The synoptic process of a super Arctic cyclone in August 2016(AC16)is investigated based on the Weather Research and Forecasting(WRF)model,and the key factors affecting the rapid intensification(RI)of AC16 and their r...The synoptic process of a super Arctic cyclone in August 2016(AC16)is investigated based on the Weather Research and Forecasting(WRF)model,and the key factors affecting the rapid intensification(RI)of AC16 and their relative contributions are analyzed by diagnosing a new surface pressure tendency equation(SPTE).The major physical mechanisms behind the two RI stages of AC16 are revealed.The trajectory,intensity changes,and structural characteristics of AC16 are well simulated by the WRF model.A diagnosis based on the SPTE promisingly reproduces the two RI stages of AC16.The leading factor that influenced the intensity of AC16 was identified to be the air-column potential temperature tendency,while the pressure change at the upper boundary had less of an impact.Further analysis reveals that the horizontal potential temperature advection was the decisive factor in a warming of the air column.Specifically,the upper-level warm advection generated by the strong wind field of the upper-level jet played a dominant role in warming the air column,which caused the initial RI of AC16.The AC16 movement into a strong potential temperature gradient generated by tropopause polar vortices increased the upper-level warm advection,which warmed the air column and thereby induced the second RI of AC16.However,the net effect of vertical potential temperature advection and latent heating,as well as radiation processes,caused a cooling of the air column and thereby negatively contributed to the RI of AC16.展开更多
In this study we investigated the problems involved in assimilating surface pressure in the current global and regional assimilation and prediction system, GRAPES. A new scheme of assimilating surface pressure was pro...In this study we investigated the problems involved in assimilating surface pressure in the current global and regional assimilation and prediction system, GRAPES. A new scheme of assimilating surface pressure was proposed, including a new interpolation scheme and a refreshed background covariance. The new scheme takes account of the differences between station elevation and model topography, and it especially deals with stations located at elevations below that of the first model level. Contrast experiments were conducted using both the original and the new assimilation schemes. The influence of the new interpolation scheme and the updated background covariance were investigated. Our results show that the new interpolation scheme utilized more observations and improved the quality of the mass analysis. The background covariance was refreshed using statistics resulting from the technique proposed by Parrish and Derber in 1992. Experiments show that the updated vertical covariance may have a positive influence on the analysis at higher levels of the atmosphere when assimilating surface pressure. This influence may be more significant if the quality of the background field at high levels is poor. A series of assimilation experiments were performed to test the validity of the new scheme. The corresponding simulation experiments were conducted using the analysis of both schemes as initial conditions. The results indicated that the new scheme leads to better forecasting of sea level pressure and precipitation in South China, especially the forecast of moderate and heavv rain.展开更多
Experimental and numerical methods were used to investigate the Magnus phenomena over a spinning projectile.The pressure force acting on the surface of a spinning projectile was measured for various cases by employing...Experimental and numerical methods were used to investigate the Magnus phenomena over a spinning projectile.The pressure force acting on the surface of a spinning projectile was measured for various cases by employing a relatively novel experimental technique.A set of miniature pressure sensors along with a data acquisition board,battery and storage memory were placed inside a spinning model and the surface pressure were obtained through a remotely controlled system.Circumferential pressures of the model for both rotational and static conditions were obtained at two different free stream Mach numbers of 0.4 and 0.8 and at different angles of attack.The results showed the ability of this new test method to measure the very small Magnus force via surface pressures over the projectile.The results provide a deep insight into the flow structure and illustrate changes in the cross-flow separation locations as a result of rotation.Similar results were obtained by the numerical simulations and were compared with the experimental data.展开更多
A hull structure is prone to local deformation and damage due to the pressure load on the surface.How to simulate surface pressure is an important issue in ship structure test.The loading mode of hydraulic actuator co...A hull structure is prone to local deformation and damage due to the pressure load on the surface.How to simulate surface pressure is an important issue in ship structure test.The loading mode of hydraulic actuator combined with high-pressure flexible bladder was proposed,and the numerical model of the loading device based on flexible bladder was established.The design and analysis method of high-pressure flexible bladder based on aramid-fiber reinforced thermoplastic polyurethane was proposed to break through the surface pressure loading technology of ship structures.The surface pressure loading system based on flexible bladder was developed.The ultimate strength verification test of the box girder under the combined action of bending moment and pressure was carried out to systematically verify the feasibility and applicability of the loading system.The results show that the surface pressure loading technology can be used well for applying uniform pressure to ship structures.Compared with the traditional surface loading methods,the improved device can be applied with horizontal constant pressure load,with rapid response and safe process,and the pressure load is always stable with the increase of the bending moment load during the test.The requirement for uniform loading in the comprehensive strength test of large structural models is satisfied and the accuracy of the test results is improved by this system.展开更多
The relationship between the all-India summer monsoon rainfall and surface pressure over the Indian region has been examined to obtain a useful predictor for the monsoon rainfall. The data series of all-India monsoon ...The relationship between the all-India summer monsoon rainfall and surface pressure over the Indian region has been examined to obtain a useful predictor for the monsoon rainfall. The data series of all-India monsoon rainfall and the mean pressures of three seasons before and after the monsoon season as well as the winter-to-spring pressure tendency (MAM-DJF) at 100 stations for the period 1951-1980 have been used in the analysis.The all-India monsoon rainfall is negatively correlated with the pressure of the spring (MAM) season preceding the monsoon and winter-to-spring seasonal difference as pressure tendency (MAM-DJF), at almost all the stations in India, and significantly with the pressures over central and northwestern regions. The average mean sea level pressure of six stations (Jodhpur, Ahmedabed, Bombay, Indore, Sagar and Akola) in the Western Central Indian (WCI) region showed highly significant (at 1% level) and consistent CCs of-0.63 for MAM and -0.56 for MAM-DJF for the period 1951 - 1980. Thus, the pre-monsoon seasonal pressure anomalies over WCI could provide a useful parameter for the long-range forecasting scheme of the Indian monsoon rainfall.展开更多
