Riser and J-Tube VIV Analysis Using CFD and FSI for Platform Retrofit Application

2013 ◽  
Author(s):  
David Rubinstein ◽  
Andrew Campbell ◽  
Rodney Pinna
Keyword(s):  
High Performance ◽  
Cross Flow ◽  
Mitigation Strategies ◽  
Cfd Modelling ◽  
Drag Forces ◽  
Fea Model ◽  
Ansys Cfx ◽  
Line Force ◽  
Maintenance And Inspection ◽  
Viv Suppression

INTECSEA has been supporting a client in designing, modelling and assessing a proposal to add additional riser capacity to an existing platform through spare drill slots in the jacket structure. Traditional empirical analysis indicated that the spans between the guides would be subject to Vortex Induced Vibration (VIV), prompting the use of VIV suppression strakes. Analysis was performed to quantify the effectiveness of strakes and to optimise where they are required to minimize jacket loads and operational maintenance and inspection requirements. The current models for VIV have been developed for pipelines and long dynamic risers. Traditional rigid risers installed into a traditional jacket are not well covered. Computational Fluid Dynamics (CFD) modelling was undertaken using ANSYS CFX on bare riser sections, along with strakes of various characteristic parameters based on vendor specifications. A range of current conditions were modelled to stimulate the onset of VIV. Validation of the performance against shedding frequency and mesh independence was performed. This work demonstrated the performance of the strakes in reducing cross flow force amplitude as well as the fluctuating component of the in-line force. The frequency of the force response was also shown to be more random and act on a longer timescale than the bare riser. The increase in drag forces was also found to be of the order reported by the vendors contacted as part of this project. Fluid Structure Interaction (FSI) simulations were performed for the full riser length to better capture the interdependence of the vortex shedding and the motion of the riser by two-way coupling of the CFD and an FEA model built within ANSYS. Simulations also examined the splash zone where only part of the span was submerged. Larger simulations were performed to quantify the effect of damping due to the adjacent spans which have lateral constraints at the guides within the drill slots. This has been a challenging modelling activity as the CFD model is very large and required High Performance Computing (HPC) to run the model in parallel. The work has shown that the application of strakes is an effective method of addressing VIV phenomena within this application. The FSI simulations have examined the dynamic damping along the full riser length. Further modelling work can be performed to better understand the conservativeness of these mitigation strategies saving operators significant cost and time in installation and operating costs.

Straked Riser Design With VIVA

2010 ◽  
Author(s):  
Dhyanjyoti Deka ◽  
Paul R. Hays ◽  
Kamaldev Raghavan ◽  
Mike Campbell
Keyword(s):  
Traveling Waves ◽  
Oil And Gas ◽  
Cross Flow ◽  
Oil And Gas Industry ◽  
Response Prediction ◽  
Design Tool ◽  
Mode Shapes ◽  
Fe Model ◽  
Viv Suppression ◽  
Modal Solution

VIVA is a vortex induced vibration (VIV) analysis software that to date has not been widely used as a design tool in the offshore oil and gas industry. VIVA employs a hydrodynamic database that has been benchmarked and calibrated against test data [1]. It offers relatively few input variables reducing the risk of user induced variability of results [2]. In addition to cross flow current induced standing wave vibration, VIVA has the capability of predicting traveling waves on a subsea riser, or a combination of standing and traveling waves. Riser boundary conditions including fixed, pinned, flex joint or SCR seabed interaction can be modeled using springs and dashpots. VIVA calculates riser natural frequencies and mode shapes and also has the flexibility to import external modal solutions. In this paper, the applicability of VIVA for the design of straked steel catenary risers (SCR) and top tensioned risers (TTR) is explored. The use of linear and rotational springs provided by VIVA to model SCR soil interaction and flex joint articulation is evaluated. Comparisons of the VIV fatigue damage output with internal and external modal solution is presented in this paper. This paper includes validation of the VIVA generated modal solution by comparing the modal frequencies and curvatures against a finite element (FE) model of the risers. Fatigue life is calculated using long term Gulf of Mexico (GoM) currents and is compared against the industry standard software SHEAR7. Three different lift curve selections in SHEAR7 are used for this comparison. The differences in riser response prediction by the two software tools are discussed in detail. The sensitivity of the VIVA predicted riser response to the absence of VIV suppression devices is presented in this paper. The riser VIV response with and without external FE generated modal input is compared and the relative merits of the two modeling approaches are discussed. Finally, the recommended approach for VIVA usage for SCR and TTR design is given.

