A mechanical metamaterial has been constructed using a network of interconnected isosceles triangles and right triangles by inspiration from the seesaw motion. The connections are defined as hinges with rotationally elastic restraints wherein each isosceles triangle is three neighboring rotating units while each right triangle is connected to four neighboring rotating units. The effective Poisson's ratio under on-axes loading were established using geometrical approach while the on-axes Young's moduli were developed by matching the spring rotational energy at the hinges of the metamaterial during relative rotation of the rigid units with the strain energy of deformation of the homogenized continuum. Results reveal that by adjusting the geometrical parameters, the Poisson's ratio can range from positive to negative values. The results also show that both the Poisson's ratio and Young's moduli have a wide range of geometrical parameters for fine tuning at low mechanical properties and well as a narrow range of geometrical parameters for coarse tuning at high mechanical properties. These observations suggest that the metamaterial has a wide range of applications from soft robotics to structural applications by adjustment of its geometrical parameters.
{"title":"Auxetic metamaterial inspired by the seesaw motion","authors":"Teik-Cheng Lim","doi":"10.1093/jom/ufae029","DOIUrl":"https://doi.org/10.1093/jom/ufae029","url":null,"abstract":"\u0000 A mechanical metamaterial has been constructed using a network of interconnected isosceles triangles and right triangles by inspiration from the seesaw motion. The connections are defined as hinges with rotationally elastic restraints wherein each isosceles triangle is three neighboring rotating units while each right triangle is connected to four neighboring rotating units. The effective Poisson's ratio under on-axes loading were established using geometrical approach while the on-axes Young's moduli were developed by matching the spring rotational energy at the hinges of the metamaterial during relative rotation of the rigid units with the strain energy of deformation of the homogenized continuum. Results reveal that by adjusting the geometrical parameters, the Poisson's ratio can range from positive to negative values. The results also show that both the Poisson's ratio and Young's moduli have a wide range of geometrical parameters for fine tuning at low mechanical properties and well as a narrow range of geometrical parameters for coarse tuning at high mechanical properties. These observations suggest that the metamaterial has a wide range of applications from soft robotics to structural applications by adjustment of its geometrical parameters.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141821930","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study aims to design the configuration of an aerodynamic wing kit (AWK) on a racing motorbike to achieve the highest downforce-to-drag ratio. The numerical study involves a motorbike traveling in a straight line, where the AWK improves performance and safety by generating downforce to prevent lift. The geometry of the AWK uses a NACA 4412 airfoil with a span of 0.6 m. The computational mesh is generated using SnappyHexMesh and installed on a simplified motorbike to minimize the mesh skewness. The Navier–Stokes equations are solved with OpenFOAM CFD using the RANS k-ω SST and LES turbulence models. Case 1 compares a motorbike with and without a dummy, both equipped with the AWK varying the angle of attack (AoA) from 0 to -41 degrees. Case 2 studies the single wing at different wind speeds (i.e. 20, 60, and 100 m/s) to determine the highest downforce-to-drag ratio at an AoA of -37 degrees. These results serve as the basis for Case 3, which investigates non-parallel wing configurations with a fixed upper wing and a rotating lower wing. In Case 4, where both upper and lower wings rotate simultaneously as parallel wings, the peak downforce-to-drag ratio occurs at an AoA of -41 degrees. Finally, Case 5 modifies the AoA of -41 degrees of the parallel wing of Case 4 to a closed-wing version to comply with FIM safety regulations. With the LES turbulence model, unsteady and complex turbulence structures can be visualized using the Q-criterion. A comparison of the time-averaged lift coefficient between the wingless and closed-wing configurations shows an increase in downforce of approximately 360%. Subsequently, the popularity of AWK will contribute to the safety of racing motorbike driving.
