Engineering Structures 29 (2007) 3503–3514 www.elsevier.com/locate/engstruct Hydroelastic response of a box-like floating fuel storage module modeled using non-conforming quadratic-serendipity Mindlin plate element Z.Y. Tay, C.D. Wang ∗ , C.M. Wang Department of Civil Engineering, National University of Singapore, No. 1 Engineering Drive 2, Kent Ridge, Singapore 117576, Singapore Received 16 May 2007; received in revised form 16 August 2007; accepted 17 August 2007 Available online 25 September 2007 Abstract Presented herein are the hydroelastic responses of a floating fuel storage module under wave action. The box-like fuel storage module is modeled by an equivalent solid plate. For the analysis, a non-conforming quadratic-serendipity (NC-QS) element based on the Mindlin plate theory was developed. In this element, we make use of the reduced integration method and the superposition of non-conforming modes onto the basis function of the 8-node element in order to prevent spurious modes and shear locking phenomena. Thus the element may be applied for both thick and thin plates. The solution for the hydroelastic response involves solving the coupled plate–water equation and the water equation numerically using the hybrid finite element–boundary element (FE-BE) method. The coupled plate–water equation is derived by equating the force term in the Mindlin plate equation with the wave pressure distribution obtained from the linearized Bernoulli equation; whereas the boundary integral equation relates the displacement of the plate and water velocity potential using the free-surface Green’s function. Results of the displacement and water velocity potential are found to be more accurate when compared with existing solutions for special cases. Moreover, the stress resultants computed are significantly more accurate than previous results as spurious modes are eliminated. c  2007 Elsevier Ltd. All rights reserved. Keywords: VLFS; Hydroelasticity; NC-QS Mindlin plate element 1. Introduction A pontoon-type, very large floating structure (VLFS) has large horizontal dimensions that results in the VLFS behaving like a large flexible plate on water. Suzuki and Yoshida [1] distinguished the elastic response from the rigid body response of a floating body by the ratio of the structural length to the characteristic length λ c which is a function of the flexural rigidity and buoyant spring stiffness. According to their definition, a floating body is dominated by the elastic response if this ratio is greater than unity. A VLFS usually falls into this category, and hence hydroelastic analysis needs to be carried out in order to assess correctly the dynamic response of the structure under wave action. Owing to the Mega-Float project in Japan from 1995 to 2001, numerous studies have been carried out to investigate the hydroelastic response of the VLFS. As the VLFS behaves ∗ Corresponding author. E-mail address: cynthia.wang@keppelom.com (C.D. Wang). like a floating elastic plate, the conventional way of modeling the VLFS is to adopt the classical thin plate theory (also known as the Kirchhoff plate theory) while the water wave is modeled using the linear wave theory (see for example, papers by Kashiwagi [2], Utsunomiya et al. [3], Hermans [4], Meylan [5], Watanabe et al. [6]). Although the plate deflection calculated using this theory is reasonably accurate, the stress resultants (such as the twisting moments and shear forces) are not accurately predicted and they do not satisfy the free-edge boundary conditions [7]. The inaccuracy is due to the stress resultants being computed from second and third derivatives of the approximated deflections. In addition, the effects of shear deformation and rotary inertia (that become significant in high frequencies of vibration) are neglected in the classical thin plate theory. Moreover, these effects become crucial when the wavelength is less than twenty times the thickness or when the thickness–length ratio is greater than 0.005 [8,9]. In order to obtain a better approximation of the deflection and stress resultants of an elastic plate due to wave actions, Watanabe et al. [10] adopted the Mindlin plate theory [8] where the 0141-0296/$ - see front matter c  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.engstruct.2007.08.015