Study of gas springs

equipped passive

compensators for offshore

installation of heavy modules

Authors: George Stanescu

Ruan Henrique Colombo

What we have to do with this?• The quest for more energy sources led

the mankind to the most unexpected and challenging places on the planet.

Source : IEA -Energy by power source 2008Source : The guardian

One cylinder that contains a moving piston. The piston is assumed free to move, with or without friction, either allowing or not the heat transfer between the two compartments and also maintaining or not the seal between them. The two compartments within the cylinder, containing ideal gas, might be modeled as closed systems or control volumes when appropriate. Also, the cylinder walls may be assumed either adiabatic or non-adiabatic.

Gas spring physical model

Source : Tord martinsen – sketch of the system

Source:http://www.offshore-technology.com/

Source:http://www.offshore-technology.com/

Source :Ormond, Matthew Jake

The vertical heave source is typically generated by an installation vessels motion and or crane tip motion. The SPHC is an inline tool that uses the principles of spring isolation to generate a net heave compensation effect or spring isolation effect.

Applications & Importance• Huge amount of resources is spent in exploration. Time

and equipment are very expensive and a smart plan is required to achieve the more profitable business.• Exploration and drilling operations in unfavorable

weather conditions such as strong winds and high sea states.• The module requires care in its installation, the

occurrence of abrupt shocks can result in a great loss of time and money, so the gas springs are a cheaper solution, essential for control the speed of the landing module on the seabed .• Widely used for cargo transportation, isolation of shock

and expansion of the "weather window" enables operations for longer.

Source : Tord martinsen – sketch of the system

Objectives• Investigation of the physical mechanisms of energy dissipation in

passive compensator. How are they dissipating the energy and how this affects the piston oscillation.

Kinectic energy

Frictionpiston/cylinder

Mechaical interaction gas/piston

Heat and mass transfer ;

gas in chambersgas /piston

Internal energy of gasand piston

Challenges in obtaining accurate numerical integration

• Initially the system was assumed conservative and reversible then implemented in Fortran for validation of the numerical solution obtained.• Tested methods:• Runge-Kutta order;• Runge-Kutta Cash-Karp 4/ order;• Rosenbrock method;• Newton-Stormer-Verlet-leapfrog;

Energy “destruction” due to numerical error propagation

Velocity x position

Challenges in obtaining accurate numerical integration• Successfully implemented in Fortran method: • Newton-Stormer-Verlet-leapfrog.• Long term energy conservation through several

periods of integration with energy and entropy monitoring.

Plot of the dimensionless gap energy and entropy through the cycles

• The performance of the device depends on the geometry;• Different stabilization point of

the piston from starting point, as predicted theoretically;

Studied case – Conservative, Irreversible system

Presented Results• Initial conditions P0 e T0 (1 bar e 300 K),the same for both chambers;• Fvel : Initial condition of velocity in relation to the initial energy

presente in the system;• The conservative, irreversible model describes a more realistic

performance of passive heave compensator;

Entropy monitoring in the irreversible cycle

• As known from the second law of thermodynamics, the total entropy of a isolated system tends to increase in time, aproaching a maximum value as internal constraits in the system are removed ;

Conclusion• This study is a first step on simulating the device

more closely to reality lighting a way for more studies on the passive heave compensator performance;• The better understanding of the dynamic

performance of this devices can lead in a more efficient control in its application;• Knowledge of these devices are owned by large

corporations and kept secret. This study tries to bring some light on the subject, which can be useful for future applications of the national oil industry;

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Acknowledgement: