Skip Nav Destination
Filter
Filter
Filter
Filter
Filter

Paper presented at the Modelling the Offshore Environment: Proceedings of an International Conference, April 1–2, 1987
Paper presented at the Modelling the Offshore Environment: Proceedings of an International Conference, April 1–2, 1987
Paper presented at the Modelling the Offshore Environment: Proceedings of an International Conference, April 1–2, 1987
Paper presented at the Modelling the Offshore Environment: Proceedings of an International Conference, April 1–2, 1987

Update search

Filter

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

### NARROW

Format

Subjects

Date

Availability

1-7 of 7

Keywords: upstream oil & gas

Close
**Follow your search**

Access your saved searches in your account

Would you like to receive an alert when new items match your search?

*Close Modal*

Sort by

Proceedings Papers

Publisher: Society of Underwater Technology

Paper presented at the Modelling the Offshore Environment: Proceedings of an International Conference, April 1–2, 1987

Paper Number: SUT-AUTOE-v12-327

...

**upstream****oil**&**gas**theone current profile stoke dnft wave crest wave zone wave theone soluhon wave-current theory fenton offshore design process expansion wave cycle 1987. The Society for Underwater Technology ...
Abstract

A brief outline is given of the way in which waves and currents have traditionally been treated in the offshore design process. Emphasis is put on three unsatisfactory features: the arbitrary selection of one of a range of mequivalent wave-kinematic theories the lack of a sound theoretical basis for extension of the current velocity profile above the mean sea level up to the wave crest the neglect of any interaction between the wave and current flows, both in the measurement of currents in the wave zone and in calculations of the total fluid flow This chapter reports some developments in non-linear wave-current interaction theory which promise to help resolve these problems. INTRODUCTION In the design of an offshore structure, a major input, which largely constrains the overall design, is the load due to extreme environmental forces, and in particular that due to waves and currents. Although in reality the fluid flow giving rise to such forces is a three-dimensional stochastic process, in the great majority of offshore designs this is modelled by a regular two-dimensional wave motion, superimposed on a one-dimensional current flow aligned along the direction of wave propagation, with a prescribed vertical profile. The parameters required to specify this flow- the wave height and period, the still-water depth, and the depth-average current-are supplied by an oceanographer, who may draw on local measurement or computer hindcast, and who will provide some elements of analysis and interpretation, including assessments of appropriate extreme value distributions, joint probabilities of extreme surge and tidal currents etc. The present chapter is not concerned with the justification for his two-dimensional idealization of the three-dimensional reality, or with the process by which the ‘environmental design parameters’ are selected. Nor is it concerned with the use made of the two-dimensional fluid velocity profile in the design rather, it is concerned with the intermediate steps between these. In traditional design practice, these staps are: to compute the wave velocity profile, using a suitably chosen non-linear wave theory, and ignoring the presence of the current to establish the current profile up to the still-water level, using any available ‘engineering’ or ‘oceanographic’ insights to extend the current profile up to the instantaneous sea surface, in particular up to the wave crest, using any available hydrodynamic insights to superimpose the wave and current flows by liner addition of the velocity and acceleration vector fields, taking no account of any effect due to interaction of the wave and current These four steps are considered in more detail in the following sections. Non-linear Wave Kinematics A range of non-linear wave theories is available, and there is a widespread belief that for any given set of environmental design parameters, one or more of these theories is applicable, and that if several are applicable they yield similar results. The range of applicability of the different wave theories is considered in some detail by Sarpkaya and Isaacson (1981).

