Dynamic Analysis of Fan Foundation Mahendra Madhavan

Potential Power Plant Problems Requiring Dynamic Analysis Machinery Vibration Piping Vibration Heavy-load drops Tornado missile impact Dry cask accidents During design, operation and maintenance of power plants, we encounter the following forms of vibration. Machinery vibration includes 1. Induced or Forced Draft Fan, 2. Cooling Tower Fan Deck, 3. Turbine generator Foundations Piping vibration includes 1. Flow induced, 2. Water hammer, 3. Acoustic resonance

Need for Vibration Analysis Meet the vendor’s performance criteria Industry guidelines or SCS standards Operation / Maintenance Vibration not generated or transmitted to other areas Foundation is free from structural resonance Vibration not annoying to people Operation and Maintenance: To prevent forced outages; Not to do maintenance more often than necessary.

Four basic components of Vibration Mass (m) Stiffness (k) Damping (c) Forcing Function (F)

Equation of motion Inertial force, Damping force and Stiffness resistance

Types of Vibration When F = 0 (Free vibration) F = F0sinωt (Forced Vibration) c = 0 (Undamped system) c ≠ 0 (Damped system) During design, operation and maintenance of power plants, we encounter the following forms of vibration

How to quantify vibration components? Mass from Machine and Foundation drawings Stiffness and Damping from DYNA5 (pile-soil interaction) Force from vendor or make an estimate F During design, operation and maintenance of power plants, we encounter the following forms of vibration

Fan Foundation Mat foundation (Soil supported) Pile / Caisson foundations

Types of Analysis Modal Analysis Response Analysis

Single Degree of Freedom Vibration modes are analogous to DOF in a node m: Mass of the system k: Stiffness of the system c: Damping

Forced vibration of a damped system Damping (c) Mass (m) Stiffness (k) DAF Vibration modes are analogous to DOF in a node m: Mass of the system k: Stiffness of the system DAF : Dynamic Amplification Factor ω: Operating frequency ωn: Natural frequency τ : Damping ratio

Vibration Acceptance Criteria (Commonly used) (Vendor’s requirement and SCS Standards) MODAL ANALYSIS Natural freq away from ± 20% of operating freq Bearing Housing disp ≤ 0.125 mils pk-pk for 1 oz of wheel unbalance at outer radius (Sensitivity check) Shaft velocity ≤ 0.1 in/sec (balancing grade) Dynamic stiffness of the foundation should be ≥ 11.987 x 106 lb/in per support. RESPONSE ANALYSIS Typically there are four acceptance criteria that are required to be met. To meet the first criteria we need to carry out a Modal analysis. The next three criteria requires Response analysis.

Wheel unbalance (Sensitivity check) F = m e ω2 e=50 in m = 1 oz. 1 oz of wheel unbalance ω = 2 π f The resulting displacement measured at Bearing Housing ≤ 0.125 mils pk-pk f = 900 rpm Peak to Peak F = 72 lb

How to Prevent Vibration? Trial sizing criteria Single or two degree of freedom models Detailed analysis using GTStrudl and Dyna5 GTStrudl for modal analysis and estimating the natural frequency Dyna5 is used to estimate soil-structure spring stiffness and damping Vibration modes are analogous to DOF in a node

Trial sizing criteria

Foundation Plan This is the plan of the foundation showing the locations of the 12 caissons.

Foundation/Soil Links to GTSTRUDL Combined Model

Foundation/Soil Members in GTSTRUDL Combined Model

Foundation/Soil Dynamic Properties 6 Members = 6 DOF’s for stiffness and damping

Vibration Modes Y Longitudinal Sliding (Translation in X) X Vertical (Translation in Y) Lateral Sliding (Translation in Z) Rocking (Rotation about X) Yawing (Rotation about Y) Pitching (Rotation about Z) X Z TYPICAL MODES OF CONCERN Vibration modes are analogous to DOF in a node

Isometric view X Y Z The plant is spending approximately $400 million the SCR program (SCR = Selective Catalytic Reduction) -- an environmental control system that will reduce Nox emissions -- a key ingredient in the formation of ozone. These NOX emissions will be reduced by approximately 85%. Last year’s User’s Group meeting… Scott Lange, SCS Atl -- SCR project at Bowen -- Steel structure supporting precipitator ductwork and the two SCR boxes Ed Marshal -- modifications to the boiler house.

Longitudinal Sliding (X Translation) Y Z X

Vertical (Y Translation) X Z

Lateral Sliding (Z Translation) Y X Z

Rocking (X Rotation) Y Z X

Yawing (Y Rotation) Y X Z

Pitching (Z Rotation) Y X Z

Recent Analyses Wansley 1 and 2 (Rock Foundation ) Single DOF, Using Hand calc Bowen 3 and 4 (Pile Foundation over rock) GTStrudl and Static pile stiffness Bowen 1 and 2 (Pile Foundation over rock) – changing soil properties (density, shear waves, poisson etc.) GTStrudl and DYNA5 The addition of the SCR system means that the existing ID fan output must increase to handle the additional pressure drop of the SCR system. This required the ID fan be replaced.

Vibration Testing In-situ testing to measure vibration for acceptance Use In-situ testing results to validate the math model The addition of the SCR system means that the existing ID fan output must increase to handle the additional pressure drop of the SCR system. This required the ID fan be replaced.

The addition of the SCR system means that the existing ID fan output must increase to handle the additional pressure drop of the SCR system. This required the ID fan be replaced.

The addition of the SCR system means that the existing ID fan output must increase to handle the additional pressure drop of the SCR system. This required the ID fan be replaced.

The addition of the SCR system means that the existing ID fan output must increase to handle the additional pressure drop of the SCR system. This required the ID fan be replaced.

The addition of the SCR system means that the existing ID fan output must increase to handle the additional pressure drop of the SCR system. This required the ID fan be replaced.

Thank you Questions ? The addition of the SCR system means that the existing ID fan output must increase to handle the additional pressure drop of the SCR system. This required the ID fan be replaced.

Thank you Questions ? The addition of the SCR system means that the existing ID fan output must increase to handle the additional pressure drop of the SCR system. This required the ID fan be replaced. S:\Workgroups\SCS Engineering\Fossil and Hydro-West\Engineering\ Madhavan Mahendra\Vibration Presentation_Anniston