Design conditions and load analysis of three leg jack-up platform, 2nd progressive report on reliability analysis of drag dominated offshore platforms

TU Deift

Second progressive repòrt on

reliability analysis of drag dominated offshore platforms

Design conditions and load analysis

of

a three leg jack-up platform

Daghigh M..

Apr 1994

report nr, SSL 354 Supervisors

Prof. Ir. S. Hengst

Prof. Ir. A.C.WM. Vrouwenvelder

Ir. H. Bòonstra

Faculty of Mechanical Engineering, and Marine Technology Ship Structures Laboratory

Technical University of Deift Mekelweg 2

2628 CD Deift The Netherlands

i

CONTENTS

_Page

i- Design çonditions of Neka jack-up platform

2

1.1 Design basics ₂

1.2 Basic environmental data for design purpose ₂

1.3 Reference water levels and air gap 3

1.4 Wave heights prediction ₄

1.5 Weibull distribution 8

1.6 Wind profile t 9

1.7 Prediction of wind velocity 11

Load Analysis, Functional loads, wave and wind loads

15

2 i

Functional loads 15

2.2 Idealization of lattice legs 16

2.3 Wave loads 21

2.4 Wind loads 22

Appendix A- Summary of characteristics of Neka platform

28

2

1- Design conditions of Neka jack-up platform

1.1 Design basics

Among designers today, the generally accepted practice in computing structural responses of jack-ups can be assembled by the Transit, Installation, Elevated (Sùrvival and Operation) and Ret ri val design conditions. For the specific survival condition in the elevated mode, both Functional and Environmental loads are associated while for the operational condition in the elevated mode., the accidental loads together with the environmental loads after credible failures, or after accidental flooding have to be added to the design load cases in survival condition (i.e. in total 4 relevant loading condition are combined in the operation condition). The functional loadings are contributed from the inherent loadings which are necessary as a consequence of the structure's existence (In literature this type of loading is also called the Gravity Loads). The structure is composed to the tiideal circumstances", i.e. no environmental loading as well as wind, wave and etc. are existed. In the evaluation of functional loads both Dead Load (D.L..) and Live Loads (L.L.)are included. The environmental loads are imposed to the platform from the effect of natural events as well as wind loads, current, waves, earthquake, ice, movement of ground and also the variation of hydrostatic pressures and the buoyancy forces by the variation of the sea water level due to the astronomical tides, In operational mode, the response of the structure are considered with the dynamic loadings. These loadings are contributed from the impact of the platform de to the vibration of drilling units, waves and earthqUake. The collision damage by the impact of a vessel with the platform is also included in the operational loading.

1.2 Basic environmental data for design purpose

Neka jack-up platform is originally constructed to operate in the Caspian Sea located on the

North of Iran (Lat 360 35' N ;

long 53° 20' E). The environmental data for the Caspian

Sea is not available-from-the-various-meterologicaioffices-(KNMI-in-Netherland,--Met-Office

in UK) because the Caspian sea is used in certain very special cases for the navigation purposes and there was a little Shipborne wave recorder present in the area. Therefore an attempt was given to establish the reliability analysis of jack-up structure due to the Northern part of North Sea and this can give an insight for the behaviour of jack-up platform in the original sea condition.

In the northern part of North Sea, the complete environmental description of three locations have independently reported by two reports of marex (marine exploration limited in UK). The full predictions of the wind, wave, current have derived for Hutton Area (61° 05 'N 01° 24'

E) , Stevenson Station (610 20' N 00° E) and Famita station (57° 30' N 3° E) and the joint probabilities of the meterological conditions have evalUated. The predicted wind conditions can be applied to the general East of Shetlands area of the Northern North Sea. The wave and current predictions are referenced especially to the Hutton area and a 150 metre water depth. For Stevenson Station, comprehensive environmental data (especially for wave predictions) have collected from February 1973 to February 1976 and these data are reported together

Design conditions of

3

_{Neka jack-up piaform}

with the reliable data recorded by drilling rigs in the

area. Extreme wind speeds have predicted with lower error margins than wave heights since all relevant wind records, including the North Sea, North Atlantic and coastal weather stations are incoopertaed with the data from drilling rigs and weather ships in the area. Current speeds below the.water level are expected to be more reliable than the surface current speeds since the surface current speeds have derived theoretically.

1.3 Reference water levels and air gap

For the purpose of the this investigation, the reference datum is taken

as the Lowest

Astronomical Tide (LAT). The Mean Water Level (MWL) is defined by the mean of

corresponding (LAT) and Highest Astronomical Tide (HAl) in the given location.

In design of Neka jack-up platform, the environmental conditions has been adopted from the notes on design conditions of Neka Power Plant in Iran and the main study report prepared by the rig builder in Finland. Based on the Neka power plant design conditions, in 1976 for the design of Neka power Plant, the water level has adopted by the mean sea level to be + 97.50 m. Water levels of Southern Caspian Sea (S.C.S.) between 1976 and 1986 has arisen to the mean sea-level about + 98.00 m. The rig builder assumes maximum operating water depth to be 91.5 m. which is 6.5 m lower the Neka Power Plant prediction. On the other hand, information over the future develópment of the sea level is not available and there seems to be no reason to consider the maximum sea level higher than +98.80 m for the present situation. Because the astronomiäal tide in the Caspian Sea can be neglected, the corresponding relation between three proposed depths may be taken as

{ttA7} = f WLk.8. = 98.8 m.

However, the extreme Still Water Level (SWL) shall be expressed as the Highest Astronomical

Tide (HAT) plus the Storm Surge. The storm surge height for Caspian Sea may be taken by 1.2 m, thus by assuming that the sea floor is flat, the undisturbed depth d shall be evaluated from the still water level SWL as

i-{Storrn surge}55 = 98.8 + 1.2 = 100 m. (1.2) The air gap is defined as the minimum clearance between the hull struçture and the maximum Crest Elevation (CL) With the environmental condition of Caspian Sea, above the Still Water Level (SW'L), the Crest Elevation (CE) is to be

18.28 I 2 = 9.14 m and the air gap is

determined as the distance between the CE and the underside of the hull (or any other vulnerable part attached to the hull, if lower). The minimum air gap should not be less than 10 per cent of the combined astronomical tide, storm surge and the wave crest elevation. The air gap is not required to be greater than 1.2 m in DnV classification [3,7] or 1.5 m in Recommended practice [4]. For the proposed structure in the Caspian Sea environment we

Design conditions of

4

_{Neka jack-up p1aform}

Airgap}55

= 10% x(1.2+9.14) =1.034 1m. (1.3)

For the purposes of study in the northern north sea environment, calculations will be carried out using 150 m water depth (LAT= 150 rn).