Simultaneous measurements of surface pressure and surface potential and scanning tunneling microscopy study for N-docosylpyridinium- TCNQ monolayer were carried out.These methods allow us to get more informations on p...Simultaneous measurements of surface pressure and surface potential and scanning tunneling microscopy study for N-docosylpyridinium- TCNQ monolayer were carried out.These methods allow us to get more informations on properties of the monolayer.The molecules at the final stage of compression are really in compact stack although a voluminous hydrophilic head exists in the molecule.展开更多
By means of ERA-40, JRA-25, NCEP/NCAR and NCEP/DOE reanalysis data, empirical relations between precipitable water and surface vapor pressure in spatial and temporal scale were calculated. The reliabilities of precipi...By means of ERA-40, JRA-25, NCEP/NCAR and NCEP/DOE reanalysis data, empirical relations between precipitable water and surface vapor pressure in spatial and temporal scale were calculated. The reliabilities of precipitable water from reanalysis data were validated based on comparing different W-e empirical relations of various reanalysis data, in order to provide basis and reference for reasonable application. The results showed that W-e empirical relation of ERA-40 was closest to that of sounding data in China, and precipitable water from ERA-40 was the most credible. The worldwide comparison among W-e empirical relations of four reanalysis data showed that there was little difference in annual mean W-e empirical relations in the middle latitudes and great differences in low and high latitudes. Seasonal mean W-e empirical relations in the middle latitudes of the northern Hemisphere had little difference in spring, autumn and winter, but great difference in summer. Therefore, the reliabilities of precipitable water from reanalysis data in spring, autumn and winter in the middle latitudes of the northern hemisphere were higher than other areas and seasons. W-e empirical relations of NCEP/NCAR and NCEP/DOE had good stability in different years, while there was poor stability in ERA-40 and JRA-25.展开更多
We report the anisotropy effect and the relaxation dynamics of surface pressure of silica nanoparticle monolayer at the air-water interface. The anisotropy of surface pressure occurs when the water surface is fully co...We report the anisotropy effect and the relaxation dynamics of surface pressure of silica nanoparticle monolayer at the air-water interface. The anisotropy of surface pressure occurs when the water surface is fully covered by particles and becomes more prominent with the increase of surface concentration. Hence, the conception of surface tensor was proposed to characterize the monolayer properties. The dynamics of pressure relaxation involves three timescales which are related to the damping of surface fluctuation, rearrangement of particle rafts and particle motion inside each raft. The anisotropy decays when the layer is kept static and the process is accelerated remarkably by barrier oscillation. The underlying physics mechanism is also discussed in detail for the origin of pressure anisotropy and its decay dynamics.展开更多
Reducing the linear system of two first order equilibrium equations involving normal stress σ(ρ,θ) and shearing stress v(ρ,θ), by elimination, to two decoupled second order equations in σ and v, ...Reducing the linear system of two first order equilibrium equations involving normal stress σ(ρ,θ) and shearing stress v(ρ,θ), by elimination, to two decoupled second order equations in σ and v, we find that, for pressure only case, v(ρ,θ) vanishes in the half space. Consequently, the second order equation in σ can be simplified. In the language of linear system analysis, the medium(system) function, characterizing the mechanical behavior of a particulate medium in pressure only case, is obtained from the simplified second order equation ( 2 ρ+ 2 θ)σ(ρ,θ)=0 and can be inverted to give impulse reponse explicitly. Thus, response σ α(ρ,θ) may be computed directly from input, i.e., the surface pressure φ α(ρ) , by integration. Some explicit formulas for transmission problems, including response to input of strip linearly increasing pressure, are given in the paper.展开更多
The microstructure,hardness and tensile properties have been studied in copper processed by high pressure surface rolling(HPSR)both in the as-deformed condition and after subsequent annealing at 150℃.It is found that...The microstructure,hardness and tensile properties have been studied in copper processed by high pressure surface rolling(HPSR)both in the as-deformed condition and after subsequent annealing at 150℃.It is found that a gradient structure with significant differences in the scale of microstructural features is formed by HPSR.The deformed microstructure varies from nano-and ultrafine-scale structures with a large fraction of high angle boundaries near the surface to lightly deformed grains at depths of 1-3 mm below the surface.Tensile tests of 1-mm-thick specimens demonstrate that the asdeformed material has a high strength and a low uniform elongation.Annealing at 150℃results in partial recrystallization,which creates new through-thickness gradients.Except for the topmost layer and several bands in the adjacent layer,recrystallization is more pronounced close to the surface.The fraction recrystallized is at least 80%at depths of 60-300μm after annealing for 960 min.The fraction recrystallized in the subsurface decreases with increasing depth,and the deformed layer at depths greater than 500μm re-mains largely non-recrystallized after annealing.This partially recrystallized condition demonstrates an improved combination of strength and ductility.展开更多
The expressions of the radius and the surface tension of surface of tension Rs and γs in terms of the pressure distribution for nanoscale liquid threads are of great importance for molecular dynamics （MD） simulatio...The expressions of the radius and the surface tension of surface of tension Rs and γs in terms of the pressure distribution for nanoscale liquid threads are of great importance for molecular dynamics （MD） simulations of the interfacial phenomena of nanoscale fluids; these two basic expressions are derived in this paper. Although these expressions were derived first in the literature[Kim B G, Lee J S, Han M H, and Park S, 2006 Nanoscale and Microscale Thermophysical Engineering, 10, 283] and used widely thereafter, the derivation is wrong both in logical structure and physical thought. In view of the importance of these basic expressions, the logic and physical mistakes appearing in that derivation are pointed out.展开更多
