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This paper examines the vibration response of the steel–concrete composite ultra-shallow floor beam (USFB) flooring system, which incorporates asymmetric steel perforated beams to accommodate the concrete floor slab within the depth of the flanges while allowing reinforcement and/or service ducts to pass through the web openings. This is a lightweight flooring system that can accommodate long spans, thus becoming susceptible to floor vibrations due to external resonant dynamic loads. To investigate the influence of slab thickness and boundary conditions on the natural frequencies of the USFB flooring system, parametric studies are conducted using a finite-element model and five floor spans. The model was first validated against an experimental test conducted by the authors. Emphasis is placed on the fundamental frequency to predict the possibility of resonance of this complex flooring system with typical human-induced dynamic loads in building structures. To further facilitate the practical numerical modelling and vibration analysis of buildings with USFB floors in standard commercial structural software, an analytical method of deriving equivalent isotropic plate properties is developed and its accuracy is numerically verified with regard to detailed Abaqus models. [ABSTRACT FROM AUTHOR]

Abstract Bridges will inevitably experience structural damage during long-term operation, which will decrease their structural load bearing capacity and durability. The vibration characteristics of bridge structures can be used as evaluation indicators for accurately diagnosing their deterioration. This study aimed at developing a vibration testing method for identifying bridge deck damage that does not affect traffic and is easy to implement. The vibration tests on the in-service bridge revealed it was mainly subjected to vertical vibrations, with the accelerations in the vertical direction about twice those in the horizontal direction. Based on fast Fourier transform analysis, the dominant vertical vibration frequencies were 2.34 Hz, 4.10 Hz, 10.30 Hz, 14.45 Hz and 18.75 Hz. A series of 0.1–0.3 Hz bandpass filters were used with those frequencies at the centers for modal analysis. The experimental results were then compared to the finite element analysis results. This study proposed a vibration-based damage identification method based on the differences between the bridge deck and both main steel girders. The study confirmed the convenience and effectiveness of using underneath maintenance walkways for wireless vibration testing.

This study investigates plate analyses employing the method of initial functions (MIFs) across various plate geometries and loading conditions. The conclusions derived from thick rectangular plates highlight substantial thickness‐induced effects on deflection and stress distributions. For thicker plates, the classical assumption of constant deflection fails, with maximum deflection often occurring at surfaces other than the middle plane. The classical and Reissner theories' constant deflection assumption leads to significant discrepancies in thick plate deflection estimates, emphasizing the need for MIFs more accurate approach. Similarly, in the case of thick circular plates, deviations from classical theory are evident in radial and shear stress distributions, particularly pronounced closer to the plate edge and support. These deviations dissipate further away from these regions. Moreover, the study delves into free vibration analyses for rectangular and circular plates, revealing that classical theory tends to overestimate frequencies, especially as plate dimensions increase. Mindlin's theory and MIF approaches showcase improved accuracy with increasing order, converging toward exact solutions. Additionally, Mindlin's theory effectively captures the behavior of higher vertical modes, showcasing sign changes in characteristic quantities of the plate. The findings underscore the limitations of classical theories in accurately predicting plate behaviors, especially in thicker plates and higher modes of vibration. Conversely, the MIF method, alongside Mindlin's theory, proves effective in providing nuanced insights into plate behaviors under various conditions, thus offering valuable implications for structural design and analysis. [ABSTRACT FROM AUTHOR]

Wheel-rail high-frequency interaction is closely related to the formation of railway short-wave defects. Finite element (FE) method has been widely used to simulate wheel-rail dynamic systems, but its validity in modelling high-frequency interaction has not been fully demonstrated in three dimensions (3D). This work aims at comprehensively validating the 3D FE modelling of wheel-rail high-frequency interaction using a downscale V-Track test rig. First, the FE model of the V-Track is developed that comprehensively includes the 3D track elasticity. The simulated track dynamic behaviours are validated against hammer tests, and the major vibration modes are analyzed employing modal analysis. Afterwards, the simulate wheel-rail dynamic responses are comprehensively compared with measurement results up to 10 kHz. Their characteristic frequencies are identified and correlated to the eigenmodes of the vehicle-track system. The results indicate that the proposed 3D FE model is capable of comprehensively and accurately simulating the 3D track dynamics and wheel-rail dynamic interaction of the V-Track up to 10 kHz. Rail vibrations dominate the wheel-rail dynamic contact within 10 kHz, while the wheel vibrations play an increasingly important role at higher frequencies and become decisive near the wheel eigenmode frequencies. The V-Track overall achieves dynamic similarity to the real vehicle-track system. [ABSTRACT FROM AUTHOR]

Bridges will inevitably experience structural damage during long-term operation, which will decrease their structural load bearing capacity and durability. The vibration characteristics of bridge structures can be used as evaluation indicators for accurately diagnosing their deterioration. This study aimed at developing a vibration testing method for identifying bridge deck damage that does not affect traffic and is easy to implement. The vibration tests on the in-service bridge revealed it was mainly subjected to vertical vibrations, with the accelerations in the vertical direction about twice those in the horizontal direction. Based on fast Fourier transform analysis, the dominant vertical vibration frequencies were 2.34 Hz, 4.10 Hz, 10.30 Hz, 14.45 Hz and 18.75 Hz. A series of 0.1–0.3 Hz bandpass filters were used with those frequencies at the centers for modal analysis. The experimental results were then compared to the finite element analysis results. This study proposed a vibration-based damage identification method based on the differences between the bridge deck and both main steel girders. The study confirmed the convenience and effectiveness of using underneath maintenance walkways for wireless vibration testing. [ABSTRACT FROM AUTHOR]