=150 _{m (1.4)}

In the North Sea (N.S.) environment, the Highest Astronomical Tide (HAT) is 2.3rn, the Pressure-induced surge and the wind induced surge are each one 0.6 rn. Thus the extreme Still Water Level: (SWL) shall be obtained as the Highest Astronomical Tide (HAT) plus the

Surges and that will be equal to 153.5 m (d=153.5 m).

dNRs =153.5m (1.5)

Finally, the North Sea environmental condition gives an estimate of air gap for the proposed structure. The height of wave above still water level is 16.8 m. and thus by taking into account the astronomical tide and storm surge, the calculated air gap will determined as

{Airgap}5 =10% x(16.8 +2.306)

=1.97 m> 1.5m. (1.6)

Thus the air gap in the North Sea environment is considered to be 1.5 m. 1.4 Wave heights prediction

The basis of the wave height and wave periods prediction in the Caspian Sea has been the application of empirical relationships of Darbyshire and Draper over a deep sea with a certain wind velocity and a certain fetch. Prior to design phase of Neka Power Plant, wave heights, periods and directions of the waves have been estimated on basis of wind observations at harbour Nowshahr. Visual observations have reported from Mr. Wassmer of Motor Columbos in period 1302/04-03, 1985, and by Capt. Nienhuis of Deift Hydraulics in the period of 19-02/16-03, 1986. Non of these data yield to the wave data at Neka location with sufficient confidence level because:

- The wave heights have been observed visually,

- The number of observation days and its period only covers a very limited period of year.

A large scatter between wave heights and wave periods has been estimated by both

observations and a simple relationship cannot be ascertained. Thus the following procedure for the determination of wave climate has been adopted in the South coast of Caspian Sea. In refereñce [24], a typical empirical relationship have used between wind blOwing with certain velocity, length of fetch and the consequent wave heights, periods. The applied fetch is equal to the distance to Neka as measured from the borders of the Caspian Sea in various directinns with an assumed maximum fetch length of 500 km. Wind duration is long enough to develop a fully arisen sea which is approximately 18 hours. For a 'smaller fetch length,

Design conditions of

5

_{Neka jack-up p1aform}

intermediate values are also possible, depending on the actual fetch and direction of wind blowing. The maximum significant wave height of 11.7 m in Table 1.1 seems acceptable compared with the maximum wave height of 18.18 m given by the rig builder.

Table 1.1 : Prediction for wave characteristics at Neka (Caspian Sea) [24]

Two methods have used for the prediction of wave heights in North Sea environment [251. The first way of wave prediction involves the application of Darbyshire and Draper graphs with the wind speeds and the second type is based on direct estimation of wave data which are measured or derived by hindcasting.

1) In the first approach, the highest 50-year wave height in a 6 hour storm is predicted by 21.6 m in a 10 minutes record with a period of 16.5 sec. The number of waves in 10 minutes is 600/16.5 36 waves while for a 6 hours storm, the number of waves is assumed to be

6x3600/16.5 = 1309 waves. Thus for a 6 hour storm, the maximum

wave height is Direction with

respect to Grid North

Fetch length (max.

value 500 km)

T (sec.)

H (m.) 0

<500

6 2.1 500 15.6 11,7 15

<270

6 2.7 270 12.7 8.6 30

<185

6 2.7 185 11.3 7.0 45

<110

6 2.7 110 9.5 5.5 60

<95

_{6 2.7} 95 9.0 5.2 75

<75

6 2.7 75 8.3 4.6 300

< 420

6 2.7 420 14.7 10.8 315

<460

_{6 2.7} 460 15.1 _11.2 330

< 500

6 2.7 500 15.6 11.7 345

< 500

6 2.7 500 15.6 11.7

Design conditions of

6

_{Neka jack-up platform}

calculated by the Darbyshire-Draper method with two values of F2 = 7.58 and F1 5.37 appropriate for the 1309 and 36 waves respectively. Thus for 6 hour storm in return period of 50 year:

H_max

=21.6x758-30.5

m (1.7)

For the Stevensen Station, the severity of the three years wind dàta was estimated

comparing to the eighteen years of past Lerwick Wind data to be approximately in order of 0.99. This relative wind severity has converted to the wave severity with taking into account the power relationship of about 1.5. Thus the relative wave severity is

(0.95)15_{= 0.93} (1.8)

The corrected wave data with a severity factor of (1.0/0.093) has given for the 50 year

extreme wave heights 'equal to

H_max =27.6 x -29.7 m (

0.93

Some data are available from Norwegian rescue ship Famita in the periods of seven winters of 1969 till 1976. The Famita data has to be corrected for the severity factor as has been discussed for the Stevensen Station, the effècts of including summer wave data, the instrument effect of Shipborne Wave recorder records which gives higher wave heights than the Wave rider Buoy.

From the all data in the Huuton Field, the following significant and extreme wave heights are predicted for the 1, 10, 50, 100 year conditions. The Directional effects are predicted from the directional wind speeds predicted in sectión 2.3 and the directional extreme wave heights have only given for guidance purposes in the Marex report [25]. However the predictions given below are established from thç Marex study and it has been presented that the West and North West waves represent the principle direction for the distribution of extreme wave heights.

Table 1.2 : Marex prediction for wave heights 'at Hutton field [25]

The maximum monthly wave heights distribution' has been given in the Marex report"No. 242A and the matrices of long term hourly wave heights for the Hutton area indicate that the

Recurrence Interval

i Year 10' Year 50 Year 100 Year

H (rn)

i22

', 14.6 16.,! 16.7

Design conditions of

7

_{Neka jack-up p1aform}

relative maximum wave heights will occur in the month January and the probability

distribution of this data are recorded from the monthly wave heights frequency tables: Table 1.3 : Predicted significant wave heights at Hutton field [25]

The WeibulÍ distribution have been used for both wind and wave measured data in North Sea environment The three parameter Weibull distribution [see equation (1 10)] will represent the probabilitistic characteristic of wave data better than the wind data (r = 94.14% for wave data) and the Weibull parameters. are established by the following quantities

= O (m) the Weibull location parameter,

a= 4.3428 (rn) the Weibull scaling parameter and X= 1.9665 the Weibu il shape parameter..

The mean and standard deviation of the Weibull distribution are determined by the same procedure for the wind speeds and we have = 3.85006 (rn) and a = 2.04339 (m). The procedure for evaluation of. Weibull parameters is described in the following section.

