Atmospheric pressure fuctuation is one of the most important factors afecting the climate environment and gas emission in the fre area.To obtain the infuence rule of the surface atmospheric pressure change on the gas ...Atmospheric pressure fuctuation is one of the most important factors afecting the climate environment and gas emission in the fre area.To obtain the infuence rule of the surface atmospheric pressure change on the gas sampling and abnormal emission in the mine closed goaf,the No.1 coal mine in Dananhu was taken as the research object.Using Fourier transform and Fisher harmonic analysis and other statistical methods,the infuence of the periodic variation of atmospheric pressure on the gas leakage and outfow in the closed goaf was studied.The results showed that there were three atmospheric pressure periods of 15.2 d,1 d and 182.2 d,and the probability was greater than 95%.The time period with the highest number of atmospheric pressure peaks was 7:00–8:00,which accounted for 20.2%of total occurrence number in a day.And the time periods with the highest number of atmospheric pressure trough were 2:00,15:00 and 16:00,accounting for 27.4%.The peak-to-trough transition time was mainly concentrated around 6 h,and the diurnal variation curve of atmospheric pressure was mainly bimodal.The atmospheric pressure change rate was mostly concentrated in 10–50 Pa/h.It was determined that the distance that the gas sampling pipe was pre-laid into the inner side of the closed wall should be greater than 44.4 m,and the CO concentration and atmospheric pressure in the closed goaf were both periodic and negative with atmospheric pressure.The research results have important guiding signifcance for the monitoring,early warning and environmental protection of the goaf.展开更多
The wind pressure characteristics on a saddle roof at wind direction along the connection of the low points are systematically studied by the wind tunnel test. First, the distributions of the mean and the fluctuating ...The wind pressure characteristics on a saddle roof at wind direction along the connection of the low points are systematically studied by the wind tunnel test. First, the distributions of the mean and the fluctuating pressures on the saddle roof are provided. Through the wind pressure spectra, the process of generation, growth and break down of the vortex on the leading edge is presented from a microscopic aspect and then the distribution mechanism of the mean and fluctuating pressures along the vulnerable leading edge is explained. By analysis of the wind pressure spectra near the high points, it can be inferred that the body induced turbulence reflects itself as a high-frequency pressure fluctuation. Secondly, the third-and fourth-order statistical moments of the wind pressure are employed to identify the non-Gaussian nature of the pressure time history and to construct an easy tool to localize regions with a non-Gaussian feature. The cause of the non-Gaussian feature is discussed by virtue of the wind pressure spectra. It is concluded that the non-Gaussian feature of the wind pressure originates from the effects of flow separation and body-induced turbulence, and the former effect plays an obvious role.展开更多
In order to explore the pressure relief and structure stability mechanism of lateral cantilever structure in the stope under the direct coverage of thick hard roof and its impact on the gob-side entry retaining, a lat...In order to explore the pressure relief and structure stability mechanism of lateral cantilever structure in the stope under the direct coverage of thick hard roof and its impact on the gob-side entry retaining, a lateral cantilever fractured structural mechanical model was established on the basis of clarification for the stress environment of gob-side entry retaining, and the equation of roof given deformation and the balance judgment for fracture block were obtained. The optimal cantilever length was proposed based on the comparison of roof structural characteristics and the stress, deformation law of surrounding rocks under six different cantilever lengths by numerical simulation method. Double stress peaks exist on the sides of gob-side entry retaining and the entry located in the low stress area. The pressure of gob-side entry retaining can be relieved by reducing the cantilever length. However, due to the impact of arch structure of rock beam, unduly short cantilever would result in insufficient pressure relief and unduly long cantilever would bring larger roof stress which results in intense deformation. Therefore, there is optimal cantilever length, which was 7-8 m in this project that enables to achieve the minimum deformation and the most stabilized rock structure of entry retaining. An engineering case of gob-side entry retaining with the direct coverage of 10 m thick hard limestone roof was put forward, and the measured data verified the reasonability of conclusion.展开更多
This work aimed at revealing the mechanism of strong ground pressure behaviour(SGPB)induced by high-position hard roof(HHR).Based on the supporting structures model of HHR,a modified voussoir beam mechanical model for...This work aimed at revealing the mechanism of strong ground pressure behaviour(SGPB)induced by high-position hard roof(HHR).Based on the supporting structures model of HHR,a modified voussoir beam mechanical model for HHR was established by considering the gangue support coefficient,through which the modified expressions of limit breaking span and breaking energy of HHR were deduced.Combined with the relationship between the dynamic-static loading stress of supporting body(hydraulic support and coal wall)and its comprehensive supporting strength,the criteria of ground pressure behaviour(GPB)induced by HHR were discussed.The types of Ⅰ_(1),Ⅰ_(2),Ⅱ_(1),andⅡ_(2) of GPB were interpreted.Results showed that types Ⅰ_(1) and Ⅰ_(2) were the main forms of SGPB in extra-thick coal seam mining.The main manifestation of SGPB was static stress,which was mainly derived from the instability of HHR rather than fracture.Accordingly,an innovative control technology was proposed,which can weaken static load by vertical-well separated fracturing HHR.The research results have been successfully applied to the 8101 working face in Tashan coal mine,Shanxi Province,China.The results of a digital borehole camera observation and stress monitoring proved the rationality of the GPB criteria.The control technology was successful,paving the way for new possibilities to HHR control for safety mining.展开更多
