Transactions of Nanjing University of Aeronautics & Astronautics
Volume 38,Issue 1,2021 Table of Contents
2021, 38(1):1-17.
DOI: 10.16356/j.1005-1120.2021.01.001
Abstract:
Over the past decade， multistable mechanical metamaterials have been widely investigated because of their novel shape reconfigurability and programmable energy landscape. The ability to reversibly reshape among diverse stable states with different energy levels represents the most important feature of the multistable mechanical metamaterials. We summarize main design strategies of multistable mechanical metamaterials， including those based on self-assembly scheme， snap-through instability， structured mechanism and geometrical frustration， with a focus on the number and controllability of accessible stable states. Then we concentrate on unusual mechanical properties of these multistable mechanical metamaterials， and present their applications in a wide range of areas， including tunable electromagnetic devices， actuators， robotics， and mechanical logic gates. Finally， we discuss remaining challenges and open opportunities of designs and applications of multistable mechanical metamaterials.
Over the past decade， multistable mechanical metamaterials have been widely investigated because of their novel shape reconfigurability and programmable energy landscape. The ability to reversibly reshape among diverse stable states with different energy levels represents the most important feature of the multistable mechanical metamaterials. We summarize main design strategies of multistable mechanical metamaterials， including those based on self-assembly scheme， snap-through instability， structured mechanism and geometrical frustration， with a focus on the number and controllability of accessible stable states. Then we concentrate on unusual mechanical properties of these multistable mechanical metamaterials， and present their applications in a wide range of areas， including tunable electromagnetic devices， actuators， robotics， and mechanical logic gates. Finally， we discuss remaining challenges and open opportunities of designs and applications of multistable mechanical metamaterials.
2021, 38(1):18-28.
DOI: 10.16356/j.1005-1120.2021.01.002
Abstract:
By making use of the direct integration method， an exact analysis of the general three-dimensional thermoelasticity problem is performed for the case of a transversely isotropic homogeneous half-space subject to local thermal and force loadings. The material plane of isotropy is assumed to be parallel to the limiting surface of the half-space. By reducing the original thermoelasticity equations to the governing ones for individual stress-tensor components， the effect of material anisotropy in the stress field is analyzed with regard to the feasibility requirement， i.e.， the finiteness of the stress field at a distance from the disturbed area. As a result， the solution is constructed in the form of explicit analytical dependencies on the force and thermal loadings for various kinds of transversely isotropic materials and agrees with the basic principles of the continua mechanics. The solution can be efficiently used as a benchmark one for the direct computation of temperature and thermal stresses in transversely isotropic semi-infinite domains， as well as for the verification of solutions constructed by different means.
By making use of the direct integration method， an exact analysis of the general three-dimensional thermoelasticity problem is performed for the case of a transversely isotropic homogeneous half-space subject to local thermal and force loadings. The material plane of isotropy is assumed to be parallel to the limiting surface of the half-space. By reducing the original thermoelasticity equations to the governing ones for individual stress-tensor components， the effect of material anisotropy in the stress field is analyzed with regard to the feasibility requirement， i.e.， the finiteness of the stress field at a distance from the disturbed area. As a result， the solution is constructed in the form of explicit analytical dependencies on the force and thermal loadings for various kinds of transversely isotropic materials and agrees with the basic principles of the continua mechanics. The solution can be efficiently used as a benchmark one for the direct computation of temperature and thermal stresses in transversely isotropic semi-infinite domains， as well as for the verification of solutions constructed by different means.
2021, 38(1):29-43.
DOI: 10.16356/j.1005-1120.2021.01.003
Abstract:
This paper focuses on the thermo-mechanical behaviors of functionally graded （FG） shape memory alloy （SMA） composite beams based on Timoshenko beam theory. The volume fraction of SMA fiber is graded in the thickness of beam according to a power-law function and the equivalent parameters are formulated. The governing differential equations， which can be solved by direct integration， are established by employing the composite laminated plate theory. The influences of FG parameter， ambient temperature and SMA fiber laying angle on the thermo-mechanical behaviors are numerically simulated and discussed under different boundary conditions. Results indicate that the neutral plane does not coincide with the middle plane of the composite beam and the distribution of martensite is asymmetric along the thickness. Both the increments of the functionally graded parameter and ambient temperature make the composite beam become stiffer. However， the influence of the SMA fiber laying angle can be negligent. This work can provide the theoretical basis for the design and application of FG SMA structures.
