DYNAMIC FINITE ELEMENT MODEL UPDATING BASED ON GLOBAL INFORMATION OF STRUCTURES

Finite element model updating method based on global information is proposed.Prior investigation upon design space of structural parameters is performed before updating usingstatistic analysis, including parameter screening using variance analysis and response surfacefitting using regression analysis. The parameter screening method selects the design parametersconsidering the result of hypothesis testing, which is a kind of global information. Meanwhile, thetraditional updating method considers local sensitivity which only gives the information at solepoint in the design space. Response surface fitting constructs a close-form multinomial whichdescribes the relationship between concerned structural feature and selected updating parameters. Itis an approximation to finite element models(FEM) and used as a substitution in the updatingiterations. The presented updating method can be applied without the restriction of linearassumption. In addition, there is no data exchange between the updating program and the finite-element analysis program in the updating iterations. This makes the method practical inengineering. An aircraft test structure, GARTEUR, is employed to verify the effectiveness of themethod. After updating, the error of modal frequencies is less than 3 percent.

Symplectic solution for three dimensional couple stress problem and its variational principle

A new state vector is presented for symplectic solution to three dimensional couple stress problem. Without relying on the analogy relationship, the dual PDEs of couple stress problem are derived by a new state vector. The duality solution methodology in a new form is thus extended to three dimensional couple stress. A new symplectic orthonormality relationship is proved. The symplectic solution to couple stress theory based a new state vector is more accordant with the custom of classical elasticity and is more convenient to process boundary conditions. A Hamilton mixed energy variational principle is derived by the integral method.

RELIABILITY ANALYSIS FOR A REPAIRABLE PARALLEL SYSTEM WITH TIME-VARYING FAILURE RATES

To solve a real problem:how to calculate the reliability of a system with time-varying failure rates in industry systems,this paper studies a model for the load-sharing parallel system with time-varying failure rates,and obtains calculating formulas of reliability and availability of the system by solving differential equations.In this paper,the failure rates are expressed in polynomial configuration.The constant,linear and Weibull failure rate are in their special form.The polynomial failure rates provide flexibility in modeling the practical time-varying failure rates.

A quantitative analysis on the sources of dune sand in the Hulun Buir Sandy Land:application of stepwise discriminant analysis (SDA) to the granulometric data

Quantitatively determining the sources of dune sand is one of the problems necessarily and urgently to be solved in aeolian landforms and desertification research. Based on the granulometric data of sand materials from the Hulun Buir Sandy Land, the paper employs the stepwise discriminant analysis technique (SDA) for two groups to select the principal factors determining the differences between surface loose sediments. The extent of similarity between two statistical populations can be described quantitatively by three factors such as the number of principal variables, Mahalanobis distance D 2 and confidence level 琢for F-test. Results reveal that: 1) Aeolian dune sand in the region mainly derives from Hailar Formation (Q 3 ), while fluvial sand and palaeosol also supply partially source sand for dunes; and 2) in the vicinity of Cuogang Town and west of the broad valley of the lower reaches of Hailar River, fluvial sand can naturally become principal supplier for dune sand.

PARTICLE SIZE AND MICROSTRUCTURE OF Ni NANOPOWDERS PREPARED BY ANODIC ARC PLASMA

Pure Ni nanopowders were successfully prepared by the method of anodic arc disch arged plasma with homemade experimental apparatus. The particle size, mircostruc ture and morphology of the particles by this process were characterized via X-ra y powder diffraction (XRD), transmission electron microscopy (TEM) and the corre sponding selected area electron diffraction (SAED); The specific surface area an d pore parameters were investigated by multi-point full analysis of nitrogen ads orption-desorption isotherms at 77K by Brunauer- Emmett-Teller (BET) surface are a analyzer; The chemical composition were determined by X-ray energy dispersive spectrometry (XEDS) equipped in SEM and element analyze instrument. The experime nt results indicate that the samples by this method with high purity,the crystal structure of the particles is as same as the bulk material, is fcc structure, w ith average particle sizes about 47nm, ranging from 20 to 70nm, and distributed uniformly in spherical chain shapes, the specific surface areavis 14.23m2/g, po re volume of pore is 0.09cm3/g and average pore diameter is 23nm.

