Natural Frequency Analysis Research Articles

Natural frequency and stability analysis of axially moving functionally graded carbon nanotube-reinforced composite thin plates

Natural frequency and stability analysis of axially moving functionally graded carbon nanotube-reinforced composite thin plates

Size-dependent couple stress natural frequency analysis via a displacement-based variational method for two- and three-dimensional problems

Size-dependent couple stress natural frequency analysis via a displacement-based variational method for two- and three-dimensional problems

Deflection and Natural Frequency Analysis of FG Porous Plates Embedded in Elastic Foundations Using Four-Variable Hyperbolic Quasi-3D Theory

Deflection and Natural Frequency Analysis of FG Porous Plates Embedded in Elastic Foundations Using Four-Variable Hyperbolic Quasi-3D Theory

Taguchi Analysis of Natural Frequency for Simply Supported Composite Stiffened Hypars with Perforation

Taguchi based optimization of natural frequency of perforated stiffened hypars is performed to consider the role of fibre lamination, width/thickness ratio of shell and position of perforation centre along x- and y-direction. Natural frequency of stiffened shell is obtained for simply supported boundary condition using finite element procedure based on L27 orthogonal array (OA) considering three settings of each parameter. Main effect plot is analyzed to identify the significant parameters. Natural frequency becomes maximum for a combination of 450 fibre lamination, width/thickness value of 20 and perforation centre position (0.4, 0.4). Interaction graphs identify the interaction parameters. ANOVA study provides the significant contribution of the parameters considered here. Present analysis identifies width/thickness as the most significant factor and other parameters yield very little significance while no interaction is found to be significant. Width/thickness value of shell yields major (98.64%) contribution to natural frequency and other factors yield very little significance. Residual analysis for natural frequency and confirmatory test validate the present study. S/N ratio gets improved by 38.3% at optimal condition compared to the initial parameter setting.

Влияние термической обработки на динамические характеристики балочных конструкций из полилактида, напечатанных на 3D-принтере FDM-методом

The paper presents general description of the FDM technology and a brief overview of its application in the aerospace industry. Main advantages and disadvantages of using poly-lactide in the 3D printing are considered. Influence of heat treatment on the dynamic characteristics of beam structures printed with a 3D printer from polylactide were determined. Resonance oscillation tests of the beam samples were carried out at different filling densities and various modes of preliminary thermal processing in the furnace. Comparative analysis of natural frequencies and damping coefficients of the samples depending on the preliminary heating temperature is provided. Experimental study showed that heat treatment of the beam structures made of polylactide leads to an increase in their rigidity and practically is not affecting the damping. Results of the work made it possible to determine the optimal preheating temperature for polylactide.

Natural frequency analysis of imperfect GNPRN conical shell, cylindrical shell, and annular plate structures resting on Winkler-Pasternak Foundations under arbitrary boundary conditions

The goal of the present research is to examine the Natural Frequencies (NFs) of perfect and imperfect Graphene Nanoplatelet Reinforced Nanocomposite (GNPRN) structures of revolution (conical and cylindrical shells and annular plate structures) resting on elastic foundations under general boundary conditions (BCs). The graphene nanoplatelet material is implemented to compose the nanocomposite enhanced by a polymeric matrix including porosities. The springs technique is applied to define the general BCs of GNPRN structures of revolution. Elastic foundations are described by two parameters, i.e., Winkler-Pasternak Foundations (WPFs). Additionally, Donnell's hypothesis and first-order shear deformation theory (FSDT) are employed to figure out the primary formulations associated with the GNPRN structures of revolution. In contrast, the equations of motion are found using Hamilton's principle. Then the equations of motion are then discretized using the well-known Generalized Differential Quadrature Method (GDQM). Next, the standard eigenvalue solution is assigned to obtain the NFs of the perfect/imperfect GNPRN structures of revolution. Finally, various benchmarks are addressed to verify the approach suggested for evaluating the NFs of the perfect/imperfect GNPRN structures of revolution. Furthermore, several novel examples highlight the effects of the change in geometrical and material properties, arbitrary boundary conditions, and WPFs on the NFs of the perfect/imperfect GNPRN structures of revolution.

