Transactions of Nanjing University of Aeronautics & Astronautics
Volume 38,Issue 3,2021 Table of Contents
2021, 38(3):361-372.
DOI: 10.16356/j.1005-1120.2021.03.001
Abstract:
An adaptive control scheme is presented， which can simultaneously realize vibration suppression and compliance control for flexible joint robot （FJR）. The proposed control scheme provides a unified formulation for both vibration suppression mode， where FJR tracks the desired position with little vibration， and compliance mode， in which FJR presents passive. Instead of designing multiple controllers and switching between them， both modes are integrated into a single controller， and the transition between two modes is smooth and stable. The stability of the closed-loop system is theoretically proven via the Lyapunov method， with the considering the dynamics uncertainties in both link side and motor side. Simulation results are presented to illustrate good performances of the proposed control scheme.
An adaptive control scheme is presented， which can simultaneously realize vibration suppression and compliance control for flexible joint robot （FJR）. The proposed control scheme provides a unified formulation for both vibration suppression mode， where FJR tracks the desired position with little vibration， and compliance mode， in which FJR presents passive. Instead of designing multiple controllers and switching between them， both modes are integrated into a single controller， and the transition between two modes is smooth and stable. The stability of the closed-loop system is theoretically proven via the Lyapunov method， with the considering the dynamics uncertainties in both link side and motor side. Simulation results are presented to illustrate good performances of the proposed control scheme.
2021, 38(3):373-382.
DOI: 10.16356/j.1005-1120.2021.03.002
Abstract:
Hydraulic valve block is an important part of the hydraulic system. The traditional hydraulic valve block is made by turning and milling， drilling and boring， which leads to many right-angle bending and closed cavity structure of process holes in its internal flow channel， seriously affecting the flow performance of oil. Based on the new design space provided by additive manufacturing technology， the internal hydraulic flow channel of valve block is optimized by using B-spline curve. Computational fluid dynamics analysis is carried out on the hydraulic flow channel to determine the optimal flow channel structure with the smallest pressure drop. The weight reduction of hydraulic valve block is carried out through topology optimization. According to the results of topology optimization， using the method of selective laser melting （SLM）， the printing of the hydraulic valve block is completed. The optimized hydraulic channel reduces the pressure loss by 31.4% compared with the traditional hydraulic channel. Compared with the traditional valve block， the hydraulic valve block manufactured by SLM with topology optimization reduces the weight by 33.9%. Therefore， the proposed flow channel optimization and valve block lightweight method provide a new reference for the performance improvement of the internal flow channel of hydraulic valve block and the overall lightweight design of valve block.
Hydraulic valve block is an important part of the hydraulic system. The traditional hydraulic valve block is made by turning and milling， drilling and boring， which leads to many right-angle bending and closed cavity structure of process holes in its internal flow channel， seriously affecting the flow performance of oil. Based on the new design space provided by additive manufacturing technology， the internal hydraulic flow channel of valve block is optimized by using B-spline curve. Computational fluid dynamics analysis is carried out on the hydraulic flow channel to determine the optimal flow channel structure with the smallest pressure drop. The weight reduction of hydraulic valve block is carried out through topology optimization. According to the results of topology optimization， using the method of selective laser melting （SLM）， the printing of the hydraulic valve block is completed. The optimized hydraulic channel reduces the pressure loss by 31.4% compared with the traditional hydraulic channel. Compared with the traditional valve block， the hydraulic valve block manufactured by SLM with topology optimization reduces the weight by 33.9%. Therefore， the proposed flow channel optimization and valve block lightweight method provide a new reference for the performance improvement of the internal flow channel of hydraulic valve block and the overall lightweight design of valve block.
2021, 38(3):383-392.
