Maximum Oscillation Amplitude Research Articles

Epigenetic Mechanisms of the Anti-inflammatory Action of the Opioid Peptide Leutragin: Role of Sirtuin 1

Sirtuin 1 (SIRT1) is a class III histone deacetylase that plays a key role in resolving inflammation through known epigenetic mechanisms involving histone and nuclear factor κB (NF-κB) deacetylation. Deacetylation reduces the transcriptional activity of NF-κB and the associated production of pro-inflammatory cytokines such as interleukin 1β (IL-1β), tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6). In the present study, we show for the first time that biomodeling of acute lung inflammation by a single injection of lipopolysaccharide (LPS) induces synchronous oscillations of mRNA levels of cytokines IL-1β, TNF-α, IL-6 and SIRT1 deacetylase in the lungs, the maximum amplitudes of cytokine mRNA oscillations are observed between 1.5 and 5 hours, whereas high levels of SIRT1 mRNA are observed up to 24 hours, when cytokine mRNA oscillations have already faded, which is consistent with the hypothesis about the role of SIRT1 as a factor acting in the phase of inflammation resolution. The study shows that the mechanism of anti-inflammatory action of inhaled hexapeptide Leutragin, a δ-opioid receptor agonist, is related to its ability to increase SIRT1 mRNA expression and decrease the amplitudes of IL-1β, TNF-α, and IL-6 mRNA oscillations in the lungs, which generally leads to the resolution of inflammation in the conditions of biomodeling of acute lung inflammation.

Comparing phase sensitive detection and Fourier analysis of modulation excitation spectroscopy data exemplified by Ambient Pressure X-ray Photoelectron Spectroscopy

Dynamic processes in catalysis are gaining increased attention and could very well be one of the next frontiers in surface science. One way to study such processes is to induce chemical changes on the surface for example by periodically adjusting the (electro)chemical potential in situ and identify the resulting spectral changes. Often this is referred to as Modulation Excitation Spectroscopy (MES). Using Ambient Pressure Photoelectron Spectroscopy data, we here discuss and compare the analysis of MES data using both Phase Sensitive Detection (PSD) and Fourier analysis. We discuss that PSD determines the component magnitude at a user-defined phase value while Fourier analysis provides the maximum oscillation amplitude and respective phase value of oscillating spectral features. We discuss advantages and disadvantages of the different analysis schemes and explore how the full time-evolution can be obtained.

Study on the impacts of injection parameters on knocking in HPDI natural gas engine at different combustion modes

Based on three-dimensional (3D) computational fluid dynamics (CFD) software, a 3D numerical model was constructed to investigate the effects of injection timing, pilot diesel energetic ratio (PDER), and angle between the central axis of the diesel jet and the horizontal direction (α) on combustion and knock in the natural gas mixing-limited combustion (NMLC) mode and natural gas slightly premixed combustion (NSPC) mode. The results indicate that advancing the start of injection of natural gas (NSOI) leads to a slight improvement in indicated thermal efficiency (ITE), but also an increase in peak cylinder pressure (Pmax) and maximum pressure rise rate (MPRR). In the NMLC mode, as the diesel and natural gas injection interval (IDN) decreases, the interference between the diesel and natural gas jets intensifies, ultimately leading to instability in the flame propagation process and increased fluctuations in cylinder pressure. At different NSOIs, when IDN is 0°CA, the maximum amplitude of pressure oscillations (MAPO) is the highest. When the PDER is increased from 5 % to 15 %, ITE increases by 7.1 %. Under different combustion modes, as α increases, ITE first increases and then decreases. However, the NSPC mode achieves a higher ITE, reaching up to 44.4 %.

