Increase In Oscillation Frequency Research Articles

Power-frequency performance of step-graded double Gunn diodes

Simulations of conventional Gunn diodes containing the double Gunn effect have shown a significant increase in oscillation frequency and frequency range. However, conventional Gunn diodes suffer from higher phase noise, lower efficiency, and reduced temperature stability due to the lack of a hot electron injector. A study on the performance of a Double Gunn diode with a graded gap injector is presented. The second region of negative differential mobility is gradually introduced in several temperature-dependent mobility models, which are implemented in an energy balance simulation. Devices with transit lengths of 0.7μm, 1.1μm, and 1.65μm are simulated. All devices experience an increase in oscillation frequency with increasing intensities of the double Gunn effect. The frequency range doubles at significant intensities of the effect in the devices with transit lengths of 0.7μm and 1.65μm.

Transmission shafts vibrations in transient rotating modes

The paper presents the investigation results of the transmission shaft dynamic behavior in transient modes of motion with change of the rotational speeds. Such modes occur during the transmission shaft transmits torque from engine to executive device. This process can be accompanied by vibration with change of frequency and amplitude of shaft oscillation. Therefore, the question of studying the dynamic behavior of such systems with identifying the impact of rotational speeds changing on them is relevant. In this regard, the study was done by developed software, in which a technique of computer simulation of the oscillating motion of considerable rotating rods under the action of inertia forces is implemented. Such software gives the possibility to model the oscillatory motion of rotating rods and determine the parameters by which the dynamic stability loss of the studying system can occur. Using this software, the diagrams of rod oscillating motion of the rotating shaft were drawn for definite parameters of the considered system. The process of oscillation is considered in space. The mathematical model of transverse oscillations is described by system of differential equations in rotating coordinate system that is tied to the shaft, but diagrams of oscillations is shown in inertial coordinate system. It is shown that when the speed of rotation changes, namely at the time interval of its increase, this process continues with growth of oscillation frequency during the acceleration time. Also shown that the amplitude of oscillations increases, too. After pass to next constant speed of rotation, the frequency of oscillations, as shown in diagrams, decreases back. Such increase of oscillation frequency during the acceleration can lead to undesirable consequences of destructive nature.

Microstructural evolution and performance improvement mechanism of Ti–6Al–4V fabricated by oscillating-wire laser additive manufacturing

This work proposes an oscillating wire laser additive manufacturing (O-WLAM), which is based on the wire laser additive manufacturing technology (WLAM) and combined with the laser oscillating welding technology. For different laser oscillation patterns, it shows a trend that metallurgical defects such as porosity, microstructural and columnar grain size decrease with the increase of oscillation frequency and oscillation amplitude. In solidified grains formed under laser oscillation, a complex oscillation of melt pool agitation could lead to a refining effect on the β grains size. The corresponding tendency of epitaxial growth of the prior β grains is weakened as well. The process experiments in this work provide a new idea of laser oscillation for wire laser additive manufacturing. The use of laser oscillation to achieve improvement of metallurgical defects and optimization of microstructure has some guiding significance for wire laser additive manufacturing.

An Enhanced Method for Nanosecond Time Synchronization in IEEE 1588 Precision Time Protocol

The performance of time-critical systems depends heavily on time synchronization accuracy. Therefore, it is crucial to have a synchronization method that can achieve high time synchronization accuracy. In this paper, we propose a new underlying transmission architecture and new synchronization messages. On the basis of these, aiming at the time error problem of the slave clock, we propose an enhanced time synchronization method based on new synchronization messages. Furthermore, we evaluate the performance of the enhanced time synchronization method on the OMNeT++ simulator. In addition, we compare the impact of different crystal oscillator accuracies and different crystal oscillator frequencies on time synchronization accuracy, respectively. Simulation results show that the time offset is at most ±1 clock period using the enhanced time synchronization method. We realize the purpose of timing the master clock and the slave clock by counting the period of the clock signal. Therefore, we needed to round down the time count to an integer. This is the reason why −1 and 1 appear at the same time. When the crystal oscillator frequency used is 80 MHz, the system can achieve a time synchronization accuracy of ±12.5 ns; that is, a nanosecond-level time synchronization accuracy can be achieved. With the reduction of the crystal oscillator accuracy of the slave clock, the synchronization accuracy of ±1 clock period can still be achieved. With the increase in the crystal oscillator frequency, the time synchronization accuracy that can be achieved also improves. The method proposed in this paper provides a new way of thinking and has certain guiding significance for improving the time synchronization accuracy of time-critical systems.

