Specification of dynamic amplification parameters (Input Table)
Through the input data table DYNAMPL the dynamic amplification parameters are specified. These parameters are required for the calculation of Dynamic Amplification Factors (DAF's) by which the hydrodynamic forces are multiplied.
In case of free pipeline spans vibration of the span may occur due to the cyclic character of the wave load. The amplitude of the vibration is a function of the ratio of the wave (forcing) frequency and the natural frequency of the pipeline span. The closer the wave frequency to the natural frequency, the greater the vibration amplitude and the greater the driving resulting load. Damping and support conditions are very important and may reduce the vibration amplitude considerably. The Dynamic Amplification Factor represents the influence of the vibration motion on the (statically determined) wave/current loads.
The following conditions have to be met for the application of dynamic amplification, to be detected automatically by the program:
•dynamic amplification is applied only if waves are specified
•one or more free pipeline spans must exist
•a span should be more or less straight, i.e. the actual length should not differ more than 10% from the straight length between start and end
•a span should be submerged for over 50%
A free span is defined as any pipeline section between supports or between a support and a FREE end point. As support are considered:
•a soil supported node with at least one adjacent node without soil
•a FIXED end point
•a node with spring specified in table SUPPORT
For all spans in the pipeline the same input parameters are applicable, so the support conditions are assumed to be the same too.
The mass density required for calculation of the natural frequency of a span is derived from the pipe weight in air. When table AIRWGHT does not exist, the weight from table DEADW increased by the buoyant force is used for calculation of the mass density of the pipe span. If one or more of the span quantities: weight, structural diameter, wall thickness, hydrodynamic diameter and Young's modulus vary along the span, an average value is determined to be used in the DAF calculation.
H410172, last changed: 2009-07-16