Marcelo H. Kobayashi

Numerical Study of stall delay on humpback whale flippers

this range of Re numbers is necessary. Recently was reported 2 that the humpback whale flipper is optimized to prevent stall and to improve aerodynamic performance. These features allow these animals to be extremely mobile with great turning ability which is necessary to catch prey. This observation together with the fact that the Reynolds number for the humpback whale falls in the aforementioned low Re range propelled the experimental study the humpback whale flipper. The flippers for this species display a very characteristic scalloped leading edge, whereas the flippers of other species less maneuverable are much smoother. 3 The experiments compared a flipper with tubercles with a smooth flipper. The researchers reported an improvement in the aerodynamic performance as well an increase in the angle of attack at which the flipper stalls. However no flow visualization was performed, therefore the reasons why the scalloped flipper performs better were not uncovered. In this work we performed the numerical simulation of the setup used for the experimental study. The unsteady turbulent flow field for the scalloped flipper and for the smooth flipper was accurately determined which produced detailed information necessary to fully understand the mechanism behind the reported improvement. Our goal with this work is to increase the knowledge about these lower Re number flows which will be useful for the design of more ecient UAV’s wings.

A Note on the Conservation of Energy and Volume in the Setting of Nonholonomic Mechanical Systems

This note concerns the analysis of conservation of energy and volume for a series of well known examples of nonholonomic mechanical systems, with linear and non-linear constraints, and aims to make evident some geometric aspects related with them.

Optimization of Aircraft Lifting Surfaces Using a Cellular Division Method

The development of a biologically inspired methodology for topology, shape, sizing, and control surface optimization of aircraft lifting surfaces is presented. The methodology is based on the map L-systems modeling of cellular division to generate the substructure topology. This is combined with variables for aerodynamic shape, structural sizing, and control surfaces (number, size, location, and aeroelastic trimmed settings) and constraints on stiffness, strength, local skin panel buckling, static aeroelastic response (roll performance, pitch rate, trimmed angle of attack), and flutter requirements. A dual-objective function is formulated with weight and L/D and is solved with a bilevel optimization algorithm. The map L-system rules that develop the topology are evolved using a genetic algorithm in the outer optimization loop on L/D and weight, which obtains the optimal parameter settings for topology, shape, and control surfaces, whereas the inner loop performs weight minimization with the structural siz...

Experimental Study and Numerical Analysis of Water Single-Phase Pressure Drop Across an Array of Circular Micro-Pin-Fins

This study investigates pressure drop associated with water liquid single-phase flow across an array of staggered micro-pin-fins having circular cross-section. The micro-pin-fins are micro-end milled out of oxygen free copper and have the following dimensions: 180 micron diameter and 683 micron height. The longitudinal pitch and transverse pitch are equal to 400 microns. Seven water inlet temperatures from 22 to 80 °C, and seventeen maximum mass velocities for each inlet temperature, ranging from 159 to 1475 kg/m2 s, were tested. The test module was well insulated to maintain adiabatic conditions. The experimental results were compared to those from a micro-pin-fin array having similar size and geometrical arrangement but a square cross-section. The circular micro-pin-fins were seen to yield a significantly lower pressure drop than the square micro-pin-fins. The present experimental results were also compared with the predictions of several friction factor correlations as well as the results from a three-dimensional numerical analysis. Neither was able to accurately predict the experimental data.Copyright

Topology, Shape, and Sizing Optimization of Aircraft Lifting Surfaces Using a Cellular Division Method

The development of a biologically inspired methodology for topology, shape, and sizing optimization of aircraft lifting surfaces is explored. The methodology is based on the map L systems modeling of cellular division to generate the substructure topology. This is combined with aerodynamic shape and structural sizing optimization and evaluated against strength, buckling, and flutter requirements. The rules that indirectly develop the topology are then evolved using a genetic algorithm to obtain the optimal parameter settings. The methodology is demonstrated on the design of a generic fighter aircraft wing box. This effort is an extension of the work conducted in Reference [1] by Kobayashi et al. In Reference [1] the cellular division method was developed for aircraft structural topology and sizing subject to static aeroelastic constraints. The current study extends the previous work by also including aerodynamic shape parameters and the addition of constraints for panel buckling and flutter.

