Static Frequency Research Articles

Effects of Folding Degree and Mass Fraction on the Static and Natural Frequency Characteristics of Functionally Graded Graphene Origami-Enabled Auxetic Metamaterials Annular Plates

This study addresses a critical gap in the literature by investigating the static and natural frequency characteristics of functionally graded (FG) auxetic metamaterial annular plates reinforced with graphene origami (GOri), a novel area previously unexplored in the context of composite constructions, particularly for circular plates. The governing equations are derived utilizing higher-order shear deformation theory along with Hamilton’s principle, and solved using the finite element approach. For the first time, a comprehensive parametric study including the folding degree and mass fraction, and distribution pattern of GOri, is investigated on the static and natural frequency properties of annular plates. It is found that the natural frequency generally increased with higher mass fractions and decreased with greater folding degrees, though the X and V patterns at a 3% mass fraction showed an atypical increase in frequency with higher folding degrees. The impact of distribution patterns varied with weight fraction: the X-pattern caused the highest deflection at 1% weight fraction but the lowest at 3%, while the O-pattern caused the least deflection overall.

Investigation on Dynamic and Static Modulus and Creep of Bio-Based Polyurethane-Modified Asphalt Mixture

The superior mechanical qualities of polyurethane have garnered increasing attention for its application in modifying asphalt mixtures. However, polyurethane needs to use polyols to cure, and polyols need to be produced by petroleum refining. As we all know, petroleum is a non-renewable energy source. In order to reduce oil consumption and conform to the trend of a green economy, lignin and chitin were used instead of polyols as curing agents. In this paper, a biological polyurethane-modified asphalt mixture (BPA-16) was designed and compared with a polyurethane-modified asphalt mixture (PA-16) and a matrix asphalt mixture (MA-16). The viscoelastic characteristics of the three asphalt mixtures were evaluated using dynamic modulus, static modulus, and creep tests. The interplay between dynamic and static modulus and frequency is examined, along with the variations in the correlation between dynamic and static modulus. The creep behavior of the mixture was ultimately examined by a uniaxial static load creep test. The findings indicate that the dynamic modulus of BPA-16 exceeds those of PA-16 and MA-16 by 8.7% and 30.4% at 25 Hz and −20 °C, respectively. At 25 Hz and 50 °C, the phase angle of BPA-16 decreases by 26.3% relative to that of MA-16. Lignin and chitin, when utilized as curing agents in place of polyol, can enhance the mechanical stability of asphalt mixtures at low temperatures and diminish their temperature sensitivity. A bio-based polyurethane-modified asphalt mixture can also maintain better elastic properties in a wider temperature range. At −20–20 °C, the dynamic and static moduli of BPA-16, PA-16 and MA-16 are linear, and they can be converted by formula at different frequencies. The failure stages of BPA-16, PA-16, and MA-16 are not observed during the 3600 s creep duration, with BPA-16 exhibiting the least creep strain, indicating that lignin and chitin enhance the resistance to permanent deformation in PU-modified asphalt mixes.

Computational studies of the optical properties of 4-cyano-4-hexyl biphenyl using a combination of DFT and molecular dynamics simulation

ABSTRACT In this study, we predicted the optical properties of the liquid crystal 4-cyano-4-hexylbiphenyl (6CB) by employing a combination of Density Functional Theory (DFT) and Molecular Dynamics simulation. We obtained the polarisability and anisotropy of polarisability of the liquid crystal through DFT calculations by employing a variety of basis sets and implementing them in Gaussian 09. The density and order parameters of the liquid crystal at different temperatures were determined from Molecular Dynamics simulations and implemented in NAMD. The extraordinary and ordinary refractive indices were then predicted from the Vuks equation. The effect of long-range corrected DFT calculations on polarisability and anisotropy of polarisability was also explored with the functionals LC-BLYP and CAM-B3LYP. We found that at static frequencies, the basis set B3LYP 6–31 G (2d,p) produced excellent results in determining refractive indices with maximum errors of 4.1% and 3% in the nematic and isotropic phases, respectively. However, the B3LYP functional was unsuitable for determining refractive indices at a wavelength of 589 nm. In contrast, the long-range functional CAM-B3LYP combined with the basis set 6–31 G (2d,p) resulted in maximum errors of 3.7% in the nematic phase and 2.5% in the isotropic phase when determining refractive indices at 589 nm.

