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Thermal deformation caused by temperature rise have an influence on the dynamic performance of a motorized spindle. In turn, the change in the dynamic performance will affect the temperature rise and thermal deformation of the system. However, the latter was rarely focused on in the previous literature. Therefore, a thermal network model of motorized spindle is enhanced by considering the thermal–mechanical coupling effect. Then, an iterative method is presented to solve the coupled equations, and a temperature test rig of the motorized spindle is set up to verify the proposed model. The relative error between the predicted and experimental results at two test points decreases by 9.56% and 3.44% after considering the thermal–mechanical coupling effect. The comparison with the experimental results shows that the proposed model with thermal–mechanical coupling effect can obtain a more accurate temperature field than the previous model.

As one type of latest emitters with simultaneous high efficiency and color-purity, the development of multi-resonance thermally activated delayed fluorescence (MR-TADF) materials represents an important advancement for organic light-emitting diodes (OLEDs). We herein present a new strategy to improve the performance of MR-TADF emitters by fusing sulfur element into the B-N based framework, aiming to utilize the non-metal heavy-atom effect in accelerating the reverse intersystem crossing (RISC) process of the emitter. Two compounds, namely 2PTZBN and 2PXZBN, were developed in this work through rigidifying the DABNA-1 skeleton by sulfur or oxygen atoms. The theoretical calculations and photoluminescence studies revealed that the sulfur-incorporated 2PTZBN enabled considerable rate constant of RISC (kRISC) up to 2.8 × 105 s-1 in toluene due to larger spin-orbital coupling (SOC) values and smaller singlet-triplet energy splitting (ΔEST) compared with 2PXZBN. Consequently, organic light-emitting diodes based on 2PTZBN exhibited highly efficient green emission with maximum external quantum efficiency (EQE) of 25.5%.

A new series of tetrahedral heteroleptic copper(I) complexes exhibiting efficient thermally-activated delayed fluorescence (TADF) in green to orange electromagnetic spectral regions has been developed by using D-A type N^N ligand and P^P ligands. Their structures, electrochemical, photophysical, and electroluminescence properties have been characterized. The complexes exhibit high photoluminescence quantum yields (PLQYs) of up to 0.71 at room temperature in doped film and the lifetimes are in a wide range of 4.3–24.1 μs. Density functional theory (DFT) calculations on the complexes reveal the lowest-lying intraligand charge-transfer excited states that are localized on the N^N ligands. Solution-processed organic light emitting diodes (OLEDs) based on one of the new emitters show a maximum external quantum efficiency (EQE) of 7.96%.

Highly efficient blue thermally activated delayed fluorescence (TADF) materials with high horizontal dipole orientation (Θ//) remain a big challenge due to the concentration quenching effects and serious efficiency roll-offs in their corresponding organic light-emitting diodes (OLEDs). We herein report two novel TADF compounds, namely 2TDBA-SBA and TDBA-SBA, which were facilely synthesized by utilizing a rigid oxygen-bridged cyclized triarylboron-based unit (TDBA) as the acceptor and a spiro acridine (SBA) as the donor. Benefiting from the rigid and planar skeleton of the acceptor and the linear molecular shape, high Θ//s and photoluminescence quantum yields (PLQYs) of ∼ 90% were achieved. Significantly, TDBA-SBA exhibited excellent TADF properties with a short delayed fluorescence lifetime of only 684 ns and narrow full-width at half-maximum (FWHM) of 44 nm in solution state, accompanied by the high PLQYs of over 80% at high doping concentrations, manifesting the alleviated exciton quenching effects. Consequently, OLEDs based on TDBA-SBA achieved a high maximum external quantum efficiency (EQE) of 29.3% and a maximum brightness of 27663 cd cm−2. Importantly, an EQE over 20% was realized even at the high brightness of 10000 cd cm−2, signifying a small efficiency roll-off.

