Smooth Circular Cylindrical Member

0s0.3 m. 0 * 0,3 M.

0.7 1 .2

  1. for DECKHOUSES AND SIMILAR STRUCTURES PLACED ON HORIZONTAL SURFACE THE FORMULA FOR C IS APPLICABLE TAKING £ AS THE VERTICAL DIMENSION AND d AS THE HORIZONTAL DIMENSION OF CONSIDERED AREA,
  2. for DECKHOUSES AND SIMILAR STRUCTURES PLACED ON HORIZONTAL SURFACE THE FORMULA FOR C IS APPLICABLE TAKING £ AS THE VERTICAL DIMENSION AND d AS THE HORIZONTAL DIMENSION OF CONSIDERED AREA,

FOR Coo LtSE COEFFICIENTS GIVEN IN THE TABLE ABOVE.

Fig. 1-40 Shape coefficient (2-dimensional flow).

wave and current. Therefore, only the current velocity profile to be applied is considered in this section.

Current velocity is often separated into two parts, wind-induced current due to wind shear and tide-induced current.

The variation of current velocity with distance above bottom may, if detailed field measurements are not available, be described by the following equation:

In open areas, if statistical data are not available, the wind-induced current of the still water level may be taken as:

The tide-induced current should be chosen according to field measurements, if available.

WIND FORCE kp i05

/

/

/

r O

56,3

o 10 20 30 40 50 60 70 WIND VELOCITY (M^/^) Fig, 1-41 Wind flow on jack-up drilling platform.

o 10 20 30 40 50 60 70 WIND VELOCITY (M^/^) Fig, 1-41 Wind flow on jack-up drilling platform.

The velocity profiles given above are shown graphically in Figure 1-42.

Recent research indicates that it may not be correct to add the current velocity vectorially to the water particle velocity in the wave.8 The results seem to be too conservative when the current is acting in the direction of the wave propagation.

When the current is acting in opposite direction of the wave propagation (tidal current only), the interaction between current velocity and water particle velocity may lead to more severe conditions than that obtained by vectorially adding the velocity components.

It should be emphasized that this condition will occur only occasionally as the wind-induced current in the direction of the wave propagation is normally larger than the tide-induced current in the opposite direction.

TIDE- INDUCED CURRENT IN THE SEA SURFACE (M/seC.)

WIND- INDUCED VELOCITY IN THE SEA SURFACE <^EC )

WATER DEPTH [Ml

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