Session: 04-06-01: Underwater Vehicles and Tools

Submission Number: 157354

Flow Field Investigation for a Cable-Burying Jet Trenching Tool 

Post Lay Burial of underwater cables is a well-spread protection method for the cable assets in most cases. In certain types of soil, Jet Trenching tools are used for cable burial. Such tools are Asso.subsea’s AssoJet III series of jet trenchers with swords baring cutting nozzles, custom made and tailored for Asso.subsea project needs, with in-house design, engineering and construction by the same company. This tool is investigated in terms of its flow field under operating conditions. The flow field induced post the jetting nozzles is crucial for the effective cutting ability of the tool, especially in cohesive soils with higher Undrained Shear Strength (Su/Cu), thus the knowledge of the flow field characteristics is important for assessing many operational parameters and optimizing them.

In the AssoJet III tool investigation case presented, 2 individual models were set for Computational Fluid Dynamics (CFD) assessment with the use of a commercial software (Fluent, Ansys). The first of them was dealing with the AssoJet III under steady state conditions, operating in “void” (free computational space), while the second model used feedback from first model’s outcome to be used as an input parameter, in order to assess the flow field when the tool is operating in a solid trench under steady-state condition as well. In both cases the three-dimensional volume of the model was discretized with mixed unstructured computational mesh and a variation of the SIMPLE numerical methodology for fluid mechanics was used, along with appropriate turbulence kinetic energy and dissipation modeling schemes (k-ε and SST k-ω respectively).

In the first case the steady state operating conditions involved mass inflow rate identical to the operating one, to split the flow in a manifold towards the cutting swords nozzles, or towards the cleaning swiveled blow-out nozzles. The flow field in this case was reviewed in detail with respect to cutting nozzles outflow velocity as well as to streamlines’ uniformity and internal pathlines’  topology. Velocity vectors and pressure field are assessed and compared to industry’s best practice values.

In the second case the same type of jet trencher and sword configuration is used. This time it is enclosed in a wall boundary in four of its six computational domain planes. The mass inflow for the manifold is derived by the previous model’s solution which resulted in the flow split, and the crucial factors of streamlines and velocity vectors are reviewed, along with the dynamic pressure outcome.

Validation of the outcome is done via literature comparison in terms of the velocity field on the cutting nozzles, while for the dynamic pressure field, in-situ photographic material during offshore project operations offers validation of the CFD methodology resulting field.

Presenting Author: ANASTASIOS KOPANIDIS Asso.subsea

Presenting Author Biography: Dr Anastasios Kopanidis is an experienced Researcher, Mechanical Engineer (AUTH), with a PhD on Computational Fluid Dynamics in porous media microscale flow field, appointed by University of West Macedonia, Greece.
During his research carrier he has been involved in micro and macro scale investigations of various scientific problems via CFD, including biomedical flows, industrial piping design and sophisticated underwater equipment.
His journal papers bare 277 citations by now, while he has received distinctions and honors from various associations.