Three-dimensional Multispecies Simulation of the Solar Wind Interaction with Mars Under Different Interplanetary Magnetic Field Orientations

Without the intrinsic magnetic field, the solar wind interaction with Mars can be significantly different from the interaction with Earth and other magnetized planets. In this paper, we investigate how a global configuration of the magnetic structures, consisting of the bow shock, the induced magnetosphere, and the magnetotail, is modulated by the interplanetary magnetic field (IMF) orientation. A 3D multispecies numerical model is established to simulate the interaction of solar wind with Mars under different IMF directions. The results show that the shock size including the subsolar distance and the terminator radius increases with Parker spiral angle, as is the same case with the magnetotail radius. The location and shape of the polarity reversal layer and inverse polarity reversal layer in the induced magnetotail are displaced to the y < 0 sector for a nonzero flow-aligned IMF component, consistent with previous analytical solutions and observations. The responses of the Martian global magnetic configuration to the different IMF directions suggest that the external magnetic field plays an important role in the solar wind interaction with unmagnetized planets.

Comprehensive performance analysis of a shearer drum in a complicated seam based on discrete element method

Drum of Shearer undertakes the main function of coal falling and loading, and its performance directly affects the working efficiency of the shearer. Therefore, in order to realize the analysis of the performance of the shearer drum, the MG2 × 55/250-BW shearer drum was the engineered object. Combining the physical and mechanical properties experiment results of coal samples, the coupling model of the drum cutting in complex coal seam was established using discrete element method. The falling-coal characteristics of the spiral drum were studied under different working conditions, and the falling-coal trajectories of the coal and rock particles were fitted. Based on a virtual prototype, the variations of the coal loading rate and lump coal rate with different design parameters were determined by studying the falling-coal effect and loading performance of the drum. Considering the drum performance, multi-objective optimization theory was used to determine the optimal operating and structural parameters. The results indicate that, in the process of drum cutting, the cutting depth has the most significant effect on the coal loading rate, while, the blade spiral angle has the least significant. Moreover, with the increase of the cutting depth of drum and the traction speed, the lump coal rate increases. While, with the increase of the drum rotation speed and the blade spiral angle, the lump coal rate decreases. It is found that when the cutting depth of the drum is 597 mm, the traction speed is 5.4 m/min, the drum rotation speed is 104.8 r/min, and the blade spiral angle is 12° the performance of the drum is optimal. Compared with the falling-coal trajectories before optimization, the displacements of the coal and rock particles ejected along the optimal falling-coal trajectories increase in the coal loading direction. The loading rate and lump coal rate of the drum increase by 6.05% and 12.27%, respectively. The load fluctuation of the drum decreases, and the productivity increases.

Numerical Study of Thermal-Hydraulic Performance of a New Spiral Z-Type PCHE for Supercritical CO2 Brayton Cycle

Printed circuit heat exchangers (PCHEs) have the characteristics of high temperature and high pressure resistance, as well as compact structure, so they are widely used in the supercritical carbon dioxide (S-CO2) Brayton cycle. In order to fully study the heat transfer process of the Z-type PCHE, a numerical model of traditional Z-type PCHE was established and the accuracy of the model was verified. On this basis, a new type of spiral PCHE (S-ZPCHE) is proposed in this paper. The segmental design method was used to compare the pressure changes under 5 different spiral angles, and it was found that increasing the spiral angle θ of the spiral structure will reduce the pressure drop of the fluid. The effects of different spiral angles on the thermal-hydraulic performance of S-ZPCHE were compared. The results show that the pressure loss of fluid is greatly reduced, while the heat transfer performance is slightly reduced, and it was concluded that the spiral angle of 20° is optimal. The local fluid flow states of the original structure and the optimal structure were compared to analyze the reason for the pressure drop reduction effect of the optimal structure. Finally, the performance of the optimal structure was analyzed under variable working conditions. The results show that the effect of reducing pressure loss of the new S-ZPCHE is more obvious in the low Reynolds number region.

Contact stress in helical bevel gears

Helical bevel gears have inclined or twisted teeth on a conical surface and the common types are skew, spiral, zerol, and hypoid bevel gears. However, this study does not include hypoid bevel gears. Due to the geometric complexities of bevel gears, commonly used methods in their design are based on the concept of equivalent or virtual spur gear. The approach in this paper is based on the following assumptions, a) the helix angle of helical bevel gears is equal to mean spiral angle, b) the pitch diameter at the backend is defined as that of a helical gear, and c) the Tredgold's approximation is applied to the helical gear. Upon these premises, the contact stress capacity of helical bevel gears is formulated in explicit design parameters. The new contact stress capacity model is used to estimate the contact stress in three gear systems for three application examples and compared with previous solutions. Differences between the new estimated results and the previous solutions vary from -3% and -11%, with the new estimates being consistently but marginally or slightly lower than the previous solution values. Though the differences appear to be small, they are significant because the durability of gears is strongly influenced by the contact stress. For example, a 5% reduction in contact stress may result in almost 50% increase in durability in some steel materials. The equations developed do not apply to bevel crown gears.

