Transient Pressure Behavior of CBM Wells during the Injection Fall-Off Test Considering the Quadratic Pressure Gradient.

Conventional coalbed methane (CBM) reservoir models for injection fall-off testing often disregard the quadratic pressure gradient's impact. This omission leads to discrepancies in simulating the transient behavior of formation fluids and extracting critical reservoir properties. Accurate determination of permeability, storability, and other properties is crucial for effective reservoir characterization and production forecasting. Inaccurate estimations can lead to suboptimal well placement, ineffective production strategies, and ultimately, missed economic opportunities. To address this shortcoming, we present a novel analytical model that explicitly incorporates the complexities of the quadratic pressure gradient and dual-permeability flow mechanisms, prevalent in many CBM formations where nanopores are rich, presenting a kind of natural nanomaterial. This model offers significant advantages over traditional approaches. By leveraging variable substitution, it facilitates the derivation of analytical solutions in the Laplace domain, subsequently converted to real-space solutions for practical application. These solutions empower reservoir engineers to generate novel type curves, a valuable tool for analyzing wellbore pressure responses during injection fall-off tests. By identifying distinct flow regimes within the reservoir based on these type curves, engineers gain valuable insights into the dynamic behavior of formation fluids. This model goes beyond traditional approaches by investigating the influence of the quadratic pressure gradient coefficient, inter-porosity flow coefficient, and storability ratio on the pressure response. A quantitative comparison with traditional models further elucidates the key discrepancies caused by neglecting the quadratic pressure gradient. The results demonstrate the proposed model's ability to accurately depict the non-linear flow behavior observed in CBM wells. This translates to more reliable pressure and pressure derivative curves that account for the impact of the quadratic pressure gradient.

Predicting the Pressure Behavior and Sensing Property of Elastic Pressure Exerting and Sensing Fabrics for Compression Textiles.

Using compression textiles to exert an appropriate and steady pressure on human limbs is a primary treatment method in the medical area. Compression pressure is a crucial parameter that determines the treatment efficacy. However, there is a lack of pressure-sensing fabrics that can both apply and measure the pressure of compression textiles, particularly the theoretical study of the prediction of the pressure and sensing performance of such a sensing fabric. In this study, based on the developed elastic pressure-exerting and -sensing fabrics and a setup test protocol simulating the pressure-exerting process, the relationships between the displacement of the press head, resultant fabric extension, and pressure were theoretically explored. Two finite element (FE) models, continuum and discontinuous models, were first established to predict the pressure behavior of elastic pressure-exerting and -sensing fabrics. The simulation results present good agreement with the experimental results wherein the pressure generated increases with the increase of the fabric strain in a nonlinear form. Furthermore, with the above FE models for the relationship between fabric extension and pressure generated, as well as the measured electrical resistance of the sensing fabric, a model for the electrical resistance of the sensing fabric can thus be established. Among pressure-sensing fabrics in three different structures, the sensing fabric in sateen exhibits better pressure prediction accuracy and a faster response to the pressure change. Finally, a series of numerical simulations were conducted to investigate the effects of the press head diameter, the unit cell crimp factor of fabric and the fabric pretension on the fabric extension, the resultant pressure, and electrical resistance change. The simulation results show that the pressure decreases with the increase of the press head diameter. The crimp factor and pretension of the sensing fabric also have a significant effect on the pressure and electrical resistance change generated. This simulation approach provides a new theoretical understanding of the pressure behavior and mechanism of pressure-sensing fabrics for future smart compression textiles.

Study on Influencing Factors of Ground Pressure Behavior in Roadway-Concentrated Areas under Super-Thick Nappe.

During the mining activity under the super-thick nappe formed by thrust fault, the law of mine pressure behavior is complex, and it is difficult to control the deformation and failure of surrounding rock. Combined with the actual engineering conditions, the influence of different roof lithology conditions, the thickness of nappe, the mining height, the size of the barrier coal pillar, and the creep time on mine pressure behavior was studied by UDEC numerical simulation software. The results showed that with the advancement of the coal face, due to the influence of the mining of the coal face and the slip dislocation of the super-thick nappe along the thrust faults, the roof-to-floor convergence, the two-sided convergence, and the maximum concentrated stress in the roadway-concentrated areas are significantly increased. For the above five influencing factors, the greater the thickness of the nappe and the mining height, the longer the creep time, and the stronger the ground pressure behavior. The larger the size of the barrier coal pillar, the stronger the roof lithology, and the gentler the ground pressure behavior. The research results can provide some reference for monitoring the law of ground pressure behavior in roadway-concentrated areas under super-thick nappe.

Abutment Pressure Distribution Law and Support Analysis of Super Large Mining Height Face.

