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**Industry**

**Oilfield Places**

**Technology**

Nakazono, Takefumi (Kagoshima University) | Kunitake, Masato (Miyazaki University) | Kondo, Fumiyoshi (Miyazaki University) | Inagaki, Hitone (Kagoshima University) | Nakazawa, Takao (Miyazaki University) | Kikumura, Tadayoshi (Ready-Mixed Concrete Association of Miyazaki) | Saito, Masaki (Crown Engineering Co. Ltd.) | Kakuda, Itsuro (Nihon Suiko Consultant Co. Ltd.)

In order to predict thermal cracks in coastal concrete structures, it is necessary to have a precise grasp of the hysteresis of temperatures generated by heat of hydration. Therefore, the temperatures solved by three-dimensional finite element analysis using the Galerkin method were compared with· the measured temperatures, but it was not possible to make a better approximation of their hysteresis. Accordingly, the interior concrete temperatures were calculated using a new equation that we have proposed instead of an empirical equation expressing the characteristics of heat generation in concrete structures. The hysteresis of the calculated and measured temperatures showed good agreement.

In order to predict thermal cracks in coastal concrete structures, it is necessary to have a precise grasp of the hysteresis of temperatures generated by heat of hydration. Although a large number of studies; have examined concrete temperature for a period of curing of mass concrete structures, little attention has been given to the interior temperature generated by heat of hydration in concrete structures of small volume. Two Sets of data averages for temperature and humidity were obtained from meteorological records of the last ten years in Miyazaki, Japan, and were adopted as the environmental conditions for the concrete specimens. The interior concrete temperatures were measured by a thermocouple sensor embedded at the center of each specimen, which was cured at a constant 30 °C and 80% humidity as summer conditions and at 5°C and 50% humidity as winter conditions in the laboratory (Nakazawa et al, 1987). Then, the hysteresis of temperatures generated by heat of hydration at the center of the concrete specimens was simulated by a three-dimensional unsteady heat conduction problem in a Cartesian coordinate system using finite element analysis with the Galerkin method. The partial differential equation for unsteady heat conduction in an isotropic solid body in the Cartesian coordinate system was solved using a convection boundary condition.

ISOPE-I-96-237

The Sixth International Offshore and Polar Engineering Conference

SPE Disciplines: Well Drilling > Casing and Cementing > Cement formulation (chemistry, properties) (0.86)

The tubular joints hot stress histories under ice loading are determined by the ice break forms, which are related to some factors such as pile features (erect or sloping), ice thickness and toughness, etc. A new method for the more conclusive and precise stress response analyses has been proposed according to ice thickness and contact statements between ice and piles, so that the exactness of fatigue life predictions are enhanced. The works required to refine the method in the future are point out in the end of the paper.

Bohai water is of shallow seabed and small waves relate to other waters in our country, but on the other hand, ice condition is relative severe, there are floating ices even in the least cold years. Several platforms had collapsed or seriously damaged due to ice, as brought on huge losses for the oil exploitation and production. For the platforms serviced in Bohai sea, especially in northern part, decreasing and elimination of the resonant vibrations induced by ice, precisely predicting of fatigue lives and evaluating the safe fatigue and fracture reliability, are of great pragmatic importance. However, ice crystallization and its toughness are influenced directly by temperature changing of air and water, and the sea water states, etc.; ices floating velocity magnitude and direction are judged by the factors such as wind, tide and current; its breakings are affected by the contact surface situations additionally. These all make it difficult to solve the force between ice and structures, up to now, a little knowledge about the ice loading properties are clearly known, as lower the precision of fatigue life prediction. In order to obtain the information about ice condition and the structure responses in the working area, a program had been carried out on the JZ20·2 platform in Bohai sea, which aimed to the measurements of ice and the structure dynamic responses.

ISOPE-I-96-257

The Sixth International Offshore and Polar Engineering Conference

Shin, Jong-Gye (Dept. of Naval Architecture and Ocean Engineering, Seoul National University) | Kim, Won-Don (Dept. of Naval Architecture and Ocean Engineering, Seoul National University) | Lee, Jang-Hyun (Dept. of Naval Architecture and Ocean Engineering, Seoul National University)

Press bending and line heating are two forming methods to shape the curved hull plates in shipbuilding industries. There have been many attempts to automate the forming process, but no feasible solutions are seen due to lack of information required for the automated process. In this paper, first the kinematics of final curved shells with reference to the flat plates is studied. Second, a numerical modeling of the thermo-elastic-plastic analysis of the line heating is suggested for double curvature shells. These combined information helps establish an automated process of forming curved shells.