This paper focuses on the thermo-mechanical behaviors of functionally graded （FG） shape memory alloy （SMA） composite beams based on Timoshenko beam theory. The volume fraction of SMA fiber is graded in the thickness of beam according to a power-law function and the equivalent parameters are formulated. The governing differential equations， which can be solved by direct integration， are established by employing the composite laminated plate theory. The influences of FG parameter， ambient temperature and SMA fiber laying angle on the thermo-mechanical behaviors are numerically simulated and discussed under different boundary conditions. Results indicate that the neutral plane does not coincide with the middle plane of the composite beam and the distribution of martensite is asymmetric along the thickness. Both the increments of the functionally graded parameter and ambient temperature make the composite beam become stiffer. However， the influence of the SMA fiber laying angle can be negligent. This work can provide the theoretical basis for the design and application of FG SMA structures.
2021, 38(1):44-56.
DOI: 10.16356/j.1005-1120.2021.01.004
Abstract:
This paper mainly investigates the effects of initial static shear stress and grain shape on the liquefaction induced large deformation of saturated sand under torsional shear. Nanjing sand， mainly composed of platy grains， is tested with different initial static shear stress ratio （SSR） using a hollow column torsional shear apparatus. The tests find that the saturated Nanjing sand reaches full liquefaction under the superposition of initial static shear stress and cyclic stress for both stress reversal and non-reversal cases. However， it requires a large number of loading cycles to reach full liquefaction if stress reversal does not occur. With increasing the initial static stress， the large deformation of the Nanjing sand should mainly induced by the cyclic liquefaction firstly under a smaller initial shear stress， and then it should be induced by the residual deformation failure. The critical point occurs approximately when the initial shear stress is close to the amplitude of the cyclic shear stress. Meanwhile， it shows that grain angularity increases the liquefaction resistance when the initial static shear stress is zero. A small initial static shear stress causes the larger loss of liquefaction resistance for angular sand than rounded sand. At a high initial SSR， the angular sand is more resistant to the large residual deformation failure than the rounded sand.
This paper mainly investigates the effects of initial static shear stress and grain shape on the liquefaction induced large deformation of saturated sand under torsional shear. Nanjing sand， mainly composed of platy grains， is tested with different initial static shear stress ratio （SSR） using a hollow column torsional shear apparatus. The tests find that the saturated Nanjing sand reaches full liquefaction under the superposition of initial static shear stress and cyclic stress for both stress reversal and non-reversal cases. However， it requires a large number of loading cycles to reach full liquefaction if stress reversal does not occur. With increasing the initial static stress， the large deformation of the Nanjing sand should mainly induced by the cyclic liquefaction firstly under a smaller initial shear stress， and then it should be induced by the residual deformation failure. The critical point occurs approximately when the initial shear stress is close to the amplitude of the cyclic shear stress. Meanwhile， it shows that grain angularity increases the liquefaction resistance when the initial static shear stress is zero. A small initial static shear stress causes the larger loss of liquefaction resistance for angular sand than rounded sand. At a high initial SSR， the angular sand is more resistant to the large residual deformation failure than the rounded sand.
2021, 38(1):57-67.
DOI: 10.16356/j.1005-1120.2021.01.005
Abstract:
Particles， including soot， aerosol and ash， usually exist as fractal aggregates. The radiative properties of the particle fractal aggregates have a great influence on studying the light or heat radiative transfer in the particle medium. In the present work， the performance of the single-layer inversion model and the double-layer inversion model in reconstructing the geometric structure of particle fractal aggregates is studied based on the light reflectance-transmittance measurement method. An improved artificial fish-swarm algorithm （IAFSA） is proposed to solve the inverse problem. The result reveals that the accuracy of double-layer inversion model is more satisfactory as it can provide more uncorrelated information than the single-layer inversion model. Moreover， the developed IAFSA show higher accuracy and better robustness than the original artificial fish swarm algorithm （AFSA） for avoiding local optimization problems effectively. As a whole， the present work supplies a useful kind of measurement technology for predicting geometrical morphology of particle fractal aggregates.
