Numerical Simulation of Parallel Cutting with Different Number of Empty Holes

The cutting blasting plays a key role in rock excavation construction, which determines the blasting effect and efficiency of the entire blasting project. In the cutting blasting, parallel holes are often used as the auxiliary free surface and the compensation space of blasting rock, and the empty holes have a great influence on the blasting effect. In this paper, Ansys/Ls-Dyna finite element analysis software is carried out to simulate four models with different number of empty holes. The simulation results show that the stronger the guiding effect of the empty holes on the crack propagation, the more obvious the inhibition effect on the crack in the remaining direction. The initial crack near the empty hole is generated by the continuous action of the stress wave, and the empty hole promotes the propagation of the explosion stress wave. The inconsistent guiding directions of adjacent empty holes are one of the reasons for the unsatisfactory blasting effect of multiple small diameter empty holes. The closer the empty hole is to the blasthole, the larger the maximum principal stress. By comparing the results of calculation with the numerical simulation, it is verified that the maximum principal stress near the empty hole is similar and the change rule is consistent. The above research has reference meaning to the location of the hollow hole in the actual blasting construction and the density of the empty hole

Study on the correlation between SHPC pore structure and air permeability

Mikro-porozna struktura betona od troske visokih radnih karakteristika (SHPC - Slag High Performance Concrete) od velikog je utjecaja na njegovu provodljivost i izdržljivost. Na temelju eksperimenta provodljivosti zraka i eksperimenta s ubrizgavanjem žive, autor analizira korelaciju između strukture pora SHPC i provodljivosti zraka, uzimajući parametre provodljivosti zraka i strukture pora SHPC kao slučajne varijable, tražeći mehanizam i stupanj utjecaja različitih omjera miješanja parametara strukture pora SHPC na provodljivost zraka. Istraživanje i analiza pokazuju da su promjer središnje pore i promjer praga SHPC svakako povezani s provodljivosti zraka i mogu se koristiti za predstavljanje zračne provodljivosti SHPC, dok ostali parametri nisu s njom usko povezani i ne mogu je pojedinačno predstavljati.The micro-porous structure of slag high performance concrete (SHPC) imposes great influence on its permeability and durability. Based on air permeability experiment and mercury injection experiment, the author analyses the correlation between SHPC pore structure and air permeability by taking parameters of SHPC air permeability and pore structure as random variables, finding the mechanism and level of influence of various mix proportions of SHPC pore structure parameters on air permeability. Research and analysis show that median pore diameter and threshold diameter of SHPC are certainly correlated to air permeability and can be used to represent SHPC air permeability, while other parameters are not closely correlated to it and cannot represent SHPC air permeability directly by single one

Influence of diameter of empty hole on the fragmentation effect of parallel cut blasting under confining pressure

Cut blasting is the key technology for roadway blasting excavation. High confining pressure has obvious inhibition effect on cut blasting effect, while empty hole is of great significance to improve cut blasting efficiency, but the relevant research is not sufficient so far. To study the crushing effect of the cut blasting with different empty hole diameters under the confining pressure, cubic cement mortar test blocks whose side length was 600 mm were made with sand cement ratio of 2:1. The test blocks were subjected to equal bi-axial confining pressure through an electro-hydraulic servo loading system, and the parallel cut blasting cement mortar physical model test was carried out. After the blasting fragmentation was screened and statistically analyzed, the fragmentation distribution and average particle size of model fragments under different empty hole diameters were analyzed and investigated. With fractal features of fragments characterized by fractal dimension, the fragmentation degree was quantitatively analyzed. ANSYS/LS–DYNA software was used to establish numerical models based on the parameters of the test model, and the stress contour at different times with different hole diameters was analyzed. The research result shows that, when two empty holes are charged with different charge of 2 g and 3 g, respectively, the maximum fractal dimension of the model fragment can be attained with empty holes in diameter of 24 mm and 16 mm, respectively, with the particle size of the fragment mainly concentrated in the middle segment between 19 to 75 mm, and the largest total mass of the fragment is 3.128 kg and 3.615 kg, respectively; When the sizes of empty holes are different, the stress concentration effect and the reflected tensile wave produced near the empty hole are also different, which brings the difference of cut blasting fragmentation effect and can effectively benefit from the empty hole effect. The peak value and action range of stress wave near the empty hole are bigger, with a long action time, suggesting a better crushing effect; the diameter of the empty hole is too small, the stress around the empty hole is small. An oversized empty hole will lead to the overflow of the stress wave from the hole. The compressive stress is small after the superposition of stress concentration, and the action area of tensile stress is also small. The proportion of large rock pieces will be high with extremely large or small empty hole. When charged with 3 g, the fractal dimension difference between empty hole model fragments of 32 mm and 16 mm is greater than the difference of model fragments between 16 mm and without empty hole, indicating that the influence on the fragmentation of rock is greater when the empty hole diameter is too large. When the empty hole diameter is the same as 16 mm, the average particle size of the fragments in the model charged with 3 g is less than that in the model charged with 2 g, with the greater fractal dimension and total mass of the fragments than that in the test model charged with 2 g. This shows that an increased charge can contribute to rock fragmentation and the volume of the cut cavity with the same diameter of empty holes

