Rigid Boundary Research Articles

Numerical study on the flow-induced noise from waterjet-propelled ship regarding a flexible boundary

In hydroacoustics, it is generally acknowledged that a half-space is bounded by a flexible boundary with non-constant reflection coefficients. However, limited research has focused on the impact of the flexible boundary on noise characteristics. In this paper, a hybrid method combining the unsteady Reynolds-averaged Navier-Stokes (URANS) equations with the Ffowcs-Williams–Hawkings (FW–H) equation is presented. Firstly, the hybrid method coupled with the mirror source method (MS method) is applied to predict noise in a half-space with a rigid boundary for validation. Secondly, the proposed method is extended to predict the underwater noise generated by a medium-speed, mono-hull ship. Specifically, the differences between the noise fields in a half-space and free-space are considered and investigated comprehensively. The results reveal that: (1) the hybrid method performs well in predicting the overall noise induced by complex-shaped configurations in a half-space bounded by different boundaries, and (2) the half-space boundary can influence the noise field due to constructive\\destructive interferences. Additionally, (3) the quadrupole noise generated in the non-uniform wake of a waterjet-propelled ship should be considered. The proposed method has provided an efficient approach to predict the flow-induced noise radiated from a waterjet-propelled ship regarding a flexible boundary.

Numerical multi‐span segmented trapdoor test with viscoelastic boundary for soil arching within pile‐supported embankment under cyclic loading

AbstractDynamic wave reflections would interfere with the laboratory observation of the soil arching under cyclic loading when a traditional trapdoor model with rigid boundaries was used. This problem would be prominent when investigating the soil arching in pile‐supported embankments where the stationary support (pile) would be small, making the rigid boundary close to the domain of interest affected by dynamic loads. To avoid dynamic wave reflections and narrow the calculation domain, soil arching within a pile‐supported embankment under cyclic loading is numerically investigated in a multi‐span segmented trapdoor model with flexible boundaries by the particle flow code (PFC). In addition, a pavement structure is included and the springs supporting the trapdoor follow a bi‐linear constitutive model. The energy‐absorbing flexible boundary at the bottom weakens the dynamic wave reflections and is in favor of passing vertical dynamic waves to compact the fill and weaken the influence of cyclic loading on the soil arching effect during the loading stage. Lateral flexible boundaries would facilitate realistically reproducing the effect of cyclic loading on the soil arching because they could consider the weakening of the plugging effect that occurs during the lateral expansion. The development of soil arches of mid‐span and side‐span are different when the load applied at the mid‐span is laterally transferred to adjacent spans by the arching effect.

Investigations of effective dispersion models for electroosmotic flow with rigid and free boundaries in a thin strip

Reactive flow and transport in porous media is topic of intense research since decades. Since dispersion is one of the key parameters in solute transport, its accurate modeling is essential to avoid wrong predictions of flow and transport behavior. In this research, we investigate novel effective dispersion models for reactive transport of electrically charged chemical species in a thin, potentially evolving strip taking into account Taylor–Aris and electroosmotic‐induced dispersion as well as their cross‐coupling effects. We prove positivity of the dispersion coefficient and the existence and uniqueness of strong solutions in the fixed geometry setting. Moreover, we numerically investigate scenarios for both the fixed and evolving geometry situation. The simulation results illustrate the possibility of separating charged species, such that the findings of this study can lead to a better understanding of mixing and separation processes of charged solutes and an improved prediction of breakthrough curves. Finally, we study the limits of vanishing channel width, precipitation layer thickness, and molecular diffusion. We show convergence of the solutions to the corresponding limit cases such as a hyperbolic model or the fixed geometry case. From these results, we can rate the impact of distinct dispersion mechanisms and evaluate the necessity of a detailed modeling for different parameter regimes.

On ‘Systematic theology’ and the contested shape of a discipline

This essay takes up questions about how systematic theology can understand itself in light of critical questions about the functioning of the label. In face of concerns about the exclusionary functioning of the term, the essay develops a set of philosophical distinctions that may help theologians to understand the shape of their discipline. The picture that emerges is of a discipline that is constituted by shifting constellations of historical precedents rather than rigid boundaries; that moves through epistemic justice for the sake of discovering truth, which furthers the pursuit of wider forms of justice; and that functions hermeneutically rather than analytically or critically in its understanding of language.