Particles， including soot， aerosol and ash， usually exist as fractal aggregates. The radiative properties of the particle fractal aggregates have a great influence on studying the light or heat radiative transfer in the particle medium. In the present work， the performance of the single-layer inversion model and the double-layer inversion model in reconstructing the geometric structure of particle fractal aggregates is studied based on the light reflectance-transmittance measurement method. An improved artificial fish-swarm algorithm （IAFSA） is proposed to solve the inverse problem. The result reveals that the accuracy of double-layer inversion model is more satisfactory as it can provide more uncorrelated information than the single-layer inversion model. Moreover， the developed IAFSA show higher accuracy and better robustness than the original artificial fish swarm algorithm （AFSA） for avoiding local optimization problems effectively. As a whole， the present work supplies a useful kind of measurement technology for predicting geometrical morphology of particle fractal aggregates.
2021, 38(1):68-74.
DOI: 10.16356/j.1005-1120.2021.01.006
Abstract:
Biodegradable polymers are highly attractive as potential alternatives to petroleum-based polymers in an attempt to achieve carbon neutrality whilst maintaining the mechanical properties of the structures. Among these polymers， polylactic acid （PLA） is particularly promising due to its good mechanical properties， biocompatibility and thermoplasticity. In this work， we aim to enhance the mechanical properties of PLA using mechanically-defibrated cellulose nanofibers （CNFs） that exhibit remarkable mechanical properties and biodegradability. We also employ fused deposition modeling （FDM）， one of the three-dimensional printing methods for thermoplastic polymers， for the low-cost fabrication of the products. Mechanically-defibrated CNF-reinforced PLA matrix composites are fabricated by FDM. Their tensile properties are investigated in two printing directions （0°/90° and +45°/-45°）. The discussion about the relationship between printing direction and tensile behavoir of mechanically-defibrated CNF-reinforced PLA matrix composite is the unique point of this study. We further discuss the microstructure and fracture surface of mechanically-defibrated CNF-reinforced PLA matrix composite by scanning electron microscope.
Biodegradable polymers are highly attractive as potential alternatives to petroleum-based polymers in an attempt to achieve carbon neutrality whilst maintaining the mechanical properties of the structures. Among these polymers， polylactic acid （PLA） is particularly promising due to its good mechanical properties， biocompatibility and thermoplasticity. In this work， we aim to enhance the mechanical properties of PLA using mechanically-defibrated cellulose nanofibers （CNFs） that exhibit remarkable mechanical properties and biodegradability. We also employ fused deposition modeling （FDM）， one of the three-dimensional printing methods for thermoplastic polymers， for the low-cost fabrication of the products. Mechanically-defibrated CNF-reinforced PLA matrix composites are fabricated by FDM. Their tensile properties are investigated in two printing directions （0°/90° and +45°/-45°）. The discussion about the relationship between printing direction and tensile behavoir of mechanically-defibrated CNF-reinforced PLA matrix composite is the unique point of this study. We further discuss the microstructure and fracture surface of mechanically-defibrated CNF-reinforced PLA matrix composite by scanning electron microscope.
7 Large and Recoverable Electrostrain in Strained Ferroelectric Superlattices due to Domain Switching
2021, 38(1):75-83.
DOI: 10.16356/j.1005-1120.2021.01.007
Abstract:
The ferroelectric superlattices have been widely studied due to their distinguished electromechanical coupling properties. Under different biaxial mismatch strains， ferroelectric superlattices exhibit different domain structures and electromechanical coupling properties. A three-dimensional phase field model is employed to investigate the detailed domain evolution and electromechanical properties of theP b T i O 3 ![]()
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The ferroelectric superlattices have been widely studied due to their distinguished electromechanical coupling properties. Under different biaxial mismatch strains， ferroelectric superlattices exhibit different domain structures and electromechanical coupling properties. A three-dimensional phase field model is employed to investigate the detailed domain evolution and electromechanical properties of the
2021, 38(1):84-95.