Ship hull plates at fore- and after- body have double curvature. Ship hull plate parts are traditionally formed up to the required double curved shape through the process of shell development, press bending and line heating. Two types of research on the plate forming process have been in-progress. One is how to get the desired surface, and the other is how much the deformation of a plate by the heat source is. The studies on how to get the desired surface is to determine the heating path, heat energy, and the processing sequences. Ueda et al (1994a) divided the deformation caused by line heating as bending strain and in-plane strain, and investigated the effect of each component. For the studies to get the deformation of a plate by the heat source, strip model was given by Moshaiov and Shin (1991). Kawakami et al (1985), Shin et al (1995) has modelled the line-heating process by using a general finite element analysis package. But, up to present, the studies overlooked the shell development process of the desired surface into the flat plate. Because the hull plate forming is the reversal of the shell development, plate forming and shell development process must be studied concurrently. Therefore this paper presents how to estimate the inherent strain by mapping between the shell surface and the developed plate.

ISOPE-I-96-270

The Sixth International Offshore and Polar Engineering Conference

SPE Disciplines:

The free-surface motion induced by the constant rotation of a fluid-filled cylindrical structure about a vertical axis of filet from that through the geometrical center of the cylinder is investigated theoretically. The fluid is assumed inviscid and the motion irrotational and so the theoretical development is based on potential, flow theory. A perturbation parameter is defined in terms of the axis of filet and the subsequent analysis includes terms up to second-order in this eccentricity parameter. Numerical results are presented that illustrate the influence of the various problem parameters on the free-surface elevation and the induced velocity field in the fluid at both first and second-order.

Since cylindrical structures containing fluid appear in a wide range of different engineering applications, the dynamics of fluid-filled cylinders have been the subject of many diverse studies. Although a wide range of literature exists on applications where viscosity bas important influence on the dynamics of the entrained fluid, the following discussion is restricted to situations where the dynamics of the fluid may reasonably be predicted by considering it to be inviscid. Several investigators have studied the effects of base excitation on the dynamic response of fluid-filled storage tanks The effects induced by the lateral motion of fluid storage tanks bas received considerable attention from the seismic community for many years. Although the earliest studies considered the tank containing the fluid as rigid (e.g., Housner, 1957), more recent investigations have included tank flexibility effects and have developed semi-analytical methods for the prediction of fluid-tank interactions (Haroun and Housner, 1982a, 1982b; Haroun, 1983). Recently, Barton and Parker (1987) incorporated diaplacement-based fluid finite elements to investigate the seismic response of both anchored and unanchored fluid-filled cylindrical storage tanks. The influence of soil-structure interaction on the dynamic response of fluid-filled, circular cylindrical tanks subjected to a horizontal ground excitation bas been studied by Veletsos and Tang (1990) and Veletsos et at. (1992).

ISOPE-I-96-222

The Sixth International Offshore and Polar Engineering Conference

This paper studies several, important questions in reliability analysis: 1. uncertainty analysis of enviromental loads on marine structures, 2. influence of correlations among multivariables on structural failure probability and sensitivity analysis, 3. Finally, vertical breakwater and jacket platform are taken as examples for calculation using Importance Sampling Procedure to directly solve structural failure probability.

Probability design method is devided into three levels: in the level 1 method a single characteristic value is connected to each uncertainty variable and a set of e. g. partial coefficients is introduced to provide a design basis. In the level 2 method, each uncertainty variable is characterized by two parameters (usually the expected value and the variance) and the, correlation between any pair of variables is characterized by a single measure. namely the covariance. More advanced methods are the level 3 methods characterized as being probabilistic methods of analysis based on knowledge of the joint distribution of all basic variables. Level 2 fits to the situation that limit state equation is linear. At the same time reliability index ß is the approximate expression of failure probability (P

ISOPE-I-96-306

The Sixth International Offshore and Polar Engineering Conference

In a previous paper by Chucheepsakul et al., presented at the ISOPE-95 conference, the effect of axial deformation on the equilibrium configurations of marine cables expressed in rectangular coordinates was discussed. The use of rectangular coordinates in that study has a limitation when the slope at the bottom end of the cable is very small or as the tangent line of the cable approaches horizontal. As a result it may cause numerical troubles and numerical accuracy may not be achieved. To circumvent this limitation, the use of polar coordinates is recommended. In this paper the work-energy functional of an extensible marine cable expressed in polar coordinates is formulated. Numerical procedure based on the finite element method referred to polar coordinates is used to solve the problem. The numerical results of cases with various values of Poisson''s ratio are given.

