Papers by Author: Zhi Chun Yang

Abstract: Normal mode and flutter analysis are conducted for a high aspect ratio aft swept flying wing model, and body freedom flutter is found to be the most critical aeroelastic instability for this air vehicle model. To determine the influence of various kinds of design parameters on BFF characteristics, eight factors are considered in the parametric study, i.e. wing vertical bending stiffness, weight and center of gravity of the wing root payload and the wing tip mass balance, wing half span, aft swept angle and the station of wing body blended line. After the parametric analysis, the mass and center of gravity of the wing root payload are selected as design variables, and the baseline model is utilized in the design optimization study subject to critical flutter speed constraint. Finally, the optimal mass balance design is suggested to suppress the body freedom flutter phenomenon passively and maximize the payload.

Abstract: To penetrate into the study of POGO vibration, by taking the LRC equivalent circuit analyzing method, based on two boundary conditions in document [, taking the flow pulse drive into consideration, this paper proposes four boundary conditions specific to the propelling flow system in liquid rockets, and at the same time, complements the mathematic model. Further, by way of network function, under the liquid system flow parameter, this paper infers transfer function expressions, and makes the accurate solution of the natural frequency under every boundary condition. At last, from the statistic point of view, by the method of correlation coefficient, this paper studies the influence that the flow parameter may have on the system natural frequency, and set the major influential liquid flow parameter to the system natural frequency of liquid propelling flow system in liquid rockets.

Abstract: The inner product vector (IPV) was proposed in our previous research as a damage detection algorithm which uses cross correlation functions between vibration responses under band pass white noise excitation. It was verified that the IPV of a structure is a weighted summation of the mode shapes of the structure and the weighing factors for each modes are different. Structural damage detection examples in our previous research shown that the damage location can be correctly detected if the bandwidth of the band pass white noise excitation only covers the fundamental natural frequency of the structure. However, the bandwidth of the band pass white noise excitation may cover first several natural frequencies of the structure in practice. This paper just investigates the damage detection method using IPV under the situation when the bandwidth of the band pass white noise excitation may cover first several natural frequencies of the structure, i.e. the hybrid method using IPV and low pass filter technique. Firstly, the theory of IPVs and the damage detection method using IPV are reviewed shortly. Then, the hybrid method using IPV and low pass filter technique is introduced. Finally, experimental damage detection example of a shear frame structure is presented to illustrate the method proposed in this paper.

Abstract: Mu method is a flutter solution technique based on frequency domain mu-analysis, which directly applies perturbation to dynamic pressure in aeroelastic equation of motion. In a previous study, the dynamic pressure perturbation was modeled as a purely real uncertainty, which could not guarantee the continuity of mu. To improve the continuity of mu, a small amount of complex perturbation is added to the dynamic pressure in addition to the real perturbation. Thus the mu method is improved with this mixed real/complex perturbation. Formulations and algorithm of the improved method are presented and validated with sample test cases. It is demonstrated that the improved mu method is more feasible and conservative than the original mu method due to the mixed perturbation.

Abstract: This paper investigates the stability issues of functionally graded material (FGM) panels subjected simultaneously to both aerodynamic and thermal loads. Finite Element Method is employed to model the panel structures and the supersonic aerodynamics is calculated by the first-order piston theory. The critical buckling temperature elevation of the panels is at first predicted. The nonlinear static analysis of the panels is then implemented at certain interval of temperature elevation before buckling onset to obtain structural stiffness matrix. The flutter speed of the panels with updated stiffness matrix corresponding to a certain temperature elevation is estimated. The results show that the FGM panels can offer beneficial effects, especially prevention from buckling. However, if FGM panels integrated with TPS are to be applied on supersonic vehicles, one should pay more attention to the boundary conditions to guarantee the dynamic stability.