DOI: 10.16356/j.1005-1120.2021.03.003
Abstract:
With the rapid development of the machining and manufacturing industry， welding has been widely used in forming connections of structural parts. At present， manual methods are often used for welding and quality inspection， with low efficiency and unstable product quality. Due to the requirements of visual inspection of weld feature size， a visual inspection system for weld feature size based on line structured light （LSL） is designed and built in this paper. An adaptive light stripe sub-pixel center extraction algorithm and a feature point extraction algorithm for welding light stripe are proposed. The experiment results show that the detection error of the weld width is 0.216 mm， the detection error of the remaining height is 0.035 mm， the single measurement costs 109 ms， and the inspection stability and repeatability of the system is 1%. Our approach can meet the online detection requirements of practical applications.
With the rapid development of the machining and manufacturing industry， welding has been widely used in forming connections of structural parts. At present， manual methods are often used for welding and quality inspection， with low efficiency and unstable product quality. Due to the requirements of visual inspection of weld feature size， a visual inspection system for weld feature size based on line structured light （LSL） is designed and built in this paper. An adaptive light stripe sub-pixel center extraction algorithm and a feature point extraction algorithm for welding light stripe are proposed. The experiment results show that the detection error of the weld width is 0.216 mm， the detection error of the remaining height is 0.035 mm， the single measurement costs 109 ms， and the inspection stability and repeatability of the system is 1%. Our approach can meet the online detection requirements of practical applications.
2021, 38(3):393-403.
DOI: 10.16356/j.1005-1120.2021.03.004
Abstract:
Aiming at the shortcomings of traditional contact measurement methods such as low measurement efficiency， high cost and low accuracy， a non-contact optical measurement method based on the laser displacement sensor is proposed. According to the relevant regulations of the coaxiality error evaluation standard and the structural characteristics of the compound gear shaft， we have designed and built a set of supporting software system as well as a hardware test platform. In this paper， the distance difference threshold and scale threshold methods are used to eliminate outlier data. The least squares circle is selected to calculate the center of the circle and the minimum containment cylinder axis method is used as the reference axis of the composite gear shaft. Compensated by the standard step shaft calibration， the coaxiality error of the composite gear shaft can be measured to be within 0.01 mm in less than two minutes. The range value of the multi-section measurement test is 0.065 mm. The average coaxiality error is? 0.476 m m ![]()
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Aiming at the shortcomings of traditional contact measurement methods such as low measurement efficiency， high cost and low accuracy， a non-contact optical measurement method based on the laser displacement sensor is proposed. According to the relevant regulations of the coaxiality error evaluation standard and the structural characteristics of the compound gear shaft， we have designed and built a set of supporting software system as well as a hardware test platform. In this paper， the distance difference threshold and scale threshold methods are used to eliminate outlier data. The least squares circle is selected to calculate the center of the circle and the minimum containment cylinder axis method is used as the reference axis of the composite gear shaft. Compensated by the standard step shaft calibration， the coaxiality error of the composite gear shaft can be measured to be within 0.01 mm in less than two minutes. The range value of the multi-section measurement test is 0.065 mm. The average coaxiality error is
2021, 38(3):404-414.
DOI: 10.16356/j.1005-1120.2021.03.005
Abstract:
Existing curve fitting algorithms of NC machining path mainly focus on the control of fitting error， but ignore the problem that the original discrete cutter position points are not enough in the high curvature area of the tool path. It may cause a sudden change in the drive force of the feed axis， resulting in a large fluctuation in the feed speed. This paper proposes a new non-uniform rational B-spline （NURBS） curve fitting optimization method based on curvature smoothing preset point constraints. First， the short line segments generated by the CAM software are optimally divided into different segment regions， and then the curvature of the short line segments in each region is adjusted to make it smoother. Secondly， a set of characteristic points reflecting the change of the curvature of the fitted curve is constructed as the control apex of the fitted curve， and the curve is fitted using the NURBS curve fitting optimization method based on the curvature smoothing preset point constraint. Finally， the curve fitting error and curve volatility are analyzed with an example， which verifies that the method can significantly improve the curvature smoothness of the high-curvature tool path， reduce the fitting error， and improve the feed speed.
