# Presentation: 211662

## NSLS2 Ground Motion and Vibration Studies

**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 & II

**Using 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 VibrationGoal: establish attenuation characteristics

## APS – Vibration Conditions on Ring and Experimental Floor

## Spring-8 Mechanical Motion Attenuation

## NSLS II Vibration AnalysisField 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

**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 structureAnalysis 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 OptionService building partition/isolation

## Attenuation of mechanical motion 

**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

- 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

**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**