Aiming to improve the maneuver performance of the strapdown inertial navigation attitude coning algorithm a new coning correction structure is constructed by adding a sample to the traditional compressed coning correc...Aiming to improve the maneuver performance of the strapdown inertial navigation attitude coning algorithm a new coning correction structure is constructed by adding a sample to the traditional compressed coning correction structure. According to the given definition of classical coning motion the residual coning correction error based on the new coning correction structure is derived. On the basis of the new structure the frequency Taylor series method is used for designing a coning correction structure coefficient and then a new coning algorithm is obtained.Two types of error models are defined for the coning algorithm performance evaluation under coning environments and maneuver environments respectively.Simulation results indicate that the maneuver accuracy of the new 4-sample coning algorithm is almost double that of the traditional compressed 4-sample coning algorithm. The new coning algorithm has an improved maneuver performance while maintaining coning performance compared to the traditional compressed coning algorithm.展开更多
Traditional coning algorithms are based on the first-order coning correction reference model.Usually they reduce the algorithm error of coning axis(z)by increasing the sample numbers in one iteration interval.But the ...Traditional coning algorithms are based on the first-order coning correction reference model.Usually they reduce the algorithm error of coning axis(z)by increasing the sample numbers in one iteration interval.But the increase of sample numbers requires the faster output rates of sensors.Therefore,the algorithms are often limited in practical use.Moreover,the noncommutivity error of rotation usually exists on all three axes and the increase of sample numbers has little positive effect on reducing the algorithm errors of orthogonal axes(x,y).Considering the errors of orthogonal axes cannot be neglected in the high-precision applications,a coning algorithm with an additional second-order coning correction term is developed to further improve the performance of coning algorithm.Compared with the traditional algorithms,the new second-order coning algorithm can effectively reduce the algorithm error without increasing the sample numbers.Theoretical analyses validate that in a coning environment with low frequency,the new algorithm has the better performance than the traditional time-series and frequency-series coning algorithms,while in a maneuver environment the new algorithm has the same order accuracy as the traditional time-series and frequency-series algorithms.Finally,the practical feasibility of the new coning algorithm is demonstrated by digital simulations and practical turntable tests.展开更多
The strap-down seeker,which combines the seeker's and the onboard gyro's measurements to obtain the target information,has been extensively applied by spinning missiles.The response delay of the strap-down see...The strap-down seeker,which combines the seeker's and the onboard gyro's measurements to obtain the target information,has been extensively applied by spinning missiles.The response delay of the strap-down seeker,a novel factor that could result in crosscoupling between the acceleration commands in the pitch and yaw channels and subsequently cause the significant deterioration in dynamic stability of the spinning missile equipped with a rate loop,is noted in this paper.The sufficient and necessary stability conditions are also analytically established based on the system equation with complex coefficient,which are further verified by numerical simulations.It could be indicated that the response delay of the strap-down seeker will greatly deteriorate the dynamic stability of the whole guidance system designed by the conventional method.It is also noticed from analysis that the stable region of the combined guidance coefficient is shrunken significantly with the increase of the spinning rate.展开更多
A nonlinear mathematic model taking the nutation and precession angles as variables for the coning motion of projectile was established according to a short period moment projection of the spining projectile. By intro...A nonlinear mathematic model taking the nutation and precession angles as variables for the coning motion of projectile was established according to a short period moment projection of the spining projectile. By introducing the generalized nutation angle and precession angular speed, the model that is difficult to be resolved can be transformed to a resolvable one. The interrelationship between nutation and precession was analyzed based on the linear model, and the stability condition was obtained for the spinning projectile. For the nonlinear model, the effects of the nutation and precession on the limit circle of the projectile's coning motion were investigated, and the analytical relations between the nutation angle and the precession angular speed in the steady coning motion of the spinning projectile were given.展开更多
To compensate the coning error of Strap-down Inertial Navigation Systems (SINS) under high dynamic angular motion, many rotation vector algorithms have been developed using angle increments information. However, most ...To compensate the coning error of Strap-down Inertial Navigation Systems (SINS) under high dynamic angular motion, many rotation vector algorithms have been developed using angle increments information. However, most SINS use angular rate gyros. Aimed at this problem, 18 algorithms are derived based on analysis of the conventional algorithms, and corresponding coning error expressions are given. At last simulation is made which indicates that the new algorithms have much higher precision.展开更多
The problem of water coning into the Tarim fractured sandstone gas reservoirs becomes one of the major concerns in terms of productivity, increased operating costs and environmental effects. Water coning is a phenomen...The problem of water coning into the Tarim fractured sandstone gas reservoirs becomes one of the major concerns in terms of productivity, increased operating costs and environmental effects. Water coning is a phenomenon caused by the imbalance between gravity and viscous forces around the completion interval. There are several controllable and uncontrollable parameters influencing this problem. In order to simulate the key parameters affecting the water coning phenomenon, a model was developed to represent a single well with an underlying aquifer using the fractured sandstone gas reservoir data of the A-Well in Dina gas fields.The parametric study was performed by varying six properties individually over a representative range. The results show that matrix permeability, well penetration(especially fracture permeability), vertical-to-horizontal permeability ratio, aquifer size and gas production rate have considerable effect on water coning in the fractured gas reservoirs. Thus, investigation of the effective parameters is necessary to understand the mechanism of water coning phenomenon. Simulation of the problem helps to optimize the conditions in which the breakthrough of water coning is delayed.展开更多
