• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.9
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• pp.923-928
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• 2008

Pyrotechnic shock or pyroshock is characterized as a transient vibration phenomenon which shows large acceleration and high frequency range up to 10kHz during the operation of separation devices where explosives are used. During the flight of a launch vehicle, pyroshock is mainly generated at several events such as satellite separation, fairing separation and stage separation. In this paper, wiremesh isolators are introduced and several types of isolators are manufactured for the performance tests. For the investigation of typical characteristics of wiremesh isolators, compressive loading tests are basically performed and pyroshock tests are accomplished to confirm pyroshock isolation ability of each wiremesh isolator by using 4Kg dummy mass.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.11
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• pp.1957-1964
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• 1997

Torsional vibration is to vibrate strongly when the ignition pulses of the engine is excited with natural frequency of driveline. Torsional vibration like this can cause various noises as rattle and booming. For this study multi-degree of freedom analysis model of torsional vibration, which is combined with mass moment of inertia and torsional spring, was developed toward two wheel drive, four wheel drive and torsional vibration characteristics were compared and analyzed through the natural frequences, mode shapes and frequency response characteristics which was acquired by the simulation of it. The pertinence of that model was proved by the field test and the outcome of the simulations coincided with feeling test. Therefore, four wheel drive simulation model is considered to be useful thing for reducing torsional vibration of driveline and developing full-time four wheel drive vehicles.

• Structural Engineering and Mechanics
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• v.43 no.4
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• pp.503-526
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• 2012

Pounding between closely located adjacent buildings is a serious issue of dense cities in the earthquake prone areas. Seismic responses of adjacent buildings subjected to earthquake induced pounding are numerically studied in this paper. The adjacent buildings are modeled as the lumped mass shear buildings subjected to earthquake acceleration and the pounding forces are modeled as the Kelvin contact force model. The Kelvin model is activated when the separation gap is closed and the buildings pound together. Characteristics of the Kelvin model are extensively explored and a new procedure is proposed to determine its stiffness. The developed model is solved numerically and a SDOF pounding case as well as a MDOF pounding case of multistory adjacent buildings are elaborated and discussed. Effects of different separation gaps, building heights and earthquake excitations on the seismic responses of adjacent buildings are obtained. Results show that the seismic responses of adjacent buildings are affected negatively by the pounding. More stories pound together and pounding is more intense if the separation gap is smaller. When the height of buildings differs significantly, the taller building is almost unaffected while the shorter building is affected detrimentally. Finally, the buildings should be analyzed case by case considering the potential earthquake excitation in the area.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.86-89
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• 2005

A computational work has been performed to investigate the aerodynamics of a projectile which is launched from the two-stage light gas gun. A moving coordinate method for a multi-domain technique is employed to simulate unsteady projectile flows with a moving boundary. The effect of a virtual mass is added to the axisymmetric unsteady Euler equation system. The computed results reasonably capture the major flow characteristics which we generated in launching the projectile supersonically, such as the interaction between the shock wave and the blast wave, the interaction between the vortical flow and the barrel shock, and the steady under-expanded jet. The present computational results properly predict the velocity, acceleration, and drag histories of the projectile.

• Structural Engineering and Mechanics
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• v.15 no.3
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• pp.299-314
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• 2003

This investigation presents an efficient method for identifying modal characteristics from the measured displacement, velocity and acceleration signals of multiple channels on structural systems. A Vector Backward Auto-Regressive model (VBAR) that describes the relationship between the output information in different time steps is used to establish a backward state equation. Generally, the accuracy of the identified dynamic characteristics can be improved by increasing the order of the Auto-Regressive model (AR) in cases of measurement of data under noisy circumstances. However, a higher-order AR model also induces more numerical modes, only some of which are the system modes. The proposed VBAR model provides a clear characteristic boundary to separate the system modes from the spurious modes. A numerical example of a lumped-mass model with three DOFs was established to verify the applicability and effectiveness of the proposed method. Finally, an offshore platform model was experimentally employed as an application case to confirm the proposed VBAR method can be applied to real-world structures.

