Analysis of One-Dimensional Consolidation Considering Non-Darcian Flow Described by Non-Newtonian Index Incorporating Impeded Drainage Boundaries

The nonlinear flow law and soil boundaries greatly affect the dissipation process of soil consolidation. Thus, to study the impact of nonlinear flow under impeded drainage boundaries, the classical non-Darcian flow model described by non-Newtonian index was introduced. The numerical solutions are derived in detail by the finite difference method (FDM) for one-dimensional (1-D) consolidation incorporating the impeded boundaries, and the computer program is compiled. Then, comparing two analytical solutions based on Darcy’s law and a numerical case of Forchheimeer’s flow, the validity of the present method was verified. The numerical results indicate that there is a critical depth phenomenon for the non-Darcian flow incorporating impeded drainage boundaries. The excess pore water pressure of the soil below the critical depth dissipates more slowly than that of Darcy’s law, whereas the pore pressure of the soil above the critical depth dissipates more quickly than that of Darcy’s law. Moreover, considering that the non-Darcian flow with the non-Newtonian index will still delay the overall consolidation rate of the soft ground, the greater the nondimensional parameter I0 is, the more obvious the lagging phenomenon of the overall dissipation of pore pressure is

Analysis of One-Dimensional Consolidation Considering Non-Darcian Flow Described by Non-Newtonian Index Incorporating Impeded Drainage Boundaries

The nonlinear flow law and soil boundaries greatly affect the dissipation process of soil consolidation. Thus, to study the impact of nonlinear flow under impeded drainage boundaries, the classical non-Darcian flow model described by non-Newtonian index was introduced. The numerical solutions are derived in detail by the finite difference method (FDM) for one-dimensional (1-D) consolidation incorporating the impeded boundaries, and the computer program is compiled. Then, comparing two analytical solutions based on Darcy’s law and a numerical case of Forchheimeer’s flow, the validity of the present method was verified. The numerical results indicate that there is a critical depth phenomenon for the non-Darcian flow incorporating impeded drainage boundaries. The excess pore water pressure of the soil below the critical depth dissipates more slowly than that of Darcy’s law, whereas the pore pressure of the soil above the critical depth dissipates more quickly than that of Darcy’s law. Moreover, considering that the non-Darcian flow with the non-Newtonian index will still delay the overall consolidation rate of the soft ground, the greater the nondimensional parameter I0 is, the more obvious the lagging phenomenon of the overall dissipation of pore pressure is

Large-Strain Nonlinear Consolidation of Sand-Drained Foundations Considering Vacuum Preloading and the Variation in Radial Permeability Coefficient

The vacuum preloading method effectively strengthens soft soil foundations with vertical drainage, which produces a smear effect when laying sand drains. Meanwhile, the seepage of pore water and soil deformation during consolidation exhibit nonlinear characteristics. Therefore, based on Gibson’s 1D large-strain consolidation theory, this paper developed a more generalized large-strain radical consolidation model of sand-drained soft foundations under free-strain assumptions. In this system, the double logarithmic compression permeability relationships for soft soils with large-strain properties, the variation in the radical permeability coefficient in the smear zone, and the effect of the non-Darcy flow were all included. Then, the partial differential control equations were numerically solved by the finite difference method and validated with existing radical consolidation test results and derived analytical solutions. Finally, the influences of relevant model parameters on consolidation are discussed. The analysis shows that the greater the maximum dimensionless vacuum negative pressure P0, the faster the consolidation rate of sand-drained foundations. Meanwhile, the decrease in the negative pressure transfer coefficient k1 will result in a decreasing final settlement amount. Moreover, the consolidation rate of sand-drained foundations is slower considering the non-Darcy flow, but the final settlement is unaffected

Enhancement of the Transmission Performance of Piezoelectric Micromachined Ultrasound Transducers by Vibration Mode Optimization

Ultrasound is widely used in industry and the agricultural, biomedical, military, and other fields. As key components in ultrasonic applications, the characteristic parameters of ultrasonic transducers fundamentally determine the performance of ultrasonic systems. High-frequency ultrasonic transducers are small in size and require high precision, which puts forward higher requirements for sensor design, material selection, and processing methods. In this paper, a three-dimensional model of a high-frequency piezoelectric micromachined ultrasonic transducer (PMUT) is established based on the finite element method (FEM). This 3D model consists of a substrate, a silicon device layer, and a molybdenum-aluminum nitride-molybdenum (Mo-AlN-Mo) sandwich piezoelectric layer. The effect of the shape of the transducer’s vibrating membrane on the transmission performance was studied. Through a discussion of the parametric scanning of the key dimensions of the diaphragms of the three structures, it was concluded that the fundamental resonance frequency of the hexagonal diaphragm was higher than that of the circle and the square under the same size. Compared with the circular diaphragm, the sensitivity of the square diaphragm increased by 8.5%, and the sensitivity of the hexagonal diaphragm increased by 10.7%. The maximum emission sound-pressure level of the hexagonal diaphragm was 6.6 times higher than that of the circular diaphragm. The finite element results show that the hexagonal diaphragm design has great advantages for improving the transmission performance of the high-frequency PMUT

