攻角对半穿甲战斗部侵彻航母双层靶板的效应研究

采用数值仿真方法,建立半穿甲战斗部对航母双层板侵彻效应的数值仿真计算模型,并计算战斗部以6种不同攻角侵彻目标的动态响应过程.结果表明,攻角对战斗部侵彻航母双层靶的能力有显著影响.随着初始攻角增加,战斗部的靶后余速下降,当初始攻角为20°和25°时,战斗部未能穿透航母的吊舱甲板.战斗部撞击吊舱甲板的攻角相对于初始攻角均有所增加,严重影响了战斗部对吊舱甲板的侵彻能力.战斗部对目标的侵彻破坏模式均属于延性扩孔和冲塞破坏模式.战斗部侵彻航母双层靶的过载较大且高过载持续时间长.当攻角大于10°时,战斗部在侵彻第1层靶板时,横向过载比较明显,导致战斗部结构出现不同程度的弯曲变形,这些因素给战斗部的结构完整性、装药稳定性和引信可靠性带来严峻挑战.该研究可用于指导半穿甲战斗部设计及其毁伤效应研究.     

地效翼艇纵向稳定性气动力系数研究

确定气动中心与压力中心是进行地效翼艇的整体布局以及稳定性设计的基础。通过将无地面效应的数值模拟结果与实验结果对比以验证其结果有效性后,再进行有地面效应情况下的数值模拟。数值结果显示出地面效应通过改变翼下表面的压力分布影响气动中心位置的规律。飞行速度,高度,攻角等,这些因素同时影响气动中心位置,所以气动中心位置的变化规律十分复杂。最后绘制了图表以显示变化规律,并为以后设计提供设计依据。     

攻角对半穿甲战斗部侵彻航母双层靶板的效应研究

采用数值仿真方法,建立半穿甲战斗部对航母双层板侵彻效应的数值仿真计算模型,并计算战斗部以6种不同攻角侵彻目标的动态响应过程。结果表明,攻角对战斗部侵彻航母双层靶的能力有显著影响。随着初始攻角增加,战斗部的靶后余速下降,当初始攻角为20°和25°时,战斗部未能穿透航母的吊舱甲板。战斗部撞击吊舱甲板的攻角相对于初始攻角均有所增加,严重影响了战斗部对吊舱甲板的侵彻能力。战斗部对目标的侵彻破坏模式均属于延性扩孔和冲塞破坏模式。战斗部侵彻航母双层靶的过载较大且高过载持续时间长。当攻角大于10°时,战斗部在侵彻第1层靶板时,横向过载比较明显,导致战斗部结构出现不同程度的弯曲变形,这些因素给战斗部的结构完整性、装药稳定性和引信可靠性带来严峻挑战。该研究可用于指导半穿甲战斗部设计及其毁伤效应研究。     

三维船体横摇运动数值模拟及舭龙骨阻尼特性研究（英文）

为研究舭龙骨阻尼特性及尺寸航速等因素的影响,本文基于计算流体动力学方法分别对有、无舭龙骨三维船体的自由横摇衰减运动以及强迫横摇运动进行数值模拟研究,有无舭龙骨的三维船体的横摇阻尼之差即为舭龙骨阻尼。对F_r=0.138、初始横摇角10°带舭龙骨船体的自由横摇衰减数值模拟算例作了验证与确认分析,自由横摇衰减时历曲线与实验结果吻合较好,固有周期和横摇阻尼精度较高。进一步分析研究了不同几何尺寸、初始横摇角、航速以及频率等参数对舭龙骨阻尼的影响。自由横摇衰减模拟研究中舭龙骨阻尼随着舭龙骨宽度、初始横摇角度的增大而增大;当航速为0时,舭龙骨阻尼在总阻尼占比最大,航速对舭龙骨阻尼绝对值影响较小。强迫横摇模拟研究表明:当横摇角一定,舭龙骨阻尼随着频率的增大而非线性增大,在固有频率附近,粘性效应不可忽略。     

桨叶剖面空泡形态发展特性研究

  目的  水下翼型空泡数下降到某个临界值后,翼型前缘位置的压强会降低而发生空化。在模型试验研究中,模型尺度翼型难以满足实尺度翼型的雷诺数,使得空化起始对应的空化数发生变化。  方法  为此,以航速为24 kn的标准KCS船采用的NACA 0012型船舵作为参照,基于STAR-CCM+软件,运用SST k-ω湍流模型和Schnerr-Sauer (S-S)空化模型对翼型空泡特性进行数值模拟。针对不同缩尺比模型,通过改变不同攻角时的翼型环境压强来计算翼型表面流场和空泡分布,得到空化起始对应的空化数,分析尺度效应对临界空化数的影响机理。  结果  结果表明,随着模型尺度的缩小,相应攻角下的翼型临界空化数也有一定程度的减小,说明雷诺数的差异会加剧尺度效应。  结论  因此,为防止尺度效应对起始空泡数的影响,模型试验中不宜选用较小尺度的翼型。     

