Detection of Coal and Gangue Based on Improved YOLOv8.

To address the lightweight and real-time issues of coal sorting detection, an intelligent detection method for coal and gangue, Our-v8, was proposed based on improved YOLOv8. Images of coal and gangue with different densities under two diverse lighting environments were collected. Then the Laplacian image enhancement algorithm was proposed to improve the training data quality, sharpening contours and boosting feature extraction; the CBAM attention mechanism was introduced to prioritize crucial features, enhancing more accurate feature extraction ability; and the EIOU loss function was added to refine box regression, further improving detection accuracy. The experimental results showed that Our-v8 for detecting coal and gangue in a halogen lamp lighting environment achieved excellent performance with a mean average precision (mAP) of 99.5%, was lightweight with FLOPs of 29.7, Param of 12.8, and a size of only 22.1 MB. Additionally, Our-v8 can provide accurate location information for coal and gangue, making it ideal for real-time coal sorting applications.

Research on the hydraulic support face guard mechanism and coupling characteristic of rib spalling in large mining heights.

In view of the problem of poor coupling adaptability and easy rib spalling of coal wall in large mining height comprehensive mining, based on the effective inhibition effect of face guard mechanism on coal wall spalling, the structural characteristics and bearing capacity of different structural forms of the face guard mechanism are compared and analyzed. According to the surrounding rock adaptability of the face guard mechanism, established a numerical analysis model for rigid-flexible coupling of the face guard mechanism under different spalling forms. In order to accurately simulate the stress state of the protective mechanism, a variable stiffness spring damping system is used to replace the hydraulic cylinder. The load-bearing performance and response characteristics of the face guard mechanism under rib spalling coupling conditions were analyzed by applying uniform normal load and impact load to the face guard. The findings indicated that, the integral-type face guard mechanism has a better effect on suppressing rib spalling. When the face guard mechanism bears the static load of the coal wall, the entire response process of the face guard jack can be divided into three stages: initial support, increasing resistance bearing, constant resistance bearing; both the impact load position and the coupling state of the rib spalling will affect the characteristics of force transmission at the face guard mechanism's hinge point, the hinge point between the extensible canopy and the primary face guard is most sensitive to biased load. The research results can provide reference for optimizing the face guard mechanism of large mining height hydraulic support and improving the reliability of coal wall support.

Influence of Periodic Disturbance Incoming Flow on the Supercavitation Phenomenon.

Previous studies on supercavitation flow have primarily focused on a standing water environment, neglecting the impact of periodic disturbance in a marine environment. Therefore, a series of periodic functions with different frequencies and amplitudes are defined to simulate the periodic disturbance, and a slender projectile is adopted to numerically study the effect of the periodic disturbance on the supercavitation phenomenon in this paper. Research results show that the cavity profile evolves periodically with the periodic disturbance of the external flow field. At the same time, as the frequency and amplitude increase, the minimum cavity shape gradually decreases to the point that the projectile cannot be wholly enveloped, and the maximum cavity profile gradually increases. Furthermore, the relationship between the cavity length (l i ) and the frequency (f) when the cavity cannot envelop the projectile is obtained (l i = -7.381f + 215.384). Meanwhile, the critical frequency range (7.16 ≤ f < 7.96) and amplitude range (1.1 ≤ am < 1.22) of the cavity to envelop the projectile are obtained. The key factors of periodic disturbances on supercavitation flow are revealed in this paper, which provides a theoretical foundation for maintaining supercavitation flow stability in an environment of periodic disturbance flow.

Experimental study on shearer traction vibration considering attitude disturbances.

