Values Of Natural Frequencies Research Articles

Fluid Structure Interaction Analyses of Elevated Storage Tank under Seismic Load

Elevated storage tanks are used to store fresh and waste water, cereal, oil and petrochemical materials. Therefore they serve in a wide area of utilization in this day and age. Analysis of a half full with water elevated storage tank is performed in the scope of this study. The structure is composed of a steel circular storage tank and frame typed steel stager. The structure is under the effect of earthquake loads as well as operational ones. Numerical model is generated by Finite Elements Analysis (FEA) software including fluid and structure parts. The interaction of the parts is provided by Coupled Eulerian Lagrangian (CEL) technique. While the structure constitutes the Lagrangian part, the fluid constitutes the Eulerian part. Interaction of Eulerian and Lagrangian parts are provided by general contact algorithms. Free surface movement of the water, maximum displacements and natural frequency values with related mode shapes of the structure are obtained after numerical analysis. Numerical results are verified by semi-analytical model, where the structure is modelled as single degree of freedom system. The accordance between results is numerically and visually obtained. The turbulent movement of water under the influence of an earthquake is modelled by utilizing the CEL technique. So, the effect of the dynamic pressure induced by the turbulence on the tank and the structural system has been taken into consideration.

Sensitivity Analysis of Modal Parameters of an RC Joint Subject to Progressive Damage under Cyclic Loads

This paper presents the results of an experimental study that focused on the gradual modification of the modal parameters of reinforced concrete beam–column frames subjected to progressive damage under cyclic loading. As is commonly found in structures of the 1970s, the specimen was characterized by the absence of specific shear reinforcement in the nodal panel. The frame modal parameters were investigated using the ambient vibrations test (AVT) as a modal identification technique. In particular, quasi-static cyclic tests with increasing amplitudes were performed on the reinforced concrete frame specimen and the modal parameters were assessed at various stages of frame degradation. By establishing a correlation between the changes in the modal parameters and the mechanical indicators of the structural damage in the frame, this study aimed to determine whether the ambient vibration tests could offer meaningful insights for evaluating the structural health of this type of structural component. As a result of the damage that occurred in the tested RC frame, the residual experimental value of the first natural frequency of the specimen was found to reduce at 52.7% of the original reference value (undamaged stage). Similarly, the residual value of the frame stiffness was found to be as low as 43.82% of the initial one. Both these results confirmed that changes when monitoring the modal frequencies may provide quantitative indexes to describe the structural health of RC frames. In combination with static tests for a direct measure of the structural stiffness variations, the AVT technique was shown to have interesting potential in detecting the type, level, and distribution of the progressive damage in civil structures. In particular, exponential and polynomial regression curves were defined to describe the decay of the first natural frequency as the structural damage increased in various parts of the frame, and it was shown that the variation in the first natural frequency was determined more by the damage on the beam than by the damage on the joint.

Numerical Prediction and Experimental Verification of Inherent Defect Influences on Frequencies of Adhesively Bonded Joint

The vibrational response of adhesively bonded joints with and without defects in the adhesive layer is predicted by simulation for the different overlapping lengths in this work. The eigenvalue extraction method (Block Lanczo’s) is employed within the finite element analysis (FEA) framework to predict the modal values of adhesively bonded joints. The numerical analysis has adopted a solid 20-node quadratic brick elements with reduced integration (C3D20R) to predict the realistic values. The predicted eigenvalues of adhesively bonded joints using an FEA solution are compared with published data and verified the accuracy of the FEA model through experimentation considering defective and non-defective joints. Additionally, simulation solutions are predicted for different overlap lengths (i.e., 25, 30, 35 and 40 mm) by changing the boundary conditions, adhesive bond thickness aspect ratio, adherend thickness ratio, defect position, and defect aspect ratio. The geometries of the adhesive and adherend significantly affect vibration responses through the dampening effect and structural weight, enhancing the stiffness. Defect position and geometry have negligible impact on the natural frequency values for all overlapping lengths except when located around the overlapping edges.

