基于惯导及声学浮标辅助的水下航行器导航定位系统

针对纯惯导系统误差发散和无线电信号在水下衰减快从而无法精确定位的问题,设计了一种基于声学浮标辅助惯导的水下定位系统,该系统由惯导系统和声学定位系统组成,其中声学定位系统由若干个浮标构成水听器阵,浮标的经纬度坐标由GPS提供,浮标完成对接收到的声源信号的处理,利用互相关测时延差的方法来进行定位。由于水下噪声、混响等因素会造成接收到的多路声信号出现模糊互相关峰,因此对接收信号应进行频域加权处理。最后利用声学系统的定位信息来校正惯导的误差。仿真结果表明:与基本互相关方法相比,加权处理能有效提高时延差的精度,所提出的惯导和声学浮标辅助设备导航系统能够使定位误差小于2 m,保证了水下航行器能够长时间在水下航行。     

气体非稳定爆轰波在具有声学吸收壁的直角三通弯管中传播特性研究

本文实验研究了丙烷、氧气和空气的预混气体非稳定爆轰波在具有声学吸收壁的直角三通弯管中传播特性，分析了声学吸收材料厚度对非稳定爆轰波传播特性的影响．实验结果表明，在直角三通弯管中安装声学吸收材料对气体非稳定爆轰波有明显的衰减作用，在弯管前后非稳定爆轰波的传播速度和压力都有很大程度的减小．而且随着声学吸收材料厚度的增加，气体非稳定爆轰波强度衰减幅度增大．这一实验结论对工业安全具有重要的参考价值．     

基于声学超材料的穿孔板缺陷态俘能特性研究

论文提出了一套适用于在低频段区间工作的声学超材料俘能装置.通过在含孔的声学超材料结构中制造一个局域共振缺陷态,进而将入射声波的弹性应变能集中在缺陷区域中,并利用压电晶片实现能量的转化.论文采用有限元的方法研究了元胞含孔的声学超材料在共振频率下俘获功率与电压的性能.进一步地,通过逐渐改变孔的尺寸,探究了孔径大小对俘能效果...     

导管螺旋桨气动性能的风洞试验研究

对自行研制的一船用空气推进导管螺旋桨系统的导管和桨后整流支架的空气动力学性能在试验雷诺数范围进行了风洞模型试验研究.研究结果表明,导管和桨后整流支架明显改善了系统的空气动力学性能,螺旋桨系统的推力系数和效率都有较明显提高,螺旋桨系统的原地静推力和倒车性能也得到很大改善.     

阶梯圆柱形耦合声场的特征正交-里兹法建模及声学特性分析

针对阶梯圆柱形耦合声场建模问题,提出基于特征正交-里兹能量原理的声学建模方法.该方法利用二维特征正交多项式和周向傅里叶级数表征阶梯圆柱形耦合声场子分段的声压函数,从能量角度考虑邻近子声场间声学连续性条件,并结合里兹法获得耦合声场的声学特性.基于本建模方法对不同分段的耦合声场开展声学特性分析,结果表明,本建模方法在保证计算准确性的基础上有效提高了计算效率,且对任意阶梯分段的圆柱形耦合声场普遍适用;圆柱形耦合声场固有频率会随着腔体外径增大而普遍增大,而腔深的影响规律相反;降低声学边界阻抗可抑制声学响应幅值,为此类声场的噪声控制提供了设计依据.     

三维声学特征频率灵敏度分析的边界元法

声系统特征频率的灵敏度分析为其优化设计提供了基础,具有重要意义。边界元法在声学问题的求解中具有独特优势,但因其系统方程系数矩阵的频率相关性导致的非线性特征值问题给声学特征频率的灵敏度分析带来了很大困难。为此,本文首先对非线性特征值问题进行了线性化处理,利用围道积分投影方法将非线性特征方程转换为小规模广义特征方程,然后对其关于设计变量直接求导,并引入左特征向量和转换矩阵构造了一种适用于内外声场的三维声学单/重特征频率灵敏度分析的边界元法。数值算例验证了该方法的适用性,以及对单/重特征频率灵敏度的计算精度。     

