• Journal of Ship and Ocean Technology
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• 제4권1호
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• pp.1-10
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• 2000

A low-order potential based boundary element method is applied for the prediction of the performance of flapped rudders as well as all-movable rudders in steady inflow. In order to obtain a reasonable solution at large angles of attack, the location of the trailing wake sheet is determined by aligning freely with the local flow. The effect of the wake sheet roll-up is also included with use of a high order panel method. The flow in the gap of a flapped rudder is modeled as Couette flow and its effect is introduced into the kinematic boundary conditions for flux at both the inlet and the outlet of the gap. In order to validate the present method, the method is applied for a series of rudders and the computational results on forces and moments are compared with experimental data. The effect of the gap size on the forces and moments is also presented.

• Wind and Structures
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• 제18권2호
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• pp.135-154
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• 2014

Aerodynamic characteristics of crescent and D-shape bundled conductors were measured by high frequency force balance technique in the wind tunnel. The drag and lift coefficients of each sub-conductor and the whole bundled conductors were presented under various attack angles of wind. The galloping possibility of bundled conductors is discussed based on the Den Hartog criterion. The influence of icing thickness, initial ice accretion angle and sub-conductor on the aerodynamic properties were investigated. Based on the measured aerodynamic force coefficients, a computationally efficient finite element method is also implemented to analyze galloping of iced bundled conductors. The analysis results show that each sub-conductor of the bundled conductor has its own galloping feature due to the use of aerodynamic forces measured separately for every single sub-conductors.

• 대한기계학회논문집B
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• 제32권5호
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• pp.392-399
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• 2008

Accurate measurement of speed and altitude of flying vehicles in air data system remains a critical technical issue. A highly reliable Pitot-static probe is required to obtain air data such as total pressure and static pressure. In this study, an analysis of the characteristics of flowfield around the Pitot-static probe was performed by using a Navier-Stokes CFD code. In addition, for the purpose of finding an optimal configuration, a technique based on the response surface method is applied to the problem with design parameters including shape of the nose section and cone angle. It is shown that the optimal configuration fulfills the MIL specification in wider range of high angles of attack.

• Wind and Structures
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• 제20권6호
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• pp.793-810
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• 2015

Tests were conducted at the Florida International University (FIU) Wall of Wind (WOW) to investigate the susceptibility of Variable Message Signs (VMS) to wind induced vibrations due to vortex shedding and galloping instability. Large scale VMS models were tested in turbulence representative of the high frequency end of the spectrum in a simulated suburban atmospheric boundary layer. Data was measured for the $0^{\circ}$ and $45^{\circ}$ horizontal wind approach directions and vertical attack angles ranging from $-4.5^{\circ}$ to $+4.5^{\circ}$. Analysis of the power spectrum of the fluctuating lift indicated that vertical vortex oscillations could be significant for VMS with a large depth ratio attached to a structure with a low natural frequency. Analysis of the galloping test data indicated that VMS with large depth ratios, greater than about 0.5, and low natural frequency could also be subject to galloping instability.

• International Journal of Control, Automation, and Systems
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• 제1권3호
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• pp.315-320
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• 2003

This paper presents a control augmentation system (CAS) based on the dynamic model inversion (DMI) architecture for a highly maneuverable aircraft. In the application of DMI not treating actuator dynamics, significant instabilities arise due to limitations on the aircraft inputs, such as actuator time delay based on dynamics and actuator displacement limit. Actuator input saturation usually occurs during high angles of attack maneuvering in low dynamic pressure conditions. The pseudo-control hedging (PCH) algorithm is applied to prevent or delay the instability of the CAS due to a slow actuator or occurrence of actuator saturation. The performance of the proposed CAS with PCH architecture is demonstrated through a nonlinear flight simulation.

• 한국전산유체공학회지
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• 제15권3호
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• pp.1-8
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• 2010

Laminar separation bubble and transitional flow over the NACA0012 are investigated at a moderate range of Reynolds numbers. A Reynolds-Averaged Navier-Stokes code is coupled with an empirical transition model that can predict transition onset points and the length of transition region. Without solving the boundary layer equations, approximated e-N method is directly applied to the RANS code and iteratively solved together. The computational results are compared with the experimental data for the NACA0012 airfoil. Results of transition onset point and the length are compared well with experimental data and Xfoil prediction. The present RANS results show at high angles of attack better agreement with experimental data than Xfoil results using the boundary layer equations.

