ngCFHT Design - Mechanical/Structural · ngCFHT Design – Mechanical/Structural Mechanical/Structural Design The ngCFHT mechanical and structural design is a feasibility study to

ngCFHT Design – Mechanical/Structural

ngCFHT Design

- Mechanical/Structural

Kei Szeto, Steven Bauman, David Loop, Derrick Salmon

27-29 March 2013, ngCFHT Workshop


Outline

Detail of mechanical/structural study

Adopted design guidelines

Baseline telescope and enclosure configuration

Feasibility study and findings by Dynamic Structures Limited

• Pier capacity study

• Cost estimate and construction schedule

Feasibility study and findings by University of Western Ontario

• Ventilation performance study

Summary of feasibility study


Mechanical/Structural Design

The ngCFHT mechanical and structural design is a feasibility

study to redevelop the current CFHT facility with a modern

telescope structure and enclosure system to accommodate a

10m, segmented mirror telescope equipped with dedicated

wide-field highly multiplexed fiber-fed spectrographic

capability.

Top level design requirements.

Aperture 10 m (segmented)

Field of View 1.5 deg2 (hexagonal)

Wavelength Range 370-1300 nm

Number of Fibers 3,200 (low resolution)

800 (high resolution)

Spectral Resolution R2,000 (370-1300 nm)

R20,000 (480-680 nm)


• Will minimize work at the

summit by reusing the

telescope and enclosure

piers

Redevelopment Guidelines

The Office of Mauna Kea Management (OMKM) has produced

a comprehensive Mauna Kea Science Reserve Master Plan

where redevelopment of CFHT is classified as a Type I facility

development.

Based on the OMKM considerations, we have adopted three

redevelopment guidelines that ngCFHT:

• Will not disturb the ground beyond what has already been done

• Will stay within the current CFHT space envelope

• W


Technical Feasibility Study

In early 2011, we launched the feasibility study to develop a

baseline telescope structure and enclosure configuration that

meets the scientific requirements and redevelopment

guidelines for ngCFHT.

Key mechanical/structural design studies conducted were:

• Definite baseline telescope and enclosure configuration

• Verify existing telescope pier load capacity for baseline telescope

• Verify existing enclosure pier load capacity for baseline enclosure

• Perform aero-thermal study to compare enclosure ventilation

performance with computational fluid dynamics (CFD) simulation

Based on findings of the feasibility study, cost estimate and

schedule are also developed for construction.


Baseline Configuration - Telescope

For the purpose of the feasibility

study, the following telescope

configuration is used:

• A f/2 segmented primary mirror of

10m diameter

- Building on the segmented mirror

knowledge of ELT projects

• From the M1 vertex to the top of

the telescope the distance is

19.4m

- Including the length of the wide field

corrector (WFC) and prime focus

components of the spectrograph

ngCFHT Design – Mechanical/Structural 7

Examples of Prime Focus Components

Based on WFMOS* design • Fiber positioner • Fiber handling unit • Acquisition & guide system • Calibration unit • De-rotator

*Source Ellis (2009)


A Calotte enclosure is assumed:

• Calotte design is compact and

structurally efficient over conventional

enclosure designs of the same size aperture

opening

- Present the “best-match” potential to existing

enclosure size and mass

- Lower construction and operation costs

- Findings from trade study

Baseline Configuration – Enclosure

ngCFHT Enclosure

Base Cap

Aperture

Existing pier


The enclosure functions:

•Combined base and cap structure motions provide a zenith

observing range of 0° to 65°

Enclosure Functionalities (1)

• Enclosure aperture is closed

by rotating the cap over a

fixed shutter “plug” attached

to the base structure


Other enclosure functions are:

• Enable the telescope to point to

horizon to facilitate

maintenance of the top end

components

• Supply an enclosure crane to

service optics, including M1

segments and WFC, prime

focus components and

spectrograph components

Enclosure Functionalities (2)

Crane


Feasibility Study by DSL

Due to the company’s extensive experience in design,

manufacturing, erection and commissioning of enclosures in

Hawaii and around the world, Dynamic Structures Limited

(DSL) of Port Coquitlam, BC, Canada was contracted.

