宽容性体积阵优化波束形成

为适应低频吊放声纳的发展,具有收扩功能的体积阵作为一种重要的水听器基阵结构形式得到了广泛的应用.体积阵的波束形成也受到越来越多的关注,一般利用自适应的方法对体积阵进行波束形成权系数设计.实际应用中由于基阵结构杂乱散射、反射的影响,阵列响应向量存在一定的误差.为保证系统的正常工作,权系数的宽容性格外重要.利用最差情况性能最优化的思想对权系数进行优化,通过实验验证了这种优化的有效性,大大提高了权系数的宽容性,改善了系统工作性能.     

动态载荷识别的自适应延迟逆模型方法

为减小载荷识别问题对原系统先验知识的依赖,采用系统的自适应延迟逆模型识别时域载荷。采用自适应算法辨识延迟逆模型,代替了一般识别方法中的系统特性矩阵求逆过程,避免了病态问题。随后将工作状态下的响应作为逆模型的输入,则其输出就是时域载荷的延迟估计。通过对两端简支梁结构进行载荷识别的仿真研究,以及对双层隔振试验台架的试验研究,识别了稳态激励和瞬态激励,验证了该方法的有效性。该方法不需要了解系统的数学模型及参数,因此能够应用于工程实践中。     

A new source number estimation method based on the beam eigenvalue

Most source number estimation methods based on the eigenvalues are decomposed by covariance matrix in MUSIC algorithm. To develop the source number estimation method which has lower signal to noise ratio and is suitable to both correlated and uncorrelated impinging signals, a new source number estimation method called beam eigenvalue method (BEM) is proposed in this paper. Through analyzing the space power spectrum and the correlation of the line array, the covariance matrix is constructed in a new way, which is decided by the line array shape when the signal frequency is given. Both of the theory analysis and the simulation results show that the BEM method can estimate the source number for correlated signals and can be more effective at lower signal to noise ratios than the normal source number estimation methods.     

基于小波分析的自适应谱线增强信号提取

提出一种基于小波多分辨率分析的自适应谱线增强算法,利用小波多分辨率分析理论,有效地将微弱的窄带轴频电场信号从宽带背景噪声中分离出来,把信号和噪声正交分解于不同的频率范围中,从而减少了自适应滤波器的阶数,提高了算法的收敛速度和稳定性。利用该方法对船模产生的轴频电场实测数据进行了处理,实验结果表明该算法可以有效地提取舰船轴频电场信号。     

基于改进小波能熵的水下目标识别

文章研究了基于改进小波能熵和概率神经网络的水下目标识别方法。首先对水下目标辐射噪声信号进行小波变换多分辨率分解和重构,然后引入滑动时间窗,提取各分解子带在滑动时间窗内的改进小波能熵值作为目标识别的特征矢量,最后将特征矢量输入到概率神经网络中实现水下目标识别。对信号进行小波多分辨率分解可反映信号在不同频域上的特征,而引入滑动时间窗并在此基础上定义改进的小波能熵可反映信号的时域特征,因此改进小波能熵方法能同时反映信号的时频特征,更适合于水下目标特征提取。仿真结果表明了该方法的有效性。     

大型复杂齿轮箱底架模态分析方法

本文探讨针对某复杂齿轮箱底架结构的一种模态分析方法。该齿轮箱底架尺寸较大,质量与刚度分布情况复杂。试验模态分析所需的试验条件要求高,对于力锤的选择和传感器的数量都有较高的要求。此外在有限元模态分析中会存在模态密集、模态向量繁杂、模态振型云图无法提取等问题。该齿轮箱底架结构特殊,近似案例很少,因而鲜有相关的计算参考。本文主要提出以扫频分析为理论基础,辅以虚拟梁的一种近似方法来求出该复杂大型结构的固有频率与振型。其计算结果较直接模态分析更能体现结构在工作状态下的模态情况,亦能对设备工作频率的选取以及结构刚度优化提供有益的帮助。     

基于振动法检测预应力混凝土梁有效应力的实验研究及有限元分析

在已建的预应力结构中,结构当前的应力检测一直是较难解决的问题。文中利用振动法研究无粘结预应力混凝土梁的振动特性,通过理论分析和实验研究发现,预应力改变了混凝土梁的有效刚度,从而改变了预应力混凝土梁的振动频率。因此可以通过振动频率值反推得到梁的有效应力。通过实验测试和有限元计算得到了预应力混凝土梁在不同预应力作用下的振动频率值,二者的结果吻合较好。研究表明,振动法可以用来检测无粘结预应力混凝土梁的有效应力,为结构的有效应力检测提供了一条参考途径。     

