Harmonic Oscillator Research Articles

Study on heat dissipation of torsional vibration damper for engine crankshaft

Abstract High temperatures in torsional vibration dampers can cause silicone oil to fail, increasing crankshaft vibration and shortening component fatigue life. Accurate prediction of the damper temperature field is key to the manufacture of highly reliable torsional vibration dampers. This study establishes the relationship between temperature, torsional vibration amplitude, silicone oil viscosity, rotational speed, housing and inertia ring clearance, and heat generation power based on Comsol. A bench test was carried out on a 6-cylinder inline diesel engine. The simulated temperature profile matched the tested result in terms of trend and relative value, and the established model could accurately predict the temperature field of the engine crankshaft torsional vibration damper.

Design of vibration damping system and simulation study of vibration characteristics of mine personnel carrier chassis

Design of vibration damping system and simulation study of vibration characteristics of mine personnel carrier chassis

Experimental study on vibration reduction of a cryogen-free dilution refrigerator system pre-cooled by a GM cryocooler

In order to carry out vibration reduction work on a cryogen-free dilution refrigerator system pre-cooled by a GM cryocooler, this paper first introduces the method of vibration measurement, particularly presenting the results and verification of displacement measurement obtained through acceleration integration. Subsequently, based on the construction of our dilution refrigerator, the paper reports experimental evidence of the direct impact of vibration on temperature and provides an effective vibration reduction scheme for the system. The study finds that vibrations transmitted through the path of “low-temperature part of GM- copper braid − support structure − various cold plates” have the most significant impact, hence making good internal soft connections is key. The influence of vibrations from the room-temperature part of GM can be mitigated to some extent by suspending the cold head, either by a separate frame or using the dilution refrigerator’s own frame. The use of a structure composed of air springs and honeycomb rubber in the suspension system has proven to be effective. Our final experimental results have demonstrated that with adequate vibration damping, the impact of vibrations from the GM on temperature can be essentially eliminated, allowing the dilution refrigerator to achieve a temperature level close to that when pre-cooled by a PT. The research in this paper has certain reference value for the construction and vibration mitigation of ultra-low temperature refrigeration systems.

Influence of chemical treatment of Bamboo fibers on the vibration and acoustic characterization of Carbon/Bamboo fiber reinforced hybrid composites

In the pursuit of sustainable materials, natural fibers are gaining attention because of their renewable nature and low environmental impact. However, their application in composites has been hindered by their hydrophilicity and non-homogeneity in the properties. To address these issues, chemical treatments such as Sodium Hydroxide and Potassium Permanganate have been utilized. This study explored the impact of chemical treatments on Bamboo fibers and their subsequent influence on the vibration and acoustic properties of Carbon/Bamboo fiber-reinforced hybrid composites. This study investigates the vibration damping and acoustic characteristics of hybrid composites, considering the synergistic advantages of Bamboo’s natural damping properties and Carbon fiber’s mechanical strength. The damping factor of Sodium Hydroxide treated Bamboo fiber reinforced hybrid composites is 34.55% higher than that of untreated Bamboo fiber reinforced hybrid composites. It is also 11.95% higher than that of Potassium Permanganate treated Bamboo fiber reinforced hybrid composites. The flexural modulus of untreated Bamboo fiber reinforced hybrid composites was 164.36% and 157.77% higher than that of Sodium Hydroxide treated and Potassium Permanganate treated Bamboo fiber reinforced hybrid composites, respectively. The effect of chemical treatment on the fiber properties were analysed using the FTIR spectrum. Acoustic characterization revealed that untreated Bamboo fiber composites have higher sound absorption coefficients at lower frequencies, whereas Sodium Hydroxide-treated composites have higher sound absorption coefficients at medium and high frequencies. The results indicated that chemical treatment enhanced fiber-matrix adhesion, reduced stiffness, and influenced the damping and acoustic performance of the hybrid composites.

Experimental analysis of low-velocity impact behaviour on flax-balsa biobased sandwich

This article deals with a detailed experimental study dedicated to the evaluation of the overall mechanical behaviour of a bio-based composite structure used in transportation industries. The sandwich structure is designed to increase the lightening, vibration damping, and composite recyclability. The considered materials consist of a Flax/Elium® laminate composite for skins associated with a balsa core. The sandwich structure was obtained using a one-shot liquid resin infusion process. Low-velocity impact tests were carried out on different sandwich configurations with the aim of characterizing the effects of the stacking sequence and the density and thickness of the core. Furthermore, an experimental comparative analysis was conducted involving two composite laminate types: Glass/Elium and Flax/Elium to enhance the specific behaviour of flax fibre composite to be used as skins in the sandwich structures. The impact tests were carried out at low velocities and at different levels of impact energy using a drop-weight test bench. Notable damage mechanisms have been identified, and a chronological sequence of their development has been suggested. Ultrasonic analyses using C-Scan imaging were applied to the opposite side of the impacted specimen. The research proves the efficient energy-absorbing capability of the biobased sandwich structure during impact. Finally, this study enables a deeper understanding of various parameters that influence the behaviour of sandwiches during low-velocity impacts, thereby facilitating more informed material selection for practical applications.