半潜航行器纵平面流体动力数值计算与试验研究

半潜航行器因航行深度介于水面航行器和潜器之间而得名。为预报半潜航行器纵平面流体动力性能,开展数值仿真与风洞试验。研究航行器不同攻角、不同舵角下受力情况,计算速度系数、舵角系数以及耦合系数,并与风洞试验数据进行对比。针对耦合工况中舵效降低的情况进行了流场分析。仿真和试验结果表明：CFD仿真结果与试验结果吻合较好,具有较高预报精度;增加航行器攻角会影响前、后舵板贴体端稍涡的形成,迫使稍涡向上偏移,在吸力面形成一个直径与舵板弦长相当的涡。研究结论可指导航行器运动控制和前后舵布局优化。     

粘性流场中船舶操纵水动力导数计算与验证

以软件Fluent作为仿真软件,应用其能够计算流体力学的特点,对操纵船舶的水动力进行预报。其方法为使用软件的动网格及后处理功能,计算出粘性流场中船舶在不同的状态以及在做不同运动时的水动力导数。首先根据船舶的运动状态计算出作用于船舶上的水动力力矩,然后对力矩进行曲线拟合,从而得到粘性流场中船舶操纵水动力导数。仿真计算结果表明,在不同运动状态下船舶的操纵水动力与次频率没有明显关联,所以该粘性流场中船舶操纵水动力导数计算方法完全可行。     

小攻角水下航行体定常空泡外形计算方法

水下航行体上的空泡在攻角、重力及航行体的外形影响下,空泡的迎水面外形与背水面外形并不对称,这种不对称空泡外形对空泡水动力或航行体弹道有极大影响。本文结合动量原理和空泡独立膨胀原理,在小攻角条件下建立了定常三维空泡外形的方法。     

小攻角水下航行体定常空泡外形计算方法

水下航行体上的空泡在攻角、重力及航行体的外形影响下,空泡的迎水面外形与背水面外形并不对称,这种不对称空泡外形对空泡水动力或航行体弹道有极大影响.本文结合动量原理和空泡独立膨胀原理,在小攻角条件下建立了定常三维空泡外形的方法.     

超空泡航行体操纵过程流体动力特性数值模拟研究

超空泡航行体操舵过程会引起空泡变形,导致航行体流体动力学特性发生变化。为了了解超空泡航行体操舵过程中航行体的动力学特性,文中采用基于欧拉两流体模型的CFD数值模拟方法及动网格技术对超空泡航行体空化器、尾舵操舵过程以及航行体攻角变化过程中的空泡形态及航行体瞬态流体动力特性变化规律进行了研究。研究结果表明空化器操舵过程中空化器升力随偏转角基本呈线性规律变化,对航行体尾部滑行力的影响相对于攻角变化对滑行力的影响为小量;尾舵操舵过程改变了空泡尾部流场,对于航行体尾部滑行力会产生重要影响。     

Interaction of two-dimensional impulsively started airfoils

Continuous vortieity panels were used to model general unsteady inviscid, incompressible, two-dimensional flows. The geometry of the airfoil was approximated by series of short straight segments having endpoints that lie on the actual surface. A piecewise linear, continuous distribution of vorticity over the airfoil surface was used to generate disturbance flow. The no-penetration condition was imposed at the midpoint of each segment and at discrete times. The wake was simulated by a system of point vortices, which moved at local fluid velocity. At each time step, a new wake panel with uniform vortieity distribution was attached to the trailing edge, and the condition of constant circulation around the airfoil and wake was imposed. A new expression for Kutta condition was developed to study the interference effect between two impulsively started NACA0012 airfoils. The tandem arrangement was found to he the most effective to enhance the lift of the rear airfoil. The interference effect between tidal turbine blades was shown clearly.     

地效翼气动力特性的数值预报

本文采用CFD技术,对存在地面效应时二维机翼在粘性流场中的空气动力特性进行了研究.结果表明:与模型试验数据相比,基于RANS方程的CFD方法能够准确预报机翼的气动升力和力矩.同时,除相对飞高外,翼剖面的厚度和拱度对地效翼的气动力特性也有重要影响.进而,作者对应用CFD分析或辅助地效翼气动力风洞试验进行了探讨.认为采用固定地板模拟地面效应与采用活动地板的模型风洞试验结果之间有很大差别,而风洞的壁面效应相比较而言可以忽略.     

