Ji-an Chen

Fiber Bragg grating-based plane strain monitoring of aerostat envelope structures

A theoretical analysis of fiber Bragg grating (FBG)-based plane strain monitoring of aerostat envelope structures is presented. Plane strain analysis of FBG-based aerostat envelope structures is much more complex than the case along the axis of the optical fiber because the effect of transverse stress on the FBG should be taken into consideration. To achieve accurate strain measurement of the aerostat envelope, a theoretical model is set up by using two perpendicular fibers in the monitoring. An analytical formula that evaluates the relationship between the strain measured by FBG sensors and the real one in the aerostat envelope is established. On the other hand, the real strain of aerostat envelope strain is affected by two unknown parameters, axial transfer rate K(L) and the radial transfer rate K(R). An equation is derived to calculate the axial transfer rate K(L). Then, the finite element method results show that K(R) is a very small value, but it cannot be ignored in accurate measurement. This paper would lay a theoretical groundwork for the research and design of FBG sensors in the structural health monitoring of aerostat envelope structures.

Finite time attitude tracking control of an autonomous airship

The problem of station-keeping attitude tracking control for an autonomous airship with system uncertainties and external disturbances is investigated. Adaptive laws are applied to estimate the upper bounds of uncertainties and disturbances, and a nonlinear finite time control scheme is proposed by combing input/output feedback linearization with integral sliding mode technique. Different from the existing works on attitude control of airship, the developed controller can guarantee the yaw, pitch and roll angle trajectories track the desired attitude in finite time in spite of uncertain system uncertainties and external disturbances. Simulation results are provided to illustrate the attitude tracking performance.

Analysis of strain transfer of six-layer surface-bonded fiber Bragg gratings

A theoretical analysis of strain transfer of six-layer surface-bonded fiber Bragg gratings (FBGs) subjected to uniform axial stress is presented. The proposed six-layer structure consists of optical fiber, protective coating, adhesive layer, substrate layer, outer adhesive layer, and host material, which is different from the four-layer case of common acknowledgement. A theoretical formula of strain transfer rate from host material to optical fiber is established to provide an accurate theoretical prediction. On the basis of the theoretical analysis, influence parameters of the middle layers that affect the average strain transfer rate of the six-layer surface-bonded FBG are discussed. After the parametric study, a selection scheme of sensor parameters for numerical validation, which makes the average strain transfer rate approach unity, is determined. Good agreement is observed between numerical results and theoretical predictions. In the end, the six-layer model is extended to the general situation of multiple substrate layers, which lays a theoretical groundwork for the research and design of surface-bonded FBGs with substrate layers in the future.

Modified digital image correlation for balancing the influence of subset size choice

Abstract. A modified digital image correlation (DIC) method is presented to balance the influence of subset size choice, improve the calculation efficiency, and enhance the measurement accuracy. The relations between pixels and the central pixel are investigated. A relatively large subset size is selected in the method and all the pixels in a subset are treated nonuniformly. Weight is assigned to each pixel dependent on the significance of the pixel to track a subset from deformed images, and weights are computed by Butterworth function based on the distances between the pixels and the central pixel in the subset. Compared with classical DIC, the proposed method is a compromise between a small and a large subset. The choice of subset size for classical DIC is displaced by choice of parameters of Butterworth function in the presented method. The influence of subset size is reduced, and the calculation efficiency is improved with enhanced measurement accuracy by the modified method. Computer-simulated speckle patterns and real experiments are applied to verify the proposed method.

Configuration Analysis of a High-Altitude Airship’s Regenerative Power System

AbstractIn the design of the power system of a high-altitude airship (HAA), the principal target is to satisfy the needs of the power demand and achieve the best balance of minimum weight and maximum reliability. To handle this problem, configuration analysis of the power system is performed. Mathematical models of output power, reliability, and weight are presented. Relationships between weight, reliability, and configurations are discussed in detail. Several design rules related to the design of the HAA’s power system are deduced. For obtaining the optimal configuration, the self-adaptive genetic algorithm (GA) is applied. Results show that the optimal configuration, compared to the configuration without redundancy, has a 258% increase in reliability and a 55.9% increase in weight. The weight increase is necessary to achieve more reliability improvement.