Study on the dynamic characteristics of the head cover-bolts-stay ring of a variable-speed pump-turbine

Abstract The design and operation of variable-speed pump-turbine units is more difficult than that of conventional units due to their adjustable speed, frequent start stop, and forward and reverse operation. Due to the development of variable-speed pump-turbines towards variable-speed, high head, and large capacity, the vibration instability caused by frequent switching between turbine and pump operating conditions is more prominent. The study on the dynamic characteristics of the head cover-bolts-stay ring system is an important guarantee for the long-term safe and stable operation of the units. This article uses the finite element method to conduct modal analysis on the head cover-bolts-stay ring system of a variable-speed pump-turbine. The natural frequency and mode shape are analyzed, and resonance analysis is carried out in combination with the dynamic and static interference characteristics of the variable-speed unit. The research results show that the dynamic and static interference frequency of the unit during the variable-speed process may be close to the natural frequency of the head cover-bolts-stay ring system, which needs to be paid attention to during operation. The results and findings in this article provide theory and practical basis for the research and design of high head, large capacity, and variable-speed pump-turbine units.

LADRC‐based non‐characteristic harmonic suppression strategy for pumped storage power plants

AbstractThe static frequency converter (SFC) in a pumped storage power plant often causes harmonic problems in the dragging processes, which may lead to the false operation of automatic devices in the power station, and even damage to the power equipment. These harmonics caused by SFC contain both characteristic and non‐characteristic degrees, and the components are more complex. Hence, the existing harmonic suppression methods using active power filter or passive power filter compensation all have some problems. The SFC starting control strategy based on linear active disturbance rejection control (LADRC) is proposed here to reduce the non‐characteristic harmonics. First, the factors affecting the non‐characteristic harmonic content are analysed, and a mathematical model of the conventional SFC starting transfer function is established. On this basis, the LADRC controller is used as the speed loop of SFC starting to replace the proportional integral (PI) controller. The stability is judged by drawing the Bode plot and the zero‐pole plot. Finally, a Matlab/Simulink simulation model of LADRC‐based SFC starting is established in a pumped storage power plant with actual parameters, and simulation accurate measurements verify the effectiveness of the proposed control strategy for non‐characteristic harmonic current suppression.

Influence of d-d transition electrons and thickness variations on the excited-state optical properties: Nonlinear optical characterization of Cr2O3 thin film

The structural, morphological, linear, and nonlinear optical properties of Cr2O3 thin films with different thicknesses deposited by the thermal deposition, were measured. The structural and morphological parameters of films, determined by XRD, FESEM, and AFM images, are compared to the linear and nonlinear optical characteristics of these media. The bandgap of prepared thin films was obtained from DRS spectra. The electron effective mass (me∗/m0), linear refractive index (n0), optical static, and high frequency dielectric constant (ε0 , ε∞) values were calculated by using the band gap energy values. Increasing the thicknesses of thin films causes to decrease the band gap, an increase RMS, increase the size of nanoparticles and the nonlinear responses of thin films. The high magnitude of n2, and β belonged to the Cr2O3 (300 nm-thickness) in the order of 10−5 cm2/W, and 10−1 cm/W respectively. The fluctuations in nonlinear responses observed at different thicknesses are attributed to d-d transitions and intraband scattering of equilibrium electrons influenced by laser radiation, as indicated by the nonlinearity data. The considerably elevated refractive non-linearity values in the analyzed film materials suggest their potential for practical applications in optoelectronic devices.

A frequency-secured planning method for integrated electricity-heat microgrids with virtual inertia suppliers

The integrated electricity-heat microgrid (IEHM) is characterized by low inertia and a high share of renewable generation. Although sector coupling in the IEHM enhances energy efficiency, the integration of electricity and heat systems restricts the primary frequency regulation (PFR) ability of coupling equipment, further threatening frequency security. This paper presents a frequency-secured planning method for virtual inertia suppliers and combined heat and power (CHP) units in the IEHM. First, we examine the PFR in IEHMs from both device and system perspectives. We develop steady-state models for sector-coupled equipment, specifically CHP units and large-scale heat pumps, for PFR and sizing purposes. To describe the system’s frequency response under emergency conditions, we explicitly derive frequency constraints that account for varying system inertia of heterogeneous resources. Furthermore, we conduct a comprehensive analysis of the impact of PFR on heating systems within the IEHM. Second, we propose a frequency-constrained planning model for IEHMs based on the aforementioned modeling framework. This model balances the power supply, heating supply, and PFR reserves deployment of IEHM by properly sizing the regulation resources. It also leverages distributionally robust (DR) chance constraints to address uncertain wind power generation. To improve the tractability of this model, we introduce a well-tailored reformulation approach that handles the nonconvexity of system inertia and DR chance constraints. Case studies conducted on two test systems demonstrate the effectiveness of the proposed method in securing frequency stability while improving the economic performance of IEHM. This method ensures both dynamic and static frequency security across 100% of time steps by optimally deploying system inertia and PFR reserves. Moreover, by coordinating heterogeneous PFR resources with time-varying system inertia, the proposed approach yields superior economic performance, achieving over a 9% reduction in total capacity compared to average benchmarks.