•To study the feasibility of the baseline telescope and enclosure

configuration

•To verify existing telescope pier load capacity for new telescope

•To verify existing enclosure pier load capacity for new enclosure

•To develop cost estimate and schedule for construction of the

telescope structure and enclosure

- Not including of optics and spectrograph costs

ngCFHT Design – Mechanical/Structural 12 TMT.ENC.PRE.11.

001.REL01

DSL Enclosures at Mauna Kea Summit

Photo copyright 1998, Richard Wainscoat

Existing DSL constructed

enclosures on Mauna Kea

Subaru

Keck I & II

CFHT

Gemini N


DSL completed final design, detailed

cost estimate and schedule for the

construction of the TMT enclosure

DSL also completed conceptual

design, budgetary cost estimate and

schedule for the construction of the

TMT telescope structure

Other DSL Work on Mauna Kea Summit

DSL manufactured and

erected the Keck II telescope


The objective of the load capacity studies is to verify the

capacity of the existing inner telescope and outer enclosure

piers to support ngCFHT under modern design codes:

• ASCE-7, [Minimum Design Loads of Buildings and Other

Structures], American Society of Civil Engineers, Reston, (2010)

• ACI 318-08, [Building Code

Requirements for Structural

Concrete and Commentary],

American Concrete Institute,

Farmington Hills (2008)

• AISC 360-05, [Specification for

Structural Steel Buildings],

American Institute of Steel

Construction, Chicago (2005)

Pier Load Capacity Studies


The inner and outer piers are modeled and analyzed using

finite element analysis (FEA) with information derived from the

original construction drawings.

• The inner telescope pier is a three storey cylindrical reinforced

concrete structure

Inner and Outer Pier Modeling

- 16.6m outside dia. and 14.4m tall

- Structural mass is 1,343 tons

• The outer enclosure pier is a four

storey steel frame structure

- 28.8m outside dia. and 14.9m tall

- Inside dia. sets a ~80mm gap

between the inner and outer piers

- Structural mass is 893 tons


Dead, live and seismic loads are

applied in the analysis with baseline

telescope configuration.

• Telescope mass is 270 tons*, 6.0%

increase from the existing telescope

• Telescope mass is 17% of total mass

- Total mass of the telescope and pier

system is 1,613 tons

- Telescope mass is modeled in FEA as a

lumped mass at the correct CG location

and connected to the pier ring girder via a

beam element frame with spring elements

to account for the dynamic interactions

Telescope Pier Load Analysis

The FEA performed using the structural analysis software SAP2000.

*Set based on Keck telescope mass

Lumped mass


Dead, live, environmental and seismic loads are applied in the

analysis with baseline enclosure configuration.

Enclosure Pier Load Analysis

The FEA performed using the structural analysis software SAP2000.

Lumped mass

• Snow load is 150 kg/m2

• Ice load is 68 kg/m2

• Wind load at 78 m/s

• Enclosure mass is 510 tons, 32%

increase over the existing enclosure

• Enclosure mass is 36% of total mass

- Total mass of the enclosure and pier

system is 1,403 tons

- Enclosure mass is modeled in FEA as a

lumped mass with the same analysis

considerations as for the telescope pier.


Telescope Pier Enclosure Pier Comment

Wall Beam All load combinations

Slab Column All load combinations

Footing Footing All load combinations

Soil Soil All load combinations

Bracing x Seismic capacity = 24% of load

All inner and outer pier structural elements have sufficient load capacity except for the enclosure pier bracing.

•Due to the “insufficient” bracing, the predicted enclosure pier seismic deflection exceeds the 80mm gap thus posing potential collision between the two piers during seismic events

- However, cost effective options are available to reinforce the bracing in-situ to increase load capacity and at the same time reducing the seismic motion of the outer enclosure pier

Findings of Load Capacity Verification


Baseline Configuration Status

With further optimization of the telescope and enclosure geometry,

the overall height can be reduced to meet the design guidelines.

The Calotte

enclosure

height is

2.5m taller

than the

existing

enclosure


Cost Estimate and Schedule (1)

DSL also produces cost and schedule estimates.

