You can use the createDynamicCluster.jacl script to create a dynamic cluster.
wsadmin -profile createDynamicCluster.jacl node_group_name dynamic_cluster_nameIn place of node_group_name and dynamic_cluster_name use the name of the node group that you want to associate with your new dynamic cluster. You might need to modify the wsadmin command to wsadmin.sh or wsadmin.bat, depending upon your operating environment.