Experimental and numerical investigations on the intact and damage survivability of a floating–moored oscillating water column device

This paper investigates the intact and damage survivability of a floating–moored Oscillating Water Column (OWC) device using physical model experiments and Computational Fluid Dynamics (CFD) simulations. Different extreme wave conditions have been tested using irregular and regular wave conditions. The device was moored to the tank floor via four vertical taut lines and the effect of the mooring line pre–tension on the device response was studied. It was found that the instantaneous position of the floating device was a key factor in the survivability analysis such that a certain irregular wave train that might not include the largest wave could induce the maximum response. Reducing the pre–tension minimized the maximum surge, but significantly increased the maximum tension due to mooring slack events causing snatch loads. A design regular wave with a period equal to the peak period and a height of 1.9–2.0 times the significant wave height could reasonably predict the same maximum line tension as the irregular sea state, but a smaller wave height was required to achieve the maximum surge. A single failure in the mooring system increased the maximum tension by 1.55 times the intact tension. For a damaged mooring system, using the same design regular wave condition derived from the survivability analysis with an intact mooring system could result in overestimating the maximum tension by more than 20% in comparison to the tension from the irregular sea state, but a smaller regular wave height or a different regular wave condition representing another sea state could lead to the same maximum tension. This highlighted the importance of investigating survival conditions with a damaged mooring system instead of simply using the same conditions derived for the intact mooring system.     

Experimental evaluation of design methods for in-site detention ponds

In this study,the detention rate of detention pond was defined to include both reduction and delay of peak flow.Flood routing experiments,with various combinations of inflow hydrographs and outlet devices in an in-site detention pond,were performed to examine the effectiveness of two analysis methods,namely the simplified method and the hydrological routing method;and to compare the detention rate of two types of outlet,namely the rectangular sharp-crested weir and the rectangular orifice.Comparison between...     

Rethinking urban water management: Experimentation as a way forward?

There is widespread acceptance regarding the need to transition towards more sustainable urban water practices. Supporting such a transition requires new governance frameworks that can accommodate complexity and uncertainty, and organisational cultures that embrace experimentation and learning. This empirically focused research paper examines how eleven, alternative local-scale experiments were initiated while operating in an unsympathetic regime. Furthermore, the perceptions of more than 150 urban water practitioners across Australia are presented, regarding the importance of and difficulty in undertaking experimentation in the urban water sector, and the necessary mechanisms for influencing a step change to sustainable urban water management practices. Interviewees revealed perceived limitations in experimenting with new technologies and practices when operating within a hierarchical and market-based governance paradigm. Also, industry conservatism and the dominant risk-based management approach both operate as significant constraints to promoting an experimentation culture, and are closely related to concerns about public health and financial implications. Overall, the research highlights the Australian urban water sector is willing to embrace learning-by-doing; however, a stronger emphasis on promoting an organisational and industry-wide culture of experimentation and learning is required. Policy implications for future water governance are discussed.     

Determination of discharge coefficients for a cross-flooding duct

Cross-flooding ducts are used to equalize asymmetric flooding and, thus, to decrease the heel angle of a ship in an emergency. The present design guidelines for cross-flooding arrangements involve uncertainties associated with the effect of variable structural factors. In this study, scale model experiments were carried out to determine discharge coefficients of a typical cross-duct, with a focus on the effect of structural components such as the girders, stiffeners, and web frame. Flow conditions and configuration of the components were varied in the experiments. The structural stiffeners in the cross-duct were found to notably increase the discharge coefficient whereas the effects of the web frame and the inclination of the duct at an angle of 7° were negligible. The experimentally obtained discharge coefficient values for the cross-duct were considerably lower than the corresponding values computed according to the generally used guidelines of the IMO Resolution MSC.245(83). This indicates that the geometrical properties of the girders in the cross-ducts need to be properly addressed to avoid overestimating the discharge coefficients. Overall, the experimental results formed an indispensable dataset for the validation and further development of CFD approaches.     

Distinguishing Propagation vs. Launch Physics of Astrophysical Jets and the Role of Experiments

The absence of other viable momentum sources for collimated flows leads to the likelihood that magnetic fields play a fundamental role in jet launch and/or collimation in astrophysical jets. To best understand the physics of jets, it is useful to distinguish between the launch region where the jet is accelerated and the larger scales where the jet propagates as a collimated structure. Observations presently resolve jet propagation, but not the launch region. Simulations typically probe the launch and propagation regions separately, but not both together. Here, I IDentify some of the physics of jet launch vs. propagation and what laboratory jet experiments to date have probed. Reproducing an astrophysical jet in the lab is unrealistic, so maximizing the benefit of the experiments requires clarifying the astrophysical connection.     

