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The combined interface boundary condition (CIBC) method has been recently proposed for fluid-structure interaction. The CIBC method employs a Gauss-Seidel-like procedure to transform traditional interface conditions into velocity and traction corrections whose effect is controlled by a dimensional parameter. However, the original CIBC method has to invoke the uncorrected traction when forming the traction correction. This process limits its application to fluid-rigid body interaction. To repair this drawback, a new formulation of the CIBC method has been developed by using a new coupling parameter. The reconstruction is simple and the structural traction is removed completely. Two partitioned subiterative coupling versions of the CIBC method are developed. The first scheme is an implicit strategy while the second one is a semi-implicit strategy. Iterative loops are actualised by the fixed-point algorithm with Aitken accelerator. The obtained results agree with the well-documented data, and some famous flow phenomena have been successfully detected.Keywords: fluid-structure interaction; aeroelasticity; partitioned subiterative coupling scheme; finite element method; combined interface boundary condition method IntroductionIn real life, fluid-structure interaction (FSI) contains the sophisticated principles of mathematics and the abundant essences of physics. Today, FSI has become one of the most challenging topics in computational fluid dynamics and has received a great deal of attention. It is a frequent issue in a rich variety of engineering realms such as civil engineering, ocean engineering, aerospace engineering, mechanical engineering and biomedical engineering. A major paradigm of FSI concerns the aeroelasticity, of which a typical application is the interplay of natural wind with a high-rise building or a suspension bridge in civil engineering. In this case, a catastrophe is likely to occur if failing to consider the FSI effect. The old Tacoma Narrows Bridge in the 1940s is the most well-known example. As a consequence, FSI is a significant consideration for the design of some practical structures.Except for the most simplified cases, FSI is too complicated (i.e. high nonlinearity and uncertainty) to be solved analytically. Instead, it has to be analysed by means of physical or numerical experiments. For numerical researches, FSI comprises three ingredients: computational fluid dynamics, computational structural dynamics and computational mesh dynamics (Wall and Ramm 1998); or, in other words, it is dominated by a three-field nonlinear formulation (Farhat, Lesoinne, and Maman 1995). Of these fields, the scientific

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The characteristic-based split (CBS) scheme has been extensively utilized to address the fluid subproblem within fluid-structure interaction (FSI) analyses over the past decade. To cope with FSI, this article develops a CBS-based partitioned semi-implicit coupling algorithm where the CBS scheme serves not only for the fluid component but also for the entire coupling algorithm. At each time instant, the first step of the CBS scheme is explicitly treated together with the fluid mesh movement, while the remaining two steps are implicitly coupled with the structural motion on the fluid mesh frozen temporarily. To retrieve the semi-implicit coupling style, a mass source term is iteratively updated in the pressure Poisson equation for elements adhering to the fluid-structure interface. The present algorithm provides the stabilized solution of the Navier-Stokes equations and the computational reduction without stability drop, thus inheriting the virtues of the CBS scheme and the projection-based semi-implicit coupling method. Within our coupling algorithm, FSI is achieved by the modified combined interface boundary condition (MCIBC) method which is re-derived in a more concise fashion. A weak implementation of the MCIBC method is proposed to avoid deteriorating the numerical results. The MCIBC method rectifies the limitations of its original counterpart, making itself applicable to fluid-rigid/flexible body interaction. Flow-induced vibrations of various bluff bodies are analyzed to test the feasibility of the proposed methodology. The overall numerical results agree well with the existing data, demonstrating the validity and the applicability of the present approach.