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1.
The ice resistance on ships in escort operations in level ice are investigated using the discrete element method (DEM). A dilated polyhedron—generated by the Minkowski sum of a sphere and a polyhedron—is employed in the DEM; this dilated polyhedron-based DEM (DPDEM) is adopted to simulate the ship–ice interaction, wherein the contact force and bond-failure criterion are considered for the collision and fracture of sea ice, respectively. A three-point bending test was simulated with DPDEM, and a field test was conducted in the Bohai Sea to validate the DEM results. Further, a parametric analysis of flexural strength was conducted to identify the parameters involved in the bond-failure criterion. The ice resistance on icebreakers and cargo ships in level ice are simulated using DPDEM. The simulated ice resistances are compared with the Lindqvist and Riska formulas and the model test, which proves the validity of the DEM simulation. The interaction between ships and level ice is simulated parametrically to investigate the ice resistance on cargo ships with and without the icebreaker escort. Influencing factors such as ship speed, ice thickness, and ship breadth were examined to investigate the ice resistance on the escorted cargo ship. Analysis and change rules of the ice resistance on cargos affected by those factors were given. 相似文献
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Numerical study of ice-induced loads on ship hulls 总被引:1,自引:0,他引:1
A numerical model is introduced in this paper to investigate both global and local ice loads on ship hulls. This model is partly based on empirical data, by which the observed phenomena of continuous icebreaking can be well reproduced. In the simulation of a full-scale icebreaking trial, the interdependence between the ice load and the ship’s motion is considered, and the three degree-of-freedom rigid body equations of surge, sway and yaw are solved by numerical integration. The variations in the level ice thickness and in the strength properties of ice can also be taken into account. The simulated ice loads on ship hulls are discussed through two case studies, in which the ship’s performance, the statistics of ice-induced frame loads, and the spatial distribution of ice loads around the hull are analyzed and compared with field measurements. As far as we know the present paper is the first to integrate all the features above. It is hoped that further studies on this numerical model can supplement the field and laboratory measurements in establishing a design basis for the ice-going ships especially for ships navigating in the first-year ice. 相似文献
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船舶在冰区航行时的冰阻力性能一直是国内外关注和研究的重点。冰阻力的研究主要集中在经验方法、数值模拟和实验研究三个方面。同时,由于冰区船舶在航行过程中频繁地与冰层或浮冰产生碰撞,海冰的材料结构和力学性质对冰阻力的研究有重要影响。文章从冰的物理力学特性出发,简要回顾几种重要的冰本构关系模型及其适用性;并从经验方法及试验与数值模拟相结合两个角度,回顾和讨论浮冰区和平整冰区中船舶的冰阻力性能研究进展;最后,基于研究现状提出尚需进一步解决的问题。文章旨在介绍冰区船舶冰阻力性能的研究进展,望能为后续冰阻力研究提供参考。 相似文献
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在船舶和海洋工程结构中,裂纹扩大时的载荷流泄现象已被大尺度疲劳试验中裂纹扩展速度减慢所证实。影响疲劳裂纹扩展的因素具有随机性质,因而研究载荷流泄对船舶和海洋工程结构疲劳可靠性的影响是有意义的。本文用Paris公式,结合改进的第二水准法,计算了一个实例,给出了考虑和不考虑载荷流泄疲劳可靠性分析的两种结果。结果的区别表明,如果要期望得到更合理的结果,则在船舶和海洋工程结构的疲劳分析中必须计及载荷流泄。 相似文献
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This study investigates the repeatability of ice-tank tests with broken ice. Ice-tank test campaigns normally do not perform multiple repetitions of tests with the same initial conditions. Therefore, the repeatability of ice-tank tests with broken ice is not well understood. Data from two test campaigns are analysed. The first test campaign studied the interaction between a 4-legged structure with a vertical waterline and several broken and intact level ice conditions. In the second test campaign, a ship hull geometry was tested. We analyse selected test cases from each test campaign. The ice-tank tests are reproduced using a 3-D discrete element method (DEM) model. Each analysed test case is simulated 20 times. The only difference between each simulation is the initial position of the ice floes. The numerical simulation results show that changes in the initial floe positions can cause large changes in the statistical properties of the ice load. Often, a single random interaction event can be identified that is responsible for the change in the results. Such interaction events can cause additional floe accumulation ahead of the structure, thereby influencing the load statistics for a large portion of the interaction length. The observed events occur both in the numerical simulations and in the physical ice-tank tests. This result indicates that ice-tank tests with broken ice have a poor repeatability; a change in an uncontrolled condition, such as the exact initial floe positions, can lead to a large variation in the experimental results. 相似文献
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Yasumi Toyama 《Marine Structures》2009,22(1):24-41
