Robust change detection method with application in vibration structures monitoring

The current study considers piezoelectric ceramic electromechanical transducers utilizing axisymmetric vibrations of complete and incomplete spherical shells. Analysis is focused on generating the modes of vibration that can be employed in the design of multimode unidirectional electroacoustic transducers for underwater applications and on determining the electrode configurations that achieve optimal electromechanical coupling for the different modes of vibration considered. Analytical expressions are presented for the modal and intermodal equivalent parameters characterizing the energy state of the shell vibration. Results of calculation and experimental verification of the resonance frequencies and effective coupling coefficients for different modes of vibration of the complete and incomplete spherical shells are in good agreement.

Design of dynamic absorbers to control the flexural resonant vibration of structures characterized by multiple natural modes

Fault Detection of Dynamical Systems with Nonstationary Inputs

Modal analysis for implant stability assessment: Sensitivity of this methodology for different implant designs

The paper investigates the influence of dynamic characteristics of building structures on the mechanisms of progressive collapse development. It is shown that natural frequencies, mode shapes, and damping levels significantly affect the propagation pattern of collapse following the initial failure of one or more load-bearing elements. Based on the obtained results, vulnerability assessment criteria are formulated that take into account the dynamic properties of structures. Purpose of the article. The purpose of this study is to establish the relationship between the dynamic characteristics of a structural system and the mechanisms of progressive collapse development. Special attention is given to the effect of natural frequencies, vibration modes, and damping level on the likelihood of structural excitation leading to instability or further collapse. Based on a numerical analysis of a steel-framed building, a direct relationship is demonstrated between local damage and the redistribution of stiffness in the structural system. The analysis of changes in dynamic characteristics makes it possible to identify potentially vulnerable zones with reduced resistance to progressive collapse. To assess collapse vulnerability, it is advisable to determine the first 3–5 natural frequencies and corresponding mode shapes, as well as damping properties. A significant reduction in stiffness leads to the localization of vibrations, increased amplitudes, and potential energy accumulation. If the system is unable to dissipate vibrations due to insufficient damping, cascading failure may occur. Critical warning signs include a frequency decrease of more than 30 %, an increase in deformation amplitude by over 50 %, the emergence of localized vibration modes, and a reduction in damping. Clarifications are proposed to the conditions of the energy-based approach for evaluating the propagation of progressive collapse, taking into account dynamic characteristics and the localization of deformations within vibration modes (i. e., structural vulnerability). The criteria for determining the dynamic coefficient are refined to consider the frequency spectrum and damping. Design tasks are formulated based on dynamic analysis to enhance resistance to progressive collapse. Conclusions. The use of dynamic coefficients (impact factors) recommended by building codes is justified but insufficient without considering the individual properties of the specific structure. The analysis of structural vibration modes can reveal potential weak spots where deformations and stresses are expected to be the highest. This is crucial for predicting the mechanisms of progressive collapse propagation. The results of this research can be applied in assessing the vulnerability of existing buildings and in designing new structures resistant to progressive collapse in accordance with modern safety requirements.

Drillstring and down-hole tool failure usually results from failing to control one or more of the vibration mechanisms. The solution starts with the ability to measure different modes of vibration, hence identifying different vibration mechanisms. Lateral, torsion and axial are vibration modes that take place when drill pipes run into problems downhole. Due to the three modes of vibration mechanisms such as bit bounce, stick-slip, lateral shocks, bit and bottom hole assembly (BHA) whirl, parametric and torsional resonance occur. Understanding the causes of the destructive loads is the main step towards developing approaches to prevent or reduce their effects, hence improving drilling performance. Vibration modes and mechanisms lead to failure of the drill pipes, BHA and drill bits. Drill pipes fatigue failure is very common due to capability of producing all vibration modes and mechanisms. Drill pipe and downhole tool assembly failure usually result from failing to have power over one or more of these vibration mechanisms. A novel in house experimental setup has been developed to mimic downhole axial, lateral and torsional vibration modes and mechanisms in drilling operations. In this paper, we focus on the design and construction of the testing facility. A number of tests were conducted to validate the capability and performance of the test setup. Drill pipe fatigue failure due to lateral cyclic stresses induced in the drill pipe has also been investigated and presented in this paper. The results show that operating on a rotation speed higher than 90% of the drillstring critical speed leads to yielding in the drillstring.