Proceedings Papers

Publisher: Society of Underwater Technology

Paper presented at the Modelling the Offshore Environment: Proceedings of an International Conference, April 1–2, 1987

Paper Number: SUT-AUTOE-v12-003

... A 407,3-23. T~ago de Ohveua, J 1963 Dec~s~on results for the parameters of the extreme value (Gumbel) d~s t r~but~on based on. the mean and the standard devlahon. Trabajos de Estadzstzca l4 ,61-81 wth whch simple model three-hourly value underwater technology equatlon mdicate

**upstream****oil**...
Abstract

INTRODUCTION The term ‘numerical model’ means different thing to different people. To a mathematician it provides a numerical solution to a problem which cannot be solved analytically; the numerical solution can be obtained to any required degree of accuracy-given sufficient computing power and assuming a finite number of solutions. The classic example is the problem of the motion of three point masses in space, form specified initial conditions. (The motion of two masses has an analytic solution). To a scientist, a model is a mathematical approximation of part of the real world which attempts to evaluate a few parameters describing that world, wither deterministically or in statistical terms. Thus, the scientist's model is a simplification of reality, so while we might solve the model with increasing accuracy, we cannot expect it to give increasingly accurate answers to the real problem. Validations is necessary. The scientist's model has two further problems: he initial conditions and other input values are not known, and they can only estimated from measurements, and as with the mathematical model, computing power may be inadequate. Environmentalists have especial difficulty with validation and input values for their models. Controlled, repeatable experiments are not possible (except with an analogue model such as a wave tank), and measurements are often difficult and expensive to make-particularly oceanic measurements, including meteorological measurements over the sea. With all these difficulties and problems, why do we use models? Essentially they have two roles: To further scientific investigation and understanding. To provide answers for immediate application An example of (a) is the use of a climate model to investigate the significance of atmospheric carbon dioxide. Suppose carbon dioxide continues its present rate of increase. What would be the effect upon our climate by the middle of the next century? What change of air temperature or sea level does the model predict for the increase in CO 2 since the Industrial Revolution, and are these changes large enough to measure? If the model prediction and observations do not agree, how can the model- and our understanding of the processes involved-be improved? A model might suggest where measurements could usefully be made. For example, models of the Equatorial Pacific have shown how ocean waves trapped at the Equator might be involved in the El Nino which affects the climate and fisheries of Peru; measurements have confirmed the existence and importance of these waves (Philander, 1986). This use of models, in furtherance of scientific investigation, is perfectly sound. The model is the hypothesis which can be disproved by measurements. Design engineer and offshore operators generally use a model in role (b), and this is more questionable. They require estimates of environmental parameters-such as tomorrow's wave height or the 50-year surge level-which can often only be obtained from models which simplify the problem and which have to be chosen to utilize the available data. These estimates cannot be correct and it is important to appreciate the order of the possible error.

Proceedings Papers

Publisher: Society of Underwater Technology

Paper presented at the Modelling the Offshore Environment: Proceedings of an International Conference, April 1–2, 1987

Paper Number: SUT-AUTOE-v12-013

... duration penod theoretical model

**upstream****oil**&**gas**engmeenng dlstnbutlon distnbution dstnbution random sea cdf houmb The adequacy or otherwise of various existing theoretical models for surface elevation, wave height, period and wave group statistics are tested against an extensive...
Abstract

The adequacy or otherwise of various existing theoretical models for surface elevation, wave height, period and wave group statistics are tested against an extensive data set from the BP Forties field. Discussion then moves to the description of the long-term wave climate and the modelling of individual storm events. Some useful extensions to the presently available models are described, covering the joint probabilities of H s and T z and the prediction of storm duration and intensity. INTRODUCTION It is common practice to differentiate between the properties of wave climates and random seas as judged (a) in the short term, over durations of 20minutes to three hours when statistical properties of the sea are assumed sensibly constant and (b) in the long-term, when non-stationary, seasonal and annual variability is central to the prediction of weather windows, fatigue environments and extreme design wave. In the short term, the work of Rice, Longuest-Higgins and many others established the properties of a linear random wave theory with a Gaussian distributed surface elevation spectra and the well known Rayleigh wave height distribution for zero-crossing waves. The analysis of long-term data has necessarily been more reliant upon empirical distributions. Ochi(1982) provides a most useful review of both short- and long-term models. The programme of probabilistic description of random seas mainly using surface elevation (¿) data collected by a Waverider buoy at the BP Forties field during six particularly severe storms, and data from Forties and elsewhere, spanning several years, in terms of summary statistics such as significant wave height (H s and average zero-crossing period (T z ). It has been shown (James, 1986) that non-linearities in wave records from floating measurement systems can be suppressed, or at least attenuated, by the horizontal motion of the buoy. Therefore, the data used in the first section of this discussion has been drawn from one of the fixed instruments mounted on the Forties FB platform. Non-Liner Surface Elevation Properties It has been commonly noted that there are consistent departures from the symmetrical Gaussian distribution of surface elevation in terms of positive skewness coefficients which may be related to finite amplitude, non-linear effects accentuating crest heights against trough depths. Variations of the Gram-Charlier perturbation on a Gaussian distribution have been proposed by Longuet-Higgins (1963) and Bitner (1980). Normalising surface elevation as y= ¿/ ¿' , Longuet-Higgins proposed the probability density function (pdf) of y as (Formula available in full paper) Where H J (y) is the J th Hermite polynomial, and¿, is µJ/s ¿ J , with µ J being the J th central moment of the surface elevation: (Formula available in full paper) Perhaps of more interest than the instantaneous surface elevation, the cumulative distribution function (cdf) of those crests (a c ) and troughs (a t ) which constitute individual up-crossing wave heights (H=a c + a t ) can be approximated on the basis of narrow-bonded seas for which ¿ and ¿ (= d¿/dt) are statistically independent by (Formula available in full paper) Where p(a c is the pdf of surface elevation form equation (1) and ¿ m is the mode (mpv) of the pdf Figure 1 shows the distribution of normalized crests.