Influence From Helical Strakes on Vortex Induced Vibrations and Static Deflection of Drilling Risers

2005 ◽  
Author(s):  
Carl M. Larsen ◽  
Gro Sagli Baarholm ◽  
Halvor Lie
Keyword(s):  
Dynamic Response ◽  
Test Data ◽  
Oscillation Amplitude ◽  
Cross Flow ◽  
Current Profile ◽  
Dynamic Stresses ◽  
Drag Forces ◽  
Vortex Induced Vibrations ◽  
Bending Stresses ◽  
Helical Strakes

Helical strakes are known to reduce and even eliminate the oscillation amplitude of vortex induced vibrations (VIV). This reduction will increase fatigue life, and also reduce drag magnification from cross-flow vibrations. But sections with strakes will also have a larger drag coefficient than the bare riser. Hence, the extension of a section with strakes along a riser should be large enough to reduce oscillations, but not too long in order to limit drag forces from current and waves. The optimum length and position for a given riser will therefore vary with current profile. Dynamic response from waves should also be taken into account. The purpose of the present paper is to illustrate the influence from strakes on VIV, as well as on static and dynamic response for a drilling riser. Hydrodynamic coefficients for a cylinder with helical strakes are found from experiments and applied in an empirical model for the analysis of VIV. The result from the VIV analysis is used for a second calculation of drag forces that are applied in an updated static analysis. Dynamic stresses from regular waves are also presented, but VIV are not considered for these cases. A simple study of length and position of the section with strakes is carried out for some standard current profiles. Results are presented in terms of oscillation amplitudes, fatigue damage, bending stresses and riser angles at ends. The study is based on test data for one particular strake geometry, but the analysis method as such is general, and the computer programs used in the study can easily apply other test data.

Drilling Riser VIV Tests With Prototype Reynolds Numbers

2013 ◽  
Author(s):  
Halvor Lie ◽  
Henning Braaten ◽  
Jamison Szwalek ◽  
Massimiliano Russo ◽  
Rolf Baarholm
Keyword(s):  
Cross Flow ◽  
Effect Study ◽  
Full Scale ◽  
Scale Model ◽  
Small Scale ◽  
Scaling Effects ◽  
Research Activity ◽  
Forced Motion ◽  
Auxiliary Lines ◽  
Viv Suppression

For deep-water riser systems, Vortex Induced Vibrations (VIV) may cause significant fatigue damage. It appears that the knowledge gap of this phenomenon is considerable and this has caused a high level of research activity over the last decades. Small scale model tests are often used to investigate VIV behaviour. However, one substantial uncertainty in applying such results is scaling effects, i.e. differences in VIV response in full scale flow and small scale flow. To (partly) overcome this obstacle, a new innovative VIV test rig was designed and built at MARINTEK to test a rigid full scale riser model. The rigid riser model is mounted vertically and can either be elastically mounted or be given a forced motion. In the present version, the cylinder can only move in the cross-flow (CF) direction and is restricted in the in-line (IL) direction. The paper reports results from a drilling riser VIV experiment where the new rest rig has been used. The overall objective of the work is to study possible VIV suppression to improve operability of retrievable riser systems with auxiliary lines by adding riser fins. These fins are normally used as devices for protection of the auxiliary lines. The test program has recently been completed and analysis is an on-going activity. However, some results can be reported at this stage and more results are planned to be published. A bare riser model was used in a Reynolds number (Rn) scaling effect study. The riser model was elastically mounted and towed over a reduced velocity range around 4 – 10 in two different Rn ranges, 75 000 – 192 000 (subcritical regime) and 347 000 – 553 000 (critical regime). The difference in the displacement amplitude to diameter ratio, A/D, is found to be significant. The elastically mounted riser was also towed with various drilling riser configurations in order to study VIV/galloping responses. One configuration included a slick joint riser model with 6 kill & choke lines; another has added riser fins too. The riser model is based on a specific drilling riser and the kill and choke lines have various diameters and have a non-symmetrical layout. The various riser configurations have also been used in forced motion tests where the towed model has been given a sinusoidal CF motion. Forces have been measured. Determination of the force coefficients is still in progress and is planned to be reported later. Scaling effects appear to be a significant uncertainty and further research on the subject is recommended. The slick joint drilling riser configuration generally increased the displacements compared to displacements of the bare riser model. The drilling riser configuration with protection fins, kill and choke lines generally reduced the displacements compared to displacements of the bare riser model. For both riser systems, tests showed that the response is sensitive to the heading of the current.