Mathieu–Hill Equation Stability Analysis for Trapped Ions: Anharmonic Corrections for Nonlinear Electrodynamic Traps

The stability properties of the Hill equation are discussed, especially those of the Mathieu equation that characterize ion motion in electrodynamic traps. The solutions of the Mathieu-Hill equation for a trapped ion are characterized by employing the Floquet theory and Hill’s method solution, which yields an infinite system of linear and homogeneous equations whose coefficients are recursively determined. Stability is discussed for parameters a and q that are real. Characteristic curves are introduced naturally by the Sturm–Liouville problem for the well-known even and odd Mathieu equations cem(z,q) and sem(z,q). In the case of a Paul trap, the stable solution corresponds to a superposition of harmonic motions. The maximum amplitude of stable oscillations for ideal conditions (taken into consideration) is derived. We illustrate the stability diagram for a combined (Paul and Penning) trap and represent the frontiers of the stability domains for both axial and radial motion, where the former is described by the canonical Mathieu equation. Anharmonic corrections for nonlinear Paul traps are discussed within the frame of perturbation theory, while the frontiers of the modified stability domains are determined as a function of the chosen perturbation parameter and we demonstrate they are shifted towards negative values of the a parameter. The applications of the results include but are not restricted to 2D and 3D ion traps used for different applications such as mass spectrometry (including nanoparticles), high resolution atomic spectroscopy and quantum engineering applications, among which we mention optical atomic clocks and quantum frequency metrology.

Predicting distribution of aeolian vibration amplitude of undamped overhead transmission lines

The most widely accepted estimation procedure of the severity of aeolian vibration is by calculating the maximum oscillation amplitudes of the conductor using Energy Balance Principle (EBP). However, the EBP is based on wind tunnel results where only one frequency is excited, while observations and experimental results show that multiple resonant modes are excited simultaneously. Furthermore, the required number of cycles of each amplitude level is not provided by current EBP-based methods. In this paper, vibration data from an experimental undamped ACSR Bersfort test line in Quebec, Canada, is recorded and analyzed. For each record of aeolian vibrations, amplitudes are fitted to a Rayleigh distribution based on the narrow-band assumption. The number of cycles and Rayleigh parameter are then related to wind conditions through a modified Strouhal frequency and EBP methodology. A statistical model is proposed to relate vibration profiles and wind input while considering wind turbulence intensity. The proposed method performs well and gives accurate estimates of both vibration amplitudes and number of cycles for ACSR Bersfort conductor. Physical and statistical theory is provided for each step of the method in order to extend the application of the method to other types of conductors or different line configurations.

Functional state of dermal circulation in patients with lichen planus

Lichen planus belongs to the group of the most common dermatoses. The etiology and mechanisms of development of lichen planus are not fully understood. This dermatosis is characterized by a variety of clinical forms, as well as a chronically relapsing course, and a fairly frequent resistance to traditional therapies. The chronically relapsing course and susceptibility to complications and deterioration in the quality of life of patients with lichen planus give this dermatosis the status of a medical and social problem. Objective — to investigate the state of blood circulation in the areas of skin lesions of patients with lichen planus, depending on the stage of the clinical course of dermatosis. Materials and methods. We observed 37 patients with lichen planus with a typical (classical) clinical form (22 men and 15 women) aged 20 to 44 years. The comparison group consisted of 30 apparently healthy individuals, comparable by sex and age. In 19 patients, the progressive stage of dermatosis was diagnosed, in 18 — the stationary stage. The duration of the course of the disease in the subjects ranged from two weeks to six months. In all the examined patients, the microcirculation index (MI), the mean quadratic deviation of the microcirculation indicators, the coefficient of variation (KV), as well as maximum amplitude of slow oscillations (ALF), maximum amplitude of rapid oscillations (AHF), maximum amplitude of pulse oscillations (ACF) were determined. The first component of the active mechanism of regulation of tissue circulation was calculated according to the formula ALF/PM; the second component — according to the formula σ/ALF; the first component of the passive mechanism of modulation of tissue circulation was calculated according to the formula ACF/σ; the second component — according to the formula AHF/σ. In addition, the intravascular resistance ACF/PM · 100 % and the microcirculation efficiency coefficient ALF/(AHF + ACF) were studied. The study was carried out on a Doppler flowmeter Vingmed SD-100 (Sweden). Results and discussion. The obtained results indicate a low level of tissue perfusion, insufficient functioning of tissue blood circulation modulation mechanisms and reduced vasomotor activity of microvessels in the areas of affected skin of patients with lichen planus. It was also established that the modulation of tissue blood circulation was redistributed in the direction of reducing the passive mechanism, that is, in the direction of disturbances of cardiac and respiratory rhythms of fluctuations. Conclusions. In the examined patients with a typical (classical) form of the clinical course of lichen planus, a stagnant­static type of hemodynamics in the dermis was established during the examination by laser Doppler flowmetry in the skin areas affected by a specific papular rash.It has also been proved that in patients with lichen planus, in particular, in skin areas with specific lichenoid lesions, there is a redistribution of modulation of tissue blood circulation towards a decrease in the passive mechanism, that is, towards cardiac and respiratory rhythm disorders of fluctuations.The established disorders of dermal vascularization in the areas of skin lesions of patients with lichen planus expand the understanding of the pathogenesis of this dermatosis and need to be taken into account when developing the tactics of its complex, individualized therapy, which will contribute to increasing the effectiveness of treatment.

