Coupled poromechanical problems appear in a variety of disciplines, from reservoir engineering to biomedical applications. This work focuses on efficient strategies for solving the matrix systems ...that result from discretization and linearization of the governing equations. These systems have an inherent block structure due to the coupled nature of the mass and momentum balance equations. Recently, several iterative solution schemes have been proposed that exhibit stable and rapid convergence to the coupled solution. These schemes appear distinct, but a unifying feature is that they exploit the block-partitioned nature of the problem to accelerate convergence. This paper analyzes several of these schemes and highlights the fundamental connections that underlie their effectiveness. We begin by focusing on two specific methods: a fully-implicit and a sequential-implicit scheme. In the first approach, the system matrix is treated monolithically, and a Krylov iteration is used to update pressure and displacement unknowns simultaneously. To accelerate convergence, a preconditioning operator is introduced based on an approximate block-factorization of the linear system. Next, we analyze a sequential-implicit scheme based on the fixed-stress split. In this method, one iterates back and forth between updating displacement and pressure unknowns separately until convergence to the coupled solution is reached. We re-interpret this scheme as a block-preconditioned Richardson iteration, and we show that the preconditioning operator is identical to that used within the fully-implicit approach. Rapid convergence in both the Richardson- and Krylov-based methods results from a particular choice for a sparse Schur complement approximation. This analysis leads to a unified framework for developing solution schemes based on approximate block factorizations. Many classic fully-implicit and sequential-implicit schemes are simple sub-cases. The analysis also highlights several new approaches that have not been previously explored. For illustration, we directly compare the performance and robustness of several variants on a benchmark problem.
We develop a numerically stable sequential formulation of thermoporomechanics for largely deformable gas hydrate deposits, extended from the fixed stress split of infinitesimal transformation. ...Constitutive equations are based on the total Lagrangian approach for both flow and geomechanics, including dynamic full tensor permeability and thermal conductivity updated from the deformation gradient. For space discretization, we take the cell‐centered finite volume and node‐based finite element method for flow and geomechanics, respectively. Then, we propose a sequential implicit method for all‐way coupled thermoporomechanics, where the nonisothermal multiphase flow problem of gas hydrates is solved implicitly first and then the geomechanics problem is solved implicitly at the next step. During solution of the flow problem, we fix the rate of first Pioal total stress for numerical stability as well as apply porosity correction and entropy correction to account for geomechanical effects. We test numerical examples where flow and geomechanics parameters are based on deep oceanic gas hydrate deposits. When applying depressurization, even though the results between the infinitesimal transformation and finite strain geomechanics are similar in the early stages due to small deformation, we find differences between them in the late times as deformation becomes large. Accordingly, permeability and thermal conductivity tensors become nonisotropic full tensors although they are initially isotropic. We identify numerical stability of the developed sequential method from the test cases that exhibit the highly complex coupled gas hydrate systems with large deformation. Thus, the proposed sequential formulation can be applied in largely deformable gas hydrate systems.
•Splits can exhibit plane change, branching and interaction with other splits.•Splits can grow after having been arrested.•Splits present distortion after their occurrence.•Micro-splits do not cause ...measurables pop-ins during fracture toughness tests.
Split is a brittle stochastic phenomenon sometimes observed in fracture toughness tests of hot rolled steels in T-L and L-T orientations. At present, there is no standard criteria to assess this event in R-curves due, among other things, to the lack of understanding of its characteristics and evolution during the test. This study analyzes the geometrical and morphological characteristics of splits as well as, their evolution and interaction during fracture toughness tests. The tests were performed according to ASTM E1820-20 in DH36 steel using SE(B) specimens in T-L orientation at −60 °C. Split’s geometrical characteristics in the intermediate or final stages of the fracture toughness test were analyzed through Computed Tomography (CT). Also, Scatter Electron Microscopy and Optic Microscopy analysis were performed on the specimen fracture surfaces to study the split’s morphological characteristics. The concomitant occurrence of two splits and micro-splits at the crack growth region are reported. The micro-splits did not cause measurables pop-ins in the load vs. displacement record. CT slices showed that some splits exhibit plane change, branching, and interaction with other splits. These phenomena are not necessarily noticeable on the fracture surface. Also, a split can grow after arrested and present distortion after their occurrence. The sequence of multiple split events can be determined by analyzing both the position on the fracture surface and the degree of distortion of the splits.
