Resonance and Bifurcation of Fractional Nonlinear Systems with Power Damping Term for Robot Grinding

A fractional nonlinear system with power damping term is introduced to study the forced vibration system in order to solve the resonance and bifurcation problems between grinding wheel and steel bar during robot grinding.The robot,grinding wheel and steel bar are reduced to a spring-damping second-order system model.The implicit function equations of vibration amplitude of the dynamic system with coulomb friction damping,linear damping,square damping and cubic damping are obtained by average method.The stability of the system is analyzed and explained,and the stability condition of the system is proposed.Then,the amplitude-frequency characteristic curves of the system under different fractional differential orders,nonlinear stiffness parameters,fractional differential term coefficients and external excitation amplitude are analyzed.It is shown that the fractional differential term in the dynamic system is the damping characteristic.Then the influence of four kinds of damping on the vibration amplitude of the system under the same parameter is investigated and it is proved that the cubic damping suppresses the vibration of the system to the maximum extent.Finally,based on the idea that the equilibrium point of the system is the constant part of the Fourier series expansion term,the bifurcation behavior caused by the change of damping parameters in linear damping,square damping and cubic damping systems with different values of fractional differential order is investigated.

General M-lumps, T-breathers, and hybrid solutions to (2+1)-dimensional generalized KDKK equation

A special transformation is introduced and thereby leads to the N-soliton solution of the(2+1)-dimensional generalized Konopelchenko-Dubrovsky-Kaup-Kupershmidt(KDKK) equation.Then,by employing the long wave limit and imposing complex conjugate constraints to the related solitons,various localized interaction solutions are constructed,including the general M-lumps,T-breathers,and hybrid wave solutions.Dynamical behaviors of these solutions are investigated analytically and graphically.The solutions obtained are very helpful in studying the interaction phenomena of nonlinear localized waves.Therefore,we hope these results can provide some theoretical guidance to the experts in oceanography,atmospheric science,and weather forecasting.

The Cyclic Behavior of Mountain Gravity Waves Generated by Flow over Topography

The cyclic behavior of lee wave systems, generated by stratified flow over mountains is investigated by the Advanced Regional Prediction System (ARPS) model. The results show that, surface friction has a direct impact upon the number and timing of mountain gravity waves cycle generation. Cyclic generation of mountain lee waves and down-slope winds was found to be extremely sensitive to the magnitude of the surface drag coefficient, where mountain waves amplitude and intensity varies with the magnitude of the drag coefficient, and the interaction of mountain waves and boundary layer process determinates the wave characteristics. For the typical drag Cd = 10–3, surface friction promotes the formation of the stationary mountain lee waves and hydraulic jump, especially, promotes boundary layer separation, the generation of low-level turbulent zones and rotor circulation or reversal flow within boundary layer. When drag coefficient becomes Cd = 10–4, lee waves remain steady states and the first evolution cycle maintains much longer than that of Cd = 10–3. In the case of the highest drag coefficient Cd = 10–2, surface friction suppresses wave breaking and the onset of hydraulic jump, and reduces greatly the amplitude and intensity of lee waves and down slope wind.

Analyses and Numerical Modeling of Gravity Waves Generated by Flow over Nanling Mountains

Although there have been many observational and modeling studies of gravity waves excited by topograpghy, the detailed structure and its changes in real world are still poorly understood. The interaction of topography and background flow are described in details for a better understanding of the gravity waves observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery over Nanling Mountains. The evolutionary process and spatial structure of gravity waves were investigated by using almost all available observational data, including MODIS satellite imagery, the Final Analyses (FNL) data issued by National Centers for Environmental Prediction (NCEP), the aerosol backscattering signal data from Lidar, the surface observational data and the sounding data of Nanling mountain regions. In order to study its development mechanism, choosing the initial sounding of Jiangxi Gaizhou station located in the upstream of Nanling regions, and using the Advanced Regional Prediction System (ARPS), the numerical simulation was performed. It is shown that the ARPS model reproduced the main features of gravity waves reasonably well, where the gravity waves and turbulent mixed layer are consistent with the satellite image and the aerosol backscattering signal from Lidar observation. It is well-known that gravity wave-induced turbulence and thus turbulent mixing could affect the local composition of chemical species, which plays a significant role in the formation of low visibility and precipitation associated with local orography.

