Gas Permeability Change With Deformation and Cracking of a Sandstone Under Triaxial Compressiongas Permeability Change With Deformation and Cracking of a Sandstone Under Triaxial Compression

In this paper, a THMC (Thermal-Hydrological-Mechanical-Chemical) multi-field coupling triaxial cell was used to systematically study the evolution of gas permeability and the deformation characteristics of sandstone. The effects of confining pressure, axial pressure, and air pressure on gas permeability characteristics were fully considered in the test. The gas permeability of sandstone decreases with increasing confining pressure. When the confining pressure is low, the variation of gas permeability is greater than the variation of gas permeability at high confining pressure. The gas injection pressure has a significant effect on the gas permeability evolution of sandstone. As the gas injection pressure increases, the gas permeability of sandstone tends to decrease. At the same confining pressure, the gas permeability of the sample during the unloading path is less than the gas permeability of the sample in the loading path. When axial pressure is applied, it has a significant influence on the permeability evolution of sandstone. When the axial pressure is less than 30 MPa, the gas permeability of the sandstone increases as the axial pressure increases. At axial pressures greater than 30 MPa, the permeability decreases as the axial pressure increases. Finally, the micro-pore/fracture structure of the sample after the gas permeability test was observed using 3D X-ray CT imaging.

Beulverhalten von ringversteiften Kreiszylinderschalen unter Axialdruck – Teil 1: Versuche und geometrische Imperfektionsanalyse/Buckling behavior of ring-stiffened cylinder shells under axial pressure – Part 1: Tests and geometric imperfection analysis

Moderne Behälter werden oft als ringversteifte Kreiszylinderschalen ausgeführt. Der traglaststeigernde Effekt eng liegender Ringsteifen unter Axialdruck erfuhr in der Forschung bis heute nur geringe Beachtung. Er ist bisher ungeregelt und infolge unnötig hohen Materialeinsatzes bleiben Stahlbehältern Marktanteile und bessere Nachhaltigkeit verwehrt. Anhand von Versuchen und einer numerischen Studie werden die neuesten Forschungsergebnisse des Einflusses der Ringsteifen auf das Axialbeulverhalten von Kreiszylinderschalen erläutert. Die Ergebnisse zeigen, dass die ringversteiften Kreiszylinder unter Axialdruck nach der aktuellen Bemessungspraxis unwirtschaftlich bemessen werden.   Im Teil 1 dieses Beitrags werden Versuche im verkleinertem Maßstab durchgeführt, um den Einfluss der Ringsteifen auf das Beulverhalten der Kreiszylinderschalen unter Axialdruck zu erforschen. Gemäß einem Vergleich von Versuchsergebnissen wird eine mehrfach höhere Tragfähigkeit ringversteifter Schalen gegenüber unversteiften Schalen ermittelt. Die geometrischen Imperfektionen des Probekörpers werden durch eine 3D-Scan-Technologie gemessen und danach mittels der Methode der Fourier-Reihen analysiert. Im Teil 2 folgen die numerische Simulation und das Ableiten eines Ingenieurmodells.

Research of pressure pulsations during gas outlet to closed pipe area with liquid and installed disc barrier

A numerical simulation of the gas outflow to a closed region filled with liquid with a barrier disk was performed. The calculations were carried out using the VOF method, supplemented by the k-e turbulence model. Calculations were performed for three cases of 100, 200, and 300 mm distances of the disk from the injector with a gas outflow into water and liquid lead. The pulsations of axial pressure on a disk obstacle were investigated. It was found that the maximum pressure during pulsations of the upper gas volume in lead can be greater than the pressure in the gas receiver.

Experimental Study on Mechanical Properties of Freeze-Thaw Damaged Red Sandstone under Combined Dynamic and Static Loading

Using the freeze-thaw cycle test chamber, the red sandstone samples are subjected to cyclic freeze-thaw tests. The physical properties, static mechanical properties of freeze-thaw damage rocks, and the compressional wave velocity at specific axial pressure are measured using conventional physical tests and uniaxial compression tests. The mechanical properties of freeze-thaw damage rocks under dynamic and static loading were studied using Hopkinson pressure bar which can exert axial pressure. The studies show that, with the increase of freeze-thaw cycles, the surface layer of the rock sample undergoes spalling phenomenon, the weight gradually decreases, the sample compactness becomes worse, there are microcracks between the cemented particles, and the compressive strength and elastic modulus decrease. Under the static loading, the longitudinal wave velocity of freeze-thaw damaged samples change significantly compared with that of samples without freeze-thaw. The freeze-thaw damage degree, axial pressure, and strain rate are coupled with each other, which together affect the dynamic mechanical properties of samples, and make the variation of mechanical parameters, such as dynamic peak strength and dynamic elastic modulus of rock. The combined action of freeze-thaw damage and axial pressure weakens the strain rate effect of samples, but when the incident wave of SHPB test is same, the dynamic strength and elastic modulus of freeze-thaw damaged samples are reduced compared with those without freeze-thaw. Combining with strain equivalence principle, the constitutive relation of freeze-thaw damage of red sandstone under dynamic and static combined loading can reflect the influence of coupling damage of axial pressure and freeze-thaw, dynamic impact parameters, and other factors, which are in good agreement with the test results.

