scholarly journals Assessment of bridge natural frequency as an indicator of scour using centrifuge modelling

2020 ◽  
Vol 10 (5) ◽  
pp. 861-881
Author(s):  
Kasun D. Kariyawasam ◽  
Campbell R. Middleton ◽  
Gopal Madabhushi ◽  
Stuart K. Haigh ◽  
James P. Talbot
Keyword(s):  
Natural Frequency ◽  
Structural Damage ◽  
Full Scale ◽  
Shallow Foundation ◽  
Scale Model ◽  
Deep Foundation ◽  
Reliable Technique ◽  
Centrifuge Testing ◽  
Frequency Sensitivity ◽  
Bridge Failure

Abstract One of the most prevalent causes of bridge failure around the world is “scour”—the gradual erosion of soil around a bridge foundation due to fast-flowing water. A reliable technique for monitoring scour would help bridge engineers take timely countermeasures to safeguard against failure. Although vibration-based techniques for monitoring structural damage have had limited success, primarily due to insufficient sensitivity, these have tended to focus on the detection of local damage. High natural frequency sensitivity has recently been reported for scour damage. Previous experiments to investigate this have been limited as a result of the cost of full-scale testing and the fact that scaled-down soil-structure models tested outside a centrifuge do not adequately simulate full-scale behaviour. This paper describes the development of what is believed to be the first-ever centrifuge-testing programme to establish the sensitivity of bridge natural frequency to scour. A 1/60 scale model of a two-span integral bridge with 15 m spans was tested at varying levels of scour. For the fundamental mode of vibration, these tests found up to a 40% variation in natural frequency for 30% loss of embedment. Models of three other types of foundation, which represent a shallow pad foundation, a deep pile bent and a deep monopile, were also tested in the centrifuge at different scour levels. The shallow foundation model showed lower frequency sensitivity to scour than the deep foundation models. Another important finding is that the frequency sensitivity to “global scour” is slightly higher than the sensitivity to “local scour”, for all foundation types. The level of frequency sensitivity (3.1–44% per scour depth equivalent to 30% of embedment of scour) detected in this experiment demonstrates the potential for using natural frequency as an indicator of both local and global scour of bridges, particularly those with deep foundations.

scholarly journals Study on Dynamic Behavior of Bridge Pier by Impact Load Test Considering Scour

2020 ◽  
Vol 10 (19) ◽  
pp. 6741
Author(s):  
Myungjae Lee ◽  
Mintaek Yoo ◽  
Hyun-Seok Jung ◽  
Ki Hyun Kim ◽  
Il-Wha Lee
Keyword(s):  
Natural Frequency ◽  
Evaluation Method ◽  
Impact Load ◽  
Full Scale ◽  
Load Test ◽  
Scale Model ◽  
Second Mode ◽  
Surcharge Load ◽  
The Stability ◽  
The Impact

In this study, for the establishment of a safety evaluation method, non-destructive tests were performed by developing a full-scale model pier and simulating scour on the ground adjacent to a field pier. The surcharge load (0–250 kN) was applied to the full-scale model pier to analyze the load’s effect on the stability. For analyzing the pier’s behavior according to the impact direction, an impact was applied in the bridge axis direction, pier length direction, and pier’s outside direction. The impact height corresponded to the top of the pier. A 1-m deep scour was simulated along one side of the ground, which was adjacent to the pier foundation. The acceleration was measured using accelerometers when an impact was applied. The natural frequency, according to the impact direction and surcharge load, was calculated using a fast Fourier transform (FFT). In addition, the first mode (vibratory), second mode (vibratory), and third modes (torsion) were analyzed according to the pier behavior using the phase difference, and the effect of the scour occurrence on the natural frequency was analyzed. The first mode was most affected by the surcharge load and scour. The stability of the pier can be determined using the second mode, and the direction of the scour can be determined using the third mode.

Effect of mesh on CFD aerodynamic performances of a container ship

2020 ◽  
Vol 20 (3) ◽  
pp. 343-353
Author(s):  
Ngo Van He ◽  
Le Thi Thai
Keyword(s):  
Water Surface ◽  
Reference Model ◽  
Full Scale ◽  
Scale Model ◽  
Container Ship ◽  
Ansys Fluent ◽  
Remarkable Effect ◽  
Aerodynamic Performances ◽  
Mesh Convergence

In this paper, a commercial CFD code, ANSYS-Fluent has been used to investigate the effect of mesh number generated in the computed domain on the CFD aerodynamic performances of a container ship. A full-scale model of the 1200TEU container ship has been chosen as a reference model in the computation. Five different mesh numbers for the same dimension domain have been used and the CFD aerodynamic performances of the above water surface hull of the ship have been shown. The obtained CFD results show a remarkable effect of mesh number on aerodynamic performances of the ship and the mesh convergence has been found. The study is an evidence to prove that the mesh number has affected the CFD results in general and the accuracy of the CFD aerodynamic performances in particular.

