Principal Modes Of Vibration Research Articles

Machine learning-based prediction of statically equivalent seismic forces in pin-supported cylindrical reticulated shells

Reticulated shells exhibit complex vibrations during earthquakes, encompassing components in horizontal and vertical directions, and multiple vibration modes occur. In particular, single-layer reticulated shells with a small depth relative to their span exhibit many vibration modes, and the shapes of these modes can vary depending on the geometry. The method for rapidly setting equivalent static seismic forces remains unexplored. In response to the above background, this study proposes a novel approach for calculating the seismic forces on single-layer reticulated shells using machine learning techniques. The shells in focus are pin-supported cylindrical reticulated shells, typically for the roofs of gymnasiums used as evacuation facilities during severe earthquakes in Japan. Machine learning uses numerical analysis results for approximately 20,000 shells, with varied spans, half-open angles, and aspect ratios. A method for preprocessing the principal vibration modes as image data is proposed, after which the imaged vibration modes are predicted from the shape parameters of the shell using a neural network. The prediction accuracy is analyzed, and a method for rapidly calculating seismic loads based on combining predicted vibration modes is proposed. These seismic loads are compared with the response spectrum method results, and their effectiveness is discussed.

Experiments on flow-induced vibration of four flexible cylinders with large aspect ratio in a square configuration

A system consisting of four cylinders positioned in the quadrilateral arrangement represents the prevalent and fundamental constituent within pipe bundles and tube banks in numerous engineering scenarios. This research presents a laboratorial study on flow-induced vibration (FIV) exhibited by four flexible cylinders positioned within a square geometric arrangement. The uniform flows were produced by a carriage on the top of a towing tank. Considering flow velocities and structural parameters, Reynolds number could reach 16000. The spacing between the cylindrical centres was selected as 6.0 D (D denotes the outer diameter of cylinders), and two typical incidence angles 0° and 45° were examined. For each flexible cylinder model, strain gages at seven distinct measuring positions were utilized to collect the oscillation data in cross-flow (CF) and in-line (IL) directions. Principal vibration modes, response frequencies, response amplitudes and motion trajectories were presented to understand the FIV features. For incidence angles 0°, considering the four flexible cylinders as two sets of tandem cylinders arranged in parallel is not appropriate due to the proximate effect. The behaviours of the two upstream cylinders resembles those of the pair of cylinders positioned in a side-by-side configuration, whereas behaviours for the downstream cylinders are influenced by wake interference generated from leading cylinders. IL response frequencies decrease to the values close to the CF response frequencies, resulting in the elliptical-shaped motion trajectories with large IL displacements. For incidence angles 45°, the upstream cylinder displays characteristics akin to those of a solitary cylinder experiencing vortex-induced vibration (VIV). Reactions for the central pair of cylinders result from the amalgamation of VIV and wake-induced flutter. While, reactions observed for downstream cylinder are characterized by low frequencies, significant IL displacements and more chaotic trajectories.

The process correlation interaction construction of Digital Twin for dynamic characteristics of machine tool structures with multi-dimensional variables

Digital Twin (DT) has become the foundation for intelligent manufacturing as a breakthrough application technology framework and can solve complex vibration problems in the machining process. However, this technology is mainly aimed at application development in a specific domain or a particular factor. The process correlation and interaction characteristics of the system have not been reflected, thus making it challenging to capture the dynamic characteristics of the machining process. This paper presents a system-oriented DT framework with process correlation interaction mechanism that integrates multiple models for dynamic process modeling. The data model is constructed as the core driving model of DT. Based on structural dynamics theory, the weak machine components are taken as digital threads of the data model to correlate position variables and cutting excitation variables. Then, the Frequency Response Function (FRF) corresponding to the principal mode of vibration at the weak machine component is used as an intermediate data for overall online process performance characterization and DT model interaction to enable mirror synchronization of the operation process. The results show that the presented DT can provide multifunctional applications such as cutting parameters optimization, process correlated variables visualization, and machining stability assessment.

