1. How to analyze ultra-large scale structures?

Today's topic is "simplification of analysis models" for structures.
 

When a structure of ultra-large scale comparable to the size of a building moves, it instills a great sense of fear first and foremost. In reality, however, regardless of scale, design proceeds for a wide variety of structures through CAE with a level of safety far higher than we might expect.

When a human lifts a heavy load such as a barbell, they shift their center of gravity and maintain balance while transferring force. In ultra-large scale structures such as the bucket wheel excavator, asymmetric loading in particular gives rise to very significant risks, making careful design a primary requirement.

2. Why is the process of simplifying the analysis model of a structure necessary?

The bucket wheel excavator structure, the subject of this topic, is an ultra-large scale structure comparable in size to a building, composed of various components and members of different sizes connected together. The size of an analysis model built through CAE or FEM algorithms is determined in practice by the level of detail implemented rather than by the physical scale. Depending on the scale, the elements that make up the analysis model are simply applied at a larger or smaller size, while the actual quantity of elements is applied in a similar manner regardless of scale.

However, the more detailed the description of every component, the greater the number of local elements can become, and it is this that ultimately determines the size of the analysis model. In practice, FEM models are constructed and analysis verification is carried out for a wide range of structures, from the nanometer scale to the kilometer scale.

The degree of detailed implementation is generally determined by the purpose of the analysis. In the case of an analysis model built as a full model, the objective is to examine the force transfer mechanism and overall deformation, so it is constructed as a simplified model using coarse element sizes, simplified geometry, and 1D/2D elements.

A part model, conversely, is used for detailed review purposes after being built with dense element sizes at local positions combined with higher-order elements.

3. What should be considered When Using 1D CFD Analysis?

The bucket wheel excavator structure is used for large-scale operations or for lifting heavy objects. Since a large concentrated mass is applied at the tip of a cantilever-type member, significant bending deformation occurs; to prevent overturning, a counter weight is used in conjunction with cables so that the sum of moments at both supports equals zero.

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