Roof and rib instability is an important issue in underground mining. To optimize ground support design,enhance ground stability, and reduce the possibility of roof or rib failure with minimal use of artificial ground...Roof and rib instability is an important issue in underground mining. To optimize ground support design,enhance ground stability, and reduce the possibility of roof or rib failure with minimal use of artificial ground support, it is essential to have an accurate understanding of ground conditions. This includes the location of voids, cracks, and discontinuities, as well as information about the different strata in the immediate roof. This paper briefly introduces ongoing research on void detection by using the roof bolter feed and rotation pressure. The goal of this project is to improve the sensitivity of detection programs to locate smaller joints and reduce the number of false alarms. This paper presents a brief review of the testing procedures, data analysis, logic, and algorithms used for void detection. In addition, this paper discusses the results of preliminary laboratory tests and statistical analysis of the data from these two drilling parameters used for void detection.展开更多
This paper analyzed the strata behaviors of solid-coal roadway, gob-side entry driving and deformation law of surrounding rock in depth under high stress and thick composite roof based on the dynamic pressure roadway ...This paper analyzed the strata behaviors of solid-coal roadway, gob-side entry driving and deformation law of surrounding rock in depth under high stress and thick composite roof based on the dynamic pressure roadway as engineering background in Fengcheng mining area, Jiangxi province. The results, both field measurement and numerical simulation show that gob-side entry driving results the deformation of coal roadway main wall, however, entity-coal roadway driving results deformation of main roof and floor. The maintenance state of gob-side entry driving is better than entity-coal roadway, this situation is relevant to thick composite roof layered and easy collapse characteristics. At the same time, this paper put fox'ward and proved proper dynamic pressure roadway supporting scheme under the surrounding rock condition and stress environment.展开更多
An rCHO cell line expressing recombinant human prourokinase (pro-UK) at the level of 5μg/ 10^6cells/d was cultivated on Cytopore cellulose porous microcarriers in a 7.5L Biostat CT stirred tank reactor. A periodic ...An rCHO cell line expressing recombinant human prourokinase (pro-UK) at the level of 5μg/ 10^6cells/d was cultivated on Cytopore cellulose porous microcarriers in a 7.5L Biostat CT stirred tank reactor. A periodic pressure oscillation of 0.04 MPa and 0.04 Hz was adopted to introduce a physical stimulus on the rCHO cells and to improve mass transfer characteristic between cells and medium in the process of porous microcarrier CHO cell culture. Compared to constant pressure culture, the oscillation culture didn't influence specific cell growth rate significantly, but could enhance the pro-UK specific production by 10% - 40%, and reduce production of lactate by 10% - 30%. In the perfusion culture of recombinant CHO cell with serum-free medium for 67 days, cell density could reach 2.64×10^7/ml, the maximal prourokinase concentration in harvested supernatant was about 118mg/L, a total of 21.1 grams of prourokinase was produced in 313 liters of supernatant. In conclusion, the perfusion cell culture with periodic pressure oscillation can enhance the production of recombinant protein and increase the reactor specific productivity.展开更多
The influence of periodic pressure with low and high frequencies on microstructure and dendritic sidebranching was studied by using 3-D phase field method. In both low and high frequency cases, the variation trend of ...The influence of periodic pressure with low and high frequencies on microstructure and dendritic sidebranching was studied by using 3-D phase field method. In both low and high frequency cases, the variation trend of SDAS (secondary dendritic arm spacing) with increasing pressure frequency is opposite to that of sidebranching frequency, while the variation trend of the average length of secondary arms is consistent with that of sidebranching frequency. The high sidebranching frequency indicates that more secondary arms share the whole driving force of dendrite growth, resulting in lower driving force for each one and leading to less developed secondary arms. The smallest SDAS is obtained when perturbed by the periodic pressure with the frequency of 0.157/τ0 (τ0 is the physical unit of time in the dimensionless phase field model) and 2.200/τ0 in low and high frequency cases, respectively. Comparisons of dendritic morphology and secondary arms are made between the low and high frequency cases. Firstly, in the low frequency case, secondary arms are luxuriant especially when pressure frequency is low, with many high-order side branches stretching out. Secondly, the average length of secondary arms in primary dendrite is longer in the low frequency case than that without pressure, and much longer than that in the high frequency case. Thirdly, the dendrite tip without side branches in the high frequency case is much longer than that in the low frequency case. All of the differences in dendritic morphology and sidebranching in the two cases can be attributed to the different modulation mechanism. In the low frequency case, periodic pressure determines tip velocity and then modulates sidebranching directly. While in the high frequency case, periodic pressure cannot determine sidebranching directly, but via modulating tiny protuberances in dendrite tip, part of which evolves into side branch. In this case, the tiny protuberances take part of the whole driving force, leading to less developed secondary arms.展开更多
