Vibration Properties Of Structure Research Articles

General Methodology to Investigate the Effect of Process Parameters on the Vibration Properties of Structures Produced by Additive Manufacturing Using Fused Filament Fabrication

General Methodology to Investigate the Effect of Process Parameters on the Vibration Properties of Structures Produced by Additive Manufacturing Using Fused Filament Fabrication

Damage detection under temperature conditions using PCA – an application to the Z24 Bridge

Vibration properties of civil structures, which are commonly analysed for damage detection, are affected by changing environmental and operational conditions, and most notably are subjected to bilinear effects from changing ambient temperature conditions. Therefore, damage detection in structures during the past decade has focused on eliminating the effects of these changing environments that affect the vibration properties of the structures. Several methods have been proposed in the literature to tackle the non-linear effects from changing environments. However, these methods can only analyse systems (e.g. natural frequency–environmental and operational system) that have an incremental change in relationship; they cannot model the bilinear effects from the changing temperature conditions, which may lead to false alerts. Hence, a damage detection method is proposed in this paper to tackle the piecewise effects from changing temperature conditions. The method makes use of a Gaussian mixture model to separate the different effects acting on the structures and uses principal component analysis for data processing. The method is applied to the Z24 Bridge, in Switzerland, which was subjected to bilinear effects from changing temperature conditions. The results obtained demonstrate that the proposed method successfully takes into account the piecewise effects to indicate the presence of damage.

A regression-based damage detection method for structures subjected to changing environmental and operational conditions

Damage detection of civil engineering structures during the past decade has focused on eliminating the effects of the changing environmental and operational conditions, from the effects of damage. In the literature, a regression analysis has been adopted to construct a model between the vibration properties of structures, and the environmental and operational parameters to represent the undamaged state of the structures, for damage detection. However, using the environmental and operational parameters in the analysis has several limitations. For example, these parameters are not always available which may affect the performances of the damage detection methods. Regression between the vibration properties only has also been proposed in the literature where multivariate statistical tools have been adopted to extract the relationships among the properties. However, these methods have the problem that it is more difficult to detect damage in the multivariate situations and a regression target is usually needed, which is difficult to determine. Therefore, a damage detection method which uses the simple regression analysis, is developed in this paper. The vibration properties of structures are used as both the independent and dependent variables in the developed method. This has the advantages that the environmental and operational conditions are not needed and the multivariate statistical tools are not required for data processing. The developed method is applied to a beam structure model and the Z24 Bridge, in Switzerland, and the results obtained demonstrate that the method can successfully classify between undamaged and damaged states. The traditional regression analysis method is also applied to the two structures and it was found that better results are obtained using the method developed in this paper.

Sparse Bayesian learning for structural damage detection under varying temperature conditions

Structural damage detection inevitably entails uncertainties, such as measurement noise and modelling errors. The existence of uncertainties may cause incorrect damage detection results. In addition, varying environmental conditions, especially temperature, may have a more significant effect on structural responses than structural damage does. Neglecting the temperature effects may make reliable damage detection difficult. In this study, a new vibration based damage detection technique that simultaneously considers the uncertainties and varying temperature conditions is developed in the sparse Bayesian learning framework. The structural vibration properties are treated as the function of both the damage parameter and varying temperature. The temperature effects on the vibration properties are incorporated into the Bayesian model updating on the basis of the quantitative relation between temperature and natural frequencies. The structural damage parameter and associated hyper-parameters are then solved through the iterative expectation–maximization technique. An experimental frame is utilized to demonstrate the effectiveness of the proposed damage detection method. The sparse damage is located and quantified correctly by considering the varying temperature conditions.

Orange photoluminescence emission and multi-photon Raman scattering from microscale Zn2SnO4 tetrapods

Zinc stannate (Zn2SnO4) and zinc oxide (ZnO) tetrapods were synthesized in air atmosphere through a one-step, high-temperature, gas-solid process. Analysis of the samples’ morphological and structural vibration properties were performed via scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. Raman spectra show that Zn2SnO4 tetrapods are mainly distributed in the vicinity of the source material. The optical properties of the samples were studied using a fluorescence spectrometer, which showed that Zn2SnO4 tetrapods had an asymmetric, broad emission in the wavelength range of 450–800 nm. The mechanism of the broad emission is discussed.