Practical Design Considerations for Managing Marine Growth on VIV Suppression Devices

2015 ◽  
Author(s):  
Don W. Allen ◽  
Li Lee ◽  
Dean Henning ◽  
Stergios Liapis
Keyword(s):  
Reynolds Number ◽  
Fatigue Life ◽  
Strong Influence ◽  
Low Reynolds Number ◽  
Vortex Induced Vibration ◽  
Design Considerations ◽  
Drag Forces ◽  
Practical Design ◽  
Helical Strakes ◽  
Viv Suppression

Most deepwater tubulars experiencing high currents frequently require vortex-induced vibration (VIV) suppression to maintain an acceptable fatigue life. Helical strakes and fairings are the most popular VIV suppression devices in use today. Marine growth can significantly affect the VIV of a bare riser, often within just a few weeks or months after riser installation. Marine growth can have a strong influence on the performance of helical strakes and fairings on deepwater tubulars. This influence affects both suppression effectiveness as well as the drag forces on the helical strakes and fairings. Unfortunately, many VIV analyses and suppression designs fail to account for the effects of marine growth at all, even on a bare riser. This paper utilizes results from both high and low Reynolds number VIV test programs to provide some design considerations for managing marine growth for VIV suppression devices.

Vibration Excitation Forces in a Normal Triangular Tube Bundle Subjected to Two-Phase Cross Flow

2011 ◽  
Author(s):  
E. S. Perrot ◽  
N. W. Mureithi ◽  
M. J. Pettigrew ◽  
G. Ricciardi
Keyword(s):  
Tube Bundle ◽  
Cross Flow ◽  
Random Excitation ◽  
Two Phase ◽  
Constant Frequency ◽  
Fluid Forces ◽  
Drag Forces ◽  
Wide Range ◽  
Drag And Lift ◽  
Lift And Drag

This paper presents test results of vibration forces in a normal triangular tube bundle subjected to air-water cross-flow. The dynamic lift and drag forces were measured with strain gage instrumented cylinders. The array has a pitch-to-diameter ratio of 1.5, and the tube diameter is 38 mm. A wide range of void fraction and fluid velocities were tested. The experiments revealed significant forces in both the drag and lift directions. Constant frequency and quasi-periodic fluid forces were found in addition to random excitation. These forces were analyzed and characterized to understand their origins. The forces were found to be dependent on the position of the cylinder within the bundle. The results are compared with those obtained with flexible cylinders in the same tube bundle and to those for a rotated triangular tube bundle. These comparisons reveal the influence of quasi-periodic forces on tube motions.

Direct Numerical Simulations of a Transonic Tip Flow With Free-Stream Disturbances

2013 ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Richard D. Sandberg
Keyword(s):  
Heat Transfer ◽  
High Performance ◽  
Free Stream ◽  
Separation Bubble ◽  
Cross Flow ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Computational Domain ◽  
Free Stream Turbulence ◽  
Gap Height