IntroductionThe growing consumer demand for high-quality products has led to the development of new technologies for assessing the quality of agricultural products. Iran is the 9th largest orange producer in the world. Every year, large quantities of agricultural products lose their optimal quality due to mechanical and physical damage during various operations such as harvesting, packaging, transportation, sorting, processing, and storage. This study is performed to identify the natural frequencies and vibration modes of the Thomson orange fruit using finite element modal analysis by ANSYS software. In addition, physical properties including mass, volume, density, and principal dimensions were measured, and mechanical properties were determined using Instron Texture Profile Analysis. The dynamic behavior of the orange fruit was simulated using the pendulum impact test. Afterward, the obtained impact was applied to the orange fruit by force gauge and three-axis accelerometer sensors in both polar and equatorial directions. The three-dimensional geometric model of the orange fruit was drawn in the ANSYS software. After meshing and applying the boundary conditions, the first 20 modes and corresponding natural frequencies were obtained. Since the objective of this study was to identify the natural frequencies of the orange fruit, it was considered to have free movement and rotation in space. The results showed that the natural frequencies of orange fruit are in the range of 0 to 248.41 Hz. Knowledge of the texture characteristics and dynamic behavior of horticultural products is essential for the design and development of agricultural machinery. Furthermore, the design and development of agricultural machinery are directly related to the biological properties of agricultural products.Materials and MethodsThe Thomson orange variety was used in the present study. The oranges used for the experiments were harvested from the Citrus and Subtropical Fruits Research Institute in Ramsar, Iran, located at coordinates 50° 40′ E and 36° 52′ N. The oranges were subsequently divided into two groups: large (average diameter 82 mm) and small (average diameter 66 mm). Conducting the finite element analysis requires knowledge of the physical and mechanical properties of the flesh and skin of the orange fruit. The physical and mechanical properties of the tested samples include geometric dimensions, modulus of elasticity, Poisson’s ratio, and density. In the present study, the dynamic behavior of the orange fruit under dynamic loads was investigated by performing an impact test using a pendulum. The orange fruit was hung from the ceiling using a thin thread to perform experimental tests and extract the modal parameters. The orange samples were subjected to impact at three angles: 7° (below the yield point), 10° (at the dynamic yield point), and 20° (above the dynamic yield point).Results and DiscussionThe comparison of the experimental (laboratory) natural frequencies and simulation validates the simulation results. The experimental natural frequencies of the first, second, and third modes in the large-group oranges are 125.4, 146.9, and 180.4 Hz, respectively. Additionally, the simulation (modal) frequencies are 133.80, 146.16, and 196.66 Hz for the first three modes, respectively. The lowest and the highest differences were observed in the second (0.5%) and third (9.01%) modes, respectively. In the small-group oranges, the first, second, and third modes have experimental natural frequencies of 152.2, 188.8, and 242.2 Hz, respectively, and simulation frequencies are 167.79, 187.50, and 248.30 Hz. The second and first modes exhibited the smallest and largest disparities between experimental and simulated natural frequencies, respectively, at 0.68% and 10.24%.ConclusionWhile there are certain limitations, it is undeniable that Computer Aided Engineering (CAE) applications are advantageous for predicting the natural frequencies and vibration modes of spherical fruits such as oranges. Utilizing the obtained frequencies, especially the resonance frequency and the vibrational mode shape, enables us to avoid the resonance frequency in the actual transportation of oranges. This is possible through the implementation of suitable packaging and transportation methods, thereby mitigating the deterioration of fruit quality and ensuring an accurate prediction of its shelf life.

This paper attempts to utilize lower order harmonics and modes of vibration consisting of "square ratios of frequency variations" as structural damage susceptibility characteristics. This is followed by the development of the frequency-based method. Firstly, this paper derives the theoretical formulation of the square ratio of frequency variation method. Secondly, a finite element model of a single column platform is established. Then the damage is simulated using the reduced modulus of elasticity to localize the damage. The result is shown to be feasible. Thirdly, a model of the offshore single column platform is constructed, and the damage is simulated using cracks on the column. The "frequency variation square ratio" is valid, so the method can be used in reality. This method is applied to the single column platform model, suitable for a beam structure. It is very effective for the single column damage identification at different damage levels, and can also initially locate the damage. This method has high practical application value and reference value for future studies. [ABSTRACT FROM AUTHOR]

