Surface models can only be meshed with ________ elements.

Surface models are specifically constructed to represent the outer boundaries and contain geometry without defining a solid volume. Because of their nature, they can only be meshed using shell elements. Shell elements are designed for thin structures where the thickness is small compared to the other dimensions, rendering them suitable for approximating surface models effectively.

Shell elements allow for efficient analysis of these thin-walled structures, as they capture the behavior of bending, stretching, and other mechanical phenomena while minimizing the computational resources needed. This makes them ideal for analyzing surfaces in simulations where volumetric behavior is not necessary.

The other types of elements, such as beam or solid elements, are not appropriate for surface models. Beam elements are primarily used for structural members, while solid elements are designed for 3D volumetric representations. Mixed mesh is a technique that utilizes different types of elements, but it still cannot apply solid or beam elements to a surface-only model. Thus, the use of shell elements is the only suitable method for meshing surface models effectively.