Proceedings Papers

Publisher: Society of Underwater Technology

Paper Number: SUT-AUTOE-v12-061

... 101,665-673 SWIM Group 1985 A shallow water mtercompanson of three numencal wave predctlon models, (SWIM). Q J R Met Soc 111, 1087- 1112 hmdcast procedure usmg whch penod rosenthal north european storm study meteorologcal office wth gunther underwater technology gnd pomt

**upstream****oil**...
Abstract

INTRODUCTION Numerical modelling techniques for waves, surges and currents have reached a level of accuracy which for most purposes make hindcast data (i.e. data obtained by running models to represent past events), superior to measured data for purposes of extreme value estimation and climate definition. Hindcast data can cover long time periods and wide geographical areas, in contrast with the presently available intermittent and sparse measured of design environmental conditions in any sea area. The measured data cab, however, be used for validations purposes, thus extending their value beyond their limited duration and importance for the estimation of environmental conditions, by resolving of in-situ measurements of waves and currents. For example, by correct physical modelling it is possible to detect the effects of topographic variation in a manner impossible to match without very large numbers of instruments in a widespread networks. The Project The North European Storm Study (NESS) is a major computer hindcast study, designed to generate a database from which an accurate assessment can be made of environmental conditions on the European Shelf and in adjacent waters. The project is sponsored by a group of oil companies and European governmental organisations. In order to obtain a hincast database which would be generally acceptable within the European operating are, it has been necessary to gather a broadly based international team of experienced modellers, drawn from governmental agencies and scientific institutes with much experience in the running of hindcast studies and operational (real time) services. The wind modelling tasks are being performed by the United Kingdom Meteorological Office (MO) and the Norwegian Meteorological Institute (DNMI), using well established techniques for pressure field and wind field analysis. The wave modelling task is under the direction of experienced modellers of the Danish Hydraulics Institute (DHI) and the GKSS Forschungszentrum, Geesthacht GMBH (in the Federal Republic of Germany), who will tailor an existing wave model of high scientific merit (the HYPA-S model) into a system best adapted for the project. Two well known hydraulics institutes, DHI and the Delft Hydraulics (DH), are jointly responsible for the surge and current hindcast task, using a versatile and much used system from DHI (the System 21) The Royal Netherlands Meteorological Institute(KNMI) is highly experienced in the gathering and mterpretation of wave data, and hence IS qualified to perform the validation assessment of the project wavemodel. DH are again involved, being responsible for the statistical processing of the resultant database The entire project is to be managed by a small team (MO as leader, assisted by DHI and DH), backed by the joint experience and scientific knowledge of all the key personnel. The objective of the project is to prepare a database of hindcast winds, waves, surge elevations and depth integrated currents over the entire North European operating area, and to use these data to develop a uniform and sound basis for design and operational criteria m that area. The hindcast tune period will initially include the winter seasons of 1961/8662 to 1985/86.