Multi-resonance thermally activated delayed fluorescence (MR-TADF) offered exceptional solution for narrowband organic light emitting diode (OLED) devices in terms of color purity and luminescence efficiency, while the development of new MR skeleton remained an exigent task, especially for long wavelength region. We hereby demonstrate that a simple modification of the B (boron)-N (nitrogen) framework by sp3 -carbon insertion would significant bathochromic shift the short-range chargetransfer emission and improve the device performances. The bis(acridan)phenylenebased skeleton developed in this contribution presented a non-planar conformation and allowed facile introduction of isolating units to prevent triplet-involved quenching, deriving two luminophores with quantum yields approaching 90% and narrow FWMHs below 30 nm in film state. Corresponding green-emissive devices realized superior performances comparing to the planar carbazolyl-based MR-TADF analogues, with a maximum external quantum efficiency (EQEmax) up to 28.2% and small efficiency rolloff without the involvement of any sensitizing host

In this study, a modified wear model considering contact temperature for spur gears in mixed elastohydrodynamic lubrication (EHL) is proposed. The contact temperature consists of bulk temperature and flash temperature. The bulk temperature is determined by the thermal network model, whereas the flash temperature is estimated through the published method. The bulk temperature, which was rarely included in the previous works, substantially has a considerable influence on the tooth wear in mixed EHL. It is also found that the lower contact temperature contributes to the reduction of gear wear depth. Furthermore, the effects of gear basic geometrical parameter and operating parameter on wear depth are investigated. The results show that the wear depth decreases with the increased tooth width, module, pressure angle and rotational velocity but increases with the surface roughness and torque. It indicates that wear resistance of tooth surfaces can be enhanced by optimising the design parameters of gear drives.

Luminescent coinage metal complexes have shown promising applications as electroluminescent emitters, photocatalysts/photosensitizers, and bioimaging/theranostic agents, rendering them attractive alternatives to transition metal complexes based on iridium, ruthenium, and platinum that have extremely low earth abundance. In comparison to the widely studied Au(I) and Cu(I) complexes, Ag(I) complexes have seldom been explored in this field because of their inferior emission properties. Herein, we report a novel series of [Ag(N^N)(P^P)]PF6 complexes exhibiting highly efficient thermally activated delayed fluorescence by using easily accessible neutral diamine ligands and commercially available ancillary diphosphine chelates. The photoluminescence quantum yields (PLQYs) of the Ag(I) emitters are ≤0.62 in doped films. The high PLQY with a large delayed fluorescence ratio enabled the fabrication of solution-processed organic light-emitting diodes (OLEDs) with a high maximum external quantum efficiency of 8.76%, among the highest values for Ag(I) emitter-based OLEDs. With superior emission properties and an excited state lifetime in the microsecond regime, together with its potent cytotoxicity, the selected Ag(I) complex has been used for simultaneous cell imaging and anticancer treatment in human liver carcinoma HepG2 cells, revealing the potential of luminescent Ag(I) complexes for biological applications such as theranostics.

Colorectal cancer (CRC) is the second leading cause of cancer-related mortality worldwide. In coping with it, histopathology image analysis (HIA) provides key information for clinical diagnosis of CRC. Nowadays, the deep learning methods are widely used in improving cancer classification and localization of tumor-regions in HIA. However, these efforts are both time-consuming and labor-intensive due to the manual annotation of tumor-regions in the whole slide images (WSIs). Furthermore, classical deep learning methods to analyze thousands of patches extracted from WSIs may cause loss of integrated information of image. Herein, a novel method was developed, which used only global labels to achieve WSI classification and localization of carcinoma by combining features from different magnifications of WSIs. The model was trained and tested using 1346 colorectal cancer WSIs from the Cancer Genome Atlas (TCGA). Our method classified colorectal cancer with an accuracy of 94.6 %, which slightly outperforms most of the existing methods. Its cancerous-location probability maps were in good agreement with annotations from three individual expert pathologists. Independent tests on 50 newly-collected colorectal cancer WSIs from hospitals produced 92.0 % accuracy and cancerous-location probability maps were in good agreement with the three pathologists. The results thereby demonstrated that the method sufficiently achieved WSI classification and localization utilizing only global labels. This weakly supervised deep learning method is effective in time and cost, as it delivered a better performance in comparison with the state-of-the-art methods.

A novel electron donor, namely, TMDBP is designed by angularly fusing two acridine moieties. The DMAC subunits in TMDBP exhibit a dominant quasi-equatorial conformation due to steric H-H repulsion. The new TADF emitters render excellent OLED performances with EQE up to 24.2% and small efficiency roll-off.

