Zhanming Qin

On a shear-deformable theory of anisotropic thin-walled beams: further contribution and validations

Within the framework of an existing anisotropic thin-walled beam model, a number of non-classical effects are further incorporated and the model thereby developed is validated. Three types of lay-ups, namely, the cross-ply, circumferentially uniform stiffness, and circumferentially asymmetric stiffness are investigated. The solution methodology is based on the Extended Galerkins Method and the non-classical effects on the static responses and natural frequencies are investigated. Comparisons of the predictions by the present model with experimental data and other analytical as well as numerical results are conducted and pertinent conclusions are drawn. This work is the first attempt to validate a class of refined thin-walled beam model that has been extensively used towards the study, among others, of dynamic response, static aeroelasticity and structural/aeroelastic feedback control.

Aeroelastic instability and response of advanced aircraft wings at subsonic flight speeds

A unified aeroelastic model developed towards investigating the flutter instability and subcritical aeroelastic response to a sharp-edged gust load in the compressible subsonic flight speed range is presented. The aircraft wing is modeled as an anisotropic composite thin-walled beam featuring circumferentially asymmetric stiffness lay-up which generates preferred elastic couplings. A number of non-classical effects such as transverse shear, warping restraint, and the 3-D strain effects are incorporated in the structural model. The unsteady aerodynamic loads in subsonic flow are based on 2-D indicial functions in conjunction with aerodynamic strip theory extended to a 3-D wing model. The numerical results reveal that elastic tailoring and warping restraint play a significant role on the flutter instability and dynamic response of composite aircraft wings.

NONLINEAR MAGNETOTHERMOELASTICITY OF ANISOTROPIC PLATES IMMERSED IN A MAGNETIC FIELD

A geometrically nonlinear theory of magnetothermoelasticity of electroconductive anisotropic plates in a magnetic field is developed. In this context, the Kirchhoff hypothesis is adopted for the plate modeling and the geometrical nonlinearities are considered in the von Kármán sense. In addition, the assumptions related to the distribution of electric and magnetic field disturbances through the plate thickness as proposed by Ambartsumyan and his collaborators are adopted. Based on the electromagnetic equations (i.e., the ones by Faraday, Ampère, Ohm, Maxwell, and Lorentz), on the modified Fourier law of heat conduction, and elastokinetic field equations, the three-dimensional coupled problem is reduced to an equivalent two-dimensional one appropriate to the theory of plates. The theory developed herein enables one to investigate the interacting effects among the magnetic, thermal, and elastic fields in orthotropic thin plates. As a special case, the problem of the free vibration of simply supported plate strips immersed in a transversal magnetic field is considered. Effects of the directionality property of the constituent material, magnetic and temperature fields, and electric conductivity, as well as thermal expansion coefficients, on the characteristics of vibrational behavior of the plate strips are investigated.

Thermoelastic Cracked Plates Carrying Nonstationary Electrical Current

ABSTRACT Problems related to the distribution of electromagnetic field and of the Joule heating along/around the cracks in a thermo- and electroconductive plate are addressed. It is assumed that the plate carries a nonstationary electrical current and contains two finite collinear cracks that are located perpendicular to the current direction. The cracks are free of mechanical loads. The formulated problem is reduced to a system of singular integral equations with Cauchy-type singular kernels and solved numerically. The influence of interaction of the cracks as well as non-stationarity of the current on the distribution of current and Joule heating are clarified. The results are instrumental toward arrest and de-acceleration of crack propagation in electro-conductive material structures.

Aeroelasticity of Composite Aerovehicle Wings in Supersonic Flows

A comprehensive aeroelastic model developed toward investigating the static divergence, e utter, and dynamic aeroelastic response of composite aerovehicle wings to sharp-edged gust and blast loads in supersonic e owe eld is presented. The aerovehicle wings are modeled as an anisotropic composite thin-walled beam structure featuring circumferentially asymmetric stiffness lay up that generates preferred elastic couplings. A number of nonclassical effects, such as transverse shear, warping restraint, and three-dimensional strain effects, are incorporated in the structural model. Based on the concept of two-dimensional indicial functions considered in conjunction with the aerodynamicstriptheoryextendedtothree-dimensionalwingmodel,theunsteadyaerodynamicloadsinsupersonic e ows are derived. The effect of elastic tailoring and the implications of transverse shear, warping restraint on divergence and dynamic response of selected wing cone gurations are investigated, and pertinent conclusions are outlined. Nomenclature AR = wing aspect ratio, L=b a.s/ = geometric quantity; see Eq. (2) and Fig. 3 aij = one-dimensional global stiffness coefe cients a1 = undisturbed speed of sound b;d = semichord and semidepth of the beam normal cross section, respectively bi = inertia coefe cient Eij = Young’ s modulus of orthotropic materials in the material coordinate system h.s/ = wall thickness as the function of the midline

