Sea Keeping

Seakeeping Tests (with ships) Experimental Methods in Marine Hydrodynamics Lecture in week 43

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Topics • Why do seakeeping tests? • What to do?  –  Activities  – Details of model test set-up and instrumentation  – Waves and wave calibration

• In-depth topics:  –  –  –  –

Test configurations Measurement of global forces Measurement of local (slamming) forces Speed loss due to waves

• Example project 2

Why do seakeeping tests? Typical Objectives

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Determine operational limits

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Measure design loads

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Optimization of design with respect to seakeeping Identify design improvements

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Capsize and safety studies

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Development and testing of motion damping systems

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Investigate added resistance and speed loss due to waves

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Studies of propulsion in waves

 Activities (in typical sequence) 1. Manuf anufac actu ture re of model del 2. Do cal calm m wate waterr p perf erform ormanc ance e tests tests (if ordere ordered) d) 3. Inst Instru rume ment ntat atio ion n of of mod model el • •

Calibrate transducers Mount all onboard instruments

4. Dynam namic ball balla asti tin ng •

Place loadsintopitch obtain correct centre of gravity and radius ballast of gyration

5. Calib Calibrat ration ion o off wave waves s (witho (without ut m mode odell in the lab) lab) 6. Perfor rforma manc nce e of of ttes ests ts 7. Data Data ana analy lysi sis s an and d repo report rtin ing g 4

Two test modes: • Free model  – Measurement of motions and accelerations  – Possibly measurement of internal global or local (slamming) forces method – a direct modeling  – This is the most commonly used method – of the real ship behavior 

• Fixed model  – Measurement of total forces on the model  – Model might be given forced motions or being fixed in incoming waves  – Used to verify and validate numerical methods 5