In this paper,polyimide（PI）films are modified using an atmospheric pressure plasma generated by a dielectric barrier discharge（DBD）in argon.Surface performance of PI film and its dependence on exposure time from 0...In this paper,polyimide（PI）films are modified using an atmospheric pressure plasma generated by a dielectric barrier discharge（DBD）in argon.Surface performance of PI film and its dependence on exposure time from 0 s to 300 s are investigated by dynamic water contact angle（WCA）,field emission scanning electron microscopy（FESEM）,and Fourier transform infrared spectroscopy in attenuated total multiple reflection mode（FTIR-ATR）.The study demonstrates that dynamic WCA exhibits a minimum with 40 s plasma treatment,and evenly distributed nano-dots and shadow concaves appeared for 40 s and 12 s Ar plasma treatment individually.A short period of plasma modification can contribute to the scission of the imide ring and the introduction of C-O and C=O（-COOH）by detailed analysis of FTIR-ATR.展开更多
The accurate prediction for aerodynamic drag of spacecraft in very low Earth orbit(VLEO) is a fundamental prerequisite for aerospace missions in VLEO. The present work calculates aerodynamic drag of the Gravity Field ...The accurate prediction for aerodynamic drag of spacecraft in very low Earth orbit(VLEO) is a fundamental prerequisite for aerospace missions in VLEO. The present work calculates aerodynamic drag of the Gravity Field and Steady-State Ocean Circulation Explorer(GOCE) satellite using the test particle Monte Carlo(TPMC) method. The primary goal is to obtain a comprehensive understanding of surface pressure and skin friction on the spacecraft surface and assess the sensitivity of aerodynamic drag to the gas-surface interaction(GSI) models. Results indicate that surface pressure is mainly distributed on the front of the satellite body and panels while skin friction is primarily distributed on the sides. In addition, as the GSI model changes from diffuse to specular reflection, the total drag coefficient is reduced at operation altitudes above 170 km. Therefore, the satellite surface should be processed so carefully that the GSI remains far from diffuse reflection from the view point of the drag-reduce design.展开更多
To investigate the interaction of the bolt-reinforced rock and the surface support,an analytical model of the convergence-confinement type is proposed,considering the sequential installation of the fully grouted rockb...To investigate the interaction of the bolt-reinforced rock and the surface support,an analytical model of the convergence-confinement type is proposed,considering the sequential installation of the fully grouted rockbolts and the surface support.The rock mass is assumed to be elastic-brittle-plastic material,obeying the linear Mohr-Coulomb criterion or the non-linear Hoek-Brown criterion.According to the strain states of the tunnel wall at bolt and surface support installation and the relative magnitude between the bolt length and the plastic depth during the whole process,six cases are categorized upon solving the problem.Each case is divided into three stages due to the different effects of the active rockbolts and the passive surface support.The fictitious pressure is introduced to quantify the threedimensional(3D)effect of the tunnel face,and thus,the actual physical location along the tunnel axis of the analytical section can be considered.By using the bolt-rock strain compatibility and the rocksurface support displacement compatibility conditions,the solutions of longitudinal tunnel displacement and the reaction pressure of surface support along the tunnel axis are obtained.The proposed analytical solutions are validated by a series of 3D numerical simulations.Extensive parametric studies are conducted to examine the effect of the typical parameters of rockbolts and surface support on the tunnel displacement and the reaction pressure of the surface support under different rock conditions.The results show that the rockbolts are more effective in controlling the tunnel displacement than the surface support,which should be installed as soon as possible with a suitable length.For tunnels excavated in weak rocks or with restricted displacement control requirements,the surface support should also be installed or closed timely with a certain stiffness.The proposed method provides a convenient alternative approach for the optimization of rockbolts and surface support at the preliminary stage of tunnel design.展开更多
Stabilizing pile is a kind of earth shoring structure frequently used in slope engineering. When the piles have cantilever segments above the ground,laggings are usually installed to avoid collapse of soil between pil...Stabilizing pile is a kind of earth shoring structure frequently used in slope engineering. When the piles have cantilever segments above the ground,laggings are usually installed to avoid collapse of soil between piles. Evaluating the earth pressure acting on laggings is of great importance in design process.Since laggings are usually less stiff than piles,the lateral pressure on lagging is much closer to active earth pressure. In order to estimate the lateral earth pressure on lagging more accurately,first,a model test of cantilever stabilizing pile and lagging systems was carried out. Then,basing the experimental results a three-dimensional sliding wedge model was established. Last,the calculation process of the total active force on lagging is presented based on the kinematic approach of limit analysis. A comparison is made between the total active force on lagging calculated by the formula presented in this study and the force on a same-size rigid retaining wall obtained from Rankine's theory. It is found that the proposed method fits well with the experimental results.Parametric studies show that the total active force on lagging increases with the growth of the lagging height and the lagging clear span; while decreases asthe soil internal friction angle and soil cohesion increase.展开更多
To achieve an atmospheric pressure glow discharge（APGD）in air and modify the surface of polyester thread using plasma,the electric field distribution and discharge characteristics under different conditions were stu...To achieve an atmospheric pressure glow discharge（APGD）in air and modify the surface of polyester thread using plasma,the electric field distribution and discharge characteristics under different conditions were studied.We found that the region with a strong electric field,which was formed in a tiny gap between two electrodes constituting a line-line contact electrode structure,provided the initial electron for the entire discharge process.Thus,the discharge voltage was reduced.The dielectric barrier of the line-line contact electrodes can inhibit the generation of secondary electrons.Thus,the transient current pulse discharge was reduced significantly,and an APGD in air was achieved.We designed double layer line-line contact electrodes,which can generate the APGD on the surface of a material under treatment directly.A noticeable change in the surface morphology of polyester fiber was visualized with the aid of a scanning electron microscope（SEM）.Two electrode structures-the multi-row line-line and double-helix line-line contact electrodes-were designed.A large area of the APGD plasma with flat and curved surfaces can be formed in air using these contact electrodes.This can improve the efficiency of surface treatment and is significant for the application of the APGD plasma in industries.展开更多