• Earthquakes and Structures
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• v.18 no.2
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• pp.263-273
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• 2020

The use of energy concepts in seismic analysis and design of structures requires the understanding of the input energy response of multi-degree-of-freedom (MDOF) systems subjected to strong ground motions. For design purposes and non-time consuming analysis, however, it would be beneficial to associate the input energy response of MDOF systems with those of single-degree-of-freedom (SDOF) systems. In this paper, the theoretical formulation of energy input to MDOF systems is developed on the basis that only a particular portion of the total mass distributed among floor levels is effective in the nth-mode response. The input energy response histories of several reinforced concrete frames subjected to a set of eleven horizontal acceleration histories selected from actual recorded events and scaled in time domain are obtained. The contribution of the fundamental mode to the total input energy response of MDOF frames is demonstrated both graphically and numerically. The input energy of the fundamental mode is found to be a good indicator of the total energy input to two-dimensional regular MDOF structures. The numerical results computed by the proposed formulation are verified with relative input energy time histories directly computed from linear time history analysis. Finally, the elastic input energies are compared with those computed from time history analysis of nonlinear MDOF systems.

• Journal of Multimedia Information System
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• v.2 no.2
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• pp.233-240
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• 2015

Mobile devices are becoming increasingly sophisticated and the latest generation of smartphones now incorporates many diverse and powerful sensors. These sensors include acceleration sensor, magnetic field sensor, light sensor, proximity sensor, gyroscope sensor, pressure sensor, rotation vector sensor, gravity sensor and orientation sensor. The availability of these sensors in mass-marketed communication devices creates exciting new opportunities for data mining and data mining applications. In this paper, we describe and evaluate a system that uses phone-based accelerometers to perform activity recognition, a task which involves identifying the physical activity that a user is performing. To implement our system, we collected labeled accelerometer data from 10 users as they performed daily activities such as "phone detached", "idle", "walking", "running", and "jumping", and then aggregated this time series data into examples that summarize the user activity 5-minute intervals. We then used the resulting training data to induce a predictive model for activity recognition. This work is significant because the activity recognition model permits us to gain useful knowledge about the habits of millions of users-just by having them carry cell phones in their pockets.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.2
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• pp.193-201
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• 1998

A heat exchanging system employing the impinging air jet is still widely used In the various fields due to its inherent merits that include the easiness in engineering applications and the high heat and/or mass transfer characteristics. The purpose of this study is to investigate the enhancement of heat transfer and flow characteristics by placing a turbulence promoters in front of heat exchanging surface. In this study, a series of circular rods are placed at the upstream of a flat plate heat exchanger that is located at potential core region(H/W=2) of a two-dimensional impinging air jet. Heat transfer enhancement is achieved by inserting turbulence promoter that results in the flow acceleration and disturbance of boundary layer. The average Nusselt number of the flat plate with the turbulence promoters is found to be around 1.42 times higher than that of the flat plate without the turbulence promoters. Based on the results of flow visualization with a smoke wire, it is confirmed that the heat transfer enhancement is caused by the flow separation and disturbance of boundary layer by inserting the turbulence promoter.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.2126-2131
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• 2005

Interactions of a humanoid with a human are important, when the humanoid is requested to provide people with human-friendly services in unknown or uncertain environment. Such interactions may require more complicated and human-like behaviors from the humanoid. In this work the arm motions of a human are discussed as the early stage of human motion imitation by a humanoid. A motion capture system is used to obtain human-friendly arm motions as references. However the captured motions may not be applied directly to the humanoid, since the differences in geometric or dynamics aspects as length, mass, degrees of freedom, and kinematics and dynamics capabilities exist between the humanoid and the human. To overcome this difficulty a method to adapt captured motions to a humanoid is developed. The geometric difference in the arm length is resolved by scaling the arm length of the humanoid with a constant. Using the scaled geometry of the humanoid the imitation of actor's arm motions is achieved by solving an inverse kinematics problem formulated using optimization. The errors between the captured trajectories of actor arms and the approximated trajectories of humanoid arms are minimized. Such dynamics capabilities of the joint motors as limits of joint position, velocity and acceleration are also imposed on the optimization problem. Two motions of one hand waiving and performing a statement in sign language are imitated by a humanoid through dynamics simulation.

• Journal of Korean Society of Steel Construction
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• v.28 no.6
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• pp.383-394
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• 2016

This study is intended to predict the seismic behavior of the down-scaled 3-story steel frame structures subjected to the real ground motion, and evaluate their structural damage through advanced finite element (FE) analysis results. The FE frame models are designed by considering the effect of the soft story. In addition, the effect of structural asymmetry is also taken into consideration during the nonlinear dynamic analyses. After observing the analysis results, it is reconfirmed that the damage of the steel frame building under the ground motion should be governed by the soft story column rather than the structural mass asymmetry.