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Full Girder Modal Analysis

This analysis focuses on the natural frequencies of a girder design, identifying a key frequency near 50Hz. Findings indicate that altering bracket height and width significantly impacts these frequencies. Additionally, changes in the positioning and design of the brackets, along with the added mass from components like vacuum pumps and waveguides, must be accounted for in the model. Feedback from Juha's MBQ analysis emphasizes the dependence of dominant frequencies on the stiffness of base structures and highlights the necessity of experimental modal analysis for more accurate results.

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Full Girder Modal Analysis

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  1. Full Girder Modal Analysis 07-08-19

  2. Feedback from Henri's Analysis: • Current design appears to show a natural frequency at or around 50Hz • Changing the position of the brackets on the girder can have a significant effect on the natural frequencies • Increasing the height of the brackets was shown to be significant • The additional mass added to the Accelerating Structures (e.g. vacuum pumps, waveguides, manifolds) also has a significant effect and should be accounted for

  3. Credit: Henri Berg, 31/07/2019

  4. Increasing Mounting Height

  5. Increasing Mounting Width

  6. Bracket Position/Design Affect • The natural frequencies can be tuned away from 50Hz by altering the height/width of the mounting brackets • However this is highly dependent on the additional mass added to the Accelerating Structures • More accurate models including more the vacuum pumps and wave guides should be used

  7. Feedback from Juha’s MBQ Analysis: • The dominant frequencies were highly dependent upon the stiffness's of the base and supporting structures • Some of the frequencies were not identified until they carried out an Experimental Modal Analysis • The tunnel floor • The levelling wedge mounts

  8. Effect of the Base Design on Natural Frequencies - Current

  9. Effect of the Base Design on Natural Frequencies - Current

  10. Effect of the Base Design on Natural Frequencies – High Brackets

  11. Effect of the Base Design on Natural Frequencies – High Brackets

  12. Notes About Analysis • Using a relatively simple models: • Flexures are modelled as 1-dimensionally-rigid joints, and are not meshed. • SAS adjustment flexures • Girder level flexures • Springs are included as Ansys ‘springs’ • Following Henri’s assumption of 150kg distributed mass across the accelerating structure sides

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