A novel optimizing Pulsed Plasma Gas Variable Polarity Plasma Arc Welding (PPG-VPPAW) method for improving weld quality

To enhance the reliability of aluminum alloy welding quality, a novel Pulsed Plasma Gas Variable Polarity Plasma Arc Welding (PPG-VPPAW) system is proposed. This system enables independent control and rapid adjustment of the plasma gas, allowing for flexible modulation of arc pressure output under constant thermal conditions, thereby reducing porosity and refining grain structure. The research analyzed the impact of parameters of different plasma gas on arc characteristics, welding porosity, and welding microstructure. The results reveal that the periodic changes in pulsed plasma gas induce corresponding variations in arc temperature, arc shape, arc pressure, arc voltage, and the morphology of the weld pool keyhole. The magnitude of the difference between the base value and peak value of pulsed plasma gas determines the extent of arc pressure fluctuations and the behavior of the backside keyhole. The maximum oscillation amplitude of the backside keyhole can reach up to 4.5 mm². Additionally, the oscillation of pulsed plasma gas within the molten pool has been demonstrated to effectively reduce weld porosity and refine grain size. Under this process, the grain size of the weld metal can be reduced by up to approximately 25%. Current work provides an important direction for fabricating highly reliable aluminum alloy weldments.

Convergence-free mapping of non-linear damper-blade performance

In the bladed disks of turbomachinery, the problem arises of finding a damping device that reduces as much as possible the amplitude of the alternating stresses produced by the forced vibrations excited by the gas flow. Dry friction solid underplatform dampers are an established solution.The shape and size of the damper, in association with those of the platform, neck and airfoil, determine the non-linear response curves having as parameter the intensity of external excitation, here synthetically represented by a “proof” excitation force. Of greatest importance are the combinations (frequency, excitation force) that realise the maximum amplitude of forced oscillation (measured, for example, at the blade tip) and the maximum value of the amplitude of the variable stress produced by the vibrations at a critical point of the blade. Since the design of the damper-blade coupling is High-Cycle Fatigue driven, this stress amplitude is taken as a reference and related to the value of the excitation force. This can finally take the well-known form of the damper performance curve.Especially in the case of parametric explorations concerning shape, size and contact parameters, the current approach to this non-linear response problem, based on iterative convergence, is numerically prohibitive unless one uses special search techniques, such as the surrogate models of various types that are favoured today.An alternative computational process is presented here, that of integrating PCR (Platform Centred Reduction) with a new approach called Amplitude Layered (excitation) Force Mapping. This process reduces the amount of computation by up to three orders of magnitude compared to standard techniques and is a winning alternative to surrogate models.

