Shear 7

SBM Atlantia is the purveyor to the industry and maintainer of the SHEAR7 VIV program.  SHEAR7 is a program which performs Vortex Induced Vibration (VIV) analysis of riser-like members in sheared flow.  It was developed at MIT under joint industry sponsorship.  We work closely with MIT in providing this program to the industry, and maintain a user group of over 40 companies world-wide who are active users. 

For information on licensing please contact:

Liz Alexander
+1 281-899-4520
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Technical questions should be directed to:

Steve Leverette                                   or         Christopher Wajnikonis

+1 281-899-4431                                            +1 281-899-4439
.(JavaScript must be enabled to view this email address)                .(JavaScript must be enabled to view this email address)

 

 

SHEAR7 Description

With over 15 years of industry use and continuous development, SHEAR7 is one of the leading modeling tools for the prediction of vortex-induced vibration (VIV). The program’s forte is the VIV response prediction of offshore structures subjected to spatially varying currents; realistic of ocean environments. The program enables users to estimate structural responses, mean drag force amplification factors and predict fatigue damage. It is simple and fast to run with all the results summarized in a convenient standard output file. The new release allows for more accurate modeling of Strakes.

SHEAR7 is a mode superposition program, which evaluates which modes are likely to be excited by vortex shedding and estimates the steady state, cross-flow, VIV response in uniform or sheared flows. It is capable of evaluating multi-mode, non-lock-in response, as well as single mode lock-in response.

The program evaluates natural frequencies and mode shapes of cables and beams with linearly varying or slowly varying tension and with a variety of boundary conditions, including cantilevers and free hanging risers. The program is capable of evaluating the natural frequencies and mode shapes and VIV response of horizontal catenary cables and uses an approximate structural model for inclined catenary cables.

The user may choose to compute natural frequencies and mode shapes in a separate program, such as a finite element program and provide them as input to SHEAR7. In this way, structures which are not in the standard solution set of SHEAR7 may be evaluated.

SHEAR7 can be used to predict the cross flow RMS displacement and stress; as well as fatigue damage rate and local drag amplification coefficients.

Structures are not required to be of constant cross-section. The user may also model sections of risers with VIV suppression devices (strakes and fairings) as well as staggered buoyancy modules.

The basic solution technique used is modal analysis and iteration (to account for the non-linear relationship between response and lift coefficient.) The physical assumption is that the power input (by lift force) and power output (through damping) for each mode should be in balance in a steady state. From initial values of lift and damping coefficients, the program finds the lift and damping coefficients in a balanced state through iteration. The converged lift and damping coefficients are used to compute cylinder response.

Throughout the years of development, SHEAR7 has remained a very simple to use program, that can quickly be run.

Recent version updates have provided the following improvements:

Version 4.3

• Much improved modeling of the behavior of Strakes.  Added formula description of lift coefficient.
• Incorporate your user lift coefficient and damping data from experiments to predict behavior of long flexible structures.
• The ability to define the lift and damping behavior separately for each zone on the structure.
• Results can be produced in the time domain for rainflow fatigue calculations or incorporation with other modeling programs.

Version 4.4

• Modification of lift coefficient formulations.
• New iteration scheme for Positive/Negative Lift power – increased accuracy of the solution resulting in a dramatic improvement of program accuracy and reliability for very small hydrodynamic diameters (< 1 inch) & single mode excitations.

Version 4.5 

• SHEAR7 is similar to that of versions 4.0-4.4 but the way in which the program works has been changed considerably. This reflects the findings of recent research; in particular that of the MIT/DEEPSTAR program involving towing slender pipes in the Gulf Stream offshore Miami. The most significant modification introduced in version 4.5 involves a change in the way power-in regions are apportioned in time and space.
• All earlier versions of the program utilized a ‘competing modes’ model of VIV, whereas all potentially responding modes competed among each other for power-in length on the riser. Whenever response in more than one mode was feasible, the whole power-in region was subdivided into individual power-in regions, one per mode. Any overlaps between modal power-in regions were removed. The greater the number of modes left above the cutoff power level, the smaller the individual power-in regions became. This had the effect of reducing the response of each mode. Recent research has shown that this in not seen on typical risers. Rather, each mode appears one at a time. Over a long period several modes may come and go, sharing the time that VIV is experienced. Each mode has a much larger power-in region than would be permitted by removing spatial overlap in power-in regions. Each mode has more power-in and responds with larger amplitude than would be predicted in the old method of response computation

For a more in-depth description of Shear7, please visit: http://web.mit.edu/shear7/shear7.html