Tomoaki Tatsukawa

Interactive Simulation of the Human Eye Depth of Field and Its Correction by Spectacle Lenses

This paper describes a fast rendering algorithm for verification of spectacle lens design. Our method simulates refraction corrections of astigmatism as well as myopia or presbyopia. Refraction and defocus are the main issues in the simulation. For refraction, our proposed method uses per‐vertex basis ray tracing which warps the environment map and produces a real‐time refracted image which is subjectively as good as ray tracing. Conventional defocus simulation was previously done by distribution ray tracing and a real‐time solution was impossible. We introduce the concept of a blur field, which we use to displace every vertex according to its position. The blurring information is precomputed as a set of field values distributed to voxels which are formed by evenly subdividing the perspective projected space. The field values can be determined by tracing a wavefront from each voxel through the lens and the eye, and by evaluating the spread of light at the retina considering the best human accommodation effort. The blur field is stored as texture data and referred to by the vertex shader that displaces each vertex. With an interactive frame rate, blending the multiple rendering results produces a blurred image comparable to distribution ray tracing output.

Many-objective evolutionary computation for optimization of separated-flow control using a DBD plasma actuator

In this paper, an algorithm for many-objective evolutionary computation, which is based on the NSGA-II with the Chebyshev preference relation, is applied to multi-objective design optimization problem of dielectric barrier discharge plasma actuator (DBDPA). The present optimization problem has four design parameters and six objective functions. The main goal of the paper is to extract useful design guidelines to predict control flow behavior based on the DBDPA parameter values using the resulting approximation Pareto set obtained by the optimization.

An Eyeglass Simulator Using Conoid Tracing

This paper proposes a method for displaying images at the fovea of the retina taking visual acuity into account. Previous research has shown that a point light source projected onto the retina forms an ellipse, which can be computed with wavefront tracing from each point in space. We propose a novel concept using conoid tracing, with which we can acquire defocusing information several times faster than that acquired by previous methods. We also show that conoid tracing is more robust and produces higher quality results. In conoid tracing the ray is regarded as a conoid, a thin cone‐like shape with varying elliptical cross‐section. The viewing ray from the retina is traced as a conoid and evaluated at each sample location. Using the sampled and pre‐computed data for the spatial distribution of blurring, we implemented an interactive eyeglass simulator. This paper demonstrates some visualization results utilizing the interactivity of the simulator, which an eyeglass lens design company uses to evaluate the design of complex progressive lenses.

On the fast hypervolume calculation method

We propose a new algorithm FHV (Fast HyperVolume) for exact hypervolume (HV) calculation using divide and conquer algorithm. FHV divides the original set of non-dominated solutions into several fractions first, calculate the value of HV of each fraction separately, sum up the each value, and finally obtain the value of HV of the original set. Therefore there are three very strong points: 1. Calculation cost is reduced significantly because each fraction contains less number of non-dominated solutions; 2. Complete parallelism is possible because each divided fraction is independent each other; 3. An arbitrary HV calculation method such as HOY (Hypervolume by Overmars and Yap) and WFG (Walking Fish Group) can be used together with FHV. Using these features computation time of HV becomes considerably reduced. For example, in a case number of objective functions is 5 and number of solutions is 1 × 106, it takes about 21 hours using WFG, however it takes only less than 30 minutes using FHV.

A New Multiobjective Genetic Programming for Extraction of Design Information from Non-dominated Solutions

We propose a new type of multi-objective genetic programming (MOGP) for multi-objective design exploration (MODE). The characteristic of the new MOGP is the simultaneous symbolic regression to multiple objective functions using correlation coefficients. This methodology is applied to non-dominated solutions of the multi-objective design optimization problem to extract information between objective functions and design parameters. The result of MOGP is symbolic equations that are highly correlated to each objective function through a single GP run. These equations are also highly correlated to several objective functions. The results indicate that the proposed MOGP is capable of finding new design parameters more closely related to the objective functions than the original design parameters. The proposed MOGP is applied to the test problem and the practical design problem to evaluate the capability.

