Journal of Marine Science and Application 2011 no. 1
Wei Zhang, Wenyong Tang, Nianzhong Chen and Shengkun Zhang
Journal of Marine Science and Application,2011(No. 1): 1-6
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The effects of stochastic characteristics of materials on the reliability of ship hulls made of composite materials under longitudinal moment were extensively studied using reliability and sensitivity calculations of a composite ship hull which was sagging. The reliability indices and failure probabilities of the ship in three kinds of failure modes (buckling, material failure, and ultimate collapse) were calculated by the surface response method and JC method. The importance factors of random variables in stochastic models, such as the model errors in predicting the ultimate longitudinal strength of ship and the longitudinal bending moment that the ship withstands, as well as the stochastic characteristics of materials in the models used, were calculated. Then, the effects of these random variables, including the stochastic characteristics of materials on the reliability index and the failure probability of ships which were sagging, were discussed with their importance factors. The results show that the effects of stochastic characteristics of materials on the reliability of ship hulls made of composite materials should be considered during the reliability assessment of composite ships. Finally, some conclusions and recommendations were given for high-speed ship design and safety assessment.

Puspendu Rakshit and Sudeshna Banerjea
Journal of Marine Science and Application,2011(No. 1): 7-16
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In the present paper, the effect of a small bottom undulation of the sea bed in the form of periodic bed form on the surface waves generated due to a rolling oscillation of a vertical barrier either partially immersed or completely submerged in water of non uniform finite depth is investigated. A simplified perturbation technique involving a non dimensional parameter characterizing the smallness of the bottom deformation is applied to reduce the given boundary value problem to two independent boundary value problems upto first order. The first boundary value problem corresponds to the problem of water wave generation due to rolling oscillation of a vertical barrier either partially immersed or completely submerged in water of uniform finite depth. This is a well known problem whose solution is available in the literature. From the second boundary value problem, the first order correction to the wave amplitude at infinity is evaluated in terms of the shape function characterizing the bottom undulation, by employing Green’s integral theorem. For a patch of sinusoidal ripples at the sea bottom, the first order correction to the wave amplitude at infinity for both the configuration of the barrier is then evaluated numerically and illustrated graphically for various values of the wave number. It is observed that resonant interaction of the wave generated, with the sinusoidal bottom undulation occurs when the ratio of twice the wavelength of the sinusoidal ripple to the wave length of waves generated, approaches unity. Also it is found that the resonance increases as the length of the barrier increases.

Zhixiong Li, Xinping Yan1, Chengqing Yuan, Jiangbin Zhao and Zhongxiao Peng
Journal of Marine Science and Application,2011(No. 1): 17-24
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A marine propulsion system is a very complicated system composed of many mechanical components. As a result, the vibration signal of a gearbox in the system is strongly coupled with the vibration signatures of other components including a diesel engine and main shaft. It is therefore imperative to assess the coupling effect on diagnostic reliability in the process of gear fault diagnosis. For this reason, a fault detection and diagnosis method based on bispectrum analysis and artificial neural networks (ANNs) was proposed for the gearbox with consideration given to the impact of the other components in marine propulsion systems. To monitor the gear conditions, the bispectrum analysis was first employed to detect gear faults. The amplitude-frequency plots containing gear characteristic signals were then attained based on the bispectrum technique, which could be regarded as an index actualizing forepart gear faults diagnosis. Both the back propagation neural network (BPNN) and the radial-basis function neural network (RBFNN) were applied to identify the states of the gearbox. The numeric and experimental test results show the bispectral patterns of varying gear fault severities are different so that distinct fault features of the vibrant signal of a marine gearbox can be extracted effectively using the bispectrum, and the ANN classification method has achieved high detection accuracy. Hence, the proposed diagnostic techniques have the capability of diagnosing marine gear faults in the earlier phases, and thus have application importance.

