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1.
The blade frequency noise of non-cavitation propeller in a uniform flow is analyzed in time domain. The unsteady loading (dipole source) on the blade surface is calculated by a potential-based surface panel method. Then the time- dependent pressure data is used as the input for Ffowcs Williams-Hawkings formulation to predict the acoustics pressure. The integration of noise source is performed over the true blade surface rather than the nothickness blade surface, and the effect of hub can be considered. The noise characteristics of the non-cavitation propeller and the numerical discretization forms are discussed. 相似文献
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船舶螺旋桨尾流场的数值分析 总被引：16，自引：1，他引：16
利用基于速度势的低阶面元法计算船舶螺旋桨的尾流场。采用计算较为简捷的关于扰动速度势的基本积分微分方程，并采用双曲面形状的面凶以消除面元间的缝隙。Newton-Raphson迭代过程被用来在桨叶随边满足压力Kutta条件，使桨叶面上表面的压力在随边有良好的一致性。在计算面元的影响系数时，应用了Morino导出的解析计算公式，加快了数值计算的速度。从解面元法的基本积分方程得到的偶极强度和源汇强度，直接求得尾流场的速度分布。 相似文献
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对于现代舰船而言噪声是其关键性能之一,目前水下航行体的流激噪声预测方法已经较为成熟,但是水面舰船的水动力噪声研究起步较晚,还没有形成系统的预报方法和控制手段。使用开源CFD工具包OpenFOAM求解器,流场通过大涡模拟方法求解,自由液面则依靠VOF方法捕捉,通过Curle方程预测远场噪声,基于镜像法考虑自由面的反射作用,数值模拟近自由面圆柱周围的声场分布。开展了Re=3 900下距离自由液面不同高度的圆柱辐射噪声求解,主要结合流场分析自由面对声场的扰动作用和不同深度对水下几何体流噪声的影响。初步考虑了自由液面波形对辐射噪声的反射作用,为后续预测水面舰船的水动力噪声特性提供依据,自由面对辐射噪声的阻抗等作用还需进一步研究。 相似文献
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A higher order panel method based on B-spline representation for both the geometry and the solution is developed for the analysis of steady flow around marine propellers. The self-influence functions due to the normal dipole and the source are desingularized through the quadratic transformation, and then shown to be evaluated using conventional numerical quadrature. By selecting a proper order for numerical quadrature, the accuracy of the present method can be increased to the machine limit. The far- and near-field influences are shown to be evaluated based on the same far-field approximation, but the near-field solution requires subdividing the panels into smaller subpanels continuously, which can be effectively implemented due to the B-spline representation of the geometry. A null pressure jump Kutta condition at the trailing edge is found to be effective in stabilizing the solution process and in predicting the correct solution. Numerical experiments indicate that the present method is robust and predicts the pressure distribution on the blade surface, including very close to the tip and trailing edge regions, with far fewer panels than existing low-order panel methods. 相似文献
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Traditionally, propeller design has been focused on all activities necessary to obtain a propeller featuring a high efficiency, avoiding erosive cavitation for given operating conditions and having adequate structural strength. In recent years, more and more challenging requirements have been imposed, such as the reduction of radiated noise and pressures pulses, requiring more precise analyses and methods in the optimization of the propeller performance. On the other hand, the evaluation of the propeller strength still relies on simplified methods, which basically consider the blade as a cantilever beam subjected to characteristic static forces. Since the loads acting on a blade are variable in the blade revolution and in different operating conditions throughout the ship life, a procedure to account for the influence of fatigue phenomena is proposed. The fatigue assessment could reduce the safety factor in the propeller scantling rules and allow improving the quality of propeller design (e.g. obtaining higher efficiency, margin on cavitation phenomena, less noise). 相似文献
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The field of biomimetics seeks to distill biological principles from nature and implement them in engineering systems in an effort to improve various performance metrics. In this paper, a biology-based approach is used to address the problem of radiated propulsor noise in underwater vehicles using active control. This approach is one of "tail articulation" of a stator blade, which is carried out using a suitable strategy that effectively alters the flow field impinging on a rotor downstream and in turn changes the radiated noise characteristics of the rotor blades. A reduced-order two-dimensional noise model is developed by characterizing the impact of the articulation as a point circulation input, which is then used to develop an active control strategy. An experimental investigation of such a control strategy is also carried out in this paper using a simple benchtop open-channel water tunnel at Re=4000 and stepper motor controlled articulation. Tail articulations using sinusoidal and transient motion were able to reduce the wake deficit behind the stator by as much as 40-60%. The implications of the proposed method for reducing blade tonal noise in autonomous underwater vehicles are briefly discussed at the end of the paper. 相似文献
