Transactions of Nanjing University of Aeronautics & Astronautics
Volume 36,Issue 5,2019 Table of Contents
2019, 36(5):693-702.
DOI: 10.16356/j.1005-1120.2019.05.001
Abstract:
The air-gap flux density formula and thrust expression of long primary double sided linear induction machine (DLIM) in the secondary motion reference frame are deduced by using the Maxwell equations firstly. Then, by analyzing the factors that affect the thrust ripple in the thrust expression, a shuttle type secondary structure of long primary DLIMs is proposed, and its thrust performances of the machine with different shuttle size combinations are simulated and compared with that of plate secondary long primary DLIM. Comparison results show that the new secondary structure can suppress the thrust ripple and improve the stability of system acceleration.
The air-gap flux density formula and thrust expression of long primary double sided linear induction machine (DLIM) in the secondary motion reference frame are deduced by using the Maxwell equations firstly. Then, by analyzing the factors that affect the thrust ripple in the thrust expression, a shuttle type secondary structure of long primary DLIMs is proposed, and its thrust performances of the machine with different shuttle size combinations are simulated and compared with that of plate secondary long primary DLIM. Comparison results show that the new secondary structure can suppress the thrust ripple and improve the stability of system acceleration.
2019, 36(5):703-714.
DOI: 10.16356/j.1005-1120.2019.05.002
Abstract:
The Vienna rectifier with unbalanced input voltage and load transient is analyzed. A nonlinear control strategy for Vienna rectifier under unbalanced input is proposed. From the view of positive and negative sequence components, the proposed nonlinear control strategy suppresses the twice frequency ripple and guarantees the dynamic response characteristic at the same time. Thanks to the proposed nonlinear control strategy, the DC bus capacitor can be reduced a lot since the voltage ripple and drop can be suppressed. A 10 kW Vienna rectifier is built to verify the proposed control strategy. After applying the proposed nonlinear control strategy, the voltage ripple is only 7 V and decreases over 75% over the traditional PI control when the unbalanced degree is 20%. The voltage drop can be reduced about 80% than former control strategy which is helpful to reduce the DC bus capacitor and achieve higher power density. The volume of the capacitor can be reduced by 83.3% with the new control method.
The Vienna rectifier with unbalanced input voltage and load transient is analyzed. A nonlinear control strategy for Vienna rectifier under unbalanced input is proposed. From the view of positive and negative sequence components, the proposed nonlinear control strategy suppresses the twice frequency ripple and guarantees the dynamic response characteristic at the same time. Thanks to the proposed nonlinear control strategy, the DC bus capacitor can be reduced a lot since the voltage ripple and drop can be suppressed. A 10 kW Vienna rectifier is built to verify the proposed control strategy. After applying the proposed nonlinear control strategy, the voltage ripple is only 7 V and decreases over 75% over the traditional PI control when the unbalanced degree is 20%. The voltage drop can be reduced about 80% than former control strategy which is helpful to reduce the DC bus capacitor and achieve higher power density. The volume of the capacitor can be reduced by 83.3% with the new control method.
TANG Jiacheng
,
YAO Kaiqi
,
ZHU Wenming
,
GAO Zhesi
,
XU Zhiwei
,
ZHANG Zhiliang
,
REN Xiaoyong
,
CHEN Qianhong
2019, 36(5):715-723.
DOI: 10.16356/j.1005-1120.2019.05.003
Abstract:
Design method of split planar resonant inductor in 1 kV SiC logical link control(LLC) converter is proposed, which ensures the converter power density of 93.59 W/ in3 and peak efficiency of 95.73%. Split resonant inductor helps to provide symmetrical resonant current by symmetrical impedance, and improves the distortion of resonant current, which ensures the efficiency of the whole converter. An interleaved winding connecting scheme improves the power density of the planar magnets, which contributes to power density improvement. Design method and calculation process of such split planar resonant inductor are provided. To verify the feasibility of the proposed design method, a 1 kV/ 48 V 6.6 kW, 210 kHz SiC LLC prototype was built, and the experimental results are given.
