Resonance Avoidance

As weight and water depths are increasing, the concept of resonance avoidance is of increased importance. The problem may occur when the wave period of the surface waves, and thus the frequency of the heave, generate boom tip movements which correspond to the system frequency of the load and wire.

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Operational Challenges

  • When the wave period of the surface waves, and thus the frequency of the heave, generate boom tip movements which correspond to the system frequency of the load and wire.
  • The heave creates resonance movements in the subsea load and wire with destructive energy.
  • Crossing of structures with large variation between weight in water and air.

Cranemaster benefits

  • Uncontrolled dynamic forces and escalating movements of load during deep water operations avoided.
  • With Cranemaster included in the rigging, system resonance period will be increased.
Resonance Avoidance - picture of cranemaster in use lowering load into the sea
Resonance Avoidance - picture of cranemaster in subsea action
Picture of resonance avoidance through a Cranemaster at sea

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We’re always excited to help our clients tackle their challenges when it comes to lifting operations. Our competent engineers will help you find the correct product for your requirements!
  • Object to be lifted, weight, water depth etc.
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Subsea resonance avoidance with Cranemaster

The system frequency is primarily dependent on the properties of the load and on the overall wire stiffness. Since the wire stiffness changes with length, and thus with water depth, the system frequency will also change with water depth. At deep water operation it is therefore high probability that at some point during the lowering operation the system frequency and wave period interfere to create resonance which may cause uncontrolled dynamic forces on the load and wire.

This example shows the system frequency/period (red line) for an object of 400 t (added mass 1000 t) lowered from the surface down to 2400 m with a typical setting on crane and wire stiffness. The average stiffness of the Cranemaster® is 200 kN/m. The system frequency without Cranemaster® scan periods that with high probability will match the wave induced movements during the lowering, and resonance with escalating movements and forces to load and crane may occur. When Cranemaster® is included in the rigging, the system frequency will be shifted upwards (blue line), avoiding the match with the wave induced frequencies.

Case Studies