Synthesis and Characterization of Nickel-Iron Bimetallic Oxide Nanoparticles via Microwave Irradiation

Bimetallic oxide nanoparticles is of great interest because of the increased potential application for which they can be applied, mainly in industrial catalytic applications owing to the synergic mechanism of two metallic elements within a nano system. Present study investigates an efficient synthesis of Ni-Fe bimetallic oxide nanoparticles in ethylene glycol using microwave irradiation technique. Nickel and iron oxide nanoparticles were synthesized separately using microwave assisted polyol synthesis method. This are then combined together in ratio 1:1 molar and is treated under microwave radiation to get Ni-Fe bimetallic oxide .The product was calcined in a muffle furnace for three different temperatures viz., 500oC, 700 oC and 900 oC. The structure and composition of nanoparticles were characterized by UV-Visible Spectroscopy, FT-IR Spectroscopy, X-Ray Diffraction (XRD), Energy-dispersive X-ray Spectroscopy (EDS) and Transmission Electron Microscopy (TEM). From the FT-IR measurements ascertains the principal vibrational modes such as Ni-O, Fe-O-Fe, Ni-Fe stretching bands and from XRD measurements grain size of the nanoparticles are determined. The empirical formula of the nanoparticle is found as Ni1Fe1.6O2.9 at 500◦C, Ni1Fe1.5O2.6 at 700◦C and Ni1Fe2O2.7 at 900◦C. Antibacterial and antifungal activity studies reveals that the nanoparticles show no appreciable biological activity.

Hyperspectral Chemical Imaging of Single Bacterial Cell Structure by Raman Spectroscopy and Machine Learning

In this work, biomolecules, such as membrane proteins, lipids, and DNA, were identified and their spatial distribution was mapped within a single Escherichia coli cell by Raman hyperspectral imaging. Raman spectroscopy allows direct, nondestructive, rapid, and cost-effective analysis of biological samples, minimizing the sample preparation and without the need of chemical label or immunological staining. Firstly, a comparison between an air-dried and a freeze-dried cell was made, and the principal vibrational modes associated to the membrane and nucleic acids were identified by the bacterium’s Raman chemical fingerprint. Then, analyzing the Raman hyperspectral images by multivariate statistical analysis, the bacterium biological status was investigated at a subcellular level. Principal components analysis (PCA) was applied for dimensionality reduction of the spectral data, then spectral unmixing was performed by multivariate curve resolution–alternating least squares (MCR-ALS). Thanks to multivariate data analysis, the DNA segregation and the Z-ring formation of a replicating bacterial cell were detected at a sub-micrometer level, opening the way to real-time molecular analysis that could be easily applied on in vivo or ex vivo biological samples, avoiding long preparation and analysis process.

Calcination process and kinetic carbonation effect on the hydrated and anhydrate phases of the OPC matrix at early age of hydration

ABSTRACT This study aims to improve the understanding of the effect of both calcination temperature and the carbonation process on cement pastes by analyzing the Fourier-transform infrared spectroscopy (FTIR) principal vibration modes. In this regard, six samples of cement pastes, identified as (CS1, CS2, CS3, CS4, CS5 and CS6), mixed with white sugar with different concentrations (X = 0, 0.2, 0.4, 0.6, 0.8, and 1.1 %), respectively, were prepared. These blended cement samples were heated (calcined) at a temperature of about 600°C. Moreover, an additional sugar-free sample tagged as CS0 was prepared and cured at room temperature for 7 days. Afterward, these samples were subjected to FTIR spectroscopy and X-ray diffraction to investigate the effect of the calcination and the carbonation process on the principal mode of vibrations and the microstructure of the ordinary Portland cement (OPC) matrix as well. The characteristics of the FTIR principal modes of vibrations were investigated. Besides, the relaxation time and the rotational energy barrier were calculated for different sugar concentrations. This study revealed that the kinetic reaction of the carbon contained in the different samples with the C3S, C2S, C–S–H and CH phases leads to the formation of calcium carbonate CaCO3, where the rate of formation depends upon the carbonation rate of samples. The critical variation for the relaxation time and rotational energy barrier clearly appeared at X = 0.6%. Moreover, the kinetic carbonation of both clinker phases and the hydrated phases in the OPC matrix system mainly depends upon the rate of the polymerization of the silicate group inside the matrix of OPC.

