1 brookhaven science associates nick simos nsls2 ground motion and vibration studies

1 BROOKHAVEN SCIENCE ASSOCIATES

Nick Simos

NSLS2 Ground Motion and Vibration Studies


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.)


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


NSLS2 Vibration Environment & Source Identification


NSLS II Site Field Studies

NSLS II Subsurface Characterization• Well-settled; stable sands (~870 ft/s Vs)• Water table ~ 30 ft below grade


PHASE I & IIUsing CFN Facility to help identify

Cultural noise and filtering effects


PHASE III: NSLS II ground motion environment


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


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)


CFN – Filtering of Motion Power & Response spectra on Floor Slab


APS: Operating Systems & Induced VibrationGoal: establish attenuation characteristics


APS – Vibration Conditions on Ring and Experimental Floor


Spring-8 Mechanical Motion Attenuation


NSLS II Vibration AnalysisField data Modeling


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


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


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


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


NSLS II Operations Cultural noise generation/minimization


Interface Options: Service Building and RING/Experimental Floor


Revised Baseline OptionService building partition/isolation


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


How do we ensure that the computational models are leadings us to correct estimates?


Validation of Mathematical Model & Processes Comparing with THEORETICAL Model/Results

Radiating Boundary Verification Rayleigh wave field verification


Validation of Mathematical Model & Processes Comparing with EXPERIMENTAL Results

Prediction of complex system below performed using same computational procedures and software


Benchmarking against dedicated tests APS Access Corridor and Experimental Floor


RING foundation mat optimization based on the established modeling and analysis


Noise Suppression for NSLS2 Sensitive Lines


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


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

1 brookhaven science associates nick simos nsls2 ground motion and vibration studies

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