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41.
为指导轮缘推进器(RDT)水动力学设计,借助CFD方法,对RDT各主要几何特征对其水动力性能影响开展研究。首先,验证CFD数值方法分析RDT水动力特性的有效性;然后,基于CFD研究RDT水动力性能的各主要影响因素,主要包括导管的长径比、扩散比、导管收缩比和桨叶梢径比。结果表明:RDT最佳长径比随载荷系数递增,并趋于一极限值,相比于导管扩散比和收缩比,导管长径比因素更能主导RDT的设计优化;RDT最佳扩散比随载荷系数递减,并趋于一极限值,最佳扩散比随长径比递减;RDT的收缩比对水动力性能影响不及扩散比和长径比显著,最佳收缩比随载荷系数呈线性递增,随长径比递减;RDT的最佳梢径比随载荷系数递增,无毂RDT比有毂RDT具有更小的最优梢径比。研究结果可为轮缘推进器的水动力学设计和优化提供参考。 相似文献
42.
The mathematical modeling group (MMG) model is well known and is widely used in the field of ship maneuverability. However,
the MMG model can be applied only after determination of the hydrodynamic coefficients either from comprehensive captive model
tests or from general empirical data. Around the cruising speed, when a ship's drift angle is relatively small, several methods
have been developed to predict hydrodynamic coefficients from the ship's principal particulars, e.g., Kijima's method. Kijima's
method is efficient in predicting the ship's maneuverability at the initial design stage and is even able to assess the effect
of changes in stern design. Similarly, for the low speed range when a ship's drift angle is relatively large, several methods
for predicting the ship's hydrodynamic coefficients have been proposed, based on captive model tests, such as those by Kose,
Kobayashi, and Yumuro. However, most of the methods developed for low speeds cannot be applied to general ship types without
additional experiments being performed. In contrast, Karasuno's method uses theoretical and empirical approaches to predict
the hydrodynamic forces, even for large drift motions. Although Karasuno's model utilizes the ship's principal particulars
and is applicable to a general vessel, it has not been widely used. This is because the form of Karasuno's model is relatively
complicated and its accuracy around the cruising speed is less than that for other methods that have been specifically developed
for the cruising speed range. A practical method for predicting hydrodynamic forces for the entire operating speed range of
blunt-body ships is proposed in this article. It is based on the MMG model and predicts hydrodynamic coefficients based on
a ship's principal particulars. A regression model for the proposed method has also been proposed by analyzing 21 different
blunt-body ships. Finally, simulations of a very large 4-m crude carrier (VLCC) model using the proposed method were carried
out and the results compared with free-running experiments (both at the cruising speed and at low speeds) to validate the
efficacy of the model. 相似文献
43.
This paper investigates the hydrodynamic damping of a smooth circular cylinder undergoing forced oscillations at Keulegan-Carpenter (KC) numbers smaller than 5 and Reynolds (Re) numbers from 103–105 with and without background steady currents. A series of experiments are conducted with a circular cylinder oscillating in still water, in-line currents and cross currents. The measured drag coefficients of the smooth cylinder in the still water condition match with the well-published results and the theoretical solution of Stokes and Wang at very small KC numbers. The hydrodynamic damping increases with the in-line steady current whereas it remains almost constant at small transverse velocities and increases notably when the latter becomes large. To predict the hydrodynamic damping in in-line steady currents, the performance of the Morison equation based on relative velocity and independent velocity is explored, respectively. The latter model, by separating the drag into two independent parts, leads to a better fit of the drag force than the former, which is not surprising. However, the former is still a preferable option for engineering design due to its simplicity. The experimental data suggest that the existing design guidelines such as ISO-19902 or DNVGL-RP-C205 should be used with caution for KC < 5. 相似文献
44.
45.
Ken Takagi 《Journal of Marine Science and Technology》2006,11(2):100-110
The diffraction and radiation problems of a two dimensional multihull structure were investigated by application of the scattering
matrix theory. The scattering matrix theory is widely used to analyze wave interaction problems in various scientific fields.