The pressure wave generated by an urban-rail vehicle when passing through a tunnel affects the comfort of passengersand may even cause damage to the train and related tunnel structures.Therefore,controlling the trains...The pressure wave generated by an urban-rail vehicle when passing through a tunnel affects the comfort of passengersand may even cause damage to the train and related tunnel structures.Therefore,controlling the trainspeed in the tunnel is extremely important.In this study,this problem is investigated numerically in the frameworkof the standard k-εtwo-equation turbulence model.In particular,an eight-car urban rail train passingthrough a tunnel at different speeds(140,160,180 and 200 km/h)is considered.The results show that the maximumaerodynamic drag of the head and tail cars is most affected by the running speed.The pressure at selectedmeasuring points on the windward side of the head car is very high,and the negative pressure at the side windowof the driver’s cab of the tail car is also very large.From the head car to the tail car,the pressure at the same heightgradually decreases.The positive pressure peak at the head car and the negative pressure peak at the tail car aregreatly affected by the speed.展开更多
A downburst is a strong downdraft generated by intense thunderstorm clouds,producing radially divergent and highly destructive winds near the ground.Its characteristic scales are expressed through random variations in...A downburst is a strong downdraft generated by intense thunderstorm clouds,producing radially divergent and highly destructive winds near the ground.Its characteristic scales are expressed through random variations in jet height,velocity,and diameter during an event.In this study,a reduced-scale parked wind turbine is exposed to downburst wind fields to investigate the resulting extreme wind loads.The analysis emphasizes both the flow structure of downbursts and the variations of surface wind pressure on turbine blades under different jet parameters.Results show that increasing jet velocity markedly enhances the maximum horizontal wind speed,while greater jet height reduces the horizontal wind speed and shifts the peak velocity closer to the jet center.Increasing jet diameter primarily affects the radial position of the maximum horizontal wind speed.For the wind turbine,the maximum equivalent stress and blade displacement increase almost linearly with jet velocity,but exhibit the opposite trend with jet diameter.Specifically,as jet velocity rises from 10 m/s to 20 m/s,the surface pressure coefficient at the blade tip increases by approximately 4.5 times.Changes in jet diameter indirectly alter the turbine’s relative position within the wind field,leading to variations in wind load direction and exposure area.Conversely,increasing jet height extends the dissipation path of the downdraft,thereby reducing the intensity of the airflow acting on the blades.For example,when jet height increases from 0.3 m to 1.2 m,the surface pressure coefficient at the blade tip decreases by nearly 50%.展开更多
With the increasing noise pollution, low noise optimization of centrifugal pimps has become a hot topic. However, experimental study on this problem is unacceptable for industrial applications due to unsustainable cos...With the increasing noise pollution, low noise optimization of centrifugal pimps has become a hot topic. However, experimental study on this problem is unacceptable for industrial applications due to unsustainable cost. A hybrid method that couples computational fluid dynamics （CFD） with computational aeroacoustic software is used to predict the flow-induced noise of pumps in order to minimize the noise of centrifugal pumps in actual projects. Under Langthjem＇s assumption that the blade surface pressure is the main flow-induced acoustic source in centrifugal pumps, the blade surface pressure pulsation is considered in terms of the acoustical sources and simulated using CFX software. The pressure pulsation and noise distribution in the near-cutoff region are examined for the blade-passing frequency （BPF） noise, and the sound pressure level （SPL） reached peaks near the cutoff that corresponded with the pressure pulsation in this region. An experiment is performed to validate this prediction. Four hydrophones are fixed to the inlet and outlet ports of the test pump to measure the flow-induced noise from the four-port model. The simulation results for the noise are analyzed and compared with the experimental results. The variation in the calculated noise with changes in the flow agreed well with the experimental results. When the flow rate was increased, the SPL first decreased and reached the minimum near the best efficient point （BEP）; it then increased when the flow rate was further increased. The numerical and experimental results confirmed that the BPF noise generated by a blade-rotating dipole roughly reflects the acoustic features of centrifugal pumps. The noise simulation method in current study has a good feasibility and suitability, which could be adopted in engineering design to predict and optimize the hydroacoustic behavior of centrifugal pumps.展开更多
Distributed leading-edge （LE） roughness could have significant impact on the aerodynamicperformance of a low-Reynolds-number （low-Re） airfoil, which has not yet been fully understood.In the present study, experime...Distributed leading-edge （LE） roughness could have significant impact on the aerodynamicperformance of a low-Reynolds-number （low-Re） airfoil, which has not yet been fully understood.In the present study, experiments were conducted to study the effects of distributed hemisphericalroughness with different sizes and distribution patterns on the performance of a GA （W）-1 airfoil.Surface pressure and particle image velocimetry （PIV） measurements were performed undervarious incident angles and different Re numbers. Significant reduction in lift and increase in dragwere found for all cases with the LE roughness applied. Compared with the distribution pattern,the roughness height was found to be a more significant factor in determining the lift reductionand altering stall behaviors. It is also found while the larger roughness advances the aerodynamicstall, the smaller roughness tends to prevent deep stall at high incident angles. PIV results alsosuggest that staggered distribution pattern induces higher fluctuations in the wake flow than thealigned pattern does. Results imply that distributed LE roughness with large element sizes areparticularly detrimental to aerodynamic performances, while those with small element sizes couldpotentially serve as a passive control mechanism to alleviate deep stall conditions at high incidentangles.展开更多
基金sponsored by the funding of the National Natural Science Foundation of China(Grant Nos.42075011,42192552,42005025,and 42075035).