Output Voltage Harmonics Mitigation in Static Frequency Converter for Shore to Ship Power Connection Supplying Nonlinear Loads using Multi-frequency Quasi Resonant Controller

Output Voltage Harmonics Mitigation in Static Frequency Converter for Shore to Ship Power Connection Supplying Nonlinear Loads using Multi-frequency Quasi Resonant Controller

Single-crystal growth, crystal structure, and molecular dynamics of organic–inorganic [NH3(CH2)2NH3]CuBr4

As part of obtaining excellent properties that can be used as lead-free hybrid solar cells, the crystal growth, crystal structure, phase transition temperature, and thermal properties for [NH3(CH2)2NH3]CuBr4 were discussed. The crystal structure at 300 K was determined to be monoclinic by single-crystal X-ray diffraction (XRD) analysis. The phase transition temperatures were determined to be 447 and 473 K, and the results were consistent with the powder XRD patterns. Thermogravimetric analysis revealed thermal stability up to ~ 460 K. The continuous changes in the 1H and 13C chemical shifts and 14N static resonance frequency with increasing temperature are related to variations in the local environment and coordination geometry. The significant differences in activation energies obtained from the 1H and 13C spin–lattice relaxation times (t1ρ) at low and high temperatures were discussed. The activation energy results suggested that the energy barrier at low temperatures was related to the reorientation of the NH3 and CH2 groups around the three-fold symmetry axis, and the energy barrier at high temperatures was related to the reorientation of the [NH3(CH2)2NH3] cation. These physical properties will be provide important insights or potential applications of this crystal.Please check and confirm that the corresponding author and their respective corresponding affiliation have been correctly identified and amend if necessary.OK !

Energetic and Kinetic Competition on the Stability of Pd13 Clusters: Ab Initio Molecular Dynamics Simulations.

Material stability is the focus on both experiments and calculations, which includes the energetic stability at the static state and the thermodynamic stability at the kinetic state. To show whether energetics or kinetics dominates on material stability, this study focuses on the Pd13 clusters, because of their observable magnetic moment in experiment. Energetically, the CALYPSO searching method and first-principles calculations find that Pd13(C2) is the ground state at 0 K while the static frequency calculations demonstrate that the icosahedron Pd13(Ih) becomes more favorable on free energy as temperature increases. However, their magnetic moments (8 μB) are not in agreement with the experimental value (<5.2 μB). Kinetically, ab initio molecular dynamics simulations reveal that Pd13(C3v) (6 μB) has supreme isomerization temperature and the other 11 low-lying isomers transform to Pd13(C3v) directly or indirectly, demonstrating that Pd13(C3v) has the maximum probability to be observed in experiment. The magnetic moment difference between experiment (<5.2 μB) and this calculation (6 μB) may be due to the spin multiplicities. Our result suggests that the magnetic moment disparity between theory and experiment (in Pd13 clusters) originates from the kinetic stability.

Lower magnetic field measurement limit of the coupled dark state magnetometer

Abstract The Coupled Dark State Magnetometer (CDSM) is an optically pumped magnetometer. For the Jupiter Icy Moons Explorer (JUICE) mission, the CDSM and two fluxgate magnetometers are combined in the J-MAG instrument to measure the static and low frequency magnetic field in the Jupiter system. During certain calibration manoeuvres, the CDSM has to be able to measure magnetic field strengths down to 100 nT with an accuracy of 0.2 nT (1 σ). At such low magnetic fields, the CDSM’s operational parameters must be carefully selected to obtain narrow resonance structures. Otherwise, the coupled dark state resonances, used for the magnetic field detection in different instrument modes, overlap and result in a systematic error. In this paper we demonstrate that with the found instrument settings the CDSM is able to measure magnetic field strengths below 100 nT with a systematic error less than 0.2 nT resulting from the overlap of the resonances.

