Wind oscillation analysis of a suspension bridge coupled with CFD

This study conducted a CFD-2D coupled analysis of a suspension bridge subjected to wind loads. Previous studies found that rotational oscillation was due to differences in the restoring force at hanger cables and could generate torsional oscillations. However, due to uncertain external force terms, the previous studies could not be applied to analyze actual structures. To enable application in a real design process, this study proposed a methodology for determining the external force terms. The external force terms were determined with CFD, and a moment force term was added to equations of motion derived from dynamic equilibrium conditions. All constants and properties were calculated from an assumed cross section of superstructure. This methodology can be used not only to avoid torsional resonance but also in preliminary analysis in the bridge design stage

Pseudo-static calculation method of the seismic residual deformation of a geogrid reinforced soil retaining wall with a liquefied backfill

The geogrid reinforced soil retaining wall is a flexible retaining wall. It will produce large deformations during earthquakes, especially on liquefied backfill soils. An index of liquefaction extent is applied to express the effect of excess pore water pressure in reinforced backfill sand during earthquakes. A geogrid reinforced soil retaining wall is represented by an isotropic vertical elastic beam. The calculation method of the seismic residual deformation of the geogrid reinforced soil retaining wall is based on the Rayleigh-Ritz method and the the Mononobe-Okabe pseudo-static method. The effect of liquefaction extent in the backfill sand is studied for seismic active earth pressures acting on a reinforced wall back and seismic residual deformations of a reinforced wall. Some influence parameters on seismic residual deformations of geogrid reinforced soil retaining walls are investigated in detail, such as the internal friction angles in the backfill sand, friction angles of the wall, horizontal seismic intensities, reinforcement length of the geogrid and soil properties. Finally, the calculated results are compared with test results of a model on large-scale shaking table. The conclusions about the parameters will be helpful for seismic designs of geo-grid reinforced soil retaining walls on liquefied foundations. The proposed pseudo-static calculation method can be used to predict safe seismic deformations of geogrid reinforced soil retaining walls

Optimization design for ultrasonic horn with large amplitude based on genetic algorithm

With the functions of amplitude amplification, impedance matching and protecting the transducer in ultrasonic machining system, ultrasonic horn is an important component in design of power ultrasonic vibration system. A new horn with large amplitude is designed. The profile of the horn is a cubic Bezier Curve. Based on genetic algorithm, the horn with large vibration amplitude ratio was obtained by optimizing the control points at the starting point and the end point of Bezier Curve. Simulation comparison was also carried out on the vibration performances of other four kinds of horns. Bezier horn and conical horn were manufactured by numerical control (NC) technology, in addition, measurement and comparison were carried out on their performances by combining with a vibrator. Results show that the amplitude of the optimized Bezier horn is 73.5 % larger than that of conical horn. Under the excitation voltage of 200 Vp-p, the amplitude of the Bezier horn can reach 108 µm

A hybrid prognostics approach to estimate the residual useful life of a planetary gearbox with a local defect

A hybrid prognostics approach for the monioring of a planetary gearbox with the local defect is presented. This hybrid method can predict the remaining useful life (RUL) of planetary gearbox with a fatigue crack. The method consists of a dynamical model for simulation data generation, a statistical algorithm for feature selection and weighting, and a modified grey model for RUL prediction. Experimental studies are conducted to validate and demonstrate the feasibility of the proposed method for RUL prediction of a cracked sun gear in planetary gearbox. And the validation has a promising result

3-Dimensional advanced solution for lunar descent and landing

A 3-dimensional advanced guidance scheme is necessary to perform a successful precise lunar landing mission. This paper outlines a 3-dimensional comparison of different methods of solution of motion control equations for guidance scheme of lunar descent. It also proposes a 3-dimensional advanced solution that allows a full depiction for a descent vehicle motion from orbital states down to the final landing event. In the conventional 2-dimensional methods of solution, some inadequate assumptions exist that limit the validity of the solutions. The proposed research solves those problems and eventually allows a complete representation of the descent module motion for successful pinpoint lunar landing

The moment stability of response on a rectangular thin plate under in-plane narrow band random excitation

A dynamical model of a thin rectangular plate under in-plate parametrical narrow band noise excitation was proposed based on the elastic theory and the Galerkin’s method. Firstly, the model was perturbed applying the multiple scale method, subsequently the averaged equation in Ito form was obtained. Subsequently, the stochastic moment stability of the steady state responses was studied by Floquet theory and the moment method. Finally, the second order moment of the system was calculated. The moments can be used to estimate the statistical characters such as mean and variance of the responses. The numerical simulation was carried out and the results are consistent with the theatrical analysis