Coupled mooring analysis using CFD with dynamic mooring models is becoming an established field. This is an important step for better predictions of responses of moored marine structures in extreme sea states and also for capturing the low-frequency response correctly. The coupling between the CFD and mooring solvers are most often carried out by exchanging the fairlead/anchor points and fairlead forces. In this paper we will discuss the effects of using (i) viscous fluid flow on a mooring component level (submerged buoys and clump weights) and (ii) the fluid-structure coupling between the viscous fluid solver and the mooring system.
In this paper, we contribute to the literature on uncertainty and the drivers of social exchange. We explore the 2008 financial crisis and hand-collect unique data on more than 2,700 vessel chartering deals closed in the container shipping industry from 2000 to 2011. Our contribution is twofold. We challenge the literature by finding that low and high status players use different collaborative strategies under uncertainty: the high status players are more prone to coopetition and the low status ones reach out to external buyers. We also extend the literature on social exchange and uncertainty and introduce other constructs: strategic versatility and country-level long-term orientation of the suppliers that we study in our model. Our findings are relevant for policy and managerial decision-makers in the industry.
Autonomous surface vessels comprise complex automated systems with advanced onboard sensors. These help establish situation awareness and perform many of the complex tasks required for safe navigation. However, situations occur that require assistance by a human proxy. If not physically present on board, information digestion and sharing between human and machine become crucial to maintain safe operation. This paper addresses the co-design of on-board systems and a Remote Control Centre (RCC). Using the international regulations on watch-keeping (STCW) as a basis, the paper discuss how an autonomous system is designed to meet the STCW requirements. It is discussed how the autonomous system is made aware of the state of the vessel, its surroundings, on-board defects or navigational challenges and shared with the RCC in a collaborating system perspective.
We present the results of a numerical model which has been developed for estimating the contribution to the methane slip from different sources in a four-stroke dual-fuel marine engine running on natural gas. The model is a thermodynamic three-zone zero-dimensional full engine cycle model and considers methane slip contributions from short-circuiting, crevices and wall quenching. The model is applied to analyze the methane slip from a four-stroke dual-fuel medium speed marine engine using natural gas as primary fuel. At low loads, wall quenching is found to be the dominant contribution to the methane slip. At full load, the wall quenching contribution is comparable to the level of the short-circuiting and crevice contributions which only vary relatively little with load. At 75% load, the contribution from short-circuiting is highest. In addition, we found that in-cylinder post-oxidation of unburned fuel remaining after the main combustion is negligible.
A conceptual design framework for collision and grounding analysis is proposed to evaluate the crashworthiness of double-hull structures. This work attempts to simplify the input parameters needed for the analysis, which can be considered as a step towards a design-oriented procedure against collision and grounding. Four typical collision and grounding scenarios are considered: (1) side structure struck by a bulbous bow, (2) side structure struck by a straight bow, (3) bottom raking, (4) bottom stranding. The analyses of these scenarios are based on statistical data of striking ship dimensions, velocities, collision angles and locations, as well as seabed shapes and sizes, grounding depth and location. The evaluation of the damage extent considers the 50- and 90-percentile values from the statistics of collision and grounding accidents. The external dynamics and internal mechanics are combined to analyse systematically the ship structural damage and energy absorption under accidental loadings.
The paper outlines a rational design procedure for bridge piers and pylons against ship collision impacts. Firstly, a set of risk acceptance criteria are proposed. This is followed by a mathematically based procedure for calculation of the probability of critical ship meeting situations near the bridge, and the probability of ship collision accidents caused by human errors as well as technical errors. This first part of the paper leads to identification of the largest striking ship, “design vessels”, a given bridge pier must withstand without structural failure in order for the bridge connection to fulfil the risk acceptance criteria. The final part of the paper is devoted to an analysis of the needed impact capacity for the bridge pylons and piers exposed to ship bow impact loads from these “design vessels”. For a number of different ship types and different tonnage merchant vessels, load – displacement relations for ship bow collisions against rigid walls are derived. Based on these comprehensive numerical results, a new empirical relation is derived which is suited for design against bow collisions. This expression for maximum bow collision forces is compared with a previously published expression for ice-strengthened ships and with existing standards for assessment of bow crushing forces. It is shown that there is need for an update of these existing standards. For design of piers and pylons against local impact pressure loads, a pressure - area relation for bulbous bow impacts is derived.