H&TECH

The flow around a cylinder at high Reynolds numbers is turbulence that can be compressed. Turbulence is an extraordinarily complex three-dimensional flow, which is unsteady, erratic and composed of eddies. The characteristic of turbulence is the fluctuation of physical quantity generated by a random motion of vortex at different scales [8] performed the DES of flow around a cylinder in a uniform cross-flow in the subcritical(laminar-separation) and postcritical(turbulent-separation) flow regimes. The results were very similar to those of the experiment and also with LES, especially at a subcritical Reynolds number of 5.0 × 10 4 . Gu et al. [10] used the DES method based on the SST two-equation turbulence model to stimulate the incompressible viscous flow around a cylinder. They proved that the DES method is valid and reliable to simulate the flow around a cylinder with a low or higher subcritical Reynolds number. Xu et al. ABSTRACT The combined section structure has been extensively used in engineering practice. However, there has been little research on the flow around a combined structure. Based on this situation, the numerical simulations of the flow around a combined pier with Reynolds numbers in the range of 1.0×10 6~2 .76×10 6 are performed. The time histories of lift coefficient and drag coefficient of three combined piers with different types (such as combined cylindrical pier, truncated-cone pier, combined truncated-cone pier) in different water depths are analyzed based on detached eddy simulation (DES) by using the fluid dynamics software FLUENT. The results show that the lift coefficient and drag coefficient between the combined cylindrical pier and the truncated-cone pier are basically the same under the condition of the same water depth. When the water depth is 3.0m, the drag coefficient of the combined truncated-cone pier is smaller than that of the combined cylindrical pier and truncated-cone pier. When the water depth is 4.0m or 5.0m, the drag coefficient of the combined truncated-cone pier is greater than that of the combined cylindrical pier and the truncated-cone pier. The form of the cross section of the submerged portion of the combined pier has a significant influence on the average drag coefficient under the condition of a different water depth

Study on the Influence of the Joint Angle between Blast Holes on Explosion Crack Propagation and Stress Variation

The joints and fissures in a natural rock mass can affect the mechanical properties of the rock mass, the propagation of a blasting stress wave, and the blasting effect of the smooth surface of roadways. In the process of roadway drilling and blasting, there will inevitably be some joints between the two blast holes. Taking the joint angle as the starting point, this paper studies the rule of rock explosion crack propagation and stress variation when there are joints with different angles between two blast holes and analyzes the influence of joints on rock mechanical properties and blasting effects. The numerical simulation method and the software ANSYS/LS-DYNA are used to establish 7 rock mass models with various joint angles. When there is no joint between two holes and joints of 15°, 30°, 45°, 60°, 75°, and 90°, the propagation of explosive cracks and stress variations in the rock mass are discussed. The results show that the joints at different angles have obvious guiding and blocking effects on the propagation of explosive cracks, and as joint angles increase, the guiding effect becomes more apparent and the blocking effect becomes weaker. The effective stress of the rock mass will vary depending on the angles of the joints between the hole and the joint. As the joint angle increases, the joint’s influence on the reflection and superposition of stress waves gradually weakens, and the peak value of the effective stress of the rock mass gradually decreases. The peak effective stress of the rock mass on the blasting side of the joint is similarly impacted by the superposition of stress waves, and the extreme value may be seen at the critical node of each change curve. The explosive crack will break through at the critical location because the maximal effective stress of the rock mass is distributed in a “W” form on the blasting side of the joint

Genomic Dissection of Leaf Angle in Maize (Zea mays L.) Using a Four-Way Cross Mapping Population.

Increasing grain yield by the selection for optimal plant architecture has been the key focus in modern maize breeding. As a result, leaf angle, an important determinant of plant architecture, has been significantly improved to adapt to the ever-increasing plant density in maize production over the past several decades. To extend our understanding on the genetic mechanisms of leaf angle in maize, we developed the first four-way cross mapping population, consisting of 277 lines derived from four maize inbred lines with varied leaf angles. The four-way cross mapping population together with the four parental lines were evaluated for leaf angle in two environments. In this study, we reported linkage maps built in the population and quantitative trait loci (QTL) on leaf angle detected by inclusive composite interval mapping (ICIM). ICIM applies a two-step strategy to effectively separate the cofactor selection from the interval mapping, which controls the background additive and dominant effects at the same time. A total of 14 leaf angle QTL were identified, four of which were further validated in near-isogenic lines (NILs). Seven of the 14 leaf angle QTL were found to overlap with the published leaf angle QTL or genes, and the remaining QTL were unique to the four-way population. This study represents the first example of QTL mapping using a four-way cross population in maize, and demonstrates that the use of specially designed four-way cross is effective in uncovering the basis of complex and polygenetic trait like leaf angle in maize