On the variational mechanics with non-linear constraints

Abstract This paper concerns a geometric formulation of the so-called variational mechanics for mechanical systems with non-linear constraints. Given a smooth Lagrangian L on the tangent bundle of the configuration space M of the constrained mechanical system, its variational trajectories are defined, through a generalization of Hamiltons principle of stationary action, as extremals of the smooth Lagrangian functional γ↦∫ L ( γ ) defined on a convenient Banach manifold of curves compatible with the constraint manifold C ⊂ TM . In the particular case of a Lagrangian given by the positive definite quadratic form induced by a metric tensor onxa0 M , this amounts to a generalization of sub-Riemannian geometry. Among the main results, it is proven that, under a regularity condition on the Lagrangian L, the normal extremals of the Lagrangian functional are given by the projections onxa0 M of a Hamiltonian vector field defined on the generalized mixed bundlexa0 W .

Nonholonomic Systems and the Geometry of Constraints.

In a recent paper [9] we analyze conservation of volume for a series of examples of mechanical systems with linear, affine and non linear constraints aiming to make evident some geometric aspects related with them. Here, we only consider examples with linear constraints (defined by a constant rank distribution), in which we have conservation of volume. Conservation of volume means, equivalently, that the orthogonal distribution (the metric is defined by the kinetic energy) is minimal (see [15]) and so, if it is integrable, the corresponding foliation has minimal leaves. Properties of the falling penny and of the vertical disc rolling on a horizontal plane without slipping are very special. A dynamically symmetric sphere that rolls without slipping on a given surfaceS⊂ℝ3 conserves volume, and the orthogonal distribution is integrable if, and only if,S isparallel to a surface with a fixed constant mean curvature. Semi-simple Lie groups endowed with suitable metrics have foliations with minimal leaves. Geometric questions related with the kinematics of the rolling motion of two surfaces are also considered.

Hybrid Genetic Programming With Accelerating Genetic Algorithm Optimizer for 3-D Metamaterial Design

The computational efficiency of existing genetic programming (GP) software is improved through the addition of parallelization and hybridization with a low-level optimizer. The low-level optimizer is implemented using genetic algorithm, and two different versions of the developed hybrid GP program are presented. Timing and efficiency performance are discussed, which includes a method of making the original optimizer more than eight times faster. Efficiency results indicate that through the use of the optimizer, with sufficient variables included, significantly fewer (about ¼ to ½) GP generations are required to achieve working metamaterial designs. Two low-frequency broadband (225-450 MHz) ground plane design examples, which are 25.3% thinner than a previously published design covering the same frequency band, are included.

Vibration reduction using biologically inspired topology optimization method: optimal stiffeners distribution on an acoustically excited plate

This paper presents the development of a biologically inspired method for topology optimization and its application to a vibration suppression problem. The proposed method is based on modeling the structure topology (distribution of stiffening ribs) by replicating the natural growth of dendritic structures, which are ramified branches as those e.g. in leaves or in insect wings. The test case is a plate excited by acoustic pressure. The multi-objectives topology optimization aims to reduce both the vibration amplitude and mass of the plate. Experimental tests are performed for baseline plate model validation and identification of acoustic excitation distribution. A set of solutions are designed by the proposed method and numerically compared with traditional optimization approaches, showing improved performances. Finally, in order to evaluate industrial applicability, the robustness of the solutions to uncertainty in branch widths is demonstrated.

Vehicle Configuration Design Using Cellular-Division and Level-Set Based Topology Optimization

In this research, a combination of global-local optimization with the possibility of multi-objective trade-off solutions is considered for vehicle configuration design. At global-level, many potential configurations are created as initial designs using cellular-division method for design space exploration. At local-level, level-set method optimizes these initial shapes for strict constraint satisfaction. A combination of these two approaches with their individual strengths are synergistically integrated for evolving a configuration from an open-ended design space for better optima. This research demonstrates the framework using several benchmark problems of topology optimization.