Torsional Frequencies Research Articles

Interactive Modelling and Simulation of Micromirror MEMS Devices

This paper presents an interactive software package for the modelling and simulation of microelectromechanical system (MEMS) devices utilizing the MATLAB high-level programming language and its interactive environment. The package provides a dynamic analysis and frequency responses of a 1-D torsional micromirror electrostatically actuated with staggered vertical comb-drives. Applying a frequency sweep to the micromirror equation, the torsional mode natural frequency may be estimated. The developed package consists of several graphical user interfaces used for modeling MEMS devices. The software package is useful for computing the forces and torques for different micromirror geometries.

Pervasive interactions between methyl torsion and low frequency vibrations in S0 and S1p-fluorotoluene.

We report two dimensional laser induced fluorescence spectral images exploring the lower torsion-vibration manifolds in S0 (E < 560 cm-1) and S1 (E < 420 cm-1) p-fluorotoluene. Analysis of the images reveals strong torsion-vibration interactions and provides an extensive set of torsion-vibration state energies in both electronic states (estimated uncertainty ±0.2 cm-1), which are fit to determine key constants including barrier heights, torsional constants, and torsion-vibration interaction constants. The dominant interactions in both electronic states are between methyl torsion (internal rotation) and the lowest frequency out-of-plane modes, D20 and D19, both of which involve a methyl wagging motion. This is the second aromatic (following toluene) for which a significant interaction between torsion and methyl out-of-plane wagging vibrations has been quantified. Given the generic nature of this motion in substituted toluenes and similar molecules, this mechanism for torsion-vibration coupling may be common in these types of molecules. The inclusion of torsion-vibration coupling affects key molecular constants such as barrier heights and torsional (and rotational) constants, and the possibility of such an interaction should thus be considered in spectral analyses when determining parameters in these types of molecules. p-Fluorotoluene is the first molecule in which the role of methyl torsion in promoting intramolecular vibrational energy redistribution (IVR) was established and the observed torsion-vibration coupling provides one conduit for the state mixing that is a precursor to IVR, as originally proposed by Moss et al. [J. Chem. Phys. 86, 51 (1987)].

A Fiber Bragg Grating Based Torsional Vibration Sensor for Rotating Machinery.

This paper proposes a new type of torsional vibration sensor based on fiber Bragg grating (FBG). The sensor has two mass ball optical fiber systems. The optical fiber is directly treated as an elastomer and a mass ball is fixed in the middle of the fiber in each mass ball fiber system, which is advantageously small, lightweight, and has anti-electromagnetic interference properties. The torsional vibration signal can be calculated by the four FBGs’ wavelength shifts, which are caused by mass balls. The difference in the two sets of mass ball optical fiber systems achieves anti-horizontal vibration and anti-temperature interference. The principle and model of the sensor, as well as numerical analysis and structural parameter design, are introduced. The experimental conclusions show that the minimum torsional natural frequency of the sensor is 27.35 Hz and the torsional vibration measurement sensitivity is 0.3603 pm/(rad/s2).

On the torsional vibrations of restrained nanotubes embedded in an elastic medium

In this paper, torsional dynamics of nanotubes embedded in an elastic medium with arbitrary elastic boundary conditions is studied. The proposed mathematical model in this study developed based on the nonlocal elasticity theory gives us opportunity to include small-scale parameter. Two springs in torsional direction are attached to a nanotube at both boundaries. Angular rotation function based on the nonlocal elasticity theory is represented by a Fourier sine series. A coefficient matrix including torsional effects is obtained by using Stoke transformation and nonlocal boundary conditions. This coefficient matrix can be used to obtain the torsional vibration frequencies with restrained or rigid (fixed-free) boundary conditions. In order to validate the performance of the present analytical method, results calculated for rigid boundary cases (fixed-free) are presented for a comparison with those given in the literature, and the results agree with each other exactly. It is shown that nonlocal parameter, torsional spring coefficients and elastic medium have a notable impact on the torsional dynamics of carbon nanotubes.

Torsional vibration characteristics of power transmission system

Torsional vibration is a frequent perturb for heavy rotating and high speed machinery. Development of large torsional vibrations produce torsional stresses which leads to increase in bearing loads and results in generation of cracks in the high stress areas of the transmission system and propeller. So, it is important to model and analyze the torsional characteristics of Power transmission system. The information obtained regarding torsion vibration characteristics will be useful to study the system dynamics and prevent premature failure caused due to resonance at critical speeds. In this paper, torsional vibration analysis is carried out for a marine power transmission system. The propulsion system is modeled as a flexible shaft with multiple inertias as lumped masses and shaft sections with torsional stiffness. Holzer method is employed to calculate the torsional resonant frequencies and their corresponding mode shapes. An algorithm for Holzer method is designed and programmed using MATLAB software.