DOI: 10.16356/j.1005-1120.2021.01.008
Abstract:
In order to investigate the dynamic behavior of non-conservative systems， the Lie symmetries and conserved quantities of fractional Birkhoffian dynamics based on quasi-fractional dynamics model are proposed and studied. The quasi-fractional dynamics model here refers to the variational problem based on the definition of Riemann-Liouville fractional integral（RLFI）， the variational problem based on the definition of extended exponentially fractional integral（EEFI）， and the variational problem based on the definition of fractional integral extended by periodic laws（FIEPL）. First， the fractional Pfaff-Birkhoff principles based on quasi-fractional dynamics models are established， and the corresponding Birkhoff’s equations and the determining equations of Lie symmetry are obtained. Second， for fractional Birkhoffian systems based on quasi-fractional models， the conditions and forms of conserved quantities are given， and Lie symmetry theorems are proved. The Pfaff-Birkhoff principles， Birkhoff’s equations and Lie symmetry theorems of quasi-fractional Birkhoffian systems and classical Birkhoffian systems are special cases of this article. Finally， some examples are given.
In order to investigate the dynamic behavior of non-conservative systems， the Lie symmetries and conserved quantities of fractional Birkhoffian dynamics based on quasi-fractional dynamics model are proposed and studied. The quasi-fractional dynamics model here refers to the variational problem based on the definition of Riemann-Liouville fractional integral（RLFI）， the variational problem based on the definition of extended exponentially fractional integral（EEFI）， and the variational problem based on the definition of fractional integral extended by periodic laws（FIEPL）. First， the fractional Pfaff-Birkhoff principles based on quasi-fractional dynamics models are established， and the corresponding Birkhoff’s equations and the determining equations of Lie symmetry are obtained. Second， for fractional Birkhoffian systems based on quasi-fractional models， the conditions and forms of conserved quantities are given， and Lie symmetry theorems are proved. The Pfaff-Birkhoff principles， Birkhoff’s equations and Lie symmetry theorems of quasi-fractional Birkhoffian systems and classical Birkhoffian systems are special cases of this article. Finally， some examples are given.
2021, 38(1):96-105.
DOI: 10.16356/j.1005-1120.2021.01.009
Abstract:
This paper proposes a straightforward and concise approach to analyze the Saint-Venant’s torsion of a circular shaft containing multiple elliptical inclusions or cracks based on the complex variable method. The complex potentials are first derived for the shaft with N elliptical inclusions by introducing Faber series expansion， and then the shear stresses and torsional rigidity are calculated. When the inclusions degenerate into cracks， the solutions for the intensity factors of stress are obtained. Finally， several numerical examples are carried out to discuss the effects of geometry parameters， different shear modulus ratios and array-types of the elliptical inclusions/cracks on the fields of stresses. The obtained results show that the proposed approach has advantages such as high accuracy and good convergence.
This paper proposes a straightforward and concise approach to analyze the Saint-Venant’s torsion of a circular shaft containing multiple elliptical inclusions or cracks based on the complex variable method. The complex potentials are first derived for the shaft with N elliptical inclusions by introducing Faber series expansion， and then the shear stresses and torsional rigidity are calculated. When the inclusions degenerate into cracks， the solutions for the intensity factors of stress are obtained. Finally， several numerical examples are carried out to discuss the effects of geometry parameters， different shear modulus ratios and array-types of the elliptical inclusions/cracks on the fields of stresses. The obtained results show that the proposed approach has advantages such as high accuracy and good convergence.
2021, 38(1):106-116.
DOI: 10.16356/j.1005-1120.2021.01.010
Abstract:
A buffer bag mechanism is designed， which can provide axial impact protection under small displacement. The stiffness characteristics of the structure under impact load are studied.The stiffness of the mechanism and the internal pressure change of the buffer bag are compared and analyzed， when the filling materials are liquid and gas respectively. Finally， the influence of initial fluid bag pressure， bulk modulus and shell thickness on the stiffness of the mechanism and the change of bag pressure are studied. The results show that the stiffness of the liquid bag is better than that of the gas bag when the filler is liquid and gas； the liquid bag has obvious pressure rise after the mechanism is subjected to axial force by 300 kN， and the gas bag has almost no pressure rise； the change of bulk modulus， which is 1 000， 1 500， 2 000 and 2 500 MPa， has an obvious effect on the liquid bag， and it is positively correlated with the stiffness of the mechanism. The change of gas modulus， which is 28 and 44， has little effect on the stiffness of the mechanism； the thickness of the buffer bag， which is 5， 10 and 15 mm， also has an obvious effect on the stiffness. The stiffness of the liquid bag is greater， and the protection for flexible joint is better in the same condition.