Fang Ji, Xiongliang Yao and Xi Ye
Journal of Marine Science and Application,2011(No. 1): 25-32
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Rigid blocking masses are located in the typical base structure of a power cabin based on the impedance mismatch principle. By combining the acoustic-structural coupling method and statistical energy analysis, the full-band vibration and sound radiation reduction effect of vibration isolation masses located in a base structure was researched. The influence of the blocking mass’ cross-section size and shape parameters and the layout location of the base isolation performance was discussed. Furthermore, the effectiveness of rigid vibration isolation design of the base structure was validated. The results show that the medium and high frequency vibration and sound radiation of a power cabin are effectively reduced by a blocking mass. Concerning weight increment and section requirement, suitably increasing the blocking mass size and section height and reducing section width can result in an efficiency-cost ratio.

Lotfollahi-Yaghin Mohammad Ali, Moosavi Sayyid Mehdi and Lotfollahi-Yaghin Amin
Journal of Marine Science and Application,2011(No. 1): 33-40
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The wave force exerted on vertical piles of offshore structures is the main criterion in designing them. In structures with more than one large pile, the influence of piles on each other is one of the most important issues being concerned in past researches. An efficient method for determining the interaction of piles is introduced in present research. First the wave force is calculated by the exact method using the diffraction theory, then in the finite difference numerical method the force is calculated by adding the velocity potentials of each pile and integration of pressure on their surface. The results showed that the ratio of the wave force on each of the double piles to a single pile has a damped oscillation around unity in which the amplitude of oscillation decreases with the increase in the spacing parameter. Also different wave incident directions and diffraction parameters were used and the results showed that the numerical solution has acceptable accuracy when the diffraction parameter is larger than unity.

Zhi Zong, Zhangrui Li and Jing Dong
Journal of Marine Science and Application,2011(No. 1): 41-48
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The localized differential quadrature (LDQ) method is a numerical technique with high accuracy for solving most kinds of nonlinear problems in engineering and can overcome the difficulties of other methods (such as difference method) to numerically evaluate the derivatives of the functions. Its high efficiency and accuracy attract many engineers to apply the method to solve most of the numerical problems in engineering. However, difficulties can still be found in some particular problems. In the following study, the LDQ was applied to solve the Sod shock tube problem. This problem is a very particular kind of problem, which challenges many common numerical methods. Three different examples were given for testing the robustness and accuracy of the LDQ. In the first example, in which common initial conditions and solving methods were given, the numerical oscillations could be found dramatically; in the second example, the initial conditions were adjusted appropriately and the numerical oscillations were less dramatic than that in the first example; in the third example, the momentum equation of the Sod shock tube problem was corrected by adding artificial viscosity, causing the numerical oscillations to nearly disappear in the process of calculation. The numerical results presented demonstrate the detailed difficulties encountered in the calculations, which need to be improved in future work. However, in summary, the localized differential quadrature is shown to be a trustworthy method for solving most of the nonlinear problems in engineering.

Huaifeng Yang, Qun Zheng, Mingcong Luo, Lanxin Sun and Rakesh Bhargava
Journal of Marine Science and Application,2011(No. 1): 49-62
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In order to study the effects of wet compression on a transonic compressor, a full 3-D steady numerical simulation was carried out under varying conditions. Different injected water flow rates and droplet diameters were considered. The effect of wet compression on the shock, separated flow, pressure ratio, and efficiency was investigated. Additionally, the effect of wet compression on the tip clearance when the compressor runs in the near-stall and stall situations was emphasized. Analysis of the results shows that the range of stable operation is extended, and that the pressure ratio and inlet air flow rate are also increased at the near-stall point. In addition, it seems that there is an optimum size of the droplet diameter.

Qiangyong Wang, Youmin Lu, Xianzhong Wang and Xiongliang Yao
Journal of Marine Science and Application,2011(No. 1): 63-69
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Based on the principle of impedance mismatching, the performance of rigid vibration isolation mass in impeding vibration wave propagation was discussed from the perspective of wave approach. Based on FEM, the influence of its weight as well as the cross-section shape parameters on the isolation performance of rigid vibration isolation mass was studied through numerical simulation. The results show that rigid vibration isolation mass can effectively impede the propagation of the medium and high frequency vibration waves, and the heavier the vibration isolation mass, the better the isolation performance. For low frequency waves, the vibration isolation effect is not so obvious; for a rectangular vibration isolation mass, the isolation performance could be effectively improved by increasing the cross-section height and reducing the cross-section width. A useful reference was provided for the application of rigid vibration isolation masses to the vibration isolation and noise reduction of ship structure.

