8 results on '"Zhiwei Shi"'
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2. Investigation of heat and mass transfer of flow structures generated by a pulsed surface arc discharge actuator in quiescent air
- Author
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Zhikun Sun, Zhiwei Shi, Xi Geng, Zheng Li, and Qijie Sun
- Subjects
Aerospace Engineering - Published
- 2023
3. Study on propagation mechanisms of the actuations generated by plasma synthetic jet actuator in a supersonic flow
- Author
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Weilin Zhang, Zhiwei Shi, Zheng Li, Xi Geng, Chuanhong Zhang, and Quanbing Sun
- Subjects
Aerospace Engineering - Published
- 2022
4. Energy optimization and investigation for Z-shaped sun-tracking morphing-wing solar-powered UAV
- Author
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Tianhang Xiao, Zhiwei Shi, Mingjian Wu, and Haisong Ang
- Subjects
0209 industrial biotechnology ,Wing ,business.industry ,Energy conversion efficiency ,Aerospace Engineering ,02 engineering and technology ,Energy minimization ,Tracking (particle physics) ,Solar energy ,01 natural sciences ,010305 fluids & plasmas ,Latitude ,020901 industrial engineering & automation ,0103 physical sciences ,Environmental science ,Daylight ,Electricity ,Aerospace engineering ,business - Abstract
To achieve perpetual flight, solar-powered UAVs (SPUAVs) need to convert sufficient solar energy into electricity during daylight flight. However, perpetual flight at middle and high latitude regions in winter days still poses great challenges for gaining enough solar energy due to the low sun elevation angle and short daylight duration. Among measures for flight endurance enhancement, tracking the sun through changing geometry of wing and orienting flight direction may be an effective design scheme for gaining more solar energy. In this paper, the energy optimization method for Z-shaped sun-tracking morphing-wing SPUAV is developed and used to investigate the advantages on energy performance of the optimal Z-shaped wing over the conventional planar wing. Energy optimization for a whole year's flight shows that the optimal Z-shaped wing is capable of achieving longer flight endurance, improving perpetual flight latitude and extending perpetual flight date efficiently compared with the planar wing, especially for the middle and high latitude regions during winter days. The investigation on implications of conversion efficiency of solar cells indicates that, with higher conversion efficiency of solar cells, the optimal Z-shaped wing is more effective to collect more net energy, retain more energy margin and achieve perpetual flight at higher latitude. The Z-shaped sun-tracking morphing-wing design combined with the energy optimization method proposed is helpful to increase flight endurance and improve perpetual flight latitude for SPUAVs.
- Published
- 2019
5. Self-learned suppression of roll oscillations based on model-free reinforcement learning
- Author
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Zhiwei Shi, Zhangyi Yao, Kun Chen, and Yizhang Dong
- Subjects
0209 industrial biotechnology ,Computer science ,Counterintuitive ,Aerospace Engineering ,02 engineering and technology ,Model free ,Space (mathematics) ,01 natural sciences ,010305 fluids & plasmas ,020901 industrial engineering & automation ,Control theory ,0103 physical sciences ,Reinforcement learning ,Current sensor - Abstract
The high-angle-of-attack uncommanded roll oscillations are dangerous and cause significant challenges in flight control. This paper focuses on investigating the feasibility and performance of an artificial-intelligence method - “model-free reinforcement learning” (MFRL) on this issue, in both simulation and experiment. In simulation, two algorithms TD3 and SAC were used to learn the policies to suppress the roll oscillations of a widely used mathematical model. The agents only utilized current states as observation vector, and achieved perfect results. In the experiments, these two algorithms were used to learn the policies to suppress the roll oscillations of a flying-wing model which utilized spanwise blowing as its roll effectors. It is worth noting that unlike in simulation, the experiments investigated the influence of the observation vectors' memory size on training results. The results show that for both algorithms, the agents cannot learn good-enough policies when their observation spaces were constructed only by the current sensor data. This phenomenon, which is a big difference between experiments and simulations of MFRL, is due to the non-Markovian characteristic of the real-world dynamics caused by inevitable latencies. However, constructing the observation space using current and past sensor data help both the TD3 and SAC agents to learn great policies to suppress the oscillations using spanwise blowing in real world. Surprisingly, the trained agents showed some counterintuitive “smart” behaviors in tests.
