Identification of excitation and reaction forces spectra for offshore platforms

2010 ◽  
Vol 37 (1) ◽  
pp. 66-76 ◽  
Author(s):  
A. A. Elshafey ◽  
M. R. Haddara ◽  
H. Marzouk
Keyword(s):  
Bending Moment ◽  
Offshore Platforms ◽  
Random Waves ◽  
Measurement Instruments ◽  
Offshore Structure ◽  
Simple Method ◽  
Random Decrement Technique ◽  
Random Decrement ◽  
Reaction Forces ◽  
Fixed Offshore Platform

A simple method is used to predict damping and natural frequencies of a fixed offshore platform subjected to wind-generated random waves using its stationary response. The method also predicts the reaction forces and bending moment at the foundation of the platform. The method uses the random decrement signature as a tool to identify the parameters in the equation of motion. Excellent agreements were obtained between the estimated and actual values of the parameters as well as for the reaction and moment at the platform foundation. The method can be applied without any interruption to the operation of the offshore structure. The method is easy to apply and uses inexpensive motion measurement instruments. The estimated forces and bending moments can be used as a tool for an on-line foundation check. A study on the limitations of applying the random decrement technique is also presented.

Damage Detection in Offshore Structures by the Random Decrement Technique

1984 ◽  
Vol 106 (1) ◽  
pp. 38-42 ◽  
Author(s):  
J. C. S. Yang ◽  
J. Chen ◽  
N. G. Dagalakis
Keyword(s):  
Wind Waves ◽  
The United States ◽  
Offshore Structures ◽  
Naval Research ◽  
United States Geological Survey ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Damage Scenarios ◽  
Random Decrement Technique ◽  
Random Decrement

The Random Decrement Technique has shown promise as an inspection technique for offshore structures. The major advantage of this technique is that it requires only measurements of the dynamic response of the structure and not the input excitation causing the response. On offshore platforms, such random input forces occur from wind, waves, and currents. The Random Decrement Technique was evaluated together with a number of other NDE techniques under the NDE round robin testing program sponsored by the United States Geological Survey and the Office of Naval Research. A series of tests, damage scenarios, were conducted on a model of an offshore structure in a blind-mode by an independent neutral agent. Test data were given to the corresponding advocates to be analyzed and interpreted to predict the damages. Initial results indicated that the Random Decrement Technique was able to identify all the damage and non-damage situations with the usage of only four accelerometers mounted on each of the legs of the structure.

scholarly journals The use of random decrement technique for long term health monitoring of concrete structures

2021 ◽  
Author(s):  
Rana Morsy
Keyword(s):  
Damage Detection ◽  
Health Monitoring ◽  
Nuclear Power ◽  
Concrete Beams ◽  
Dynamic Properties ◽  
Offshore Platforms ◽  
Random Decrement Technique ◽  
Power Stations ◽  
Random Decrement ◽  
Detection Approach

This investigation deals with the development of an advanced strategy for Structural Health Monitoring (SHM) of concrete beams and girders for important structures such as bridges, offshore platforms and nuclear power stations using smart monitoring systems, including an effective diagnostic approach for damage detection with a reliability-based performance ranking. The proposed strategy can be classified into four main sections: identification of the existence of damage, determination the localization of the damage, estimation the level of damage, and assessing the seriousness of the damage regarding the structure’s service life. Random Decrement (RD) is an accurate dynamic analysis diagnostic tool that has been used effectively for SHM; the technique has been used within various fields in mechanical, aerospace, and, recently, civil engineering. The damage detection approach is based on the RD technique. A theoretical, numerical, and experimental investigation has been conducted on concrete beams using the RD technique for damage detection in terms of changes in the dynamic properties and used at successive multiple points under certain leading point conditions to determine the location of damage through the development of the Multi-Channel Random Decrement (MCRD).

scholarly journals The use of random decrement technique for long term health monitoring of concrete structures

2021 ◽  
Author(s):  
Rana Morsy
Keyword(s):  
Damage Detection ◽  
Health Monitoring ◽  
Nuclear Power ◽  
Concrete Beams ◽  
Dynamic Properties ◽  
Offshore Platforms ◽  
Random Decrement Technique ◽  
Power Stations ◽  
Random Decrement ◽  
Detection Approach

This investigation deals with the development of an advanced strategy for Structural Health Monitoring (SHM) of concrete beams and girders for important structures such as bridges, offshore platforms and nuclear power stations using smart monitoring systems, including an effective diagnostic approach for damage detection with a reliability-based performance ranking. The proposed strategy can be classified into four main sections: identification of the existence of damage, determination the localization of the damage, estimation the level of damage, and assessing the seriousness of the damage regarding the structure’s service life. Random Decrement (RD) is an accurate dynamic analysis diagnostic tool that has been used effectively for SHM; the technique has been used within various fields in mechanical, aerospace, and, recently, civil engineering. The damage detection approach is based on the RD technique. A theoretical, numerical, and experimental investigation has been conducted on concrete beams using the RD technique for damage detection in terms of changes in the dynamic properties and used at successive multiple points under certain leading point conditions to determine the location of damage through the development of the Multi-Channel Random Decrement (MCRD).

Generation of Wave-Field Time Histories by the Modulated Discrete Fourier Transformation

2003 ◽  
Author(s):  
Yousun Li
Keyword(s):  
Wave Field ◽  
Fourier Transformation ◽  
Time Instant ◽  
Discrete Fourier Transformation ◽  
Fast Fourier Transformation ◽  
Structural Members ◽  
Random Waves ◽  
Offshore Structure ◽  
Time Histories ◽  
The Time Domain

In the time domain simulation of the response of an offshore structure under random waves, the time histories of the wave field should be generated as the input to the dynamic equations. Herein the wave field is the wave surface elevation, the water particle velocities and accelerations at structural members. The generated time histories should be able to match the given wave-field spectral descriptions, to trace the structural member motions if it is a compliant offshore structure, and be numerically efficient. Most frequently used generation methods are the direct summation of a limited number of cosine functions, the Fast Fourier Transformation, and the digital filtering model. However, none of them can really satisfy all the above requirements. A novel technique, called the Modulated Discrete Fourier Transformation, has been developed. Under this method, the wave time histories at each time instant is a summation of a few time-varying complex functions. The simulated time histories have continuous spectral density functions, and the motions of the structural members are well included. This method seems to be superior to all the conventional methods in terms of the above mentioned three requirements.

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