The pore structure characteristics of tight sandstone are of significance for the exploration and development of tight oil reservoirs. However， little attention is paid to the flow characteristics and influencing factors of different types of pores. This restricts the understanding of the flow and storage capacity of tight sandstone and affects the evaluation and prediction of favorable areas for tight oil reservoirs. Therefore， this paper focuses on the tight sandstone in the Chang 7 member of the Triassic Yanchang Formation in Ordos Basin， and casting thin sections， scanning electron microscopy， nuclear magnetic resonance， and the fractal method are adopted to research the pore structure characteristics of tight sandstone. The results indicate that the pore structure of tight sandstone is a binary pore system composed of bound pores and movable pores. The morphological characteristics and connectivity of different types of pores vary greatly. Bound pores are mainly composed of intergranular pores， and the pore model is the envelope surface of clay accumulation. The pore radius is small， the connectivity is poor， and the fluid flow is poor. The pore features a regular shape， weak heterogeneity， low fractal dimension， and an average value of 1.306 3. The movable pores are mainly combined pores with a spiky-spherical shape. This type of pore has a large radius and multiple connecting channels formed by dissolution， resulting in strong connectivity. The shape of movable pores is irregular， with strong heterogeneity， a large fractal dimension， and an average value of 3.241 6. The influence of different types of pores on physical properties is also different. The average contribution of bound pores to porosity is 47.7%， and that of movable pores to porosity is 52.3%. The two types of pores have similar content but are affected by differences in connectivity. The average contribution of bound pores to permeability is 0.2%， while that of movable pores to permeability is 99.8%. Movable pores are the main factor affecting the permeability of tight sandstone. The fractal dimension can characterize the pore structure of tight sandstone. Sandstone is mainly composed of composite pores and located near the source rocks is a favorable area for exploration and development of tight sandstone.
A high-speed train with wings (HSTW) is a new type of train that enhances aerodynamic lift by adding wings, effectively reducing gravity, to reduce the wear and tear of wheels and rails. This study, based on the RNG k−ε turbulence model and employing a sliding grid method, investigates the aerodynamic effects of HSTWs with different angles of attack when passing through tunnels. The precision of numerical simulation method is validated by data obtained through a moving model test. The results show that the lift of the HSTW increases upon entering the tunnel, with an average lift in the tunnel of 33.3
The properties of low-modulus (m≤1) sodium silicate and pre-desilication solutions in alkali systems were studied by measuring their electrical conductivity, viscosity, and surface tension. The results show that the property of high concentration pre-desilication solution is similar to that of sodium silicate solution. The electrical conductivity of sodium silicate solution increases with increasing the temperature and silica concentration but decreases with increasing the modulus. Further, the viscosity of the solution increases with increasing the silica concentration and linearly decreases with increasingthe temperature, whereas its surface tension gradually decreases with increasingsilica concentration and temperature, indicating that the sodium silicate solution is an oligomer with strong surface activity. At room temperature, the electrical conductivity and surface tension of sodium silicate solution are higher than those of pre-desilication solution, whereas its viscosity is smaller than that of pre-desilication solution. A turning point exists at a silica concentration of 44.7 g/L. When the silica concentration is less than 44.7 g/L, the ionic structure of the solution is dominated by monomeric silicate ions. In contrast, when the silica concentration changes from 44.7 to 50 g/L, the migration number of silicate anions significantly decreases.
Using engine exhaust heat to partially convert methanol to syngas and then co-combust is a favored strategy to optimize combustion in methanol engines. In the present work, experiments of methanol pyrolysis and methanolsyngas oxidation were conducted using flow reactors at 1.0-5.0 MPa. The substitution ratio of syngas to methanol varied from 0 to 50%. Experimental results show that high pressure slightly promotes methanol pyrolysis and reduces CH2O generation; syngas inhibits methanol oxidation and reduces CH2O generation. Otherwise, experimental results were used to validate the recently published methanol model, and Mech15.34 captures the experimental data well. The kinetic analysis revealed the effects of substitution ratio on methanolsyngas co-oxidation can be divided into dilution and chemical effects. The dilution effect refers to the reduction of methanol, which directly decreases the CH2O generation. The chemical effect refers to the competition of H2 and CO for OH radicals, which decelerates the CH3OH oxidation. Meanwhile, the reaction H2O2 + H = H2 + HO2 proceeds in reverse direction with H2 blending, generating more H radicals, which enhances the CH2O consumption through the reaction CH2O + H = HCO + H2.
Mechanical metamaterials have been pursuing as valuable properties attribute to the unique internal architecture, but are generally limited to the predetermined properties after manufacturing, resulting in the inability to continuously change the properties during application. Aiming for the continuously adjustable property under environments with high reliability requirements, this research developed two types of mechanical metamaterials based on planetary gear train. The principle of continuously adjustable mechanical property and dynamic characteristics of metamaterial based on planetary gear train is researched though a theoretical model of curved beam under varying radial load. Further, mechanical metamaterials based on double-layers planetary gear (DLPG) train and Ravigneaux planetary gear (RPG) train are designed. The compressive elastic modulus, shear modulus, and amplitude-frequency response are calculated and investigated with finite element simulation. The results, with an adjustable range respectively within 9–15 times and 2–3 times in compressive elastic modulus of and shear modulus, show a good agreement between the theoretical and simulated results, and illustrate the adjustability and reliability of the mechanical metamaterials based on planetary gear train. Finally, the potential configurations and applications of metamaterial based on planetary gear train are presented.