Impact load estimation of drift-wood hitting against the bow structure of high-speed vessels has been investigated. It may be difficult for the craft operator to detect in advance a drift-wood floating just below the ocean surface and to avoid the collision with it. It is particularly difficult for operators of the high-speed vessels in night cruising mode. The probability of the accident may be higher than that of the collision with rocks or other ships because of the difficulties of early detection of the floating object. Impact loads are estimated for drift-wood of different sizes and craft speed considering whipping motion and local crushing of the wood at the hitting region. A simplified formula for the load estimation is proposed based on the modal approach and the energy balance. Predicted impact loads can be applied to the initial design of the bow structure and collision bulkhead of the craft to secure the structural safety against a possible accident. 相似文献
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冰阻力是影响船舶在冰区航行性能的关键因素。当前主要的冰阻力研究方法有经验公式法、模型/实船试验法和数值模拟方法。数值模拟方式能够对船舶破冰的全过程进行快速模拟,且模拟成本低,参数易于控制 、结果较为准确,是一种比较适宜的冰阻力预报方法。随着计算技术的进步,各种数值模拟方法层出不穷,其中包括基于网格单元的有限元模型,基于无网格方法的离散元模型、SPH法、近场动力学模型等;近年来,网格模型与无网格模型的耦合方法也逐渐发展起来。文章简要梳理了冰区航行船舶冰阻力数值研究的进展,并基于研究现状提出尚需进一步解决的问题,意在为进一步提高冰阻力数值模拟精度提供参考。 相似文献
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In the structural design of the Polar Class ships, glancing impact with ice has been considered as the governing load scenario for dimensioning the bow structure. At present, non-linear transient dynamic analysis has been reckoned as a fundamental requirement in the assessment of the structural strength of ships with higher ice classes. Under such requirement, understanding of the dynamic characteristics of the ship-ice impact load appears significant importance. The present study aims to investigate the spatial and temporal variations of the impact loads by simulating the glancing impact events between a polar research vessel and giant ice floes in ice tank. The ship-ice impact loads were recorded by a grid-based tactile sensor attached on the bow area of the model ship. To achieve a reasonable simulation on the design scenario described by the IACS Unified Requirements for Polar Class Ships (UR I), a series of methodological calibration tests were preliminarily carried out to determine the key parameters that should be carefully monitored and controlled, accompanying with thorough discussions on the ship-ice impact process. This paper provides detailed information on the preliminary methodological calibrations and the tactile data processing techniques, including the identification of the ship-ice contact area, the depiction of the ice loading trail and the outline of the spatial distributions of local ice pressures. A companion paper provides detailed analyses and discussions regarding the spatial and temporal variation of the ice impact loads from the formal tests based on the proposed testing procedures obtained by the methodological calibrations. 相似文献
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Ice loads are important environmental loads that can influence the structural safety of ships during navigation in ice-covered waters. The identification of ice loads on ship hulls is the core of ice load monitoring. In this study, a new ice load identification model based on Green kernel and regularization methods is established. First, the forward model for ice load identification is developed through the discretised convolution integral of ice loads. Next, three commonly used regularization methods, including Tikhonov, truncated singular value decomposition, and least square QR-factorization (LSQR) are adopted to reduce solution errors. The LSQR method is thereafter selected as the optimal regularization operator, and its regular property is proved by numerical cases with ice-induced strains that contain noise. Finally, two load identification cases are conducted on an experimental rig to evaluate the feasibility of the model in ice load identification. The identified loads can determine the signal features of applied loads in the time domain with good accuracy. This identification model provides new insights for full-scale ice load monitoring. 相似文献
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Glacial ice features in the northern and central Barents Sea may threaten ships and offshore structures. Particularly, small glacial ice features, which are difficult to detect and manage by concurrent technologies, are of concern. Additionally, small glacial ice features are more susceptible to wave-driven oscillatory motions, which increases their pre-impact kinetic energy and may damage ships and offshore structures. This paper is part of three related papers. An initial paper (Monteban et al., 2020) studied glacial ice features’ drift, size distribution and encounter frequencies with an offshore structure in the Barents Sea. The following two papers (Paper I and Paper II) further performed glacial ice impact studies, including impact motion analysis (Paper I) and structural damage assessment (Paper II). This paper (Paper I) studies the wave-driven motion of small glacial ice features and their subsequent impact with a given offshore structure. The aim here is to develop a numerical model that is capable of efficiently calculating the