• 인터넷정보학회논문지
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• 제22권3호
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• pp.67-73
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• 2021

본 논문에서는 드론의 추락을 예방하기 위해 드론의 프로펠러와 연결된 모터로부터 진동 데이터를 수집하고 순환 신경망(recurrent neural network, RNN)과 long short term memory (LSTM)을 사용하여 드론의 비정상 진동을 예측하는 연구를 진행하였다. 드론의 비정상 진동 데이터를 수집하기 위해 드론의 프로펠러와 연결된 모터에 진동 센서를 부착하여 정상, 바(bar) 손상, 로터(rotor) 손상, 축 휨에 대한 진동 데이터를 수집하고 LSTM과 RNN을 통해 비정상 진동을 예측한 결과의 평균 제곱근 오차 (root mean square error, RMSE) 값을 비교분석 하였다. 시뮬레이션 비교 결과, RNN과 LSTM을 통해 예측한 결과 모두 비정상 진동 패턴을 매우 정확하게 예측하는 것을 확인하였으며 LSTM을 통해 예측한 진동이 RNN을 통해 예측한 진동보다 RMSE값이 평균 15.4% 낮은 것을 확인하였다.

• Clinics in Shoulder and Elbow
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• 제21권2호
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• pp.105-110
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• 2018

Since the introduction of shoulder arthroplasty by Neer in 1974, the design of not only the glenoid component but also the humeral component used in shoulder arthroplasty has continually evolved. Changes to the design of the humeral component include a gradually disappearing proximal fin; diversified surface finishes (such as smooth, grit-blasted, and porous coating); a more contoured stem from the originally straight and cylindrical shape; and the use of press-fit uncemented fixation as opposed to cemented fixation. Despite the evolution of the humeral component for shoulder arthroplasty, however, stem-related complications are not uncommon. Examples of stem-related complications include intraoperative humeral fractures, stem loosening, periprosthetic fractures, and stress shielding. These become much more common in revision arthroplasty, where patients are associated with further complications such as surgical difficulty in extracting the humeral component, proximal metaphyseal bone loss due to stress shielding, intraoperative humeral shaft fractures, and incomplete cement removal. Physicians have made many attempts to reduce these complications by shortening the stem of the humeral component. In this review, we will discuss some of the limitations of long-stem humeral components, the feasibility of replacing them with short-stem humeral components, and the clinical outcomes associated with short-stemmed humeral components in shoulder arthroplasty.

• Applied Microscopy
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• 제26권2호
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• pp.177-195
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• 1996

Fine structure of the processes of intramembranous ossification and endochondral ossification at the tip of the distal phalanx of human fetuses was studied by electron microscopy. In 50 mm fetus, intramembranous ossification of the tip of cartilaginous phalanx was first noted. The osteoblasts of the perichondral zone of tip of cartilaginous phalanx started to lay down a thick membranous bony lamella. Most of the hypertrophied chondrocytes in the marginal parts of tip of the distal phalanx remained viable after being embeded in mineralized cartilaginous septa. The tuberosity of the distal phalanx was formed by membranous bony trabeculae on the exterior of the subperiosteal cap at 80 mm fetus. At this stage endochondral ossification was first observed in distal extremity of the distal phalanx. The maority of hypertrophied chondrocytes in the center of distal extremity appeared to be disintegrating. Resorption of calcified matrix was undertaken by perivascular cells and chondroclasts. From the periosteum, zone of calcification, vascular sprouts expanded within a recently opened lacunae, and the invading osteoblasts laid down osteoid and bone. After 120 mm fetus, endochondral and subperiosteal ossification proceeded in only one direction, just proximally. These findings demonstrate that intramembranous ossification, calcification, and endochondral ossification start at tip of the distal phalanx instead of at the center of the shaft, as was the case in other long bones.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 추계 학술발표회
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• pp.562-573
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• 2006

Incheon Bridge which will be the world's 5th long cable-stayed bridge in 2009 has been built under the management by Korea Highway Corporation. Incheon Bridge consists of several special-featured bridges and construction sections are divided into two groups, the private investment section with the foreign concessionaire and the government-financed section. 8 pile load tests were performed to investigate the behavior of rock-embedded large-diameter drilled shafts at both sections. Among these, 4 tests at the government-financed section have been utilized to adjust the detailed designs that were carried out individually as well as to find the actual bearing capacity of the ground prior to the commencement of constructions under the joint control of all contractors. Comprehensive procedures of the design and the construction of foundations using pile load tests were introduced.

• Journal of Electrical Engineering and Technology
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• 제12권4호
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• pp.1495-1502
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• 2017

The Theory of operation of switched reluctance motors (SRM) depends on the reluctance torque, where energy is transferred to stator winding only. Although its construction is simple, the electrical design is complex, due to the switching configuration needed to deliver power to stator coils. However, because of the nonlinearly of magnetic circuit, SRM has torque ripple. This paper proposes a new strategy to drive SRM from a single-phase AC supply. Each stator winding is connected to AC-DC or AC-AC converters, which is called branch. All branches are connected in parallel to a single-phase AC supply. A shaft encoder allows current production in stator winding during the positive torque production region and terminates it during the negative torque production region. A magnetic flux is produced between stator poles when current is supplied from AC supply to stator coil and repeats many cycles as long as the rate of change of stator inductance is positive. Different possibilities for the configurations of AC-AC or AC-DC converters are introduced to drive SRM from the single-phase AC supply. A case study is presented for a SRM fed from AC supply through semi-controlled AC-DC converter is presented. A simulation model is introduced and verified by experimental rig for two-phase SRM.

