共查询到20条相似文献,搜索用时 203 毫秒
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HUANG Sheng WANG Pei-sheng HU Jian 《船舶与海洋工程学报》2007,6(2):6-11
The hydrodynamic performance of a propeller in unsteady inflow was calculated using the surface panel method. The surfaces of blades and hub were discreted by a number of hyperboloidal quadrilateral panels with constant source and doublet distribution. Each panel's corner coordinates were calculated by spline interpolation between the main parameter and the blade geometry of the propeller. The integral equation was derived using the Green Formula. The influence coefficient of the matrix was calculated by the Morino analytic formula. The tangential velocity distribution was calculated with the Yanagizawa method, and the pressure coefficient was calculated using the Bonuli equation. The pressure Kutta condition was satisfied at the trailing edge of the propeller blade using the Newton-Raphson iterative procedure, so as to make the pressure coefficients of the suction and pressure faces of the blade equal at the trailing edge. Calculated results for the propeller in steady inflow were taken as initialization values for the unsteady inflow calculation process. Calculations were carried out from the moment the propeller achieved steady rotation. At each time interval, a linear algebraic equation combined with Kutta condition was established on a key blade and solved numerically. Comparison between calculated results and experimental results indicates that this method is correct and effective. 相似文献
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《中国远洋航务》2013,(11):10-13
The China Shipping Prosperity Index (CSPI) for the third quarter has climbed 15 points from the second quarter to 101.7 points, back to positive territory, which is above 100 points, according to the latest report form Shanghai International Shipping Institute (SISI). This is the first time since the third quarter of 2011 that the CSPI returned to above the critical level. In the past two years, withering trade and overcapacity pushed the Chinese shipping industry down to a historical bottom. In the third quarter of 2012, when the CSPI fell to only 78 points, about 60 per cent of carriers in China suffered severe loss. Since the second quarter of this year, the Chinese government's policies to secure growth have taken effect and spurred an obvious growth in the country's investments and exports, which brought hope to the shipping market. The Baltic Dry Index has risen to over 2,100 points by far, a sharp increase of 180 per cent from the beginning of this year. The index surged nearly 80 per cent in September. The container shipping industry also shares the general improvement of the market. Since July, there have been several attempts to introduce rate increase. The spot rate from Shanghai to Europe was once more than doubled. Part of the carriers might be able to reverse their loss in the third quarter. However, the recovery might not be sustainable, as China is very likely to be able to meet the GDP target of 7.5 per cent growth and there will not be further policies to boost domestic economy. Meanwhile, the rebound of rates has stimulated deployment of new tonnage. Statistics show, capacity on Asia-Europe lane grew about three per cent in September but demand is not stable. The supply-demand imbalance caused a decrease of over US$100 per TEU in the container shipping rates in the last week of September.SISl's report estimated that the CSPI in the fourth quarter will be 99.56 points, falling again below the critical level. In face of such challenges, 相似文献
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ZHANGJing LIUQun BaikunthNath 《船舶与海洋工程学报》2004,3(1):71-74
lmage segment is a primat.‘y step in image analysis of unexploded ordnance (UXO) detection by ground penetrating radar (GPR) sensor which is accompanied with a lot of noises and other elements that affect the recognition of real target size. In this paper we bring forward a new theory, that is, we look the weight sets as target vector sets which is the new cues in semi-automatic segmentation to form the final image segmentation. The experiment results show that the measure size of target with our method is much smaller than the size with other methods and close to the real size of target. 相似文献
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WANG Bai-he HUANG Jian-guo 《船舶与海洋工程学报》2007,6(4):13-17