文摘The synoptic process of a super Arctic cyclone in August 2016(AC16)is investigated based on the Weather Research and Forecasting(WRF)model,and the key factors affecting the rapid intensification(RI)of AC16 and their relative contributions are analyzed by diagnosing a new surface pressure tendency equation(SPTE).The major physical mechanisms behind the two RI stages of AC16 are revealed.The trajectory,intensity changes,and structural characteristics of AC16 are well simulated by the WRF model.A diagnosis based on the SPTE promisingly reproduces the two RI stages of AC16.The leading factor that influenced the intensity of AC16 was identified to be the air-column potential temperature tendency,while the pressure change at the upper boundary had less of an impact.Further analysis reveals that the horizontal potential temperature advection was the decisive factor in a warming of the air column.Specifically,the upper-level warm advection generated by the strong wind field of the upper-level jet played a dominant role in warming the air column,which caused the initial RI of AC16.The AC16 movement into a strong potential temperature gradient generated by tropopause polar vortices increased the upper-level warm advection,which warmed the air column and thereby induced the second RI of AC16.However,the net effect of vertical potential temperature advection and latent heating,as well as radiation processes,caused a cooling of the air column and thereby negatively contributed to the RI of AC16.
基金This study was supported by the China Meteorological Administration，the Natural Science Foundation，the Foundation of Guangzhou Institute of Tropical and Marine Meteorology
文摘In this study we investigated the problems involved in assimilating surface pressure in the current global and regional assimilation and prediction system, GRAPES. A new scheme of assimilating surface pressure was proposed, including a new interpolation scheme and a refreshed background covariance. The new scheme takes account of the differences between station elevation and model topography, and it especially deals with stations located at elevations below that of the first model level. Contrast experiments were conducted using both the original and the new assimilation schemes. The influence of the new interpolation scheme and the updated background covariance were investigated. Our results show that the new interpolation scheme utilized more observations and improved the quality of the mass analysis. The background covariance was refreshed using statistics resulting from the technique proposed by Parrish and Derber in 1992. Experiments show that the updated vertical covariance may have a positive influence on the analysis at higher levels of the atmosphere when assimilating surface pressure. This influence may be more significant if the quality of the background field at high levels is poor. A series of assimilation experiments were performed to test the validity of the new scheme. The corresponding simulation experiments were conducted using the analysis of both schemes as initial conditions. The results indicated that the new scheme leads to better forecasting of sea level pressure and precipitation in South China, especially the forecast of moderate and heavv rain.
文摘Experimental and numerical methods were used to investigate the Magnus phenomena over a spinning projectile.The pressure force acting on the surface of a spinning projectile was measured for various cases by employing a relatively novel experimental technique.A set of miniature pressure sensors along with a data acquisition board,battery and storage memory were placed inside a spinning model and the surface pressure were obtained through a remotely controlled system.Circumferential pressures of the model for both rotational and static conditions were obtained at two different free stream Mach numbers of 0.4 and 0.8 and at different angles of attack.The results showed the ability of this new test method to measure the very small Magnus force via surface pressures over the projectile.The results provide a deep insight into the flow structure and illustrate changes in the cross-flow separation locations as a result of rotation.Similar results were obtained by the numerical simulations and were compared with the experimental data.
文摘A hull structure is prone to local deformation and damage due to the pressure load on the surface.How to simulate surface pressure is an important issue in ship structure test.The loading mode of hydraulic actuator combined with high-pressure flexible bladder was proposed,and the numerical model of the loading device based on flexible bladder was established.The design and analysis method of high-pressure flexible bladder based on aramid-fiber reinforced thermoplastic polyurethane was proposed to break through the surface pressure loading technology of ship structures.The surface pressure loading system based on flexible bladder was developed.The ultimate strength verification test of the box girder under the combined action of bending moment and pressure was carried out to systematically verify the feasibility and applicability of the loading system.The results show that the surface pressure loading technology can be used well for applying uniform pressure to ship structures.Compared with the traditional surface loading methods,the improved device can be applied with horizontal constant pressure load,with rapid response and safe process,and the pressure load is always stable with the increase of the bending moment load during the test.The requirement for uniform loading in the comprehensive strength test of large structural models is satisfied and the accuracy of the test results is improved by this system.
