Robust Output Tracking Control of Uncertain Nonaffine Systems With Guaranteed Tracking Error Bounds

Zhixiang Chen,Wenyan Bai,Lingjian Kong 제어·로봇·시스템학회 2024 International Journal of Control, Automation, and Vol.22 No.4

This paper considers the output tracking problem for uncertain nonaffine systems. A robust output tracking controller for a class of uncertain nonaffine strict-feedback systems with guaranteed tracking error bounds is proposed. First, a diffeomorphism is employed to convert the strict-feedback nonaffine system with mismatched uncertainties into a feedback linearization nonaffine system (FLNS). Second, for the transformed FLNS, an error transformation and sliding surface technique are combined to transform the constrained tracking problem of a highorder system into an unconstrained stabilization problem of a first-order system when visualizing the guaranteed tracking error bound as a tracking error constraint. Then, a saturated approximate dynamic inversion scheme and an extended state observer are combined to achieve the stabilization of the transformed first-order nonaffine system. The stability of the closed-loop system is analyzed rigorously and it is sufficient to guarantee that the tracking error constraint can be achieved and all system states are semi-globally uniformly bounded for the original system. Simulation results clarify and verify the effectiveness of the proposed method.

Sensitivity of Extreme Temperature Events to Urbanization in the Pearl River Delta Region

Zhixiang Xiao,Ziqian Wang,Weijuan Pan,Yongli Wang,Song Yang 한국기상학회 2019 Asia-Pacific Journal of Atmospheric Sciences Vol.55 No.3

The urbanization effect on extreme temperature related to heat wave events in the Pearl River Delta (PRD) of China is investigated using a regional model. Several experiments with different urbanization levels are carried out. Results indicate that the air temperature of heat wave events is sensitive to urban land cover and the urbanized warming intensifies along with urban expansion. The regional model performs better on the simulations of maximum and minimum 2-m air temperature when urban land cover is close to the observed value. Because of the urbanization effect, the surface skin temperature shows a maximum warming (~2.5 °C) at daytime, while the maximum warming of 2-m air temperature (~1.5 °C) occurs at nighttime. Consequently, an increased (a decreased) diurnal range in surface skin temperature (2-m air temperature) is induced. According to the diagnostic equations, the 2-m air temperature is not only related to surface skin temperature, but also regulated by surface sensible heat flux. At daytime, although the increased solar absorption and the decreased upward latent heat flux (due to the deficit of surface evaporation) sharply enhance the surface skin temperature in the higher urbanization experiment, the simultaneously increased sensible heat flux suppresses the 2-m air temperature. At nighttime, however, the difference in surface sensible heat flux is relatively small, thus 2-m air temperature largely depends on surface skin temperature influenced by ground heat release. This study emphasizes the different variations and physical mechanisms of surface skin temperature and 2-m air temperature under the urbanization in the PRD region.

Wind tunnel tests and CFD simulations for snow redistribution on 3D stepped flat roofs

Zhixiang Yu,Fu Zhu,Ruizhou Cao,Xiaoxiao Chen,Lei Zhao,Shichun Zhao 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.28 No.1

The accurate prediction of snow distributions under the wind action on roofs plays an important role in designing structures in civil engineering in regions with heavy snowfall. Affected by some factors such as building shapes, sizes and layouts, the snow drifting on roofs shows more three-dimensional characteristics. Thus, the research on three-dimensional snow distribution is needed. Firstly, four groups of stepped flat roofs are designed, of which the width-height ratio is 3, 4, 5 and 6. Silica sand with average radius of 0.1 mm is used to model the snow particles and then the wind tunnel test of snow drifting on stepped flat roofs is carried out. 3D scanning is used to obtain the snow distribution after the test is finished and the mean mass transport rate is calculated. Next, the wind velocity and duration is determined for numerical simulations based on similarity criteria. The adaptive-mesh method based on radial basis function (RBF) interpolation is used to simulate the dynamic change of snow phase boundary on lower roofs and then a time-marching analysis of steady snow drifting is conducted. The overall trend of numerical results are generally consistent with the wind tunnel tests and field measurements, which validate the accuracy of the numerical simulation. The combination between the wind tunnel test and CFD simulation for three-dimensional typical roofs can provide certain reference to the prediction of the distribution of snow loads on typical roofs.

Experimental study on the influence of Reynolds number and roll angle on train aerodynamics

Zhixiang Huang,Wenhui Li,Tanghong Liu,Li Chen 한국풍공학회 2022 Wind and Structures, An International Journal (WAS Vol.35 No.2

When the rolling stocks run on the curve, the external rail has to be lifted to a certain level to balance the centrifugal force acting on the train body. Under such a situation, passengers may feel uncomfortable, and the slanted vehicle has the potential overturning risks at high speed. This paper conducted a wind tunnel test in an annular wind tunnel with φ=3.2 m based on a 1/20th scaled high-speed train (HST) model. The sensitivity of Reynolds effects ranging from Re = 0.37×106 to Re = 1.45×106 was tested based on the incoming wind from U=30 m/s to U=113 m/s. The wind speed covers the range from incompressible to compressible. The impact of roll angle ranging from γ=0° to γ=4° on train aerodynamics was tested. In addition, the boundary layer development was also analyzed under different wind speeds. The results indicate that drag and lift aerodynamic coefficients gradually stabilized and converged over U=70 m/s, which could be regeared as the self-similarity region. Similarly, the thickness of the boundary layer on the floor gradually decreased with the wind speed increase, and little changed over U=80 m/s. The rolling moment of the head and tail cars increased with the roll angle from γ=0° to γ=4°. However, the potential overturning risks of the head car are higher than the tail car with the increase of the roll angle. This study is significant in providing a reference for the overturning assessment of HST.

