To solve the problem of large deformation soft rock roadway with complicated stress condition in Baluba copper mine, the characteristics of roadway deformation and failure modes are analyzed deeply on the basis of geological survey. Combined with the theoretical analysis and numerical simulation, the new reinforcement technology with floor mudsill and grouting anchor cable is proposed. Moreover, the three dimension numerical simulation model is established by the software FLAC-3D, the support parameter is optimized by it. The results show that the optical array pitch of the U-steel shelf arch is 0.8 m, and the optical array pitch of the grouting anchor cable is 2.4 m. At last, the field experiments are done all over the soft rock roadway. Engineering practice shows that the deformation of soft rock roadway in Baluba copper mine is effectively controlled by adopting the new reinforcement technology, which can provide certain references for similar engineering.
In order to optimize the stope structure parameters in broken rock conditions, a novel method for the optimization of stope structure parameters is described. The method is based on the field investigation, laboratory tests and numerical simulation. The grey relational analysis (GRA) is applied to the optimization of the stope structure parameters in broken rock conditions with multiple performance characteristics. The influencing factors include stope height, pillar diameter, pillar spacing and pillar array pitch, the performance characteristics include maximum tensile strength, maximum compressive strength and ore recovery rate. The setting of influencing factors is accomplished using the four factors four levels Taguchi experiment design method, and 16 experiments are done by numerical simulation. Analysis of the grey relational grade indicates the first effect value of 0.219 is the pillar array pitch. In addition, the optimal stope structure parameters are as follows: the height of the stope is 3.5 m, the pillar diameter is 3.5 m, the pillar spacing is 3 m and the pillar array pitch is 5 m. In-situ measurement shows that all of the pillars can basically remain stable, ore recovery rate can be ensured to be more than 82%. This study indicates that the GRA method can efficiently applied to the optimization of stope structure parameters.
The evaluation accuracies of rock mass structures based on the ratings of the Rock Quality Designation (RQD) and discontinuity spacing (S) in the Rock Mass Rating (RMR) system are very limited due to the inherent restrictions of RQD and S. This study presents an improvement that replaces these two parameters with the modified blockiness index (Bz) in the RMR system. Before proceeding with this replacement, it is necessary for theoretical model building to make an assumption that the discontinuity network contains three sets of mutually orthogonal disc-shaped discontinuities with the same diameter and spacing of discontinuities. Then, a total of 35 types of theoretical DFN (Discrete Fracture Network) models possessing the different structures were built based on the International Society for Rock Mechanics (ISRM) discontinuity classification (ISRM, 1978). In addition, the RQD values of each model were measured by setting the scanlines in the models, and the Bz values were computed following the modified blockiness evaluation method. Correlations between the three indices (i.e., Bz, RQD and S) were explored, and the reliability of the substitution was subsequently verified. Finally, RMR systems based on the proposed method and the standard approach were applied to real cases, and comparisons between the two methods were performed. This study reveals that RQD is well correlated with S but is difficult to relate to the discontinuity diameter (D), and Bz has a good correlation with RQD/S. Additionally, the ratings of RQD and S are always far from the actual rock mass structure, and the Bz ratings are found to give better characterizations of rock mass structures. This substitution in the RMR system was found to be acceptable and practical.
In the presented paper, a problem of nonholonomic constrained mechanical systems is treated. New methods in nonholonomic mechanics are applied to a problem of a Forklift-truck robot motion. This method of the geometrical theory of general nonholonomic constrained systems on fibered manifolds and their jet prolongations, based on so-called Chetaev-type constraint forces. The relevance of this theory for general types of nonholonomic constraints, not only linear or affine ones, was then verified on appropriate models. On the other hand, the equations of motion of a Forklift-truck robot are highly nonlinear and rolling without slipping condition can only be expressed by nonholonomic constraint equations. In this paper, the geometrical theory is applied to the above mentioned mechanical problem. The results of numerical solutions of constrained equations of motion, derived within the theory, are presented.
Abstract Magnetic-geared permanent magnet (MGPM) electrical machine is a new type of machine by incorporating magnetic gear into PM electrical machine, and it may be in operation with low-speed, high-torque and direct-driven. In this paper, three types of MGPM machines are present, and a quantitative comparison among them is performed by finite element analysis (FEA). The magnetic field distribution, stable torque and back EMF are obtained at no-load. The results show that three types of MGPM machine are suitable for different application fields respectively according to their own advantages, such as high torque and back EMF, which form an important foundation for MGPM electrical machine research.