文摘The relationship between the all-India summer monsoon rainfall and surface pressure over the Indian region has been examined to obtain a useful predictor for the monsoon rainfall. The data series of all-India monsoon rainfall and the mean pressures of three seasons before and after the monsoon season as well as the winter-to-spring pressure tendency (MAM-DJF) at 100 stations for the period 1951-1980 have been used in the analysis.The all-India monsoon rainfall is negatively correlated with the pressure of the spring (MAM) season preceding the monsoon and winter-to-spring seasonal difference as pressure tendency (MAM-DJF), at almost all the stations in India, and significantly with the pressures over central and northwestern regions. The average mean sea level pressure of six stations (Jodhpur, Ahmedabed, Bombay, Indore, Sagar and Akola) in the Western Central Indian (WCI) region showed highly significant (at 1% level) and consistent CCs of-0.63 for MAM and -0.56 for MAM-DJF for the period 1951 - 1980. Thus, the pre-monsoon seasonal pressure anomalies over WCI could provide a useful parameter for the long-range forecasting scheme of the Indian monsoon rainfall.
文摘Simultaneous measurements of surface pressure and surface potential and scanning tunneling microscopy study for N-docosylpyridinium- TCNQ monolayer were carried out.These methods allow us to get more informations on properties of the monolayer.The molecules at the final stage of compression are really in compact stack although a voluminous hydrophilic head exists in the molecule.
基金Supported by National Natural Science Foundation of China (40775048)Major State Basic Research Development Program (2006CB400504)National Key Technology R & D Program (2007BAC294)
文摘By means of ERA-40, JRA-25, NCEP/NCAR and NCEP/DOE reanalysis data, empirical relations between precipitable water and surface vapor pressure in spatial and temporal scale were calculated. The reliabilities of precipitable water from reanalysis data were validated based on comparing different W-e empirical relations of various reanalysis data, in order to provide basis and reference for reasonable application. The results showed that W-e empirical relation of ERA-40 was closest to that of sounding data in China, and precipitable water from ERA-40 was the most credible. The worldwide comparison among W-e empirical relations of four reanalysis data showed that there was little difference in annual mean W-e empirical relations in the middle latitudes and great differences in low and high latitudes. Seasonal mean W-e empirical relations in the middle latitudes of the northern Hemisphere had little difference in spring, autumn and winter, but great difference in summer. Therefore, the reliabilities of precipitable water from reanalysis data in spring, autumn and winter in the middle latitudes of the northern hemisphere were higher than other areas and seasons. W-e empirical relations of NCEP/NCAR and NCEP/DOE had good stability in different years, while there was poor stability in ERA-40 and JRA-25.
基金supported by the NPU Foundation for Fundamental Research (Grant No. NPU-FFR-JC20100242)
文摘We report the anisotropy effect and the relaxation dynamics of surface pressure of silica nanoparticle monolayer at the air-water interface. The anisotropy of surface pressure occurs when the water surface is fully covered by particles and becomes more prominent with the increase of surface concentration. Hence, the conception of surface tensor was proposed to characterize the monolayer properties. The dynamics of pressure relaxation involves three timescales which are related to the damping of surface fluctuation, rearrangement of particle rafts and particle motion inside each raft. The anisotropy decays when the layer is kept static and the process is accelerated remarkably by barrier oscillation. The underlying physics mechanism is also discussed in detail for the origin of pressure anisotropy and its decay dynamics.
文摘Reducing the linear system of two first order equilibrium equations involving normal stress σ(ρ,θ) and shearing stress v(ρ,θ), by elimination, to two decoupled second order equations in σ and v, we find that, for pressure only case, v(ρ,θ) vanishes in the half space. Consequently, the second order equation in σ can be simplified. In the language of linear system analysis, the medium(system) function, characterizing the mechanical behavior of a particulate medium in pressure only case, is obtained from the simplified second order equation ( 2 ρ+ 2 θ)σ(ρ,θ)=0 and can be inverted to give impulse reponse explicitly. Thus, response σ α(ρ,θ) may be computed directly from input, i.e., the surface pressure φ α(ρ) , by integration. Some explicit formulas for transmission problems, including response to input of strip linearly increasing pressure, are given in the paper.
基金supported by the National Natural Science Foundation of China(No.52071038).QYH acknowledges funding from the Natural Science Foundation of Chongqing(grant cstc2021jcyj-msxmX1185).
文摘The microstructure,hardness and tensile properties have been studied in copper processed by high pressure surface rolling(HPSR)both in the as-deformed condition and after subsequent annealing at 150℃.It is found that a gradient structure with significant differences in the scale of microstructural features is formed by HPSR.The deformed microstructure varies from nano-and ultrafine-scale structures with a large fraction of high angle boundaries near the surface to lightly deformed grains at depths of 1-3 mm below the surface.Tensile tests of 1-mm-thick specimens demonstrate that the asdeformed material has a high strength and a low uniform elongation.Annealing at 150℃results in partial recrystallization,which creates new through-thickness gradients.Except for the topmost layer and several bands in the adjacent layer,recrystallization is more pronounced close to the surface.The fraction recrystallized is at least 80%at depths of 60-300μm after annealing for 960 min.The fraction recrystallized in the subsurface decreases with increasing depth,and the deformed layer at depths greater than 500μm re-mains largely non-recrystallized after annealing.This partially recrystallized condition demonstrates an improved combination of strength and ductility.
基金RαProject supported by the National Natural Science Foundation of China(Grant No.11072242)the Research and Development Program of Science and Technology of Higher Education of Shanxi Province,China(Grant No.20121029)
文摘The expressions of the radius and the surface tension of surface of tension Rs and γs in terms of the pressure distribution for nanoscale liquid threads are of great importance for molecular dynamics （MD） simulations of the interfacial phenomena of nanoscale fluids; these two basic expressions are derived in this paper. Although these expressions were derived first in the literature[Kim B G, Lee J S, Han M H, and Park S, 2006 Nanoscale and Microscale Thermophysical Engineering, 10, 283] and used widely thereafter, the derivation is wrong both in logical structure and physical thought. In view of the importance of these basic expressions, the logic and physical mistakes appearing in that derivation are pointed out.