In this paper we use direct numerical simulation to investigate the unsteady flow over a model turbine blade-tip at engine scale Reynolds and Mach numbers. The DNS is performed with a new in-house multi-block structured compressible Navier-Stokes solver purposely developed for exploiting high-performance computing systems. The particular case of a transonic tip flow is studied since previous work has suggested compressibility has an important influence on the turbulent nature of the separation bubble at the inlet to the gap and subsequent flow reattachment. The effects of free-stream turbulence, cross-flow and pressure-side boundary-layer on the tip flow aerodynamics and heat transfer are investigated. For ‘clean’ in-flow cases we find that even at engine scale Reynolds numbers the tip flow is intermittent in nature (neither laminar nor fully turbulent). The breakdown to turbulence occurs through the development of spanwise modes with wavelengths around 25% of the gap height. Cross-flows of 25% of the streamwise gap exit velocity are found to increase the stability of the tip flow, and to significantly reduce the turbulence production in the separation bubble. This is predicted through in-house linear stability analysis, and confirmed by the DNS. For the case when the inlet flow has free-stream turbulence, viscous dissipation and the rapid acceleration of the flow at the inlet to the tip-gap causes significant distortion of the vorticity field and reductions of turbulence intensity as the flow enters the tip gap. This means that only very high turbulence levels at the inlet to the computational domain significantly affect the tip heat transfer. The DNS results are compared with RANS predictions using the Spalart-Allmaras and k–ω SST turbulence models. The RANS and DNS predictions give similar qualitative features for the tip flow, but the size and shape of the inlet separation bubble and shock positions differ noticeably. The RANS predictions are particularly insensitive to free-stream turbulence.

Reynolds Number Effect on the Flow Demeanorin a Vertical Circular Free Turbulent Jet with Cross Flow

2021 ◽  
Vol 409 ◽  
pp. 158-178
Author(s):  
Abdelkader Feddal ◽  
Abbes Azzi ◽  
Ahmed Zineddine Dellil
Keyword(s):  
Reynolds Number ◽  
Cross Flow ◽  
Turbulence Models ◽  
Turbulent Jets ◽  
Turbulent Jet ◽  
Low Velocity ◽  
Transverse Current ◽  
Ansys Cfx ◽  
The Cross ◽  
Two Jets

This paper deals with studying numerically two circular turbulent jets impinging on a flat surface with a low velocity cross flow by using ANSYS CFX 16.2, with the aim of proving the effect ofReynolds number on the flow demeanor in a vertical circular free turbulent jet with cross flow. Five turbulence models of the RANS (Reynolds Averaged Navier–Stokes) approach were tested and the k -ω SST model was chosen to validate CFD results with the experimental data. Average velocity profiles, velocity and turbulent kinetic energy contours and streamlines are presented for four case configurations. In the first three cases, the following parameters have been varied: Reynolds number at the level of the two jets ( ), wind velocity at the level of the cross-flow ( ), and the distance between the two jets (S = 45mm, 90mm and 135mm). In the last case, a new configuration of the phenomenon not yet studied so far was treated, where horizontal cross-flows were introduced from both sides in order to simulate gusts of wind disrupting a VSTOL aircraft which tries to operate close to the ground. This case was carried out for Reynolds number based on the crossflow of 4 104, 10 104 and 20 104 .The numerical results obtained show that the deflection of the jets is minimal when the Reynolds number at the level of the jets is greater than that of the cross-flow. The increase of Reynolds number at the level of the cross-flow reveals a significant deviation of the two jets with an intensity which always remains less for the second jet. As for the space parameter between the two jets, it turns out that the fact of further spacing the two jets makes the first jet even more vulnerable and leads to a greater deflection. Finally, the simulation of the wind gusts from the front and the back caused a zone of turbulence which resulted from a form of "interlacing" of the two jets under the effect of the transverse current imposed by the two sides.

scholarly journals Biofouling Mitigation Approaches during Water Recovery from Fermented Broth via Forward Osmosis

Membranes ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 307
Author(s):  
Stavros Kalafatakis ◽  
Agata Zarebska ◽  
Lene Lange ◽  
Claus Hélix-Nielsen ◽  
Ioannis V. Skiadas ◽  
...  
Keyword(s):  
Flow Velocity ◽  
Forward Osmosis ◽  
Cross Flow ◽  
Feed Solution ◽  
Mitigation Strategies ◽  
Water Recovery ◽  
Operational Parameters ◽  
Solution Ph ◽  
Sustainable Solutions ◽  
Cross Flow Velocity

