34
Coastal Engineering: Theory and Practice
Fig. 2.4 Shield’s curve (the hjulstorm approach).
easy to find the critical value (at the intersection of the line and the curve;
since the limits are not sharp, the “curve” is indicated by a hatched band).
As the original shields curve was difficult to use because of the presence
of same variables in both axes, the graph became implicit. In order to
make the graph explicit, many researchers created équations to approximate
shield’s curve. The graph was transformed to another axis System with
dimensionless grain diameter D*. Figure 2.5 shows the shield’s parameter
as a function of dimensionless parameter.
1(3-1)911/3
n* = B50
(2.28)
where s = ˣ-. p
Whether or not there is any movement of grains thus dépends on the
parameters of velocity, V (or critical shear stress, rcr) and the diameter, D.
These three parameters are taken into account in nearly ail sédiment transport théories.
Scveral features of the Shields diagram are particularly noteworthy.
The Shields stress is a minimum for sand whose grain diameter is in the
range of (0.06-2.0mm). Sand is small enough to hâve small mass but too
large for adhesion forces to corne into play.
Silt/clay, in spite of the smaller size, requires a higher shear stress for
motion than sand. Here adhesion forces become overwhelmingly large
Coastal Engineering: Theory and Practice
Fig. 2.4 Shield’s curve (the hjulstorm approach).
easy to find the critical value (at the intersection of the line and the curve;
since the limits are not sharp, the “curve” is indicated by a hatched band).
As the original shields curve was difficult to use because of the presence
of same variables in both axes, the graph became implicit. In order to
make the graph explicit, many researchers created équations to approximate
shield’s curve. The graph was transformed to another axis System with
dimensionless grain diameter D*. Figure 2.5 shows the shield’s parameter
as a function of dimensionless parameter.
1(3-1)911/3
n* = B50
(2.28)
where s = ˣ-. p
Whether or not there is any movement of grains thus dépends on the
parameters of velocity, V (or critical shear stress, rcr) and the diameter, D.
These three parameters are taken into account in nearly ail sédiment transport théories.
Scveral features of the Shields diagram are particularly noteworthy.
The Shields stress is a minimum for sand whose grain diameter is in the
range of (0.06-2.0mm). Sand is small enough to hâve small mass but too
large for adhesion forces to corne into play.
Silt/clay, in spite of the smaller size, requires a higher shear stress for
motion than sand. Here adhesion forces become overwhelmingly large