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OBJECTIVE
Based on experience data (including measurements at operating facilities) integrated with large-scale, state-of-the-art computational models:
• make the best possible estimate as to what the vibration levels will be once the NSLS II structure is placed on the “green-field”
• assist in the optimization of the design of a “quiet” facility (treatment of in-house sources, disruption of vibration paths, structural interfaces, mat thicknesses, etc.)
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BASIC APPROACH
• QUANTIFY the vibration criteria which key elements of the NSLS2 (ring and experimental lines) MUST meet
• Establish the “green-field” conditions at the NSLS2 site
• Make the link between the “green-field” and the NSLS2 infrastructure using
– “experience” data– state-of-the-art computational methods (the only available tool)
and as a result• estimate vibration levels on the ring and experimental floor• identify structural provisions ensuring stability requirements
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NSLS II Site Field Studies
NSLS II Subsurface Characterization• Well-settled; stable sands (~870 ft/s Vs)• Water table ~ 30 ft below grade
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PHASE I & IIUsing CFN Facility to help identify
Cultural noise and filtering effects
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Comparison with other “green-field” sites
Spring-8 free-field conditions are remarkably “quiet” due to rocky subsurface
HOWEVER, as shown later, rock is both a blessing and a detriment
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Field Studies at Relevant Facilities
• CFN• Same site conditions as well as natural ground motion and
cultural vibration• Benchmarking of ground motion filtering (foundation
interaction with ground motion)• APS & SPring-8
• Quantification of in-house generated noise• Effectiveness of noise-arrest schemes• Identification of “achieved” vibration levels for ring and
experimental floor (including spatial variability)
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APS: Operating Systems & Induced VibrationGoal: establish attenuation characteristics
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The challenge is to best estimate the transfer of the measured “green-field” ground motion
?
Measured Free-field Vibration at NSLS2 site
Resultant field dependent on type of waves arriving at site
BNL site with deep sand primarily RAYLEIGH Waves
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Qualitative assessment of ground motion filtering
NSLS II structure neither RIGID nor simple
TRUE interaction can only be established through detailed, comprehensive wave interaction analysis
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Computed Ground Motion Filtering
TAB HSHS )]([)()()( *
Input Power Spectra = actual record from the NSLS II site
Transfer Function H(w) = extracted from the wave propagation
and scattering analysis
Analysis represents the computing of the transient response to
an impulse (white noise) – USE of explicit formulation that enables the analysis of very large problems
Rayleigh waves are primarily generated and propagated
toward the NSLS II structure
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NSLS II Ground Motion Filtering due to the presence of the structureAnalysis CONFIRMED that placement of NSLS II infrastructure will reduce the “green-field” ground
vibration conditions
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Attenuation of mechanical motion
TAB HSHS )]([)()()( *
Input Power Spectra = actual recordings at Spring-8 and APS
mechanical rooms (pumps; chillers, etc.)
Transfer Functions = extracted from the detailed analysis
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How do we ensure that the computational models are leadings us to correct estimates?
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Validation of Mathematical Model & Processes Comparing with THEORETICAL Model/Results
Radiating Boundary Verification Rayleigh wave field verification
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Validation of Mathematical Model & Processes Comparing with EXPERIMENTAL Results
Prediction of complex system below performed using same computational procedures and software
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Benchmarking against dedicated tests APS Access Corridor and Experimental Floor
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RING foundation mat optimization based on the established modeling and analysis
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SUMMARY
• Field vibration studies confirmed that the stability limits set for NSLS II (<25 nm; 4-50 Hz) are satisfied by the selected site
• Field studies at operating facilities have provided realistic levels of in-house generated vibration as well as motion attenuation characteristics
• Studies at other facilities also provided a good understanding of what measures for noise suppression work and can be implemented into the design of NSLS II
• The use of benchmarked, large-scale dynamic analysis models combined with data recorded at other facilities have provided a powerful tool for assessing the anticipated motion at the NSLS II experimental and ring floors
• The combined computational model/actual noise data also provide the means to optimize• The in-house noise suppression• The ring and/or experimental floor thicknesses
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PATH FORWARD• Utilize the newly installed network of ground motion measuring
stations to monitor both the long-term vibration stability of the site as well as its spatial variation
• Expand the site vibration study to include slow ground motions (low frequency end of the spectrum) and assess their space and time coherence for the NSLS II site
• Continue to fine-tune the large-scale vibration analysis models based on specific and NSLS II-related field tests as well as on data generated at similar but operating
• Complete the optimization of the NSLS II ring and experimental floor thicknesses (especially parts of exp. floor with extra-sensitive beam lines)
• Assess the effectiveness of noise suppression features for implementation and integration into the final NSLS II design