• Journal of Sensor Science and Technology
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• v.31 no.2
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• pp.96-101
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• 2022

As the elderly population gradually increases, the risk of fatal fall accidents among the elderly is increasing. One way to cope with a fall accident is to determine the fall direction before impact using a wearable inertial measurement unit (IMU). In this context, a previous study proposed a method of classifying fall directions using a support vector machine with sensor velocity, acceleration, and tilt angle as input parameters. However, in this method, the IMU signals are processed through several processes, including a Kalman filter and the integration of acceleration, which involves a large amount of computation and error factors. Therefore, this paper proposes a machine learning-based method that classifies the fall direction before impact using IMU raw signals rather than processed data. In this study, we investigated the effects of the following two factors on the classification performance: (1) the usage of processed/raw signals and (2) the selection of machine learning techniques. First, as a result of comparing the processed/raw signals, the difference in sensitivities between the two methods was within 5%, indicating an equivalent level of classification performance. Second, as a result of comparing six machine learning techniques, K-nearest neighbor and naive Bayes exhibited excellent performance with a sensitivity of 86.0% and 84.1%, respectively.

• The Journal of the Korea Contents Association
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• v.8 no.8
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• pp.244-252
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• 2008

This research differentiate the technique of Jungkwon-jirugi, one of the basic movements of Taekwondo, into two movements stop-jirugi and push-jirugi and gives analysis of the impulse, acceleration and velocity in the point of motor control. For this, we tried graphic analysis using an acceleration sensor and high speed camera which was made from USA in 2005 and took pictures at 250 frames per second. We reached the following conclusions. First, the acceleration wave of push-jirugi was a period longer than stop-jirugi, meaning that the push-jirugi motion asserts force for a longer time. Second, the acceleration and velocity graph shows that the highest velocity occurs on the point when the acceleration begins to decrease right after reaching its maximum. Third, according to the image analysis using the high speed camera, we could find out that the shoulder is pushed a little even in the stop-jirugi motion.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• v.6 no.1
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• pp.44-50
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• 2003

If the accelerometers are used in measuring the response, the absolute values of the velocity and displacement are not usually obtainable because their initial values are not accounted for in the integration of the acceleration response. A new dynamic response conversion algorithm of both the time domain and the frequency domain is proposed for the problem in estimating the displacement data by defining the transformed responses. In this algorithm, the displacement response can be obtained from the measured acceleration records by integration without requiring the knowledge of the initial velocity and displacement information. The applicability of the technique is tested by an example problem using the real bridge's superstructure under several cases of moving load. In the response conversion procedure of the frequency domain, the identified response according to the frequency can be estimated by changing over the limits of integration. If the reliability of the identified responses is ensured, it is expected that the proposed method for estimating the impact factor can be useful in the bridge's dynamic test. This method can be useful in those practical cases when the direct measurement of the displacement is difficult as in the dynamic studies of huge structure.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.812-818
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• 2001

The drop type impact test and finite element analysis are established for examining the buckling behavior of a square tube under the lateral impact load. Based on these results, the effects by the boundary conditions for supporting the structure are reviewed, which are as follows. One is pinned condition by screw; the other is fixed by welding. The critical impact force and acceleration by test are nearly same between two cases. However, the critical impact velocity of the pinned condition is higher than that of the fixed case. Therefore, the dynamic buckling behavior of a pinned structure is better than the fixed condition in view of critical impact velocity. These test and analysis results will be adaptable for predicting the dynamic structural integrity of a tube structure not only the axial impact event but the lateral impact event.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.505-508
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• 2004

단열완충재 제품간의 경량충원 저감성능 평가를 객관적이고 신속하게 판별하기 위하여 실험실용 시험장치를 개발하였다. EVA계열 및 EPPㆍEPS계열의 단열완충재들에 대한 경량충격원 시험에서 제품간의 성능비교가 가능하였으며, 동탄성계수 및 손실계수 측정과 병행함으로써 제품들간의 우열성을 보다 정밀하게 평가할 수 있었다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.19 no.3
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• pp.305-325
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• 2015

In this paper, missile homing guidance laws to control the impact angle and time are proposed based on the polynomial function. To derive the guidance commands, we first assume that the acceleration command profile can be represented as a polynomial function with unknown coefficients. After that, the unknown coefficients are determined to achieve the given terminal constrains. Using the determined coefficients, we can finally obtain the state feedback guidance command. The suggested approach to design the guidance laws is simple and provides the more generalized optimal solutions of the impact angle and time control guidance.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.12
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• pp.2982-2994
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• 1993