Significant Wave height H(m) Probability Density Distribution Cumulative Probability Distribution

0.0-0,2

0 o

0.3 - 0.6

0.0146 0.0,146

07 - Li

. 0.0365. 0.0511 1.2 - 1.6 0.07299 0.12409 1.7 - 2.3 '0.16788 r 0.29197 2.4 - 3.2 0.15328 0.44525 3.3 - 4.4 0.24817 0.69342

4.5-5.9

0.14598 0.8394

6.0- 7.6

0.11679 0.95619 7.7'- 9:.5 0.0292 0.98539 9.6 - 11.6 0.0073 0.99269 1.7 -, 13.8 0.0073 0.99999

> 13.9

', 0.0000,1 1

Design conditions of

8

_{Neka jack-up piaform}

1.5 Weibull distribution

The cumulative probability diagram represented by a Weibull distribution and the statistical parameters are obtained

where VR is the wind velocity in reference height. The Weibull distributión was originally

proposed for the interpretation of fatigue data,, and in the analysis of data it is common to assume the Weibull location parameter is equal to zero. The alternative form is called the 2-parameter Weibuli distribution and is considerably simpler than the three 2-parameter type. However taking the natural logarithms from equation (1.10)

LnLn

-ALn(v-p.)-().Lna)

(1.11)

1 -F(vR)

This equatión has a form Y = X X + C, where Y=LnLn

i -F(v)

X=Ln(vR-')

Thus if the value of_¡ in equation (1. 13) is known, the equation Y = X X + C represents a straight line with a slope Xand the intercept C on the cartesian X, Y coordinates. In order to determine the Weibúll parameters for, say., wind speeds, the following steps are required: For a prescribed value, of the Weibull lòcation parameter., jx,. the slópe Xand the intercept C are determined by the least. square method.

The correlation cefficient r is defined as the degree of association of variables in linear equilibrium equation:

r

1=1 i=1 n n n n i .15) ([n

x -

(,x)2]

_[nE

2

_(E')2]'2

(.1.12) (1.13) (1.14;) (1

3. The analysis is repeated for the iterative values of Weibull location parameter, ,

F(vÁ)=1-e

VR P)

and the Weibull parameters, a and X, corresponding, to the maximum correlation coefficient r are selected.

The mean and standard deviation of Weibull distribution (Minima Type 3 distribution) can be obtained from the nth moment of distributión as follöws

E[x"] =fx'f(x)dx

(1.16)

where ftx). is the probability density of Weibull distributiòn. The mean and standard deviation are given by the gamma function as follows (see Manual of Super-Form program [29]).

i

=«.r(1 +)

(1.17)

(1.1.8)

where F(1 ± nia)

= J x'. exp(-x). dx, and the integral is taken from zero to infinity.

1.6 Wind profile

Horizontal differentiation of air pressure due to the horizontal differentiation of temperature, which creates by the sun radiation, is the original reason of the wind

in the sphere The

Coriolis forces relocate the air mass between'equator and poles. In addition to the so-called rotational windj in the world, there are some special locations that the seasonal winds are

generated in those area's. In Asia, the seasonal winds regularly change their directions 1200 alternatively in the summer and the next winter. The air transportation stops near the earth and the wind velocity increases with the height from the zero level.

The variation of wind profile with height is contributed from the differentiation of airmass

density in different temperatures and moisture with heights. In the recent DnV classification notes (1992)., the wind velocity is taken as a function of height above the still water level by a logarithmic function:

v=vR(i +0.137Ln--)

(1.19)

z0

This equation has given for the first time by JI. Lumley and H.A. Panofsky in 1964 (see' reference [20]). in Joint Industry Jack-up Committee (Recommended practice) [4], the variation of wave velocity with height in vertical distance from the stili water surface is sustained by an additional factor which 'is called the shape coefficient (G). In that case, the wind force is calculated for a vertical extend not more than 15 m and appropriâte height coefficients are given n Table 4.1 of the Recommended practice (page 24). In general for

Design conditions of

10

_{Neka jack-up p1aform}

platforms not higher than loo m, the variation of wind velocity

with height can be determined from the following equation

Z0 10m

where

z

=

height of load point above the still water level,

z0 = reference height (z 10 m

even if it is not

specified),

VR = wind velocity in reference height,

profile

n ='

mode, that is dependent to the sea and the

distance from land and the

duration of wind blowing.

The mode n is taken 7 n 13 and in Recommended practice [4] the appropriate value

is given by n

= 10 unless site specific data indicate that an alternative value isiitting. However for storm 'n 13 and for continuous winds in the open sea n = 8 is considered.

In reference [7], the wind velocity has defined with equatiOn (2.20) bya factor of l/n =

0.09. The variation in wind profile with variation of height above the still water level is given by Figure 2.1 [3,7]. Usually the measurements of wind speed are obtained using visual estimation of the Beaufort wind forces or direct one minute mean values measured by an

anemometer. These measurements then are recorded continuously on chart rolls which are read for values of hourly mean wind velocity, maximum gust velocity and wind direction. The observation are usually made three-hourly. In case that, the observátions are taken in shorter or longer time of 1 hour, then the reference wind velocity should be multiplied' to the

gustfactor-br(tjwllere-for_t_l_hour,_thegust_factojsgreaterthanL[b1 (t,1)

> i] awl for

t >

1 hour, the gustfactor is less than 1 [b1 (t,7) < 1].

1.7 Prediction of wind velocity

With reference to the Wind load for Neka jack-up structure, the reference wind velocity has

given by VR = 51.4 mIs _{for the Caspian Sea by the rig builder. Spot winds observations}

indicates a wind frequency distribution at the Lenkoran (a harbour of Caspian Sea) for the month Janùary of the years 1983-'91. These data has been published by the Met Office in UK which can only give a useful guidance to directiOnal extreme wind speeds and should be treated with some caution because of some transmission errors. However it can be observed that the predicted wind speed by' rig builder is in the same order of magnitude as has been obtained by the results of Met Office where the 50 years' wind velocity is predicted to be 65.7 rn/s for the West winds.

VVR ()

(1.20)

z0

Table 1.4 : Prediction for wind speed at Caspian Sea [24]

The maximum wind speeds will occur in the west direction and the probability distributions of hourly maximum wind speeds are determined in Table 1.5:

Table 1.5: Probabilistic distribution of wind speed at Caspian Sea Direction Recurrence Interval (velocities per mis)

1 year 10 years 50 years 100 years

North 10.36222 12.25834 13.52696 14.06115 North East 4.364635 4.927004 5.289118 5.438618 East 4.790379 5.338355 5.687908 5.831527 South East 12.16015 15.47914 17.8299 18.84924 South 35.4231 49.87226 60.93172 65.9231 South West 20.86493 34.08234 45.56071 51.09024 West 40 16923 54 79184 65 71158 70 57764 North West 28.21281 36.6504 42.71765 45.36916

Wind velocity (mis) Probability Density

Distribution Cumulative Probability Distribution

0.0 - 0.2

0.003559 0.003559 0.3 - 1.5 0.295374 0.298932 1.6 - 3.3 0.508897 0.807829

3.4-5.4

0.120996 0.928826 5.5 - 7.9 0.05694 0.985765 8.0 - 10.7 0.003559 0.989324 10.8 - 13.8 0 0.989324 13.9 - 17.1 0 0.989324 17.2 - 20.7 0 0.989324 20.8 - 24.4 0 0.989324 24.5 - 28.4 0 0.989324 28.5 - 32.6 0 0.989324

Design conditions of

The three parameter Weibull distribution is used in order to extrapolate the predicted wind speeds in long term and its parameters are obtained as

= 0.099 (mis) the Weibull location parameter,

a

= 1.925 (mIs) the Weibull scaling parameter and X= 0.7266 the Weibull shape parameter

The mean and standard deviation of Weibuil distribution for the wind speed in Caspian Sea environment are determined by j = 2.4538 (mIs) and a 3.3007 (mIs) respectiely. For the seek of analysis in the North Sea environment, the wind speeds have adopted from the marex reports in the directional estimators. The wind distributions at O.W.S. India, Mike and Lerwick have corrected for the predictions of directional extreme wind speeds. For each of eight main directions, the wave data are incorporated in a Weibull Scale plots from which the extreme wind speeds expected to occur with recurrence intervals of 1, 10, 50 and 100 years. The predictions given below are established from the Marex results and it can be seen that the West and North West winds represent the principle direction for the distributiòn of wind speeds.