Quantum Gravity Corrections to the Inflationary Spectrum in a Bohmian Approach

A precise interpretation of the universe wave function is forbidden in the spirit of the Copenhagen School since a precise notion of measure operation cannot be satisfactorily defined. Here, we propose a Bohmian interpretation of the isotropic universe quantum dynamics, in which the Hamilton–Jacobi equation is restated by including quantum corrections, which lead to a classical trajectory containing effects of order ℏ2. This solution is then used to determine the spectrum of gauge-invariant quantum fluctuations living on the obtained background model. The analysis is performed adopting the wave function approach to describe the fluctuation dynamics, which gives a time-dependent harmonic oscillator for each Fourier mode and whose frequency is affected by the ℏ2 corrections. The properties of the emerging spectrum are discussed, outlining the modification induced with respect to the scale-invariant result, and the hierarchy of the spectral index running is discussed.

Modeling the Dynamic Loads Affecting a Bridge Crane during Start-Up

Introduction. The dynamic loads during the start-up of a bridge crane can cause excessive stress in the structure and components, leading to potential safety hazards and increased wear and tear. To reduce the influence of the dynamic loads, various strategies can be implemented including optimization of the acceleration and deceleration profiles, using the soft start controls, implementing the vibration damping systems. It is vital to ensure that the proper crane maintenance and inspection protocols are in place. By reducing the impact of dynamic loads during the start-up, the overall performance and longevity of a bridge crane can be improved, ultimately enhancing safety and efficiency of the industrial operations. The present research offers a new approach to improving the efficiency and safety of industrial operations by providing a more precise account of the dynamic loads during the start-up of a bridge crane. The objective of this study is to develop a mathematical model for investigating the mechanical properties of the bridge cranes by analyzing the dynamic loads that occur during lifting operations.Materials and Methods. The development of the mathematical model was based on the kinetic model of the system, which included three connecting blocks and two flexible connections for a more accurate description of the bridge crane structure. Lagrange’s equations incorporating the information about the geometry and structure of a bridge crane were used. They made it possible to describe the motion of a system with the multiple elements and degrees of freedom. Processing and analysis of the results of the mathematical model were carried out in the MATLAB program using the Runge-Kutta method.Results. As a result of the research, a mathematical model was developed to study the dynamic loads affecting a bridge crane during lifting operations. Graphs describing the dependences of speed, acceleration, load, and rope angle over time, and their influence on the crane beam were plotted. The changes in these parameters over time, including their maximum values, were analyzed. The reasons for load changes and factors influencing the extension of lifting machines’ service life as well as reducing metal consumption during production thereof were identified.Discussion and Conclusion. The developed mathematical model and its numerical solution using the specialized software (MATLAB) allow for conducting the dynamic analysis of the bridge crane structures and determining the optimal design solutions. The analysis of the factors influencing the load changes leads to the conclusion that the use of this model can significantly reduce the load magnitudes and metal consumption, as well as increase the service life of lifting machines. The results obtained with the developed mathematical model and its numerical solution are useful for optimizing the crane structures, providing compliance with the operational requirements, and extending the service life of lifting machines.

Учет динамических нагрузок при проектировании металлоконструкций портальных кранов

The design calculation of crane metal structures is usually performed according to load combinations, for which the dynamic coefficients are strictly defined in the regulatory documentation. In fact, these coefficients depend on the departure and the length of the suspension of the load, they are different when lifting loads of different weights. A review of the literature has revealed a clear gap in the studies of the dynamics of gantry cranes, which are characterized by a change in the characteristics of their design even during one cycle of their operation. In this paper, to study the influence of the parameters of the gantry crane system on the magnitude of the dynamism coefficients, a dynamic model consisting of the mass of the crane’s metal structure brought to the point of suspension of the load and the weight of the load is applied. The weight of the rope, the elasticity of the lifting mechanism, and the damping of vibrations are not taken into account, and the characteristic of the drive is considered absolutely rigid. A method for determining the parameters of a dynamic model such as structural rigidity, its reduced masses is presented, and the results of calculating the dynamism coefficients for the metal structure of a crane and a rope suspension under various parameters and operating modes are presented. Calculations for a gantry crane with a lifting capacity of 10 tons have shown that with small departures, the dynamic load coefficient in the rope is always less than for a metal structure, while its value is maximum. For large departures, the values of the dynamics coefficients are close to those accepted for calculations according to regulatory documents. These circumstances should be taken into account both in the static calculation of portal cranes and in the calculation of their elements for durability, which will increase their reliability in determining the loading of metal structures.