Enhancement of the Transmission Performance of Piezoelectric Micromachined Ultrasound Transducers by Vibration Mode Optimization

Ultrasound is widely used in industry and the agricultural, biomedical, military, and other fields. As key components in ultrasonic applications, the characteristic parameters of ultrasonic transducers fundamentally determine the performance of ultrasonic systems. High-frequency ultrasonic transducers are small in size and require high precision, which puts forward higher requirements for sensor design, material selection, and processing methods. In this paper, a three-dimensional model of a high-frequency piezoelectric micromachined ultrasonic transducer (PMUT) is established based on the finite element method (FEM). This 3D model consists of a substrate, a silicon device layer, and a molybdenum-aluminum nitride-molybdenum (Mo-AlN-Mo) sandwich piezoelectric layer. The effect of the shape of the transducer’s vibrating membrane on the transmission performance was studied. Through a discussion of the parametric scanning of the key dimensions of the diaphragms of the three structures, it was concluded that the fundamental resonance frequency of the hexagonal diaphragm was higher than that of the circle and the square under the same size. Compared with the circular diaphragm, the sensitivity of the square diaphragm increased by 8.5%, and the sensitivity of the hexagonal diaphragm increased by 10.7%. The maximum emission sound-pressure level of the hexagonal diaphragm was 6.6 times higher than that of the circular diaphragm. The finite element results show that the hexagonal diaphragm design has great advantages for improving the transmission performance of the high-frequency PMUT

Design and Fabrication of High-Frequency Piezoelectric Micromachined Ultrasonic Transducer Based on an AlN Thin Film

A piezoelectric micromachined ultrasonic transducer (PMUT) is a microelectromechanical system (MEMS) device that can transmit and receive ultrasonic waves. Given its advantages of high-frequency ultrasound with good directionality and high resolution, PMUT can be used in application scenarios with low power supply, such as fingerprint recognition, nondestructive testing, and medical diagnosis. Here, a PMUT based on an aluminum nitride thin-film material is designed and fabricated. First, the eigenfrequencies of the PMUT are studied with multiphysics coupling simulation software, and the relationship between eigenfrequencies and vibration layer parameters is determined. The transmission performance of the PMUT is obtained via simulation. The PMUT device is fabricated in accordance with the designed simple MEMS processing process. The topography of the PMUT vibration layer is determined via scanning electron microscopy, and the resonant frequency of the PMUT device is 7.43 MHz. The electromechanical coupling coefficient is 2.21% via an LCR tester

Composite g-C3N4/NiCo2O4 with Excellent Electrochemical Impedance as an Electrode for Supercapacitors

For the development of supercapacitors, electrode materials with the advantages of simple synthesis and high specific capacitance are one of the very important factors. Herein, we synthesized g-C3N4 and NiCo2O4 by thermal polymerization method and hydrothermal method, respectively, and finally synthesized NiCo2O4/g-C3N4 nanomaterials by mixing, grinding, and calcining g-C3N4 and NiCo2O4. NiCo2O4/g-C3N4 nanomaterials are characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The microscopic morphology, lattice structure, and element distribution of NiCo2O4/g-C3N4 nanomaterials were characterized by scanning electron microscopy (SEM), transmission electron microscopy, high resoultion transmission electron microscopy, and mapping methods. The electrochemical performance and cycle stability of NiCo2O4/g-C3N4 were tested in a 6 M KOH aqueous solution as electrolyte under a three-electrode system. Due to the physical mixing structure of g-C3N4 and NiCo2O4 nanomaterials, the electrochemical energy storage performance of NiCo2O4/g-C3N4 supercapacitor electrodes is better than that of NiCo2O4 supercapacitor electrodes. At a current density of 1 A/g, the capacitances of NiCo2O4 and NiCo2O4/g-C3N4 are 98.86 and 1,127.71 F/g, respectively. At a current density of 10 A/g, the capacitance of NiCo2O4/g-C3N4 supercapacitor electrode maintains 70.5% after 3,000 cycles. NiCo2O4/g-C3N4 electrode has excellent electrochemical performance, which may be due to the formation of physical mixing between NiCo2O4 and g-C3N4, which has broad application prospects. This research is of great importance for the development of materials in high-performance energy storage devices, catalysis, sensors, and other applications