실시간 DGPS를 이용한 헬리콥터 착륙 시스템 개발

기창돈,장재규,황덕호,김정한,박성민 서울대학교 항공우주신기술연구소 2000 항공우주신기술연구소 연구보고 Vol.1 No.1

최근 수년간, GPS와 관련된 연구들이 항공분야를 비롯한 다양한 분야에서 진행되었다. 특히 GPS를 항공기의 착륙 유도 시스템에 이용하려는 연구가 많이 이뤄지고 있다. 이러한 시도들은 GPS의 경제성, 신뢰성, 정확성 등의 장점들을 십분 활용하기 위한 것이라고 할 수 있다. 서울대학교 GPS 실험실에서도 이러한 경향에 보조를 맞추어, GPS를 기반으로 하는 항공기 착륙 시스템을 개발하고, 헬리콥터를 이용한 비행실험을 수행하고 있다, 그 동안 누적된 실시간 DGPS 시스템 개발기술들을 바탕으로 항공기 착륙 시스템을 확장, 보강하여 최근의 비행실험을 실시하였다. 본 논문에서는 새롭게 구성된 항공기 착륙 시스템을 소개하고 이를 이용한 비행 실험 결과를 분석하였다. 기존의, 기본적인 실시간 DGPS 시스템에서 추가, 발전된 부분은 세 가지로 분류할 수 있다. 첫번째는, 단일 GPS 안테나를 이용하여 항공기의 자세를 추정하는 부분이고, 두 번째는, 통합적인 cockpit display이다. 이 display는 가상현실을 이용하여 조종사에게 기존의 ILS정보와 그 이외의 다양한 정보들을 보여준다. 마지막으로, 공항의 기상상태에 관계없이 조종사가 공항에 접근할 수 있도록, 전자지도를 삽입하여 안전한 착륙을 시도할 수 있도록 시스템을 구성하였다. 이렇게 새롭게 구성된 시스템을 이용하여 김해 국제 공항에서 비행실험을 수행하였다. 분석된 결과를 바탕으로, 이 시스템이 정확도 측면에서, CAT-Ⅰ을 충분히 만족시킴을 확인하였으며, 신뢰도 높은 자세결정이 이뤄지고 있음을 확인하였다. In recent, there has been remarkable progress in the field of GPS applications. In a few years, an appreciable number of aircraft will adopt GPS as a landing guidance system because GPS is more economic, more reliable and more accurate than any other aviation systems. In this respect, we have performed several helicopter landing flight tests based on the real-time DGPS system made in SNUGL (Seoul National University GPS Laboratory). From the experimental results, we found several problems which should be fixed to adopt DGPS as a aircraft landing guidance system. In this paper, we will introduce the problems found in tests and also suggest modifications to solve the problems. Our modifications can be classified into three parts. The first is about the attitude determination with single GPS antenna. The second deals with the cockpit display module. The display was devised to integrate the Instrument Landing System (ILS) with tunnel-in-the-sky using virtual reality. With the display, pilot can achieve more safe landings. The last part is the digital map. We inserted digital map into our system and put direction indicator on the map using position information from GPS. It is very useful for pilot to find airports even in bad weather. Using the newly designed DGPS landing system, we conducted flight test at Kimhae International Airport, Pusan, Korea. It was successful! Our system can also satisfy Category-Ⅰ criterion for aircraft landing approach and determine attitude angle with a high level of reliability. It is supported by video materials.

Automatic Control of Miniature Vehicle Using Indoor Navigation System

Yun, Doo-Hee,Jun, Hae-Young,Kim, Do-Yoon,Kee, Chang-Don 서울대학교 항공우주신기술연구소 2001 항공우주신기술연구소 연구보고 Vol.2 No.1

Nowadays, the field of GPS navigation is being extended indoors. Pseudolite is thought to play a key role in this area. Indoor navigation system is a typical example of pseudolite application. After rigorous efforts, we have implemented the indoor navigation system successfully using CDGPS. Error analysis shows that the RMS value of horizontal kinematic positioning error is below 1cm. In this system, a miniature truck is equipped with all the devices for real-time operation, Our final research goal is automatic control of miniature vehicle using indoor navigation system. To achieve this, we have mounted 2 GPS antennas on the vehicle to obtain yaw angle. From experimental results, we can conclude that the indoor navigation system is a sufficient position and 2D attitude sensor for vehicle control in indoor environment such as factory, hanger, indoor amusement park, and etc.