To achieve the production information management of the coning,drawing and twisting's workshop,and promote a good and fast development of the textile enterprise,firstly,we analyze the information technology develo...To achieve the production information management of the coning,drawing and twisting's workshop,and promote a good and fast development of the textile enterprise,firstly,we analyze the information technology development status of the textile enterprise at home and abroad,study the weaknesses of the existing computer monitoring system,introduce the system design project,and propose a system network model based on client/server(C/S)mode.Secondly,a multi-agent production monitoring and control system is developed,and the communication of the single-port-multi-protocol and a multi-thread data collection technology are studied via the multi-thread and standard template library(STL)technologies.Thirdly,the system management functions,the structure design of the database,and the technical difficulties in the process of software design are also introduced.As proved in practice,the system satisfies the production management requirements of the workshop,and implements the network management of the production information.展开更多
Both the asymptotical stability criterion and the bounded stability criterion of the coning motion for wrap around fin(WAF) rockets are proposed through the analy-sis of coning motion equations,which can be easily use...Both the asymptotical stability criterion and the bounded stability criterion of the coning motion for wrap around fin(WAF) rockets are proposed through the analy-sis of coning motion equations,which can be easily used to determine the exis-tence of the coning motion during the rocket design. The correctness of the crite-rions is verified by mathematical simulation examples of a WAF rocket with differ-ent setting angles. It is also found that the setting angle of WAF has great effects on the rolling moment and side moment of the rocket.展开更多
In this short paper,we have treated the aerodynamic performance of micro downwind rotor with coning soft blades experimentally.The test wind rotor has the tip diameter of 1.5 m and three two-dimensional NACA0018 blade...In this short paper,we have treated the aerodynamic performance of micro downwind rotor with coning soft blades experimentally.The test wind rotor has the tip diameter of 1.5 m and three two-dimensional NACA0018 blades of 0.15 m chord whose material is light,soft and pliable foam plastic for perfect safety.From the wind tunnel test,it is realized that the performance is manageable by the coning angle of the rotor blade.In the present case,an improvement of the performance in lower wind speeds is achieved by using the coning blade of 20°.Besides,owing to the torsional deformation of very soft blade,the self-power control characteristic is observed in every test rotor regardless of coning angle in the range of 0°-20° under the wind speed less than 12 m/s.展开更多
目的探讨应用Wagner Cone生物型股骨柄假体联合转子下横行截骨治疗CroweⅣ型成人髋关节发育不良(developmental dysplasia of the hip,DDH)的临床疗效。方法回顾性分析2021年1月至2024年1月济宁医学院附属医院收治的15例(20髋)CroweⅣ型...目的探讨应用Wagner Cone生物型股骨柄假体联合转子下横行截骨治疗CroweⅣ型成人髋关节发育不良(developmental dysplasia of the hip,DDH)的临床疗效。方法回顾性分析2021年1月至2024年1月济宁医学院附属医院收治的15例(20髋)CroweⅣ型DDH患者资料,其中女13例(17髋),男2例(3髋);年龄32~67岁,平均(51.7±10.5)岁。所有患者均采用改良髋关节Hardinge入路,选择股骨小转子下横行截骨技术结合Wagner Cone生物型股骨柄假体进行人工髋关节置换。应用Harris髋关节评分评价患者临床功能恢复情况,疼痛视觉模拟评分(visual analogue scale,VAS)评估患者疼痛程度;收集手术时间、术中出血量、患者手术前后下肢长度等临床资料并进行分析比较。随访期间观察截骨处的愈合及并发症情况。结果患者均获随访7~36个月,平均(19.7±8.7)个月。手术时间72~235 min,平均(142.2±44.1)min;术中出血量为200~1800 mL。术后即刻X线片示股骨柄与髓腔均紧密压配,假体髓腔填充良好。Harris髋关节评分由术前(49.9±6.3)分提高至末次随访时的(91.1±2.7)分,手术前后比较差异有统计学意义(P<0.05);VAS评分由术前(5.1±1.0)分改善至术后(1.6±0.5)分,手术前后比较差异有统计学意义(P<0.05)。末次随访时患者双下肢不等长相差(0.4±0.3)cm,与术前(4.0±0.6)cm比较,差异有统计学意义(P<0.05)。术后截骨端不愈合患者1例,无感染、神经损伤和假体松动、下沉患者。结论Wagner Cone生物型股骨柄联合转子下横形截骨治疗CroweⅣ型髋关节发育不良,能获得满意临床疗效,术后并发症少,可有效平衡双下肢长度,减轻患者髋关节疼痛,并且能简化手术流程,值得临床推广使用。展开更多
AIM:To identify topographic determinants of the anterior chamber angle(ACA)in patients with keratoconus(KCN).METHODS:Four hundred and ten eyes of 294 patients with KCN were recruited for this study.First,complete ocul...AIM:To identify topographic determinants of the anterior chamber angle(ACA)in patients with keratoconus(KCN).METHODS:Four hundred and ten eyes of 294 patients with KCN were recruited for this study.First,complete ocular examinations were performed for all patients,including visual acuity measurement,refraction,and slit-lamp biomicroscopy.Then,all participants underwent corneal imaging by the Oculus Pentacam HR.RESULTS:The mean age of the participants was 32.40±8.52y(15-60y)and 69.5%of them were male.The mean ACA was 38.47°±5.75°(range:14.40°to 56.50°)in the whole sample,38.24°±6.00°in males,and 38.98°±5.11°in females(P=0.447).The mean ACA was significantly different among different groups of cone morphology,as patients with nipple cones showed the lowest mean ACA.Moreover,there were statistically significant differences in the mean ACA among different groups of cone locations,with patients having central cones exhibiting the lowest mean ACA(P<0.001).Anterior and posterior Q values were significantly,directly correlated with ACA(anterior Q:r=0.122,P=0.014,posterior Q:r=0.192,P<0.001).CONCLUSION:This study provides critical insights into the risk factors for ACA narrowing in KCN patients,which is essential for planning intraocular surgeries.Patients with nipple and central cones exhibited the most significant ACA narrowing.Additionally,more negative Q-values are associated with increased ACA narrowing,highlighting the need for targeted diagnostic and therapeutic strategies.展开更多