Benchmarking of Truss Spar Vortex Induced Motions Derived From CFD With Experiments

2005 ◽  
Author(s):  
John Halkyard ◽  
Senu Sirnivas ◽  
Samuel Holmes ◽  
Yiannis Constantinides ◽  
Owen H. Oakley ◽  
...  
Keyword(s):  
Scale Up ◽  
Vertical Cylinder ◽  
Reynolds Numbers ◽  
Full Scale ◽  
Scale Model ◽  
Current Direction ◽  
Test Results ◽  
Helical Strakes ◽  
Truss Spar ◽  
Scale Data

Floating spar platforms are widely used in the Gulf of Mexico for oil production. The spar is a bluff, vertical cylinder which is subject to Vortex Induced Motions (VIM) when current velocities exceed a few knots. All spars to date have been constructed with helical strakes to mitigate VIM in order to reduce the loads on the risers and moorings. Model tests have indicated that the effectiveness of these strakes is influenced greatly by details of their design, by appurtenances placed on the outside of the hull and by current direction. At this time there is limited full scale data to validate the model test results and little understanding of the mechanisms at work in strake performance. The authors have been investigating the use of CFD as a means for predicting full scale VIM performance and for facilitating the design of spars for reduced VIM. This paper reports on the results of a study to benchmark the CFD results for a truss spar with a set of model experiments carried out in a towing tank. The focus is on the effect of current direction, reduced velocity and strake pitch on the VIM response. The tests were carried out on a 1:40 scale model of an actual truss spar design, and all computations were carried out at model scale. Future study will consider the effect of external appurtenances on the hull and scale-up to full scale Reynolds’ numbers on the results.

Drilling Riser VIV Tests With Prototype Reynolds Numbers

2013 ◽  
Author(s):  
Halvor Lie ◽  
Henning Braaten ◽  
Jamison Szwalek ◽  
Massimiliano Russo ◽  
Rolf Baarholm
Keyword(s):  
Cross Flow ◽  
Effect Study ◽  
Full Scale ◽  
Scale Model ◽  
Small Scale ◽  
Scaling Effects ◽  
Research Activity ◽  
Forced Motion ◽  
Auxiliary Lines ◽  
Viv Suppression

For deep-water riser systems, Vortex Induced Vibrations (VIV) may cause significant fatigue damage. It appears that the knowledge gap of this phenomenon is considerable and this has caused a high level of research activity over the last decades. Small scale model tests are often used to investigate VIV behaviour. However, one substantial uncertainty in applying such results is scaling effects, i.e. differences in VIV response in full scale flow and small scale flow. To (partly) overcome this obstacle, a new innovative VIV test rig was designed and built at MARINTEK to test a rigid full scale riser model. The rigid riser model is mounted vertically and can either be elastically mounted or be given a forced motion. In the present version, the cylinder can only move in the cross-flow (CF) direction and is restricted in the in-line (IL) direction. The paper reports results from a drilling riser VIV experiment where the new rest rig has been used. The overall objective of the work is to study possible VIV suppression to improve operability of retrievable riser systems with auxiliary lines by adding riser fins. These fins are normally used as devices for protection of the auxiliary lines. The test program has recently been completed and analysis is an on-going activity. However, some results can be reported at this stage and more results are planned to be published. A bare riser model was used in a Reynolds number (Rn) scaling effect study. The riser model was elastically mounted and towed over a reduced velocity range around 4 – 10 in two different Rn ranges, 75 000 – 192 000 (subcritical regime) and 347 000 – 553 000 (critical regime). The difference in the displacement amplitude to diameter ratio, A/D, is found to be significant. The elastically mounted riser was also towed with various drilling riser configurations in order to study VIV/galloping responses. One configuration included a slick joint riser model with 6 kill & choke lines; another has added riser fins too. The riser model is based on a specific drilling riser and the kill and choke lines have various diameters and have a non-symmetrical layout. The various riser configurations have also been used in forced motion tests where the towed model has been given a sinusoidal CF motion. Forces have been measured. Determination of the force coefficients is still in progress and is planned to be reported later. Scaling effects appear to be a significant uncertainty and further research on the subject is recommended. The slick joint drilling riser configuration generally increased the displacements compared to displacements of the bare riser model. The drilling riser configuration with protection fins, kill and choke lines generally reduced the displacements compared to displacements of the bare riser model. For both riser systems, tests showed that the response is sensitive to the heading of the current.