Flow Characteristics of Liquid Ramjet Engines using Two Color PIV

Ahn, Kyubok,Yoon, Youngbin 서울대학교 항공우주신기술연구소 2001 항공우주신기술연구소 연구보고 Vol.2 No.2

A two color PIV technique has been developed for visualization of complex and high speed flow in a ramjet combustor. Two color PIV has the advantages that velocity distributions in high speed flowfields can be measured simply by varying the time interval between two different laser beams and a directional ambiguity problem can be solved by color separation, and then a signal-to-noise ratio can be increased through nearly perfect cross-correlation. As a basic research of the ramjet engine, a 2-D shaped combustor with two symmetric air intakes has been manufactured and an experimental study has been conducted using a two color PIV technique. The flow characteristics such as recirculation zones, intake air mixing and turbulent kinetic energy have been investigated varying inlet angles and dome heights. It was found that the primary recirculation zone is affected mainly by the dome height, whereas the secondary recirculation zone is influenced by the air inlet angle.

매개변수최적화를 이용한 실시간 유도탄 궤적최적화 연구

김유단,이태영,안재명 서울대학교 항공우주신기술연구소 2000 항공우주신기술연구소 연구보고 Vol.1 No.1

Missile trajectory optimization is performed to obtain the optimal intercept trajectories against a descending target. The missile is assumed to be a point mass moving in three dimensional space, and thrust, gravity and aerodynamic forces are assumed to dominate the forces acting on it. Burnout velocity is considered as the performance index, inequality constraints on the control variables are considered, and inequality constraints on the dynamic pressure multiplied by the angle of attack is also considered to guarantee structural safety. The direct method is used to solve this problem, and only the control variables are parameterized. When the pre-computed optimal input is implemented, the missile may deviate from the pre-computed optimal trajectory due to external disturbances as well as internal uncertainties. To compensate for these effects, a real time trajectory optimization algorithm is proposed. ※ This paper has been presented at JSASS 13th International Sessions in 37th Aircraft Symposium which has held at Tokyo on October 13-15, 1999.

REALIZATION OF INTERNET PARALLEL SUPERCOMPUTING FOR LARGE-SCALE STRUCTRAL ANALYSIS

Kim, Seung Jo,Lee, Chang Sung,Ha, Byung Un,Choi, Ji Duck,Cho, Jin Yeon,Kim, Jeong Ho 서울대학교 항공우주신기술연구소 2001 항공우주신기술연구소 연구보고 Vol.2 No.2

In this work, Internet Supercomputing methodology is introduced and the concept is materialized for large-scale finite element analysis. The primary resources of Internet Supercomputing are numerous idling PCs connected by Internet with no regards to their locations. Under the above concept, virtual supercomputing system InterSup I is constructed and tested. To establish the InterSup I system, 64 PC nodes, which are located in several places and connected by Internet, are conscripted, and the finite element code, IPSAP(Internet Parallel Structural Analysis Program) based on parallel multifrontal solver is developed for solving structural analysis problems. And mesh-partitioner based on graph-partitioning algorithms with WVEM(Weight Vertex and Edge Method) proposed in this work also developed. By the establish InterSup I system, analysis of finite element structural model having around 10 million DOFs are solved and the elapse time is 28,194 sec. From these results, it is confirmed that the proposed Internet Supercomputing methodology has a great promise and potential as a next-generation.

STRESS RECOVERY IN LAMINATED COMPOSITE AND SANDWICH PANELS UNDERGOING FINITE ROTATION

Park, Byung Chul,Park, Jin Woo,Kim, Yong Hyup 서울대학교 항공우주신기술연구소 2001 항공우주신기술연구소 연구보고 Vol.2 No.2

Laminated composite and sandwich panels are susceptible to mechanical damages in the transverse direction due to their relatively low strength in the transverse direction. For such damages to occur, laminated composite and sandwich panels usually experience geometrically nonlinear deformations. Therefore, analysis taking into account large deformations is required for predicting mechanical damages such as delamination. In the present study, a nonlinear predictor-corrector procedure is adopted for the accurate recovery of stress in laminated composite and sandwich panels undergoing geometrically nonlinear deformations. It is a post-processing procedure based on the three-dimensional equilibrium equations, combined with the eighteen-node assumed strain solid finite element model based on the Hellinger-Reissner principle tailored for large rotation analysis of laminated composite and sandwich panels. The effectiveness of the proposed approach is demonstrated by means of numerical examples of laminated composite and sandwich panels subjected to mechanical loading.

