Mark C. Hyman

A Comprehensive Sub-Grid Air Entrainment Model for RaNS Modeling of Free-Surface Bubbly Flows

The simulation of free surface bubbly flows using a two-fluid model remains a challenging problem in part due to the lack of a comprehensive air entrainment model that can predict the rate and location of air entrainment for a wide range of flows. In this study we derive a sub-grid model and implement it in a computational multiphase fluid dynamics (CMFD) framework to solve the Reynolds-averaged two-fluid equations. We assess the performance of our model in simulating bubbly flows underneath a plunging liquid jet and a hydraulic jump while varying the characteristic velocity. We compare the void fraction predictions with their experimental counterparts and conclude that the air entrainment model and the two-fluid modeling approach yield accurate results everywhere for the plunging jet and in the turbulent shear layer for the hydraulic jump. The inability of the proposed approach to recover the high void fraction in the roller region of the hydraulic jump is attributed to the failure of RaNS model to resol...

Simulation of three-dimensional finite-depth wave phenomenon for moving pressure distributions

The flow field and the bottom pressure signatures due to an air cushion vehicle are calculated by analytical and computational means. The singularities in the integrals from the theoretical analyses are removed by using the Cauchy`s residue theorem and the resulting integrals are numerically evaluated by the adaptive quadrature routines of QUADPACK.

Simulation of surface ship dynamics

We present a summary of the three-year Challenge Project (C68), begun in 2001, with the objective of demonstrating a capability to simulate time-dependent six-degree-of-freedom motions of ships in waves and the associated near-field flow using unsteady Reynolds-Averaged Navier-Stokes (RANS) codes. The efforts involved a team of researchers using two state-of-the-art unsteady RANS codes for a progression of building-block simulations at both model- and full-scales and for practical configurations including detailed resolution of propulsors and appendages. The two RANS codes used for this project are UNCLE, developed at the Mississippi State University, and CFDSHIP-IOWA, developed at the University of Iowa. The three-year efforts have successfully demonstrated a capability to simulate coupled pitch/heave motions, coupled pitch/heave/roll motions, maneuvers in the horizontal plane, and near-field wake, including propeller and viscous effects. The predictive capability demonstrated in this project has clearly paved the way for more challenging computations that involve large-amplitude motions in high sea states for a new generation of naval ships, including surface combatant and other future hull forms.

Three-dimensional flow around a submerged body in finite-depth water

Abstract The three-dimensional fluid flow around an axisymmetric body submerged in a finite-depth fluid is calculated by an analytical/numerical method based on a Greens function formulation. The flow around a submerged axisymmetric body, such as the infinite-fluid analogue of a Rankine body, can be constructed by superposition of a source and a sink along the axis of symmetry. Analytical evaluation is complicated because of the singular Cauchy-type principal-value integrals with infinite and semi-infinite limits. In this study these integrals are evaluated by using a set of adaptive numerical quadratures. This approach is direct, and it does not require an asymptotic expansion. The results for the three-dimensional flow calculations are applied for the evaluation of pressure signatures of several Rankine-type bodies with different Froude numbers. Streamlines were determined by a second-order finite-difference algorithm that follows a fluid particle by solving an appropriate initial-value problem. As expected, the shape distortion from the infinite-fluid Rankine body geometry was significant when the slenderness and the linearity (small-wave elevation and slope) approximations became inappropriate.

CALCULATION OF MAGNETIC FLOW NOISE INSIDE AN ENCLOSURE IN A SEA-STATE

An algorithm is presented that enables the computation of flow-induced magnetic noise that would be detected by a sensor inside an enclosing body. The generated magnetic field is the sum of a body surface current as well as a volume component. In the present paper, the magnetic field is computed under the assumptions of slowly varying ambient and irrotational flows. The flow field is computed by applying the low order panel method PMARC with modifications to allow a first order surface gravity wave field. It is determined that such a representation (both the irrotational as well as low order method) is adequate for general application, though not if high accuracy is required and that at shallow depths, sea-induced noise will dominate the total, sensed ambient noise.