ON DETECTION OF DEFECTS IN BEAMS AND TRUSSES FROM DYNAMIC RESPONSES

2000 ◽  
Vol 24 (1A) ◽  
pp. 1-31
Author(s):  
S. Lukasiewicz ◽  
K. Palka
Keyword(s):  
Bending Stiffness ◽  
Least Square ◽  
Dynamic Responses ◽  
Axial Stiffness ◽  
Mathematical Form ◽  
The Finite Element Method ◽  
Identification Procedure ◽  
Identification Method ◽  
Model Equations ◽  
Source Of Information

This paper presents an identification method to detect cracks and corroded members in vibrating structures. The mathematical identification procedure based on the least square technique uses the measured dynamic response of a structure as the source of information. The application of the Finite Element Method (FEM) for the representation of all constraints and model equations allows presentation of the identification process in a simple and very efficient mathematical form. Propagation of cracks and other failures of the members cause changes in the bending and axial stiffness of the members. One can detect the crack by observing the change in the bending stiffness caused by the closing and opening of the crack in two different configurations. The proposed identification method provides highly precise calculated results which allows detection of small changes in the bending stiffness of the members resulting from cracks and corrosion. The method was tested on simulated experimental data.

A NUMERICAL TECHNIQUE TO EVALUATE THE FLEXURAL STIFFNESS OF LONG BONES AFFECTED BY CRACKS AND POROSITY

2011 ◽  
Vol 11 (01) ◽  
pp. 131-148 ◽  
Author(s):  
HADI MOHAMMADI ◽  
FERESHTEH BAHRAMIAN ◽  
KIBRET MEQUANINT ◽  
AMIN RIZKALLA
Keyword(s):  
Numerical Technique ◽  
Least Square ◽  
Dynamic Responses ◽  
Computational Technique ◽  
Flexural Stiffness ◽  
Long Bones ◽  
Surface Cracks ◽  
The Finite Element Method ◽  
Computational Investigation ◽  
Stiffness Properties

Bone maintains its structure through a constant process of resorption and formation, in a process called bone remodeling. An imbalance in this process caused by disease, abnormal mechanical demands, or fatigue may predispose bone to fracture injuries. Increase in bone resorption can increase the number of surface cracks and structural porosity of the bone and thus change its stiffness properties. In this study, a computational technique is proposed to investigate the stiffness properties in long bones based on dynamic responses. As the first attempt, defects such as porosity and cracks are detected based on changes in stiffness properties of the sample. The least square algorithm and the finite element method are used as tools in this study. The Wilson-θ numerical method is employed to generate artificially experimental results for acceleration vectors. The data obtained from the artificial experiment is later employed to the proposed computational investigation model as raw data.

In-Place FE Modeling of Unbonded Flexible Pipelines Capturing Pressure Stiffening and Decoupled Axial/Nonlinear Bending Stiffness

2010 ◽  
Author(s):  
Edvin Hanken ◽  
Evelyn R. Hollingsworth ◽  
Lars S. Fagerland
Keyword(s):  
Water Injection ◽  
Bending Stiffness ◽  
Axial Stiffness ◽  
Fe Model ◽  
Nonlinear Bending ◽  
Upheaval Buckling ◽  
History Effects ◽  
System Integrity ◽  
Non Linear ◽  
Bending Behaviour

For fast track pipeline projects the need for costly installation vessels and sophisticated materials for rigid pipeline water injection systems, have made flexible pipelines a competitive alternative. They can be installed with less costly construction vessels, provide a competitive lead time and a corrosion resistant compliant material. Flexible pipelines have relative high axial stiffness and low non-linear bending stiffness which is a challenge to model correctly with FE for in-place analyses of pipelines. Whilst some FE programs can model the non-linear bending behaviour of a flexible pipeline at a given pressure, current FE tools do not include the effect of increased bending resistance as the system is pressurized. Therefore, a 3D FE model in ANSYS was developed to simulate the decoupled axial and nonlinear bending behaviour of a flexible, including the bend stiffening effect for increasing pressure. A description of the model is given in this paper. It will be demonstrated how the FE model can be used to simulate the 3D nonlinear catenary behaviour of an high pressure flexible pipeline tied into a manifold during pressurization. Due to high manifold hub loads during pressurization it is essential that such a model is capable of capturing all effects during pressurization to achieve an acceptable confidence level of the system integrity. It is also described how the FE model is used for upheaval buckling design, capturing non-linearities and load history effects that can reduce the conservatism in the design.

