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排序方式: 共有163条查询结果,搜索用时 78 毫秒
111.
Kamlesh S.?VaryaniEmail author Appapillai?Thavalingam Parmeswarn?Krishnankutty 《Journal of Marine Science and Technology》2004,9(1):24-31
To improve the formulation of ship–ship interaction forces and moments in a mathematical model of a ship maneuvring simulator, we developed a new generic mathematical model for the overtaking maneuver. This process involves using the numerical results, which provide a potentially complete set of data from which (within the constraints of the numerical modelling) everything necessary can be acquired. We found that the new generic mathematical model is as accurate as the numerical model. It is also more accessible to a navigator, master, or pilot, who could use it on a palmtop computer by keying in a few numberical estimates of the size, position, and speed of the neighboring ship and receive almost instant aneous results, giving time for a refined strategy to be validated if necessary. These results can also readily be used by simulation program developers to simulate the worst possible scenarios. 相似文献
112.
Goutam Kumar?SahaEmail author Kazuo?Suzuki Hisashi?Kai 《Journal of Marine Science and Technology》2004,9(2):51-62
A computational method for improving hull form in shallow water with respect to wave resistance is presented. The method involves coupling ideas from two distinct research fields: numerical ship hydrodynamics and nonlinear programming techniques. The wave resistance is estimated by means of Morinos panel method, which is extended to free surface flow and considers the influence of finite depth on the wave resistance of ships. This is linked to the optimization procedure of the sequential quadratic programming (SQP) technique, and an optimum hull form can be obtained through a series of iterations giving some design constraints. Sinkage is an important factor in shallow water, and this method considers sinkage as a hydrodynamic design constraint. The optimization procedure developed is demonstrated by selecting a Wigley (C
B = 0.444) hull and the Series 60 (C
B = 0.60) hull, and new hull forms are obtained at Froude number 0.316. The Froude number specified corresponds to a lower than critical speed since most of the ships operating in shallow water move below their critical speed. The numerical results of the optimization procedure indicate that the optimized hull forms yields a reduction in wave resistance. 相似文献
113.
Roberto?MuscariEmail author Andrea?Di Mascio 《Journal of Marine Science and Technology》2004,9(4):158-170
A new model for the simulation of spilling breaking waves in naval flows is presented. The hydrostatic pressure is used in order to mimic the weight of the breaker on the underlying flow, as in the model of Cointe and Tulin, whereas the algorithm for detecting the breaking inception and the definition of its geometry are completely new and are suitable for the simulation of three–dimensional flows around ships hulls. The model has been implemented in a finite-volume code developed for naval flows, and its performances have been validated against experimental data for a submerged profile, an S60 hull in drift motion, and the US Combatant DTMB 5415 model on a straight course. 相似文献
114.
A 2D+T VOF fully coupled formulation for the calculation of breaking free-surface flow 总被引:1,自引:0,他引:1
Yann?AndrillonEmail author Bertrand?Alessandrini 《Journal of Marine Science and Technology》2004,8(4):159-168
We present the results of simulations obtained with a free-surface flow solver based on the following method. The free surface is simulated by the volume-of-fluid interface capturing method. This code solves the Navier–Stokes equations using a finite-volume method adapted to a structured or unstructured mesh. The system is constructed using a fully coupled approach. This global approach allows the simulation of complex flow as a breaking or merging wave. Moreover, with the use of a 2D+T decomposition, it is possible to simulate three-dimensional steady flow. 相似文献
115.
Choung Mook?LeeEmail author Dong Gi?Han Kwan Hyoung?Kang Sang Joon?Lee 《Journal of Marine Science and Technology》2004,8(3):117-125
The behavior of the flow passing a tandem oil fence, and the performance of the fence, were investigated by experimental and numerical methods. The flow characteristics between tandem fences were measured by the particle image velocimetry (PIV) method for the rigid and open free surface between the two fences in order to gather reference data for numerical investigations. A method of assessing a tandem fence by tracing the movement of an oil droplet around the fence is introduced. The effect of the current speed, the separation distance between the two fences, the relative draft of the two fences, and the water depth on the oil containment between the fences was investigated. 相似文献
116.
In actual control systems, many types of restrictions or nonlinearities exist. For example, owing to nonlinearities in the actuators or sensors, the controller may not be applicable in some practical situations. Such a nonlinearity is amplitude saturation in actuators. Although it may sometimes be ignored, failure to consider actuator saturation may severely degrade the performance of a closed-loop system, and even lead to instability. On the other hand, limiting the controller gain to avoid saturation sacrifices control effort, and may lead to loss of performance. Many approaches have been tired in order to overcome these undesirable problems, and some good results have been obtained. The saturation has been replaced with a gain which is calculated as a function of the variance of the signal at its inputs. Based on this assumption, some attractive control theories have been introduced. Here, we introduce a useful anti-wind-up control system. In other words, the control system proposed has a very simple design process and can guarantee good control performance, as it is based on the assumption that the saturation is replaced with a varying gain. The validity of the proposed control system will be shown by comparing some simulation results. 相似文献
117.
