A Level考试素有“英国高考”之称。其制度演进大致经历了发轫与探索、扩张与调适、回归与重塑三个阶段,其主要变革内容包括四个方面:组织形式从年终末考的线性考试模式发展为一年多考的模块化考试,再回归线性考试模式;考试评价从常模...A Level考试素有“英国高考”之称。其制度演进大致经历了发轫与探索、扩张与调适、回归与重塑三个阶段,其主要变革内容包括四个方面:组织形式从年终末考的线性考试模式发展为一年多考的模块化考试,再回归线性考试模式;考试评价从常模参照转变为标准参照,评价手段逐步优化;考试要求从注重学科深度转变为强调知识广度,再发展为追求广度和深度并重;考试内容从偏重学术性转变为普职并重,再发展为职普融通和强调基础学科。变革的动因既有来自外部的国际竞争加剧和国内政党轮替,也有来自内部的文化价值观驱动和考试选才效度追求。A Level考试制度对我国高考改革有一定启发,我国可结合国情,以基础学科为支点、职普融通为路径、多样化的考试选择为依托、预测效度为导向,开展本土化探索。展开更多
Groundwater level(GWL)is a key indicator used to accurately assess groundwater resources and form the foundation for ef-fective groundwater management.This paper integrates a Gate Recurrent Unit(GRU)model with a Multi...Groundwater level(GWL)is a key indicator used to accurately assess groundwater resources and form the foundation for ef-fective groundwater management.This paper integrates a Gate Recurrent Unit(GRU)model with a Multi-head Self-attention mechan-ism(MSAM-GRU)to simulate GWLs in both confined and unconfined aquifers simultaneously.The model innovatively captures the lag times between GWLs in the unconfined aquifer and precipitation,as well as between GWLs in the confined aquifer and the upper aquifer.We have assessed the effectiveness of the proposed model using a case study in the Beijing Plain,China from January 2005 to December 2020.With the consideration of lag times,the results indicated that the MSAM-GRU model exhibits a maximum 67%and 73%reduction in RMSE compared to the Attention mechanism-GRU(AM-GRU)and GRU model,respectively.MSAM-GRU model exhibited a 31%reduction in RMSE and a 0.12 increase in R^(2) compared to the same model that do not account for lag time.In Region I,the shortest lag time of GWL in the unconfined aquifer was two months,while that in the confined aquifer was three months,indicating a longer delayed response in the confined aquifer.MSAM-GRU model considering lag time,was then applied to simulate the GWLs in the unconfined aquifer under different scenarios and to analyze whether GWL fluctuations affect subway operations.The simulation res-ults showed that under the scenario 1,the GWL in the unconfined aquifer would rise above the depth of subway station floor,threaten-ing the operation of subways.This study can provide reliable technical support for the accurate simulation of GWLs in multi-aquifer systems.展开更多
The devastating Ms8.0 Wenchuan earthquake ruptured two large parallel thrust faults along the middle segment of the Longmenshan thrust belt. Preseismic and postseismic leveling data indicated the hanging wall of the Y...The devastating Ms8.0 Wenchuan earthquake ruptured two large parallel thrust faults along the middle segment of the Longmenshan thrust belt. Preseismic and postseismic leveling data indicated the hanging wall of the Yingxiu-Beichuan-Nanba thrust fault mainly presented coseismic uplift with respect to the reference point at Pingwu county town, and the observed maximum uplift of 4.7 m is located at Beichuan county （Qushan town） which is about 100 m west of the fault scarp. The foot wall of the Yingxiu-Beichuan-Nanba thrust fault mainly showed subsidence with maximum subsidence of 0.6 m near the rupture. By employing a listric dislocation model, we found that the fault geometry model of exponential dip angle δ=88°×[1-exp（-9/h）] with depth of 18 km and uniform thrust-slip of 5.6 m could fit the observed coseismic vertical deformation very well, which verifies the listric thrust model of the Longmenshan orogenic zone.展开更多
Investigation of unloading rock failure under differentσ_(2)facilitates the control mechanism of excavation surrounding rock.This study focused on single-sided unloading tests of granite specimens under true triaxial...Investigation of unloading rock failure under differentσ_(2)facilitates the control mechanism of excavation surrounding rock.This study focused on single-sided unloading tests of granite specimens under true triaxial conditions.The strength and failure characteristics were studied with micro-camera and acoustic emission(AE)monitoring.Furthermore,the choice of test path and the effect ofσ_(2)on fracture of unloading rock were discussed.Results show that the increasedσ_(2)can strengthen the stability of single-sided unloading rock.After unloading,the rock’s free surface underwent five phases,namely,inoculation,particle ejection,buckling rupture,stable failure,and unstable rockburst phases.Moreover,atσ_(2)≤30 MPa,the b value shows the following variation tendency:rising,dropping,significant fluctuation,and dropping,with dispersed damages signal.Atσ_(2)≥40 MPa,the tendency shows:a rise,a decrease,a slight fluctuation,and final drop,with concentrated damages signal.After unloading,AE energy is mainly concentrated in the micro-energy range.With the increasedσ_(2),the micro-energy ratio rises.In contrast,low,medium and large energy ratios drop gradually.The increased tensile fractures and decreased shear fractures indicate that the failure mode of the unloading rock gradually changes from tensile-shear mode to tensile-split one.The fractional dimension of the rock fragments first increases and then decreases with an inflection point at 20 MPa.The distribution of SIF on the planes changes asσ_(2)increases,resulting in strengthening and then weakening of the rock bearing capacity.展开更多