Proceedings Papers

Publisher: Society of Underwater Technology

Paper Number: SUT-AUTOE-v12-117

... problems. prediction model result storm wave height spectrum astensk target position

**upstream****oil**&**gas**spectra coefficient empirical ray reservoir characterization whist 3 formulae frequency frequency spectrum wth wave energy equation underwater technology wave model...
Abstract

A ray tracing model that includes the effects of refraction in shallow water has been developed to allow the evaluation of a set of empirical formulae for the prediction of directional wave spectra. The formulae have been tested by hindcasting the waves at eight offshore sites in the North Sea during WHIST storms 3, 5 and 6. At the peak of a storm the model predicted significant wave heights that agreed with observed values to within the ±10% accuracy suggested by the Department of Energy. Although the model is first-generation and cannot resolve non-linear interactions, it is computationally efficient and may be suitable for many engineering applications. In particular, it could be used in sensitivity tests for determining the grid spacing and coastal wind correction factors that should be applied during the use of second-and third-generation wave models. The good results obtained during high wave conditions are the result of the high directional resolution of the model coupled with the use of a realistic formula for the energy in the saturated wave spectrum. INTRODUCTION Hydrodynamic models of the currents and surface elevations associated with tides and surges can give results of high accuracy (e.g. Heaps and Jones, 1979). This is because the physics of the problem is well understood, and the equations that describe the motion contain only a relatively small amount of empiricism (with empirical formulae being used to represent the surface and bottom stresses, and the vertical eddy viscosity in the case of a three-dimensional model), in contrast wave models contain a fair degree of empiricism. For example, the BMO model (Gloding 1983), which is a second-generation model, attempts to take account of the effect of the non-linear interactions by replacing the wind-sea part of the spectrum by a JONSWAP spectrum with the same energy. Consequently, the model results depend not only on the empirical formulae used to describe the wave growth, but also on the empirical constants that appear in the JONSWAP spectrum. The lack of our understanding of the true physics of wave generation is reflected in the predictions made by wave models which can show appreciable errors. The Department of Energy has suggested that a wave model should be accurate to±10% of peak wave height, and existing second-generation models have been evaluated by applying them to the WHIST storms (Department of Energy, 1986). Recent wave models (the third-generation models) are becoming even more complex as they attempt to solve explicitly the non-linear interactions, thus necessitating the use of high-powered computers. Ultimately, this may lead to a better understanding of the physics of wave generation, but it limits the work to those researchers who have access to parallel processing computers, and the computational costs are likely to be high. An alternative approach is to accept the empirical nature of much wave modelling, and to investigate the use of purely empirical methods for the practical prediction of wave spectra. This may not advance our understanding of wave dynamics, but may produce practical models that will be suitable for many engineering problems.

Proceedings Papers

Publisher: Society of Underwater Technology

Paper Number: SUT-AUTOE-v12-223

... hydrauhc institute shell expro surge system 21 whch

**upstream****oil**&**gas**operation gnd model fine gnd model west east shell uk exploration 1987. The Society for Underwater Technology ...
Abstract

