## 1 Introduction  
The dynamic responses of a buried tunnel in general, and its seismic responses, in particular, are of much interest [1; 2; 3]. The water conveyance tunnel, as one kind of urban underground tunnel, guarantees domestic water for residents in metropolises, and is considered as the lifeline to a city. Actual seismic events have shown that tunnels are easily damaged during earthquakes [4; 5]. Thus, the seismic analysis and anti-seismic design of the tunnels are important and necessary. The traditional analytical method and two dimensional or simplified three dimensional analysis methods may create some inaccuracies, such as the overestimation or underestimation of tunnel deformations [6]. Due to the fact that the soil-structure interaction (SSI) is complicated and the underground structures may induce wave diffraction [7], it may need the help of the finite element method (FEM) to get accurate results especially under realistic conditions [8; 9; 10]. Although the water conveyance tunnel characterized by the inner water is different from normal immersed tunnels, general analysis approaches are still suitable. The study of a water conveyance tunnel under seismic loadings involves interaction between inner water and tunnel structures. The interaction between fluid and structure of the liquid storage vessels under seismic loading was first studied by [PERSON] [11]. Afterwards, lots of pioneering work was performed by [PERSON] [12], and the added mass method provided by him has been widely used in relation to structure design codes and standards. On the basis of the previous work, other scholars have studied and developed the relevant algorithms [13]. All the above-mentioned studies mainly focus on the responses of the vertical cylindrical or rectangular tanks and the analogous morphing structures. On the contrary, studies on seismic responses of the horizontal cylindrical liquid storage vessels to which the water conveyance tunnel with water-structure interaction belongs are limited. The earliest research of this kind of problems can be found in the literature [14]. After that researchers have made further studies [15; 16]. With the development of high-performance computing, full scale numerical simulations considering fluid-structure interaction (FSI) emerge constantly, among which the Arbitrary Lagrangian Eulerian (ALE) based fluid structure coupling algorithm has been used widely. [PERSON], _et al._[17] have analyzed the dynamic responses of a flexible container subjected to wind actions using the ALE based fluid-structure interaction method. [PERSON], _et al._[18] have used the ALE to simulate the fluid-structure interaction of the AP1000 water tank subjected to earthquakes and obtained the optimal height of water to reduce seismic responses. It is thus clear that the ALE based fluid-structure interaction algorithm can be used to deal with the coupling of liquid and its corresponding storage vessel [19; 20; 21]. Thus, the ALE based fluid-structure interaction approach is adopted in this study for analyses of the water conveyance tunnel subjected to earthquakes. To solve the efficiency problem arising from a large-scale finite element calculation, the aids from high-performance computers and parallel algorithms are necessary. Though a number of ideas for parallelized finite element computational methods have been developed [22], the further study for one such scale model with lots of detections and computations for contact (including SSI) and FSI is still needed to obtain more even load distribution and higher parallel efficiency. In this paper, a modified domain decomposition technique derived from the recursive coordinate bisection (RCB) method, which is named the modified RCB (MRCB), is proposed. This method splits the model based on its topological distribution of the computation loads as well as its geometric shape. Not only is the number of nodes and elements in each partition approximately equal, but also the extra coupling loads including contact and FSI are almost balanced.