Dynamic Performance of the National Technical University of Athens Double-chine Series Hull Forms in Random Waves

2014 ◽  
Vol 30 (03) ◽  
pp. 101-108
Author(s):  
Gregory J. Grigoropoulos ◽  
Dimitra P. Damala
Keyword(s):  
Dynamic Performance ◽  
Experimental Results ◽  
Random Waves ◽  
Hull Form ◽  
Marine Hydrodynamics ◽  
National Technical ◽  
Calm Water ◽  
Technical University ◽  
Hull Forms ◽  
Scaled Models

A systematic series of double-chine, wide-transom hull forms with warped planing surface has been developed at the Laboratory for Ship & Marine Hydrodynamics (LSMH) of the National Technical University of Athens during the last two decades. The series are suitable for medium and large ships operating at high but preplaning speeds and consist of five hull forms. Two scaled models for each hull form have been constructed and tested in calm water and in waves. In this article, systematic experimental results in random waves are presented.

Hull Form Optimization for Hydrodynamic Performance

2004 ◽  
Vol 41 (04) ◽  
pp. 167-182
Author(s):  
Gregory J. Grigoropoulos
Keyword(s):  
Water Resistance ◽  
Optimization Procedure ◽  
Hydrodynamic Performance ◽  
Hull Form ◽  
Principal Characteristics ◽  
Calm Water ◽  
Rough Water ◽  
Hull Forms ◽  
Scaled Models ◽  
Formal Optimization

A method for optimizing hull forms with respect to their hydrodynamic performance in calm and rough water is presented. The method is based on an initial optimization of a parent hull form for seakeeping and the improvement of the resulting optimum hull form for calm water resistance. In the first part of the method, variant hull forms differing from a parent in the main dimensions and/or in one or more hull form parameters, such as CWP, LCF, CB, LCB, KB, CP, are automatically generated and their seakeeping qualities evaluated. When appropriate ranges for the principal characteristics and parameters of the hull form under investigation are prescribed, a formal optimization procedure is used to obtain the variant with the best seakeeping behavior. The weighted sum of the resonant values of selected ship responses for a number of ship speeds and headings in regular waves forms the objective function. The Hooke and Jeeves algorithm is used to accomplish the optimization. The procedure results in a set of trends regarding the proposed variations of the selected hull form parameters, within the specified constraints. These trends are then applied on the parent hull to derive an optimized hull form with fair lines. Subsequently, this hull form can be locally modified to improve its calm water resistance or, as it should be done, its propulsion characteristics. The applicability of the method is demonstrated in two cases: a conventional reefer ship and a naval destroyer. Scaled models of the parent and the optimized hull forms have been tested for calm water resistance and seakeeping. In both cases the validity of the methodology is demonstrated.

Geometrical Characteristics of Fishing Boats Series of ITU

2007 ◽  
Vol 44 (02) ◽  
pp. 125-137
Author(s):  
Muhsin Aydin ◽  
Aydin Salci
Keyword(s):  
Computer Program ◽  
The Body ◽  
Hull Form ◽  
The Third ◽  
Geometrical Characteristics ◽  
Fishing Boat ◽  
Technical University ◽  
Hull Forms

In the present paper, first 13 hull forms of fishing boats with different block coefficients were generated. Later, 26 hull forms of fishing boats with two different ratios of length to beam were generated by utilizing previous hull forms of fishing boats mentioned. In total, 39 fishing boats were generated. This series is called "Fishing Boats Series of ITU" (Istanbul Technical University). In this Series, the forms of the body stations and beams of the boats are the same for equal block coefficient and different lengths. The ratio of the beam of any station at any waterline to the beam of boat, Bz/B varies with respect to block coefficient, CB. These variations have been represented with the third-degree polynomials. Thus, a hull form of the fishing boat in the desired length and block coefficient can be obtained by using these polynomials. For this purpose, a computer program called "Turetme" was developed. Finally, by using this program, three hull forms of fishing boats were obtained and presented here.