A classical time-varying signal,the multi-component Chirp signal has been widely used and the ability to estimate its instantaneous frequency(IF) is very useful. But in noisy environments,it is hard to estimate the IF of a multi-component Chirp signal accurately. Wigner distribution maxima(WDM) are usually utilized for this estimation. But in practice,estimation bias increases when some points deviate from the true IF in high noise environments. This paper presents a new method of multi-component Chirp signal IF estimation named Wigner Viterbi fit(WVF) ,based on Wigner-Ville distribution(WVD) and the Viterbi algorithm. First,we transform the WVD of the Chirp signal into digital image,and apply the Viterbi algorithm to separate the components and estimate their IF. At last,we establish a linear model to fit the estimation results. Theoretical analysis and simulation results prove that this new method has high precision and better performance than WDM in high noise environments,and better suppression of interference and the edge effect. Compared with WDM,WVF can reduce the mean square error(MSE) by 50% when the signal to noise ration(SNR) is in the range of -15dB to -11dB. WVF is an effective and promising IF estimation method. 相似文献
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CAI Cheng-tao ZHU Qi-dan YAN Yong-jie 《船舶与海洋工程学报》2005,4(4):43-46
Helicopter blade running elevation measurement is an important measure target in helicopter blade dynamic balance experimentation. The elevation influences the helicopter' s security and other performance capabilities. In testing, however, it has been difficult to measure the elevation when the rotor reaches high speeds. To get a simple, fast and highly accurate measurement system, photo electricity technology was applied to measuring the blade running elevation. Discussed is the measurement principle of blade running elevation, tire design of the measurement system and analysis of the measurement precision. 相似文献
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A new multi-level analysis method of introducing the super-element modeling method, derived from the multi-level analysis method first proposed by O. F. Hughes, has been proposed in this paper to solve the problem of high time cost in adopting a rational-based optimal design method for ship structural design. Furthermore,the method was verified by its effective application in optimization of the mid-ship section of a container ship. A full 3-D FEM model of a ship,suffering static and quasi-static loads, was used as the analyzing object for evaluating the structural performance of the mid-ship module, including static strength and buckling performance. Research results reveal that this new method could substantially reduce the computational cost of the rational-based optimization problem without decreasing its accuracy, which increases the feasibility and economic efficiency of using a rational-based optimal design method in ship structural design. 相似文献
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YAO Bin LI Hai-sen ZHOU Tian SUN SHENG-he 《船舶与海洋工程学报》2006,5(4):42-47
The effective method of the recognition of underwater complex objects in sonar image is to segment sonar image into target, shadow and sea-bottom reverberation regions and then extract the edge of the object. Because of the time-varying and space-varying characters of underwater acoustics environment, the sonar images have poor quality and serious speckle noise, so traditional image segmentation is unable to achieve precise segmentation. In the paper, the image segmentation process based on MRF (Markov random field) model is studied, and a practical method of estimating model parameters is proposed. Through analyzing the impact of chosen model parameters, a sonar imagery segmentation algorithm based on fixed parameters' MRF model is proposed. Both of the segmentation effect and the low computing load are gained. By applying the algorithm to the synthesized texture image and actual side-scan sonar image, the algorithm can be achieved with precise segmentation result. 相似文献
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A new method to solve the boundary value problem arising in the study of scattering of two-dimensional surface water waves by a discontinuity in the surface boundary conditions is presented in this paper. The discontinuity arises due to the floating of two semi-infinite inertial surfaces of different surface densities. Applying Green’s second identity to the potential functions and appropriate Green’s functions, this problem is reduced to solving two coupled Fredholm integral equations with regular kernels. The solutions to these integral equations are used to determine the reflection and the transmission coefficients. The results for the reflection coefficient are presented graphically and are compared to those obtained earlier using other research methods. It is observed from the graphs that the results computed from the present analysis match exactly with the previous results. 相似文献
