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Collaborating Authors
Huang, Weiping
ABSTRACT In order to study vortex-induced motions (VIM) response of floating cylinders, a model experiment was conducted in a water flume at reduced velocity from 1.3 to 10.2. Considering the aspects of response amplitude, vortex shedding frequency, force analysis, and motion trajectories, the VIM characteristics of cylinders with and without helical strakes were analyzed. According to the results, the ratio of vortex shedding frequency to natural frequency increased linearly with increasing reduced velocity before and after the lock-in district, with St≈0.18 before lock-in district and St≈0.14 after it. Helical strakes change the motion trajectories and frequencies very obviously and deliver remarkable VIM suppression effects. INTRODUCTION For a long time, the phenomena of vortex-induced vibrations (VIV) has drawn the attention of many researchers. In the field of ocean engineering, many studies have been conducted on the vortex-induced vibrations of flexible structures that have extremely high aspect ratio, such as submarine oil pipelines and risers. Since the 1990s when Spar platform was used in 588m deep water of the Gulf of Mexico for the first time, low-frequency and large-amplitude motions caused by the action of the Gulf Stream have become a focus of industrial research (Kokkinis et al.,2004). On the one hand, the main structure of the Spar platform is a deep draft column, which will also cause vortex shedding at a certain flow velocity. Therefore, the Spar platform performs the corresponding motion characteristics which is similar to the theory of VIV. On the other hand, the platform structure is rigid, has a relatively low aspect ratio and floats on the surface of water, altering its motion significantly from the predictions of VIV theory. To distinguish the two, researchers refer to the motion of floating structures as vortex-induced motions (VIM) (Mehernosh et al.,2008). Large-amplitude vortex-induced motions (VIM) will lead to fatigue damage to risers and anchor chains, shorten fatigue lifetime. On engineering, helical strakes are often used to reduce the amplitude of VIM. Irani (2005) conducted model tests to study the effectiveness of Truss Spar helical strakes. The tests simulated several important parameters, including the geometrical shape and quality of the platform hull and truss, the mooring system characteristics, and the different shapes of strakes. Wang (2010) designed vortex suppression helical strakes for a new concept Cell-Truss Spar platform and obtained an optimal parameter combination with a combination of model experiments and numerical simulations. With orthogonal experimental designs and numerical simulation, Wei (2013) studied the influence of pitch, strake height, current velocity and other parameters on the vortex suppression offered by helical strakes. Wei also performed range analysis and variance analysis on the data to observe the effects of strake parameters and interactions on the efficiency of the VIM suppression.
- Research Report > New Finding (0.40)
- Research Report > Experimental Study (0.40)
Study on Typical Design Load Cases of Semi-Submersible FOWTs
Meng, Xun (Ocean University of China, Shandong Provincial Key Laboratory of Ocean Engineering) | Liu, Meng (Ocean University of China) | Huang, Weiping (Ocean University of China, Shandong Provincial Key Laboratory of Ocean Engineering) | Fu, Qiang (Ocean University of China, CIMC Offshore Engineering Institute Company Limited)
ABSTRACT This paper studies on the typical design load cases that dominate the characteristics of structural stress distributions. The OC4-DeepCwind conceptual semi-submersible substructure with the 5.0MW floating offshore wind turbine (FOWT) is adopted as the target structure. Parametric finite element method (FEM) is employed for idealized numerical modelling. Different environmental load cases controlled by random variable parameters such as wave directions, phases, heights and periods are imported into static probabilistic design system (PDS) as samples. Core areas with localized stress concentration based on probability statistics and corresponding typical design load cases are summarized. This study presents a method of effectively simplifying the complicated dynamic strength analysis procedures and would serve as a reference of reasonable optimization of main dimensions of the semi-submersible FOWTs. INTRODUCTION Due to the depletion reserves and negative environmental influences of fossil fuels, human beings have been forced to seeking for alternative energy sources. According to the report of Intergovernmental Panel on Climate Change (IPCC), nearly 80 percent of the world's energy supply could be provided by renewable energy resources in 2050, and wind energy would make up one of the largest contributions to the energy system by then (Sun, Huang and Wu, 2012). Nowadays wind energy industry has moved its interest offshore. Reference shows that offshore wind power will cover 14% of European electricity demand by 2030 (Athanasia, Anne-Bénédicte, and Jacopo, 2012). In the first half of 2017, developers have totally installed about 6.1GW of capacity, including 1.3GW in Europe. The activity in the offshore market is 2.6 times higher than for the first half of 2016 (WindEurope, 2017). Most offshore wind farms so far are installed and operating in shallow waters (<30m), where bottom-fixed foundations with simplified structure concepts such as monopile and gravity concrete caisson are widely used (Failla and Arena, 2015). At water depths between 30m and 60m, multi-foot foundations such as tripod or jacket support are considered (Lozano-Mjinguez, Kolios and Brennan, 2011). For the benefits of relatively unrestricted space, lower social impacts and rich wind resources, wind farms are pushed into deeper waters. For cost-effective solutions, floating offshore wind turbines (FOWTs) become feasible options to extract energy (Meng, Lou and Shi, 2014).