Design method of split planar resonant inductor in 1 kV SiC logical link control(LLC) converter is proposed, which ensures the converter power density of 93.59 W/ in3 and peak efficiency of 95.73%. Split resonant inductor helps to provide symmetrical resonant current by symmetrical impedance, and improves the distortion of resonant current, which ensures the efficiency of the whole converter. An interleaved winding connecting scheme improves the power density of the planar magnets, which contributes to power density improvement. Design method and calculation process of such split planar resonant inductor are provided. To verify the feasibility of the proposed design method, a 1 kV/ 48 V 6.6 kW, 210 kHz SiC LLC prototype was built, and the experimental results are given.
2019, 36(5):724-732.
DOI: 10.16356/j.1005-1120.2019.05.004
Abstract:
Considering the promotion effect of interlaminar normal tensile stress and the inhibition effect of interlaminar normal compressive stress, two kinds of elimination initial criteria were proposed in this paper. Based on these two delamination initial criteria, a modified cohesive zone model (CZM) was established to simulate the delamination behavior in laminated composites. Numerical simulations of double cantilever beam (DCB), mixed-mode bending (MMB) and end notched flexure (ENF) tests were conducted. The results show that the proposed model can do a better job than common ones when it is used to predict laminates’ delamination under interlaminar compression stress. Moreover, a factor r, named cohesive strength coefficient, was defined in this paper on account of the difference between cohesive strength and interlaminar fracture strength. With changing factor r, it shows that a moderate variation of cohesive strength will not cause significant influences on global load-displacement responses. Besides, in order to obtain a good balance between prediction accuracy and computational efficiency, there shall be two or three numerical elements within the cohesive zone.
Considering the promotion effect of interlaminar normal tensile stress and the inhibition effect of interlaminar normal compressive stress, two kinds of elimination initial criteria were proposed in this paper. Based on these two delamination initial criteria, a modified cohesive zone model (CZM) was established to simulate the delamination behavior in laminated composites. Numerical simulations of double cantilever beam (DCB), mixed-mode bending (MMB) and end notched flexure (ENF) tests were conducted. The results show that the proposed model can do a better job than common ones when it is used to predict laminates’ delamination under interlaminar compression stress. Moreover, a factor r, named cohesive strength coefficient, was defined in this paper on account of the difference between cohesive strength and interlaminar fracture strength. With changing factor r, it shows that a moderate variation of cohesive strength will not cause significant influences on global load-displacement responses. Besides, in order to obtain a good balance between prediction accuracy and computational efficiency, there shall be two or three numerical elements within the cohesive zone.
2019, 36(5):733-746.
DOI: 10.16356/j.1005-1120.2019.05.005
Abstract:
The weighted-sum-of-gray-gas (WSGG) model and Mie theory are applied to study the influents of particle size on the radiative transfer in high temperature homogeneous gas-particle mixtures, such as the flame in aero-engine combustor. The radiative transfer equation is solved by the finite volume method. The particle size is assumed to obey uniform distribution and logarithmic normal (L-N) distribution, respectively. Results reveal that when particle size obeys uniform distribution, increasing particle size with total particle volume fraction f v unchanged will result in the decreasing of the absolute value of radiative heat transfer properties, and the effect of ignoring particle scattering will also be weakened. Opposite conclusions can be obtained when total particle number concentration N 0 is unchanged. Moreover, if particle size obeys L-N distribution, increasing the narrowness index σ or decreasing the characteristic diameter with the total particle volume fraction f v unchanged will increase the absolute value of radiative heat transfer properties. With total particle number concentration N 0 unchanged, opposite conclusions for radiative heat source and incident radiation terms can be obtained except for radiative heat flux term. As a whole, the effects of particle size on the radiative heat transfer in the high-temperature homogeneous gas-particle mixtures are complicated, and the particle scattering cannot be ignoring just according to the particle size.