The Dynamic Analysis of Hydropower House and Unit System in Coupled Hydraulic-mechanical-electric Factors

A hydraulic-mechanical-electric and structures coupled model of hydropower station system including subsystem models of the penstock, hydro-turbine model, speed governor, synchronous generator as well as grid, rotor-bearing system and powerhouse structure is established. This model is used to simulate the small fluctuation transient process of 10% load-up in the part load condition for hydropower station. Mechanical eccentric force, unbalanced magnetic pull and vortex pressure fluctuation at inlet of draft tube are considered in the numerical calculation. The interaction between hydraulic-mechanical-electric coupled factors and structural vibration properties during the small fluctuation transient process is studied. The results indicate that the speed regulation for turbine has very litter impact on the transient process of generator. In the process of small fluctuation with loading method in this paper, structure of powerhouse is greatly influenced by vortex pressure pulse in the draft tube, and the vibration of unit is excited by loads which caused by itself rotating.

Ambient vibration tests of an arch dam with different reservoir water levels: experimental results and comparison with finite element modelling.

This paper deals with the ambient vibration tests performed in an arch dam in two different working conditions in order to assess the effect produced by two different reservoir water levels on the structural vibration properties. The study consists of an experimental part and a numerical part. The experimental tests were carried out in two different periods of the year, at the beginning of autumn (October 2012) and at the end of winter (March 2013), respectively. The measurements were performed using a fast technique based on asynchronous records of microtremor time-series. In-contact single-station measurements were done by means of one single high resolution triaxial tromometer and two low-frequency seismometers, placed in different points of the structure. The Standard Spectral Ratio method has been used to evaluate the natural frequencies of vibration of the structure. A 3D finite element model of the arch dam-reservoir-foundation system has been developed to verify analytically determined vibration properties, such as natural frequencies and mode shapes, and their changes linked to water level with the experimental results.

A study of variability and applicability of various signal processing techniques in structural system identification

The structural responses and vibration properties such as frequencies and mode shapes are directly related to the structural mass and stiffness. Changing structural conditions will affect the structural responses and vibration properties. Structural conditions can thus be identified through measurements of structural vibration. However, certain uncertainties associated with structure models, changing ambient environmental conditions, changing loading conditions, equipment noises and various signal processing techniques used in extracting structural vibration properties, etc. is inevitable. The influences of these uncertainties on structural vibration properties might be more significant than that of the structural damage, therefore, cause false identification or result in the true structural damage not identifiable. This paper studies the applicability and reliability of a few popularly used modal identification methods including time-domain, frequency-domain and time-frequency domain methods for civil structural system identification. The results indicate that on average a 2% to 3% error tends to be yielded by using different signal processing techniques for vibration frequencies identification when the signal is not heavily noise contaminated, which should be taken into account when estimating the damage detection results. The applicability of the time-frequency domain methods to the identification of time-varying system either with sudden change or continuous variance is also discussed.

A Study of Variability and Applicability of Various Signal Processing Techniques in Structural System Identification

The structural responses and vibration properties such as frequencies and mode shapes are directly related to the structural mass and stiffness. Changing structural conditions will affect the structural responses and vibration properties. Structural conditions can thus be identified through measurements of structural vibration. However, certain uncertainties associated with structure models, changing ambient environmental conditions, changing loading conditions, equipment noises and various signal processing techniques used in extracting structural vibration properties, etc. is inevitable. The influences of these uncertainties on structural vibration properties might be more significant than that of the structural damage, therefore, cause false identification or result in the true structural damage not identifiable. This paper studies the applicability and reliability of a few popularly used modal identification methods including time-domain, frequency-domain and time-frequency domain methods for civil structural system identification. The results indicate that on average a 2% to 3% error tends to be yielded by using different signal processing techniques for vibration frequencies identification when the signal is not heavily noise contaminated, which should be taken into account when estimating the damage detection results. The applicability of the time-frequency domain methods to the identification of time-varying system either with sudden change or continuous variance is also discussed.

