• 한국산림과학회지
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• 제76권1호
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• pp.27-32
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• 1987

강원도(江原道) 원주시(原州市) 우산동(牛山洞)에 소재(所在)한 상지대학(尙志大學) 구내(構內)에 생육중(生育中)인 8종(種)의 조경수목(造景樹木)을 대상(對象)으로 기공형질(氣孔形質)(기공형(氣孔型), 밀도(密度) 및 기공장(氣孔長))을 조사(調査)하였다. 개나리, 수수꽃다리, 느티나무 및 모과나무의 기공(氣孔)은 irregular-celled type(anomocytic)이며, 백당나무, 튜울립나무 및 목련의 기공(氣孔)은 parallel-celled type(paracytic)이었다. 개나리의 경우, 엽신장(葉伸長)에 따른 기공장(氣孔長)의 변화(變化)는 거의 없었고, 단위엽면적당(單位葉面積當) 기공수(氣孔數)는 크게 감소(減少)했으며, 개체엽당(個體葉當) 기공수(氣孔數)는 증가(增加)하였다. 주목의 경우, 침엽신장(針葉伸長)에 따라 기공장(氣孔長)은 계속 증가(增加)했으며, 단위엽면적당(單位葉面積當) 기공수(氣孔數)는 감소(減少)하였다.

• 대한기계학회논문집B
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• 제25권12호
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• pp.1721-1729
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• 2001

The performance of gas turbines is decreased as their operating hours increase. Fouling in the axial compressor is one of main reasons for the performance degradation of gas turbine. Airborne particles entering with air at the inlet into compressor adhere to the blade surface and result in the change of the blade shape, which is closely and sensitively related to the compressor performance. It is difficult to exactly analyze the mechanism of the compressor fouling because the growing process of the fouling is very slow and the dimension of the fouled depth on the blade surface is very small compared with blade dimensions. In this study, an improved analytic method to predict the motion of particles in compressor cascades and their deposition onto blade is proposed. Simulations using proposed method and their comparison with field data demonstrate the feasibility of the model. It if found that some important parameters such as chord length, solidity and number of stages, which represent the characteristics of compressor geometry, are closely related to the fouling phenomena. And, the particle sloe and patterns of their distributions are also Important factors to predict the fouling phenomena in the axial compressor of the gas turbine.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.416-416
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• 2016

Organic-inorganic metal halide perovskite solar cells have received attention because it has a number of advantages with excellent light harvesting, high carrier mobility, and facile solution processability and also recorded recently power conversion efficiency (PCEs) of over 20%. The major issue on perovskite solar cells have been reached the limit of small area laboratory scale devices produced using fabrication techniques such as spin coating and physical vapor deposition which are incompatible with low-cost and large area fabrication of perovskite solar cells using printing and coating techniques. To solution these problems, we have investigated the feasibility of achieving fully printable perovskite solar cells by the blade-coating technique. The blade-coating fabrication has been widely used to fabricate organic solar cells (OSCs) and is proven to be a simple, environment-friendly, and low-cost method for the solution-processed photovoltaic. Moreover, the film morphology control in the blade-coating method is much easier than the spray coating and roll-to-roll printing; high-quality photoactive layers with controllable thickness can be performed by using a precisely polished blade with low surface roughness and coating gap control between blade and coating substrate[1]. In order to fabricate perovskite devices with good efficiency, one of the main factors in printed electronic processing is the fabrication of thin films with controlled morphology, high surface coverage and minimum pinholes for high performance, printed thin film perovskite solar cells. Charge dissociation efficiency, charge transport and diffusion length of charge species are dependent on the crystallinity of the film [2]. We fabricated the printed perovskite solar cells with large area and flexible by the bar-coating. The morphology of printed film could be closely related with the condition of the bar-coating technique such as coating speed, concentration and amount of solution, drying condition, and suitable film thickness was also studied by using the optical analysis with SEM. Electrical performance of printed devices is gives hysteresis and efficiency distribution.

• 한국생산제조학회지
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• 제23권2호
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• pp.178-185
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• 2014

This paper describes a fabrication multiplexing sensor probe that employs a fiber Bragg grating(FBG) based on multiple measurements to determine the blade deflection of a wind power generator the reliability analysis of this probe is also presented. To diminish the temperature sensitivity of the FBG sensor, we form multiple CFRPs onto the upper and lower layers of the FBG and package it with an epoxy resin. As a result, the depth of the CFRP is 1mm, and the temperature sensitivity is $2.39pm/^{\circ}C$. We construct a sensor network utilizing the fabricated sensor with a blade beam model. As the number of pendulums is increased on the fore-end of the beam, the strain value is measured. The strain variation is calculated from the measurement of the load on the blade beam model by monitoring the strain of the FBG sensor. When the linear equation is applied, the strain error is 0.4% and when the finite difference method is used, the tip deflection error is 3.3%. The displacement error derived from the strain value of the FBG sensor is 4.39%. The calculated result between the measured value of the dead-end of the beam and the strain is less than 2.46% tip distortion error. Therefore, our proposed multiplexing sensor probe is a low-cost and high-reliability solution for a commercial wind power generator.

