STRUCTURAL MECHANICS

Solid cantilever as a baseline structure before being redesigned.

The structural mechanics research focus area has ongoing projects in structural redesign, damage mechanics, structural dynamics, and structural acoustics. Researchers are investigating several areas of vital importance in the design and analysis of marine structures. Research spans from the microscale of material cracking to the mesoscale distortion of welded ship plating to macroscale residual stress in large offshore structures. For example, methodologies for structural and topological redesign of complex structures by large admissible perturbations have been under development since 1983; this approach leads to algorithms capable of establishing a desired structure which satisfies design requirements without trial and error and without repeated finite element analysis.

Topology redesign of solid cantilever. Numerical results show finite elements with different strain energy levels. Smoothing produces a gothic arch structure as shown in the upper corner.

New methods for analyzing the response of structures which are subjected to damage are also being addressed. Materials and structures may suffer a loss of stability as they deform and as damage develops; techniques for describing these types of failure mechanisms are being developed within the structural mechanics group. Shown below is a typical-stress strain relation for a porous brittle solid indicating a sudden failure caused by a material instability. Finite element based models for computing distortion, high frequency vibrations, and acoustic response are also being developed in current projects. Highlights of additional research include impact analysis of ship and offshore platforms subject to ice collision and grounding.

Nondimensional compressive stress versus lateral strain curves for biaxial loading of a brittle material containing defects. The axial stress s11 and lateral strain e22 are nondimensionalized with respect to the flaw size, a, and the fracture toughness of the parent material KIC. The ratio of lateral to axial stress is a. The material fails due to a loss of stability at the peak stresses as indicated.

FACULTY: Bernitsas, Karr, Troesch, Vlahopoulos