It should be possible to deduce the necessary acoustical information concerning the bounding surfaces of a room from steady-state measurements of the transmission between a source and a receiver appropriately placed in the room. This problem is being studied by using a small model chamber yielding discrete normal modes of vibration in the range from 200 to 1500 cycles. A small sound source having substantially constant output over this frequency range was developed and comprises a multiple capillary formed by packing a brass tube with parallel round wires, the sound from a dynamic receiver passing down the canals between the wires. Resonant pressure peaks in the chamber corresponding to the first fifty normal modes of vibration have been observed and identified. Analysis and experiment indicate that the total absorption in the chamber for a given mode of vibration can be measured by observing the width of the resonance curve at the half-intensity height. By selection of different modes of vibration, absorption coefficients are obtained as functions of both frequency and angle of incidence, the latter including grazing incidence. The decay rates predicted by these measurements have been checked experimentally. Plans will be discussed for the extension of these results to large scale rooms by an appropriate statistical analysis.

The χT parameter, a simplified method recently presented, allows to estimate the global second-order effects on reinforced concrete frames using the natural period of vibration. This parameter was developed based on the fact that both natural period of vibration and global second-order effects depend essentially on the stiffness and mass matrices of the structure, being thus related. In this paper, numerical analyses are conducted on nine models with different patterns of irregularity in terms of geometry in plan and stiffness. The main purpose of these analyses is to evaluate the applicability of the χT parameter in asymmetric structures as well as that can present torsional modes as the fundamental mode of vibration. In addition, different hypotheses are tested in order to verify the influence of the different modes of vibration in the structural sensitivity to global second-order effects. Results of the simplified analyses were compared to the final bending moment values obtained through a nonlinear numerical analysis considering the P-Δ effect. It is observed that the parameter χT is a promising indicator for a simplified estimation of the global second-order effects for concrete frames, especially when higher modes of vibration are taken account in the analysis.

This article presents a probabilistic model based on a bipartite convolutional architecture for unsupervised change detection. We aim to develop a robust change detection method that can adapt to different types of data and scenarios for multitemporal coregistered remote sensing images of the same spatial resolution. On the premise of coregistration, unsupervised change detection usually suffers from the distinct appearances (different intensities or data structures) of the same object in multitemporal images, such as images obtained in different climatic conditions (season, illumination, and so on), and by different and even heterogeneous sensors. Since change detection in heterogeneous images can also adapt to other scenarios, many methods have been proposed recently focusing on such data, but most of them are limited by the need for labeled data or by specific assumptions. With the excellent and flexible feature learning capability of neural networks, we model the change detection into a Gibbs probabilistic model based on a bipartite neural network. The model is driven by an energy function defined as the squared feature distance, which is the core of change detection. Via optimizing the model, the difference degree of each pixel is automatically obtained for further identification. The probabilistic model learns to capture the distribution in an unsupervised way. Therefore, the proposed method can adapt to various scenarios without being trained by labeled data. Experiments on different types of data and scenarios demonstrate the superiority of the proposed method.

The contribution is aimed at phenomenological modelling and analysis of fundamental properties of non-synchronous vibrations in chosen coupled structures. A van der Pol reduced-order model is employed to simulate the aero-elastic interaction between flexible bodies and fluid. Non-synchronous vibration and frequency lock-in, along with hysteresis, are captured in the main resonance area. Moreover, the model reveals subharmonic resonances accompanied by the existence of unstable solutions and frequency lock-in. The study is further extended to investigate the dynamical behaviour of a coupled cyclic structure, where different modes of vibration due to the aero-elastic interaction are analysed.

