Study On The Structural Anti-Impact Mechanical Behavior Characteristic Analysis And Optimization Design Of The Marine Umbilical Cable

The exploration and development of offshore oil and gas has gradually developed into the deep sea.The umbilical cable,as the link of power,control and hydraulic transmission between top floating devices and subsea production systems,is one of the important equipment for deep sea oil and gas exploration.The umbilical is a typical multi-layer unbonded structure,which is mainly composed of functional components and reinforced components through helically wound form.The domestic and foreign research works on this complex structure mainly focus on the structural mechanical behavior analysis and failure problems of dynamic umbilical cables under marine environmental loads.However,for the static umbilical cables laid on the seabed,the structural damage and failure caused by accidental impacts such as trawl equipments or ship anchors are also important factors affecting the safe operation of the umbilical during its life cycle,which need to be considered in the design process.The structural mechanical behavior characteristic of the umbilical under the impact of heavy objects are analyzed in this paper.First,the possible impact risks of umbilicals are classified and described,and the impact risk assessment method and impact form of umbilicals caused by ship anchoring and trawling activities are given.Then,considering the interaction form between the impact object-umbilical-seabed and the nonlinear factors of the material,a numerical analysis model of the umbilical by the impact of the heavy obj ect is established.On this basis,a typical double-layer armored steel tube umbilical is taken as an example.Based on the ABAQUS/Explicit solver,the impact process of the umbilical under the rigid plate is simulated by the dynamic explicit algorithm.The deformation characteristics and damage behavior of the structure under different impact angles are obtained.Subsequently,the impact test device for the umbilical was built to verify the validity of the numerical model.Based on the verified numerical model,a relatively extensive parametric study has then been carried out to reveal the damage and deformation laws of the umbilical internal components under different impact energies,as well as the influence of the structural parameters of the umbilical itself,the shape of the impact object and the seabed environment on the structural response of the umbilical.It is found that the umbilical can effectively resist the lateral impact load due to the increase in the radial stiffness of the inner core in the full filling form,but this filling form will increase the weight and cost of the umbilical.Therefore,considering the radial stiffness of the umbilical core,a topology optimization design method of the filling bodies is proposed,which aims to ensure its carrying capacity while reducing the mass.A design example is used to illustrate the optimization and result verification process.For the umbilical in the case,under the premise of ensuring its cross-sectional mechanical properties and impact resistance,the mass of the filling bodies of the umbilical per unit length is reduced by 14%after topology optimization,and it has little effect on the uniformity of the force and deformation of the internal components of the umbilical.The feasibility of the topology optimization method in the optimization design of filling bodies is verified.In a summary,these above research achievements are helpful to guide the impact resistance evaluation of umbilicals and the design of protective measures.It can provide a reference for the engineering design of umbilicals.