Identification of Bearing Coefficients of Flexible Rotor-Bearing Systems

2000 ◽  
Author(s):  
Tachung Yang ◽  
Wei-Ching Chaung
Keyword(s):  
Industrial Applications ◽  
Operating Conditions ◽  
Least Square ◽  
Flexible Rotor ◽  
Fem Modeling ◽  
Identification Method ◽  
Reaction Forces ◽  
Manufacturing Assembly ◽  
Stiffness And Damping

The accuracy of stiffness and damping coefficients of bearings is critical for the rotordynamic analysis of rotating machinery. However, the influence of bearings depends on the design, manufacturing, assembly, and operating conditions of the bearings. Uncertainties occur quite often in manufacturing and assembly, which causes the inaccuracy of bearing predictions. An accurate and reliable in-situ identification method for the bearing coefficients is valuable to both analyses and industrial applications. The identification method developed in this research used the receptance matrices of flexible shafts from FEM modeling and the unbalance forces of trial masses to derive the displacements and reaction forces at bearing locations. Eight bearing coefficients are identified through a Total Least Square (TLS) procedure, which can handle noise effectively. A special feature of this method is that it can identify bearing coefficients at a specific operating speed, which make it suitable for the measurement of speed-dependent bearings, like hydrodynamic bearings. Numerical validation of this method is presented. The configurations of unbalance mass arrangements are discussed.

Dynamic Responses Analysis of Permeable Breakwater Subjected to Random Waves

2014 ◽  
Vol 1061-1062 ◽  
pp. 809-812
Author(s):  
Hu Ping
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Dynamic Responses ◽  
Exceedance Probability ◽  
Random Waves ◽  
The Finite Element Method ◽  
Wave Load ◽  
Power Spectral ◽  
Density Analysis ◽  
Element Method

In this paper, based on the finite element method and ANSYS software, the dynamic responses of permeable breakwater under wave load response is analyzed and studied. Taking the method of combining modal analysis and power spectrum analysis research on dynamic response of breakwater in the frequency domain and the principal stress and displacement distribution of the structure in the exceedance probability of 0.7%. The results prove that the finite element method of power spectral density analysis can provide effective guidance for the actual engineering.

New Step to Improve the Accuracy of Blade Synchronous Vibration Parameters Identification Based on Combination of GARIV and LM Algorithm

2017 ◽  
Author(s):  
Weimin Wang ◽  
Sanqun Ren ◽  
Shan Huang ◽  
Qihang Li ◽  
Kang Chen
Keyword(s):  
Experimental Study ◽  
Parameters Identification ◽  
Least Square ◽  
Experimental Result ◽  
Blade Vibration ◽  
Vibration Displacement ◽  
Campbell Diagram ◽  
Identification Method ◽  
Blade Tip ◽  
Vibration Parameters

Generally, turbine blade vibration can be divided into asynchronous vibration and synchronous vibration. Comparing to parameters identification of asynchronous vibration, that of the synchronous vibration is more difficult and needs more sensors. The applicability of the synchronous identification method is more stringent than that of asynchronous identification method. A new method is presented to identify the blade synchronous vibration parameters based on the blade tip-timing (BTT) method and previous achievements in this region. Here, the parameters, such as the frequency of harmonic resonance center, blade vibration amplitude and the initial phase, are obtained by the nonlinear least square fitting algorithm based on relationships between the rotation speed and the blade tip displacement. We call this way as sweep frequency fitting (SFF) method. As the blade is operated at a constant speed that is near the frequency of resonance center, the blade vibration displacement can be obtained by the sensors at different positions, so the blade synchronous vibration Engine Order (EO) can be obtained by the global autoregressive with instrumental variables (GARIV) method. Furthermore the Campbell diagram of blade synchronous vibration can be plotted by the parameters obtained by GARIV method and SFF method. In the experimental study, the parameter identification of blade synchronous vibration is completed and the Campbell diagram of blade vibration is accurately plotted under the excitation of six magnets. Meanwhile, the experimental study and analysis on the harmonic vibration of blade with different numbers of excitation are carried out. The relative deviation of the dynamic frequency of blade between the experimental result and simulation result is less than 1%.

scholarly journals Assessment of Physician's Knowledge of Potential Drug-Drug Interactions: An Online Survey in China

2021 ◽  
Vol 8 ◽  
Author(s):  
Jing Yuan ◽  
Chunying Shen ◽  
Chengnan Wang ◽  
Gang Shen ◽  
Bing Han
Keyword(s):  
Drug Interactions ◽  
Online Survey ◽  
Mobile Apps ◽  
Least Square ◽  
Common Source ◽  
Potential Drug ◽  
Cross Sectional Survey ◽  
Online Questionnaire ◽  
Cross Sectional ◽  
Source Of Information