Under the condition of the shallow coal seam, the laws of roof activity after large mining height longwall face mining and prevention measures for large-area roof weighting are problems that need to be solved urgently. In the background of the super large mining height working face in the upper 108 working face of Jinjitan Coal Mine 12-2, the spatial distribution characteristics of the development and change of the mining-induced abutment pressure and the related support design in the 8.2 m super large mining height and fully mechanized mining face were conducted. It reveals the distribution characteristics of the dynamic stress field and internal and external stress fields. The influence range of the abutment pressure of the super high mining height working face was measured on site. The numerical simulation is carried out, the roadway support structure is analyzed, and the improvement measures are proposed. The research results demonstrate that: The influence range of abutment pressure is 234 m, the obvious influence range of the leading pressure is 47-60 m, and the peak position of the influence of the leading pressure is 15-20 m. The 5 m range is the lateral inward stress field of the coal pillar, the 10-15 m range is the outward stress field of the coal pillar, and the 20 m range is the original rock stress field of the coal pillar. Therefore, it is proposed that the reasonable size of the coal pillar for roadway protection is 20-22 m. Adjusting the distance between screw steel and FRP bolts from 1000 mm to 1200 mm, the length of the roof prestressed anchor cable should be appropriately reduced to 5.5-6 m according to the lithology of the roof.

Engineering Elastic Properties of Isostructural Molecular Perovskite Ferroelectrics via B-Site Substitution.

Managing elastic properties of ABX3 type molecular perovskite ferroelectrics is critical to their future applications since these parameters determine their service durability and reliability in devices. The abundant structural and chemical viability of these compounds offer a convenient way to manipulate their elastic properties through a facile chemical approach. Here, the elastic properties and high-pressure behaviors of two isostructural perovskite ferroelectrics, MDABCO-NH4 I3 and MDABCO-KI3 (MDABCO = N-methyl-N'-diazabicyclo[2.2.2]octonium) is systematically investigated, via the first principles calculations and high-pressure synchrotron X-ray diffraction experiments. It is show that the simple replacement of NH4 + by K+ on the B-site respectively results in up to 48.1%, 52.4%, and 56.3% higher Young's moduli, shear moduli and bulk moduli, which is attributed to the much stronger KI coordination bonding than NH4 …I hydrogen bonding. These findings demonstrate that it is possible to tune elastic properties of molecular perovskite ferroelectrics via simply varying the framework assembling interactions.

Pressure behavior of different PEEK materials for dental implants.

Due to its mechanical properties, the biocompatible high-performance material PEEK (polyetheretherketone) and PEEK-based compounds may represent viable alternatives to titanium in the field of dental implantology. Therefore we performed static pressure tests with 11 PEEK materials (two unfilled grades, two grades filled with titanium-dioxide-powder, two grades filled with barium-sulfate-powder, two grades reinforced with short carbon fibers, one grade reinforced with glass fibers and two grades reinforced with continuous carbon fibers) in the form of cylindrical specimens with a diameter of 4, 5 and 6mm. The specimens had a height to diameter ratio of 2:1 and were therefore 8, 10 and 12mm high. The parameters elastic modulus, elastic limit and pressure strength were evaluated. The elastic moduli ranged between 2.65±0.03GPa for specimens of a titanium-dioxide-filled grade and 106.71±14.83GPa for specimens reinforced with continuous carbon fibers. The elastic limits ranged between 808.1±42.44N for specimens of a barium-sulfate-filled grade and 7256.4±519.86N for specimens reinforced with continuous carbon fibers. The lowest pressure strength of 122.77MPa was observed for specimens of an unfilled grade, whereas the highest pressure strength of 712.67±66.02MPa could be evaluated for specimens containing continuous carbon fibers. Regarding the maximum bite force of a first molar, all tested materials seem to be suitable for the use as dental implants.

A Study on the Effect of Degree of Freedom of Ankle Motion on Gait of Transfemoral Amputees with SNS Control Prosthesis / 대한정형외과연구학회지

Using three different types of the ankle joint, i.e., the fixed, single-axis, and multi axis type, the gait characteristics of transfemoral amputees were investigated to understand the biomechanics of ankle joint motion during gait of transfemoral amputees with a SNS (swing and stance phase) control prosthesis controlling the flexion-extension of knee in the stance phase unlike conventional swing control prostheses. The socket pressure was measured to explain the resulting gait characteristic of the transfemoral amputees for different ankle joint components. Based on the results from the gait characteristics, socket pressure, knee flexion-extension behavior, and ground reaction vector, the fixed type ankle joint could be considered as the most appropriate ankle joint for the transfemoral amputees using the SNS control prosthesis.

A Study on the Effect of Degree of Freedom of Ankle Motion on Gait of Transfemoral Amputees with SNS Control Prosthesis / 대한정형외과연구학회지

Using three different types of the ankle joint, i.e., the fixed, single-axis, and multi axis type, the gait characteristics of transfemoral amputees were investigated to understand the biomechanics of ankle joint motion during gait of transfemoral amputees with a SNS (swing and stance phase) control prosthesis controlling the flexion-extension of knee in the stance phase unlike conventional swing control prostheses. The socket pressure was measured to explain the resulting gait characteristic of the transfemoral amputees for different ankle joint components. Based on the results from the gait characteristics, socket pressure, knee flexion-extension behavior, and ground reaction vector, the fixed type ankle joint could be considered as the most appropriate ankle joint for the transfemoral amputees using the SNS control prosthesis.