Introduction The growing consumer demand for high-quality products has led to the development of new technologies for assessing the quality of agricultural products. Iran is the 9th largest orange producer in the world. Every year, large quantities of agricultural products lose their optimal quality due to mechanical and physical damage during various operations such as harvesting, packaging, transportation, sorting, processing, and storage. This study is performed to identify the natural frequencies and vibration modes of the Thomson orange fruit using finite element modal analysis by ANSYS software. In addition, physical properties including mass, volume, density, and principal dimensions were measured, and mechanical properties were determined using Instron Texture Profile Analysis. The dynamic behavior of the orange fruit was simulated using the pendulum impact test. Afterward, the obtained impact was applied to the orange fruit by force gauge and three-axis accelerometer sensors in both polar and equatorial directions. The three-dimensional geometric model of the orange fruit was drawn in the ANSYS software. After meshing and applying the boundary conditions, the first 20 modes and corresponding natural frequencies were obtained. Since the objective of this study was to identify the natural frequencies of the orange fruit, it was considered to have free movement and rotation in space. The results showed that the natural frequencies of orange fruit are in the range of 0 to 248.41 Hz. Knowledge of the texture characteristics and dynamic behavior of horticultural products is essential for the design and development of agricultural machinery. Furthermore, the design and development of agricultural machinery are directly related to the biological properties of agricultural products. Materials and Methods The Thomson orange variety was used in the present study. The oranges used for the experiments were harvested from the Citrus and Subtropical Fruits Research Institute in Ramsar, Iran, located at coordinates 50° 40' E and 36° 52' N. The oranges were subsequently divided into two groups: large (average diameter 82 mm) and small (average diameter 66 mm). Conducting the finite element analysis requires knowledge of the physical and mechanical properties of the flesh and skin of the orange fruit. The physical and mechanical properties of the tested samples include geometric dimensions, modulus of elasticity, Poisson's ratio, and density. In the present study, the dynamic behavior of the orange fruit under dynamic loads was investigated by performing an impact test using a pendulum. The orange fruit was hung from the ceiling using a thin thread to perform experimental tests and extract the modal parameters. The orange samples were subjected to impact at three angles: 7° (below the yield point), 10° (at the dynamic yield point), and 20° (above the dynamic yield point). Results and Discussion The comparison of the experimental (laboratory) natural frequencies and simulation validates the simulation results. The experimental natural frequencies of the first, second, and third modes in the large-group oranges are 125.4, 146.9, and 180.4 Hz, respectively. Additionally, the simulation (modal) frequencies are 133.80, 146.16, and 196.66 Hz for the first three modes, respectively. The lowest and the highest differences were observed in the second (0.5%) and third (9.01%) modes, respectively. In the small-group oranges, the first, second, and third modes have experimental natural frequencies of 152.2, 188.8, and 242.2 Hz, respectively, and simulation frequencies are 167.79, 187.50, and 248.30 Hz. The second and first modes exhibited the smallest and largest disparities between experimental and simulated natural frequencies, respectively, at 0.68% and 10.24%. Conclusion While there are certain limitations, it is undeniable that Computer Aided Engineering (CAE) applications are advantageous for predicting the natural frequencies and vibration modes of spherical fruits such as oranges. Utilizing the obtained frequencies, especially the resonance frequency and the vibrational mode shape, enables us to avoid the resonance frequency in the actual transportation of oranges. This is possible through the implementation of suitable packaging and transportation methods, thereby mitigating the deterioration of fruit quality and ensuring an accurate prediction of its shelf life. [ABSTRACT FROM AUTHOR]

Abstract The macaw palm is a palm tree with wide geographic distribution. The aim of this work was to determine the modal properties of the macaw palm fruit-rachilla system subjected to mechanical vibrations. Three-dimensional models were elaborated using a computational program for 3D CAD modeling. The three-dimensional model developed was validated as a function of the real displacements observed during laboratory vibration tests. The average values observed for the system natural frequencies in the vibration tests were 20.09 Hz for the immature stage and 19.86 Hz for the mature stage. The average values of natural frequencies obtained by the numerical simulations were 28.41 Hz and 25.56 Hz for the immature and mature maturation stages, respectively. The vibration mode corresponding to the natural frequencies evaluated was characterized as pendulum displacements of the macaw palm fruit-rachilla system.

In this work, we have considered a cantilever beam with a rectangular plastic cross-section, reinforced by four wire reinforcements made of ductile Iron. It was studied using numerical resolution based on theoretical formulae and then simulated using Solidworks software. A comparison of the results on the frequency ratios between the theoretical and numerical by Solidworks models gave a low error of 1.389% with a high correlation coefficient of around 0.959. Then, two top reinforcements inside the beam were cut in order to study the behavior of the intact beam and the damaged beam. Using the simulation results, we found an accurate damage severity using a mathematical method based on error deviation indicators or Model Performance Analysis (MPA).

This paper aims to perform modal and harmonic response analyses to show how the piston skirt length reacts. The studied aluminium piston was generated in CATIA CAD Software and consequentially this was simulated in ANSYS software using modal and harmonic response tools. The piston finite element model was built to predict the basic modal parameters such as: natural frequencies, vibration modes and deformations. Different grid sensitivity tests have been done to improve the accuracy of the piston model. The piston with larger skirt has shown 77% higher vibration deformations than piston with smaller skirt. The proposed methodology can be easily used by a design engineer to perform dynamic behaviour studies of moving components and assemblies in Internal Combustion engines and not only. [ABSTRACT FROM AUTHOR]

This paper proposes a local resonance-type pentagonal phononic crystal beam structure for practical engineering applications to achieve better vibration and noise reduction. The energy band, transmission curve, and displacement field corresponding to the vibration modes of the structure are calculated based on the finite element method and Bloch-Floquet theorem. Furthermore, an analysis is conducted to understand the mechanism behind the generation of bandgaps. The numerical analysis indicates that the pentagonal unit oscillator creates a low-frequency bandgap between 60–70 Hz and 107–130 Hz. Additionally, the pentagonal phononic crystal double-layer beam structure exhibits excellent vibration damping, whereas the single-layer beam has poor vibration damping. The article comparatively analyzes the effects of different parameters on the bandgap range and transmission loss of a pentagonal phononic crystal beam. For instance, increasing the thickness of the lead layer leads to an increase in the width of the bandgap. Similarly, increasing the thickness of the rubber layer, intermediate plate, and total thickness of the phononic crystals results in a bandgap at lower frequencies. By adjusting the parameters, the beam can be optimized for practical engineering purposes. [ABSTRACT FROM AUTHOR]

Understanding the vibrational characteristics of power transformers is significantly important in their design and monitoring. In this contribution, a model with a multi-physics coupling simulation of the electrical circuit, magnetic field, and solid mechanics is developed to investigate the characteristics of the transformer vibration. After describing the model, the harmonic contents of the vibration signals and their variation in the case of mechanical faults are studied. It is shown that under normal operating conditions, the fundamental vibration frequency of 100 Hz has the maximum amplitude, while in the case of mechanical faults, the amplitudes of 200 Hz and 300 Hz harmonics increase dramatically compared to the fundamental harmonic. The influence of vibration sensor position is investigated too, which indicates that the area near the tank bottom is the best position to gather vibration signals. Moreover, the mechanical resonance frequencies of the transformer, along with their mode shapes, are addressed in this paper. Finally, the influence of mechanical changes on the vibration energy distribution in the tank surface is explored. The results of the paper suggest possible diagnosis methods for condition monitoring of transformers, such as using the vibration energy distribution on the tank surface or analyzing the vibration harmonics. [ABSTRACT FROM AUTHOR]