Existing curve fitting algorithms of NC machining path mainly focus on the control of fitting error， but ignore the problem that the original discrete cutter position points are not enough in the high curvature area of the tool path. It may cause a sudden change in the drive force of the feed axis， resulting in a large fluctuation in the feed speed. This paper proposes a new non-uniform rational B-spline （NURBS） curve fitting optimization method based on curvature smoothing preset point constraints. First， the short line segments generated by the CAM software are optimally divided into different segment regions， and then the curvature of the short line segments in each region is adjusted to make it smoother. Secondly， a set of characteristic points reflecting the change of the curvature of the fitted curve is constructed as the control apex of the fitted curve， and the curve is fitted using the NURBS curve fitting optimization method based on the curvature smoothing preset point constraint. Finally， the curve fitting error and curve volatility are analyzed with an example， which verifies that the method can significantly improve the curvature smoothness of the high-curvature tool path， reduce the fitting error， and improve the feed speed.
2021, 38(3):415-426.
DOI: 10.16356/j.1005-1120.2021.03.006
Abstract:
The flexible job-shop scheduling problem（FJSP） with combined processing constraints is a common scheduling problem in mixed-flow production lines. However， traditional methods for classic FJSP cannot be directly applied. Targeting this problem， the process state model of a mixed-flow production line is analyzed. On this basis， a mathematical model of a mixed-flow job-shop scheduling problem with combined processing constraints is established based on the traditional FJSP. Then， an improved genetic algorithm with multi-segment encoding， crossover， and mutation is proposed for the mixed-flow production line problem. Finally， the proposed algorithm is applied to the production workshop of missile structural components at an aerospace institute to verify its feasibility and effectiveness.
The flexible job-shop scheduling problem（FJSP） with combined processing constraints is a common scheduling problem in mixed-flow production lines. However， traditional methods for classic FJSP cannot be directly applied. Targeting this problem， the process state model of a mixed-flow production line is analyzed. On this basis， a mathematical model of a mixed-flow job-shop scheduling problem with combined processing constraints is established based on the traditional FJSP. Then， an improved genetic algorithm with multi-segment encoding， crossover， and mutation is proposed for the mixed-flow production line problem. Finally， the proposed algorithm is applied to the production workshop of missile structural components at an aerospace institute to verify its feasibility and effectiveness.
2021, 38(3):427-436.
DOI: 10.16356/j.1005-1120.2021.03.007
Abstract:
For comprehensive characteristics of flow in a gas bearing， lattice Boltzmann method （LBM） is applied for study of the two-dimensional flow between two eccentric cylinders with the inner one rotating at a high speed. The flow pattern and circumferential pressure distribution are discussed based on critical issues such as eccentricity ranging from 0.2 to 0.9， clearance ratio varying from 0.005 to 0.01 and rotating speed in the range of 3×104—1.8×105 r/min. The analysis and discussion on the circumferential pressure distribution affirmed the quasilinear relation between the extremum pressure and rotating speed. Furthermore， a high eccentricity and small clearance ratio contributes most to the fluctuation of the circumferential pressure distribution. The flow pattern inside the channel exhibits separation vortex under a large eccentricity. The conclusions drawn in this work give rise to prediction of the flow pattern in the gas bearing which is beneficial for evaluating the performance of as well as instructing the design and development.
For comprehensive characteristics of flow in a gas bearing， lattice Boltzmann method （LBM） is applied for study of the two-dimensional flow between two eccentric cylinders with the inner one rotating at a high speed. The flow pattern and circumferential pressure distribution are discussed based on critical issues such as eccentricity ranging from 0.2 to 0.9， clearance ratio varying from 0.005 to 0.01 and rotating speed in the range of 3×104—1.8×105 r/min. The analysis and discussion on the circumferential pressure distribution affirmed the quasilinear relation between the extremum pressure and rotating speed. Furthermore， a high eccentricity and small clearance ratio contributes most to the fluctuation of the circumferential pressure distribution. The flow pattern inside the channel exhibits separation vortex under a large eccentricity. The conclusions drawn in this work give rise to prediction of the flow pattern in the gas bearing which is beneficial for evaluating the performance of as well as instructing the design and development.