Ionic Liquid Electrospray Thrusters(ILETs)are well suited for micro-nano satellite applications due to their small size,low power consumption,and high specific impulse.However,the limited thrust of a single-emitter IL...Ionic Liquid Electrospray Thrusters(ILETs)are well suited for micro-nano satellite applications due to their small size,low power consumption,and high specific impulse.However,the limited thrust of a single-emitter ILET restricts its use in space missions.To optimize the performance of ILETs and make them suitable for a wider range of space missions,we designed a Circular-emitter ILET(CILET)to convert a one-dimensional(point)emission into a twodimensional(line)emission.The CILET can self-organize multiple Taylor cones simultaneously.The cones were photographed and the axial emission currents were measured under different voltage and pressure difference conditions with a CILET experimental system.The emission can be divided into two stable states and one unstable state based on the flow and current characteristics.The current in Stable state Ⅰ increases non-linearly with the voltage,while that in Stable state Ⅱ is nearly linear with respect to the voltage.The number of cones increases with the voltage in stable states,while the cones become short and crowded under high-voltage conditions.The variation law of the number of cones can be explained with the self-organization theory.The variation in the current exhibits a good correlation with the number of cones.This study demonstrates the feasibility of circular emitters and experimentally indicates that the emission current is improved by approximately two orders of magnitude compared to that of a single capillary.展开更多
Geotechnical parameters derived from an intrusive cone penetration test(CPT)are used to asses mechanical properties to inform the design phase of infrastructure projects.However,local,in situ 1D measurements can fail ...Geotechnical parameters derived from an intrusive cone penetration test(CPT)are used to asses mechanical properties to inform the design phase of infrastructure projects.However,local,in situ 1D measurements can fail to capture 3D subsurface variations,which could mean less than optimal design decisions for foundation engineering.By coupling the localised measurements from CPTs with more global 3D measurements derived from geophysical methods,a higher fidelity 3D overview of the subsurface can be obtained.Machine Learning(ML)may offer an effective means to capture all types of geophysical information associated with CPT data at a site scale to build a 2D or 3D ground model.In this paper,we present an ML approach to build a 3D ground model of cone resistance and sleeve friction by combining several CPT measurements with Multichannel Analysis of Surface Waves(MASW)and Electrical Resistivity Tomography(ERT)data on a land site characterisation project in the United Arab Emirates(UAE).To avoid a potential overfitting problem inherent to the use of machine learning and a lack of data at certain locations,we explore the possibility of using a prior Geo-Statistical(GS)approach that attempts to constrain the overfitting process by“artificially”increasing the amount of input data.A sensitivity study is also performed on input features used to train the ML algorithm to better define the optimal combination of input features for the prediction.Our results showed that ERT data were not useful in capturing 3D variations of geotechnical properties compared to Vs due to the geographical location of the site(200 m east from the Oman Gulf)and the possible effect of saline water intrusion.Additionally,we demonstrate that the use of a prior GS phase could be a promising and interesting means to make the prediction of ground properties more robust,especially for this specific case study described in this paper.Looking ahead,better representation of the subsurface can lead to a number of benefits for stakeholders involved in developing assets.Better ground/geotechnical models mean better site calibration of design methods and fewer design assumptions for reliability-based design,creating an opportunity for value engineering in the form of lighter construction without compromising safety,shorter construction timelines,and reduced resource requirements.展开更多
Harrat Lunayyir,a volcanic field in western Saudi Arabia,exhibits diverse geomorphological and topographical features shaped by volcanic,tectonic,and climatic processes.This study integrates field observations,remote ...Harrat Lunayyir,a volcanic field in western Saudi Arabia,exhibits diverse geomorphological and topographical features shaped by volcanic,tectonic,and climatic processes.This study integrates field observations,remote sensing,and GIS analysis to investigate the spatial distribution and relationships between volcanic landforms,lava flows,and topographical variation result obtained is a morphological classification of the cinder cones of Harrat Lunayyir,which can be sub-divided into four types:tephra rings,horseshoe-shaped volcanoes,multiple volcanoes and volcanoes without craters.All of these are monogenetic volcanoes,unlike central volcanoes(stratovolcanoes)which live for tens or hundreds of thousands of years and erupt numerous times.In Harrat Lunayyir,there is a clear dominance of arched horseshoe-shaped volcanoes(58)over ring-shaped cinder cones(10),A1_symmetric cones(circular,uniform cinder cones with a single crater)(32),A2_asymmetric cones(elongated,irregular cones and may feature one or more craters)(8),volcanoes without craters(55)and multiple volcanoes(20).The classification presented in this paper makes it possible to include all morphological types of volcanoes found in the region.This fact also renders the present classification a useful tool to apply in other,both insular and continental volcanic areas to eventually analyze and systematize the study of eruptive edifices with similar traits.Hence,this research will explore the standard physical volcanology literature so as to follow accepted definitions.展开更多
The stress wave profile at the frictional interface is crucial for investigating the frictional process.This study modeled a brittle material interface with a micro-contact to analyze the fine stress wave structure as...The stress wave profile at the frictional interface is crucial for investigating the frictional process.This study modeled a brittle material interface with a micro-contact to analyze the fine stress wave structure associated with frictional slip.Employing the finite element simulation alongside the related wave theory and experiments,two new wave structures were indentified:A Mach cone symmetric to the frictional interface associated with incident plane wave propagation,and a new plane longitudinal wave generated across the entire frictional interface at the moment when the incident wave began to propagate.The time and space of its appearance implies that the overall response of the frictional interface precedes the local wave response of the medium.Consequently,a model involving characteristic line theory and the idea of Green’s function has been proposed for its occurrence.The analysis results show that these two new wave phenomena are independent of the fracture of micro-contacts at the interface;instead,the frictional interface effect may be responsible for the generation of such new wave structures.The measured wave profiles provide a proof for the existence of the new wave structures.These results display new wave phenomena,and suggest a wave profile for investigating the dynamic mechanical properties of the frictional interface.展开更多