Shilong Wang, Yuru Xu and Yongjie Pang
Journal of Marine Science and Application,2011(No. 1): 70-75
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The S/N of an underwater image is low and has a fuzzy edge. If using traditional methods to process it directly, the result is not satisfying. Though the traditional fuzzy C-means algorithm can sometimes divide the image into object and background, its time-consuming computation is often an obstacle. The mission of the vision system of an autonomous underwater vehicle (AUV) is to rapidly and exactly deal with the information about the object in a complex environment for the AUV to use the obtained result to execute the next task. So, by using the statistical characteristics of the gray image histogram, a fast and effective fuzzy C-means underwater image segmentation algorithm was presented. With the weighted histogram modifying the fuzzy membership, the above algorithm can not only cut down on a large amount of data processing and storage during the computation process compared with the traditional algorithm, so as to speed up the efficiency of the segmentation, but also improve the quality of underwater image segmentation. Finally, particle swarm optimization (PSO) described by the sine function was introduced to the algorithm mentioned above. It made up for the shortcomings that the FCM algorithm can not get the global optimal solution. Thus, on the one hand, it considers the global impact and achieves the local optimal solution, and on the other hand, further greatly increases the computing speed. Experimental results indicate that the novel algorithm can reach a better segmentation quality and the processing time of each image is reduced. They enhance efficiency and satisfy the requirements of a highly effective, real-time AUV.

Lei Yuan and Hansong Wu
Journal of Marine Science and Application,2011(No. 1): 76-81
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In considering the characteristic of a rudder, the maneuvers of a ship were described by an unmatched uncertain nonlinear mathematic model with unknown virtual control coefficient and parameter uncertainties. In order to solve the uncertainties in the ship heading control, specifically the controller singular and paramount re-estimation problem, a new multiple sliding-mode adaptive fuzzy control algorithm was proposed by combining Nussbaum gain technology, the approximation property of fuzzy logic systems, and a multiple sliding-mode control algorithm. Based on the Lyapunov function, it was proven in theory that the controller made all signals in the nonlinear system of unmatched uncertain ship motion uniformly bounded, with tracking errors converging to zero. Simulation results show that the demonstrated controller design can track a desired course fast and accurately. It also exhibits strong robustness peculiarity in relation to system uncertainties and disturbances.

Jing Li, Jianyun Chen and Xiaobo Chen
Journal of Marine Science and Application,2011(No. 1): 82-87
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The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens. The blades are the key components of offshore wind turbines, and their dynamic characteristics directly determine the effectiveness of offshore wind turbines. With different rotating speeds and blade length, the rotating blades generate various centrifugal stiffening effects. To directly analyze the centrifugal stiffening effect of blades, the Rayleigh energy method (REM) was used to derive the natural frequency equation of the blade, including the centrifugal stiffening effect and the axial force calculation formula. The axial force planes and the first to third order natural frequency planes which vary with the rotating speed and length were calculated in three-dimensional coordinates. The centrifugal stiffening coefficient was introduced to quantitatively study the relationship between the centrifugal stiffening degree and the rotating speed, and then the fundamental frequency correction formula was built based on the rotating speed and the blade length. The analysis results show that the calculation results of the fundamental frequency correction formula agree with the theoretical calculation results. The error of calculation results between them is less than 0.5%.

Guoyong Jin, Xiaolin Liu, Zhigang Liu and Tiejun Yang
Journal of Marine Science and Application,2011(No. 1): 88-97
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A numerical and experimental study was presented on active control of structurally radiated sound from an elastic cylindrical shell. An analytical model was developed for the active structural acoustic control (ASAC) of the cylindrical shell. Both global and local control strategies were considered. The optimal control forces corresponding to each control strategy were obtained by using the linear quadratic optimal control theory. Numerical simulations were performed to examine and analyze the control performance under different control strategies. The results show that global sound attenuation of the cylindrical shell at resonance frequencies can be achieved by using point force as the control input of the ASAC system. Better control performance can be obtained under the control strategy of minimization of the radiated sound power. However, control spillover may occur at off-resonance frequencies with the control strategy of structural kinetic energy minimization in terms of the radiated sound power. Considerable levels of global sound attenuation can also be achieved in the on-resonance cases with the local control strategy, i.e., minimization of the mean-square velocity of finite discrete locations. An ASAC experiment using an FXLMS algorithm was implemented, agreement was observed between the numerical and experimental results, and successful attenuation of structural vibration and radiated sound was achieved.