Quantum degenerate Bose–Fermi atomic gas mixture of 23Na and 40K

We report a compact experimental setup for producing a quantum degenerate mixture of Bose23Na and Fermi40K gases. The atoms are collected in dual dark magneto–optical traps(MOT) with species timesharing loading to reduce the light-induced loss, and then further cooled using the gray molasses technique on the D2line for23Na and D1line for40K. The microwave evaporation cooling is used to cool23Na in |F = 2, mF= 2〉 in an optically plugged magnetic trap, meanwhile,40K in |F = 9/2, mF= 9/2〉 is sympathetically cooled. Then the mixture is loaded into a large volume optical dipole trap where23Na atoms are immediately transferred to |1, 1〉 for further effective cooling to avoid the strong three-body loss between23Na atoms in |2, 2〉 and40K atoms in |9/2, 9/2〉. At the end of the evaporation in optical trap, a degenerate Fermi gas of40K with 1.9 × 10^(5) atoms at T/TF= 0.5 in the |9/2, 9/2〉 hyperfine state coexists with a Bose–Einstein condensate(BEC) of23Na with 8 × 10^(4) atoms in the |1, 1〉 hyperfine state at 300 n K. We also can produce the two species mixture with the tunable population imbalance by adjusting the 23Na magneto–optical trap loading time.

The Formation of Lee Reversal Flow and Moisture Distribution Effect on the Characteristics of Precipitation

Moist flow over a bell-shaped mountain is investigated using the advanced regional prediction system (ARPS). Three closely related issues are addressed: the upslope precipitation mechanism, periodic evolution of precipitation associated with mountain waves, and lee precipitation induced by reversal flow. The results show that precipitation is strongly the moist distribution and terrain scale dependent. Beginning with the case of uniformly stratified flow over mountain, upslope precipitation and lee wave precipitation pattern are obtained. Most importantly, lee precipitation induced by reversal flow can be caused by layered flow over mountain, wherein lee reversal flow exerts a significant influence on the orographic precipitation.

Analysis of Terrain Height Effects on the Asymmetric Precipitation Patterns during the Landfall of Typhoon Meranti (2010)

The predictions of heavy rainfall in an accurate and timely fashion are some of the most important challenges in disastrous weather forecast when a typhoon passes over land. Numerical simulations using the advanced weather research and forecasting (WRF) model are performed to study the effect of terrain height and land surface processes on the rainfall of landfall typhoon Meranti (2010). The experimental results indicate that terrain height could enhance convection and precipitation. The heavy rainfall is concentrated on the west side of typhoon track, which is mainly associated with the distribution of deep convection. The terrain height exacerbated the asymmetric distribution of heavy rainfall. The most striking feature is that enhanced rainfall is mainly caused by secondary circulation, which is induced by terrain height and can be explained by a highly simplified theoretical model. Finally, it is worth pointing out that perturbation potential temperature or buoyancy processes forced by terrain height could be taken as an indicator for accurate prediction of heavy rainfall during the landfall of a tropical cyclone.

Removing and recycling mercury from scrubbing solution produced in wet nonferrous metal smelting flue gas purification process

Wet purification technology for nonferrous metal smelting flue gas is important for mercury removal;however, this technology produces a large amounts of spent scrubbing solution that contain mercury. The mercury in these scrubbing solutions pose a great threat to the environment. Therefore, this research provides a novel strategy for removing and recycling mercury from the scrubbing solution, which is significant for decreasing mercury pollution while also allowing for the safe disposal of wastewater and a stable supply of mercury resources. Some critical parameters for the electrochemical reduction of mercury were studied in detail. Additionally, the electrodeposition dynamics and electroreduction mechanism for mercury were evaluated. Results suggested that over 92.4% of mercury could be removed from the scrubbing solution in the form of a Hg-Cu alloy under optimal conditions within 150 min and with a current efficiency of approximately 75%. Additionally, mercury electrodeposition was a quasi-reversible process, and the controlled step was the mass transport of the reactant. A pre-conversion step from Hg(Tu)_(4)^(2+) to Hg(Tu)_(3)^(2+) before mercury electroreduction was necessary. Then, the formed Hg(Tu)_(3)^(2+) on the cathode surface gained electrons step by step. After electrodeposition, the mercury in the spent cathode could be recycled by thermal desorption. The results of the electrochemical reduction of mercury and subsequent recycling provides a practical and easy-to-adopt alternative for recycling mercury resources and decreasing mercury contamination.

Interpretable discovery of semiconductors with machine learning

Machine learning models of material properties accelerate materials discovery,reproducing density functional theory calculated results at a fraction of the cost1–6.To bridge the gap between theory and experiments,machine learning predictions need to be distilled in the form of interpretable chemical rules that can be used by experimentalists.Here we develop a framework to address this gap by combining evolutionary algorithm-powered search with machine-learning surrogate models.We then couple the search results with supervised learning and statistical testing.This strategy enables the efficient search of a materials space while providing interpretable design rules.We demonstrate its effectiveness by developing rules for the design of direct bandgap materials,stable UV emitters,and IR perovskite emitters.Finally,we conclusively show how DARWIN-generated rules are statistically more robust and applicable to a wide range of applications including the design of UV halide perovskites.

