• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2017년도 추계학술논문요약집
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• pp.189-190
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• 2017

For the concept design of the device, a tool was made to test the simulated fuel rods and cutting force and the cutting force was measured. When 2-CUT and 3-CUT modules were used, the maximum force in 2-CUT at 12.5 mm/s speed change was $197.5kg_f$ and the maximum force at 3-CUT was $363.2kg_f$. The change of force in 2-CUT rapidly increases from about 1 second, and you can see that there are increase and decrease of the force change from about 5 seconds to 18 seconds, and it was rapidly decreased and the cut was made. The force change in 3-CUT has higher force at about 5 seconds later than 2-CUT at the speed of 12.5 mm/s, and you can see that it has the same tendency afterwards. If you search for the force at adequate speed from this cutting force test, 2-CUT module requires less slitting force than 3-CUT module, and the cutting time for 250 mm at 12.5 mm/s was 21 seconds, which can cut 4 m fuel rod in 5 minutes. But, there are cases of not completely slitting with 2-CUT module, so it is necessary to supplement this in the future through experiments.

• 대한기계학회논문집B
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• 제37권12호
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• pp.1153-1157
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• 2013

증기터빈의 터빈 블레이드는 발전소 핵심설비 중 하나로, 로터의 디스크에 결합되어 회전함으로 써 증기 에너지를 기계적 에너지로 변환시켜주는 역할을 하고 있다. 최근 터빈의 잦은 기동정지로 인해 블레이드 회전에 따른 원심하중이 반복적 작용하고 이에 따른 저압 증기터빈 최종단 블레이드의 손상이 자주 보고되고 있다. 본 논문에서는 터빈 블레이드에 발생되는 손상을 분석하여 블레이드에 발생되는 저주기 피로수명을 평가하였다. 증기터빈 최종단 블레이드의 균열발생 수명을 결정하기 위해 유한요소법으로 계산한 탄성응력에 Neuber's rule을 적용하여 진변형율 진폭을 계산하였으며, 예측된 수명과 블레이드 실제 기동정지횟수가 잘 일치됨을 보였다.

• 한국가시화정보학회지
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• 제18권2호
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• pp.59-65
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• 2020

Vertical axis wind energy systems including 3 and 4 blades are numerically investigated in a two-dimensional (2D) computational domain. The power coefficient (C_p) is adopted to measure the efficiency of the system and the effect of the rotating velocity on the power coefficient is analyzed for the two different systems. The rotating velocity varies from 30 rad/s to 90 rad/s, which corresponds to the tip speed ratio (T.S.R) of 0.5 to 1.5. The torque exerted on the blades is mainly determined by the aerodynamic force in the x-direction and maximized when the blade is positioned at around θ = 186°. The efficiency of the 4-blade system is higher than that of the 3-blade system within the tip speed ratio range between 0.5 and 0.67, besides where the 3-blade system shows a better performance. For the 3-blade system, the maximum efficiency is reached to 0.082 at the tip speed ratio of 1.083. The maximum efficiency of the 4-blade system is 0.071 at T.S.R. = 0.92. The velocity fields in the x-direction, pressure fields, and the vorticity magnitude are analyzed in detail for the optimal cases of the 3- and 4-blades systems, respectively.

• 제어로봇시스템학회논문지
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• 제18권2호
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• pp.76-80
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• 2012

This paper demonstrates how to implement inherent pitching stability in an insect-mimicking flapping-wing system for vertical takeoff. Design and fabrication of the insect-mimicking flapping-wing system is briefly described focusing on the recent modification. Force produced by the flapping-wing systems is estimated using the UBET (Unsteady Blade Element Theory) developed in the previous work. The estimation shows that the wing twist placed in the modified system can improve thrust production for about 10 %. The estimated thrust is compared with the measured thrust, which proves that the UBET provides fairly good estimations for the thrust produced by the flapping-wing systems. The vertical takeoff test shows that inherent pitching stability can be implemented in an insect-mimicking flapping-wing system by aligning the aerodynamic force center and center of gravity.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.71-84
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• 2020

In order to improve the performance of marine centrifugal pump, a centrifugal pump whose specific speed is 66.7 was selected for the research. Outlet diameter D2, outlet width b2, blade outlet angle β2, blade wrap φ and blade number z of the impeller were chosen as the variables. The maximum weighted average efficiency and the minimum vibration intensity at the base were calculated as objectives. Based on the Latin Hypercube method, the impeller was numerically optimized. The numerical results show that after optimization, the amplitudes of pressure fluctuation on the main frequency at different monitoring points decrease in varying degrees. The radial force on impeller decreases obviously under off-design flow rates and is more symmetrical during the operation of the pump. The variation of the axial force is relatively small, which has no obvious relationship with the rotating angle of the impeller. The energy performance and vibration experiment was performed for verifying. The test results show that the weighted average efficiency under 0.8Qd, 1.0Qd and 1.2Qd increases by 4.3% after optimization. The maximal vibration intensity at M1-M4 on the pump base reduced from 0.36 mm/s to 0.25 mm/s, decreasing by 30.5%. In addition, the vibration velocities of bracket in pump side and outlet flange also have significant reductions.

