Youngmyung Lee

Non-linear dynamic response structural optimization for frontal-impact and side-impact crash tests

Vehicle crash optimization is a representative non-linear dynamic response structural optimization that utilizes highly non-linear vehicle crash analysis in the time domain. In the automobile industries, crash optimization is employed to enhance the crashworthiness characteristics. The equivalent-static-loads method has been developed for such non-linear dynamic response structural optimization. The equivalent static loads are the static loads that generate the same displacement field in linear static analysis as those of non-linear dynamic analysis at a certain time step, and the equivalent static loads are imposed as external loads in linear static structural optimization. In this research, the conventional equivalent-static-loads method is expanded to the crash management system with regard to the frontal-impact test and a full-scale vehicle for a side-impact crash test. Crash analysis frequently considers unsupported systems which do not have boundary conditions and where adjacent structures do not penetrate owing to contact. Since the equivalent-static-loads method uses linear static response structural optimization, boundary conditions are required, and the impenetrability condition cannot be directly considered. To overcome the difficulties, a problem without boundary conditions is solved by using the inertia relief method. Thus, relative displacements with respect to a certain reference point are used in linear static response optimization. The impenetrability condition in non-linear analysis is transformed to the impenetrability constraints in linear static response optimization.

Optimization of the loading path for the tube-hydroforming process

In general, hydroforming optimization aims to make a desired shape of a plastically deformed structure under dynamic forces. The automotive industry has shown great interest in tube hydroforming, which is a metal-forming process. The forces from the hydraulic fluid are utilized to deform a tube. The internal pressures and the axial feedings (of the axial forces) determine the quality of the deformed product. In this research, an optimization process is employed to evaluate the appropriate external forces but defects are prevented. The equivalent static loads method for non-linear static response structural optimization is used for the optimization process because the tube-hydroforming process is analysed by non-linear dynamic response analysis. The equivalent static loads are the static loads that generate the same response field as that of non-linear dynamic analysis and are utilized as the loading conditions in linear static response optimization. A novel process is added to the original equivalent static loads method for non-linear static response structural optimization to address the objective function and the design variables for tube-hydroforming optimization. A new technique is proposed to use the external forces as the design variables in linear static response optimization. A few hydroforming examples are solved by using the newly proposed techniques.

Detection, motion planning and control of human tracking mobile robots

In this paper, a method combining detection, motion planning and control of human tracking mobile robots is discussed. Using face recognition and detection of a pair of human legs via a stereo vision camera and 2D laser scanner, respectively, the human position is estimated. Based on the differential flatness property of the kinematic model of the mobile robot, the trajectory of the robot to the moving human is planned in real-time. The combined motion planning and control method is used for tracking a detected human.

Crash Optimization of an Automobile Frontal Structure Using Equivalent Static Loads

Abstract : Automobile crash optimization is nonlinear dynamic response structural optimization that uses highly nonlinear crash analysis in the time domain. The equivalent static loads (ESLs) method has been proposed to solve such problems. The ESLs are the static load sets generating the same displacement field as that of nonlinear dynamic analysis. Linear static response structural optimization is employed with the ESLs as multiple loading conditions. Nonlinear dynamic analysis and linear static structural optimization are repeated until the convergence criteria are satisfied. Nonlinear dynamic crash analysis for frontal analysis may not have boundary conditions, but boundary conditions are required in linear static response optimization. This study proposes a method to use the inertia relief method to overcome the mismatch. An optimization problem is formulated for the design of an automobile frontal structure and solved by the proposed method. Key words : Structural optimization(구조최적설계), Size optimization(치수최적설계), Inertia relief method(관성제거법), Equivalent static loads( 등가정하중), Frontal structure(전방구조물)

Case studies of a robot enhanced walker for training of children with cerebral palsy

Cerebral palsy (CP) is a disorder of movement and posture in children caused by non-progressive insult of the immature brain. The characteristic features are weakness, spasticity, muscle contractures, and poor motor coordination. The gait patterns of children with CP are slow, uncoordinated, and unstable. Our hypothesis is that these impaired children will benefit from robot enhanced walkers to improve their balance, coordination, and speed during gait. In addition, this experience will also impact their clinical scores that relate to their functional performance and caregiver assistance. In this study, we used a specially-designed robotic walker which children used to perform a series of walking tasks, in increasing order of difficulty. This study was performed in 30 training sessions over a period of 3 months. Each training session lasted for 20 minutes. The outcome measures were variables recorded by the robot such as travel distance, average speed, and clinical measured variables that characterize their disability profiles.