The development of the thermally activated delayed fluorescence (TADF) emitters with circularly polarized luminescence (CPL), particularly those exhibiting deep-blue emission is still a formidable challenge. In this work, we reported a simple and easily accessed molecular design strategy for deep-blue circularly polarized TADF (CP-TADF) enantiomers. Two chiral compounds, namely (S)-NPE-AcDPS and (R)-NPE-AcDPS, were successfully designed and synthesized, which featured concurrently TADF, CPL, and aggregation-induced enhanced emission (AIEE) properties. The CPL exhibited a maximum gPL value of 3.0 × 10−4. These emitters exhibited deep blue emission peaking at 451 nm in doped film with a high photoluminescence of 86% and a small singlet-triplet splitting of 0.05 eV. Furthermore, the deep blue OLED based on (S)-NPE-AcDPS demonstrated a high external quantum efficiency (EQE) up to 18.5%.

Passive surface wave methods utilizing traffic noise have been studied in recent years to estimate shear wave velocity in urban near-surface explorations. Suitable processing scheme is necessary for the emergence of coherent signal, and even to account for the azimuthal effects in acquired noise data. We propose a new ambient noise data selection technique based on the asymmetry of the cross-correlation functions to refine the quality of data processing in the complex city environment. The asymmetry coefficient is defined by the logarithmic energy ratio of the casual and acausal surface waves to measure the correlation asymmetry, and two kinds of symmetric functions are taken into account to establish the screening conditions. The underlying physics for the symmetries of the correlation functions are demonstrated to prove the feasibility of our algorithm. Two numerical tests suggest that the bidirectional inline sources are adequately highlighted, and the high velocity anomalies caused by the offline sources are eliminated by our method. Furthermore, the significances of the applications of time window and normalization are investigated to improve the reliability of the algorithm. We also apply the method to three-component field data acquired from the city pavement. The comparisons between the results of raw and selected data confirmed that the random noise and the artifacts can be effectively suppressed, and the dispersion energy trends emerge clearly and become more convergent toward the lower frequency. Finally, our method is concluded to be practical for urban bidirectional traffic noise.

A novel prediction method for gear friction coefficients with or without lubrication is developed with a computational inverse technique. A surrogate model is introduced to describe the mapping between the friction coefficients and root stresses, according to an adaptive radial basis function. The convergence criterion for solving the friction coefficients is determined based on the calculated and measured root stresses. A nonzero friction coefficient at the pitch point, which is closely relative to the action of rolling friction, is detected using the proposed method. Results show that the gear friction coefficients decrease with an increase in rotation speed or a decline in applied torque. Moreover, the friction coefficients without lubrication are more than twice those with lubrication.

An adhesive wear prediction method for double helical gears is proposed according to enhanced coordinate transformation and generalized sliding distance model in conjunction with Archard's wear equation. To describe transient contact ellipse and identify the contact point pairs conveniently, a transform coordinate plane is set in coincidence with the plane of action and a coordinate axe parallels to the contact line. The contact pressure distribution is determined by contact line length, contact width and normal force, and a modified sliding distance model is proposed by generalized moving distance replacement of Hertz contact width. As the wear coefficient, contact pressure and sliding distance are given, the tooth wear depths are predicted by a developed numerical procedure. Effects of major geometrical and working parameters on the wear depth are investigated. The results show that the wear depth becomes smaller, which is mainly determined by the contact force per unit length, equivalent curvature radius and sliding distance as normal module, normal pressure angle, helix angle, tooth width or transmission ratio increases. However, the wear depth becomes larger when input torque is improved. It is indicated that rational parameters match in gear design and uniform wear distribution are beneficial for wear resistance.