Characterization and suppression of cutting vibration under the coupling effect of varied cutting excitations and position-dependent dynamics

Vibration characteristics of cutting vary with the change of the cutting excitation and the change of structure dynamics. To analysis and reduce the vibration, this paper presents a method of identifying the principal mode of vibration to analysis the coupling effect of cutting excitation and position-dependent structure dynamics on cutting vibration. Next, the modal mass distributions corresponding to the principal modes at different positions are calculated to optimize the selection of machining position and reduce vibration. The method is verified through simulation and cutting tests. The vibration can be reduced through the optimally selected cutting position based on the proposed method.

Impact of genetically nonlinear application of external loads on the stress-strain state and on the principal vibration modes of reinforced concrete frame buildings on elastic subsoil

In this paper authors discuss the impact of genetically nonlinear application of external loads on the stress-stain state and on principal vibration modes of reinforced concrete frame structures on elastic foundation. The reader will find a methodology for integrated numerical and instrumental analysis. Six examples of linear and nonlinear FEA-models calculated in SCAD Office are given in comparison.

Generalization of soft phonon modes

Soft phonon modes describe a collective movement of atoms that transform a higher-symmetry crystal structure into a lower-symmetry crystal structure. Such structural transformations occur at finite temperatures, where the phonons (i.e., the low-temperature vibrational modes) and the static perfect crystal structures provide an incomplete picture of the dynamics. Here, principal vibrational modes (PVMs) are introduced as descriptors of the dynamics of a material system with $N$ atoms. The PVMs represent the independent collective movements of the atoms at a given temperature. Molecular dynamics (MD) simulations, here in the form of quantum MD using density functional theory calculations, provide both the data describing the atomic motion and the data used to construct the PVMs. The leading mode, ${\mathrm{PVM}}_{0}$, represents the $3N$-dimensional direction in which the system moves with greatest amplitude. For structural phase transitions, ${\mathrm{PVM}}_{0}$ serves as a generalization of soft phonon modes. At low temperatures, ${\mathrm{PVM}}_{0}$ reproduces the soft phonon mode in systems where one phonon dominates the phase transformation. In general, multiple phonon modes combine to describe a transformation, in which case ${\mathrm{PVM}}_{0}$ culls these phonon modes. Moreover, while soft phonon modes arise in the higher-symmetry crystal structure, ${\mathrm{PVM}}_{0}$ can be equally well calculated on either side of the structural phase transition. Two applications demonstrate these properties: first, transitions into and out of bcc titanium, and, second, the two crystal structures proposed for the $\ensuremath{\beta}$ phase of uranium, the higher-symmetry structure of which stabilizes with temperature.

Implementation of a Simplified Method in Design of Hysteretic Dampers for Isolated Highway Bridges

AbstractUsing seismic isolation systems for highway bridges modifies the structure’s principal vibration modes and effectively reduces the seismic base shear conveyed from the superstructure to the substructure. However, for some low-damping rubber isolation bearings, large displacements can be a problem. Supplemental hysteretic dampers can be introduced into the base-isolated bridge, which might nevertheless increase the structure base shear, and the merit of adding dampers has to be evaluated properly. In this paper, a simplified method was implemented for the design of a low-cost hysteretic damper, and the resulting isolator-damper system was tested experimentally. The design method used is based on an equivalent linearization approach. A full-scale elastomeric isolation bearing was characterized and used in the design of a hysteretic damper. Both the isolator and the damper went through cyclic testing and real-time dynamic substructuring (RTDS) methods to verify the capacity of the method to design ba...

A numerical study on the fatigue life design of concrete slabs for railway tracks