Active and passive soil wedges influence on the natural frequency of retaining structures

Studying the behavior of retaining structures has been very important issue due to their large application in civil engineering. An accurate determination of the earth pressure and the natural frequency is elemental for studying the dynamic behavior of these structures. In the most previous investigations, the soil backfill was considered sufficient width as rectangular mass whereas in the real. the backfill behind retaining structures repartitioned as triangular active and passive soil wedges. Rectifying this weakness, this study proposed an analytical model for calculating the natural frequency of retaining structures by considering the triangular active and passive soil failure wedges, which take into account the variation of earth pressure behind retaining structures. The soil wedge causes an increase in the value of natural frequency. It is clarified that the soil wedge has a large influence on the natural frequency of retaining structures. In this regard, the consideration of active and passive soil wedges behind retaining structures plays an important influence in determining of the natural frequency.

Experimental and Numerical Studies on the Vibration of Hybrid Composite with an Edge Crack

The hybrid composite plate is increasingly used in marine, robotic arm, and other applications. Edge crack is the greatest common fault in the structural systems during its working time. In this research, the successful fabrications of a hybrid composite of epoxy-based composites reinforced with bamboo and glass fibers have been done to examine the vibration characteristics under free vibration. First-order shear deformation theory is used to study the fundamental natural frequencies of asymmetrically hybrid composite beam with edge cracks for cantilever beam boundary conditions. Both numerical (FEM) using ABAQUS software and experimental investigations are done for the vibration analysis of unidirectional bamboo/glass fiber epoxy hybrid composite (BGHC) beam with edge cracks using fracture mechanics theory. It is observed that implications edge crack with different crack depth and various fiber weight ratio parameters have a major effect on vibration analysis. Also, it is clear that the natural frequencies of the hybrid composite are significantly affected due to the fiber weight ratio and crack depth of the hybrid composite materials. So, crack lengths are playing a vital role in the dynamic or vibration characteristics of the hybrid composite materials. The results of natural frequencies have been shown that they are decreased with an increase in crack depth and an increase in the bamboo fiber weight. Thus, BGHC-2 made from 30% bamboo and 10% glass fiber can be a viable candidate for applications that will produce good vibration properties. Generally, the first-third natural frequency of the hybrid composite beam decreases within the increase of bamboo fiber and decreases in glass fiber. The composite materials having 60% of epoxy with 20% bamboo and 20% glass fiber, and 60% of epoxy with 10% glass and 30% bamboo fibers, are observed with a gradual decrease in the values of natural frequencies with respect to increasing in crack depth. A fine agreement was accomplished between the simulation and experimental results. Therefore, the present approach can be used to identify cracks for mechanical health monitoring by linking the variation in natural frequencies of the hybrid composite beams.

Собственные колебания упругой прямоугольной CFCF-пластинки при одноосном растяжении-сжатии ее плоскости

The influence of a uniaxial distributed load in the plane of a thin rectangular plate on the value of the first natural frequency of its oscillations has been studied. We considered a plate, two opposite faces of which are clamped, and the other two are free (CFCF-plate, C-clamped edge, F-free edge). The load is applied to the clamped edges. The main differential equation for the coordinate component of the deflection function and all the boundary conditions of the problem are fulfilled exactly using two hyperbolic-trigonometric series in two coordinates and an additional function depending on one variable x. The problem was reduced to an infinite system of linear algebraic equations with respect to one sequence of uncertain coefficients, containing as parameters the magnitude of the load and the frequency of oscillations. For a number of load values, the natural frequencies of oscillations were found by enumerating frequency values in combination with the method of successive approximations when solving a reduced system of linear algebraic equations. To ensure acceptable accuracy of calculations, the number of terms in the series (the size of the reduced system), the number of iterations and the number of significant digits in the mantissa when calculating non-trivial coefficients of the system were changed. A square plate was considered as an example. Based on the calculation results, a graph was constructed of the dependence of the first natural frequency of oscillations on the magnitude of tension-compression forces, which is a curve close to a parabola. Under Eulerian compressive load, the oscillations stop. The shapes of natural vibrations changed slightly and were similar to the shape of the curved surface of a plate under the action of a uniform transverse load. The purpose of this study is to create an effective algorithm for calculating the natural frequencies of oscillations of a CFCF-plate when the uniaxial tensile-compression load of its clamped faces changes.