船舶振动声学优化设计中设备运动激励的等效反演力方法

当设备振动载荷以运动激励形式给出时,常采用大质量法或直接加速度法进行结构动力响应分析。但基于这两种方法的动力学模型无法用于船舶振动模态分析以及振动声学优化设计迭代过程中的动力学重分析。本文基于动力设备内源激振力的不变性,提出等效反演力法,将设备运动激励转换为设备等效内源力载荷,用于船舶水下辐射噪声的预报以及结构声学优化设计。以某舱段为例,对比分析了不同加载方法对应的动力学模型的固有频率与水下辐射噪声声功率,实测水声声功率为92.33 dB,基于等效反演力法输入的水声声功率数值计算结果为93.84 dB,两者相差1.51 dB。研究表明,等效反演力法是在振源设备载荷以运动激励给定时计算水下辐射噪声并用于声学优化设计的优选方法。     

一种改进的水下三阵元辅助惯导系统的定位算法

针对水下惯导系统定位误差随时间发散的缺陷,设计了一种基于DVL、声学定位辅助惯导的组合导航系统。声学定位系统由安装在水下潜器上的换能器阵和布放在海底的三阵元定位基阵组成,传统长基线定位水下至少要布放四个阵元,三个阵元无法直接定位求解。根据三阵元测得的距离信息和惯导系统输出的位置信息建立距离耦合模型,给出了惯导、DVL和声学定位系统的状态方程和量测方程;同时针对水下声速垂直分布特性,提出了一种等效声速的修正方法。仿真结果表明:在三阵元定位基阵作用范围内,组合导航系统能有效修正惯导位置误差,定位误差小于4 m,具有良好的适用性。     

五零能模式材料设计的非线性有限元计算方法

五零能模式材料是一种新型人工超材料,特征为其弹性模量矩阵的6个特征值中5个为零,可用等效体积模量来描述,表现出类似流体的性质,可被应用于声学隐声斗篷的设计中。然而,根据A.N.Norris[1]提出的理论,设计五零能模式材料时,与应用变换声学方法设计一般声学人工超材料不同,要求其满足一非线性偏微分方程约束。本文利用非线性有限元的完全拉格朗日方法,推导了这一偏微分方程的弱形式,并给出了相应的非线性有限元计算列式,以及迭代求解的具体算法。最后,给出了五零能摸式材料设计的二维和三维坐标变换数值算例。     

气体爆轰波在声学吸收壁下游的再加强过程

实验研究了爆轰波在声学吸收段下游发生的再恢复过程。利用声学吸收段首先将一个稳定的爆轰波衰减,于是产生一个非稳定爆轰波,速度降为 45% ~60?J。该非稳定爆轰波传出声学吸收段后再次加强,并在距声学吸收段出口端一定距离处突然发展成超驱动爆轰。实验利用烟迹技术捕捉了爆轰波从发生衰减到再次加强的全过程,获得了爆轰波再加强距离随初压变化的实验规律。由此,本文建立了再加强段内加速传播火焰的理论模型,称为激波 -爆燃波复合态,并解释了火焰加速和超驱动爆轰形成的机理。     

A new phenomenon of acoustic streaming

This paper describes a new phenomenon of acoustic streaming which takes place when a Helmholtz resonator is excited by an inside sound source with resonant frequency, and takes the form of a strong turbulent jet. The flow visualizations, hot wire and LDV measurements are combined to investigate the process of acoustic streaming. It is found that this kind of acoustic streaming results from the contribution of Reynolds stress.     

Acoustic Doppler velocimeter-induced acoustic streaming and its implications for measurement

The acoustic Doppler velocimeter (ADV) is widely used for the characterization of fluid flow. Secondary flows (“acoustic streaming”) generated by the ADV’s acoustic pulses may affect the accuracy of measurements in experiments with small velocities. We assessed the impact of acoustic streaming on flow measurement using particle image velocimetry. The probes of two different ADVs were successively mounted in a tank of quiescent water. The probes’ ultrasound emitters were aligned with a laser light sheet. Observed flow was primarily in the axial direction, accelerating from the ultrasound emitter and peaking within centimeters of the velocimeter sampling volume before dropping off. We measured the dependence of acoustic streaming velocity on ADV configuration, finding that different settings induce streaming ranging from negligible to more than 2.0 cm s⁻¹. From these results, we describe cases where acoustic streaming affects velocity measurements and also cases where ADVs accurately measure their own acoustic streaming.     

Acoustic streaming measurements in standing wave resonator using Particle Image Velocimetry

This paper experimentally investigates the measurement of acoustic streaming in a 7 m long-standing wave air-filled acoustic resonator. One can describe the acoustic streaming as a second-order steady flow, which is superimposed on the dominant acoustic velocity. It is induced by the nonlinearities of the acoustic propagation inside the resonator. The exploration of the acoustic velocity field by the synchronized PIV (stands for Particle Image Velocimetry) technique enabled to highlight and quantify these secondary flows. The PIV measurements of the acoustic velocity fields at different phases over the excitation signal period gave information on streaming profiles and the post processing applied allowed plotting the acoustic velocity over time. These results were compared to the outcome of a 2D numerical study performed with the commercial software Fluent, where good agreements were found. It indicates the ability of this method to accurately measure second order steady flow variations of the acoustic velocity field.     