Simulation of the deformable lateral boundaries in biaxial test using DEM

Applying the discrete element method (DEM) in soil mechanics can provide abundant information at the particle-scale and facilitates illustration of the macro-mechanical behaviour of soils based on the inter-particle mechanisms. The triaxial test is one of the most common laboratory methods to study the macro-mechanical behaviour of particulate materials such as soil. However, many problems in geotechnical design can be assumed and simplified as a plane strain phenomenon. Therefore a biaxial test can be conducted to reproduce the macro-mechanical behaviour of soil, where the sample is enclosed by two horizontal rigid platens and a vertical latex membrane, which is a deformable continuous element and allows the enclosed specimen to deform freely while maintaining confining stress during loading. This paper presents an algorithm to represent physical and mechanical characteristics of latex membrane in the 2D DEM simulation of biaxial test using the PFC2D code. To investigate the impact of the lateral boundary conditions on the micro-macro mechanical behaviours of soil samples, two sets of DEM biaxial tests are conducted, i.e. with rigid and deformable lateral boundary conditions. The DEM modeling results indicate that the lateral boundary conditions have a significant effect on the micro-scale fabric properties, thickness and inclination of the shear band. The comparison between these two simulations also demonstrates that the lateral boundary conditions play a major role in the peak and post-peak stress-strain behaviours as well as the dilation and critical state behaviours of granular soils.

Accumulation and Cross-Shelf Transport of Coastal Waters by Submesoscale Cyclones in the Black Sea

High- and medium-resolution satellite optical imagery show that submesoscale cyclonic eddies (SCEs) trap coastal waters and induce their rapid cross-shelf transport. Due to the presence of a rigid boundary, the convergence is observed in the coastal part of SCEs. It causes accumulation of suspended matter, which spins inward in a spiral motion toward the SCE core. Small SCEs with a radius of 1–10 km transport waters with local anomalies in the concentration of chlorophyll, total suspended matter and temperature to a distance of up to 150 km and are observed for more than 10 days. Lagrangian calculations based on realistic NEMO numerical model are used to estimate the fate of the coastal waters in such SCEs. The eddy entrains the largest number of particles during its separation from the coast when its vorticity reaches the maximum. Then, the SCE weakens, which is accompanied by the flattening of initially risen isopycnals and deepening of the trapped coastal waters. The described mechanism shows that coastal SCEs may cause intense short-period cross-shelf transport of the biological and chemical characteristics, and is another process affecting the functioning of the marine ecosystems.

The Onset of Darcy–Brinkman Convection in a Porous Layer with Mutual Impact of Thermal Non-Equilibrium and Non-Uniform Temperature Gradients

The two-field thermal conditions of local thermal nonequilibrium (LTNE) were used to investigate linear stability of thermal convection in a liquid-saturated, porous layer via the extended Brinkman–Darcy model for different non-uniform basic thermal gradients. The critical values were numerically computed by the Galerkin method for rigid isothermal boundaries. The impact of LTNE and different forms of non-uniform basic temperature gradients on the onset of porous convection was examined. The porosity modified conductivity ratio has no influence on system stability at a small inter-phase heat transport coefficient limit. However, for higher values of the inter-phase heat transport coefficient, an increase in the porosity modified conductivity ratio hastens the onset of convection. An increase in the Darcy number delays the convective motions. The results for different basic temperature profiles are symmetric qualitatively. In addition, the possibility of control of convection by a basic temperature profile was studied in detail.

Integrating one health: exploring the global dialogue on bioethics.

Unesco's World Bioethics Day, whose theme this year is the protection of future generations, reveals the centrality of the concept of one-health, as the main way to guarantee a future for the planet seen as the common home of all living beings. The recent pandemic has sufficiently shown how animal health is linked to human health and how only the balance of the entire planet guarantees both. Living on earth as human beings, no longer blinded by the Anthropocene's arrogance, but conscious of having a fundamental responsibility for the health care and well-being of every species is the imperative that should guide scientific research, education and social life. Thus, a renovating of the education system is essential to break down rigid boundaries between disciplines and promote complex and critical thinking.

Triaxial Shear Analysis Using Discrete Element Methods for Sandy Soil with an Improved Flexible Membrane Boundary