2021, 38(3):437-449.
DOI: 10.16356/j.1005-1120.2021.03.008
Abstract:
In wind tunnel tests， long cantilever stings are usually used to support aerodynamic models. However， this kind of sting support system is prone to vibration problems due to its low damping， which limits the test envelope and affects the data quality. It is shown in many studies that the sting vibration can be effectively reduced by using active sting dampers based on piezoelectric actuators. This paper attempts to review the research progress of piezoelectric vibration control in wind tunnel tests， covering the design of active sting dampers， control methods and wind tunnel applications. First of all， different design schemes of active sting dampers are briefly introduced， along with the vibration damping principle. Then， a comprehensive review of the control methods for active sting dampers is presented， ranging from classic control methods， like PID control algorithm， to various intelligent control methods. Furthermore， the applications of active sting dampers and controllers in different wind tunnels are summarized to evaluate their vibration damping effect. Finally， the remaining problems that need to be solved in the future development of piezoelectric vibration control in wind tunnel tests are discussed.
In wind tunnel tests， long cantilever stings are usually used to support aerodynamic models. However， this kind of sting support system is prone to vibration problems due to its low damping， which limits the test envelope and affects the data quality. It is shown in many studies that the sting vibration can be effectively reduced by using active sting dampers based on piezoelectric actuators. This paper attempts to review the research progress of piezoelectric vibration control in wind tunnel tests， covering the design of active sting dampers， control methods and wind tunnel applications. First of all， different design schemes of active sting dampers are briefly introduced， along with the vibration damping principle. Then， a comprehensive review of the control methods for active sting dampers is presented， ranging from classic control methods， like PID control algorithm， to various intelligent control methods. Furthermore， the applications of active sting dampers and controllers in different wind tunnels are summarized to evaluate their vibration damping effect. Finally， the remaining problems that need to be solved in the future development of piezoelectric vibration control in wind tunnel tests are discussed.
2021, 38(3):450-461.
DOI: 10.16356/j.1005-1120.2021.03.009
Abstract:
Motion behavior of grinding balls plays a vital role in improving efficiency of particle crushing. A method of preparing micro-particles by changing ball-motion behavior in a flutter mill is proposed and multiple grinding experiments are conducted. Crushing performance parameters， such as breakage rate Si， production rates of fine particles Fi and Fi*， are studied in different motion conditions. From the results， a better crushing performance is attained in the coupled motion modes of rotating speed ratio of 85%， with a vibrating amplitude of 8 mm and a frequency of 12 Hz. In addition， the influence of ball-motion behavior on particle crushing performance is discussed. The ball-motion behaviors， such as the collision energy loss E， among grinding balls have some relationship with the particle crushing performance of Si. Therefore， this study not just provides an efficiency way of accumulating micro-particles， but also reveals how the ball-motion behavior influence particle crushing performance in the flutter mill.
Motion behavior of grinding balls plays a vital role in improving efficiency of particle crushing. A method of preparing micro-particles by changing ball-motion behavior in a flutter mill is proposed and multiple grinding experiments are conducted. Crushing performance parameters， such as breakage rate Si， production rates of fine particles Fi and Fi*， are studied in different motion conditions. From the results， a better crushing performance is attained in the coupled motion modes of rotating speed ratio of 85%， with a vibrating amplitude of 8 mm and a frequency of 12 Hz. In addition， the influence of ball-motion behavior on particle crushing performance is discussed. The ball-motion behaviors， such as the collision energy loss E， among grinding balls have some relationship with the particle crushing performance of Si. Therefore， this study not just provides an efficiency way of accumulating micro-particles， but also reveals how the ball-motion behavior influence particle crushing performance in the flutter mill.
2021, 38(3):462-473.
