Fundamental Vibrational Modes Research Articles

Multi-resonant TVA formed by a tree of deflated composite beams with core structured fabrics

Abstract This paper presents a study on a multi-resonant tuneable vibration absorber for the control of flexural vibrations of thin structures in a low frequency band where the response is characterized by distinct lightly damped resonances of low order flexural modes. The absorber is formed by a tree of deflated composite beams made by a core structured fabric wrapped on a plastic skin. The beams have increasingly smaller length and are fixed in the middle on a mast that works as a base-post and vacuum-junction too. The fabric in each beam is made by a lattice of interlocked truss-like rigid particles. The uniform pressure exerted by the deflated skin forces the particles to jam such that the fabric moves from its natural fluid-like state to a solid state whose rigidity depends on the confining pressure exerted by the skin. Hence, each beam is characterized by a fundamental flapping vibration mode whose response resembles that of a classical mass-spring-damper vibration absorber and can be suitably tuned by adjusting the level of vacuum. The paper first analyses the working principles of single-beam and three-beams absorbers with respect to their vibration transmissibility and base impedance frequency response functions. Then, it presents the vibration control generated by the single-beam and the three-beams absorbers tuned to minimise the resonant responses of a single or three low order flexural modes of a thin plate. The paper shows that the operational frequency of each beam-absorber can be suitably adapted in a band of 8 Hz by varying the vacuum pressure in a 5 – 80 kPa range. Also, it shows that the single-beam or multi-beams absorbers reduce the resonant response of the target flexural modes by 10 to 20 dB.

A Computational Study of Temperature Driven Low Engine Order Forced Response In High Pressure Turbines

Abstract This paper reports the results of computational studies of the effect of combustor exit temperature distortions on Low Engine Order (LEO) forced response of a High Pressure Turbine (HPT). Forced response of this kind occurs at frequencies below the Stator Vane Passing Frequency (SVPF) and can be a major cause of High Cycle Fatigue (HCF) in turbines due to its tendency to excite fundamental modes of vibration. This paper investigates the extent through which temperature distortions act as a forcing stimulus in HPT rotor rows, through measuring unsteady pressure and modal force magnitude recorded from full annulus unsteady simulations of the MT1 stage: a low temperature, unshrouded, HPT rig. Rotor relative incidence angle variations are shown to be the key mechanism through which temperature acts as a forcer in HPT rotor rows, whilst temperature driven forced response is shown to be dependent on the magnitude of the modal content of the upstream temperature waves. These findings are used to build a reduced domain tool for blocked burner forced response prediction, which is shown to be accurate to an RMS error of 2.66%, far beyond the current accepted standard for forcing prediction of this kind.

Crystal Growth, Structural Elucidation, Chemical Reactivity, Topology Exploration (ELF, LOL, AIM, RDG) and NLO Activity of 4-Cumyl Phenol Crystal Using Quantum Chemical Calculation

The main objective of the study is to analyze the structural behavior and NLO activity of 4-cumyl phenol by experimental and theoretical spectroscopic techniques. Its computational result is compared with the cumene compound. The optimized structural parameters of the title compound were computationally obtained at the B3LYP/6-31G (d, p) basis set. The fundamental modes of vibration were examined by experimental FT-IR, and FT-Raman techniques. The distribution of the vibrational bands was carried out with the help of normal coordinate analysis (NCA). The resulting harmonic wavenumbers were scaled by using NCA method. Topological analysis, such as Electron localization function (ELF), natural bond orbital analysis (NBO), reduced density gradient (RDG) and atoms in molecule (AIM) analysis, molecular electrostatic potential (MEP) have been used to evaluate the intermolecular interaction, especially the hydrogen bonds. UV-visible spectrum of the compound was recorded in the region 200–900 nm and the electronic properties and HOMO-LUMO energies were calculated by time dependent density functional theory approach.

Hunting for Sulfur-containing Molecules in Space: A Spectroscopic Characterization of Cyclopropenethione Based on High-level Ab Initio Calculations

Cyclopropenethione falls into the class of complex organic molecules but has not yet been observed in the interstellar medium or any circumstellar disks. However, its existence is very likely, and thus this study provides high-level ab initio predictions, which may serve as reference data for future observations or experimental work. Rovibrational configuration interaction theory based on multidimensional potential energy surfaces being obtained from explicitly correlated coupled-cluster calculations has been used to predict the fundamental vibrational modes, the microwave spectrum, and low-lying rovibrational transitions. Rotational constants as well as quartic and sextic centrifugal distortion constants were obtained from vibrational perturbation theory.

