Green Water on FPSO Analyzed by a Coupled Potential-Flow-NS-VOF Method

2014 ◽  
Author(s):  
Csaba Pakozdi ◽  
Anders Östman ◽  
Carl-Trygve Stansberg ◽  
Daniel Fonseca de Carvalho e Silva
Keyword(s):  
Potential Theory ◽  
Model Test ◽  
Cfd Simulation ◽  
Impact Force ◽  
Vof Method ◽  
Green Water ◽  
Wave Kinematics ◽  
Water Height ◽  
Good Agreement

The nowadays frequent use of FPSOs for offshore oil production in areas prone to green water events has increased the industrys focus on wave-induced impact loads as an important design parameter. This is a complex hydrodynamic problem where simplified engineering methods are often used in connection with model testing. Various efforts have been presented during the recent 10–15 years to establish reasonably good industry design tools, while the use of fully nonlinear methods and CFD is still in its development. The main focus of this paper is to investigate the potential of a simplified coupled method between a potential theory based Green Water engineer tool (Kinema3) and the commercial CFD tool Star-CCM+ based on its Navier-Stokes Solver (NS) and the Volume of Fluid (VOF) method. Results from a case study application on a large FPSO are validated against model test data. The case study contains analyses of the FPSO in long crested regular seas, both in fixed and in moored conditions. Three different heading directions are included. The approach for modeling green water events uses a Finite-Volume-VOF method with a complex velocity inlet boundary condition. Thus the Kinema3 engineering tool is used to generate simplified spatio-temporal inlet conditions from the relative wave elevation and wave kinematics at the bulwark, based on linear potential theory combined with nonlinear random wave kinematics. The VOF method is then used to model the detailed flow on deck, including impact forces on deck structures. Kinema3 can also generate simplified estimates for the peak water height, velocity as well as impact force values assuming an extended dam-break approach together with a simplified, local 2D deck layout, and comparisons to the CFD results show an overall fairly good agreement although flow details on deck can of course not be expected to be modeled that well. Comparisons of the above results to model test data show good agreement both for the relative wave height, water height and impact force level, in regular and irregular waves. Detailed time histories, including force rise time, from the coupled Kinema3 - Star-CCM+ CFD simulation analysis are quite similar to the measured ones. The CPU time consumption for the coupled simulation is moderate compared to a full CFD simulation of the FPSO in waves. Hence the achieved calculation time and the simplicity of the simulation setup of the numerical simulation makes this method an interesting candidate for industrial use. This work is a part of the research project “Green Water and Wave Impact on FPSO” carried out for and in cooperation with PETROBRAS.

Ultra-Deepwater Model Testing of a Semisubmersible and Hybrid Verification

2008 ◽  
Author(s):  
Timothy E. Kendon ◽  
Ola Oritsland ◽  
Rolf J. Baarholm ◽  
Svein I. Karlsen ◽  
Carl-Trygve Stansberg ◽  
...  
Keyword(s):  
Model Test ◽  
Water Depth ◽  
Deep Water ◽  
Low Frequency ◽  
Line Tension ◽  
Model Tests ◽  
Test Results ◽  
Test Verification ◽  
Good Agreement

Model test verification of floater systems in ultra-deep water meets limitations when it comes to available laboratory sizes. Systems in depths beyond 1000–1500 m cannot be tested at reasonable scales without the truncation of the mooring and riser system. The development of methods and procedures to overcome this problem has been addressed through extensive research programs at MARINTEK (VERIDEEP, VERIDEEP Extension, NDP, DEMO2000). This led to a hybrid verification procedure which combines reasonable truncation principles, model tests of the truncated system, and numerical simulations, to estimate the system’s response at full depth. There is, however, still a need to address the actual influence from the truncation procedure, and from the integration with simulations, on the final extrapolated full depth results. This paper presents a case study for the validation of the procedure, that compares full depth model test results of a semisubmersible in water depth 1250m against the extrapolated full depth results obtained from a truncated system of 500m. Results are presented for line tension and vessel responses in 3 seastates. In general the extrapolated full depth results were found to be in good agreement with the full depth model tests. However, the results confirmed expectation that the low frequency response has the greater uncertainties and presents the greatest challenge for the procedure.