Research studies on the analysis of extensible cables and marine cables have been dealt mostly based on the use of arc length as the independent variable with a specified total unstrained arc length (e.g., Henghold and Russell, 1976; Goodman and Breslin, 1976; Henghold and Russell, 1976; Goodman and Breslin, 1976; De Zoysa, 1976; Huddleston, 1981; Irvine, 1975; Triantafyllou, 1982; Banjwu and Iradj, 1984; Burgress, .1993; and Huddleston and Ham, 1994). In some cases, the total unstrained arc length may be unavailable but the top tension of cable is· specified or can be indentified. Therefore, the use of arc length as the independent variable, as is commonly done, may cause numerical difficulty which results in inefficient method of analysis. To alleviate this difficulty, a more efficient method of solving this practical case was given by Chucheepsakul et al. (1995) and Laohapotjanart (1995) in which a variational equation and an equilibrium equation are used.

ISOPE-I-96-116

The Sixth International Offshore and Polar Engineering Conference

Motions and associated transfer functions of a wave-following buoy with a single-point slack mooring are studied by using two buoy/cable numerical models (one time domain model and one frequency domain model) and field-measured data. Field data were measured by a National Data Buoy Center (NDBC) 30m discus buoy that has an all-chain slack mooring with a significant amount of excess chain lying on the sea floor. Motion transfer functions obtained from the two numerical models and field data are compared. This study shows that the buoy responses are weakly nonlinear within the meaningful wave frequency range (f < 0.4 Hz). The time domain model compares more favorably to the measured data than the frequency domain model.

Ocean buoys are used for various purposes that include navigational aides, data collection, and communication relays. A buoy needs to be designed correctly to properly perform the desired functions. Some design considerations for ocean buoys were discussed by Timpe and Teng (1993). It is important to know the buoy characteristics and performance through analysis and testing to properly design and use a buoy. Teng and Timpe (1994) reviewed and discussed various tools used for analysis and testing of ocean buoys. These include mathematical and numerical analysis, physical model testing, and prototype testing. NDBC, an element of the National Weather Service (NWS) of the National Oceanographic and Atmospheric Administration (NOAA), maintains a network of data buoys that are deployed off the coast of the United States to measure environmental information and report data in real time. Currently, NDBC has 73 moored data buoys at the U.S. east and west coasts, Gulf of Mexico, Great Lakes, and Hawaiian Islands. Depending on missions, locations, and environmental conditions expected at the buoy location, a variety of buoy types are used, including 2.4-, 3-, 10-, and 12-m discus and 6-m boat-shaped NOMAD buoys (see NDBC, 1994).

ISOPE-I-96-211

The Sixth International Offshore and Polar Engineering Conference

SPE Disciplines:

SUMMARY

The nonlinear effects of the steady flow on wave diffraction-radiation at low forward speed are analyzed via a new theoretical method. The method is based on a decomposition of the time-harmonic potential into linear and nonlinear components. The linear time-harmonic potential satisfies the classical linearized free-surface condition while the nonlinear potential takes into account nonlinear interactions between the local steady flow and the linear time-harmonic potential. Both the linear and nonlinear potentials are evaluated by using the source method which involves the Green function of wave diffraction-radiation at small forward speed given in Noblesse and Chen (1995). Within the approximation of order 0 (τ), the present method leads to a consistent solution of the time-harmonic potential. The limitation of application to bodies of large size by the previous analysis based on a perturbation expansion, due to secular terms, is removed. The present method gives correctly fluid kinematics at any point in the fluid domain, in addition to first-order, second-order loadings, and wave drift dampings. It is shown that the nonlinear effects of the steady flow at the free surface give substantial contribution to above quantities. **INTRODUCTION**