文摘In this paper,polyimide（PI）films are modified using an atmospheric pressure plasma generated by a dielectric barrier discharge（DBD）in argon.Surface performance of PI film and its dependence on exposure time from 0 s to 300 s are investigated by dynamic water contact angle（WCA）,field emission scanning electron microscopy（FESEM）,and Fourier transform infrared spectroscopy in attenuated total multiple reflection mode（FTIR-ATR）.The study demonstrates that dynamic WCA exhibits a minimum with 40 s plasma treatment,and evenly distributed nano-dots and shadow concaves appeared for 40 s and 12 s Ar plasma treatment individually.A short period of plasma modification can contribute to the scission of the imide ring and the introduction of C-O and C=O（-COOH）by detailed analysis of FTIR-ATR.
文摘The accurate prediction for aerodynamic drag of spacecraft in very low Earth orbit(VLEO) is a fundamental prerequisite for aerospace missions in VLEO. The present work calculates aerodynamic drag of the Gravity Field and Steady-State Ocean Circulation Explorer(GOCE) satellite using the test particle Monte Carlo(TPMC) method. The primary goal is to obtain a comprehensive understanding of surface pressure and skin friction on the spacecraft surface and assess the sensitivity of aerodynamic drag to the gas-surface interaction(GSI) models. Results indicate that surface pressure is mainly distributed on the front of the satellite body and panels while skin friction is primarily distributed on the sides. In addition, as the GSI model changes from diffuse to specular reflection, the total drag coefficient is reduced at operation altitudes above 170 km. Therefore, the satellite surface should be processed so carefully that the GSI remains far from diffuse reflection from the view point of the drag-reduce design.
基金funding support from the Fundamental Research Funds for the Central Universities(Grant No.2023JBZY024)the National Natural Science Foundation of China(Grant Nos.52208382 and 52278387).
文摘To investigate the interaction of the bolt-reinforced rock and the surface support,an analytical model of the convergence-confinement type is proposed,considering the sequential installation of the fully grouted rockbolts and the surface support.The rock mass is assumed to be elastic-brittle-plastic material,obeying the linear Mohr-Coulomb criterion or the non-linear Hoek-Brown criterion.According to the strain states of the tunnel wall at bolt and surface support installation and the relative magnitude between the bolt length and the plastic depth during the whole process,six cases are categorized upon solving the problem.Each case is divided into three stages due to the different effects of the active rockbolts and the passive surface support.The fictitious pressure is introduced to quantify the threedimensional(3D)effect of the tunnel face,and thus,the actual physical location along the tunnel axis of the analytical section can be considered.By using the bolt-rock strain compatibility and the rocksurface support displacement compatibility conditions,the solutions of longitudinal tunnel displacement and the reaction pressure of surface support along the tunnel axis are obtained.The proposed analytical solutions are validated by a series of 3D numerical simulations.Extensive parametric studies are conducted to examine the effect of the typical parameters of rockbolts and surface support on the tunnel displacement and the reaction pressure of the surface support under different rock conditions.The results show that the rockbolts are more effective in controlling the tunnel displacement than the surface support,which should be installed as soon as possible with a suitable length.For tunnels excavated in weak rocks or with restricted displacement control requirements,the surface support should also be installed or closed timely with a certain stiffness.The proposed method provides a convenient alternative approach for the optimization of rockbolts and surface support at the preliminary stage of tunnel design.
基金financially supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China under Grant No. 2012BAJ22B06
文摘Stabilizing pile is a kind of earth shoring structure frequently used in slope engineering. When the piles have cantilever segments above the ground,laggings are usually installed to avoid collapse of soil between piles. Evaluating the earth pressure acting on laggings is of great importance in design process.Since laggings are usually less stiff than piles,the lateral pressure on lagging is much closer to active earth pressure. In order to estimate the lateral earth pressure on lagging more accurately,first,a model test of cantilever stabilizing pile and lagging systems was carried out. Then,basing the experimental results a three-dimensional sliding wedge model was established. Last,the calculation process of the total active force on lagging is presented based on the kinematic approach of limit analysis. A comparison is made between the total active force on lagging calculated by the formula presented in this study and the force on a same-size rigid retaining wall obtained from Rankine's theory. It is found that the proposed method fits well with the experimental results.Parametric studies show that the total active force on lagging increases with the growth of the lagging height and the lagging clear span; while decreases asthe soil internal friction angle and soil cohesion increase.
文摘To achieve an atmospheric pressure glow discharge（APGD）in air and modify the surface of polyester thread using plasma,the electric field distribution and discharge characteristics under different conditions were studied.We found that the region with a strong electric field,which was formed in a tiny gap between two electrodes constituting a line-line contact electrode structure,provided the initial electron for the entire discharge process.Thus,the discharge voltage was reduced.The dielectric barrier of the line-line contact electrodes can inhibit the generation of secondary electrons.Thus,the transient current pulse discharge was reduced significantly,and an APGD in air was achieved.We designed double layer line-line contact electrodes,which can generate the APGD on the surface of a material under treatment directly.A noticeable change in the surface morphology of polyester fiber was visualized with the aid of a scanning electron microscope（SEM）.Two electrode structures-the multi-row line-line and double-helix line-line contact electrodes-were designed.A large area of the APGD plasma with flat and curved surfaces can be formed in air using these contact electrodes.This can improve the efficiency of surface treatment and is significant for the application of the APGD plasma in industries.
