Cooperative Motion Control Of Dynamic Positioning Platforms And Motion Responses Analysis Of A Gangway

With the offshore oil & gas exploitation approaching to deepwater,the Accommodation support platform(ASP)or Floatel is widely used to provide onsite construction,commissioning or maintenance services for offshore engineering activities.The ASP can not only offer more comfortable living conditions and completed facilities for entertainment and medical treatment but also bring more variable load for the product platform(PP).Usually a gangway is connected between an ASP and a PP,providing accessibility of walk-to-work for stuffs.It is crucial to make sure that the gangway is safe under the complicated ocean environment,which can not only guarantee life security of people but also extend the uptime and save costs of a project.To maximize the safety connection time of the gangway,the relative distance between two platforms should not be beyond the gangway's telescoping scope,which comes from cooperative motion control of the two platforms.In this paper,the study is conducted for an ASP equipped with dynamic positioning(DP)system,a mooring-assisted dynamic positioning product platform and a gangway between them.The two connected platforms set the problem of floating multi-body system,so the first problem to be solved is hydrodynamic analysis in the frequency domain.Then the slow drift force is transformed from frequency domain to time domain,which is an important input for DP system.Secondly,a tracking controller is proposed based on consensus method,and its control law is proved to be convergence by Lyapunov Funtions,achieving the goal of cooperative motion control of the two platforms so that the stroke of the gangway is within its safety range.Finally,the motion responses including expansion amount and angle of the gangway under different orientation of sea loads are investigated,aiming to provide references for operations and maintenance of offshore industry.