Nonlinear Vibrations of a Unbalanced Rotor Supported by PMR Magnetic Bearings

Zhixiang Xu,Hideyuki Tamura,Kunisato Seto 대한기계학회 1997 Asia-Pacific Vibration Conference Vol.2 No.1

Active Fault Tolerant Control of an Unmanned Surface Vehicle

Zhixiang Liu,Youmin Zhang,Chi Yuan 제어로봇시스템학회 2015 제어로봇시스템학회 국제학술대회 논문집 Vol.2015 No.10

This paper presents an active fault tolerant control methodology with application to an unmanned surface vehicle (USV). Firstly, an augmented linear quadratic regulator (LQR) scheme is developed to guarantee the desired control performance and stability of USV in the absence of actuator faults. Secondly, an additional control mechanism incorporating a fault estimator and an adaptive fault compensator are synthesized to asymptotically stabilize the closedloop system in the event of actuator faults. Based on a nonlinear USV model, simulation results validated the effectiveness of the proposed control approach in either the absence or presence of actuator faults.

Effects of cyclic loads on viscoelastic behavior of brain tissue on the implanting trajectory of STN-DBS

Zhixiang Huang,Chunyang Pan,Panling Huang,Jun Zhou,Xueen Li 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.4

During deep brain stimulation of the sub-thalamic nucleus (STN-DBS), frequently adjusting the position of the cannula may lead to changes in tissue viscoelasticity. To investigate the mechanical properties of tissue on implant path at repeated loads, three cyclic tension and relaxation tests were carried out at 10 % and 20 % strains. Results indicated that white matter was about 25 %-140 % stiffer than gray matter. Within 20 % strain, the natural viscoelasticity of tissue was not affected by the repeated tension. Whereas at 20 % strain, irreversible internal structure rearrangements occurred at the first relaxation due to the persistent strain action, and almost 60 % of the attenuation modulus generated in the initial 5 s of the process, which leads to a softer transformation of the tissue. Further simulated puncture experiments revealed that an irreversible depression occurred when the cerebral hemisphere was subjected to a constant pressure of cannula for 5 s.

Ternary blends for large area flexible organic solar cells

Zhixiang Wei 한국고분자학회 2016 한국고분자학회 학술대회 연구논문 초록집 Vol.41 No.2

A Comparative Study on the Offshore Intensification of Supertyphoon Rammasun (2014) and Typhoon Rumbia (2013): the Role of Summer Monsoon

Zhixiang Xiao,Cai Yao,Xiaoli Luo,Hongmei Sun 한국기상학회 2021 Asia-Pacific Journal of Atmospheric Sciences Vol.57 No.3

The offshore intensificationmechanisms of Supertyphoon Rammasun (2014) and Typhoon Rumbia (2013) are analyzed and compared based on the best track typhoon data provided by the Shanghai Typhoon Institute of China Meteorological Administration (STI/CMA), ECMWF (CMA and JMA) objective (subjective) predicted typhoon track and intensity, and reanalysis data of the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). Results show that the offshore sea surface temperature over 28 °C was conducive to the intensification of the two typhoons in the coastal area prior to their landfall in South China. Rammasun was embedded in an extremely active phase of a 10–20-day oscillation in the summer monsoon over the South China Sea and western North Pacific prior to its landfall. The low-level jet transported warm and moist air to the inner core of Rammasun and the deepening of the southwesterly monsoon flow up to 200 hPa reduced vertical wind shear, both favorable for the offshore rapid intensification of Rammasun. In 2013, the summer monsoon over the South China Sea and western North Pacific experienced quasi-20-day and quasi-10-day oscillations. The out of phase of the two oscillations resulted in relatively weak tropical and subtropical summer monsoon flow prior to the landfall of Rumbia. As a result, the low-level monsoon flow transported relatively less moist air into Rumbia, and the shallow monsoon flow was not conducive to the weakening of vertical wind shear, resulting in a less rapid offshore intensification of Rumbia than Rammasun.

Progress of China Nuclear Data Evaluation

Zhixiang X. Zhao,Zhigang G. Ge 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.23

Recent years, a lot of achievements on nuclear data evaluation and nuclear database set up et al., are obtained by China Nuclear Data Centre (CNDC). A new evaluated neutron data library CENDL-3.1, which contained 240 nuclei data file with ENDF6 format, is released and a lot of benchmark and data validation for this library have been performed. The nuclear data model study and code system improvement are done at CNDC and some code systems (UNF, MEND et al.) based on the updated study results is being used in the evaluation activities. As an important tendency of nuclear data application, the evaluated covariance les are become more and more important, so establishment of the producing method for the covariance files is one of the most important tasks for nuclear data researchers. A new evaluation system for evaluation the covariance le is being developing and some good results are obtained at CNDC. Some good improvements on the study of fission yield data evaluation and relative field have been carried out. A new semi-empirical model, which used to analyze and to describe the yield-energy relations and a new systematics on independent yield with Zp model are developed. The progress at CNDC about nuclear data evaluation, data process, validation and related research fields studies are mentioned in this presentation.