• Korean Journal of Applied Biomechanics
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• v.34 no.1
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• pp.34-44
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• 2024

Objective: This study aimed to investigate how the movements occurring during the follow-through phase after releasing an arrow among elite compound archers, are associated with the arrow impact points on the target. Method: Nine elite archers performed consecutive compound archery shooting under conditions identical to actual competitions using their own bows and equipment. Motion capture system and force platform were utilized to record the changes in joint positions and center of pressure, respectively. Principal component analysis was employed to identify the patterns in which multidimensional joint positions and COP changes were organized with horizontal and vertical coordinates of arrow impact points. Subsequently, correlation analysis quantified the relationship between individual variables and the coordinates of arrow impacts on the target. Results: We found a common organizational pattern in which the two axes of the impact point coordinates were grouped into the first two principal components. The movements of the upper and lower limbs following release exhibited opposite patterns in the anterior-posterior axis, with significant correlations observed between the arrow impact points of the horizontal axis and the left shoulder, right elbow, left hip, and both knees. Additionally, the lateral movements induced by the reaction force upon arrow release showed significant associations with the vertical coordinates of the impact points. Particularly, the correlations between the movements of the left shoulder and elbow, as well as the bilateral hip and right knee, were consistently observed among all participants. Conclusion: These findings implied that the post-release movements could significantly influence the trajectory and impact points of the arrows in compound archery. We suggest that a consistent and controlled movement during the follow-through phase may be more beneficial for optimizing shooting accuracy and precision rather than minimizing movements.

• Geomechanics and Engineering
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• v.11 no.2
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• pp.253-267
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• 2016

The stability of surrounding rock will be poor when the tunnel is excavated through nearly horizontal stratum. In this paper, the instability mechanism of local nearly horizontal stratum in super-large section and deep buried tunnel is revealed by the analysis of the macro failure and micro fracture. A structural model is proposed to explain the mechanics of surrounding rock collapse under the action of stress redistribution and shed light on the macroscopic analytical approach of the stability of surrounding rock. Then, some highly effective formulas applied in the tunnel engineering are developed according to the theory of mixed-mode micro fracture. And well-documented field case is made to demonstrate the effectiveness and accuracy of the proposed analytical methods of mixed-mode fracture. Meanwhile, in order to make the more accurate judgment about yield failure of rock mass, a series of comprehensive failure criteria are formed. In addition, the relationship between the nonlinear failure criterion and $K_I$ and $K_{II}$ of micro fracture is established to make the surrounding rock failure criterion more comprehensive and accurate. Further, the influence of the parameters related to the tension-shear mixed-mode fracture and compression-shear mixed-mode fracture on the propagation of rock crack is analyzed. Results show that ${\sigma}_3$ changes linearly with the change of ${\sigma}_1$. And the change rate is related to ${\beta}$, angle between the cracks and ${\sigma}_1$. The proposed simple analytical approach is economical and efficient, and suitable for the analysis of local nearly horizontal stratum in super-large section and deep buried tunnel.

• Journal of Biosystems Engineering
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• v.41 no.2
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• pp.67-74
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• 2016

Purpose: Many tractors have adopted the horizontal control system designed to maintain the three-point mounted implements in horizontal position when they are tilted sideways. The control system rotates the implement in the opposite direction to the inclination of rear axle of the tractor. However, the current control system was found to have poor performance in accuracy and response. A new control system was therefore developed to improve the performance. Methods: The new control system was designed to get the response of the implement to be started earlier by using the tilt information from the front axle of the tractor. By this approach, the rotation of the implement can be adjusted as required to make it horizontal at the expected time, even though the response is slow. The optimal values of the control parameters for the new system were determined by computer simulation and validated by a performance test conducted with an obstacle of 120 mm height on a flat concrete surface. The performance of the control system was evaluated by the root mean square error (RMSE) of the rotation angle of the implement with respect to the actual inclination of the rear axle. Results: The new control system reduced the RMSE of the current control system by 44.6% indicating a high performance improvement. The inclination of the front axle was easily obtained from a sensor mounted on the front axle of the tractor and used as input to the new control system. Conclusions: The method of getting the response of the implement to be started earlier by utilizing the inclination information of the front axle can be applied to improve the performance of the current control system at least cost.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.155-160
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• 2002

Recently, the development of aerospace and automobile industries has brought new technological challenges, rebated to the growing complexity of products and the new geometry of the models. High speed milling with a 5-Axis milling machine has been widely used fur 3D sculptured surface parts. When turbine blades are machined by a 5-axis milling, their thin and cantilever shape causes vibrations, deflections and twists. Therefore, the surface roughness and the waviness of the workpiece are not good. In this paper, the effects of cutter orientation and the lead/tilt angle used to machine turbine blades with a 5-axis high speed ball end-milling were investigated to improve geometric accuracy and surface integrity. The experiments were performed using a lead/tilt angle of 15$^{\circ}$ to the workpiece with four cutter directions such as horizontal outward, horizontal inward, vertical outward, and vortical inward directions. Workpiece deflection, surface roughness and the machined surface were all measured with various cutter orientations such as cutting directions, and lead/tilt angle. The results show that the best cutting strategy for machining turbine blades with a 5-axis milling is horizontal inward direction with a tilt angle.

