int index = 0;
// Iterate through the visible panels which are not owned by other panels.
while(index < dockManager1.RootPanels.Count) {
   DockPanel panel = dockManager1.RootPanels[index];
   // Hide the panel if it's floating.
   if(panel.FloatForm == null)
      index++;
   else
      panel.Hide();
}

Dim index As Integer = 0
' Iterate through the visible panels which are not owned by any other panels.
While index < dockManager1.RootPanels.Count
   Dim panel As DockPanel = dockManager1.RootPanels(index)
   ' Hide the panel if it's floating.
   If (panel.FloatForm Is Nothing) Then
      index = index + 1
   Else
      panel.Hide()
   End If
End While