Effects of oscillation frequency on the flow characteristics of a centrifugal pump impeller with sinusoidal flow rate

This study uses large eddy simulation to investigate the flow characteristics of a centrifugal pump impeller with sinusoidal flow rate and constant rotational speed. Five different oscillation frequencies ( f/f0 = 1.0, 1.2, 1.5, 2.0, and 3.0, where f0 indicates one-ninth of the rotational speed) are selected to isolate the influence of oscillation frequency on the flow characteristics. Studies show that the pressure deviation between dropping and rising stages concentrates at the impeller inlet at instantaneous 0.5 Qd ( Qd is the design load), and its value increases with the increase in oscillation frequency. The lowest period of many flow characteristics, including pressure fluctuation and head, equals to that of flow rate. The differences in pressure fluctuation between adjacent channels decreases with the increase in oscillation frequency. The first and second dominant frequencies of pressure fluctuation are mainly affected by the oscillation frequency in the nonstall passage, and they have an important relationship with the stall vortex in the stall passage. With the increase in oscillation frequency, the amplitude of lowest order head pulsation increases, and the high order head pulsation gradually weakens. The average head is approximately 2.36 m.

Characteristic of keyhole, molten pool and microstructure of oscillating laser TIG hybrid welding

In this research, the dynamic change of laser keyhole of vertical oscillating laser keyhole was studied, and it was found that the laser keyhole depth was periodic. The keyhole depth decreased with the increase of oscillation amplitude and frequency, but the stability of the keyhole increased. This was closely related to the energy distribution of oscillating laser. The special energy distribution made the “two molten pools“ phenomenon appear in oscillating laser tungsten inert gas (TIG) hybrid welding, and the grains in the keyhole molten pool were smaller than those in the conduction molten pool. The narrow gap (NG) oscillating laser TIG hybrid welding (OL-T) was carried out, and the microstructure and mechanical properties of OL-T welding were compared with that of TIG welding and general laser TIG hybrid welding (L-T). The grain of the OL-T welding seam was refined because the OL-T welding had a lower line energy, which changed the crystalline morphology of the welding seam. The tensile strength of the weld joint was almost equivalent to that of TIG welding and base metal, reaching 559 MPa. It was observed that there was no lack of sidewall fusion in the welding seam of the NG OL-T welding, and the weld efficiency was much higher than that of TIG welding. The morphology of the molten pool in oscillating laser-TIG hybrid welding and the arc shape in the groove were collected using high-speed cameras. It was observed that the elimination of lack of sidewall fusion in NG welding mainly depended on the direct heating on the sidewall and stirring molten pool by oscillation laser.

Numerical study of beam oscillation and its effect on the solidification parameters and grain morphology in remote laser welding of high-strength aluminium alloys

This study investigated the effect of beam oscillation on the solidification behaviour during laser welding of Al-5754 to Al-6061 alloy. In this study, a finite element model has been developed to simulate temperature and fluid flow fields by implementing different combinations of volumetric heat source models. Solidification parameters such as temperature gradient (G), solidification rate (R), cooling rate (G × R) and G/R are evaluated to understand the mechanism of microstructure formation. It was found that beam oscillation improves the tensile strength by 21.4% for full penetration welding due to an increase in the percentage of formation of equiaxed grains. Modelling results revealed that the cooling rate increases with an increase in oscillation frequency. However, tensile strength followed a parabolic distribution with a peak at the oscillation frequency of 300 Hz.

