Pawel Woelke

Ship Impact Study: Analytical Approaches and Finite Element Modeling

The current paper presents the results of a ship impact study conducted using various analytical approaches available in the literature with the results obtained from detailed finite element analysis. Considering a typical container vessel impacting a rigid wall with an initial speed of 10 knots, the study investigates the forces imparted on the struck obstacle, the energy dissipated through inelastic deformation, penetration, local deformation patterns, and local failure of the ship elements. The main objective of the paper is to study the accuracy and generality of the predictions of the vessel collision forces, obtained by means of analytical closed-form solutions, in reference to detailed finite element analyses. The results show that significant discrepancies between simplified analytical approaches and detailed finite element analyses can occur, depending on the specific impact scenarios under consideration.

Stress resultant based elasto-viscoplastic thick shell model

The current paper presents enhancement introduced to the elasto-viscoplastic shell formulation, which serves as a theoretical base for the finite element code EPSA (Elasto-Plastic Shell Analysis) [1–3]. The shell equations used in EPSA are modified to account for transverse shear deformation, which is important in the analysis of thick plates and shells, as well as composite laminates. Transverse shear forces calculated from transverse shear strains are introduced into a rate-dependent yield function, which is similar to Iliushins yield surface expressed in terms of stress resultants and stress couples [12]. The hardening rule defined by Bieniek and Funaro [4], which allows for representation of the Bauschinger effect on a moment-curvature plane, was previously adopted in EPSA and is used here in the same form. Viscoplastic strain rates are calculated, taking into account the transverse shears. Only non-layered shells are considered in this work.

Finite Element Modeling of Fatigue in Fiber–Metal Laminates

Innovative hybrid materials developed at Delft University of Technology (e.g., ARALL and GLARE) dramatically reduce life-cycle costs and offer a great opportunity for service life extension of legacy aircraft. Replacement or repair of damaged aircraft components requires high-strength composite materials with high tailorability, fatigue, and impact-damage resistance, all of which are offered by the advanced hybrid materials. In addition, a reliable fatigue-life evaluation methodology for hybrid structures of arbitrary layup, configuration, constituent materials, and geometry is necessary. An efficient computational framework is presented for simulation of fatigue fracture in fiber–metal laminates based on the homogenized laminate modeled with large shell elements and cohesive zone used to simulate crack propagation. The cohesive traction–separation relationship is calibrated against the analytical solution for the strain-energy release rate, which explicitly accounts for the effect of fiber bridging. Appr...

INVESTIGATION OF SHIP IMPACT SCENARIOS AND MITIGATION MEASURES

Ship impact is an important loading scenario for analysis and design of bridges, oil platforms, and other marine structures. Ships collision is also a very important design consideration for ship hulls. Designing structures to resist both accidental and intentional ship impact requires characterization of the impact loading history. Standard design practice relies on simplified methods to determine the impact loads, which typically consider only speed and mass of the vessel. However, ship impact is a complicated non-linear structural dynamic event that depends not just on the size and mass of the vessel, but also local stiffening pattern, location and function of the bulkheads, possible ice-strengthening classification, draft, presence of the bulbous bow, and many other factors. Neglecting these factors can lead to overestimation or underestimation of the loads, depending on a specific scenario. The discrepancies between simplified load estimates and detailed finite element analyses are investigated in this paper.Copyright

Ductile Fracture Prediction for Marine Structures

Reliable modelling of fracture on a structural scale restricts the type of the finite elements used in the analyses to shell elements with in-plane dimension larger than the thickness. Thus, we consider a comprehensive constitutive formulation embedded in the shell mechanics framework. We propose a three-invariant plasticity model that accounts for dependence of the strain at fracture on both stress triaxiality and the third invariant of the deviatoric stress, which has a significant influence for shear-dominated stress states. This is achieved through a phenomenological damage evolution equation that includes both the dilatational term and plastic deviatoric energy term. The latter is dependent on the omega parameter, which can be considered a normalization of the Lode angle. A consistent calibration procedure is also developed based on a small number of carefully selected coupon-level experimental tests.Copyright

Characterization of the Pressure Wave Emitted From Implosion of Submerged Cylindrical Shell Structures

Buckling of submerged cylindrical shells is a sudden and rapid implosion which emits a high pressure pulse that may be damaging to nearby structures. The characteristics of this pressure pulse are dictated by various parameters defining the shell structure such as the length to diameter ratio, shell thickness, material, and the existence and configuration of internal stiffeners. This study examines, through the use of high fidelity coupled fluid-structure finite element computations, the impact of various structural parameters on the resulting pressure wave emanating from the implosion. The results demonstrate that certain structural configurations produce pressure waves with higher peak pressure and impulse thereby enhancing the potential for damage to nearby structures.Copyright

Impact Mitigation for Buried Structures: Demolition of the New Haven Veterans Memorial Coliseum

We present an overview of the analysis and design of mitigation schemes for buried structures subjected to impact loading, with a focus on the hazard evaluation to underground utilities from the demolition by implosion of the Veterans Memorial Coliseum in New Haven, CT. We discuss the analytical and numerical investigations validated by field testing conducted prior to the implosion and leading to the design of the mitigation schemes aimed at protecting the utilities buried under ground. All the designed and constructed mitigation schemes proved successful during the January 2007 implosion of the Veterans Memorial Coliseum.

Shell Element Based on the Refined Theory of Thick Spherical Shells

Formulation of a computational model for thick shells presents many problems, as briefly described in Sect. 1.3.2. In the following sections, we discuss the most important of these problems-shear and membrane locking and mesh instabilities along with the remedies we adopted to overcome them. After the introducing the details of the finite element procedure, which lead, to the formulation of the stiffness matrix of the element, we verify the reliability of the numerical algorithm through a series of discriminating examples.