The weighted-sum-of-gray-gas (WSGG) model and Mie theory are applied to study the influents of particle size on the radiative transfer in high temperature homogeneous gas-particle mixtures, such as the flame in aero-engine combustor. The radiative transfer equation is solved by the finite volume method. The particle size is assumed to obey uniform distribution and logarithmic normal (L-N) distribution, respectively. Results reveal that when particle size obeys uniform distribution, increasing particle size with total particle volume fraction f v unchanged will result in the decreasing of the absolute value of radiative heat transfer properties, and the effect of ignoring particle scattering will also be weakened. Opposite conclusions can be obtained when total particle number concentration N 0 is unchanged. Moreover, if particle size obeys L-N distribution, increasing the narrowness index σ or decreasing the characteristic diameter
2019, 36(5):747-759.
DOI: 10.16356/j.1005-1120.2019.05.006
Abstract:
The ejector-powered engine simulator (EPES) system is an important piece of equipment in conducting an influence test of the intake and jet flow in low-speed wind tunnels. In this work, through the analysis of the structure and principle of EPES, three parts of the internal flow force were obtained, namely, the additional resistance before the inlet, the internal flow force in the inlet and the thrust produced by the ejector. On the assumption of one-dimensional isentropic adiabatic flow, the theoretical formulae for calculating the forces were derived according to the measured total pressure, static pressure and total temperature of the internal flow section. Subsequently, a calibration tank was used to calibrate the EPES system. On the basis of the characteristics of the EPES system, the process and method of its calibration were designed in detail, and the model installation interface of the calibration tank was reformed. By applying this method, the repeatability accuracy of the inlet flow rate calibration coefficient was less than 0.05%, whereas that of the exhaust flow rate and velocity was less than 0.1%. Upon the application of the calibration coefficients to the correction of the wind tunnel experiment data, the results showed good agreement with the numerical simulation results in terms of regularity and magnitude before stall, which validates the reasonableness and feasibility of the calibration method. Analysis of the calibration data also demonstrated the consistency in the variation law and trend between the theoretical calculation and actual measurement of internal flow force, further reflecting the rationality and feasibility of the theoretical calculation. Nevertheless, the numerical difference was large and further widened with a higher ejection flow rate mainly because of the accuracy of flow measurement and the inhomogeneity of internal flow. The thrust deflection angle of EPES is an important factor in correcting this issue. In particular, the thrust deflection angle becomes larger with small ejection flow and becomes smaller with an increase in flow rate, essentially exhibiting a general change of less than 10°.
The ejector-powered engine simulator (EPES) system is an important piece of equipment in conducting an influence test of the intake and jet flow in low-speed wind tunnels. In this work, through the analysis of the structure and principle of EPES, three parts of the internal flow force were obtained, namely, the additional resistance before the inlet, the internal flow force in the inlet and the thrust produced by the ejector. On the assumption of one-dimensional isentropic adiabatic flow, the theoretical formulae for calculating the forces were derived according to the measured total pressure, static pressure and total temperature of the internal flow section. Subsequently, a calibration tank was used to calibrate the EPES system. On the basis of the characteristics of the EPES system, the process and method of its calibration were designed in detail, and the model installation interface of the calibration tank was reformed. By applying this method, the repeatability accuracy of the inlet flow rate calibration coefficient was less than 0.05%, whereas that of the exhaust flow rate and velocity was less than 0.1%. Upon the application of the calibration coefficients to the correction of the wind tunnel experiment data, the results showed good agreement with the numerical simulation results in terms of regularity and magnitude before stall, which validates the reasonableness and feasibility of the calibration method. Analysis of the calibration data also demonstrated the consistency in the variation law and trend between the theoretical calculation and actual measurement of internal flow force, further reflecting the rationality and feasibility of the theoretical calculation. Nevertheless, the numerical difference was large and further widened with a higher ejection flow rate mainly because of the accuracy of flow measurement and the inhomogeneity of internal flow. The thrust deflection angle of EPES is an important factor in correcting this issue. In particular, the thrust deflection angle becomes larger with small ejection flow and becomes smaller with an increase in flow rate, essentially exhibiting a general change of less than 10°.
2019, 36(5):760-768.
