The saturated and unsaturated soil were widely studied by many researchers nowadays. With the development of calculation mechanics and computer, the discrete element method (DEM), as a powerful technique, has been implemented in saturated soil mechanics. This paper review the development of DEM and its application in saturated soil research. Meanwhile, it also prospect the application of DEM in unsaturated soil research. Besides, it also raised some problems that might be met in the real practice and it also tried to put forward some reasonable methods to solve these problems. In the end, this paper put forward a new DEM contact model based on the surface energy to analysis unsaturated soil.
Abstract The vibration signal of a diesel engine contains a large amount of fault information, and an accurate collection of vibration signals will provide reliable data support for diesel engine condition monitoring. This paper designs a diesel engine vibration signal acquisition system based on the powerful Zynq chip. IEPE piezoelectric acceleration sensors are selected to collect diesel engine vibration signals, and a signal conditioning circuit is designed to filter out interference during signal transmission using the characteristics of differential signals and to adjust the voltage amplitude of the signal to ensure compliance with the input voltage level requirements of the AD conversion module. Considering the excellent performance of the AD7771, it is selected as the AD conversion chip, and the peripheral circuit design is completed. With the help of Vivado software, the software and hardware design based on the Zynq chip is completed, controlling the AD7771 to sample 8 channels of vibration signals. Finally, a signal conditioning circuit simulation model is established in Multisim 14.1 software to verify its good performance, and upper computer software is developed to monitor the fault information of the diesel engine.
As a quick, accurate and efficient inspecting equipment, the Portable Falling Weight Deflectometer (PFWD) is widely used in subgrade modulus evaluation in the foreign countries. However, most analysis methods used in the modulus back calculation of PFWD is based on the classical Boussinesq solution or empirical formulas, which could hardly reflect the resilient of subgrade accurately. In this paper, the elastic half-space theory is introduced into the analysis of modulus back calculation, and with the integral transform and the numerical analysis, this paper provides an approximate method to evaluate the elastic modulus of subgrade.
This paper presents a micro-displacement sensing circuit, which can detect sensing capacitors of levitated rotor. To ensure the high resolution, noise analysis of pre-amplifier of micro-displacement sensing circuit is conducted. The results show that choosing low noise amp and decreasing Cf /C1 can reduce the electronic noise.
Based on extended finite element coupled with field variable method, fatigue damage numerical test of three point-bending beam with initial notch has been made to predict crack propagation path, numerical results showed : under the fatigue loading with 200Hz, and amplitude is 20KN, length of crack expanding was the biggest and crack grew as some angles with the initial crack during the first loading, crack propagated parallel to the initial angle during the other loading cycle. These results can fit the experiment very well. Using Fortran, A new user subroutine named USDFILD (User subroutine to redefine field variables at a material point) was also provided on the platform of ABAQUS, which can modal the change of physic material with time. This user subroutine can also import fatigue characterize of material into the model.
Tobacco stems are an important part of the tobacco leaf, containing a lot of cellulose, result in the low utilization of tobacco leaves in cigarettes. The pre-treatment technology of tobacco stems is a key to increase the utilization of tobacco stems. In this work, steam explosion treatment was carried out on tobacco stems with different moisture contents containing 2%, 5% and 10%, respectively. The steam explosion is carried out under different pressure and pressure holding time conditions, the changes in physical structure, chemical composition and pyrolysis volatiles of tobacco stem was investigated. The results indicate that steam explosion has a negligible impact on the crystalline structure of cellulose and low-order polysaccharide crystals, while it has an obvious effect on KCl. Steam explosion increases the specific surface area by destroying the amorphous structure on tobacco stems. The contents of chemical constituents and pyrolytic volatiles indicate that there is a significant leaching effect of lignin, but no change in cellulose content. Soluble polysaccharides, the main component of hemicellulose, were converted into pyrolytic volatiles e.g., furfural and furfuryl alcohol. In conclusion, the technology of steam explosion promotes the leaching, decomposition and chemical transformation of amorphous structures on tobacco stems, thus destroying the structure of the cell walls.
This paper presents an electromechancial interface model of liquid floated micro-gyroscope, which can analyze sensing capacitors and resistance of gyroscope. The impacts of them are analyzed and simulated with the simulation software of circuit. The analytic results indicate that the reasonable interface circuit can substantially remove the impacts of these parasitic capacitances, increase the signal noise ratio. To ensure the high resolution, the model of liquid floated micro-gyroscope with ANSOFT conducted. The results show the transfer characteristics of the sensor and nonlinear error of transfer characteristics.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)