{"title":"Numerical Study of Motorbike Aerodynamic Wing Kit","authors":"Han Chien, Chin-Cheng Wang","doi":"10.1093/jom/ufae025","DOIUrl":"https://doi.org/10.1093/jom/ufae025","url":null,"abstract":"\u0000 This study aims to design the configuration of an aerodynamic wing kit (AWK) on a racing motorbike to achieve the highest downforce-to-drag ratio. The numerical study involves a motorbike traveling in a straight line, where the AWK improves performance and safety by generating downforce to prevent lift. The geometry of the AWK uses a NACA 4412 airfoil with a span of 0.6 m. The computational mesh is generated using SnappyHexMesh and installed on a simplified motorbike to minimize the mesh skewness. The Navier–Stokes equations are solved with OpenFOAM CFD using the RANS k-ω SST and LES turbulence models. Case 1 compares a motorbike with and without a dummy, both equipped with the AWK varying the angle of attack (AoA) from 0 to -41 degrees. Case 2 studies the single wing at different wind speeds (i.e. 20, 60, and 100 m/s) to determine the highest downforce-to-drag ratio at an AoA of -37 degrees. These results serve as the basis for Case 3, which investigates non-parallel wing configurations with a fixed upper wing and a rotating lower wing. In Case 4, where both upper and lower wings rotate simultaneously as parallel wings, the peak downforce-to-drag ratio occurs at an AoA of -41 degrees. Finally, Case 5 modifies the AoA of -41 degrees of the parallel wing of Case 4 to a closed-wing version to comply with FIM safety regulations. With the LES turbulence model, unsteady and complex turbulence structures can be visualized using the Q-criterion. A comparison of the time-averaged lift coefficient between the wingless and closed-wing configurations shows an increase in downforce of approximately 360%. Subsequently, the popularity of AWK will contribute to the safety of racing motorbike driving.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141343114","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Aiming at the problem of performance degradation and large deformation of sandy mudstone after immersion in water, the compression test is carried out. The damage and deterioration law of strength and elastic modulus of immersed rock mass is analyzed, and the function relationship between rock damage variable and soaking time is obtained by fitting. Combined with Hoek-Brown criterion and Mohr-Coulomb criterion, the calculation method of instantaneous cohesion and instantaneous internal friction angle of damaged rock mass is derived based on tangent method, and the equivalent Mohr-Coulomb criterion which can effectively characterize the nonlinear strength characteristics of damaged rock mass is given. Based on the built-in creep model Cvisc of Flac3D, a damage creep model is given by introducing the damage factor and nonlinear strength criterion of immersed rock mass, which is more suitable for describing the creep characteristics of immersed sandy mudstone. The validity of the model is verified by comparing with the measured results.
{"title":"Damage Creep Model and Application for Sandy Mudstone Considering the Effect of Immersion Deterioration","authors":"Zhitao Ma, Wenhu Liu, Hanwen Xu, Yujia Huo, Yipeng Wang, Shunhai Li","doi":"10.1093/jom/ufae026","DOIUrl":"https://doi.org/10.1093/jom/ufae026","url":null,"abstract":"\u0000 Aiming at the problem of performance degradation and large deformation of sandy mudstone after immersion in water, the compression test is carried out. The damage and deterioration law of strength and elastic modulus of immersed rock mass is analyzed, and the function relationship between rock damage variable and soaking time is obtained by fitting. Combined with Hoek-Brown criterion and Mohr-Coulomb criterion, the calculation method of instantaneous cohesion and instantaneous internal friction angle of damaged rock mass is derived based on tangent method, and the equivalent Mohr-Coulomb criterion which can effectively characterize the nonlinear strength characteristics of damaged rock mass is given. Based on the built-in creep model Cvisc of Flac3D, a damage creep model is given by introducing the damage factor and nonlinear strength criterion of immersed rock mass, which is more suitable for describing the creep characteristics of immersed sandy mudstone. The validity of the model is verified by comparing with the measured results.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141341799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this study, low-frequency-based numerical methods were used to predict the noise radiating from rotating horizontal axis wind turbine (HAWT) blades. The flow parameters in the vicinity of blade surfaces, which are required for the Ffowcs Williams–Hawkings (FW–H) equation, were calculated using ANSYS FLUENT. The numerical model was verified against the experimental re-sults from the National Renewable Energy Laboratory Phase VI wind turbine blades. The coupling analysis was integrated with four Reynolds-averaged Navier–Stokes turbulence models and FW–H equation under various boundary conditions. The standard k-ε, SST k-ω, and V2f turbulence models produced results in agreement with the available experimental pressure coefficient and relative velocity distribution data in the flow fields. Under the verification of aeroacoustic results, the SST k-ω turbulence model were more consistent with the LES data. An Institute of Nuclear Energy Research (INER) 25-kW HAWT was employed to predict noise frequency distribution at nine points on the tower on the windward and leeward sides under different operating conditions. Noise frequency distributions on the windward and leeward sides exhibited slight differences, whereas those on the left and right sides of the tower were different because of wind-shear influence. Under operating conditions, the decibels of the low-frequency noise at 0–200 Hz were ∼25–40 dB, and the noise frequency distributions on the windward and leeward sides were similar. With increasing distance, the decibel number of the monitoring point ∼25 m away dropped to 0 dB. For the noise prediction in Case 2 (wind speed = 12 m/s, pitches = 18°), the decibel number at 50 m was ∼25 dB and was ∼15 dB at 70 m. In Case 3 (wind speed = 18 m/s, pitches = 33°), the decibel number at 50 m was ∼30 dB and was ∼20 dB at 70 m. The peak amplitude of the noise was inversely proportional to the increasing distance from the tower but proportional to the wind and rotational speeds.