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次重力波（Infragravity Wave，IGW）是一种频率较低（0.05~0.005 Hz），波长较长（约10 km）的表面重力波。由IGW引起的海表面高度变化会被宽刈幅干涉高度计SWOT （Surface Water and Ocean Topography，SWOT）卫星观测到，因此在使用SWOT观测的海表面高度来反演中尺度、次中尺度大洋环流时，IGW是一种重要的误差来源。根据数值模型模拟的全球IGW时空分布特征，本文以IGW最为活跃的东北太平洋和欧洲西北陆架附近大西洋为研究海域，估算了上述海域由IGW所引起的海表面高度变化，并将计算结果与SWOT Simulator模拟的轨道噪声（±5 cm）比较，首次定量地估算了IGW在SWOT观测海表面高度时的干扰程度。研究表明，IGW所引起的厘米量级的海表面高度变化在SWOT卫星观测海表面流场时是一种重要的，不可忽略的误差来源。在大西洋欧洲西北陆架海域，冬季IGW对海表面高度的贡献可达到SWOT卫星噪声要求水平的25%；然而，对于大陆架狭窄的美国西岸太平洋而言，由岸线产生的IGW将迅速传入深海海域，在广阔的范围内产生显著的"噪声"影响，在SWOT反演海表面流场时由IGW引起的误差将达到SWOT卫星噪声要求水平的15%。 相似文献
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近海海上风电场水下噪声传播模型适用性研究 总被引：1，自引：0，他引：1
通过现场采集近海海上风电场工程区运营期风机水下噪声和背景噪声数据,计算了噪声信号的倍频带声压级,功率谱级和峰值声压级,确定了海上风电场水下噪声总声源级为148.3 d B,以此开展近海海上风电工程风机水下噪声频域特性、功率密度谱特性等研究。在此基础上使用Kraken简正波模型和Bellhop射线模型对风电场运营期风机水下噪声在水平与垂直方向上的传播进行模拟,模拟了噪声在不同频带内的衰减程度,结果显示模型模拟结果在不同频率下的衰减趋势有着很大差异,产生了明显的多途干涉现象,通过实测数据对建立的噪声传播模型进行验证,发现Kraken简正波模型在500 Hz以下,Bellhop射线模型在500 Hz以上适合模拟实际水下噪声传播情形,同时海区本身背景噪声的存在会对预测的准确性产生影响。这些结论可用于进一步对近海海上风电场水下噪声传播的研究。 相似文献
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由于海面噪声源都可以抽象成偶极子辐射源,因此,研究海水表面偶极子辐射模型的噪声場的时空相关函数是有实际意义的。 设偶极子辐射源均勻而独立地分布在海水表面上,其辐射谱为S,则具有时延为的两点 相似文献
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This paper is the continuation of the work described in [14], dedicated to the presentation of the results of propeller performance in behind-hull during straight ahead motion obtained by a novel experimental set-up for the measurements of single blade loads. In the present case, the study shows and discusses the single blade and propeller loads developed during steady turning conditions, that were simulated by means of free running, self propelled maneuvering tests for a twin screw configuration. Maneuvering conditions are critical for the ship propulsion system, because the performance of the propeller and the side effects related to its functioning (propeller–hull induced pressure and vibrations, noise) are completely different with respect to the design condition in straight ahead motion. Thrust and torque and generation of in-plane loads (force and moments), developed by the blade during the period, evolve differently for the two propellers, due to different propeller–wake interactions. The understanding and the accurate quantification of propeller loads, in these realistic operative scenarios, are pivotal to design low emission and comfortable ships, fulfilling the requirements of safety and continuity of operations at sea. The analysis is carried out revisiting the investigation in [14] for three different speeds (FN = 0.26, 0.34 and 0.40) and a large set of rudder angles that span moderate and tight maneuvers. 相似文献
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海上风电场建设期风机打桩会产生高强度的水下噪声,研究水下冲击打桩噪声的监测方法、特性分析及对海洋生物的影响是非常重要的。采用自容式水下声音记录仪,多点同步测量了福建省兴化湾海上风电场二期工程建设期单次完整的水下冲击打桩噪声,从时频域特性进行了分析,并利用最小二乘法拟合得到了打桩声源级和声暴露级。结果表明：水下冲击打桩噪声是典型的低频、高强度的脉冲信号,单个脉冲持续时间约90~100 ms,峰值声源级约209.4±2 dB,声暴露级约197.7±2 dB;主要能量分布在50 Hz~1 kHz频段,750 m测量点的该频段声压级相比海洋环境背景噪声,提高了约40~50 dB。水下冲击打桩噪声频域能量分布与大黄鱼的听觉敏感频段相重叠,对大黄鱼影响程度和范围较大,实际工程应用中宜采用声暴露级作为评价指标。 相似文献
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Recovery of surface-wave time series from pressure gage data is a time-consuming process and is not customarily carried out. Such information is, however, useful particularly in real-time for warning of freak waves or waves of unusual characteristics. Two simple numerical filters are developed here to serve such purpose. The first method is a linear filter with a built-in window to suppress high-frequency noise. The second method recovers the surface wave by computing the local surface curvature. These filters are very simple and can be programmed into a microprocessor to be integrated into field instrument packages.Both filters have been tested satisfactorily against conventional linear filters using simulated wave data and wave data collected in intermediate water depth. Neither filter requires pre-filtering of noise from raw data, which is commonly required to recover surface-wave information from sub-surface pressure data. 相似文献
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Savonius桨叶是一种典型的垂直轴阻力型桨叶,在风力发电中广泛应用。这种桨叶具有在多风向作用下单向转动的特性。利用该特性,将其应用于捕获水质点运动方向发生周期性或非周期性改变的波浪能的相关研究。采用Fluent数值仿真软件并基于UDF二次开发技术建立桨叶三维数值模型,分析叶片重叠率、相对入水深度和开口率等参数对桨叶动转矩和功率等水动力特性的影响,搭建实验平台,开展物理模型对照试验。研究结果表明:叶片重叠率有助于减小S型桨叶负转矩;当桨叶在水面上高度与波幅相等时,其功率系数达到最大;在叶片上增加弹片阀开口,可以增大桨叶动转矩系数,当开口面积达到一半时,动转矩系数比未开口桨叶提高28.3%。 相似文献
