Evanescent wave induced fluorescence spectroscopy and time-correlated single-photon counting have been combined to provide a method of studying the fluorescence decay profiles of fluorophores at a solid/solution interface. Using these techniques the photophysical properties of tetrasulphonated aluminium phthalocyanine (AlS₄Pc) in methanol and water solution have been studied at a fused silica interface. In a poor solvent, such as methanol, AlS₄Pc is shown to form an adsorbed monolayer on the fused silica surface and exhibit a fluorescence decay profile that deviates from the simple, first-order, single-exponential kinetics of the bulk solution. By changing the solvent to water, which is a good solvent for AlS₄Pc, the surface/bulk differences are not observed. The ability of time-resolved fluorescence spectroscopy to distinguish between concentration and quantum-yield effects on evanescent wave induced fluorescence intensity, is clearly demonstrated.

This work describes the development of a hybrid framework of Runge–Kutta (RK), discontinuous Galerkin (DG), level set (LS) and direct ghost fluid (DGFM) methods for the simulation of near-field and early-time underwater explosions (UNDEX) in early-stage ship design. UNDEX problems provide a series of challenging issues to be solved. The multi-dimensional, multi-phase, compressible and inviscid fluid-governing equations must be solved numerically. The shock front in the solution field must be captured accurately while maintaining the total variation diminishing (TVD) properties. The interface between the explosive gas and water must be tracked without letting the numerical diffusion across the material interface lead to spurious pressure oscillations and thus the failure of the simulation. The non-reflecting boundary condition (NRBC) must effectively absorb the wave and prevent it from reflecting back into the fluid. Furthermore, the CFD solver must have the capability of dealing with fluid–structure interactions (FSI) where both the fluid and structural domains respond with significant deformation. These issues necessitate a hybrid model. In-house CFD solvers (UNDEXVT) are developed to test the applicability of this framework. In this development, code verification and validation are performed. Different methods of implementing non-reflecting boundary conditions (NRBCs) are compared. The simulation results of single and multi-dimensional cases that possess near-field and early-time UNDEX features—such as shock and rarefaction waves in the fluid, the explosion bubble, and the variation of its radius over time—are presented. Continuing research on two-way coupled FSI with large deformation is introduced, and together with a more complete description of the direct ghost fluid method (DGFM) in this framework will be described in subsequent papers.

The Navy's early-stage design tools are integrated with the Leading Edge Architecture for Prototyping Systems (LEAPS) data repository, thus enabling a streamlined, cohesive approach to the creation, storage and access of data pertinent to a ship design. The Smart Ship System Design (S3D) design environment currently under development within the Electric Ship Research and Development Consortium (ESRDC) recently completed development of S3D as a LEAPS application and is extending its capability to include the LEAPS application framework, multi-platform compatibility, and added functionality.

The prediction of surface ship response to a far‐field underwater explosion (UNDEX) requires the simulation of shock wave propagation in the fluid, cavitation, fluid‐structure interaction, and structural response. Effective approaches to model the fluid include cavitating acoustic finite element (CAFE) and cavitating acoustic spectral element (CASE) methods. Although the spectral element method offers the potential for greater accuracy at lower computational cost, it also generates more spurious oscillations around discontinuities which are difficult to avoid in shock‐related problems. Thus, the advantage of CASE remains unproven. In this paper, we present a 3D‐partitioned FSI framework and investigate the application of CAFE and CASE to a surface ship early‐time far‐field UNDEX problem to determine which method has the best computational efficiency for this problem. We also associate the accuracy of the structural response with the modeling of cavitation distribution. A further contribution of this work is the examination of different nonmatching mesh information exchange schemes to demonstrate how they affect the structural response and improve the CAFE/CASE methodologies.

Traditionally, the Concept and Requirements Exploration process is the first stage of ship design. Concept and Requirements Exploration responds to a stated mission need with early high-level assessment of a broad range of ship design options and technologies. Our design group uses a Multi-Objective Optimization approach to explore the design space and identify non-dominated designs ranked by cost, risk, and effectiveness. Our method of calculating effectiveness in this approach has, in the past, been based on expert opinion. In this study, the use of a more direct physics-based Operational Effectiveness Model approach is considered to provide greater confidence in the validity of effectiveness results and a perception that results are more unbiased and rational. This approach requires significant early investment. How much analysis is enough and is there significant payoff for this significant effort? This paper presents this approach and explores these questions.

This work presents a Direct Ghost Fluid Method (DGFM) as part of a two-fluid numerical framework suitable to model explosive gas and water flows resulting from underwater explosion (UNDEX). Due to the presence of explosive gas and water with shock waves in the modeling domain, classic Eulerian methods with inherent diffusion may not be effective. Numerical diffusion occurs due to nonphysical diffused density at material interfaces, which creates spurious pressure oscillations and significantly degrades the quality of the numerical results. To eliminate or minimize numerical diffusion, sharp interface methods having no mixed elements may be used in multifluid flow computations. The Direct Ghost Fluid Method (DGFM) described in this paper uses direct extrapolation of density (vice pressure) and tangential velocity from real to ghost fluid. The spurious pressure oscillations near the material interface are therefore minimized. One-, two-, and three-dimensional computational fluid dynamics (CFD) solvers that have DGFM as an essential part in their framework to model UNDEX interface conditions are developed, explored, and applied to the simulation of a series of benchmark problems. Excellent agreement is obtained among the simulations, the analytical solutions, and the experiments.