Abstract A method based on Reynolds number similarity, of the vortex-induced vibration (VIV) of circle cylinders is proposed to achieve VIV similarity between prototype and tested model. Because the mode of vortex shedding highly depends on Reynolds number, the VIV response of a circle cylinder is closely related to Reynolds number and reduced velocity. However, the scaled model test of circle cylinder's VIV is nowadays designed based on Froude number similarity but Reynolds number not similar under the same fluid for both model and prototype. Therefore, the VIV response of tested model is not similar to that of the prototype because they have different vortex shedding modes. It means that the test results can not be used to predict the VIV response of the prototype according to the scaling law based on Froude number similarity. In this paper, the relationship between prototype and model based on Reynolds number similarity has been deduced. The prototype and three scaled models with different similarity schemes have been simulated using CFD to validate the method. The results show that the similarity between prototype and model is satisfied by the Reynolds number similarity and both Froude number and Reynolds number similarity. But the similarity between prototype and model is not satisfied by Froude number similarity.
- North America (0.69)
- Asia > China > Shandong Province (0.29)
- Research Report > New Finding (0.49)
- Research Report > Experimental Study (0.34)
ABSTRACT Steel Catenary Risers (SCRs) became the preferred riser systems with the development of deepwater oil and gas exploration. A new model for the dynamic analysis of SCRs is proposed in the paper, the rigid motion, which is the rigid rotation about the axis from the hanging point to the touch down point (TDP), is simulated in the new model. The rigid motion of SCRs is coupled with bending vibration model as inertial force and hydrodynamic damping, and then the out-of-plane motion of SCRs with both bending vibration and rigid motion are simulated. The case studies show that the rigid motion affects the dynamic response of SCRs greatly and can not be ignored in their dynamic analysis.
- Asia > China (0.30)
- North America > United States (0.28)
ABSTRACT In this paper, a new concept of ETLP has been proposed. It is composed of four square columns and a ring pontoon which is consisted of four box beams. The new platform has lesser blocks and welds compared to ETLP, so it can be built at a lower cost and in a shorter construction period. Meanwhile, the pontoon extensions in the new platform is part of pontoons, therefore, the fatigue problem in the welds at the root of extensions in ETLP is solved. A hydrodynamic analysis is conducted to prove the structure's dynamically stabilities. The results showed the new design has a reasonable hydrodynamic characteristic.
- North America > United States (0.47)
- Europe > United Kingdom (0.28)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Ewing Bank > Block 958 > Prince Field (0.99)
- North America > United States > Gulf of Mexico > Central GOM > East Gulf Coast Tertiary Basin > Ewing Bank > 1003 > Prince Field (0.99)
ABSTRACT The User-Defined Function (UDF)and dynamic mesh technique are used to simulate the circular cylinder motion. An Elastically supported cylinder placed in uniform flow and also in combination of uniform and oscillating flows at low Reynolds number values are simulated. The uniform and oscillating flows are both in the x direction. SIMPLE algorithm is used to solve the Navier-Stokes equations. In the paper, we compute the lift and oscillating motion amplitude as functions of Reynolds number and time. Simulations show the vortex induced vibration process of an elastically supported circular cylinder in uniform flow and compare the oscillating motion amplitude and amplitude of lift coefficient in uniform flow and combination of uniform and oscillating flow.
Numerical Analysis of Circular Cylinder In Combination of Uniform Flow And Oscillating Flow At Low-Reynolds Number
Deng, Yue (Department of Ocean Engineering, Ocean University of China) | Huang, Weiping (Department of Ocean Engineering, Ocean University of China) | Zhao, Jingli (Marine Technology Center, Shandong Marine Fisheries Research Institute)
ABSTRACT: The dynamic mesh technique and User-Defined Function (UDF) are used to simulate the cylinder motion. A transversely oscillating circular cylinder in combination of uniform flow and oscillating flow at low Reynolds number is simulated. The uniform flow and oscillating flow both are x direction. SIMPLE algorithm is used to solve the Navier- Stokes equations. In this paper, we compute the lift and drag coefficient changing with time and draw the map of vorticity isolines at phase angleφ = 3π / 2. Force time histories are shown for uniform flow at Reynolds number (Re) of 200 and for the combination of uniform and oscillating flow. INTRODUCTION In recent years, increasingly more and more exploration and production have shifted to deeper waters. Marine risers remain to be technically challenging in deep sea. More and more pivotal components of the circular cylinder shape represented by marine risers are widely used in the offshore platform and subsea pipeline systems. Many works focus on the research of circular cylinder in uniform flow and oscillating flow. Gu et al. (1994) found that vortex from one side of the cylinder to the other reach to a high degree of concentration of vorticity next to cylinder when the s f / f increased (f is the oscillating frequency of cylinder, s f is he shedding frequency for the fixed cylinder). Lu and Dalton (1996) studied the vortex shedding from a transversely oscillating circular cylinder in a uniform flow by numerical solutions. The impact of increasing the amplitude of oscillating cylinder and Reynolds number are shown to lower the value of s f / f at which vortex switching. Wang and Zhou (2005) studied a circular cylinder oscillating transversely in a uniform flow and verified the conclusion of Lu & Dalton.