• 한국항공우주학회지
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• 제39권8호
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• pp.725-734
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• 2011

높은 받음각에서 항공기는 Wing Rock 이라고 알려진 Limit cycle 형태의 횡방향 진동 운동을 보일 수 있다. 이 논문에서는 이러한 불안정 진동운동과 관련한 불확실성에 적응하여 안정화시키는 고전 및 신경회로망기반 적응제어기법들의 상세 설계내용을 제시하였다. 모든 기법들은 80도 후퇴각을 가진 삼각날개를 갖는 모델에 적용하여 시뮬레이션하였고 그 결과를 비교분석하였다.

• 해양환경안전학회지
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• 제27권7호
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• pp.1059-1066
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• 2021

우리나라는 해상활동의 중요성이 크며, 산업화에 따른 이상기후 현상 등을 규명하기 위해 육상에 많은 자동기상 관측설비를 운영 중이지만 해상에서는 그 수가 매우 부족하다. 또한, 해양안전정보 구축 등을 위해 해양조사선을 운영 중이나 접근이 어려운 곳이 많고 높은 운영비용이 요구된다. 따라서 다양한 해양관측 등이 가능한 소형무인화선박의 개발이 필요하다. 한편 소형 무인화 선박에서 세일(Sail)은 항해 성능에 큰 영향을 미치므로 이에 대한 많은 연구가 진행되고 있다. 본 연구에서는 기존 에어포일 형상보다 높은 공기역학적 성능을 갖는 것으로 알려진 트윈커브세일(Twin curvy sail)의 설계변수인 캠버(Camber)효과에 대해 검토하였다. 5 종류의 캠버에 대해 유동해석 결과, 캠버 크기가 9 %일 때 가장 높은 양력계수를 나타내었다. 트윈커브세일의 경우 Port sail과 Starboard sail의 상호작용에 의해 받음각 23°에서 가장 높은 양력계수를 갖고, Port sail의 경우 받음각 20°에서 가장 높은 양력계수를 Starboard sail의 경우 받음각 15°에서 가장 낮은 양력계수를 나타내었다. 또한, 트윈커브세일은 모든 받음각에서 에어포일 형상인 NACA 0018보다 높은 양력계수를 나타내었다.

• Wind and Structures
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• 제1권3호
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• pp.225-241
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• 1998

The high-rise supporting towers of long-span suspension and cable-stayed bridges commonly comprise a pair of slender prisms of roughly square cross-section with a center-to-centre spacing of from perhaps 2 to 6 widths and connected by one or more cross-ties. The tower columns may have a constant spacing as common for suspension bridges or the spacing may reduce towards the top of the tower. The present paper is concerned with the aerodynamics of such towers and describes an experimental investigation of the overall aerodynamic forces acting on a pair of square cylinders in two-dimensional flow. Wind tunnel pressure measurements were carried out in smooth flow and with a longitudinal intensity of turbulence 0.10. Different angles of attack were considered between $0^{\circ}$ and $90^{\circ}$, and separations between the two columns from twice to 13 times the side width of the column. The mean values of the overall forces proved to be related to the bias introduced in the flow by the interaction between the two cylinders; the overall rms forces are related to the level of coherence between the shedding-induced forces on the two cylinders and to their phase. Plots showing the variation of the force coefficients and Strouhal number as a function of the separation, together with the force coefficients spectra and lift cross-correlation functions are presented in the paper.

• Wind and Structures
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• 제18권1호
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• pp.37-56
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• 2014

The evaluation of pressure fields acting on slender structures under wind loads is currently performed in experimental aerodynamic tests. For wind-sensitive structures, in fact, the knowledge of global and local wind actions is crucial for design purpose. This paper considers a particular slender structure under wind excitation, representative of most common high-rise buildings, whose experimental wind field on in-scale model was measured in the CRIACIV boundary-layer wind tunnel (University of Florence) for several angles of attack of the wind. It is shown that an efficient reduced model to represent structural response can be obtained by coupling the classical structural modal projection with the so called blowing modes projection, obtained by decomposing the covariance or power spectral density (PSD) wind tensors. In particular, the elaboration of experimental data shows that the first few blowing modes can effectively represent the wind-field when eigenvectors of the PSD tensor are used, while a significantly larger number of blowing modes is required when the covariance wind tensor is used to decompose the wind field.