This paper proposes a new dc-side active filter for wind generators that combines 12-pulse polygon auto-transformer rectifier with dc-side current injection method and dual-buck full-bridge inverter having not the “shoot-through” problem in conventional bridge-type inverters, and therefore this system with the character low harmonic distortion and high reliability. The proposed dc-side active filter is realized by using dual-buck full bridge converter, which directly injects compensation current at dc-side of two six-pulse diode bridges rectifiers. Compared with the conventional three-phase active power filter at ac-side, the system with the dc-side active filter draws nearly sinusoidal current by shaping the diode bridges output current to be triangular without using the instantaneous reactive power compensation technology, only using simple hysteretic current control, even though under load variation and unbalanced voltage disturbances, and while an acceptable linear approximation to the accurate waveform of injection current is recommended. The perfor- mance of the system was simulated using MATLAB/Simulink, and the possibility of the dc-side active filter eliminating current harmonics was confirmed in steady and transient states. The simulation results indicate, the system has a total harmonic distortion of current reduced closely to 1%, and a high power factor on the wind generator side.
In order for the working status of the aluminum alloyed hydraulic valve body to be controlled in actual conditions, a new friction and wear design device was designed for the cast iron and aluminum alloyed valve bodies comparison under the same conditions. The results displayed that: (1) The oil leakage of the aluminum alloyed hydraulic valve body was higher than the corresponding oil leakage of the iron body during the initial running stage. Besides during a later running stage, the oil leakage of the aluminum alloyed body was lower than corresponding oil leakage of the iron body; (2) The actual oil leakage of different materials consisted of two parts: the foundation leakage that was the leakage of the valve without wear and wear leakage that was caused by the worn valve body; (3) The aluminum alloyed valve could rely on the dust filling furrow and melting mechanism that led the body surface to retain dynamic balance, resulting in the valve leakage preservation at a low level. The aluminum alloy modified valve body can meet the requirements of hydraulic leakage under pressure, possibly constituting this alloy suitable for hydraulic valve body manufacturing.
Microwave sintering process was employed to agglomerate ferromanganese alloy powders. The effects of sintering temperature, holding time and particle size composition on the properties and microstructure of sintering products were investigated. The results was shown that increasing sintering temperature or holding time appropriately is beneficial to increase the compressive strength and volume density. SEM and EDAX analysis shows that the liquid phase formed below the melting point in the sintering process, which leads to densification. XRD patterns indicate that the main reaction during microwave sintering is the decarbonization and carburization of iron carbide phase. The experiment demonstrate that the optimum microwave sintering process condition is 1150°C, 10 min and 50% content of the powders with the size of –75 μm
The friction and wear properties of 201HT aluminum alloys and the corresponding competitive coupons were tested on an electrohydraulic servo face friction and wear testing machine (MM-U10G). The microstructures of the competitive coupons were investigated by scanning electron microscopy (SEM) and consequently the corresponding friction and wear mechanisms were studied. The results demonstrated that: (1) the best competitive material of friction and wear performance of the 201HT was the 201HTC. (2) the 201HTC modified by carbon following the initial mill for oil storage of the micro-groove to be produced, increased the corresponding lubrication performance reduced the friction coefficient and wear rate effectively. (3) the 201HT-201HTC could obtain both better friction and wear mainly due to the initial process of grinding following the 201HT plastic deformation occurred in the surface and the formation of a series of re-melting welding points, whereas the 201HT material hardness would be similar to the 201HTC material hardness, which led into the competitive material friction and wear performance improvement.
An efficient system of micropropagation via somatic embryogenesis from root-derived callus was established in Arabica coffee (Coffea arabica L.). Twenty-six callus lines were induced on MS (Murashige and Skoog, 1962) medium supplemented with combinations of NAA (0, 0.1, 0.5, 1 and 2 mg/L) plus BA (0, 1 and 2 mg/L), or 2,4-D (0, 0.1, 0.5, 1 and 2 mg/L) plus TDZ (0, 1 and 2 mg/L). Subsequently, two types of somatic embryos were obtained from callus cultures and named S-type and I-type embryos. The S-type embryos were obtained from an 18-monthold callus line which was induced and maintained at 2 mg/L TDZ and 0.1 mg/L 2,4-D near the end of each period of the subculture. These embryos have a developmental barrier, which did not pass through the torpedo stage and could be overcome by a supplement of 2 or 5 mg/L BA. The I-type embryos were induced from 3-month-old callus when transferred onto induction media, i.e., MS supplemented with TDZ (2 and 5 mg/L) plus 2,4-D (0 and 0.1 mg/L). The significantly highest response, i.e., 13.3 embryos per callus clump was obtained at 2 mg/L TDZ. In this study, the results reveal that TDZ has a crucial effect on embryogenic callus induction, proliferation and subsequent somatic embryogenesis.