Dynamic Aeroelastic Response of Aircraft Wings Modeled as Anisotropic Thin-Walled Beams

The dynamic aeroelastic response of aircraft wings modeled as anisotropic composite thin-walled beams in an incompressible flow and exposed to gust and blast loads is examined. The structural model incorporates a number of nonclassical effects, such as transverse shear, material anisotropy, warping inhibition, and rotatory inertia. The circumferentially asymmetric stiffness layup is used to generate preferred elastic couplings, and in this context, the implication of elastic coupling, warping inhibition on the response is investigated. The unsteady incompressible aerodynamics for arbitrary small motion in the time domain is based on the concept of indicial functions. The implication of directionality property of composite material is revealed, the influence of the gust/blast profiles on the response is discussed, and a number of conclusions are outlined.

Magnetoelastic modeling of circular cylindrical shells immersed in a magnetic field. Part I: Magnetoelastic loads considering finite dimensional effects

Abstract Determination of magnetoelastic loads acting on a perfectly electro-conductive circular cylindrical shell immersed in a uniform applied magnetic field is addressed. The finite dimensional effects related to the finite length and finite thickness of the shell are taken into consideration. Fourier integral method is used to derive the singular integral equations governing the distributed magnetoelastic loads. As special cases, determination of magnetoelastic loads via discarding the thickness effect are obtained from the general formulation, and the magnetoelastic loads of infinitely long shells are derived. Magnetoelastic loads on plate strips or infinite plates are also reduced from the general formulation. To the best of the authors’ knowledge, this represents the first work devoted to the analytical determination of magnetoelastic loads on circular cylindrical shells considering the finite length and thickness effects.

Magnetoelastic modeling of circular cylindrical shells immersed in a magnetic field Part II: Implications of finite dimensional effects on the free vibrations

In the context of free vibration analysis of axi-symmetric perfectly electro-conductive circular cylindrical shells, four simplified magnetoelastic load models are investigated. Concerning the model of circular cylindrical shells, a linear theory based on Love–Kirchhoff hypothesis is adopted. Due to the high complexities involving singularity of integral equations, infinite integral domains and excessive time needed to evaluate some kernels, special treatments are designed toward achieving highly efficient and highly accurate numerical computation. The influence of applied magnetic field, thickness ratio and dimensionless radius on free vibrations of circular cylindrical shells are further investigated and pertinent conclusions are outlined.

Joule Heating and its Implications on Crack Detection/Arrest in Electrically Conductive Circular Cylindrical Shells

Distribution of Joule heating and the corresponding electromagnetic field in the vicinity of the crack in a thermo- and electro-conductive thin-walled shell carrying a non-stationary electrical current is investigated. Specifically, a circular cylindrical shell with one finitely long crack that is perpendicular to the current direction is considered. The crack is free of mechanical loads. The underlying boundary-value problem is addressed via the use of Fourier series expansion and the solution reduces to that of a singular integral equation with Hilbert-type singular kernel. The influence of the presence of crack, and the effect of non-stationarity of the current on the distribution of current and Joule heating in the shell are investigated and pertinent conclusions are drawn. The results are instrumental toward crack detection and active arrest of crack propagation in structures made of electro-conductive materials or aged structure components in aerospace industry.

Diffraction of harmonic flexural waves in a cracked elastic plate carrying electrical current

The scattering effect of harmonic flexural waves at a through crack in an elastic plate carrying electrical current is investigated. In this context, the Kirchhoffean bending plate theory is extended as to include magnetoelastic interactions. An incident wave giving rise to bending moments symmetric about the longitudinal x-axis of the crack is applied. Fourier transform technique reduces the problem to dual integral equations, which are then cast to a system of two singular integral equations. Efficient numerical computation is implemented to get the bending moment intensity factor for arbitrary frequency of the incident wave and of arbitrary electrical current intensity. The asymptotic behaviour of the bending moment intensity factor is analysed and parametric studies are conducted.