Oscillating Laser-Arc Hybrid Additive Manufacturing of AZ31 Magnesium Alloy

To overcome the instability of the traditional magnesium alloy additive process, the research on oscillating laser-arc hybrid additive manufacturing (O-LHAM) for AZ31 Mg alloy was developed first, and it focused on the effect of beam oscillation on process characteristics, such as macroscopic morphology, porosity defects, microstructure, and mechanical properties of thin-walled components. The increasing oscillation frequency was effective in suppressing the defects, including lack of fusion, wavy hump, internal porosity, etc. Compared with the case without oscillation, the average grain size of O-LHAM samples was refined from 22–32 μm to 18–20 μm at 300 Hz, while the percentage of Al8Mn5 and Mg17Al12 precipitation increased from 1.42–1.61% to 2.55–3.32%. For this reason, a stirring laminar flow was induced using the oscillating laser in the melt pool, with the ability to disrupt the grain structure and provide more nucleation sites, which is beneficial in reducing the average grain size and promoting the precipitation of the precipitated phase. Meanwhile, for the component without pores, the ultimate tensile strength is 205 MPa, slightly less than the base, but the elongation is 20.7%, twice that of the base. The tensile fracture is characterized by a large number of dimples and some ductile tearing ridges, demonstrating good ductility, which is associated with the grain refinement and precipitation strengthening induced using the oscillating laser. The results indicated that O-LHAM would be an effective method for manufacturing Mg alloy fast and well.

Effect of calcium on rheological properties of Abelmoschus esculentus (okra) pod polysaccharide and its application in Annona squamosa

The fruit softening seriously affected the quality of Annona squamosa, and the edible coating combined with exogenous calcium had a positive effect on inhibiting the softening of A. squamosa. In this paper, the rheological properties of C-AeP-P solution and the effect of Ca2+ on the rheological properties of the solution were studied. Based on this, the indicators of fruit hardness, freshness and plumpness were used to monitor the softening effect of A. squamosa. The results show that: C-AeP-P solution showed non-Newtonian shear-thinning behavior over the range of 0.2-1.0%. With the increase of C-AeP-P concentration, the apparent viscosity and solids like properties increased. After the addition of Ca2+, C-AeP-P had apparent differences on apparent viscosity. The G′ and G″ of C-AeP-P were increased with increasing oscillation frequency. C-AeP-P and C-AeP-P+Ca2+ treatment can slow down rapidly decline of fruit hardness, increase of soluble solid content, loss of water, change peel color and regulate the expression of key enzyme genes AI and Ni. It was concluded that the coating treatment of C-AeP-P alleviates the adverse effects of quality changes during storage, so as to improve the quality and prolong the shelf life of A. squamosa.

Thermal energy storage technology and its application in power data remote transmission

In order to meet the current situation of the strong growth of energy demand, the authors put forward the research of thermal energy storage technology and its application in power data remote transmission. The main content of the technology is based on heat energy storage technology, discuss the advantages of heat energy storage technology, and study the stability analysis in the remote transmission of power data, finally, the stability performance of heat energy storage technology in power data remote transmission is obtained through experiments. The experimental results show that the energy storage is added at bus 6 of the power supply end, and the transmission distance between the energy storage power station and bus 6 is changed and the energy storage output is kept at 100 MW, the power of the connecting line is 400 MW. With the increase of the transmission distance, the variation trend of the interregion oscillation mode and the oscillation mode in Region 1 and Region 2 is that the oscillation frequency increases, the characteristic root moves to the left and the damping ratio increases, but the change is small. In conclusion it proves that heat energy storage technology has outstanding advantages, it has a broad development prospect and an important role in power data remote transmission.

