• Current Optics and Photonics
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• 제1권5호
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• pp.468-473
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• 2017

We determined the feasibility of a fishing camera system using an optical fiber as the fishing line by testing a power-over-fiber (POF) module and multimode optical fiber. Operation of the remote camera module (RCM) without the battery was preferred because the removal of the charging or battery replacement section enabled a waterproof single-body type design. The average efficiency of the photovoltaic power converter (PPC) in the tested POF module was 32.6% at 820 nm, and thus, a high-power laser of at least 1.27 W was required for operating the developed RCM with an electrical dissipation of 413 mW. Because the optical fiber was wound on a fishing reel, composite loss composed of bending and tensile loss occurred. To mitigate the composite loss, we employed a simple holder that showed an improvement in the composite loss of 0.38 dB to 0.8 dB, which was considerably better than the losses without the holder.

• Smart Structures and Systems
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• 제24권3호
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• pp.361-377
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• 2019

The stiffness of shape memory alloy (SMA) spring while in actuation is represented by an empirical model that is derived from the logistic differential equation. This model correlates the stiffness to the alloy temperature and the functionality of SMA spring as active variable stiffness actuator (VSA) is analyzed based on factors that are the input conditions (activation current, duty cycle and excitation frequency) and operating conditions (pre-stress and mechanical connection). The model parameters are estimated by adopting the nonlinear least square method, henceforth, the model is validated experimentally. The average correlation factor of 0.95 between the model response and experimental results validates the proposed model. In furtherance, the justification is augmented from the comparison with existing stiffness models (logistic curve model and polynomial model). The important distinction from several observations regarding the comparison of the model prediction with the experimental states that it is more superior, flexible and adaptable than the existing. The nature of stiffness variation in the SMA spring is assessed also from the Dynamic Mechanical Thermal Analysis (DMTA), which as well proves the proposal. This model advances the ability to use SMA integrated mechanism for enhanced variable stiffness actuation. The investigation proves that the stiffness of SMA spring may be altered under controlled conditions.

• Steel and Composite Structures
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• 제46권6호
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• pp.731-744
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• 2023

Vehicle load information is an important role in operating and ensuring the structural health of cable-stayed bridges. In this regard, an efficient and economic method is proposed for vehicle load detection based on the observed cable tension and vehicle position using a graph neural network (GNN). Datasets are first generated using the practical advanced analysis program (PAAP), a robust program for modeling and considering both geometric and material nonlinearities of bridge structures subjected to vehicle load with low computational costs. With the superiority of GNN, the proposed model is demonstrated to precisely capture complex nonlinear correlations between the input features and vehicle load in the output. Four popular machine learning methods including artificial neural network (ANN), decision tree (DT), random forest (RF), and support vector machines (SVM) are refereed in a comparison. A case study of a cable-stayed bridge with the typical truck is considered to evaluate the model's performance. The results demonstrate that the GNN-based model provides high accuracy and efficiency in prediction with satisfactory correlation coefficients, efficient determination values, and very small errors; and is a novel approach for vehicle load detection with the input data of the existing monitoring system.

• 풍력에너지저널
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• 제15권1호
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• pp.30-42
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• 2024

This paper examines the design feasibility of cage aquaculture coexistent with an offshore wind farm in the southwestern sea of South Korea. Among the many types of fish farms, 2 × 3 cage aquaculture was selected for the investigation and the initial design including mooring lines, bridles, etc. was drawn with iterative numerical simulations using Orcaflex. Experimental campaigns were conducted to validate the numerical results, and they were found to be in good agreement with the experiments. Using a validated numerical model, the tension of mooring lines and the deformed volumes of the facility were examined under given operating and survival conditions. The validated model will be further used to investigate various aspects of the cage farm design for design optimization.