DOI: 10.16356/j.1005-1120.2019.05.007
Abstract:
For the enhancement of heat transfer efficiency, a novel turbulator inspired by the morphology of barchan dunes, called the mimetic barchan dune (MBD) turbulator, is designed and evaluated in the simplified gas turbine transition section. By using computational fluid dynamics(CFD), the numerical simulations for comparison have been carried out, concluding the smooth thermal surface, a thermal surface with riblet-shaped turbulator and a thermal surface with MBD turbulator. Then, two indicators are investigated for evaluating the coolant performance which are the heat transfer efficiency ( ) on the outlet and the pressure loss ( ) in the coolant chamber. The numerical results show that the coolant has the best heat transfer efficiency with less pressure loss in the coolant chamber with the MBD turbulator. Then, the effect of the MBD turbulator sizes on heat transfer efficiency is investigated. When the height of the MBD turbulator (h) is set at 8 mm, the maximum amount of heat that could be transfered by the coolant is up to 566.2 K and the corresponding heat transfer efficiency is 26.62%. The detail flows have been shown to elucidate the function of the MBD surface which may greatly arouse more design for solving harsh circumstance.
For the enhancement of heat transfer efficiency, a novel turbulator inspired by the morphology of barchan dunes, called the mimetic barchan dune (MBD) turbulator, is designed and evaluated in the simplified gas turbine transition section. By using computational fluid dynamics(CFD), the numerical simulations for comparison have been carried out, concluding the smooth thermal surface, a thermal surface with riblet-shaped turbulator and a thermal surface with MBD turbulator. Then, two indicators are investigated for evaluating the coolant performance which are the heat transfer efficiency (
2019, 36(5):769-778.
DOI: 10.16356/j.1005-1120.2019.05.008
Abstract:
High-speed airflow in wind tunnel tests usually causes dramatic vibration of ejector structure, which may lead to fatigue and even destruction of the wind tunnel. Therefore, analyzing and solving the flow-induced vibration problem is a tough and indispensable part of the wind tunnel security design. In this paper, taking a kind of two-stage ejector as the study object, multiple numerical simulation methods are adopted in order to carry out research on the analysis technique of the flow-induced vibration characteristics of ejector structure. Firstly, the structural dynamics characteristic is analyzed by using the ejector structural dynamics numerical model, which is built on the basis of finite element method. Secondly, the complex flow phenomenon is explored applying numerical fluid-dynamics model of the inner flow field of the ejector, which is constructed on the basis of finite volume method. Finally, based on the two numerical models above, the vibration response of the ejector structure induced by the high-speed airflow is computed via the fluid-solid coupling technique. The comparison of the simulation results with the actual vibration test indicates that these numerical simulation methods can accurately figure out the rule of flow-induced vibration of ejectors.
High-speed airflow in wind tunnel tests usually causes dramatic vibration of ejector structure, which may lead to fatigue and even destruction of the wind tunnel. Therefore, analyzing and solving the flow-induced vibration problem is a tough and indispensable part of the wind tunnel security design. In this paper, taking a kind of two-stage ejector as the study object, multiple numerical simulation methods are adopted in order to carry out research on the analysis technique of the flow-induced vibration characteristics of ejector structure. Firstly, the structural dynamics characteristic is analyzed by using the ejector structural dynamics numerical model, which is built on the basis of finite element method. Secondly, the complex flow phenomenon is explored applying numerical fluid-dynamics model of the inner flow field of the ejector, which is constructed on the basis of finite volume method. Finally, based on the two numerical models above, the vibration response of the ejector structure induced by the high-speed airflow is computed via the fluid-solid coupling technique. The comparison of the simulation results with the actual vibration test indicates that these numerical simulation methods can accurately figure out the rule of flow-induced vibration of ejectors.
2019, 36(5):779-788.