Currently,the cranes used at sea do not have enough flexibility,efficiency,and safety.Thus,this study proposed a floating multirobot coordinated towing system to meet the demands for offshore towing.Because of the fle...Currently,the cranes used at sea do not have enough flexibility,efficiency,and safety.Thus,this study proposed a floating multirobot coordinated towing system to meet the demands for offshore towing.Because of the flexibility of rope-driven robots,the one-way pulling characteristics of the rope,and the floating characteristics of the base,towing robots are easily overturned.First,the spatial configuration of the towing system was established according to the towing task,and the kinematic model of the towing system was established using the coordinate transformation.Then,the dynamic model of the towing system was established according to the rigid-body dynamics and hydrodynamic theory.Finally,the stability of the towing system was analyzed using the stability cone method.The simulation experiments provide a reference for the practical application of the floating multirobot coordinated towing system,which can improve the stability of towing systems by changing the configuration of the towing robot.展开更多
We explore some necessary and sufficient conditions for the boundedness of the Forelli-Rudin type operator T on the weighted Lebesgue space associated with tubular domains over the forward light cone.Our approach invo...We explore some necessary and sufficient conditions for the boundedness of the Forelli-Rudin type operator T on the weighted Lebesgue space associated with tubular domains over the forward light cone.Our approach involves conducting precise computations for a series of complex integrals to identify appropriate test functions,and through a detailed analysis of these test functions,we derive the boundedness properties of the operator T.This work is significant in the study of the Bergman projection operators.展开更多
In hilly regions,the existence of surface cracks in rock mass induces a potential threat to structural stability.Thus,the present research aims to explore the impact of surface cracks on the loadbearing capacity of st...In hilly regions,the existence of surface cracks in rock mass induces a potential threat to structural stability.Thus,the present research aims to explore the impact of surface cracks on the loadbearing capacity of strip footing placed on the rock mass.By taking into account the various boundary constraints across the surface of crack edges,the study investigates the presence of two categories of surface cracks,namely(1)separated crack,and(2)fine crack.The lower bound limit analysis is employed in conjunction with the finite element method(LBFELA)to conduct the numerical analysis.In order to evaluate rock mass yielding,the power conic programming(PCP)method is utilized to implement the generalized Hoek-Brown(GHB)failure criterion.The stability of the strip footing is analyzed by determining the bearing capacity factor(Nσγ),which is presented in the form of design charts by varying the strength parameters of rock,including the Geological Strength Index(GSI),Hoek-Brown material parameter(mi),Disturbance factor(D),and Normalised Uniaxial Compressive Strength(σci/γB),whereγis the unit weight of rock mass,and B is the width of strip footing.The study also investigates the impact of cracks on strip footings,considering different positions of the crack(LC)and depths of the crack(DC).The results demonstrate that the influence of the fine crack is only noticeable until the LC/B ratio reaches 6.However,for the separated crack,its impact remains significant even when the LC/B ratio exceeds 16.The appearance of fine crack at the edge of the footing results in a decrease in the magnitude Nσγof up to 45%,indicating a substantial reduction in the stability of the footing.The failure patterns are presented and discussed in detail for various cases in this study to examine the effect of surface cracks on the strip footing and to address the extent of the plastic collapse.展开更多
Oral and maxillofacial diagnostic imaging is of paramount importance in dental clinical diagnosis,treatment planning,and follow-up procedures.Periapical ra-diographic examination and numerous panoramic systems are use...Oral and maxillofacial diagnostic imaging is of paramount importance in dental clinical diagnosis,treatment planning,and follow-up procedures.Periapical ra-diographic examination and numerous panoramic systems are used in routine clinical dental practice.Cone beam CT is widely used and currently the method of choice in oral and maxillofacial implantology,endodontics,maxillofacial surgery,periodontics,degenerative temporomandibular joint disease,orthodontics,airway studies,sleep disorders,and forensic dentistry.Another innovative laboratory re-search tool that offers three-dimensional(3D)detailed high-resolution images of in vitro teeth and neighboring structures with submicrometric accuracy is micro-computed tomography.Ultra-high radiation doses,long scanning times,and high costs preclude its routine clinical use.In response to the high demand for a te-chnique that could provide real-time images using a cost-effective,rapid,user-friendly,and portable technique without ionizing radiation,some authors pro-posed ultrasound imaging methods as an alternative to X-ray imaging techniques.Ultrasonography can be used in the dentomaxillofacial region for various diagno-stic purposes such as salivary gland and superficial tissue examination.Recently,dedicated dental magnetic resonance imaging with appropriate software,hard-ware,sequences,and field of view tailored to fit dentomaxillofacial anatomy was introduced.Lately,3D printing technologies and their application in dentistry has attracted attention.During 3D printing a given material is added in successive layers to create a 3D object.The application of this technology has the potential to decrease operation time and minimize operator bias and the possibility of proce-dural errors.Another hot topic regarding dentomaxillofacial radiology is artificial intelligence,which is a field related to computer science dedicated to developing systems or machines that can perform tasks traditionally associated with human intelligence.It is obvious that further investigation and research in the field of dentomaxillofacial radiology will make great contributions to diagnostic imaging for various dental specialties.展开更多