Exploring the effect of thin film thicknesses on linear and nonlinear optical properties of MoO3 thin film

The structural, morphological, linear, and nonlinear optical properties of MoO3 thin films deposited by thermal deposition were measured. The effect of various thicknesses of films was studied. The structural and morphological parameters of films, determined by x-ray diffraction, field emission scanning electron microscopy, and AFM images, are compared to the linear and nonlinear optical characteristics of these media. The bandgap of the prepared thin films was obtained from the diffuse reflectance spectroscopy spectra. The electron’s effective mass (me*/m0), linear refractive index (n0), and optical static and high frequency dielectric constant (ɛ0, ɛ∞) values were calculated by using the bandgap energy values. Increasing the thicknesses of thin films decreased the bandgap, increased the root mean square, and increased the size of nanoparticles and the nonlinear response of thin films. The high magnitude of n2 and β was because of MoO3 (300 nm-thickness), which were of the order of 10−5 cm2/W and 10−1 cm/W, respectively. The fluctuations in nonlinear responses observed at different thicknesses are attributed to d–d transitions and intraband scattering of equilibrium electrons influenced by laser radiation, as indicated by the nonlinearity data. The considerably elevated refractive nonlinearity values in the analyzed film materials suggest their potential for practical application in optoelectronic devices.

Static output feedback LFC for semi‐Markov type interconnected multi‐area power systems: A non‐fragile PI strategy

AbstractThis article addresses the static output feedback load frequency control (LFC) problem for semi‐Markov type interconnected multi‐area power systems (IMAPSs) through non‐fragile proportional‐integral (PI) strategy. Primarily, by roundly exploiting the dynamical properties and considering random mutations of the IMAPSs, the semi‐Markov jump process (MJP) is elaborately scheduled for establishing the dynamical model with precision. Subsequently, on account of the characteristic of geographical isolation, a memory‐like sampled‐data LFC mechanism considering time‐varying transmission delay for the semi‐Markov jump IMPASs is formulated accordingly. Additionally, the non‐fragile issue is explored for the PI controller gain fluctuations to meet the actual operation scenario. After that, a mode‐dependent two‐side polynomial‐type looped Lyapunov functional is constructed for enhancing flexibility. Then, in virtue of the stochastic analysis technique, some relaxed conditions guaranteeing stochastic stability with prescribed performance are thereby derived in the shape of linear matrix inequalities (LMIs). Ultimately, a numerical example is carried out to validate the efficacy of the developed control methodology.

Dynamic Modeling and Analysis of a Temperature- Dependent Axially Translating Functionally Graded Cantilever Beam

In this paper, the dynamics of an axially translating functionally graded cantilever beam (FGCB) with time-varying length are studied under environmental temperature variations. Firstly, the governing partial differential equation for the FGCB under different temperatures is established based on the Euler–Bernoulli beam theory. Secondly, the Galerkin discretization and the assumed mode method (AMM) are employed to derive the vibration equations for each mode. Then, the coupling effects of the axial translation motion and the bending deformation on the vibration response of the FGCB are analyzed through numerical simulation. The results showed that different initial lengths, velocities and accelerations can influence the dynamic response greatly. Moreover, the increase in temperature will increase the response amplitude and decrease the frequency of FGCB, but the increase in functionally gradient parameter will decrease both the amplitude and the frequency of the FGCB. Finally, the wavelet transform (WT) is utilized to perform a time–frequency analysis. It is found that the time-dependent frequency obtained by using WT is consistent with the first-order static frequency obtained theoretically. The variation of frequency with time can be obtained quickly and accurately by using WT. The results of this research are of great significance for the application of composite axially translating beams in practical engineering.

Dynamic hydroelasticity of composite appendages with reverse-mode algorithmic differentiation

Composite materials enable the tailoring of load-dependent, passive, shape adaptation because of the directional stiffness of the fibers. However, excessive flow-induced vibrations and dynamic instabilities represent a design challenge for composite marine appendages. We develop DCFoil, a dynamic composite foil solver that uses one-dimensional models—composite beam elements and unsteady lifting line theory—to perform static and dynamic frequency domain analysis. The program is differentiated to provide derivatives of an aggregated flutter function with respect to design variables. The flutter function characterizes dynamic hydroelastic stability. We apply the solver to investigate the hydroelastic performance of a composite fin bulb keel based on the IMOCA 60 class of racing yachts, which were reported to have flutter problems. Based on the derivatives computed for this bulb keel, we found that the foil thickness has the most significant impact on flutter speed. This work shows both the development of and utility of a program with flutter derivatives for flexible composite marine appendage design.