A Transient Event-Capturing Circuit and Adaptive PI Control for a Voltage Mode Superbuck Converter

This paper proposes a transient event-capturing circuit and adaptive PI control to monitor and improve the transient response of a superbuck converter. The transient event-capturing circuit is composed of coupling and capturing circuits. The coupling circuit converts the output voltage to the sensed voltage, whereas the DC and ripple components are eliminated. By counting the up-crossing and down-crossing numbers of the sensed voltage, the capturing circuit classifies the output voltage response into different transient events according to oscillation cycles. The transient events carry the stability information that can be used to adjust the bandwidth and phase margin. Finally, an adaptive PI controller is implemented with the proposed transient event-capturing circuit to improve the stability and transient response. Experimental results of the 100 W superbuck converter verify the effectiveness of the adaptive PI controller for improving the transient response and stability. The adaptive PI controller eliminates the oscillations due to deviated parameters and operating conditions. The maximum oscillation amplitude is reduced from 2 V to 400 mV at the reference voltage change.

Large eddy simulation of combustion instabilities in a co-axial stratified model combustor under transient operating conditions

This work conducted large eddy simulation investigation on the effect of transient time and transient direction on the combustion instabilities in a co-axial stratified model combustor under transient operating conditions. Two transient times, which is greater than and less than the time delay, respectively, 0.1 s and 0.1 ms, were studied in different transient direction. The transient combustion process is analyzed by the global HRR, temperature, CH and CO. The time–frequency analysis of the pilot-stage and main-stage are carried out by FFT and SWT. The mode transition characteristics of the pilot-stage and main-stage are discussed based on the recurrence plots and Poincare plots. Finally, the bifurcations of the HRR and temperature caused by the transient time are analyzed. It was found that the shorter transient time is associated with larger oscillation amplitude of temperature, as well as the greater temperature and HRR gradient, and the maximum oscillation amplitude is larger. Furthermore, due to the shorter transient time in case ⅠⅡ-, the changing rate of heat release rate is approximately 725 J·m−3·s−2, which is significantly greater than the 72 J·m−3·s−2 in case ⅠⅡ+. In case ⅠⅡ-, the maximum CH is 2.0e-12, which is approximately 11 % higher than the maximum value in other cases. Different modes were observed in different transient time and transient direction. Longer transient time is associated with both a greater number of modes and frequency of mode transitions, and higher possibility of excitation oscillation occurring. Under a specific global average mixture fraction of 0.0345, two different flame shapes were observed in separate cases: a stratified flame and an M-shaped flame.

Laser Vibrometry of Shear Waves in a Layer of a Gel-Like Medium

Abstract—A laser scanning vibrometer was used to measure the amplitudes and phases of the vibrational velocity of shear waves excited by a one-dimensional source in the form of a narrow rectangular bar in a gellike medium. The vibrations of 26 plates reflecting the laser beam and located inside an optically transparentphantom along a segment with a length of 84.5 mm at a distance of 20 mm from the source were measured.The angular distributions of the amplitude and phase of shear waves at discrete frequencies from 59 to 500 Hz were measured in continuous mode. In pulsed mode, the vibrator excited a pulse in the medium with a durationof 1.5 periods of the 300 Hz frequency. The amplitudes and phases of shear waves were calculated by fastFourier transform of the time profile of the vibration velocity of the plates with a duration of 50 ms. The angular amplitude distributions measured in the pulsed and continuous modes are qualitatively the same. At all frequencies, the distributions are symmetrical with respect to the vertical axis. The maximum oscillation amplitude is observed at angles close to ±45°. The velocity of shear waves, calculated from the measured phase distributions, increases from 2 to 2.5 m/s with a change in frequency from 50 to 500 Hz. It is shown that this velocity behavior is well described by a relaxation model of the medium with one relaxation time equal to 0.3 ms. Shear wave attenuation depends on frequency and exceeds 1 cm-1 for waves with frequencies above250 Hz. The maximum attenuation per wavelength is observed near the relaxation frequency of the medium in the 300–400 Hz range. The results can be used to optimize devices for measuring the elasticity of soft tissues.