Cold-rolled thin strip steel of high flatness quality undergoes multistage deformation during tension leveling. Thus, the parameters of set-up and manipulating are more difficult. With the aid of FE code MSC. MARC, th...Cold-rolled thin strip steel of high flatness quality undergoes multistage deformation during tension leveling. Thus, the parameters of set-up and manipulating are more difficult. With the aid of FE code MSC. MARC, the tension leveling process of thin strip steel was numerically simulated. Concentrating on the influence of the roll intermeshes in 2# anti-cambering on the distribution and magnitude of residual stresses in leveled strip steel, several experiments were clone with the tension leveler based on the results from the simulation. It was found from the simulation that the magnitude of longitudinal residual stresses in the cross-section of the leveled strip steel regularly presents obvious interdependence with the roll intermeshes in 2# anti-cambering. In addition, there is a steady zone as the longitudinal residual stresses of the surface layers in leveled strip steel vary with the roll intermeshes of 2# anticambering, which is of importance in the manipulation of tension levelers. It was also found that the distribution of strains and stresses across the width of strip steel is uneven during leveling or after removing the tension loaded upon the strip, from which it was found that 3D simulation could not be replaced by 2D analysis because 2D analysis in this case cannot represent the physical behavior of strip steel deformation during tension leveling.展开更多
A model based on the curvature integration method has been applied in an online plate leveling system. However, there are some shortcomings in the current leveling models. On the one hand, the models cannot deal with ...A model based on the curvature integration method has been applied in an online plate leveling system. However, there are some shortcomings in the current leveling models. On the one hand, the models cannot deal with the leveling process of plates with a random curvature distribution. On the other hand, the current models are suitable only for stable leveling processes and ignore the biting in and tailing out stages. This study presents a new plate-leveling model based on the curvature integration method, which can describe the leveling process of plates with random curvature distribution. Further, the model is solved in two cases in order to take the biting in and tailing out stages into consideration. The proposed model is evaluated by comparing with a plate leveling experiment. Finally, the leveling process of a plate with a wave bent is studied using the proposed model. It is found that the contact angles vary greatly during the biting in and tailing out stages. However, they are relatively steady during the 5 roller leveling stage. In addition, the contact angle of roller No. 2 is the smallest, which is close to 0. Roller leveling can effectively eliminate bending in the plate, but there are regions in the head and tail of the plate, where roller leveling is not effective. The non-leveling region length is about 2 times that of the roller space. This study proposes a quasi-static plate-leveling model, which makes it possible to analyze the dynamic straightening process using a curvature integration method. It also makes it possible to analyze the straightening process of a plate with random curvature distribution.展开更多
Roller leveling process of longitudinal profile （LP） plate is hardly studied because plate thickness changes. Deformation characteristics and residual curvature during LP plate leveling process were investigated bas...Roller leveling process of longitudinal profile （LP） plate is hardly studied because plate thickness changes. Deformation characteristics and residual curvature during LP plate leveling process were investigated based on curva ture integral by elastic plastic differences. It was found that entry intermesh section is reduced with increasing thick- ness and entry intermesh should be from 0.7 to 1.1 mm for LP plate with 42/54 mm in thickness. In order to get satisfactory flatness along longitudinal direction, small entry intermesh should be selected and exit intermesh should be 0 ram. In addition, thickness section for I.P plate which can be leveled by 11 roller leveler is from 24 to 60 mm. Finally, there is an intermesh schedule that could level LP plate with initial curvature less than elastic limit curvature.展开更多
The accurate control for the vehicle height and leveling adjustment system of an electronic air suspension(EAS) still is a challenging problem that has not been effectively solved in prior researches. This paper propo...The accurate control for the vehicle height and leveling adjustment system of an electronic air suspension(EAS) still is a challenging problem that has not been effectively solved in prior researches. This paper proposes a new adaptive controller to control the vehicle height and to adjust the roll and pitch angles of the vehicle body(leveling control) during the vehicle height adjustment procedures by an EAS system. A nonlinear mechanism model of the full?car vehicle height adjustment system is established to reflect the system dynamic behaviors and to derive the system optimal control law. To deal with the nonlinear characters in the vehicle height and leveling adjustment processes, the nonlinear system model is globally linearized through the state feedback method. On this basis, a fuzzy sliding mode controller(FSMC) is designed to improve the control accuracy of the vehicle height adjustment and to reduce the peak values of the roll and pitch angles of the vehicle body. To verify the effectiveness of the proposed control method more accurately, the full?car EAS system model programmed using AMESim is also given. Then, the co?simulation study of the FSMC performance can be conducted. Finally, actual vehicle tests are performed with a city bus, and the test results illustrate that the vehicle height adjustment performance is effectively guaranteed by the FSMC, and the peak values of the roll and pitch angles of the vehicle body during the vehicle height adjustment procedures are also reduced significantly. This research proposes an effective control methodology for the vehicle height and leveling adjustment system of an EAS, which provides a favorable control performance for the system.展开更多