Nonlinear effects are significant in the vicinity of floating bodies, as is convincingly shown in some recent studies by using hybrid calculation methods based on zonal coupling of an inner nonlinear and/or viscous flow with an outer linear potential flow. Even within potential theory, nonlinear interactions between the (unsteady) time-harmonic flow and the local steady flow are important for blunt bodies, as shown in Faltinsen (1994). A body advancing at constant speed in regular waves generates a steady Kelvin pattern plus several systems of linear time- harmonic waves. The general interaction between the steady flow and the time-harmonic flows may be solved by using a zonal approach, which needs considerable effort in solving numerical problems associated with higher-order derivatives of the velocity potential and in required CPU time.

ISOPE-I-96-214

The Sixth International Offshore and Polar Engineering Conference

A detailed study of the influences of the stochasticities in sand Density, coefficient of earth pressure, angle of interface friction and pile diameter on the axial load capacity and probability of failure of single piles is presented. Practical significance of this work, for researchers and practitioners, is discussed. One of the important conclusions drawn is that methods should be developed to improve the estimates of not only the average value but also of the probability distribution of the density of soils.

The Challenge of prediction of load carrying capacity of piles is a natural consequence of the physical, statistical, model and human uncertainties. The main challenge, in the context of this paper is presented by the lack of satisfactory understanding of the soil-pile interactions as well as limited, incomplete and unreliable soil information. The stochastic nature of loading imposes additional uncertainties. At the ISOPE.94, the authors presented a philosophical and practical basis for a methodology that acknowledges the above stated uncertainties and helps in carrying out design of piles using reliability analysis, with Monte Carlo simulation (Singh et al, 1994). The main thrust of the argument was that the prevalent practice of using factors of safety is not only deterministic and irrational but it also discourages clearer understanding of the relative importance of the various influencing factors. It was also argued that reliability/probabilistic approaches· encourage healthy scepticism towards assumptions in modelling and design as well as towards the test data and design inputs. It was pointed out that this approach is more rational and reliable as compared to the most prevalent probabilistic approach of using reliability index, ß.

ISOPE-I-96-075

The Sixth International Offshore and Polar Engineering Conference

analysis, Berezantsev, capacity, density, design, diameter, Load, machine learning, mean, medium, model, parameter, pile, probability, profile, sand, sensitivity, SOIL, study, uncertainty, value

SPE Disciplines:

Dijkstra, O.D. (TNO Building and Construction Research) | van Manen, S.E. (Rijkswaterstaat) | Gijsbers, F.B.J. (TNO Building and Construction Research) | van der Weijde, H. (Rijkswaterstaat)

This paper is a summary of a study ''on the tubular joints in the steel gates of the Eastern ScheIdt storm surge barrier in the Netherlands''. This study was commissioned by the Directorate-General for Public Works and Water Management (Rijkswaterstaat) and carried out in the period 1985-1992. At a late stage during the fabrication of the Eastern ScheIdt storm surge barrier it was found that, due to improper control during rolling, many tubes were made of steel with a relatively coarse grain. It was therefore decided to use probabilistic methods to determine the failure probability and optimum inspection strategy. The optimum strategy was determined on economic grounds, based on a consideration of the investments, costs of inspection, costs of repair and failure costs. Safety was included as a boundary condition. The study indicated that it was necessary for financial reasons to differentiate inspection schedules, depending on the load and type of material.

When fabricating the steel gates for the Eastern ScheIdt storm surge barrier in the Netherlands it was discovered that the tubes of the main structure contained coarse-grained steel. This was due to insufficient control during hot rolling of the plates to produce these tubes. Coarse-grain material may lead to brittleness. This was confirmed by further tests (Charpy V and CTOD). When the barrier is closed and exposed to a large difference in water levels and high wave loads, unstable cracks may grow from weld defects (undercuts, or slag inclusion) or fatigue cracks in the tubular joints. Experiments on coarse-grain Y-joints removed from the structure showed that a chord could fail completely due to such cracks. At the time the presence of coarse grain structures was discovered a number of gates had already been installed, while others were ready for installation.

ISOPE-I-96-250

The Sixth International Offshore and Polar Engineering Conference

SPE Disciplines:

- Well Drilling (0.68)
- Reservoir Description and Dynamics > Reserves Evaluation (0.34)