Roll Damping Coefficients Assessment and Comparison for Round Bilge and Hard Chine Hullforms

2013 ◽  
Author(s):  
Ermina Begovic ◽  
Carlo Bertorello ◽  
Jasna Prpic Orsic
Keyword(s):  
Experimental Tests ◽  
Relative Speed ◽  
Roll Damping ◽  
Hull Form ◽  
Fundamental Parameters ◽  
Damping Coefficients ◽  
Displacement Mode ◽  
Calm Water ◽  
Hull Forms ◽  
Metacentric Height

The sustainable design of small passenger vessels and large size pleasure craft indicates new trends: lower speed, reduced fuel consumption and better seakeeping in all range of velocities. Small amplitudes of roll motion are considered one of the most important comfort parameter. These trends call for reviewing some commonly used concepts and designer practice. Fundamental parameters as metacentric height and midsection form affect comfort as well as ship safety in counteracting way. Round bilge, due to good seakeeping characteristics and to large amount of available data from systematic series is the most common hull form choice when cruising speed implies displacement or semi displacement mode. Hard chine hull forms are generally chosen when relative speed leads to some hydrodynamic lift, although recently they have been considered for low relative speed. They allow simplified and cheaper construction and among their interesting features is higher roll damping. This appears very attractive for craft that are generally fitted with stabilizing systems and ask for the most reduced roll motions at any and zero speed. This paper presents the results of experimental tests relative to roll decay of two ship models of the same dimensions, displacement and GM values: they have the same warped bottom hull form developed at University of Naples, the first is hard chine and the second has round bilge from transom to midship. Both of them are suitable for displacement and semi-displacement craft operating at medium-low relative speed. The tests have been carried out at University of Naples towing tank, in calm water, at Fn ranging from 0.0 to 0.45. Natural roll frequencies and linear and non linear damping coefficients are reported for all tested speeds allowing a fair comparison of the roll characteristics due to the variation in hull form.

scholarly journals Mixed-Fidelity Design Optimization of Hull Form Using CFD and Potential Flow Solvers

2021 ◽  
Vol 9 (11) ◽  
pp. 1234
Author(s):  
Gregory J. Grigoropoulos ◽  
Christos Bakirtzoglou ◽  
George Papadakis ◽  
Dimitrios Ntouras
Keyword(s):  
Potential Flow ◽  
Stokes Equations ◽  
Computing Time ◽  
Navier Stokes ◽  
Design Parameters ◽  
Geometrical Parameters ◽  
Viscous Effects ◽  
Hull Form ◽  
Calm Water ◽  
Hull Forms

The present paper proposes a new mixed-fidelity method to optimize the shape of ships using genetic algorithms (GA) and potential flow codes to evaluate the hydrodynamics of variant hull forms, enhanced by a surrogate model based on an Artificial Neural Network (ANN) to account for viscous effects. The performance of the variant hull forms generated by the GA is evaluated for calm water resistance using potential flow methods which are quite fast when they run on modern computers. However, these methods do not take into account the viscous effects which are dominant in the stern region of the ship. Solvers of the Reynolds-Averaged Navier-Stokes Equations (RANS) should be used in this respect, which, however, are too time-consuming to be used for the evaluation of some hundreds of variants within the GA search. In this study, a RANS solver is used prior to the execution of the GA to train an ANN in modeling the effect of stern design geometrical parameters only. Potential flow results, accounting for the geometrical design parameters of the rest of the hull, are combined with the aforementioned trained meta-model for the final hull form evaluation. This work concentrates on the provision of a more reliable framework for the evaluation of hull form performance in calm water without a significant increase of the computing time.

Numerical evaluation of hydrodynamic characteristics of planing hulls by using a hybrid method

2021 ◽  
pp. 147509022199024
Author(s):  
Emre Kahramanoglu ◽  
Silvia Pennino ◽  
Huseyin Yilmaz
Keyword(s):  
Experimental Data ◽  
Hybrid Method ◽  
Design Stage ◽  
Hydrodynamic Characteristics ◽  
Calm Water ◽  
Preliminary Design Stage ◽  
Reduction Function ◽  
Hull Forms ◽  
Good Agreement

The hydrodynamic characteristics of the planing hulls in particular at the planing regime are completely different from the conventional hull forms and the determination of these characteristics is more complicated. In the present study, calm water hydrodynamic characteristics of planing hulls are investigated using a hybrid method. The hybrid method combines the dynamic trim and sinkage from the Zarnick approach with the Savitsky method in order to calculate the total resistance of the planing hull. Since the obtained dynamic trim and sinkage values by using the original Zarnick approach are not in good agreement with experimental data, an improvement is applied to the hybrid method using a reduction function proposed by Garme. The numerical results obtained by the hybrid and improved hybrid method are compared with each other and available experimental data. The results indicate that the improved hybrid method gives better results compared to the hybrid method, especially for the dynamic trim and resistance. Although the results have some discrepancies with experimental data in terms of resistance, trim and sinkage, the improved hybrid method becomes appealing particularly for the preliminary design stage of the planing hulls.

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