Protección sísmica de estructuras civiles mediante dispositivo INERTER en la provincia de Huancayo

This research work proposes the use of a Tuned-Mass-Damper-Inerter (TMDI), which combines a new configuration of passive vibration control using an “Inerter”. This two-terminal mechanical flywheel device, based on the well-known Tuned-Mass-Damper (TMD), generates resistance forces proportional to the relative acceleration of its terminals. TMDI takes advantage of the “mass amplification effect” of Inerter to improve performance compared to TMD. For harmonically excited primary linear systems, closed-form analytical software is modeled to obtain optimal design and tuning parameters of the TMDI, using established methods. It is observed that, with proper distribution of the dampers, the TMDI system is more effective in suppressing vibrations close to the natural frequency of the uncontrolled primary system and is more resistant to the effects of detuning and misdistribution. Furthermore, the results of the modeled structures show the effectiveness of the TMDI, modeled as a classical damper, in suppressing the fundamental mode of vibration for linear MDOF structures. The incorporation of the Inerter in the proposed TMDI configuration can replace part of the vibrating mass, achieving lightweight passive vibration control solutions or improving structural performance. The solution proposed and modeled with traditional dampers behaves linearly, in line with current performance trends for minimally damaged structures protected by passive control devices. Additionally, optimized TMDI is applied for vibration suppression and displacement control, offering optimal seismic protection.

Temperature-controlled synthesis of novel boron nanofibers by laser ablation technique

The synthesis of boron nanofibers (BNFs) at different temperatures using the double-pulsed laser ablation (DPLA) technique were reported. Q-switched Nd: YAG laser with 532 and 1064 nm dual beam wavelengths of laser used to ablate a solid boron target. A vapor–solid process at a furnace temperature and pressure supported boron 'nanofibers' growth with the active metal catalysts of 1 % Ni and 1 % Co in a quartz tube furnace in flowing argon (Ar) gas. The crystalline phase purity of the synthesized BNFs at 950, 1050, and 1150 °C were determined by X-ray diffraction (XRD), and the results from XRD confirm that each BNF is preferentially grown in the c-axis (100) direction of alpha boron (α-B). Electron microscopy revealed that each BNF exhibit a length of 1–5 μm and a diameter width of 5–100 nm, while the elemental chemical compositional nature of the BNFs is identified from energy dispersive X–ray spectroscopy (EDX). Image analysis shows the average diameter of each BNF synthesized to be 23.10, 19.13, and 16.09 nm. The lattice distance of each BNF is found to be 0.40, 0.39, and 0.38 nm, respectively. Fingerprint Raman spectroscopy revealed the fundamental vibrational modes of BNFs at Eg and A1g.

Quantification of Crystal Chemistry of Fe‐Mg Carbonates by Raman Microspectroscopy and Near‐Infrared Remote Sensing

AbstractOn Earth, carbonate minerals are widely used as recorders of the geological environments in which they formed. Here, we present a method designed to retrieve the crystal chemistry of Fe‐Mg carbonate minerals using infrared remote sensing or Raman spectroscopy. We analyzed a suite of well‐characterized Fe‐Mg carbonate minerals for which Raman spectra were obtained in two different laboratories, and IR spectra were measured in reflectance and transmission from the visible range to 25‐μm. We built calibration lines for the dependence of fundamental and harmonic vibrational modes position to the Mg# (defined as Mg# = 100 × Mg/(Mg + Fe + Ca + Mn)). These calibrations should enable retrieval of Mg# based on spectroscopic observations with a typical accuracy of 10. We discuss the framework of applicability of these calibrations and apply them to a typical CRISM spectrum of carbonates from the Nilli Fossae region of Mars.