Low-velocity impact responses of composite laminates are investigated using the finite element method based on various theories. In two-dimensional nonlinear analysis, a displacement field considering higher order shear deformation and large deflection of the laminate is assumed and a finite element formulation is developed using a C$^{o}$-continuous 9-node plate element. Also, three-dimensional linear analysis based on the infinitesimal strain-displacement assumptions is performed using 8-node brick elements with incompatible modes. A modified Hertzian contact law is incorporated into the finite element program to evaluate the impact force. In the time integration, the Newmark constant acceleration algorithm is used in conjuction with successive iterations within each time step. Numerical results from static analysis as well as the impact response analysis are presented including impact force histories, deflections, strains in the laminate. Impact responses according to two typical low-velocity impact conditions are compared each other.

• Journal of the Korean Society of Safety
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• v.27 no.2
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• pp.98-104
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• 2012

Current [Guideline for Installation and Management of Sidewalks and Safety Facilities on Roads] suggests that the types of curbs should be Barrier curb ($85^{\circ}$). Although Barrier curbs ($90^{\circ}$) were not specified in the guideline. The curbs installed on the roads currently are Barrier curbs ($90^{\circ}$) which are not specified in the installation standard. Therefore, it is critical to prepare for the installation standard of curbs by researching types of curbs and driving safety. This research have assessed the driving safety throughout Full Scale Crash Test according to type of curbs (Barrier curbs ($85^{\circ}$) and Barrier curbs ($90^{\circ}$)). Barrier curbs ($90^{\circ}$) showed higher figure in Theoretical head Impact Velocity, Post-impact Head Deceleration, Vehicle Damage when Crash, Passenger's Wounds Severity, and every other items than Barrier curbs ($85^{\circ}$). Barrier curbs ($85^{\circ}$) were found to have better Occupant Safety Index. Analysis of Behavior Using Full-Scale Crash Test showed difference depending on the Impact Condition between Barrier curbs ($85^{\circ}$) and Barrier curbs ($90^{\circ}$). Generally, Barrier curbs ($85^{\circ}$) were superior than Barrier curbs ($90^{\circ}$) in terms of protecting the passengers and vehicle damages. When an impact angle increases, Acceleration of Vehicle, Variations of Speed, and Contact Relationship between Wheels and Curbs, two types of curb showed similarity. However, if an impact of an angle decreases, Barrier Curbs ($85^{\circ}$) showed excellence in Driving Safety such as Acceleration of Vehicle, Variations of Speed, and Contact Relationship between Wheels and Curbs.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1125-1131
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• 2014

This work presents a vulnerability assessment procedure for a complex structure using vibration characteristics. The structural behavior of a three-dimensional framed structure subjected to impact forces was predicted using the spectral element method. The Timoshenko beam function was applied to simulate the impact wave propagations induced by a high-velocity projectile at relatively high frequencies. The interactions at the joints were analyzed for both flexural and longitudinal wave propagations. Simulations of the impact energy transfer through the entire structure were performed using the transient displacement and acceleration responses obtained from the frequency analysis. The kill probabilities of the crucial components for an operating system were calculated as a function of the predicted acceleration amplitudes according to the acceptable vibration levels. Following the proposed vulnerability assessment procedure, the vulnerable positions of a three-dimensional combat vehicle with high possibilities of damage generation of components by impact loading were identified from the estimated vibration responses.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.3
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• pp.281-292
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• 2014

We propose a novel cooperative guidance law design method based on the finite time disturbance observer (FTDO) for multiple near space interceptors (NSIs) with impact time control. Initially, we construct a cooperative guidance model with head pursuit, and employ the FTDO to estimate the system disturbance caused by target maneuvering. We subsequently separate the cooperative guidance process into two stages, and develop the normal acceleration command based on the super-twisting algorithm (STA) and disturbance estimated value, to ensure the convergence of the relative distance. Then, we also design the acceleration command along the line-of-sight (LOS), based on the nonsingular fast terminal sliding mode (NFTSM) control, to ensure that all the NSIs simultaneously hit the target. Furthermore, we prove the stability of the closed-loop guidance system, based on the Lyapunov theory. Finally, our simulation results of a three-to-one interception scenario show that the proposed cooperative guidance scheme makes all the NSIs hit the target at the same time.