Detection technology application based on spectral subtraction and vibro acoustic principle in the measurement of ship reliability level

Introduction: As an important part of ship manufacturing, parts are of great significance in the calculation of its reliability level.Methods: To achieve rapid damage detection of ship parts, a method for measuring the reliability level of ship casting and forging parts based on spectral subtraction and vibration-acoustic principles was proposed. This method improves the spectral subtraction method by adding a percussion vibration signal and time-frequency analysis, and uses the principle of resonance acoustics to complete the construction of the test platform to obtain the natural frequency of the part and achieve non-destructive testing of the part.Results: The results show that using the Fabric data set as the task data set for experiments, the accuracy of the research method is 98.54%; the uncertainty is 5.58; the sensitivity detection is 0.26 μm. In the comparison of the spectrogram of the sound signal after noise reduction, this method has fewer yellow spots remaining on the spectrogram of the noise reduction sound signal, and almost no excess noise remains. In the comparison of modal simulation data of ship parts, the maximum relative error between the simulation data obtained by this method and the natural frequency value obtained from the experimental data is 2.3%, and there is no value exceeding 2.5%, so the error is small.Discussion: The above results show that this method can obtain more accurate natural frequencies of parts, can effectively calculate the reliability level of ship casting and forging parts, and provides a new method reference for the safe operation of ships.

Vibration Fatigue Analysis of Two Different Variants of Oil Suction Pipes.

In order to reduce the overall mass of the product, an improved variant of the engine oil suction pipe in hybrid design is developed and analysed as part of this paper. The vibration fatigue analysis of a simple all-metal suction pipe and the new hybrid suction pipe variant is derived using computer FEA simulations and vibration measurements on the shaker. The hybrid design of the technical components makes it possible to combine different types of materials in order to achieve the best possible properties and behaviours for the components under the influence of external loads. In our case, we combine a suction pipe made of S235JR mild steel with a 3D-printed polyamide intake funnel featuring a grid designed to prevent particles from entering the engine's lubrication circuit. This design reduces the mass and shifts the centre of gravity closer to the attachment point of the pipe, as well as to the engine crankcase, which has a positive effect on the values of natural frequencies and vibration amplitudes. The main objective of such a hybrid suction pipe is precisely to reduce vibrations, and thus extend the service life of the components.

The influence of material’s surface modification on the structure’s dynamics-initial test results

Laser Doppler Vibrometry (LDV) is a still inexhaustible source of research knowledge. Continuous development of the hardware and software makes it possible to employ this technique to new applications. Among plenty of LDV research ideas, the analysis of the influence of material’s surface modification on the structure’s dynamics is not widely investigated. The aim of the paper is to verify a research hypothesis, which assumes that by applying a thin layer of material (coating) to an existing structure or by physical modification of structure’s surface, it is possible to measurably change the dynamics features of the analysed structure in terms of values of natural frequencies and oscillations amplitudes. To perform the assumed research and measurement of vibration a doppler laser vibrometer Polytec PSV-500 was used. Measurement outcomes for different titanium alloy plates surface modifications are depicted. In article’s summary research-based conclusions are formulated.

CRACK EFFECT ON THE NATURAL FREQUENCY OF COMPOSITE BEAM: FINITE ELEMENT ANALYSIS WITH EXPERIMENTAL STUDY

Cracks in structural elements can significantly affect their dynamic behaviour and lead to detrimental consequences. This study investigates the influence of cracks on the natural frequency of a laminated beam under free vibration, employing a combination of finite element method (FEM) analysis and experimental work. The numerical computation is done using ABAQUS simulation software by developing a comprehensive FEM model that accurately represents the laminated beam's mechanical behaviour, considering material anisotropy, geometry and crack propagation. The finite element model is validated through experimental tests conducted on both intact and cracked laminated beam specimens. The experimental setup utilizes Fast Fourier Transform (FFT) analyzer high-precision measurement tool to obtain accurate natural frequency values. The parametric study is conducted to analyze the impact of crack location, size, and orientation on the laminated beam's natural frequency. The FEM simulations reveal that the presence of cracks leads to a reduction in natural frequency, indicating a decrease in structural stiffness. The extent of frequency reduction is found to be influenced by crack characteristics and their proximity to critical locations within the beam. The experimental investigations corroborate the FEM findings, highlighting the consistency between numerical predictions and actual measurements.