The object of the research is the reinforced concrete frame of an industrial building. A review of publications on methods of dynamic calculation of reinforced concrete structures is presented. Computational studies were carried out using the finite element method. The initial data for the calculation are the physical characteristics of the material of concrete, steel and base, the geometric parameters of the reinforced concrete frame obtained as a result of laser scanning. The resulting point cloud was combined with a mathematical model built based on design documentation. Based on a cloud of terrestrial laser scanning points, the computational model was refined. A comparison was made between the actual and design dimensions of columns and nodes. Discrepancies in the geometric dimensions of columns, nodes and connections were determined. The strength and stability of the reinforced concrete frame were not included in the methodology, but were used to determine the geometric dimensions of the structure, which are the initial data for the research. To determine the natural frequencies and vibration modes of the reinforced concrete frame, dynamic calculations of the equipment-frame-based system were performed. The equipment is presented in the form of distributed point masses on the marks of the frame consoles. An analysis of vibrations of the frame, based on which the structure was strengthened, is presented. The dynamic load from equipment operation is specified based on the measurements of vibration values in the longitudinal direction of the frame. The resonance zone during equipment operation was determined. Based on the results of the dynamic calculation, the frame structure was strengthened to prevent resonance phenomena. Test calculations and measurements showed the efficiency of the proposed method. The first translational (in the longitudinal direction) natural frequency increased from 3.609 Hz to 6.4258 Hz.

We consider the time dependent Euler–Bernoulli beam equation with discontinuous and singular coefficients. Using an extension of the Hörmander product of distributions with non-intersecting singular supports (L. Hörmander, 1983 [25]), we obtain an explicit formulation of the differential problem which is strictly defined within the space of Schwartz distributions. We determine the general structure of its separable solutions and prove existence, uniqueness and regularity results under quite general conditions. This formalism is used to study the dynamics of an Euler–Bernoulli beam model with discontinuous flexural stiffness and structural cracks. We consider the cases of simply supported and clamped-clamped boundary conditions and study the relation between the characteristic frequencies of the beam and the position, magnitude and structure of the singularities in the flexural stiffness. Our results are compared with some recent formulations of the same problem. [ABSTRACT FROM AUTHOR]

Non-contact vibration measurement of civil engineering structures is one of the most emphasized areas in structural health monitoring. Conventional methods have many limitations and challenges when used for the vibration testing of large civil engineering structures. Devices such as accelerometers must be mounted at appropriate locations to be able to record structure's motion, which can pose a major accessibility issue. Laser-based far-field displacement measurement systems that can only measure motion in the direction of the laser beam also require mounting of reflectors at the point of interest. Other limitations include upper and lower frequency limits and greater inaccuracies at higher frequencies, higher cost and multichannel applications for plotting mode shapes are impractical. In this research, a previously validated microwave interferometric radar is used for taking the response of cable-stayed bridge under impact and ambient conditions. The apparatus namely VirA can image the target in 3-dimensions from a single point of measurement with a least count of ≤ 0.1 mm. The accuracy of VirA was checked by the identification of lower-order modes of vibrations of the main girder. Several stay cables were then measured to identify natural frequencies for potential use in the condition monitoring of the bridge. VirA was found to be reliable in the measurement of natural frequencies of different structural components. Lower modes of vibrations were identified but mode shapes showed variation. Lower-order natural frequencies for cables were identified by VirA which suggests that it may be used for condition monitoring of cable-stayed bridges. [ABSTRACT FROM AUTHOR]

This research focuses on calculating the translational vibration modes of a three-level frame building, in order to determine its periods and way of vibrating, the evaluation was carried out using interactive methods of Stodola and Holzer, the numerical method of Jacobi, and the results obtained were verified using functions of the eigenvals vector and eigenvecs matrix of the Mathcad software. In addition, a verification was carried out with modeling in the Etabs software, following the properties established by the Technical Standard E.030 for Seismic-Resistant Design of the Reglamento Nacional de Edificaciones (RNE). Throughout the investigation, accurate results were obtained through manual calculations as well as verifications with the use of Mathcaf and ETABS software. In each instance, it was determined that these methods represent the most appropriate way to obtain approximate values with respect to the verification carried out with its period and way of vibrating. These reliable results underline the effectiveness of the tools and methods used, highlighting the deep understanding of the dynamic characteristics of the analyzed building. [ABSTRACT FROM AUTHOR]

In this work, we have considered a cantilever beam with a rectangular plastic cross-section, reinforced by four wire reinforcements made of ductile Iron. It was studied using numerical resolution based on theoretical formulae and then simulated using Solidworks software. A comparison of the results on the frequency ratios between the theoretical and numerical by Solidworks models gave a low error of 1.389% with a high correlation coefficient of around 0.959. Then, two top reinforcements inside the beam were cut in order to study the behavior of the intact beam and the damaged beam. Using the simulation results, we found an accurate damage severity using a mathematical method based on error deviation indicators or Model Performance Analysis (MPA). [ABSTRACT FROM AUTHOR]

Pipa fretting and pitch measurement are crucial aspects of playing. In this paper, Pipa’s string vibration is simplified to bounded string vibration, and a simplified structural model of Pipa is built. Transverse free vibration is used to establish the vibration equations of Pipa strings, and differential analysis is used to analyze the standing waves. Meanwhile, the vibration of the resonance panel of the Pipa was abstracted into a dynamic model, and the modal analysis was performed using coordinate transformation. In the actual test, the sound signal generated by the vibration was also processed with the help of the Fourier transform, and the pitch of the Pipa was measured by analyzing the time and frequency domains. The vibration of the Pipa panel is complex but regular, with the vibration pitch line at 32.5 hz being a central axis and the vibration pitch line at the frequency of 85 hz being on the upper side, while the vibration corresponding to the frequencies of 32.5 hz and 85 hz can be regarded as a synthesis of the vibration corresponding to the frequency of 175.5 hz. Under the viewpoint of vibration modal analysis, the performance effect of the Pipa has a more refined expression.