Computational study of steady streaming from oscillating microbubbles with uniform and wavy wall motions

Steady streaming flow fields of a 5 μm bubble oscillating with uniform radial wall motion and a 500 μm bubble oscillating with wavy wall motion were simulated using a computational fluid dynamics method that incorporated fluid–structure interactions. The steady streaming flow fields for both bubbles were calculated, and they exhibited upward jet flow with two symmetrical counter-rotating vortices. The maximum streaming velocity ranged from a few to tens of millimeters per second. The simulated flow fields were compared with the theory and experimental measurements using particle image velocimetry. The simulation results agreed well with the theoretical and experimental data. Therefore, the proposed computational method would provide a useful tool to predict steady streaming flow fields of oscillating bubbles.     

Surface Probing with Streaming Potential: The Polymer Flooding Scenario

Transport in Porous Media - The first experimental evidence of polymer adsorption in natural carbonates obtained from streaming potential measurements is presented. The surface probing of the...     

Shear induced phase transitions in highly dilute aqueous detergent solutions

Aqueous solutions of some cationic detergents show rheopectic behaviour at very low concentrations. Rheological measurements and the electrical anisotropy of the streaming solutions indicate that the rheopectic behaviour of the solutions is due to a shear induced phase transition.     

Instability of Streaming Viscoelastic Fluids in the Presence of ��Effective Interfacial Tension�� Through Porous Medium

The ??effective interfacial tension?? effect on the instability of the plane interface between two uniform, superposed, and streaming Rivlin?CEricksen viscoelastic fluids through a porous medium is considered. The case of two uniform streaming Rivlin?CEricksen viscoelastic fluids separated by a horizontal boundary is studied. In the absence of ??effective interfacial tension??, stability/instability of the system as well as perturbations transverse to the direction of streaming are found to be unaffected by the presence of streaming if the perturbations in the direction of streaming are ignored, whereas for perturbations in all other directions, there exists instability for a certain wave number range. ??Effective interfacial tension?? is able to suppress this Kelvin?CHelmholtz instability for small wavelength perturbations, the medium porosity reduces the stability range given in terms of a difference in streaming velocities.     

Forced Convective Cooling via Acoustic Streaming in a Narrow Channel Established by a Vibrating Piezoelectric Bimorph

Forced convection in a narrow channel is investigated both numerically and experimentally. The flow field is established through the mechanism of acoustic streaming. This is accomplished by high frequency vibration of one of the channel walls, which is composed of a piezoelectric bimorph. In the numerical computations, the Navier-Stokes equations are decomposed into the acoustic equations and the streaming equations by the perturbation method. The acoustic field is first numerically obtained, which provides the driving force for the streaming field. The streaming field and the associated temperature field are then obtained numerically. Heat losses from a heat source are measured to determine the efficiency of this as a cooling method. The air-flow patterns in the channel between the heat source and the bimorph actuator are visualized using the particle tracking velocimetry. The visualization clearly shows that vortical streaming (acoustic streaming) can be induced by bimorph vibration, which enhances heat transfer between the heat source and the surrounding air. The temperature decreases obtained computationally and experimentally are in good agreement.     

Acoustic streaming on spheres

The phenomenon of secondary motion (acoustic streaming) created by the oscillation of a fluid past a sphere is investigated through numerically solving the full Navier-Stokes equations. The main parameters that affect the structure of acoustic streaming are Reynolds number and Strouhal number. The results are presented in the form of steady streaming patterns as well as the relation between Reynolds and Strouhal numbers and the dimensions of the streaming region.     

加载速率对骨的流动电位的影响

骨受力变形时所引起的压力驱动骨内哈佛氏管或骨小管内的液体流动,是骨内出现流动电位的外部原因.由于人体经常受动态载荷作用,研究骨在动态加载过程中流动电位的变化,更有助于了解骨细胞周围电环境的性质.为此,设计了流动电位测试系统,在骨试样两端施加梯形压力波.实验测量了在不同加载速率下流动电位的变化波形.结果显示,加载速率越高,流动电位有减小的趋势.分析认为这是由于微管中局部产生的湍流引起的.