DOI: 10.16356/j.1005-1120.2019.05.009
Abstract:
Digital micro-thruster arrays can be used for special missions of micro/nano-satellites with the requirements of high precision and small impulse. This paper presents a novel control allocation algorithm for the digital micro-thruster array, namely status graph based control allocation (SGBCA) algorithm, which aims at finding the optimal micro thrusters combination scheme to realize the sequential control synthesis for micro/nano-satellite during real-time orbit control tasks. A mathematical model is set up for the control allocation of this multivariate over-actuated system. Through dividing thrusters into disjoint segments by offline calculation and combining segments dynamically online to provide a sequence of the required impulse for the micro/nano-satellite, the time complexity of the control allocation algorithm decreases significantly. All levels of impulse can be generated by the digital micro thruster arrays and the service life of the arrays can be extended using the segment converting strategy proposed in this paper. The simulation indicates that the algorithm can satisfy the requirements of real-time orbit control for micro/nano-satellites.
Digital micro-thruster arrays can be used for special missions of micro/nano-satellites with the requirements of high precision and small impulse. This paper presents a novel control allocation algorithm for the digital micro-thruster array, namely status graph based control allocation (SGBCA) algorithm, which aims at finding the optimal micro thrusters combination scheme to realize the sequential control synthesis for micro/nano-satellite during real-time orbit control tasks. A mathematical model is set up for the control allocation of this multivariate over-actuated system. Through dividing thrusters into disjoint segments by offline calculation and combining segments dynamically online to provide a sequence of the required impulse for the micro/nano-satellite, the time complexity of the control allocation algorithm decreases significantly. All levels of impulse can be generated by the digital micro thruster arrays and the service life of the arrays can be extended using the segment converting strategy proposed in this paper. The simulation indicates that the algorithm can satisfy the requirements of real-time orbit control for micro/nano-satellites.
2019, 36(5):789-797.
DOI: 10.16356/j.1005-1120.2019.05.010
Abstract:
The temperature field in unsteady phase greatly affects the quality of friction plug welding (FPW). An analytical model is put forward to correlate the process parameters and the temperature field in unsteady phase of FPW. Applying the von Mises criterion for plastic deformation and linearizing the heat flux, the model is achieved by Laplace transformation. The predicated peak temperature and peak time agree with the experiment data, with errors of about 4% and 8%, of AA7075-T6 FPW.
The temperature field in unsteady phase greatly affects the quality of friction plug welding (FPW). An analytical model is put forward to correlate the process parameters and the temperature field in unsteady phase of FPW. Applying the von Mises criterion for plastic deformation and linearizing the heat flux, the model is achieved by Laplace transformation. The predicated peak temperature and peak time agree with the experiment data, with errors of about 4% and 8%, of AA7075-T6 FPW.
2019, 36(5):798-807.
DOI: 10.16356/j.1005-1120.2019.05.011
Abstract:
A thermoviscoelastic modeling approach is developed to predict the recovery behaviors of the thermally activated amorphous shape memory polymers (SMPs) based on the generalized finite deformation viscoelasticity theory. In this paper, a series of moduli and relaxation times of the generalized Maxwell model is estimated from the stress relaxation master curve by using the nonlinear regression (NLREG) method. Assuming that the amorphous SMPs are approximately incompressible isotropic elastomers in the rubbery state, the hyperelastic response of the materials is well modeled with a hyperelastic model in Ogden form. In addition, the Williams-Landel-Ferry (WLF) equation is used to describe the horizontal shift factor obtained with time-temperature superposition principle (TTSP). The finite element simulations show good agreement with the experimental thermomechanical behaviors. Moreover, the possibility of developing a temperature-responsive intravascular stent with the SMP studied here is investigated in terms of its thermomechanical property.Therefore, it can be concluded that the model has good prediction capabilities for the recovery behaviors of amorphous SMPs.