On the natural frequency investigation of the thick hollow cylinder with 2D-FGM Mori-Tanaka scheme

ABSTRACT In this paper, we conduct the natural frequency analysis for a 2D-FGM (functionally graded material) finite-length, thick-walled cylinder by the graded finite element method. The material properties gradations are considered along with the thickness and the longitudinal axis of the cylinder according to the Mori-Tanaka scheme and power-law volume fraction distributions. Therefore, the graded properties are implemented by user subroutine UMAT in ABAQUS/Standard™. The eigenvalue problem is solved using three-dimensional elasticity equations, and the current technique has been confirmed by earlier research. The major purpose of this study is to see how FGM configurations affect the vibration behaviour of the cylinder. The variation of the cylinder's first natural frequencies for various thickness-to-outer-radius and length-to-outer-radius ratios is presented, taking into account varied material distributions. According to the findings, raising the power exponents, particularly the radial one, increases the natural frequencies.

The analysis and validation of natural frequencies and mode shapes of 3D plates in the framework of the generalized thermoelastic theory

This article considers thermal effects that induce thermoelastic damping and, which, consequently, because of the absorbed thermal energy, cause thermal stresses. The problem is stated in the framework of the generalized thermoelastic theory. The natural frequency and mode shape analyzes of 3D plates are presented under uniform and nonuniform heating. From the modeling point of view, this results in the quadratic eigenvalue problem where complex frequencies and modes are obtained. Moreover, the quality factor related to the thermoelastic damping is also calculated in terms of the imaginary and the real parts of the frequencies for both the uniform and nonuniform thermal distributions. The variation of natural frequencies with temperature is investigated and compared with the experimental results for the plates with free boundary conditions. The first two mode shapes are also examined for all clamped edges for the uniform and nonuniform cases. Complex frequencies and complex modes are observed due to the thermal effects. For the uniform case, the real part of the modes decreases and the complex part increases, while the mode’s norm remains the same as in the classical modes as temperature increases. For the nonuniform case, the mode shape analysis is performed under the assumption that the elasticity modulus, thermal expansion, and specific heat parameters are functions of temperature. The peak point of the out-of-plane displacement is shown to be shifted toward the warm zone. The obtained outcomes may help design thermal structures and allow for future extensions.

Diagnosis of femoral implant loosening after total hip replacement by analysis of natural frequency

Clinical follow-up and normal plain radiology are common protocols for detecting implant loosening in Total Hip Replacement (THR), which cannot detect it at very early stages. There are more accurate radiological techniques (arthrography, radio-stereometric analysis) which are not widely employed due to their cost and invasiveness. The shift detection of natural frequencies by vibration analysis has been also used as a more sensitive alternative. However, interpreting the data is not easy in clinical environments. An experiment with three stem models with a very different design in artificial femurs was performed in this work. Strain gauges were employed as the dynamic sensor, and free decay bending and bending + torsion tests were performed for two extreme situations including completely loose and well-fixed stem. The strain gauges signal was processed in time-domain and frequency domain, and resonant shifting and increases in dumping ratio were analyzed. Resonant shifting was not easy to recognize, especially for some models. However, dumping ratio showed very significant changes in all models and did not need transforming signals into frequency-domain for its computing. The findings indicated that dumping ratio is a highly suitable parameter and easier to compute in searching for implant loosening.

Natural frequency analysis of deep-sea mining riser considering varying tension and buffer station

The natural frequency of tensioned marine riser is important for deep sea mining pipe. The effects of varying tension along pipe and buffer station on natural frequencies and mode shapes are analyzed based on simplified beam model. The explicit expression of natural frequencies are given in terms of dimensionless weight of buffer and constant tension for cases of ω≫α and ω≪α through separation variable method. The results agree well with numerical results and regressions. Variation relations between natural frequency and dimensionless parameters of deep sea mining riser are given. Large variation tension along pipe are analyzed by power series method without buffer, the maximums of higher order mode shapes located nearer the upper end.

Numerical Analysis of Natural Frequency for U-Shaped Expansion Bellows in Fixed-Fixed and Fixed-Free Conditions

In this study, MATLAB code was used to analyze the natural frequency in two types of U-shape metal expansion bellows with various supporting conditions (fixed-fixed and fixed- free). The first bellow has a 10 mm inner diameter., and a length of (100, 200, 300) mm, has (36, 75, and 111) convolutions. While the second bellow, with an inner diameter of 20mm and (100,200,300) mm, has a number of convolutions (25,54 and 82). The result shows that by lowering the bellow length and increasing the bellow diameter, the natural frequency was raised. Were. Where, the maximum frequency was recorded at a maximum value of 20 mm in diameter and a length of 100 mm, about (13549.167 Hz) in the case of fixed-fixed and (13097.528 Hz) in the case of fixed-free. In general, the natural frequency depends directly on the stiffness and total mass of the pipe conveying fluid. The stiffness of the material is determined by the moment of inertia. As a result, increasing the diameter will increase the moment of inertia, which will result in an increase in stiffness, which will result in an increase in natural frequency.