A broad view of present-day 3D deformation field around the Northeast China region was derived from GPS and leveling observations. We draw the following conclusions： First, the Northeast China region moved towards no...A broad view of present-day 3D deformation field around the Northeast China region was derived from GPS and leveling observations. We draw the following conclusions： First, the Northeast China region moved towards northwest with an average velocity of 5 ram/a, with respect to South China. The entire Northeast China region was in a low strain state from the strain rate field. Second, we processed two periods of first- order leveling data in 1970s and 1990s, showing the vertical deformation of the Northeast China region is ＂uplift in western part and subsidence in eastern part＇展开更多
Leveler is widely used to improve the quality of defective mild steel plates.Its typical ranges of the leveling capacity are constrained by three criteria,namely the maximum stroke of rollers,allowable total leveling ...Leveler is widely used to improve the quality of defective mild steel plates.Its typical ranges of the leveling capacity are constrained by three criteria,namely the maximum stroke of rollers,allowable total leveling force and motor power.In this work,an optimization model with equality and inequality constraints was built for the maximum yield stress search of each thickness of plates.The corresponding search procedure with three loops was given.The approximate range by the simplification model could be used as the initial value for the actual range search of the leveling capacity.Therefore,the search speed could be accelerated compared with a global search.The consistency of the analytical results and field data demonstrates the reliability of the proposed model and procedure.The typical ranges of the leveling capacity are expressed by several boundary curves which are helpful to judge whether the incoming plate can be leveled quickly or not.Also,these curves can be used to find the maximum yield stress for a specific thickness or the maximum thickness for a yield stress for plates.展开更多
Waves occurring in cold-rolled plates or sheets can be divided into longitudinal and transverse waves. Classical leveling theories merely solve the problem of longitudinal waves, while no well accepted method can be e...Waves occurring in cold-rolled plates or sheets can be divided into longitudinal and transverse waves. Classical leveling theories merely solve the problem of longitudinal waves, while no well accepted method can be employed for transverse waves. In order to investigate the essential deformation law of leveling for plates with transverse waves, a 2.5-dimensional （2.5- D） analytical approach was proposed. In this model, the plate was transversely divided into some strips with equal width; the strips are considered to be in the state of plane strain and each group of adjacent strips are assumed to be deformation compatible under stress. After calculation, the bending deformation of each strip and the leveling effect of overall plate were obtained by comprehensNe consideration of various strips along with the width. Bending of roller is a main approach to eliminate the transverse waves, which is widely accepted by the industry, but the essential effect of bending of roller on the deformation of plates and the calculation of bending of roller are unknown. According to the 2.5-D analytical model, it can be found that, for plates, it is neutral plane offsetting and middle plane elongation or contraction under inner stress that can effectively improve plate shape. Taking double side waves as an example, the appropriate values of bending of roller were obtained by the 2.5-D analytical model related to different initial unevenness, which was applicable to the current on-line adjusting of bending of roller in rolling industry.展开更多
Through the analysis of the principle, error sources and precision of trigonometric leveling, this paper points out the key problems about first order leveling replaced by trigonometric leveling; and for the first tim...Through the analysis of the principle, error sources and precision of trigonometric leveling, this paper points out the key problems about first order leveling replaced by trigonometric leveling; and for the first time puts forward that, in some given conditions, it is not only feasible but also valuable to replace first order leveling by precise trigonometric leveling, and proves it by experimentation as well. The content and conclusion of this paper have consulting significance and practicable value for our setting down relational criterion and production practice.展开更多
The inter-electrode gap(IEG) is an essential parameter for the anode shaping process in electrochemical machining(ECM) and directly affects the machining accuracy. In this paper, the IEG during the leveling process of...The inter-electrode gap(IEG) is an essential parameter for the anode shaping process in electrochemical machining(ECM) and directly affects the machining accuracy. In this paper, the IEG during the leveling process of an oval anode workpiece in counter-rotating ECM(CRECM)is investigated. The variation of the minimum IEG is analyzed theoretically, and the results indicate that rather than reaching equilibrium, the minimum IEG in CRECM expands constantly when a constant feed speed is used for the cathode tool. This IEG expansion leads to a poor localization effect and has an adverse influence on the roundness of the machined workpiece. To maintain a small constant IEG in CRECM, a variable feed speed is used for the cathode based on a fitted equation. The theoretical results show that the minimum IEG can be controlled at a small value by using an accelerated feed speed. Experiments have been conducted using a specific experimental apparatus in which the cathode tool is designed as a combined structure of two sectors and a thin sheet. By detecting the machining currents flowing through the minimum IEG, how the latter varies is obtained indirectly. The results indicate that using an accelerated feed speed is effective for controlling the IEG, thereby improving the roundness of the machined workpiece.展开更多