Spectral Dynamic Analysis of Torsional Vibrations of Thin-Walled Open Section Beams Restrained Against Warping at One End and Transversely Restrained at the Other End

The present paper deals with spectral dynamic analysis of free torsional vibration of doubly symmetric thin-walled beams of open section. Spectral frequency equation is derived in this paper for the case of rotationally restrained doubly-symmetric thin-walled beam with one end rotationally restrained and transversely restrained at the other end. The resulting transcendental frequency equation with appropriate boundary conditions is derived and is solved for varying values of warping parameter and the rotational and transverse restraint parameter. The influence of rotational restraint parameter, transverse restraint parameter and warping parameter on the free torsional vibration frequencies is investigated in detail. A MATLAB computer program is developed to solve the spectral frequency equation derived in this paper. Numerical results for natural frequencies for various values of rotational and transverse restraint parameters for various values of warping parameter are obtained and presented in both tabular as well as graphical form showing the influence of these parameters on the first fundamental torsional frequency parameter.

Multibody Simulation for the Vibration Analysis of a Turbocharged Diesel Engine

In this paper, a multibody calculation methodology has been applied to the vibration analysis of a 4-cylinder, 4-stroke, turbocharged diesel engine, with a simulation driven study of the angular speed variation of a crankshaft under consideration of different modeling assumptions. Moreover, time dependent simulation results, evaluated at the engine supports, are condensed to a vibration index and compared with experimental results, obtaining satisfactory outcomes. The modal analysis also considers the damping aspects and has been conducted using a multibody model created with the software AVL/EXCITE. The influence of crankshaft torsional frequencies on the rotational speed behavior has been evaluated in order to reduce the vibration phenomena. The focus of this work is related to industrial aspects since, for an existing and commercialized engine, a numerical and experimental complex study has been performed to enable design improvements aimed at reducing noise and vibrations. Existing procedures and algorithms are combined here to reach the abovementioned objectives in the most efficient way.

Three-Dimensional Atomic Force Microscopy for Sidewall Imaging Using Torsional Resonance Mode.

This article presents an atomic force microscopy (AFM) technique for true three-dimensional (3D) characterization. The cantilever probe with flared tip was used in a home-made 3D-AFM system. The cantilever was driven by two shaking piezoceramics and oscillated around its vertical or torsional resonance frequency. The vertical resonance mode was used for upper surface imaging, and the torsional resonance mode was used for sidewall detecting. The 3D-AFM was applied to measure standard gratings with the height of 100 nm and 200 nm. The experiment results showed that the presented 3D-AFM technique was able to detect the small defect features on the steep sidewall and to reconstruct the 3D topography of the measured structure.

Spectroscopy and formation of lanthanum-hydrocarbon radicals formed by C-H and C-C bond activation of 1-pentene and 2-pentene.

La atom reactions with 1-pentene and 2-pentene are carried out in a laser-vaporization molecular beam source. The two reactions yield the same metal-hydrocarbon products from the dehydrogenation and carbon-carbon bond cleavage of the pentene molecules. The dehydrogenated species La(C5H8) is the major product, whereas the carbon-carbon bond cleaved species La(C2H2) and La(C3H4) are the minor ones. La(C10H18) is also observed and is presumably formed by La(C5H8) addition to a second pentene molecule. La(C5H8) and La(C2H2) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species from the two reactions exhibit the same transitions. Adiabatic ionization energies and metal-ligand stretching frequencies are determined for the two species, and additional methyl bending and torsional frequencies are measured for the larger one. Five possible isomers are considered for La(C5H8), and a C1 metallacyclopentene (Iso A) is identified as the most possible isomer. La(C2H2) is confirmed to be a C2v metallacyclopropene. The ground electronic state of each species is a doublet with a La 6s1-based electron configuration, and ionization yields a singlet state. The formation of the lanthanacyclopentene includes La addition to the C=C double bond, La insertion into two C(sp3)-H bonds, and concerted dehydrogenation. For the 2-pentene reaction, the formation of the five-membered ring may also involve 2-pentene to 1-pentene isomerization. In addition to the metal addition and insertion, the formation of the three-membered metallacycle from 1-pentene includes C(sp3)-C(sp3) bond breakage and hydrogen migration from La to C(sp3), whereas its formation from 2-pentene may involve the ligand isomerization.