Innovative stiffness and damping models for oil films are developed to account for the impacts in both normal and tangential directions. Given that these models are applied to a gear drive in line contact elastohydrodynamic lubrication (EHL), the combined stiffness is derived from the stiffness of both the oil film and gear tooth while the combined damping is established from the damping of these parts. The effects of three fundamental parameters (contact force, rotation speed, and tooth numbers) of the gear drive in line contact EHL on the combined stiffness and damping are then investigated. The results reveal that the small normal and tangential stiffness of the lubricant can alleviate meshing impact and shear vibration, while the impact and friction heat can be reduced by using an oil film with either a large normal damping or small tangential damping. Given that its amplitude and fluctuation are closely related to shear rate, effective viscosity, entrainment velocity, and curvature radii, the improved combined stiffness and damping can be obtained by rationally matching the geometric and operating parameters.

Excited-state properties (characteristics and composition) play a crucial role in luminescence properties of the new-generation organic light-emitting materials. As a special excited species, the hybridized local and charge-transfer (HLCT) state is composed of locally excited (LE) state and charge-transfer (CT) state, which can harvest simultaneous high photoluminescence (PL) efficiency and high exciton utilization in organic light-emitting diodes. In this work, we designed and synthesized three donor (D)–acceptor (A) compounds with different donor units and a typical electron-deficient unit acridine as the acceptor unit to investigate the different hybridization statuses among them. As is revealed by the molecular design, the three compounds precisely show the different hybridization statuses: LE-dominated hybridization (CZP-1AC), quasi-equivalent HLCT (qHLCT, TPA-1AC), and CT-dominated hybridization (PTZ-1AC). As a result, TPA-1AC exhibits the highest PL efficiency and multifold device performance, meri...

To develop colorless and soluble polyimide films, a novel dianhydride containing 1,4:3,6-dianhydro-D-mannitol unit, 2,5-bis(3,4-dicarboxyphenoxy)-1,4:3,6-dianhydromannitol dianhydride (IMDA) was synthesized. And two series of polyimides were prepared via a two-step thermal imidization, PI−(1–4) were obtained from IMDA and four kinds of aromatic diamines while PI−(5–7) from IMDA and three kinds of semiaromatic diamines. All the polyimides were readily soluble in common polar solvents and could afford flexible, tough and colorless films with transparency up to 89% at 450 nm. Especially, polyimides simultaneously containing 1,4:3,6-dianhydrohexitol units in diamine and dianhydride exhibited comparable optical and soluble performance with the alicyclic fluorinated ones. Meanwhile, it was certified that 1,4:3,6-dianhydrohexitol fragment in dianhydride was more determinant in solubility and transmittance of polyimides than that in diamine. An overall investigation of these polyimides on thermal, mechanical, morphological, soluble, optical and dielectric properties was presented, and their structure-property relationships were discussed in detail.

This paper provides a method coupling the 2D microtopography filtered by ISO Gaussian filter of spur gears, which is typically used in power transmission devices, and Transmission error (TE) together. A gearbox with certain transmission ratio is selected as a research object for analysis. This gearbox comprises a mathematical model of TE calculation based on the Monte Carlo method and the coordinate transformation method, which couples the 2D microtopography of spur gears and TE. Two TE models are established to study their effects on the coupling results: a) The single TE model, which means only one gear owns TE, and b) the synthetic TE model, which means both gears possess TE. The new model of the 2D microtopography of tooth surfaces can be utilized further to investigate the mechanism of engagement and the approximate contact position of asperities on the tooth surface. The new model is also significant in studying the tooth root bending stress.

As one type of latest emitters with simultaneous high efficiency and color-purity, the development of multi-resonance thermally activated delayed fluorescence (MR-TADF) materials represents an important advancement for organic light-emitting diodes (OLEDs). We herein present a new strategy to improve the performance of MR-TADF emitters by fusing sulfur element into the B-N based framework, aiming to utilize the non-metal heavy-atom effect in accelerating the reverse intersystem crossing (RISC) process of the emitter. Two compounds, namely 2PTZBN and 2PXZBN, were developed in this work through rigidifying the DABNA-1 skeleton by sulfur or oxygen atoms. The theoretical calculations and photoluminescence studies revealed that the sulfur-incorporated 2PTZBN enabled considerable rate constant of RISC (kRISC) up to 2.8 × 105 s-1 in toluene due to larger spin-orbital coupling (SOC) values and smaller singlet-triplet energy splitting (ΔEST) compared with 2PXZBN. Consequently, organic light-emitting diodes based on 2PTZBN exhibited highly efficient green emission with maximum external quantum efficiency (EQE) of 25.5%.