The development of GPS(Global Positioning System) technology has led to increasingly widely and successful applications of GPS surveys for monitoring crustal movements. However, multi-period GPS survey solutions have ...The development of GPS(Global Positioning System) technology has led to increasingly widely and successful applications of GPS surveys for monitoring crustal movements. However, multi-period GPS survey solutions have not been applied in monitoring vertical crustal movements with normal backgrounds. In this paper, we carried out a comparative study on the vertical deformation of the comprehensive profile of the cross-fault zone in Shanyin, Shanxi province, China, based on GPS and precise leveling observation data for multiple time periods. The vertical deformation rates observed with repeating GPS survey are obviously different(over 20 mm/y at some sites) from those with repeating leveling survey within a relatively short period. However, the deviations in the vertical displacement between GPS and leveling in a long-term survey(over three years) showed good consistency at 3-4 mm/y at most sites, on GPS forced offset surveying and fixed survey instruments in a long-term survey(over three years). Therefore, GPS vertical displacement results can be applied to the study of vertical crustal movements.展开更多
Single-sided linear induction motors(SLIMs)are widely used as traction components in maglev transportation systems.It is of great practical value to study speed sensorless control methods of SLIM.End-effect which is r...Single-sided linear induction motors(SLIMs)are widely used as traction components in maglev transportation systems.It is of great practical value to study speed sensorless control methods of SLIM.End-effect which is related to the speed of mover is considered,and the M-axis equivalent circuit of SLIM is asymmetric to T-axis.The secondary flux is chosen as the state variable,and the speed identification function is deduced.展开更多
Leveling process plays an important role in delivering the desired material properties and product standards.An analytical method for the rotational leveling process of bars was presented.First,each cross section of t...Leveling process plays an important role in delivering the desired material properties and product standards.An analytical method for the rotational leveling process of bars was presented.First,each cross section of the bar in the leveling area was discretized with the roller gap-curvature relations established in both planes XYand XZ.Second,a numerical procedure with two steps was developed to simulate both pressing and leveling processes.This approach can be easily implemented to produce simulation results of the curvature and trajectory distributions during the leveling process,as well as the bending and residual stresses.It is found that curvature and trajectory distributions follow a sine-shape due to the characteristic of rotational movement,which also results in a helical pattern of residual stress after leveling.Based on the results obtained,it is also observed that the rotational movement is beneficial for adding the number of bending cycle.This is the reason why there are only a few pairs of rollers on the bar leveler.展开更多
Stagnating yield and declining input use efficiency in irrigated wheat of the Indo-Gangetic Plain (IGP) coupled with diminishing availability of water for agriculture is a major concern of food security in South Asia....Stagnating yield and declining input use efficiency in irrigated wheat of the Indo-Gangetic Plain (IGP) coupled with diminishing availability of water for agriculture is a major concern of food security in South Asia. The objective of our study was to establish an understanding of how wheat yield and input use efficiency can be improved and how land leveling and crop establishment practices can be modified to be more efficient in water use through layering of precision-conservation crop management techniques. The “precision land leveling with raised bed” planting can be used to improve crop yield, water and nutrient use efficiency over the existing “traditional land leveling with flat” planting practices. We conducted a field experiment during 2002-2004 at Modipuram, India to quantify the benefits of alternate land leveling (precision land leveling) and crop establishment (furrow irrigated raised bed planting) techniques alone or in combination (layering precision-conservation) in terms of crop yield, water savings, and nutrient use efficiency of wheat production in IGP. The wheat yield was about 16.6% higher with nearly 50% less irrigation water with layering precision land leveling and raised bed planting compared to traditional practices (traditional land leveling with flat planting). The agronomic (AE) and uptake efficiency (UE) of N, P and K were significantly improved under precision land leveling with raised bed planting technique compared to other practices.展开更多