An Optimal Sensitivity-Enhancing Feedback Control Approach via Eigenstructure Assignment for Structural Damage Identification

2007 ◽  
Vol 129 (6) ◽  
pp. 771-783 ◽  
Author(s):  
L. J. Jiang ◽  
J. Tang ◽  
K. W. Wang
Keyword(s):  
Feedback Control ◽  
Frequency Shift ◽  
Natural Frequency ◽  
Structural Damage ◽  
Closed Loop ◽  
Damage Identification ◽  
Frequency Measurement ◽  
Sensitivity Enhancement ◽  
Stiffness Reduction ◽  
Structural Damage Identification

The concept of using sensitivity-enhancing feedback control to improve the performance of frequency-shift-based structural damage identification has been recently explored. In previous studies, however, the feedback controller is designed to alter only the closed-loop eigenvalues, and the effect of closed-loop eigenvectors on the sensitivity enhancement performance has not been considered. In this research, it is shown that the sensitivity of the natural frequency shift to the damage in a multi-degree-of-freedom structure can be significantly influenced by the placement of both the eigenvalues and the eigenvectors. A constrained optimization problem is formulated to find the optimal assignment of both the closed-loop eigenvalues and eigenvectors, and then an optimal sensitivity-enhancing control is designed to achieve the desired closed-loop eigenstructure. Another advantage of this scheme is that the dataset of frequency measurement for damage identification can be enlarged by utilizing a series of closed-loop controls, which can be realized by activating different combinations of actuators in the system. Therefore, by using this proposed idea of multiple sensitivity-enhancing feedback controls, we can simultaneously address the two major limitations of frequency-shift-based damage identification: the low sensitivity of frequency shift to damage effects and the deficiency of frequency measurement data. A series of case studies are performed. It is demonstrated that the sensitivity of natural frequency shift to stiffness reduction can be significantly enhanced by using the designed sensitivity-enhancing feedback control, where the optimal placement of closed-loop eigenvectors plays a very important role. It is further verified that such sensitivity enhancement can directly benefit the damage identification accuracy and robustness.

scholarly journals Identification of Corrosion on a Hollow Tube Using Vibration

2014 ◽  
Vol 564 ◽  
pp. 176-181
Author(s):  
S.T. Cheng ◽  
Nawal Aswan Abdul Jalil ◽  
Zamir A. Zulkefli
Keyword(s):  
Free Boundary ◽  
Boundary Conditions ◽  
Natural Frequency ◽  
Impact Loading ◽  
Structural Damage ◽  
Natural Frequencies ◽  
Localized Corrosion ◽  
Free Boundary Conditions ◽  
The Impact ◽  
Impact Vibration

Vibration based technique have so far been focused on the identification of structural damage. However, not many studies have been conducted on the corrosion identification on pipes. The objective of this paper is to identify corrosion on pipes from vibration measurements. A hollow pipe, 500 mm in length with 63.5 mm in diameter was subjected to impact loading using an impact hammer to identify the natural frequency of the tube in two conditions i) without any corrosion and ii) with an induced localized 40 mm by 40 mm corrosion at the middle of the pipe. The shift of natural frequencies of the structures under free boundary conditions was examined for each node of excitation. The results showed that there is a shift in natural frequency of the pipe, between 3 and 4 Hz near to the corrosion area. It can suggested that that the impact vibration is capable of identifying of localized corrosion on a hollow tube.

Dynamic Property Evaluation of a Long-Span Cable-Stayed Bridge (Sutong Bridge) by a Bayesian Method

2018 ◽  
Vol 19 (01) ◽  
pp. 1940010 ◽  
Author(s):  
Yan-Chun Ni ◽  
Qi-Wei Zhang ◽  
Jian-Feng Liu
Keyword(s):  
Natural Frequency ◽  
Dynamic Characteristics ◽  
Structural Damage ◽  
Dynamic Properties ◽  
Modal Identification ◽  
Modal Parameters ◽  
Modal Parameter ◽  
Cable Stayed Bridge ◽  
Long Span ◽  
Sutong Bridge

Modal identification aims at identifying the dynamic properties including natural frequency, damping ratio, and mode shape, which is an important step in further structural damage detection, finite element model updating, and condition assessment. This paper presents the work on the investigation of the dynamic characteristics of a long-span cable-stayed bridge-Sutong Bridge by a Bayesian modal identification method. Sutong Bridge is the second longest cable-stayed bridge in the world, situated on the Yangtze River in Jiangsu Province, China, with a total length of 2 088[Formula: see text]m. A short-term nondestructive on-site vibration test was conducted to collect the structural response and determine the actual dynamic characteristics of the bridge before it was opened to traffic. Due to the limited number of sensors, multiple setups were designed to complete the whole measurement. Based on the data collected in the field tests, modal parameters were identified by a fast Bayesian FFT method. The first three modes in both vertical and transverse directions were identified and studied. In order to obtain modal parameter variation with temperature and vibration levels, long-term tests have also been performed in different seasons. The variation of natural frequency and damping ratios with temperature and vibration level were investigated. The future distribution of the modal parameters was also predicted using these data.

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