Strength enhancement of a flame‐retardant hybrid composite by incorporating graphene nanoparticles for structural applications

AbstractHybrid composite's flame retardancy properties play a dynamic role in structural applications. When inorganic nanomaterials form organic/inorganic nanocomposites, they exhibit superior flame‐retardant effects. Therefore, the current work investigates the combined effects of halogen‐free fire‐retardant ammonium polyphosphate (APP) and graphene (GR) nanofillers on the mechanical, and fire‐resistant behavior of hybrid composite fabricated using a vacuum bag process. Mechanical study affirmed that the concurrent incorporation of APP and GR hybrid composite improved the hardness, flexural, and tensile properties by 7%, 26%, and 16%, respectively. Scanning electron microscopy (SEM) confirms that the dispersion of 0.75 wt% GRs improved the mechanical properties by preventing crack propagation and strong binding between fiber‐matrix in the hybrid composite. The vibrational analysis reveals an improved natural frequency (NF) value was obtained with 0.75 wt% GR; further addition of GR increased the damping due to an increase in nanoparticle agglomeration. The combined effect of APP and GR decreased the hybrid composite's water uptake and porosity by 52% and 80%, respectively. The flammability study (Vertical burning) affirmed that the composite's grade score was improved from V‐1 to V‐0. Therefore, the current study emphasizes that this optimized hybrid composite can be utilized in fire‐sensitive structural applications.Highlights UL‐94 VB test reveals the flammability of the hybrid composite. Examine the combined effect of APP and GR in strength and flame‐retardant properties. GR and APP added sample shows better mechanical and flame resistance properties. The optimized wt% of GR and APP for better results is 0.75% and 9.25%. The prepared composite may suitable fire‐sensitive structural applications.

Vibration Characteristics of FML Cylindrical Shell Bonded by Thin Piezoelectric Actuator and Sensor Layer with and Without Fluid–Structure Interaction Resting on Pasternak Elastic Foundation

The present study investigates the vibration analysis of cylindrical shells composed of fiber metal laminate (FML) with embedded piezoelectric layers, undergoing fluid-structure interaction (FSI) and resting on a Pasternak elastic foundation based on the principles of three-dimensional elasticity theory. Using the state space approach, the equations of motion were derived under simply supported boundary conditions. The natural frequencies of the FML cylindrical shell, accounting for the presence of a moving fluid, were computed by solving the eigenfrequency equations. The study examined the influence of various parameters, including boundary conditions, length-to-radius ratio, fluid type, fluid velocity, circumferential wave number, and radius-to-thickness ratio, on glass-reinforced aluminum laminate (GLARE), aramid-reinforced aluminum laminate (ARALL), and carbon-reinforced aluminum laminate (CARALL). A constant composite/metal volume ratio was assumed. The results obtained were validated by comparing with natural frequency values from the existing literature, confirming the agreement and convergence with previous studies. The results confirm that the highest natural frequency values are assigned to the CARALL, ARALL and GRALE structures in descending order. Furthermore, an increase in fluid flow velocity through the cylindrical shell correlates with a reduction in natural frequency.

Vibration Analysis of Suspension System for 3DOF Quarter Car Model with Tire Damping

Quarter car model is the simplest way for the analysis of vehicle suspension system. The objective of this study is to propose the natural frequency and to identify the displacement analysis of 3 Degree of Freedom (3DOF) suspension system using Matlab software. Research methodology are state space modelling method and logarithmic decrement method. From the state space modelling, seat mass, sprung mass and unsprung mass displacement have been calculated. Logarithmic decrement method is a time domain technique to obtain experimental damping ratio. The novelty of this research has demonstrated the experimental approach by using Quantum X (catman AP v5 software). Natural frequency and acceleration results are obtained from the time domain response of experimental data. The value of sprung mass natural frequency for theoretical (1.23 Hz) and experimental (1.134 Hz) result are within 1Hz to 2Hz. The maximum displacement transmissibility values for theoretical (2.7) and experimental (2.54) approach are less than the reference value (3.5) at the resonance point. The findings demonstrated that the results of natural frequency and damping ratio are within the acceptable limit. So, the obtained results are validated the suspension system of Nissan Sunny model for vehicle safety and passenger comfort.

