Measured and Predicted Wave Plus Current Loading on a Laboratory-Scale, Space Frame Structure

Allender, J.H.; Petrauskas, C.

doi:10.4043/5371-ms

Cited by 12 publications

(7 citation statements)

References 1 publication

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“…The numerical predictions on the total forcetime histories compare well with the measurements for all range of cases with a single and Figure 4. It is worth emphasising that for the present industry practice (or standard Morison equation) to fit the peak forces for all cases, different Cd values would be required, consistent with Allender and Petrauskas [4]. This work is reported in Santo et al [12].…”

Section: Static Casesupporting

confidence: 64%

“…Our research shows that the presence of unsteady large waves on top of a steady current introduces additional blockage, interpreted as 'wave-current blockage'. This work was largely motivated by the findings from Allender and Petrauskas [4], who measured the peak forces on a complete 3 m high model of a Gulf of Mexico platform in regular waves and current in a very large wave tank. Using the then standard design methodology (before the simple current blockage model), they reported the necessity to use a lower value for the Morison drag coefficient ( = 0.7 − 0.8) in order to fit the measured peak forces for waves with in-line current.…”

Section: Introductionmentioning

confidence: 99%

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Wave-Current Blockage: Reduced Forces for the Re-Assessment of Ageing Space-Frame Offshore Structures

Santo

Taylor

Day

et al. 2018

Day 3 Wed, May 02, 2018

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This paper summarises extensive research work on the accurate calculation of extreme loads from waves and current on space-frame offshore structures. Although relevant to new builds, improved prediction of extreme loads is also key to the re-assessment of old and ageing offshore platforms. Current blockage is a field effect. Due to the presence of the rest of the structure, the flow velocity on each structural member is reduced on average leading to smaller overall loads. The first model to account for this 'current blockage' was first by Taylor [1], and incorporated into standard industry practice (API, DNV and ISO). This is a simple improvement to the original Morison equation (Morison et al. [2]), which predicts forces using the undisturbed open ocean flow properties. 2 OTC-29036-MS jacket structure under all range of wave and current conditions, only a single pair of values of Morison drag and inertia coefficients is required to reproduce the complete total force-time histories on the jacket model. This is in contrast to the present industry practice whereby different Morison drag coefficients are required in order to fit the measured peak forces over the wide range of cases considered. For the dynamic tests, we find that the relative velocity formulation of the Morison equation for space-frame structures is valid for dynamically sensitive structures. All of these effects can be captured using our numerical porous block model. Nomenclature , = drag and inertia force, respectively , , = Morison drag coefficient, inertia coefficient, and added mass coefficient, respectively ,̇ = wave orbital velocity and acceleration = current velocity = water density , , = solid drag area, frontal area and volume of a structure,

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Section: Static Casesupporting

confidence: 64%

Section: Introductionmentioning

confidence: 99%

Wave-Current Blockage: Reduced Forces for the Re-Assessment of Ageing Space-Frame Offshore Structures

Santo

Taylor

Day

et al. 2018

Day 3 Wed, May 02, 2018

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“…Many studies have considered periodic waves only without current (or periodic oscillation without steady flow), whilst some examined the effect of waves and steady current simultaneously, see e.g. Sarpkaya and Isaacson (1981), Sarpkaya et al (1984), Heideman and Sarpkaya (1985), Rodenbusch and Källström (1986), Allender and Petrauskas (1987), Reed et al (1990), and Chaplin et al (1992). Large scatter in the Morison drag and inertia coefficients (C d and C m ) is observed, and no general conclusions have been drawn, because of the complexity of the problem due to the presence of a current interacting with waves and the structure.…”

Section: Introductionmentioning

confidence: 99%

“…It should be noted that the estimation of loads on space-frame structures as a topic has not been an active area of research over the last few decades. Allender and Petrauskas (1987) measured the peak forces on a complete 3 m high model of a Gulf of Mexico platform in regular waves and current in a very large wave tank. They observed what we interpret as significant wavecurrent blockage for a wide range of regular wave heights and steady tow speeds.…”

Section: Introductionmentioning

confidence: 99%

Current blockage and extreme forces on a jacket model in focussed wave groups with current

Santo

Taylor

Day

et al. 2018

Journal of Fluids and Structures

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This paper documents large laboratory-scale measurements of hydrodynamic force time histories on a realistic 1:80 scale space-frame jacket structure exposed to combined waves and in-line current. The aim is to investigate the fluid flow (and the associated hydrodynamic force) reduction relative to ambient fluid flow due to the presence of the jacket structure as an obstacle array, interpreted as wave-current blockage. Transient focussed wave groups, and embedded wave groups in a smaller regular wave background are generated in a towing tank, and the jacket is towed under different speeds opposite to the wave direction to simulate wave loading with different in-line uniform currents. The measurements are compared with numerical predictions using Computational Fluid Dynamics (CFD), with the actual jacket represented in a three-dimensional numerical wave tank as a porous tower modelled as a uniformly distributed Morison stress field. Good agreement is achieved, both in terms of incident surface elevation as well as total force time histories, all using a single set of Morison drag (C d) and inertia (C m) coefficients. Substantial force reduction is observed under transient large crest relative to prediction from the present industry design guideline with the same Morison coefficients. We demonstrate the generality of our findings: without influence of Keulegen-Carpenter (KC) number effect, a single invariant set of C d and C m is all that is required to numerically explain and reproduce the measured total force time histories on a realistic jacket model for a large range of wave heights and non-zero current speeds.

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“…Also, the use of the sloped foundations beneath the structures and some provisions for the constructing podium in depth and at further points were began in those years, and now the tallest casted platform has been placed at a depth of 315.5 meters in the Gulf of Mexico [1]. The extraction of oil from the marine resources is often performed through the platforms and offshore constructions.…”

Section: Introductionmentioning

confidence: 99%

Modeling the Pressure Distribution and the Changes of Water Level around the Offshore Platforms Exposed to Waves, Using the Numerical Model of Flow 3D

RashidiNasab¹,

Askar²

2017

CWEEE

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The humans' need to use the oceans for exploration and extraction of oil has led to the development of engineering science in the field of offshore structures. Since it's important to examine the offshore structures from different aspects and perspectives, we would have to evaluate many different parameters about them. So categorizing these parameters can help to perform their related analysis with more accuracy and more details. Due to the efficient force it exerts on the structure, the pressure distribution around every marine or hydraulic structure has a significant importance, and it even accounts for one of the dominant issues in designing and building of such structures. In the present study, an oil platform located in Phase 15 of South Pars oil fields, located in the Persian Gulf waters, has been analyzed using the FLOW 3D software. The outputs indicate that the pressure of water is distributed almost hydrostatically with the depth, and its maximum reaches 0.6 MPa at the bottom.

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Measured and Predicted Wave Plus Current Loading on a Laboratory-Scale, Space Frame Structure

Cited by 12 publications

References 1 publication

Wave-Current Blockage: Reduced Forces for the Re-Assessment of Ageing Space-Frame Offshore Structures

Wave-Current Blockage: Reduced Forces for the Re-Assessment of Ageing Space-Frame Offshore Structures

Current blockage and extreme forces on a jacket model in focussed wave groups with current

Modeling the Pressure Distribution and the Changes of Water Level around the Offshore Platforms Exposed to Waves, Using the Numerical Model of Flow 3D

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