Амплитудно-частотные характеристики виброзащитной системы сиденья с трехсегментной статической силовой характеристикой и участком квазинулевой жесткости

Vibration protection for heavy equipment operators is important. Exposure to vibration is harmful to health. Vibration protection seats are used for protection. Reliable passive systems with quasi-zero stiffness are promising. For the developed design of the seat on the basis of parallelogram mechanism, spring, cable and rollers, the study of vibration-protective properties is carried out. The design scheme has been developed, key parameters have been selected, and their study on vibration protection parameters has been carried out. The static force response was approximated by three linear segments with a horizontal mean. The known dynamic model describing forced oscillations of the mass was used. The displacement of the base was given by a harmonic function. Vibration protection systems with three-segment and with one-segment static force response were compared. The comparison was carried out in terms of transmission coefficients, accelerations and suspension displacement. The results of the computational experiment are presented in the form of graphs: amplitude-frequency characteristics in the form of transmission coefficients in acceleration and displacement, at different amplitudes of base vibrations, damp-ing and stiffness coefficients. Dependences of average values of transmission coefficients in the investigated frequency range are given. Vibration damping is effective when the maximum suspension travel does not exceed the middle section of the static characteristic. The most effective vibration damping, according to the average value of the acceleration transfer coefficient, is achieved at minimum, and for a single-segment characteristic — zero values of the stiffness coefficient. The presence of extreme segments in the characteristic significantly increases the average values of the accelera-tion and displacement transfer coefficients of the suspension. Seat vibration protection systems in real conditions should have a limitation of suspension displacement for ergonomic reasons. The values of the stiffness coefficients of the extreme parts of the static force response, according to the criterion of minimizing the average value of the acceleration transfer coefficient, should be minimized. To substantiate the optimal values of the stiffness coefficients of the extreme sections of the characteristic and viscous friction coefficients, it is advisable to conduct additional studies under step and stochastic impacts.

Identifying Factors Influencing the Properties of Vibroacoustic Metamaterials Using Three Different Acoustic Methods

Vibroacoustic metamaterials offer an approach for the targeted damping of unwanted structural vibrations and noise by integrating periodically arranged resonators into a matrix of bulk material. Fabrication using the laser bed powder fusion process allows the targeted integration of bulk resonators and powder depots, leading to an extension of the designable damping properties. Herein, the adaptation of acoustic methods is focused on the characterization of the properties of metamaterial plates. The investigated vibroacoustic metamaterial plates are made of polyamide PA1.2, combining material and structural damping. The vibration behavior of the plates over a range of frequencies using acoustic impedance measurements in a custom‐built measurement tube is investigated and it is compared with structural dynamics experiments using an electrodynamic shaker. The measurements allow for the identification of stop bands (frequency range with high damping) and influencing factors such as metamaterial design, mass, powder amountand surface on the frequency‐dependent damping properties. The adapted technique investigated in this work provides an experimental platform to characterize the complex interplay of acoustic metamaterial design and holds promise for scaling up metamaterial technology for industrial applications due to its simplicity, small space requirement, and low cost.

Synergistic effect of graphene and carbon black on the mechanical and vibration damping characteristics of styrene-butadiene rubber

Synergistic effect of graphene and carbon black on the mechanical and vibration damping characteristics of styrene-butadiene rubber

Unveiling the temperature-dependent mechanisms of viscoelasticity of sand-enhanced epoxy

The viscoelastic behavior of epoxy is critical for its engineering performance and applications. This work focused on the improvement of its viscoelastic performance by using natural sand particles as fillers. Experiments were carried out to investigate the static and dynamic viscoelastic properties of epoxy with various sand particle contents. Static mechanical tests demonstrated an increase in the elastic modulus, albeit at the cost of reduced strength at a higher sand content due to stress concentrations. Dynamic tests indicated substantially improved storage modulus and damping of epoxy after being filled with sand particles. Moreover, the glass transition temperature of epoxy showed a substantial rise upon the addition of sand particles, signifying an augmentation in its heat resistance. Static viscoelastic characterization revealed an elevation in both room- and high-temperature relaxation moduli upon incorporating sand. By applying time–temperature superposition principles, long-term relaxation curves were obtained, which could provide a reference for engineering design. These viscoelastic investigations offer insights into the underpinning mechanisms governing the performance of sand-reinforced epoxy. This enables the rational design of sand-particle-reinforced epoxy for customized durability, heat resistance and vibration damping.