Double helical gears are widely applied in the aviation, marine and energy equipment, and generally required to be modified as the crowned since the machining error and assembling error of the gear drive are inevitable. The crowned gears usually operate in point contact mixed elastohydrodynamic lubrication (EHL), and adhesive wear has been one of the most prominent problems, but few previous researches were focused on this problem. In this work, a wear life prediction model of crowned double helical gears in point contact mixed EHL is proposed. The tooth profiles of the crowned gears are obtained according to the generating principle, and the load is attained in consideration of multi-tooth pairs contact. The contact pressure is derived from Hertzian elastic contact theory and load sharing concept, and the sliding distance is determined by a generalized model. Then, the wear rate in point contact mixed EHL is evaluated by extending the Archard theory to lubricated case, and the extended Archard's wear model is used to formulate the gear tooth wear. Moreover, the wear life prediction model which takes account of rotation speed and input torque is established, and the influences of surface roughness and crowned amount on the wear life of the crowned gears are further studied. Results show that surface roughness has a great influence on the wear life at different rotational speeds, while input torque has a great influence on the wear life at different crowned amount. It indicates that the wear life of the crowned double helical gears can be improved by reasonable matching lubrication, modification and working parameters.

Wear is directly related to rough surface contact, and the accuracy of a wear prediction model depends on the accurate determination of contact pressure. In this work, a numerical model with high computational accuracy for rough surface contact is developed and applied to the wear prediction of spur gears. To acquire contact pressure, the integral equation that contact pressure should satisfy is discretized into a set of linear equations by piecewise linear interpolating contact pressure. Then, a gear wear model including rough surface contact is established. The proposed contact model is verified by comparing with smooth and rough surface contact, and the wear depths of a spur gear drive with geometry and pressure updates are analyzed. Result shows that a small roughness value among contact surfaces may cause a large change in contact pressure. The effects of main design parameters on gear wear are subsequently investigated. Gear wear is found to decrease with increased module and pressure angle but increases with increased transmission ratio and input torque. These findings indicate that reasonable parameter matching is beneficial to improving gear wear resistance.

Non-Newtonian thermal elastohydrodynamic lubrication (EHL) theory in point contact which deals with the lubrication for a crowned herringbone gear drive is developed, combined with the verified numerical procedure. Effects of the major geometry and working parameters on the lubrication performance (the pressure, film thickness, temperature rise and shear stress), are investigated. The results show that the enlargement of normal module, normal pressure angle, helix angel, and transmission ratio is beneficial for pitting resistance, and that the excessive crowned can debase the contact fatigue strength. It is indicated that severe thermal deformation and scuffing are prone to generation under large load and speed.

An enhanced flexible dynamic model for a valve train with clearance and multi-directional deformations is proposed based on finite element method (FEM), and verified by experiment. According to the measured cam profile, the available internal excitations in numerical solution to the model are achieved by using piecewise cubic Hermite interpolating polynomial. The comparative analysis demonstrates that the bending deformation of the rocker arm is much larger than the radial deformation, signifying the necessities of multi-directional deformations in dynamic analysis for the valve train. The effects of valve clearance and cam rotation speed on contact force, acceleration and dynamic transmission error (DTE) are investigated. Both theoretical predictions and experimental measurements show that the amplitudes and fluctuations of contact force, acceleration and DTE become larger, when the valve clearance or cam speed increases. It is found that including the elasticity and the damping will weaken the impact between the rocker arm and the valve on the components (not adjacent to the valve) at either unseating or seating scenario. Additionally, as valve clearance or cam rotation speed becomes larger, the valve lift and the working phase decrease, which eventually leads to inlet air reduction. Furthermore, our study shows that the combustion rate improvement, input torque, and components durability can be improved by tuning valve clearance or adjustment the cam profile.