Exploring strain localization has substantial potential to significantly impact the disaster resilience and mitigation capabilities of infrastructure, thus influencing project sustainability. Consequently, the field of sustainable geotechnical engineering is progressively directing attention toward studying soil strain localization. This research focuses on triaxial testing to deepen our understanding of this phenomenon by applying discrete element methods, thereby fostering the advancement of sustainable geotechnical engineering practices. While rigid-wall-based discrete element triaxial tests have been extensively studied, using flexible boundaries in these tests has received limited attention. This study introduces a three-stage method to enhance stress application in flexible membranes by applying confining pressure. A comparison of triaxial tests was conducted at both macroscopic and microscopic scales, utilizing flexible and rigid boundaries. Moreover, numerical simulations were performed on flexible membrane samples with various particle sizes to identify appropriate dimensions for flexible boundaries. Our results demonstrate that the improved flexible membrane provides more accurate representations of macroscopic and microscopic sample variations than rigid walls. Keeping the particle sizes for flexible membranes within the range of 0.2 to 0.8 times the characteristic particle size (r) is essential for striking a balance between simulation accuracy and computational efficiency. These findings enhance the accuracy of triaxial compression test simulations and offer a valuable foundation for studying strain localization in soils. Understanding these phenomena is essential for various geotechnical engineering applications, such as foundation design and slope stability analysis. Furthermore, these findings form a pivotal foundation for resource optimization and enhancing the reliability of engineered structures, thereby driving the advancement of sustainable geotechnical engineering practices.

Non-Quadratic Strain Gradient Plasticity Theory and Size Effects in Constrained Shear

Abstract A previously proposed strain gradient plasticity theory is extended to incorporate a non-quadratic power law function of the plastic strain gradient in the free energy expression with an exponent of N + 1. The values of N are taken to vary from N = 1 to N = 0. A simple shear problem of a metal layer between rigid boundaries is analyzed. Two stages of plastic deformation are considered. In stage I, the plastic strain is taken to be zero at the boundaries. Stage I ends when a specified magnitude of the plastic strain gradient is attained at the boundaries. In stage II, the magnitude of the plastic strain gradient at the boundaries is fixed at the specified value. With N = 0, a critical plastic strain gradient cannot be specified at the boundaries because the plastic strain gradient is infinite at the boundaries. The theory with N = 0 predicts a constant plateau stress immediately after initial yield, and the dependence of the plateau stress on the layer thickness can fit experimentally observed plateau stress values. However, with N = 0, a stress gap occurs between the initial yield stress and the plateau stress. The theory with 0 < N ≤ 1 and with stage II also can reproduce the experimentally observed dependence of the plateau stress on the layer thickness for any value of N in that range, with an appropriate value of critical plastic strain gradient at the boundaries. The solution for 0 < N ≤ 1 includes that for N = 0 as a limiting case.

“They're training us to be helpless:” Medical student socialization around social determinants of health

Social factors are the primary drivers of health inequity in the United States. Yet, medical trainees remain underprepared to address the social determinants of health in practice, despite curricular innovations. Therefore, there is a critical need to explore how social determinants of health curricula is taken up by medical students. This study, which draws upon ethnographic fieldwork and in-depth interviews at a medical school in the United States, explores how medical students understand their role in addressing social determinants of health. I find that epistemic invulnerability, defined as the closure to affect or to be affected in relation to others, generates feelings of helplessness, closure to alternate possibilities, and rigid professional boundaries that prevent medical students from incorporating the responsibility to act on the social determinants into their clinical purview. These findings provide novel epistemological context to better align health equity curricula in medical education with the aim to train physicians that both understand and address the social determinants of health.

Dynamics of a laser-induced buoyant bubble near a vertical rigid boundary

Dynamics of a laser-induced buoyant bubble near a vertical rigid boundary

Linear stability of longitudinal convective rolls in a non-Darcy porous layer filled with nanofluid due to viscous dissipation effect: A realistic approach

The onset of longitudinal convective rolls of nanofluid flow inside a horizontal porous material using Brinkman theory due to the viscous dissipation effect has been addressed numerically. An infinitely long horizontal porous region has been considered which is confined between two rigid boundaries. The boundaries of the channel are considered adiabatic (lower) and isothermal (upper). Brownian motion and thermophoresis properties are taken into consideration for nanofluid. In the linear stability analysis, oblique roll disturbances with arbitrary orientation are taken into account, where the preferred mode of instability i.e., longitudinal rolls (when P=0 or ϑ=π/2) are shown. Finally, the resulting eigenvalue problem is solved in MATLAB using the bvp4c technique. The impact of improving the modified diffusivity ratio (NA<10), Lewis number (Le<,=,>1), concentration Rayleigh number (Rn) and modified particle density increment (NB≈10−2−10−5) is to accelerate the instability boundaries, while the switching parameter (ξ) has a dual character on it. Further, the pattern of the streamlines are slightly compressed in the channel’s center for large values of ξ, whereas no markable changes are noticed for higher values of NA. The isotherms lines are closer near the adiabatic boundary when ξ takes small values.

