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1.
The main objective of this paper is to develop an efficient numerical method which can predict the underwater acoustic field
and pressure fluctuation on a ship hull due to unsteady propeller sheet cavitation by linear acoustic theory. In addition,
the noise scattered from the ship hull and reflected from the free surface are included. Concerning the computation of the
acoustic field induced by unsteady sheet cavitation and forces of a marine propeller, a method is derived without making any
approximation about the distance function between the noise source and field point. Thus, this method can be used to predict
acoustic pressure at both far and near fields, and this is very important for the scattering problem because the ship hull
is located very close to the propeller. For the computation of the scattering problem, a more efficient and robust method
is derived in time domain, which can treat multi-frequency waves scattered from underwater obstacles. The acoustic fields
of a container ship radiated by the propeller and scattered from the ship hull with free surface is investigated in this paper.
The pressure fluctuations of low blade rate on the ship hull induced by the propeller are also computed by the present method
and are found to be similar to the results obtained by a panel method satisfying the Laplace equation for the points near
the propeller due to the small retarding time. However, for the points on the ship hull away from the propeller, the differences
of the results between two methods will increase. 相似文献
2.
在梳理流噪声数值预报方法的基础上,采用流场大涡模拟(large eddy simulation,LES)和声学边界元(boundary element method,BEM)方法在频域内计算预报了船体流噪声谱曲线,求取了其等效声中心.LES计算时选用动力学Smagorinsky-Lilly(dynamic Smagorinsky-Lilly,DSM)亚格子应力模型,流噪声由船体壁面脉动压力和法向速度特性决定,声源节点和声节点变量传递采用一对一的守恒传递方式.结果表明:某型船在航速14 kn时,裸船体流噪声在20 Hz~2 kHz频段内总声源级为133dB;当计算有效频段扩展到20 kHz时,总声源级达143.3 dB.流噪声主要来源于兴波引起的涡量,且主要集中于100 Hz~10 kHz频段.球首尾流区和船体尾涡区对流噪声辐射量贡献明显,特别是球首尾流区,对全频段都有明显的贡献,为水面舰艇流噪声研究提供了一条新的途径. 相似文献
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《船舶与海洋工程学报》2020,(1)
Despite their high manufacturing cost and structural deficiencies especially in tip regions, highly skewed propellers are preferred in the marine industry, where underwater noise is a significant design criterion. However, hydrodynamic performances should also be considered before a decision to use these propellers is made. This study investigates the trade-off between hydrodynamic and hydroacoustic performances by comparing conventional and highly skewed Seiun Maru marine propellers for a noncavitating case.Many papers in the literature focus solely on hydroacoustic calculations for the open-water case. However, propulsive characteristics are significantly different when propeller-hull interactions take place. Changes in propulsion performance also reflect on the hydroacoustic performances of the propeller. In this study, propeller-hull interactions were considered to calculate the noise spectra.Rather than solving the full case, which is computationally demanding, an indirect approach was adopted; axial velocities from the nominal ship wake were introduced as the inlet condition of the numerical approach. A hybrid method based on the acoustic analogy was used in coupling computational fluid dynamics techniques with acoustic propagation methods, implementing the Ffowcs Williams-Hawkings(FW-H) equation. The hydrodynamic performances of both propellers were presented as a preliminary study.Propeller-hull interactions were included in calculations after observing good accordance between our results, experiments, and quasi-continuous method for the open-water case. With the use of the time-dependent flow field data of the propeller behind a nonuniform ship wake as an input, simulation results were used to solve the FW-H equation to extract acoustic pressure and sound pressure levels for several hydrophones located in the near field. Noise spectra results confirm that the highest values of the sound pressure levels are in the low-frequency range and the first harmonics calculated by the present method are in good accordance with the theoretical values. Results also show that a highly skewed propeller generates less noise even in noncavitating cases despite a small reduction in hydrodynamic efficiency. 相似文献
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Using a time domain acoustic analogy, we develop a method to predict the sound field and hull pressure fluctuation generated by unsteady sheet cavitation on marine propellers. Formulation 1A of Farassat is introduced to enhance theoretical understanding of this work, and it is applied to modeling the scattered sound field created by the fuselage boundary. To express the direct sound field resulting from sheet cavitation, a new solution is studied which considers the Doppler effect and also separately expresses the near and far fields. A small cube model is used to verify the method. Computed acoustic field pressures around the cube are compared with the boundary element method, and the numerical results show good agreement. Finally, the pressure fluctuation on a ship stern model is calculated. 相似文献
6.