Delamination Detection in Concrete Plates using a Laser Ablation Impact Echo Technique

This study investigates the detection of delaminations in concrete plates using non-contact laser ablation instead of the conventional hammer excitation. Tests were performed on two specimens of which one had an artificial delamination. 5 mm to 15 mm diameter steel tip hammers were used as a reference source and compared to a 7 ns pulsed 1064 nm Nd:YAG laser with 150 mJ pulse energy. Signals were recorded by surface- mounted accelerometers and in air by microphones and a laser Doppler vibrometer. Frequencies up to 150 kHz are excited with a broad frequency spectrum and little energy compared to the narrower frequency spectra of the hammers. The characteristic thickness resonance frequency of the intact plates can be accurately detected by the hammer excitation. The laser can excite low frequency flexural vibration modes over a shallow delamination at 3 cm depth, but does not excite the thickness resonance frequency. The low frequency flexural vibrations are verified by numerical natural frequency analysis.

New low-order continuum models for the dynamics of a Timoshenko beam lattice with next-nearest interactions

In this paper, the dynamic behaviour of a novel Timoshenko beam lattice with long-range interactions, accounting for both bending and shear deformations, is investigated. Several new non-classical continuum models are developed with the aim of capturing its dispersive behaviour with a lower computational cost. For this, innovative continualization procedures are used, comparing them with techniques commonly used in lattices continualization, as well as with advanced ones. Moreover, low-order continuum governing equations are pursued, thus avoiding the need for extra boundary conditions, whose physical meaning is unclear. A comprehensive analysis of the transition frequency, which initiates the shear propagation spectrum, has been performed here for the first time for this lattice and the corresponding continuum models. The capability of these continuum models in capturing the behaviour of the lattice is assessed by conducting both dispersion and natural frequency analyses, for the latter providing an original method to treat the edges for the three possible boundary conditions in Timoshenko beam lattices. The influence of long-range interactions is analysed, and the way shear effect affects the shape vibration modes of the discrete model is interestingly illustrated, finally concluding that some of the new developed continuum models accurately capture the behaviour of the lattice.

Design and implementation of Crossed-circle MEMS ciliary vector hydrophone

MEMS ciliary vector hydrophone is used for underwater low-frequency acoustic signal testing, but it is limited by mutual inhibition of bandwidth and sensitivity. A crossed-circle bionic vector hydrophone is proposed in this paper. It uses two circular structures to increase receiving area of sound waves and improve sensitivity. At the same time, it improves working bandwidth of the hydrophone by reducing thickness of circular structure and adopting hollow cylinder. In this paper, COMSOL simulation software was used to carry out simulation and analysis of stress distribution and natural frequency, and determine the optimal size of crossed-circle structure. Experiments show that sensitivity of the hydrophone was measured to reach −184.5 dB@1250 Hz（0dB = 1 V/μPa）, and the working bandwidth was 20–1250 Hz, the sensitivity reaches −186.7 dB at 1000 Hz, 10.4 dB higher than that of single-cylinder structure. The depth of pit exceeds 30 dB at 315 Hz and 630 Hz, indicating that the hydrophone has excellent dipole directivity.

Variable Natural Frequency Damper for Minimizing Response of Offshore Wind Turbine: Principle Verification through Analysis of Controllable Natural Frequencies

Resonance causes extreme stress, acceleration of fatigue, and reduction in lifespan of offshore wind structures. The main factors that cause resonance are environmental loads such as wind and waves, and dynamic loads caused by rotor movement. Estimation of the natural frequency at the design stage is highly uncertain, and natural frequency changes occur due to various factors during long-term operation. Therefore, it is important to ensure structural safety from resonance through a vibration-monitoring system or an additional damper. In this study, the effect of seawater existing inside the substructure on the natural frequency of the structure was dealt with. The natural frequency estimation equation for a fixed offshore wind structure was derived with the “inner fluid simplification assumption”. The finite element modal analysis was performed to verify the principle of Variable Natural Frequency Damper (VNFD), a system that controls the natural frequency of offshore wind structures through a pump, and to find the range of natural frequency control. As a result, interior fluid affects the natural frequency of the wind turbine support structure. Specifically, the variable natural frequency range was very low, at about 0.027% for the monopile model at a depth of 10 m, but increased rapidly to about 3.66% at a depth of 70 m. Furthermore, when estimating the natural frequency of a fixed offshore wind turbine in deep water without consideration of interior fluid, the estimates can be higher than with consideration of it.