A Compact Impact Rotary Motor Based on a Piezoelectric Tube Actuator with Helical Interdigitated Electrodes.

This paper presents a novel impact rotary motor based on a piezoelectric tube actuator with helical interdigitated electrodes which has a compact structure and high resolution. The assembled prototype motor has a maximum diameter of 15 mm and a length of 65 mm and works under a saw-shaped driving voltage. The LuGre friction model is adopted to analyze the rotary motion process of the motor in the dynamic simulations. From the experimental tests, the first torsional resonant frequency of the piezoelectric tube is 59.289 kHz with a free boundary condition. A series of experiments about the stepping characteristics of different driving voltages, duty cycles, and working frequencies are carried out by a laser Doppler vibrometer based on a fabricated prototype motor. The experimental results show that the prototype rotary motor can produce a maximum torsional angle of about 0.03° using a driving voltage of 480 Vp-p (peak-to-peak driving voltage) with a duty ratio of 0% under a small friction force of about 0.1 N. The motor can produce a maximum average angle of about 2.55 rad/s and a stall torque of 0.4 mN∙m at 8 kHz using a driving voltage of 640 Vp-p with a duty ratio of 0% under a large friction force of about 3.6 N. The prototype can be driven in forward and backward motion and is working in stick-slip mode at low frequencies and slip-slip mode at high frequencies.

Torsional Oscillation Damping Control for DFIG-Based Wind Farm Participating in Power System Frequency Regulation

Large-scale wind farms (WFs) are gradually required to participate in power system frequency regulation, especially in a weak grid. Corresponding ancillary frequency control functionalities and the contribution of the WF to system frequency stability are well studied. However, the impact of WF ancillary frequency control on wind turbine generators (WTGs) is rarely considered. It is found in this paper that the ancillary frequency control deteriorates drive-train torsional oscillation of the WTG, which restricts application of the ancillary control. To overcome this problem, this paper proposes an adaptive damping control scheme based on reactive power modulation of the WTG to suppress the drive-train torsional oscillation, which can assist the WF to meet the grid code requirements. Superior to the traditional active power modulation method, the proposed adaptive control scheme can achieve satisfactory damping improvement with less control effort. Furthermore, the adaptive scheme with a torsional frequency updating mechanism can effectively counteract torsional damping deterioration caused by parameter uncertainties, operating condition or control mode variations. Feasibility and effectiveness of the proposed damping control are validated by simulations and real-time experiments.

Effect of Fiber Orientation and Position of Circular Hole on Torsional Natural Frequency of Laminated Composite Beam

Effect of Fiber Orientation and Position of Circular Hole on Torsional Natural Frequency of Laminated Composite Beam

Free Vibration Analysis of Fibre-Metal Laminated Beams via Hierarchical One-Dimensional Models

This paper presents a free vibration analysis of beams made of fibre-metal laminated beans. Due to its attractive properties, this class of composites has gained more and more importance in the aeronautic field. Several higher-order displacements-based theories as well as classical models (Euler-Bernoulli’s and Timoshenko’s ones) are derived, assuming Carrera’s Unified Formulation by a priori approximating the displacement field over the cross section in a compact form. The governing differential equations and the boundary conditions are derived in a general form that corresponds to a generic term in the displacement field approximation. The resulting fundamental term, named “nucleus”, does not depend upon the approximation order N, which is a free parameter of the formulation. A Navier-type, closed form solution is used. Simply supported beams are, therefore, investigated. Slender and short beams are considered. Three- and five-layer beams are studied. Bending, shear, torsional, and axial modes and frequencies are presented. Results are assessed for three-dimensional FEM solutions obtained by a commercial finite element code using three-dimensional elements showing that the proposed approach is accurate yet computationally effective.

