Abstract: With a focus on the intake tower of the Yanshan Reservoir, this paper discusses the method of modeling in the 3D CAD software SolidWorks and the interface processing between SolidWorks and the ANSYS code, which decreases the difficulty in modeling complicated models in ANSYS. In view of the function of the birth-death element and secondary development with APDL (ANSYS parametric design language), a simulation analysis of the temperature field and thermal stress during the construction period of the intake tower was conveniently conducted. The results show that the temperature rise is about 29.934 over 3 or 4 days. The temperature differences between any two points are less than 24 . The thermal stress increases with the temperature difference and reaches its maximum of 1.68 MPa at the interface between two concrete layers.Key words: SolidWorks; ANSYS; APDL; birth-death element; temperature field; thermal stress1 IntroductionMass concrete is widely used in civil and hydraulic engineering nowadays, and its thermal stress increasingly attracts attention during design and construction. It is necessary to analyze the temperature field and thermal stress of important mass concrete structures with both routine methods and the finite element method (FEM). Some researchers have done a large amount of simulation analyses using FEM software (Tatro 1985; Barrett et al. 1992; Kawaguchi and Nakane 1996; Zhu and Xu 2001; Zhu 2006), but difficulties in these methods remain. There are two main difficulties: (1) Most mass concrete structures are complex and difficult to model with FEM software. (2) Complete simulation is difficult with FEM software because of the complex construction processes and boundary conditions of concrete. The structure of the intake tower of the Yanshan Reservoir is complex. It is 34.5 m high and there is a square pressure tunnel at the bottom, the side length of which is 6 m. The intake tower was modeled in the 3D CAD software SolidWorks and imported into ANSYS with an interface tool. Then, using the APDL program, analysis of the temperature field and thermal stress during construction was conducted.2 Modeling in SolidWorks and interface processing between SolidWorks and ANSYS2.1 Modeling in SolidWorksSolidWorks is a CAD/CAE/CAM/PDM desktop system, and the first 3D mechanical CAD software in Windows developed by the SolidWorks company. It provides product-level automated design tools (Liu and Ren 2005). The outside structure of the intake tower is simple but the internal structure is relatively complex. Therefore, the process of modeling is undertaken from the inside to the outside. The integrated and internal models of the intake tower are shown in Fig. 1 and Fig. 2.图片 Fig. 1 Integrated model Fig. 2 Cross section2.2 Interface processing between SolidWorks and ANSYSANSYS is a type of large universal finite element software that has a powerful ability to calculate and analyze aspects of structure, thermal properties, fluid, electromagnetics, acoustics and so on. In addition, the interface of ANSYS can be used to import the CAD model conveniently (Zhang 2005), which greatly reduces the difficulties of dealing with complex models. The interface tools are given in Table 1.Table 1 CAD software packages and preferred interface tools图 表 1After modeling in SolidWorks, it is necessary to save the model as a type of Parasolid (*.x_t) so as to import it into ANSYS correctly. Then, in ANSYS, the importing of the model is completed with the command “PARAIN, Name, Extension, Path, Entity, FMT, Scale” or the choice of “FileDImportDPARA.” in the GUI interface. There are two means of importing: selecting or not selecting “Allow Defeaturing”，the differences of which are shown in Fig. 3 and Fig. 4.图图片片 Fig. 3 Importing with defeaturing Fig. 4 Importing without defeaturing3 Analysis of temperature field of intake towerThe temperature analysis of the intake tower during the construction period involves aspects of the temperature field and thermal stress. The calculation must deal with the problems of simulation of layered construction, dynamic boundary conditions, hydration heat, dynamic elasticity modulus, autogenous volume deformation of concrete and thermal creep stress, which are difficult to simulate directly in ANSYS. APDL is a scripting language based on the style of parametric variables. It is used to reduce a large amount of repetitive work in analysis (Gong and Xie 2004). This study carried out a simulation analysis of the temperature field considering nearly all conditions of construction, using the birth-death element and programming with APDL.3.1Solving temperature field principle3.1.1 Unsteady temperature field analysisThe temperature of concrete changes during the construction period due to the effect of hydration heat of cement. This problem can be expressed as a heat conduction problem with internal heat sources in the area. The unsteady temperature field T(x, y, z,D ) is written as (Zhu