- Published
- 2021
6. Effect of wingtip connection on the energy and flight endurance performance of solar aircraft
- Author
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Tianhang Xiao, Zhiwei Shi, Mingjian Wu, and Haisong Ang
- Subjects
Battery (electricity) ,0209 industrial biotechnology ,Lift-induced drag ,business.industry ,Aerospace Engineering ,02 engineering and technology ,Energy consumption ,01 natural sciences ,Aspect ratio (image) ,010305 fluids & plasmas ,020901 industrial engineering & automation ,Solar cell efficiency ,Range (aeronautics) ,Physics::Space Physics ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Environmental science ,Daylight ,Astrophysics::Earth and Planetary Astrophysics ,Aerospace engineering ,business ,Oswald efficiency number ,Physics::Atmospheric and Oceanic Physics - Abstract
This study explores the effects of wingtip connection on decreasing energy consumption and increasing flight endurance for solar aircraft. The Oswald efficiency factor, induced drag coefficient and power consumption are derived as the models of the number of wingtip connected aircraft. As the energy margin model is related to the number of connected solar aircraft, a flight endurance margin model is proposed to evaluate the advantages of wingtip connection quantitatively. With the numerical method developed, researches on the energy and flight endurance performance for a given example wingtip-connected solar aircraft are performed. Moreover, the impacts of solar cell efficiency, flight date and latitude on the advantages of wingtip connection for solar aircraft are explored. The results suggest that the wingtip connection design enables solar aircraft to decrease induced drag coefficient, increase flight endurance and range effectively when the aircraft is only powered by battery. The wingtip connection design is more effective to increase the flight endurance and improve the maximum perpetual flight latitude with more connected solar aircrafts and higher solar cell efficiency, especially in the flight condition with high solar elevation angle and more daylight hours. However, as the number of connected solar aircraft increases, the effect of one more connected aircraft on these advantages decreases because the effect of wingtip connection on decreasing induced drag coefficient decreases with increasing aspect ratio.
- Published
- 2021
7. Study on inner characteristics of plasma synthetic jet actuator and geometric effects
- Author
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Weilin Zhang, Shoulin Jin, Zhiwei Shi, and Xi Geng
- Subjects
0209 industrial biotechnology ,Jet (fluid) ,Materials science ,Computer simulation ,Turbulence ,Oscillation ,Flow (psychology) ,Aerospace Engineering ,02 engineering and technology ,Plasma ,Mechanics ,01 natural sciences ,010305 fluids & plasmas ,020901 industrial engineering & automation ,Speed of sound ,0103 physical sciences ,Body orifice - Abstract
In order to further study the inner characteristics of the plasma synthetic jet actuator (PSJA) which consists of a cavity, two electrodes and a lid with orifice, a two-dimensional numerical simulation is carried out with SST k-ω turbulence model. The evolutions of the flow parameters inside the cavity with a single pulse, such as pressure, density, temperature and velocity, are analyzed in detail. The oscillation mechanisms of the flow parameters at the orifice of the cavity is also investigated. To study the effects of geometric factors on the performance of the PSJA, five widths and heights of the cavities are considered. The results suggest that the base frequencies are inversely proportional to the width and height of the cavity respectively. The proportional constant is equal to the sound speed. Besides, shortening the width or height of the cavity can obtain a faster peak velocity of the jet. The peak of the jet velocity occurs earlier with a shorter height of the cavity.
- Published
- 2020
8. The suppression of flying-wing roll oscillations with open and closed-loop spanwise blowing
- Author
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Yizhang Dong, Dechen Wei, Zhiwei Shi, Shengxiang Tong, and Kun Chen
- Subjects
Flow control (data) ,Physics ,0209 industrial biotechnology ,Wing ,Angle of attack ,Control variable ,Aerospace Engineering ,02 engineering and technology ,Mechanics ,01 natural sciences ,Trim ,010305 fluids & plasmas ,Vortex ,020901 industrial engineering & automation ,Duty cycle ,0103 physical sciences ,Order of magnitude - Abstract
Uncommanded self-induced roll oscillations cause significant challenges in flight control and are ubiquitous in high-attack-angle flights in the flying-wing configuration. Spanwise blowing slots were designed in this article to suppress these roll oscillations with nonzero mean angles of a 53° swept flying-wing model. Three flow control strategies were proposed and studied successively. The open-loop symmetric blowing successfully suppressed oscillations below the nominal angle of attack of 24° before losing its effectiveness. Subsequently, adaptive continuous blowing using the proportion-integral-differential algorithm was performed with symmetric pre-blowing to eliminate the ineffective region with a small blowing coefficient. Using this strategy, roll oscillations under all tested nominal angles of attack were successfully addressed as the nonzero trim angles were eliminated and the oscillations were suppressed. However, the air consumption needed to maintain the model balance was too large, which necessitated the development of pulsed blowing. Static force measurements showed that the blowing-induced rolling moment had a linear relationship with the duty cycle of blowing. The results from the particle-image-velocimetry tests revealed that the mechanism of the linear relationship was the increased duration of coherent vortices over a period at longer duty cycles. Based on the static experimental results, the model was stabilized via proportion-integral-differential adaptive blowing, which utilized the duty cycle as the control variable. Compared to the second strategy, the last one reduced the required mean blowing momentum coefficient by two orders of magnitude while maintaining a great control effect.
- Published
- 2020
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