Jung-Sun Choi

Optimization of an automobile curtain airbag using the design of experiments

A side collision of an automobile poses a higher risk of injury than a frontal collision does. Throughout the world, governments and insurance companies tend to establish and implement new safety standards for side collisions in order to ensure the safety of the occupants of vehicles. Most of the standards aim to reduce the head injury criterion. Currently, curtain-airbag systems are widely used and known to be the most effective means to reduce the head injury criterion in the event of a side collision. A curtain-airbag design procedure which uses modern optimization methods based on a newly defined design scenario to reduce the head injury criterion risks of the occupants of vehicles is introduced in this paper. The design scenario has two phases. In phase 1, various elements of the curtain airbag are defined as the design parameters. The variables are determined in a discrete space using an orthogonal array as well as in a continuous space using optimization where each function is approximated. In phase 2, important variables are extracted via a statistical method and those variables are determined in the same manner as in phase 1. As a result, the head injury criterion of the occupant is decreased significantly. The final design is discussed from a practical viewpoint.

Analysis and Fabrication of Unconventional Flapping Wing Air Vehicles

ßRecently, numerous research groups are actively studying the design of the flapping wing air vehicles (FWAV). The FWAV was inspired by flying birds and insects. The lift and thrust forces are simultaneously generated from the flapping motion. The FWAV design is classified into either a biomimetic design or a biomorphic design. First, the bird-mimicking FWAV, which has one pair of wings, is fabricated as a biomimetic design. The driving mechanism is simplified to implement the flapping motion in the vertical plane. Second, unconventional FWAVs, which are the X-type wing FWAV, two pairs of X-type wings FWAV and three pairs of X-type wings FWAV, are developed to improve the performance of the bird-mimicking FWAV. The X-type wing FWAV is developed as a biomorphic design. The two pairs of X-type wings FWAV and three pairs of X-type wings FWAV are developed as a combination of the biomimetic and biomorphic designs. Various flight tests are carried out and the performances of FWAVs are analyzed by measuring the thrust-to-weight ratio and the lift-to-weight ratio. The results indicate that the unconventional FWAV with an appropriate combination of biomimetic and biomorphic designs has superior performance to the bird-mimicking FWAVs with a biomimetic design.

Kinematic Optimization of a Flapping Motion for Maneuverability and Sustainability Flights

The design of a biomimetic micro air vehicle with flapping wings is an essential challenge in the military/civilian field to conduct various missions. The success of a micro-air-vehicle flight is strongly related to the maneuverability and sustainability of an unsteady aerodynamic performance of the flapping motion. Appropriate flapping kinematics need to be established that are amenable to various flight purposes under a fluctuating environment. In this research, kinematics of flapping motion are determined by the study of aerodynamic performance of a flapping airfoil for appropriate maneuverability and sustainability. The flapping motion of an airfoil is formulated by a combined sinusoidal plunging and pitching motion in various angles of the stroke plane. The optimization process is carried out to determine the efficient motions based on a well-defined surrogate model that is made from the results of two-dimensional computational-fluid-dynamics analysis. The kriging method and genetic algorithm are use...

Multidisciplinary design optimization of the flapping wing system for forward flight

The success of a flapping wing air vehicle flight is strongly related to the flapping motion and wing structure. Various disciplines should be considered for analysis and design of the flapping wing system. A design process for a flapping wing system is defined by using multidisciplinary design optimization. Unsteady aeroelastic analysis is employed as the system analysis. From the results of the aeroelastic analysis, the deformation of the wing is transmitted to the fluid discipline and the dynamic pressure is conveyed to the structural discipline. In the fluid discipline, a kinematic optimization problem is solved to maximize the time-averaged thrust coefficient and the propulsive efficiency simultaneously. In the structural discipline, nonlinear dynamic topology optimization is performed to find the distribution of reinforcement by using the equivalent static loads method for nonlinear static response structural optimization. The defined design process is applied to a flapping wing air vehicle model and the flapping wing air vehicle model is fabricated based on the optimization results.

Optimization of the Flapping Motion for the High Maneuverability Flight

The study considers the high maneuverability flight and path optimization is conducted to investigate the appropriate generation of the lift and thrust considering the angle of the stroke plane. The path optimization problem is defined according to the various purposes of the high maneuverability flight. The flying purposes are to maximize thrust force, lift force and both lift and thrust forces. The flapping motion of the airfoil is made by a combined sinusoidal plunging and pitching motion in each problem. The optimization process is carried out by using well-defined surrogate models. The surrogate model is determined by the results of two-dimensional computational fluid dynamics analysis. The Kriging method is used to make the surrogate model and a genetic algorithm is utilized to optimize the surrogate model. The optimization results show the flapping motions for the high maneuverable flight. The effects on the generation of lift and thrust forces are confirmed by analyzing the vortex.

Optimization of the flapping motion for the hovering flight

The kinematics of a flapping plate is determined by solving a path optimization problem for the hovering flight. The flapping motion of the flat plate is described by a combined sinusoidal plunging and pitching motion in the horizontal plane. The optimization process is carried out based on a well defined surrogate model which is made from the results of 2-dimensional computational fluid dynamics analysis. The Kriging method and genetic algorithm are utilized for the path optimization problem. The design variables are the pitching amplitude, the phase angles, and frequency of the flapping motion. The optimization results show that the drag force and the thrust force in the flapping motion cancel each other out because the flapping motion is almost symmetric. The lift force, which is almost the same as the weight of the flapping wing micro air vehicle, is only generated by the flapping motion.

Topology Optimization of a Flapping Wing using Equivalent Static Loads

The flapping wing of a micro air vehicle is optimized to enhance performance while some rigidity is kept with minimum mass. A work flow for the design of the flapping wing is defined. The performances to be enhanced are thrust coefficient and propulsive efficiency. The flapping kinematics of the flapping wing is determined by solving a path optimization problem which maximizes the performances. The optimization process is carried out based on a well defined surrogate model. The surrogate model is made from the results of two-dimensional fluid dynamic analysis. The Kriging method is employed to establish the surrogate model and a genetic algorithm is utilized for the multi-objective function problem. Dynamic topology optimization is performed to find the distribution of reinforcement. Certain rigidity can be kept by the results of topology optimization. A dynamic topology optimization method is developed by modification of the equivalent static loads method for non linear static response structural optimization. Three-dimensional computational fluid dynamic analysis is performed based on the optimum values of the path optimization to evaluate the external loads for the topology optimization process. It is found that the topology results are quite similar to the practical product. The process of the defined work flow is materialized by interfacing various software systems.