Hydrodynamic Coefficients for Riser In-Line VIV in Sheared Currents

2007 ◽  
Author(s):  
Djoni E. Sidarta ◽  
Kostas F. Lambrakos ◽  
Carl M. Larsen
Keyword(s):  
Fatigue Damage ◽  
Laboratory Tests ◽  
Ad Hoc ◽  
Science And Technology ◽  
Cross Flow ◽  
Hydrodynamic Coefficients ◽  
Simply Supported ◽  
Hydrodynamic Damping ◽  
Uniform Current ◽  
Mode Response

A methodology for analyzing risers for in-line VIV fatigue damage has been developed that is based on the code SHEAR7, and laboratory in-line VIV coefficients. The in-line VIV fatigue in many instances governs the design of the riser since in-line VIV starts at a reduced velocity of about 1 whereas the threshold reduced velocity for cross flow VIV is about 4. The methodology can treat sheared currents on the basis of the cross flow VIV modeling in SHEAR7. Through the SHEAR7 modeling, the methodology removes conservatism implicit in the present ad hoc procedures for calculating riser in-line VIV response on the basis of the DNV-RP-F105 code. The reduction in conservatism is due to accounting properly for the power-in region in the VIV excitation, the hydrodynamic damping, and competing modal excitation (multiple mode response). The inline VIV coefficients have been derived from laboratory tests at the Norwegian University of Science and Technology (NTNU). The paper presents the in-line VIV coefficients, and examples to demonstrate the methodology for riser in sheared currents. The coefficients derived from the NTNU tests are functions of both the in-line VIV response amplitude and the reduced velocity. The coefficients presented in the paper are scaled test coefficients. The scaling of the NTNU coefficients assures that the methodology calculates in-line VIV amplitudes that are consistent with the response amplitudes in DNV-RP-F105 for the case of a simply supported riser in uniform current. This DNV code, although written for pipelines, has been extended to risers in sheared currents on the basis of conservative approaches.

Frequency Domain Model for Prediction of Stochastic Vortex Induced Vibrations for Deep Water Risers

2008 ◽  
Author(s):  
Halvor Lie ◽  
Carl M. Larsen ◽  
Karl Erik Kaasen
Keyword(s):  
Fatigue Damage ◽  
Travelling Waves ◽  
Cross Flow ◽  
Higher Order ◽  
Domain Model ◽  
Limited Information ◽  
Time Sharing ◽  
New Model ◽  
Discrete Frequency ◽  
Uniform Current

This paper describes a new model for prediction of fatigue damage from VIV in risers. The method will overcome some of the shortcomings of previous methods. A fully 3D model is proposed, “cross-flow” and “in-line” response are predicted, response at higher order harmonic components will be added, and the stochastic nature of the response is accounted for by introducing a time varying envelope function combined with “time sharing” between dominating response frequencies. A model that reflects this behaviour is considered to be more realistic and is more likely to predict lower fatigue damage than the traditional discrete-frequency models. The model will predict a response that will appear as a combination of standing and travelling waves depending on boundary conditions, damping and load distribution. Fatigue damage will therefore become more evenly distributed along the riser, and less concentrated at anti-nodes for (dominating modes) than seen from traditional discrete frequency models. The proposed model needs empirical coefficients for simultaneous IL and CF response. In principle this requires a data base of added mass, excitation and damping coefficients for varying flow conditions and response frequencies, combinations of response amplitudes in both directions, varying phase between the two response components and even the presence of higher order motion components. Such data do not exist. We have therefore proposed to use the limited information we have on this matter at present. Future improvement of the model might therefore be possible if more data becomes available. The new model will be implemented in the VIVANA program and the enhancement of the code is in progress. The paper will present the background of the model, the basic assumption of the new model and a comparison between preliminary results obtained from a preliminary code and model test results. The cases include both 2D uniform current conditions and 3D (non-uniform) current conditions.

Experimental and Numerical Analysis of Forced Motion of a Circular Cylinder

2011 ◽  
Author(s):  
Decao Yin ◽  
Carl M. Larsen
Keyword(s):  
Influence Factor ◽  
Amplitude Ratio ◽  
Cross Flow ◽  
Flexible Beam ◽  
Hydrodynamic Coefficients ◽  
Forced Motion ◽  
Vortex Pattern ◽  
Severe Fatigue ◽  
Vortex Induced Vibrations ◽  
Uniform Current