Effects of surface roughness on the aerodynamic performance of a high subsonic compressor airfoil at low Reynolds number

The aerodynamic performance of compressor airfoil is significantly affected by the surface roughness at low Reynolds number(Re).In the present study,numerical simulations have been conducted to investigate the impact of surface roughness on the profile loss of a high subsonic compressor airfoil at Re=1.5×10^(5).Four roughness locations,covering 10%,30%,50%and 100%of the suction surface from the leading edge and seven roughness magnitudes(Ra)ranging from 52 to525 lm were selected.Results showed that the surface roughness mainly determined the loss generation process by influencing the structure of the Laminar Separation Bubble(LSB)and the turbulence level near the wall.For all the roughness locations,the variation trend for the profile loss with the roughness magnitude was similar.In the transitionally rough region,the negative displacement effect of the LSB was suppressed with the increase of roughness magnitude,leading to a maximum decrease of 14.6%,16.04%,16.45%and 10.20%in the profile loss at Ra=157 lm for the four roughness locations,respectively.However,with a further increase of the roughness magnitude in the fully rough region,the stronger turbulent dissipation enhanced the growth rate of the turbulent boundary layer and increased the profile loss instead.By comparison,the leading edge roughness played a dominant role in the boundary layer development and performance variation.To take fully advantage of the surface roughness reducing profile loss at low Re,the effects of roughness on suppressing LSB and inducing strong turbulent dissipation should be balanced effectively.

Vortex dynamics and entropy generation in separated transitional flow over a compressor blade at various incidence angles

The transition process within a Laminar Separation Bubble(LSB)that formed on a compressor blade surface was investigated using Large Eddy Simulations(LESs)at a Reynolds number of 1.5×10;and incidence angles of 0°,+3°,and+5°.The vortex dynamics in the separated shear layers were compared at various incidence angles and its effects on the loss generation were clarified through entropy analysis.Results showed that transition onset,which was accurately identified by the Linear Stability Theory(LST),was significantly promoted at the increased incidence angle.As such,the development of LSB was suppressed and the relative role of viscous instability played in the transition process was weakened.At the incidence angle of 0°,two-dimensional spanwise vortices detached from the blade surface and roiled up periodically,which were further stretched and eventually evolved into large-scale hairpin vortices.As time passed,the fully developed hairpin vortices broke down into small-scale eddies.Meanwhile,the flow near the wall reversely ejected into the outer separated shear layers and a sweeping process happened subsequently,forcing the separated shear layers to reattach and accelerating the generation of turbulent fluctuations.By comparison,the strength of vortex rolling-up was weakened at higher incidence angles,and the vortex pairing and breakdown of large-scale vortices were less pronounced.Therefore,the level of turbulent fluctuations that generated in the separated shear layers was reduced.Detailed entropy analysis showed that the turbulent dissipation effect related to the Reynolds shear stresses determined the largest amount of positive entropy generation,which declined to a lower level as the incidence angle increased from 0°to+5°.Correspondingly,the profile loss was reduced by 50.4%.

Numerical investigation of flow mechanisms of tandem impeller inside a centrifugal compressor

This study numerically investigated a single stage centrifugal compressor "Radiver" with a wedge diffuser and several tandem-designed impellers to explore the flow phenomena within the tandem impeller and the potential to enhance compressor performance.The results demonstrate that tandem design and clocking fraction(ks)significantly affects the compressor performance.The compressor stage with tandem impellers of Series A of boundary layer growth interruption alone are observed to have a widely operating range but efficiency and total pressure ratio penalty compared with that of conventional impeller.The tandem impeller with at least the same impeller efficiency as the conventional design is considered as a critical design criteria so that further modification process based on the flow characteristic of tandem impeller is necessary.In order to restrain the inducer wake and exducer shock losses,parameters modification of blade angle and thickness distributions are necessary and the modified tandem impeller of Series B is obtained.The modified tandem impeller with 25%clocking arrangement shows an 8.45%stall margin increase and maintains the total pressure ratio and efficiency as the conventional design,which proves the potential of tandem impeller to improve compressor stage performance.It is noteworthy that the tandem impellers of Radiver have not shown obviously balanced exit flow field and the fundamental mechanism of stall margin extending of tandem impeller lies on the improved impeller/diffuser matching performance resulting from the incidence angle variation at diffuser inlet.