Extensive study on the design loads used for strength assessment of tanker and bulk carrier structures

ClassNK has undertaken wide-ranging basic research covering many aspects related to the safety of ship structures, including design loads, structural analysis, strength assessment of buckling, collapse, and fatigue, and rational corrosion margins to develop new design standards which have transparency and consistency. Among the wide-ranging basic research, this article summarizes the results of extensive work on the design loads used for strength assessments of tanker and bulk carrier structures. The main aim of the research was to develop practical estimation methods of design loads with rational technical backgrounds relating to the actual loads acting on the primary structural members of tankers and bulk carriers. During this study, we proposed the following methodology. Design sea states that closely resemble the actual sea states which are considered to be the most severe for hull structures. Find practical estimation methods for the design sea states by parametric studies using the results of series calculations on representative tankers and bulk carriers. Find practical estimation methods for design regular waves which will result in the same level of stresses as those induced in irregular waves under the design sea states. We also briefly introduced some practical estimation methods for the design loads, such as ship motions, accelerations, hull-girder bending moments, and hydrodynamic pressures that are induced under design regular waves. The findings in this study have been summarized and implemented in the new design standards for tanker and bulk carrier structures.Updated from the Japanese original which won the 2003 SNAJ prize (J Soc Nav Archit Jpn 2002; 191:195–207; 2002; 191:208–220; and 2002; 192:723–733)     

Evaluation of added resistance in regular incident waves by computational fluid dynamics motion simulation using an overlapping grid system

A computational fluid dynamics simulation method called WISDAM-X was developed to evaluate the added resistance of ships in waves. The Reynolds-averaged Navier–Stokes (RANS) equation was solved by the finite-volume method and a MAC-type solution algorithm. An overlapping grid system was employed to implement rigorous wave generation, the interactions of ships with incident waves, and the resultant ship motions. The motion of the ship is simultaneously solved by combining the solution of the motion of the ship with the solution of the flow about the ship. The free surface is captured by treatment by the density-function method. The accuracy of WISDAM-X is examined by a comparison with experimental data from a container carrier hull form, and shows a fairly good agreement with respect to ship motion and added resistance. Simulations were also conducted for a bow-form series of a medium-speed tanker to examine the effectiveness of the WISDAM-X method as a design tool for a hull form with a smaller resistance in waves. It was confirmed that the WISDAM-X method can evaluate the added resistance with sufficient relative accuracy and can be used as a design tool for ships.     

Flexural gravity wave generation by initial disturbances in the presence of current

The effect of uniform current on the generation of flexural gravity waves resulting from initial disturbances at a point was analyzed in two dimensions. The problem was formulated as an initial boundary value problem under the assumptions of the linearized theory of water waves. By direct application of the Laplace transform and then the Fourier transform, explicit expressions for the velocity potential and free surface elevation were obtained in integral forms; these were evaluated asymptotically for large distances and times by the application of the method of the stationary phase to obtain the far field behavior of the surface elevations in specific cases. Simple numerical computations were performed to illustrate the effect of uniform current on the surface elevation, wavelength, phase velocity, and group velocity of the flexural gravity waves and on the far field behavior of the progressive waves in two different cases, namely, when there is an initial depression concentrated at the origin and an initial impulse concentrated at the origin.     

Wave and sea level monitoring and prediction in the service module of the Global Ocean Observing System (GOOS)

The need for a Global Ocean Observing System Global (GOOS) is now widely appreciated. Parts of GOOS are currently being implemented already. In this paper, written on the request of the joint Scientific and Technical Committee of GOOS, we present some of the scientific issues that need to be addressed for the further development of the Ocean and Marine Meteorology Service module of GOOS. This module is concerned with monitoring and prediction of sea level (both tsunamis and storm surges) and wind driven waves (wind–sea and swell), among other things. For each of these we discuss the current state-of-the-art, indicate what observations are needed and make suggestions for future modelling development.     

坡度对波浪统计特征的影响

为了明确坡度对不同波浪统计特征的影响,利用数值模型对波浪在不同坡度斜坡上的传播进行模拟,分析波浪的非线性参数和波高分布等,比较不同坡度下波浪的传播特性。结果表明,在相同条件下,随着波浪在斜坡地形上传播,波高会随着水深的变浅逐渐增大;坡度对于波浪的波高分布具有较大影响,当坡度较大时,波浪传播至斜坡较浅水深时的波高分布接近瑞利分布,当坡度逐渐减小时,相同波高的发生概率逐渐减小;而Ursell参数则不会随着坡度的变化有明显的变化。     

舰船风浪航行失速的估算方法

将舰船常用的在风浪中失速的估算方法概括为7种,比较了各种方法的普适性、精确性和局限性,以便使用者选用.     

Capacity drops at merges: An endogenous model

The Newell-Daganzo merge model is not only very simple but also accurately reproduces experimental findings. However, the capacity downstream of the merge is an exogenous variable in the model. This is a serious limitation for merges that behave as active bottlenecks because their downstream capacity is a direct consequence of the merging behavior. This paper proposes an analytical model that extends the Newell-Daganzo model by incorporating, endogenously, the capacity drop related to the merging process. Two cases are investigated depending on the traffic states on the on-ramp. The model properties are analyzed and a sensitivity analysis is performed to quantify the relative contribution of the each parameter in the capacity drop. Finally, the extended Newell-Daganzo model is validated with experimental data coming from an active merge bottleneck on the M6 freeway in UK.     

Railway wheel-flat detection and measurement by ultrasound

This work presents an innovative ultrasound technique designed to detect and quantify flats formed in the rolling surface of railway wheels. Differently from other approaches, ultrasonic pulses (Rayleigh waves) are sent over a measuring rail. The variations in the round-trip time of flight (RTOF) of the ultrasound pulse to the rail-wheel contact point allow detecting and quantifying the wheel-flats. In spite of the wear state of the irregularity, the method provides the loss of material and the length of the flat originally formed by abrasion. A theoretical background supports the technique which offers many advantages for railway maintenance. Simulations and experimental results match the expected ones.     

井筒与输油管线的物理防蜡技术综述

文中通过对大量相关文献的分析总结,对目前各大油田常用的物理防蜡技术的发展历史、工作原理、适用环境以及使用条件进行了归纳、介绍,并对这些防蜡技术在实验室中的实验结果和近年来油田使用后的效果进行了分析总结.这些防蜡技术的分类介绍为各大油田在实践中面临不同采油条件和原油组分时筛选防蜡方法提供了理论性的依据,也为防蜡技术的进一...     

A macroscopic theory of two-lane rural roads

A macroscopic theory for predicting the operation on two-lane, two-way roads is proposed. In this theory, the interaction between fast and slow vehicles obeys Newell’s kinematic wave theory of moving bottlenecks. Calibration is not required as all parameters are fully observable. Closed-form expressions for the capacity, average speed, percent time spent following and overtaking rates are proposed and the biases of current practice are identified. Comparisons between the proposed theory and empirical data are also included.