Charge-transfer (CT) state is becoming a useful excited state to design next-generation luminescence materials for high-performance organic light-emitting diode (OLED). However, strong CT state usually causes serious decrease in photoluminescence (PL) efficiency due to the small overlap between HOMO and LUMO. In order to harvest both high exciton utilization and high PL efficiency in fluorescent OLEDs, figuring out the strategy of fine modification of CT component in excited state through structural modulation is important. In this work, four donor–acceptor structure triphenylamine (TPA) - acridine (AC) isomers (TPA-9AC, TPA-1AC, TPA-2AC and TPA-3AC) were designed and synthesized to investigate structure-property relationship between isomerization effect and excited state properties. Density functional theory (DFT) calculations and solvatochromic absorption, emission and photoluminescence decay spectra are carried out for the deep understanding of their emissive state character. The four isomers exhibit gradually increased PL efficiency from low-polarity hexane to medium-polarity tetrahydrofuran (THF), which could be assigned to the formation of hybridized local and charge-transfer (HLCT) states and effectively suppressed non-radiative transition arised from acridine in medium-polarity solvents. Among four isomers, TPA-3AC achieved the best EL performance, due to the proper LE and CT compositions in the emissive state, demonstrating that isomerization of donor and acceptor functional moieties is an effective approach for structural modification for high-efficiency fluorescent OLED emitters.

Friction is not considered in the calculation of load capacity for spiral bevel gears according to either ISO or AGMA gear standard, and friction effects on the bending, contact and shear of the gears have rarely been discussed. In this regard, the present work establishes analytical solutions to calculate bending and contact strength for spiral bevel gears incorporating friction on the tooth surface, which are verified by ISO gear standard and finite element method (FEM). The bending strength is calculated based on Lewis cantilever beam approximation, utilizing the modified normal force and the friction component. The modified normal force is derived at the highest point of single tooth contact (HPSTC) in the normal equivalent gear. Follow Hertz contact theory, the contact strength is calculated when the modified normal force and the friction component are exerted at the lowest point of single tooth contact (LPSTC) in the normal equivalent gear. The calculated bending and contact stresses agree well with those obtained from the FEM analysis while considering the influence of friction. Both theoretical predictions and FEM analysis have shown that friction has a crucial effect on load capacity of a spiral bevel gear drive, and that it exerts stronger influence on the bending strength (compared with the contact strength). When friction coefficients become larger (with the same input torque), the bending stress considering only the modified normal force decreases at HPSTC, whereas it increases if both the modified normal force and the friction component are included. In comparison, the contact stress will increase at LPSTC under both scenarios. Furthermore, it is illustrated that shear strength check of the tooth is necessary as large friction occurs in the contact zone. This developed analytical solution can be well applied to the determination of load capacity of spiral bevel gears, especially under harsh working conditions or in the demand for higher performance.

Polyaromatic compounds are significant members of leading candidates for organic semiconductors and optical materials. However, a thorny problem of polyaromatic materials is that their good emissive abilities in solutions are seriously weakened in solids due to strong π–π interactions between aromatics. As a typical case, the intermolecular π–π interaction tends to form excimers for polyaromatic system, which were always considered to quench fluorescence and decrease luminous efficiency in the past decades. Herein, anthracene is modified by meta-substituted bromobenzene to facilitate the formation of discrete dimeric stack in solids, leading to the enhanced anthracene excimer fluorescence. Particularly, instead of excimer quenching fluorescence, the more anthracene dimers in solids, the higher fluorescence efficiency, namely, excimer-induced enhanced solid-state emission. This work not only provides a meta-substituted strategy for molecular design to form excimer in solids but also demonstrates that high-...

A new normal stiffness model of the oil film is established by the viscous-elastic fluid between a spur gear drive being equivalent to a massless spring element, and the tangential stiffness model is proposed according to the hypothesis of equal shear stress on laminar element surfaces. Effects of operating parameters (contact force and rotation speed) and geometry parameters (module, tooth number, pressure angle and modification) on the oil film stiffness from the root to the tip are investigated. The results show that the amplitude and fluctuation of the stiffness are closely related to the shear rate, effective viscosity and curvature radii. It is indicated that the rational parameter match is valid in mesh impact reduction and stationarity enhancement.

