Abstract. 1 Introduction

Transcription

1 Parametric analysis of hull structure of mono- and catamaran-type inland vessels T. Jastrzebski & Z. Sekulski Faculty ofmaritime Technology, Technical University of Szczecin, AL Piastow 41, Szczecin, Poland Abstract The parametric calculations are applied for the hull structure weight optimisation of three models of inland vessels with restricted main dimensions. The general assumptions of the ship model topology and material are described atfirst.then an algorithm and a new computer code developed for the purpose of the study are presented The results of parametric calculations of mass of hull structure dependant on the geometrical data and material strength are performed. The conclusions from the study for design complete the paper. 1 Introduction The hull structure weight optimisation is one of the main design criteria also in the case of inland vessels especially when the main ship dimensions are restricted due to the specified water way limits. A most commonly method used in the inland vessel hull design is still the one based on classification society rules. Therefore the algorithms for the hull strength element dimensioning according to the Polish Register of Shipping and Germanisher Lloyd Rules were chosen in the present study. There are several practical optimisation approaches for use in hull structure analysis but the systematic, parametric calculations are still most often used method due to their simplicity and close relation to design practice. This method was also selected for this work. Its practical easy application was assured by the preparation of a computer code developed especially for this analysis. The code is based on the above mentioned classification rules. The systematic calculations were performed to study the influence of geometrical and material models on ship mass and ship dimensions. Two types of geometrical ship models were taken into consideration: a monohull and catamaran. The ships were designed to carry containers and liquid cargoes. As

2 516 Marine Technology II design vanables the frame spacing, framing system and matenal strength were taken. 2 Ship and material models Three models of vessels were taken into consideration in the analysis: - container ship: monohull - Model CM, catamaran - Model CC, - tanker: monohull - Model TM. The cross section topology of the hull models is shown in Fig. 1. r^t \ \ Engine room Holds W ^... to. / /[ 1 CONTAINER CARRIER HI H\ B J A MODEL CM MODEL CC TANKER B Figure 1: Investigated models of inland vessels The data of the vessels are grouped in Table 1. The analysis of mass coefficients, discussed in the next chapter, was performed for a specific vessel on the base of the mass estimation for a hull module of defined length and with fixed lay out of the cross section as shown in Fig. 1.

3 Marine Technology II 517 The influence of variation of the following parameters was analysed: - variation of frame spacing: s = (390, 445, 520, 620) mm for Models CM and CC, s = (520, 560, 600) mm for Model TM - variation of hull material quality - mild and higher tensile (HT) steels: A - mild steel, yield stress Re = 23 5 MPa, AH32 - HT steel, Re = 315 MPa, AH36 - HT steel, Re = 355 MPa, AH40 - HT steel, Re = 390 MPa, The analysed hulls were designed for the following framing systems: Model CM and Model CC - container ships: transverse framing at bottom, side and deck, Model TM - tanker: 1. Transverse framing at bottom, side and deck, 2. Mixed framing - longitudinal at bottom and deck, transverse at side, 3. Longitudinal framing at bottom, side and deck. Model Type of ship Hull type Rules Hull material Length overall L^ Length b.p. L^ Depth H Breadth Draught Block coeff. B T CK Table 1. Data of investigated inland vessels CM Cargo - container Monohull PRS Steel 85.00m m 2.90m 9.50m 2.50m 0.90 CC Cargo - container Catamaran PRS Steel m m 2.90m 9.50m 2.50m 0.90 TM Tanker Monohull GL Steel 85.00m m calculated for WD< m 1.20m Computer code for hull structure dimensioning Two classification rules were chosen to evaluate the scantlings of the hull members: Rules of the Polish Register of Shipping [1] and Germanisher Lloyd [2]. The calculation algorithm was composed with several modules containing the programmed calculation procedures according to the rule formulae. Three separate codes were created for the study aims. All transverse and longitudinal elements of the hull in the hold part can be calculated for the modelled cross sections. Plate and profile elements according to the Polish Standards can be