典型阵列声纳束控演示软件开发研究

典型阵列声纳波束形成（束控）技术,即直线阵和平面阵指向性函数及其波束图的研究可为其它复杂基阵（圆柱阵、球阵）的束控技术研究提供借鉴和参考。文章通过最典型的均匀间隔阵列对束控技术进行研究,利用MATLAB编写制作了一个具有仿真演示界面的程序,用于演示不同坐标系下、不同参数时的波束图,并可在课堂教学演示中使用。     

A method of multi-channel reference signals acquiring in broadband ANC

In a flank array on an unmanned underwater vehicle （UUV）, self-generated noise which has broadband and colored spectrum property in frequency and spatial domain is the main factor affecting the performance of weak signal detection, so the technique of adaptive noise cancellation （ANC） as well as physical denoising and active noise cancellation are often used in practice. Because ANC is based on correlations, improvements in performance come from better correlation between reference signals and primary signals. Taking full advantage of the characteristics of flank arrays and the characteristics of information obtained from hydrophones, a new method for reference signal acquisition for adaptive noise cancellation is proposed, in which the multi-channel reference signals are obtained by accurate delaying for a given direction of arrival （DOA） and differencing between adjacent outputs of array elements. The validity of the proposed method was verified through system modeling simulations and lake experiments which showed good performance with little additional computational burden.     

任意结构形状传感器阵方向图的最佳化

本文介绍一种处理传感器阵方向图最佳化问题的新方法,即所谓凹槽噪声场法。这种方法将通过计算机仿真来实现。原理上说,这种方法可以用来计算任意结构传感器阵的最佳权系数矢量和最佳方向图,以满足主瓣方向和宽度的要求,并使旁瓣级为最小。因此这种方法有可能用来解决传感器阵设计、应用中的许多实际问题,例如少数传感器失效、阵的尺寸误差过大,单个传感器的方向图互不一致,以及阵的结构形状复杂等。文中提供了一些计算实例,以说明本方法的优点,包括有一个“随机阵”的方向性设计。     

基于均匀法的风雨载荷下折叠式舱口盖拓扑优化设计研究

本文以48500DWT散货船舱口盖为研究对象,提出改变传统折叠式舱口盖设计方法,引入拓扑优化的方法对舱口盖横梁腹板、纵桁腹板进行优化设计。通过ANSYS模拟仿真分析,找出最佳力传递路径的结构布置形式,根据优化结果提取节点信息,经过对拓扑优化后的模型进行二次优化,完善了拓扑优化的结果,使其材料布局形式更合理,研究结果表明,基于均匀法的拓扑优化方法运用于折叠式舱口盖的设计中,可改善舱口盖横梁腹板、纵桁腹板结构,保证其强度并且达到轻量化设计的目的,为舱口盖横梁腹板、纵桁腹板的结构设计提供参考依据。     

用谐波小波变换法研究船舶横摇的非线性动力特性

本文探索了一种用小波分析的方法来研究船舶非线性横摇系统的运动.对于非线性非自治系统的响应主要有周期、准周期和混沌几种状态.而在系统参数变化时,又由周期分叉形成了准周期和混沌.因此,需要对周期解做更多的研究.当系统响应是周期的,通过小波变换,可以得到一些不同频率的谐波,这些谐波与谐波平衡法得到的解非常相似,因此也就可以作为系统的近似解.如果系统响应是混沌的,通过小波变换,始终都得不到周期的信号,这一点明显区别于周期运动.也就是说通过小波变换这种方法,可以明显地区别出混沌和周期.     

基于ADS的锁相环瞬态响应仿真

在使用ADS(Advanced Design System)软件搭建了对锁相环的瞬态响应仿真的平台后,对分频比改变和参考频率相位抖动时的输出响应进行仿真,得到输出响应的各种指标,并进行了分析.此仿真技术可为锁相环的设计分析提供参考.     

一种通用型基于经验模态分解的小波阈值滤波方法研究

首先针对中高频水声信号,提出一种改进的经验模态分解加小波软阈值滤波方法;然后将信号进行带通滤波处理及经验模态分解,将分解得到的各个模态转换为频域信号,采用小波软阈值方法在频域上对这些模态进行滤波,最后对信号进行重构,并将其转换为时域信号。分别采用本方法和原时域上的小波阈值方法对不同频率的水声信号进行滤波,经计算分析可知,对频率小于800 Hz的水声信号,采用原方法可获得较好的滤波效果;当信号频率大于800 Hz时,采用本方法的滤波效果更好,因此应针对不同频率的水声信号,选择合适的滤波方法,以获得满意的滤波效果。     