The hydrogen-enriched direct reduction shaft furnace addresses the high CO_(2) emissions associated with the blast furnace process.A discrete element method(DEM)model was introduced to explore how the structure of the...The hydrogen-enriched direct reduction shaft furnace addresses the high CO_(2) emissions associated with the blast furnace process.A discrete element method(DEM)model was introduced to explore how the structure of the diversion cone affects particle descent behavior in a hydrogen-enriched shaft furnace.The results indicated that in the absence of a diversion cone,the descending velocity near the furnace wall zone is significantly lower than that at its center,resulting in a‘V’-shaped burden flow pattern.The discharge velocity has a minor impact on the flow pattern in the shaft furnace.Upon installation of a diversion cone,burden descending velocity becomes more uniform,leading to a‘-’-shaped burden flow pattern.As the bottom of the diversion cone ascends(i.e.,the lower end of the diversion cone is progressively closer to the top),there is an increase in the volume fraction of the dead zone within the shaft furnace.This is particularly evident in the formation of a triangular dead zone at the base of the diversion cone.It is suggested that the lower cone of the bi-conical diversion cone should maintain a sufficient height.展开更多
基金The National Natural Science Foundation of China(No.51375087)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20110092110039)+2 种基金the Public Science and Technology Research Funds Projects of Ocean(No.201205035)the Scientific Innovation Research of College Graduates in Jiangsu Province(No.CXZZ12_0097)the Scientific Research Foundation of Graduate School of Southeast University(No.YBJJ1349)
文摘Aiming to improve the maneuver performance of the strapdown inertial navigation attitude coning algorithm a new coning correction structure is constructed by adding a sample to the traditional compressed coning correction structure. According to the given definition of classical coning motion the residual coning correction error based on the new coning correction structure is derived. On the basis of the new structure the frequency Taylor series method is used for designing a coning correction structure coefficient and then a new coning algorithm is obtained.Two types of error models are defined for the coning algorithm performance evaluation under coning environments and maneuver environments respectively.Simulation results indicate that the maneuver accuracy of the new 4-sample coning algorithm is almost double that of the traditional compressed 4-sample coning algorithm. The new coning algorithm has an improved maneuver performance while maintaining coning performance compared to the traditional compressed coning algorithm.
基金Supported by the National Natural Science Foundation of China(61104188,91016019)the National Basic Research Program of China(2009CB724002)the Research Funding of Nanjing University of Aeronautics and Astronautics(NS2010084,NP2011049)
文摘Traditional coning algorithms are based on the first-order coning correction reference model.Usually they reduce the algorithm error of coning axis(z)by increasing the sample numbers in one iteration interval.But the increase of sample numbers requires the faster output rates of sensors.Therefore,the algorithms are often limited in practical use.Moreover,the noncommutivity error of rotation usually exists on all three axes and the increase of sample numbers has little positive effect on reducing the algorithm errors of orthogonal axes(x,y).Considering the errors of orthogonal axes cannot be neglected in the high-precision applications,a coning algorithm with an additional second-order coning correction term is developed to further improve the performance of coning algorithm.Compared with the traditional algorithms,the new second-order coning algorithm can effectively reduce the algorithm error without increasing the sample numbers.Theoretical analyses validate that in a coning environment with low frequency,the new algorithm has the better performance than the traditional time-series and frequency-series coning algorithms,while in a maneuver environment the new algorithm has the same order accuracy as the traditional time-series and frequency-series algorithms.Finally,the practical feasibility of the new coning algorithm is demonstrated by digital simulations and practical turntable tests.
基金the financial support from National Science Foundation of China(No.11532002)。
文摘The strap-down seeker,which combines the seeker's and the onboard gyro's measurements to obtain the target information,has been extensively applied by spinning missiles.The response delay of the strap-down seeker,a novel factor that could result in crosscoupling between the acceleration commands in the pitch and yaw channels and subsequently cause the significant deterioration in dynamic stability of the spinning missile equipped with a rate loop,is noted in this paper.The sufficient and necessary stability conditions are also analytically established based on the system equation with complex coefficient,which are further verified by numerical simulations.It could be indicated that the response delay of the strap-down seeker will greatly deteriorate the dynamic stability of the whole guidance system designed by the conventional method.It is also noticed from analysis that the stable region of the combined guidance coefficient is shrunken significantly with the increase of the spinning rate.
基金Sponsored by the National Science Foundation of China (10972034)
文摘A nonlinear mathematic model taking the nutation and precession angles as variables for the coning motion of projectile was established according to a short period moment projection of the spining projectile. By introducing the generalized nutation angle and precession angular speed, the model that is difficult to be resolved can be transformed to a resolvable one. The interrelationship between nutation and precession was analyzed based on the linear model, and the stability condition was obtained for the spinning projectile. For the nonlinear model, the effects of the nutation and precession on the limit circle of the projectile's coning motion were investigated, and the analytical relations between the nutation angle and the precession angular speed in the steady coning motion of the spinning projectile were given.
