• 한국안전학회지
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• 제34권6호
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• pp.88-95
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• 2019

It has been only a few years since drones have been introduced to Korea, and as the use of drones has increased in industrial sites as well as in hobby activities, accidents such as workers' body parts coming into contact with rotating propellers have been occurring since 2016. Industrial accident cases are being filed. In the case of a remote control vehicle, if you release the remote controller in the event of an abnormal situation, it stops in place and no further danger occurs but in case of drones flying over the sky is different. Sudden motor stops during flight, uncontrolled changes in flight posture, loss of radio waves, loose propeller, etc, numerous factors can lead to accidents due to unintentional movements. Therefore, drone operators need safety knowledge as well as high knowledge about drones. However, drones with a weight of less than 12 kg can fly without a pilot's certification, and therefore, a minimum accident prevention measure is required. 10 accidents approved as industrial accidents since 2016, 23 accidents surveyed by general drone operator, 40 accidents surveyed by the Korean Consumer Resources Unfortunately for the purpose of writing this paper, drones are a new species and do not have many parameters for analysis but my experience has shown that the type of disaster does not deviate significantly. In addition, there is no paper that analyzes drone related industrial accidents not only in Korea but also in other countries. However, even if you watch an overseas drone accident video through YouTube, it is not much different from the case that occurs in Korea. I hope that this study will be of little help to all the drone pilots as well as the work safety of industrial drones used in industrial sites.

• 한국운동역학회지
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• 제20권4호
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• pp.429-436
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• 2010

The purpose of this study was to analyze the kinematic factors and throwing variables for the 3-turn and 4-turn techniques and for release as well as to provide technical advice for improving athletic performance in hammer throwing. Data analysis led to the following conclusions: To increase the rotation speed for the 3-turn and 4-turn techniques, the time elapsed during the 1-foot support period should be decreased the distance between the rotating foot and the rotation axis should be small and the height of the hip joint should be increased at the times of release The throwing angle at the moment of release should be more than 40 degrees, and the throwing position should be taken vertically high at the shoulder joints. To accelerate the motion of the hammer, the speed should not be reduced during the 1-foot support period but should be increased during the 2-foot support period for much greater acceleration. In the 3-turn technique, the angles of the shoulder axis and hummer string should be dragged angle at the maximum point and lead angle at the minimum point, and dragged angle at the maximum and minimum points in the 4-turn at the time of relase The upper body should be quickly bent backward, the knee angle should be extended, and the angles of the shoulder axis and hammer string should be dragged angle close to 90 degrees.

• Tribology and Lubricants
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• 제31권6호
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• pp.302-307
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• 2015

The use of turbocharger in internal combustion engines has increased as it is a key components for improving system efficiency without increasing engine size. Because of increasing demand, many studies have evaluated rotordynamic performance so as to increase rotation speed. This paper presents a linear and nonlinear analysis model for a turbocharger rotor supported by a floating ring bearing. We constructed rotor model by using the finite element method and approximated bearings as being infinitely short. In the linear model, we considered fluid film force as stiffness and damping element. In nonlinear analysis, calculation of the fluid film force involved solving the time dependent Reynolds equation. We verified the developed model by comparing the results to those of previous research. The analysis results show that there are four unstable modes, which are rigid body modes combining ring and rotor motion. As the rotating speed increases, the logarithmic decrement shows that certain unstable modes goes into the stable area or the stable mode goes into the unstable area. These unstable modes appear as sub-synchronous vibrations in nonlinear analysis. In nonlinear analysis frequency jump phenomenon demonstrated in several experimental studies appears. The analysis results also showed that frequency jump phenomenon occurs when the vibration mode changes and the sequence of unstable mode matches the linear analysis result. However, the natural frequency predicted using linear analysis differs from those obtained using nonlinear analysis.

• 품질경영학회지
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• 제49권4호
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• pp.581-594
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• 2021

Purpose: The purpose of this study is to compare machine learning models for anomaly detection of mechanical facility equipment and suggest an anomaly detection system for mechanical facility equipment in subway stations. It helps to predict failures and plan the maintenance of facility. Ultimately it aims to improve the quality of facility equipment. Methods: The data collected from Daejeon Metropolitan Rapid Transit Corporation was used in this experiment. The experiment was performed using Python, Scikit-learn, tensorflow 2.0 for preprocessing and machine learning. Also it was conducted in two failure states of the equipment. We compared and analyzed five unsupervised machine learning models focused on model Long Short-Term Memory Variational Autoencoder(LSTM-VAE). Results: In both experiments, change in vibration and current data was observed when there is a defect. When the rotating body failure was happened, the magnitude of vibration has increased but current has decreased. In situation of axis alignment failure, both of vibration and current have increased. In addition, model LSTM-VAE showed superior accuracy than the other four base-line models. Conclusion: According to the results, model LSTM-VAE showed outstanding performance with more than 97% of accuracy in the experiments. Thus, the quality of mechanical facility equipment will be improved if the proposed anomaly detection system is established with this model used.