Vehicle crash optimization considering a roof crush test and a side impact test

The vehicle performances for the side impact test and the roof crush test are dependent on the side structure design of a vehicle. Crash optimization can be employed to enhance the performances. A meta-model-based structural optimization technique is generally utilized in the optimization process since the technique is simple to use. However, the meta-model-based optimization is not suitable for problems with many design variables such as topology and topometry optimizations. A crash optimization methodology is proposed to consider both the side impact test and the roof crush test. The equivalent static loads method is adopted for the side impact test and the enforced displacement method is adopted for the roof crush test, and the two methods are integrated. A design formulation is defined. The survival distance from the side impact test and the roof strength for the roof crush test are used for the design constraints. Crash optimization is performed for a practical large-scale structure. For conceptual design, reinforcement of the B-pillar is determined by using topometry optimization, and size and shape optimizations are employed for a detailed design to satisfy the design constraints while the mass is reduced.

Pedestrian Protection System Design for SUV Using the Design of Experiments

The mortality rate of car-pedestrian accidents is quite high, compared to the frequency of accidents. Researches on pedestrian protection are being actively performed worldwide. The A-pillar and lower part of the wind shield cause the most serious damage to the pedestrians. Typical devises to protect the pedestrians are the hood lift system and pedestrian airbag. The design of such devices for an sport utility vehicle is performed based on a design process using design of experiments (DOE). The design results are obtained by an orthogonal array (OA), analysis of mean (ANOM) and analysis of variance (ANOVA). A metamodel is also used in the design process.The mortality rate of car-pedestrian accidents is quite high, compared to the frequency of accidents. Researches on pedestrian protection are being actively performed worldwide. The A-pillar and lower part of the wind shield cause the most serious damage to the pedestrians. Typical devises to protect the pedestrians are the hood lift system and pedestrian airbag. The design of such devices for an sport utility vehicle is performed based on a design process using design of experiments (DOE). The design results are obtained by an orthogonal array (OA), analysis of mean (ANOM) and analysis of variance (ANOVA). A metamodel is also used in the design process.

Robot-Enhanced Mobility Training of Children With Cerebral Palsy: Short-Term and Long-Term Pilot Studies

Mobility is a causal factor in infant development. Neural impaired infants, e.g., with cerebral palsy (CP), are at risk for further developmental delays due to lack of self-generated mobility. It is possible that these infants may benefit from robot-enhanced mobility, where the mobility comes from a robot that the child drives via a joystick. We believe that such a mobility experience will enrich the child and minimize further delays in attaining some of the childhood developmental and social milestones. In order to address the broad goal posed earlier, one can ask the following simpler questions: 1) Will children with CP learn to drive a robot using a joystick? 2) Will these children with CP sustain interest in doing so over multiple training sessions? 3) Will such a robot-enhanced mobility impact development scores in this group of children? 4) Will a larger number of robotic training sessions be more effective to enhance these developmental scores? This paper reports the first results from two pilot studies conducted by our research group on robot-assisted mobility training, where children with CP performed two tasks across multiple training sessions. We found that, after training with the robot, children who performed 30 training sessions, labeled as “long-term study,” advanced in their driving skills and showed significant improvements in clinical scores such as Gross Motor Function Measure, Quality of Upper Extremity Skills Test, and Pediatric Evaluation of Disability Inventory (mobility with/without caregiver and social function with/without caregiver).