文摘To compensate the coning error of Strap-down Inertial Navigation Systems (SINS) under high dynamic angular motion, many rotation vector algorithms have been developed using angle increments information. However, most SINS use angular rate gyros. Aimed at this problem, 18 algorithms are derived based on analysis of the conventional algorithms, and corresponding coning error expressions are given. At last simulation is made which indicates that the new algorithms have much higher precision.
基金Project(50150503-12)supported by National Science and Technology Major Program of the Ministry of Science and Technology of ChinaProject(2010E-2103)supported by Research on Key Technology in Tarim Oilfield Exploration and Development,China
文摘The problem of water coning into the Tarim fractured sandstone gas reservoirs becomes one of the major concerns in terms of productivity, increased operating costs and environmental effects. Water coning is a phenomenon caused by the imbalance between gravity and viscous forces around the completion interval. There are several controllable and uncontrollable parameters influencing this problem. In order to simulate the key parameters affecting the water coning phenomenon, a model was developed to represent a single well with an underlying aquifer using the fractured sandstone gas reservoir data of the A-Well in Dina gas fields.The parametric study was performed by varying six properties individually over a representative range. The results show that matrix permeability, well penetration(especially fracture permeability), vertical-to-horizontal permeability ratio, aquifer size and gas production rate have considerable effect on water coning in the fractured gas reservoirs. Thus, investigation of the effective parameters is necessary to understand the mechanism of water coning phenomenon. Simulation of the problem helps to optimize the conditions in which the breakthrough of water coning is delayed.
文摘To achieve the production information management of the coning,drawing and twisting's workshop,and promote a good and fast development of the textile enterprise,firstly,we analyze the information technology development status of the textile enterprise at home and abroad,study the weaknesses of the existing computer monitoring system,introduce the system design project,and propose a system network model based on client/server(C/S)mode.Secondly,a multi-agent production monitoring and control system is developed,and the communication of the single-port-multi-protocol and a multi-thread data collection technology are studied via the multi-thread and standard template library(STL)technologies.Thirdly,the system management functions,the structure design of the database,and the technical difficulties in the process of software design are also introduced.As proved in practice,the system satisfies the production management requirements of the workshop,and implements the network management of the production information.
文摘Both the asymptotical stability criterion and the bounded stability criterion of the coning motion for wrap around fin(WAF) rockets are proposed through the analy-sis of coning motion equations,which can be easily used to determine the exis-tence of the coning motion during the rocket design. The correctness of the crite-rions is verified by mathematical simulation examples of a WAF rocket with differ-ent setting angles. It is also found that the setting angle of WAF has great effects on the rolling moment and side moment of the rocket.
文摘In this short paper,we have treated the aerodynamic performance of micro downwind rotor with coning soft blades experimentally.The test wind rotor has the tip diameter of 1.5 m and three two-dimensional NACA0018 blades of 0.15 m chord whose material is light,soft and pliable foam plastic for perfect safety.From the wind tunnel test,it is realized that the performance is manageable by the coning angle of the rotor blade.In the present case,an improvement of the performance in lower wind speeds is achieved by using the coning blade of 20°.Besides,owing to the torsional deformation of very soft blade,the self-power control characteristic is observed in every test rotor regardless of coning angle in the range of 0°-20° under the wind speed less than 12 m/s.
基金Supported by Iranian University of Medical Sciences(code:IR.IUMS.REC.1401.371).
文摘AIM:To identify topographic determinants of the anterior chamber angle(ACA)in patients with keratoconus(KCN).METHODS:Four hundred and ten eyes of 294 patients with KCN were recruited for this study.First,complete ocular examinations were performed for all patients,including visual acuity measurement,refraction,and slit-lamp biomicroscopy.Then,all participants underwent corneal imaging by the Oculus Pentacam HR.RESULTS:The mean age of the participants was 32.40±8.52y(15-60y)and 69.5%of them were male.The mean ACA was 38.47°±5.75°(range:14.40°to 56.50°)in the whole sample,38.24°±6.00°in males,and 38.98°±5.11°in females(P=0.447).The mean ACA was significantly different among different groups of cone morphology,as patients with nipple cones showed the lowest mean ACA.Moreover,there were statistically significant differences in the mean ACA among different groups of cone locations,with patients having central cones exhibiting the lowest mean ACA(P<0.001).Anterior and posterior Q values were significantly,directly correlated with ACA(anterior Q:r=0.122,P=0.014,posterior Q:r=0.192,P<0.001).CONCLUSION:This study provides critical insights into the risk factors for ACA narrowing in KCN patients,which is essential for planning intraocular surgeries.Patients with nipple and central cones exhibited the most significant ACA narrowing.Additionally,more negative Q-values are associated with increased ACA narrowing,highlighting the need for targeted diagnostic and therapeutic strategies.
基金co-supported by the National Key R&D Program of China(No.2020YFC2201001)the Shenzhen Science and Technology Program,China(No.20210623091808026)。
文摘Ionic Liquid Electrospray Thrusters(ILETs)are well suited for micro-nano satellite applications due to their small size,low power consumption,and high specific impulse.However,the limited thrust of a single-emitter ILET restricts its use in space missions.To optimize the performance of ILETs and make them suitable for a wider range of space missions,we designed a Circular-emitter ILET(CILET)to convert a one-dimensional(point)emission into a twodimensional(line)emission.The CILET can self-organize multiple Taylor cones simultaneously.The cones were photographed and the axial emission currents were measured under different voltage and pressure difference conditions with a CILET experimental system.The emission can be divided into two stable states and one unstable state based on the flow and current characteristics.The current in Stable state Ⅰ increases non-linearly with the voltage,while that in Stable state Ⅱ is nearly linear with respect to the voltage.The number of cones increases with the voltage in stable states,while the cones become short and crowded under high-voltage conditions.The variation law of the number of cones can be explained with the self-organization theory.The variation in the current exhibits a good correlation with the number of cones.This study demonstrates the feasibility of circular emitters and experimentally indicates that the emission current is improved by approximately two orders of magnitude compared to that of a single capillary.