Mathematical model for takeoff simulation of a wing in proximity to the ground

Aircraft flying close to the ground benefit from enhanced efficiency owing to decreased induced drag and increased lift. In this study, a mathematical model is developed to simulate the takeoff of a wing near the ground using an Iterative Boundary Element Method (IBEM) and the finite difference scheme. Two stand-alone sub-codes and a mother code, which enables communication between the sub-codes, are developed to solve for the self-excitation of the Wing-In-Ground (WIG) effect. The aerodynamic force exerted on the wing is calculated by the first sub-code using the IBEM, and the vertical displacement of the wing is calculated by the second sub-code using the finite difference scheme. The mother code commands the two sub-codes and can solve for the aerodynamics of the wing and operating height within seconds. The developed code system is used to solve for the force, velocity, and displacement of an NACA6409 wing at a 4° Angle of Attack (AoA) which has various numerical and experimental studies in the literature. The effects of thickness and AoA are then investigated and conclusions were drawn with respect to generated results. The proposed model provides a practical method for understanding the flight dynamics and it is specifically beneficial at the pre-design stages of a WIG effect craft.     

非均匀表面上移动的冲翼艇的横摇-垂荡-纵摇运动建模（英文）

Ground-effect vehicles flying close to water or ground often employ ram wings which generate aerodynamic lift primarily on their lower surfaces. The subject of this paper is the 3-DOF modeling of roll, heave, and pitch motions of such a wing in the presence of surface waves and other ground non-uniformities. The potential-flow extreme-ground-effect theory is applied for calculating unsteady pressure distribution under the wing which defines instantaneous lift force and moments. Dynamic simulations of a selected ram wing configuration are carried out in the presence of surface waves of various headings and wavelengths,as well as for transient flights over a ground obstacle. The largest amplitudes of the vehicle motions are observed in beam waves when the periods of the encounter are long. Nonlinear effects are more pronounced for pitch angles than for roll and heave. The present method can be adapted for modeling of air-supported lifting surfaces on fast marine vehicles.     

Numerical solutions for a two-dimensional airfoil undergoing unsteady motion

Continuous vorticity panels are used to model general unsteady inviscid, incompressible, and two-dimensional flows. The geometry of the airfoil is approximated by series of short straight segments having endpoints that lie on the actual surface. A piecewise linear, continuous distribution of vorticity over the airfoil surface is used to generate disturbance flow. The no-penetration condition is imposed at the midpoint of each segment and at discrete times. The wake is simulated by a system of point vortices, which move at local fluid velocity. At each time step, a new wake panel with uniform vorticity distribution is attached to the trailing edge, and the condition of constant circulation around the airfoil and wake is imposed. A new expression for Kutta condition is developed to study (i) the effect of thickness on the lift build-up of an impulsively started airfoil, (ii) the effects of reduced frequency and heave amplitude on the thrust production of flapping airfoils, and (iii) the vortex-airfoil interaction. This work presents some hydrodynamic results for tidalstream turbine.     

浮式风机气动-水动耦合特性数值模拟（英文）

The exploration for renewable and clean energies has become crucial due to environmental issues such as global warming and the energy crisis. In recent years,floating offshore wind turbines(FOWTs) have attracted a considerable amount of attention as a means to exploit steady and strong wind sources available in deep-sea areas. In this study, the coupled aero-hydrodynamic characteristics of a spar-type 5-MW wind turbine are analyzed. An unsteady actuator line model(UALM) coupled with a twophase computational fluid dynamics solver naoe-FOAM-SJTU is applied to solve three-dimensional Reynolds-averaged NavierStokes equations. Simulations with different complexities are performed. First, the wind turbine is parked. Second, the impact of the wind turbine is simplified into equivalent forces and moments. Third, fully coupled dynamic analysis with wind and wave excitation is conducted by utilizing the UALM. From the simulation, aerodynamic forces, including the unsteady aerodynamic power and thrust, can be obtained, and hydrodynamic responses such as the six-degrees-of-freedom motions of the floating platform and the mooring tensions are also available. The coupled responses of the FOWT for cases of different complexities are analyzed based on the simulation results. Findings indicate that the coupling effects between the aerodynamics of the wind turbine and the hydrodynamics of the floating platform are obvious. The aerodynamic loads have a significant effect on the dynamic responses of the floating platform, and the aerodynamic performance of the wind turbine has highly unsteady characteristics due to the motions of the floating platform. A spar-type FOWT consisting of NREL-5-MW baseline wind turbine and OC3-Hywind platform system is investigated. The aerodynamic forces can be obtained by the UALM. The 6 DoF motions and mooring tensions are predicted by the naoe-FOAM-SJTU. To research the coupling effects between the aerodynamics of the wind turbine and the hydrodynamics of the floating platform, simulations with different complexities are performed. Fully coupled aero-hydrodynamic characteristics of FOWTs, including aerodynamic loads, wake vortex, motion responses, and mooring tensions, are compared and analyzed.     