基于改进BP-GA方法的FPSO舷侧结构耐撞性能优化设计

基于遗传算法和ABAQUS参数化有限元仿真技术,对传统的BP-GA优化方法进行改进,并采用改进的BP-GA方法对浮式生产储油卸油装置(FPSO)舷侧结构的耐撞性能进行优化,以验证其可行性和准确性。结果表明,与传统的BP神经网络相比,经遗传算法优化的BP神经网络具有更高的预测精度和更强的泛化能力;改进的BP-GA优化方法可在结构减重的基础上进一步提高结构的耐撞性能,能较好地适用于复杂的FPSO舷侧结构耐撞性优化设计。采用的优化方法具有通用性,可为抗爆性能的优化设计提供参考。     

The research on signal-obtaining pattern for a new type of gyroscope

In this paper, a photoelectric signal obtained scheme via equator triangle pattern engraved on rotor is discussed and the mathematic model is deduced in the case which is deflexion between rotor axis and the coordinate frame of case. The deflexion error and coupling error under the situation are analyzed. Finally, three methods of engraving based on the spherical triangle pattern are presented. The error models of various methods are built up and the simulation curves are provided respectively. We have done the primary experiments on the surface of rotor using this method. It can be seen from the enlarged figures that the rim of the pattern is smooth and the demand of sensor resolution is satisfied by and large. The results of study supply reference for signal obtaining.     

基于双树复小波的被动目标特征提取方法研究

针对水下目标辐射噪声特征提取困难的问题,提出一种基于双树复小波变换的特征提取方法。首先,采用一种改进的小波阈值去噪方法去除水下目标辐射噪声信号中的噪声成分,该方法可以获得优于经典小波阈值去噪方法的结果;其次,在特征提取过程中,采用具有近似平移不变性的双树复小波变换,该方法能够克服信号时移带来的影响,得到稳定的目标特征向量。仿真试验和实航数据处理结果表明,本文方法提取的目标特征向量比使用离散小波变换提取的结果更稳定。     

Numerical weight function method for the structural analysis of ships: a speedy direct calculation with condensed structural information

The weight function method was originally derived for crack problems to calculate stress intensity factors for arbitrary loading conditions. In this article, a numerical weight function method has been extended to formulate the structural response analyses of two-dimensional elasticity, plate-bending, and three-dimensional plate-structures by using the finite-element method. The solution procedure is based on the well-known Maxwell–Betti reciprocal theorem, which is applied to the original and properly defined auxiliary problems. The present numerical weight function may be considered as a finite-element version of a Green’s function in an integral equation solution scheme. Although ship structures are certainly analysed by the finite-element method in a practical design procedure, the weight function approach has not yet been realized. The method is very useful for the analysis of structures subjected to a vast range of loading conditions, because structural responses can simply be calculated by the inner product of the universal weight function and load vectors. The validity and convergence characteristics of the present method are investigated by two-dimensional elastic and plate-bending problems, respectively. Finally, the method is applied to the calculation of the response amplitude operator of a stress component at a critical structural detail of a double-hull tanker, and the speed and efficiency of the method are quantitatively discussed based on the practical results.     

Crack detection using a frequency response function in offshore platforms

Structural cracks can change the frequency response function (FRF) of an offshore platform. Thus, FRF shifts can be used to detect cracks. When a crack at a specific location and magnitude occurs in an offshore structure, changes in the FRF can be measured. In this way, shifts in FRF can be used to detect cracks. An experimental model was constructed to verify the FRF method. The relationship between FRF and cracks was found to be non-linear. The effect of multiple cracks on FRF was analyzed, and the shift due to multiple cracks was found to be much more than the summation of FRF shifts due to each of the cracks. Then the effects of noise and changes in the mass of the jacket on FRF were evaluated. The results show that significant damage to a beam can be detected by dramatic changes in the FRF, even when 10% random noise exists. FRF can also be used to approximately locate the breakage, but it can neither be efficiently used to predict the location of breakage nor the existence of small hairline cracks. The FRF shift caused by a 7% mass change is much less than the FRF shift caused by the breakage of any beam, but is larger than that caused by any early cracks.     

主瓣干扰下平面阵自适应波束优化方法

在自适应波束形成中,若干扰信号从主瓣进入,往往引起副瓣增高、主瓣变形且峰值偏移,波束性能明显恶化。针对平面阵,通过构造干扰阻塞矩阵,首先对主瓣内的干扰进行相消预处理,再进行自适应波束形成,最后进行权系数补偿,消除主波束偏移。仿真结果表明,该方法能有效消除主瓣干扰和解决波束畸变问题,提高自适应波束的性能。