• Korean Chemical Engineering Research
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• 제47권6호
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• pp.720-726
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• 2009

가압으로 운전되는 삼상슬러리 기포탑에서 기포 체류량과 압력강하를 목적함수로하여 기포탑의 설계 및 scale-up을 위한 수력학적 similarity를 고찰하였다. 또한, 본 연구에서 선택한 각 실험변수가 기포탑의 직경변화에 따라 기포탑 내 기포 체류량에 미치는 영향을 분석하였다. 슬러리 기포탑에서 기체체류량 및 압력강하의 결정에 영향을 미치는 주요 인자로써 기체유속($U_G$), 연속 슬러리 상의 점도(${\mu}_{SL,eff}$) 및 표면장력(${\rho}_{SL}$), 운전압력의 변화에 따라 변화하는 기체상의 밀도(${\rho}_G$)와 슬러리 밀도(${\rho}_{SL}$)의 차($\rho_{SL}$-${\rho}_G$), 기포탑 내부에서 단위길이 당 압력강하(${\Delta}P/L$), 기포탑의 직경(D) 그리고 기포탑에서 다상흐름에 작용하는 중력의 영향을 고려하기 위해 중력가속도(g) 등을 선정하였다. 선정된 7개의 슬러리 기포탑의 수력학적 특성에 영향을 미치는 파라메타들과 3개의 기본차원들로부터 차원해석에 의해 수력학적 특성을 지배하는 4개의 무차원 군을 도출하였다. 도출된 무차원 군인 레이놀즈 수, 프라우드 수 그리고 웨버 수 등이 기포탑에서 기포체류량에 미치는 영향을 검토하였다. 기포탑 내부에서의 압력강하와 기체 체류량 등을 무차원 군의 상관식으로부터 효과적으로 예측할 수 있었다. 본 연구의 결과는 가압슬러리 기포탑의 설계 및 scale-up 등에 매우 유용한 정보를 제공할 수 있을 것으로 사료된다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.389-396
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• 2002

In XXI century it is necessary to expect the recommencement and development of activities on mastering the Moon. In the long term it is construction of manned lunar bases with industrial, astrophysical, procuring, repair equipment and services. Interplanetary flights from the Moon demand smaller power expenditures, than from the Earth, therefore it is favourable to use its surface for the construction of space-vehicle launching sites. Flights of devices in libration points in the system 'Earth - Moon' are considered. Experience of engineering system creation for the Moon displays the great complexity in provision of serviceability and reliability of friction units. Open friction units should operate under following conditions on the Moon: pressure of environment (vacuum) $p\;>10\;^{-10}$ Pa; wide range of temperature change $+150^{\circ}C\;...170^{\circ}C$; high evaporability of lubricants; influence of temperature gradients and warping of constructions; sublimation of elements of constructional materials; irradiation of different physical nature; effect of micrometeorites; reduced gravitation; influence of abrasive particles of lunar ground; requirements on minimization of size and weight characteristics of a construction (high tension); undesirability (impossibility) of application of liquid and plastic lubricants; vibration, shock, acoustic loadings during start and landings to the Earth; difficulties in repair-regenerative operations in conditions of the Moon etc. Adhesive interaction of conjugated surfaces is the principal reason of possible failures of rubbed units on the Moon. In the research of the Moon automatic interplanetary stations of 'Luna' (USSR), 'Surveyer', 'Apollo' (USA) series were used. Stations executed functions of flying, landing, artificial satellites of the Moon, moon-rovers and manned spacecrafts such as 'Apollo'. The experimental- theoretical researches carried out in the sixtieth years on tribology for conditions of the Moon appeared to be rather useful to engineering of an outer space exploration and the decision of complex problems for the friction units operating in extreme conditions on the Earth. For the creation of highly loaded friction units for the long service life on the Moon it is required not only to use accumulated experience and designed technologies, but also to carry out wide scientific research.

