• 한국소음진동공학회논문집
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• 제25권2호
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• pp.75-82
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• 2015

Noises from the large scale marine propeller are calculated numerically on non-cavitation condition. The hydrodynamic analysis is carried out by potential based panel method with time marching free wake approach. The distribution of hydrodynamic loads on the propeller surface and noise signals are obtained using the unsteady Bernoulli's equation and the Farasssat's formula respectively. It turns out that the noise signal at the narrow band shows strong peak at the blade passage frequency, and the peak value at the 1/3 octave band also shows the same trend. Noise signals and directivity patterns for both the thickness and the loading noise are compared with each other. The directivity pattern for the loading noise shows minor lobe at the backward side of the rotating disc plane.

• Ocean Systems Engineering
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• 제13권2호
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• pp.147-172
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• 2023

This study investigates the influence of loading and inflow conditions on tidal turbine performance from a hydrodynamic and hydroacoustic point of view. A boundary element method is utilized for the former to investigate turbine performance at various loading conditions under zero/non-zero yaw inflow. The boundary element method is selected as it has been selected, tested, and validated to be computationally efficient and accurate for marine hydrodynamic problems. Once the hydrodynamic solutions are obtained, such as the time-dependent surface pressures and periodic motion of the turbine blade, they are taken as the known noise sources for the subsequence hydroacoustic analysis based on the Ffowcs Williams-Hawkings formulation given in a form proposed by Farassat. This formulation is coupled with the boundary element method to fully consider the three-dimensional shape of the turbine and the speed of sound in the acoustic analysis. For validations, a model turbine is taken from a reference paper, and the comparison between numerical predictions and experimental data reveals satisfactory agreement in hydrodynamic performance. Importantly, this study shows that the noise patterns and sound pressure levels at both the near- and far-field are affected by different loading conditions and sensitive to the inclination imposed in the incoming flow.

• International Journal of Aeronautical and Space Sciences
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• 제18권1호
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• pp.17-27
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• 2017

The treatment of rotor wake has been a critical issue in the field of the rotor aerodynamics. This paper presents a new free wake model for the unsteady analysis for a wind turbine. A blade-wake-tower interaction is major source of unsteady aerodynamic loading and noise on the wind turbine. However, this interaction can not be considered in conventional free wake model. Thus, the free wake model named Finite Vortex Element (FVE hereafter) was devised in order to consider the interaction effects. In this new free wake model, the wake-tower interaction was described by dividing one vortex filament into two vortex filaments, when the vortex filament collided with a tower. Each divided vortex filaments were remodeled to make vortex ring and horseshoe vortex to satisfy Kelvin's circulation theorem and Helmholtz's vortex theorem. This model was then used to predict aerodynamic load and wake geometry for the horizontal axis wind turbine. The results of the FVE model were compared with those of the conventional free wake model and the experimental results of SNU wind tunnel test and NREL wind tunnel test under various inflow velocity and yaw condition. The result of the FVE model showed better correlation with experimental data. It was certain that the tower interaction has a strong effect on the unsteady aerodynamic load of blades. Thus, the tower interaction needs to be taken into account for the unsteady load prediction. As a result, this research shows a potential of the FVE for an efficient and versatile numerical tool for unsteady loading analysis of a wind turbine.

• 대한조선학회지
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• 제26권3호
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• pp.29-40
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• 1989

고효율 및 캐비테이션 특성이 우수한 프로펠러 날개단면을 개발하기 위한 일련의 설계 제작 시험 및 해석과정을 기술하였다. 여러 날개단면의 양력-항력곡선과 캐비테이션 특징을 비교하기 위하여 11개의 2차원 날개 단면을 설계 제작 시험하였다. 개발된 단면(KH18 단면)은 양력-항력 곡선과 캐비티 초생 곡선에서 기존 단면에 비하여 폭이 넓기 때문에 불균일한 선미후류에서 작동하는 프로펠러의 날개 단면으로서 적합하리라 생각된다. 개방단면을 사용한 프로펠러 설계법을 제시하였다. 코오드 방향 부하분포 형상이 프로펠로 성능에 미치는 영향을 고찰하기 위하여 3가지 기준 부하 형상에 대한 프로펠러를 각각 설계하였다. 또한 날개단면이 프로펠러 성능에 미치는 영향을 비교하기 위하여 기존 날개단면만을 사용한 프로펠러를 2개 설계하였다.

• 한국산림과학회지
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• 제97권4호
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• pp.431-436
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• 2008