Symmetric and asymmetric vibration and buckling of a thermal rotating annular-plate with Pasternak foundation

This paper studies the symmetric and asymmetric vibration and buckling modes of a rotating thermal annular plate resting on a Pasternak foundation. With considering the von Kármán geometric nonlinearity and the first-order shear deformation theory, the governing equations of the system are established via Hamilton's principle, and then solved by using the differential quadrature method. With both inner and outer boundaries constrained, the modes of the rotating system vary differently depending on the mode symmetry. The symmetric modes are mainly affected by the generated centrifugal force, while the asymmetric ones are affected by both centrifugal and Coriolis forces. The additional Coriolis, with mainly two directions, strengthens the forward travelling parts of the asymmetric modes, but makes the backward counterparts buckled more easily. Also, the thermal effect, as well as boundary elasticity and foundation coefficients, are also investigated from the viewpoint of mode symmetry. Results show that the temperature rise can shift the fundamental vibration mode from the symmetric one to the asymmetric one and backward travelling waves for rotation, which also adds to the complexity of mode variation with joint parameters. For the joint effect of the temperature rise and rotating, the annular plate tends to buckle more readily while the effects of the two factors are linearly superimposed.

Millimeter-Wave and High-Resolution Infrared Spectroscopy of the Ground and Seven Lowest Fundamental States of 1H-1,2,4-Triazole.

A combined analysis of millimeter-wave (70-700 GHz) and rotationally resolved infrared (400-1200 cm-1) spectra of the ground state and seven fundamental vibrational modes of 1H-1,2,4-triazole is reported. While the lowest-energy vibrationally excited state (ν18) is well-treated using a single-state distorted-rotor Hamiltonian, the second (ν17) and third (ν16) vibrationally excited states are involved in strong c-type Coriolis coupling and require an appropriate two-state Hamiltonian. The oblate nature of 1H-1,2,4-triazole is sufficiently close to the oblate symmetric-top limit that the analysis requires the use of A-reduced, sextic centrifugally distorted-rotor Hamiltonian models in the Ir representation in order to achieve low σfit values. The coupling between ν17 (A″) and ν16 (A″) resulted in many transitions with slightly perturbed frequencies, many highly displaced resonant intrastate transitions, and 165 nominal interstate transitions. Modeling the spectra of ν17 and ν16 required three c-axis Coriolis-coupling terms (Fab, FabJ, and FabK) to treat the interaction. Many of the nominal interstate transitions form clearly discernible Q-branch bands, comprising degenerate sets of a- and b-type transitions. The rotational spectra of four higher-energy vibrationally excited states (ν15, ν14, ν13, and ν12), which form a complex polyad involving Coriolis and anharmonic coupling interactions, were analyzed by single-state models, thus producing only effective spectroscopic constants. Inclusion of rotationally resolved infrared transitions enabled the accurate and precise determination of vibrational band origins for the four lowest-energy fundamental states: ν18 = 542.601 824 3 (28) cm-1, ν17 = 665.183 128 5 (43) cm-1, ν16 = 682.256 910 5 (43) cm-1, and ν15 = 847.557 400 (11) cm-1.

Computational aspects of DFT, HOMO-LUMO, PED, molecular docking and basic characterisations of Octadec-9-Enoic Acid (C18H34O2)

Finding a few potential ‘green’ inhibitors has been a long-term goal because these products that are derived from plants enable prescription drug costs reduced, side effects minimised and biodegradable. Known by its common name, Hybanthusenneaspermus (L.) F. Muell, which is a member of the Violaceae family, is a herb or shrub found worldwide in tropical and subtropical climates. Knowing the applicability of H. enneaspermus for the treatment of a variety of acute or chronic diseases with a diverse nature of phytoconstituents will be made easier with the information provided in this comprehensive article. The majority of the information in this research article was gathered from different scientific sources that focused on H. enneaspermus research. Plant extraction, optimised geometry, thorough vibrational assignment, and characterisation of the fundamental vibrational modes of Octadec-9-Enoic Acid were conducted using experimental FT-IR and UV-Vis data in addition to quantum chemistry research. The actual vibrational data were compared to the wavenumbers computed theoretically for the chemical's optimal shape using DFT/B3LYP gradient calculations with the 6-311G ++ (d,p) basis set. A computation has been performed utilising the energy gap between HOMO and LUMO. Intramolecular interactions (NBO), molecular electrostatic potential (MEP) at a specific point p (x,y,z), atomic charge values, NMR & UV-vis computation, and molecular docking studies with protein-ligand interactions were all interpreted using natural bond orbital analysis.