• Ocean and Polar Research
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• 제39권3호
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• pp.205-211
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• 2017

This paper seeks to provide a dynamic analysis of a 150 ton winch based on ocean environmental data. The winch model that was subjected to analysis was modeled from CAD to each subsystem by the commercial software DAFUL. The winch model has tree brake systems (disk brake, band brake and ratchet brake). The rotation motion of the motor and contact elements of the brake are applied to the winch model in order to analyze its dynamic characteristics. In addition, a crane-barge was modeled to apply ocean environmental data. The motion data of the crane-barge was produced by means of the RAO(Response Amplitude Operator) of the barge and wave spectrum. The reaction force of the translational joint was measured instead of the tension of the cable. The brake performance of the winch was produced and assessed based on the operating motion of the crane-barge.

• 대한기계학회논문집A
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• 제30권11호
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• pp.1494-1501
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• 2006

Mechanical and physical properties of a copper alloy for a liquid rocket engine(LRE) combustion chamber liner application were tested at various temperatures. All test specimens were heat treated with the condition they might experience during actual fabrication process of the LRE combustion chamber. Physical properties measured include thermal conductivity, specific heat and thermal expansion data. Uniaxial tension tests were preformed to get mechanical properties at several temperatures ranging from room temperature to 600$^{\circ}C$. The result demonstrated that yield stress and ultimate tensile stress of the copper alloy decreases considerably and strain hardening increases as the result of the heat treatment. Since the LRE combustion chamber operates at higher temperature over 400$^{\circ}C$, the copper alloy can exhibit time-dependent behavior. Strain rate, creep and stress relaxation tests were performed to check the time-dependent behavior of the copper alloy. Strain rate tests revealed that strain rate effect is negligible up to 400$^{\circ}C$ while stress-strain curve is changed at 500$^{\circ}C$ as the strain rate is changed. Creep tests were conducted at 250$^{\circ}C$ and 500$^{\circ}C$ and the secondary creep rate was found to be very small at both temperatures implying that creep effect is negligible for the combustion chamber liner because its operating time is quite short.

• 한국정밀공학회지
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• 제17권12호
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• pp.209-216
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• 2000

The lateral behavior of the moving web is critical to the quality of the web products. The alignment of the rollers carrying the web is found to be one of important factors to the lateral behavior of the moving web. But, the study on the effect of the tilting roller in the direction of the normal to the moving web on the lateral behavior has not been reported in the literature yet. For example, the contact roller often contacts the winding roll in a tilted fashion and causes the lateral motion of the winding web, which induces the offset on the wound roll. The lateral dynamics of the moving web induced by a tilted roller in normal direction of a web is investigated in this paper. The two-dimensional dynamic model developed by Shelton is extended to investigate the effect of a titled roller in a normal direction of the moving web on the lateral motion of the moving web. New boundary conditions are developed to solve the extended model. Computer simulation study proved that the model developed can be used to predict the lateral motion of the moving web ？ to a tilted roller in normal direction of the moving web. The lateral deflection is increased exponentially a the tilting angle is increased. As the length of web span is increased, the amount of lateral deflection was increased almost linearly for the same tilting angle. The lateral dynamics turned out to be almost independent to the operating tension. The model developed can be used to solve the offset problem of the staggered winding and also to design a new web guiding mechanism.

• 한국해양공학회지
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• 제26권4호
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• pp.77-85
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• 2012

A study was performed on the design of a mooring line to maintain the position of a floating WEC (wave energy conversion) system. The procedure to design a mooring line is set up and the safety of the designed mooring system is evaluated using commercial software, Orcaflex. The characteristics curve for one line is analyzed to determine the properties and pretension of a mooring line. While considering the ocean environmental condition and importance of a floating WEC system, a multi-line layout is determined. A 4-point mooring system with 4 lines shows the instability in the yaw motion of the floating WEC system under a designed ocean environmental condition. The redesigned 4-point mooring system with 8 lines is found to be safe on the condition of a harsh ocean environment. The floating WEC system with the redesigned mooring system also shows stable motion in surge and pitch under operating conditions. From a parametric study on the mooring line length, the extreme value of the mooring line tension is found to be very sensitive to the pretension and length of mooring line. The results of this study can contribute to the establishment of a design procedure for mooring lines.