Shell Expro operates a 36-inch oil pipeline which runs from Cormorant Alpha to Sullom Voe, through Yell Sound in the Shetlands. Yell Sound is noted for its complex tidal regime with frequent occurrences of disturbed and very fast-moving water masses. Access to the pipeline is required for inspection purposes and for maintenance/repair if inspection should reveal the need for that to be carried out. As the area is largely sheltered form stray wave action, access to the pipeline is determined by the strength of the tidal currents. Extensive measuring programmes carried out for the northern part of Yell Sound (1976–1978) and the southeastern parts (1982) have revealed the presence of considerable variations (surges) in current speeds which could not be explained as part of the ordinary tidal regime. It was suggested that the surges reflect the appearance of gyres (vortices) in the area, but until recently it was not possible to test this theory nor to assess the spatial extent of the surges or to identify the tracks along which the gyres move. In order to obtain an improved understanding of the complex current pattern in the area around the Brent System Pipeline, Shell Expro commissioned the Danish Hydraulis Institute (DHI) to set up a computer based model of the Shetland area. The results of the study will be used also for planning and scheduling diving work in Yell Sound and to assist in the establishment of Pipeline Maintenance Systems. This chapter describes how the model was established using Systems 21, DHL's numerical modelling systems for two-dimensional, nearly horizontal flow. The model was validated using measurements form five different locations in the 1982 survey. The results confirm the gyre theory and show the spatial extent of the gyres as well as the tracks followed by them. Finally, a program (for an IBM PC) which makes use of the model results to predict current velocities along the pipeline, and the amount of time available for diving, is described. Fig 1 Brent and Ninian systems pipeline routes to Sullom Voe oil terminal: existing facilities (available in full paper) INTRODUCTION Shell UK Exploration and Production (Shell Expro) on behalf of a consortium of 17 participants, operates the Brent System Pipeline which runs from Cormorant Alpha platform to Sullom Voe in the Shetkand Isles (see Fig 1). The pipeline is 914 mm (36 in) in diameter and carries live crude from a number of fields in the Northern sector of the United Kingdom's North Sea continental shelf, for separation at Sullow Voe and re-export via tanker. The approaches to Yell Sound, from the north and from the east, both act like funnels, with the width of the channel and its depth both reducing as the centre of Yell Sound is approached (see Fig 2 and 3). The reducing cross-sectional area gives rise to very high current speeds; surface currents in the region of five knots have been measured and higher currents have been predicted in the once-per-100 years condition.

Proceedings Papers

Publisher: Society of Underwater Technology

Paper Number: SUT-AUTOE-v12-313

... this review to only one are of the problem of wave-current interactions. jonsson free surface peregnne gravlty wave equation interaction

**upstream****oil**&**gas**wave-current interaction water wave fenton deep water hear shear mterachon phase speed dalrymple water depth current profile...
Abstract

INTRODUCTION One of the continuing topics of interest in the field of design of offshore structures is that of wave-current interactions and their effects on structures. The standard approach to this problem appears to be to ignore any interaction between the waves and the current and simply to add the two together (vectorially), in order to calculate the forces on a structure. This approach carries with it certain difficulties; for example, it is not clear whether it will lead to an under or over-estimate of the forces. Additionally, as the current profile is usually only defined up to the mean level, it is necessary to make ad hoc assumptions about the form of the profile between the mean level and the wave crests. These assumptions are difficult to justify and are therefore unsatisfactory. Beiboer (1984) has discussed wave-current interactions in relation to engineering design applications. He notes the need for a better understanding of the interactions and also the need for a better statistical description of the joint probability of occurrence of extreme wave and currents. We will not repeat his discussion her, instead, we will pursue only one aspect of the problem he identified. The aim of this chapter is to review the interaction of waves with a current which is steady and uniform in the horizontal plane, but varies with depth. The reasons for restricting our attention to this specific problem are two-fold: first, it is one that is of practical interest to those designing offshore structures; and secondly, to cover all aspects of wave-current interactions would require a much more comprehensive review than it is possible to give here. For the benefit of readers who want to pursue aspects of the problem not considered here, we recommend the review papers by Peregrine (1976) and Peregrine and Jonsson (1983) Additionally, Peregrine et al. (1983) gave an annotated bibliography of papers on wave-current interaction, while Dalrymple (1973) describes various methods for calculating such interactions in more detail than it is possible to do here. Finally, for more general background information regarding wave kinematics and forces on structures, Carter et al (1986) and Sarpkaya and Isaacson (1981) may be consulted. It is perhaps worth nothing that most of the above references deal with deterministic aspects of the problem, much less is known about the statistics of wave-current interactions. In this chapter, we will outline the mathematical models that are available for calculating the interaction of waves with a vertically varying current. These models will be considered in the light of such experimental evidence as exists presently, in order to assess their applicability. This will allow us to see where there are theoretical or practical difficulties in the application of the models. On the basis of our review we will give some indication as to which methods are suitable for practical application and also which aspects of the problem require further research. As we have restricted this review to only one are of the problem of wave-current interactions.