A mathematical model of the viscoelastic phenomenon, employing the fractional derivative Maxwell Model (FDMM) is analyzed in order to determine its consistency with thermodynamic principles. In particular, the development of constraints on the parameters of the model guarantees that the FDMM will predict a nonnegative rate of energy dissipation and a nonnegative internal work. The creep compliance and relaxation modulus of the FDMM are obtained in an easier way. It is found that the monotonic non-decreasing creep compliance and monotonic non-increasing relaxation moduli prove a well-behaved viscoelastic phenomenon of the FDMM. The analysis of relaxation modulus indicates that the FDMM represents viscoelastic fluid behavior, with arbitrary fractional derivatives of stress and strain, only if the thermodynamic constraints are satisfied. The steady state sinusoidal response expressions derived in this article are verified using comparisons with experimental force-displacement loops.

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In this paper, a sensing device specifically for measuring deformations of high temperature pipes is designed, and its applicability is verified both experimentally and theoretically. First, the design procedure and the working principle of the sensing device are described in detail. Then, experiments are carried out to prove the accuracy and the long-term stability of the sensing device. To verify the accuracy of the device, numerical simulation of the deformation of a pipe model is carried out using finite element method. Results from the experimental measurements are in good agreement with results from the numerical simulation. The long-term stability of the device is validated by monitoring the deformation. Conclusions are drawn that the designed sensing device has high accuracy and excellent stability and can be used for measuring deformations of high temperature pipes in power plants.

In this study, parametric assessment of the main geometric design features of a pressure relief valve (PRV) with a backpressure chamber and two adjusting rings was conducted using a response surface methodology. This design approach was established by using computational fluid dynamics (CFD) to model the dynamic performance of the opening and closing of a nuclear power main steam pressure relief valve (NPMS PRV). An experimental facility was established to test the NPMS PRV in accordance with the standard ASME PTC 25, and to validate the CFD model. It was found that the model can accurately simulate the dynamic performance of the NPMS PRV; the difference in blowdown between the simulation and experiment results is found to be below 0.6%. Thus, the model can be used as part of a design analysis tool. The backpressure chamber assisted in the reseating and decreased the blowdown of the NPMS PRV from 18.13% to 5.50%. The sensitivity to valve geometry was investigated, and an explicit relationship between blowdown and valve geometry was established (with a relative error less than 1%) using the response surface methodology; this will allow designers to assess the valve settings without the need for a CFD model.

A general model of a rub-impact rotor-bearing system with initial permanent bow is set up and the corresponding governing motion equation is given. The nonlinear oil-film forces from the journal bearing are obtained under the short bearing theory. The rubbing model is assumed to consist of the radial elastic impact and the tangential Coulomb type of friction. Through numerical calculation, rotating speeds, initial permanent bow lengths and phase angles between the mass eccentricity direction and the rotor permanent bow direction are used as control parameters to investigate their effect on the rub-impact rotor-bearing system with the help of bifurcation diagrams, Lyapunov exponents, Poincaré maps, frequency spectrums and orbit maps. Complicated motions, such as periodic, quasi-periodic even chaotic vibrations, are observed. Under the influence of the initial permanent bow, different routes to chaos are found and the speed when the rub happens is changed greatly. Corresponding results can be used to diagnose the rub-impact fault in this kind of rotor systems and this study may contribute to a further understanding of the nonlinear dynamics of such a rub-impact rotor-bearing system with initial permanent bow.