The research is focused on the zeros of the wave exciting force near resonance, which occurs both in the diffraction problem
and the radiation problem. At the zeros of the wave exciting force, the wave exciting force for the overall structure is zero,
but each demihull undergoes wave excitation. At near-resonant frequencies, the amplitude of the traveling wave between adjacent
demihulls becomes very large and the demihulls experience very large wave forces. A number of simple equations for representing
the hydrodynamic properties of the multihull structure at the zeros and near-resonant frequencies are obtained. Numerical
examples show that these simple equations well explain the hydrodynamic forces and the wave system in the spaces between the
demihulls. 相似文献
46.
David C.M. Miller Coleen L. Moloney Carl D. van der Lingen Christophe Lett Christian Mullon John G. Field 《Journal of Marine Systems》2006,61(3-4):212
A particle-tracking individual-based model (IBM) coupled with a 3-D hydrodynamic model was used to investigate how spatial variability in spawning and nursery grounds may influence transport and retention of sardine (Sardinops sagax) eggs and larvae in the southern Benguela ecosystem. A temperature-dependent Bělehrádek development model based on laboratory growth data was used to determine the duration of one egg and two larval stages. Successful transport/retention depended on each particle's stage of development rather than its age. Results show that recruitment could occur in two distinct nursery areas on the west and south coasts of South Africa. Three viable recruitment ‘systems’ were identified: two are retention-based (spawned and retained on the west coast (WC–WC) or the south coast (SC–SC)) and one is transport-based (spawned on the south coast and transported to the west coast (SC–WC)). In the WC–WC system, the vertical distribution of eggs influenced retention; at intermediate depths of spawning (25–50 m) eggs avoided both offshore Ekman drift and deep cold water. In the SC–SC system, the area of spawning was important; > 50% of eggs from the eastern Agulhas Bank (EAB) were retained in the south coast nursery grounds, whereas very few eggs were transported there from west of Cape Agulhas. In the SC–WC system, area of spawning was also important; 40% of the eggs spawned on the western Agulhas Bank (WAB) were transported to the west coast nursery ground. Sardine life history strategy could be divided between two main systems: the west coast system (spawning on the WAB and WC, and recruiting to the WC) and the Agulhas Bank system (spawning on the central and eastern Agulhas Bank, and recruiting to the SC). 相似文献
47.
Torpedo anchors are an innovative and cost-effective technology in marine foundation engineering; however, there is a lack of systematic and comprehensive studies on the influence of torpedo anchor geometry on its hydrodynamic characteristics, especially the effect of anchor fin configuration on the hydrodynamic characteristics is rarely reported in the existing literature. Therefore, this study investigates the influence of geometric characteristics of both finless and finned torpedo anchors on their terminal velocity, drag coefficient and installation directional stability in water through CFD numerical analysis in a systematical manner. The considered geometric characteristics include the center of gravity position, shape and angle of anchor tip, shaft and fin aspect ratio, fin number, fin thickness, fin shape, fin position and fin area. Based on the obtained numerical results, some practical design recommendations and impact weighting charts of different anchor geometric factors are provided, which enables a quick qualitative and quantitative assessment of torpedo anchors. In addition, a simple weight-based approach for estimation of terminal velocity and drag coefficient of torpedo anchors considering multiple geometric configuration factors is proposed, which may provide some reference and scientific guidance for experimental and engineering design of torpedo anchors. 相似文献
48.
船舶操纵水动力导数的灵敏度分析是简化和重建船舶操纵运动数学模型的主要手段。本文使用平方损失函数方法对船舶操纵水动力导数进行灵敏度分析,并基于灵敏度分析结果对Mariner船的操纵运动数学模型进行简化。通过基于简化模型和原始数学模型的操纵运动仿真对比,验证了基于损失函数法的船舶操纵水动力导数灵敏度分析方法的有效性。 相似文献
49.
用源分布方法求解浅水中二维任意剖面在自由表面上垂荡的附加质量和阻尼系数 总被引:2,自引:1,他引:2
用源分布方法求解了二维任意剖面在浅水中垂向振荡问题,计算了系列60方型系数0.7船型剖面在不同水深吃水比情况下的垂荡水动力系数,讨论了水深对水动力系数的影响,并与Frank无限水深的结果作了比较。研究结果表明,水深对二维船型剖面水动力系数具有较大的影响。这种影响在水深吃水比小于5.0时已相当明显,当水深吃水比小于2.0时将变得显著。另外,水深对水动力系数的影响与振荡频率有关,并且在低频处更为明显。 相似文献
50.