The flow induced vibration of tubes in the steam generator gradually attracts great attention. The natural frequency of the tube is the basic parameter for vibration analysis. The supporting structures of the tube bundle in steam generator are the cinquefoil orifice-baffle and the anti-vibration bar which is different from the common baffle plate. The issue that researchers focus on is how these supporting structures affect the natural frequency. A simplified method of the special support in the tube bundle was studied based on the numerical simulation. According to the characteristics of supporting structures, the effect of stiffness of the supporting structures on the natural frequency was studied by the spring element constraints. The results show that when the stiffness of the support structure is larger than the magnitude of 105 N/m, the stiffness has no influence on the natural frequency. The frictional force of the circumferential constraint inside the plane is too weak to constrain the tube so we need to pay more attention on the vibration inside the plane. Through changing the contact length of the support component and tubes, the effect of the contact condition on the natural frequency is studied. The results show that the contact condition has a certain effect on the natural frequency. When the support is simplified as simple support, the influence on natural frequency is small and the deviation is less than 1.5%. And there is a certain safety margin under the simplified method. In the calculation process, the special support can be simplified as simple support and the calculation results are relatively accurate and conservative.

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