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481.
Comprised by a swarm of acoustically linked and cooperative autonomous underwater vehicles (AUVs) with onboard sensors, an
underwater mobile sensing network (UMSN) will be a complementary means to fixed observatory networks, e.g. seafloor observatory
networks and moored buoy arrays. It has obvious advantages over a single large AUV in higher efficiency due to parallel observation,
stronger robustness to vehicle failures and lower cost. Although an UMSN can be viewed as a counterpart of wireless mobile
sensing networks for air and terrestrial applications, it is much more challenging due to poor performance of underwater acoustic
communication, poor performance of underwater positioning and high degree of uncertainty in vehicle dynamics and underwater
environment. In order to verify key technologies involved in an UMSN, e.g. cooperation of multi-AUVs based on acoustic communication,
a low cost testbed has been developed for experimental study. The design of both hardware and software is introduced. Also
the results of a functional test for verification of the effectiveness of the testbed are presented. 相似文献
482.
A combination of methods was developed that can determine hydrodynamic forces on a planing hull in steady motion. Firstly, a potential-based boundary-element method was used to calculate the hydrodynamic pressure, induced resistance and lift. Then the frictional resistance component was determined by the viscous boundary layer theory. Finally, a particular empirical technique was applied, to determine the region of upwash geometry and determine spray resistance. Case studies involving four models of Series 62 planing craft were run. These showed that the suggested method is efficient and capable, with results that are in good agreement with experimental measurements over a wide range of volumetric Froude numbers. 相似文献
483.
Detection of weak underwater signals is an area of general interest in marine engineering. A weak signal detection scheme
was developed; it combined nonlinear dynamical reconstruction techniques, radial basis function (RBF) neural networks and
an extended Kalman filter (EKF). In this method chaos theory was used to model background noise. Noise was predicted by phase
space reconstruction techniques and RBF neural networks in a synergistic manner. In the absence of a signal, prediction error
stayed low and became relatively large when the input contained a signal. EKF was used to improve the convergence rate of
the RBF neural network. Application of the scheme to different experimental data sets showed that the algorithm can detect
signals hidden in strong noise even when the signal-to-noise ratio (SNR) is less than −40d B. 相似文献
484.
It can be beneficial to reduce vibrations in shipboard piping, so the authors designed a new kind of piping damper with a
plunger-type accumulator. Special requirements for the piping damper included low impact displacement, low speed, as well
as an appropriate locking speed. Inside the damper, a plunger-type accumulator was installed and on the outside of the piston
rod, a tube with exposed corrugations was added. Between the piston and the cylinder, a clearance seal was added. Using mathematical
modeling, the effects of the dynamic performance of the damper’s impact displacement on vibrations were observed. Changes
to the clearance between the piston and the cylinder, the stiffness of the spring in the accumulator, the throttle valve size,
and locking speed resistance of the damper were respectively simulated and studied. Based on the results of the simulation,
dampers with optimal parameters were developed and tested with different accumulator spring stiffnesses and different throttles.
The simulation and experimental results showed that parameters such as seal clearance between piston and cylinder, accumulator
spring stiffness and throttle parameters have significant effects on the damper’s impact displacement, low speed resistance
and locking speed. 相似文献
485.
水下潜器改进S面控制及控制系统仿真(英文) 总被引:1,自引:0,他引:1
S surface controllers have been proven to provide effective motion control for an autonomous underwater vehicle (AUV). However,
it is difficult to adjust their control parameters manually. Choosing the optimum parameters for the controller of a particular
AUV is a significant challenge. To automate the process, a modified particle swarm optimization (MPSO) algorithm was proposed.
It was based on immune theory, and used a nonlinear regression strategy for inertia weight to optimize AUV control parameters.
A semi-physical simulation system for the AUV was developed as a platform to verify the proposed control method, and its structure
was considered. The simulation results indicated that the semi-physical simulation platform was helpful, the optimization
algorithm has good local and global searching abilities, and the method can be reliably used for an AUV. 相似文献
486.
边界任意弹性约束薄板的横向振动(英文) 总被引:1,自引:0,他引:1
This paper presents an analytical study on the influence of edge restraining stiffness on the transverse vibrations of rectangular
plate structure. An improved Fourier series method was employed to analyze the transverse vibration of plate structure with
general elastically restrained boundary conditions. A linear combination of a double Fourier series and eight auxiliary terms
was sought as the admissible function of the flexural displacement of the plate, each term being a combination of a polynomial
function and a single cosine series expansion. The auxiliary terms were introduced to ensure and improve the smoothness of
the original displacement function and its derivatives at the boundaries. Several numerical examples were given to demonstrate
the validity and accuracy of the current solution. The influences of translational and rotational stiffness on the natural
frequencies and mode shapes of plate were analyzed by numerical results. The results show that the translational stiffness
has bigger influence on the natural frequencies than the rotational stiffness. It is generally well known that little change
of the rotational stiffness has little influence on the mode shapes of plate. However, the current work shows that a very
little change of rotational stiffness value may lead to a large change of the mode shapes of a square plate structure. 相似文献
487.
水面无人船的发展与使命(英文) 总被引:5,自引:0,他引:5
488.
船舶在规则纵浪中的混沌运动 总被引:2,自引:0,他引:2
Parametric resonance can lead to dangerously large rolling motions, endangering the ship, cargo and crew. The QR-factorization method for calculating (LCEs) Lyapunov Characteristic Exponents was introduced; parametric resonance stability
of ships in longitudinal waves was then analyzed using LCEs. Then the safe and unsafe regions of target ships were then identified.
The results showed that this method can be used to analyze ship stability and to accurately identify safe and unsafe operating
conditions for a ship in longitudinal waves. 相似文献
489.
Solid oxide fuel cell (SOFC) has been identified as an effective and clean alternative choice for marine power system. This
paper emphasizes on the dynamic modeling of SOFC power system and its performance based upon marine operating circumstance.
A SOFC power system model has been provided considering thermodynamic and electrochemical reaction mechanism. Subcomponents
of lithium ion battery, power conditioning unit, stack structure and controller are integrated in the model. The dynamic response
of the system is identified according to the inertia of its subcomponent and controller. Validation of the whole system simulation
at steady state and transit period are presented, concerning the effects of thermo inertia, control strategy and seagoing
environment. The simulation results show reasonable accuracy compare with lab test. The models can be used to predict performance
of a SOFC power system and identify the system response when part of the component parameter is adjusted. 相似文献
490.
Line heating process is a very complex phenomenon as a variety of factors affects the amount of residual deformations. Numerical
thermal and mechanical analysis of line heating for prediction of residual deformation is time consuming. In the present work
dimensional analysis has been presented to obtain a new relationship between input parameters and resulting residual deformations
during line heating process. The temperature distribution and residual deformations for 6 mm, 8 mm, 10 mm and 12 mm thick
steel plates were numerically estimated and compared with experimental and published results. Extensive data generated through
a validated FE model were used to find co-relationship between the input parameters and the resulting residual deformation
by multiple regression analysis. The results obtained from the deformation equations developed in this work compared well
with those of the FE analysis with a drop in the computation time in the order of 100 (computational time required for FE
analysis is around 7 200 second to 9 000 seconds and where the time required for getting the residual deformation by developed
equations is only 60 to 90 seconds). 相似文献