Abstract: The flow of gas and solid particles in DD-precalciner in the cement plant with capacity of 5000t/d was studied by numerical calculation using Fluent software. The DD-precalciner includes four eccentric burners, two eccentric tertiary air ducts and four feed boxes. The standard k-ε model was proposed to simulate the three-dimension turbulence flow and the movement of solid particles was simulated by particle stochastic trajectory model. The speed contours and velocity vector of different sections as well as the trajectories of solid particles were calculated and analyzed. It indicates that the structure design of DD-precalciner can great improve the combustion of coal power and decomposition of CaCO3 particles.
Abstract: Damage occurs in components and joints while the structure is affected by strong ground motions. Dynamic characteristics of the structure will change with the deterioration of strength and stiffness. Analyzing and processing the vibration signals is one of the mainstream ways for structural health monitoring and damage identification. In this paper, Hilbert-Huang transform is adopted to identify structural damage. Time-varying instantaneous frequency and instantaneous energy is used to identify the damage evolution of the structure. And relative amplitude of Hilbert marginal spectrum is used to identify the damage location of the structure. Finally, the acceleration records at gauge points from the shaking table test of a 12-storey reinforced concrete frame model are processed. Evolution and location of the model damage are identified. Identification results agree well with experimental observation. This indicates that the proposed approach is capable to identify damage of the structure.
Abstract: The pavement condition index (PCI), a numerical rating from 0 to 100, gives a good indication of the pavement condition. However, the pavement distress survey is a labor-intensive procedure which is performed quite subjectively by experienced pavement engineers. Then, a highly complicated calculation is required to determine the PCI of a road network. It is advantageous to determine the PCI from relevant pavement parameters. This study demonstrates how to develop a PCI assessment model based on pavement parameters by combining data mining technique and group method of data handling (GMDH) method. Records from provincial and county roads with asphalt surface and wide variety of pavement structure in Taiwan were employed. After conducting the find dependencies (FD) algorithm in data mining techniques, 120 dependent records were extracted from 253 raw records. For the PCI model development, 100 records were randomly selected as the training dataset. GMDH was successfully applied to develop a PCI assessment model that uses 7 critical pavement parameters and PCI as inputs and output, respectively. The R2 for the training dataset is 0.849. The rest of 20 records were utilized as the testing dataset, which has 0.851 of R2 based on the PCI assessment model. This study confirms that combining data mining technique and GMDH method has the potential to provide significant assistance in pavement condition assessment. The model proposed in this study provides a good foundation for further refinement when additional data is available.
Abstract: The chemical hydration involves complex multiphysical processes including mass and energy transfer, chemical reactions and consequently stress development and shrinkage. This paper proposed a multiphysics numerical model to predict the kinetics cement paste. The chemical reaction theory, heat transfer theory, diffusion theory, and continuum mechanics were coupled in the theoretical model. A comprehensive theoretical model is established with partial different equation system, auxiliary functions, and typical boundary conditions.
Abstract: Freeze-thaw is a major source of damages for infrastructures located in cold regions. Investigating the effects of freeze-thaw on soil mechanical and thermal properties is important for the design and maintenance of infrastructures such as pavements and pipelines. Most existing research investigates soil behaviors in complete freeze or complete thaw conditions. Tools to assist the determination of freeze-thaw status are currently lacking. In this paper, we introduced the design of an innovative guided electromagnetic wave sensor called Time Domain Reflectometry (TDR) that can non-destructively monitoring the freeze-thaw process in standard specimens of soil and concrete. An analysis algorithm is developed to interpret TDR signals. Compared with the existing technologies, the new method not only accurately determines the various stages in the freezing and thawing processes, but also the degree of freeze-thaw status. This analyses algorithm is also independent of soil types and thus can be widely applied. Experiments were conducted on typical types of soils to validate the sensor performance. With the aid of this new sensor, the effects of the degree of freeze-thaw on soil mechanical properties (such as the modulus, strength and volume change) are determined. The success of our preliminary study indicates the innovative sensor and analyses we developed can be a useful tool for investigating the fundamentals of freeze-thaw effects on geomaterials.
Abstract: On basis of the existed TCK model, the establishment process of a new rock blasting damage model is discussed by considering the relationship of crack density Cd, which indicates the shock damage extent of rock, and sound wave attenuation coefficient ap. Then, this model is inserted into the user-defined material model library of ANSYS/LS-DYNA3D software to construct the new damage model. Numerical simulation of damage to retained rock mass of dam foundation caused by rock blasting excavation in dam region with this model. Calculation results show that: as far as the blasting parameters and geological conditions in this paper, the damage to retained rock mass below caused by rock blasting excavation above is basically limited to the scope of 1.5m below the bottom of blasthole, and damage degree gradually reduces from the bottom of blasthole to faraway. Meanwhile, blasting will not cause rock mass to open along soft layer inside, whose maximum calculation displacement is only 3mm. The calculation result can be referred by the practical engineering.
Abstract: Shock accumulation damage failure of rock is often seen in engineering at present. The damage model based on stress wave attenuation is firstly adopted to improve the linear elastic constitutive relationship and load type used in original numerical manifold method program, then the influence of load intensity, action time and rock initial damage on accumulation damage is discussed with it. The simulation results show that: (1) Rock shock accumulation damage shows a nonlinearly rise with increase of load action time; (2) Rock shock accumulation damage shows a non-proportional rise with increase of load intensity, and there will be a load threshold which cannot produce accumulation damage; (3) The initial damage of rock has little influence on accumulation damage of time effect.