Hydrofoil fixture load analysis
Pozhidaev, Kirill (2022)
Pozhidaev, Kirill
2022
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:amk-202203223831
https://urn.fi/URN:NBN:fi:amk-202203223831
Tiivistelmä
The purpose of this thesis is to quantify the fixture loads of a hydrofoil structure. A fixture is a device that transfers a load between a mast and a hull of a hydrofoil. These loads are dependent on the vessels operational modes, (i) accelerating, (ii) foiling, (iii) deceleration. The loads are in all cases combinations of compressive and bending loads.
The thesis demonstrates the largest loads exist during acceleration, before the vessel reached the foiling mode.
The bending fixture loads are biggest before the vessel is completely lifted out the water. Compressive stress in the fixture however increases the more the vessel is lifted from the water due to fact that buoyant force gradually stops to affect on a hull, and its’ mass shifts on a cross section of a mast. As soon as the craft’s hull leaves the water, and whole hull’s mast renders compressive load on a fixture and mast.
A detailed FEA analysis with COMSOL is performed in 2 steps, in the first step a pressure field on the hydrofoil is calculated at a given flow speed. The FEA solver uses turbulent model. In second step the pressure field is used as input to calculate the static stresses on the hydrofoil. The hydrofoil fixture must transfer these loads. The first step of the fluid dynamic FEA analysis is computationally more demanding than the second step. Calculation time per velocity was approximately 20 minutes per iteration. The solutions are found using fluid mechanics simulation of a given foil shape while demonstrating the lift off or onset of foiling at the speed 5.42 meters per second. The vessel’s hull had a mass of 1500 kilograms, the wingspan of a hydrofoil was 2 meters, the height of a mast was 1 metre.
Maximum combined (compressive and bending) load observed to be 0.86 MPa and occurs at liftoff speed in corners of a leading and a trailing edge of a mast. The model included a compression stress from the hull’s mast. Hull’s technical data is included in appendix. Maximum bending stress observed to be 0.12 MPa. The speed was limited to 20 meters per second since latter speed is an optimal and is rarely exceeded in real life operation. The sudden crash mode was not studied in current thesis due to abundance of factors that the software must consider in order to achieve proper results.
The thesis demonstrates the largest loads exist during acceleration, before the vessel reached the foiling mode.
The bending fixture loads are biggest before the vessel is completely lifted out the water. Compressive stress in the fixture however increases the more the vessel is lifted from the water due to fact that buoyant force gradually stops to affect on a hull, and its’ mass shifts on a cross section of a mast. As soon as the craft’s hull leaves the water, and whole hull’s mast renders compressive load on a fixture and mast.
A detailed FEA analysis with COMSOL is performed in 2 steps, in the first step a pressure field on the hydrofoil is calculated at a given flow speed. The FEA solver uses turbulent model. In second step the pressure field is used as input to calculate the static stresses on the hydrofoil. The hydrofoil fixture must transfer these loads. The first step of the fluid dynamic FEA analysis is computationally more demanding than the second step. Calculation time per velocity was approximately 20 minutes per iteration. The solutions are found using fluid mechanics simulation of a given foil shape while demonstrating the lift off or onset of foiling at the speed 5.42 meters per second. The vessel’s hull had a mass of 1500 kilograms, the wingspan of a hydrofoil was 2 meters, the height of a mast was 1 metre.
Maximum combined (compressive and bending) load observed to be 0.86 MPa and occurs at liftoff speed in corners of a leading and a trailing edge of a mast. The model included a compression stress from the hull’s mast. Hull’s technical data is included in appendix. Maximum bending stress observed to be 0.12 MPa. The speed was limited to 20 meters per second since latter speed is an optimal and is rarely exceeded in real life operation. The sudden crash mode was not studied in current thesis due to abundance of factors that the software must consider in order to achieve proper results.