The pressure pulsation induced by the pumped periodic pulsation fluid is the main factor of causing fluid resonance and stimulating pipelines vibrations and noise. In order to reduce the f...The pressure pulsation induced by the pumped periodic pulsation fluid is the main factor of causing fluid resonance and stimulating pipelines vibrations and noise. In order to reduce the faults caused by the vibrations of pipelines, two aspects have been researched: one is to develop high quality filters, weaken and restrain the crest of pulsation pressure; the other is to design structural parameters of the piping network and eliminate the fluid resonance. Both need calculating the pressure pulsations of different structural parameters and frequencies, and knowing the amplitude frequency. In this paper the stiffness matrix technique is used for treating the coupling of subsystems of pipelines and calculating the pressure distribution of the piping network and it is tested by simulation and experiments.展开更多
A wind tunnel test was conducted for a large steel gymnasium structure. Simultaneous pressure measurements were made on its entire ellipsoidal roof in a simulated suburban boundary layer flow field. Special attention ...A wind tunnel test was conducted for a large steel gymnasium structure. Simultaneous pressure measurements were made on its entire ellipsoidal roof in a simulated suburban boundary layer flow field. Special attention is paid to the charaeteristics of fluctuating wind pressures in different zones on the roof. Some selected results are presented: 1) correlations between fluctuating wind pressures on both roof surfaces, 2) eigenvalues and eigenvectors of covariance matrices of the fluctuating wind pressures, 3) probability distributions of the fluctuating wind pressures, and 4) statistical characteristics of peak factor. Furthermore, the applicability of the quasi-steady approach is discussed in detail. Based on the results, an empirical formula for estimating the minimum pressure coefficients, using a peak factor approach, is presented. Comparison of the minimum pressure coefficients determined by the proposed formula and those obtained from the wind tunnel tests is made to examine the applicability and accuracy of the proposed formula.展开更多
The distinctions of dendritic morphology and sidebranching behavior when solidified under atmosphere pressure,constant pressure which is higher than atmosphere pressure (hereinafter referred to as constant pressure) a...The distinctions of dendritic morphology and sidebranching behavior when solidified under atmosphere pressure,constant pressure which is higher than atmosphere pressure (hereinafter referred to as constant pressure) and periodic pressure were investigated using 3-D phase field method.When growing at atmosphere pressure,side branches (secondary dendritic arms) are irregular.When solidified under constant pressure with a relatively high value,side branches are much more luxuriant,with more developed high-order side branches.When applied with periodic pressure,resonant sidebranching happens,leading to many more regular side branches and the smallest secondary dendritic arm spacing (SDAS) in the three cases.The significant difference in dendritic morphology is associated with tip velocity modulated by total undercooling including pressure and temperature undercooling.In the case of constant pressure,tip velocity increases linearly with total undercooling,and it varies periodically in periodic pressure case.The different variation trend in tip velocity is the reason for the distinct dendrite growth behavior in different cases.Unlike the phenomenon in constant pressure case where the dendrite grows faster with higher pressure,the dendrite grows slower under periodic pressure with higher amplitude,resulting in less developed primary dendrite and side branches.This is influenced by tip remelting due to low undercooling or even negative undercooling.It is revealed that the accelerated velocity of tip remelting increases with the decline of undercooling.The greater the amplitude of periodic pressure,the faster the tip remelting velocity during one period.This is the reason why the average tip velocity decreases with the rise of amplitude of periodic pressure.展开更多
Pressure and proximity measurements made in a tunnel indicate that a typical vehicle passage produced on the tunnel roof an initial pressure increase of small magnitude,followed by a sharp and more substantial drop in...Pressure and proximity measurements made in a tunnel indicate that a typical vehicle passage produced on the tunnel roof an initial pressure increase of small magnitude,followed by a sharp and more substantial drop in pressure below atmospheric.The magnitude of the pressure drop was found to increase with smaller clearances between the vehicle top and the tunnel roof,consistent with the Bernoulli relation and the vehicle speed.The dynamic pressures potentially may have significant effects on the vibration and noise environments on the lower floors of“air rights construction”buildings that span highways.展开更多