DOI: 10.16356/j.1005-1120.2021.03.010
Abstract:
Optimization of machining parameters is of great importance for multi-pass end milling because machining parameters adversely or positively affect the time and quality of production. This paper develops a second-order full-discretization method （2ndFDM）-based 3-D stability prediction model for simultaneous optimization of spindle speed， axial cutting depth and radial cutting depth. The optimal machining parameters in each pass are obtained to achieve the minimum production time comprehensive considering constraints of 3-D stability， machine tool performance， tool life and machining requirements. A cloud drop-enabled particle swarm optimization （CDPSO） algorithm is proposed to solve the developed machining parameter optimization， and 13 benchmark problems are used to evaluate CDPSO algorithm. Numerical results show that CDPSO algorithm has a certain advantage in computational cost as well as comparable search quality and robustness. A demonstrative example is provided.
Optimization of machining parameters is of great importance for multi-pass end milling because machining parameters adversely or positively affect the time and quality of production. This paper develops a second-order full-discretization method （2ndFDM）-based 3-D stability prediction model for simultaneous optimization of spindle speed， axial cutting depth and radial cutting depth. The optimal machining parameters in each pass are obtained to achieve the minimum production time comprehensive considering constraints of 3-D stability， machine tool performance， tool life and machining requirements. A cloud drop-enabled particle swarm optimization （CDPSO） algorithm is proposed to solve the developed machining parameter optimization， and 13 benchmark problems are used to evaluate CDPSO algorithm. Numerical results show that CDPSO algorithm has a certain advantage in computational cost as well as comparable search quality and robustness. A demonstrative example is provided.
11 Optimization Design and Comprehensive Evaluation of Screw Contact of Space Battery Based on ANSYS
2021, 38(3):474-483.
DOI: 10.16356/j.1005-1120.2021.03.011
Abstract:
In order to improve the safety of the battery of satellite side mounting， and prevent the screw from producing excess due to frequent assembly and disassembly， the YS-20 material replacement and structure optimization design of the screw body are carried out under the premise of not changing the original tooling. The double-shear test of YS-20 bar is carried out， and the ANSYS optimization design module is used to design 7×7×6， a total of 294， calculation cases of D1， D2， T， the three important dimension parameters of screw structure. The actual bearing state of screw composite structure is accurately simulated by using asymmetric contact model. Three comprehensive evaluations are established， and the calculation examples satisfying the conditions are evaluated comprehensively. The final results are T=12.2 mm， D1=16 mm， D2=2 mm. The stress verification and contact analysis are carried out for the final scheme and the bearing state and contact state optimized screw structure are obtained.
In order to improve the safety of the battery of satellite side mounting， and prevent the screw from producing excess due to frequent assembly and disassembly， the YS-20 material replacement and structure optimization design of the screw body are carried out under the premise of not changing the original tooling. The double-shear test of YS-20 bar is carried out， and the ANSYS optimization design module is used to design 7×7×6， a total of 294， calculation cases of D1， D2， T， the three important dimension parameters of screw structure. The actual bearing state of screw composite structure is accurately simulated by using asymmetric contact model. Three comprehensive evaluations are established， and the calculation examples satisfying the conditions are evaluated comprehensively. The final results are T=12.2 mm， D1=16 mm， D2=2 mm. The stress verification and contact analysis are carried out for the final scheme and the bearing state and contact state optimized screw structure are obtained.
2021, 38(3):484-491.
DOI: 10.16356/j.1005-1120.2021.03.012
Abstract:
TIG welding experiments of TC2 titanium alloy sheet was carried out， and the well-formed weld was obtained. After welding process， the cross-section microstructure， mechanical properties， fracture morphology and quality inspection of the joint were studied. The results show that the microstructure of the weld consists of a large number of acicular α′ and β block. The microhardness curve shows that the microhardness value in the fusion zone （FZ） of the joint is significantly higher than that in the heat affected zone （HAZ） and the base metal （BM）， and the microhardness of the base metal is the lowest. The tensile strength of the joint is equivalent to that of the base metal， and the fracture morphology shows that the fracture mechanism of the joint is mixed ductile-brittle fracture mode. The weld quality is excellent through chemical inspection， penetrant inspection and X-ray inspection.