Hyperelasticity of blood clots: Bridging the gap between microscopic and continuum scales

The biomechanical properties of blood clots, which are dictated by their compositions and micro-structures, play a critical role in determining their fates, i.e., occlusion, persistency, or embolization in the human circulatory system. While numerous constitutive models have emerged to describe the biomechanics of blood clots, most of these models have primarily focused on the macroscopic deformation of the clots and the resultant strain-stress correlations without depicting the microscopic contributions from their structural components, such as fibrin fibers, fibrin network and red blood cells. This work addresses the gap in current scientific understanding by quantifying how changes in the microstructure of blood clots affect its mechanical responses under different external stresses. We leverage our previous published work to develop a hyperelastic potential model for blood clots, which incorporates six distinct strain-energy components to describe the alignment of fibers, the entropic and enthalpic stretching of fibrin fibers, the buckling of these fibers, clot densification, and clot jamming. These strain-energy components are represented by a combination of simple harmonic oscillators, one-sided harmonic potentials, and a Gaussian potential. The proposed model, which is C0, C1, and C2 continuous with a total of 13 parameters, has been validated against three datasets: 1) fibrin clot in tension, 2) blood clot in compression, and 3) blood clots in shear, demonstrating its robustness. Subsequent simulations of a microscopic blood clot model are performed to uncover mechanistic correlations for a majority of the hyperelastic potential's stiffness/strain parameters. Our results show that only one proposed term concerning fiber buckling needs further refinement, while the remaining five strain-energy terms appear to describe precisely what they were intended to. In summary, the proposed model provides insight into the behavior of thromboembolisms and assistance in computer-aided design of surgical tools and interventions such as thrombectomy.

Strain modal response and vibration damping optimization of tower for wind power equipment

The safety of wind power equipment under dynamic load is one of the key factors to ensure sustainable energy recovery. In order to effectively improve the reliability of tower structure, the damage identification of flange bolt fracture based on strain mode was studied, and the vibration control and optimization scheme was proposed and verified. The dynamic response of the tower to wind load was calculated using the theory of Davenport spectrum. Combined with computational fluid dynamics, the dynamic load change law of the tower was obtained. Based on ANSYS Workbench, the modal simulation and analysis of the tower were carried out. Under different bolt damage conditions, the distribution characteristics of the strain modal shape of the tower in the axial and radial directions were obtained. The vibration damper was applied to the inside of the tower, and the vibration and stress at different positions under wind load were compared and analyzed to verify the specific vibration reduction and optimization effect. The results show that the strain modal shape of the tower cylinder has a significant peak at the damage site, and the peak height is positively correlated with the damage degree, indicating that the strain modal shape is highly sensitive to the damage. In addition, the vibration and maximum stress of the flange and top position of the tower have been effectively reduced by the shock absorber. The average amplitude of tower top can be reduced by 22.5 %, and the peak stress at the bottom flange position can be reduced by about 38 %.

Frequency dependent polarizability of confined harmonic oscillators

The D-dimensional Schrödinger equation for a confined harmonic potential perturbed by a time-dependent dipole field is analysed. The model uses exact confined solutions for the harmonic potential whereas the time-dependent field is treated using first-order time-dependent perturbation theory. Exact analytic solutions are obtained in terms of generalised Laguerre functions. This system has applications to nanostructures where there are strong confinement potentials in some dimensions and example calculations are carried out to illustrate the effect of the dimension.

High signal-to-noise ratio harmonic mode-locking Mamyshev oscillator at 1550 nm

Harmonic mode-locking is the effective method to improve ultrafast pulse repetition rate for the current research. However, this way of increasing the repetition rate based on pulse splitting has inherent instability characteristics, manifested as low signal-to-noise ratio and loss of mode-locking. In this paper, Mamyshev regenerative oscillation mode-locking technique is used to effectively improve the signal-to-noise ratio of pulses by compressing the nonlinear chirp in the cavity under the condition of near-zero dispersion. In the experiment, we successfully achieved a harmonic mode-locked pulse of up to 16 orders, corresponding to a repetition rate of 78.56 MHz, and the signal-to-noise ratio of the highest harmonic order reached 70 dB. Our research not only solves the inherent defect of low repetition rate of Mamyshev oscillator, but also effectively improves the signal-to-noise ratio of harmonic mode-locked pulse. This mode-locked structure based on Mamyshev oscillator provides reference and operability for improving the stability of ultrafast fiber lasers.

