Impact Of Boundary Conditions Research Articles

A Modified Reentrant Metamaterial with Equal and Enhanced Orthogonal Elastic Properties

Herein, an improved mechanical metamaterial is proposed, which is derived from the decomposition, rotation, and reassembly of reentrant structures. The structure is parametric, allowing for rapid redesign. The study focuses on the variations in equivalent stiffness and Poisson's ratio of the structure within the linear elastic range when internal rib angle θ changes. First, based on homogenization simulation analyses, it has been verified that this design achieves the tailorable equivalent elastic modulus and Poisson's ratio over a wide range, meanwhile, maintaining equal elastic properties in the orthogonal direction at all times. Second, to reduce future repetitive experiments, an interpolation model is established to expand the design domain. The fitting formula indicates that by modifying θ and relative wall thickness t/L0, the elastic performance of the structures can be tailored. Additionally, the impact of boundary conditions is discussed to minimize experimental costs. Finally, the accuracy of the simulations is validated through uniaxial compression tests.

The impact of boundary conditions on the acoustical behavior of lightweight granular particle stacks

The acoustical behavior of air-saturated granular stacks can differ significantly from that of more traditional sound absorbing materials such as fibrous webs and foams when tested in a standing wave tube. The latter materials can often be modeled as equivalent fluids by using one-dimensional theory, with the further assumption that their behavior does not depend on the input signal level. In contrast, level dependence of the response of lightweight granular materials such as glass bubbles has been consistently observed in previous studies. At low input levels, the absorption coefficient of glass bubble stacks shows solid-like behavior with multiple peaks associated with radial modes of the solid phase of the edge-constrained stack: i.e., the response is two-dimensional. In contrast, at high input levels, glass bubble stacks show one-dimensional fluid-like behavior, with the quarter wave depth resonance dominating the response. It is hypothesized here that at high input levels the particles slip axially at the circumferential boundary, thus showing a one-dimensional response, while at low levels, the particles are constrained to have zero axial velocity, thus creating a two-dimensional response. It is shown here that a two-dimensional finite difference implementation of the poro-elastic Biot theory can accurately reproduce the observed level-dependent behavior.

Buckling instability analysis of delaminated beam-like structures by using the exact stiffness method

In multilayered structures, delamination not only reduces local strength but also induces buckling instability, compromising structural safety even before reaching the critical buckling load. This paper introduces a novel model for buckling analysis of structures with delamination damage. The model utilizes exact stiffness formulations derived from Timoshenko theory, enabling precising modelling of beam-like structures with through-thickness delamination. The Wittrick-Williams algorithm is utilized to calculate the critical buckling loads, which are validated against results from the finite element software ANSYS. Additionally, a modified Euler buckling formula for the approximate yet closed-form critical buckling load of delaminated beam-like structures is proposed, with comparisons made to the exact stiffness method results. The study investigates the effects of position and length of delamination and boundary conditions of beam on the critical buckling loads. The findings indicate that the buckling reduction factors of delaminated beam is primarily influenced by the thickness-wise position of the delamination, followed by the delamination length, and then the length-wise position of the delamination. Furthermore, the impact of boundary conditions becomes more significant when the delamination is near the beam’s end. This research provides practical guidelines for preventing buckling instability in delaminated beam-like structures.

Analytical and FE modeling of a bi-directional functionally graded Timoshenko beam under thermomechanical loading

Functionally graded materials (FGMs) have variable volume fractions in different directions, making structural analysis challenging due to shear deformation. This study investigates the behavior of a two-directional functionally graded material (TDFGM) Timoshenko beam under thermomechanical loads. Varied material properties in both axial and transverse directions are analyzed using a mathematical approach and a finite element model. The mathematical approach involves transforming the system of two ordinary differential equations to a single fourth-order differential equation to determine deflection and rotation. Additionally, a bilinear quadrilateral element is used to validate the mathematical solution. The results show that increasing grading parameters reduced transverse deflection, with a maximum reduction of 38.97% for CF beams and 39.26% for SS beams when the gradation index az increased from 0 to 1 under mechanical loading. Under combined mechanical and thermal loading, higher temperatures on the beam’s hot side lead to increased deflection, with notable increases at higher gradation indices. Moreover, increased maximum deflection by 6.29% for CF beams and 4.05% for SS beams when considering temperature-dependent properties. It was observed that when TDFGM Timoshenko beams were heated for thermal loading, the SS beam deflected in the opposite direction of the applied mechanical load. The results agree with previous research and indicate alignment between mathematical and finite element solutions. The impact of boundary conditions on the deflection of Timoshenko beams made of TDFGM is discussed. The introduced methodology enhances TDFGM beam bending analysis, allowing control over behavior through grading parameters and boundary conditions selection.

Bending-bearing capacity design of transformed triangular corrugated steel plates with top stringers

This study investigates the bending-bearing capacity and design method of Transformed Triangular Corrugated Steel Plates (TT-CSPs) with top stringers adopted in trestles subjected to possible pure bending. Elastic buckling load and ultimate strength are derived through theoretical deduction and numerical analysis. Exploration focuses on the impact of boundary conditions, aspect ratio, corrugation density, and top stringers on buckling behavior and ultimate strength. This paper advances a design approach for the bending-bearing capacity of TT-CSPs with top stringers. Findings indicate that the vertical boundaries of TT-CSPs cannot meet the plane assumption and are close to being free-warping. Higher corrugation densities increase structural stiffness and uniformity, while TT-CSP height variations significantly affect stability. Top stringers behave as lateral constraints and undergo significant bending stresses, with their various buckling modes influencing the bending-bearing stability capacity of TT-CSPs.