• 대한조선학회논문집
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• 제55권6호
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• pp.474-481
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• 2018

This paper is to compare by numerical analysis the flow characteristics and propulsion performance of stern with the shape change of K-duct, a pre-swirl duct developed by Korea Research Institute of Ships & Ocean Engineering (KRISO). First, the characteristics of the propeller and the resistance and self-propulsion before and after the attachment of the K-duct to the ship were verified and the validity of the calculation method was confirmed by comparing this result with the model test results. After that, resistance and self-propulsion calculations were performed by the same numerical method when the K-duct was changed into five different shapes. The efficiency of the other five cases was compared using the delivery horsepower in the model scale and the flow characteristics of the stern were analyzed as the velocity and pressure distributions in the area between the duct end and the propeller plane. For the computation, STAR-CCM +, a general-purpose flow analysis program, was used and the Reynolds Averaged Navier-Stokes (RANS) equations were applied. Rigid Body Motion (RBM) method was used for the propeller rotating motion and SST $k-{\omega}$ turbulence model was applied for the turbulence model. As a result, the tangential velocity of the propeller inflow changed according to the position angle change of the stator, and the pressure of the propeller hub and the cap changes. This regulated the propeller hub vortex. It was confirmed that the vortex of the portion where the fixed blade and the duct meet was reduced by blunt change.

• 한국산업융합학회 논문집
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• 제25권6_3호
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• pp.1239-1246
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• 2022

This paper introduces the effect of grease on the degradation characteristics of bearings used as key components of packaging equipment and automation systems. Bearings parts are installed to fix and support the rotating body of the system, and performance degradation of the bearings has a great effect on the life of the system too. When bearings are used in various devices and systems, the grease is applied to reduce friction and improve fatigue life. Determining the type of lubricant (grease) is important because it has a great influence on the operating environment and lifespan and ensures long lifespan of systems and facilities. However, studies that simultaneously compared and analyzed the change in mechanical degradation characteristics and the comparison of chemical degradation characteristics according to grease types under actual operating conditions are insufficient. In this paper, three types of small harmonic drive, high-load reducer, and low-load reducer grease used in power transmission joint modules are experimentally selected and finally injected into ball bearings with a load (19,500N) to improve bearing durability. Degradation characteristics were tested by attaching to test equipment. At this time, after the durability test under the same load conditions, the mechanical degradation characteristics, that is temperature, vibration according to the three greases types. In addition, the chemical degradation characteristics of the corresponding grease was compared to present the results of mutual correlation analysis.

• Steel and Composite Structures
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• 제49권5호
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• pp.487-502
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• 2023

In the realm of nanotechnology, the nonlocal strain gradient theory takes center stage as it scrutinizes the behavior of spinning cantilever nanobeams and nanotubes, pivotal components supporting various mechanical movements in sport structures. The dynamics of these structures have sparked debates within the scientific community, with some contending that nonlocal cantilever models fail to predict dynamic softening, while others propose that they can indeed exhibit stiffness softening characteristics. To address these disparities, this paper investigates the dynamic response of a nonlocal cantilever cylindrical beam under the influence of external discontinuous dynamic loads. The study employs four distinct models: the Euler-Bernoulli beam model, Timoshenko beam model, higher-order beam model, and a novel higher-order tube model. These models account for the effects of functionally graded materials (FGMs) in the radial tube direction, giving rise to nanotubes with varying properties. The Hamilton principle is employed to formulate the governing differential equations and precise boundary conditions. These equations are subsequently solved using the generalized differential quadrature element technique (GDQEM). This research not only advances our understanding of the dynamic behavior of nanotubes but also reveals the intriguing phenomena of both hardening and softening in the nonlocal parameter within cantilever nanostructures. Moreover, the findings hold promise for practical applications, including drug delivery, where the controlled vibrations of nanotubes can enhance the precision and efficiency of medication transport within the human body. By exploring the multifaceted characteristics of nanotubes, this study not only contributes to the design and manufacturing of rotating nanostructures but also offers insights into their potential role in revolutionizing drug delivery systems.