Nonlinear analysis of parametric rolling in longitudinal and quartering seas with realistic modeling of roll-restoring moment 总被引:4,自引:0,他引:4
Hirotada?HashimotoEmail author Naoya?Umeda 《Journal of Marine Science and Technology》2004,9(3):117-126
Parametric rolling of a containership in longitudinal and quartering seas is examined by applying nonlinear dynamics to a 1DOF mathematical model with realistic modeling of the wave effect on roll-restoring moment. In our previous work, we confirmed that a mathematical model with a roll-restoring moment in waves calculated with the Froude–Krylov assumption could considerably overestimate the danger of capsizing associated with parametric rolling. Therefore, in the present work, all numerical calculations based on nonlinear analysis were carried out with the direct aid of a measured roll-restoring moment in waves. For this purpose, captive model experiments were conducted for various sets of wavelengths in longitudinal seas. This experiment demonstrates that the Froude–Krylov prediction could not explain the wavelength effect on restoring moment as the wave-steepness effect. Using the numerical model with the aid of this measured roll-restoring moment, the Poincaré mapping technique was applied to identify bifurcation structures of roll motions not only in longitudinal seas, but also in quartering seas. As a result, it was confirmed that capsizing associated with parametric rolling is more likely to occur in following seas than in quartering seas. However, period-doubling and chaos appeared in quartering seas. Finally, an averaging method assuming a period-2 orbit was applied to the same model with the same conditions as the Poincaré map. Reasonably good agreement was obtained between the numerical results with a Poincaré map and those with the averaging method in longitudinal seas, but the averaging method has limited capability in quartering seas. 相似文献
118.
Investigation of cavitation inception characteristics of hydrofoil sections via a viscous approach 总被引:1,自引:0,他引:1
Shiu-Wu?ChauEmail author Kun-Lin?Hsu Jen-Shiang?Kouh Yen-Jen?Chen 《Journal of Marine Science and Technology》2004,8(4):147-158
Unlike traditional approaches based on potential theory, this work investigated the cavitation inception characteristics of hydrofoil sections by solving Reynolds-averaged Navier–Stokes (RANS) equations. The viscous effects at high Reynolds numbers were taken into account through calculation of the eddy viscosity using a k- model. This viscous approach delivers the lift and drag forces in a more self-contained way, which cannot be obtained directly from the potential theory. A comparison with smooth surface measurements validates the proposed numerical method. Two approaches to include the roughness effects are also described. The predictions of cavitation bucket characteristics based on potential theory are more conservative than those reached by the proposed viscous computations. Hydrofoil sections with different camber ratios, foil thicknesses, and Reynolds numbers were studied numerically. A decrease in the Reynolds number tends to increase the cavitation-free region without changing the shape of the steep region. An increase in foil thickness gives a range increase in the angle of attack where no cavitation is expected. An increase in the camber ratio moves the cavitation-free location of the angle of attack, and slightly increases its range. 相似文献
119.
D.?Savitski V.?IvanovEmail author B.?Shyrokau T.?Pütz J.?De?Smet J.?Theunissen 《International Journal of Automotive Technology》2016,17(2):327-338
Functions of anti-lock braking for full electric vehicles (EV) with individually controlled wheel drive can be realized through conventional brake system actuating friction brakes and regenerative brake system actuating electric motors. To analyze advantages and limitations of both variants of anti-lock braking systems (ABS), the presented study introduces results of experimental investigations obtained from proving ground tests of all-wheel drive EV. The brake performance is assessed for three different configurations: hydraulic ABS; regenerative ABS only on the front axle; blended hydraulic and regenerative ABS on the front axle and hydraulic ABS on the rear axle. The hydraulic ABS is based on a rule-based controller, and the continuous regenerative ABS uses the gain-scheduled proportional-integral direct slip control with feedforward and feedback control parts. The results of tests on low-friction road surface demonstrated that all the ABS configurations guarantee considerable reduction of the brake distance compared to the vehicle without ABS. In addition, braking manoeuvres with the regenerative ABS are characterized by accurate tracking of the reference wheel slip that results in less oscillatory time profile of the vehicle deceleration and, as consequence, in better driving comfort. The results of the presented experimental investigations can be used in the process of selection of ABS architecture for upcoming generations of full electric vehicles with individual wheel drive. 相似文献
120.
This study investigates the effects of sociodemographic and economic status on the differences in environmental awareness, risk perception, and stewardship of the Mekong Delta residents based on a survey conducted in person with 1,006 households across the delta system. Spatial visualization and a multiple correspondence analysis (MCA) were performed on the survey results to discover underlying factors of the participants' responses. The study results revealed that public environmental awareness in the Mekong Delta is still limited. The level of environmental awareness, risk perception, and understanding of stewardship of local people varies by location. Furthermore, how the Mekong Delta dwellers perceive environmental risks and behave toward environmental protection is unlikely to be influenced by their demographic profiles. However, they are significantly affected by the economic status including income levels and sources. Poor economic status was found to significantly hamper pro-environmental behavior of Mekong Delta people regardless of their knowledge of environmental degradation and the related consequences. These findings provide key information to assist policymakers in developing a successful and sustainable disaster risk reduction mitigation plan for the Mekong Delta region. The implications may also be applicable for other coastal zones, which are composed of similar sociodemographic, economic, and environmental conditions. 相似文献