A buffer bag mechanism is designed， which can provide axial impact protection under small displacement. The stiffness characteristics of the structure under impact load are studied.The stiffness of the mechanism and the internal pressure change of the buffer bag are compared and analyzed， when the filling materials are liquid and gas respectively. Finally， the influence of initial fluid bag pressure， bulk modulus and shell thickness on the stiffness of the mechanism and the change of bag pressure are studied. The results show that the stiffness of the liquid bag is better than that of the gas bag when the filler is liquid and gas； the liquid bag has obvious pressure rise after the mechanism is subjected to axial force by 300 kN， and the gas bag has almost no pressure rise； the change of bulk modulus， which is 1 000， 1 500， 2 000 and 2 500 MPa， has an obvious effect on the liquid bag， and it is positively correlated with the stiffness of the mechanism. The change of gas modulus， which is 28 and 44， has little effect on the stiffness of the mechanism； the thickness of the buffer bag， which is 5， 10 and 15 mm， also has an obvious effect on the stiffness. The stiffness of the liquid bag is greater， and the protection for flexible joint is better in the same condition.
2021, 38(1):117-123.
DOI: 10.16356/j.1005-1120.2021.01.011
Abstract:
Investigation of paper cutting process is vital for the design of cutting tools， but the fracture mechanism of paper cutting is still unclear. Here， we focus on the cutting process of paper， including the key parameters of cohesive zone model （CZM） for the orthotropic paper， to simulate the shear fracture process. Firstly， the material constants of the orthotropic paper are determined by longitudinal and transverse tensile test. Secondly， based on the tensile stress-strain curves， combined with damage theory and numerical simulations， the key parameters of the CZM for the orthotropic paper are obtained. Finally， a model III fracture is simulated to verify the accuracy of the model. Results show that the load-displacement curves obtained by the simulation is consistent with the test results.
Investigation of paper cutting process is vital for the design of cutting tools， but the fracture mechanism of paper cutting is still unclear. Here， we focus on the cutting process of paper， including the key parameters of cohesive zone model （CZM） for the orthotropic paper， to simulate the shear fracture process. Firstly， the material constants of the orthotropic paper are determined by longitudinal and transverse tensile test. Secondly， based on the tensile stress-strain curves， combined with damage theory and numerical simulations， the key parameters of the CZM for the orthotropic paper are obtained. Finally， a model III fracture is simulated to verify the accuracy of the model. Results show that the load-displacement curves obtained by the simulation is consistent with the test results.
2021, 38(1):124-131.
DOI: 10.16356/j.1005-1120.2021.01.012
Abstract:
The explosive demands for facial masks as vital personal protection equipment （PPE） in the wake of Covid-19 have challenged many industries and enterprises in technology and capacity， and the piezoelectric ceramic （PZT） transducers for the production of facial masks in the welding process are in heavy demand. In the earlier days of the epidemic， the supply of ceramic transducers cannot meet its increasing demands， and efforts in materials， development， and production are mobilized to provide the transducers to mask producers for quick production. The simplest solution is presented with the employment of Rayleigh-Ritz method for the vibration analysis， then different materials can be selected to achieve the required frequency and energy standards. The fully tailored method and results can be utilized by the engineers for quick development of the PZT transducers to perform precise function in welding.
The explosive demands for facial masks as vital personal protection equipment （PPE） in the wake of Covid-19 have challenged many industries and enterprises in technology and capacity， and the piezoelectric ceramic （PZT） transducers for the production of facial masks in the welding process are in heavy demand. In the earlier days of the epidemic， the supply of ceramic transducers cannot meet its increasing demands， and efforts in materials， development， and production are mobilized to provide the transducers to mask producers for quick production. The simplest solution is presented with the employment of Rayleigh-Ritz method for the vibration analysis， then different materials can be selected to achieve the required frequency and energy standards. The fully tailored method and results can be utilized by the engineers for quick development of the PZT transducers to perform precise function in welding.
