Application of FEM strength reduction method to geotechnical engineering with the consideration of tension and shear failures

The failure characteristic of geomatertials in different stress states is analyzed, and it is found that the stability of geotechnical structure depends on not only shear strength index c and tanφ, but also tensile strength index T. The overvalued of tensile strength of materials could lead to non-conservative results in the primary strength reduction method. Therefore, the FEM strength reduction method should take identical reduction of both tensile strength index and shear strength index into account. In other word, tension and shear strength reduction method (TSSR) in the process of strength reduction should be adopted. The necessity and correctness of TSSR is validated by stimulating four typical example models, i.e. the general slope, the stalactite, the tunnel and the steep slope. Studies show that the modified strength reduction method has universal applicability in geotechnical engineering.     

Dynamic Influence of Sustained Small Rainfall Infiltration on Stability of Unsaturated Soil Slope

Taking the moisture content as main control parameter of shear strength of the soil, we analyze the variational properties of moisture content and shear strength with the change of rainfall time during the small sustained rainfall infiltration, and establish the relationships between total cohesion as well as effective angle of friction and the time of sustained small rainfall infiltration into an unsaturated slope. With the rainfall infiltration, the influence area of slope expands. Through the strength reduction method based on FLAC3D, the dynamic safety factor of slope in different time and the duration time before the failure of the slope are obtained. The results show that the slope critical sliding surface is yet unsaturated during a sustained small rainfall.     

Effects of nitrite on the growth and competition of Microcystis aeruginosa and Scendesmus quadricauda

Not only population densities of phytoplankton but also its community structure can be influenced by nitrite concentration.To investigate this effect,the growth and competition of Microcystis aeruginosa and Scendesmus quadricauda under different nitrite concentrations are studied by using batch cultures,and the competition relation is analyzed by the competition parameters.The results indicate that there is competition between M.aeruginosa and S.quadricauda in present experiment conditions,and S.quadricauda is dominant in competition.Meanwhile,the increase of nitrite concentration can strengthen S.quadricauda dominance,because under high nitrite concentration (20 mg/L,30 mg/L),M.aeruginosa is more damaged and the allelopathy between M.aeruginosa and S.quadricauda is intenser.     

Experimental Analysis on the Deformation of Sandstone underPore Pressure and Constant Time

In order to discuss the deformation characteristics of rock mass under different water levels changing between 145 and 175 meter in the Three Gorges reservoir area, an experiment was carried out for the studying sandstone deformation under the conditions of three different axial stresses(σ1=55.54,34.18,12.82 MPa), two cyclic pore pressures(Pmin=2 MPa,Pmax=6 MPa) and two kinds of constant time(the upper limit time and the lower limit time(ΔT=120,240 s).With ε1-T curves and p-T curves, as well as p-ε1  hysteresis curves, it was found that the curves were continuous sine wave-shaped curves.At first, the strain decreased with loading pore pressure.And then, it decreased to valley value with pore pressure at stable upper limit.Next, it increased with unloading pore pressure and increased to peak value with pore pressure at stable lower limit.The p-ε1  hysteresis curves of the sandstone had two typical stages.And one was caused by the closure of some primary pores and crack under increasing compaction, in which the strain did not form obviously hysteresis curves, and the other was pore pressure coupling stage which showed obvious hysteresis curve in form of the anti-clockwise from the dispersed to the dense.In addition, Δε-n curves in four sections (loading, unloading, steady upper limit, steady lower limit) of p-ε1 curves were compared and respectively ananlyzed in the condition of various axial stress and different constant time .     

Design and optimization of the precision rollforging on a heavy truck front axle

The under-filling defect of I-beam in a heavy truck front axle which occurs in the process debugging of the precision roll-forging and die-forging is studied. Finite element models of precision roll-forging and die-forging are established based on FEM software and the previous productive results. Then, the mechanism of the under-filing defect in I-beam is studied. And the effects of the three variables including width B, radius R and slope A of I-beam in the third step on the forging quality are investigated. In addition, the roll-forging die constructions for I-beam in previous three steps are redesigned and manufactured. The productive results show that I-beam can be fully filled, the debugging cycle is reduced significantly and the products quality is guaranteed.     

