Abstract
No rules specifically stipulate the structural foundation of a ship’s main engine from the perspective of resonance vibration. Additionally, a main engine is usually set on a more rigid foundation on land in shop tests conducted by an engine manufacturer. This means that the soundness of the main engine onboard the ship relies on the shipyard accounting for the difference in stiffness of the foundation between land and ship. Furthermore, we would like to adopt a less rigid foundation to reduce the hull weight, so we needed to demonstrate the soundness of the less-rigid foundation. First, we validated a method of estimating the natural frequency of the H-mode vibration of the main engine by comparing the results of finite element analyses with excitation test results for a real ship with a rigid foundation. Second, we calculated the natural frequency for the less-rigid foundation and found that it was not appreciably different when top bracings were used. Third, we clarified quantitatively that the effect of the foundation was less than that of the top bracings on the H-mode vibration using a simple mathematical model. We can therefore adopt the less-rigid foundation for a new merchant ship with effective top bracings.