• Journal of the Korean Institute of Navigation
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• v.12 no.2
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• pp.23-32
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• 1988

This paper offers a method of magnetic compass adjustment for the vessel alongside the wharf using newly designed magnetic north former, which makes the same magnetic field-change as the turning vessel does. The characteristics of the magnetic north former was examined by observing the deviation curves of the magnetic compass installed on the compass deviascop at laboratory. The magnetic north former consists of A and B arms which hold the permanent bar magnets at the both ends of each arm. The arm is to rotae in the horizontal plane about the vertical axis fixed at the center boss of the magnetic compass and it is to compensate the horizontal plane about the vertical axis fixed at the center boss of the magnetic compass and it is to compensate the horizontal component of the earth's field. The B arm makes the artificial magnetic north around the magnetic compass for every ship's heading. The results of investigation are summarized as follows ; 1. The observation and correction of magnetic compass deviation can be done without swinging the ship, of the effect of D coefficient is negligible. 2. The residual deviation curve of the magnetic compass depends on the accuracy of deduced value of ship's multplier($\lambda$). 3. The errors due to the inaccuracy of deduced value of ship's multiplier change in the same way as the B and C coefficient do.

• Earthquakes and Structures
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• v.14 no.2
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• pp.179-186
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• 2018

We present the accurate investigation the seismic behavior of the gravity retaining wall built near rock face based on numerical method. The retaining wall is a useful structure in geotechnical engineering, where the earthquake is a common phenomenon; therefore, the evaluation of the behavior of the retaining wall during an earthquake is essential. However, in all previous studies, the backfill behind the wall was usually approximated by a homogeneous region, while in contrast, in practice, in many cases retaining walls are used to support the soil pressure in, inhomogeneous, mountainous area. This suggests an accurate investigation of the problem, i.e., numerical analysis. The numerical results will be compared with some of recently proposed analytical methods to show the accuracy of the proposed method. We show that increasing the volume of the rock face yields decreasing the permanent horizontal displacement of the gravity retaining wall built near rock face. Besides, we see that the permanent horizontal displacement of the gravity retaining wall with homogenous backfill is more than permanent horizontal displacement of the gravity retaining wall case of the built near rock face in different frequency contents.

• Nuclear Engineering and Technology
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• v.36 no.2
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• pp.142-152
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• 2004

The liquid entrainment and vapor pull-through offtake model of RELAP5/MOD3 had been developed for SBLOCA (Small Break Loss of Coolant Accident). The RELAP5/MOD3 model for horizontal volumes accounts for the phase separation phenomena and computes the flux of mass and energy through a branch when stratified conditions occur in the horizontal pipe. In the case of CANDU reactor, this model should be used in the coolant flow of 95 feeders connected to the reactor header component under the horizontal stratification in header. The current RELAP5 model can treat the only 3 directions junctions; vertical upward, downward, and side oriented junctions, and thus improvements for the liquid entrainment and vapor pull-through model were needed for considering the exact angles. The RELAP5 off-take model was modified and generalized by considering the geometric effect of branching angles. Based on the previous experimental results, the critical height correlation was reconstructed by use of the branch line connection angle and validation analyses were also performed using SET. The new model can be applied to vertical upward, downward and angled branch, and the accuracy of the new correlations is more improved than that of RELAP5.

• Journal of Welding and Joining
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• v.16 no.3
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• pp.102-110
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• 1998

The horizontal fillet welding is prevalently used in heavy and ship building industries to fabricate the large scale structures. A deep understanding of the horizontal fillet welding process is restricted, because the phenomena occurring in welding are very complex and highly non-linear characteristics. To achieve the satisfactory weld bead geometry in robot welding system, the seam tracking algorithm should be reliable. The number of seam tracker was developed for arc welding automation by now. Among these seam tracker, the arc sensor is prevalently used in industrial robot welding system because of its low cost and flexibility. However, the accuracy of arc sensor would be decreased due to the electrical noise and metal transfer. In this study, the signal processing algorithm based on the neural network was implemented to enhance the reliability of measured welding current signals. Moreover, the seam tracking algorithm in conjunction with the signal processing algorithm was implemented to trace the center of weld line. It was revealed that the neural network could be effectively used to predict the welding current signal at the end of weaving.

• Geomechanics and Engineering
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• v.34 no.1
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• pp.43-49
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• 2023

Knowledge of minimum horizontal stress (S_hmin) is a significant step in determining full stress tensor. It provides crucial information for the production of sand, hydraulic fracturing, determination of safe mud weight window, reservoir production behavior, and wellbore stability. Calculating the S_hmin using indirect methods has been proved to be awkward because a lot of data are required in all of these models. Also, direct techniques such as hydraulic fracturing are costly and time-consuming. To figure these problems out, this work aims to apply the long-short-term memory (LSTM) algorithm to S_hmin time-series prediction. 13956 datasets obtained from an oil well logging operation were applied in the models. 80% of the data were used for training, and 20% of the data were used for testing. In order to achieve the maximum accuracy of the LSTM model, its hyper-parameters were optimized significantly. Through different statistical indices, the LSTM model's performance was compared with with other machine learning methods. Finally, the optimized LSTM model was recommended for S_hmin prediction in the well logging operation.

• Korean Journal of Remote Sensing
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• v.30 no.1
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• pp.37-45
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• 2014

This paper reports the geolocation accuracy of KOMPSAT-3 imagery. KOMPSAT-3 was launched successfully on May 18, 2012 and has been released last March. In this paper, we have checked the geolocation accuracy of initial sensor model, precise sensor model and stereo-and multi-image model using four KOMPSAT-3 images covering the same area. The KOMPSAT-3 images without GCPs provided the geolocation accuracy of about 30m and the geocorrected KOMPSAT-3 images provided the geolocation accuracy of about 1m or less. KOMPSAT-3 stereo- and multi-images models yield threedimensional points with sub-meter accuracy in horizontal and vertical direction. Overall, KOMPSAT-3 showed much improved performance in terms of the geolocation accuracy over KOMPSAT-2. KOMPSAT-3 is expected to be able to replace foreign satellite data with sub-meter accuracy level for achieving accurate geometric information.