• 대한조선학회논문집
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• 제50권2호
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• pp.95-103
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• 2013

Prediction of the running posture is important to evaluate the resistance by the numerical calculation for a high speed vessel. Especially for a planing craft having a large variation of running attitude it becomes more essential, but it can not be obtained easily because the running posture and the hydrodynamic forces including the resistance are interacted with each other. So iterative calculation to obtain the dynamic forces according to the changes in attitude is necessary, in this study, considering the calculated hydrodynamic force at the assumed draft as the additional buoyancy the corrected draft is calculated through satisfying the equilibrium between the buoyancy and the hull weight. To verify the derived method three kinds of hull forms were used with the results of model tests, R/V ATHENA and 150 tons class guide vessel for middle-speed semi-planing crafts, 28 feet fast boat for a high-speed planing boat. For all cases with several iterations the converged value of draft can be obtained, lastly the resistance and flow around hull were simulated by using VOF method.

• 한국전산유체공학회지
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• 제14권4호
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• pp.67-77
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• 2009

This paper is a continuation of a recent development on the Hermite-based divergence-free element method and deals with a non-isothermal fluid flow driven by the buoyancy force in a square cavity with temperature difference across the two sides. Two Hermite functions are considered for numerical computations in this paper. One is a cubic function and the other is a quartic function. The degrees-of-freedom of the cubic Hermite function are stream function and its first and second derivatives for the velocity field, and temperature and its first derivatives for the temperature field. The degrees-of-freedom of the quartic Hermite function include two second derivatives and one cross derivative of the stream function in addition to the degrees-of-freedom of the cubic stream function. This paper presents a brief review on the Hermite based divergence-free basis functions and its finite element formulations for the buoyancy driven flow. The present algorithm does not employ any upwinding or a stabilization term. However, numerical values and contour graphs for major flow variables showed good agreements with those by De Vahl Davis[6].

• 한국해양공학회지
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• 제32권6호
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• pp.466-473
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• 2018

This paper presents an estimation method for the static configuration of a steel lazy wave riser (SLWR) using the dynamic relaxation method applied to estimate the configuration of structures with strong geometric non-linearity. The lumped mass model is introduced to reflect the flexible structural characteristics of the riser. In the lumped mass model, the tensions, shear forces, buoyancy, self-weights, and seabed reaction forces at nodal points are considered in order to find the static configuration of the SLWR. The dynamic relaxation method using a viscous damping formulation is applied to the static configuration analysis. Fictitious masses are defined at nodal points using the sum of the largest direct stiffness values of nodal points to ensure the numerical stability. Various case studies were performed according to the bending stiffness and size of the buoyancy module using the dynamic relaxation method. OrcaFlex was employed to validate the accuracy of the developed numerical method.

• KIEAE Journal
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• 제15권2호
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• pp.123-131
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• 2015

Purpose : Improvement of indoor thermal comfort and reduction of the energy consumption in building can be obtained by applying a double skin facade system. In order to achieve effectively this purpose, design team would have to perform easy and appropriate performance analysis for making better design decision during the design process. Method : This paper focus on the natural ventilation performance of a multi-story type double skin facade with main causes which are pressure difference according to the wind and temperature difference between indoor and outdoor (Buoyancy Effect). Using this main causes, the natural ventilation ratio of wind effect-to-buoyancy effect in cavity of multi-story type double skin facade were analyzed through the performance analysis results of CFD (Computational Fluid Dynamics) simulation. Result : When the wind velocity was 2m/s, the ventilation rate in the cavity was highest. If wind velocity was slower than 2m/s wind velocity, buoyancy effect has more influence on the ventilation rate in the cavity, and if wind velocity was faster than 2m/s wind velocity, wind effect has more influence on the ventilation rate in the cavity.

• 한국재난정보학회 논문집
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• 제14권3호
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• pp.343-351
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• 2018

연구목적: 최근 기반시설물이 대형화 됨에 따라 콘크리트 구조물의 경우는 중량감소를 위하여 중공 슬래브가 대안의 하나로 제시되고 있다. 연구방법: 중공부재의 시공 시 부력으로 인하여 시공이 어려운 점과 콘크리트 단면적이 줄어 전단성능이 부족하게 되는 구조적인 단점이 있으므로, PVC관과 같은 중공체를 이용하여 일방향 슬래브를 제작하고 시공성과 구조성능을 검토하는 실험을 실시하였다. 연구결과: PVC관을 이용한 일방향 중공슬래브의 경우 부력방지장치를 이용하면 타설 시 발생하는 중공체의 부상 및 침강을 예방하여 시공성능이 크게 개선되었으며, 휨 및 전단성능도 적합한 성능을 가진 것으로 확인되었다. 결론: 중공율과 휨성능은 큰 관계가 없지만 중공율이 큰 경우는 항복 후 2차 강성이 낮으므로 이에 대한 고려가 필요하며, 중공율의 증가에 따른 전단성능의 감소는 전단철근을 배근하면 보완될 수 있을 것으로 사료된다.