Design and Investigations on Dry Gas Seal of the Shaft End for 450MWe Supercritical Carbon Dioxide Compressor

The dry gas seal is a promising sealing technology to control the leakage flow through the clearance between the stationary and rotational components of Supercritical Carbon Dioxide (SCO2) turbomachinery. The dry gas seal is firstly designed for the SCO2 compressor shaft end of the GE’s 450MWe Brayton cycle power generation system. Then the effects of the spiral angle and gas film thickness on the designed dry gas seal performance are numerically investigated using the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and SST turbulence model. The accuracy of the numerical method is validated by comparison of the previous research data done by Gabriel et al. with air as the working fluid. The Current study analyzed the sealing performance parameters of the designed dry gas seal for SCO2 compressor shaft end at five gas film thicknesses and four spiral angles. These parameters include: opening force, leakage rate, stiffness, and opening force leakage ratio. Also, the impacts of the spiral angle on flow direction in the fluid film are analyzed. The obtained results show that the designed dry gas seal meets the requirement of the leakage flow rate of the SCO2 compressor shaft end. The dry gas seal with a spiral angle of 15° is the best solution due to its low leakage rate and its’ best comprehensive sealing performance. On some occasions where high stability is required, the dry gas seal with a spiral angle of 30° can be selected due to its’ highest film stiffness. The present work provides the reference of the dry gas seal design for the SCO2 compressor shaft end.

Research on spiral angle optimization for longitudinal road header's cutting head

The cutting head is the key component of a road header in tunnel excavation, where the concept of the spiral angle design directly affects the comprehensive performance, which includes cutting resistance, fluctuation coefficient, specific energy consumption, cutting head stress distribution, and so on. Based on the theory of rock-breaking by pick, the mechanical model of pick was established, and the three-dimensional force vector in the WORKBENCH coordinate system was determined. The 3D model of the proposed cutting head was designed using PRO/E and the static simulation was carried out using WORKBENCH, while the stress information of key parts was obtained. Furthermore, a four-dimensional fitting method was used to investigate the influence of the horizontal swing speed, rotational speed, and spiral angle of the cutting head, on the stress of the cutting head assembly. By setting the horizontal swing speed, rotational speed and the spiral angle as design variables and the specific energy consumption, total cutting resistance, fluctuation coefficient, power consumption, and stress on cutting head assembly as the objective function; the multiobjective optimization function of the cutting head was established. By using genetic algorithm, the complex problem has been solved. The solution of this optimization function provides the horizontal swing speed, rotational speed, and spiral angle values, where the optimal performance is achieved, in the aspect of energy consumption, cutting resistance, fluctuation coefficient, cutting power, and cutting motor power. This method provides solid guidance and is a great reference in spiral angle design and optimization.

Research on the effect of magnet parameters on the isochronous field of a superconducting cyclotron

It is a complicated task to obtain an isochronous field of a cyclotron magnet. Due to non-linear property of iron, iterated simulation of magnet design takes a long time to get an isochronous field. As an example, for a magnet design of a 240 MeV (SC240) superconducting cyclotron, the effect of main parameters of a magnet system on the magnetic field was studied, among them the azimuthal sector width, the spiral sector angle, the gap between sectors, the depth of valley region, the position of the coil, the shape of the coil and the excited current of the superconducting coil. It was found that the azimuthal average magnetic field can be increased by any of the following methods, including enlarging azimuthal width, increasing excited current of the superconducting coil, narrowing of the gap between sectors, reducing the depth of the valley region or decreasing the distance between the coil and the mid-plane. In addition, axial oscillation frequency can be improved by increasing the spiral angle, the depth of the valley region, or decreasing the gap between sectors.

On hydrodynamic lubrication characteristics of ferrofluid film in a spiral groove mechanical seal

Purpose The purpose of this study is to investigate the hydrodynamic lubrication characteristics of ferrofluid film for spiral groove mechanical seal in external electromagnetic field and to analyze the effects of the volume fraction of ferrofluid, parameters of the electromagnetic field, operating parameters and geometrical parameters of mechanical seal on the characteristics of ferrofluid film. Design/methodology/approach The relationship between the ferrofluid viscosity and the intensity of external electromagnetic field was established. Based on the Muijderman narrow groove theory, the pressure distribution was calculated with the trial method by trapezoid formula. Findings It was found that pressure, average viscosity, average density and opening force of ferrofluid between end faces increase with the increase in intensity of current, volume fraction of ferrofluid, rotating speed, pressure differential and spiral angle; decrease with the increase in temperature; and increase at first and then decrease with the increase in the ratio of groove width to weir and the groove length. All of them reach the maximum value when the ratio of width of groove to weir is 0.7 and the ratio of groove length is 0.6. Leakage of ferrofluid increases with an increase in intensity of current, volume fraction of ferrofluid, rotating speed, pressure differential, spiral angle and ratio of groove length; decreases with an increase in temperature; and increases at first and then decreases with the increase in the ratio of groove width to weir. The tendencies of characteristics of silicone oil are consistent with those of ferrofluid, and the characteristics of silicone oil are smaller than those of ferrofluid under the same condition. Originality/value The volume fraction of ferrofluid, rotating speed, spiral angle, ratio of groove width to weir, groove length and temperature have a significant influence on the characteristics of ferrofluid film; however, intensity of current and the pressure differential have slight influence on the characteristics of ferrofluid film. An analytical method for analyzing hydrodynamic lubrication characteristics of ferrofluid film in a spiral groove mechanical seal was proposed based on the Muijderman narrow groove theory.