Background: Drug interactions are the most common preventable cause of adverse drug reaction, which may result in drug toxicity or undesired therapeutic effect with harmful outcomes to patients. Given the rising use of combination therapies, the main objectives of this study were to estimate the degree to which physicians can identify potential drug-drug interactions (PDDIs) correctly and to describe the common source of information used by physicians when they need to check PDDIs.Methods: A cross-sectional survey utilizing a self-administered online questionnaire was conducted among physicians in China. Participants were asked to classify 20 drug pairs as “no interaction,” “may be used together with monitoring,” “contraindication,” and “not sure.” We also collected data on the physician's source of information and altitude toward the PDDIs. An ordinary least square regression model was performed to investigate the potential predictors of PDDI knowledge.Results: Eligible questionnaires were obtained from 618 physicians. The respondents classified correctly 6.7 out of 20 drug pairs, or 33.4% of the drug interactions investigated. The number of drug pairs recognized by respondents was ranged from 0 to 16. The percentage of physicians who recognized specific drug pairs ranged from 8.3% for no interactions between conjugated estrogens and raloxifene, to 64.0% for the interaction between dopamine and phenytoin. When the respondents want to check PDDI information, the most commonly used source of information was package inserts (n = 572, 92.6%), followed by the Internet or mobile Apps (n = 424, 68.6%), consultation with clinical pharmacists (n = 384, 62.1%), medical textbooks (n = 374, 60.5%), knowledge base in Chinese (n = 283, 45.8%), and other physicians (n = 366, 59.2%). In the multiple regression analysis, the significant predictors of a higher number of recognized drug pairs were years of practice and altitudes toward PDDIs.Conclusion: In this online survey accessing physician's ability to detect PDDIs, less than half of the drug pairs were recognized, indicating unsatisfactory level of knowledge about the clinically significant drug interactions. Continuing education and accessible electronic database can help physicians detecting PDDIs and improve drug safety.

Galloping response of sector-shape iced eight bundle conductors

2020 ◽  
Vol 47 (10) ◽  
pp. 1201-1213
Author(s):  
Meng-qi Cai ◽  
Lin-shu Zhou ◽  
Qian Xu ◽  
Xiao-hui Yang ◽  
Xiao-hui Liu
Keyword(s):  
Transmission Lines ◽  
Theoretical Basis ◽  
Wind Tunnel Test ◽  
Dynamic Responses ◽  
Test Results ◽  
The Finite Element Method ◽  
Aerodynamic Coefficients ◽  
Aerodynamic Loads ◽  
Natural Modes ◽  
Wind Velocities

Wind tunnel test results of the aerodynamic coefficients of sector-shape iced eight bundle conductors varying with wind attack angles are presented. Then, by means of the user-defined cable elements, the aerodynamic loads are applied on the cable elements of each sub-conductor through the finite element method (FEM). In addition, the galloping responses of sector-shape iced eight bundle conductors are discussed. Finally, galloping responses, including dynamic responses (natural modes and frequencies), galloping orbits, and amplitudes of typical sector-shape iced eight bundle conductor transmission lines in the cases of different span lengths, wind velocities, and angles of wind attack are studied, respectively. These results provide useful references for a theoretical basis for the study of galloping and the technique of anti-galloping in cold regions.

Simultaneous Scatterer Shape Estimation and Partial Aperture Far-Field Pattern Denoising

2012 ◽  
Vol 11 (2) ◽  
pp. 271-284 ◽  
Author(s):  
Yaakov Olshansky ◽  
Eli Turkel
Keyword(s):  
Scattering Problem ◽  
Least Square ◽  
Field Pattern ◽  
Error Estimator ◽  
Far Field ◽  
The Finite Element Method ◽  
Shape Estimation ◽  
Ill Posed ◽  
Filtering Technique ◽  
Far Field Pattern

AbstractWe study the inverse problem of recovering the scatterer shape from the far-field pattern(FFP) in the presence of noise. Furthermore, only a discrete partial aperture is usually known. This problem is ill-posed and is frequently addressed using regularization. Instead, we propose to use a direct approach denoising the FFP using a filtering technique. The effectiveness of the technique is studied on a scatterer with the shape of the ellipse with a tower. The forward scattering problem is solved using the finite element method (FEM). The numerical FFP is additionally corrupted by Gaussian noise. The shape parameters are found based on a least-square error estimator. If ũ∞ is a perturbation of the FFP then we attempt to find Γ, the scatterer shape, which minimizes ∣∣ũ∞ − ũ∞∣∣ using the conjugate gradient method for the denoised FFP

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