• Reinforcement of the outer pier

• Deconstruction of the existing telescope structure and enclosure

• Design and manufacturing of the baseline telescope structure

and enclosure

• Trial assembly and on-site construction

Estimates are based on:

• Original construction drawings

• Original erection procedures

• Parametric construction cost relationships

- Keck telescope construction

- TMT estimates


Cost Estimate and Schedule (2)

DSL cost and schedule estimates:

• Total cost is $68.2 M, including profit and contingency

- Not including of optics and spectrograph costs

• On-site construction duration is 2.8 years

- Total overall schedule is 5.5 years


The objective of the CFD study is to compare “dome-flushing”

performance of passive and active ventilation configurations.

•Passive ventilation is provided by vent openings on the base

structure of the enclosure

- Optimal vent area is determined parametrically based on TMT

ventilation requirement

•Active ventilation provided by floor-mounted exhaust fans

- Optimal flow rate is determined parametrically using existing Keck

ventilation configuration

- A median case is modeled and compared

- Wind approaching from the east at 5 m/s

- Telescope pointing normal to the wind direction at 30° zenith

Study of Ventilation Performance (1)

Enclosure with vent openings


The WindEEE Research Institute at the University of Western

Ontario in London, ON, Canada was contracted for the study.

Assessment criteria for performance used in the comparison study:

• Volume fraction of outside air inside the enclosure

- High volume fraction indicates efficient dome-flushing

• Temperature distribution, mean and RMS, along the optical path

- Uniform temperature indicates minimum dome-seeing

• Wind velocity and turbulent kinetic energy along the optical axis

- Low velocity and turbulence indicate minimum wind-shake

Study of Ventilation Performance (2)

CFD simulation domain Mesh presentation


Findings of Ventilation Study (1)

Passive ventilation provides superior dome-flushing while

maintaining uniform temperature and low turbulence level.

•Optical path contains 99% outside air after 372 seconds of

“flushing”

•Optical path reaches uniform air temperature within the same time

with a RMS temperature variation of <0.04°K

•Low turbulent kinetic energy, <0.5 m2/s2, is observed

Active ventilation does not provide the same degree of dome-

flushing performance even at twice the optimal flow rate.

Mesh of optical path

• Optical path contains only 14% outside air after

368 seconds of “flushing”

• Less uniform temperature distribution

- RMS temperature variation observed is ~0.08°K


Floor exhaust

Findings of Ventilation Study (2)

*Flow rate at 90,000 cubic

foot per minute (cfm)

Passive ventilation

Active ventilation*

• Passive ventilation

provides uniform

dome-flushing.

• For active ventilation,

flow follows inside

curvature of curvature of the enclosure resulting in

non-uniform flushing in the optical path. 2 x active ventilation flow rate

Floor exhaust

Volume fraction plots, central cross

section view parallel to the wind.

•Dark blue indicates 100% original air

•Red indicates 100% flushed “new” air


Feasibility is established with the proposed baseline

•Load capacity studies that they did not identified major structural

deficiencies

• By optimizing the telescope and enclosure geometry, we can

reduce the overall height to meet the design guidelines

•CFD analysis is planned to evaluate aero-thermal

performance of the proposed “minimal” facility

• Dome ventilation efficiency through floor vents, same as Keck

• Flow profile over aperture opening and inside

Summary of Feasibility Study Summary of Feasibility Study

The proposed baseline ngCFHT telescope and enclosure

configuration meets the adopted design guidelines.

• No additional ground disturbances

• Stay within the current CFHT space envelope

- By optimizing the telescope and enclosure geometry, we will meet the space

envelope guideline

• Existing telescope and enclosure piers can be reused

- Enclosure pier bracing can be reinforced economically

• Cost estimate is $68.2M with 2.8 years of on-site

construction, and an overall duration of 5.5 years

Preliminary CFD analysis indicated passive

ventilation has superior aero-thermal performance.

• Cost of passive ventilation is included in the DSL

estimate


Backup Slides


Calotte Enclosure Motion Principle

Centre

Coincident with

the Telescope

Centre

Azimuth Axis

Aperture Opening

at Maximum

Zenith Angle = 650

Rotating Cap Structure

Fixed Outer Pier

Rotating Base Structure

Cap Axis Fixed @

Zenith Angle = 32.50


Enclosure Aperture Positions

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ngCFHT Design - Mechanical/Structural · ngCFHT Design – Mechanical/Structural Mechanical/Structural Design The ngCFHT mechanical and structural design is a feasibility study to