Preventing the plug-holing phenomena of a natural ventilation system in a shallow underground tunnel is important for improving the ventilation performance, and the tunnel slope has a significant influence on the smoke flow. In this study, the effect of the tunnel slope on plug-holing in a shallow underground tunnel was analyzed by numerical method. The tunnel slope was increased by 0–8 degrees and the fire source was assumed to be 5 MW, which is equivalent to one sedan vehicle. As a result, the possibility of plug-holing decreased as the tunnel slope increased. However, when the tunnel slope is more than 4°, the fresh air from the entrance of the tunnel and smoke are diluted before reaching the shaft, so the flow temperature passing through the shaft is lowered, and the ventilation performance begins to decrease. In particular, plug-holing does not occur at the tunnel slopes of 6 and 8°, but the ventilation performance is expected to decrease because the temperature of the smoke discharged to the shaft is much lower than the general smoke temperature. Therefore, it is necessary to design the natural ventilation system considering the influence of the tunnel slope.

The hematocrit is increased during hemodialysis and a stenosis is associated with the critical range of hemodynamic characteristics that are affected by the hematocrit. However, the effect of hematocrit on unsteady hemodynamic characteristics during hemodialysis is still unclear. Hence, a numerical research is performed on the effect of hematocrit on unsteady hemodynamic characteristics using a multiphase blood model during one cardiac cycle. The effect of hematocrit appears clearly on high wall shear stress (HWSS) at the floor of the vein vessel. At the peak systole velocity, the HWSS varies from about 1% to 2% when the hematocrit varies by about 1%. At the end distal velocity, the HWSS varies by about 1% when hematocrit varies by 1%. On the other hand, the hematocrit has a very small effect on HWSS at the top of vein anastomosis. Also, these effects of hematocrit are the same on low wall shear stress and oscillatory shear index. Consequently, the variation of hematocrit at the floor of the vein anastomosis should be considered before other anastomosis regions at peak systole velocity.

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Numerical analysis was performed for the effect of the venous anastomosis angle in a forearm arteriovenous graft for hemodialysis using a multiphase blood model. The geometry of the blood vessel was generated based on the patient-computed tomography data. The anastomosis angles were set at 15°, 30°, and 45°. The hematocrit was set at 34%, 45%, and 58%. The larger anastomosis angle, high wall shear stress area >11 Pa, increases to the side of the vein wall away from the anastomosis site. Further, the relatively low wall shear stress area, <3 Pa, occurs near the anastomosis site in larger anastomosis angles. Therefore, the effect of high wall shear stress has advantages in the vicinity of the anastomosis, as the anastomosis angle is larger, but disadvantages as the distance from the anastomosis increases. Moreover, patients with low hematocrit are advantageous for WSS area.