Due to the influence of structural clearances, the shearer's oscillates and jumps concerning the scraper are frequent, which induces the collision and vibration impact of the traction components and exacerbates the traction failure of the shearer. Therefore, to explore the correlation between attitude disturbance and traction vibration, an experiment on the traction vibration is carried out, the spatial swaying of the shearer and vibration differences between two traction components are obtained, the influence of the lifting angle of the rocker arm is discussed, and the influence mechanism of the shearer attitude disturbance on traction vibration is elucidated. The results indicate that the rolling swing intensity of the shearer is the highest while the yawing swing intensity is the lowest, and the pitch swing intensity increases with the increase of the lifting angle of the rocker arm. Besides, the vibration impact indices of the two walking mechanisms have a competitive relationship of one decreasing but the other increasing, which can be used as a reference signal to judge the rolling swing and load-sharing performance of the traction part. Moreover, with the swing attitude, the competitive relationship of the average of vibration peaks is shown in the two support shoes, and it can be used as a reference signal to judge the pitching swing and the load-sharing performance of the traction part. This result reveals the impact mechanism of attitude disturbances on traction vibration and proposes a signal monitoring approach for judging the traction attitude disturbance and load-sharing performance, providing a reference for reducing traction faults.

Digital Control Method and Performance Analysis of the Double-Compound Axial Piston Pump.

The flow control range of the double-compound axial piston pump with the traditional mechanical-hydraulic feedback servo control is limited and the accuracy is poor. Accordingly, this paper proposes a digital control scheme and its control strategy using a linear stepper motor direct drive servo valve for the precise control and double pumps cooperation of the double-compound axial piston pump. A numerical model of the digital control double-compound axial piston pump is established, and the validity of the model is verified by experimental tests. The performance advantages of the digital control method relative to the mechanical-hydraulic feedback servo control method are analyzed, as is the performance of the control strategy for double pumps. The results show that the digital control method can achieve a wider range of flow control than the traditional mechanical-hydraulic feedback servo control method and avoid the torque impact on the prime mover caused by the active control. The combination of the flow control and the power control including four control modes can meet the performance requirements of the double-compound axial piston pump. The highest priority is given to the energy-saving control, which can reduce the displacement of the main pump in the nonworking state to reduce the additional power loss. The study provides a basis for the accurate matching and optimization of power to load and flow to operating speed of the double-compound axial piston pump.

Vibration response difference of caving mechanism under coal rock impact based on mechanical-hydraulic coupling.

Top coal caving in fully mechanized caving mining will cause an irregular impact on the caving mechanism of hydraulic support. The vibration response of the caving mechanism varies under different forms of impact. This response difference is a prerequisite for new coal rock identification technology in intelligent mining. Therefore, this work studies the difference in vibration response of the caving mechanism under different forms of impact. An innovative mechanical-hydraulic coupling system model of the caving mechanism impact by coal rock is established. The metal plate impact test proved the significant difference in vibration response of the caving mechanism under coal rock impact of different materials. Afterward, a more improved mechanical-hydraulic co-simulation model analyzed the difference in the vibration response of the caving mechanism under different rock materials, volumes, velocities and impact positions. The results show that the vibration response is more intense under rock impact than under coal impact. A lower position, a faster velocity and a larger volume correspond to a more noticeable response difference in the caving mechanism. The vibration and fault sensitive areas of the caving mechanism are determined. This study has a reference significance for improving the caving mechanism's structural design and failure prevention. The conclusions provide guidance for a new intelligent coal rock identification technology based on vibration signals.

Impact Response of the Tail Beam Jack Based on Bidirectional Fluid-Structure Coupling Simulation.

In top coal caving mining, the coal rock collapse will cause an irregular impact on the tail beam jack of the caving control mechanism. The severe impact will lead to jack failure. The bidirectional fluid-structure coupling model is built on Fluent and Mechanical software to study the impact response of the tail beam jack. The dynamic flow velocity streamlines, hydraulic pressure distribution, stress field, and strain field of the jack under impact load are extracted. The response characteristics of the jack in the stationary state and motion state are analyzed. The conclusions are as follows: the stress and strain of the rodless cavity are much larger than those of the rod cavity, which is more likely to be damaged. The hydraulic pressure in the jack cavity is in vertical layered distribution. The flow velocity streamlines present spiral shapes. The response degree of the hydraulic pressure signal in the rodless cavity is stronger than that in the rod cavity, and the response degree of the flow velocity signal in the rod cavity is stronger than that in the rodless cavity. The impact response of the jack in the motion state is more sensitive and stronger than that in the stationary state. The coal rock collapse situation can be most effectively identified only by comprehensively analyzing the rodless cavity's pressure signal and the rod cavity's velocity signal. This paper innovatively visualizes the flow velocity streamlines and pressure distribution together. The bidirectional fluid-structure coupling method is innovatively applied to the tail beam jack. The findings of this study can help for better understanding of the tail beam jack's structural design and failure prevention. This study provides a certain research basis for the intelligent coal rock identification technology in mining coal based on jack vibration signals.

