Analysis And Discussion On Hydrodynamic Characteristics Of Aircraft During Ditching

Since last20s, designers of marine aircraft have focused on ditching characteristics. At last60s, ditching has been introduced into airworthiness regulation by civil aviation administration of each country. Thus, problems of aircrafts’performance safety during ditching need to be solved, in order to succeed national airworthiness validation.While studying performance safety of aircrafts during ditching, there are three evaluations to confirm that ditching is successful:1. whether deformation and dynamic attitude of structure affect seriously passengers’escape;2. whether crew and passengers can afford overload of water impact;3. whether there is enough time for crew and passengers to escape from cabin.In order to examine and approve the three evaluations above, it is necessary to get deep understanding about ditching characteristics (such as, water impact load, crashworthiness and floatation performance). Among them, water impact load and crash worthiness are main contents presented in the paper.Actually, interaction between water and aircraft is a classical interdisciplinary problem of fluid mechanics and solid mechanics, and fluid-solid interaction refers to non-linear behavlor of fluid. It’the premier to describe fluid boundary and simulate the coupling force between fluid and solid for solving water impact problem.The main aim of this paper is to build ditching model for computation. With introducing ALE method to describe fluid boundary and penalty coupling method to define fluid-solid interaction, ditching is simulated by means of explicit dynamics. By simulating the ditching test of subscale model and comparing experimental results with numerical result, validation of the method is verified. Meanwhile, regularities of key physical parameters (e.g. angle of attack, overload acceleration) have been analyzed.The research results have been presented as follows:1. Based on the detailed investigations of related literatures, geometrical model of aircraft A320and related data are obtained. With the use of CAD and CAE codes, geometry of aircraft and numerical model for ditching has been modeled successfully.2. By using ALE algorithm and penalty coupling method, the interaction between aircraft and water is successfully simulated. Compared with test-experimental results, it can be observed that the numerical time-history results agreed with the experimental. The times when peak accelerations appear for experimental and numerical results are identical. The maximum error between them is less than the engineering requirements20%.3. Through observing dynamic characteristics during ditching, conditions’(e.g. angle of attack, velocity and gravity center position) effects and regularity of key physical parameters (overload accelerations and dynamic attitudes) have been investigated. From the data, it’s shown that angle of attack and weight affect attitude angle sharper than other factors. In addition, the affect of horizontal velocity on attitude angle and overload is not clear, and the regular affects of other factors on overload of different components are not the same.The paper hopes to build a reasonable method to simulate ditching, and provide safe suggestion for ditching in offshore region, in order to promote numerical research for ditching.