The areas used to be covered by shifting sand dunes have been reclaimed rapidly in recent years.However,it is a challenge to reclaim high sand dunes because it is rather costly to level the high dunes to gentle arable...The areas used to be covered by shifting sand dunes have been reclaimed rapidly in recent years.However,it is a challenge to reclaim high sand dunes because it is rather costly to level the high dunes to gentle arable lands.In this study,a wind guide plate was used to change the characteristics of natural wind to level the sand dunes.The use of wind energy could significantly increase the efficiency of dune leveling and decrease the cost.Low wind velocity is a typical characteristic in Ulan Buh Desert of China where the average wind speed is much lower than the threshold velocity for sand movement.The experiment of this study was conducted to accelerate the wind velocity by a wind guide plate to level a sand dune.Results show that the threshold velocity for sand movement is 3.32 m/s at 10 cm above the sand surface in Ulan Buh Desert.A wind guide plate set at an angle less than 50°could significantly increase the wind velocity.The wind velocity could be accelerated up to the threshold velocity for sand movement behind a plate when the plate is at the angles of 20°,25°,35°and 40°.The most significant acceleration of wind velocity appears at 1.5 and 3.0 m behind the plate with an angle of 25°.An obvious wind velocity acceleration zone exists behind the wind guide plate when the angles are at 25°,35°,40°and 45°,with the most obvious zone under the angle of 45°.The results also show that the total amount of sand transferred over the experimental period increased by 6.1%under the effects of wind guide plates compared to the sand moved without wind guide plates.The results of the study will provide theoretical and practical supports for desert management in sand dune areas.展开更多
基金Under the auspices of the National Key Research and Development Program of China(No.2024YFC3713102)。
文摘Groundwater level(GWL)is a key indicator used to accurately assess groundwater resources and form the foundation for ef-fective groundwater management.This paper integrates a Gate Recurrent Unit(GRU)model with a Multi-head Self-attention mechan-ism(MSAM-GRU)to simulate GWLs in both confined and unconfined aquifers simultaneously.The model innovatively captures the lag times between GWLs in the unconfined aquifer and precipitation,as well as between GWLs in the confined aquifer and the upper aquifer.We have assessed the effectiveness of the proposed model using a case study in the Beijing Plain,China from January 2005 to December 2020.With the consideration of lag times,the results indicated that the MSAM-GRU model exhibits a maximum 67%and 73%reduction in RMSE compared to the Attention mechanism-GRU(AM-GRU)and GRU model,respectively.MSAM-GRU model exhibited a 31%reduction in RMSE and a 0.12 increase in R^(2) compared to the same model that do not account for lag time.In Region I,the shortest lag time of GWL in the unconfined aquifer was two months,while that in the confined aquifer was three months,indicating a longer delayed response in the confined aquifer.MSAM-GRU model considering lag time,was then applied to simulate the GWLs in the unconfined aquifer under different scenarios and to analyze whether GWL fluctuations affect subway operations.The simulation res-ults showed that under the scenario 1,the GWL in the unconfined aquifer would rise above the depth of subway station floor,threaten-ing the operation of subways.This study can provide reliable technical support for the accurate simulation of GWLs in multi-aquifer systems.
基金jointly sup-ported by National Key Basic Research 973 project(2004CB418403)National Natural Science Foundation of China(40974062)
文摘The devastating Ms8.0 Wenchuan earthquake ruptured two large parallel thrust faults along the middle segment of the Longmenshan thrust belt. Preseismic and postseismic leveling data indicated the hanging wall of the Yingxiu-Beichuan-Nanba thrust fault mainly presented coseismic uplift with respect to the reference point at Pingwu county town, and the observed maximum uplift of 4.7 m is located at Beichuan county （Qushan town） which is about 100 m west of the fault scarp. The foot wall of the Yingxiu-Beichuan-Nanba thrust fault mainly showed subsidence with maximum subsidence of 0.6 m near the rupture. By employing a listric dislocation model, we found that the fault geometry model of exponential dip angle δ=88°×[1-exp（-9/h）] with depth of 18 km and uniform thrust-slip of 5.6 m could fit the observed coseismic vertical deformation very well, which verifies the listric thrust model of the Longmenshan orogenic zone.
基金This work was supported by the Scientific Research Project of Anhui Province Universities,China(No.YJS20210388)the National Natural Science Foundation of China(Nos.51974009,52004006,and 52004005)+2 种基金the Major Science and Technology Special Project of Anhui Province,China(No.202203a07020011)the Collaborative Innovation Project of Anhui Province Universities,China(No.GXXT-2021-075)the Huaibei City Science and Technology Major Program(No.Z2020005).
文摘Investigation of unloading rock failure under differentσ_(2)facilitates the control mechanism of excavation surrounding rock.This study focused on single-sided unloading tests of granite specimens under true triaxial conditions.The strength and failure characteristics were studied with micro-camera and acoustic emission(AE)monitoring.Furthermore,the choice of test path and the effect ofσ_(2)on fracture of unloading rock were discussed.Results show that the increasedσ_(2)can strengthen the stability of single-sided unloading rock.After unloading,the rock’s free surface underwent five phases,namely,inoculation,particle ejection,buckling rupture,stable failure,and unstable rockburst phases.Moreover,atσ_(2)≤30 MPa,the b value shows the following variation tendency:rising,dropping,significant fluctuation,and dropping,with dispersed damages signal.Atσ_(2)≥40 MPa,the tendency shows:a rise,a decrease,a slight fluctuation,and final drop,with concentrated damages signal.After unloading,AE energy is mainly concentrated in the micro-energy range.With the increasedσ_(2),the micro-energy ratio rises.In contrast,low,medium and large energy ratios drop gradually.The increased tensile fractures and decreased shear fractures indicate that the failure mode of the unloading rock gradually changes from tensile-shear mode to tensile-split one.The fractional dimension of the rock fragments first increases and then decreases with an inflection point at 20 MPa.The distribution of SIF on the planes changes asσ_(2)increases,resulting in strengthening and then weakening of the rock bearing capacity.