With the growing use of high-speed trains, non-ballasted tracks have become more popular compared to ballasted ones. However, the study on fatigue evaluation in concrete slabs under train load has been rather limited. This work presents a numerical study on the fatigue life design of concrete slabs for railway tracks. A finite element model for a three-slab track system is established for extracting the principal vibration modes and transient analysis under time-dependent loads. The fatigue evaluation procedure is first validated against full-scale experiments on slabs carried out in a three-point-bend load configuration under fatigue. Next, techniques in the context of digital signal processing, i.e., random phases combined with each constituent frequency amplitude to generate new load pulses, are employed to obtain the most unfavourable load scenario from numerous measured real-time train loads. A novel fatigue criterion which singles out the significance of stress amplitude (proper to concrete-like materials) is implemented to obtain the critical load direction. Fatigue damage under compression is evaluated under this most unfavourable load situation. Meanwhile, parametric analyses on material strength and slab geometry are carried out, recommendations for improved designs towards fatigue life are given accordingly. Even though the established procedure is demonstrated for fatigue under compression, damage evaluation based on the Model Code, extension to tension or mixed tension–compressive stress evaluations, as well as damage calculations with alternative criterions can be easily implemented.

FTIR Studies of Silicon Carbide 1D-Nanostructures

Stable 1D silicon carbide nanostructures (nanowires) have been obtained via combustion synthesis route. Infrared absorption and reflection spectra for as-obtained and purified SiC nanowires were compared with the spectra of commercially available SiC nanomaterials. Principal vibrational modes have been identified. Reflectivity spectrum has been reconstructed by modeling of the dielectric function

The local seismic response of the Fosso di Vallerano valley (Rome, Italy) based on a high-resolution geological model

The main purpose of this study is the analysis of the local seismic response in the Fosso di Vallerano valley, an alluvial basin located in a recently urbanized area of Rome (Italy). A high-resolution geological model was obtained starting from 250 available borehole log stratigraphies and pressiometer in-site tests; the model highlighted a complex and heterogeneous setting of both the local substratum and the alluvial fill. The local seismo-stratigraphy was derived based on several noise measurements as well as one cross-hole test. A preliminary validation of the stratigraphic model was performed by modeling the amplification functions (SSR) derived from weak motions recorded on August 2009 through a temporary velocimetric array. The obtained results show that the recent alluvial deposits have one principal mode of vibration at about 0.8 Hz and different secondary vibrational modes due to the characteristic stratigraphic setting of the alluvia. The seismic bedrock can be located within the Paleo Tiber 4 deposits (Santa Cecilia Formation) by assuming a velocity gradient in these deposits (i.e. corresponding to the Vs increment from about 500 m/s up to 1100 m/s).

Influence of alloy inhomogeneities on the determination by Raman scattering of composition and strain in Si1–xGex/Si(001) layers

In this work, we investigate the influence of alloy composition inhomogeneities on the vibrational properties of strained Si1−xGex/Si layers with x ranging from 0 to 0.5. We show that the frequencies of the principal alloy vibrational modes (Ge-Ge, Si-Ge, and Si-Si) are strongly influenced by the distribution of Ge atoms within the alloy layers, which becomes gradually random following a series of sequential annealing steps. Our measurements suggest that the composition dependence of the optical phonon frequencies in fully random and unstrained alloys is well described by the results previously published by Alonso and Winer [Phys. Rev. B 39, 10056 (1989)]. In the general case of an alloy layer with unknown degree of compositional inhomogeneity and/or strain relaxation, though the analysis of the Raman spectra is not straightforward. Therefore, we propose an analytical/graphical method to accurately estimate the Ge content and residual strain of SiGe layers exhibiting any level of compositional disorder or strain status, by performing a single Raman measurement. This would be extremely useful in situations where x-ray measurements cannot be conducted. We show that our procedure to treat the Raman data holds for the whole compositional range but with different accuracy depending upon the case: (i) For annealed SiGe layers (mostly strain relaxed) the Ge content x can be directly determined with high accuracy of ±0.01. (ii) For strained samples (usually as-grown samples) an extra criterion must be adopted seeking for a graphical solution, accounting for the degree of compositional inhomogeneity. In this case, the error in the determination of Ge content depends on alloy composition, being the upper bound ±0.02 for x<0.3 and ±0.03 for x>0.3.