Microseismic oscillations as an indicator of tropical cyclones

The paper presents the results of recording microseismic oscillations in the frequency range of infrasonic waves performed during the periods of active influence of tropical cyclones on the water area of the Sea of Japan. The data were obtained by a coastal laser-interference measuring complex consisting of a two-axis laser strainmeter and a laser nanobarograph. A case study using remote sensing data shows that the world meteorological agencies stopped tracking the typhoon too early, while the cyclone retains its vortex structure and energy characteristics. The dynamics of changes in the characteristics of infrasound microseismic oscillations, which depend on the trajectory of typhoons and the duration of their impact on the sea area, is shown. Generalised results are given for some groups of typhoons having similar trajectories of movement, as a result of which the maximum amplitudes of microseismic infrasonic oscillations are manifested at different frequencies. During the passage of a category 5 typhoon in 2022, a microseismic signal formed by the interaction of the atmospheric vortex in the rear part of the cyclone with the field of quicksand waves was registered near the measuring site. As a result of registration by ground-based remote sensing methods of certain characteristics of microseismic signals generated during the passage of typhoons, it is possible to use the information to determine the parameters of tropical cyclone movement.

Revitalizing Inert Materials: Grafting Self‐Oscillating, Stimuli‐Responsive Organometallic Polymers for Pulsating Systems

AbstractA major challenge in materials science is dynamically adjusting material properties using sensors and control systems. This contribution develops a new approach using a self‐oscillating copolymer to autonomously change material surface properties in response to environmental changes. A redox‐sensitive terpolymer of N‐isopropylacrylamide (NIPAM), dimethylacrylamide (DMAc), and an iron‐based comonomer ([(phen)2(phen‐5‐yl‐acrylamide)FeII](PF6)2) is synthesized via Reversible Addition‐Fragmentation Chain Transfer (RAFT) polymerization, catalyzing an oscillating redox reaction (Belousov‐Zhabotinsky, BZ). The terpolymer oscillates from soluble to insoluble around 35 °C based on the iron's oxidation state. A catechol unit is incorporated to enhance versatility, enabling grafting onto different surfaces. Optimal BZ reagent concentrations are explored for maximum oscillation amplitude and frequency. By selecting a working temperature between redox transition points, the copolymer's oscillation from coil to globular conformation is observed due to redox oscillations. The self‐oscillating copolymer is grafted onto an ultrafiltration membrane, where conformational changes cause variations in pore size, leading to rapid negative flux peaks that disrupt the flux and reduce membrane fouling during protein filtration. This study highlights self‐oscillating polymers' ability to impart dynamic properties to inert materials, paving the way for smart materials with self‐regulating properties to adapt to changing conditions.

Aspect ratio influence on the vortex induced vibrations of a pivoted finite height cylinder at low Reynolds number

The effect of the aspect ratio on the vortex induced vibrations (VIV) of a pivoted finite length circular cylinder is investigated. A fixed value of the Reynolds number Re = 100 with four values of the aspect ratio AR=2, 3, 5, 7 is considered. Different values of the reduced velocity ur* in the range 2≤ur*≤11 were used for each AR value with a fixed value of the reduced mass mr*=5. Results on the oscillatory response of the cylinder, hydrodynamic forces, and wake structures are reported. In order to compare the VIV of the different length cylinders, the displacement of the center of mass (which coincides on each case) was analyzed. It is found that the maximum oscillation amplitudes, the extent of the synchronization region, and the wake structures are influenced by the aspect ratio. Also, a steady symmetrical flow is obtained for the small AR=2, 3 cases with relatively low values of ur*, which is found to be unstable when increasing ur*.