In this paper,the wind load on an arc-shaped canopy roof was studied with numerical wind tunnel method(NWTM) .Three-dimensional models were set up for the canopy roof with opened or closed skylights.The air flow aroun...In this paper,the wind load on an arc-shaped canopy roof was studied with numerical wind tunnel method(NWTM) .Three-dimensional models were set up for the canopy roof with opened or closed skylights.The air flow around the roof under wind action from three directions was analysed respectively.Wind pressure coefficients on the canopy roof were determined by NWTM.The results of NWTM agreed well with those of wind tunnel test for the roof with opened skylights,which verified the applicability and rationality of NWTM.The effect of the closure of skylights was then investigated with NWTM.It was concluded that the closure of the skylights may increase the wind suction on the top surface of the roof greatly and should be considered in the structure design of the canopy roof.展开更多
The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechan...The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechanism of wind pressure pulse events, the peak over threshold method was employed to study properties of this kind of events. The event duration time, the energy contribution, the number of the pulse events, and the distribution of average peak pressure were calculated. Probability density functions of some typical samples in separation region were also given. Results show that the non-Gaussian roof pressure is strong in the flow separation region owing to the wind pressure pulse events. Evaluations of the extreme peak pressures, which can be determined by the peak over threshold method effectively, are important to the design of building cladding.展开更多
Based on study of the influence of main roof fracture on ground pressure, this paper considered the immediate roof as a semi-infinite long beam on a Winkler elastic foundation. In the model the coal seam is the founda...Based on study of the influence of main roof fracture on ground pressure, this paper considered the immediate roof as a semi-infinite long beam on a Winkler elastic foundation. In the model the coal seam is the foundation and the pressure caused by mian roof deflection is the load. Having solved the model and analyzed relevant factors,the authors indicate that the disturbance caused by the breakage of the mian roof can be observed in both gates of longwall face and explain why it can be. The paper points out that the applicability of the method to obtain the disturbance information by measuring the loads on supports is wider than that by measuring the roof convergence rate. The results are useful for monitoring and predicting ground pressure.展开更多
Evolution of periodic orbits in Sun-Mars and Sun-Earth systems are analyzed using Poincare surface of section technique and the effects of solar radiation pressure of bigger primary and actual oblateness...Evolution of periodic orbits in Sun-Mars and Sun-Earth systems are analyzed using Poincare surface of section technique and the effects of solar radiation pressure of bigger primary and actual oblateness of smaller primary on these orbits areconsidered. It is observed that solar radiation pressure of bigger primary has substantial effect on period, orbit’s shape, size and their position in the phase space. Since these orbits can be used for the design of low energy transfer trajectories, so perturbations due to solar radiation pressure has to be understood and should be taken care of during trajectory design. It is also verified that stability of such orbits are negligible so they can be used as transfer orbit. For each pair of solar radiation pressure q and Jacobi constant C we get two separatrices where stability of island becomes zero. In this paper, detailed stability analysis of periodic orbit having two loops is given when q = 0.9845.展开更多
Liquid storage,particularly oil and petrochemical products which are considered hazardous liquid,are an important part of the oil industry.Thin-walled vertical cylindrical steel storage tanks are widely used in recent...Liquid storage,particularly oil and petrochemical products which are considered hazardous liquid,are an important part of the oil industry.Thin-walled vertical cylindrical steel storage tanks are widely used in recent years.Due to high sensitivity of these structures in an earthquake and other external excitations may lead to catastrophic consequences.For instance,huge economic losses,environmental damages,and casualities,many studies have been done about these structures.past studies showed that liquid storage tanks,equipped with a floating roof,are potentially vulnerable while subjected to seismic loads and earthquake has been considered as one of the most destructive natural hazards.The reason is that such tanks are made of two separated parts(shell and roof)which each may have its own responses;sometimes causing resonance phenomenon and so that,roof movements,rooffluid interaction,roof-shell interaction,and also the way they are attached should still be investigated.Experimental tests of floating roof’s vertical fluctuation was performed in a full-scale reservoir tank and assessing of the results demonstrated that presence of a seal between floating roof and shell plate can significantly increase damping ratio in liquid sloshing and also suppress the roof`s vertical displacements.In other words,seal can control a floating roof and make it stop moving vertically over few cycles.展开更多
基金This work was financially sponsored by the National Natural Science Foundation of China(51864045,51804161,52074156 and 51804355)And Central University Basic Scientifc Research Business Expenses Special Funds(2023ZKPYAQ03).