Damage Identification of Steel Beams Using Local and Global Methods

Structural condition monitoring methods can be generally classified as local and global. While the global method needs only a small number of sensors to measure the low-frequency structural vibration properties, the acquired information is often not sufficiently sensitive to minor damages in a structure. Local methods, on the other hand, could be very sensitive to minor damages but their detection range is usually small. To overcome the drawbacks and take advantage of both methods, an integrated condition monitoring system has been recently developed for structural damage detection, which combines guided wave and structural vibration tests. This study aims at finding a viable damage identification method for steel structures by using this system. First, a spectral element modelling method is developed, which can simulate both wave propagation and structural vibration properties. Then the model is used in updating analysis to identify crack damage. Extensive numerical simulations and model updating works are conducted. The experimental and numerical results suggest that simply combining the objective functions cannot provide better structural damage identification. A two-stage damage identification scheme is more suitable for identifying damage in steel beams.

Seismic Response Analysis of High-Speed Railway Bridge Fabricated Round-Ended Piers

The responses of high-speed railway bridge subjected to seismic load were investigated by numerical simulation, the whole finite element model of the multi-span bridge simply supported bridge was set up, and natural vibration properties of structure were analyzed. According to theory of elasticity and elastic-plasticity, parametric study was conducted to assess the influences of different speeds, strong motion record, pier height and earthquake acceleration on the seismic capability of high-speed bridge subjected to different strength of the earthquake, the finite element soft ware and moment-curvature program were employed to calculate the earthquake responses of bridge. The calculation results show that, with the increase of train speed, pier height and earthquake intensity, the earthquake responses of bridge are increase in general, and the bottom of piers step into states of elastic-plasticity under high-level earthquake, elastic-plastic deformation is larger, the stirrup encryption measures should be carried out.

Substructuring Technique for Damage Detection Using Statistical Multi-Stage Artificial Neural Network

Artificial Neural networks (ANN) have been proven in many studies to be able to efficiently detect damage from vibration measurements. Their capability to recognize patterns and to handle non-linear and non-unique problems provides an advantage over traditional mathematical methods in correlating the vibration data to damage location and severity. However, one shortcoming of ANN is they require enormous computational effort and sometimes prohibitive time and computer memory for training a reliable ANN model, especially when structures with many degrees of freedom are involved. Therefore, in most cases, rather large elements are used in the structure model to reduce the degrees of freedom. This results in the structural vibration properties not being sensitive to small damage in a large element. As a result, direct application of ANN to detecting damage in a large civil engineering structures is not feasible. In this study, a multi-stage ANN incorporating a probability method is proposed to tackle this problem. Through this method, a structure is divided into several substructures, and each substructure is assessed independently. In each subsequent stage, only the damaged substructures are analyzed, and eventually the location and severity of small structural damage can be detected. This approach greatly reduces the computational time and the required computer memory. Moreover, a probabilistic method is also used to include the uncertainties in vibration frequencies and mode shapes in damage detection analysis. It is found that this method reduces the uncertainty effect in frequencies due to duplication error in the multi-stage ANN model and reduces the uncertainty effect in mode shapes due to the damage in other substructures. The developed approach is applied to detect damage in numerically simulated and laboratory tested concrete slab. The results demonstrate that the proposed method can detect small damage with a higher level of confidence, and the undamaged elements are less likely to be falsely detected.

360369 A SIMPLE IDENTIFICATION METHOD FOR MEMBER VIBRATION PROPERTIES OF RAILWAY VIADUCTS(Condition Monitoring,Technical Session)

For train speed-up, resonance response of structures and these environmental performance of it such as ground vibration and noise are critical issues from the viewpoints of safety and serviceability, respectively. To adequately tackle these issues, the vibration properties of structures must be thoroughly understood on an each member. In this study, we estimated the vibration mode shape and the natural frequency of RC rigid frame railway viaducts based on results of simultaneous multipoint measurement and proposed an estimation method for member vibration.

Continuous and Damped Vibration Detection Based on Fiber Diversity Detection Sensor by Rayleigh Backscattering

An optical fiber vibration sensor based on a polarization diversity scheme has been developed to study structural vibration properties under external disturbance. The polarization diversity scheme has improved signal-to-noise ratio (SNR) by over 13 dB with capability of detection frequency of sub-hertz to tens of kilo- hertz. The minimum dynamic strain we have detected is 3 nepsiv, and the SNR of the sensor is >37 dB without any averaging. For the first time, Rayleigh backscattering has been utilized to detect continuous and damped vibration generated by a piezo fiber stretcher and vibrating cantilever with a frequency range of sub-hertz to 16 kHz. We also use this sensor and polarization analyzer to characterize the polarization state change and phase shift of the piezo fiber stretcher in transmission and Rayleigh backscattering up to kilohertz frequency, both results agrees quantitatively.