传统的水面舰船声学设计评价方法在应用上存在着局限性,为进一步发展和完善,通过对总声级声学特性类比、声频范围和超声频段声学特性、实船检测声学特点和实船声隐身战术技术要求制订等进行广泛论述与类比探讨的基础上,指出了现有方法在总声级确定、声学特性预报和实船检测等方面的不足,提出了较为合理的水面舰船声学特性的类比及其评价方法,即以特定频段的线谱分析来评定其声学性能。 相似文献
7.
以某船舶的噪声振动控制为目的,探讨了船舶结构声学设计技术。针对某船舶机舱结构,在初步设计的基础上,运用FEM/BEM方法,对比了不同设计参数下的船舶振动响应和水下辐射噪声声压级。通过调整机舱段结构参数,避免船体结构共振的发生,确定了低噪声设计方案。模型试验表明,振动传递特性的计算值与试验值有很好的一致性,所建立的船舶振动噪声预报模型是可信的。 相似文献
8.
In this paper the Acoustic Analogy is used to predict the underwater noise from a complete scaled ship model in a steady course. The numerical investigation is performed by coupling an incompressible RANS code, equipped with a level-set approach to account for the fundamental time evolution of the free surface, to a FWH-based hydroacoustic solver, here suitably designed to manage the huge set of data coming from a full-unsteady hydrodynamic simulation. The results reveal the overall limited contribution from the propeller thickness and loading noise components and the fundamental one from the nonlinear quadrupole sources. The comparison between the hydrodynamic and hydroacoustic solutions point out the noticeable scattering effects due to the hull surface, the possible influence of sound refractions at the free surface and, above all, the leading role played by the turbulent fluctuating component of the velocity field. Finally, by computing the pressure time histories at a prescribed set of virtual hydrophones and turning them into the frequency domain, the ship noise footprint in dB is traced out, thus showing how the Acoustic Analogy can be effectively used to analyze the ship hydroacoustic behavior, both in terms of amplitude and directivity. 相似文献
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螺旋桨激振力作用下船体振动及水下辐射噪声研究 总被引:1,自引:0,他引:1
利用有限元法和边界元方法分析比较了螺旋桨激振力三个方向分力(轴向、横向、垂向)分别作用以及同时作用时引起的船体结构振动与水下辐射噪声。结果表明,船体结构在螺旋桨激振力作用下在轴频、叶频、一倍叶频、二倍叶频以及船体固有频率处振动响应出现线谱;横向螺旋桨激振力引起的船体水下辐射噪声最大,垂向力其次,最小是轴向力;三个方向激振力同时作用时船体最大辐射声功率出现在叶频处,主要由横向力引起,其次是轴频处,主要由轴向力引起。分析其原因主要是横向激振力在叶频时最大,而且与船体固有频率接近,产生共振,轴向力在轴频处次之。 相似文献
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The aim of this work is to analyze the hydroacoustic behavior of a marine propeller through the acoustic analogy and to test the versatility and effectiveness of this approach in dealing with the many (and relatively unexplored) issues concerning the underwater noise and its numerical prediction. In particular, a propeller in a noncavitating open water condition is examined here by coupling a Reynolds averaged Navier–Stokes hydrodynamic solver to a hydroacoustic code implementing different resolution forms of the Ffowcs Williams–Hawkings (FWH) equation. The numerical results suggest that unlike the analogous aeronautical problem, where the role played by the nonlinear quadrupole sources is known to be relevant just at high transonic or supersonic regime, the pressure field underwater seems to be significantly affected by the flow nonlinearities, while the contribution from the linear terms (the thickness and loading noise components) is dominant only in a spatially very limited region. Then, contrary to popular belief and regardless of the low blade rotational speed, a reliable hydroacoustic analysis of a marine propeller cannot put aside the contribution of the nonlinear noise sources represented by the turbulence and vorticity three-dimensional fields and requires the computation of the FWH quadrupole source terms. 相似文献
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在流声耦合领域中,水下航行体复杂流动与流激噪声研究具有重要的学术意义与实用价值。文章对FW-H声学类比方法、渗流FW-H声学类比方法、Kirchhoff方法与Powell涡声理论进行了物理内涵与数学公式的详细比较;然后利用大涡模拟结合四种声计算方法数值计算了三维NACA0015机翼、机翼/圆柱结合体、方腔产生的流激辐射噪声,并与国内外试验结果进行了对比,分析了四种声计算方法的计算精度与计算效率;最后,对围壳流激噪声进行了数值预报与试验验证,计算了围壳在不同水速下的流激噪声变化规律,并探讨了声学积分面对计算结果的影响。 相似文献