The rock damage mechanism of combined rock breaking with saw blade and conical pick.

The combined rock breaking method with the saw blade and conical pick is proposed to improve the rock breaking efficiency. The numerical simulation of combined rock breaking with the saw blade and conical pick is established to investigate the rock damage mechanism. And verified and modified the numerical simulation model with the rock breaking comprehensive test bench, the quantitative analysis error is less than 0.05, indicated quantitative analysis system is accuracy. The result indicated that the cutting parameters of the saw blade and conical pick affect the rock damage. And the cutting parameters of conical pick and structural parameters of rock plate have been studied to influence rock breaking volume. The research result could help optimize the cutting parameters of the saw blade and conical pick to improve the rock breaking efficiency.

Simulation Research on Impact Contact Behavior between Coal Gangue Particle and the Hydraulic Support: Contact Response Differences Induced by the Difference in Impacted Location and Impact Material.

In the process of top coal caving, coal gangue particles may impact on various parts of the hydraulic support. However, at present, the contact mechanism between coal gangue and hydraulic support is not entirely clear. Therefore, this paper first constructed the accurate mathematical model of the hydraulic cylinder equivalent spring stiffness forming by the equivalent series of different parts of emulsion and hydraulic cylinder, and then built the mesh model of the coal gangue particles and the support's force transmission components; on this basis, the rigid-flexible coupling impact contact dynamic model between coal gangue and hydraulic support was established. After deducing contact parameters and setting impact mode, contact simulations were carried out for coal particles impacting at the different parts of the support and coal/gangue particles impacting at the same component of the support, and the contact response difference in the support induced by the difference in impacted component and coal/gangue properties was compared and studied. The results show that the number of collisions, contact force, velocity and acceleration of impacted part are different when the same single coal particle impact different parts of the support. Various contact responses during gangue impact are more than 40% larger than that of coal, and the difference ratio can even reach 190%.

Investigation of fragment separation during a circular saw blade cutting rock based on ANSYS/LS-DYNA.

Circular saw blades are widely used in stone processing. The circular saw blade cutting hard rock numerical simulation model based on ANSYS/LS-DYNA was established to investigate the complex dynamic problem in rock cutting. The failure mechanism of the rock and the influence of cutting parameters on the cutting force and rock fragments were studied by numerical simulation. The results demonstrated that the failure modes of the rock were mainly tensile failure with some shear failure and compressive failure. The cutting force and the number of fragments increased with the feed speed. With the increasing circular saw blade rotational speed, the cutting force and the number of fragments decreased and tended to stabilize. With the distance between the circular saw blades increasing, the cutting force and rock fragments number increase and then maintain basic stability, and when the distance between double circular saw blades reaches 25 mm, it will form a completed rock plate and the interaction of circular saw blades will decrease. The numerical simulation can accurately simulate rock breakage and force when a circular saw blade cuts rock.

Analysis of the vibration characteristics of tail beam of the hydraulic support under random coal gangue particle slip conditions.

To study the influence of the gangue content of coal gangue particles on the vibration signal of the tail beam under sliding condition, this paper combines three-dimensional(3D) laser scanning technology with the finite element method, establishes a finite element model of the real shape of coal gangue particles and the hydraulic support in top coal caving in LS-DYNA, analyzes the influence of gangue content on some characteristics of the acceleration signal on the tail beam in the time and frequency domains, and then studies the influence of the size and total mass of the rock, and the angle of the tail beam on the characteristics. The following conclusions are obtained: when the coal gangue particles slip on the tail beam, an increase in gangue content significantly improves the effective value of the acceleration signal of the tail beam in the time domain and the average power and average amplitude in the frequency domain. With different sizes, total masses, and tail beam angles, the increase in gangue content always causes an increase in acceleration signal characteristics. In terms of the influence of various factors on the same gangue content, at the same total mass, the larger the rock mass size is, the faster the characteristic value increases with the increase in gangue content. The greater the total mass, the greater the value of the acceleration signal characteristics. A smaller angle between the tail beam and the ground increases the value of each characteristic. The results of this study provide a reference for further research on coal gangue identification based on vibrations.

