International Shipbuilding Progress - Volume 63, issue 1-2

Authors: Kumar, S. | Nagarajan, V. | Sha, O.P.

Article Type: Research Article

Abstract: In this paper, the results of experimental investigations of the characteristics of the flow behind a twin-propeller twin-rudder hull are presented. An Acoustic Doppler Velocity meter (ADV) was used to measure the flow field behind the twin propeller and twin rudder. The measurements were mainly carried out in zero speed condition. Additionally, few experiments were carried out with model moving in bare hull condition, i.e. without rudder and propeller. This data was used for verification of CFD simulation result. In the zero speed condition, experiments were carried out with propeller rotating in inward and outward configuration respectively. Phase averaged measurements …were also carried out for the port propeller in outward rotating configuration, in the zero speed condition. Numerical prediction of propeller thrust and torque at zero speed condition are under development. The experiment data presented in this paper will be useful for validation of numerical methods under development. Show more

Keywords: ADV (Acoustic Doppler Velocity meter), twin-propeller, twin-rudder

DOI: 10.3233/ISP-160121

Citation: International Shipbuilding Progress, vol. 63, no. 1-2, pp. 1-40, 2017

Authors: Cecchini, Andres | Serrano, David | Just-Agosto, Frederick

Article Type: Research Article

Abstract: This paper presents a novel computational technique for fatigue life assessment of hull structures subjected to repeated water slamming loads. The proposed approach combines numerical results from finite element (FE) models of a single impact event with statistical distributions of experimental peak pressures from the literature. Numerical stresses are extrapolated using Peak over Threshold (POT) analysis to simulate the effect of small variations of the angle of incidence and impact velocity in a scenario of multiple impacts. POT analysis is used to model stress exceedances above and below certain threshold levels based on a statistical distribution. In this paper, stress …exceedances are assumed to follow a similar statistical distribution to that of the peak pressures. The resulting extrapolated stresses contain modified peaks and valleys which are highly dependent on the threshold levels. The stress cycles are then classified and counted using the Rainflow method. The level of structural damage associated with each cycle is computed and the individual contributions are combined using a linear damage accumulation model (Palmgren–Miner’s law). In this paper, fatigue of a component in the pressure-affected zone is considered. The proposed approach predicts more damage, for a particular number of impacts, than the classical approach without stress exceedances. Damage predictions are also highly dependent on the threshold levels. A significant reduction of fatigue life is observed when small variations of the impact conditions are considered. Show more

Keywords: Wave slamming, stress-time extrapolation, Rainflow cycle counting, fatigue

DOI: 10.3233/ISP-160122

Citation: International Shipbuilding Progress, vol. 63, no. 1-2, pp. 41-58, 2017

Authors: Dong, Zong-ran | Lin, Yan

Article Type: Research Article

Abstract: Ship pipe route design (SPRD) is to search the near optimal pipe routes that meet various constraints and objectives in a constrained ship space, which is one of the most time-consuming and difficult process in ship production. This paper proposes an automatic approach for solving the SPRD problem based on the grid theory and particle swarm optimization (PSO) algorithm. The fitness functions which are used in the PSO algorithm are formulated to evaluate the engineering objectives and constraints. A fixed-length particle encoding is improved according to the characteristics of ship pipe routing in 3-D space to overcome the shortcomings of …variable-length encoding. Mutation operation is combined with the computing process of PSO to avoid the problem of local optimum and to accelerate the convergence rate. Based on the proposed algorithm, the multi-swarms optimization with co-evolution mechanism is applied to solve the problem of multiple pipes and branch pipe routing. The simulations of pipe routing examples are conducted by using VC++ and OpenGL, which demonstrate the feasibility and efficiency of the proposed algorithm. Results show that our approach can route the most common variations of ship pipes automatically under certain constraints in 3-D space. Moreover, the approach can also be applied to other similar path-planning or pipe-routing problems. Show more

Keywords: Particle swarm optimization (PSO), ship pipe route design (SPRD), multiple pipes routing, branch pipe routing, grid theory

DOI: 10.3233/ISP-160123

Citation: International Shipbuilding Progress, vol. 63, no. 1-2, pp. 59-84, 2017