Shengqi Yu, Yiwang Huang and Weiqi Jiao
Journal of Marine Science and Application,2011(No. 1): 98-104
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Acoustic vector sensor consists of pressure and particle velocity sensors, which measure the three-dimensional acoustic particle velocity, as well as the pressure at one location at the same time. By preserving the amplitude and phase information of the pressure and particle velocity, they possess a number of advantages over traditional scalar sensors. Signal-to-noise ratio (SNR) gain (which is often called array gain) is one of such advantages and is always interested by all of us. But it is not unchangeable if the spatial correlation of the noise field varies. Much more important, it is difficult to be given if the noise becomes complex. In this paper, spatial correlation of the vector field of isotropic volume-noise and surface-generated noise has been introduced briefly. Based on the results, the combined SNR output of a vector linear array is investigated and the maximum gain is given in the specified noise. Computer simulation shows that the output of one array in the same noise is not the same in different gestures. And then we find the best gesture through SNR calculation and obtain the biggest gain, which has important meaning to guide how to deploy an array in practice. We also should use the array with respect to the characteristics of the real ambient noise, especially in anisotropic noise field.

Li Zhu1, Qingfen Li and F. G. Buchholz
Journal of Marine Science and Application,2011(No. 1): 105-112
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Fracture processes in ship-building structures are in many cases of a 3-D character. A finite element (FE) model of an all fracture mode (AFM) specimen was built for the study of 3-D mixed mode crack fracture behavior including modes I, II, and III. The stress intensity factors (SIFs) were calculated by the modified virtual crack closure integral (MVCCI) method, and the crack initiation angle assessment was based on a recently developed 3-D fracture criterion––the Richard criterion. It was shown that the FE model of the AFM-specimen is applicable for investigations under general mixed mode loading conditions, and the computational results of crack initiation angles are in agreement with some available experimental findings. Thus, the applicability of the FE model of the AFM-specimen for mixed mode loading conditions and the validity of the Richard criterion can be demonstrated.

Yinbing Zhang, Junwei Zhao, Yecai Guo and Jinming Li
Journal of Marine Science and Application,2011(No. 1): 113-120
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The problem of blind adaptive equalization of underwater single-input multiple-output (SIMO) acoustic channels was analyzed by using the linear prediction method. Minimum mean square error (MMSE) blind equalizers with arbitrary delay were described on a basis of channel identification. Two methods for calculating linear MMSE equalizers were proposed. One was based on full channel identification and realized using RLS adaptive algorithms, and the other was based on the zero-delay MMSE equalizer and realized using LMS and RLS adaptive algorithms, respectively. Performance of the three proposed algorithms and comparison with two existing zero-forcing (ZF) equalization algorithms were investigated by simulations utilizing two underwater acoustic channels. The results show that the proposed algorithms are robust enough to channel order mismatch. They have almost the same performance as the corresponding ZF algorithms under a high signal-to-noise (SNR) ratio and better performance under a low SNR.

Qiang Chen and Jianbo Liu
Journal of Marine Science and Application,2011(No. 1): 121-126
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The construction and shape of UUVs are described in the paper. UUV design is the shape of the overall design of unmanned underwater vehicle should first be resolved UUV underwater vehicle directly affects the shape of the resistance and noise, which is related to energy, payload, maneuverability and concealment UUV problem The main characteristic and parameter tables for foreign torpedo shape, flat shape and anomalous shape are also given in the paper. The general layout of typical foreign UUVs is analyzed in detail. And the total layout figure and interior constructive figure are introduced. Torpedo-type because of its good water power and low noise, no one has been the main form of underwater vehicle-like, and many designers are now highly favored because of its stable performance, anti-environmental interference capability. Other irregular shapes designed primarily for the completion of a specific task, according to the specific environment and mission requirements. According to comparing and summarizing, some suggestions and conclusions are presented.