文摘Atmospheric pressure fuctuation is one of the most important factors afecting the climate environment and gas emission in the fre area.To obtain the infuence rule of the surface atmospheric pressure change on the gas sampling and abnormal emission in the mine closed goaf,the No.1 coal mine in Dananhu was taken as the research object.Using Fourier transform and Fisher harmonic analysis and other statistical methods,the infuence of the periodic variation of atmospheric pressure on the gas leakage and outfow in the closed goaf was studied.The results showed that there were three atmospheric pressure periods of 15.2 d,1 d and 182.2 d,and the probability was greater than 95%.The time period with the highest number of atmospheric pressure peaks was 7:00–8:00,which accounted for 20.2%of total occurrence number in a day.And the time periods with the highest number of atmospheric pressure trough were 2:00,15:00 and 16:00,accounting for 27.4%.The peak-to-trough transition time was mainly concentrated around 6 h,and the diurnal variation curve of atmospheric pressure was mainly bimodal.The atmospheric pressure change rate was mostly concentrated in 10–50 Pa/h.It was determined that the distance that the gas sampling pipe was pre-laid into the inner side of the closed wall should be greater than 44.4 m,and the CO concentration and atmospheric pressure in the closed goaf were both periodic and negative with atmospheric pressure.The research results have important guiding signifcance for the monitoring,early warning and environmental protection of the goaf.
基金The National Natural Science Foundation of China (No.50678036)Jiangsu Civil Engineering Graduate Center for Innovation and Academic Communication Foundation
文摘The wind pressure characteristics on a saddle roof at wind direction along the connection of the low points are systematically studied by the wind tunnel test. First, the distributions of the mean and the fluctuating pressures on the saddle roof are provided. Through the wind pressure spectra, the process of generation, growth and break down of the vortex on the leading edge is presented from a microscopic aspect and then the distribution mechanism of the mean and fluctuating pressures along the vulnerable leading edge is explained. By analysis of the wind pressure spectra near the high points, it can be inferred that the body induced turbulence reflects itself as a high-frequency pressure fluctuation. Secondly, the third-and fourth-order statistical moments of the wind pressure are employed to identify the non-Gaussian nature of the pressure time history and to construct an easy tool to localize regions with a non-Gaussian feature. The cause of the non-Gaussian feature is discussed by virtue of the wind pressure spectra. It is concluded that the non-Gaussian feature of the wind pressure originates from the effects of flow separation and body-induced turbulence, and the former effect plays an obvious role.
基金Project(51404251)supported by the National Natural Science Foundation of ChinaProject(BK20140198)supported by the Natural Science Foundation of Jiangsu Province of China+1 种基金Project(2014XT01)supported by the Fundamental Research Funds for the Central UniversitiesChina
文摘In order to explore the pressure relief and structure stability mechanism of lateral cantilever structure in the stope under the direct coverage of thick hard roof and its impact on the gob-side entry retaining, a lateral cantilever fractured structural mechanical model was established on the basis of clarification for the stress environment of gob-side entry retaining, and the equation of roof given deformation and the balance judgment for fracture block were obtained. The optimal cantilever length was proposed based on the comparison of roof structural characteristics and the stress, deformation law of surrounding rocks under six different cantilever lengths by numerical simulation method. Double stress peaks exist on the sides of gob-side entry retaining and the entry located in the low stress area. The pressure of gob-side entry retaining can be relieved by reducing the cantilever length. However, due to the impact of arch structure of rock beam, unduly short cantilever would result in insufficient pressure relief and unduly long cantilever would bring larger roof stress which results in intense deformation. Therefore, there is optimal cantilever length, which was 7-8 m in this project that enables to achieve the minimum deformation and the most stabilized rock structure of entry retaining. An engineering case of gob-side entry retaining with the direct coverage of 10 m thick hard limestone roof was put forward, and the measured data verified the reasonability of conclusion.