• 한국지반환경공학회 논문집
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• 제24권10호
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• pp.33-39
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• 2023

지하공간의 이용에 관심이 높아짐에 따라 지하구조물에 작용하는 수압에 대한 안전성 확보가 요구되고 있다. 국내에서는 이와 같은 지하수압을 제어하기 위한 방법으로 여러가지 부력방지공법을 사용하고 있으며, 그 중 최근 경제성과 시공성이 뛰어나고, 안정성이 좋은 연직배수공법을 도입하여 적용하고 있다. 그러나 현장에서 설계 시공되는 연직배수공법의 경우 수치해석에 의존하여 설계 시공되는 경우가 많아 실측적인 안정성 판단을 기대하기 힘들다. 이에 본 연구에서는 모형토조를 이용해 연직배수시스템을 설치하여 양압력을 측정하는 실험을 진행하였다. 실험에 의한 측정값과 수치해석값을 바탕으로 작용양압력을 비교·분석하여 현장적용이 가능한 기초자료로 사용하고자 한다.

• 대한조선학회논문집
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• 제52권3호
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• pp.236-247
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• 2015

In this paper, the experimental equipments for ventilated supercavitation in cavitation tunnel is constructed and the basic data of ventilated supercavitation regard to the entrainment coefficient and Froude number is fulfilled. The experiments are conducted for the disk cavitator with injecting air and the pressure inside cavity and the shape of cavity are measured. As the entrainment coefficient increases while the Froude number is kept constant, the ventilated cavitation number decreases to a minimum value which decreases no more even with increasing the air entrainment. The minimum value of ventilated cavitation number, caused by the blockage effect, decreases according to increasing the diameter ratio of test section to cavitator. The cavity length is rapidly enlarged near the minimum cavitation number. In low Froude numbers, the cavity tail is floating up due to buoyancy and the air inside the cavity is evacuated from its rear end with twin-vortex hollow tubes. However, in high Froude numbers, the buoyancy effect is almost negligible and there is no more twin-vortex tubes so that the cavity shape becomes close to axisymmetric. In order to measure the cavity length and width, the two methods, which are to be based on the cavity shapes and the maximum width of cavity, are applied. As the entrainment coefficient increases after the ventilated cavitation number gets down to the minimum cavitation number, the cavity length still increases gradually. These phenomenon can be confirmed by the measurement using the method based on the cavity shapes. On the other hand, when the method based on the maximum width of cavity is used, the length and width of the cavity agree well with a semi-empirical formular of natural cavity. So the method based on the maximum width of cavity can be a valid method for cavitator design.

• 해양환경안전학회지
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• 제24권6호
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• pp.686-693
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• 2018

2014년 세월호 침몰사고 이후 해상에서의 안전에 대한 국민적 관심이 높아져 왔다. 해상에서 인명구조에 필요한 초기 대응시간을 확보하기 위해 구조기관의 골든타임뿐만 아니라 조난자도 구조대원이 현장에 도착하기까지 필요한 시간을 확보할 필요가 있다. 본 연구는 유류오염방제정(이하 방제정)에 비치된 오일펜스를 활용하여 다수의 인명들을 구조할 때 조난자의 심리적 안정을 유지하고 안전하게 인명을 구조하는 방안에 대한 연구를 진행하였다. 실 해역 실험을 통해 오일펜스의 측면에 구명줄 설치 시 1 m 당 70 kg 성인 2명의 부력을 유지할 수 있고 양측면에는 4명을 유지할 수 있음을 확인하였다. 또한 오일펜스 상부에 탑승 시 8 m 당 성인 3명에 대한 부력이 유지되고 있음을 확인하였다. 구조 방법으로는 방제정에서 설치한 오일펜스 후단을 잡고 고속단정이 조난자에게 접근시키는 것이 가장 신속하고 정확하게 구조하는 방법임을 확인하였다. 이 결과로 오일펜스를 활용하여 구조기관이 구조에 필요한 시간을 확보하고 아울러 조난자가 구조 시까지 심리적 안정을 가질 수 있어 다수의 인명들을 구조할 때 구조 방안으로 활용할 수 있음을 확인하였다.

• 한국수소및신에너지학회논문집
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• 제16권1호
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• pp.1-8
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• 2005

Transition of momentum-controlling hydrogen jet to buoyant jet is experimentally investigated in order to develop a prediction model for the moving trajectory of hydrogen leaked from hydrogen devices. In the experiments, room-temperature helium, that has a similar density to the hydrogen leaked from high pressure tank, is horizontally injected through a 4mm tube and its moving trajectory is visualized by the shadowgraph method. The moving trajectories are found to be parabolic, thereby exhibiting increasing influence of the buoyancy. In analyzing the experimental results, the vertical movement is assumed to be controlled by the buoyancy while the horizontal movement is controlled by the air entrainment caused by the initial momentum. The resealing based on this assumption yields a single curve fitting to the all experimental results.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.333-336
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• 2003

For long time, the takeoff and landing control of airship was worked by human handling. With the development of the autonomous control system, the exact controls during the takeoff and landing were required and lots of methods and algorithms were suggested. This paper presents the result of airship take-off and landing by buoyancy control using air ballonet volume change and performance control of pitch angle for stable flight within the desired altitude. For the complexity of airship's dynamics, firstly, simple PID controller was applied. Due to the various atmospheric conditions, this controller didn’t give satisfactory results. Therefore, new control method was designed to reduce rapidly the error between designed trajectory and actual trajectory by learning algorithm using an artificial neural network. Generally, ANN has various weaknesses such as large training time, selection of neuron and hidden layer numbers required to deal with complex problem. To overcome these drawbacks, in this paper, the RBFN (radial basis function network) controller developed.