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When an elliptical manhole is installed in a steel tower-type vessel, to meet the strength requirements, it is optimal for the long axis of the manhole to be ( ) to the axis of the vessel barrel； It is optimal when the long-axis direction of the manhole on the skirt seat is perpendicular to the axis direction (). 1) Parallel, 2) Perpendicular, 3) Angle of 30 degrees, 4) Angle of 45 degrees
When an elliptical manhole is installed in a steel tower-type vessel, to meet strength requirements, it is optimal for the long axis of the manhole to be at 90° to the axis of the vessel shell； The optimal position for the manhole on the skirt is when its long axis is aligned with the axis direction (0°).
I think the second floor is correct. Both cases are related to the weakening of the cylinder caused by the openings, that is, to the reinforcement resulting from those openings. According to the principles of elasticity, when an elliptical hole is made in a cylinder and its long axis is perpendicular to the cylinder’s axis, the maximum stress occurs at the ends of the long axis when the ratio of the long axis to the short axis is greater than 2. The openings in the skirt reduce the capacity to withstand moments caused by wind loads, as well as vertical gravity and seismic forces; therefore, the smaller the size of the openings in the cross-section perpendicular to the cylinder axis, the better, in order to ensure Zsm, Asm.
2) Vertical (the length-diameter ratio is generally less than or equal to 2; when the length-diameter ratio is greater than 2, it is generally parallel)； 1) Parallel