Forward Osmosis (FO) is a promising technology that can offer sustainable solutions in the biorefinery wastewater and desalination fields, via low energy water recovery. However, microbial biomass and organic matter accumulation on membrane surfaces can hinder the water recovery and potentially lead to total membrane blockage. Biofouling development is a rather complex process and can be affected by several factors such as nutrient availability, chemical composition of the solutions, and hydrodynamic conditions. Therefore, operational parameters like cross-flow velocity and pH of the filtration solution have been proposed as effective biofouling mitigation strategies. Nevertheless, most of the studies have been conducted with the use of rather simple solutions. As a result, biofouling mitigation practices based on such studies might not be as effective when applying complex industrial mixtures. In the present study, the effect of cross-flow velocity, pH, and cell concentration of the feed solution was investigated, with the use of complex solutions during FO separation. Specifically, fermentation effluent and crude glycerol were used as a feed and draw solution, respectively, with the purpose of recirculating water by using FO alone. The effect of the abovementioned parameters on (i) ATP accumulation, (ii) organic foulant deposition, (iii) total water recovery, (iv) reverse glycerol flux, and (v) process butanol rejection has been studied. The main findings of the present study suggest that significant reduction of biofouling can be achieved as a combined effect of high-cross flow velocity and low feed solution pH. Furthermore, cell removal from the feed solution prior filtration may further assist the reduction of membrane blockage. These results may shed light on the challenging, but promising field of FO process dealing with complex industrial solutions.

Finite Element Modeling of Pad Deformation due to Diamond Disc Conditioning in Chemical Mechanical Polishing (CMP)

2012 ◽  
Author(s):  
Emmanuel A. Baisie ◽  
Z. C. Li ◽  
X. H. Zhang
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Material Removal ◽  
High Performance ◽  
Removal Rate ◽  
Chemical Mechanical Planarization ◽  
Element Analysis ◽  
Fea Model ◽  
Pad Wear ◽  
Diamond Disc

Chemical mechanical planarization (CMP) is widely used to planarize and smooth the surface of semiconductor wafers. In CMP, diamond disc conditioning is traditionally employed to restore pad planarity and surface asperity. Pad deformation which occurs during conditioning affects the material removal mechanism of CMP since pad shape, stress and strain are related to cut rate during conditioning, pad wear rate and wafer material removal rate (MRR) during polishing. Available reports concerning the effect of diamond disc conditioning on pad deformation are based on simplified models of the pad and do not consider its microstructure. In this study, a two-dimensional (2-D) finite element analysis (FEA) model is proposed to analyze the interaction between the diamond disc conditioner and the polishing pad. To enhance modeling fidelity, image processing is utilized to characterize the morphological and mechanical properties of the pad. An FEA model of the characterized pad is developed and utilized to study the effects of process parameters (conditioning pressure and pad stiffness) on pad deformation. The study reveals that understanding the morphological and mechanical properties of CMP pads is important to the design of high performance pads.

An Analytical Study of the Optimized Performance of an Impingement Heat Sink

2004 ◽  
Vol 126 (4) ◽  
pp. 528-534 ◽  
Author(s):  
S. B. Sathe ◽  
B. G. Sammakia
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Sink ◽  
High Performance ◽  
Cross Flow ◽  
High Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Flow Through

The results of a study of a new and unique high-performance air-cooled impingement heat sink are presented. An extensive numerical investigation of the heat sink performance is conducted and is verified by experimental data. The study is relevant to cooling of high-power chips and modules in air-cooled environments and applies to workstations or mainframes. In the study, a rectangular jet impinges on a set of parallel fins and then turns into cross flow. The effects of the fin thickness, gap nozzle width and fin shape on the heat transfer and pressure drop are investigated. It is found that pressure drop is reduced by cutting the fins in the central impingement zone without sacrificing the heat transfer due to a reduction in the extent of the stagnant zone. A combination of fin thicknesses of the order of 0.5 mm and channel gaps of 0.8 mm with appropriate central cutout yielded heat transfer coefficients over 1500 W/m2 K at a pressure drop of less than 100 N/m2, as is typically available in high-end workstations. A detailed study of flow-through heat sinks subject to the same constraints as the impingement heat sink showed that the flow-through heat sink could not achieve the high heat transfer coefficients at a low pressure drop.

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