{"title":"Numerical Prediction of the Aerodynamics and Aeroacoustics of a 25 kW Horizontal Axis Wind Turbine","authors":"Wen-Yu Wang, Y. Ferng","doi":"10.1093/jom/ufae024","DOIUrl":"https://doi.org/10.1093/jom/ufae024","url":null,"abstract":"\u0000 In this study, low-frequency-based numerical methods were used to predict the noise radiating from rotating horizontal axis wind turbine (HAWT) blades. The flow parameters in the vicinity of blade surfaces, which are required for the Ffowcs Williams–Hawkings (FW–H) equation, were calculated using ANSYS FLUENT. The numerical model was verified against the experimental re-sults from the National Renewable Energy Laboratory Phase VI wind turbine blades. The coupling analysis was integrated with four Reynolds-averaged Navier–Stokes turbulence models and FW–H equation under various boundary conditions. The standard k-ε, SST k-ω, and V2f turbulence models produced results in agreement with the available experimental pressure coefficient and relative velocity distribution data in the flow fields. Under the verification of aeroacoustic results, the SST k-ω turbulence model were more consistent with the LES data. An Institute of Nuclear Energy Research (INER) 25-kW HAWT was employed to predict noise frequency distribution at nine points on the tower on the windward and leeward sides under different operating conditions. Noise frequency distributions on the windward and leeward sides exhibited slight differences, whereas those on the left and right sides of the tower were different because of wind-shear influence. Under operating conditions, the decibels of the low-frequency noise at 0–200 Hz were ∼25–40 dB, and the noise frequency distributions on the windward and leeward sides were similar. With increasing distance, the decibel number of the monitoring point ∼25 m away dropped to 0 dB. For the noise prediction in Case 2 (wind speed = 12 m/s, pitches = 18°), the decibel number at 50 m was ∼25 dB and was ∼15 dB at 70 m. In Case 3 (wind speed = 18 m/s, pitches = 33°), the decibel number at 50 m was ∼30 dB and was ∼20 dB at 70 m. The peak amplitude of the noise was inversely proportional to the increasing distance from the tower but proportional to the wind and rotational speeds.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141358909","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We report analytical solutions to the problem of non-Newtonian power-law fluid flows in the annular space between a pair of concentric spherical surfaces rotating at distinct angular velocities with the inner and outer wall boundaries subject to general asymmetric hydrodynamic slip conditions. Analytical solutions are possible because of assuming constant valued apparent hydrodynamic slip lengths in the linearized kinematic slip conditions, and our solutions can be validated against the limiting results of Newtonian fluids, no-slip conditions, or a single rotating sphere reported in previous literature. Comprehensive systematic parametric studies show that (additional to the power-law fluid flow behavior index) the degree of hydrodynamic slip at the inner surface is the dominant factor that determines the limiting values of the viscous torque exerted on the inner sphere as the outer-to-inner radius ratio assumes significantly large values. Nonetheless, the flow behavior index and outer slip length prove to be the crucial key parameters responsible for a variety of torque responses, which can be categorized by a compact analytical expression, as the outer-to-inner radius ratio is increased in the small to moderate regime. We propose a criteria which identifies the proper slip length and outer-to-inner radius ratio combinations for a given power-law flow behavior index such that the hydrodynamic slip wall effects of the outer surface can be minimized or eliminated. A simple method is also presented to characterize and quantify the apparent hydrodynamic slip effects by use of the concentric rotating spheres viscometer.