TIG welding experiments of TC2 titanium alloy sheet was carried out， and the well-formed weld was obtained. After welding process， the cross-section microstructure， mechanical properties， fracture morphology and quality inspection of the joint were studied. The results show that the microstructure of the weld consists of a large number of acicular α′ and β block. The microhardness curve shows that the microhardness value in the fusion zone （FZ） of the joint is significantly higher than that in the heat affected zone （HAZ） and the base metal （BM）， and the microhardness of the base metal is the lowest. The tensile strength of the joint is equivalent to that of the base metal， and the fracture morphology shows that the fracture mechanism of the joint is mixed ductile-brittle fracture mode. The weld quality is excellent through chemical inspection， penetrant inspection and X-ray inspection.
2021, 38(3):492-500.
DOI: 10.16356/j.1005-1120.2021.03.013
Abstract:
The common Au nanostructures （nanospheres， nanorods and nanosheets） were prepared by the seed growth method to explore the cold welding phenomenon of these non-single crystal nanostructures at room temperature. Systematic studies show that the concentration of surfactant cetyltrimethylammonium bromide（CTAB） and drying conditions are important factors to determine the evolution and final configuration of nanostructures during welding. The key factor of cold welding is the concentration of surfactant as low as 0.3 mm / L， and the welding should be carried out under the condition of slow evaporation and sufficient relaxation time， rather than rapid drying process. At the same time， the structural evolution during the welding process of gold rod head and tail is simulated by combining the electronic microscope characterization and density functional theory， which reveals that the stability of the welding nanostructure is better than that of the dispersed nanostructure.In the slow evaporation process of Au nanostructures with the same crystal structure， the low surfactant attached to the surface of the nanoparticles increases the attraction between the nanoparticles， which makes the nanoparticles close to each other adhere due to the interaction， and improves the physical properties of the intersection due to the diffusion， epitaxy and surface relaxation of the metal surface atoms. The results provide a research basis for the physical property analysis of nanostructures and the construction of defect devices.
The common Au nanostructures （nanospheres， nanorods and nanosheets） were prepared by the seed growth method to explore the cold welding phenomenon of these non-single crystal nanostructures at room temperature. Systematic studies show that the concentration of surfactant cetyltrimethylammonium bromide（CTAB） and drying conditions are important factors to determine the evolution and final configuration of nanostructures during welding. The key factor of cold welding is the concentration of surfactant as low as 0.3 mm / L， and the welding should be carried out under the condition of slow evaporation and sufficient relaxation time， rather than rapid drying process. At the same time， the structural evolution during the welding process of gold rod head and tail is simulated by combining the electronic microscope characterization and density functional theory， which reveals that the stability of the welding nanostructure is better than that of the dispersed nanostructure.In the slow evaporation process of Au nanostructures with the same crystal structure， the low surfactant attached to the surface of the nanoparticles increases the attraction between the nanoparticles， which makes the nanoparticles close to each other adhere due to the interaction， and improves the physical properties of the intersection due to the diffusion， epitaxy and surface relaxation of the metal surface atoms. The results provide a research basis for the physical property analysis of nanostructures and the construction of defect devices.
2021, 38(3):501-511.
DOI: 10.16356/j.1005-1120.2021.03.014
Abstract:
The scene matching navigation is a research focus in the field of autonomous navigation， but the real-time performance of image matching algorithm is difficult to meet the needs of real navigation systems. Therefore， this paper proposes a fast image matching algorithm. The algorithm improves the traditional line segment extraction algorithm and combines with the Delaunay triangulation method. By combining the geometric features of points and lines， the image feature redundancy is reduced. Then， the error with confidence criterion is analyzed and the matching process is completed. The simulation results show that the proposed algorithm can still work within 3° rotation and small scale variation. In addition， the matching time is less than 0.5 s when the image size is 256 pixel×256 pixel. The proposed algorithm is suitable for autonomous navigation systems with multiple feature distribution and higher real-time requirements.