Analysis of cable-stayed bridges under multi-component random ground motion by response spectrum method

Segregation of granular materials by virtue of density or size is a commonly encountered phenomenon in nature. Despite its widespread interest among many researchers in recent years, a complete and unified understanding of granular segregation remains elusive to date. Using molecular dynamics simulations, we report a novel technique of inducing density segregation in a binary mixture of granular materials subjected to vibrations by the use of a bumpy vibrating base. Density segregation in the vertical directions may be induced by oscillating the bumpy base composed of discrete solid particles vertically or horizontally. In both cases, lighter particles tended to rise to the top of the granular bed and form a layer above the heavier particles. We suggest that differences in granular temperature profiles arising from the two different modes of vibrations may play an important role in determining the extent of density segregation occurring in binary granular mixtures. © 2010 American Institute of Chemical Engineers AIChE J, 2010

ABSTRACTSolid solution compositions of Sr2(NbxTa1−x)2O7 ceramics with Tr ranging from 450°C to 1342°C were fabricated utilizing a hot-forging technique to achieve preffered grain orientation and thus enhance poling. Translucent samples with greater than 99% theoretical density were obtained using this process. Depending on composition, the degree of orientation as determined by x-ray diffraction was found to be 75% to 95%. The thermal expansion, resistivity, and dielectric constant were shown to be very anisotropic. The direction perpendicular to the forging axis proved to be the ferroelectric “easy” direction, exhibiting hysteresis behavior. Piezoactivity in PLS polycrystals was measured for the first time. Hot-forged samples were electrically poled and the electromechanical properties determined using the five different modes of vibration. For Sr2(Nb0.5Ta0.5)2O7: N24=1504 Hz-m, s44=18.2×10-12m2/N, k24=3.0%, d24=2.6 pC/N, g24=6.3×10-3 Vm/N, and Qm=1100. This material was also shown to resist depoling when exposed to temperatures as high as 650°C.

In the present investigation, efforts have been made to find effect material on cantilever beam under vibration. Specimens were modelled and analysed using FEM package (Abacus). Analysis was done by setting maximum frequency value as 60 Hz. It was found that a cantilever beam attains different modes of vibration. For mode-I of vibration the value of ‘strain energy’ and ‘deflection of beam’ along the cantilever beam from fixed end towards free end were obtained and tabulated. Aluminium, Copper and Steel were selected as three different materials for analysis. Numerical data obtained from FEM analysis were further tabulated and plotted for further useful analysis. Using numerical techniques, polynomial equations were also developed so that intermediate data can be determined.

The recent escalade of the oil prices encourages the search and exploration of new oil fields. This represents a challenge to engineers, due to more difficult conditions of operation in harsh environments and deeper reservoirs. The offshore industry faces, in the edge of technology with new necessities and limiting conditions imposed by the environment, an increase in the cost of production. It is, therefore, of vital importance to have the equipments operating at the most optimized conditions in order to reduce these costs. VIV software developed in the frequency domain was successful in designing risers and pipelines using large safety factors and making conservative assumptions. These tools only predict single-mode vibrations. In this perspective, the present paper describes the results obtained from a new time-domain code developed to assess the vortex-induced vibrations of a long flexible cylinder. A time-domain analysis was chosen because this suits the problem well, since it is able to predict and calculate different modes of vibrations. In the model, a cylinder is divided into elements that can be exposed to an arbitrary current profile. Each of these elements is free to oscillate parallel and transversely to the flow, and is coupled to a pair of van der Pol’s wake oscillators. This simulates the vortex shedding and, therefore, the fluctuating nature of drag and lift coefficient during the occurrence of VIV. The governing equations are solved by 4th-Order Runge-Kutta schemes in time domain. The new time-domain model is compared with small scale model test data from benchmarking.