2021, 38(1):132-139.
DOI: 10.16356/j.1005-1120.2021.01.013
Abstract:
The rotor initial unbalance of an aeroengine gas generator of turboshaft engine seriously affects rotor assembly process. To reasonably optimize rotor assembly process， the effect analyses of rotor initial unbalance of single disc and combined discs on rotor dynamic characteristics are firstly implemented in respect of the dispersity of rotor initial unbalance. It is found that the most important factors contributing to rotor vibration are the unbalances of the first stage compressor disc and the second stage turbine disc. However， reducing the mass of two discs conflicts with the control of the whole gas generator rotor balance resulting from the unbalance increase of single components. Thus， we further analyze the key control factors of affecting rotor initial unbalance， and give the strict control measures of centrifugal impeller runout in the assembly process by adjusting the angle of central tie rod axis. The purpose of this measures to make the assembly process simpler and more effective for timely controlling rotor initial unbalance. The efforts of this study validate that the proposed method is workable for the rotor tightened by a central tie rod and possesses the significant meaning of practical application in engineering.
The rotor initial unbalance of an aeroengine gas generator of turboshaft engine seriously affects rotor assembly process. To reasonably optimize rotor assembly process， the effect analyses of rotor initial unbalance of single disc and combined discs on rotor dynamic characteristics are firstly implemented in respect of the dispersity of rotor initial unbalance. It is found that the most important factors contributing to rotor vibration are the unbalances of the first stage compressor disc and the second stage turbine disc. However， reducing the mass of two discs conflicts with the control of the whole gas generator rotor balance resulting from the unbalance increase of single components. Thus， we further analyze the key control factors of affecting rotor initial unbalance， and give the strict control measures of centrifugal impeller runout in the assembly process by adjusting the angle of central tie rod axis. The purpose of this measures to make the assembly process simpler and more effective for timely controlling rotor initial unbalance. The efforts of this study validate that the proposed method is workable for the rotor tightened by a central tie rod and possesses the significant meaning of practical application in engineering.
2021, 38(1):140-152.
DOI: 10.16356/j.1005-1120.2021.01.014
Abstract:
Structural health monitoring （SHM） in-service is very important for wind turbine system. Because the central wavelength of a fiber Bragg grating （FBG） sensor changes linearly with strain or temperature， FBG-based sensors are easily applied to structural tests. Therefore， the monitoring of wind turbine blades by FBG sensors is proposed. The method is experimentally proved to be feasible. Five FBG sensors were set along the blade length in order to measure distributed strain. However， environmental or measurement noise may cover the structural signals. Dual-tree complex wavelet transform （DT-CWT） is suggested to wipe off the noise. The experimental studies indicate that the tested strain fluctuate distinctly as one of the blades is broken. The rotation period is about 1 s at the given working condition. However， the period is about 0.3 s if all the wind blades are in good conditions. Therefore， strain monitoring by FBG sensors could predict damage of a wind turbine blade system. Moreover， the studies indicate that monitoring of one blade is adequate to diagnose the status of a wind generator.
Structural health monitoring （SHM） in-service is very important for wind turbine system. Because the central wavelength of a fiber Bragg grating （FBG） sensor changes linearly with strain or temperature， FBG-based sensors are easily applied to structural tests. Therefore， the monitoring of wind turbine blades by FBG sensors is proposed. The method is experimentally proved to be feasible. Five FBG sensors were set along the blade length in order to measure distributed strain. However， environmental or measurement noise may cover the structural signals. Dual-tree complex wavelet transform （DT-CWT） is suggested to wipe off the noise. The experimental studies indicate that the tested strain fluctuate distinctly as one of the blades is broken. The rotation period is about 1 s at the given working condition. However， the period is about 0.3 s if all the wind blades are in good conditions. Therefore， strain monitoring by FBG sensors could predict damage of a wind turbine blade system. Moreover， the studies indicate that monitoring of one blade is adequate to diagnose the status of a wind generator.
2021, 38(1):153-163.