Design and FPGA Implementation of animproved structure of digital matched filter

An improved structure of digital matched filter(DMF)is presented. Two same pseudorandom spread spectrum sequences with the length of N are used to spread the same baseband symbol at the transmitter, which is equal to spread the baseband symbol with a spread spectrum sequence with the length of 2N. At the receiver, only a spread spectrum sequence with the length of N is needed to de spread the data, and then cumulates the two correlation peaks and exports to the output. The detection probability(Pd)and the false alarm probability(Pf)are analyzed and simulated. The improved structure of DMF is implemented based on the recursive and folded principle. Experimental results show that, for the same spread gain, the improved structure has the same Pd and Pf as the basic DMF, while saves the hardware resources greatly compared with the recursive and folded structure.     

Numerical analysis on the evolutionary features of deformation and failure modes of slopes

The failure of slope is a gradual accumulation process. Under the effect of many interior and exterior factors, some parts in the slope reach yield with the increase of stress, and sliding surface forms gradually till complete transfixion. With continuous increase of the plastic strain, overall failure happens on the slope. Traditional analysis method cannot display the mechanic conditions and the whole process of deformation, transfixion of sliding surfaces and failure. Meanwhile, FEM strength reduction can quantitatively show the deformation features and the process of occurrence and development of sliding surface. Based on the previous researches, the paper classifies slopes according to the features of rock and soil and the slope structure. Through analyzing the graphs of deformation and the nephograms of plastic strain under different reduction factors or safety factors, the researchers can directly find the deformation tendency of slopes and the whole process of the extension, transfixion and failure of sliding surface with the reduction of safety factor. So, the failure mechanism of slope can be found intuitively, which can provide effective basis for the prevention and governance of slopes.     

Mechanical property prediction model of AZ31 magnesium alloys based on an artificial neural network with parameter optimization

The tensile strength, yield strength and elongation of AZ31 magnesium alloys on different annealed conditions are tested by mechanical properties experiments. A model of corresponding mechanical properties is built by applying artificial neural network, and it is optimized by a new method,namely all permutations and combinations training of parameters. The results show that the network model has an excellent performance, which is based on optimal parameters obtained from all permutations and combinations training. Compared with traditional model, whose parameters are obtained from conventional heuristic, the improved model has higher average correlation coefficient and lower average error. Therefore, it can predict the mechanical properties of AZ31 magnesium alloy on different annealed conditions more accurately.     

Two-level Safety Evaluation and Structural Optimization of Steel Truss Bridge

A robust method for determining the component safety factor and structural safety factor of steel truss bridge is developed based on elastic modulus reduction method (EMRM). A procedure of two-level safety analysis and structural optimization is presented by means of the linear FEA iteration and the generalized yield criterion to take multiple internal forces into consideration. The strategy of elastic modulus adjustment is derived according to the principle of conversation of energy. The element bearing ratio (EBR) in every step can be obtained, and the first and last EBRs are employed to determine component safety factor and the structural safety factor for two-level structural safety evaluation of steel truss bridge. Those components with higher or lower EBR than the referenced EBR can be identified. By taking the quantitative relationship of the two level safety factors, a structural optimization scheme with better distribution of the EBR and saving material consumption can be achieved by adjusting the sectional strength of components with higher and lower EBR. Numerical examples show that the proposed method is promising with satisfying accuracy. The analysis of structural safety and optimization can be implemented by using the linear iteration while complicated nonlinear analysis in classical scheme is avoided.     

Application of GA in Calculating Factor of Safety in SlopeStability

How to ascertain the sliding surface and the factor of safety(FS) is the key problem of slope stability.The failure model of a slope is supposed at first and then the sliding surface and the factor of safety are computed approximately during analyzing the slope stability all over the world.However,the hypothesis cannot reflect the real state of slope sliding.In this paper,the critical failure surface with the lowest value of FS is computed and the better result is got by means of GA.     