Vortex induced vibrations (VIV) of long, slender marine structures may cause severe fatigue damage. However, VIV is still not fully understood, which calls for further research on this topic. This paper discusses results from experimental and numerical investigations of forces on rigid cylinders subjected to combined in-line (IL) and cross-flow (CF) motions, and it aims at improving the understanding of the interaction between IL and CF response components. Model tests with a long flexible beam were conducted at MARINTEK for the Norwegian Deepwater Programme (NDP). The model was 38 m long and it was towed horizontally so that both uniform and linear sheared current profiles could be obtained. Orbits for cross section motions at selected positions along the beam were identified in these tests. Forced motion experiments using these orbits were later carried out in the Marine Cybernetic Laboratory at Norwegian University of Science and Technology (NTNU). A 2 m long rigid cylinder was towed horizontally and forced to follow the measured orbits with identical amplitude ratio, non-dimensional frequency and Reynolds number as for the flexible beam tests. Parts of the results from these tests were published by Yin & Larsen in 2010. In this paper results from an investigation of trajectories for six positions along the beam in a uniform current condition will be shown. Three orbits have nearly the same CF amplitude ratio at the primary CF frequency, and the other three have similar IL amplitude ratio at the primary IL frequency, which is twice the CF frequency. Hydrodynamic coefficients have been found from experiments and numerical computations were carried out to find vortex shedding patterns for these cases. The main conclusions are that the IL motion component is a significant influence factor, and that higher order displacement components are more pronounced in IL direction than CF. Significant displacements in IL direction at 6 times the primary CF frequency were also observed, the ‘2T’ vortex pattern was captured when strong IL motion components were present. It is also seen that hydrodynamic coefficients should be found for combined CF and IL orbits and thereby improve the empirical models for prediction of VIV.

A Methodology for In-Line VIV Analysis of Risers in Sheared Currents

2006 ◽  
Author(s):  
Djoni E. Sidarta ◽  
Kostas F. Lambrakos ◽  
Hugh M. Thompson ◽  
Roger W. Burke
Keyword(s):  
Fatigue Damage ◽  
Laboratory Data ◽  
Cross Flow ◽  
Multiple Constraints ◽  
Current Profile ◽  
Sheared Flow ◽  
Hydrodynamic Damping ◽  
Mode Excitation ◽  
Exploration And Production ◽  
The Cross

As exploration and production move to even deeper water and more severe environment, the need to have a methodology for analyzing risers for in-line VIV fatigue damage without undue conservatism increases. The methodology presented in this paper reduces the conservatism in available methods by accounting for (1) the power-in region, (2) the power-out region (hydrodynamic damping), (3) competing modal excitation in the case of multiple mode excitation, and (4) the multiple constraints, if available, in the riser that result in irregular modal shapes. This methodology requires the use of a cross-flow VIV code with sheared flow capability such as SHEAR7, VIVA, or VIVANA. In this methodology the riser over the current profile is split into sections of cross-flow excitation and sections that have potential for in-line VIV excitation only. The cross-flow VIV code defines the sections for cross-flow excitation. All sections are analyzed for in-line VIV with the cross-flow VIV code using the appropriate in-line VIV force coefficients and Strouhal numbers. The assumptions implicit in the cross-flow VIV code regarding power-in, power-out, etc., are assumed valid for the in-line VIV analysis. The in-line VIV coefficients used in the analysis reported in this paper have been obtained from laboratory data, and are functions of both the VIV response amplitude and reduced velocity. The coefficients have been modified to give in-line VIV response amplitudes with the methodology presented that are consistent with DNV-RP-F105. The fatigue damage along the riser represents the sum of the damages produced by in-line VIV excitation for each of the riser sections.

scholarly journals Conceitos de Arte, Design e Arquitetura aplicados: Utilização de tecnologias aliadas a processos e procedimentos intuitivos e racionas em ateliês-laboratórios para a concepção e materialização de projetos / Concepts of Applied Art, Design and Architecture: Use of Technologies Coupled with Intuitive Processes and Procedures and Rationalized in Workshops-Laboratories for the Design and Materialization of Projects

2017 ◽  
Vol 4 (1) ◽  
pp. 25-35
Author(s):  
Celio Martins da Matta ◽  
Andre Martins da Matta
Keyword(s):  
Laboratory Tests ◽  
Science And Technology ◽  
A Priori ◽  
Academic Experience ◽  
Doctoral Thesis ◽  
Applied Art ◽  
De Se ◽  
Art Design ◽  
Artistic Works

ABSTRACTProcess of study of two binomials considered inseparable: creative-rational and conceptualization-materialization. Translates the academic experience with classes, orientations, disciplines, coordination of laboratories and doctoral thesis: Artemídia Influente: Ateliê-Laboratório in the Interfaces Art, Science and Technology. This mixture provided information on laboratory tests for the conception, materialization and understanding of art and its derivatives in the art, science and technology interfaces. Emphasis on the use of materialization processes, which a priori served as a didactic tool and were subsequently used to make artistic works, concomitantly the awareness and scientific artistic appropriation of these didactic prototypes of courses in design, architecture and art.RESUMOO artigo relata a vivência acadêmica do autor com aulas, orientações, disciplinas ministradas, coordenação de laboratórios e parte da tese de doutoramento intitulada: Artemídia Influente: Ateliê-Laboratório nas Interfaces Arte, Ciência e Tecnologia. Essa mistura forneceu informações sobre ensaios e tentativas laboratoriais de se conceber, materializar e entender arte, e seus derivados nas interfaces arte, ciência e tecnologia. Ênfase para a utilização de processos avançados de materialização, que a priori serviam de instrumento didático nos estudos em ateliês-laboratórios, mas que posteriormente foram utilizados para a confecção de obras de arte, concomitantemente a uma tomada de consciência, de apropriação artístico científica de protótipos didáticos. Para a materialização foram utilizadas técnicas híbridas, manuais e tecnológicas, em diversos espaços de ateliês-laboratórios.