DOI: 10.16356/j.1005-1120.2021.01.015
Abstract:
This study develops a method for the full-size structural design of blade， involving the optimal layer thickness configuration of the blade to maximize its bending stiffness using a genetic algorithm. Numerical differentiation is employed to solve the sensitivity of blade modal frequency to the layer thickness of each part of blade. The natural frequencies of first-order flapwise and edgewise modes are selected as the optimal objectives. Based on the modal sensitivity analysis of all design variables， the effect of discretized layer thickness on bending stiffness of the blade is explored， and 14 significant design variables are filtered to drive the structural optimization. The best solution predicts an increase in natural frequencies of first-order flapwise and edgewise blade modes by up to 12% and 10.4%， respectively. The results show that the structural optimization method based on modal sensitivity is more effective to improve the structural performance.
This study develops a method for the full-size structural design of blade， involving the optimal layer thickness configuration of the blade to maximize its bending stiffness using a genetic algorithm. Numerical differentiation is employed to solve the sensitivity of blade modal frequency to the layer thickness of each part of blade. The natural frequencies of first-order flapwise and edgewise modes are selected as the optimal objectives. Based on the modal sensitivity analysis of all design variables， the effect of discretized layer thickness on bending stiffness of the blade is explored， and 14 significant design variables are filtered to drive the structural optimization. The best solution predicts an increase in natural frequencies of first-order flapwise and edgewise blade modes by up to 12% and 10.4%， respectively. The results show that the structural optimization method based on modal sensitivity is more effective to improve the structural performance.
16 Reliability Analysis of Numerical Simulation of Sea-Crossing Bridge Deformation Under Wave Forces
2021, 38(1):164-172.
DOI: 10.16356/j.1005-1120.2021.01.016
Abstract:
To study on the numerical simulation calculation reliability of sea-crossing bridge under complex wave forces， the paper applied GPS deformation monitoring and numerical simulation calculation by researching Qingdao Jiaozhou Bay Sea-Crossing Bridge. The db3 wavelet three-layer decomposition was used on the horizontal movement of the sea-crossing bridge and the wind speed of the waves to analyze their correlation. The complex wave forces value of Qingdao Jiaozhou Bay Sea-Crossing Bridge was loaded on FLAC3D software successfully to make numerical simulation calculation of bridge deformation. Since the accuracy of the GPS deformation monitoring reaches millimeter level， it was used to monitor the exact value of the bridge deformation to judge the reliability of numerical simulation. The relative errors of displacement in X， Y and Z directions were between 33% and 41% through comparison. It could be seen that the numerical simulation error was relatively large， which was mainly due to various environmental factors and the deviation of applied wave forces. However， numerical simulation generally reflects the deformation law of the sea-crossing bridge under complex wave forces， providing an effectively technical support for the safe operation assessment of the sea-crossing bridge.
To study on the numerical simulation calculation reliability of sea-crossing bridge under complex wave forces， the paper applied GPS deformation monitoring and numerical simulation calculation by researching Qingdao Jiaozhou Bay Sea-Crossing Bridge. The db3 wavelet three-layer decomposition was used on the horizontal movement of the sea-crossing bridge and the wind speed of the waves to analyze their correlation. The complex wave forces value of Qingdao Jiaozhou Bay Sea-Crossing Bridge was loaded on FLAC3D software successfully to make numerical simulation calculation of bridge deformation. Since the accuracy of the GPS deformation monitoring reaches millimeter level， it was used to monitor the exact value of the bridge deformation to judge the reliability of numerical simulation. The relative errors of displacement in X， Y and Z directions were between 33% and 41% through comparison. It could be seen that the numerical simulation error was relatively large， which was mainly due to various environmental factors and the deviation of applied wave forces. However， numerical simulation generally reflects the deformation law of the sea-crossing bridge under complex wave forces， providing an effectively technical support for the safe operation assessment of the sea-crossing bridge.
2021, 38(1):173-180.