Table 1.6: Marex prediction for wind speed at Hutton field [25]

12

_{Neka jack-up pia çform}

Based on the above predictions, the maximum wind speeds will occur over the west or north west directions. The maximum monthly wind data distribution has been given in the Marex rçport No. 242A andEthe matricesof-long ternrhourly--wind--speeds-for-the-I-Iajtjan--area

Direction Recurrence Interval (velOcities per mis)

1-Year 10 Year 50 Year 100 Year

North 28.0 31.0 33.0 34.0 North East 26.0 29.0 30.5 31.5 East 26.0 28.5 30.5 31.5 South East 27.0 30,5 32.5 33.0 South 29.5 32.5 34.5 35.5 South West 29.5 33.0 35.0 36.0 West 3OE5 34.0

363

37,5 North West 30.5 34.0 36.5 37.5 32.7 0.010676

_i

Design conditions of

13

_{Neka jack-up p1afòrtn}

indicate that the relative maximum wind speeds will occur in the month January and the probability distribution of this data are recorded from the monthly wind frequency tables:

Table 1.7: Probabilistic distribution of wind speed at Hutton field' [25]

There are different distributions which have been used for the long term distributiòn of wind velocities The marex report has recommended the application of Weibull distribution for the

Haitian area and thus the Weibull distribution is used heir for the predictión of

wave

velocities.

The iterative procedure for evaluation of Weibull parameters has been performed by a 'simple computer' programme and the Weibull parameters for the given set of wind speed data are obtained as

= O (mis) the Weibuli location parameter,

a= 12280

(mis) the Weibull scaling parameter and X= 1.8756 the Weibull shape parameter

Wind velocity (mis) Probability Density Distribution Cumilative Probability Distribution

0.O-Ö.2

0 0

0.3- 1.5

0.0146 _0.0146

1.6 - 3i

0.0365 0.0511 3:.4 - 5.4

_0.0299

' 0.12409

5.5-7.9

' 0.16788 0.29197 8.0 -. 10.7 0.15328'

₄₄₅₂₅

10.8 - 13.8 0.248,17 ₀₆₉₃₄₂ 13.9- 17.1 0.14598 0.8394

17.2-20.7

0.11679

,

0.95619

20.8-24.4

0.0292 , 0.98539 24.5 - 28.4 0,0073 0.99269 28.5 - 32.6 0.0073 ' 0.99999 32,7 0.00001 1

Design conditions of

14

_{Neka jack-up p1aform}

The mean and standard deviation of Weibull distribution for the wind speed in North Sea environment are determined by _{= lo! 9016 (mIs) and a = 6.03815 (m/s respectively.}

Load analysis, Functional Ioad,

15

_{Wave and Wind loads}

2- Load Analysis, Functional loads, wave and wind loads

2.1 Functional loads

For the structural analysis of the selected jack-up, consider the characteristics_{and dimensions} given m Table A i Based on the surface capacities and the density of used materials for different parts of the platform, a preliminary Dead Loads (D.L..) or fixed weight loads have been calculated as indicated in Table 2.1.

Table 2.1 Determination of Fixed Loads for NEKA platform

Similar to the fixed weights, the variable weights can be evaluated by summing up the live loads on different decks. The design deck loads are used from Table A. i (in appendix) and the surface capacities-have-beendetermined_inthedesign_manuaLofthe_jackup{17j.nie following results are drawn by the analysis of variable weights:

Table 2.2 Determination of Variable Loads (+ Live Loads) for NEKA platform Fixed weight breakdown _{Preliminary weights}

Hull + Jack house 1808 tonnes

Living quarters 111 tonnes

Cantilever and drilling substructures _{306 tonnes}

Heliport _{71 tonnes}

Equipment and outfits 1679 tonnes

Legs above the hull (height 11 m) 8.93 X 11 X 3 295 tonnes

Total lightship weight (excluding leg below the hull and the spudtanks)

4270 tonnes

Deck Load Area Total load

Pipe rack on main deck . 2.6 tIm2 147 m2 382.2 ts.

Pipe rack on cantilever deck 2.6 tIm2 239 in2 62.1.4 ts.

Machinary deck 0.725 tim2 1890 m2 1370.25 ts.

Main deck 2 tIm2 1273 m2 2546 ts.

Quarter's deck 0.435 tIm2 3 x470 in2 613.. 35 ts.

House top (main deck) _{0.435 t/in 3Ô.46 m2 13.25 ts.} House top (drilling deck) 0.435 tim2 38.55 m2 16.77 ts. 0.194 dm2

3783n2

73:4f9ts

The drilling equipment has a derrick with the dimension of44.8 m high, 9.14 m X _{9.14 m}

base and 590 metric tonnes static hook load. The substructure is designed in_{accordance with} API norms and specified design criteria with the drilling load, rotary load and set back load which in total will be 1390 metric tonnes from the data given in Table A. 1.

The total gravity load is obtained by adding of the results in Tables A. 1, 2.1 and 2.2.

W=427O+5M6 + 1390 = 11306 tonnes (2.1)

It should be emphasized that indetermination of WT, the weight of legs below deck level and

the weight of spud tanks were not included. The spud tanks weight have obtained

approximately (WPUd = 338 tonnes) and the weight of remainder parts of legs can be assumed

'by

vertical tubular

located at the geometric centre of the actual leg. The equivalent

model has to be

evaluated for both the drag force and inertia force.

For drag

component, the _{Figure 2.2 Chords with bracings}

product'

of

equivalent CO3X

D and

.for the inertia component, the product of equivalent GMX A (or GMX D2) are

contributed in the idealized model. .

The section parameters for chord' and brace elements are given in Table 1 6. With these structural parameters, the weight of one 'bay is determined and the total weight of leg is

Load analysis, Functional loads,.

