DarcyTools:A Computer Code for Hydrogeological Analysis of Nuclear Waste Repositories in Fractured Rock

A computer code for simulation of groundwater flow and transport is described. Both porous and fractured media are handled by the code. The main intended application is the analysis of a deep repository for nuclear waste and for this reason flow and transport in a sparsely fractured rock is in focus. The mathematical and numerical models are described in some detail. In short, one may say that the code is based on the traditional conservation and state laws, but also embodies a number of submodels (subgrid processes, permafrost, etc). An unstructured Cartesian grid and a finite volume approach are the key elements in the discretization of the basic equations. A multigrid solver is part of the code as well as a parallelization option based on the SPMD (Single-Program Multiple-Data) method. The main application areas are summarized and an application to a deep repository is discussed in some more detail.

Propeller cavitation viscous simulation and low-frequency noise prediction with non-uniform inflow

Aiming at predicting ship propeller＇s cavitation low-frequency noise spectrum, a hy- brid method combining the cavitation multi-phase flow unsteady simulation with the pulsating spherical bubble radiated noise theory was proposed. Then, both of the NSRDC4383 5-bladed propeller and a 7-bladed highly-skewed propeller＇s cavitation low-frequency noise spectrum sub- jected to the full appended SUBOFF submarine＇s nominal wake were investigated. The effects of thrust loading and cavity extension on the discrete line spectrum frequency and its spectrum source level were analyzed. The improved Sauer cavitation model and modified shear stress transport turbulence models were adopted to simulate the propeller sheet cavitation along with integrated verification. The cavity volume acceleration related to the characteristic length rep- resenting the unsteady sheet cavitation extension, which was more reasonable than the spherical cavity hypothesis, was used to the cavitation low-frequency noise spectrum prediction. Results show that the 7-bladed propeller truly appreciates the advantages of smaller loads, latter cav- itation inception and lower cavitating tonal noise comparing to that of the 5 blades. Under the same cavitation index based on ship speed, the interaction of wake inflow and blades will induce significantly low frequency line spectrums and strengthen their source level. Given the submarine wake, cavitation index and rotating speed condition, the thrust, torque and cavity area of blades will decrease with the decreasing load, but the fluctuated acceleration amplitude of cavity volume and the tonal noise spectrum level increases, and the discrete line spectrum components shift mainly to the even times of the BPF harmonics from the odd. If the cavita- tion extension lightens, the BPF harmonics line spectrums will be depressed, and the spectrum level at 1 kHz reduces 2.54 dB. The numerical method above constructs a numerical system to measure the cavitating hydrodynamics and noise performances of ship propellers, which can be productive for the numerical design of wake adapted low noise submarine propeller.