4 518 Marine Technology II selected from the data bank by a user. Scantlings of elements finally accepted by a designer are used for estimation of the weight of structure. Mass is normally calculated for an frame spacing and then extended for the specified ship length. 4 Results of parametric calculations 4.1 Container ships For two container ship Models CM and CL a section of normalised length of m was first analysed. The scantlings of all members together with the corresponding weight of structure were calculated. Then the results were extended for the hold space length and for the entire vessel hull. The calculations were performed for the specified variation of frame spacing and material grades. The scantlings of the members are in accordance with the Polish Register Rules. 4.2 Tanker According to the assumed different frame spacing the hull sections of three different length were analysed: 10.40, 8.96 and 9.60 m. A hull section in the case of the tanker was equivalent to the length of the cargo tank. For each framing system of the hull the calculations were performed for a specified frame spacing and for four steel grades as explained in Chapter 2. The computer code was used for the calculation of scantlings of hull members in accordance with the Germamsher Lloyd Rules. Structure weight of the hull sections was calculated too. The weight data was extended for the full length for the cargo space and for the whole ship. 4.3 Design curves Systematic calculations of the effect of variation of the framing system, frame spacing and material grades supplied rich set of design data. Some results are presented in Figures 2,3,4 and 5. Mass coefficient of the structure weight related to the main ship dimensions (LBH) was used for comparison and to demonstrate the influence of the varied parameters. The influence of frame spacing and steel grade on the structure weight for the container vessels is demonstrated in Fig.2 and Fig. 3 for the monohull and catamaran models respectively. It is shown that decrease of the frame spacing has strong influence on the structure weight but no minimum of this function was found in the investigated range of spacing. In Fig.4 a weight coefficient is shown with respect to frame spacing and material grade of the monohull tanker. The very significant influence of matenal grade is observed but the influence of the frame spacing is practically very small. Fig.5 demonstrates changes of the weight according to different frame spacing and framing system for the same vessel. The mixed framing system turned out optimal and the minimum of the function was found for frame spacing equal to 0.56 m.

5 Marine Technology II 519 CM-AH CM-AH36! - CM-AH4Q 0,06 415mm 520mm Space of frame Figure 2: Monohull container vessel - influence of frame spacing and steel grade on weight coefficient X *CD * O) CC-AH CC-AH36 I - CC-AH40 1 <D o 2 to "5 X 0,06 415mm 520mm Space frame 620mm Figure 3: Catamaran container vessel - influence of frame spacing and steel grade on weight coefficient

6 520 Marine Technology II TM-A TM-AH32 TM-AH36 Steel for hull structure TM-AH40 Figure 4: Monohull tanker vessel - influence of framing system and steel grade on weight coefficient Hull structure weight/l*b*h u, iu - 0, 14-0, 13-0, 12- j Mixed.. Lingitudinal. Transverse _ 0, 11 i i i - i 520 mm 560 mm 600 Frame spacing Figure 5: Monohull tanker vessel - influence of frame spacing and framing system on weight coefficient (mild steel A)

7 5 Conclusions Marine Technology II 521 The parametric studies on influence of the important hull design parameters such as frame spacing, framing system and material grade on the weight characteristics of monohuil and catamaran type inland vessels were presented in the paper. It was proved by the parametric studies that weight coefficient of the investigated vessels is dependant on the material and geometrical hull characteristics. The curves presented in the paper can be used for designing inland vessels. Such investigation can be easily extended to other inland vessels of similar destination and geometrical configuration. Acknowledgements The author gratefully acknowledges the financial support of the Polish Committee of Scientific Research and Dr. Lech Tolkacz and Dr. Maciej Taczala from the Technical University of Szczecin for their co-operation and assistance. References 1. Rules for Classification and Construction of Inland Vessels - Part II, Hull Polish Register of Shipping, Gdansk 1987 (in Polish) 2. Ship Technology - Rules for Classification and Construction. Part 2 - Inland Waterway Vessels. Germanischer Lloyd, 1990