• 대한기계학회논문집A
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• 제38권6호
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• pp.609-617
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• 2014

풍력터빈 블레이드의 가변 피치제어는 풍력발전기의 과풍속 영역 설계에 있어 중요한 요소로 알려져 있으나 원가문제 때문에 소형 풍력터빈에는 적용되지 못하고 실속제어가 많이 적용되고 있다. 하지만, 블레이드 주변의 난류 때문에 설계된 실속이 구현되지 않는 실속지연 현상이 종종 발생되고, 이에 따른 풍력 블레이드의 과회전과 발전기의 과출력 위험이 발생하고 있다. 이에 따라 블레이드에서 발생되는 공력으로 피치가 변하고 스프링의 복원력으로 복귀되는 수동형 피치제어 모듈이 주목 받고 있다. 본 연구에서는 회전하는 블레이드의 익형에서 발생되는 양력과 항력을 이용하여 회전면으로 작용되는 토크와 블레이드의 Flap 방향으로 작용되는 추력을 계산하는 방법을 제시하고, 이러한 힘들의 크기를 여러 가지 익형에 대해 비교하였으며, 블레이드의 피치모멘트를 정량적으로 산출하여 수동 피치제어 모듈의 설계자료로 활용될 수 있도록 하였다.

• 한국항공우주학회지
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• 제39권8호
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• pp.735-743
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• 2011

본 연구에서는 직선형 터빈 캐스케이드 장치를 이용하여 분사영역으로 진입하고 퇴각하는 익형의 허브, 평균반경, 팁에 형성되는 표면에서의 압력을 정상상태에서 측정하였다. 익형은 축류형으로 코드가 200mm이며, 분사 노즐은 단면은 사각형으로 그 크기는 $200mm{\times}200mm$이다. 실험은 코드 기준으로 레이놀즈수 $3{\times}10^5$에서 수행되었다. 탈설계 성능을 측정하기 위하여 노즐의 설치각을 $58^{\circ}$, $65^{\circ}$와 $72^{\circ}$로 변경하면서, 노즐의 설치각 변화에 대한 익형에서 표면압 변화의 특성을 파악하였다. 또한 현절비를 1.25, 1.38, 1.67로 변경하면서 현절비 변화에 대한 익형의 표면압 변화를 측정하였다. 실험의 결과에서 익형이 분사영역으로 진입할 때 현절비가 적을수록 흡입면에서는 표면압력의 감소가 발생되었고 낮은 노즐설치각인 경우에는 역회전방향의 힘이 형성되었다. 아울러 양의 입사각으로 익형이 분사영역으로 진입할 때 흡입면의 앞부분에 낮은 압력이 형성되었다.

• Coupled systems mechanics
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• 제2권3호
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• pp.231-253
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• 2013

The impact of spar-nacelle-blade coupling on edgewise dynamic responses of spar-type floating wind turbines (S-FOWT) is investigated in this paper. Currently, this coupling is not considered explicitly by researchers. First of all, a coupled model of edgewise vibration of the S-FOWT considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar and mooring system, the hydrodynamic effects, the restoring moment and the buoyancy force is proposed. The aerodynamic loads are combined of a steady wind (including the wind shear) and turbulence. Each blade is modeled as a cantilever beam vibrating in its fundamental mode. The mooring cables are modeled using an extended quasi-static method. The hydrodynamic effects calculated by using Morison's equation and strip theory consist of added mass, fluid inertia and viscous drag forces. The random sea state is simulated by superimposing a number of linear regular waves. The model shows that the vibration of the blades, nacelle, tower, and spar are coupled in all degrees of freedom and in all inertial, dissipative and elastic components. An uncoupled model of the S-FOWT is then formulated in which the blades and the nacelle are not coupled with the spar vibration. A 5MW S-FOWT is analyzed by using the two proposed models. In the no-wave sea, the coupling is found to contribute to spar responses only. When the wave loading is considered, the coupling is significant for the responses of both the nacelle and the spar.

• 대한기계학회논문집B
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• 제27권10호
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• pp.1457-1463
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• 2003

In this paper, the response surface method using three-dimensional Navier-Stokes analysis to optimize the shape of a multi-blade centrifugal fan, is described. For numerical analysis, Reynolds-averaged Navier-Stokes equations with standard k - c turbulence model are transformed into non-orthogonal curvilinear coordinate system, and are discretized with finite volume approximations. Due to the large number of blades in this centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models for economic calculations. Linear Upwind Differencing Scheme(LUDS) is used to approximate the convection terms in the governing equations. SIMPLEC algorithm is used as a velocity-pressure correction procedure. Design variables, location of cur off, radius of cut off, expansion angle of scroll and width of impeller were selected to optimize the shapes of scroll and blades. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, the efficiency was successfully improved. It was found that the optimization process provides reliable design of this kind of fans with reasonable computing time.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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• pp.129-136
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• 2000

Centrifugal fans are widely used and the noise generated by these machines causes one of the most serious problems. In general, the centrifugal fan noise is often dominated by tones at BPF(blade passage frequency) and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the cutoff in the casing. However, only a few researches have been carried out on predicting the noise because of the difficulty in obtaining detailed Information about the flow field and casing effects on noise radiation. The objective of this study is to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan, and to calculate the effects of small vanes that are attached in original impeller - Splitter impeller. We assume that the impeller rotates with a constant angular velocity and the flow field around the impeller is incompressible and inviscid. So, a discrete vortex method (DVM) is used to model the centrifugal fan and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. The splitter impeller changes the acoustic characteristics as well as performance. Two-splitter type impeller and splitter impeller which splitter locates in jet region are good for acoustic characteristics.