文摘Geotechnical parameters derived from an intrusive cone penetration test(CPT)are used to asses mechanical properties to inform the design phase of infrastructure projects.However,local,in situ 1D measurements can fail to capture 3D subsurface variations,which could mean less than optimal design decisions for foundation engineering.By coupling the localised measurements from CPTs with more global 3D measurements derived from geophysical methods,a higher fidelity 3D overview of the subsurface can be obtained.Machine Learning(ML)may offer an effective means to capture all types of geophysical information associated with CPT data at a site scale to build a 2D or 3D ground model.In this paper,we present an ML approach to build a 3D ground model of cone resistance and sleeve friction by combining several CPT measurements with Multichannel Analysis of Surface Waves(MASW)and Electrical Resistivity Tomography(ERT)data on a land site characterisation project in the United Arab Emirates(UAE).To avoid a potential overfitting problem inherent to the use of machine learning and a lack of data at certain locations,we explore the possibility of using a prior Geo-Statistical(GS)approach that attempts to constrain the overfitting process by“artificially”increasing the amount of input data.A sensitivity study is also performed on input features used to train the ML algorithm to better define the optimal combination of input features for the prediction.Our results showed that ERT data were not useful in capturing 3D variations of geotechnical properties compared to Vs due to the geographical location of the site(200 m east from the Oman Gulf)and the possible effect of saline water intrusion.Additionally,we demonstrate that the use of a prior GS phase could be a promising and interesting means to make the prediction of ground properties more robust,especially for this specific case study described in this paper.Looking ahead,better representation of the subsurface can lead to a number of benefits for stakeholders involved in developing assets.Better ground/geotechnical models mean better site calibration of design methods and fewer design assumptions for reliability-based design,creating an opportunity for value engineering in the form of lighter construction without compromising safety,shorter construction timelines,and reduced resource requirements.
文摘Harrat Lunayyir,a volcanic field in western Saudi Arabia,exhibits diverse geomorphological and topographical features shaped by volcanic,tectonic,and climatic processes.This study integrates field observations,remote sensing,and GIS analysis to investigate the spatial distribution and relationships between volcanic landforms,lava flows,and topographical variation result obtained is a morphological classification of the cinder cones of Harrat Lunayyir,which can be sub-divided into four types:tephra rings,horseshoe-shaped volcanoes,multiple volcanoes and volcanoes without craters.All of these are monogenetic volcanoes,unlike central volcanoes(stratovolcanoes)which live for tens or hundreds of thousands of years and erupt numerous times.In Harrat Lunayyir,there is a clear dominance of arched horseshoe-shaped volcanoes(58)over ring-shaped cinder cones(10),A1_symmetric cones(circular,uniform cinder cones with a single crater)(32),A2_asymmetric cones(elongated,irregular cones and may feature one or more craters)(8),volcanoes without craters(55)and multiple volcanoes(20).The classification presented in this paper makes it possible to include all morphological types of volcanoes found in the region.This fact also renders the present classification a useful tool to apply in other,both insular and continental volcanic areas to eventually analyze and systematize the study of eruptive edifices with similar traits.Hence,this research will explore the standard physical volcanology literature so as to follow accepted definitions.
基金supported by the National Natural Science Foundation of China(Grant No.12272127)the Construction Project of Double First Class in Safety Discipline of the Universities of Henan Province(Grant No.AQ20230751).
文摘The stress wave profile at the frictional interface is crucial for investigating the frictional process.This study modeled a brittle material interface with a micro-contact to analyze the fine stress wave structure associated with frictional slip.Employing the finite element simulation alongside the related wave theory and experiments,two new wave structures were indentified:A Mach cone symmetric to the frictional interface associated with incident plane wave propagation,and a new plane longitudinal wave generated across the entire frictional interface at the moment when the incident wave began to propagate.The time and space of its appearance implies that the overall response of the frictional interface precedes the local wave response of the medium.Consequently,a model involving characteristic line theory and the idea of Green’s function has been proposed for its occurrence.The analysis results show that these two new wave phenomena are independent of the fracture of micro-contacts at the interface;instead,the frictional interface effect may be responsible for the generation of such new wave structures.The measured wave profiles provide a proof for the existence of the new wave structures.These results display new wave phenomena,and suggest a wave profile for investigating the dynamic mechanical properties of the frictional interface.
基金Supported by the National Natural Science Foundation of China under Grant No.51965032the Natural Science Foundation of Gansu Province of China under Grant No.22JR5RA319+2 种基金the Excellent Doctoral Student Foundation of Gansu Province of China under Grant No.23JRRA842the Sichuan Province Engineering Technology Research Center of General Aircraft Maintenance under Grant No.GAMRC2023YB05the Key Research and Development Project of Lanzhou Jiaotong University under Grant No.LZJTUZDYF2302.
