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The limit cycle oscillations (LCOs) exhibited by long-span suspension bridges in post-flutter condition are investigated. A parametric dynamic model of prestressed long-span suspension bridges is coupled with a nonlinear quasi-steady aerodynamic formulation to obtain the governing aeroelastic partial differential equations adopted herewith. By employing the Faedo–Galerkin method, the aeroelastic nonlinear equations are reduced to their state-space ordinary differential form. Convergence analysis for the reduction process is first carried out and time-domain simulations are performed to investigate LCOs while continuation tools are employed to path follow the post-critical LCOs. A supercritical Hopf bifurcation behavior, confirmed by a stable LCO, is found past the critical flutter condition. The analysis shows that the LCO amplitude increases with the wind speed up to a secondary critical speed where it terminates with a fold bifurcation. The stability of the LCOs within the range bracketed by the Hopf and fold bifurcations is evaluated by performing parametric analyses regarding the main design parameters that can be affected by uncertainties, primarily the structural damping and the initial wind angle of attack.

Localized bending waves in a thin elastic orthotropic cantilever plate reinforced by a rigid rib are studied. A condition under which the edge waves can be eliminated is determined. The condition requires that the rib have a certain minimal stiffness. Such waves are time-varying, and have spatially nonuniform bending perturbations that are localized in the proximity of free surface and are quickly decaying to zero. A general solution is presented and the particular case of an isotropic reinforced plate is shown. An inverse method is described for identifying the elastic properties of the rib.

This paper describes an efficient reduced order model (ROM) applied in the aerodynamic analysis of bluff bodies. The proposed method, which is based on eigensystem realization algorithm (ERA), uses the impulse response of the system obtained by computational fluid dynamics (CFD) analysis to construct a ROM that can accurately predict the response of the system to any arbitrary input. In order to study the performance of the proposed technique, three different geometries including elliptical and rectangular sections as well as the deck cross section of Great Belt Bridge (GBB) were considered. The aerodynamic coefficients of the impulse responses of the three sections are used to construct the corresponding ROM for each section. Then, the aerodynamic coefficients from an arbitrary sinusoidal input obtained by CFD are compared with the predicted one using the ROM. The results presented illustrate the ability of the proposed technique to predict responses of the systems to arbitrary sinusoidal and other generic inputs, with significant savings in terms of CPU time when compared with most CFD codes. The methodology described in this paper has wide application in many offshore engineering problems where flexible structures interact with unsteady fluid flow, and should be useful in preliminary design, in design optimization, and in control algorithm development.

This paper addresses the problem of the aerothermoelastic modeling behavior and analyses of skin curved panels with static and dynamic edge movability effect in high supersonic flow. Flutter and post-flutter behavior will be analyzed toward determining under which conditions such panels will exhibit a benign instability, that is a stable limit cycle oscillation, or a catastrophic instability, that is an unstable LCO. The aerothermoelastic governing equations are developed from the geometrically non-linear theory of infinitely long two dimensional curved panels. Von Kármán non-linear strain-displacement relation in conjunction with the Kirchhoff plate-hypothesis is adopted. A geometrically imperfect curved panel forced by a supersonic/hypersonic unsteady flow is numerically investigated using Galerkin approach. These equations are based on the third-order piston theory aerodynamic for modeling the flow-induced forces. Furthermore, the effects of thermal degradation and Kelvin’s model of structural damping independent of time and temperature are also considered in this model. Computational analysis and discussion of the finding along with pertinent conclusions are presented.

This paper deals with the magnetoelastic interactions for a structure consisting of two elastic current carrying superconducting substrates, separated by a gap (vacuum). The two elastic substrates, which have no acoustic contacts, are coupled by a magnetic field generated by the deformations of the substrates. The surface magnetoelastic waves of Rayleigh type, decaying exponentially with distance from substrates surfaces, are studied. For a plane harmonic wave the dispersion equation is derived and solved to obtain the coupled wave frequencies. The magnetomechanical coupling effects are investigated in detail and simulations show that the magnetoelastic coupling effect is quite significant when the gap relative thickness is rather small. The existence of two surface gap waves with two different velocities is shown. In superconducting media the constitutive relations of magnetic field and electrical current of primary nondeformed state are given by means of London’s equations.

This paper describes an advanced monitoring system for fouling phenomenon in a wide range of tubular heat exchangers such as condensers and intercoolers. First, a mathematical model of fouling resistance in tubular heat exchangers is adapted. The model is based on the applied thermal power, the inside heat transfer coefficient, and geometrical characteristics of the heat exchanger under consideration. The resulting model is a function of measured quantities such as water and tube wall temperatures, fluid flow velocity, and some physical properties of the fluid flowing inside the tubes, such as viscosity, conductivity, and density. Second, an on-line fouling monitoring system was prepared, and the heat transfer resistance for selected solutions was measured in real time by this system. The effect of concentration and chemical reactions on fouling was studied experimentally using contaminants such as sodium bicarbonate, sodium chloride, calcium chloride, and a mixture of sodium bicarbonate and calcium chloride. Experimental results provide quantitative information of liquid-side fouling on heat transfer surfaces, and its effects on the thermal efficiency. Experimental data are critical for heat exchanger design and for planning operating and cleaning schedules of the heat exchanger. Uncertainty analysis shows that the experimental results are acceptable and the experimental setup is appropriate for measuring fouling resistance in industrial applications.

This work investigates the behavior of an electroconductive plate under the action of a nonconservative load and subjected to a transversal magnetic field. The governing equation of the bending vibrations of an electroconductive plate, subjected to a transverse magnetic field and a follower type force at one edge, is presented. The assumption of an elongated plate leads to a simplified equation, which is conveniently written in dimensionless terms. For a cantilevered configuration, the characteristic equation relative to the magnetoelastic modes of vibration of the system is derived. Approximate solutions based on Galerkin method and an adjoint formulation are also presented and compared with the semi-analytical results. Root loci plots are computed as a function of the proper dimensionless parameters. The behavior of the system is very similar to the one exhibited by other structures subjected to nonconservative loads when damping is present. A relaxed definition of stability is used to regain continuity in the instability envelope.