Dynamic response modeling of high-speed planing craft with enforced acceleration

Small fast vessels with planing hulls are designed to rise up and glide on top of the water when enough power is supplied. Ideally, the planing hull is strategically placed to increase the speed of the vessel. The planing hull locally generates high hydrodynamic pressure in high speed to reduce friction drag and wave resistance. Conversely, the vessels operate like displacement hulls when at rest or at slow speeds but climb towards the surface of the water as they move faster. It has been observed that a planing hull craft often encounters high slamming loads with high encountering frequency. Such slamming has the potential to suddenly alter sailing direction and speed. In addition, the slamming effect creates hazardous conditions, not only for those individuals aboard but also for the traversing sea vessel itself, from boat hull to onboard equipment. Therefore, to avert risk, it is crucial that considerable measures be taken to ensure the sea vessel is structurally sound for safe operation.

It is well documented that the slamming phenomena of a planing hull involves fully coupled dynamic interaction between fluid, structure, wind, wave and the vessel itself. It is a very challenging undertaking to fully understand the slamming phenomena and its consequences on the design and operation of a planing hull. Consequently, much research focus has been directed here where many drop-wedge tests, towing tank tests, sea trials and numerical simulations have been conducted to collect the data on pointwise accelerations, pressures and strains on planing hulls.

On this account, researchers from the Old Dominion University: Professor Gene Hou, Brian Johnson, Jonathan Degroff, Steven Trenor and Dr. Jennifer Michaeli developed new methods and procedures that could facilitate better comprehension of the dynamic responses of high-speed planing hulls to wave impacts. They believed that such development would help mitigate risk to crew and equipment. Simply put, they employed the base excitation method for dynamic analysis of a high-speed craft with the enforced acceleration based upon the sea trial data. Their work is currently published in the research journal, Ocean Engineering.

In their approach, the structure dynamic analysis of a high-speed planing craft was completed by enforcing the collected pointwise acceleration data on a valid finite element model.  In the first phase of their study, the researchers validated the proposed method by focusing on nine single wave impacts, each of which was associated with one specific seakeeping condition selected from the available sea trial data. For the second, phase, the issue about the number and the placement of input accelerometers was investigated. Lastly, the enforced acceleration method was extended successfully to conduct the dynamic analysis of an isolated pilot cabin.

The results demonstrated that the output of the proposed method matched well with those of sea trial data. Specifically, the proposed method achieved higher accuracy for the higher peak acceleration case than for the lower ones. The authors also reported that the accelerometers aligned along the keel and near the bottom hull were more important to the accuracy of the simulation than those away and off the centerline.

In summary, the study by Old Dominion University scientists presented the first attempt to adopt the base excitation technique for dynamic analysis of a high-speed craft with the enforced acceleration based upon the sea trial data. Typically, the method was structure-based, and neither involved computational fluid dynamics nor fluid structure interaction. In a statement to Advances in Engineering, Professor Gene Hou highlighted that their proposed approach could indeed be extended to rigid-flexible body coupling analysis of a high-speed craft when it is running with large pitching and yawing motion. Overall, the successful demonstration presented open the door for more broad investigation of the proposed method.