A thermoviscoelastic modeling approach is developed to predict the recovery behaviors of the thermally activated amorphous shape memory polymers (SMPs) based on the generalized finite deformation viscoelasticity theory. In this paper, a series of moduli and relaxation times of the generalized Maxwell model is estimated from the stress relaxation master curve by using the nonlinear regression (NLREG) method. Assuming that the amorphous SMPs are approximately incompressible isotropic elastomers in the rubbery state, the hyperelastic response of the materials is well modeled with a hyperelastic model in Ogden form. In addition, the Williams-Landel-Ferry (WLF) equation is used to describe the horizontal shift factor obtained with time-temperature superposition principle (TTSP). The finite element simulations show good agreement with the experimental thermomechanical behaviors. Moreover, the possibility of developing a temperature-responsive intravascular stent with the SMP studied here is investigated in terms of its thermomechanical property.Therefore, it can be concluded that the model has good prediction capabilities for the recovery behaviors of amorphous SMPs.
2019, 36(5):808-816.
DOI: 10.16356/j.1005-1120.2019.05.012
Abstract:
For investigating the back pressure characteristics of turbine channel of an external-parallel turbine-based combined cycle (TBCC) inlet during the mode transition with the freestream air Mach number of 1.8, wind tunnel tests and numerical simulations are carried out. The results show that the critical back pressure of the turbine channel decreases linearly with the decrease of the open degree of splitter plate. The turbine channel has self-starting capacity when the open degree of the turbine channel is 100%. The total pressure recovery coefficient increases with the increase of back pressure when turbine channel is at supercritical and critical state. The mass capture ratio, total pressure recovery coefficient and outlet pressure ratio decrease obviously when turbine channel is at subcritical state. Results of the research would provide scheme reference and technology storage for TBCC propulsion evolution.
For investigating the back pressure characteristics of turbine channel of an external-parallel turbine-based combined cycle (TBCC) inlet during the mode transition with the freestream air Mach number of 1.8, wind tunnel tests and numerical simulations are carried out. The results show that the critical back pressure of the turbine channel decreases linearly with the decrease of the open degree of splitter plate. The turbine channel has self-starting capacity when the open degree of the turbine channel is 100%. The total pressure recovery coefficient increases with the increase of back pressure when turbine channel is at supercritical and critical state. The mass capture ratio, total pressure recovery coefficient and outlet pressure ratio decrease obviously when turbine channel is at subcritical state. Results of the research would provide scheme reference and technology storage for TBCC propulsion evolution.
2019, 36(5):817-827.
DOI: 10.16356/j.1005-1120.2019.05.013
Abstract:
Oscillatory failure cases (OFC) detection in the fly-by-wire (FBW) flight control system for civil aircraft is addressed in this paper. First, OFC is ranked four levels: Handling quality, static load, global structure fatigue and local fatigue, according to their respect impact on aircraft. Second, we present voting and comparing monitors based on un-similarity redundancy commands to detect OFC . Third, the associated performances, the thresholds and the counters of the monitors are calculated by the high fidelity nonlinear aircraft models. Finally, the monitors of OFC are verified by the Iron Bird Platform with real parameters of the flight control system. The results show that our approach can detect OFC rapidly.
Oscillatory failure cases (OFC) detection in the fly-by-wire (FBW) flight control system for civil aircraft is addressed in this paper. First, OFC is ranked four levels: Handling quality, static load, global structure fatigue and local fatigue, according to their respect impact on aircraft. Second, we present voting and comparing monitors based on un-similarity redundancy commands to detect OFC . Third, the associated performances, the thresholds and the counters of the monitors are calculated by the high fidelity nonlinear aircraft models. Finally, the monitors of OFC are verified by the Iron Bird Platform with real parameters of the flight control system. The results show that our approach can detect OFC rapidly.
2019, 36(5):828-837.
DOI: 10.16356/j.1005-1120.2019.05.014
Abstract:
To improve the combustor performance of multi-point injection combustion, lobe nozzle design was applied to the aero-engine model combustor, by presetting the swirl through a certain twisted angle of the edge of the lobe outlet. Numerical simulation in combination with modelling test is used in this paper. The effects of swirl vorticity presetting onto the vortex structure, the characteristics of combustion temperature field, the combustor exit temperature field quality, the combustion efficiency, and the NO x emissions of multi-point injection combustion chamber are investigated. Compared with the conventional vortex flow at the lobe outlet edge, the results of numerical simulation and water modelling test of the swirl vorticity presetting show that the swirl presetting can efficiently enhance the range and intensity of the lobe-induced vorticities. Besides, it can improve the uniformity of the combustion temperature in the combustor chamber, together with the reduced emissions of the pollutant NO x . Moreover, compared with the conventional lobe nozzle chamber, the swirl vortex presetting can effectively improve its combustion performance. The flow simulation test results demonstrate the fluid vortex structure in the combustion chamber and validate the simulation results.