희귀수종 망개나무의 유전자원 보존 전략 수립을 위해 7개 집단의 지리적 위치에 따른 엽의 9가지 형태적 특성에 대한 변이를 조사하고 다변량분석을 실시하였다. 평균생장은 엽신장 10.25 cm, 최대엽폭 4.10 cm, 엽신장/최대엽폭 2.52, 상1/3폭 3.22 cm, 하1/3폭 3.42 cm, 상1/3폭/하1/3폭 0.95, 엽병길이 1.24 cm, 엽신장/엽병길이 8.91, 엽맥수 8.16개로 나타났다. Nested 분산분석 결과 9가지 양적특성들 모두에서 집단간 및 집단내 개체 간에 유의적인 차이를 보였으며, 대부분의 형질들은 총 분산 가운데 집단내 개체 간 차지하는 비율이 집단간 차지하는 비율보다 큰 것으로 나타났다. 9가지 양적특성들에 대한 집단간 유연관계는 거리지수 1.2에서 크게 2개의 그룹(충북과 경북지역)으로 나뉘었으며, 유집군의 유형은 제3주성분까지가 전체 변이의 87.3%를 설명하였다. 제1주성분의 기여율은 51.1%로 엽신장, 엽신장/최대엽폭 및 엽신장/엽병길이, 제2주성분의 기여율은 23.1%로 최대엽폭, 상1/3폭 및 하1/3폭, 제3성분은 13.1%로 엽병길이 인자가 망개나무 엽 특성 분류에 중요한 정보를 주는 요인으로 나타났다.

• 대한기계학회논문집B
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• 제20권8호
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• pp.2707-2720
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• 1996

The aerodynamic design of the two-stages of centrifugal compressors in an 1.2MW industrial gas turbine is completed with the application of numerical analyses. The final shape of an intake, the axial guide vanes and a return channel is determined using several interactions between design and two-dimensional turbulent flow analysis, focused on the minimum loss of internal flows. The one-dimensional turbulent flow analysis, focused on the minimum loss of internal flows. The one-dimensional design and prediction of aerodynamic performances for the compressors are performed by two different methods; one is a method with conventional loss models, and the other a method with the two-zone model. The combination methods of the Betzier curves generate three-dimensional geometric shapes of impeller blades which are to be checked with a careful change of aerodynamic blade loadings. The impeller design is finally completed by the applications of three-dimensional compressible turbulent flow solvers, and the effect of minor change of design of the second-stage channel diffuser is also studied. All the aerodynamic design results are soon to the verified by component performance tests of prototype centrifugal compressors.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2421-2428
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• 2002

In this study, the failure probability of the degraded LP turbine blade steel was performed using the Monte Carlo simulation to apply variation of applied stress and strength. For this purpose, applied stress under the service condition of steady state was obtained by theoretical stress analysis and the maximum Von-Mises stress was 219MPa. The fatigue strength under rotating-bending load was evaluated by the staircase method. Furthermore, 3-parameter Weibull distribution was found to be most appropriate among assumed distributions when the probabilistic distributions of tensile and fatigue strength were determined by the proposed analysis. The failure probability with various loading conditions was derived from the strength-stress interference model and the characteristic factor of safety was also estimated.

• Journal of Mechanical Science and Technology
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• 제20권7호
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• pp.1077-1088
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• 2006

This paper describes a numerical investigation on the performance deteriorations of a low speed, single-stage axial turbine due to use of rough blades. Numerical calculations have been carried out with a commercial CFD code, CFX-Tascflow, by using a modified wall function to implement rough surfaces on the stator vane and rotor blade. To assess the stage performance variations corresponding to 5 equivalent sand-grain roughness heights from a transition ally rough regime to a fully rough regime, stage work coefficient and total to static efficiency were chosen. Numerical results showed that both work coefficient and stage efficiency reduced as roughness height increased. Higher surface roughness induced higher blade loading both on the stator and rotor which in turn resulted in higher deviation angles and corresponding work coefficient reductions. Although, deviation angle changes were small, a simple sensitivity analysis suggested that their contributions on work coefficient reductions were substantial. Higher profile loss coefficients were predicted by higher roughness heights, especially on the suction surface of the stator and rotor. Furthermore sensitivity analysis similar to the above, suggested that additional profile loss generations due to roughness were accountable for efficiency reductions.

• 소음진동
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• 제8권5호
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• pp.870-878
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• 1998

The cross-flow fan which constitutes a fan-duct system with a stabilizer and a scroll casing is widely used in many air-ventilating and air-conditioning devices. Its ooperating points of high efficiency and loading conditions frequently induce a annoying sharp tonal component of discrete frequency on the noise spectrum, which is open called as a BPF(Blade-Passing-Frequency) noise and degrades the sound quality of the devices. this BPF tone has been one of the defects of the cross-flow fan. This study proposes two methods in order to reduce this tonal noise component, which are the random distributions of the fan blades and the skewed shapes of the stabilizer. The proposed methods are verified by a simple analytical model and are applied in manufacturing the cross-flow fan and the stabilizer samples. Some experiments are carried out to verify the reduction capability of BPF tones of above two schemes and the experimental results are analyzed. The comparison between two method is also carried out.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.965-980
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• 2014

This paper presents a new estimation method of full scale propulsive performance for the pulling type podded propeller. In order to estimate the drag of pod housing, a drag velocity ratio, which includes the effects of podded propeller loading and Reynolds number, is presented and evaluated through the comparison of model test and numerical analysis. By separating the thrust of propeller blade and the drag of pod housing, extrapolation method of pod housing drag to full scale is deduced, and correction method of propeller blade thrust and torque to full scale is presented. This study utilized the drag coefficient ratio of the pod housing as a measure for expanding it to full scale, but in order to increase the accuracy of performance evaluation, additional study is necessary on the method for the full scale expansion via separating the drag of pod body, strut and fin which consist the pod housing.