ABSTRACT This paper introduces a new concept of Spar platform called S-Spar which is designed accounting for significant features of environmental conditions in South China Sea. First order wave exciting force RAO and motion RAO are captured. Its motion response under internal solitary wave with mooring system is determined. Mooring stiffness is calculated with catenary theory, and wave force exerted by internal solitary wave on Spar platform is estimated with Morison Equation. INTRODUCTION The floating structure Spar is recognized as one of the preferred deepwater solutions for the production of oil and gas in the offshore industry. Compared with other floating structures, Spar platforms have excellent stability, motion behavior and adaption to wide range of water depth. On the other perspective, rigid risers and dry tree system are available on Spar platforms. According to those merits, Spar platforms are then regarded as an attractive and economic solution for the development of deepwater. Three types of production Spars have been built to date: the "Classic" and "Truss" Spars, and third generation Cell Spar. With the rapid development of deepwater oil industry, many new technologies and innovative Spar concepts are introduced to adapt to new operation conditions and ultra-deep water depth. So far, Spar concept has been almost exclusively in the Gulf of Mexico, where it has proved a competitive solution for small fields in deep water. Meanwhile, lots of attentions are focused on South China Sea for its rich storage of oil and natural gas. The South China Sea region has been proven that oil reserves estimated at about 7.5billion barrels, and oil production in the region is currently over 1.3 million barrels per day. While, it was also noted (Xu, 2002) that the depth of the basin of the South China Sea is over 3,600 meters and the environment conditions are relatively severe.
ABSTRACT This paper presents a new type of Spar platform named S-Spar. Its midsection is a cylinder with the same diameter as the centre well. And the centre well and midsection is designed as an integrated structure. Heave plates are attached appropriately along the connection section. With the unique midsection, S-Spar is suitable for operating at the special oceanic environment and ultra-deep water depth in South China Sea. The paper will discuss both structural design and hydrodynamic analysis. Detail motion analysis results show that the platform offers excellent motion characteristics, and optimizing to carry large payloads in ultra-deep water. Finally, the effect of potential and viscous damping in different region has been analyzed. INTRODUCTION As the offshore oil exploitation activities expending to deep water and even ultra-deep water, many new types of floating structures suitable for this depth are being developed concomitantly. Compared with other floating structures, Spar platform has excellent stability, benign motion behavior and adaptation to wide range of water depth. Besides, the rigid risers and dry tree system can be used in Spar platforms. Due to so many advantages depicted above, Spar platform is then regarded as an attractive design solution for regions of deep water. Since the first generation of Classic Spar has come to use, the Spar platform has been evolved into the second generation of Truss Spar and the latest Cell Spar (Finn, Maher and Gupta, 2003). With the rapid development of deep-water oil industry, many new technologies and innovative Spar concepts are frequently being proposed to adapt to new operation conditions and ultra-deep water depth. Nowadays, the South China Sea has focused the attention due to the rich storage of oil and natural gas. So the exploitation of the South China Sea is a hot and attractive task and has broad prospects.
Fatigue Damage of Risers With Two-Degrees-of-Freedom Vortex-Induced-Vibration
Tang, Shizhen (Shandong Key Laboratory of Ocean Engineering, Ocean University of China) | Huang, Weiping (Shandong Key Laboratory of Ocean Engineering, Ocean University of China) | Deng, Yue (Shandong Key Laboratory of Ocean Engineering, Ocean University of China) | Liu, Jianjun (Shandong Key Laboratory of Ocean Engineering, Ocean University of China)
ABSTRACT The more practical case of vortex-induced vibration in two degrees of freedom has been presented. The mass ratio is low and equal to m*=1.78. The response amplitude showed three branches namely, the initial branch, the super-upper branch and the lower branch. The reason for the appearance of the super-upper branch is owed to the power increase. The fatigue damage in two degrees of freedom has been compared with that in one degree of freedom. The results showed the in-line fatigue damage can not be neglected especially in the initial branch and the super-upper branch. The in-line fatigue damage could be a main contributor under low reduced velocity and distinctly have a positive influence on that in cross-flow direction in the super-upper branch. INTRODUCTION The problems of vortex-induced vibration (VIV) have been paid more attention in recent years due to the demand of petroleum industry moving towards deep water. Many efforts have been devoted to the prediction of VIV of deepwater marine risers and free span pipelines response mainly in the cross-flow direction for structural design according to the fatigue damage criterion. Vandiver (1987) discovered that there was an interaction between inline vibration and cross-flow VIV that showed as a chart of ‘eight-offigure’. Moe and Wu (1990) carried out two studies for systems enabling x-ymotion of a cylinder, the mass ratios in the xand y directions were quite different, and also the natural frequencies were set in the ratio fx/fy=2.18. Under these special conditions, they found a broad regime of reduced velocity Un(where Un = U/fND, U =freestream velocity, fN= natural frequency; D= diameter) over which resonant amplitudes were found (with transverse normalised amplitude close to Ay/D=1, Ayis the response amplitude in cross flow direction), but without any evidence of distinct response branches.