with a high aspect ratio. The computational approach presented in this paper is the first in the literature wherein the FMM has been implemented for an UVLM-based nonlinear, unsteady aerodynamic simulator. The approach has broad applicability for the study of aerodynamic and aeroelastic responses of aircraft systems and related decision support systems in dynamic data-driven application systems.Fil: Kebbie-Anthony, Abu. University of Maryland; Estados UnidosFil: Gumerov, Nail A.. University of Maryland; Estados UnidosFil: Preidikman, Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Balachandran, Balakumar. University of Maryland; Estados UnidosFil: Azarm, Shapour. University of Maryland; Estados Unido
Numerical and Experimental Shape Optimal Design of a Hole in a Tall Beam
No full textShape optimal design is a structural optimization process in which the boundary shapes of structures are optimized to meet a set of requirements. This is in contrast with early strategies which dealt mostly with the so-called sizing variables such as cross-section, length and width, rather than with the shape of boundaries. This thesis deals with the optimization of the shape of an interior discontinuity (hole) in a two-dimensional strucure, namely a tall beam. The objective is to find hole shapes with approximately uniform boundary stress to reduce the weight of the beam without increasing the maximum tensile stress originally present in the beam. Two approaches are used: 1. A numerical approach using finite element analysis, non-linear programming and interactive graphics.2. An experimental approach using photoelasticity. The hole shapes obtained from the two approaches match quite well. A CAD approach is also presented to simulate the photoelastic method. The methods described in the thesis can be used for a wide variety of two-dimensional structural problems, including reduction of weight, minimization of stress concentration and other design objectives
Parameter Sensitivity Measures for Single Objective, Multi-Objective, and Feasibility Robust Design Optimization
No full textUncontrollable variations are unavoidable in engineering design. If ignored, such variations can seriously deteriorate performance of an optimum design. Robust optimization is an approach that optimizes performance of a design and at the same time reduces its sensitivity to variations. The literature reports on numerous robust optimization techniques. In general, these techniques have three main shortcomings: (i) they presume probability distributions for parameter variations, which might be invalid, (ii) they limit parameter variations to a small (linear) range, and (iii) they use gradient information of objective/constraint functions. These shortcomings severely restrict applications of the techniques reported in the literature.
The objective of this dissertation is to present a robust optimization method that addresses all of the above-mentioned shortcomings. In addition to being efficient, the robust optimization method of this dissertation is applicable to both single and multi-objective optimization problems.
There are two steps in our robust optimization method. In the first step, the method measures robustness for a design alternative. The robustness measure is developed based on a concept that associated with each design alternative there is a sensitivity region in parameter variation space that determines how much variation a design alternative can absorb. The larger the size of this region, the more robust the design. The size of the sensitivity region is estimated by a hyper-sphere, using a worst-case approach. The radius of this hyper-sphere is obtained by solving an inner optimization problem. By comparing this radius to an actual range of parameter variations, it is determined whether or not a design alternative is robust. This comparison is added, in the second step, as an additional constraint to the original optimization problem. An optimization technique is then used to solve this problem and find a robust optimum design solution.
As a demonstration, the robust optimization method is applied to numerous numerical and engineering examples. The results obtained are numerically analyzed and compared to nominal optimum designs, and to optimum designs obtained by a few well-known methods from the literature. The comparison study verifies that the solutions obtained by our method are indeed robust, and that the method is efficient
Plate Heat Exchanger Optimization Using Different Approximation Assisted Multiobjective Optimization Techniques
No full textThis paper presents a comparison between different multiobjective optimization approaches that can be used to optimize the design of thermal equipment. Plate heat exchanger is taken as case study to apply different optimization techniques. The thermal-hydrodynamic characteristics of single phase turbulent flow in chevron-type plate heat exchangers with sinusoidal-shaped corrugations have been used in this paper. The computational domain contains a corrugation channel and the simulations adopted the shear-stress transport (SST) κ-ω model as the turbulence model. Two different approximation assisted optimization approaches are tested. Offline approximation assisted optimization, and online approximation assisted optimization are compared to optimize plate heat exchanger design. For both approximation techniques (offline and online), design optimization is performed using multiobjective genetic algorithm based on meta-models that are built to represent the entire design space. In offline approximation, globally accurate meta-models are built which requires adding more samples. However in online approximation assisted optimization, samples are added just to improve the metamodels performance in the expected optimum region. Approximated optimum designs are validated using computationally expensive actual CFD simulations. Finally, a comparison between offline and online approximation assisted optimization is presented with guidelines to apply both approaches in the area of heat exchanger design optimization. The methods presented in this paper are generic and can be applied to optimize different types of heat exchangers, electronic cooling devices and other thermal system components
Local Monotonicity in Optimal Design.
No full textIn design optimization, there usually exists a large number of inequality constraints, many of them satisfied as equalities at the optimum (active). The method of monotonicity was developed to identify these active constraints analytically and globally. The analytical approach may be inhibited by the need for extensive algebraic manipulations and a computational implementation of the method is desirable. A monotonicity-based strategy for selecting active constraints in a constrained nonlinear design optimization problem is implemented computationally. The concept of local monotonicity is introduced as the basis for iterating on the active set. A prototype algorithm is developed utilizing a local monotonicity strategy, constrained derivatives, and descent-type techniques such as gradient and Golden-Section. The algorithm (called ACCME, for Automated Constraint Criticality by Monotonicity Evaluations) is applied to several demonstration examples as well as five engineering design problems, namely, helical compression spring, ride-ring for rotary kilns, passive vehicle suspension, gear reducer, and flywheel for a punch-press. For these problems the results are compared with those obtained from global monotonicity analysis. The algorithm is also tested on a set of 40 test problems with different mathematical forms from the collection of Hock and Schittkowski {25}. Although the algorithm in its current form needs numerical refinements, the test results are judged to be fairly competitive with the other techniques tested, i.e., generalized reduced gradient and sequential quadratic programming. A strategy for constraint activity identification that couples the local algorithm with global information possibly available for a given problem, is also implemented. This information may be provided by global monotonicity analysis or a design expert. The strategy is a first attempt towards development of iteration procedures for optimal design which may use knowledge or information other than the one provided by traditional local calculations.PhDMechanical engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/160088/1/8422190.pd
New Generation of Air Cooled Heat Exchanger 1 kW Module Design Optimization
No full textThe objective of this paper is to evaluate and optimize the performance of 1 kW integrated heat exchanger module for new generations of air cooled heat exchangers. The first objective is to minimize the ratio of the header frontal area to the entire heat exchanger frontal which will help to reduce the header size. The second objective is to minimize the pressure drop for the entire heat exchanger, i.e., inside the inlet and outlet headers in addition to pressure drop inside the tubes. A three step approach is proposed. First step involves selecting the header design based on previous header optimization studies and then simulating the header using a new 3D CFD simulation approach. Second step includes solving the heat exchanger using information from the header simulation that accounts for the variation in refrigerant mass flow rate inside the tubes and obtain the performance for the entire heat exchanger. Finally, a solver is used to evaluate the overall module performance. Three different headers are investigated with different header height and size ratio. Then parametric studies are conducted to explore the effect of header size ratio on the optimum designs. Lastly, design guidelines to optimize the integrated heat exchange module are provided based on the study results
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