Grid-Optimized Dispersion-Relation-Preserving Schemes On General Geometries for Computational Aeroacoustics

Cheong, Cheol Ung,Lee, Soo Gab 서울대학교 항공우주신기술연구소 2001 항공우주신기술연구소 연구보고 Vol.2 No.2

In this paper, we investigate dispersion-relation-preserving property of finite difference scheme on general geometries for computational aeroacoustics, where non-dispersive and non-dissipative properties are of critical importance. The analysis pertains to the application of the optimization-algorithm of the dispersion-relation-preserving(DRP) scheme in wave number space to the general geometries - non-uniform Cartesian and curvilinear grids. In many computational aeroacoustics applications, the DRP schemes have often been favored for their accuracy and efficiency. The DRP scheme, however, is implemented only on uniform Cartesian grids. Practical problems in aeroacoustics, however, are seldom confined to the uniform Cartesian grids with the associated computing grids often being non-uniform Cartesian or curvilinear. Grid-optimized dispersion-relation-preserving (GODRP) finite difference schemes are proposed, based on optimization that make finite differential equations possess locally the same dispersion relation as the original partial differential equations on the grid points in the non-uniform Cartesian or curvilinear mesh. This local dispersion-relation-preserving property guarantees global accuracy of numerical schemes in the wave number space over full domain. The basic idea behind mathematical formulations of GODRP schemes is that the optimization in the wave number space is carried out not on the computation domain but on the physical domain. Because of the different properties between the Cartesian and curvilinear grids - whether the coupling of the coordinate variables between the physical and computation domain exists or not, different mathematical formulations are developed for each grid type. To investigate the effectiveness of GODRP schemes, a sequence of benchmark problems are executed. Through many numerical test problems, it is shown that the use of GODRP scheme can broaden the application area of the conventional DRP scheme to aeroacoustic phenomena, enhancing both the speed and accuracy of the computation using non-uniform Cartesian or curvilinear grids.

Efficient prediction methods for the micro-pressure wave form a high-speed train entering a tunnel using the Kirchhoff formunlation

Yoon, Tae Seok,Lee, Soo Gab 서울대학교 항공우주신기술연구소 2001 항공우주신기술연구소 연구보고 Vol.2 No.2

The compression wave generated by a high-speed train emerging from the exit portal of a tunnel gives rise to an impulsive noise called a micro-pressure wave. In this study, new methods for the prediction of sonic-boom noise are proposed. The first method combines acoustic monopole analysis and the method of characteristics with the Kirchhoff method. The compression wave from a train entering a tunnel is calculated by an approximate compact Green's function, and the resultant noise at the tunnel exit is predicted by a linear Kirchhoff formulation. The second method couples the Kirchhoff formulation with the Euler equation, which is solved numerically for the generation and propagation of the compression wave. Numerical prediction of the compression wave, the propagation in the tunnel, and the micro-pressure wave obtained by the present methods are compared with measured data. The numerical results exhibit reasonable agreement with the experimental data. The proposed methods in this study are shown to be very useful design tools for the nose shape of trains and the geometry of tunnels, and they can be utilized to minimize the pressure fluctuation in the tunnel and the corresponding booming noise.

Large Deflection of Laminated Composite Plates with Viscoelastic Properties

Kim, Tae-Woo,Kim, Ji-Hwan 서울대학교 항공우주신기술연구소 2000 항공우주신기술연구소 연구보고 Vol.1 No.2

Dynamic behavior of laminated composite plates undergoing moderately large deflection is investigated taking into account the viscoelastic behavior of material properties. Based on von Karman's non-linear deformation theory and Boltzmann's superposition principle, non-linear and hereditary type governing equations are derived. Finite element analysis and the method of multiple scales is applied to examine the effect of large amplitude on the dissipative nature of viscoelastic laminated plates. It is shown that geometric nonlinearity does not have so much effect on the dissipative behavior as on frequency and limit of the method used in this work is also discussed.

Dynamic Stall Control Using Aerodynamic Sensitivity Analysis

Ahn, Tai-Sul,Kim, Hyoung-Jin,Kim, Chong-Am,Rho, Oh-Hyun 서울대학교 항공우주신기술연구소 2000 항공우주신기술연구소 연구보고 Vol.1 No.2

This paper presents methods for dynamic stall control utilizing an optimal approach. Unsteady aerodynamic sensitivity code is developed using a direct difference method from discrete two-dimensional unsteady compressible Navier-Stokes code including two-equation turbulence model. Dynamic stall control is conducted by minimizing objective function defined at an instant instead of integrating a response for a period of time. Unsteady sensitivity derivative of the objective function is calculated by the sensitivity code, and optimization is conducted using a linear line search method at every physical time level. Examples of dynamic stall control utilizing airfoils nose radius or maximum thickness variation show very satisfactory results.