In this paper we extend the state-of-the-art stochastic programming models for the Maritime Fleet Renewal Problem (MFRP) to explicitly limit the risk of insolvency due to negative cash flows when making maritime shipping investments. This is achieved by modeling the payment of ships in a number of periodical installments rather than in a lump sum paid upfront, representing more closely the actual cash flows for a shipping company. Based on this, we propose two alternative risk control measures, where the first imposes that the cash flow in each time period is always higher than a desired threshold, while the second limits the Conditional Value-at-Risk. We test the two models on realistic test instances based on data from a shipping company. The computational study demonstrates how the two models can be used to assess the trade-offs between risk of insolvency and expected profits in the MFRP.
Marine cables are primarily designed to support axial loads. The effect of bending stiffness on the cable response is therefore often neglected in numerical analysis. However, in low-tension applications such as umbilical modeling of ROVs or during slack events, the bending forces may affect the slack regime dynamics of the cable. In this paper, we present the implementation of bending stiffness as a rotation-free, nested local Discontinuous Galerkin (DG) method into an existing Lax–Friedrichs-type solver for cable dynamics based on an hp-adaptive DG method. Numerical verification shows exponential convergence of order P and P + 1 for odd and even polynomial orders, respectively. Validation of a swinging cable shows good comparison with experimental data, and the importance of bending stiffness is demonstrated. Snap load events in a deep water tether are compared with field-test data. The bending forces affect the low-tension response for shorter lengths of tether (200–500 m), which results in an increasing snap load magnitude for increasing bending stiffness. It is shown that the nested LDG method works well for computing bending effects in marine cables.
Closed-form expressions to estimate the energy absorption and damage extent for severe ship collision damages were initially developed in 1999 [1, 2], and further validated with experimental data in 2016 [3]. To gain further confidence for applications within design using the proposed analytical procedure, it is evident that more detailed and comprehensive comparisons and validations with experiments and numerical simulations are necessary. The purpose of the present paper is to use the analytical approach and finite element analyses to study in depth model-scale and full-scale collision tests so that to further quantify key calculation parameters and to verify the capability and accuracy of the proposed analytical method. In total 18 experimental tests and one full-scale collision accident are evaluated. The 18 experimental energy absorption-penetration and collision force-penetration curves, and the associated finite element simulations, are compared with results obtained from the analytical calculations. It can be concluded that the analytical method gives consistently good agreement with all experiments analysed here. Finally, an application of the analytical method is demonstrated by an example where speed restrictions are determined in a port to avoid LNG cargo leakage in an event of an LNG carrier being struck by another ship.
Ship collision and grounding events constitute a major hazard for ship operations, and ship collision risk analyses have to be carried out for installations such as offshore structures for extraction of hydrocarbons, offshore wind farms, and bridges spanning waterways. This book provides assessment procedures for ship collision and grounding analysis and includes probabilistic methods for collision and grounding risk assessment, estimation of the energy released during collisions, and prediction of the extent of damage on the involved structures.
The main feature of the book is that it encapsulates reliable and fast analysis methods for collision and grounding assessment and the methods have been extensively validated with experimental and numerical results. In addition, all the described analysis methods include realistic calculation examples so as to provide confidence in their use to eventually conduct the required assessment according to the rules and design codes. The book is intended as a handbook for professionals and researchers in the industry dealing with design and analysis of ships and offshore structures. The book can also be used as a text book for postgraduate courses orientated towards the design and analysis of ship and offshore structures.