Optimization of column-in-column system based on non-conventional TMD concept

Previous studies showed that the non-conventional tuned mass damper (TMD) with large mass ratio outperforms the traditional one in respect to the structural vibration control efficiency and robustness. The authors recently proposed a novel control system based on the non-conventional TMD concept, namely the column-in-column (CIC) system, which was composed of a primary column, a secondary column and a series of interconnected springs/dashpots. In this novel system, the secondary column connected to the primary one with springs/dashpots could act as a large TMD to attenuate adverse vibration of the primary structure, and its control effectiveness was preliminarily verified through numerical investigations. However, the control robustness was found not sufficient based on the existing optimal formulae in the literature for CIC optimization. This paper presents a new design method for optimizing the CIC system for better harnessing its control effectiveness and robustness in reducing structural response. The CIC system consists of two columns with distributed mass and uniform flexural rigidity, connected by springs along the column height. The effective modal mass and modal stiffness of a specific vibration mode of the system can be straightforwardly calculated by using the Euler-Bernoulli beam theory. Considering the fundamental vibration mode of the system as the target response mode for vibration control, the multiple degree-of-freedom (DOF) CIC is simplified into a two DOF with three springs (2DOF3S) structural model, the design parameters, i.e., the optimal tuning frequency ratio and damping ratio of this system are derived to minimize the displacement response of the primary structure. To demonstrate the proposed design method, the effectiveness and robustness of the CIC system in controlling seismic induced structural vibrations are assessed in both the frequency and time domains. Results show that the derived optimum formulae are applicable for optimizing the TMD system with consideration of the distributed mass and deformation of the mass damper, i.e., a column in this study. The optimized CIC system has good control robustness even if the CIC is mistuned with its design parameters deviate from the optimal values by ±50 %. The conventional TMD system with lumped mass as the mass damper is a special case of the proposed CIC system. The optimized CIC system has favorable control efficiency in mitigating the seismic responses of structures with reduction ratios averagely varying within the range of 15 % ∼ 55 % with a probability of 92.67 %. It is concluded that the proposed method is reliable and can be used for the optimum design and control of the CIC system.

Vibrational Self-Consistent Field (VSCF) and Post-VSCF Method Calculations Combined with the Reference Interaction Site Model Self-Consistent Field Method Coupled with the Constrained Spatial Electron Density Distribution: Applications to NaHCOO in Aqueous Phase.

Investigating vibrational behavior in solution is crucial for understanding molecular dynamics within a solvent environment. Notably, the analysis of Raman spectra for molecules in solution is important owing to its ability to unveil intricate solute-solvent interactions. Previous studies have effectively employed frequency calculations utilizing the reference interaction site model self-consistent field method in conjunction with constrained spatial electron density distribution (RISM-SCF-cSED) to understand molecular vibrations in solution, primarily focusing on fundamental vibrational modes. However, the oversight of overtones and combination tones in these studies prompted us to combine the vibrational self-consistent field (VSCF) and vibrational second-order Mo̷ller-Plesset perturbation (VMP2) methods with RISM-SCF-cSED to address these aspects theoretically. Illustrating the efficacy of this integrated approach, we computed the Raman spectra of sodium formate (NaHCOO) in water, revealing the necessity of accounting for molecular anharmonicity in solution vibrational analysis. Our findings underscore the potency of VSCF and VMP2 in conjunction with RISM-SCF-cSED as a robust theoretical framework for such calculations.