• 핵의학기술
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• 제23권1호
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• pp.54-58
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• 2019

Capillary tube 10개를 $^{99m}Tc$로 채워서 고정식-초점형 SPECT와 회전식-평형 SPECT 장비를 이용하여 선예도와 감도를 평가하였다. 그리고 이 데이터를 이용하여 검출-조사야 내에서의 평균값과 표준편차를 이용하여 균일도를 나타내는 변동계수를 평가하였다. 고정식-초점형 SPECT의 선예도 균일도와 감도 균일도는 회전식-평형 SPECT 에 비해 각각 68%, 110% 높게 평가되었다.

• 헤리티지:역사와 과학
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• 제44권4호
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• pp.112-129
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• 2011

본고에서는 백제 한성기 중심지역에 해당되는 서울 몽촌토성, 서울 풍납토성, 서울 석촌동고분군, 하남 미사리유적에서 출토된 취사용기의 형태, 제작기법 등을 분석하여 그 전개양상에 대해 살펴보았다. 형태적 분석에서는 심발형토기는 동최대경이 동체상부에 위치하고 장란형토기는 동최대경이 동체중부에 위치하는 것으로 나타났고, 경부잘록도는 두 기종 모두 미비한 편이었다. 유적별로는 심발형토기의 경우 서울 석촌동고분군이 용량이 적고, 심도가 깊으며, 동최대경이 높은 것으로 확인되었다. 장란형토기는 서울 풍납토성이 하남 미사리유적보다 심도가 깊고, 동최대경은 동중부에 위치하며 경부잘록도가 큰 것으로 확인되었다. 제작기법 분석에서는 심발형토기는 용량군의 폭이 커질수록 유문내박자를 이용하여 타날하였는데, 외면에는 승문이 주로 확인되었다. 또한 기벽이 가장 얇은 것으로 나타났다. 이는 기술적 변화를 나타내는 것으로 시간성을 포함하고 있다. 장란형토기에서도 유문내박자를 사용한 토기가 기벽이 가장 얇고 경부의 잘록도는 약해지는 것으로 나타났으며, 구순부에 강한회전력에 의한 정면흔적이 관찰되었다. 두 기종 모두 유문내박자를 사용하면서 더욱 기벽을 얇게 제작할 수 있게 된 것으로 확인되었다. 백제 한성기 중심지역에서 출토된 심발형토기와 장란형토기는 태토나 소성에서는 시간성이 명확하지 않지만 제작기법상에서 그 전개양상을 확인할 수 있었다. 또한 그 제작기법의 변화양상에는 시간성도 반영되어 있는 점도 확인 할 수 있었다.

• 한국수산과학회지
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• 제28권4호
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• pp.457-468
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• 1995

현재 유수식 방법으로 양식되고 있는 넙치(Paralichthys olivaceus)의 육상수조 양식에서 환수율, 월동시가온 및 양식배수 등의 문제를 해결하기 위하여, 실제 양식장에 설치한 반폐쇄식 순환여과 사육시스템을 이용하여 1992년 2월부터 1994년 1월까지 2년 동안(실험 I , 실험II) 넘치를 사육하면서 그 실용성을 연구하였다. 실험 I에서는 평균전장 7.5cm, 평균체중 3.4g, 실험II에서는 각각 5.0cm, 1.8g의 종묘를 사용하였다. 실험 I의 사육수 용존 무기태질소량은 $NH_4-N\;0.247-0.512ppm,\;NO_2-N\;0.010-0.043ppm,\;NO_3-N\;0.108-0.342ppm$ 실험II에서는 각각 0.091-0.715ppm, 0.002-0.045 ppm, 0,007-0.277 ppm 범위에서 변화하였다. 일간섭식률은 실험 I $0.67-2.41\%$, 실험II $0.69-2.22\%$, 사료효율은 각각 $34.8-59.8\%,\;40.5-88.4\%$였다. 실험 I에서의 어체는 사육 340일만에 전장 40.0-42.8cm, 체중 695.0-852.6g으로 성장하였고, 실험II에서는 사육 365일후에 전장 36.7-39.7cm, 체중 552.4-706.4g으로 자라났다. 사육종료시 어체의 평균 생존율은 실험 $192.0\%$, 실험II $96.0\%$였다. 어체의 체표면적이 수조바닥을 덮는율(covering rate)은 넙치의 수용밀도의 지표로 활용 가능하였다. 사육시 어체의 최대 수용량은 실험 I에서 덮는율 2.2, 중량 $34.1kg/m^2$였고, 실험II에서는 각각 $2.6,\;36.3kg/m^2$였다. 순환여과식 양식시스템은 현행의 유수식 양식시스템에 비해 양식 생산성 및 연안 환경오염 방지에 기여도가 높은 양식방법으로 평가되었다.