Crashworthiness Evaluation of Electric Vehicle Battery Packs Using Honeycomb Structures and Explicit Dynamic Analysis

The battery pack system is crucial to safeguard battery units during any collision. The crashworthiness of battery packs could be improved with the incorporation of honeycomb structures. The objective of the current study is to evaluate the structural characteristics of battery encasing using ANSYS explicit dynamic analysis. The modal analysis is conducted to determine the natural frequency, mode shape, and peak displacement values. The CAD model of the battery pack is developed in Creo parametric design software. The use of a honeycomb structure enabled the reduction of the effect of impact on battery units. At the time of the collision, the honeycomb structure would absorb maximum crash impact and would save the battery unit cells from major damage. The natural frequency of a battery pack with a honeycomb structure has a higher first, 2nd, and 3rd natural frequency. At the time of impact and without any honeycomb structure, the internal energy of the battery unit is 1021.8mJ while with the honeycomb lattice structure, it is 0.80376mJ. The results have shown that with the incorporation of a honeycomb structure, there is a substantial reduction in the internal energy of the cell with the incorporation of the lattice structure.

Is Acoustic modal analysis a reliable substitution for Osstell® device in dental implant stability assessment? An experimental and finite element analysis study.

Different methods have been proposed to investigate the fixation stability of dental implants, each of which has its limitations. Among these methods, resonance frequency analysis (RFA) has been widely utilized to measure dental implant stability. This study aimed to assess dental implants with two non-destructive RFA and acoustic modal analysis (AMA) validated with a finite element simulation of the fundamental natural frequency (NF) of the bone analog-implant structure. A total number of 18 implants were inserted into two Polyurethane (PU) bone blocks with different densities (0.16 g/cc and 0.32 g/cc). AMA was used to measure NF; First, the sound originating from the axial tapping of the implant was recorded with a simple microphone. Secondly, a fast Fourier transformation algorithm was conducted to determine the NF of the implant-bone analog structure. In parallel, the ISQ (Implant Stability Quotient) value was measured using the Osstell® device. Finally, using finite element analysis (FEA), the implant-bone analog structure was modeled for validation. Doubling the bone analog density resulted in an average increase of 82% and 47% in the NF and ISQ using AMA and Osstell®, respectively (P-value<0.05). Furthermore, a strong linear relationship (R2= 0.93) was observed between the measured NF and ISQ values in the linear regression analysis. The NF of the dental implant predicted by FEA was overestimated by about 15.2% and 15.0% than those in the low- and high-density PUs, respectively. Moreover, the FEA predicted an increase of 83% in NF by increasing the bone analog density from 0.16 to 0.32 g/cc. Having required the minimum process combined with easily available equipment makes it an ideal method for fixation strength studies. The good correspondence between the ISQ values and NFs, in addition to the good accuracy and reliability of the later method, confirms its application for fixation stability assessment.

Dynamic Stability of a Three-Layer Beam – Generalisation of the Sandwich Structure Theory

Abstract The work focuses on the dynamic stability problem of a simply supported three-layer beam subjected to a pulsating axial force. Two analytical models of this beam are developed: one model takes into account the non-linear hypothesis of cross-section deformation, and the other takes into account the standard “broken line” hypothesis. Displacements, strains and stresses for each model are formulated in detail. Based on the Hamilton principle, equations of motion are determined for each of these models. These systems of two differential equations for each model are approximately solved with the consideration of the axial pulsating force, and the fundamental natural frequencies, critical forces and the Mathieu equation are determined. Detailed studies are performed for an exemplary family of beams. The stable and unstable regions are calculated for the three pulsating load cases. The values of fundamental natural frequencies and critical forces of exemplary beams calculated from two models are compared.