Microwave synthesis of magnesium phosphate-rGO as an effective electrode for supercapacitor application

Abstract Transition metal phosphate based materials is being used for energy storage because of P–O covalent bond which facilitates more storage compared to other transition metals and this covalent bond enhanced the electrochemical performance for supercapacitor applications. Pure magnesium phosphate (Mg3(PO4)2) were synthesized via microwave synthesis as the composite varies with rGO (MgPO-XrGO) X=25,50,75,100mg. The prepared composite materials were examined employing XRD, Raman, FT-IR, SEM and XPS studies. Electrochemical studies (CV, EIS, GCD) of three electrode system for the prepared electrodes were performed using Biologic SP-150 with 2M (H2SO4) as electrolyte. From the XRD results, triclinic structured MgPO was confirmed (JCPDS card #35–0329) and rGO has enhanced the crystallinity of MgPO composite. From Raman analyses, the well graphitization nature of rGO in composite MgPO was identified and from XPS analysis chemical composition of the elements was analyzed. The FT-IR fundamental modes of vibrations of PO 4 3 − ${\text{PO}}_{4}^{3-}$ (γ 1,γ 3,γ 4) were obtained. The electrochemical analysis of the prepared material such as pure and composite materials showed better performance. The high specific capacitance was obtained for MgPO-50rGO because MgPO has high coordination with rGO. As Mg2+ oxidation state has high chemical reactivity compared to other earth metals and other advantage is P–O covalent bond that enhanced the performance of the electrode. By facilitating these advantages, rGO is included as composite to develop the electrode to favor the practical applications. By using the optimum level rGO composite with MgPO4-50rGO a better new candidate was successfully developed for supercapacitor applications. The fabricated MgPO-50rGO//Activate carbon full cell set up exhibited the specific capacitance 61 Fg−1 at 1 Ag−1, 21.7 Wh kg−1 energy density and 790.0 W kg−1 power densities and explored outstanding capacitive retention in 2 electrode full cell setup cyclic stability of 99.1 % over the 5000 cycles.

Crystal structures and photoluminescence properties of undoped and Fe3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowders

Undoped and Fe3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowders were produced by a solid-state reaction process. The prepared samples underwent characterizations using XRD, SEM with EDS, HR-TEM with SAED, FTIR, Raman, UV-Vis, EPR and PL techniques. The XRD analysis confirms the orthorhombic crystal structure of the prepared samples and unit cell parameters were evaluated. The samples exhibited stone-like structures with low aggregation based on the micrographs obtained from SEM and HR-TEM images. Additionally, the grain and particle sizes of the powder samples were evaluated. The elements Li, O, P, Ba and Fe were confirmed to be present in the produced samples by EDS spectra. FT-IR and Raman spectral investigation revealed the fundamental vibrational and bending modes of various phosphate groups. The energy bands, identified as characteristic bands of Fe3+ ions, were produced in the UV–visible region of the optical absorption spectrum for the doped sample. The crystal field and inter-electronic parameters (Dq = 915, B = 700 and C = 2715 cm−1) were also evaluated. Furthermore, the refractive index and metallization criteria properties were calculated using energy bandgap values of 4.46 and 4.38 eV of the produced samples. The doping of Fe3+ ions led to a reduction in the bandgap energy, resulting in a red-shift. A resonance signal was observed in the EPR spectrum at g = 2.05, which can be ascribed to iron ions entering the host lattice at a distorted octahedral symmetry sites and this was also supported by optical absorption studies. The produced sample showed emission peaks at 354, 440 and 530 nm in the ultraviolet, blue and green regions of its photoluminescence spectrum. Photometric parameters, such as CCT, CRI and CIE chromatic coordinates, reveal that the prepared samples could bee used in LEDs applications. This work offers novel visions into diphosphate compounds doped with transition metal ions.

Modeling Nonlinear Dynamics of Functionalization Layers: Enhancing Gas Sensor Sensitivity for Piezoelectrically Driven Microcantilever.