The role of process and geometrical parameters of gate stack Inverted-T shape junction less FET at 20 nm technology node

In the present era, FET devices are seamlessly integrated with complex circuits that can be used to realize chips capable of operating at a significantly higher speed. These designed devices can meet the requisite of circuits used in designing mobile phones, tablets and laptops, thereby enhancing the overall performance. The present work focuses on designing of gate stack inverted-T junctionless FET at 20 nm technology node. Both static and low frequency characteristics of device such as threshold voltage (VTh), transconductance (gm), on (ION) & off (IOFF) state currents, as well as its high-frequency characteristics like total gate capacitance (Cgg), cut-off frequency (fT), maximum oscillation frequency (fmax) and gain bandwidth product (GBW) are methodically demonstrated with alterations in the device process and geometrical variations. The parameters such as height of fin, width of fin and work function are varied to study their impact. The SS, DIBL, ION/IOFF (current switching ratio) and VTh, for 20 nm gate length are observed as 67.94 mV/dec, 34.32 mV/V, 108, 0.32 V, respectively. The fmax is determined to be in the THz range and has early voltage of approximately 6.12V. Additionally, the effect of temperature is also studied by varying it in the range of 250 K–450 K. Analysis and virtual modelling of device is carried out using Visual TCAD. In addition, p-channel transistor is designed along with the n-channel configuration to investigate the device performance for CMOS based circuits. The noise margin and average delay of the inverter circuit are observed to be 0.37 V and 36.7 ps respectively.

The SF and remanence evaluation of magnetic shields based on SST for low-frequency and degaussing situation

As the dominant shielding functional material, the permalloy sheet primarily determines the static and low-frequency shielding performances of magnetically shielded room (MSR). However, the lack of measurement of shielding sheets for practical use would lead to a non-negligible evaluation error in MSR performance. Therefore, an estimation technique of shielding factor (SF) and the remanence of MSR is proposed in this paper while considering the nonlinear magnetic characteristics of the permalloy sheet tested by a single sheet tester for low-frequency field and degaussing situation (L-D-SST). First, a high-accuracy measurement system, comprising L-D-SST (for exciting magnetic field and sensing the corresponding B and H) and the control system (for applying excitation to L-D-SST and amplifying, filtering, and collecting B and H signals), is established. Weak magnetic fields at low frequencies and decaying alternating demagnetizing field excitations are separately applied to the L-D-SST for basic magnetization curves (BM curves) and an anhysteretic magnetization curve (AM curve) tests. Furthermore, the BM and AM curves are respectively integrated with the FEM algorithm for accurate and reliable estimations of the SF and remanence of MSR in an operational state. In addition, the tested magnetic properties are applied for the optimization of MSR shielding quality.

An enhanced static frequency converter with integrated energy storage for pumped storage plants

An enhanced static frequency converter with integrated energy storage for pumped storage plants

Experimental comparison of a NACA0021 airfoil in large plunging and surging motions at 90 ◦ angle of attack

The topic of vortex-induced vibrations on a wind turbine blade has recently gained much attention due to its growing size and flexibility. To address this concern, a wind tunnel test was conducted to study the forced plunging and surging motion of a NACA0021 airfoil at 90° angle of attack. Results indicate that vortex lock-in occurred for a motion amplitude of one chord length even for a small frequency ratio (between motion frequency and static Strouhal frequency) of 0.39. Analysis of the drag coefficient, derived from the phase-averaged Particle Image Velocimetry (PIV) data, shows that a plunging airfoil experiences higher average loading than a surging airfoil, which is deemed to be more harmful considering the higher loading in the crossflow-direction due to the variation of effective angle of attack.

Principle of the electromagnetic testing based on the varied frequency domain and its realization

With the development of modern industry, the types and quantities of industrial equipment are increasing. In the long-term production process, various failure modes such as corrosion and cracks will occur, therefore the workload of inspection will increase dramatically. It is extremely urgent to study the combined non-destructive testing (NDT) technology and develop corresponding multi-functional instruments to achieve rapid inspection. In this paper, an electromagnetic testing principle based on the varied frequency domain is proposed. In the first place, spatial uniformity and spatial periodic static fields are generated by the arrangement of the permanent magnetizers, these static fields are fields with different spatial frequencies. In the second place, dynamic fields with different frequencies are generated by different frequencies excitations. Under the time-space electromagnetic field coupling, a new combined electromagnetic testing principle of magnetic flux leakage (MFL), guided wave (GW) and electromagnetic acoustic transducer (EMAT) is proposed. The MFL testing method can be realized based on the uniform static field, GW based on the interaction of spatial periodic static field and low frequency dynamic field, while EMAT based on the combination of uniform static field and high frequency dynamic field. According to the above principle, a multi-functional instrument is developed, which includes a medium-low frequency excitation unit for GW, a high frequency excitation unit for EMAT, corresponding receiving amplifiers for GW/EMAT/MFL, and USB-based data transmitters. Finally, the relevant performance tests are carried out, which laid the foundation for field application.