The Lift Force on a Cylinder Vibrating in a Current

1990 ◽  
Vol 112 (4) ◽  
pp. 297-303 ◽  
Author(s):  
G. Moe ◽  
Z.-J. Wu
Keyword(s):  
Free Vibration ◽  
Forced Vibration ◽  
Cross Flow ◽  
Reference Frequency ◽  
Average Force ◽  
Vibrational Response ◽  
Uniform Current ◽  
Extensive Program ◽  
Vibration Tests ◽  
Lock In

This paper reports an extensive program of forced and free vibration tests on a single circular cylinder moving mainly perpendicularly to a uniform current. For both free and forced vibration tests, two cases were investigated: one in which the cylinder was restrained in the in-line direction and the other in which it was supported on suitable springs. The cross-flow vibrational response and hydrodynamic forces on the cylinder were measured. Large variations of motion frequency in the “lock-in” range were found from the free vibration tests. This leads to two different definitions of reduced velocity, namely, a so-called nominal reduced velocity based on one reference frequency and the true reduced velocity based on the actual vibration frequency. When different results are compared, the true reduced velocity should be used. The forced vibration tests showed, as may be expected, that the transverse force in the “lock-in” range on the average will add energy to the cylinder at moderate motion amplitudes and subtract energy at large amplitudes. Some conditions resulting in a steady-state vibration of a flexibly mounted cylinder were analyzed. The actual force traces also show very large and apparently random deviations from the average force amplitude. The results from the forced and the free vibration tests are consistent with each other if the true reduced velocity and reduced amplitude are the same.

Experimental Investigation on the Suppression Device of VIV of a Flexible Riser

2014 ◽  
Author(s):  
Yun Gao ◽  
Shixiao Fu ◽  
Leijian Song ◽  
Tao Peng ◽  
Runpei Lei
Keyword(s):  
Fatigue Damage ◽  
Experimental Results ◽  
Experimental Investigations ◽  
Flexible Riser ◽  
Excited Mode ◽  
Response Characteristics ◽  
Helical Strakes ◽  
Uniform Current ◽  
Viv Suppression ◽  
Synchronization Regime

Experimental investigations were conducted on a flexible riser with and without helical strakes. A uniform current was obtained by towing a riser model in a tank, and the vortex-induced vibration (VIV) suppression of strakes with different heights and pitches was studied. The results of the bare riser show that the characteristics of the synchronization of the VIV for a flexible riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical strakes, and the suppression performance depends on the geometry of the helical strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser fitted with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that strake height has a greater influence on the VIV response than the strake pitch, and the drag exerted on the riser increases with strake pitch and height.

Response of Pipelines Under VIV: An Experimental Investigation

2010 ◽  
Author(s):  
Prashant K. Soni ◽  
Carl M. Larsen
Keyword(s):  
Response Pattern ◽  
Dynamic Properties ◽  
Cross Flow ◽  
Flexible Beam ◽  
Hydrodynamic Coefficients ◽  
Response Model ◽  
Flexible Pipe ◽  
Damping Force ◽  
Robust Response ◽  
A Current

Pipelines laid on an uneven bottom often have free spans. For cases with long spans, one may have several modes and eigenfrequencies that can be excited by vortex shedding. Furthermore, due to the sag effect of a long free-span, the dynamic properties are different in vertical and in horizontal directions. This causes a complex response pattern in the cross-flow (CF) and in-line (IL) directions. From previous research we know that pure IL response at relatively low current velocities may significantly contribute to fatigue damage. This response type must be studied in addition to the combined IL and CF response. The objective of this paper is to present experimental results from flexible beam experiments where both response types are studied, as well as to present results from an empirical response model for the same cases. The empirical model is based on two types of experiments. The first set of experiments were conducted with a flexible pipe for both single and double span configuration. Pure IL and combined IL and CF motions were observed. In the second set of experiments, forces on a rigid cylinder were measured under forced motions in a current. The motions were found from measurements of cross section in the flexible pipe tests. Hydrodynamic coefficients such as drag, added mass, excitation and damping force coefficients were found and then applied in the empirical response model. In the present paper the results from the flexible beam experiments are presented and also compared with the results from the empirical response model. The results so far are encouraging, but further work and more data are needed in order to have a general and robust response model for combined CF and IL VIV.

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