Electroconvection in Rotating Jeffrey Nanofluid Saturating Porous Medium: Free–Free, Rigid-Free, Rigid–Rigid Boundaries

The impact of rotation and the boundaries on the initiation of convective instability in a rheological nanofluid layer heated beneath saturated by a porous media with the inclusion of an AC electric field (vertical) is studied employing linear stability analysis. The stationary convective stability of rheological nanofluid is customarily established utilizing Buongiorno model for nanoparticles and Jeffrey model for rheological behavior of regular fluid. The Buongiorno model deployed for nanofluids incorporates the influence of thermophoresis and Brownian motion. Using the normal mode technique, the set of coupled differential equations is solved analytically for both stress-free boudaries and numerically by using the Galerkin-type Weighted Residual Method (GWRM) for top-free, bottom-rigid and rigid–rigid bounding surfaces. The numerical computed values of stationary thermal Rayleigh number are presented graphically for three distinct combinations of boundary conditions. The Taylor number accounting for rotation parameter, Jeffrey parameter, and nanofluid Lewis number delay the start of stationary convection, whereas electric field and concentration Rayleigh number destabilize a system for three groups of boundaries. The bottom-/top-heavy nanofluids are found to be more/less stable. Rigid–rigid boundaries augment the stability in a more pronounced manner than that of the stress-free and rigid-free boundaries. The conditions for non-occurrence of over stability are also derived. This study is of great significance in many metallurgical processes including megma flow, deep convective chimneys, polymer solutions, microfluidic devices and blood flow in micro circulatory systems. An excellent coincidence is found admist present paper and the earlier published work.

Brinkman–Bénard Convection with Rough Boundaries and Third-Type Thermal Boundary Conditions

The Brinkman–Bénard convection problem is chosen for investigation, along with very general boundary conditions. Using the Maclaurin series, in this paper, we show that it is possible to perform a relatively exact linear stability analysis, as well as a weakly nonlinear stability analysis, as normally performed in the case of a classical free isothermal/free isothermal boundary combination. Starting from a classical linear stability analysis, we ultimately study the chaos in such systems, all conducted with great accuracy. The principle of exchange of stabilities is proven, and the critical Rayleigh number, Rac, and the wave number, ac, are obtained in closed form. An asymptotic analysis is performed, to obtain Rac for the case of adiabatic boundaries, for which ac≃0. A seemingly minimal representation yields a generalized Lorenz model for the general boundary condition used. The symmetry in the three Lorenz equations, their dissipative nature, energy-conserving nature, and bounded solution are observed for the considered general boundary condition. Thus, one may infer that, to obtain the results of various related problems, they can be handled in an integrated manner, and results can be obtained with great accuracy. The effect of increasing the values of the Biot numbers and/or slip Darcy numbers is to increase, not only the value of the critical Rayleigh number, but also the critical wave number. Extreme values of zero and infinity, when assigned to the Biot number, yield the results of an adiabatic and an isothermal boundary, respectively. Likewise, these extreme values assigned to the slip Darcy number yield the effects of free and rigid boundary conditions, respectively. Intermediate values of the Biot and slip Darcy numbers bridge the gap between the extreme cases. The effects of the Biot and slip Darcy numbers on the Hopf–Rayleigh number are, however, opposite to each other. In view of the known analogy between Bénard convection and Taylor–Couette flow in the linear regime, it is imperative that the results of the latter problem, viz., Brinkman–Taylor–Couette flow, become as well known.

What We Talk About When We Talk About Ethnicity: Hispanic Self-classification and Appraisal in an Online College Forum

Research has frequently remarked on the conceptual overlap of racial versus ethnic categories at the macro-level, as well as on individual-level inconsistencies across multiple dimensions of race. Less research has focused on the interpersonal negotiation of racial self-classification and identity claims-making, or on the norms that govern racial appraisal. This study uses a case at the boundaries of the Hispanic category to ask: what norms of self-classification and social appraisal do interlocuters draw on in their interpretation of ethnic categories? I answer this question using a unique dataset of posts from a college admissions forum, in which prospective applicants ask, “Am I Hispanic?” Findings reveal that ancestry forms the most rigid boundary, though interlocuters debate whether ancestry is biological or cultural. Cultural identity is also necessary, though more loosely defined. Specific, noninstitutionalized traits, such as phenotype, language, and surname, are considered neither necessary nor sufficient. Findings highlight the enduring primacy of ancestry and the importance of social appraisal in the college application context.

