1 3 Dynamic Stability

Information about 1 3 Dynamic Stability

Published on November 6, 2007

Author: Garrick

Source: authorstream.com

Content

Slide1:  DYNAMIC STABILITY LT Tom DeNucci (860) 444-8672 Slide2:  G Station Coos Bay 47’ MLB training Nov 1999 Dynamic Stability Objectives:  Dynamic Stability Objectives Understand heeling moments Determine dynamic stability Determine max roll from righting and heeling moment curves Understand the Navy Criteria for dynamic stability Heeling Moments:  Heeling Moments Moments of forces are what cause a ship to heel, list, return to equilibrium or capsize. A righting moment tends to rotate a vessel towards its initial position A heeling moment tends to rotate a vessel away from its initial (stable) position. Causes of heeling moments Off-Center Weights Beam Winds Off Center Weights (Weights over the side) High Speed Turns Crowding of passengers Icing Heeling Moment Curve:  Heeling Moment Curve Plot of the Heeling Moment versus angle of heel, for any externally applied force. Heeling Moment curves usually start at a maximum value, and then decrease to zero at 90 degrees of heel. Slide6:  Angle of Heel Heeling Moment Curve (From - wind, turns, etc.) Moment Static Stability Curve:  Static Stability Curve Area under the curve represents work performed to heel the ship and stored energy available to return the ship to 0. Righting Moment Curve:  Angle of Heel Righting Moment Curve Righting Moment Curve Moment Slide9:  Angle of Heel Heeling Moment Curve Moment Righting Moment Curve Slide10:  Angle of Heel Moment Excess Heeling Energy Slide11:  Angle of Heel Moment Excess Heeling Energy Excess Righting Energy Slide12:  Angle of Heel Moment Excess Heeling Energy Excess Righting Energy Max Angle of Roll The ship will roll until excess heeling energy equals excess righting energy Slide13:  Angle of Heel Moment Excess Heeling Energy Excess Righting Energy Max Angle of Roll Static Angle of Heel If everything stays constant, the ship will settle out to a constant angle of heel Slide14:  Angle of Heel Moment Excess Heeling Energy Excess Righting Energy Excess heeling energy greater than excess righting energy Ship will capsize CGC JARVIS - November 15, 1972:  CGC JARVIS - November 15, 1972 Prior to damage Added weight only Added weight & Free Surface Effect Dynamic Stability curve CGC JARVIS - November 15, 1972:  CGC JARVIS - November 15, 1972 Prior to damage Added weight only Added weight & Free Surface Effect Max roll Dynamic Stability curve Heel U.S. Navy Criteria:  U.S. Navy Criteria In 1960’s, U.S. Navy developed dynamic stability design criteria for their ships Compares energy used to heel the ship to energy available to right the ship Applies a safety factor to ensure positive dynamic stability Similar criteria used by shipbuilders worldwide U.S. Navy Criteria:  U.S. Navy Criteria Navy criteria addresses specific hazards We’ll briefly look at criteria for: Beam winds with rolling Operating with a weight over the side High speed turns Crowding of Passengers to one side Beam Winds With Rolling:  Beam Winds With Rolling DRAFT H - LEVER ARM (feet) - From Center of SAIL AREA to 1/2 DRAFT A - SAIL AREA (square feet) [cross-hatched area] Vw - VELOCITY of WIND in knots H HEELING ARM created by WIND = 0.004 V A H 2 w 2240 ² cos ø 2 Beam Winds With Rolling:  Beam Winds With Rolling Weight Over the Side:  D D Weight Over the Side Weight Over the Side:  Weight Over the Side Stability Criteria: 1 (Angle of Heel at Point C)  15 A1 (Excess Righting Energy)  40% A2 (Total Righting Energy) c) Righting Arm at Point C (RA 1)  60% of Maximum Righting Arm (RA 2) High Speed Turn:  High Speed Turn High Speed Turn:  High Speed Turn Stability Criteria: a) 1 (Angle of Heel at Point C)  10 for Newly constructed ships 1 (Angle of Heel at Point C)  15 for Existing ships b) A1 (Excess Righting Energy)  40% A2 (Total Righting Energy) c) Righting Arm at Point C (RA 1)  60% of Maximum Righting Arm (RA 2) A1 Crowding of Passengers:  Crowding of Passengers D Crowding of Passengers:  Crowding of Passengers Stability Criteria: 1 (Angle of Heel at Point C)  15 A1 (Excess Righting Energy)  40% A2 (Total Righting Energy) c) Righting Arm at Point C (RA 1)  60% of Maximum Righting Arm (RA 2) 87’ WPB addition:  87’ WPB addition Does this meet Navy Criteria? Not all the time!

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