This paper first introduces the vibration modal analysis system and its general design, then improves the smoothing function and wavelet function transform algorithms in the system, and then determines and verifies the characteristic parameter algorithms in the structure of the improved wavelet transform vibration modal algorithms based on longitudinal waves, transverse shear waves, and bending waves in beams. The application of vibrational modes in sight-singing and ear training is examined and analyzed. The results show that the wavelet transform algorithm has the highest accuracy in calculation results. The calculation of vibration modes can be more effective using this basis. The investigation of students’ attitudes towards sight-singing and ear-training learning found that 52.3% of the students like sight-singing and ear-training learning, 40.13% and 7.37% of the students have no feeling for sight-singing and ear-training learning as well as disliking sight-singing and ear-training classes.48.68% and 37.45% of the students agree that sight-singing and ear-training training can help to improve their music literacy, and 25.79% and 56.14% of them think that Less gain in sight-singing ear training class is caused by boring teaching mode and single content. The investigation of vibrational modes in the teaching process of sight-singing and ear training found that 63.27% of the students had a better understanding of the learning process of vibrational modes; 68.59% of the students liked the teaching process of vibrational modes and the teaching method; and 70.79% of the students thought that the vibrational modes were helpful to the learning of sight-singing and ear training.

For the successful production of NiO/NiCo2O4 nanocomposites, the environmentally friendly method of egg white supplementation has been used. Several analytical techniques were employed to characterize the morphology, purity, and crystal structure of the as-prepared nanocomposites. These techniques included transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The physical adsorption and magnetic properties of the investigated composite were determined using the Brunauer–Emmett–Teller (BET) method and a vibrating-sample magnetometer (VSM), respectively. The results have shown that the as-prepared composite particles had diameters of about 10–25 nm, with uniform distribution. The XRD analysis showed that the as-synthesized composites consisted entirely of cubic structures of both NiO and spinel NiCo2O4 nanoparticles, with a space group of Fd3m. The FTIR analysis showed characteristic vibration modes related to metal oxides, confirming the formation of composites containing NiO and NiCo2O4 crystallites. The investigated composites' saturation magnetization (MS) and coercivity (HC) were easily controllable because of the ingredients' ferromagnetic (NiCo2O4) and antiferromagnetic (NiO) characteristics. The excellent combination of the NiO/NiCo2O4 nanocomposites' properties is anticipated to make this system suitable for a wide range of applications. [ABSTRACT FROM AUTHOR]

A square metal plate (Chladni plate) is excited harmonically by a vibration shaker, while the whole system is set in an anechoic chamber to stop reflections, isolate the system from sound entering from the surroundings, and deal with direct sounds only. As far as the authors are aware, such an arrangement has not been achieved so far. Vibration modes are visualized by using poppy grains scattered over the upper surface of the plate and are also recorded by a camera located above it, inserted among the acoustic wedges on the roof of the chamber, which made it possible to record the patterns and avoid unpleasant sounds associated with some of them. Four distinctive vibration modes of the plate are then originally identified using vibrational and acoustic mode identification. These responses from the plate are measured both by an accelerometer attached to the central point of the plate and by a microphone set on the same vertical line as the accelerometer but above it, measuring the direct sound. The signals from the accelerometer and the microphone are then compared in two experimental arrangements, and their forms and the frequency contents are found to be equivalent. It is shown that the existing symmetry, i.e., the exact correspondence between vibrational and acoustic responses, can be used as the identifier of the patterns formed on the plate and the associated modal frequency. [ABSTRACT FROM AUTHOR]

This paper addresses two aspects of the metrology of spherical, petal polymer reflectors which are part of an effort by the European Space Agency (ESA) to develop actively controlled foldable reflectors, enabling larger apertures on CubeSats and small satellites. The first problem is that of measuring the surface figure error of the spherical reflector alone during the development phase, and to assess the quality before assembling the telescope (large stroke, low accuracy). The SCOTS (Software Configurable Optical Testing System) appears to provide a fast and satisfactory solution to this problem. The second problem is the wavefront error reconstruction when the petal reflector is mounted on the telescope, because parts of the petals are obscured by the secondary mirror, in such a way that the petals appear completely disconnected, making the gradient-based metrology impossible. Using the fact that the petals have common mechanical boundary conditions at the central support ring, the problem is solved by using a set of orthogonal modes satisfying the same boundary conditions. The vibration modes are used for this purpose; the modal amplitudes are reconstructed from slope data outside the obstruction, allowing for wavefront error reconstruction over the entire surface. [ABSTRACT FROM AUTHOR]

In this paper, an electromechanical coupled dynamics model of a two-stage movable tooth drive system plus a motor is proposed. The electromechanical coupled dynamics equations of the system are derived. Based on it, the equations of the sensitivity of the natural frequencies to the system parameters are deduced. Natural frequencies and vibration modes of the drive system are investigated. The sensitivity of the natural frequencies to the system parameters is analyzed. Results show that the whole system has the low-speed mode, the whole vibration mode and the high-speed mode. The low-speed mode mainly occurs in the second stage drive. The high-speed mode mainly occurs in the first stage drive. The whole vibration mode occurs in the first and the second stage drives. For the three modes, sensitivity of the natural frequency to the coil current increases linearly. The natural frequencies increase quicker with the coil current for a large current. The rotation position angle of the wave generator has an important effect on the natural frequencies. [ABSTRACT FROM AUTHOR]