Breathing oscillations excitation mechanism and influence factors in Hall thrusters

Breathing oscillations as one of the low frequency, large amplitude discharge instabilities have serious influence on the performance and lifetime of Hall thrusters. In order to acquire a better understanding of the breathing-oscillation in the Hall thrusters and provide the effective suppression methods for breathing-oscillation, the excitation mechanism and influence factors of the breathing oscillations are investigated by utilizing the two-zone predator-prey (P-P) model in this paper. The two-zone P-P model divides the discharge channel of Hall thruster into two parts according to the working principle of Hall thruster: one is the near anode zone and the other e is the ionization zone. The model includes the ion radial diffusion effect and electrons-wall interaction effect. The four-order Range-Kuttle method is utilized to solve the nonlinear two-zone P-P model equation. The research results show that the interaction of electrons with the wall has the inhibition effect on the breathing oscillations caused by the energy consumption due to the colliding with discharge channel wall. However, ion radial diffusion effect which is near anode has an excitation effect on the breathing oscillation. The ion and neutral atom dynamic behaviors obviously show the P-P feature in the phase space. In other words, there is a phase difference between the change of ion density and the change of neutral particle density. Relying on the intensity of the ions radial diffusion effect, the mode oscillation frequency and oscillation amplitude of discharge current present non monotonic change trend. More specifically, with the increase of intensity of ion radial diffusion effect, the oscillation frequency first increases and then decreases. However, the discharge peak current first decreases and then increases. Furthermore, the breathing oscillations excitation is irrelevant to the length of ionization zone, and the oscillation frequency increases (oscillation period) with length of ionization zone increasing (decreasing), provided that the length of discharge channel is constant. The research results of this paper will provide support to make clear the excitation mechanism and propose the new method of suppressing the breathing oscillations in the hall thrusters.

Device and circuit-level evaluation of a zero-cost transistor architecture developed via process optimization

In this work, ring oscillator test structures are designed and characterized to evaluate the in-circuit performance of a new medium-voltage (around 2–5 V) transistor architecture developed via process optimization in a 40 nm embedded non-volatile memory (eNVM) CMOS technology. The transistor is zero-cost in terms of photomask and process steps. It is compared to an existing transistor available in the technology. A SPICE model (Simulation Program with Integrated Circuit Emphasis) of the new device is developed to evaluate its circuit-level performance through electrical simulations. The simulation results are complemented by experimental results, and both show a large increase in the ring oscillator frequency for the new transistor, compared to the existing one. In addition, the reliability of the new transistor is evaluated at the device level with hot-carrier injection (HCI) stress tests and at the circuit level with power-supply stress tests.

Unsteady Flow Transition Effects on a Pitching Transonic Laminar Airfoil

This paper presents a computational study of unsteady transonic effects on a pitching supercritical laminar airfoil using high-order implicit large-eddy simulation. A CAST10-2 airfoil operating at a chord-based Reynolds number of , a transonic freestream Mach number of , and a small nominal angle of attack of deg was subjected to forced pitching oscillations about the quarter-chord with a small amplitude of deg and reduced frequencies of , 0.23, and 0.285. Complex interactions between flow separation, the motion of multiple shocks, and excursions of transitional flow were elucidated and compared against inviscid simulations. The boundary layer was found to be highly sensitive to pitch frequency, due in large part to the effects of frequency on shock motion. was found to be indirectly affected by the impact of shock motion on the boundary-layer state. Aerodynamic damping diminished with increasing oscillation frequency until becoming negative at , indicating potential for aeroelastic instability.

Numerical simulation of transport phenomena and its effect on the weld profile and solute distribution during laser welding of dissimilar aluminium alloys with and without beam oscillation

Remote Laser Welding (RLW) of Aluminium alloys has significant importance in lightweight manufacturing to decrease the weight of the body in white. It is critical to understand the physical process of transport phenomena during welding which is highly related to the mechanical performance of the joints. To investigate the underlying physics during welding and to understand the influence of beam oscillation on heat transfer, fluid flow and material mixing a transient three-dimensional Finite Element (FE) based Multiphysics model has been developed and validated from the experiments. The effect of welding speed, oscillation amplitude and oscillation frequency on the fusion zone dimensions, flow profile, vorticity profile, cooling rate and thermal gradient during the butt welding of Al-5754 to Al-6005, with sinusoidal beam oscillation, is analysed. It was found that one additional vortex is formed during beam oscillation welding due to the churning action of the oscillating beam. With the increase in oscillation amplitude, welds become wider and the depth of penetration decreases. An increase in oscillation frequency leads to an increase in the flow rate of the molten metal suggesting that the beam oscillation introduces a churning action that leads to an increase in mixing. It was highlighted that the material mixing depends on both diffusion and convection.