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This paper describes an analytical investigation into synchrophasing, a vibration control strategy on a machinery installation in which two rotational machines are attached to a beam-like raft by discrete resilient isolators. Forces and moments introduced by sources are considered, which effectively represent a practical engineering system. Adjusting the relative phase angle between the machines has been theoretically demonstrated to greatly reduce the cost function, which is defined as the sum of velocity squares of attaching points on the raft at each frequency of interest. The effect of the position of the machine is also investigated. Results show that altering the position of the secondary source may cause a slight change to the mode shape of the composite system and therefore change the optimum phase between the two machines. Although the analysis is based on a one-dimensional Euler–Bernoulli beam and each machine is considered as a rigid-body, a key principle can be derived from the results. However, the factors that can influence the synchrophasing control performance would become coupled and highly complicated. This condition has to be considered in practice. 相似文献
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Based on the traditional Smoothed Particle Hydrodynamics (SPH) algorithm, the linked-list search algorithm combined with the variable smoothing length and square support domain was put forward to improve the calculation efficiency and guarantee the calculation accuracy. The physical process of high velocity fragment impact on a broadside liquid cabin was programmed for simulation. The numerical results agreed well with those of the general software ANSYS AUTODYN, which verifies the effectiveness and feasibility of the numerical method. From the perspective of the outer plate thickness of the liquid cabin, the width of the liquid cabin, and incident angle of the fragment, the influence of these parameters on protective mechanisms was analyzed to provide a basis for protective design of a broadside liquid cabin. Results show that the influence of outer plate thickness is not obvious; therefore, the conventional design can be adopted in the design of the outer plate. The width of the liquid cabin has a great influence on the residual velocity of the fragment and the width of the liquid cabin should be designed to be as wide as possible under the premise of meeting other requirements. There is a certain incident angle in which the velocity attenuation of the fragment is most obvious, and the high-pressure zone near the inner plate is asymmetric. The inner plate of liquid cabin should be strengthened according to the hull form, principal dimensions, and vulnerable points. 相似文献
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红外序列图像帧间匹配算法研究 总被引:1,自引:0,他引:1
文章在现有单帧图像检测算法的基础上,提出了一种可同步跟踪运动目标的帧间匹配算法。算法采取对相邻两帧间像素点匹配,匹配过程与当前两帧外的其余帧无关,把匹配结果兴趣区域像素点对应的另一个全零矩阵位置值赋为1,顺利输入检测后的单帧图像,执行匹配操作,实时形成目标运动轨迹。该算法结构简单、存储量少、计算速度快,硬件平台要就低,可有效地完成对多个目标、交叉目标、迎头目标的检测与跟踪。根据仿真和实拍照片的试验,证实了算法理论上的优点,有较高的应用价值。 相似文献
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一种简单易行的摄像机标定方法 总被引:1,自引:0,他引:1
提出一种适用于电视测量系统中的方便的投影参数求取方法,主要着眼于方法的易用性,并在此基础上设计出了一套用于自动测量船模运动参数的电视测量系统。它首先利用测试卡上的方格线求出摄像机镜头的变形修正系数,然后利用已知的5个地面坐标与图像中的对应点的关系求出摄像机的标定参数。根据上述两步得出的参数,可以通过图像上的任何一个像素点计算出其在地面上的对应坐标值。实验证明,本文提出的方法是有效的,且能够比较方便地解决视觉监控中摄像机标定的问题。 相似文献
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Jenhwa Guo 《Journal of Marine Science and Technology》2008,13(2):147-153
This study presents a localization system using visual information for guidance and navigation of a biomimetic autonomous
underwater vehicle (BAUV). The BAUV tracks a mooring cable using two cameras and sonar. Sonar has good accuracy in detecting
longitudinal distances but is poor in detecting lateral distances. Since a stereo image has quantization errors, for the cameras,
measurement errors in lateral directions are less than those in the optic-axis direction. An extended Kalman filter was employed
to combine observational information derived from the cameras and sonar of the mooring cable position with the navigation
data of the BAUV. This work demonstrates, using water tank experiments, the effectiveness of the proposed tracking technique
in decreasing uncertainty in position estimations of the BAUV and mooring cable. 相似文献
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船舶发动机盖外板与内板之间常涂覆一层防震密封胶,但具体涂胶形态难以观测,常用机器视觉手段获取产品涂胶图片。针对涂胶区域分割和检测精度低,效率慢的问题,提出一种新的边缘提取算法获取涂胶区域。为了避免传统Canny边缘检测方法易受噪声干扰的缺点,采用具有保边特性的加权最小二乘法滤波器对图像滤波去燥,增加45°和135°两个方向计算图像梯度,利用改进后的Canny算法获取边缘,对获取到的边缘点用区域生长方式将涂胶区域提取出来,最后将提取到的涂胶区域与标准涂胶区域进行配准和减影,得到减影结果即为涂胶缺陷。试验仿真表明:本算法能够很好的提取到胶水区域,并且获取胶水缺陷。 相似文献