基金Item Sponsored by Korea Research Foundation (KRF-2004-005-D00111)
文摘Cold-rolled thin strip steel of high flatness quality undergoes multistage deformation during tension leveling. Thus, the parameters of set-up and manipulating are more difficult. With the aid of FE code MSC. MARC, the tension leveling process of thin strip steel was numerically simulated. Concentrating on the influence of the roll intermeshes in 2# anti-cambering on the distribution and magnitude of residual stresses in leveled strip steel, several experiments were clone with the tension leveler based on the results from the simulation. It was found from the simulation that the magnitude of longitudinal residual stresses in the cross-section of the leveled strip steel regularly presents obvious interdependence with the roll intermeshes in 2# anti-cambering. In addition, there is a steady zone as the longitudinal residual stresses of the surface layers in leveled strip steel vary with the roll intermeshes of 2# anticambering, which is of importance in the manipulation of tension levelers. It was also found that the distribution of strains and stresses across the width of strip steel is uneven during leveling or after removing the tension loaded upon the strip, from which it was found that 3D simulation could not be replaced by 2D analysis because 2D analysis in this case cannot represent the physical behavior of strip steel deformation during tension leveling.
基金Supported by National Hi-tech Research and Development Program of China(863 Program,Grant No.2013AA031302)National Natural Science Foundation of China(Grant No.51805024)
文摘A model based on the curvature integration method has been applied in an online plate leveling system. However, there are some shortcomings in the current leveling models. On the one hand, the models cannot deal with the leveling process of plates with a random curvature distribution. On the other hand, the current models are suitable only for stable leveling processes and ignore the biting in and tailing out stages. This study presents a new plate-leveling model based on the curvature integration method, which can describe the leveling process of plates with random curvature distribution. Further, the model is solved in two cases in order to take the biting in and tailing out stages into consideration. The proposed model is evaluated by comparing with a plate leveling experiment. Finally, the leveling process of a plate with a wave bent is studied using the proposed model. It is found that the contact angles vary greatly during the biting in and tailing out stages. However, they are relatively steady during the 5 roller leveling stage. In addition, the contact angle of roller No. 2 is the smallest, which is close to 0. Roller leveling can effectively eliminate bending in the plate, but there are regions in the head and tail of the plate, where roller leveling is not effective. The non-leveling region length is about 2 times that of the roller space. This study proposes a quasi-static plate-leveling model, which makes it possible to analyze the dynamic straightening process using a curvature integration method. It also makes it possible to analyze the straightening process of a plate with random curvature distribution.
基金Item Sponsored by National Natural Science Foundation of China(50604006,50974039)
文摘Roller leveling process of longitudinal profile （LP） plate is hardly studied because plate thickness changes. Deformation characteristics and residual curvature during LP plate leveling process were investigated based on curva ture integral by elastic plastic differences. It was found that entry intermesh section is reduced with increasing thick- ness and entry intermesh should be from 0.7 to 1.1 mm for LP plate with 42/54 mm in thickness. In order to get satisfactory flatness along longitudinal direction, small entry intermesh should be selected and exit intermesh should be 0 ram. In addition, thickness section for I.P plate which can be leveled by 11 roller leveler is from 24 to 60 mm. Finally, there is an intermesh schedule that could level LP plate with initial curvature less than elastic limit curvature.
基金Supported by National Natural Science Foundation of China(Grant Nos.51375212,61601203)Priority Academic Program Development(PAPD)of Jiangsu Higher Education Institutions of China+1 种基金Key Research and Development Program of Jiangsu Province(BE2016149)Jiangsu Provincial Natural Science Foundation of China(BK20140555)
文摘The accurate control for the vehicle height and leveling adjustment system of an electronic air suspension(EAS) still is a challenging problem that has not been effectively solved in prior researches. This paper proposes a new adaptive controller to control the vehicle height and to adjust the roll and pitch angles of the vehicle body(leveling control) during the vehicle height adjustment procedures by an EAS system. A nonlinear mechanism model of the full?car vehicle height adjustment system is established to reflect the system dynamic behaviors and to derive the system optimal control law. To deal with the nonlinear characters in the vehicle height and leveling adjustment processes, the nonlinear system model is globally linearized through the state feedback method. On this basis, a fuzzy sliding mode controller(FSMC) is designed to improve the control accuracy of the vehicle height adjustment and to reduce the peak values of the roll and pitch angles of the vehicle body. To verify the effectiveness of the proposed control method more accurately, the full?car EAS system model programmed using AMESim is also given. Then, the co?simulation study of the FSMC performance can be conducted. Finally, actual vehicle tests are performed with a city bus, and the test results illustrate that the vehicle height adjustment performance is effectively guaranteed by the FSMC, and the peak values of the roll and pitch angles of the vehicle body during the vehicle height adjustment procedures are also reduced significantly. This research proposes an effective control methodology for the vehicle height and leveling adjustment system of an EAS, which provides a favorable control performance for the system.