Numerical evaluation of a new hybrid bucket-group pile foundation for offshore wind turbines

ABSTRACT An innovative foundation combining a bucket foundation and group piles (BGP) is proposed and investigated in this paper. Sleeve structures are added on the skirt of the mono-bucket, and piles can be inserted through the sleeves and connected with the bucket by grouting. With the same amount of steel, four finite element models of BGPs with different pile diameter and length combinations are established by ABAQUS, as well as a mono-bucket to study the unidirectional bearing capacity and failure mechanism. The results show that the bearing capacity of the BGP with suitable pile length and pile diameter is considerably higher than that of the mono-bucket foundation. Finally, static analysis and natural frequency analysis of the BGP are carried out based on the loading and geotechnical conditions at Yangjiang area of China. The results show that the BGP meet the design requirements, and the new BGP has engineering practicability.

Analysis and Optimization of Composite Propeller Shaft for Automotive Applications

In the field of automotive engineering polymeric composites played vital role due to its outstanding properties such as high strength, low weight and high stiffness. The purpose of this research is to develop a single piece steel (Cr–Mo SCM440) drive shaft using computer aided modelling tool and finite element method was used for analysing static analysing and free vibration. These results were compared with the propeller shaft made by carbon and glass epoxy composites. ANSYS software is used for accomplish total deflection, natural frequency, and modal analyses. From this work it was noted that the propeller shaft made using carbon epoxy offered better results as compared with steel and glass epoxy composite propeller.

Natural frequency analysis of a dual rotor system with model uncertainty

Natural frequency analysis of a dual rotor system with model uncertainty

Experimental parametric study on hydroelastic behaviour of a 15000-TEU container ship based on segmented ship model

ABSTRACT Large-scale ships with high elasticity and low natural frequency, behave high dynamic response amplitude under impulsive wave loads (whipping) and short period waves (springing), which could result in serious ultimate loads and fatigue damage. The segmented model test is a more powerful approach for the ship hydroelastic analysis compared with ship seakeeping test. However, the effect of some test parameters on the hydroelastic responses is still not a clear statement. Therefore, the number of segments, propulsion mode and backbone form are chosen for the parametric study on ship hydroelastic behaviour. A three-dimensional (3-D) nonlinear time-domain hydroelastic method is developed, in which the nonlinearity of instantaneous wetted surface and slamming force are considered. Through the analysis of natural frequencies and vertical bending moments (VBM), the impact on hydroelastic behaviour is discussed. Results show that self-propelling models with variable cross-section backbones are more suitable and reliable in studying nonlinear hydroelastic behaviour.

Dynamic calculation and optimization design of arbitrary planar branch piping system

The absorbing transfer matrix method (ATMM) is applied to dynamics calculation and optimization design of planar branch piping systems combined with the response surface model or method (RSM) and a new proposed hybrid RSM (HRSM). A main path is chosen to absorb the influences of sub-branches, and the branch point transfer matrix in the main transfer path is established and proved by the ANSYS simulation and experimental results. It shows that the errors between the ATMM and the finite element method are less than 0.36% in the calculation of the natural frequencies of the two-branch piping system, and the ATMM also agrees well with the dynamics response experimental results of the cross-branch piping system. Then, based on the initial design model of a double-branch piping system, first order natural frequency analysis samples are selected for the branch point positions optimization using the uniform design method (UD) and calculated by the ATMM; the minimum value of the RSM, obtained by fitting the samples with a second-order polynomial (SOP) function, is solved as the best design scheme using the genetic algorithm (GA). Finally, for the problem of supporting positions optimization of a T-branch piping system, a HRSM using the SOP function to fit the variation law with different supporting positions in the samples of the dynamics response optimization target, which is the total x-directional vibration acceleration level (TAC) of three supporting points in the frequency 1–300 Hz and the Fourier basis function to fit the relationship of SOP function error with independent variables is proposed combining the Minimize Prediction (MP) adding point criterion to gradually update the samples, until the HRSM reaches stability and obtains the wanted design solution.