{"title":"Power-law fluid annular flows between concentric rotating spheres subject to hydrodynamic slip","authors":"Hsin-Fu Huang, Po-Han Tseng","doi":"10.1093/jom/ufae023","DOIUrl":"https://doi.org/10.1093/jom/ufae023","url":null,"abstract":"\u0000 We report analytical solutions to the problem of non-Newtonian power-law fluid flows in the annular space between a pair of concentric spherical surfaces rotating at distinct angular velocities with the inner and outer wall boundaries subject to general asymmetric hydrodynamic slip conditions. Analytical solutions are possible because of assuming constant valued apparent hydrodynamic slip lengths in the linearized kinematic slip conditions, and our solutions can be validated against the limiting results of Newtonian fluids, no-slip conditions, or a single rotating sphere reported in previous literature. Comprehensive systematic parametric studies show that (additional to the power-law fluid flow behavior index) the degree of hydrodynamic slip at the inner surface is the dominant factor that determines the limiting values of the viscous torque exerted on the inner sphere as the outer-to-inner radius ratio assumes significantly large values. Nonetheless, the flow behavior index and outer slip length prove to be the crucial key parameters responsible for a variety of torque responses, which can be categorized by a compact analytical expression, as the outer-to-inner radius ratio is increased in the small to moderate regime. We propose a criteria which identifies the proper slip length and outer-to-inner radius ratio combinations for a given power-law flow behavior index such that the hydrodynamic slip wall effects of the outer surface can be minimized or eliminated. A simple method is also presented to characterize and quantify the apparent hydrodynamic slip effects by use of the concentric rotating spheres viscometer.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141356439","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Friction stir welding (FSW) is a well-established technique developed extensively over the past two decades for various applications. This study investigates the effect of repositioning the tool pin shoulder (0.18 mm) above the surface of a 12 mm thick dissimilar aluminum alloy (AA6063-AA5083) on tensile strength, welding temperature, and micro-hardness. Trials were conducted according to the L9 Taguchi method and further simulated using ABAQUS software. The input parameters spindle speed (SS), tool pin length (TPL), and traversing speed (TS) were each tested at three levels. The impact of these parameters on weld quality was analyzed using ANOVA. Optimization of the process to achieve desired temperature and tensile strength was carried out using grey relational analysis (GRA) for both experimental and simulated results. Mathematical models were generated using the multi-variable regression method (MVRM) and response surface method (RSM). Predicted data from the RSM model were compared to experimental outcomes, revealing a maximum deviation of 8.69% for temperature and 5.17% for tensile strength. Furthermore, the study demonstrated that ABAQUS accurately simulates the FSW process with an accuracy of up to 93.71%.
{"title":"Multi-objective analysis of solid-state joints: Effect of tool pin shoulder clearance on thick dissimilar aluminum plates","authors":"Deepika Mishra, Ravi Shankar Prasad, Sudhir Kumar","doi":"10.1093/jom/ufae022","DOIUrl":"https://doi.org/10.1093/jom/ufae022","url":null,"abstract":"\u0000 Friction stir welding (FSW) is a well-established technique developed extensively over the past two decades for various applications. This study investigates the effect of repositioning the tool pin shoulder (0.18 mm) above the surface of a 12 mm thick dissimilar aluminum alloy (AA6063-AA5083) on tensile strength, welding temperature, and micro-hardness. Trials were conducted according to the L9 Taguchi method and further simulated using ABAQUS software. The input parameters spindle speed (SS), tool pin length (TPL), and traversing speed (TS) were each tested at three levels. The impact of these parameters on weld quality was analyzed using ANOVA. Optimization of the process to achieve desired temperature and tensile strength was carried out using grey relational analysis (GRA) for both experimental and simulated results. Mathematical models were generated using the multi-variable regression method (MVRM) and response surface method (RSM). Predicted data from the RSM model were compared to experimental outcomes, revealing a maximum deviation of 8.69% for temperature and 5.17% for tensile strength. Furthermore, the study demonstrated that ABAQUS accurately simulates the FSW process with an accuracy of up to 93.71%.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141385020","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The declaration on the “natural frequency of rock” exists in many engineering areas, and it has caused many misunderstandings. Different from the mass-spring model usually used, the circular plate model and cylinder model are respectively established to clarify the relationship between the vibration characteristics (including natural frequency and vibration mode) and their influencing factors of rock by modal analysis. The effect of dimension, geometric shape, and boundary condition on the vibration characteristics of rock with plate structure is investigated, in which the semi-analytical solutions agree well with the simulation results. By using the cylinder model based upon the Lamé-Navier Eq., the effect of such influencing factors on the vibration characteristics of the block rock sample is further studied and verified by numerical simulation and experimental results. The results suggest that the natural frequency of “rock” (including the experimental rock sample) is strongly dependent on the dimension, geometric shape, and boundary condition. The resonance frequency observed in the excitation experiment is not only closely associated with the natural frequency of a specific order, but also dependent on the dominance of the particular vibration mode. These findings contribute to a better understanding of the rock-breaking mechanism under dynamic loads with a certain excitation frequency.