Coupling Model Analysis on Fluid Structure Interaction in Lifting Pipeling Based on ADINA

Using finite element software ADINA, three coupling models on fluid-structure interaction among internal fluid—pipe—external fluid in the lifting pipeline were researched. Firstly, coupling finite element model on fluid structure interaction of lifting pipeline was established and the first sixth order natural frequencies and principal vibration modes were attained at different ore conveying volume concentration and cross-section size of pipeline;Then natural frequencies of three couplings were compared with two couplings and no coupling according to the above condition, and FSI effect on natural frequency of pipeline was discussed. The calculation results were shown that the natural frequency of the pipe and its relative error reduced with the volume concentration and the relative wall thickness increased, which explain the reason that has better accuracy considering three couplings than other .These results have certain directive significance on the dynamic response, structure design and study of reduction vibration of lifting pipeline.

Active force cancellation of a near resonance vibrating system using robust H<SUB align="right">∞ control

In this study, the active force cancellation performance of a robust H∞ controller is investigated on a near resonance vibrating system consisting of a rotating machine hard mounted on a flexible base. This configuration and phenomenon can be present in vehicle engine mounts. The model of the vibrating system was first identified experimentally. The uncompensated system frequency response is then used to design the controller. The control objective is to reduce the system (RMS) gain. The effectiveness of the controller has been demonstrated experimentally through implementation on a digital signal processor. Results show reductions of the measured RMS transmitted forces at different mount locations when the machine is operated at speeds near the principal mode of vibration. However at frequency where the vibration is not significant, the reduction in transmitted force level can be minimal.

Raman and structural characterization of LuAlO 3

The structural and vibrational properties of lutetium orthoaluminate perovskite (LuAlO 3) were investigated by means of Raman spectroscopy and EXAFS measurements. The analysis of Raman spectra taken in four different polarized configurations along the principal axes at 20 K and room temperature conditions permits to assign the principal vibrational modes in LuAP single crystals and to confirm the belonging to the D 2 h 16 space group. EXAFS measurements were performed at room temperature in order to obtain local structural informations on the first and next nearest neighbors around lutetium absorptions sites. Unit cell parameters and bond lengths were determined by the analysis of the EXAFS spectroscopy at the L 3 absorption edge of lutetium. The informations thus gathered on this compound can offer a useful addition in the framework of a full structural characterization of LuAlO 3.

Research on Natural Characteristics of Helical Gear in Gearbox for Wind Turbine Generator

The three-dimensional helical gear model based on the geometric parameters is created by using software called PROE3.0. The natural characteristics of helical gear are analyzed by using the finite element method. The natural frequency of the helical gear is calculated by the software ANSYS and the principal mode of vibration is discussed. There are four vibration modes, which are circular vibration, torsional vibration, radial vibration and umbrella vibration. The phenomenon of resonance of the helical gear can be avoided by choosing suitable parameters and changing the natural frequency of the helical gear.

Modeling and characterization of piezoelectric transducers by means of scattering parameters. Part II: Application on colloidal suspension monitoring

This paper illustrates the application of the S-parameter concept for the analysis of the response of a piezoelectric sensor exploited for the discrimination of bentonite colloids of interest in construction engineering. The device is a millimeter-sized cantilever beam fully immersed in the suspension under examination. The beam is energized by a sweeping sinusoidal voltage: the electrical admittance is measured and the corresponding S-parameter is calculated. A procedure for the extraction of the lumped element circuital model is presented and the identification process clearly improves when the S-parameter response is used. Dealing with variable loading conditions, any change on density and/or viscosity of the interacting fluid determines a well-behaved variation of the frequency response associated with the principal modes of mechanical vibration. Inspection of response variations, especially in the S-parameter Smith chart and in the neighborhoods of resonance, allows the discrimination of different loading mixtures. Experimentation was carried out with 2.5%, 5.0%, 7.5% and 10.0% bentonite mixtures and the sensor has been able to fully discriminate between these different bentonite colloidal suspensions.

Influence of shear strains on damping the vibrations of a rectangular plate with piezoelectric actuators

The problem of active damping of the nonstationary vibrations of a hinged rectangular plate with distributed piezoelectric actuators is solved using Timoshenko’s hypotheses. To this end, two methods are employed: (i) a classical method of balancing the principal vibration modes by applying the appropriate potential difference to the actuator and (ii) the dynamical-programming method that reduces the problem to the matrix algebraic Riccati equation. The results obtained by both approaches are compared. The effect of the shear modulus on the amplitude of the damping potential difference and the deflection of the plate is analyzed