16

_{Wave and Wind loads}

Total variable weight _{5646 ts.}

WkgS=893Xli6X3 3108 tonnes. (2.2) 2.2 Idealization of lattice legs' FLOW DIRECTION By definition, the

i d e a i

i z. e d hydrodynamic leg

model

is

comprised of one,

'equivalent'

Load analysis, Fünctional loads,

17

_{Wave and hind loads}

evaluated by the number of bays ( _{1134 tonnes). In order to define a suitable alternative} for the shape of jack-up bays, it has been accepted to detennine the equivalent drag and me rtia coefficients for a proposed equivalent diameter. The equivalent diameter for a bay is chosen in accordance with the geometrical characteristics and it has been given by an

equivalent diameter for bay height which occupies the same volume as well as the detailed model of the bay. Each bay Of the parametric jack-up platform has 18 elements and thus with reference to Figure. 2.2, the hydrodynamic equivalent diameter is determined as follows

Table 2.3 Evaluation of equivalent hydrodynamic tube model for lattice. leg

The total volume of one bay is summed up by addition of A1 X l on the läst column of the Table 1.6, where A1 denotes the equivalent area of element or ir D12 I 4

The equivalent diameter is then determined by: Tube. No. From To

D X t

(mmxmm)

l (m)

_{A X l}

1 1 4

800 x 50

_{6 3.015929} 2 2 6 800 X 50 6 3.015929 3 3 8 800 X 50 6 3.0,15929 4 4 5

400 x 28

' 4.95 ' 0.622035 5 4 9'

400 x28

4.95 0.622035 6 6 5 400 X 28 4.95 0.622035 7 6 7 400 X 28 4.95 0.622035 8 8 7

400 x 28

4.95 0.622035 9 8 9

400 x 28

4.95 0622035 10 1 5

360 x 28

7.78 0.791908 11 1 9 360 X 28 7.78 0.791908 12 2 5 360 X 28 ' 7.78 0.791908 13 2 7 360 X 28 7.78 0.791908 14 3 7

360 x 28

7.78 0.791908 15 3 9 360 X 28 7.78 0.791908 16 5 7 200 X 12 4.95 ' 0. 155509 17 7 9

200 x 12

4.95 ' 0. 155509 18 9 5

200 x 12

4.95 0. 155509

¡= 18

Vß= A.11,= 17.998 m3

14V

DE=Aj__!_1.954 m

where s = 6 m. denotes the height of one bay.. The .equivalént drag coefficient is given by:

¡= 18

=R

CD

The. equivalent drag coefficient for each member, GDE , is determined by.

[sin2 _{cos2Il,sin2«1]2 C,} 'DES

In which:

GD = Drag coefficient of element i'

D1 = _{reference diameter of element i '(including marine growth as applicablé)}

length of member i

= Angle which determines the flow direction (Figure 2.2)

Angle which determines the inclination of element from horizontal (Figure 2.2). By .a similar procedure, the equivalent values of inertia coefficient, cMR, representing the bay

interia can be found by summing up the hydrodynamic coefficients of individual members as ¡r 18

CM=E

CM (2.7)

The equivalent inertia coefficient of an element,,GMEI, is defined by the equivalent area of 'leg

AE, the equivalent'.area of element A1 and the inertia coefficient of the element GMj,as follows

:CM=[l 'i-(sin23.,.+cos2 I5iSin2i)(CM- 11)] (2.8)

The computation of equivalent drag and inertia coefficients has been performed for heading

600 _{The appropriate drag coefficient for the leg chords is recommended by the following}

equations [41:

(2.3)

(2.4)

(2.5)

(2.6)

Load analysis, Functional loads,

19

_{Wave and Wind loads}

CD( ¿x)=C

çD()=CD(CDl_CDo)srn2(a_200)]

; 20°<a<90°

(2.9)

Table 2.4 Equivalent Hydrodynamic Coefficients for use in design wave analysis (2.10)

where a = _{O indicates the case that the direction of wave is parallel to the rack plate. The}

CDO and CDI are the drag coefficients of leg chorrds for flow parallel and nonna! to the rack. The drag coefficient for the flow normal (a = 900) _{to the rack, CDI, is related to the}

projected diameter of W and is varied between 1.8 and 2.0 for different ratio of WID (W is the mid depth of racks and D is the diameter). For simplicity, it has been concluded that the equivalent drag coefficient for the leg chord can be expressed by equation (1.29) given in the Marine Technology Division (see reference [3]).

In the first report, the drag coefficients are given by G

65 for zero (0 min.) marine

growth thickness. Because that the site specific data for marine growth is not available, it has decided to use the minimum marine growth thickness_{tm = 12.5 mm for the jack-up studied.} Thus the new diamater of all elements below the MWL + 2 m is obtained by adding the

total of 25 mm. to the prior diameter., Further below the water level, the increase of

roughness leads to the increase of drag coefficient which is assumed to be C = 0.70 for the parametric study. It has also assumed that the inertia coefficient may be applied for all

directions with the same value C'M = 2.0. By the procedure explained before, the following (Table 2.4) presents the hydrodynamic coefficients of jack-up legs for the heading

_a

600.

The stiffness of a cylindrical jack-up leg is characterized by the beam properties [3,4,7]. The equivalent cylinderical leg parameters are defined in term of the "equivalent shear area" of a two dimensional lattice structure [3,7]. The equivalent stiffness of the leg gives the same stiffness for all directions. The validity of equivalent beam:, parameters is restricted for the symmetrical configuration of leg components. This is not the case for legs with racks on only two of the chords. However, the eqUivalent shear area for a K-braced configuration i's given by the following equation [3,4,7]:

Marine growth (t,,, = 0 mm.) Marine growth (t,,, = 12.5mm.)

2.478 ' 2.697

GM 1.830 _1.824

Load analysis, Functional loads,

20

_{Wàve and Wind loads}

A=

A.-

Qa s3 where p = Poison ratio 0.3

s = height of one bay

6m

h = side length cf the leg 9.9 m d =' length of diagonal bracing = 7.78 m

AD= cross sectional area of diagonal element 292,04 cm2

= cross sectional area of horizontal bracing = 327.23 cm2

A Ach+Ar= area of one chord including racks (2 X 10 X _{140 mm)}

C= 1178.10 ± 280 = 1458.1 cm2.

The leg shear area is determined to be AQ;= 383.10 cm2. In the equivalent beam models, each leg shall be modelled as a continuous beam with the following section properties, which are

constant over the entire length of leg. Note that the leg shear area is to be included and the values of Is,, I given below make no allowance for shear effects. The stiffness parameters for legs with three chords are given by (see also Figure 1.8):

A =3A1 =3 x 1458.1 =4374.3 cm2 =4374.3x iO4 rn2 (2.13)

(1 v)sh2

AD 84 l2A

(2.12) =-

22

A .=. x383.10=574.66 crn2=574.66x1Ø4 in2

I =1

ï

_z

=!

