水上无人机成为无人机研究的新热点，其船体构型对离水特性影响巨大，构型参数设计合理可以减小滑跑距离和需用功率，反之会造成离水困难，甚至可能出现增加发动机功率水上飞机也无法离水的情况。这是由于其特殊的起降环境使得水上无人机起飞过程受力情况较常规飞行器更加复杂，常规飞行器起飞性能计算方法对于水上无人机不再适用，所以对水上飞机起飞离水特性的求解十分重要。CFD的发展使得利用数值计算方法代替常规的试验手段成为了可能，但直接利用CFD软件仿真求解水上无人机/飞机的离水过程难度大，耗时长，可行性低。可根据CFD计算中库朗数条件对气动力和水动力求解要求的不同，采用解耦方法分别求解不同条件下水上无人机完整构型的气动力和船体构型的水动力；同时水上无人机在起飞滑跑过程中，垂向受力小、加速度小，可将垂向受力看做近平衡状态，这成为分段插值求解方法的基础。将离水起飞过程离散化，利用分段插值方法求解得到其起飞离水特性，计算结果可以很好体现水上无人机水面滑跑的特性，与试验结果吻合良好。
The sea-UAV has become a hot spot of UAV research recently. Sea-UAV's hull is a key factor for the takeoff procedure. The well-designed hull can reduce engine power and takeoff distance; otherwise, the UAV would hardly take off, and engine power would even increase. Because the sea-UAV has a more complex force condition due to the particular takeoff environment, the takeoff performance analysis method applied to conventional aircraft is no longer available for the sea-UAV. Therefore, it is important to analyze the takeoff performance of the sea-UAV. The development of CFD makes it possible to use numerical calculation method to replace the experimental method, but it is not realizable to predict the multiphase performance of the sea-UAV by using CFD directly for it is time consuming and has enormous amount of calculation. In this paper, a decoupled calculation method is developed to predict the aerodynamic and hydrodynamic forces separated based on the different demands of Courant number. Meanwhile, the force in the vertical direction is assumed to be near balanced due to quite small resultant force and acceleration in this direction during takeoff. Based on this assumption, the discrete takeoff procedure is calculated by the piecewise interpolation method. The results can explain sea-UAV's takeoff characteristics, and match the experimental data well.
[1] JASON W, GILBERT L. Preliminary design optimization of an amphibious aircraft[C]//Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2012:3613-3668.[2] JOHNSON E R. American flying boats and amphibious aircraft:An illustrated history[M]. Jefferson, North Carolina:McFarland & Company Inc. Publishers, 2009:213-228.[3] WILLIAM N. Seaplane design[M]. London:Mcgraw-Hill Book Company Inc., 1934:75-111.[4] CARTER A W. Research on high length-beam ratio hulls[J]. Journal of the Aeronautical Sciences, 1949, 17(3):167-183.[5] HERRMANN H. Seaplane floats and hulls[R]. Washington, D.C.:NACA, 1927.[6] HUGLI W C, AXT W C. Hydrodynamic investigation of a series of hull models suitable for small flying boats and amphibians:NACA-TN-2503[R]. Washington, D.C.:NACA, 1951.[7] PAOLA C P, DANIELE D, FRANCO M. Preliminary design of an amphibious aircraft by the multidisciplinary design optimization approach[C]//48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference. Reston, VA:AIAA, 2007:1075-1105.[8] FREDIANI A, CIPOLLA V, OLIVIERO F. Design of a prototype of light amphibious prandtlplane[C]//56th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference. Reston, VA:AIAA, 2015:176-187.[9] MAYANK V B, RAJKUMAR S, SCOTT E. Conceptual design and sizing of an amphibian transport aircraft[C]//2013 Aviation Technology, Integration, and Operations Conference, 2013:2177-2185.[10] 褚林塘. 水上飞机水动力设计[M]. 北京:航空工业出版社, 2014:179-222. CHU L T. Hydrodynamic design of seaplane[M]. Beijing:Aviation Industry Press, 2014:179-222(in Chinese).[11] YANG X, WANG T, LIANG J, et al. Survey on the novel hybrid aquatic-aerial amphibious aircraft:Aquatic unmanned aerial vehicle (Aqua UAV)[J]. Progress in Aerospace Sciences, 2015, 74:131-151.[12] HESS J L, SMITH A M O. Calculation of potential flow about arbitrary bodies[J]. Progress in Aeronautics Sciences, 1967, 8(8):138-149.[13] MELTON J E, BERGER M J, AFTOSMIS M J. 3D application of a cartesian grid euler method[C]//33rd Aerospace Sciences Meeting and Exhibit. Reston, VA:AIAA,1995.[14] CLARENCE O E B, KIDAMBI S, DANIEL G H, et al. Unstructured nonlinear free surface flow solutions:Validation and verification[C]//32nd Fluid Dynamic Conference and Exhibit. Reston, VA:AIAA, 2002.[15] BEDDHU M, JIANG M Y, TAYLOR L K, et al. Computation of steady and unsteady flows with a free surface around the wigley hull[J]. Applied Mathematics and Computation, 1998, 89(1-3):67-84[16] YANG M Q, MA D L. Asymmetric ground effects of a tailless unmanned aerial vehicle model[J]. Proceedings of the Institution of Mechanical Engineers, Part G:Journal of Aerospace Engineering, 2014, 14(28):2652-2661.[17] 倪崇本. 基于CFD的船舶阻力性能综合研究[D]. 上海:上海交通大学, 2011:51-88. NI C B. A comprehensive investigation of ship resistance prediction based on CFD theory[D]. Shanghai:Shanghai Jiao Tong University, 2011:51-88(in Chinese).[18] 上官纯飞. 某型水上飞机水动力性能数值验证研究[D].武汉:华中科技大学, 2012:23-50. SHANGGUAN C F. Numerical validation of hydrodynamic performance on a seaplane[D]. Wuhan:Huazhong University of Science and Technology, 2012:23-50(in Chinese).[19] 邱良骏. 两栖飞机综合气动性能优化设计[D]. 上海:上海交通大学, 2013:27-50. QIU L J. Integrated aerodynamic and hydrodynamic optimization of amphibious aircraft[D]. Shanghai:Shanghai Jiao Tong University, 2013:27-50(in Chinese).[20] 卢晓平. 舰船原理[M]. 北京:国防工业出版社, 2009:103-130. LU X P. Theory of ships[M]. Beijing:Defense Industry Press, 2009:103-130(in Chinese).[21] ANDERSON J D. Computational fluid dynamics[M]. New York:Mcgraw-Hill Book Company Inc., 1995:78-90.[22] PARK I R, KIM K S, KIM J A. Volume of fluid method for incompressible free surface flows[J]. International Journal for Numerical Method in Fluids, 2009, 61(12):1331-1362.[23] BEDDHU M, JIANG M Y, WHITFIELD D L, et al. CFD validation of the free surface flow around DTMB model 5415 using Reynolds averaged Navier-Stokes equations[C]//Proceedings of the Third Osaka Colloquiumon Advanced CFD Applications to Ship Flow and Hull Form Design,1998.
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