• 한국기계가공학회지
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• 제4권2호
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• pp.37-42
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• 2005

Recently $6{\sigma}$ quality control is an most important strategy to many enterprises in order to be a top company in the world, because it is an excellent scientific method to achieve the best quality control for their management and products. SY company is a small and medium one that has the quality problem for a long time such as occurring cracks on the surface of commutator at his assembly line while being assembled a rotor shaft and commutator of DC motor. This research was started to improve this problem by $6{\sigma}$ process, and as the results of this study, first, to find three vital fews, second, to get an achievement of about 21% improvement for the fracture strength of commutator, and third, to be recognized to change into $6{\sigma}$ quality control in SY company.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.338-350
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• 2010

As existing materials for ground reinforcement, chemical grout material using cementitous materials and waterglass was used. But many problems in terms of ground reinforcement effects were implicated. In this study, for development and applicability verification of new materials, viscosity, fluidity, permeability, Self-Leveling, keeping of drilled hole, antiwashout underwater, resistance of water (groundwater dilution and minimize material eluting) and the early strength and long-term strength characteristics of developed materials was confirmed, and material standards, and establishing construction standards for the various model tests were conducted. As a result, high viscosity, flowability, permeability and keeping of drilled hole characteristics are excellent, in addition to the early strength properties, dilution does nat occur to groundwater, including groundwater is available for dealing with environmental issues. Application of basic and reinforcement method by Filler function in addition to structure can also or development of a new concept can be expected. In addition, middle and large-diameter drilled shaft, micropile, ground anchors, soil-nailing, steel pipes multi-grouting reinforcement for cement injection process could be used enough to even be considered.

• 한국기계가공학회지
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• 제13권1호
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• pp.115-120
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• 2014

Wind power is a type of clean energy source which does not produce carbon dioxide. The wind turbine industry is considered as a major growth industry in many countries. The main cause of wind turbine failure arises in the wind turbine gearbox, and the main type of damage occurs in the bearings and gears. Therefore, predictions of gear and bearing damage are very important to ensure the reliability of the wind turbine reducers used in these systems. In this research, in order to optimize the wind turbine reducer, a series of simulations and redesigns was done using the tool RomaxDesigner. The RomaxDesigner model was used to analyze the bearing life of the duty cycle for a 5 MW wind-turbine pitch drive and to calculate the load in operating states. The reducer was designed to satisfy the life requirement by analyzing bearing damage and calculating the stress values of the main parts of the reducer.

• Journal of Advanced Marine Engineering and Technology
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• 제10권2호
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• pp.146-155
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• 1986

Until recently, the calculation of torsional vibration for the marine diesel engine shafting has been performed only for vibratory stresses of resonant points and vibratory stresses for other engine speeds are determined by the estimation. With the advent of energy-saving engines which have a long stroke and a small number of cylinders, the first major critical torsional vibration of the propulsion shaft appears ordinarily near the MCR speed of engine and the flank of its vibratory stress exceeds now and then the limit stress defined by the rules of Classification Society. In order to know the above condition in the design stage of propulsion shafting, it is necessary to calculate the forced torsional vibration with the damping of propulsion shafting for all orders and to synthesize its calculated results according to their phase angles. In this study, the forced torsional vibrations with the damping of propulsion shafting are calculated for several orders by mechanical impedance method, and their results are synthesized. A computer program for above calculations are developed and some test-runs of the developed program are performed for propulsion shaftings of actual ships. The results of calculations are compared with measured values and also with those of the modal analysis method. They show fairly good agreements and the developed program is checked up on its reliability.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.1049-1052
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• 1997

The pupose of this study on the surface finishing is to examine the performance of brushing as a means of reducing the surface roughness of the precision theaded shafts in ball screw assemblies. Ball screws provide superior performance compared to other types of screw feeds in terms of static and dynamic rolling resistance,backlash,and wear characteristics. The Reduction of the surface roughness of the lead shaft in ball screw assembiles is essential for precision movement,high speed/low noise tracel, and for low wear/long life. To reduce machine dependent errors that would influence the surface roughness compared with other lapping or polishing techniques,experiments will be performed using special wire brushes to polish precision ground shafts. The best results were obtained using the Al /sab 2/O /sab3/ brushes, with the Al /sab 2/O /sab3/ #500 grit brush producing a surface finish of approximately 0.7 .mu.m, and the Al /sab 2/O /sab3/ #600 grit producing a surface finish of approximately 0.8 .mu.m. Both of these results were produced at the highest wheel polishing speed of 3520 rpm. The SiC #500 brush produced a surface roughness of approximately 1 .mu.m at 3520 rpm.