Anti-chloride permeability and anti-chloride corrodibility of a green high performance concrete admixture in concrete

The effects of green high performance concrete (GHPC) admixture on the anti-chloride permeability and anti- chloride corrodibility of concrete are studied by a series of experiments designed on the basis of the diffusion principle and electro-chemical principle. The GHPC admixture consists of fly ash, gangue, slag, red mud, etc., of which the mass fraction of industrial residues is over 96 %. The anti-permeabilities and anti-corrodibilities of the tested GHPC and normal concrete (NC) are evaluated by the Diffusion Coefficients of chloride which was obtained by measuring the concentration of chloride in the tested systems by the voltage difference method. It is found that the adoption of GHPC admixture greatly improves the anti-chloride permeability and anti-chloride corrodibility by modifying the inner structure and contracting the porosity of concrete to the reduce considerably the diffusion rate of chloride. The admixture is desirable regarding its engineering performances as well as economical and environmental interests.

MODEL FOR PREDICTING SHEAR STRENGTH OF SATURATED SOFT CLAY AFTER IMPACT LOADING

Previous studies showed that the samples of saturated soft clay undergoing several stages of impact loading and reconsolidation show obvious quasi-overconsolidation state, and have an increased shear strength. In this paper, the definition of quasi-overconsolidation ratio is given, and furthermore a model for predicting the shear strength of saturated soft clay after impact loading is suggested. In this model, the conditions of partial drainage and stages of impact are taken into account. The calculation results by the proposed model are in good accordance with test data. Besides, the effect of disturbance consolidation on the undrained shear strength by this model is discussed.

Experimental research on the compressibility of stale waste

The compressibility of stale waste is studied based on the investigation into the composition and properties of stale waste in the Chongqing City. Stale waste sampled at a landfill closed for over 8 a was analyzed indoors for its natural density, natural water content, relative density, grain size distribution curve, uniformity coefficient and curvature coefficient. Indoor compression tests for the stale waste were performed to find out the void ratio and its dependence upon applied pressure, compressibility coefficient, constrained modulus and volume compressibility coefficient. From the experimental data, the curvature coefficient and the preconsolidation pressure of the stale waste were worked out. The results indicates that the stale waste is of high compressibility, which is different from the other kinds of common soil, and is underconsolidated soil. The measured compressibility parameters are applicable to settlement calculation of closed landfills.

Crucial problems on security assessment of a building site adjacent to an excavated high slope

The subject of this work is the assessment on the stability of an excavated high slope in order to insure the security of the building site adjacent to the slope, which is frequently encountered in town construction in mountainous areas due to terrain limit. On the base of some typical engineering cases in Chongqing, several crucial problems on security assessment of building site adjacent to an excavated high slope, including the natural geological conditions and man-destroyed degree, engineering environment, potential failure pattern of the high slope, calculation parameters and analysis methods, are roundly discussed. It is demonstrated that the conclusion of security assessment can be determined according to the aspects above-mentioned, and the security assessment is one of the fundamental data to insure the safety of the related construction, site and buildings.

A combined gray neural network model of seasonal heating load forecast

Seasonal heating load time sequence has the double trends of increasing and fluctuating, so it''s difficult to select a model to forecast it. In this paper, a combined model of gray model and artificial neural network model was presented to forecast seasonal heating load. A concrete model was established and was verified through actual examples.

Benefit Evaluation Model of Small Watershed Control Based on Projection Pursuit

A projection pursuit model is presented in this paper for comprehensive evaluation of benefits of small watershed control.By using the model,small watershed control samples with many benefit evaluation indexes can be synthesized projective values with one dimension.The samples can be naturally evaluated according to the projective values.The parameters of the model is optimized by using real coding beased accelerating genetic aglrothm,which overcomes the shortcomings of large computation amount and difficulty of computer programming in traditional projection prusuit methods,and provides a new way for wide applications of projection pursuit technique to different evaluation problems in agricultural systems engineering.