A h2=-!.xOE14'581x9.92=7i45 in4 2 Ci 2 (2.14) (2.15)

x3.83 x IO2x.9.92 O939 in4 (2.16)

The implementation of idealized model for leg structure requires specialcare to establish equal weight and buoyancy for both modeIs The additional mass is appended to the leg model to give the same weight of the lattice legó The buoyancy of equivalent model shall be evaluated with an iteration procedure which is applied by changing the diameters that regulates the buoyancy..

2.3 Wave loads

distances,, the total forces on the legs _{are composed of three loads F1 , F2 and F3 in} uni-directional long crested wave model. Each of leg forces are contributed from the lumped forces on leg parts and can be projected in two hoEizontal directions

_{x and y. Thus the}

relation between nodal lumped forces and total force for leg is given by

F1 = _{J. V i = 1,2,3 =leg number (2.17)}

J lumped nodú

In which fj denotes the wave force on leg number i for lumped joint j. Thus by this way,.

the internal forces on elements are correlated to the external loads for

three legs. By performing an analysis for each of three loads F1 , F and F3 , the response of each element

and its probabilistic characteristics are evaluated and the internal forces for elements are

obtained from the structural: analysis results knowing the ratio's a1, a2 and a3:

S=a1F1 +a2F2+a3F3 (2.18)

where a1, a2 and a3 are the ratio's of internal forces in the element to the total applied forces on legs F1 , F2 and F3.

Consider the simplest wave theory (linear Airy wave theory) for the computation of wave. kinematics Basically the common wave theories are used in order to determine the wave

velocity potential 4'. The velocity potential is determined in term of wave characteristics by the following expression

gH coshk

cos®

2c coshkd

where s

=z±d

O

wt-k.x

By substitution of wave kinematics in the Morison equation, the wave force for an element with unit length is obtained by the following equation

f,(:) =p 1! D2CMl + !._{p DCD !u,Iu.} . (2.20)

where i = 1,2,3 indicates the leg number. Substitution of water particle velocity and

accelerations in the Morison equation, the wave force model for the element (withunit length)

is calculated form

fj(t)=pgkC0[

D2GM(a.cos8)+!DGDI,(8/a5mø) (2.21)

Integrating this equation with respect to the length of vertical idealized cylinder, thewave

forces on the structure are obtained by

(2.19)

Load analysis, Functional loads,

22

_{Wave and Wind loads}

F1(t) _{FM,(t) +FDÍ(t) (2.22)}

and for an element located in the range of _{s s} we have

FM,(t) pg(sinhks -sinhk) D2.CÇH.cose 2coshkd (2.23) pg2k2 S S0 Slnhks.COSI]ks smhks0.coshks0 ).DCH2.Sin2 (2.24) FDI(t) = 8 w2cosh2kd 2 2k 2.4 Wind Loads

Designers of floating structures use wind load as a part of design criteria when righting levers

must be adequate to withstand overturning moments from the wind. Moored

semi-submersibles, tension leg platforms (TPLs) are especially sensitive to dynamic wind loads. The deviation of dynamic wind theory from steady state behaviour may be a problem in slender offshore structures where the high frequency range increases the self-excitation of the body due to elastic vibrations and wind turbulence are interested as well as the vortex shedding [18]. In a steady static condition, the static wind force _{component for the wind} direction perpendicular to the cross sectional plane of the block of a member are computed by the following equations [3,4,7]:

F,=P1A

(2.25)

where

F1

= the steady state wind force component normal to the element axis,

P

= the pressure at the centre of the block considered

p = the mass density of air ( = 1.2224 Kg/rn3 for dry air unless an alternative value have been justified for the location ),

4Wi

=

projected area normal to the element axis,

y

=

design wind velocity defined by equation (1.19) or (1.20),

Ç

= the shape coefficient shall be derived from Table 4.2 of 1Recommended practice (page 25 in reference [4]).

For calculation of wind forces on lattice legs, the shape coefficient Ç i

given by the

equivalent drag coefficient Cd and the equivalent diameter DE as given in Rulesj The projected

area A1 may be chosen as the product of the equivalent diameter DE and the desired leg length. For the idealization of lattice legs with equivalent cylinder, the reader is referredto

Load analysis, Functional loads,

23

_{Wave and Wind loads}

the following references [3,4,7] (see section 1.7.)

The wind forces are calculated for the parts of the jack-up outside of the water, the helicopter landed on the helideck and the life saving boats hooked to the platform near the quarters. In different elevations the wind velocities shall be obtained with taking into account the variation of wind velocity for each 5 metres.. The wind loads on lattice legs and hull structure are considered in the following elevations:

The legs from the SWL till the lower guide elevation, i.e. air gap (±0.0 m +8.7 m)

The hull depth (+8.7 m - + 16.32 m)

The leg reserve parts (+16.32 m - + 29 m),.

The wind loads for the drilling unit (with dimensions of 147' X 30' X 30' 44.8m X 9.14

m X

_{9.14 m, the drilling deck depth, 4 m) and the quarters shall be evaluated in the}

following range of elevations

Derrick open lattice structure (+25.5 m

- + 70.3 m)

Derrick hull (+ 21.5 m ± 25.5 m)

Quarters (+ 16.32 m 16.32 + 4 X 3.90 m = + 31.92 m, the width of quarter at each level is 43.35 m).

Helideck with dimensions 10 rn X 2.5 m. Boat with dimension 9 m X 0.75 m.

First we determine the area that should be used for the evaluation of wind forces in the different parts and then by determination of wind velocity and pressure, the total wind load is found in terms of KN. [n = IO in equation (1 .20)].

1) The whole area of the each leg and its shape's coefficient are obtained as follows:

A. =8.7 [3.xO.8x6 +1 xO.4x9.9 +2x0.4x4.95 i-6x7.78x0.36/sin(5477°)] 6.0

A1=63.95 in2 _; C3=2.478

(2.27)

(2.28) 2) The projected area for the deck and its shape's coefficient are determined in the following

way.

A2 F[43.74 +2 x20.19 xcos(30° ) +(53.3443.74) xsin(30°)]x7.62 =969.65 rn2 (2.29)

3) The wind loads on reserve parts of legs are determined as item (1).

-

4)_Derricks are constructed from 4 corner pipes with 40 cm diameter with internal bracings

Load analysis, Functional loads,

24

_{Wave and Wi,ìd loads}

at different elevations by 20 cm diameters. The real slope of corners are 1:10 while the apparent shape is equal to 1.10 v'2. Thus taking into account the height of derrick _{and the} distance between the corners of the structure, the distribution of heightand slope of: mooring

guys are calculated on the basis of expressions given by AISC (American Institute of Steel Construction).