文摘Currently,the cranes used at sea do not have enough flexibility,efficiency,and safety.Thus,this study proposed a floating multirobot coordinated towing system to meet the demands for offshore towing.Because of the flexibility of rope-driven robots,the one-way pulling characteristics of the rope,and the floating characteristics of the base,towing robots are easily overturned.First,the spatial configuration of the towing system was established according to the towing task,and the kinematic model of the towing system was established using the coordinate transformation.Then,the dynamic model of the towing system was established according to the rigid-body dynamics and hydrodynamic theory.Finally,the stability of the towing system was analyzed using the stability cone method.The simulation experiments provide a reference for the practical application of the floating multirobot coordinated towing system,which can improve the stability of towing systems by changing the configuration of the towing robot.
基金Liu’s research was supported by the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(31610030)Deng’s research was supported by the NSFC(11971042,12071035)the National Key R&D Program of China(2021YFA1002600).
文摘We explore some necessary and sufficient conditions for the boundedness of the Forelli-Rudin type operator T on the weighted Lebesgue space associated with tubular domains over the forward light cone.Our approach involves conducting precise computations for a series of complex integrals to identify appropriate test functions,and through a detailed analysis of these test functions,we derive the boundedness properties of the operator T.This work is significant in the study of the Bergman projection operators.
基金supported by the Centre for Development of Advanced Computing (CDAC), Pune
文摘In hilly regions,the existence of surface cracks in rock mass induces a potential threat to structural stability.Thus,the present research aims to explore the impact of surface cracks on the loadbearing capacity of strip footing placed on the rock mass.By taking into account the various boundary constraints across the surface of crack edges,the study investigates the presence of two categories of surface cracks,namely(1)separated crack,and(2)fine crack.The lower bound limit analysis is employed in conjunction with the finite element method(LBFELA)to conduct the numerical analysis.In order to evaluate rock mass yielding,the power conic programming(PCP)method is utilized to implement the generalized Hoek-Brown(GHB)failure criterion.The stability of the strip footing is analyzed by determining the bearing capacity factor(Nσγ),which is presented in the form of design charts by varying the strength parameters of rock,including the Geological Strength Index(GSI),Hoek-Brown material parameter(mi),Disturbance factor(D),and Normalised Uniaxial Compressive Strength(σci/γB),whereγis the unit weight of rock mass,and B is the width of strip footing.The study also investigates the impact of cracks on strip footings,considering different positions of the crack(LC)and depths of the crack(DC).The results demonstrate that the influence of the fine crack is only noticeable until the LC/B ratio reaches 6.However,for the separated crack,its impact remains significant even when the LC/B ratio exceeds 16.The appearance of fine crack at the edge of the footing results in a decrease in the magnitude Nσγof up to 45%,indicating a substantial reduction in the stability of the footing.The failure patterns are presented and discussed in detail for various cases in this study to examine the effect of surface cracks on the strip footing and to address the extent of the plastic collapse.
文摘Oral and maxillofacial diagnostic imaging is of paramount importance in dental clinical diagnosis,treatment planning,and follow-up procedures.Periapical ra-diographic examination and numerous panoramic systems are used in routine clinical dental practice.Cone beam CT is widely used and currently the method of choice in oral and maxillofacial implantology,endodontics,maxillofacial surgery,periodontics,degenerative temporomandibular joint disease,orthodontics,airway studies,sleep disorders,and forensic dentistry.Another innovative laboratory re-search tool that offers three-dimensional(3D)detailed high-resolution images of in vitro teeth and neighboring structures with submicrometric accuracy is micro-computed tomography.Ultra-high radiation doses,long scanning times,and high costs preclude its routine clinical use.In response to the high demand for a te-chnique that could provide real-time images using a cost-effective,rapid,user-friendly,and portable technique without ionizing radiation,some authors pro-posed ultrasound imaging methods as an alternative to X-ray imaging techniques.Ultrasonography can be used in the dentomaxillofacial region for various diagno-stic purposes such as salivary gland and superficial tissue examination.Recently,dedicated dental magnetic resonance imaging with appropriate software,hard-ware,sequences,and field of view tailored to fit dentomaxillofacial anatomy was introduced.Lately,3D printing technologies and their application in dentistry has attracted attention.During 3D printing a given material is added in successive layers to create a 3D object.The application of this technology has the potential to decrease operation time and minimize operator bias and the possibility of proce-dural errors.Another hot topic regarding dentomaxillofacial radiology is artificial intelligence,which is a field related to computer science dedicated to developing systems or machines that can perform tasks traditionally associated with human intelligence.It is obvious that further investigation and research in the field of dentomaxillofacial radiology will make great contributions to diagnostic imaging for various dental specialties.
基金the National Key R&D Program of China(Nos.2021YFC2902400 and 2021YFC2902401)the project of State Key Laboratory of Intelligent Optimized Manufacturing in Mining&Metallurgy Process(No.BGRIMM-KZSKL-2023-14).
文摘The hydrogen-enriched direct reduction shaft furnace addresses the high CO_(2) emissions associated with the blast furnace process.A discrete element method(DEM)model was introduced to explore how the structure of the diversion cone affects particle descent behavior in a hydrogen-enriched shaft furnace.The results indicated that in the absence of a diversion cone,the descending velocity near the furnace wall zone is significantly lower than that at its center,resulting in a‘V’-shaped burden flow pattern.The discharge velocity has a minor impact on the flow pattern in the shaft furnace.Upon installation of a diversion cone,burden descending velocity becomes more uniform,leading to a‘-’-shaped burden flow pattern.As the bottom of the diversion cone ascends(i.e.,the lower end of the diversion cone is progressively closer to the top),there is an increase in the volume fraction of the dead zone within the shaft furnace.This is particularly evident in the formation of a triangular dead zone at the base of the diversion cone.It is suggested that the lower cone of the bi-conical diversion cone should maintain a sufficient height.