Tomographic entanglement indicators in a coupled oscillator model

We study entanglement in a simple model comprising two coupled linear harmonic oscillators of the same natural frequency. The system is separable in the center of mass (COM) and relative coordinates into two oscillators of frequency ω c and ω r. We compute standard entanglement measures (subsystem linear entropy and subsystem von Neumann entropy) as well as several tomographic entanglement indicators (Bhattacharyya distance, Kullback–Leibler divergence, and inverse participation ratio) as functions of the frequency ratio η = ω c/ω r, keeping the COM oscillator in its ground state. We demonstrate that, overall, the entanglement indicators reflect quite faithfully the variations in the standard measures. The entanglement is shown to be minimum at η = 1 and maximum at η → 0 or ∞.

Frequency Recognition of a Free Damped Vibration Signal Based on Improved Elias Aboutanios Interpolation Method

The free damped vibration signal of engineering structures is an energy-limited signal, and the effective signal length is limited by the damped factor. The classical periodic graph method is affected by signal damped coefficient and noise, and it is difficult to obtain satisfactory recognition accuracy. This article proposes the IEAI method for frequency estimation of freely damped vibration signal, considering the influence of initial phase. By combining discrete Fourier transform with complex operations, the signal is iteratively interpolated to improve the accuracy of frequency estimation .The simulation results show that the mean error of the IEAI method is 1.3%~26.5% of the traditional Periodogram method, A&M method and Welch method, and the Root-mean-square deviation is 7.4%~40.3% of the latter three methods under the condition of high signal-to-noise ratio; In the case of low signal-to-noise ratio, the mean error of the IEAI method is 16.2%~43.0% of the latter three, and the Root-mean-square deviation is 20.8%~81.8% of the latter three. The experimental results of cantilever beam damage identification show that the IEAI method is more sensitive to small structural damages and can be used for the identification and diagnosis of small structural damages.

General framework for quantifying dissipation pathways in open quantum systems. I. Theoretical formulation.

We present a general and practical theoretical framework to investigate how energy is dissipated in open quantum system dynamics. This is performed by quantifying the contributions of individual bath components to the overall dissipation of the system. The framework is based on the Nakajima-Zwanzig projection operator technique, which allows us to express the rate of energy dissipation into a specific bath degree of freedom by using traces of operator products. The approach captures system-bath interactions to all orders, but is based on second-order perturbation theory on the off-diagonal subsystem's couplings and a Markovian description of the bath. The usefulness of our theory is demonstrated by applying it to various models of open quantum systems involving harmonic oscillators or spin baths and connecting the outcomes to existing results such as our previously reported formula derived for locally coupled harmonic baths [Kim and Franco, J. Chem. Phys. 154, 084109 (2021)]. We also prove that the dissipation calculated by our theory rigorously satisfies thermodynamic principles such as energy conservation and detailed balance. Overall, the strategy can be used to develop the theory and simulation of dissipation pathways to interpret and engineer the dynamics of open quantum systems.

Numerical modeling of the heat and mass transfer of rarefied gas flows in a double-sided oscillatory lid-driven cavity

In micro/nano research and engineering applications, internal flows of rarefied gas in confined geometries with moving parts are of great interest. The rarefied gaseous flows in an oscillating lid-driven cavity are investigated numerically in this work, taking into account both the parallel and antiparallel motion of the driving walls. The discrete unified gas kinetic scheme (DUGKS) is applied to the evolution of the flow and temperature fields. The Shakhov collision model is incorporated into DUGKS to account for flows of non-unit Prandtl numbers. The validity of the Shakhov-DUGKS is confirmed in both single-sided oscillating and steady lid-driven cavity flows. The effects of gas compressibility, rarefaction, and lid oscillation frequency on the mass and heat transport are then thoroughly examined. The corresponding parameter spaces of the Mach, Knudsen and Stokes numbers are 0.16 ≤ Ma ≤ 1.2, 0.075 ≤ Kn ≤ 10 and 0.5 ≤ St ≤ 5, respectively. The shear force and Nusselt number Nu on the cavity walls, as well as the velocity, temperature, and heat flux lines in the cavity, are measured and analyzed. The results suggest that the anti-Fourier heat transfer phenomenon might also occur in the rarefied double-sided oscillating cavity flow. Nu is prone to non-simple harmonic oscillation in its evolution. Furthermore, in the parallel motion as opposed to the anti-parallel motion, the left wall experiences a greater intensity of heat transmission. Compressibility, expansion cooling, and viscous heating compete to provide the complicated flow and heat transfer characteristics found in cavities.