67. Piles

The identification tag for this tutorial is PDS-ACF. Pregenerated input files for this tutorial are found in the folder named PDS-ACF in the provided tutorial input files.

67.1. Tutorial overview

This tutorial covers:

• Simulating multiple piles connected to a floating structure which can respond to waves, current, and wind
• Determination of loads on base of piles and at connection with the floating structure
• Understanding how to use ABA connections and force connections between rigid bodies to simulate parallel mechanisms

Fig. 67.1 Breakwater3300 moored with two piles

67.2. Breakwater 3300 RigidBody

Note

• The Breakwater3300 RigidBody created in the Floating breakwater tutorial will be moored with piles in this tutorial.

• Open tutorial input files for the Floating breakwater tutorial.
• Delete all mooring lines and two of the breakwater RigidBody DObjects.
• Set (i.e. update) the state of the Breakwater3300 RigidBody to have a Z Position of 0.429 m, as shown in Fig. 67.2. Set the pitch, roll, and all translational and rotational velocities to zero.

Fig. 67.2 State of Breakwater3300

67.3. Add piles

• Add two RigidBody DObjects called pile1 and pile2
• Add a Cylinder to pile1 and pile2.
• Make the cylinder 20 m long and 0.5 m in diameter.
• Set the mass properties as shown in the listing below.

// Mass properties
$Ix 3.33e5 //M*L^2/12
$Iy 3.33e5 //M*L^2/12
$Iz 312.5 //0.5*M*R^2 
$Ixy 0
$Ixz 0
$Iyz 0
$DefineInertiaAboutCG 1
$CGPosition 0 0 -5
$Mass 10e3

// Numerical
$Kinematic 0

$Cylinder pileCylinder 0 0 -5 0 0 0

67.4. Make connections

Note

• The prismatic joint capability of the ABA connection would be ideal for connecting the breakwater to the piles, however, the breakwater cannot be the follower of pile1 and pile2 in this connection. Thus Breakwater3300 will be the master DObject, and the piles the followers.
• The piles must be fixed to the seabed. The strategy employed in this tutorial will be to create a fixed Seabed RigidBody DObject, and then make a force connection between it and the piles. Recall a force connection restricts translation and rotation at the connection location between the two RigidBody DObjects.

• Create a RigidBody called seabed
• Set $Kinematic to 1 for the seabed
• Create an ABA connection between the Breakwater3300 and pile1, and Breakwater3300 and pile2
• Set the connection properties for Breakwater3300 and pile1 as per the listing below.

// Mechanical
$MasterConnectionLocation 0 0 0 0 0 0
$FollowerConnectionLocation 0 0 -5 0 0 0
$Joint 0
$FollowerJointAxis 2

// Uncategorized properties
$PrismaticJointLinear jointProperties

• Set the connection properties for Breakwater3300 and pile2 as per the listing below.

// Mechanical
$MasterConnectionLocation 20 0 0 0 0 0
$FollowerConnectionLocation 0 0 -5 0 0 0
$Joint 0
$FollowerJointAxis 2

// Uncategorized properties
$PrismaticJointLinear jointProperties

• For each of the piles, set the ABA state to one degree of freedom and to have a joint deflection (position) of -0.429. This will place the bottom of the pile and the local frame of the pile at the seabed (5 m depth).
• Make a force connection between seabed and each of the piles using the connection information listed below.
• Set the connection properties for pile1 and seabed as per the listing below.

// Connection configuration
$MasterConnectionLocation 0 0 0 0 0 0
$FollowerConnectionLocation 0 0 5 0 0 0
$ActiveConstraintDirection 1 1 1 1 1 1

// Rotational stiffness
$FCRKJoint 1e7
$FCRCJoint 1e7

// Translational stiffness
$FCKJoint 1e7
$FCCJoint 1e7

• Set the connection properties for pile2 and seabed as per the listing below.

// Connection configuration
$MasterConnectionLocation 0 0 0 0 0 0
$FollowerConnectionLocation 20 0 5 0 0 0
$ActiveConstraintDirection 1 1 1 1 1 1

// Rotational stiffness
$FCRKJoint 1e6
$FCRCJoint 1e6

// Translational stiffness
$FCKJoint 1e6
$FCCJoint 1e6

67.5. Analysis of loads

• Set the simulation run time to 30 seconds.
• Set the wave height to 1 m and period to 5 seconds, and ramp the waves over 5 seconds.
• Run the simulation.
• View the results in PostPDS.

Note

• Notice that the piles roll due to the hydrodynamic forces acting on them and the waves.
• The breakwater heaves relative to the piles in the waves. To introduce friction or end-stops, the joint properties can be adjusted.

• To assess the loads acting at the base of the piles, view the rigidBodyForceConnection.dat and rigidBodyMomentConnection.dat.
• To assess the loads acting on the breakwater at the joint connection location, view rigidBodyABAConnection.dat in the Breakwater3300 results.