American Journal of Innovative Research and Applied Sciences. ISSN 2429-5396 I www.american-jiras.com

| Mahar, Jasem Alhasan

| and | Adnan, Mohamed Ibrahim

Tishreen University | Department of water engineering and irrigation | Lattakia | Syria |

ABSTRACT

Background The efficiency and safe design of marine platforms depend on a complex structure of mutual influence between these

facilities and the surrounding environment and the degree of resistance to different loading patterns during the entire investment

period. Fixed jacket platforms are huge steel framed structures used for the exploration and extraction of oil and gas from the earth’s

crust. Jacket type structures are appropriate for relatively shallow water depth. Objectives: the objective of this study is to select

specific parameters for the elements of a fixed platform (jacket) and conduct an static analysis study to resist these elements for the

influence of the basic loads that are subject to it within the environment of the Syrian coast , using the software SACS. Methods: the

jacket is modeled in SACS finite element program and static analysis is conducted with fixed boundary conditions. Critical conditions

are taken into account, which include structure and equipment weight, wind load, hydrodynamic load using Morison equation.

Results: Linear static analysis is performed for the four legged jacket considering (3) loading directions. The maximum base shear

and overturning moment are calculated in normal environmental conditions and stormy. as well as the unit check values, for all

member are obtained it. Conclusions: the environmental conditions of the Syrian coast are suitable for the construction of jacket

offshore, therefore a great importance to support the Syrian national economy.

Keywords

Unity Check, Jacket,

Linear Static Analysis

SACS software

1. INTRODUCTION

Offshore platforms are huge steel or concrete structures used for the exploration and extraction of oil and gas from the

earth’s crust. Offshore structures are designed for installation in the open sea, lakes, gulfs, etc., many kilometers from

shorelines. these structures may be made of steel, reinforced concrete or a combination of both [7].

The total number of offshore platform in various bays, gulf and oceans of the world is increasing year by year, most of

which are of fixed jacket-type platforms located in 100 ft (32 m) to 650 ft (200 m) depth for oil and gas exploration

purposes [8]. The analysis, design and construction of offshore structures compatible with the extreme offshore

environmental conditions is a most challenging and creative task. Over the usual conditions and situations met by land-

based structures, offshore structures have the added complication of being placed in an ocean environment where

hydrodynamic interaction effects and dynamic response become major considerations in their design [6].

The jacket structure typically consists of tubular members of various diameters and wall thicknesses. the air gap between

the sea surface and the bottom of the topside structure is made high enough to prevent waves from hitting the topside

structure. At the bottom, the jacket is normally outfitted with a temporary foundation which supports the jacket until the

permanent foundation is installed. Bracing configurations consist of the vertical, horizontal and diagonal members, who

connect jacket legs forming a stiff truss system, transfer the loads acting on the platform to its foundation [4]. The

primary function of a jacket structure is to support the weight of the topside structure by transferring the weight to the

foundation. The jacket structure is subjected to different environmental loads during their lifetime. These loads are

imposed on platforms through natural phenomena such as wind, current, wave, earthquake, snow and earth movement.

Among various types of environmental loading, wave forces loading is dominated loads [9]. Offshore structures may be

analyzed using static or dynamic analysis methods. Static analysis methods are sufficient for structures, which are rigid

enough to neglect the dynamic forces associated with the motion under the time-dependent environmental loadings. On

the other hand, structures which are flexible due to their particular form are to be used in deep water must be checked

for dynamic loads [2]. The calculation of the wave loads on vertical tubular members is always of major concern to

engineers. The analysis of wave effects on offshore structures, such as wave loads and corresponding responses, are of

ORIGINAL ARTICLE

ANALYSIS OF OFFSHORE JACKET STRUCTURE IN THE SYRIAN

COAST BY USING COMPUTER MODELING

and Applied Sciences are the property of Atlantic Center Research Sciences, and is protected by copyright laws CC-BY. See: http://creativecommons.org/licenses/by-nc/4.0/.

American Journal of Innovative Research and Applied Sciences. ISSN 2429-5396 I www.american-jiras.com

great importance to ocean engineers in the design, and for the operational safety of offshore structures, especially

recently when such studies are motivated by the need to build solid marine structures in connection with oil and natural

gas productions [3]. The effects of various wave patterns on offshore structure have been investigated by numerous

researchers in the past [10, 11].

From the simulations of wave loading and structural analysis on few model tests, it can be concluded that the developed

programs are able to reproduce results from the model tests with satisfactory accuracy [5].

The present paper deals the static responses of an four legged jacket platform under the environmental conditions of the

Syrian coast, in order to determine the design parameters necessary for the stability of a typical platform at a specific

depth by using the computer program SACS. SACS (structural analysis computer systems), a design and analysis software

for offshore structures and vessels, is used for the modeling and analysis of the jacket.

2. MATERIALS AND METHODS

2.1 Study site and data availability:

Environmental data of the platform model for static analysis are based on study conducted by the Institute Kaspmornii

proekt, to implement the technical project to expand the port of Lattakia, which is located in the northwestern part of

Syrian territory. The wave system was determined in the study area based on the processing of wind data taken from the

overall weather maps of the Eastern Mediterranean between 1975 and 1951 (25 years).

Wind speeds at 10m above mean sea level from three main geographical directions with 1 and 100- years return period

are shown in table (1).

Table 1: The table presents the wind speeds with 1 and 100- years return period.

Geographical

Direction(from)

Wind Velocity (m/s)

1-year

100-years

south

11,0

South-west

14,0

North-west

10,0

2.2 Data processing:

The values of the significant wave heights and their periods were calculated in the study area Depending on the CEM

relationship for wave prediction. The wave height and period of wave with 1 and 100- year return period shown in table

(2).

Table 2: The table presents the wave height and period of wave with 1and 100- year

return period.

Geographical

Direction(from)

wave

1-year 100-year





(m) 



(s)





(m) 



(s)

south

1.98 6.1

4.4 8.1

South-west

2.4 6.4

6.7 9.94

North-west

1.5 5.3

4.4 8.2

2.3 Environmental loads:

Water force can be classified as forces due to waves and forces due to current. Wind blowing over the ocean’s surface

drags water along with it, thus forming current and generating waves. The forces induced by ocean waves on platform

are dynamic in nature. However, it is the accepted practice to design shallow water platforms by static approach. As a

water depth increases and platforms become flexible, dynamic effect becomes significant [9].

2.4 Waves:

Regular wave theories used for calculation of wave forces on fixed offshore structures are based on the three

parameters water depth (d), wave height (h) and wave period (T) as obtained from wave measurements adapted to

different statistical models, as The figure1 presents. Wave plus current kinematics (velocity and acceleration fields) are