Vibration Response Analysis of the Tail Beam of Hydraulic Support Impacted by Coal Gangue Particles with Different Shapes.

The existing research on coal gangue identification based on vibration usually assumes that coal gangue particles are ideal shapes. To understand the vibration response difference in hydraulic support caused by coal and gangue with real shapes, this paper uses a three-dimensional (3D) scanning technology to determine the real shape of coal particles. The process of coal and gangue impacting the tail beam at different angles was simulated in the LS-DYNA software package, and the effects of shape parameters, velocity, and coal strength on the difference in vibration signals caused by the two were analyzed statistically. The conclusions are as follows: the vibrational response of the tail beam is concentrated mainly in the area between the ribs. The regularity of the velocity signal caused by gangue is better than the regularity of the velocity signal caused by coal, and the attenuation speed of the acceleration signal of gangue is slower than the attenuation speed of the acceleration signal of coal. The probability distributions of the velocity and acceleration responses were analyzed statistically, and the results show that the results from coal can be well fitted by a logarithmic normal function, and the standard deviations of velocity and acceleration are 0.05591 and 489.8, respectively. The gangue results are fitted by the gamma function and the Weibull function, and the standard deviations are 0.13531 and 737.9, respectively, showing that the fitting function has the potential to be used as the basis for coal gangue identification. The change in coal strength has little effect on the vibration response of the tail beam. With increasingly falling velocity, the vibration signal intensity of the tail beam increases, but the discrimination between coal and gangue weakens; therefore, measures should be taken to reduce the falling velocity of the rock mass. The research results of this paper can provide a reference for further study of coal gangue identification methods based on vibration.

Research on Cutting Performance of Conical Pick Cutting Rock Plate with One Side Constrain and Three Sides Free.

To improve the conical pick cutting performance by per cutting to the free surface. The cutting performance of rock and rock plate breaking are investigated by theoretical and experimental methods. Analyzed the fracture position of the rock plate with constrained one side by the pick to study the effect of rock properties and the rock plate structural parameters on cutting force. The results indicated that the rock plate fracture is mainly from the constrained side and center of the rock plate. The cutting force of the conical pick is significantly affected by the rock plate structural parameters and the constraint sides of the rock plate number. The cutting force increases obviously with the increase of plate thickness, cutting point depth, and the rock uniaxial compressive strength. However, the influence of rock plate constrains sides number is opposite. It provides a basis for improving the cutting performance of pick and predicting the rock plate fracture.

Research on cutting performance and fatigue life of conical pick in cutting rock process.

The conical pick is the most crucial tool of roadheader for breaking rock, establishing the conical pick cutting rock and conical pick fatigue life numerical simulation models to investigate the influence of cutting parameters on rock damage, average peak cutting force, specific cutting energy and the conical pick fatigue life. The research results indicate that the width and depth of rock damage increase with increasing cutting depth and cutting speed. The average peak cutting force and the specific cutting energy have the same changing tendency. The changing trend of conical pick fatigue life and conical pick stress is opposite relationship. The optimum cutting angle of the conical pick cutting rock is 45°. Applying the research results for guiding the optimization of the cutting parameters reduces the specific cutting energy and stress and improves the conical pick fatigue life.

The design and analysis of a new slipper-type hydraulic support.

To improve the safety and the stability of the support under mines and reduce the cost, we design a new slipper-type hydraulic support with energy-efficiency and high reliability. To study its dynamics, we build a reverse kinematics model. We analyze the motion and the force for each component of the new support with a simulation in Matlab/Simulink. The results show that it has appropriate structures with the required four-bar linkages. To compare the performance between the new slipper-type support and the traditional support, we design their mechanics models, deduce their mechanics relations and obtain the force curves for each component of both supports under the same loads. The results prove that the new slipper-type support has less demand on oil pressure for the hydraulic cylinder when working at middle and high positions and it has a larger supporting force and a higher supporting stability which would be more energy-efficient.