relative motion between the ice feature and structure and to sample a sufficient amount of impact events from which statistical information can be obtained. The statistical information entails the distributions of the impact location and associated impact velocities. Given the distributions of the impact velocities at different locations, we can quantify the kinetic energy for related impact scenarios for a further structural damage assessment in Paper II (Yu et al., 2020).In Paper I, a numerical model that separately calculates the wave-driven oscillatory motion and the mean drift motion of small glacial ice features is proposed, implemented and validated. Practical and fit-for-purpose hydrodynamic simplifications are made to simulate and sample sufficient impact events. The numerical model has been favourably validated against existing numerical results and experimental data. A case study is presented where a 10 m wide glacial ice feature is drifting under the influence of surface waves towards an offshore structure. The case study shows that if an impact happens, the overall impact location and impact velocity can be best fitted by the Normal and Weibull distributions, respectively. Additionally, the impact velocity increases with impact height. Moreover, the impact velocity increases and the impact range is more dispersed in a higher sea state. It is also important to notice that the approaches and methods proposed in this paper adhere to and reflect the general requirements stated in ISO19906 (2019) and NORSOK N-003 (2017) for estimating the design kinetic energy for glacial ice impacts. 相似文献
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Based on the design ice load that corresponds to a certain return period, a practical approach for designing the frames behind the side-shell or the bow of a ship subject to ice loading is proposed. Four typical types of section profiles have been selected for modelling and numerical analysis. Non-linear finite element analyses that involve both the geometric and material non-linearity were performed. From the analyses, the relationships between the loads and the beam's cross-section properties were obtained for different permanent set requirements. These relationships were then used for finding the section modulus from which the cross-section of the beam can be decided. Finally, a design example is presented for illustration. 相似文献
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The interaction of ice with a polar ship is complex, which may involve several ice failure mechanisms such as local crushing, tensile, cracking, bending, shearing, sliding and the ship structures could attain permanent deformations. A reasonable modeling of ice behavior is, therefore, critical to the analysis of ship-ice interactions. This paper reports an experimental and numerical study on the behavior of stiffened panels subject to the impact of a wedge-shaped ice block/indenter. The tested stiffened panel was mounted to a Falling Weight Impact Tester, and measurements were taken to help understand the dynamic responses of the structure and the ice, and also the permanent deformations. Finite element analyses using ABAQUS/EXPLICIT were also performed for the lab tests. The proposed ice model features a multi-surface yield function, empirical failure criteria for a few ice failure modes, and a representation of the remaining load carrying capacity of crushed ice. This ice model is implemented in a user-defined subroutine VUMAT and uses the cohesive element in a numerical solution. The predicted and measured impact force and structural deformation compared very well with the tests, indicating that the proposed ice model coded in VUMAT is reasonable. A series of parametric studies was then carried out to identify the key parameters of this new ice model that would have major effects on the prediction of ice impacts. The paper intends to provide test data that may be useful in understanding the complex ice-ship interaction and to introduce a numerical solution with a new ice model that improves the simulation of high-energy ice-ship impacts. 相似文献
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传统的平头方尾型运输船舶具有载重大、吃水浅的优点,但航行阻力大,航速低。本文针对该船型开展了开槽减阻的研究,通过在船底开设纵向槽道对艏部高压区进行引流减阻,来实现该船型高航速运输的要求。船体流场及阻力采用RANS方法进行数值模拟,并计及航行姿态的变化。通过改变槽道长度、宽度以及槽道顶板的形状,研究了减阻效果与槽道几何尺度的关系。针对某型船船的研究表明,船底槽道的引流量是影响减阻效果的主要因素,当采用纵向贯穿的槽道,且槽道顶板的折角点设在船中时,可使原船30节时的减阻率达到24%以上。 相似文献
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铝合金游艇外板由于造型面积与曲率变化较大,且包含许多局部深抽等复杂特征,使其冲压成形较为困难。为分析其成形缺陷并进行优化设计,采用有限元法对铝合金游艇外板进行冲压特征、缺陷成因及影响因素分析,并提出一种具有平缓特征的工艺补充面设计来克服成形缺陷。数值计算结果表明:降低压料力可改善局部拉伸,但厚度增加较少,通过优化外型参数可改善球鼻艏区域的破裂缺陷,但反向船脊区域的褶皱也因压料力的减小而更加严重;阻料条使反向船脊的褶皱大幅度减少,船首褶皱完全改善;基于平缓特征的工艺补充面造型设计可解决球鼻艏尖点造型所产生的局部拉伸,反向船脊缺陷也得到改善,船尾底壳褶皱缺陷经造型往外延伸得以移至工艺补充面部分。经优化设计后,铝合金游艇外板冲压缺陷均得到改善。 相似文献
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在冰区油气开发中,锥体结构可以有效降低冰力,避免强烈的冰激振动,是目前渤海油气平台的主要结构形式。为研究海冰与锥体结构的相互作用过程,文章建立了适用于模拟海冰破碎特性的离散单元模型。该模型将海冰离散为若干个具有粘接-破碎功能的颗粒单元,并通过海冰弯曲试验确定了单元间的粘接强度;然后对海冰与锥体结构的作用过程进行了数值计算,获得了相应的动冰荷载及冰振响应;在此基础上讨论了不同锥角影响下冰荷载及结构振动响应的变化规律。结果表明,水平方向冰荷载及结构冰振响应随锥角的增加明显增加,而竖直方向冰荷载则显著降低。该离散单元模型还可进一步应用于不同类型抗冰结构的冰荷载分析,有助于解决冰区结构物的抗冰结构设计和冰致疲劳分析。 相似文献