DBD Plasma Actuator Multi-Objective Design Optimization at Reynolds Number 63,000: Baseline Case

The working parameters of the dielectric barrier discharge (DBD) plasma actuator were optimized to gain an understanding of the flow control mechanism. Experiments were conducted at a Reynolds number of 63,000 using a NACA 0015 airfoil which was fixed to the stall angle of 12 degrees. The two objective functions are: 1) power consumption (P) and 2) lift coefficient (Cl). The goal of the optimization is to decrease P while maximizing Cl. The design variables consist of input power parameters. The algorithm was run for 10 generations with a total population of 260 solutions. Although the number of generations and population size was limited due to experimental constraints, the algorithm was able to converge and the approximate Pareto-front was obtained. From the objective function space, we observe a relatively linear trend where Cl increases with P and after a certain threshold, the value of Cl seems to saturate. We discuss the results obtained in the objective space in addition to scatter plot matrix and color maps. This article, with its experiment-based approach, demonstrates the robustness of a Multi-Objective Design Optimization method and its feasibility for wind tunnel experiments.Copyright

Design Exploration of Low-Thrust Space Trajectory Problem for DESTINY Mission

The present study focuses on exploring optimal transfer solutions for the Demonstration and Experiment of Space Technology for INterplanetary voYage (DESTINY) mission, which was proposed as an Inst...

Design Exploration of a DBD Plasma Actuator for Massive Separation Control

The main aim of this paper is to elucidate the mechanism of massive separation control by using a dielectric barrier discharge plasma actuator (DBDPA). A technique of design exploration is applied to find good operating-parameter combinations for the DBDPA. We consider a NACA 0015 airfoil with 16◦ angle of attack and Reynolds number Re = 63000. The flow without the control is massively separated, however we can suppress the separation using the DBDPA with the relevant operating parameters. Using good parameter combinations obtained by design exploration technique, the nature of the flow around the airfoil with and without control is explored in detail.

Multiobjective Design Exploration of an Aeroacoustic Design Problem for Rocket Launch Site with Evolutionary Computation and Large Eddy Simulations

In this study, multiobjective design exploration for a rocket launch site is conducted using the evolutionary computation with the large eddy simulation to understand the acoustic characteristics associated with various launch sites and find design information such as trade-off relation among objective functions. The launch site is described by the curved surface. The flat plate inclined with 45 degree is considered as the reference configuration. The objective functions of multiobjective aeroacoustic design optimization are, 1) minimization of averaged sound pressure level near the payload fairing, 2) minimization of maximum pressure on the curved surface of the rocket launch site, and 3) minimization of the difference of the curved surface from the flat plate inclined with 45 degree. Threedimensional compressible Navier-Stokes equations are solved with the modified weighted compact nonlinear scheme. The total number of evaluation in multiobjective evolutionary computation is 2500, and the evaluation of one configuration necessitates the use of 130 nodes(1040 total cores) using ”K” supercomputer. Firstly, the analysis of non-dominated solutions clearly shows that there are various trade-off relations and correlations among the objective functions. Furthermore, the analysis of flow fields shows that as the curved surface around the impingement region becomes steeper, the acoustic waves generated from the impingement region weaken. This is because the curved surface becomes steeper, the separation bubble near the impingement region becomes smaller, and finally disappears. The proper orthogonal decomposition(POD) analysis is conduced to extract the characteristic modes from characteristic non-dominated solutions.

Three-Dimensional Wing Design Towards the Future Mars Airplane

The effects of aspect ratio and Reynolds number on aerodynamic characteristics of three-dimensional rectangular wing at low Reynolds number of 103 to 105 , are investigated with Reynolds-averaged Navier-Stokes solver with the Baldwin-Lomax model. Present results show that lift coefficient decreases drastically at lower aspect ratio than 4. Besides, the much larger viscous drag coefficient is obtained at the lower Reynolds number, especially lower than 104 . In order to focus on designing practical wings, the particular cases under the condition of fixed wing-surface area and fixed main stream velocity are conducted. The results show that there is trade-off between the decrease in viscous drag coefficient with increasing Reynolds number and the increase in lift coefficient with increasing aspect ratio. At the lower Reynolds number condition, as the former effect is stronger than the latter one, maximum lift-to-drag ratio is obtained at lower aspect ratio.Copyright