Two Dimensional Analyses
Figure 10 shows the finite element mesh for the dam considering the facing
and the gallery for conventional approach. The mesh was build using the map mesh
with different spacing ratios for the regions with high temperature and stresses
gradients (in Figures 10 & 11 this is not visible). The total numbers of elements is 796
including those of the foundation for conventional model and 7745 elements for
actual model. Because of the non-linear nature of the transient analysis, non-linear
solution with automatic time stepping is used to control convergence. The full
Newton – Rhapson method with adaptive descent is used to solve the non-linear
equations. Automatic time stepping is used to increase the number of sub- steps when
convergence is not occurring within a given number of equilibrium iterations. When
convergence occurs rapidly the number of sub-steps decreases to speed run-time. The
non-linear solution control functions are implicit to ANSYS, and default parameters
are used.
The rock foundation was modeled in the region bounded between 30 m
upstream, 30 m downstream and 30 meters under the dam. The rock elements
simulate the heat dissipation through the foundation. The dam was divided into 15
layers, each layer has thickness of 3 m constructed in 10 days called from now on
conventional approach, and the last layer has a thickness of 4 m and according to the
actual approach, the dam body was divided into 153 layers; each layer has thickness
11
of 0.3 meter constructed in one day. PLANE77 element type available in ANSYS
element library was used. Each element has one degree of freedom temperature at
each of its 8 nodes to simulate irregular shape, and is applicable to a two-dimensional
steady-state or transient thermal plain strain analysis. Plane strain is the condition for
which the strains perpendicular to the plane of the analysis maintain at zero. The
effect of non-linearity of modulus of elasticity is not included in the structural
analysis in this stage of analysis. Moreover, the element can be used to carry out
structural analysis by replacing it by an equivalent structural element called
PLANE82.
Chia sẻ với bạn bè của bạn: |