Tank Test and Numerical Simulation of Spar Type Floating OTEC

2021 ◽  
Author(s):  
Shunka C. Hirao ◽  
Jun Umeda ◽  
Kentaroh Kokubun ◽  
Toshifumi Fujiwara
Keyword(s):  
Numerical Simulations ◽  
Cold Water ◽  
Scaling Law ◽  
Internal Flow ◽  
Bending Moment ◽  
Floating Structure ◽  
Waves And Currents ◽  
Tank Test ◽  
Safety Assessments ◽  
Ocean Thermal Energy

Abstract National Maritime Research Institute, NMRI, had been studying the analytical method on safety assessments of floating power generation facilities for ten years more. As a part of these studies, an Ocean Thermal Energy Conversion (OTEC) was also studied in our institute. The OTEC normally has a very long and thick Cold-Water Pipe (CWP) with an unanchored end to pump up a large amount of cold-water continuously. From the viewpoints of the safety assessments of the OTEC operation, it is noteworthy to confirm the effect of the existing long pipe against a floating unit/body and an effect of internal flowing water. It is necessary, moreover, to consider the Vortex Induced Vibration (VIV) effect for floater motions and structural analysis of the pipe itself and a connecting point of the floating structure. In this paper, the results of model tests and numerical simulations of a spar type floating OTEC with a single CWP in waves and currents are presented. The CWP model was made of material fitting the scaling law for a planned full scale OTEC. The specific and unique phenomena of the floating OTEC were confirmed from the model test results. Based on the results of the tank tests and the numerical simulations, we confirmed the necessary items and arrangements for safety evaluations. In detail, the internal flow increased the bending moment at the connection point.

Reliability Analysis of a Steel Catenary Riser With Environmental, Geometry, and Operational Uncertainties

2014 ◽  
Author(s):  
C. Y. Ma ◽  
U. Alibrandi ◽  
C. G. Koh
Keyword(s):  
Failure Probability ◽  
Bending Moment ◽  
External Pressure ◽  
Engineering Practice ◽  
Floating Structure ◽  
Steel Catenary Riser ◽  
Waves And Currents ◽  
Uncertainty Parameters ◽  
Environmental Geometry ◽  
Scr Model

Steel Catenary Riser (SCR) offers an attractive solution to deepwater floating structure due to its economical effectiveness, large diameters, high resistance to internal and external pressure, simple and robust installation methods. SCR forms a prolongation of a subsea flowline attached to a fixed platform or a floating unit in a catenary shape. Due to the relatively large motion under waves and currents, SCR lines are sensitive to dynamic effects and vulnerable to damage in deep water. They are commonly subjected to high top tension and large bending moment due to platform or FPSO movements which may lead to fatigue damage. There are many uncertainties that can affect the safety and cost-effectiveness of the SCR. Offshore design codes typically adopt empirical safety factors to account for these uncertainties but this approach does not permit the prediction of failure probability of the riser system. To address the above issue, this paper presents the coupling of the stochastic analysis concept to the deterministic computational model for the dynamic analysis of SCR. The finite element solution is developed for hydrodynamic and structural analysis accounting for nonlinear and dynamic coupling effects. Methods for reduction of dimensionality of uncertainties are investigated to help to make the analysis computationally feasible. Uncertainty and numerical realization of specific uncertainty parameters are modeled through riser dynamics software and uncertainty analysis software. Distributions of effective tension, bending moment, and API RP 2RD stress are illustrated for a specified SCR model. The correlation effects between structural responses and random variables are investigated. In addition, the failure probability of SCR API RP 2RD stress is investigated through Monte Carlo simulations. This will help to evaluate the behavior and reliability of SCR realistically, incorporating the environmental, geometry and operational uncertainties in engineering practice.