Abstract: Smoothed particle hydrodynamics (SPH) method is used to simulate the lift-off phenomenon of sand particles in the air flow. Whether the sand particles make any form of movement in the air flow, firstly, they always jump into the air from a standstill condition, so it is helpfull to understand the saltation mechanism of sand particles. Because the computitional region is discreted into particles in the SPH method, the movement of each particle can represent the machnical behavior of sand particles if the particle dispersion has the same characteristic with the sand particles. The foundmental theory of SPH method and its key elements are reviewed in detail, such as the kernel function, the choice of smoothing length and their influence on the numerical simulation results.In this study a numerical simulation model of wind-blown sand two-phase flow using SPH model is proposed and then the model is discreted to simulate the take-off process of sand particles with adquate boundary conditions. Simulation results show that the proposed model can be used to simulate the dynamic characteristics of sand particles in lift-off.

Abstract: This paper investigates aeroelastic tailoring and optimal trailing edge control surface deflection to minimize induced drag for a HALE UAV flying wing configuration. The analysis process is conducted on the Finite Element(FE) model of a composite slender wing. Genetic Algorithm(GA) is employed to aeroelastically tailor the wing by setting the composite ply orientation. The study examined conformal and traditional flaps and explored two optimization formulations to minimize drag. The impacts of the conformal control surface are recognized as required deflection saving which can be translated to drag reduction. The results also show that the control demands for the optimal trim can be further reduced if the wing is properly tailored.

Abstract: Wind-Blown sand movement is a complicated, non-linear, self-organized and two-phase flow. Conventional theory of mechanics and existing experimental observation method can’t describe that inherent mechanism exactly, and then appeared much difficulty of numerical method for computational simulation of wind-blown sand movement. In this paper, the smoothed particle hydrodynamics (SPH) method is used for simulating the wind-blown sand movement process. According to the characteristic of wind-blown sand movement the sand grains phase and the gas phase are modeled by considering the different kernel function and the particles size, mass, density, velocity and other physical quantities, which can movement along with controlling equation. Finally the numerical simulations are conducted for wind-blown sand movement and some reasonable results are obtained.

Abstract: An investigation on the stability of heated panels in supersonic airflow is performed. The nonlinear aeroelastic model for a two-dimensional panel is established using Galerkin method and the thermal effect on the panel stiffness is also considered. The quasi-steady piston theory is employed to calculate the aerodynamic load on the panel. The static and dynamic stabilities for flat panels are studied using Lyapunov indirect method and the stability boundary curve is obtained. The static deformation of a post-buckled panel is then calculated and the local stability of the post-buckling equilibrium is analyzed. The limit cycle oscillation of the post-buckled panel is simulated in time domain. The results show that a two-mode model is suitable for panel static stability analysis and static deformation calculation; but more than four modes are required for dynamic stability analysis. The effects of temperature elevation and dimensionless parameters related to panel length/thickness ratio, material density and Mach number on the stability of heated panel are studied. It is found that panel flutter may occur at relatively low aerodynamic pressure when several stable equilibria exist for the aeroelastic system of heated panel.

Abstract: The analytical evaluation and finite element methods are used to analyze the critical stability of the shallow spherical roof of oil storage tank with an axial symmetrical corrosion region. At first, the nonlinear finite element method is adopted to calculate the global critical load of the storage tank roof, and the local corrosion region is equivalent to a circular corrosion pit with uniform depth. The results show that the tank wall and inner pressure of the stored oil have slight effects on the stability of the roof. To build the formula of local critical load of the tank roof, the circular corrosion pit is separated from the whole roof and treated as a shallow spherical shell which is elastically supported on the rest part of the roof. The equivalent support stiffness is obtained by the deformation compatibility at the edge of the corrosion pit. The resulted nonlinear stability equation is solved with a modified iteration method to determine the local critical load. The local critical load for an in-service corroded oil tank roof is analyzed by the proposed approach and the results are compared with those calculated by the conventional nonlinear finite element method with good agreement and the geometrical parameter of the corrosion region corresponding to the minimal critical load is 9.5.