The scene matching navigation is a research focus in the field of autonomous navigation， but the real-time performance of image matching algorithm is difficult to meet the needs of real navigation systems. Therefore， this paper proposes a fast image matching algorithm. The algorithm improves the traditional line segment extraction algorithm and combines with the Delaunay triangulation method. By combining the geometric features of points and lines， the image feature redundancy is reduced. Then， the error with confidence criterion is analyzed and the matching process is completed. The simulation results show that the proposed algorithm can still work within 3° rotation and small scale variation. In addition， the matching time is less than 0.5 s when the image size is 256 pixel×256 pixel. The proposed algorithm is suitable for autonomous navigation systems with multiple feature distribution and higher real-time requirements.
2021, 38(3):512-519.
DOI: 10.16356/j.1005-1120.2021.03.015
Abstract:
A compact antenna formed by three concentric split rings for ultra-high frequency （UHF） radio frequency identification （RFID） tag is proposed in this paper. The antenna is composed of two parts， an outer short-circuited ring modified from a traditional split-ring resonator （SRR） antenna and an inner SRR load， so the antenna can be regarded as a short-circuited ring loaded with SRR. According to the transmission line theory， to conjugate match with the capacitive input-impedance of a tag chip， the length of the short-circuited ring is λg/4 shorter than that of an open-circuited dipole of a traditional SRR antenna， whereλ g ![]()
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A compact antenna formed by three concentric split rings for ultra-high frequency （UHF） radio frequency identification （RFID） tag is proposed in this paper. The antenna is composed of two parts， an outer short-circuited ring modified from a traditional split-ring resonator （SRR） antenna and an inner SRR load， so the antenna can be regarded as a short-circuited ring loaded with SRR. According to the transmission line theory， to conjugate match with the capacitive input-impedance of a tag chip， the length of the short-circuited ring is λg/4 shorter than that of an open-circuited dipole of a traditional SRR antenna， where
2021, 38(3):520-534.
DOI: 10.16356/j.1005-1120.2021.03.016
Abstract:
When the frigate moves forward， due to the ship motion such as pitching and rolling， the flow over the flight deck becomes very complex， which may seriously threaten the taking off and landing of the ship-borne helicopter. The flow fields over the different modified simple frigate shape （SFS） models， consisting of the hangar and flight deck， were numerically studied by changing the ratio of hangar height and length in the static state and pitching state. For different models， the contours of velocity and pressure above the flight deck， as well as the variations of velocity components of the observation points and line in static state and pitching state were compared and analyzed. The results show that the size of recirculation zone and the location of the reattachment point have distinct differences for diverse models， and reveal the tracks of recirculation zone’s center and reattachment position in a pitching period. In addition， the velocity components at two observation positions also change periodically with the periodic motion. Furthermore， the deviations of the velocity components in static state and pitching state are relatively large， therefore， the flow fields in static state cannot be used to simulate that in pitching state correctly.
When the frigate moves forward， due to the ship motion such as pitching and rolling， the flow over the flight deck becomes very complex， which may seriously threaten the taking off and landing of the ship-borne helicopter. The flow fields over the different modified simple frigate shape （SFS） models， consisting of the hangar and flight deck， were numerically studied by changing the ratio of hangar height and length in the static state and pitching state. For different models， the contours of velocity and pressure above the flight deck， as well as the variations of velocity components of the observation points and line in static state and pitching state were compared and analyzed. The results show that the size of recirculation zone and the location of the reattachment point have distinct differences for diverse models， and reveal the tracks of recirculation zone’s center and reattachment position in a pitching period. In addition， the velocity components at two observation positions also change periodically with the periodic motion. Furthermore， the deviations of the velocity components in static state and pitching state are relatively large， therefore， the flow fields in static state cannot be used to simulate that in pitching state correctly.
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