Experimental Verification of Dynamic Properties of a Hollow Aluminum Beam

In this study, analytical and computational analyses are performed to determine the dynamic properties of an aluminum hollow beam and an experimental analysis is also performed. The experimental model is taken as a reference model and the computational model is updated accordingly using model updating tools. The damping behavior inherent in all physical structures is measured experimentally. According to the results of the cross-correlation modal assurance criterion, the experimental and computational results match well. The average error between the computational and experimental results for the first five damped natural frequency values is 1.5%.

Buckling Stability and Vibration Characteristics of Functionally Graded Graphene Platelet-Reinforced Composites Multi-Arc Concave Honeycomb Sandwich Panels Under Thermal Loading

The utilization of functionally graded graphene platelet-reinforced composites (FG-GPLRC) and honeycomb sandwich constructions is prevalent in the field of engineering. Therefore, it is crucial to investigate the buckling and vibration properties of these materials under heat circumstances. This paper specifically focuses on the vibration and thermal buckling characteristics of a novel multi-arc concave honeycomb sandwich plate (MACHSP) equipped with an adjustable positive-negative Poisson’s ratio. The governing equations of motion for the system are derived based on the first-order shear deformation theory in conjunction with Hamilton’s principle. The formulation of the system’s characteristic equation involves the establishment of displacement functions that satisfy distinct boundary conditions. Using computational programming, natural frequencies, mode shapes, and critical buckling temperatures of MACHSP with three different FG-GPLRC distributions under thermal influences are determined. Subsequently, these results are compared with outcomes from finite element simulations and findings from previously published literature. Additionally, the amplitude-frequency response characteristics of the structure under harmonic excitation are analyzed, followed by a discussion of the impact of structural parameters on its buckling and vibration characteristics. The results indicate that the established theoretical model for predicting the buckling and vibration characteristics of MACHSP with FG-GPLRC distribution aligns well with simulation models and prior research. In contrast to solid plates, MACHSP not only achieves a substantial reduction in weight but also demonstrates a significant increase in natural frequency. Furthermore, graphene platelets have the potential to enhance the structure’s natural frequency values and critical buckling temperatures. Lastly, various structural parameters exert a notable influence on the structure’s performance.

Structural Optimization of MicroMED Dust Analyzer

This research work describes the structural optimization of the MicroMED Dust Analyzer, an Optical Particle Counter developed for the ESA ExoMars 2022 mission. Topology Optimization, a non-conventional design technique was adopted to obtain a lighter component, a valuable achievement for aerospace and space scientific instruments design. In particular, two solutions for the instrument optical bench were proposed and assessed relying on a classical finite element approach, comparing the improved performance with the current design. The optimization outcome proved the adopted design workflow robustness and provided promising results in view of a possible mechanical design enhancement of the MicroMED Dust Analyzer instrument. Indeed, a mass budget saving of about 55% of the considered design domain was achieved, and the dynamic behaviour of the optical bench was improved by up to 50% of the first natural frequency value. Finally, a mockup of the lightened optical bench was manufactured, and the redesign effectiveness was proven by comparing the numerical mechanical resonances with the ones obtained experimentally. An error smaller than 5% was found on the first natural frequency, validating the performed optimization approach.

The Vibration Analysis Based on Experimental and Finite Element Modeling for Investigating the Effect of a Multi-Notch Location of a Steel Plate

Vibration is challenging and significant in solving engineering problems. The issue of vibration in loaded objects by utilizing a three-dimensional model and experiments. Typically, an object is subjected to a random frequency, which changes the notch shape depending on the frequency model. The investigations determined the performance difference by conducting modal analysis with the finite element method and examining the various forms of each mode. We simulated metal plates with V notch and multiple notch locations on both sides and one side of the notch. The test kits included an accelerometer and a force sensor for correcting the national frequency via Simulink Matlab® and verifying the result from the finite element methods. The V-shaped vibration testing provided significant insights into its accuracy and potential for predicting damage and fracture through experimentation and the finite element method. The tested specimen analyzed the behavior of two models and found that the two V-shaped exhibited varying natural frequency values. Specifically, the double-sided V-shaped increased natural frequency, whereas the single-sided notched V-shaped cutting showed a significant decrease in natural frequency. Accordingly, this investigative approach, the result of the experiment, and the finite element shows that correlation disposition can be utilized to forecast various random frequencies for vibration analysis.