Electrohydrodynamic Couette–Poiseuille Flow Instability of Two Viscous Conducting and Dielectric Fluid Layers Streaming through Brinkman Porous Medium

The electrohydrodynamic plane Couette–Poiseuille flow instability of two superposed conducting and dielectric viscous incompressible fluids confined between two rigid horizontal planes under the action of a normal electric field and pressure gradient through Brinkman porous medium has been analytically investigated. The lower plane is stationary, while the upper one is moving with constant velocity. The details of the base state mathematical model and the linearized model equations for the perturbed state are introduced. Following the usual procedure of linear stability analysis for viscous fluids, we derived two non-dimensional modified Orr–Sommerfeld equations and obtained the associated boundary and interfacial conditions suitable for the problem. The eigenvalue problem has been solved using asymptotic analysis for wave numbers in the long-wavelength limit to obtain a very complicated novel dispersion relation for the wave velocity through lengthy calculations. The obtained dispersion equation has been solved using Mathematica software v12.1 to study graphically the effects of various parameters on the stability of the system. It is obvious from the figures that the system in the absence of a porous medium and/or electric field is more unstable than in their presence. It is found also that the velocity of the upper rigid boundary, medium permeability, and Reynolds number have dual roles on the stability on the system, stabilizing as well as destabilizing depending on the viscosity ratio value. The electric potential, dielectric constant and pressure gradient are found to have destabilizing influences on the system, while the porosity of the porous medium, density ratio and Froude number have stabilizing influences. A depth ratio of less than one has a dual role on the stability of the system, while it has a stabilizing influence for values greater than one. It is observed that the viscosity stratification brings about a stabilizing as well as a destabilizing effect on the flow system.

Situated Interior

The idea of a situated interior reflects the conceptual understanding of an expanded range of interiority from the self to the outside world; it involves traversing rigid boundaries to allow fluidity and continuity. The situated interior considers the critical role of other things in defining the interior practice, from the practice of inhabitation and the practice of making and designing to the dynamic formation of the discipline. The collection of articles in this issue of Interiority demonstrates the numerous ways particular situations define the practice of design, inhabitation, and the discipline of the interior. The narratives of various situations presented in this issue of Interiority demonstrate the relational qualities of self, interior, and context manifested in the continuous process of making, inhabiting, and experiencing. They highlight the critical role of such relational qualities as a foundation for a better understanding of interior practice and interior inhabitation that are dynamic and meaningful.

Numerical investigation of the cavitation bubble near the solid wall with a gas-entrapping hole based on a fully compressible three-phase model

The solid surface with several cavities containing gas strongly influences the bubble’s dynamical behaviors. To reveal the underlying physical mechanism of the cavitation bubble near a rigid boundary with a gas-entrapping hole, a fully compressible three-phase model, accounting for the three-phase volume transport equation, was implemented in OpenFOAM. The predicted bubble shape was validated with the corresponding experimental photos, and good agreement was achieved. The bubble’s primary physical features (e.g., the expanding shock wave, upward and downward liquid jet, and high-pressure region) are well reproduced, which helps understand the underlying mechanisms. The numerical results show that the solid wall with a gas-entrapping hole could affect the morphology of both the bubble and liquid jet, as well as shortens the bubble's first oscillation period in comparison to an intact rigid wall. The relationship among the prolongation factor, the standoff distance, and the relative size ratio is analyzed. It is found the prolongation factor increases as the relative size ratio decrease. As the standoff distance decreases, the gas entrapping hole plays a significant role in the oscillation period of the bubble. The current model can be further extended to reveal the microscopic mechanism of aeration avoiding cavitation damage and investigate the interaction between air bubbles and cavitation bubbles, which is of great interest to practical applications.

The Rayleigh–Bénard problem for water with maximum density effects

Linear stability and weakly nonlinear stability analyses are developed for Rayleigh–Bénard convection in water near 3.98 °C subject to isothermal boundary conditions. The density–temperature relationship (equation of state) is approximated by a cubic polynomial, including linear, quadratic, and cubic terms. The continuity equation, the Navier–Stokes momentum equation, the equation of state, and the energy equation constitute the governing system. Linear stability analysis is used to investigate how the maximum density property of water affects the onset of convective instability and the choice of unstable wave number for four different types of boundary conditions. Then, a weakly nonlinear stability study is done using the spectral Fourier method for isothermal tangential stress-free boundary conditions to quantify the heat transport of the system and demonstrate the transition from regular/periodic convection to chaotic convection. A Stuart-Ginzburg–Landau equation is obtained using the multiscale expansion method. Streamlines and isotherms are presented and analyzed. The influence of maximum density has been shown to delay the onset of instability and is, therefore, a stabilizing mechanism for thermal instability. Due to the maximum density, the onset of chaotic convection is also delayed. Among four different boundaries, the impermeable rigid boundaries require the highest Rayleigh number for instability to begin. Increasing boundary temperatures advance the onset of chaotic convection and improve the heat transport situation.