A description of the stand based on a digital speckle interferometer with a diffuse reference wave and separated branches is given, which allows determining the natural frequencies and vibration modes of objects in real time. In the frequency range 100...4000 Hz, an experimental study of the vibration characteristics of a turbine rotor blade of a gas turbine engine was carried out, with rigid fastening of the blade fir tree part, which was achieved by fixing the blade in the lock and then fixing it in the clamping device. In the frequency range from 100 to 4000 Hz, 9 blade vibration modes were identified. The object of the study is the turbine rotor blade of a gas turbine engine with a height along the trailing edge of 288 mm and a chord in the middle section of 88.5 mm. A solid-state geometric model of a rotor blade based on a faceted body obtained from 3D scanning has been created. Concerning the frequency range 100...4000 Hz, using the ANSYS Workbench software package, a series of calculations of the resonant frequencies of the blade by the finite element method was carried out. Many vibration modes have been obtained, and the data obtained from experiments and calculations have been compared. The analysis of the spectrum of the natural vibration frequencies of the blade showed that the root-mean-square value of the deviations between the results obtained is 5.5% for the same modes. To verify the software calculation, the values of the resonance frequencies were recalculated using a three-dimensional model of the blade fixed in the lock. To determine the influence of the boundary conditions for fixing a gas turbine blade on its vibration characteristics, a series of calculations of the resonance frequencies and vibration modes of the blade model with cutting off a part of the blade at different heights was carried out. It is shown that cutting off the fir tree part of the blade root when modeling the boundary conditions of fixing makes it possible to simplify the calculation process by simplifying the geometry of the three-dimensional model of the blade under study, with a minimum loss of calculation accuracy.

Objective. The article substantiates the need for digital simulation of emergency impact in the study of the stability of a building to progressive collapse by creating a simulator of local destruction.Method. To ensure the unique architectural appearance of the projected multifunctional high-rise complex, a complex shape has been developed with recesses in which elevator shafts are located. The principle of control of the structure due to the influx of external energy is observed. Energy conversion and the necessary protection is provided by the presence in the spatial frame of the building of balancing connections near architectural recesses, which allow stabilizing the state of a complex system. The spatial rigidity of the structural scheme of a high-rise building is ensured by the use of symmetrically located diaphragms and stiffening cores, rigid nodes for interfacing with the supporting structures of outrigger systems.Result. The calculation algorithm for progressive collapse includes the calculation of the stress-strain state of the building frame elements during normal operation. An analogue of the emergency action is created by excluding from the design model the bearing element, the instantaneous removal of which is modeled by a force with the opposite sign, determined by the results of the calculation in the normal operation stage.Conclusion. The stress-strain state of the frame, which occurs during local destruction, is a criterion for resistance to progressive collapse. The question of the need and the established form of outrigger floors in relation to a specific building has been investigated. The dependence of the dynamic characteristics when changing the structural solutions of the frame of a unique building is given.

In this manuscript, static and free vibration responses on Euler–Bernoulli beams with a Koch snowflake cross-section are studied. By applying the finite element method, the transversal displacement in static load condition, natural frequencies, and vibration modes are solved and validated using Matlab. For each case presented, the transversal displacement and natural frequency are analyzed as a Hausdorff dimension function. It is found that the maximum displacement increases as the Hausdorff dimension increases, with the relationship y m a x = k 0.79 ln d H + 0.37 , being k the iteration number of pre-fractal. The natural frequencies increase as ω ∼ M 2.51 , whereas the bending stiffness is expressed as E I = 1165.4 ln (d H + k) . Numerical examples are given in order to discuss the mechanical implications. [ABSTRACT FROM AUTHOR]

For the successful production of NiO/NiCo2O4 nanocomposites, the environmentally friendly method of egg white supplementation has been used. Several analytical techniques were employed to characterize the morphology, purity, and crystal structure of the as-prepared nanocomposites. These techniques included transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The physical adsorption and magnetic properties of the investigated composite were determined using the Brunauer–Emmett–Teller (BET) method and a vibrating-sample magnetometer (VSM), respectively. The results have shown that the as-prepared composite particles had diameters of about 10–25 nm, with uniform distribution. The XRD analysis showed that the as-synthesized composites consisted entirely of cubic structures of both NiO and spinel NiCo2O4 nanoparticles, with a space group of Fd3m. The FTIR analysis showed characteristic vibration modes related to metal oxides, confirming the formation of composites containing NiO and NiCo2O4 crystallites. The investigated composites’ saturation magnetization (MS) and coercivity (HC) were easily controllable because of the ingredients’ ferromagnetic (NiCo2O4) and antiferromagnetic (NiO) characteristics. The excellent combination of the NiO/NiCo2O4 nanocomposites’ properties is anticipated to make this system suitable for a wide range of applications.