A capacitive transformer-based class-C oscillator

This paper presents a novel class-C VCO by exploiting a capacitive transformer-based (CT-based) resonator. Assuming the same Q-factor, the CT-based resonator has a lower equivalent resistance than the conventional LC resonator, which results in reduction of the phase noise. Moreover, using the second node of resonator for biasing core transistors’ gates enhances the loop gain and provides a robust start-up for biasing MOS gates of the active pair. Furthermore, compared to the conventional oscillator, a larger tail capacitance can be used in the proposed class-C oscillator, which results in greater phase noise improvement. Additionally, the oscillation amplitude calculated accurately in this paper demonstrates that using the CT-based resonator negligibly affects the maximum oscillation amplitude in the CMOS class-C oscillator in the deep-submicron processes. The proposed oscillator is implemented in standard 90-nm CMOS technology and operates at 3.5–3.7 GHz. Its phase noise at 1 MHz and 3 MHz offset frequencies are −129 dBc/Hz and −138.4 dBc/Hz in 3.6 GHz, respectively. The proposed structure occupies 0.49 mm2 core area and consumes 9.2 mW power with the FoM 190.3 dBc/Hz at 3 MHz offset frequency.

On Accounting for Own Fields of Emitters when Describing Generation Modes

The paper discusses three different modes of electromagnetic field generation by an ensemble of oscillators placed at the radiation wavelength in the one-dimensional case. The excitation of the resonator field is considered, which, as a rule, is determined by the geometry of the system, with and without taking into account the eigenfields of the emitters. The superradiance regime of the same ensemble of oscillators is also analyzed. In fact, superradiance is formed due to the emitters' own fields even in the absence of a resonator. It is noted that the maximum achievable amplitudes of induced fields both in the superradiance regime and in the regime of excitation of the resonator field are comparable. This makes us think about the role of the self-fields of emitters in electronic devices. It is shown that in describing the resonator excitation mode, in addition to the resonator field, it is also necessary to take into account the sum of the natural fields of the emitters in the active zone. Synchronization of emitters leads not only to an increase in the resonator field, but also, as in the superradiance regime, it significantly increases the amplitude of the sum of the oscillator fields. It is shown that in the practically interesting case of open systems (dissipative generation modes), taking into account the eigenfields of the emitters significantly reduces the characteristic time for the development of the generation process and increases the maximum achievable oscillation amplitude. This account also changes the conditions for achieving the maximum energy flow from the system. This can change the operating point of the generation process, which is determined by the requirement for the maximum rate of energy output from the system.

Prediction of knock intensity and validation in an optical SI engine

To provide fundamental insights into the underlying mechanisms of knock occurrence in a spark-ignition (SI) engine, optical diagnostic measurements were performed at advanced spark timing under boosted conditions. Employing high-speed imaging, deflagration-to-detonation transition (DDT) processes were recorded. The states and locations of the unburned mixture more susceptible to autoignition were identified by statistically analyzing the recorded images of the spatial distribution of flame propagation and end-gas autoignition under distinct combustion modes. The relationships between the unburned mixture fraction (UMF) and two metrics associated with the knock intensity levels, namely the maximum amplitude of pressure oscillation (MAPO) and the peak in-cylinder pressure, Pmax, were examined. In contrast to common beliefs, we found that the knock intensity represented by MAPO is not strongly correlated with UMF because UMF alone is inherently insufficient to represent the thermo-chemical properties of the bulk mixture inhomogeneities and its chemical reactivity at the onset of end-gas autoignition occurrence. Instead, a much stronger correlation was found between UMF and a newly proposed normalized-peak-pressure metric, allowing an a prior prediction of Pmax, which is a critical parameter associated with the propensity of engine failure if Pmax exceeds the strength limit of the engine. To quantitatively predict MAPO under SI-engine conditions, a refined model was proposed by imposing the pressure and temperature traces into the zero-dimensional (0-D) reactor model, such that the thermochemical properties of the transient mixture state at the onset of end-gas autoignition are properly incorporated into the predictive criteria. The model was validated against a large experimental dataset consisting of 619 cycles under various operating conditions. The results show that the model can reliably predict the end-gas autoignition and the knock intensity levels dictated by MAPO regardless of the stochastic nature of the knock development process.

