Offshore Structures Design Based on

Concept of Modularization

BRUNO ČALIĆ and NIKŠA FAFANDJEL

Faculty of Engineering University of Rijeka

Department for Naval Architecture and Ocean Engineering

51000 Rijeka, Vukovarska 58

Croatia

Phone: ++ 385 51 651453; Fax: ++ 385 51 675 818

E-mail: calic@riteh.hr

TOMISLAV ČALIĆ

Faculty of Engineering University of Rijeka

Department for Naval Architecture and Ocean Engineering

51000 Rijeka, Vukovarska 58

Croatia

Phone: ++ 385 51 651455; Fax: ++ 385 51 675 818

ABSTRACT

Authors propose a novel design and building concept of offshore structures designated for various purposes. Improvement in design and building solutions of surface and underwater structures including also underwater restaurants, habitats, diving chambers, gondolas, tunnels, towers, bridges, etc., is based on concept of modularization. Together with modular construction concept, possible contents, communications, building materials, exploitation locations, energy supply, wastage disposal, ventilation and air conditioning, as well as marine structures protection, safety and rescue are discussed.

The main objective of this article is to present theoretical and practical results and possibilities of different space joint types implementation in mentioned structures. After introducing of new space joint types in light conventional grid structures, the authors are suggesting their implementation also in various shipbuilding areas.

The main new grid structures building concept is characterized with structure lightness, simple assembly and adjusting procedures, "maintenance free" and "ecology friendly" structure characteristics, accommodation system modules with simplified on board erection possibilities, and multiple usage configurations.

Analyzing various present construction solutions in offshore unit superstructures, masts, communication facilities, furniture, gangways, telescopic roofs, etc. the authors pointed out concrete proposals for new solutions regarding implementation of mentioned space joint types. Advantages with argumentation for particular topics were described and presented.

INTRODUCTION

Space joint is a new constructional element for synchronous fastening of crossover rods in and/or on space joint body. At the same time the space joint represents a fastening node within grid structure. New grid structures solutions are based on Patent Cooperation Treaty (PCT), Patent Application No. PCT/GB97/00944, with International Publication Number W 97 / 38229 and some additional research results in this field. Some of present research activities supported by the Ministry of Science and Technology of the Republic of Croatia (Scientific project name: Marine structures and equipment in coastal zone and sub-sea) have also been presented.

There are many grid structure types with various solutions for rods (bars) fastening in grid nodes. Fastening problem can be very complex in cases where various opposite requirements have to be achieved, such as: mounting time restriction, maintenance cost restrictions (maintenance free structures), ecology requirements, user friendly structures, disassembling requirements, short replacement time, mass restrictions, low static and dynamic weights, etc.

The most of present structures do not comply with these requirements.

In this article, those problems were approached by implementation of CROCKA system of building, partitioning and adaptation, which is based on introducing new types of dismounting joints (Čalić Bruno (1(). Figure 1 shows one type of joints in which rods are fastened on friction principle. In this paper some theoretical, experimental and practical solutions are pointed out.

Developed computer model for one space joint type was described. Computer modeling was performed on basis of finite element method. Special attentions were pointed out regarding contact pressures, deformations, as well as stresses. Up to date testing was mainly realized concerning small-reinforced polyamide type of space joint body and fastening bodies.

Preparations for testing procedures of different types from various materials and dimensions have been discussed, too. Special consideration was given to compare theoretical and experimental results concerning forces, deformations, strengths, and contact problems, based on some scientific research results achieved at Faculty of Engineering University of Rijeka.

In addition, different aspects of ecology, maintenance, mounting and dismounting procedures, safety, replacement, etc. have been discussed. On basis of mentioned theoretical, experimental and some exploitation results authors proposed usage of different space joint types for implementation in shipbuilding. Authors are also suggesting further research regarding implementation of new predicted space joint types to different fields in shipbuilding and marine structures.

Figure 1 CROCKA system with space joint – type I b and appertaining rods

OFFSHORE STRUCTURES DESIGN BASED ON CONCEPT OF MODULARIZATION

System description

CROCKA system aims to solve mentioned technical problems through space joints by achieving the following:

enabling problem solution by central tightening or loosing of rods, in easy, fast, sustainable, cost effective and synchronous manner;

enabling problem solution by synchronous, central tightening of rods from internal part of space joint, in a mode to retreat rods into corresponding space joint body holes;

enabling problem solution by synchronous, central tightening of rods from the external of space joint, in a mode to retreat rods into corresponding space joints body holes, while rods' tightening or loosening is executed through tightening bodies (covers);

enabling problem solution by synchronous, central tightening of rods in such mode that rods' tightening is performed by tightening body “separated part” of space joint;

enabling problem solution in a mode as the space joint, if necessary, become non-disconnected, and of more difficult type to disconnect, as to ensure higher joint load capacity;

enabling problem solution in a mode as the space joint, if necessary, become non-disconnected, and of easier type to disconnect, as to ensure higher joint load capacity; and enabling problem solution in a mode that the space joint internal becomes isolated from the surrounding fluid, and in such way to prevent joint parts deterioration due to surrounding fluid aggressive influence.

Theoretical Approach

Objective of the space joint is to join or connect structure rods within structure nodes.

Determination of stresses in rod, which is usually assumed to be a one-dimensional constructional element, is relatively an easy task. Nevertheless, the behavior of space joint body under load should be investigated more in details.

Joining of structure rods is based on friction between rods and space joint body. Analysis of space joint body employing friction principle was performed during the first stage of research.

The needed friction force for joining structure rods is achieved by tightening of two special elements inside space joint body.

A simulation of space joint body behavior was performed by finite element method with emphasis on contact problem, Figure 2.