The article deals with the complete modeling and characterization of thick piezoelectric ceramics. Modeling is based on radial and longitudinal mode determination of a thick piezoelectric disk. Shear modes are inserted in the modeling using the properties of partial derivatives. Displacements calculation of the three vibration modes leads to the determination of the general impedance of a thick disk. Modeling leads to new electromechanical coupling factors (EMC factors) showing the influence of coupling between: longitudinal-radial, longitudinal-shear and also shear-longitudinal modes. Using one-dimension hypotheses, longitudinal and radial 3D-EMC factors reduce to the well-known EMC factors defined by Standards. EMC factors related to coupling between longitudinal and shear modes are new. Complete characterization of the piezoelectric ceramic disk has been carried out for calculating all the constant-E and constant-D elastic constant (2 × 6) and the three piezoelectric coefficients related to the disk. Calculated elastic constant matrix is consistent because it does not depend on compliances. [ABSTRACT FROM AUTHOR]

The natural frequencies and modes of cantilever isotropic thin closed corrugated circular cylindrical shells with arbitrary number of corrugations are determined using the finite-element method. Two test problems for longitudinally corrugated open circular cylindrical shells are solved. The frequencies determined with our method and with the spline-collocation method in combination with the method of discrete orthogonalization are in good agreement (the difference is no greater than 5.5%). The natural frequencies of corrugated shells with different number of corrugations are compared. The dependence of the natural frequency of corrugated shells on the number of corrugations and vibration modes is established. The symmetric and antisymmetric modes of vibrations including those of tensile, shear, flexural, and torsional vibrations for all the corrugated shells considered are found. [ABSTRACT FROM AUTHOR]

Acoustic Resonance Testing is a nondestructive testing method based on the analysis of eigenfrequencies of structures. While it is a well-established technique for conventionally manufactured parts, more research is needed to use the technique to quantify the properties of complex, filigree structures like additively manufactured parts. Therefore, this work examines simulation-based generation of synthetic data to estimate influencing factors caused by additive manufacturing. Using numerical eigenfrequency analysis, a systematic study of the vibration modes of a Ti6Al4V metamaterial unit cell with multistable mechanical behaviour reveals the interplay between the material properties, geometrical parameters and manufacturing-induced defects. The simulations enable the identification of specific eigenfrequencies for which the highest influence of manufacturing variations on the vibration modes are to be expected in experiments, for example, with regards to the Young's modulus, spring width, or deflection-induced change in geometry. Frequency shift plots visualize the predicted effects of different parameters and form the basis for future guided experimental design and analysis for complex structures. The simulation-based approach allows a screening of multiple influencing factors, which is not possible experimentally. The simulation-based generation of synthetic data will contribute to the improvement of the interpretation of acoustic spectra and will extend the acoustic resonance testing for more complex structures. • Extension of acoustic resonance testing for complex 3D-structures and metamaterials. • Simulation-based quantification of the influence of manufacturing induced defects. • Simulation-aided design of experiments and enhanced interpretability of results. [ABSTRACT FROM AUTHOR]

This paper is focused on the study of the dynamic behaviour of two large arch dams, and it presents some innovations for the improvement of Seismic and Structural Health Monitoring (SSHM) systems for dams. The work describes a methodology based on the integrated use of software for automatic monitoring data analysis and of computational 3D finite element (3DFE) models for dam dynamic behaviour simulation. The monitoring data analysis software was developed for automatic modal identification, in order to obtain natural frequencies and mode shapes, for automatic detection of vibrations induced by seismic events, to be distinguished from those caused by other operational sources, and for comparison between results retrieved from measured vibrations and numerical results from 3DFE modelling. The numerical simulations are carried out using a 3DFE program developed for dynamic analysis of dam-reservoir-foundation systems, based on a solid–fluid coupled formulation and considering the dam-water dynamic interaction, including calculation modules for complex modal analysis and for linear and non-linear seismic analysis. The case studies are two large arch dams that have been under continuous dynamic monitoring over the last ten years: Cabril dam (132 m high), the highest dam in Portugal, and Cahora Bassa dam (170 m high), in Mozambique, one of the highest dams in Africa. The SSHM systems installed in both dams have similar schemes and were designed to continuously record accelerations in several locations at the upper part of the dam body and near the dam-foundation interface, using uniaxial and triaxial accelerometers. The most significant experimental results from continuous dynamic monitoring are presented and compared with numerical results for both dams, with emphasis on the evolution of natural frequencies over time, including the vibration mode shapes for various water levels, and on the measured accelerations during low-intensity seismic events. Furthermore, the main results of non-linear seismic response simulations are provided, considering the effects due to joint movements and tensile and compressive concrete damage, aiming to assess the seismic performance of both dams based on the Endurance Time Analysis method. [ABSTRACT FROM AUTHOR]

The AC conductivity response of disordered materials follows a universal power law of the form σ ′ (ω) ∝ ω n at the low frequency regime, with the power exponent values in the range 0 < n < 1. At the high frequency regime, in many experimental data of different disordered materials, superlinear values of the power exponent n were observed. The observed superlinear values of the power exponent are usually within 1 < n < 2 , but in some cases values n > 2 were detected. The present work is based on the definitions of electromagnetic theory as well as the Havriliak–Negami equation and the damped harmonic oscillator equation, which are widely used for the description of dielectric relaxation mechanisms and vibration modes in the THz frequency region, respectively. This work focuses mainly on investigating the parameters that affect the power exponent and the range of possible n values. [ABSTRACT FROM AUTHOR]

In this paper, a simple example to illustrate what is basically known from the Gauss’ times interplay between geometry and mechanics in thin shells is presented. Specifically, the eigen-mode spectrum in spontaneously curved (i.e., up-down asymmetric) extensible polymerized or elastic membranes is studied. It is found that in the spontaneously curved crystalline membrane, the flexural mode is coupled to the acoustic longitudinal mode, even in the harmonic approximation. If the coupling (proportional to the membrane spontaneous curvature) is strong enough, the coupled modes dispersions acquire the imaginary part, i.e., effective damping. The damping is not related to the entropy production (dissipation); it comes from the redistribution of the energy between the modes. The curvature-induced mode coupling makes the flexural mode more rigid, and the acoustic mode becomes softer. As it concerns the transverse acoustical mode, it remains uncoupled in the harmonic approximation, keeping its standard dispersion law. We anticipate that the basic ideas inspiring this study can be applied to a large variety of interesting systems, ranging from still fashionable graphene films, both in the freely suspended and on a substrate states, to the not yet fully understood lipid membranes in the so-called gel and rippled phases.