基金This work was jointly supported by the National Natural Science Foundation of China(No.51974042)the Shanxi Province Science and Technology Plan Exposed Bidding Project(No.20191101015)+3 种基金the Open Project Program of Key Laboratory of Mine Disaster Prevention and Control(No.JMDPC202102)the Scientific Research Project of Introducing Talents in Guizhou University(No.202045)the Open Project Program of National Engineering Technology Research Center of Development and Utilization for Phosphorus Resources(NECP202210)the Growth Project of Young Scientific and Technological Talents in Universities of Guizhou Province(KY2022139).
文摘This work aimed at revealing the mechanism of strong ground pressure behaviour(SGPB)induced by high-position hard roof(HHR).Based on the supporting structures model of HHR,a modified voussoir beam mechanical model for HHR was established by considering the gangue support coefficient,through which the modified expressions of limit breaking span and breaking energy of HHR were deduced.Combined with the relationship between the dynamic-static loading stress of supporting body(hydraulic support and coal wall)and its comprehensive supporting strength,the criteria of ground pressure behaviour(GPB)induced by HHR were discussed.The types of Ⅰ_(1),Ⅰ_(2),Ⅱ_(1),andⅡ_(2) of GPB were interpreted.Results showed that types Ⅰ_(1) and Ⅰ_(2) were the main forms of SGPB in extra-thick coal seam mining.The main manifestation of SGPB was static stress,which was mainly derived from the instability of HHR rather than fracture.Accordingly,an innovative control technology was proposed,which can weaken static load by vertical-well separated fracturing HHR.The research results have been successfully applied to the 8101 working face in Tashan coal mine,Shanxi Province,China.The results of a digital borehole camera observation and stress monitoring proved the rationality of the GPB criteria.The control technology was successful,paving the way for new possibilities to HHR control for safety mining.
文摘Roof and rib instability is an important issue in underground mining. To optimize ground support design,enhance ground stability, and reduce the possibility of roof or rib failure with minimal use of artificial ground support, it is essential to have an accurate understanding of ground conditions. This includes the location of voids, cracks, and discontinuities, as well as information about the different strata in the immediate roof. This paper briefly introduces ongoing research on void detection by using the roof bolter feed and rotation pressure. The goal of this project is to improve the sensitivity of detection programs to locate smaller joints and reduce the number of false alarms. This paper presents a brief review of the testing procedures, data analysis, logic, and algorithms used for void detection. In addition, this paper discusses the results of preliminary laboratory tests and statistical analysis of the data from these two drilling parameters used for void detection.
基金Supported by the National Natural Science Foundation of China (51074071) the Scientific Research Fund of Hunan Provincial Education Department (12cy013)
文摘This paper analyzed the strata behaviors of solid-coal roadway, gob-side entry driving and deformation law of surrounding rock in depth under high stress and thick composite roof based on the dynamic pressure roadway as engineering background in Fengcheng mining area, Jiangxi province. The results, both field measurement and numerical simulation show that gob-side entry driving results the deformation of coal roadway main wall, however, entity-coal roadway driving results deformation of main roof and floor. The maintenance state of gob-side entry driving is better than entity-coal roadway, this situation is relevant to thick composite roof layered and easy collapse characteristics. At the same time, this paper put fox'ward and proved proper dynamic pressure roadway supporting scheme under the surrounding rock condition and stress environment.
文摘An rCHO cell line expressing recombinant human prourokinase (pro-UK) at the level of 5μg/ 10^6cells/d was cultivated on Cytopore cellulose porous microcarriers in a 7.5L Biostat CT stirred tank reactor. A periodic pressure oscillation of 0.04 MPa and 0.04 Hz was adopted to introduce a physical stimulus on the rCHO cells and to improve mass transfer characteristic between cells and medium in the process of porous microcarrier CHO cell culture. Compared to constant pressure culture, the oscillation culture didn't influence specific cell growth rate significantly, but could enhance the pro-UK specific production by 10% - 40%, and reduce production of lactate by 10% - 30%. In the perfusion culture of recombinant CHO cell with serum-free medium for 67 days, cell density could reach 2.64×10^7/ml, the maximal prourokinase concentration in harvested supernatant was about 118mg/L, a total of 21.1 grams of prourokinase was produced in 313 liters of supernatant. In conclusion, the perfusion cell culture with periodic pressure oscillation can enhance the production of recombinant protein and increase the reactor specific productivity.
基金This wurk was supputed by lhe Nativual Higl Teeltwlugy Research and Development Program of China(Grant No.2018YF E0204300)Institute Guo Qiang,Tsinghua University(Grant No.2019GQG1010).
