Structural Response of Bow Structures with Sonar Domes

Abstract

Naval vessels are designed to remain operational in severe conditions, sea-state 6 or higher, and have to maintain a minimum forward speed in these conditions. These seakeeping conditions may result in severe impact loads on the bow of the vessel, called slamming. Sonar domes are often used at naval vessels to detect objects under water and are located at the forefoot of the vessel. The sonar dome used by the Royal Netherlands Navy is a composite structure connected under the steel bow structure of the vessel and is filled with water. Slamming and other seakeeping loads at the composite sonar dome have to be transferred to the steel bow structure through the composite and water inside the dome. Slamming loads have an impact type of character, which is described as a sudden quick increase of the load and with a short duration. Previous research has shown that neglecting the loads at the dome structure results in a serious underprediction of local structural response of the bow of the vessel. Besides that, little is known about the load transfer from the dome towards the bow structure. First, the dynamic response of a fluid filled composite sonar dome is studied. Different load types are applied at the sonar dome model to study the influence of the internal fluid on the response. Second, the effect of the loading transferred from the sonar dome on the stress levels in steel bow structure is studied. Slamming loads at the dome structure do not result in a highly dynamic response for the considered design. The rise-times of the loads have a relative long duration compared to the lowest natural response period of the sonar dome. The rise-times observed in the studied seakeeping conditions is in general much longer compared to the natural response periods of the dome. Including the internal fluid in the dome results in a reduction of the deformation and stresses of the composite shell. During seakeeping loading the pressure in the internal fluid rises, resulting in a pressure load on the bow structure above the dome. The reduction of internal pressure due to the outflow of water from the dome to an expansion container seems to be rather limited The presence of a sonar dome results in additional loads at the bow structure. These loads are a force at the dome flange and a pressure load on the bow structure above the dome. This leads to an increased stress level of the structural elements directly above the dome. It is concluded that the contribution of the internal pressure within the dome to the stress levels of the bow structure is most relevant. Vessels without a sonar dome do not have a deck in the forefoot of the vessel that is loaded by a fluid pressure. It is concluded that the loads from the sonar dome should not be neglected in a structural analysis of the bow structure.Mechanical, Maritime and Materials EngineeringMarine and Transport TechnologyScience Ship & Offshore Stucture