Numerical analysis of combustion process and pressure oscillation phenomena in low-pressure injection natural gas/diesel dual fuel low speed marine engine

Dual fuel strategy is a promising way to achieve low-carbon emission for marine engines, but engine knock restricts the compression ratio and engine thermal efficiency by adopting premixed combustion mode. Engine knock of natural gas/diesel dual fuel low speed marine engine is not well understood under high compression ratio. The characteristics of combustion process and pressure oscillation phenomena were investigated by varying compression ratio, pre-chamber number, energy proportion of pilot diesel with a single-cylinder engine model with numerical simulation. The results show that, with increase in pre-chamber number using the same energy proportion of pilot diesel under compression ratio of 16, the maximum amplitude of pressure oscillation can be significantly reduced from 0.62 MPa to 0.23 MPa in main chamber, while both resonance modes follow (1,0) mode. With double pre-chamber, when the energy proportion of pilot diesel increases from 0.6% to 1.2%, due to the stronger intensity of jet flame, the heat release rate is accelerated as well as the accumulation of H2O2 radical become less before high speed spontaneous combustion, resulting in lower amplitude of pressure oscillation. When the energy proportion of pilot diesel increases from 1.2% to 3.0%, excessive amount of pilot diesel cannot strengthen the jet flame obviously while the amplitude of pressure oscillation increases slightly. These results suggest that about 1.0% in energy proportion of pilot diesel should be optimal by considering the thermal efficiency, pressure oscillation and NOx emission together.

Hamiltonian Additional Damping Control for Suppressing Power Oscillation Induced by Draft Tube Pressure Fluctuation

The power oscillation induced by pressure fluctuation in the draft tube of the hydraulic turbine is one of the limiting factors preventing the Francis turbine from operating in the vibration zone. At the present power grid with a high proportion of renewable energy resources, we try to improve the load regulation ability of the hydropower units by extending the stable operation zone to the vibration zone. By the mathematical modelling of pressure fluctuation, this paper gives an analytical expression of the power oscillation. We derive the extended Hamiltonian model of the hydropower unit where power oscillation is external excitation. Secondly, the damping injection method introduces some desired interconnection and damping matrices as the Hamiltonian damping factor into the additional damping control. Finally, through theoretical analysis and experimental simulation, this research discusses the resonance characteristics of pressure fluctuation and power oscillation, the equivalent analysis between the damping factor and equivalent damping coefficient, and the control design of vibration zone crossing during the start-up. Simulation results show that when r25 = 1.3, the minimum power oscillation amplitude is 0.5466, which is equivalent to an increase in D by 20. The maximum oscillation amplitude decreases by 4.6%, and the operation limited zone is reduced by 10.1%. The proposed additional damping control can effectively suppress the power oscillation and expand the regulation range.

Nonlinear dynamic modeling and analysis of spur gears considering dynamic contact state under misalignment errors

Traditional gear dynamic models take the mesh stiffness obtained under static conditions as an internal excitation. Under practical conditions, misalignment errors are unavoidable and will affect the contact state and mesh stiffness. The contact state and mesh stiffness under misalignment errors are dynamic force-dependent (DFD) since they are also affected by the violently fluctuating dynamic meshing force (DMF). Consequently, developing a dynamic model based on statically obtained mesh stiffness is inappropriate under misalignment errors. This study presents a torsional dynamic model of spur gears considering the DFD mesh stiffness and contact state change caused by misalignment errors. The mesh stiffness and torsional dynamic model of the proposed model are jointly solved. Parametric studies are conducted to reveal the differences in the dynamic responses between the proposed and traditional models under different misalignment errors. The dynamic responses of spur gears in resonance and off-resonance regions show that, compared with the traditional model, the proposed model under misalignment errors is more likely to undergo non-periodic and chaotic motion due to contact loss. In addition, misalignment errors lead to a significant increase in the maximum value and oscillation amplitude of the DMF of the proposed model.