Experimental Study of Nonlinear Moored-Buoy Responses
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Experimental Study of Nonlinear Moored-Buoy Responses. Objectives : To Identify and Classify Highly Nonlinear Experimental Structural Responses Under Combined Deterministic and Random Waves To Validate Analytical Model Predictions and Investigate Fluid-Structure Interactions.

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Experimental Study of Nonlinear Moored-Buoy Responses

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Experimental study of nonlinear moored buoy responses

Experimental Study of Nonlinear Moored-Buoy Responses

  • Objectives:

  • To Identify and Classify Highly Nonlinear Experimental Structural Responses Under Combined Deterministic and Random Waves

  • To Validate Analytical Model Predictions and Investigate Fluid-Structure Interactions

Experimental Configuration (SDOF)

  • Principal Investigator:

  • Prof. Solomon C.S. Yim Civil Engineering Department Oregon State University

  • Approach:

  • Modifying Existing ID Techniques and/or Developing New Tools to Classify Degree of Nonlinearity

  • Comparing Overall Behaviors of Experimental Data and Simulations to Validate Analytical Model

  • Conducting Sensitivity Study to examine Hydrodynamic Properties


Experimental study of nonlinear moored buoy responses

Highly Nonlinear Experimental Structural Responses

Possible Chaos (Poincare Map)

  • Observations:

  • Primary and Secondary Resonances in Frequency Response Diagram

  • Harmonic, Subharmonic, Superharmonic, and Possibly Chaotic Responses

  • Transition Behavior of Multiple Coexisting Response Attractors

Possible Chaos (Poincare Time History)

Coexisting Harmonics and Subharmonics


Experimental study of nonlinear moored buoy responses

Poincare Analysis of Multiple Coexisting Responses

Sections I & V

Sections III & VII

Sections II & VI

Sections IV & VIII


Experimental study of nonlinear moored buoy responses

Comparisons of Experimental Results and Analytical Predictions

Time-Averaged PDF

Numerical Model:

where

Frequency Response Diagram

Distributions of Large Excursions


Experimental study of nonlinear moored buoy responses

On-Going/Future Research

Cd versus Reynolds Number

  • On-Going Research:

  • Identifying Best-Fit Fluid-Structure Models

  • Investigating Hydrodynamic Properties

  • Predicting Occurrence of (Noisy) Chaos

  • Verifying Inter-Domain Transitions as Analytically Predicted

Cm versus Reynolds Number

  • Future Research:

  • Formulating Models Based on Large Body Theory

  • Extending Analysis Procedure to MODF Experimental Results

  • Comparing SDOF and MDOF Results


Experimental study of nonlinear moored buoy responses

Stochastic Analysis of Nonlinear System under Narrowband Excitation

  • Objectives:

  • Improve accuracy of prediction using semi-analytical method

  • Apply semi-analytical method to nonlinear-structure nonlinearly-damped (NSND) model

  • Compare prediction with experimental data

  • Principal Investigator:

  • Prof. Solomon C.S. Yim

  • Civil Engineering Department

  • Oregon State University

  • Approach:

  • Identify typical nonlinear response behavior under deterministic excitation

  • Employ semi-analytical method to predict system response

  • Validate prediction method through comparison with experimental data


Experimental study of nonlinear moored buoy responses

Stochastic Analysis of Nonlinear System under Narrowband Excitation

Response under Deterministic Excitation

Typical Nonlinear Response Behavior

Progress:

System Configuration

(a) Plan view (b) Profile view

Fig.1 Experimental model of nonlinear system

Fig.2 Four different response behavior under same excitation

Coexisting Attraction Domain

Response Amplitude Curve

Fig 3. Small amplitude harmonic, 1/3 subharmonic, 1/2 subharmonic and large amplitude harmonic

Fig 4. Response amplitude curve of system in subharmonic region


Experimental study of nonlinear moored buoy responses

Stochastic Analysis of Nonlinear System under Narrowband Excitation

Jump Phenomena

Inter-Domain Transition

Fig 5. Amplitude jump from large amplitude to small amplitude harmonic domain

Fig 6. Schematic diagram of inter-domain transitions

Response under Narrowband Excitation

Stochastic behavior of the excitation parameter

Intra-Domain Transition

Where, A(1),A(2) = excitation amplitude of current and next cycles,  = phase angle difference, (1)-(2)

Fig 7. Intra-domain transitions within four different attraction domains


Experimental study of nonlinear moored buoy responses

Stochastic Analysis of Nonlinear System under Narrowband Excitation

Numerical simulation

Large amplitude harmonic response

1/2 subharmonic response

1/3 subharmonic response

small amplitude harmonic response

Fig 8. Time series of narrowband excitation amplitude (top) and corresponding response amplitude (bottom)

Fig 9. Amplitude response map correspond to time series shown in Fig 8.

Result

Overall Response Amplitude Probability Distribution

  • Future study:

  • Apply semi-analytical method to NSND model

  • Predict response of NSND model with coefficient determined by system identification technique

  • Verify prediction using experimental data

Fig 10. Overall response amplitude probability distributions (compared with simulation result)


Experimental study of nonlinear moored buoy responses

Modeling and Validation of

Nonlinear Stochastic Barge Motions

Modeling and Validation of

Nonlinear Stochastic Barge Motions

Objectives:

- To examine predictive capability of

coupled Roll-Heave-Sway models

to estimate stochastic properties of

nonlinear barge response behavior

- To develop probability-based analysis

and design methodology

FIG. 1. Roll-Heave-Sway Model

Approach:

- Develop Roll-Heave-Sway

barge-motion models

(and lower order ones)

- Identify system coefficients

- Examine and compare numerical

predictions with measured data

- Develop nonlinear extreme-value

prediction techniques

Principal Investigator:

- Prof. Solomon C.S. Yim

Civil Engineering Department

Oregon State University


Experimental study of nonlinear moored buoy responses

Modeling and Validation of

Nonlinear Stochastic Barge Motions

Identification of System Coefficients

for Roll-Heave Model

- Regular Waves

Comparison of Model Predictions

with Measured Data

- Measured Random Waves

- Simulated Random Waves

measured

predicted

FIG. 1. Roll vs Roll Velocity

(Regular Waves, Case SB27)

measured

predicted

Future Research:

- Examine complex nonlinear

behavior including resonance and

possible chaos

- Perform and compare simulations

- Use model to verify proposed

theories on capsize

FIG. 2. Roll vs Heave

(Regular Waves, Case SB27)


Experimental study of nonlinear moored buoy responses

Modeling and Validation of

Nonlinear Stochastic Barge Motions

measured

predicted

FIG.3. Roll Distribution

(measured random waves)

FIG.5. Roll vs Wave

(measured random waves)

measured

predicted

FIG.4. Heave Distribution

(measured random waves)

FIG.6. Roll vs Heave

(measured random waves)


Experimental study of nonlinear moored buoy responses

Modeling and Validation of

Nonlinear Stochastic Barge Motions

measured

predicted

FIG.7. Roll Distribution

(simulated random waves)

FIG.9. Roll vs Wave

(simulated random waves)

measured

measured

FIG.8. Heave Distribution

(simulated random waves)

FIG.10. Roll vs Heave

(simulated random waves)


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