文摘The influence of periodic pressure with low and high frequencies on microstructure and dendritic sidebranching was studied by using 3-D phase field method. In both low and high frequency cases, the variation trend of SDAS (secondary dendritic arm spacing) with increasing pressure frequency is opposite to that of sidebranching frequency, while the variation trend of the average length of secondary arms is consistent with that of sidebranching frequency. The high sidebranching frequency indicates that more secondary arms share the whole driving force of dendrite growth, resulting in lower driving force for each one and leading to less developed secondary arms. The smallest SDAS is obtained when perturbed by the periodic pressure with the frequency of 0.157/τ0 (τ0 is the physical unit of time in the dimensionless phase field model) and 2.200/τ0 in low and high frequency cases, respectively. Comparisons of dendritic morphology and secondary arms are made between the low and high frequency cases. Firstly, in the low frequency case, secondary arms are luxuriant especially when pressure frequency is low, with many high-order side branches stretching out. Secondly, the average length of secondary arms in primary dendrite is longer in the low frequency case than that without pressure, and much longer than that in the high frequency case. Thirdly, the dendrite tip without side branches in the high frequency case is much longer than that in the low frequency case. All of the differences in dendritic morphology and sidebranching in the two cases can be attributed to the different modulation mechanism. In the low frequency case, periodic pressure determines tip velocity and then modulates sidebranching directly. While in the high frequency case, periodic pressure cannot determine sidebranching directly, but via modulating tiny protuberances in dendrite tip, part of which evolves into side branch. In this case, the tiny protuberances take part of the whole driving force, leading to less developed secondary arms.
文摘The pressure pulsation induced by the pumped periodic pulsation fluid is the main factor of causing fluid resonance and stimulating pipelines vibrations and noise. In order to reduce the faults caused by the vibrations of pipelines, two aspects have been researched: one is to develop high quality filters, weaken and restrain the crest of pulsation pressure; the other is to design structural parameters of the piping network and eliminate the fluid resonance. Both need calculating the pressure pulsations of different structural parameters and frequencies, and knowing the amplitude frequency. In this paper the stiffness matrix technique is used for treating the coupling of subsystems of pipelines and calculating the pressure distribution of the piping network and it is tested by simulation and experiments.
基金Project(50978063) supported by the National Science Foundation of ChinaProject(NCET-09-0082) supported by the Program for New Century Excellent Talents in Chinese UniversitiesProject(121072) supported by the Fok Ying-Tong Education Foundation for Young Teachers in the Higher Education Institutions of China
文摘A wind tunnel test was conducted for a large steel gymnasium structure. Simultaneous pressure measurements were made on its entire ellipsoidal roof in a simulated suburban boundary layer flow field. Special attention is paid to the charaeteristics of fluctuating wind pressures in different zones on the roof. Some selected results are presented: 1) correlations between fluctuating wind pressures on both roof surfaces, 2) eigenvalues and eigenvectors of covariance matrices of the fluctuating wind pressures, 3) probability distributions of the fluctuating wind pressures, and 4) statistical characteristics of peak factor. Furthermore, the applicability of the quasi-steady approach is discussed in detail. Based on the results, an empirical formula for estimating the minimum pressure coefficients, using a peak factor approach, is presented. Comparison of the minimum pressure coefficients determined by the proposed formula and those obtained from the wind tunnel tests is made to examine the applicability and accuracy of the proposed formula.
基金supported by the National High Technology Research and Development Program of China(Grant No.2018YFE0204300)Institute Guo Qiang,Tsinghua University(Grant No.2019GQG1010)。
文摘The distinctions of dendritic morphology and sidebranching behavior when solidified under atmosphere pressure,constant pressure which is higher than atmosphere pressure (hereinafter referred to as constant pressure) and periodic pressure were investigated using 3-D phase field method.When growing at atmosphere pressure,side branches (secondary dendritic arms) are irregular.When solidified under constant pressure with a relatively high value,side branches are much more luxuriant,with more developed high-order side branches.When applied with periodic pressure,resonant sidebranching happens,leading to many more regular side branches and the smallest secondary dendritic arm spacing (SDAS) in the three cases.The significant difference in dendritic morphology is associated with tip velocity modulated by total undercooling including pressure and temperature undercooling.In the case of constant pressure,tip velocity increases linearly with total undercooling,and it varies periodically in periodic pressure case.The different variation trend in tip velocity is the reason for the distinct dendrite growth behavior in different cases.Unlike the phenomenon in constant pressure case where the dendrite grows faster with higher pressure,the dendrite grows slower under periodic pressure with higher amplitude,resulting in less developed primary dendrite and side branches.This is influenced by tip remelting due to low undercooling or even negative undercooling.It is revealed that the accelerated velocity of tip remelting increases with the decline of undercooling.The greater the amplitude of periodic pressure,the faster the tip remelting velocity during one period.This is the reason why the average tip velocity decreases with the rise of amplitude of periodic pressure.