Experimental investigation of axial pressure drop analysis on the additively manufactured porous regenerator

Regenerators are used in cryogenics for nitrogen and helium liquefaction through reversed Stirling cycle to achieve a low operating temperature of 40 K. An ideal regenerator has critical properties such as low thermal conductivity, optimum porosity, high heat transfer, and specific heat. In general, the matrix of the porous materials is in the form of wire mesh, fibrous wool, granules, or foams. The recent technological development in additive manufacturing (AM) allows it to extend its application to porous structure-based energy exchanging devices. Direct metal laser sintering (DMLS) is one of the AM processes used to fabricate complex geometry with uniform porosity, of considerably low cost compared with the conventional processes. This paper presents the development of an experimental setup to investigate the steady axial pressure drop analysis through various types of regenerators. These regenerators have been tested for multiple working fluids such as Argon and Helium gas at room temperature. The axial pressure drop results of the additive regenerator have been compared with the woven wire mesh and copper wool type of regenerators. The additively manufactured regenerator has a lower pressure drop of 9% and 14% than the copper wool and woven wire mesh type regenerators.

Experimental Study on Mechanical Properties and Seepage Laws of Raw Coal under Variable Loading and Unloading Rates

This manuscript studied the effects of variable axial pressure loading rate and variable confining pressure unloading rate on the deformation behavior and seepage characteristics of raw coal under alternate loading and unloading of axial pressure and confining pressure. It believed that as axial stress increases, axial strain ε 1 decreases, radial strain ε 3 increases, and permeability k decreases, and ε 1 ′ , ε 3 ′ , and k ′ increase when confining pressure is decreases. With the loading of axial stress and the unloading of confining pressure, the variation amplitudes of ε 1 ′ , ε 3 ′ , and k ′ values reduce gradually. During axial stress loading, the rise in the amplitude of ε 1 is larger than that of ε 3 and the reduction in the amplitude of k , indicating that ε 1 is more sensitive to axial stress than ε 3 and k . During unloading of confining pressure, the increase rate of ε 3 is larger than that of ε 1 and k ; also, ε 3 showed a high sensitivity to confining pressure. In the stage of axial stress loading and confining pressure unloading, the evolution law of deformation and permeability parameters is basically consistent with the change in loading and unloading rate.

Physical and Mechanical Properties of Turfy Soils under Confining and Axial Pressure Increases Stress Paths in Jilin Province, Northeast China

In recent years, highways have been built rapidly in China’s turfy swamp areas to accommodate economic development. Turfy soil is a type of special soil with high humus and incompletely decomposed plant contents, so its properties are complex and unique. Both the axial and confining pressures of turfy soil increase during embankment filling. Therefore, in this study, three soil tests for analysing the decomposition degree, organic matter content, and triaxial compression under confining and axial pressure increases stress paths were performed to achieve insights into the stress-strain properties of turfy soil. The volumetric and deviatoric strains of turfy soil were summarised to reveal the inner mechanisms of turfy soil, culminating in the establishment of a constitutive model for turfy soil. The results of the constitutive model were compared with the experimental test results to verify the accuracy of the constitutive model. The results showed that the stress-strain and strength of turfy soil are closely related to the organic matter content and decomposition degree. The calculated stress and strain results are also consistent with the experimental results, indicating that this constitutive model can be used to better indicate the original deformation state and strength characteristics of the turfy soil.

IFAR liner benchmark challenge #1 – DLR impedance eduction of uniform and axially segmented liners and comparison with NASA results

This paper presents the contribution from the German Aerospace Center (DLR) to the first liner benchmark challenge under the framework of the International Forum for Aviation Research (IFAR). Therefore, two sets of acoustically damping wall treatments, called ‘liner samples’, have been produced by additive manufacturing based on the design data provided by NASA coordinating this benchmark. These liner samples have been integrated and acoustically characterized in the liner flow test facility DUCT-R at DLR Berlin as well as in the liner flow test facility GFIT at NASA Langley. Besides the dissipation coefficients and the axial pressure profiles, the liner wall impedance was educed by first determining the axial wave numbers and then applying a straightforward method based on the one-dimensional Convected Helmholtz Equation. Finally, the comparison of the liner impedance values to the NASA results show a fairly good agreement.