基金supported by the Spark Programs of Earthquake Sciences(XH14069Y)the Special Earthquake Research Project of the China Earthquake Administration(201208009)
文摘A broad view of present-day 3D deformation field around the Northeast China region was derived from GPS and leveling observations. We draw the following conclusions： First, the Northeast China region moved towards northwest with an average velocity of 5 ram/a, with respect to South China. The entire Northeast China region was in a low strain state from the strain rate field. Second, we processed two periods of first- order leveling data in 1970s and 1990s, showing the vertical deformation of the Northeast China region is ＂uplift in western part and subsidence in eastern part＇
文摘Leveler is widely used to improve the quality of defective mild steel plates.Its typical ranges of the leveling capacity are constrained by three criteria,namely the maximum stroke of rollers,allowable total leveling force and motor power.In this work,an optimization model with equality and inequality constraints was built for the maximum yield stress search of each thickness of plates.The corresponding search procedure with three loops was given.The approximate range by the simplification model could be used as the initial value for the actual range search of the leveling capacity.Therefore,the search speed could be accelerated compared with a global search.The consistency of the analytical results and field data demonstrates the reliability of the proposed model and procedure.The typical ranges of the leveling capacity are expressed by several boundary curves which are helpful to judge whether the incoming plate can be leveled quickly or not.Also,these curves can be used to find the maximum yield stress for a specific thickness or the maximum thickness for a yield stress for plates.
基金Sponsored by National Science and Technology Major Project of China(2012ZX04012011)National Natural Science Foundation of China(51375306)
文摘Waves occurring in cold-rolled plates or sheets can be divided into longitudinal and transverse waves. Classical leveling theories merely solve the problem of longitudinal waves, while no well accepted method can be employed for transverse waves. In order to investigate the essential deformation law of leveling for plates with transverse waves, a 2.5-dimensional （2.5- D） analytical approach was proposed. In this model, the plate was transversely divided into some strips with equal width; the strips are considered to be in the state of plane strain and each group of adjacent strips are assumed to be deformation compatible under stress. After calculation, the bending deformation of each strip and the leveling effect of overall plate were obtained by comprehensNe consideration of various strips along with the width. Bending of roller is a main approach to eliminate the transverse waves, which is widely accepted by the industry, but the essential effect of bending of roller on the deformation of plates and the calculation of bending of roller are unknown. According to the 2.5-D analytical model, it can be found that, for plates, it is neutral plane offsetting and middle plane elongation or contraction under inner stress that can effectively improve plate shape. Taking double side waves as an example, the appropriate values of bending of roller were obtained by the 2.5-D analytical model related to different initial unevenness, which was applicable to the current on-line adjusting of bending of roller in rolling industry.
文摘Through the analysis of the principle, error sources and precision of trigonometric leveling, this paper points out the key problems about first order leveling replaced by trigonometric leveling; and for the first time puts forward that, in some given conditions, it is not only feasible but also valuable to replace first order leveling by precise trigonometric leveling, and proves it by experimentation as well. The content and conclusion of this paper have consulting significance and practicable value for our setting down relational criterion and production practice.
基金supported by the National Natural Science Foundation of China (51535006, 51805259)Natural Science Foundation of Jiangsu Province of China (BK20180431)+2 种基金Fundamental Research Funds for the Central Universities of China (3082018NP2018406)Young Elite Scientists Sponsorship Program by CAST of ChinaJiangsu Key Laboratory of Precision and Micro-Manufacturing Technology of China
文摘The inter-electrode gap(IEG) is an essential parameter for the anode shaping process in electrochemical machining(ECM) and directly affects the machining accuracy. In this paper, the IEG during the leveling process of an oval anode workpiece in counter-rotating ECM(CRECM)is investigated. The variation of the minimum IEG is analyzed theoretically, and the results indicate that rather than reaching equilibrium, the minimum IEG in CRECM expands constantly when a constant feed speed is used for the cathode tool. This IEG expansion leads to a poor localization effect and has an adverse influence on the roundness of the machined workpiece. To maintain a small constant IEG in CRECM, a variable feed speed is used for the cathode based on a fitted equation. The theoretical results show that the minimum IEG can be controlled at a small value by using an accelerated feed speed. Experiments have been conducted using a specific experimental apparatus in which the cathode tool is designed as a combined structure of two sectors and a thin sheet. By detecting the machining currents flowing through the minimum IEG, how the latter varies is obtained indirectly. The results indicate that using an accelerated feed speed is effective for controlling the IEG, thereby improving the roundness of the machined workpiece.