Simplified Wave In Deck Analysis In Irregular Seas

2007 ◽  
Author(s):  
Thomas B. Johannessen
Keyword(s):  
Model Test ◽  
Impact Force ◽  
Surface Elevation ◽  
Test Results ◽  
Free Surface Elevation ◽  
Offshore Structure ◽  
Wave Elevation ◽  
Practical Design ◽  
Good Agreement ◽  
Linear Shape

Using a simple von Karman approach, Baarholm (2005) obtained good agreement between measured and predicted impact force underneath the deck of a GBS. This method rested, however, on a very careful second order modelling of the diffracted free surface elevation underneath the deck. In particular, the method was found to be very sensitive to the maximum wave elevation (i.e. the magnitude of the negative airgap). These requirements limit the applicability of the method since an accurate representation of the surface elevation is not usually available. In the design of an offshore structure, however, much effort is spent on determining the airgap underneath the deck. Zones with negative airgap are found by approximate calculations or by extrapolating on model test results. The method described in the present paper simplifies the problem by using Baarholm’s method subject to a known negative airgap height above the deck rather than attempting to solve the whole problem. With a known negative airgap height and using the well known expected linear shape of the wave around this maximum, a robust and conservative estimate of the deck loading can be obtained. The nonconservative property of linear theory that it underestimates the crest height is thus removed and replaced with the conservative property that too much water is present above the deck level. The paper describes this method, provides a practical design example and compares the results with model test results. The agreement with model test results is good for the single event which has been compared, but there is a clear scope for further comparison.

A Study on the Performance of Stratified Air Conditioning Design in Assembly Halls – A Case Study at the Dazhi Cultural Center in Taiwan

2013 ◽  
Vol 368-370 ◽  
pp. 599-602 ◽  
Author(s):  
Ian Hung ◽  
Hsien Te Lin ◽  
Yu Chung Wang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Indoor Air ◽  
Air Conditioning ◽  
Cfd Simulation ◽  
Indoor Temperature ◽  
Cultural Center ◽  
Computational Fluid Dynamics Cfd

This study focuses on the performance of air conditioning design at the Dazhi Cultural Center and uses a computational fluid dynamics (CFD) simulation to discuss the differences in wind velocity and ambient indoor temperature between all-zone air conditioning design and stratified air conditioning design. The results have strong implications for air conditioning design and can improve the indoor air quality of assembly halls.

Structural Analysis of an Offshore Jacket Model Under Seismic Excitation

2008 ◽  
Author(s):  
Helder J. D. Correia ◽  
Anto´nio C. Mendes ◽  
Carlos A. F. S. Oliveira
Keyword(s):  
Point Of View ◽  
Shaking Table ◽  
Seismic Excitation ◽  
Model Structure ◽  
Structural Members ◽  
Jacket Structures ◽  
Reaction Forces ◽  
Nodal Displacements ◽  
Good Agreement

In the present work the action of earthquakes upon offshore jacket structures is analysed by means of ADINA software. Our case-study refers to an existing model structure, previously constructed at the Laboratory of Fluid Mechanics of UBI, which has been analysed from the hydrodynamic point of view — Mendes et al. [1, 2]. The seismic excitation will be imposed at the base of this model structure, with frequencies and amplitudes corresponding to actual earthquake conditions transposed to the model scale of 1:45. The FEM software is utilised to calculate the natural frequencies of the model and to obtain stresses at selected members, as well as their nodal displacements. Our purpose is to quantify maximum stresses occurring in critical structural members and to verify the survivability criterion. The predictions of the numerical model, in terms of the reaction forces at the base and acceleration at the top of the structure, are then correlated with the experimental measurements performed when the model structure is excited in an especially designed shaking table (Correia [3]), revealing a good agreement between both results.

Numerical Simulation of Ship Collision and Validations With Experimental Results

2021 ◽  
Author(s):  
Xiangbiao Wang ◽  
Chun Bao Li ◽  
Ling Zhu
Keyword(s):  
Numerical Simulation ◽  
Model Test ◽  
Structural Damage ◽  
Added Mass ◽  
Ship Motion ◽  
Time Dependent ◽  
Structural Deformation ◽  
Structure Interaction ◽  
Ship Collision ◽  
Good Agreement

Abstract Ship collision accidents occur from time to time in recent years, and this would cause serious consequences such as casualties, environmental pollution, loss of cargo on board, damage to the ship and its equipment, etc. Therefore, it is of great significance to study the response of ship motion and the mechanism of structural damage during the collision. In this paper, model experiments and numerical simulation are used to study the ship-ship collision. Firstly, the Coupled Eulerian-Lagrangian (CEL) was used to simulate the fluid-structure interaction for predicting structural deformation and ship motion during the normal ship-ship collision. Meanwhile, a series of model tests were carried out to validate the numerical results. The validation presented that the CEL simulation was in good agreement with the model test. However, the CEL simulation could not present the characteristics the time-dependent added mass.