In this study, a new transceiver system is presented for detecting the location and orientation of narrow bone fractures. The system comprises a multilayer patch resonator integrated with a reactive ...impedance surface as the transmitter and a three-element array of split-ring resonator (SRR) probes as the receiver. It operates at 2.45 GHz in the Industrial, Scientific, and Medical (ISM) frequency band. Dielectric plano-concave lenses are used in the transmitter and receiver to improve impedance matching and adapt to the human body curvature. By using three adjacent SRR probes to divide the area being investigated into smaller sections, the system concentrates power in the fractured region, improving image resolution. The high capacitance of the split gap in the SRR probes allows for precise tracking of small changes. The system performs longitudinal and rotational raster scans to localize bone cracks and achieves an impressive resolution of 1 mm. The experimental measurements were conducted using a gelatin-based arm phantom and a real arm with various healthy and broken bones. The dual-polarized configuration of the system enables effectively detecting the orientation of fractures. The presence of fractures can be determined by comparing the power received from the three SRR probes. When the crack is parallel to the incident <inline-formula> <tex-math notation="LaTeX">{E} </tex-math></inline-formula>-field, the probe directly facing the crack receives more power than the adjacent probes. This power difference is significantly reduced in healthy bone and also when the incident wave is perpendicular to the crack. The results from both measurement and simulation support each other, validating the reliability of the proposed transceiver system.
Pumped thermal energy storage is a novel energy storage technology with features of high efficiency, geographical independence and suitable for bulk capacity energy storage. As a subset of pump ...thermal energy storage system, the transcritical CO2 arrangements have received widespread attention due to their excellent thermodynamic performance. However, the high cost and low efficiency of heat exchange progress caused by CO2 phase transition hinder the transformation of this system from scientific theory to practical application. CO2 binary mixtures is innovatively employed as working fluid in proposed system. The temperature of mixture is variable rather than remaining constant during the evaporation and condensation progresses. R134a, R290, R600 and R601 are selected respectively to mix with CO2 to form the new working fluids. Advanced thermodynamic and economic models are established to investigate the performance of novel systems. Results indicate that the system driven by CO2/R134a with a refrigerant mass fraction of 0.15 exhibits the optimal overall performance. At the optimal point of the 10 MW/8h system, the round trip efficiency and levelized cost of storage are 66.18 % and 0.146 $/kWh, respectively. Moreover, the investigation of system performance with various energy storage capacities is put forward. It is shown that when the energy system capacity reaches 300 MW, the levelized cost of storage can be reduced to 0.122 $/kWh. To adapt to different peak and valley periods in different regions, systems with different charge and discharge times are investigated and it is found that the charge duration should better be equal to the discharge duration.
•The CO2 mixture cycled high temperature pumped heat storage is given.•The CO2/R134a with fraction 0.85/0.15 is most suggested as working fluid.•The system efficiency can be 66.18 % in the optimal condition.•The system levelized cost of storage ranges from 0.122 to 0.146 $/kWh.
We propose a new split ring resonator engraved metamaterial MIMO patch antenna design which applies in 6–11 THz frequency band. Four different THz antennas are investigated and their results are ...compared to find the optimized antenna design with superstrate. The four antenna designs evolved by adding superstrate layers and metamaterials in the form of complementary split ring resonators are investigated. They are THz patch antenna (TPA), THz complementary split ring resonator patch antenna (TCPA), THz patch antenna with complementary split ring resonator superstrate (TPACS), and THz complementary split ring resonator patch antenna with complementary split ring resonator superstrate (TCPACS). The results show that the complementary split ring resonator metamaterial added in the patch as well as in the superstrate affects the antenna gain and bandwidth while the addition of the superstrate affects the multiband and gain characteristics. All four designs are optimized and show the multiband response. The TCPACS design exhibits the highest bandwidth of 900 GHz 8.88%) and the highest gain of 9.19 dB. The TCPA design is having highest bandwidth of 530 GHz (5.3%) and the highest gain of 8.05 dB. The TPACS design is having highest bandwidth of 300 GHz (3%) and the highest gain of 7.47 dB. The TPA design is having highest bandwidth of 60 GHz (0.6%) and the highest gain of 6.42 dB. The proposed antenna design with multiband, broadband, high-gain and optically transparent characteristics can be used in Terahertz Wireless Area Networks, Terahertz Wi-Fi, 6 G, Internet of Things, Sensing and Imaging applications.