H; ∞ non-fragile observer-based sliding mode control of singular Markovian jump systems with state delay

This paper is concerned with the state estimation and H∞ sliding mode control for delayed singular Markovian jump systems. A non-fragile observer is designed to estimate the system states, and the sliding mode control law is established to ensure the reachability of the sliding surface in the state-estimation space. Then, some sufficient conditions for the stochastic admissibility of the overall closed-loop system with H∞ disturbance attenuation level are derived in terms of strict linear matrix inequality (LMI).

Force identification based on a comprehensive approach combining Taylor formula and acceleration transmissibility

Abstract Force identification is a crucial inverse problem in structural dynamics. In this paper, a new method integrating Taylor formula algorithm and acceleration transmissibility concept is put forward to identify the magnitude and location of loads in time domain. The Taylor formula algorithm expresses the response vectors as Taylor-series expansion and then, a series of deductions are implemented. Ultimately an explicit discrete equation which associates output acceleration response, structure characteristic and input excitation together is established. After establishing the explicit discrete equation, acceleration transmissibility concept is utilized to identify the location of forces. Under the premise of knowing the acceleration response and structure characteristic, force magnitude can be calculated. To verify the effectiveness of proposed method, one builds up a theoretical simulation model in which different types of dynamic excitations are exerted on an inflatable cantilever beam. Meanwhile, classical state space algorithm is made a contrast with Taylor formula algorithm in the step of force magnitude identification. Calculation results demonstrate that the integration method is capable of identifying the location of excitations precisely. Reconstruction of force time history reaches a higher accuracy compared to state space algorithm as well. In addition, the anti-noise ability of proposed algorithm is discussed.

Preliminary reliability analysis of a high-altitude airship’s envelope

To analyze the reliability of an airship’s envelope, the methodology of structural reliability analysis is adopted. The basic theory and the detailed steps of the algorithm of the first-order reliability method are discussed. For finding multiple design points, the method of adding bulge to the limit-state function is applied. With regard to the problem of envelope’s reliability, the safety criterion and limit state function of the airship’s envelope are analyzed. The mathematical model of the envelope’s maximum stress is also presented. The reliability simulation of a stratospheric airship’s envelope is taken as an example. Results of sensitivity analyses of the envelope are also obtained.

Applications of FBG Sensors for Airship Structural Health Monitoring

The application of structural health monitoring (SHM) based on fiber Bragg grating (FBG) for airships is investigated. In order to verify the validity of the FBG-based SHM in the field of airships, a qualitative strain monitoring experiment for ZHIYUAN-1 airship nosecone has been carried out. A commercial FBG interrogation system (Micron Optics sm130) is used in this experiment to measure the strain. Moreover, a finite element (FE) analysis is proceeded to confirm the result of the experiment. Results indicate the effectiveness of the FBG-based SHM system for the strain monitoring in the airship field. Finally, some proposals for future researches are provided.

Reliability Analysis for the Power and Propulsion System of Stratospheric Airship

For meeting requirements of staying in the stratosphere for a long time period more than one year and less of maintenance, the power and propulsion system of the stratospheric airship is required to have high reliability. In this regard, reliability design is a key procedure in the design phase of the power and propulsion system of stratospheric airship. This paper focuses on the quantitative analysis of the reliability for the power and propulsion system of the stratospheric airship. Firstly, the reliability of the solar cell array and the fuel cell of power system are discussed respectively. Then, different topologies of the power system are discussed and compared. The reliability of the propulsion system is also analyzed in different configurations. The reliability of the basic combination of the power and propulsion system is discussed. For improving reliability, a new type of combination for the power and propulsion system is proposed. Reliability models of proposed combination are created through simplification. The ZhiYuan-1 is used as a demonstration problem to show the capability of this reliability-improved method. The result shows that the reliability of ZhiYuan-1 power and propulsion system increases by 12.8%.