Influence of yaw-roll coupling on the behavior of a FPSO: An experimental and numerical investigation

An inconvenience in the experimental set-up of a FPSO in regular waves highlighted occurrence of parametric-roll events promoted by yaw-roll coupling and motivated a combined physical and numerical analysis on the relevance of this phenomenon on the roll resonance, as well as on the water shipping. The model tests examine the ship in head- and bow-sea waves in the zone of the first parametric resonance. Numerically, it is adopted a 3D Domain-Decomposition (DD) strategy combining a weakly-nonlinear potential-flow solver based on the weak-scatterer theory with a shallow-water approximation for the shipped liquid and with a bottom-slamming solution. Detailed comparisons against these and other seakeeping experiments validated the numerical method in its different aspects with global success.At first, a 2-dof equivalent linearized yaw-roll coupled system is examined and the measurements are used to estimate hydrodynamic coefficients required to complete the mathematical model of the problem. Then the DD method is applied to verify the instability occurrence and compared against the experiments. From the analysis, the parametric-roll instability does not occur if all nonlinearities in the roll restoring load are not accounted for. However the amplitude of the resonant roll is affected by the coupling with the other degrees of freedom. Especially the coupling with yaw tends to increase the steady-state roll amplitude. It also affects the water shipping with the trend in reducing its severity for the vessel, this is opposite to the influence of the parametric roll in head-sea waves on the water on deck, as documented in Greco et al. (2014) [4].     

旋转扰动流体中壁面湍流不稳定及其拟序结构研究I：实验

重点介绍和讨论了中性条件下旋转扰动流体中边界层强迫不稳定及其相关的一些问题,阐述了旋转体系中切变驱动边界层不稳定的动力学特征。这些不稳定状态的研究在大气物理学、流体动力学、海洋学等多个领域中引起科学家极大的兴趣,近年来在实验和理论研究中都得到了不断的发展。意大利都灵大学基础物理系地球科学实验组通过水槽旋转实验方法,不断改变水槽启动或结束时的旋转运动速度,以及底部壁面粗糙度等要素,所得到的实验结果与SDBL理论非常一致。     

EXPERIMENTS ON FLOW AROUND A CYLINDER IN A SCOURED CRANNEL BED

1 INTRODUCTION'LOcal scour around a pier is a result of the interatiOn amongst the pier, the aPproach flow and theerodible bed. The Presence of a pier results in a stagnation pressure build-up in front of the pier and athree-dimensional tUrbulent flow echaracterized by the downward flow ahead of the pier and the so-called horseshoe vortex along the base of the Pier forms itself The flow modifies the erothe bed inthe vicinity of the pier when local scour takes place (Graf and AJhnakar l…     

岩石波速温度和压力系数的测量方法及其应用

概述了高温高压实验技术在研究地球深部物质组成和结构等方面所起的作用，认为它是把地球物理模型同地球深部物质组成结合起来必不可少的一个中间环节，通过分析典型的试验结果，介绍了在实验室测定岩石波速温度系数（ρ↓V/ρ↓T）P、压力系数（ρ↓T／ρ↓P）T和岩石本征波速（VO）的方法，以及运用它们进行波速外推的原理，结合前人工作实例，阐明了将此技术与地质及地球物理研究结合，为地球物理测深资料的解释提供实验约束的研究思路，针对在前人工作中实验参数及实验结果存在差异的现象，着重探讨了实验条件和流程对实验结果的影响，认为，在用回归方法计算（ρ↓V／ρ↓P）T时，通常应在大于300MPa的压力段上采集实验数据，以消除岩石内部先存微裂隙的影响；在计算（ρ↓V／ρ↓P）T时，为抑制热裂隙的产生，还应满足不小于1MPa/℃的压力增量；另外，测定（ρ↓V／ρ↓T）P时，实验温度不宜太高，以避免引起岩石内部的矿物相变和物态变化。     

格栅结构复合地基的应用研究

格栅结构复合地基是一种有侧限结构复合地基。通过载荷试验和相关测试研究表明:格栅结构的侧向变形受到相邻桩的限制,侧向变形减少;格栅内的地基土没有侧向位移;地基土内有应力集中和应力分担比增加的规律。