The data supporting the findings in this work are available from the corresponding author with a reasonable request.
Some well-known graph irregularity indices of a connected graph G are investigated. Our study is focused mainly on the comparison of the Bell’s degree-variance (Var(G)) and the Collatz–Sinogowitz ...irregularity index (CS(G)) with the recently introduced σ(G) irregularity index. It is a degree-based topological invariant calculated as σ(G)=F(G)−2M2(G) where M2(G) is the second Zagreb index, F(G)=∑d3(v), and d(v) is the degree of the vertex v in G. By introducing the notion of the complete split-like graphs representing a broad subclass of bidegreed connected graphs, it is shown that for these graphs the equality σ(G)=n2Var(G) holds.
In this paper, a highly sensitive differential Hexagonal Split Ring Resonator (HSRR) sensor is presented operating at 5.3 GHz for permittivity characterization of organic liquids. The hexagonal ...design has a smaller surface area for better field concentration and also possesses a long lateral interaction length for better power transfer from the feed to the resonators. The sensor is designed by loading a 50Ω transmission line with a pair of symmetrically placed HSRRs on either side of the transmission line. Differential sensing is achieved by using one of the resonating elements as the reference and the other as the material sensing unit. The sensor is designed and fabricated on an FR4 substrate to keep the cost low without sacrificing sensitivity. The sensor’s performance is investigated using six Liquid Under Tests (LUTs), covering a wide range of dielectric constants (εr′) from 1 to 20.6, while two LUTs are taken as unknown samples, and their complex permittivity is accurately determined. Due to the high concentration of the electric field, the sensor delivers an extremely high normalized sensitivity of 4.646% (246.48MHz of average sensitivity). The sensor is capable of determining the complex permittivity of unknown LUTs with less than 1.15%error, with the additional advantage of differential sensing, thus making it immune to environmental fluctuations.
Display omitted
•SRR-based differential microwave sensor has been designed and fabricated.•A hexagonal design has been introduced for better coupling of the resonators.•Liquids with a wide range of dielectric constants have been carefully selected to validate the sensor’s performance.•The sensor posesses normalised sensitivity of 4.646 % and average sensitivity of 246.48 MHz.•The sensor predicts permittivity of unknown samples with high accuracy and can be a good alternative to commercial sensors.
It is well known that both the specimen size and the loading rate can affect the tensile strength of rock specimens. In this study, the combined effect of loading rate and specimen size on tensile ...strength was investigated by performing some physical and numerical Brazilian tests on specimens with notch and without notch. The dynamic tests were performed using the Split Hopkinson Pressure Bar apparatus. A type of dental gypsum commercially known as Snow Rock was used to prepare the molded gypsum specimens for the physical tests. The CA3 computer program was utilized for the numerical simulation. The bonded particle model for simulation of the rock together with the implemented micromechanical model was able to capture many features of the physical test results. It was shown that the notched specimens were much more sensitive to the loading rate. Furthermore, the results suggested that there is a critical stress rate at which the specimen size has no effect on the specimen strength. For loading rates greater than the critical one, with the increase in the specimen size, greater tensile strength was obtained. Fracture mechanics size effect was partially observed for the applied loading rates smaller than the critical rate.
This article describes a novel minimally invasive technique for bilateral sagittal split osteotomy (BSSO) that aims to reduce surgical trauma while maintaining bone overlap and rigid internal ...fixation for proper consolidation of the bone segments. The technique involves a small vestibular mucoperiosteal incision made on the lateral aspect of the mandible between the first and second molars, enabling a standard ramus split, surgical segment movement, and miniplate fixation. A retrospective evaluation of 67 consecutive patients who underwent BSSO using this protocol showed favorable split of the mandible with no unfavorable splits or non-union. Patients were discharged from hospital within an average of 17 h with minimal postoperative complications. This technique provides good surgical visualization with a very small incision and allows standard BSSO surgery without difficulty.
PDF