Laser welding of TC4 titanium alloy to 7075 aluminum alloy with infinite-shape oscillating beam

Laser welding of TC4 titanium (Ti) and 7075 aluminum (Al) alloys were accomplished in an overlap Ti-on-Al configuration with infinite-shape oscillating beam, microstructure and mechancial properties of joints were analyzed, energy-saving rate, interfacial heat transfer and energy-saving production were also investigated. The results suggested that the performance of TC4/7075 dissimilar joint can be maintained from 1663 N to 1672 N without obvious fluctuations by the use of oscillating laser beam with the corresponding increasing 50 Hz frequency for every 100 W decrease in laser power, which is derived from the promotion of heat transfer in penetration depth direction, thus keeping the melting amount of base metal to maintain an effective connection. In addition, the energy-saving rate rises as laser power decreases and oscillating frequency increases. Under 900 W laser power and 150 Hz oscillating frequency, the energy-saving rate reaches the highest value of 21.62% compared to the initial conventional laser welding process at 1200 W laser power. The conclusions can provide a basis for energy-saving rate evaluation of the green manufacturing in Ti/Al novel process.

Sensitivity of the thermomagnetic instability in superconducting film to magnetic perturbation for electromagnetic interference detection

The time-varying magnetic field with electromagnetic perturbation is regarded as an important parameter for the thermomagnetic stability of superconducting film devices. In this work, using a thermomagnetic model, we investigate the sensitivity of thermomagnetic instability in superconducting films exposed to a linear ramp magnetic field, superposed by the additional AC magnetic perturbation with tunable amplitude and oscillation frequency. Surprisingly, we find that the thermomagnetic instability is a non-monotonic function with the increasing oscillation frequency of the magnetic perturbation, depending on the working temperature and oscillation amplitude. The unexpected non-monotonic sensitivity of the thermomagnetic instability is revealed by the characteristic oscillation of the electric field, which cannot be aggravated by the AC magnetic perturbation at very high frequencies. The findings of this paper demonstrate that the magnetic perturbation at very low or high frequencies is not the main factor that triggers the thermomagnetic instability of superconducting films. Furthermore, using the magnetic moment measurement, we propose possible electromagnetic interference detection by the superconducting film based on such non-monotonic sensitivity of the thermomagnetic instability, which can be used to detect the tunable target electromagnetic interference with characteristic frequency in a complex electromagnetic environment.

Moffatt eddies in electrohydrodynamics flows: numerical simulations and analyses

We study numerically a sequence of eddies in two-dimensional electrohydrodynamics (EHD) flows of a dielectric liquid, driven by an electric potential difference between a hyperbolic blade electrode and a flat plate electrode (or the blade–plate configuration). The electrically driven flow impinges on the plate to generate vortices, which resemble Moffatt eddies (Moffatt, J. Fluid Mech., vol. 18, 1964, pp. 1–18). Such a phenomenon in EHD was first reported in the experimental work of Perri et al. (J. Fluid Mech., vol. 900, 2020, A12). We conduct direct numerical simulations of the EHD flow with three Moffatt-type eddies in a large computational domain at moderate electric Rayleigh numbers ( $T$ , quantifying the strength of the electric field). The ratios of size and intensity of the adjacent eddies are examined, and they can be compared favourably to the theoretical prediction of Moffatt; interestingly, the quantitative comparison is remarkably accurate for the two eddies in the far field. Our investigation also shows that a larger $T$ strengthens the vortex intensity, and a stronger charge diffusion effect enlarges the vortex size. A sufficiently large $T$ can further result in an oscillating flow, consistent with the experimental observation. In addition, a global stability analysis of the steady blade–plate EHD flow is conducted. The global mode is characterised in detail at different values of $T$ . When $T$ is large, the confinement effect of the geometry in the centre region may lead to an increased oscillation frequency. This work contributes to the quantitative characterisation of the Moffatt-type eddies in EHD flows.