Analysis of plastic flow characteristics based on bridge steel 16Mn ratcheting

Abstract:The analysis of the plastic flow characteristics on the basis of the ratcheting experimental results for the bridge steel 16Mn are carried out by calculatig the plastic modulus H and the angle θ between the backstress rate deviator and the plastic flowdirection. The different mechanisms causing uniaxial andmultiaxial non proportional ratchetting are illustrated, that is, the starting and evolution of uniaxial ratchetting is due to the different values of the plastic modulus H at the symmetric loading points with respect to the mean stress. On the other hand, the staring and evolution of multiaxial non proportional ratcheting is driven by H and θ variations. The influence of loading history on ratchetting is the result of the influence of loading history on the angle θ.     

CFD Optimization on Coupling Smoke Control Parameters in Tunnel with Non symmetry laid Damper

With respect to three vents located on both sides of the fire source in an asymmetrical arrangement, series of CFD simulations and reduced scale experimental tests are carried out. And further analysis is undertaken for several parameters, such as airflow distribution, flue gas temperature and smoke horizontal diffusion distance etc, with different combinations of the longitudinal velocity and exhaust rate. It is found that horizontal diffusion distance of smoke is confined in three vents bordering the fire source and optimization design with minimal exhaust rate is further proposed. With multiple CFD simulations, series of dimensionless correlations are recommended for further tunnel fire safety design with some parameters, such as heat release rate, tunnel inclination and optimized parameters with slope variation.     

RESEARCH ON A KIND OF GREY LINEAR PROGRAMMING AND THEIR DUAL THEORIES

In this paper, a kind of grey linear programming with grey interval coefficients is discussed,the definitions of the first and second whitenized linear programmlngs and the grey dual linear programmings are presented, the relationships between the solutions of the above three kinds of programming and the solution of the primal programming are explored, and some new conclusions are obtained.     

Experimental Analysis of Mechanical Properties of Thick Plate in Steel Structure at Low Temperature

Thick steel plates are widely used in high-rise buildings and large-span steel structures. However, the increase of steel plate thickness will induce variations of mechanical properties of steel plates, especially the thickness properties. The mechanical properties of structural steel Q345B with plate thickness from 60 to 150 mm were tested at low temperature through round bar tensile specimens which included two types, i.e. transverse specimen that is perpendicular to the rolling direction and Z-direction (or through thickness) specimen. The indices of yield strength fy, ultimate tensile strength fu, percentage reduction of area ψ and their variations with temperature and sampling locations were measured in the experiments; the corresponding indices for thorough thickness properties were also obtained. it is indicated that: (1) when temperature decreases, fy and fu of thick plate increase while ψ value decreases; (2) from surface to center of the thick plate, ψ values for transverse specimens decrease; (3) with the increase of plate thickness, ψ values for Z-direction specimens decrease and are smaller than those of transverse specimens. Useful material property data of thick steel plate are provided for thick plate steel structures.     

Experimental Study on Channel Characteristic and Refrigerating Effect in Vortex Tubes

Taking compressed air as the working medium, the performances of energy separation and temperature distribution in various kinds of vortex tubes are experimentally studied. Temperature distribution and refrigerating effect curve in vortex tubes are attained. The results show that the refrigerating effect of vortex tube with four nozzles is better than the other three kinds of vortex tube under the condition of ordinary temperature and 0.7 MPa pressure, and the refrigerating effect of vortex tube with six nozzles is worst in the four kinds of vortex tube. The refrigerating effect of nozzle with Achimid curve is best compared with other kinds of curves. The experiment shows that there is a boundary between cold and hot airflow at 0.7R of the tube, where cold airflow is inside the boundary and hot airflow is outside the boundary.     

