The erect column piles have an important effect on the stability of the foundation pit. Based on the three-dimensional explicit finite-difference program, this paper analyzes the impact of the tension force, the location of the maximum tension force and the heave of piles on the column piles with consideration of the interaction between soil and piles. It is shown that the influence of the excavation on the erect column piles has an obvious spatial characteristic, with the maximum influence on the center pile and the minimum on the corner pile. The tension force is induced by excavation, the location of the maximum value moves upward of the column pile, and finally stops at half of the effective insertion depth of pile foundation, the maximum tension force of the center pile in pile group is larger than that of a single pile; the heave of the pile top increases with the numbers of piles, and then decreases when the pile number is increased to a certain value.
The seismic behaviors of composite steel-concrete structures are widely studied due to their extensive engineering applications in the major national construction projects and are reviewed in this paper, including the composite beams, the composite columns, the composite joints and the composite frames, as well as the characterization of the transfer of forces and the damage evolution. The modeling schemes, to simulate the seismic behaviors of steel-concrete composite frames are discussed, including the micro finite element modeling, the macro finite element modeling, and the multi-scale finite element modeling. The seismic performance evaluation of composite structure systems is also discussed.
The reliability simulation is a very effective method for reliability analysis of complicated structural systems. The characteristics of the Monte-Carlo (MC) method, the method to estimate the limit state function and the stochastic finite element method (SFEM) are discussed in this paper, with emphasis on the simulation of the solid rocket motor (SRM).
The artificially upstream flux vector splitting (AUFS) scheme is extended into a gridless method successfully. This gridless method is based on the polynomial basis least-squares method, the curve fitting of linear basis function and AUFS scheme are employed to calculate the spatial derivatives, and a four-stage Runge-Kutta algorithm is applied to advance the Euler equations in time. In order to demonstrate the effciency and the accuracy of this method, a Riemann problem, a supersonic flow in channel, and a transonic flow of NACA0012 airfoil at di?erent attack angles are simulated, and the results are in good agreement with the results calculated by the HLLC (Harten-Lax-van Leer-contact) scheme and other references. Besides, the time spent in the AUFS scheme is about 15% less than in the HLLC scheme.
According to the requirement proposed by the Sixth National Structure Design Contest for college students (NSDCCS), a four-storey bamboo frame model raised floor house is built and experimented under a lateral impact load. The acceleration response is measured.and the FEA software LS-DYNA is used to carry out the finite element analysis to investigate the dynamic mechanism of the frame. The numerical simulation results are in a good agreement with the experimental acceleration time history curves. Furthermore, a parametric analysis is conducted to study the peak of the acceleration. The results indicate that the models with a higher initial relaxation offset of the tension rods or with a lighter contact plate will increase the acceleration of the frame. With regards to the mass of the impact ball, the velocity affects the peak of the acceleration more sensitively, and the peak acceleration increases with the increase of the ball velocity.
The theoretical model of a new-type turbine flowmeter is proposed based on the theorem of moment of momentum and the boundary layer theory of fluids, for analyzing the influence of the rotor's geometry on the flowmeter's metrological performance. The meter factor of a DN50 turbine flowmeter is calculated with the theoretical model and by using a standard volume tube. The effectiveness of the model is verified as it is shown that the calculated results are in a good agreement with the experiment results with an error in the range of ±3.5%, and the model provides a theoretical basis for the meter's optimization design.
It is very important to locate the explosion source in the impact test. In this paper, a dynamic model of the buoy-cable system is established based on the force on cylinders in the uniform water flows. With the new model, the location of the buoy is dermined by using a numerical method based on the Runge-Kutta method and the Newton iteration.
This paper studies the vibration characteristics of continuous spans with only one galloping span. The finite element model of continuous spans is set up by means of ABAQUS softwart,and the aerodynamic load is determined by the UEL. The time domain solutions for the vibrations of the continuous spans are obtained with consideration of the non-linear influence. The effects of span and galloping amplitude are investigated, which may provide some guidance for prevention of conductor galloping.
To ensure the flight safety under the condition of the wing damage in the aircraft, a new online fault diagnosis method is proposed based on the nonlinear aerodynamic model of the wing damage. Firstly, according to the input and output characteristics of the aircraft, the aerodynamic derivatives can be identified online using the recursive least squares algorithm with a forgetting factor, and the wing damage model can be established as the aerodynamic derivatives are substituted into the equation of the aircraft motion. Secondly, the fault diagnosis approach is proposed based on the multi-model algorithm and the central difference Kalman filter algorithm, and the adaptive capacity of the central difference Kalman filter algorithm can be strengthened as the sampling points are updated online using the strategy of a strong tracking filter. Lastly, in the presence of various wing damage faults, the simulation results indicate that the proposed algorithm can not only improve the experiment effciency but also ensure the fault coverage as compared with other algorithms.
The wellbore safety factor is used as a criterion to determine the wellbore instability area, and with the Monte-Carlo simulation, the instability area is calculated. To consider the wellbore collapse risk, the influence of the mud density, the deviation and the azimuth on the wellbore instability area is analyzed, and the effect of the well trajectory parameters on the wellbore instability in different in-situ stress fields is evaluated by the method of calculating the instability area proposed in this paper. The evaluation results agree with the actual engineering practice, which shows that this method could be used to evaluate the characteristics and the severity of the borehole instability.
Based on the theory of the soil hydro-mechanical coupling constitutive model, a chemical-hydromechanical coupling constitutive model (C-H-M model) of soil is proposed. In this model, the impact of salt and alkali ion solutes of the soil pore water on the preconsolidation pressure is considered by employing a chemical softening equation. A numerical simulation of the parameter in the softening equation is conducted on the basis of the experimental results. The C-H-M coupling constitutive model is validated by conducting a numerical simulation.
To increase the frequency and improve the wind resistance properties of cooling towers, stiffening rings and ribs are added on a cooling tower, and the influences of their dimensions, locations and amounts are analyzed. The stiffening rings at an appropriate location will increase the frequency significantly, but the stiffening ribs have no such effect. The contributions of the stiffening rings to the frequency are decided by their participation degree, so the stiffening rings will have more significant effects if they are located where the mode displacement is large or the modes have more circumferential wave numbers. In practical applications, the frequency will be increased notably if there are 3-5 stiffening rings scattered along the shells with a uniform distance.
In this paper, a nonlocal viscoelastic sandwich-beam model is developed to investigate the stability of a pulsating-fluid-conveying carbon nanotube (CNT) embedded in two-parameter elastic mediums. In the new model, thin surface layers are on the inner and outer tube surfaces and both the resulting effects of the surface elasticity and the surface residual stress are taken into account. The classical Euler-Bernoulli beam model is modified by introducing nonlocal and surface parameters. The governing equation is solved via the averaging method and the stability regions are obtained. Numerical examples show the complicated influences of the nonlocal, surface effects and the two medium parameters on the natural frequency, the critical flow velocity and the dynamic stability of the CNT. The conclusions of the present paper may be used in the structural design and vibration analysis of nanofluidic devices.