This article presents a parametrized response model that enhances the limit of detection (LOD) of piezoelectrically driven microcantilever (PD-MC) based gas sensors by accounting for the adsorption-induced variations in elastic properties of the functionalization layer (binder) and the nonlinear motional dynamics of the PD-MC. The developed model is demonstrated for quantifying cadaverine, a volatile biogenic diamine whose concentration is used to assess the freshness of meat. At low concentrations of cadaverine, an increase in the resonance frequency is observed, contrary to the expected reduction due to mass added by adsorption. The study explores the variations in the elastic modulus vis-à-vis the adsorbed mass of cadaverine and derives the resonance frequency to the adsorbed mass response function. We advance a blended technique involving the analysis of atomic force microscopy (AFM) force-distance (f-d) curves and fitting of the quartz crystal microbalance (QCM) impedance response spectrum to deduce the adsorption-induced changes in the viscoelastic properties of the functionalization layer. The findings obtained are subsequently employed in modeling the response function for a structurally nonhomogenous PD-MC, highlighting the significance of the functionalization layer to the global elastic properties. The structural composition of the PD-MC beam adopted herein features a trapezoidal base hosting the actuating piezoelectric stratum and a rectangular free end with a functionalization layer. The Euler-Bernoulli beam theory coupled with Hamilton's principle is used to develop the equation of motion, which is subsequently discretized into a set of nonlinear ordinary differential equations via Galerkin expansion, and the solutions to the first fundamental mode of vibration are determined using the method of multiple scales. The obtained solutions provide a basis for deducing the nonlinear response function model to the adsorbed mass. The derived model is validated by recorded resonance frequency changes resulting from exposure to known concentrations of cadaverine. We demonstrate that the increase in resonance frequency for low concentrations of cadaverine is due to the dominance of the variation of the elastic modulus of the functionalization layer originating from the initial binder-analyte interactions over damping due to added mass. It is concluded that the developed nonlinear response function model can reliably be used to quantify the cadaverine concentration at low concentrations with an elevated Limit of Detection.

Vibration Mitigation via Tuned Mass Damper for Adjacent Stay Cables Interconnected with Rigid Cross-Tie

The characteristics of low damping and closely spaced natural frequencies make stay cables susceptible to wind-induced vibrations. This work proposed a novel damping device consisting of tuned mass damper (TMD) and rigid cross-tie (RCT) to mitigate the vibration of stay cables effectively. Two adjacent stay cables interconnected with RCTs can provide installation locations for TMDs, thus making the novel TMD-RCT control system feasible. Experimental control tests were carried out on a two-cable model of adjacent stay cables built in laboratory, where one TMD was designed based on the fundamental vibration mode of the stay cable. The effects of CT stiffness, number of RCTs, mass ratio, and installation position on the vibration reduction effect of the device were studied. To validate the efficacy of the proposed TMD-RCT device in vibration mitigation of stay cables under different loading cases, simulation tests and corresponding control performance evaluation were conducted.

FT-IR, FT-raman and UV spectra and ab initio HF and DFT study of conformational analysis, molecular structure and properties of ortho- meta– and para–chlorophenylboronic acid isomers

In this study, the FT-IR, FT-Raman, and UV–Vis spectroscopic properties of three monosubstituted phenylboronic acid derivatives: ortho-chlorophenylboronic acid (o-ClPhBA), meta-chlorophenylboronic acid (m-ClPhBA) and para-chlorophenylboronic acid (p-ClPhBA) molecules are investigated both experimentally and theoretically using Density Functional Theory (B3LYP) and Hartree Fock (HF). In order to find the stable possible conformations of the compounds, the conformational analysis was carried out by running potential energy surface (PES) scan by means of rotation of two structural parameters, the dihedral angles indicated as φ2 (C6–B–O1–H1A) and φ3 (C6–B–O2–H2A), varying from −180° to 180° with an increment of 10° using B3LYP/6-31G level of theory. Also, to determinate the most stable conformer for all the molecules, potential energy curve (PEC) the stable possible conformations on PES scan were investigated as a function of φ1 (C1-C6–B–O1) dihedral angle from 0° up to 180° with an increment of 10° using B3LYP/6–311++G(d,p) and HF/6–311++G(d,p) level of theory. For all the studied compounds, two conformational structures (conformer anti-anti, syn-syn) that did not have imaginary frequency values outside the equilibrium state (conformer anti-syn) were detected theoretically at the both methods.Due to their conformational flexibility, the relative stabilities of the anti-syn, anti-anti, and syn-syn conformers of o-ClPhBA, m-ClPhBA, and p-ClPhBA are 0.0, 4.66, and 6.76 kcal/mol, respectively, at the B3LYP/6–311++G(d,p) level of theory. For the HF/6–311++G(d,p) level of theory, the relative stabilities are 0.00, 4.54, and 6.11 kcal/mol for o-ClPhBA; 0.00, 3.98, and 1.51 kcal/mol for m-ClPhBA; and 0.00, 4.10, and 1.44 kcal/mol for p-ClPhBA, respectively. Some of the determined stable conformations of these molecules are different in symmetry groups. It was observed that the increase in the symmetry was effective in the of molecular properties, especially for vibrational frequencies. The structural parameter, dipole moments (μ), vibrational frequencies, polarizability (α), hyperpolarizability (β), the highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) of the stable conformers were calculated by using Ab initio HF/6–311++G(d,p) and DFT/B3LYP/6–311++G(d,p) level of theory. The assignments of fundamental vibrational modes of the studied molecule were performed based on total energy distribution (TED) analysis.