Analysis of dynamic characteristics of vapor plume of oscillating laser welding of SUS301L-HT stainless steel

Investigations had made much efforts on the vapor plume dynamic characteristics of laser beam welding (LBW) but only showed a little knowledge about the oscillating laser beam welding (OLBW). The velocity magnitude and direction of OLBW varied abidingly, resulting in complicated evolution process of vapor plume. Present research attempted to elucidate the effect of oscillation frequency on the dynamic behavior of vapor plume. The vapor plume morphology was uniform at 50 Hz and 100 Hz. The abrupt change in velocity direction easily led to the occurrence of attenuation and even annihilation of the vapor plume at the frequency less than 20 Hz or greater than 150 Hz. The vapor plume area less than 31.44 mm2 or the vapor plume orientation greater than −40° could be used as the judgment criterion of keyhole instability. The coefficient of variation of vapor plume area or orientation and the proportion of keyhole instability time showed similar trends of first decreasing and then increasing with the increase of oscillation frequency. The stability of vapor plume or keyhole was the best at 50 Hz.

Control mechanisms of pathological low-frequency oscillations under different targets in Parkinson's disease

Deep brain stimulation (DBS) inhibiting excessive low-frequency (7–35 Hz) synchronization can treat Parkinson's disease (PD), although the therapeutic mechanism remains unclear. To explore the mechanism of DBS in controlling the pathological low-frequency oscillations, we stimulate the globus pallidus pars interna (GPi), globus pallidus pars externa (GPe), subthalamic nucleus (STN), indirect medium spiny neurons (iMSN) and direct medium spiny neurons (dMSN) in basal ganglia (BG) to analyze the discharge mode of each nucleus. The transition between healthy and PD condition can be achieved by whether to add dopamine-level current based on the cortex-basal ganglia-thalamus (CTx-BG-TH) loop model. In this study, we propose two mechanisms to control the abnormal oscillations, namely, increase and decrease mechanisms of oscillation frequency. The simulation results show that stimulating GPi, STN or iMSN can make the discharge frequency of GPi reach more than 35 Hz, while stimulation of dMSN or GPe targets can reduce the frequency to less than 7 Hz, indicating that the discharge frequency presents two opposite changes to eliminate the beta oscillations. Moreover, GPi-DBS and dMSN-DBS are the optimal choices that can minimize the oscillation energy in the low-frequency band under the two control mechanisms, respectively. Therefore, simultaneous stimulation in GPi and dMSN to coordinate the two control mechanisms may provide a new idea for the DBS targets selection under parkinsonian state.

Dynamic process and mechanism of crude oil release from silty intertidal sediment under different influencing factors

Under tidal scouring, residual petroleum in the intertidal sediment after oil spills could release again, causing secondary pollution in the marine ecosystem. The current study aimed to investigate the dynamic process and principles of crude oil release from silty intertidal sediment under different influencing factors and screened for the key factors. In this paper, the fitting equations and correlation between the release amount and various factors were explored through the single-factor and orthogonal experiments. Then, the key influencing factors were selected for multi-factor fitting of the release amount. The results showed that the oil release amount rose with the increase in oil concentration, oscillation frequency, and release time, but decreased with an increase in salinity. As the pH decreased, the oil release amount increased. The relationship between release amount and concentration/oscillation frequency can be equipped by the polynomial equation, and the average R2 was 0.95 and 0.84, respectively. The release amount can be fitted by the Lagergren pseudo-second-order kinetic equation with time, with the average R2 0.89. The pH was negatively correlated with the release amount in the fresh contaminated sediment but positively correlated with the weathered one. The correlation between each factor and oil release amount was ranked (from large to small) as oil concentration, oscillation frequency, salinity, time, and pH. At last, a polynomial equation can be fitted between the key influencing factors (oil concentration and oscillation frequency) and the release amount. The results can provide a theoretical basis for predicting the secondary pollution owing to the oil re-release from intertidal sediment.