Marine turbulence

Balaji, V., 2004. FMS. The GFDL Flexible Modelling System.http //www.gfdl.noaa.gov/ fms/. Baumert H. Z., Simpson J., Siindermann J.,(Eds.), 2005. Marine Turbulence Theories, Observations,... 

This type of damage is dealt with comprehensively in Section 8.8. It can be particularly severe in seawater giving rise to cavitation corrosion or cavitation erosion mechanisms, and hence can be a considerable problem in marine and offshore engineering. Components that may suffer in this way include the suction faces of propellers, the suction areas of pump impellers and casings, diffusers, shaft brackets, rudders and diesel-engine cylinder liners. There is also evidence that cavitation conditions can develop in seawater, drilling mud and produced oil/gas waterlines with turbulent high rates of flow. 

Read power number versus Reynolds number in turbulent region is based on geometry of the impellers. The lowest power number is less than l,for marine propellers. For flat bladed turbines in a turbulent region, the power number is equal to 6. The power graph is illustrated in Figure 6.6. 

In seawater, physical processes that transport water can also cause mass fluxes and, hence, are another means by which the salinity of seawater can be conservatively altered. The physical processes responsible for water movement within the ocean are turbulent mixing and water-mass advection. Turbulent mixing has been observed to follow Pick s first law and, hence, is also known as eddy diffusion. The rate at which solutes are transported by turbulent mixing and advection is usually much faster than that of molecular diffusion. Exceptions to this occur in locations where water motion is relatively slow, such as the pore waters of marine sediments. The effects of advection and turbulent mixing on the transport of chemicals are discussed further in Chapter 4. 

Reaction rates of nonconservative chemicals in marine sediments can be estimated from porewater concentration profiles using a mathematical model similar to the onedimensional advection-diffusion model for the water column presented in Section 4.3.4. As with the water column, horizontal concentration gradients are assumed to be negligible as compared to the vertical gradients. In contrast to the water column, solute transport in the pore waters is controlled by molecular diffusion and advection, with the effects of turbulent mixing being negligible. 

Both the refractory and labile fractions of HMW DOM can be lost from seawater through formation of macrogels that aggregate into marine snow. The labile fraction that is known to participate in marine snow formation are the TEPs, such as mucopolysaccharides found in the mucus sheaths surrounding fecal pellets and plankton colonies. HMW DOM is also lost from seawater via (1) adsorption onto sinking POM and minerals, (2) conversion into POM at the sea surfece by turbulence associated with bursting bubbles, and (3) photochemical degradation. 

In Figure 7.8, the curves a, b, and c correlate data for three types of impellers, namely, the six-flat blade turbine, two-flat blade paddle, and three-blade marine propeller, respectively. It should be noted that, for the range of (Re) >10, Afp is independent of (Re). For this turbulent regime it is clear from Equation 7.30 that... 

Where high levels of marine vessel motion are experienced and high product quality 1s required the secondary turbulence effects of the baffling, required to control resonant waves and primary turbulence, will not allow the product specifications to be met. These conditions require more advanced vessel Internals to be utilized that eliminate the secondary turbulence while still controlling resonant waves and primary turbulence. 

Relatively small marine vessel motions have a significant effect on the process equipment design. For example, three degrees of pitch can cause a forty percent Increase in gas velocity due to the spirit level effect, combinations of pitch and heave can cause resonant waves, further reducing the dedicated phase areas and causing primary turbulence roll and sway motions, although of lesser conse quence, add to turbulent fluid conditions Inside the vessel. In addition all motion adversely affect level control and level safety systems. 

The most useful impellers are ihe simple flat paddle, the marine-type propeller, and the turbine, If any of these are on a vertical shaft rotating on the center line of a cylindrical vessel, the fluid motion will be one of rotation. A vortex forms around which the liquid swirls. A minimum of turbulence and of vertical and lateral flow motion will result, very little power can be applied. 

---