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提出一种以势流兴波阻力理论Rankine源方法为基础,结合SHIPFLOW软件为计算工具,利用CAD-CFD集成平台FRIENDSHIP-Framework软件进行变形优化,研究船舶的最小兴波阻力型线优化设计的方法,并考察了兴波优化得到的船型总阻力变化情况。在型线优化过程中,以兴波阻力系数为目标函数,排水量变化范围为约束条件,在Wigley船体前端增加一个利用Feature建模技术参数化生成的球艏并调整艏部型线使得船体表面光顺。选取球鼻艏形状的各项参数作为基本设计变量,利用DOE方法对船艏进行优化,获得了设计航速下兴波阻力较小的船型,验证了所提方法进行船艏型线优化的有效性。相应的考察变形及优化前后总阻力变化情况表明:在高傅汝德数情况下增加球艏所带来的粘性阻力的增加小于兴波阻力的减小量,总阻力得到了改善,优化后得到的球艏能在进一步减小兴波的同时减小总阻力。此外,还运用所提方法对3100TEU船型的船艏,利用Delta Shift方法进行变形,在设计航速下,将变形的参数作为设计变量,利用DOE方法进行优化设计。结果显示:在排水量限制范围内当球鼻艏向上向前伸展一定长度时可以降低兴波阻力。与此同时,由于优化前后船体湿表面积变化很小,粘性阻力的变化并不明显,兴波的减小则使得总阻力得到了改善。 相似文献
18.
Soonhung Han Yeon-Seung Lee Young Bok Choi 《Journal of Marine Science and Technology》2012,17(1):1-17
Hydrodynamic optimizations of ship hull forms have been carried out employing parametric curves generated by fairness-optimized B-Spline form parameter curves, labeled as F-Spline. Two functionalities of the parametric geometry models are used in the present study: a constrained transformation function to account for hull form variations and a geometric entity used in full parametric hull form design. The present F-Spline based optimization procedure is applied to two distinct hydrodynamic hull form optimizations: the global shape optimization of an ultra-large container ship and the forebody hull form for the hydrodynamic optimization of an LPG carrier. Improvements of ship performance achieved by the proposed F-Spline procedure are demonstrated through numerical experiments and through correlations with experimental data. The ultra-large containership was built and delivered to the ship owner. The present study validates the effectiveness of the proposed hydrodynamic optimization procedure, ushering in process automation and performance improvement in practical ship design practices. 相似文献
19.
舰船航行时在其下方附近产生水压场。这种水压场无法消除,也极难人工模拟。水压水雷就是根据航行舰船的水压场特性而引爆的。从舰船的安全防护角度考虑,可在船体底部加装某种附体,使舰船原有水压场发生改变,从而避免引爆水压水雷。对在船底加装翼板、回转体等附体所造成的舰船水压场畸变进行了试验研究和数值计算。在拖曳水池中进行了船模水压场测量,比较了加装附体前后舰船水压场的特性,据此分析了采用舰船水压场畸变方法防御水压水雷的可行性。比较了加装翼板和回转体的防水压水雷效果。分析了在实船下加装翼板防水压水雷的可能性。 相似文献
20.
With increases in ship size and speed, shipboard vibration becomes a significant concern in the design and construction of vessels. Excessive ship vibration is to be avoided for passenger comfort and crew habitability. In addition to the undesired effects on humans, excessive ship vibration may result in the fatigue failure of local structural members or malfunctioning of machinery and equipment. The propeller induces fluctuating pressure on the surface of the hull, which induces vibration in the hull structure. These pressure pulses acting on the ship hull surface above the propeller are the predominant factor for vibrations of ship structures are taken as excitation forces for forced vibration analysis. Ship structures are complex and may be analyzed after idealization of the structure. Several simplifying assumptions are made in the finite element idealization of the hull structure. In this study, a three-dimensional finite element model representing the entire ship hull, including the deckhouse and machinery propulsion system, has been developed using solid modeling software for local and global vibration analyses. Vibration analyses have been conducted under two conditions: free–free (dry) and in-water (wet). The wet analysis has been implemented using acoustic elements. The total damping associated with overall ship hull structure vibration has been considered as a combination of the several damping components. As a result of the global ship free vibration analysis, global natural frequencies and mode shapes have been determined. Moreover, the responses of local ship structures have been determined as a result of the propeller-induced forced vibration analysis. 相似文献