Issue 53

A. Kostina et alii, Frattura ed Integrità Strutturale, 53 (2020) 394-405; DOI: 10.3221/IGF-ESIS.53.30 399 min min 100%       i i m m m err (19) where i  [0.02; 1.28] indicates the size of the element used to determine the von Mises stress value  m on the internal wall of the ice cylinder, and  min m is the von Mises stress value on the internal wall of the ice cylinder obtained in the solution of the problem with minimum element size. Fig. 2 shows the effect of size of the finite element of the grid on relative error. The results demonstrate that the optimal size of the element is 0.04m. It is interesting that if the element size is maximum (1.28m), then the relative error does not exceed 8.3%, which is well within the permissible limits of an engineering error. Figure 2: Relative error vs finite element size. R ESULTS AND DISCUSSION Comparison of numerical simulation results and analytical estimates he developed mathematical model is used for assessing the optimal ice wall thickness according to the criterion for ultimate stress-strain state. The calculation results are summarized in Tab. 6. When the optimal ice wall thickness is calculated by Eqn. (2), the ultimate uniaxial compression strength values are taken from Tab. 2. The values for the cohesion and internal friction angle used in Eqn. (4) are also given in Tab. 2. The calculation results are summarized in Tabs. 7 and 8. The obtained results demonstrate that, for all materials under study, the design thicknesses obtained by Eqn. (3) exceed those found using Eqn. (4). This can be attributed to the fact that the internal friction is ignored, which increases the strength. In general, the scatter in the estimates obtained by Eqns. (3) and (4) is great (12 times for sand); especially, when the ice wall experiences high loads. h ′ , m Sand Chalk Clay 100 1.05 0.35 0.75 200 1.75 0.50 1.2 300 2.35 0.75 1.4 500 2.5 1.05 2.6 Table 6: Ice wall thickness obtained via numerical simulation. h ′ , m Sand Chalk Clay 100 3.065 0.774 2.667 200 6.342 1.550 5.864 300 9.623 2.327 9.058 500 16.183 3.879 15.451 Table 7: Ice wall thickness calculated by formula (3). T