A gravity similitude model for studying steep rock slopes

A method of a large experimental model coupled with a smaller one and an equivalent replacement method are adopted to study the deformation and the failure mechanism of a steep rock slope, in order to solve the difficult problems in space gravity similitude of the experimental model on steep rock slope with weak layers. The experimental results on the Lianziya Precipice of the Yangtze Three Gorges are in general agreement with the field observations. The experimental method adopted is proved to be successful in molding the complex geological condition especially with the weak layers.

Applications of airtight concrete grouting to road tunnels

Road tunnel excavation often traverses coal strata, which is at risk of firedamp explosion that usually results in disaster. Airtight concrete grouting is popularly used in this kind of tunnel project. Based on the essential theory of mechanics of fluids in porous media, the principle of improving concrete airtight property and its influential factors are investigated. The proportioning tests and monitoring method for airtight concrete are introduced, which is illustrated by a case study applied to the project of the Huayinshan Tunnel. It is proved by engineering practices that the achievement of this research work is beneficial to tunneling project across coal strata.

Application of dynamic programming to structural repairing strategies

A model of dynamic programming for repairing strategies of concrete structures during a projected service period is proposed, which takes into account the degradation in strength of components and the probability of accidental load. This model takes the safety grade of a structural system as the state variable of repairing strategies, and incorporates economic factors including expected repair cost, property loss due to structure failure, goods and material loss due to structure failure, loss of production interrupt due to structure failure, and inspection cost in decision making. It is found that the optimal repairing strategies are sensitive to the probability of accidental loads as well as the failure costs. The practicality of the model is demonstrated by an example.

Characteristics of acoustic emission temporal sequences during the failure of a concrete structure under loading

The characteristics of acoustic emission (AE) signals given off in the course of the failure of a concrete structure is explored based on the laboratory experiments with concrete specimens. It is observed that the failure of a concrete structure experiences three stages divided by two inflexion points on the AE event curve, which are sequentially no damage, damage initiation and propagation, and major failure stages. In the first stage, existing micro cracks and defects are compacted by loading, but no damage propagated, hence few AE signals are detected, and it appears that there exists a nearly linear relationship between the relative stress and relative strain. In the second stage, the AE event frequency increases, implying that micro cracks begin to emerge inside the concrete structure, which is consistent with the damage mechanics. When the load is over 80 % of that breaks the structure, i.e. the maximum load, there is a vertical jump on the AE event count curve, which suggests that the failure propagation speeds up. After the second inflexion point, the AE event density increases faster than before, and there is another jump just before breaking, which indicates a quick propagation stage. These findings are valuable for evaluating the damage situations, and for studying and monitoring the dynamic process of the failure behaviors of a concrete structure.

The Automatic Control System For High-speed Material Hoist

This paper introduces the principle, software and hardware structure of automatic control system for high-speed material hoist, and analysis feature of the

NUMERICAL MODELING FOR POSITIVE AND INVERSE PROBLEMS OF 3-D SEEPAGE IN DOUBLE FRACTURED MEDIA

Three-dimensional seepage in double fractured media was modeled in this paper. The determination of hydraulic conductivity tensor of rock mass is a vital problem for the sea water intrusion or sea water encroachment and seepage of fissured medium. According to the geological and hydrogeological conditions for the 2nd-stage construction of the Three Gorges Project (TGP), the physical and mathematical models for the groundwater movement through the 3D double fractured media of rock mass during construction were established in this paper. Based on discontinuity-control inverse theory, some related parameters of double fractured media were inversed with flux being the known quantity and calibration of water table the objective function. Synchronously, the seepage field of the construction region was systematically analyzed and simulated, the results of which exhibit that the double fractured media model of fracture water can comprehensively and correctly describe the geological and hydrogeological conditions in the construction region.