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Nearshore Breakwater System

Nearshore Breakwater System. Jeffrey A. Melby, PhD. RPE Need. Nearshore JLOTS cease in sea state 3 Existing small ports may not have adequate draft Existing ports are relatively easily denied Need calm water for nearshore JLOTS operations No rapidly installable technology exists

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Nearshore Breakwater System

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  1. Nearshore Breakwater System Jeffrey A. Melby, PhD

  2. RPE Need • Nearshore JLOTS cease in sea state 3 • Existing small ports may not have adequate draft • Existing ports are relatively easily denied • Need calm water for nearshore JLOTS operations • No rapidly installable technology exists • Traditional breakwaters and piers require months to construct or repair • Floating causeways are not functional in and above SS3 and do not work nearshore • Huge breaking wave forces in nearshore zone demand a rational engineering approach for both mooring and structural integrity

  3. NBS R&D Program • Operating metrics • Deploy in SS3, Operate in SS1-SS5 • Deploy in 2-3 days • Operate in depths of 0 - 30 ft • Reduce wave heights by 50% • Identify promising ideas • Physical modeling • Numerical modeling • Full scale testing

  4. NBS Primary Concept

  5. Physical Model Study • Conducted 1:20 scale model of fabric tube structure • Wave flume 3’ x 3’ x 148’ • Scaled irregular wave climate • Included sand bed • Roughly scaled fabric elasticity

  6. Model Structures

  7. Physical Model Study • Measurements • Incident and transmitted waves • Displacement of tubes • Forces on fabric • Sediment scour

  8. Wave Overtopping Kt = Ht /Hi Rc = freeboard Hs = wave height Lp = fabric preload Hi Rc Ht

  9. Wave Forces in Fabric Conversion: 4.45 N/lb

  10. Maximum Full-Scale Force Fmax = 13.7 t/50 ft for single tube Fmax = 4.6 t/50 ft for two-tube Hs = 5 ft Hs = 10 ft

  11. Maximum Full-Scale Force

  12. Fabric Tube Connection Transfers Moment

  13. Numerical Modeling • Navier-Stokes Solver • Full solution of non-linear fundamental hydrodynamic equations with turbulence using finite elements • Very efficient mesh handling algorithms • Very large scale grids - O(10 M nodes) • Can be used as rapid prototyping tool for NBS

  14. Navier-Stokes Solver Solved using a finite element formulation with free surface tracking

  15. N-S Solver Examples

  16. waterA.mov

  17. Finite Element Fabric Model

  18. N-S Solution for NBS

  19. Conclusions • Nearshore breakwater required for nearshore logistics • Multi-tube fabric structure shows promise • Navier-Stokes implementation will speed development • Future work with modified geometry has begun

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