Motovated Skellerup 3500 Litre Tank Case Study
Skellerup Rotomould approached Motovated Design and Analysis Ltd to aid in the design of a multipurpose 3500-litre water/septic tank.
The tank was to be used both above and below ground, which presented several issues with structural strength and stability. This was a challenging problem, which was solved successfully using advanced design and Finite Element techniques.
Working from 2D sketches, Motovated developed a 3D model of the tank, accurately capturing the geometry of corrugations, ribs and the manhole port.
A non-linear Finite Element Analysis (FEA) was completed using shell elements and quarter symmetry to avoid lengthy computation times and show the overall stress and displacement behaviour of the tank. The critical area identified was the base (Figure 2).
The base & corrugations have variable section thickness due to the moulding process, and required solid elements to accurately model the stresses in these areas, as shell elements would have been inaccurate with the complex geometry involved.
An axis-symmetric model was used to investigate localised areas (Figure 3) and geometry changes, including additional ribs and an inverted dome base, were reviewed.
The final solution used the flat base to avoid costly tooling changes, but Incorporated a unique wall section profile (due to controlling the moulding process) to provide the required support.
Motovated produced manufacturing drawings for the mould, with an expansion allowance added, and ensured code compliance for the tank testing.
Figure 1: Rendered image of the final design
Figure 3: Solid element model
Figure 2: Shell element model