Hydrodynamics study of a BCF mode bioinspired robotic-fish underwater vehicle using Lighthill’s slender body model

This paper investigates the hydrodynamic characteristics of the rectilinear motion of a robotic fish underwater vehicle. This 2-joint, 3-link multibody vehicle model is biologically inspired by a body caudal fin carangiform fish propulsion mechanism. Navier–Stokes equations are used to compute the unsteady flow fields generated due to the interaction between the vehicle and the surrounding incompressible and Newtonian fluid (water) environment. The NACA 0014 airfoil aerodynamic profile has been designed to boost the swimming efficiency by reducing drag as the vehicle undergoes an undulatory/oscillatory motion. Using the Lighthill slender body model, a traveling wave mathematical function is defined to undulate the robotic fish posterior (caudal) region while the motion tracking is carried out by dynamic meshing technique. The results obtained show that though the net lift force approaches to zero, the net thrust or negative drag coefficient maintains a finite value dependent on kinematic parameters like tail beat frequency (TBF) and amplitude span (AS) at a given propulsive wavelength and the forward velocity of the vehicle. The results reveal the effects of TBF and AS on the coefficient of drag friction and the thrust force. Drag coefficients obtained from the simulations are compared and validated with the experimental results. The hydrodynamic results are found to be similar to the kinematic study results and suggest that TBF and AS play the most effective roles in the bioinspired propulsion technique. Relation of these parameters with propelling thrust force and forward velocity is also in conjunction over a given range of TBF and AS values.     

Monitoring blade loads for a floating wind turbine in wave basin model tests using Fiber Bragg Grating sensors: A feasibility study

The blade loading contains sufficient information about the unsteady aerodynamics of Floating Wind Turbines (FWTs), and it serves as the basis for advanced controller developments. Wave basin model test is among the most reliable and economical methods for FWT investigations. However, few FWTs were reported being able to monitor the blade loads during wave basin tests. The main obstacles include strict space/mass limitations in model manufacturing and problems associated with signal transmission between rotating blades and stationary signal processing unit. In this paper, the feasibility of detecting blade loads for model FWT in wave basin tests is investigated. An on-line monitoring system is developed based on Fiber Bragg Grating (FBG) sensors and a Fiber Optical Rotary Joint (FORJ). Extensive validation tests are conducted under different environmental and operational conditions. Results show that the proposed FBG-FORJ sensing system presents impressive feasibility and reliability. As the authors know, it is among the first attempts to monitor the blade loads in real-time for model FWTs in wave basin tests. The present study will serve to enrich the knowledge about unsteady aerodynamics of FWTs and lay the foundation for experimental studies on advanced FWT controllers.     

海洋悬空管道非线性振动稳定性分析

以海洋悬空管线为研究对象,根据海洋悬空管道的主要特征,将海洋悬空管道简化为两端简支梁力学模型．涡激升力简化为简谐荷载。在考虑管道非线性因素下,建立悬空管道的横向振动方程,并采用谐波平衡法对方程求解。可得出洋流涡激作用下海洋悬空管道横向振动失稳的双尖点突变模型,由此导出悬空管道失稳条件。根据失稳条件分析发现．海洋悬空管长度对稳定性影响起主导作用,并在假定其他条件不变的情况下,分析影响悬空管道稳定性的因素和悬空段临界长度之间的关系。分析结果表明：随着外流流速、管内流流速、管内压强的增加,悬空管道的临界长度减小：随着材料弹性模量、管外直径的增大．悬空段的临界长度增加：其他影响因素相比较而言可以忽略．     

水下航行体非定常垂直空泡长度的计算

带空泡航行体从水下朝水面运动时,空泡将受到重力梯度和空泡记忆效应的耦合影响而呈现出特殊的非定常特点。为了计算有限水深重力场中的空泡长度,文章在Paryshev空泡动力学数学模型(Delay Differential Equations,DDEs方程)基础上,增加了重力影响项;同时为了快速求解上述空泡DDEs方程,对DDEs的数值方法进行了改进,提出了一种效率更高的对延迟时间点进行局部拟合的方法。最后利用新方法求解了带重力影响的空泡DDEs方程,计算结果与试验结果吻合。