International Shipbuilding Progress 63 (2016/2017) 1-40 DOI 10.3233/1SP-160I2I
IDS Press
1
Measurement of flow characteristics in propeller
slipstream of a twin propeller twin rudder model ship
S. Kumar, V. Nagarajan* and O.P. Sha
DeparlmenI of Ocean Engineering Naval Aicliilecliii e, UT Kliaragpnr, Kharagpur, Jiulia E-mails: sluiial.knmar.inecli@giiiail.com, visliwanalliji@naval.iilkgp.ernel.in, ops @ naval.iilkgp.ernel.in
Received 12 May 2015 Revised 21 August 2016 Accepted 25 August 2016
In this paper, the results of experimental investigations of Ihe 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.
Keywords: ADV (Acoustic Doppler Velocity meter), twin-propeller, twin-rudder
1. Introduction
The knowledge of the flow characteristic in near wake region, where the
veloc-ity gradient and turbulence intensveloc-ity gets stabilized is important for the design of
marine propeller. Recently CFD based numerical methods for predicting propeller
thrust and torque have improved significantly. Earlier, potential flow based methods
for predicting propeller tlirust and torque were popular. These methods worked well
in open water condition. Some of these potential flow based propeller thi'ust and
torque predicting techniques are being used with CFD based solver to give propeller
'Corresponding author: Vishwanath Nagarajan, Associate Professor, Department of Ocean Engineering and Naval Architecture, IIT Kharagpur, Kharagpur, 721 302, West Bengal, India. Tels: +91 3222 283 782, +91 8016 727 912; Faxes: +91 3222 282 284, +91 3222 255 303; E-mail: vish\vanathj@naval.iitkgp.ernet.in.
Inlernational Shipbuilding Progress 63 (2016/2017) 41-58 DOI I0.3233/ISP-160122
IDS Press
4 i
A novel approach for fatigue life prediction of local hull
structures subjected to slamming loads
Andres Cecchini *, David Serrano and Frederick Just-Agosto
Department of Mechanical Engineering, Universiry' of Puerto Rico, Mayagiiez, PR, USA
Received 21 April 2015 Revised 20 September 2016 Accepted 20 September 2016
This paper presents a novel computational technique for fatigue life assessment of hull structures sub-jected 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 pres-sures from the Uterature. 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 classi-fied 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 consid-ered. 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 lev-els. A significant reduction of fatigue life is observed when small variations of the impact conditions are considered.
Keywords: Wave slamming, stress-time extrapolation, Rainflow cycle counting, fatigue
1. Introduction
Hydrodynamic impacts (slamming) are characterized by very high loads of short
duration compared to the local dominant period of vibration ofthe structure. In rough
sea conditions, a ship hull may experience repeated impact events which may induce
cyclic loading, eventually causing fatigue failure of the structure. Because of the
con-siderable possibility of this type of stmctural damage, fatigue induced by slamming
'Corresponding author: Andres Cecchini, Department of Mechanical Engineering, University of Puerto Rico, Mayagiiez, PR 00681, USA. Tel.: -i-l 787 832 4040, Ext. 3659; Fax: -i-l 787 265 3817; E-mail: andres.cecchini@upr.edu.
Internalional Shipbuilding Progress 53 (2016/2017) 59-84 DOI 10.3233/ISP-I60123
IDS Press
59
A particle swarm optimization based approach for ship
pipe route design
Zong-ran Dong" and Yan Lin ^•'^•*
" Facully of Eleclionic Infonnation and Electiical Engineering, Dalian Univeisity ofTechnology, Dalian, China
E-mail: dongzongran@j63.coni
^ School of Naval Arciiitecture, Dalian University of Technology, Dalian, China
State Key Laboratoiy of Sirucriiral Analysis for Industrial Ecimpinent, Dalian University ofTechnology, Dalian, China
E-mail: linyaiily@illut.erlu.cn
Received 14 March 2016 Revised 14 October 2016 Accepted 24 October 2016
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 over-come the shortcomings of variable-length encoding. Mutation operafion is combined with the computing process of PSO to avoid the problem of local opumum 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 con-ducted by using V C + + and OpenGL, which demonstrate the feasibility and efficiency of the proposed algorithtn. Results show that our approach can route the most common variations of ship pipes automati-cally under certain constraints in 3-D space. Moreover, the approach can also be applied to other similar path-planning or pipe-routing problems.
Keywords: Particle swarm optimization (PSO), ship pipe route design (SPRD), multiple pipes routing, branch pipe routing, grid theory
1. Introduction
Pipe route design (PRD) has been a popular research topic since 1970s. The goal
of PRD is to find optimal route or path between interface locations under various
Corresponding author: Yan Lin, School of Naval Architecture, Dalian University of Technology, Dalian 116024, China. Tel.: -1-86 0411 84707485;Fax; +86 0411 84707485; E-mail: linyanly@dlut.edu.cn.
