8
1 Introducing Sea Water
u+Au
),
),'
,
)
)'
,
~'
u
Fig. 1.3: Two layers of fluid slipping one over another in the shear flow
of another branch of fluid mechanics, so-called rheology, and is far beyond the
scope of this book.
The dynamic molecular viscosity of sea water depends on temperature, T,
and salinity, S, as follows from Table 1.1. Colder water is more 'resistant' to
motion than warmer water. The dependence of /1 on salinity is weaker than its
dependence on temperature.
As force on an element of fluid varies like /1 but the mass of that element
varies like p, the acceleration and hence the velocity field is determined by the
ratio /1/p, known as the coefficient of kinematic viscosity, II:
/1
II = - ,
p
(1.3)
where II has units of m 2 /s. For example, the kinematic viscosity for sea water
of salinity S = 35 ppm and of temperature T = 20°C is 1.064x 10- 6 m 2 /s. It
is interesting to note that there is almost no liquid with viscosity lower than
that of water, and that lIair ~ 15 x IIwater. The viscosity of water is of particular
significance in the regions close to solid boundaries and this subject will be
discussed in detail in Sect. 2.5.
Both coefficients, /1 and II, are physical properties of fluid, independent of
fluid motion. When a fluid is completely at rest or is moving very slowly, the
rate of diffusion of momentum is essentially determined by molecular motion.
Eddies are small and the velocity shear is great, and the internal resistance
of the water due to molecular viscosity smooths out the gradients in velocity.
This smoothing of the flow by viscosity is the way the energy in turbulence is
finally converted to heat and dissipated.
1 Introducing Sea Water
u+Au
),
),'
,
)
)'
,
~'
u
Fig. 1.3: Two layers of fluid slipping one over another in the shear flow
of another branch of fluid mechanics, so-called rheology, and is far beyond the
scope of this book.
The dynamic molecular viscosity of sea water depends on temperature, T,
and salinity, S, as follows from Table 1.1. Colder water is more 'resistant' to
motion than warmer water. The dependence of /1 on salinity is weaker than its
dependence on temperature.
As force on an element of fluid varies like /1 but the mass of that element
varies like p, the acceleration and hence the velocity field is determined by the
ratio /1/p, known as the coefficient of kinematic viscosity, II:
/1
II = - ,
p
(1.3)
where II has units of m 2 /s. For example, the kinematic viscosity for sea water
of salinity S = 35 ppm and of temperature T = 20°C is 1.064x 10- 6 m 2 /s. It
is interesting to note that there is almost no liquid with viscosity lower than
that of water, and that lIair ~ 15 x IIwater. The viscosity of water is of particular
significance in the regions close to solid boundaries and this subject will be
discussed in detail in Sect. 2.5.
Both coefficients, /1 and II, are physical properties of fluid, independent of
fluid motion. When a fluid is completely at rest or is moving very slowly, the
rate of diffusion of momentum is essentially determined by molecular motion.
Eddies are small and the velocity shear is great, and the internal resistance
of the water due to molecular viscosity smooths out the gradients in velocity.
This smoothing of the flow by viscosity is the way the energy in turbulence is
finally converted to heat and dissipated.