DOI: 10.16356/j.1005-1120.2021.01.017
Abstract:
Engineering change management is a special form of problem solving where many rules must be followed to satisfy the requirements of product changes. As engineering change has great influence on the cycle and the cost of product development， it is necessary to anticipate design changes （DCs） in advance and estimate the influence effectively. A process simulation-based method for engineering change management is proposed incorporating multiple assessment parameters. First， the change propagation model is established， which includes the formulation of change propagation influence， assessment score of DC solution. Then the optimization process of DC solution is introduced based on ant colony optimization （ACO）， and an optimization algorithm is detailed to acquire the optimal DC solution automatically. Finally， a case study of belt conveyor platform is implemented to validate the proposed method. The results show that changed requirement of product can be satisfied by multiple DC solutions and the optimal one can be acquired according to the unique characteristics of each solution.
Engineering change management is a special form of problem solving where many rules must be followed to satisfy the requirements of product changes. As engineering change has great influence on the cycle and the cost of product development， it is necessary to anticipate design changes （DCs） in advance and estimate the influence effectively. A process simulation-based method for engineering change management is proposed incorporating multiple assessment parameters. First， the change propagation model is established， which includes the formulation of change propagation influence， assessment score of DC solution. Then the optimization process of DC solution is introduced based on ant colony optimization （ACO）， and an optimization algorithm is detailed to acquire the optimal DC solution automatically. Finally， a case study of belt conveyor platform is implemented to validate the proposed method. The results show that changed requirement of product can be satisfied by multiple DC solutions and the optimal one can be acquired according to the unique characteristics of each solution.
2021, 38(1):181-192.
DOI: 10.16356/j.1005-1120.2021.01.018
Abstract:
In recent years， multiple-load automatic guided vehicle （AGV） is increasingly used in the logistics transportation fields， owing to the advantages of smaller fleet size and fewer occurrences of traffic congestion. However， one main challenge lies in the deadlock-avoidance for the dispatching process of a multiple-load AGV system. To prevent the system from falling into a deadlock， a strategy of keeping the number of jobs in the system （NJIS） at a low level is adopted in most existing literatures. It is noteworthy that a low-level NJIS will make the processing machine easier to be starved， thereby reducing the system efficiency unavoidably. The motivation of the paper is to develop a deadlock-avoidance dispatching method for a multiple-load AGV system operating at a high NJIS level. Firstly， the deadlock-avoidance dispatching method is devised by incorporating a deadlock-avoidance strategy into a dispatching procedure that contains four sub-problems. In this strategy， critical tasks are recognized according to the status of workstation buffers， and then temporarily forbidden to avoid potential deadlocks. Secondly， three multi-attribute dispatching rules are designed for system efficiency， where both the traveling distance and the buffer status are taken into account. Finally， a simulation system is developed to evaluate the performance of the proposed deadlock-avoidance strategy and dispatching rules at different NJIS levels. The experimental results demonstrate that our deadlock-avoidance dispatching method can improve the system efficiency at a high NJIS level and the adaptability to various system settings， while still avoiding potential deadlocks.
In recent years， multiple-load automatic guided vehicle （AGV） is increasingly used in the logistics transportation fields， owing to the advantages of smaller fleet size and fewer occurrences of traffic congestion. However， one main challenge lies in the deadlock-avoidance for the dispatching process of a multiple-load AGV system. To prevent the system from falling into a deadlock， a strategy of keeping the number of jobs in the system （NJIS） at a low level is adopted in most existing literatures. It is noteworthy that a low-level NJIS will make the processing machine easier to be starved， thereby reducing the system efficiency unavoidably. The motivation of the paper is to develop a deadlock-avoidance dispatching method for a multiple-load AGV system operating at a high NJIS level. Firstly， the deadlock-avoidance dispatching method is devised by incorporating a deadlock-avoidance strategy into a dispatching procedure that contains four sub-problems. In this strategy， critical tasks are recognized according to the status of workstation buffers， and then temporarily forbidden to avoid potential deadlocks. Secondly， three multi-attribute dispatching rules are designed for system efficiency， where both the traveling distance and the buffer status are taken into account. Finally， a simulation system is developed to evaluate the performance of the proposed deadlock-avoidance strategy and dispatching rules at different NJIS levels. The experimental results demonstrate that our deadlock-avoidance dispatching method can improve the system efficiency at a high NJIS level and the adaptability to various system settings， while still avoiding potential deadlocks.
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