Tc 67/sc 4 n date: 2005-03-9 iso/wd XXXXXX ISO tc 67/sc 4/wg 6 Secretariat: Design of dynamic risers for offshore production systems Élément introductif — Élément central — Élément complémentaire Warning
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where  = Wake half-width (see Figure 38)
 = Effective drag coefficient, any expected VIV to be taken into account by increasing its typical stationary flow value,
 = Diameter of riser generating the wake,
 = Distance in flow direction from center of riser,
 = Transverse distance from center-line of wake,
 = Wake velocity at y=0,
 = Wake velocity at arbitrary downstream coordinates x,y,
 = Inflow velocity to upstream riser.
k1 and k2 empirical constants having recommended values k1 = 0.25 and k2 = 1.0. As an example of the practical consequences of this formulation consider two cylinders of equal diameter, one sitting directly behind the other in the direction of the current. If the center-to-center spacing is 5 diameters, the drag force on the downstream cylinder is reduced by 45 percent compared to the upstream cylinder. If the spacing is 30 diameters the corresponding reduction will be 27 percent and at a spacing of 100 diameters the reduction is still as large as 16 percent. It is generally accepted that the potential flow field induced by a cylinder is negligible at distances of the order of 5 diameters or more. However, as can be seen from the above examples, the shielding effect produced by the upstream cylinder is significant even at much larger distances. The evaluation of risk of collision in top-tensioned riser arrays can be done in three phases as follows: Directory: standards standards -> Request for proposal contract form for the transit industry standards -> Indiana Academic Standards Resource Guide Grade 8 United States History – Growth and Development (to 1877) Updated April 2016 standards -> Us history Dictionary Based on the sc state Standards standards -> Integrating Standards Education into the Business School Curriculum standards -> Use of Sprint U301 3G/4g mobile Broadband usb device Installation standards -> International organisation for standardisation organisation internationale de normalisation standards -> Standards of Excellence standards -> Common Core State Standards for Mathematics (ccssm) Download 2.34 Mb. Share with your friends:
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