Present research was concentrated to the experimental analyzes on presented contact problem, and stress distribution analyzes treating one space joint type. Further research will be extended to whole array of new registered space joint types.

Future theoretical and experimental research will be dedicated to dynamical behavior investigations regarding different grid structure configurations with a variety of dismounting space joint types in grid structure nodes.

Figure 2 3D finite element mesh on space joint body

Experimental Results

Two types of patent pending space joints are under experimental stage at Faculty of Engineering University of Rijeka.

Due to complex space joint geometry it was necessary to simplify the experimental model. Therefore, experiments were performed on 2D models that were recognized as the most critical cross sections. The photoelasticimetry method was used (Mrakovčić Tomislav (6(, (Čalić Bruno et al. (5().

Application Possibilities

The space joint type I b, with dimensions 35(14(12 mm (edge length ( rod bore ( tightening subsystem element bore), made of 30 % reinforced polyamide 6 is already under production in Croatia.

Based on above mentioned space joint results (theoretical, experimental and practical), it is possible further to develop other space joints of various dimensions and from different materials.

As described (Čalić Bruno (3( and (4(), (Čalić Bruno et al. (5() new solutions for implementation of disassembling space joints cover various fields: off-shore structures, Figure 3, civil engineering and shipbuilding structures (various buildings, scaffoldings, bridges, shelves, furniture), toy industries, etc.

Also various possibilities for implementation of different space joint types are enabled within off-shore structures such as: pontoons, tourist platforms, cages for fishery, underwater parks communication supports with superstructures and energy plant foundations.

These types of dismounting space joints are also applicable in most of ocean structures where partitioning elements are required.

Authors idea is to realize the "ecology friendly" concept regarding after usage disposal of exploited off-shore constructional elements or modules, taking in consideration costs and safety requirements.

Figure 3 Multi-purpose offshore platform

Recently, CROCKA system was implemented for various purposes.

For example, it was implemented in rings of 8 and 6.5 m in diameter, designed for Turbo Limach Show, the most popular Croatian TV children show, Figure 4. Those rings are equipped with space object models, and are slowly rotating in opposite directions. The main advantage of these rings is in extremely low weight. Both rings in weight have less than 100 kg, while the whole-equipped structure equals less than 300 kg.

Figure 4 Overhead rotating structure in CROCKA system for TV scenography

Furthermore, different space joint types already registered or that are under development can be implemented for various grid structures within offshore objects and units, such as mobile and fixed platforms, bridges, auxiliary tourist and energy communication and support structures, etc. Due to mentioned characteristics, such structures can be used within space technology.

Conclusion

Regarding grid structure joint requirements that are often contradictory, solution possibilities based on new dismounting space joints are proposed.

Options of dismounting joints from world patent databases were analyzed, and compared with PCT (Čalić Bruno (3(). Furthermore, on bases of theoretical and experimental research performed on Faculty of Engineering University of Rijeka (Mrakovčić Tomislav (6(, (Čalić Bruno et al. (5(), authors are pointing out relevant advantages of several dismounting space joint types by that in context of CROCKA system is possible to improve some espied defects within existing grid structures.

Also, further theoretical and experimental research is suggested regarding new types of dismounting space joints.

Application possibilities of dismounting space joints were presented through obtained results regarding light structures that are ecologically compatible and maintenance free.

Further research activities will cover extensive experimental activities, introducing other patent pending disassembling space joint solutions in practice and new symmetric space bodies solutions, also including space joint type for very large static and dynamic loads.

Authors have analyzed the implementation of modularization within offshore structure design based on usage of new dismounting space joint types.

Special care was dedicated to the new grid structures building concept characterized with structure lightness, simple assembly and adjusting procedures, "maintenance free" and "ecology friendly" characteristics, accommodation system modules with simplified on board erection possibilities, and multiple usage configurations.

ACKNOWLEDGMENTS

The authors wish to express gratitude to the Faculty of Engineering University of Rijeka and specially to the dean Prof. Bernard Franković, D. Sc. for their understanding and support to the research and development activities in field of naval architecture and ocean engineering.

Herewith, authors also express their gratitude to the Government of the City of Rijeka and especially to the major Mr. Slavko Linić for their help and comprehension to enable participation to IOA(99 conference in IMARI.

The authors also express their gratitude to the Ministry of Science and Technology of the Republic of Croatia which have found the possibility for additional support to enable some of realized research activities at the Faculty of Engineering University of Rijeka.

REFERENCES

1. Čalić B. "New Devices in Coastal Zone and Subsea in Tourist Offer", Proceedings. International Round Table – Adriatic Coastal Zone and Subsea (ACZS) Real Challenge for Croatian Tourism, Scientific Council of Maritime Affairs of Croatian Academy of Sciences and Arts, Rijeka, pp. 99-103 (1994)

2. Čalić, B. "New Approach to Marine Structures Design", Proceedings. 4th Symposium DESIGN 96, Faculty of Engineering University of Rijeka, Rijeka, pp. 3-10 (1996)

3. Čalić B. "Space Joint", Patent Cooperation Treaty (PCT), International Publication Number: WO 97/38229, 10, London (1997)

4. Čalić, B. "Prostorna spojnica", Croatian Intellectual Property Gazette, 2, 371 (1998)

5. Čalić, B, Fafandjel N, Mrakovčić T. "Implementation of Space Joints to Grid Structure", Proceedings. 5th International Design Conference, Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Zagreb, pp. 425-430 (1998)

6. Mrakovčić, T. "Optimisation of the Space Joint Dimensions", Master thesis, Faculty of Engineering University of Rijeka, Rijeka (1998)

7. Vlaisavljević, G. "Initial Design of Concept design of Light Dismounting modular Pontoon Structure", B. Sc. Degree Thesis, Faculty of Engineering University of Rijeka (1999)

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