To improve the combustor performance of multi-point injection combustion, lobe nozzle design was applied to the aero-engine model combustor, by presetting the swirl through a certain twisted angle of the edge of the lobe outlet. Numerical simulation in combination with modelling test is used in this paper. The effects of swirl vorticity presetting onto the vortex structure, the characteristics of combustion temperature field, the combustor exit temperature field quality, the combustion efficiency, and the NO x emissions of multi-point injection combustion chamber are investigated. Compared with the conventional vortex flow at the lobe outlet edge, the results of numerical simulation and water modelling test of the swirl vorticity presetting show that the swirl presetting can efficiently enhance the range and intensity of the lobe-induced vorticities. Besides, it can improve the uniformity of the combustion temperature in the combustor chamber, together with the reduced emissions of the pollutant NO x . Moreover, compared with the conventional lobe nozzle chamber, the swirl vortex presetting can effectively improve its combustion performance. The flow simulation test results demonstrate the fluid vortex structure in the combustion chamber and validate the simulation results.
2019, 36(5):838-844.
DOI: 10.16356/j.1005-1120.2019.05.015
Abstract:
The identification result of operational mode is eurychoric while operational mode identification is investigated under ambient excitation, which is influenced by the signal size and the time interval. The operational mode identification method, which is based on the sliding time window method and the eigensystem realization algorithm (ERA), is investigated to improve the identification accuracy and stability. Firstly, the theory of the ERA method is introduced. Secondly, the strategy for decomposition and implementation is put forward, including the sliding time window method and the filtration method of modes. At last, an example is studied, where the model of a cantilever beam is built and the white noise exciting is input. Results show that the operational mode identification method can realize the modes, and has high robustness to the signal to noise ratio and signal size.
The identification result of operational mode is eurychoric while operational mode identification is investigated under ambient excitation, which is influenced by the signal size and the time interval. The operational mode identification method, which is based on the sliding time window method and the eigensystem realization algorithm (ERA), is investigated to improve the identification accuracy and stability. Firstly, the theory of the ERA method is introduced. Secondly, the strategy for decomposition and implementation is put forward, including the sliding time window method and the filtration method of modes. At last, an example is studied, where the model of a cantilever beam is built and the white noise exciting is input. Results show that the operational mode identification method can realize the modes, and has high robustness to the signal to noise ratio and signal size.
2019, 36(5):845-855.
DOI: 10.16356/j.1005-1120.2019.05.016
Abstract:
The detailed flow structures and closely-related heat transfer characteristics are investigated along the wall of a cooling channel with rib tabulator by computation. Three typical Reynolds numbers defined by the rib height are set at 200, 500, 1 300, and the Mach numbers is 0.2, respectively. Two inlet boundary conditions, including the uniform and the fully-developed turbulent conditions, are used to study the turbulence effects on the characteristics of heat transfer in the vicinity of rib and wall. Results show that the local Nusselt number increases when the Reynolds number rises from 200 to 1 300. At lower Reynolds number, the turbulent inlet condition generates more tangible heat transfer enhancement. At higher Reynolds number, however, the uniform inlet condition contributes more to the convective heat transfer effects. The paper discovers that the high Nusselt number has a consistent correlation with the positive and negative sign alteration of the shear layer on the wall, which satisfactorily explains the mechanisms of heat transfer enhancement due to the flow.