No. of panels '= 4

T=2m

B=9m

11=44.8-6 =38.8m

k

(log B - log T)

No. of panels = 0.163 log e

k ± log T

e =' 2.913 m

logp

k + log e

_p = 4.243m log q =

k + log p

q 6.179 m

a =T.H

(T + e

+ p + q) = 5.060m log f =

k + log a'

f

= 7.370 m

log r

=

k + log f

r

= 10.735 m log s = k + log r s = 15.635 m b = T.h

(T + e ± p + q)

= 5.086m log g

k + log b

g = 7.407 m log u

=

k + log g

u = 10.788 m

logw=k+logu =w= 15.713m

A42 4 xO.4x 10.735/sin(84.29° )+8x2x1 i .932/sin(64. 107) +4x0.2x4.243] 4L878 rn2

A43= _{4x4x7.370/shi(84.29°) +8 x02:x8. 193/sin64. 17)} +4xO2x2.913] =28.752 rn2

A =[4x4x5060/sin(84.29°) 4-8 xO.2x5.625/sin(64. 107) +4x0.2x6.179] =23.084 rn2

The wind load on top house of derrick structure is determined:as

A45=4x2x6=48 m2 ; C3=1

Figure 2.2 'Derrick structure

Thus the projècted area for the effect of wind on derrick structure are determined as follows A41 =[4x0.4x i5.635/sin(8429°) +8 xO.2x'17.380/sin(64.107)

+4xO2x6.i79] =60.995 m2 (2.31)

- (2.32)

(2.33)

(2.34)

. (2.35)

Load analysis, Functional loads,

25

_{Wave and Wid loads}

A5 = 2 x9. 14 x 4 x{ cos(30° j + sin(30° )} = 99.88 m2 (2.36)

6) The wind loads on quarters are determined with the loads on the projected area as follows

A6 =15.6 x [7.68 +(2 x43.35 + 768) x.sin(30°)]= 855.97 m2 (2.37) Table 2.5 Detennination of Wind Loads for the jack-up in Caspian Sea envirÓnment

The total wind force in the Caspian sea enviromnent is determined by summing üp the last column of Table 2.5.

F[TOl_{wind load/or s.c.'sj} = 10508.243 KN 10.508 MN

a

Item Elevation(m) Area (m2) Velocity Pressure Tótal load

1.1

0-5

3X3635

57.21 3.03249

56.45

1 2 5 - 8 7 3 X 27 20 63 27 i 3 70979 494 74 2.1

_{87T 10}

165.43 65.27 1.59347 430.81 2.2 10 - 15 636.25 67.19 1.68847 1755.73 2 3 15 - 16 32 167 97 68 73 1 76645 484 92 3.1

16.32-20

3 x27.05

69,75 1.81942 _597.96 3.2 20 - 25 3 X 36.75 71.26 1.89909 847.92 3.3 25 - 29 3 X 29.40' 72.57 4.88115 703.61 4.1 25.5 - 41.13 60.995 74.11 508969 507.37 4.2 41.13 - 51.87 41.878 76.63 5.44128 372.41 4.3

51.87-59.24

28.752 78.00 5.63839 264.96 4.4 59.24 - 6-43 23,084 78.83 5.75926 217.28 4.5

64.3 - 703

48 79.52 2.36435 185.48 5 21.5 - 25.5 99.88 71.56 1.91568 312.71 6.1

16.32-20

201.92 69.75 L81942 600.42 6.2 20 - 25 274.35 71.26 1.89909 851.51 6.3

25 -31.92

379.70 72.96 1.99047 1235.18 7

20 -30

10 x 2.5

72.01 1.93953 79.23 8 15.57 - 16.32 9 X 0.75 68.84 1.7727 19.55

Load analysis, Functional loads,

26

Table 2.6 Determination of Wind Loads for the jack-up in North SeaenvirOnment

The total wind force in the North Sea enviromnent is determined by summing up the last column of Table 2.6.

F10,

wind load for N.N.S.J =3242.3 KN = 3.24 MN

Wave and Wind loads

(2.35) Item Elevation(m) Area (in2) Velocity Pressure Total lOad

1.. I O - 5

3 x 36.75

31.78 1.52918 168.61 1.2 5 - 8.7 3 X 27.20 35;14 1.87072 108.40 2.1

8.7-10

165.43 36.26 0:80353 132.92 2.2 lo - 15 636.25 37.32 0.85144 _541.73 2.3 15 - 16.32 167.97 38.18 0.89076 149.62 3.1 16.32 - 20 3 X 27.05 38.74 0.91747 184.50 3.2 20 - 25 3 X 36.75 39.58

₉₅₇₆₅

_261.62. 3.3 25 - 29 3 X 29.40 40.31 2.46140 217.10 4.1

255-41.13

60.995 41.16 2.56656 156.55 4.2 41.13 - 51.87 41.878 42.56 2.74385 114.91 4.3

51.87-59.24

28.752

4333

2.84325 81.75 4.4 59.24 - 64.3 23.084 43.79 2.90420 67.04 4.5

64.3-70.3

48 44.17 1.19226 57.23 5 21.5 25.5 99.88 . 39.75

96601

i 96.48 6.1

16.32-20

201.92 38.74 0.91747 185.26 6.2 20 - 25 274.35 39.58 0.95765 262.73 6,3 25 31.92 .379.70 40.53 1.00373 381.11 7 20 - 30 10 X 2.5 40.00 0.97804 24.45 8 15.57 - 16.32 9 X 0.75 38,24 0.89391 6.03

Appendix A: Summary of characteristics of Neka platform

Table A.! Summary of characteristics of the NEKA jack-up platform General verifications Main index

Type of rig Self elevating cantilever jack-up

Purpose Production platfonn

Design RR-4513C

Owner and manager National Iranian Oil Company (N.I.O.C.)

Builder Rauma-Repola Offshore Industry and (N.I.O.C.)

Yard built Neka construction yard, Iran

Platform Size of elements

Platform length a 54.86 m

Platform breadth b = 53.34 m

Hull depth

e = 7.62 m

Hull draft (structural load line) 4.57 m Height of double bottom 152.4 cm

Legs Number and size of elemeiits

Leg type Triangular (T)

Diameter of chord

D = 800 mm

Diameter of diagonals (Oblique diameter) D0 = 360 mm

Diameter of horizontal bracing Dh = 400 mm Diameter of span breaker D9 = 200 mm

Number of legs 3

Leg design length 'leg = 127 m

Distance between leg guides

e = 14.3 m

Center-line of forward leg to centre-line of aft legs

f = 31.177 m Centre to centre of aft legs

g = 36 m

Append& A. Summary of

28

_{characteristics of Neka p1aform}

Bay height (legs) s 6.0 m

Side length of the trianguJar truss leg

h = 9.9 m

Spud tank

Size of elements

Diameter 12.09 m

Height

_4.57m

Cantilever Size of elements and capacities Cantilever beams spacing 15 .24 m

Cantilever extension 12.192 m

Transverse movement from centre 3.048 m

Displacement and draft Size

Towing displacement 7866 metric tonnes

Hull draft

427 m

Jacking system Type and capacities

Type _{Rack and pinion}

Chord with racks _{3/3 (3 chords with racks over 3 chords)}

Guiding system Tangential (T)