Strain method for synchronous dynamic measurement of elastic, shear modulus and Poisson’s ratio of wood and wood composites

In this work, the principle and method for synchronous dynamic measurement of elasticity, shear modulus and Poisson’s ratio of wood and wood composite with two strain gauges were studied and discussed. The experimental scheme, named 0°–75° scheme, was developed for synchronous dynamic measurement of elasticity (E), shear modulus (G) and Poisson’s ratio (μ) with two strain gauges of 0° and 75°. The 75° strain gauge was not only used to measure Poisson’s ratio together with the 0° strain gauge, but also to measure the first-order torsional frequency of cantilever plate. In addition, the principle of measuring elasticity and shear modulus by the 0°–75° scheme was described. Based on the stress and strain analysis of first-order bending and torsional modes of cantilever plates, the pasting position and orientation of strain gauges in the 0°–75° scheme were decided. Comparing the results of using two combinations of strain gauges, 0°–75° and 0°–90° schemes, the correspondence indicates that the 0°–75° scheme is feasible for dynamic measurement of Poisson’s ratio. By transient excitation, the strain spectrums under 0° and 75° of Poplar’s tangential section, Sitka spruce’s radial section and medium density fiberboard (MDF) cantilever plate were measured. Thus, one-hammer-excitation synchronous measurement of elasticity, shear modulus and Poisson’s ratio of materials was achieved. Its correctness was verified by axial tension and static square-plate torsion tests.

Design of a Novel MEMS Microgripper with Rotatory Electrostatic Comb-Drive Actuators for Biomedical Applications.

Primary tumors of patients can release circulating tumor cells (CTCs) to flow inside of their blood. The CTCs have different mechanical properties in comparison with red and white blood cells, and their detection may be employed to study the efficiency of medical treatments against cancer. We present the design of a novel MEMS microgripper with rotatory electrostatic comb-drive actuators for mechanical properties characterization of cells. The microgripper has a compact structural configuration of four polysilicon layers and a simple performance that control the opening and closing displacements of the microgripper tips. The microgripper has a mobile arm, a fixed arm, two different actuators and two serpentine springs, which are designed based on the SUMMiT V surface micromachining process from Sandia National Laboratories. The proposed microgripper operates at its first rotational resonant frequency and its mobile arm has a controlled displacement of 40 µm at both opening and closing directions using dc and ac bias voltages. Analytical models are developed to predict the stiffness, damping forces and first torsional resonant frequency of the microgripper. In addition, finite element method (FEM) models are obtained to estimate the mechanical behavior of the microgripper. The results of the analytical models agree very well respect to FEM simulations. The microgripper has a first rotational resonant frequency of 463.8 Hz without gripped cell and it can operate up to with maximum dc and ac voltages of 23.4 V and 129.2 V, respectively. Based on the results of the analytical and FEM models about the performance of the proposed microgripper, it could be used as a dispositive for mechanical properties characterization of circulating tumor cells (CTCs).

Design optimization of a dynamically flat resonating micro-mirror for pico-projection applications

One of the main design limitations of resonant micro-mirrors, intended for visual projection display applications, is inertia-driven dynamic deformation. In order to achieve high scan angles, micro-mirrors used for high frequency (20–30 kHz) laser beam scanning are typically operated at resonance and in the region of their torsional modal frequency. Although the optical resolution of the projected image is defined by the micro-mirror dimensions, the scanning frequency and the maximum scan angle, significant dynamic deformation (> 1/10 of the incident wavelength) can develop and give rise to a loss in contrast between adjacent projected spots. A design optimization scheme for a one directional resonant micro-mirror intended for laser projection with XGA optical resolution is performed and presented in this study. The minimization of dynamic deformation is considered as one of the main objectives but other parameters related to micro-mirror optical performance, structural reliability and gas damping characteristics are also investigated. The optimization scheme is performed using Design of Experiments and response surface methodologies. The design process demonstrates the technical feasibility of including features, such as a gimbal structure, that improve the dynamic mirror flatness without compromising the target scanning frequency, mode separation, maximum shear stress and power consumption.

Relationship of Low Temperature with Testicular Torsion.

To determine whether there is a correlation between seasonal temperature change and frequency of testicular torsion. An observational study. Departments of Urology, Hitit University Corum Training and Research Hospital, Corum and Ankara Training and Research Hospital, Turkey, from June 2005 to December 2014. Patients who had been diagnosed with testicular torsion and operated in the last 10 years were retrospectively reached through the hospital records. The seasons and the seasonal average temperature occuring in this region were recorded. The median (IQR) age of the patients was 14 (10.8 - 17.0) years. Testicular torsion was on the right side in 18 (60%) and left side in 12 (40%) patients. Twenty-four (80%) patients underwent surgical detorsion and bilateral testicular fixation while 6 (20%) patients underwent orchiectomy. There were 14 (46.6%) cases in the winter months, 7 (23.3%) in the spring months, 4 (13.3%) in the summer months, and 5 (16.6%) in the fall months. Acute testicular torsion in the winter to be statistically significant (p<0.05). Acute testicular torsion was seen more commonly in cold season with low temperature.