Strength Reduction Method of No-linear FEM Limit Analysis for Pile Group Foundation

Confined by the condition of static loading test, the ultimate load of pile group is modified by the ultimate load of static loading test of a pile, so the estimated ultimate value lacks objectivity. The variables of universal function of bearing capacity of pile group are put up. First, based on one another matching parameters of strength for geotechnical material according to simultaneity relation in the forced pile foundation, and induced the strength reduction factor, the safety storage factor (SSF) is put up, which is denoted the ratio of real ultimate load to the load on pile foundation. Second, the plastic deformation is happen at the soils around pile tie at the condition of ultimately loading, and the steady state of pile-soil system rapidly changes into a unstable state (rapid changing relation), the phenomenon of loading-settlement shows that the vertical line lies at the inflexion after the ultimate load point. Hereby, the criterion of ultimate load, which is computed by the strength reduction method of no-linear FEM limit analysis for pile group, is build. Finally, used the ANSYS softer, the screw pile group of the practical foundation engineering is analyzed by 3-d FEM strength method. At P=207 800 N, the SSF is equal to 1.16, and the ultimate load (Q) is 241 048 N, which it is small 3.35% than the estimated ultimately loading of state loading test (249 400 N). This result validated the feasibility of strength reduction method used to decide the ultimate load of pile group.     

Bamboo simulation based on fractal algorithm

Fractal theories are quite popular in modeling and simulation of objects with irregular shapes. The combination of fractal theories and virtual reality technologies may be used to generate the realistic and complex nature objects. Plants simulation is one of the most important fields in computer graphics. The simulation algorithms of Bamboo are discussed. The conventional L-system modeling approach is improved based on the single-axis characteristics of Bamboo, and the relevant method, e.g. the displacement mapping technique used in Bamboo internodes modeling and rendering is discussed as well. Moreover, based on the basic idea of particle system, an improved simulation approach for distribution pattern of Bamboo is presented.This improved simulation algorithm can make the random distribution of particles break the rules of rectangular shape. Simulation results show that the proposed methods can simulate realistic Bamboo forms and distribution patterns in the nature.     

Study on the Terzaghi Ultimate Bearing Capacity of Foundation Based on the Unified Strength Theory

The ultimate bearing capacity of foundation based on Mohr-Coulomb strength criterion did not analyze effect of intermediate principal stress on yield and failure of soil so that the disparity between results obtained using Mohr-Coulomb strength criterion and those from experimental data are produced .In the paper , The ultimate bearing capacity of foundation based on unified strength theory is established and a unified solutions are obtained. The corresponding solutions of different materials can be got from it .The unified solution can not only be used to fit the properties of the materials with different tension-pressure strength but also those with equal tension-pressure strength, Results show that ones make full use of the properties of the materials so as to reduce supports,which is of important significance for engineering.     

Analysis of Laterally Loaded Long Piles in Cohesionless Soil in Nonlinear Conditions

A method was developed for nonlinear analysis of laterally loaded long piles in cohesionless soil. It is considered that the modulus of horizontal subgrade reaction is related with groundline pile displacement by an attenuation power function based on the existing methods and it is assumed that both the modulus of horizontal subgrade reaction and the ultimate soil resistance increase linearly with depth . It is also considered that soil in front of the pile may change from elastic state into plastic state as pile displacement increase. Nonlinear differential equations of the fourth order were derived for both states and to solve the equations, the Gleser finite difference approach with iteration and the Reese Matlock approach were developed,respectively of propsed methed. It is validated by the test and numerical field calculation that the results respectively of proposed methed are more accurate than ‘m’method and simpler than ‘p y’method. And the results are in good agreement both when pile displacement is small and large,thus it can be applied to construction in place of ‘p y’ method especially when test parameters are unavailable.     

Objective evaluation methods of automobile riding comfort

There is much difference between GB4970 1996 Method of random input running test Automotive ride comfort and international evaluation methods, and the characters of automobile riding comfort is not discussed in detail. The measurement and evaluation methods are discussed. The ten axis vibrations exposed to human body in automobile are measured throughout road testing, and then the characteristic of automobile riding comfort is analyzed. An objective measurement and evaluation method of automobile riding comfort are presented. The results show that the difference generated by frequency weighting factors ωk and ωb is very little. The crest factor of vibration in automobiles is about 4~8 by time domain analysis. The percentage of each axis vibration is calculated, the results show that vertical vibration (z axis) at seat surface, horizontal vibration (x axis) at backrest and pitch vibration (rx axis) at seat surface are most important for comfort. The evaluation method in GB4970 1996 underestimates the vibration expose on the human body about 3 dB, which should be revised. Based on the results, a simple and convenient method for measuring vibration on automobiles is presented.