Simple and fast detection of chemical warfare agents vapor is necessary and urgent to fight against uncertain terrorist attacks and wars. In this contribution, inspired by the design of the hybrid locally excited and charge transfer (HLCT) excited state, two fast and highly sensitive visualization and fluorescence probes for DCP detection with relative small interstate coupling (J) TPA-2AC and TPA-9AC are reported. Upon exposure to saturated DCP vapor, the TPA-9AC test strips exhibited a rapid fluorescent response in no more than 1 s, accompanied by a change of the color from green to red. The detection limit of the test strips can be estimated as sensitive as 0.15 ppb, which is far superior to the "harmless" level (7 ppb) of human response to acute sarin exposure. More impressively, the fluorescent intensity of the test strips can be quickly restored when exposed to ammonia vapor for cyclic utilization, demonstrating an application prospect in the real-time detection of chemical warfare agents.

Near-surface ( urban sustainable development and expansion. Complex urbanized environments, however, limit the application of traditional active-source seismic surveys . Passive seismic surveys provide an alternative for investigating near-surface structures by utilizing abundant traffic noise. We presented a case study of fine-scale shear-wave velocity (Vs) structure imaging in the Hangzhou urban area (eastern China) and compared inversion results of ambient noise tomography and multichannel analysis of passive surface wave (MAPS). Noise data were recorded within one day by a dense seismic network (130 m × 120 m). The average adjacent station interval is about 10 m. Our goal is to investigate the top 100 m of the subsurface at the survey area. The two inverted Vs models by tomography and MAPS are similar and they both tally with the logging data. The subsurface geology structures are analyzed based on tomography inversion results and borehole data. The bedrock surface is determined at about 60 m depth and a high-velocity layer is found at around 45– 50 m depth. The sedimentary formation and bedrock in the survey area are further stratified under the control of borehole data.

Gearbox is required to serve for ≥ 30 min in helicopter design to improve survivability, when the gear drive loses lubrication due to battle damage. Under such loss-of-lubrication condition, tooth friction, wear and temperature pose serious problems to dynamic performance of gears. Therefore, a nonlinear tribo-dynamic model of spur gear drives is established and experimentally validated in this work. The time-varying friction coefficient is predicted under loss-of-lubrication condition on the basis of computational inverse technique. The temperature rise and tooth wear caused by friction were included by using thermal network model and dynamic wear model. The flexibility of gear shafts and the gyroscopic effect of gear rotors are also considered. The results indicate the gyroscopic effect apparently affects the natural frequency of the gear drive, while friction has negligible effect on the natural frequency but has considerable effect on the nonlinear behavior. The influence of temperature and gyroscopic effect on nonlinear behavior are reflected in the region of middle and high speed, while tooth wear mainly affects the bifurcation at the middle speed. In addition, tooth wear not only aggravates gear vibration but also can change the phase of dynamic transmission error. The analysis and experiment results can be an important reference in reducing friction and wear, restraining nonlinear behavior, and reducing vibration and noise.

This paper proposes a thermal network model to predict the contact temperature of spur gears. A crucial parameter in gear scuffing evaluation is the contact temperature, which comprises the bulk and flash temperatures. Herein, thermal network models of gear bulk temperature and flash temperature are established, by dispersing tooth into multiple temperature elements connected by the thermal resistances of heat conduction and heat convection. The thermal network model of gear bulk temperature is verified by the finite element model and previous work, and the presented model for gear flash temperature is validated by Blok flash temperature formula. Following ISO standard, gear scuffing is evaluated by comparing the contact temperature with scuffing critical temperature. The effects of geometric and operating parameters on the gear temperature are subsequently investigated. Contact temperature is found to decrease with increased tooth width, pressure angle and module, but increases with increased rotational velocity and input torque. These findings indicate that reasonable geometric and operating parameter matching are beneficial for increasing gear-scuffing resistance.

Flexibility and inner stress of transmission components are main considerations in the development of high-precision and lightweight engines. Gyroscopic effect of rotary shaft and rotor should also be considered in high-speed engines. Therefore, an elastic dynamic model of a valve train system is proposed. The model includes multiaxial flexibilities of camshaft and linkages, gyroscopic effect of the camshaft and cam rotor, centrifugal force of cams and friction force and moment of the cam–tappet pair. Then, the natural frequency, mode shape, pushrod stress and housing vibration are predicted using the proposed model. Results show that the gyroscopic effect of the rotors and camshaft apparently affects the natural frequency of the system by changing the camshaft stiffness. The proposed model can effectively predict the dynamic stress, as proven by a stress experiment. In addition, idling and maximum working speeds are recommended using the predicted model and verified by a vibration experiment. Thus, the proposed model can be an important reference in engine adjustment, improvement of component durability and determination of idling and maximum speeds.