基金supported by the China National Special Fund for Earthquake Scientific Research in Public Interest(201508009)
文摘The development of GPS(Global Positioning System) technology has led to increasingly widely and successful applications of GPS surveys for monitoring crustal movements. However, multi-period GPS survey solutions have not been applied in monitoring vertical crustal movements with normal backgrounds. In this paper, we carried out a comparative study on the vertical deformation of the comprehensive profile of the cross-fault zone in Shanyin, Shanxi province, China, based on GPS and precise leveling observation data for multiple time periods. The vertical deformation rates observed with repeating GPS survey are obviously different(over 20 mm/y at some sites) from those with repeating leveling survey within a relatively short period. However, the deviations in the vertical displacement between GPS and leveling in a long-term survey(over three years) showed good consistency at 3-4 mm/y at most sites, on GPS forced offset surveying and fixed survey instruments in a long-term survey(over three years). Therefore, GPS vertical displacement results can be applied to the study of vertical crustal movements.
文摘Single-sided linear induction motors(SLIMs)are widely used as traction components in maglev transportation systems.It is of great practical value to study speed sensorless control methods of SLIM.End-effect which is related to the speed of mover is considered,and the M-axis equivalent circuit of SLIM is asymmetric to T-axis.The secondary flux is chosen as the state variable,and the speed identification function is deduced.
文摘Leveling process plays an important role in delivering the desired material properties and product standards.An analytical method for the rotational leveling process of bars was presented.First,each cross section of the bar in the leveling area was discretized with the roller gap-curvature relations established in both planes XYand XZ.Second,a numerical procedure with two steps was developed to simulate both pressing and leveling processes.This approach can be easily implemented to produce simulation results of the curvature and trajectory distributions during the leveling process,as well as the bending and residual stresses.It is found that curvature and trajectory distributions follow a sine-shape due to the characteristic of rotational movement,which also results in a helical pattern of residual stress after leveling.Based on the results obtained,it is also observed that the rotational movement is beneficial for adding the number of bending cycle.This is the reason why there are only a few pairs of rollers on the bar leveler.
文摘Stagnating yield and declining input use efficiency in irrigated wheat of the Indo-Gangetic Plain (IGP) coupled with diminishing availability of water for agriculture is a major concern of food security in South Asia. The objective of our study was to establish an understanding of how wheat yield and input use efficiency can be improved and how land leveling and crop establishment practices can be modified to be more efficient in water use through layering of precision-conservation crop management techniques. The “precision land leveling with raised bed” planting can be used to improve crop yield, water and nutrient use efficiency over the existing “traditional land leveling with flat” planting practices. We conducted a field experiment during 2002-2004 at Modipuram, India to quantify the benefits of alternate land leveling (precision land leveling) and crop establishment (furrow irrigated raised bed planting) techniques alone or in combination (layering precision-conservation) in terms of crop yield, water savings, and nutrient use efficiency of wheat production in IGP. The wheat yield was about 16.6% higher with nearly 50% less irrigation water with layering precision land leveling and raised bed planting compared to traditional practices (traditional land leveling with flat planting). The agronomic (AE) and uptake efficiency (UE) of N, P and K were significantly improved under precision land leveling with raised bed planting technique compared to other practices.
基金supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China(2015BAC06B00)the Natural Science Foundation of the Inner Mongolia Autonomous Region of China(2014ZD03)
文摘The areas used to be covered by shifting sand dunes have been reclaimed rapidly in recent years.However,it is a challenge to reclaim high sand dunes because it is rather costly to level the high dunes to gentle arable lands.In this study,a wind guide plate was used to change the characteristics of natural wind to level the sand dunes.The use of wind energy could significantly increase the efficiency of dune leveling and decrease the cost.Low wind velocity is a typical characteristic in Ulan Buh Desert of China where the average wind speed is much lower than the threshold velocity for sand movement.The experiment of this study was conducted to accelerate the wind velocity by a wind guide plate to level a sand dune.Results show that the threshold velocity for sand movement is 3.32 m/s at 10 cm above the sand surface in Ulan Buh Desert.A wind guide plate set at an angle less than 50°could significantly increase the wind velocity.The wind velocity could be accelerated up to the threshold velocity for sand movement behind a plate when the plate is at the angles of 20°,25°,35°and 40°.The most significant acceleration of wind velocity appears at 1.5 and 3.0 m behind the plate with an angle of 25°.An obvious wind velocity acceleration zone exists behind the wind guide plate when the angles are at 25°,35°,40°and 45°,with the most obvious zone under the angle of 45°.The results also show that the total amount of sand transferred over the experimental period increased by 6.1%under the effects of wind guide plates compared to the sand moved without wind guide plates.The results of the study will provide theoretical and practical supports for desert management in sand dune areas.
