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The accurate prediction of drag coefficients for truss-type jack-up legs is an important part of a unit's design. Over the past 14 years, a series of windtunnel tests have been conducted on both square and triangular cross-section leg configurations. A calculation method which closely fits the model test data has also been adopted. A previous paper described the early testing and the MMEC calculation method for square legs. Since then, testing and research have continued on both square and triangular leg designs. This paper describes the more recent testing performed on square legs, and it details the testing and the MMEC method for triangular legs. In addition, the effects of cornerpost design and surface roughness are discussed. Several example calculations are provided in Appendices. 相似文献
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锚在船舶操纵中的应用 总被引:1,自引:0,他引:1
锚、车、舵是船舶设备的三大要素,不能忽视锚在实践中的作用。除固定船体外,在抢险、防台风及其它紧急情况下也常用的到锚。尤其是在船舶操纵时锚的作用更为突出,是船长、引航员不可缺少的得力工具。本文着重介绍锚在港口等待泊位、等候过船闸、等候过桥及离靠码头时的应用。 相似文献
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Hiroharu Kato Kento Miura Hajime Yamaguchi Masaru Miyanaga 《Journal of Marine Science and Technology》1998,3(3):122-129
The formation of air bubbles ejected through a single hole in a flat plate was observed in uniform flow of 2–10 m/s It was
confirmed that the size of the air bubbles was governed by main flow velocity and air flow rate. According to previous experiments,
the size of the bubbles is an important factor in frictional drag reduction by microbubble ejection. Usually bubbles larger
than a certain diameter (for example 1 mm) have no effect on frictional drag reduction. Three different methods were proposed
and tested to generate smaller bubbles. Among them, a 2D convex (half body of an NACA 64-021 section) with ejection holes
at the top was the best and most promising. The diameter of the bubbles became about one-third the size of the reference ejection
on a flat plate. Moreover, the bubble size did not increase with increasing flow rate. This is a favorable characteristic
for practical purposes. The skin friction force was measured directly with a miniature floating element transducer, and decreased
drastically by microbubble ejection from the top of the 2D convex shape. 相似文献
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水下航行体通气超空泡减阻特性实验研究 总被引:7,自引:1,他引:6
为了研究超空泡的减阻效果,保证在较低流速下生成超空泡,在水洞中开展了水下航行体通气超空泡的实验研究.采用通气的方法在较低水速下生成人工通气超空泡,通过改变通气率和弗劳德数,获得了不同条件下通气空泡的长度,以及不同空泡长度下的模型阻力系数.研究表明,来流速度不变时,空泡长度随通气率的增加而增加,阻力系数随空泡长度的增加先递增后递减;空化器直径对阻力系数的影响较大,在大弗劳德数条件下,阻力系数会因空化器直径过大而出现随通气量的增加而变大的趋势.利用商用软件对超空泡形态及阻力系数作了数值仿真,并与实验结果作了对比,两者符合较好. 相似文献
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Elastic FE simulation with inherent deformation and interface element is an ideal and practical computational approach for predicting welding distortion in production of thin plate structures. In this study, recent researches on inherent deformation theory and welding induced buckling investigation of ship panel were sequentially introduced. Taking bead-on-plate welding as research objective (plate with 2.28 mm in thickness), integration approach with inherent strain was proposed to accurately and conveniently evaluate magnitude of inherent deformation. Also, average temperature to clarify the mechanism of influential effect of plate width on magnitude of inherent deformation was presented and examined. With the mechanism investigation of welding induced buckling by elastic FE analysis using inherent deformation, an application for predicting and mitigating the welding induced buckling in fabrication of ship panel with thin plates by employing different welding procedure patterns was carried out. Examined intermittent zigzag welding procedure is effective to reduce the magnitude of in-plane inherent shrinkages and control the possible welding induced buckling. 相似文献
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新型透空板式防波堤消浪效果试验研究 总被引:6,自引:0,他引:6
为增大双层板式防波堤的波能耗散和防波堤结构的稳定,提出了的一种新型桩基双层板式防波堤,通过物理模型试验,对比分析了该防波堤结构(模型 c)与另两种结构型式的防波堤(模型 a、b)在不同的波浪参数下透射系数、反射系数的变化关系,探讨了新型桩基双层板式防波堤(模型 c)透射系数、反射系数随相对波高、相对水深及相对淹没深度的变化关系,分析了其波能损耗情况。结果表明,在试验范围内,对于长周期波,模型 c 比其他两种型式的防波堤消波效果好;当水深与模型顶平齐时新结构(模型 c)对波能的消耗大于淹没和出水两种情况,说明防波堤高程与水位平齐时其消波效果较好。 相似文献
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Sayed Mohammad Reza Hodaei Mohammad Reza Chamani Mohammad Navid Moghim Shahriar Mansoorzadeh Abdoreza Kabiri-Samani 《船舶与海洋工程学报》2016,15(4):382-387
A set of experiments is carried out in a towing tank to study the effects of the curvature of perforated plates on the wave reflection coefficient (C r ). The curvature of a perforated plate can be changed by rotating a reference perforated plate aboutits origin according to the parabolic equation y=?x 2. A plunger-type wave maker is used to generate regular waves. The reflection coefficients are calculated using Goda and Suzuki’s (1976) method. The results are compared with those of vertical or sloped passive wave absorbers. The comparison shows that a perforated plate with a curved profile is highly efficient in terms of reducing the wave reflection coefficient. A correlation is established to estimate the reflection coefficient of curved perforated plates as a function of both flow and geometry characteristics. 相似文献