Jacking system (Floating or Fixed) Unknown

Power system Electrical jacking power Connection type of jacks to jack house Fixed jacking system

Fixation system Rack chock system F&G design Number of Double sided racks per leg 3

Elevating units per leg 12

TOtal nominal elevatiñg capacity 7184 metric tonnes Total holding capacity i 1430 metric tonnes

Jacking speed 18.288 rn/h

Holding capacity chocks engaged 28575 metric tonnes Surface capacities Design value Deck area (less leg wells) 1890 m2

--Pipe rack on cantilever 239 m2

Pipe rack on main deck 147 rn2

Sack storage 85 rn2

Design deck loads Typical value

Pipe racks 2600 kg/rn2

Main deck outside pipe rack 2000 kg/rn2

Upper decks 725 kg/rn2

Quarter's deck 435 kg/rn2

House tops 435 kg/rn2 S

Substructure design loads Typical value (API florins) Maximum drilling load 590 metric tonnes

Rotary beam load _{450 metric tonnes}

Set back load _{350 metric tonnes}

Environmental data used in design Design value (CàspianSea)

Operating mean water depth 91.5 m

Wind velocity

y = 51.4 rn/s

Current speed _{= 0.5 rn/s} S

Wave height H 18.28 m

Wave period T 15.0 s

References

3- References

Hattori Y. et al (1982) "Full-scale measurement of natural frequency and damping ratio

of jack-up rigs and some theoritical considerations ",, Proceedings of offshore technology

con-ference, (OTC paper No. 4287).

Marine Technology Division SIPM EPD/5 (1989) "Practice for the site-specific assesment

of jackup units , Shell International Petroleum Maatschappij, May.

Det Norske Ventas Classification Notes (1992) "Strength analysis of main structures of selfelevating unit", Hovik, Norway, February.

JOint Industry Jackup Committee (192) !'Conaentaries to eleventh draft recommended practice for site specific assessment of mobile jack-up units", June.

Liu P. (1989) "Nonlinear dynamic simulation of jack-up platform models" Hydraulic Engineering Group, Faculty of Civil Engineering, Workgroup Offshore Technology,. Technical University DeIft, Nov.

Barltrop N.D. and Adams A.J. (1991) "Dynamics of fixed marine structures" Third Edition, Appendix I, pp. 670-690

Det Norske Vertias (1984) "Strength analysis of main structures of self elevating units", classification notes No. 31.5, Hovik, Norway, May

8 Joint industry jack-up committee (1992) "Commentaries to eleventh draft recommended practice for site specific. assessment of mobile jack-up units (Draft)", June.

Carlsen C.A. et al (1985) "Structural behaviour of harsh environment jack-ups", Det Norske Vertias, Paper Series No. 85P016, Hovik, Norway, Presented at the CóMerence: The jack-up drilling platform design and operation" RINA London 25-27 Sep.

Grundlehner G.J. (1989) "The development of a simple model for the deformation behaviour of leg to hull connections of jack-ups", Master of Science Thesis, Technical University Delft, Dept of Mechanical Engineering, Marine Structure Consultants (MSC) BV ref No. PF 8525-1470, Schiedam, Holland, Aug.

li- Smedstad E.N. (1993) "Stochastic dynamic analysis of jack-ups", Thesi, Technical

University Delft, Faculty of Civil Engineering, Offshore Division, The University of

Trondheim The Norwegian Institute of Technology, Department of Marine Technology, Division of Marine Structures, June

Chakrabati S.K. (1987). "Hydrodynamics of offshore structures", CML Publication, Great Britain

Sadeghi Kabir (1989) "Design of marine and offshore structures", First edition, Printed in Technical Universiiy

fK1iijéli Näi

diñèTösy, Iran

References

II

Mommaas C.J,. and Blankestijn E.P. (1984) "Development and design of two series of jack-ups for hostile waters", Marine Structure Consultants (MSC) BY. (The Netherländs), Presented in the 5th Offshore South East Asia Conference, Session 7 _{: MaÈine, pp. 7-(71-94),} 21-24 February, Singapore.

Bennett W.T. and Malcolm Sharples B.P. (1986) "Jack-up legs to stand on?", Presented at the Conference: The jack-up drilling platform (Design & Operatión) Edited by L.F. Boswell, The City Univerisity London 25-27 Sep. (1985), ISBN O-0O383218X

Friede and Goldman Limited (1981) "A jack-up rig for offshore use and a method of making such a unit with its support legs rigid", European Patent Application, Publication Number O-024-939 A2

Repola offshore Engineering (1988) "Design manual of Neka-Project", Rauma-Replola Offshore Inc., Finland.

Soding H. et al (1990). "Environmental forces on offshore structures: a state of art review"., Journal of Marine Structures (Design, construction & Safety), Elsevier applied science, Vol. 3, pp. 59-81

Blendermann W. (1987) "Umgebungsbedingungen und Lastannahmen",

Vorlesungsrnanuskript Nr.37, Institute fur schiffbau der universitat Hamburg.

Lumley J.L. and Panofsky H.A. (1964) "The structure of atmospheric turbulance", John Wiley & Sons, New York, U.S.A;

Hattori Y. et al (1982) "Natural vibration of jack-up rig" J. of Naval Architect and Ocean Engineering,, Society of Naval Architect of Japan, Vol. 26, pp. 173-181

22 Wilson E.L. and Habibullah A. (1993) "SAP9O, A Series of Computer Programs for the

Static and Dynamic Finite Element Analysis of Structures", University Of Brekely,

California.

Lipson C. and Sheth N.J. (1973)

"Statistical design and analysis of engineering experiments", McGraw-Hill Kogakusha LTD, International Student Editions.

DeIft Hydraulics. "Cooling water intake of Neka thermal power plant", Emmeloord, The Netherlands.

Marex (Marine Exploration Limited) (1979) "Hutton Area, main study report and addendum", Marex House, UK.

Ellingwood Bruce, Galambos Theodore V., MacGregor James G. and Cornell C. Alun (1980) "Development of a probability based load criterion for American National Standard

A58 - Building code requirements for minimum design loads

in buildings and other structures", Department of Commerce - Natiònal Bureau of Standards; June

References

III

Thoft-Christensen P. and Baker J.

(1982) "Structural reliability

theory and its

application", Speringer-Verlag Berlin, ieidelberg, New York.

Edwards G.E. et al. (1985) "Methodologies for limit state reliabilituy analysis of offshore jacket platforms", Fourth mt. Conf, on the Behavioür of Offshore Structures, _{BOSS 85,,}

Deift.

Koster M.J. (1993) "User Manual SUPER-FORM", Versión 1.1, Jan.

Department of Energy (1990) "Offshore Installations: Guidance on design, constructión and certification", Fourth edition, HMSO, ISBN 0-11-412961-4, June.