Bearing is an essential component in a mechanical rotating equipment system. It is no less important than lubrication to prevent wear is very important to consider in the mechanical maintenance system of rotating equipment. Bearing wear is one of the problems in wind turbines that will increase maintenance costs, shorten the wind turbines' lifespan, and cause the component or overall damage to the wind turbine. The latest technology has provided instruments for analyzing the damage of elements in a bearing according to the caused vibrations. Therefore, this study was performed on Ball Bearing Turbine Propeller to identify the dynamic characteristics of Ball Bearing with and without lubrication. The test was carried out using the Bump Test method applied in three measured parts: X, Y, and Z axes. The measuring instrument which was used was Fast Fourier Transform (FFT) Analyzer (Ono Sokki) and the data were analyzed using MATLAB. It was identified that the application of oil could reduce the amplitude and decrease the frequency. Personal frequency appearing more than once indicates the existence of global vibration modes. The frequency which only appears once in the measurement spot indicates local vibration modes. The highest frequency both after and before the application of oil was found in the Y-axis.

Damage to the rotor blade of a steam turbine is a relatively common problem and is one of the leading causes of sudden and unplanned shutdowns of a steam turbine. Therefore, the high reliability of the rotor blades is very important for the safe and economical operation of the steam turbine. To ensure high reliability, it is necessary to perform a vibration analysis of the rotor blades experimentally and in a computer environment. In this paper, a modal analysis was performed on the twisted blade of the last stage of the turbine in the Ansys software. The results of the modal analysis of the stationary rotor blade were compared with the results obtained by the bump test, which confirmed the numerical model of the blade. A modal analysis of a rotating rotor blade was performed on the same numerical model, and Campbell diagrams were plotted to determine the critical speeds

Nanotechnology is presently dealt with development in the process of becoming an indispensable phenomenon in the engineering and scientific fields. In this work, it has been proved that the (8, 0) zig-zag GaN, GaP, GaAs, InN, InP, and InAs nanotubes can act as semiconductors. For historical reasons, normal mode analysis was originally developed for describing the vibrational spectra of molecules. A very useful approach in the analysis of normal modes is to turn attention away from individual modes and towards the types of motion in the nanotube that one would like to analyze. By calculation of the normal modes using the U matrix, it is possible to get the F matrix from the multiplication of frequency to the U matrix. In this work a complete set of the linear combinations and their normalization coefficients are achieved. The fact that for zigzag tubes, the IR-active modes are different in the (8, 0) zig-zag GaN, GaP, GaAs, InN, InP, and InAs nanotubes and is due to the reduced symmetry for those compounds. In this Letter, a simple yet accurate computational frequency normal mode was derived for estimating the nanotubes that are corresponding with some behavior of them. [ABSTRACT FROM AUTHOR]

Bimetallic Au/Ag core–shell cuboid nanoparticles (NPs) exhibit a complex plasmonic response dominated by a dipolar longitudinal mode and higher-order transverse modes in the near-UV, which may be exploited for a range of applications. In this paper, we take advantage of the strong signature of these modes in the NP ultrafast transient optical response, measured by pump-probe transient absorption (TA) spectroscopy, to explore the NP vibrational landscape. The fast Fourier transform analysis of the TA dynamics reveals specific vibration modes in the frequency range 15–150 GHz, further studied by numerical simulations based on the finite element method. While bare Au nanorods exhibit extensional and breathing modes, the bimetallic NPs undergo more complex motions, involving the displacement of facets, edges and corners. The amplitude and frequency of these modes are shown to depend on the Ag shell thickness, as the silver load modifies the NP aspect ratio and mass. Moreover, the contributions of the vibrational modes to the experimental TA spectra are shown to vary with the probe laser wavelength at which the signal is monitored. Using the combined simulations of the NP elastic and optical properties, we elucidate this influence by analyzing the effect of the mechanisms involved in the acousto-plasmonic coupling. [ABSTRACT FROM AUTHOR]

To explore the effect and mechanism of bivalent ion doping on yttrium iron garnet (YIG), Zn-YIG (Zn-doped YIG) nanoparticles with a size of 60~70 nm were prepared by the sol-gel method. It was proven that Zn ion doping resulted in lattice expansion and internal stress due to crystallite size shrinkage. A Raman spectroscopic analysis proved the influence of Zn doping on the crystal structure and peak intensity by analyzing Raman vibration modes. The characteristics and chemical mechanism of mass loss and phase evolution in each temperature region were explored through TG-DSC measurements. Moreover, it was revealed that the antiferromagnetic coupling, pinning mechanisms and particle aggregation lead to coercivity, exhibiting different variation trends. A saturation magnetization (Ms) curve variation mechanism was further revealed, which was due to the thermal effects, super-exchange effect, and coupling effect between sub-lattices. Meanwhile, the influence of the thermal effect on Ms and its mechanism were explored by spin theory, and it was proven that it was mainly caused by the random arrangement of magnetic moments and thermal vibration. These results provide theoretical support for the wider application of YIG devices in microwave and high-temperature fields. [ABSTRACT FROM AUTHOR]

This paper investigates the potentials of inter-story isolation systems (IIS) for retrofitting irregular masonry buildings by means of an isolated vertical addition realised on the roof of the existing structure. By assuming a case study, a wide parametric analysis is firstly carried out on lumped-masses model for identifying the dynamic properties of the isolated superstructure that minimizes the global seismic response. Hence, a 3D FE model is adopted for the detailed design and analysis of the IIS structure, with different solutions, in order to regularize the global seismic response of the IIS complex. Finally, some general design criteria are suggested. [ABSTRACT FROM AUTHOR]