Waves Flashcards
High Frequency, Short Wave
Ripple
Distance to complete one complete wave (sine) cycle, defined as 2π radians
Period T
Low frequency, long wave and high frequency waves dissipated
Swell
Stable wave with maximized wave height and energy
Fully developed wave
A wave pattern in the typical sine pattern
Sinusoidal Waves
1 second =
9.43 radians
If spring is compressed or placed in tension, force that will try to return to its original location is
Restoring Forve
The number of radians completed in 1 second
Frequency
π =
2π =
180 deg, 360 deg/ 1 complete cycle
The magnitude of the restoring force is proportional to the magnitude of the displacement
Linear Force
The distance travelled at a given time T
Displacement (Z)
Exiting force or waves
Motion Source
Radiated Wave, eddy and viscous force
Damping Source
Unless energy is continually added, the system will eventually come at rest
Force function and Resonance
When the force function is applied at the same frequency as the oscillating system, a condition of — exists
Resonance
Condition 1: the frequency of the forcing function is much smaller than the system
Z=F/k
Condition 2: The frequency of the force function is much greater than the system
Z=0
Condition 3: The frequency of the forcing function equals the system
z = Infinity (Resonance)
Translational Motion
Surge, Sway, Heave
Simple Harmonic Motion
Heave Pitch and Roll
Rotational Motion
Roll, Pitch, Yaw
Stiff Ship, small period; bad seakeeping quality
Large GM
Tender Ship, less stable; good seakeeping quality
Small GM
Encounter Frequency = Natural Frequency
Resonance
Are well Damped due to large wave generation
Heave and Pitch
Susceptible to encounter frequency and —- are not damped well due to small damping
Roll Amplitude, roll motions
Caused by relative motion of ship and sea
Non-Oscillatory Dynamic Response
More likely to occur with roll than pitch and heave
Resonance
opposite case of shipping water where the bow of the ship is left unsupported
Forefoot Emergence
Caused by bow submergence
Shipping Water
Impact of the bow region when bow reenters into the sea. Causing severe structural Vibration
Slamming
The stern version of forefoot emergence
Racing
cause the propeller to leave the water and thus cause the whole ship power to race
severe torsion and wear in shaft
The effects of all these response is to increase the resistance
Added Power
limits Awl and TPI reducing heave acceleration
Volume is distributed higher
Limits MT1 reducing pitch acceleration
forward and aft are V-shaped
Very common passive anti rolling device
Located at the bilge turn
Reduce roll amplitude up to 35%
Bilge Keel
limits the Ixx reducing the stiffness of GZ curve thereby reducing roll acceleration
Wider water plane forward
Reduce the roll motion by throttling the fluid in the tank
relative change of G of fluid will dampen the roll
Tank Stabilizer
Very Common active anti-rolling device
Located at the Bilge Keel
Controls the roll by creating lifting force
Fin Stabilizer
A ship heading directly into the waves will meet the successive waves much more quickly and the waves will appear to be a much shorter period
Head Sea
A ship moving in a following sea, the waves will appear to have a longer period
Following Sea
If wave approaches a moving ship from the broadside there will be no difference between wave period and apparent period experienced by the ship
Beam Sea
Are periodic, uniform waves with a consistent wavelength and amplitude
They repeat at regular intervals, making them idealized representations of wave motion
Regular Waves
are more common in nature and represents complex combination of different wave frequencies, amplitudes and directions. They vary significantly over time.
Irregular Waves