文摘Pressure and proximity measurements made in a tunnel indicate that a typical vehicle passage produced on the tunnel roof an initial pressure increase of small magnitude,followed by a sharp and more substantial drop in pressure below atmospheric.The magnitude of the pressure drop was found to increase with smaller clearances between the vehicle top and the tunnel roof,consistent with the Bernoulli relation and the vehicle speed.The dynamic pressures potentially may have significant effects on the vibration and noise environments on the lower floors of“air rights construction”buildings that span highways.
文摘In this paper,the wind load on an arc-shaped canopy roof was studied with numerical wind tunnel method(NWTM) .Three-dimensional models were set up for the canopy roof with opened or closed skylights.The air flow around the roof under wind action from three directions was analysed respectively.Wind pressure coefficients on the canopy roof were determined by NWTM.The results of NWTM agreed well with those of wind tunnel test for the roof with opened skylights,which verified the applicability and rationality of NWTM.The effect of the closure of skylights was then investigated with NWTM.It was concluded that the closure of the skylights may increase the wind suction on the top surface of the roof greatly and should be considered in the structure design of the canopy roof.
基金Sponsored by the National Natural Science Foundation of China(Grant No.50708030 and 90815021)
文摘The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechanism of wind pressure pulse events, the peak over threshold method was employed to study properties of this kind of events. The event duration time, the energy contribution, the number of the pulse events, and the distribution of average peak pressure were calculated. Probability density functions of some typical samples in separation region were also given. Results show that the non-Gaussian roof pressure is strong in the flow separation region owing to the wind pressure pulse events. Evaluations of the extreme peak pressures, which can be determined by the peak over threshold method effectively, are important to the design of building cladding.
文摘Based on study of the influence of main roof fracture on ground pressure, this paper considered the immediate roof as a semi-infinite long beam on a Winkler elastic foundation. In the model the coal seam is the foundation and the pressure caused by mian roof deflection is the load. Having solved the model and analyzed relevant factors,the authors indicate that the disturbance caused by the breakage of the mian roof can be observed in both gates of longwall face and explain why it can be. The paper points out that the applicability of the method to obtain the disturbance information by measuring the loads on supports is wider than that by measuring the roof convergence rate. The results are useful for monitoring and predicting ground pressure.
文摘Evolution of periodic orbits in Sun-Mars and Sun-Earth systems are analyzed using Poincare surface of section technique and the effects of solar radiation pressure of bigger primary and actual oblateness of smaller primary on these orbits areconsidered. It is observed that solar radiation pressure of bigger primary has substantial effect on period, orbit’s shape, size and their position in the phase space. Since these orbits can be used for the design of low energy transfer trajectories, so perturbations due to solar radiation pressure has to be understood and should be taken care of during trajectory design. It is also verified that stability of such orbits are negligible so they can be used as transfer orbit. For each pair of solar radiation pressure q and Jacobi constant C we get two separatrices where stability of island becomes zero. In this paper, detailed stability analysis of periodic orbit having two loops is given when q = 0.9845.
文摘Liquid storage,particularly oil and petrochemical products which are considered hazardous liquid,are an important part of the oil industry.Thin-walled vertical cylindrical steel storage tanks are widely used in recent years.Due to high sensitivity of these structures in an earthquake and other external excitations may lead to catastrophic consequences.For instance,huge economic losses,environmental damages,and casualities,many studies have been done about these structures.past studies showed that liquid storage tanks,equipped with a floating roof,are potentially vulnerable while subjected to seismic loads and earthquake has been considered as one of the most destructive natural hazards.The reason is that such tanks are made of two separated parts(shell and roof)which each may have its own responses;sometimes causing resonance phenomenon and so that,roof movements,rooffluid interaction,roof-shell interaction,and also the way they are attached should still be investigated.Experimental tests of floating roof’s vertical fluctuation was performed in a full-scale reservoir tank and assessing of the results demonstrated that presence of a seal between floating roof and shell plate can significantly increase damping ratio in liquid sloshing and also suppress the roof`s vertical displacements.In other words,seal can control a floating roof and make it stop moving vertically over few cycles.