Frequency assignment of an assembled structure through links of its substructures

Abstract

Structural modifications for assigning desirable natural frequencies and modes are an effective passive vibration control strategy. In many assembled structures, the substructures, which may come from different manufacturers/suppliers or have intended individual functions, do not allow modifications or are difficult to modify. In such common situations, designing proper links or joints used for assembling the substructures will be an effective solution to ensure that the assembled structure possesses the right modal properties.In this paper, a receptance-based frequency assignment approach is presented, which consists of a theoretical method of frequency assignment suitable for assembled structures, an indirect method for estimating rotational recpetances and a substructuring method. It is implemented on an assembled structure, which is a simplified model of a floating raft platform installed on a ship hull. The model comprises two substructures and six links. A number of experiments are carried out to measure the required receptances systematically, including rotational receptances which are measured with the help of an auxiliary structure and two rotational accelerometers. One and two frequencies are successfully assigned by using the links with the right cross-sections determined by solving an optimisation problem. Key challenges are also discussed. This work should be practically very useful in passive vibration control of assembled structures.