The detailed flow structures and closely-related heat transfer characteristics are investigated along the wall of a cooling channel with rib tabulator by computation. Three typical Reynolds numbers defined by the rib height are set at 200, 500, 1 300, and the Mach numbers is 0.2, respectively. Two inlet boundary conditions, including the uniform and the fully-developed turbulent conditions, are used to study the turbulence effects on the characteristics of heat transfer in the vicinity of rib and wall. Results show that the local Nusselt number increases when the Reynolds number rises from 200 to 1 300. At lower Reynolds number, the turbulent inlet condition generates more tangible heat transfer enhancement. At higher Reynolds number, however, the uniform inlet condition contributes more to the convective heat transfer effects. The paper discovers that the high Nusselt number has a consistent correlation with the positive and negative sign alteration of the shear layer on the wall, which satisfactorily explains the mechanisms of heat transfer enhancement due to the flow.
2019, 36(5):856-867.
DOI: 10.16356/j.1005-1120.2019.05.017
Abstract:
The unstarted flow field in a hypersonic inlet model at a design point of Ma 6 is studied experimentally. The time-resolved spatial flow characteristics of the separation shock oscillation, which is induced by the unstarted flow, are analyzed based on a high-speed Schlieren system and an image processing method. The motion of the separation shock detected by the shock-detection algorithm is compared to the results of fast-response wall-pressure measurements, and good agreement is demonstrated by comparing the frequency components in the power spectral density contours between shock oscillation and pressure fluctuation. The hysteresis of the pressure and separation shock during oscillation cycles is observed from the time history of the shock motion, which means that the unsteady flow pattern of the unstarted hypersonic flow can be accurately clarified by time-resolved Schlieren image processing. These results convincingly demonstrate that the shock-detection technique is successfully applied to an unstarted hypersonic flow case.
The unstarted flow field in a hypersonic inlet model at a design point of Ma 6 is studied experimentally. The time-resolved spatial flow characteristics of the separation shock oscillation, which is induced by the unstarted flow, are analyzed based on a high-speed Schlieren system and an image processing method. The motion of the separation shock detected by the shock-detection algorithm is compared to the results of fast-response wall-pressure measurements, and good agreement is demonstrated by comparing the frequency components in the power spectral density contours between shock oscillation and pressure fluctuation. The hysteresis of the pressure and separation shock during oscillation cycles is observed from the time history of the shock motion, which means that the unsteady flow pattern of the unstarted hypersonic flow can be accurately clarified by time-resolved Schlieren image processing. These results convincingly demonstrate that the shock-detection technique is successfully applied to an unstarted hypersonic flow case.
2019, 36(5):868-878.
DOI: 10.16356/j.1005-1120.2019.05.018
Abstract:
It is important to improve the development efficiency of decoupling a coupling task package according to the information relevancy relation between development tasks in the collaborative development process of complicated electronic products. In order to define the task coupling model in the development process, the weighted directed graph based on the information relevancy is established, and the correspondence between weighted directed graph model and numerical design structure matrix model of coupling tasks is introduced. The task coupling model is quantized, thereby the interactivity matrix of task package is built. A multi-goal task decoupling method based on improved genetic algorithm is proposed to decouple the task coupling model, which transforms the decoupling of task package into a multi-goal optimization issue. Then the improved genetic algorithm is used to solve the interactivity matrix of coupling tasks. Finally, the effectiveness of this decomposition method is proved by using the example of task package decoupling of collaborative development of a radar’s phased array antenna.
It is important to improve the development efficiency of decoupling a coupling task package according to the information relevancy relation between development tasks in the collaborative development process of complicated electronic products. In order to define the task coupling model in the development process, the weighted directed graph based on the information relevancy is established, and the correspondence between weighted directed graph model and numerical design structure matrix model of coupling tasks is introduced. The task coupling model is quantized, thereby the interactivity matrix of task package is built. A multi-goal task decoupling method based on improved genetic algorithm is proposed to decouple the task coupling model, which transforms the decoupling of task package into a multi-goal optimization issue. Then the improved genetic algorithm is used to solve the interactivity matrix of coupling tasks. Finally, the effectiveness of this decomposition method is proved by using the example of task package decoupling of collaborative development of a radar’s phased array antenna.
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