Preliminary Design of a 1-MWe OTEC Test Plant

1982 ◽  
Vol 104 (1) ◽  
pp. 3-8 ◽  
Author(s):  
T. Kajikawa
Keyword(s):  
Cold Water ◽  
Working Fluid ◽  
Test Plant ◽  
Mooring System ◽  
Preliminary Design ◽  
Closed Cycle ◽  
Water Pipe ◽  
Thermal Energy Conversion ◽  
Design Value ◽  
Ocean Thermal Energy

An ocean-based, 1-MWe (gross) test plant has been planned to establish the feasibility of OTEC (ocean thermal energy conversion) power generation in the revised Sunshine Project. The preliminary design of the proposed test plant employs a closed-cycle power system using ammonia as the working fluid on a barge-type platform with a rigid-arm-type, detachable, single-buoy mooring system. Two types each of titanium evaporators and condensers are to be included. The steel, cold-water pipe is suspended from the buoy. The design value of the ocean temperature difference is 20 K. The paper presents an overview of the preliminary design of the test plant and the tests to be conducted.

scholarly journals On the Scaling of Bubble Cluster Collapse in Cloud Cavitating Flow Around a Slender Projectile

2015 ◽  
Author(s):  
Yiwei Wang ◽  
Chenguang Huang ◽  
Xiaocui Wu
Keyword(s):  
Phase Change ◽  
Numerical Simulations ◽  
Scaling Law ◽  
Cavitating Flow ◽  
Cavitation Model ◽  
Bubble Cluster ◽  
Collapse Pressure ◽  
Variation Range ◽  
Main Factors ◽  
Similarity Law

The scaling law of bubble cluster collapse in cloud cavitating flow around a slender projectile is investigated in the present paper. The influence of compressibility is mainly discussed. Firstly the governing parameters are obtained by dimensional analysis, and the numerical method is established in order to verify the similarity law and obtain the influence of parameters based on a mixture approach with Singhal cavitation model. Moreover, the similarity law is validated by numerical simulations. Two main factors of compressibility of mixture fluid, including compressibility of non-condensable gas and phase change, are studied, respectively. Results indicated that the phase change has little influence on both flowing and collapse pressure. In the condition that the variation range of the mixture compressibility is small, the compressibility of non-condensable gas has notable impact the local collapse pressure peaks, however the macroscopic flow pattern does not change.

Feasibility of Using Stress Joint in an Existing Flexible Joint Receptacle for a Deepwater SCR

2009 ◽  
Author(s):  
Basim Mekha ◽  
Alok Kumar ◽  
Mike Stark ◽  
Paul Barnett
Keyword(s):  
Bending Moment ◽  
Flexible Joints ◽  
Floating Structure ◽  
Element Analysis ◽  
Flexible Joint ◽  
Floating Structures ◽  
Operational Problem ◽  
Hull Structure ◽  
Hull Design ◽  
Titanium Material

In recent years, most fluid produced or exported has been transported using steel catenary risers (SCRs) attached to deepwater floating structures. The SCRs are terminated at the floating structures using Top Termination Units (TTUs) such as flexible joints or tapered stress joints. The flexible joints are usually designed to allow the riser to rotate with the floating structure motion and reduce the amount of moments transferred to the hull structure. The flexible joints depend on the flexibility and compressibility of the elastomer layers to allow for the rotation of the SCR. The stress joints, alternatively, provide fixed support at the hull and thus larger bending moment that has to be accounted for in the hull design. The stress joints can be made of steel or titanium material. The SCR TTU’s receptacle, which will be welded to the hull porch and contains the TTU basket, has to be designed to meet the force and reaction requirements associated with the selected TTU type. However, in some cases which could be due to failure of the TTU to meet the expected life or the operational requirements, the operators may have to replace the damaged TTU with another one or with a different TTU type. A few examples are available in the Gulf of Mexico. Recently the Flexible Joint TTU of the Independent Hub 20-inch export SCR had an operational problem. During the course of investigating the related issues and studying possible solutions, one option considered was the feasibility of replacing the Flexible Joint (FJ) with Titanium Tapered Stress Joint (TSJ). This paper highlights the issues that have to be considered in the design of the FJ existing receptacle to accommodate the force reactions of a Titanium TSJ. These issues are addressed and the results of the detailed finite element analysis performed are provided. The analysis conclusions, which are related to the feasibility of the existing receptacle to receive the loads imposed by TSJ and the modifications required to achieve this, are presented.