{"title":"Investigation on vibration characteristics of rock based on circular plate and cylinder model: dimension, geometric shape and boundary condition","authors":"Zhao Zhang, Bing Liu, Jianlin Liu","doi":"10.1093/jom/ufae021","DOIUrl":"https://doi.org/10.1093/jom/ufae021","url":null,"abstract":"\u0000 The declaration on the “natural frequency of rock” exists in many engineering areas, and it has caused many misunderstandings. Different from the mass-spring model usually used, the circular plate model and cylinder model are respectively established to clarify the relationship between the vibration characteristics (including natural frequency and vibration mode) and their influencing factors of rock by modal analysis. The effect of dimension, geometric shape, and boundary condition on the vibration characteristics of rock with plate structure is investigated, in which the semi-analytical solutions agree well with the simulation results. By using the cylinder model based upon the Lamé-Navier Eq., the effect of such influencing factors on the vibration characteristics of the block rock sample is further studied and verified by numerical simulation and experimental results. The results suggest that the natural frequency of “rock” (including the experimental rock sample) is strongly dependent on the dimension, geometric shape, and boundary condition. The resonance frequency observed in the excitation experiment is not only closely associated with the natural frequency of a specific order, but also dependent on the dominance of the particular vibration mode. These findings contribute to a better understanding of the rock-breaking mechanism under dynamic loads with a certain excitation frequency.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141103246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Previous studies have suggested that irregular echinoids exhibit higher survival rates than regular echinoids following mass extinctions. This study focuses on the irregular echinoid Claviaster libycus, investigating its flow field and scour behavior under extreme water flow conditions through numerical simulations and experiments. The numerical model Splash3D used in this study was modified from the open-source code Truchas developed by the U.S. National Laboratory. Splash3D solves the three-dimensional incompressible Navier-Stokes Eqs.. The fluid volume method describes the water surface kinematics and sand surface kinematics. Since Claviaster libycus is semi-submerged in the sand, a discontinuous bi-viscosity model describes the rheological behavior of the bed material. The research findings indicate that when the gonopore of Claviaster libycus faces downstream, there is no evident horseshoe vortex flow, which contributes to reducing the occurrence of localized scour. This also validates the hypothesis of this study: the transition of echinoids from pentaradial symmetry to bilateral symmetry assists in stabilizing bottom sediments and reducing localized scour.
