N121-091 TITLE: Increased Capability and Interface for Computational Code for Implosion

TECHNOLOGY AREAS: Ground/Sea Vehicles

ACQUISITION PROGRAM: EPE-FY08-06 Payload Implosion and Platform Damage Avoidance

OBJECTIVE: Develop a standard modeling procedure for implosion simulation which will be integrated into a graphical user interface (GUI) for efficient model development and increased assessment capability.

DESCRIPTION: The ONR Future Naval Capability (FNC) program on implosion will deliver a physics-based computational code at the end of FY12, which has been developed for underwater implosion modeling and simulation. Underwater implosion is a unique and complex event, such that the computational model must include strong coupling between fluid and structural solvers; the fluid model must include underwater shock propagation, and the structural model must include rapid, large deformation with material failure/fracture capability. The delivered code will be validated against deep ocean implosion experiments.

Additional research is needed to develop modeling procedures for underwater implosion. Specific areas of research include: material model and material failure criterion; shell and solid element formulation; structural element size for material fracture; relative size of fluid and structural elements with respect to fluid/structure coupling; and performance analysis of the Tillotson equation of state (EOS) for water compared to the Tait EOS. If the research listed above is not addressed, it may take longer to transition the FNC product into the NAVSEA 05P approval process for systems containing implodable volumes.

State-of-the-Art: The code is primarily a research tool, making extensive use of text input files and scripts. The available EOS within the fluid code are stiffened gas, Tait, and Jones-Wilkins-Lee (JWL). The structural code is capable of large deformation, elastic/plastic material behavior, and the extended finite element method (XFEM) for structural cracking/failure. The code will be validated against underwater explosion initiated implosion experiments.

PHASE I:
1. Identify and define the critical parameters to be included in a modeling procedure for underwater implosion.
2. Develop the concept of a GUI for underwater implosion models.
3. Determine the technical feasibility of implementing the Tillotson Equation of State for water in the fluid code.

PHASE II:
1. Develop a prototype modeling procedure and validate against underwater implosion data.
2. Build the GUI and embed the prototype modeling procedure.
3. Implement the Tillotson EOS into the physics based computational code.

PHASE III: The product will be a GUI developed specifically for underwater implosion problems of interest to the Navy. The GUI will translate user inputs into physics-based computational code input files, which adhere to the modeling procedures developed for underwater implosion. This product will transition to the Naval Warfare Centers, who are responsible for providing engineering assessments of the impact of underwater implosion close to a submarine.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The GUI and modeling procedure for implodable volumes will be available to the private sector for the design of systems that contain implodable volumes. Additionally, the modeling procedure will benefit industrial applications (e.g., aircraft, automotive, marine) which require computational analysis involving fluid structure interaction and material fracture/failure.

REFERENCES:
1. Vanzant, B.W., Russell, J.E., Schraeder, A.L., DeHart, R.C., "Near-Field Pressure Response Due To A Sphere Imploding In Water", Summary Technical Report No. 1938-1, Contract No. N00 140-66-C-0698, Southwest Research Institute, (1967).

2. Turner, S.E., "Underwater Implosion of Glass Spheres," Journal of the Acoustical Society of America, 121 (2), February 2007, p 844-852.

3. C. Farhat, A. Rallu, K. Wang, and T. Belytschko, "Robust and provably second-order explicit-explicit and implicit-explicit staggered time-integrators for highly non-linear compressible fluid-structure interaction problems," International Journal for Numerical Methods in Engineering 2010; 84:73-137.

KEYWORDS: implosion; fluid structure interaction; fracture; failure; shock; collapse; underwater

** TOPIC AUTHOR (TPOC) **

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