基金supported by the Beijing Postdoctoral Research Foundation(No.2023-ZZ-133)Scientific Research Foundation of Beijing Infrastructure Investment Co.,Ltd.(No.2023-ZB-03)Fundamental Research Funds for the Central Universities(No.2682023ZTPY036).
文摘The pressure wave generated by an urban-rail vehicle when passing through a tunnel affects the comfort of passengersand may even cause damage to the train and related tunnel structures.Therefore,controlling the trainspeed in the tunnel is extremely important.In this study,this problem is investigated numerically in the frameworkof the standard k-εtwo-equation turbulence model.In particular,an eight-car urban rail train passingthrough a tunnel at different speeds(140,160,180 and 200 km/h)is considered.The results show that the maximumaerodynamic drag of the head and tail cars is most affected by the running speed.The pressure at selectedmeasuring points on the windward side of the head car is very high,and the negative pressure at the side windowof the driver’s cab of the tail car is also very large.From the head car to the tail car,the pressure at the same heightgradually decreases.The positive pressure peak at the head car and the negative pressure peak at the tail car aregreatly affected by the speed.
基金the National Natural Science Foundation of China(Grant Nos.52276197, 52166014)Gansu Province Key Research and Development Program—Industrial Project(Grant No.23YFGA0069).
文摘A downburst is a strong downdraft generated by intense thunderstorm clouds,producing radially divergent and highly destructive winds near the ground.Its characteristic scales are expressed through random variations in jet height,velocity,and diameter during an event.In this study,a reduced-scale parked wind turbine is exposed to downburst wind fields to investigate the resulting extreme wind loads.The analysis emphasizes both the flow structure of downbursts and the variations of surface wind pressure on turbine blades under different jet parameters.Results show that increasing jet velocity markedly enhances the maximum horizontal wind speed,while greater jet height reduces the horizontal wind speed and shifts the peak velocity closer to the jet center.Increasing jet diameter primarily affects the radial position of the maximum horizontal wind speed.For the wind turbine,the maximum equivalent stress and blade displacement increase almost linearly with jet velocity,but exhibit the opposite trend with jet diameter.Specifically,as jet velocity rises from 10 m/s to 20 m/s,the surface pressure coefficient at the blade tip increases by approximately 4.5 times.Changes in jet diameter indirectly alter the turbine’s relative position within the wind field,leading to variations in wind load direction and exposure area.Conversely,increasing jet height extends the dissipation path of the downdraft,thereby reducing the intensity of the airflow acting on the blades.For example,when jet height increases from 0.3 m to 1.2 m,the surface pressure coefficient at the blade tip decreases by nearly 50%.
基金Supported by Research and Innovation Project for College Graduates of Jiangsu Province of China(Grant No.CXZZ13_0673)National Natural Science Foundation of China(Grant No.51009072)+1 种基金National Science&Technology Pillar Program of China(Grant No.2011BAF14B04)State Key Program of National Natural Science Foundation of China(Grant No.51239005)
文摘With the increasing noise pollution, low noise optimization of centrifugal pimps has become a hot topic. However, experimental study on this problem is unacceptable for industrial applications due to unsustainable cost. A hybrid method that couples computational fluid dynamics （CFD） with computational aeroacoustic software is used to predict the flow-induced noise of pumps in order to minimize the noise of centrifugal pumps in actual projects. Under Langthjem＇s assumption that the blade surface pressure is the main flow-induced acoustic source in centrifugal pumps, the blade surface pressure pulsation is considered in terms of the acoustical sources and simulated using CFX software. The pressure pulsation and noise distribution in the near-cutoff region are examined for the blade-passing frequency （BPF） noise, and the sound pressure level （SPL） reached peaks near the cutoff that corresponded with the pressure pulsation in this region. An experiment is performed to validate this prediction. Four hydrophones are fixed to the inlet and outlet ports of the test pump to measure the flow-induced noise from the four-port model. The simulation results for the noise are analyzed and compared with the experimental results. The variation in the calculated noise with changes in the flow agreed well with the experimental results. When the flow rate was increased, the SPL first decreased and reached the minimum near the best efficient point （BEP）; it then increased when the flow rate was further increased. The numerical and experimental results confirmed that the BPF noise generated by a blade-rotating dipole roughly reflects the acoustic features of centrifugal pumps. The noise simulation method in current study has a good feasibility and suitability, which could be adopted in engineering design to predict and optimize the hydroacoustic behavior of centrifugal pumps.
文摘Distributed leading-edge （LE） roughness could have significant impact on the aerodynamicperformance of a low-Reynolds-number （low-Re） airfoil, which has not yet been fully understood.In the present study, experiments were conducted to study the effects of distributed hemisphericalroughness with different sizes and distribution patterns on the performance of a GA （W）-1 airfoil.Surface pressure and particle image velocimetry （PIV） measurements were performed undervarious incident angles and different Re numbers. Significant reduction in lift and increase in dragwere found for all cases with the LE roughness applied. Compared with the distribution pattern,the roughness height was found to be a more significant factor in determining the lift reductionand altering stall behaviors. It is also found while the larger roughness advances the aerodynamicstall, the smaller roughness tends to prevent deep stall at high incident angles. PIV results alsosuggest that staggered distribution pattern induces higher fluctuations in the wake flow than thealigned pattern does. Results imply that distributed LE roughness with large element sizes areparticularly detrimental to aerodynamic performances, while those with small element sizes couldpotentially serve as a passive control mechanism to alleviate deep stall conditions at high incidentangles.