The effects of centring error and angular misalignment on crack initiation life in herringbone gears are investigated in this work. Herringbone gears with centring error or angular misalignment are modelled for contact analysis. A crack initiation life model of standard and error gears is proposed in accordance with tooth stress history and a critical plane method for nonproportional loading. Then, the effects of centring error and angular misalignment on crack initiation life in herringbone gears are investigated. Results show that centring error and angular misalignment sharply reduce crack initiation life, but a moderate tip relief can eliminate stress concentration and extend crack initiation life. Furthermore, angular adjustment balances the load distribution of the left and right teeth in herringbone gears with centring error, improving tooth crack initiation life.

It is of scientific and engineering significance to extract surface wave signals from urban ambient noise for fine-scale three-dimensional velocity structure imaging of underground medium. A series of issues such as ambient noise characteristics in urban environment, observation system design and resolution of small-scale imaging, have put forward a lot of new requirements and challenges to traditional methods and technologies. We utilized the dense array with its aperture extend below hundred meters in Hangzhou urban area, to carry out the ambient noise data acquisition experiments within one day. Based on the time-frequency analysis of noise cross-correlations, we conducted surface wave travel time tomography. Finally, the phase velocity slices were inverted to build a three-dimensional S-wave velocity structure, and the profiles were compared with the drilling data for validations. We concluded that these geometry and processing parameters adopted in the urban environment are feasible for near-surface tomography and can meet the demands of three-dimensional geological survey in cities efficiently.

This study proposes an innovative and comprehensive method for the design and analysis of a high-speed cam mechanism. In the proposed method, the displacement function of the cam follower is described using Fourier series. The coefficients of the series are obtained by constraint equations during the cam rise period and the minimum principle of displacement error function (where, error function refers to the variance between actual displacement and ideal displacement of the cam follower during the dwell). The validity of the proposed design method is verified through a case study with focus on high-speed cam mechanism design. In the design case, kinematic characteristic analysis of this cam follower shows that the order of continuous derivative of displacement transfer function is higher, the characteristic value of its dynamic torque is smaller, and its jerk at the impact point is smaller than some common disc cam mechanisms. The results indicate that the proposed method can reduce the vibration of the cam mechanisms and its impact velocity is smaller than the existing design methods.

This paper carries out the experimental and numerical investigations on the root stress of a light-load spur gear drive. An improved gear test rig is developed to enable the dynamic root stress of a light-load spur gear drive to be wirelessly measured, and the signals of root strain, rotational speeds and torques of input/output gear shafts are sent or received wirelessly. After the random electrical noise is eliminated by multi-point average method, the key parameters of dynamic contact analysis on the root stress (rotational speeds and torque) are obtained, and the root strain signal is converted into root stress. Based on the curve of the measured root stress, the impact of meshing teeth and the alternative variation in the single and double pair gear meshing can be attained quantitatively. The geometric model of gear is developed by the generative machining principle and the coordinate transformation method. Then, the dynamic contact analysis is performed by the display centre difference metho...

As key factor of numerical simulation for gear strength, namely determination of effective loads between meshing teeth profiles, their numerical calculation principles of static and dynamic finite element methods are analyzed according to the loads on gear teeth. The static analysis of gear strength can be classified to effective statics and static contact analysis, and the numerical simulation method for face distribution as the rule of Hertz contact is advanced. The differences between static and dynamic contact and their influences in results are researched. Compared with the empirical formulas, the analytical results about bearing capacity of gear drive under different effective loads show: (1) As the sequence of concentrated force, linear distribution force, face distribution force as the rule of Hertz contact, static contact analysis, the accuracy and reliability of calculating results under different effective loads are improved, especially the results from face distribution and static contact being very close. (2) Dynamic contact analysis can be used to simulated the effect well. The above studies could be referenced to calculation in bearing capacity of gear drive.