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Sound from an airborne source travels to a receiver beneath the sea surface via a geometric path that is most simply described using ray theory, where the atmosphere and the sea are assumed to be isospeed sound propagation media separated by a planar surface (the air-sea interface). This theoretical approach leads to the development of a time-frequency model for the signal received by a single underwater acoustic sensor and a time-delay model for the signals received by a pair of spatially separated underwater acoustic sensors. The validity of these models is verified using spatially averaged experimental data recorded from a linear array of hydrophones during various transits of a turboprop aircraft. The same approach is used to solve the inverse time-frequency problem, that is, estimation of the aircraft's speed, altitude, and propeller blade rate given the observed variation with time of the instantaneous frequency of the received signal. Similarly, the inverse time-delay problem is considered whereby the speed and altitude of the aircraft are estimated using the differential time-of-arrival information from each of two adjacent pairs of widely spaced hydrophones (with one hydrophone being common to each pair). It is found that the solutions to each of the inverse problems provide reliable estimates of the speed and altitude of the aircraft, with the inverse time-frequency method also providing an estimate that closely matches the actual propeller blade rate 相似文献
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导管推进器是一种普遍应用于无人遥控潜水器（ROV）等潜器中的特种推进器。在桨叶与导管之间的梢隙中存在非常复杂的流动，本研究基于大涡模拟（LES）对导管推进器的梢隙流动进行了数值模拟分析。通过对时间步长的收敛性研究，建立两套基于不同网格类型的计算模型。将计算结果与试验进行对比，比较两种不同类型网格模拟结果的差异发现，切割体网格能够更好地捕捉到泄涡的细节，并结合梢隙流场的原理分析泄涡发展的过程，梢隙涡的驱动力是吸力面与压力面之间的压差。此外，随着进速系数增大，梢隙周向的涡管轴向分布范围减小，主泄涡发生位置延后，泄出涡的长度和数量都有所减少。 相似文献
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Marine propellers usually operate in a spatially nonuniform wake and then the propeller exciting forces are produced. These exciting forces will cause serious hull vibration and noise radiation. So, there are many researches on the exciting forces of propellers. However, the effects of the shaft and blade elasticity are ignored in most studies. Therefore, firstly, considered the effects of the shaft and blade elasticity, a fluid–structure interaction dynamic model of the fluid-propeller-shaft system is established by coupled BEM and FEM. Then, based on this model, the characteristics of axial exciting force and theirs transmission mechanism to the hull via the shaft are studied. The research results show that first, there are two kinds of vibration modes for blade bending vibration: global mode and local mode. The elastic coupling effect between the blade and the shafting only affects the global mode, but hardly affects the local mode of the blade. Secondly, during the transmission of axial exciting force to the hull through the blades and shafting, only the global mode of the blades can amplify it, while the local mode cannot. These studies could provide a guideline for the optimal design of the propeller-shaft system to make the exciting force transmitted to the ship hull via the shafting be the smallest. 相似文献
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Ambient noise in the surf zone, in the frequency range 120 Hz to 5 kHz, was recorded using a broad-band hydrophone, located approximately 1 m above bottom and 1-2 m below the mean sea surface. The predominant source of this noise is breaking waves. Analysis of simultaneous land-based video observations of the sea surface in the region of the hydrophone, along with wave height data, reveals quantitative correlation between wave-breaking events and the hydrophone signal. In energetic surf, locally breaking waves appear as discrete events in the ambient noise spectra. Distant breaking events do not appear to be detected, as distinct events above the ambient background noise, by the hydrophone. The noise events associated with local breakers are characterized by an asymmetry in the time envelope: low frequencies (less than 500 Hz) are observed leading the breaking crest, followed by a broader range of frequencies peaking in intensity with the passage of the wave crest above the hydrophone, and then decreasing abruptly at all frequencies. Low frequencies are generally not observed trailing the breaking wave. The detection by the hydrophone of breaking waves in the immediate vicinity implies that ambient noise in heavy surf provides a means of studying breaking-wave statistics in the surf zone in situ: in particular, the frequency of occurrence of local breaking 相似文献