1 Loads, Responses, Failure Modes Naval Architecture and Ocean Engineering Department U.S. Naval Academy EN358 Ship Stuctures

2 Classifying Loads On Ships  Static loads  Stillwater loads  Hydrostatic, weight  Other static  Drydocking (grounding) loads  Thermal loads  Slowly-varying loads  Wave-induced dynamic pressure  Wave encounter + ship motions  Sloshing liquids  Shipping (green) water  Wave slap (sides/foredeck)  Launching, berthing  Rapidly-varying loads  Slamming  Mechanical vibration  Propeller, machinery  Other dynamic loads  Combat loads, collision, grounding, ice-breaking  Loads to be combined  Basic loads  “Live” loads  “Dead” loads  Liquid loads  Equipment loads  Sea environment loads  Hydrostatic loads –Still water, waves (sagging, hogging)  Other sea loads –Heeling, transverse waves, shipping (green) water, slamming  Ship motion loads (DAF)  Individual loads  Operational environment loads –Flooding, aircraft landing, docking, ice loads, etc.  Combat loads –UNDEX, topside missile, airblast, gun-blast (self), etc. Hughes / PNANAVSEA DDS / IMO

3 Static Loads  “Stillwater” loads  External pressures (hydrostatic/buoyancy – no waves)  Internal pressures (tanks)  All weights onboard  Fixed (“lightship”) weights –Structure (steel), machinery and piping (propulsion & non-propulsion including fluid in piping systems), fixed deck gear, outfitting/furnishing, fixed portions of weapons systems  Variable weights –Cargo (incl. “non-fixed” portion of weapons systems), fuel & lube, water (variable ballast & fresh water), holding & waste, provisions & stores, crew & effects, etc.

4 Static Loads  Special static loads  Grounding  Drydocking  Lifting, parbuckling, etc.  Thermal loads

5 Slowly-Varying Loads  Wave-induced “dynamic” pressure distribution  Due to both wave motion and ship motion  Wave-induced buoyancy distribution  Longitudinal → longitudinal bending  Transverse → transverse “racking”  Oblique → torsion/twisting, bending, racking

6 Slowly-Varying Loads  Wave-induced buoyancy distributions (longitudinal)  Hogging  Wave crest amidships  Main deck in tension  Keel & bottom plating in compression  Sagging  Wave trough amidships  Main deck in compression  Keel & bottom plating in tension  Most Navy combatants → worst case loads WHY?

7 Slowly-Varying Loads  Other slowly-varying loads  Wave slap on sides and on foredecks  Sloshing of liquids in tanks  Shipping (green) water on deck  Localized inertial loads (masts, elongated structures, other heavy objects)  Launching & berthing loads

8 Rapidly-Varying Loads  Slamming → whipping (2 or 3 node flexural vibration) → local buckling, shell plating damage  Springing  Flexural hull vibration due to increased frequency of encounter with waves in head seas  Mechanical Vibration  Propeller, machinery

9 Rapidly-Varying Loads  Other rapidly-varying dynamic loads  Combat loads  UNDEX –shock wave, bubble pulse → whipping  Above water weapons –nuclear air blast, missiles, etc.  Self-launched (missile blast, gun blast)  Impacts: collisions & groundings

10 Response Analyses  Basic types of response analyses  Static only vs. static & dynamic vs. “quasi-static”  Probabilistic vs. deterministic  Linear vs. non-linear  Naval architects usually deal with “quasi-static”, deterministic, linear analyses  Consider slowly-varying wave loads as “quasi-static” pressure/buoyancy distribution (neglect ship motions)  Sometimes deal with dynamic analyses via dynamic amplification factor (DAF) → “quasi-static”  Probabilistic nature of loads and strength capacities are addressed via factor of safety (FOS)  Suitable FOS keep material behavior in linear range –But, geometric nonlinearities may occur !