Commercial-scale aquaculture of tilapia species in Zambia.

2020 ◽  
Author(s):  
Douglas Flynn
Keyword(s):  
Oreochromis Niloticus ◽  
Inorganic Compound ◽  
Chicken Manure ◽  
Green Water ◽  
Commercial Scale ◽  
Tilapia Rendalli ◽  
Productive System ◽  
Dominant Fish ◽  
Initial Scheme

Abstract This case study describes the piloting and subsequent commercialization of an integrated pig and fish operation in Zambia. The initial scheme began in October 1981 using indigenous Zambian species including Oreochromis andersonii, Oreochromis macrochir and Tilapia rendalli. Different fertilization techniques were trialled, including organic (chicken manure) and inorganic (compound) fertilisers, and different integration systems were tested; ducks over fish and pigs over fish. Over the 29 years the project has been running, the variety of methods originally trialled have been refined to the extremely productive system in place today. Oreochromis niloticus is the dominant fish species produced, and members of the Clarias genus used as the main predator. The hatchery has been intensified (and now incorporates mono-sexing), aeration systems have been implemented in grow-out ponds and a green-water floating fish pellet has been developed. Yields have increased from an initial average of 2.5 to 3 tons/ha to present yields of over 11 tons/ha. The initial five hectare project has grown to over 45 ha of water producing over 600 tons of fish a year, and a stable herd of 200 sows producing in excess of 4100 slaughter stock per annum.

Defining soil macrofauna composition and activity for biopedological studies - A case study on two soils in the Western Australian wheat belt

Soil Research ◽  
1993 ◽  
Vol 31 (1) ◽  
pp. 83 ◽  
Author(s):  
LAL Debruyn
Keyword(s):  
Substantial Contribution ◽  
Resident Species ◽  
Pitfall Trapping ◽  
Soil Macrofauna ◽  
Major Species ◽  
Australian Wheat ◽  
Species Mapping ◽  
Western Australian ◽  
Good Agreement

In Durokoppin reserve and surrounding farmland, part of the central wheatbelt region, pitfall trapping and mapping of soil macrofauna activity were used to define the extent of soil macrofauna activity in these two environments. This type of study is a necessary precursor to determining the significance of certain invertebrate activity in soil modification in these habitats. The relative merits of the two techniques in determining the extent of soil macrofauna activity is assessed. The soil macrofauna groups identified by mapping and pitfall trapping as making a substantial contribution (in terms of relative abundance and activity) in all habitats were, in descending order, ants, spiders and scorpions (wandoo woodland only). In general there was good agreement between the two techniques in identifying the major species and trends in species composition between habitats, but mapping failed to identify the rare or cryptic species. Mapping more accurately identified the resident species in each habitat compared with pitfall trapping. Pitfall trapping data indicated that foraging activity of most soil macrofauna was depressed over winter, except for beetles, and was higher in the spring and summer sampling periods. However, mapping revealed a more constant level of soil macrofauna activity, especially for ant nests. It is argued that the two approaches complement one another and that each has value in interpreting the effects of soil macrofauna activity on soil properties in further studies. The discussion is based on the results of a study carried out in the Kellerberrin area of Western Australia.

scholarly journals Performance Evaluation of Shell-and-Tube Heat Exchanger with 3-Fluid Sets using CFD and NTU

2019 ◽  
Vol 9 (1) ◽  
pp. 1416-1420
Keyword(s):  
Heat Exchanger ◽  
Industrial Development ◽  
Cfd Simulation ◽  
Sea Water ◽  
Raw Water ◽  
Power Sector ◽  
Tube Heat Exchanger ◽  
Shell And Tube ◽  
Pass Through ◽  
Good Agreement

Energy generation to the present growing population is a crucial challenge for the power sector. Heat exchangers (HE) plays an important role in the industrial development. In this present work an attempt is made to develop a Shell-and- Tube Heat Exchanger (STHE) with segmental baffles using commercial CATIA V5 and Autodesk CFD Simulation Softwares. TEMA standards are considered for design of STHE with baffle-cut of 25%. 3-different sets of fluids are allowed to pass through the shell and tube sides i.e. Methanol - Sea Water (M-S), Distilled Water – Raw Water (D-R) and Kerosene- Crude Oil (K-C). The boundary conditions imposed for analysis are fluid inlet temperatures and velocities. ϵ-NTU is employed for the validation of simulation results and found good agreement between them. Results are plotted for temperature, pressure and velocity contours. The performance of the STHE is shown best for the K-C fluid set among other fluid sets.

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