• 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.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.192-196
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• 2005

Key part of main equipment in a gas turbine may be likely to be damaged due to operation under high temperature, high pressure, high-speed rotation, etc. Accordingly, the cost for maintenance increases and the damaged parts may cause generation to stop. The number of parts for maintenance also increases, but diagnostics technology fur the maintenance actually does not catch up with the demand. Blades are made of precipitation hardening Ni superalloy IN738 and the like for keeping hot strength. The surface of a blade is thermal-sprayed, using powder with main compositions such as Ni, Cr, Al, etc. in order to inhibit hot oxidation. Conventional regular maintenance of the coating layer of a blade is made by FPI (Fluorescent Penetrant Inspection) and MTP (Magnetic Particle Testing). Such methods, however, are complicated and take long time and also require much cost. In this study, defect diagnostics were tested for the coating layer of an industrial gas turbine blade, using an infraredthermography camera. Since the infrared thermography method can check a temperature distribution on a wide range of area by means of non-contact, it can advantageously save expenses and time as compared to conventional test methods. For the infrared thermography method, however, thermo-load must be applied onto a tested specimen and it is difficult to quantify the measured data. To solve the problems, this essay includes description about producing a specimen of a gas turbine blade (bucket), applying thermo-load onto the produced specimen, photographing thermography images by an infrared thermography camera, analyzing the thermography images, and pre-testing for analyzing defects on the coating layer of the gas turbine blade.

• 대한기계학회논문집B
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• 제26권9호
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• pp.1292-1301
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• 2002

An experimental study of turbine performance is conducted with various incidence angles on a rotating turbine rotor. 5 different incidence angles are applied from -17$^{\circ}$to 13$^{\circ}$with 7.5$^{\circ}$gaps. In order to precisely set up the incidence angles at the rotor inlet, 5 turbine discs are manufactured with the different fir tree section. Total-to-total efficiencies are obtained on the several off-design points with considering the exit total pressure, which is meas fred at 12 locations between the hub and casing using a pressure rake. The degree of reaction is 0.373 at the mean radius, and Reynolds number based on the rotor chord is 0.86$\times$10$^{5}$ at the turbine inlet on the design point experiment. The experiment on a single-stage turbine is conducted at the low-pressure and low-speed state, but it is sufficient to consider the blade loading effect due to the rotating apparatus even though the total pressure loss at the exit is increased proportionally to the turbine output power. The experimental results recommend 6$^{\circ}$as an optimum incidence angle on the turbine blade design. The total-to-total efficiency is steeply decreased when the incidence angle is over $\pm$9$^{\circ}$ from the optimum incidence angle. In the range of less than -10$^{\circ}$incidence angle, 7.5$^{\circ}$ reduction of incidence angle generates 15% decrease of total-to-total efficiency. This result is obtained on the same rotor blade by changing only the rotational speed to minimize the effect of profile and secondary flow loss in the passage. Experimental results show that the change rate of total-to-total efficiency according to the incidence angle change is unchanged although the turbine operates at the off-design condition.

• 항공우주기술
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• 제8권1호
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• pp.32-41
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• 2009

본 연구에서는 한국형기동헬기(KUH) 주로터 블레이드의 축소 설계를 수행하였다. 축소 모델은 공력하중, 익단 와류 및 소음원 측정 시험을 위해 설계되었다. 실제 로터와 동일한 공력 하중을 모사하기 위하여 마하스케일링 기법이 적용되었다. 마하스케일 모델은 블레이드의 익단 마하수가 동일하며, 정규화된 진동수 또한 동일하다. 즉, 마하스케일된 모델은 공력하중 및 구조동역학적 과점에서 상사된 모델이다. 공기역학적 축소과정은 외형 치수의 축소와 회전수의 증가를 통해 완료된다. 구조동역학적 측면에서는 블레이드 단면 설계를 통해 생성된 강성 및 관성 분포가 실제 로터의 회전고유진동수 분포를 나타내는지 확인하는 과정을 통해 완료된다. 본 연구에서는 국내에서 수급 가능한 복합재 프리프레그를 이용한 블레이드 단면 설계를 수행하고, 설계된 모델의 동역학적 특성을 고찰하였다.

• 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.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.213-217
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• 2008

This paper describes an application of centrifugal compressor optimization system, in which the blade profile of impeller is represented with NURBS(Non-Uniform Rational B-Spline) curve. A commercial CFD(Computational Fluid Dynamics) program named NUMECA fine/turbo was used to evaluate the performance of the whole centrifugal compressor flow passage including impeller and diffuser. The whole optimization design system was integrated based on iSIGHT, a commercial integration and optimization software, which provides a direct application of some optimization algorithms. To insure the practicability of optimization, the performance of centrifugal compressor under all condition was concerned during the optimizing process. That means a compositive object function considering the aerodynamic efficiency, pressure ratio and mass flow rate under different work condition was applied by using different weight number for different conditions. Using the optimization method described in this paper, an optimized design of the impeller blade of centrifugal compressor was obtained. Comparing to the original design, optimized design has a better performance not only under the design work condition, but also the off-design work condition including near stall and near choke condition.