Metamodel-Based Multi-Objective Reliable Optimization for Front Structure of Electric Vehicle

In this paper, a multi-objective reliable optimization (MORO) procedure for the front body of an electric vehicle is proposed and compared with determinate multi-objective optimization (DMOO). The energy absorption and peak crash force of the simplified vehicle model under the full-lap frontal impact condition are used as the design objectives, with the weighted sum of the basic frequency, the first-order torsional and bending frequencies of the full-size vehicle model, and the weight of the front body taken as the constraints. The thicknesses of nine components on the front body are defined as design variables, and their geometric tolerances determine the uncertainty factor. The most accurate metamodel using the polynomial response surface, kriging, and a radial basis function is selected to model four design criteria during optimization, allowing the efficiency improvement to be computed. Monte Carlo simulations are adopted to handle the probability constraints, and multi-objective particle swarm optimization is employed as the solver. The MORO results indicate reliability levels of $$R = 100$$ %, demonstrating the significant enhancement in reliability of the front body over that given by DMOO, and reliable design schemes and proposals are provided for further study.

Structural and thermochemical properties of methyl ethyl sulfide alcohols: HOCH2SCH2CH3, CH3SCH(OH)CH3, CH3SCH2CH2OH, and radicals corresponding to loss of H atom

AbstractSulfide alkoxy radicals are important intermediates during the partial oxidation of alkyl sulfides in atmospheric chemistry and in combustion. The atmospheric reaction sequence to formation of the alkoxy radicals includes (1) initial reaction with OH to create a radical on a carbon site, (2) the carbon radical then associates with 3O2 to form a peroxy radical, and (3) an NO radical reacts with the peroxy radical to form an alkoxy radical (RO•) plus NO2. This study determines structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (ΔfH°, S°, and Cp(T)) of 3 corresponding alcohols HOCH2SCH2CH3, CH3SCH(OH)CH3, and CH3SCH2CH2OH of methyl ethyl sulfides studied in order to characterize the thermochemistry of the respective alkoxy radicals. The lowest energy molecular structures were calculated using the B3LYP density functional level of theory with the 6‐311G(2d,d,p) basis set. Standard enthalpies of formation (ΔfH°298) for the radicals and their parent molecules were calculated using B3LYP/6‐31 + G(2d,p), CBS‐QB3, M062x/6‐311 + g(2d,p), and G3MP2B3 methods. Isodesmic reactions were used to determine ∆fH° values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6‐31 + G(d,p) level theory. The contributions for S°298 and Cp(T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by CBS‐QB3 calculations, with contributions from torsion frequencies replaced by internal rotor contributions. Group additivity and hydrogen bond increment values were developed for estimating properties of structurally similar and larger sulfur‐containing peroxide molecules and their radicals.

Closed manual detorsion in case of a testicular torsion in children

Aim of study. To evaluate the effectiveness of closed manual detorsion in case of testicular torsion in children of different age groups. Materials and methods. Manual detorsion was carried out according to the classical technique (Yudin Ya.B. et al., 1987) by 79 patients with a testicular torsion at the age from the neonatal period to 18 years. A comparative analysis of the effectiveness of detorsion depending on various factors (the age of the patient, the duration of ischemia, the presence of a secondary hydrocele) was performed. Results. The effectiveness of the detorsion depended on the duration of the ischemia period before manipulation in patients of all ages. The effectiveness of the detorsion is more pronounced in adolescents, which is due to the more advanced structures of the spermatic cord and the larger testicle mass. A hydrocele of a secondary nature is a factor complicating detorsion, but its puncture emptying increases the efficiency of manipulation. Conclusions. The effectiveness of manual detorsion is directly proportional to the age of the patient and inversely proportional to the duration of ischemia before the manipulation is performed. The frequency of residual torsion does not allow us to consider the method as independent in the treatment of testicular torsion, and ultrasound and ultrasound dopplerography are completely reliable evaluation criteria. The effectiveness of the method allows you to recommend it in the first day of the disease in patients of all age groups, except for newborns, but emergency surgery should be performed as soon as possible after the detorsion. Carrying out a discharge puncture in patients with a secondary hydrocele against a background of testicular vesicle significantly improves the effectiveness of manual detorsion. (For citation: Shormanov IS, Shchedrov DN. Closed manual detorsion in case of a testicular torsion in children. Urologicheskie vedomosti. 2018;8(1):34-39. doi: 10.17816/uroved8134-39).