• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.629-633
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• 2006

We investigated a new longitudinal acceleration wave decomposition method in time domain. The proposed method separates up- and down-stream waves with an axial strain and axial acceleration measured at a single point on the transmission path. The advantages such as low computation load and easy implementation would be possible by developing time domain under the following assumptions; low frequency range, uniform cross sectional area and elastic wave propagation. We confirmed the feasibility and performance of the method through experiment using Split Hopkinson Pressure Bar (SHPB). The method can be effective in several applications, including active vibration control with wave view point, where real time wave decomposition is necessary.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.430-433
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• 2003

This paper presents a system identification (SI) scheme in time domain using measured acceleration data. The error function is defined as the time integral of the least square errors between the measured acceleration and the calculated acceleration by a mathematical model. Damping parameters as well as stiffness properties of a structure are considered as system parameters. The structural damping is modeled by the Rayleigh damping in SI. The regularization technique is applied to alleviate the ill-posed characteristics of inverse problems. The validity of the proposed method is demonstrated by an experimental study on a shear building model.

• Journal of the Semiconductor & Display Technology
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• v.20 no.3
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• pp.117-119
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• 2021

With the development of the industry, the use of drones in specific mission flight is being actively studied. These drones fly a specified path and perform repetitive tasks. if the drone system will detect objects in real time, the performance of these mission flight will increase. In this paper, we implement object detection system and mount GPU acceleration to maximize the efficiency of limited device resources with drone video using Tensorflow Lite which enables in-device inference from a mobile device and Mobile SDK of DJI, a drone manufacture. For performance comparison, the average processing time per frame was measured when object detection was performed using only the CPU and when object detection was performed using the CPU and GPU at the same time.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.9
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• pp.52-60
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• 1997

This paper proposes the effective method of the software based motion control by using lenear, exponential and bell type discrete filters for acceleration and deceleration of servo motors. Recursive filters are designed in discrete time domain which can reduce computation time and vibration of motors due to load disturbance. Also it deals with the method which decides the time constants of filters when a machine tool is driven at rapid, cutting and jog feedrate. Validity of the proposed method is verified by corner cutting experiments.

• Journal of the Earthquake Engineering Society of Korea
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• v.18 no.1
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• pp.29-36
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• 2014

In industrial facilities sites, the conventional method determining the earthquake magnitude (M) using earthquake ground-motion records is generally not applicable due to the poor quality of data. Therefore, a new methodology is proposed for determining the earthquake magnitude in real-time based on the amplitude measures of the ground-motion acceleration mostly from S-wave packets with the higher signal-to-ratios, given the Vs30 of the site. The amplitude measures include the bracketed cumulative parameters and peak ground acceleration (As). The cumulative parameter is either CAV (Cumulative Absolute Velocity) with 100 SPS (sampling per second) or BSPGA (Bracketed Summation of the PGAs) with 1 SPS. The arithmetic equations to determine the earthquake magnitude are derived from the CAV(BSPGA)-As-M relations. For the application to broad ranges of earthquake magnitude and distance, the multiple relations of CAV(BSPGA)-As-M are derived based on worldwide earthquake records and successfully used to determine the earthquake magnitude with a standard deviation of ${\pm}0.6M$.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.11
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• pp.221-227
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• 2002

Tapping is a machining process that makes a female screw on parts to be assembly together. Recently, as the number of small and compact products increases the radius of tap as small as 1 mm is not unusual and more accurate tapping is needed. In complying with those needs, some high-speed tapping machines with synchronizing function have been developed. This paper describes the development of an ultra high-speed tapping machine up to 10,000rpm. The key factors in the tapping speed are the acceleration/deceleration and the synchronizing errors between spindle motor and fred motor. To minimize the acceleration/deceleration time, a low inertia spindle with a synchronous built-in servo motor was developed. To minimize the synchronizing errors, the tapping cycle algorithm was optimized on an open architecture CNC. The developed tapping machine has the acceleration/deceleration time of 0.13sec/10,000rpm for rigid tapping and the synchronizing error below 4.4%. The cycle time for tapping a female screw of M3 and depth 2 times diameter was 0.55sec.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.3
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• pp.39-47
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• 1990

The generation of artificial accelerograms considering the characteristic of earthquakes in the Korean peninsula for a time history analysis of structures is accomplised by the stochastic method. The engineering data such as a representative shape of envelope function and an effective duration are investigated from the instrumental records. The maximum ground acceleration value is based on seismic zoning map which are constructed for the Korean peninsula. The acceleration-time histories are generated for two different types of earthquake motions and two types of soil conditions. In the study, the maximum ground acceleration value of 0.2 g and effective durations of 24 seconds are used. The validity of the artificial accelerograms is obtained by the comparison with the required envelope functions and the design response spectrum.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.899-909
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• 1992

An iterative solution technique is presented to analyze the dynamic systems of rigid bodies subjected to kinematic constraints. Lagrange multipliers associated with the constraints are iteratively computed by monotonically reducing an appropriately defined constraint error vector, and the resulting equation of motion is solved by a well-established ODE technique. Constraints on the velocity and acceleration as well as the position are made to be satisfied at joints at each time step. Time integration is efficiently performed because decomposition or orthonormalization of the large matrix is not required at all. An acceleration technique is suggested for the faster convergence of the iterative scheme.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.5
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• pp.15-28
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• 1998

Recently may investigations have been studied on the high-speed machining by using machine tools. A CNC machine tool makes some tool path errors caused by software acceleration/deceleration. The faster a cutting feedrate is, the bigger the tool path errors are. Some known methods reduce these kinds of errors, but they make the total cutting time increased. This paper presents a feed-forward algorithm that can be generated by distorting the original tool path, and reduces the tool path errors and the total cutting time. The algorithm to generate a new tool path is represented as following; 1)calculating each distance of software acceleration/deceleration between two adjacent blocks, 2) estimating the distorted distance which is the adjacent-ratio-constant(k1, k2) multiply the distance of software acceleration/deceleration, 3) generating a 3-degree Bezier curve approximating the distorted tool path, 4) symmetrically transforming the Bezier curve about the intersection point between two blocks, and 5) connecting the transformed Bezier curve with the original tool path. The algorithm is applied to FANUC 0M. The study is to promote the high-precision machining and to reduce the total cutting time.

• Nuclear Engineering and Technology
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• v.43 no.4
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• pp.361-374
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• 2011

Two types of numerical modeling techniques were considered for the dynamic response of a structure subjected to a ground acceleration. One technique is based on the equation of motion relative to ground motion, and the other is based on the equation of absolute motion of the structure and the ground. The analytic background of the former is well established while the latter has not yet been extensively verified. The latter is called a large mass method, which allocates an appropriate large mass to the ground so that it causes the ground to move according to a given acceleration time history. In this paper, through the use of a single degree-of-freedom spring-mass system, the equations of motion of the two techniques were analyzed and useful theorems are provided on the large mass method. Using simple examples, the numerical results of the two modeling techniques were compared with analytic solutions. It is shown that the theorems provide a clear insight on the large mass method.