Long term vibration monitoring of an RC slab: Temperature and humidity effect

Changes in environmental conditions such as temperature and humidity affect structural vibration properties. Other researchers have reported that modal frequencies varied significantly in a single day due to temperature change. Therefore, it is necessary to discriminate the variation of modal properties due to environmental change from those caused by structural damage, and quantify the environmental effect in vibration-based structural health monitoring and damage identification. Environmental conditions affect structural vibration properties in a complicated manner; this paper only investigates the variation of frequencies, mode shapes and damping with respect to temperature and humidity changes. A reinforced concrete slab, which was constructed and placed outside the laboratory, has been periodically vibration tested for nearly two years. This paper reports results obtained over that time for the first four modes. It is found that the frequencies have a strong negative correlation with temperature and humidity, damping ratios have a positive correlation, but no clear correlation of mode shapes with temperature and humidity change can be observed. Linear regression models between modal properties and environmental factors are built. A quantification analysis shows that variation of the elastic modulus of the material is the primary cause of the variation of modal properties.

Vibration Properties of Structural FRP Composites.

Being considerably stiffer, lighter and more damped than metals, fibre reinforced plastic composites are increasingly replacing metal alloys used traditionally in weight sensitive structural applications. However, the hybrid nature of FRP composites has a far more significant bearing on vibration properties of structures made from these materials than metals. Presented here is a review of some fundamental aspects of vibration damping in general, and of vibration properties of structural FRP composites in particular. Both experimental and analytical aspects of studying these properties are considered. This, it is hoped, will provide a reasonably broad appreciation of vibration characteristics of structural FRP composites, and of the work done to study these characteristics.

Simplified Analysis Method for Structural Vibration Properties of Asymmetric Rocket for Coupling between Yaw and Roll Vibration.

A simplified analysis method is proposed to obtain eigenfrequencies and modes for yaw-bending and roll-torsional structural vibration of an asymmetric configuration rocket. The author has already proposed a simplified analysis method for axial-pitch coupling vibration of an asymmetric configuration rocket. The present method can analyze the other coupling vibration, that is yaw-roll coupling vibration for an asymmetric configuration rocket by asymmetric beam elements. The purpose of this simplified analysis method using a FORTRAN 77 program is also to prepare an analysis tool for studying on yaw-roll coupling effects in the preliminary design phase and a rough-check tool of detailed analysis. This program can generate yaw-roll coupling stiffness and mass matrices by the offset asymmetric beam element with linearly changing sectional properties using the Timoshenko-type beam theory. A sample structural vibration analysis of a hypothetical rocket with an asymmetric configuration demonstrates the capability of this simplified method. The results obtained agree well with those obtained by MSC/NASTRAN analysis, and this proposed method enables great simplification of model preparation. Based on these findings, the proposed method is judged to be an efficient structural vibration analysis tool of an asymmetric rocket.

Simplified Analysis Method for Structural Vibration Properties of Asymmetric Rocket.

A simplified analytical method is proposed to obtain eigenfrequencies and modes of an asymmetric configuration rocket. The present method is an extension of the symmetric beam element matrix method and can utilize asymmetric beam elements. The purpose of this simplified analysis method using a FORTRAN 77 program is to prepare an analysis tool in the preliminary design phase and a rough-check tool of detailed analysis. This program has three functions: (1) to generate stiffness and mass matrices for the asymmetric beam element with linearly changing sectional properties using the Timoshenko-type beam theory, (2) to calculate the dynamical matrix from which rigid body degrees of freedom are eliminated, and (3) to calculate eigenvalues and eigenvectors. A sample structural vibration analysis of a hypothetical rocket with an asymmetric configuration is conducted to demonstrate the capability of this simplified method. The results obtained agree well with those obtained by MSC/NASTRAN analysis, and this proposed method enables great simplification of model preparation. Based on these findings, the proposed method is judged to be an efficient structural vibration analysis tool of an asymmetric rocket.

2036 せん断,曲げ,回転慣性を考慮した場合の構造物の振動特性(構造)

2036 せん断,曲げ,回転慣性を考慮した場合の構造物の振動特性(構造)