The Ocean Thermal Gradient Hydraulic Power Plant and Its Scope

2003 ◽  
Author(s):  
Earl J. Beck
Keyword(s):  
Power Plant ◽  
Thermal Gradient ◽  
Cold Water ◽  
Working Fluid ◽  
Hydraulic Power ◽  
Tropical Oceans ◽  
Thermal Energy Conversion ◽  
Near Shore ◽  
Power Outputs ◽  
Ocean Thermal Energy

Heretofore, the concept of developing power from the tropical oceans, (Ocean Thermal Energy Conversion, or OTEC) has assumed the mooring of large platforms holding the plants in deep water to secure the coldest possible condensing water. As the Ocean Thermal Gradient Hydraulic Power Plant (OTGHPP) does not depend, on the expansion of a working fluid, other than forming a foam of steam bubbles. It does not need extremely cold water as would be dictated by Carnot’s concept of efficiency and the 2nd Law of Thermodynamics. Plants may be based on or near-shore on selected tropical islands, where cool but not extremely cold water may be available at moderate depths. This paper discusses the above possibilities and two possible plant locations, as well as projected power outputs. The location and utilization of large of amounts of power on isolated islands, where cabling of power to major population centers would not be feasible are discussed. Two that come to mind are the reduction of bauxite to produce aluminum and the of current interest is the electrolyzing of water to produce gaseous hydrogen fuel to be used in fuel cells, with oxygen as a by-product.

Experimental and numerical investigation of wave-current forces on coastal bridge superstructures with box girders

2019 ◽  
Vol 23 (7) ◽  
pp. 1438-1453 ◽  
Author(s):  
Jiawei Zhang ◽  
Bing Zhu ◽  
Azhen Kang ◽  
Ruitao Yin ◽  
Xin Li ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Numerical Models ◽  
Wave Forces ◽  
Vertical Force ◽  
Box Girder Bridges ◽  
Box Girder ◽  
Coastal Bridges ◽  
Girder Bridges ◽  
Wave Parameters ◽  
Waves And Currents

Coastal bridges are exposed to hurricane waves and storm surges during hurricanes, which threaten the safety of the superstructures. Since waves and ocean currents coexist in the natural marine environment and the action of currents leads to changes in wave parameters and thus affects wave loads, considering their interaction is necessary for the study of wave forces on coastal bridges. In this study, hydrodynamic loads on a box girder with the joint action of regular waves and currents are investigated with both experiments and numerical models. A series of experiments of wave forces that include conditions with different wave heights, current velocities, wave periods and submergence depths are conducted in a wave flume. Two-dimensional numerical simulations are performed to further investigate the mechanics of wave-current forces on box girder bridges. The wave parameters and wave forces of the numerical simulations are compared with the experimental results. The results indicate that a following current usually leads to higher maximum horizontal forces and lower maximum vertical forces. The opposing current results in a higher maximum hydrodynamic vertical force than following current with a low submergence depth. However, due to the joint effect of the wave parameters and structure position relationships, the behaviours of wave forces in other situations become complicated. It is anticipated that this study can provide experimental data of wave-current forces for the superstructures of box girder bridges and enhance the understanding of the mechanism of bridge damage by waves and currents.

scholarly journals CFD Code Validation against Stratified Air-Water Flow Experimental Data

2008 ◽  
Vol 2008 ◽  
pp. 1-7 ◽  
Author(s):  
F. Terzuoli ◽  
M. C. Galassi ◽  
D. Mazzini ◽  
F. D'Auria
Keyword(s):  
Experimental Data ◽  
Numerical Simulations ◽  
Water Flow ◽  
Nuclear Reactor ◽  
Cold Water ◽  
Three Dimensional ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Two Phase ◽  
Code Validation

Pressurized thermal shock (PTS) modelling has been identified as one of the most important industrial needs related to nuclear reactor safety. A severe PTS scenario limiting the reactor pressure vessel (RPV) lifetime is the cold water emergency core cooling (ECC) injection into the cold leg during a loss of coolant accident (LOCA). Since it represents a big challenge for numerical simulations, this scenario was selected within the European Platform for Nuclear Reactor Simulations (NURESIM) Integrated Project as a reference two-phase problem for computational fluid dynamics (CFDs) code validation. This paper presents a CFD analysis of a stratified air-water flow experimental investigation performed at the Institut de Mécanique des Fluides de Toulouse in 1985, which shares some common physical features with the ECC injection in PWR cold leg. Numerical simulations have been carried out with two commercial codes (Fluent and Ansys CFX), and a research code (NEPTUNE CFD). The aim of this work, carried out at the University of Pisa within the NURESIM IP, is to validate the free surface flow model implemented in the codes against experimental data, and to perform code-to-code benchmarking. Obtained results suggest the relevance of three-dimensional effects and stress the importance of a suitable interface drag modelling.

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