{"title":"Using the Discontinuous Bi-viscosity model to analyze the three-dimensional flow field and local scour behavior around the Claviaster libycus","authors":"Pin-Jie Lin, Tso-Ren Wu, Jih-Pai Lin, Mei-Hui Chuang, Yi-Xuan Huang, Jia-Jie Chi","doi":"10.1093/jom/ufae019","DOIUrl":"https://doi.org/10.1093/jom/ufae019","url":null,"abstract":"\u0000 Previous studies have suggested that irregular echinoids exhibit higher survival rates than regular echinoids following mass extinctions. This study focuses on the irregular echinoid Claviaster libycus, investigating its flow field and scour behavior under extreme water flow conditions through numerical simulations and experiments. The numerical model Splash3D used in this study was modified from the open-source code Truchas developed by the U.S. National Laboratory. Splash3D solves the three-dimensional incompressible Navier-Stokes Eqs.. The fluid volume method describes the water surface kinematics and sand surface kinematics. Since Claviaster libycus is semi-submerged in the sand, a discontinuous bi-viscosity model describes the rheological behavior of the bed material. The research findings indicate that when the gonopore of Claviaster libycus faces downstream, there is no evident horseshoe vortex flow, which contributes to reducing the occurrence of localized scour. This also validates the hypothesis of this study: the transition of echinoids from pentaradial symmetry to bilateral symmetry assists in stabilizing bottom sediments and reducing localized scour.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141111700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The particle dynamics equation’s formal logic is examined in the context of classical mechanics to investigate the nature of inertial forces. Firstly, a fresh perspective on the dual dependence of the inertial reference frame and inertial force in Newtonian dynamics is presented. The causal relationship on both sides of Newton’s second law is found to be asymmetrical and inconsistent. Secondly, a more general particle dynamics equation, applicable in any translational frame of reference without additional assumptions, is introduced. Essentially, Newton’s second law is only an extreme case of the newly generalized dynamics equation since in Newton’s second law an entire term of the forces acting on the reference object is omitted. The nature of inertial force is unveiled as the mass-ratio weighted real force acting on the reference object. This qualitative explanation is entirely naturalistic as the reference frame’s acceleration depends directly on the acceleration of its reference object(s), and the acceleration of every reference object depends directly on the forces acting on this reference object.
{"title":"Generalized dynamics equation with causal symmetry","authors":"ChiYi Chen","doi":"10.1093/jom/ufae012","DOIUrl":"https://doi.org/10.1093/jom/ufae012","url":null,"abstract":"\u0000 The particle dynamics equation’s formal logic is examined in the context of classical mechanics to investigate the nature of inertial forces. Firstly, a fresh perspective on the dual dependence of the inertial reference frame and inertial force in Newtonian dynamics is presented. The causal relationship on both sides of Newton’s second law is found to be asymmetrical and inconsistent. Secondly, a more general particle dynamics equation, applicable in any translational frame of reference without additional assumptions, is introduced. Essentially, Newton’s second law is only an extreme case of the newly generalized dynamics equation since in Newton’s second law an entire term of the forces acting on the reference object is omitted. The nature of inertial force is unveiled as the mass-ratio weighted real force acting on the reference object. This qualitative explanation is entirely naturalistic as the reference frame’s acceleration depends directly on the acceleration of its reference object(s), and the acceleration of every reference object depends directly on the forces acting on this reference object.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140240219","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A method of solving plane-strain boundary value problems for a reduced version of the double slip and rotation model is developed. It is assumed that the intrinsic spin vanishes. Elastic strains are neglected. The Mohr-Coulomb yield criterion is adopted. An analogy between the solutions for this model and classical rigid plastic solutions of pressure-independent plasticity is revealed. The method is based on introducing auxiliary variables that satisfy the equation of telegraphy in regions where both families of characteristics are curved. Therefore, Riemann's method can conveniently be applied to solving boundary value problems. The method is employed for analyzing the processes of plane strain drawing and extrusion through a wedge-shaped die. Friction is neglected. The solution is given in terms of ordinary integrals. The effect of the angle of internal friction on processes' parameters is revealed. The solution reduces to available solutions of pressure-independent plasticity if the angle of internal friction vanishes.
{"title":"A New Method of Solving Plane Strain Boundary Value Problems for the Double Slip and Rotation Model","authors":"Sergei Alexandrov, E. Lyamina, Yeau-Rean Jeng","doi":"10.1093/jom/ufae004","DOIUrl":"https://doi.org/10.1093/jom/ufae004","url":null,"abstract":"\u0000 A method of solving plane-strain boundary value problems for a reduced version of the double slip and rotation model is developed. It is assumed that the intrinsic spin vanishes. Elastic strains are neglected. The Mohr-Coulomb yield criterion is adopted. An analogy between the solutions for this model and classical rigid plastic solutions of pressure-independent plasticity is revealed. The method is based on introducing auxiliary variables that satisfy the equation of telegraphy in regions where both families of characteristics are curved. Therefore, Riemann's method can conveniently be applied to solving boundary value problems. The method is employed for analyzing the processes of plane strain drawing and extrusion through a wedge-shaped die. Friction is neglected. The solution is given in terms of ordinary integrals. The effect of the angle of internal friction on processes' parameters is revealed. The solution reduces to available solutions of pressure-independent plasticity if the angle of internal friction vanishes.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2024-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139592564","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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