Investigating thermal conductivity and mechanical properties of a hybrid material based on cellulose nanofibers and boron nitride nanotubes using molecular dynamics simulations

Cellulose nanofibers (NFCs) have emerged as a preferred choice for fabricating nanomaterials with exceptional mechanical properties. At the same time, boron nitride nanotubes (BNNTs) have long been favored in thermal management devices due to their superior thermal conductivity (k). This study uses reverse non-equilibrium molecular dynamics (MD) simulations to investigate k for a hybrid material based on NFCs and BNNTs. The result is then compared with pure NFC and BNNT-based structures with equivalent total weight content to elucidate how incorporating BNNT fillers enhances k for the hybrid system. Furthermore, the fundamental phonon vibration modes responsible for driving thermal transport in NFC-based materials upon incorporating BNNTS are identified by computing the vibrational density of states from the Fourier transform analysis of the averaged mass-weighted velocity autocorrelation function. Additionally, MD simulations demonstrate how both NFCs and BNNTs synergistically improve the constituting hybrid structure’s mechanical properties (e.g. tensile strength and stiffness). The overarching aim is to contribute towards the engineered design of novel functional materials based on nanocellulose that simultaneously improve crucial physical properties pertaining to thermal transport and mechanics.

Symmetric and asymmetric free vibrations of rotating eccentric annular plate

The symmetric and asymmetric free vibrations of rotating eccentric annular plate in uniform thermal environment are studied in present paper. The priority of research is clarifying the different combined effects of various factors on symmetric and asymmetric vibrations of eccentric annular plate. In order to conveniently obtain the natural frequency and vibration mode of eccentric annular plate with irregular physical domain, the transformed differential quadrature method is employed. Due to the rotational motion, the initial configuration caused by centrifugal force is calculated before vibration analyses. Then the traveling wave vibration arisen from the Coriolis force is investigated. By comparing the vibration characteristics of annular plate with/without eccentricity, the different impacts of interaction between the geometrical size, boundary conditions, temperature rise, rotational motion, and eccentricity on symmetric and asymmetric vibrations are discussed. Results show that eccentricity leads to the splitting phenomena only in asymmetric vibrations. And it does not affect the symmetry of vibration. Temperature rise results in that the fundamental vibration mode shape shifts from symmetric to asymmetric. However, eccentricity inhibits the change. Rotational motion causes the occurrence of traveling wave vibration in asymmetric vibration whereas not in symmetric vibration.

Passive mitigation of low-frequency vibration modes in lightweight structures based on a new generation of acoustic black holes

Topology optimization and generative design are methods used to lighten structures under specific loads. The resulting lightweight components are usually softer in the directions perpendicular to the applied efforts, such as in the case of cranes. This results in the possible excitation of structural modes at very low frequencies, which can lead to premature aging of lightweight structures. In this paper, we present a new design of acoustic black hole (ABH), able to mitigate vibration modes in a test 3D-printed lightweight structure, from 20 Hz upwards. The novel ABH weights less than 10 grams and can be readily screwed on the structure. Its design is based on that of a classic ABH, with additional winglets and/or rods, to increase the vibrating mass without significantly changing the stiffness of the ABH. This results in a strongly reduced ABH cut-on frequency. The winglets and/or rods also result in a greatly increased contact area between the ABH and the viscoelastic dissipative material, with positive effects on the ABH damping efficiency. The new ABHs could successfully be used, first to damp the fundamental vibration mode of aluminum cylinders, and then to reduce the amplitude of the first three structural modes of the test lightweight structure. The new ABH manages to damp modes at frequencies several times lower than the ones found in the literature, which are promising results.