Impact of Boundary Conditions and Radius of Curvature on Vibro-Acoustic Behavior of Cold-Rolled Carbon Steel Structure

Impact of Boundary Conditions and Radius of Curvature on Vibro-Acoustic Behavior of Cold-Rolled Carbon Steel Structure

Impact of boundary conditions on the modeled thermal regime of the Antarctic ice sheet

Abstract. A realistic initialization of ice flow models is critical for predicting future changes in ice sheet mass balance and their associated contribution to sea level rise. The initial thermal state of an ice sheet is particularly important, as it controls ice viscosity and basal conditions, thereby influencing the overall ice velocity. Englacial and subglacial conditions, however, remain poorly understood due to insufficient direct measurements, which complicate the initialization and validation of thermal models. Here, we investigate the impact of using different geothermal heat flux (GHF) datasets and vertical velocity profiles on the thermal state of the Antarctic ice sheet and compare our modeled temperatures to in situ measurements from 15 boreholes. We find that the temperature profile is more sensitive to vertical velocity than to GHF. The basal temperature of grounded ice and the amount of basal melting are influenced by both selection of GHF and vertical velocity. More importantly, we find that the standard approach, which consists of combining basal sliding speed and incompressibility to derive vertical velocities, provides reasonably good results in fast-flow regions (ice velocity >50 m yr−1) but performs poorly in slow-flow regions (ice velocity <50 m yr−1). Furthermore, the modeled temperature profiles in ice streams, where bed geometry is generated using a mass conservation approach, show better agreement with observed borehole temperatures compared to kriging-based bed geometry.

Impact of boundary conditions on Rayleigh-Bénard convection: stability, heat transfer and chaos

The paper compares the results of Rayleigh-Bénard convection problem for rigid-rigid-isothermal, rigid-free-isothermal and free-free isothermal boundaries. A minimal Fourier-Galerkin expansion yields the generalized-Lorenz-model whose scaled version is reduced to the Stuart-Landau-model using the multiscale-method. Nusselt number is estimated for both steady and unsteady regimes. Regular, chaotic, and periodic natures of the solution are studied using the Hopf-Rayleigh-number and by means of a bifurcation diagram. The linear and weakly-nonlinear-analyses reveal that the onset of regular and chaotic motions in the case of rigid-free-isothermal boundaries happens later than that of free-free isothermal boundaries but earlier than rigid-rigid-isothermal boundaries. It is shown that the scaled-Lorenz-model possesses all the features of the classical-Lorenz-model. Beyond the value of the Hopf-Rayleigh-number, we observe chaotic-motion between two consecutive spells of periodic motion. It is found that one can also have a window of periodicity for all three boundaries.

Convection in a rectangular enclosure with internally heated porous medium: impact of boundary conditions

Convection in a rectangular enclosure with internally heated porous medium: impact of boundary conditions

The impact of boundary conditions on the relationship between value creation and value appropriation in buyer-supplier relationships

Purpose This study aims to investigate whether higher value creation leads to higher value appropriation and to identify the boundary conditions in a buyer–supplier relationship that can explain why a particular supplier can appropriate higher value than others. Design/methodology/approach The study uses questionnaire surveys. The sample of the survey has 150 publicly-listed supplier firms in Taiwan. The unit of analysis is the buyer–supplier relationship. Findings In the buyer–supplier relationship, suppliers’ bargaining power, partnership and a supplier’s original brand manufacturing (OBM) business can strengthen the positive relationship between value creation and value appropriation. Research limitations/implications This study adopts the unilateral viewpoint of suppliers; however, some constructs might require dyadic evaluation. This study only explores the spillover effect of OBM business on the relationship between value creation and appropriation. Practical implications The spillover effect of a supplier’s OBM business in a buyer–supplier relationship allows the buyer to share more common benefits and the supplier to capture more private benefits as compensation. By broadening its customer base, a supplier can increase its bargaining power. A supplier can also maintain a strategic partnership with each essential buyer. Originality/value To avoid the dark-side effect of partnership, the model provides the contingency that a supplier can capture more value from a buyer–supplier relationship.

Impact of Boundary Conditions on Acoustic Excitation of Entropy Perturbations in a Bounded Volume of Newtonian Gas

Excitation of the entropy mode in the field of intense sound, that is, acoustic heating, is theoretically considered in this work. The dynamic equation for an excess density which specifies the entropy mode, has been obtained by means of the method of projections. It takes the form of the diffusion equation with an acoustic driving force which is quadratically nonlinear in the leading order. The diffusion coefficient is proportional to the thermal conduction, and the acoustic force is proportional to the total attenuation. Theoretical description of instantaneous heating allows to take into account aperiodic and impulsive sounds. Acoustic heating in a half-space and in a planar resonator is discussed. The aim of this study is to evaluate acoustic heating and determine the contribution of thermal conduction and mechanical viscosity in different boundary problems. The conclusions are drawn for the Dirichlet and Neumann boundary conditions. The instantaneous dynamic equation for variations in temperature, which specifies the entropy mode, is solved analytically for some types of acoustic exciters. The results show variation in temperature as a function of time and distance from the boundary for different boundary conditions.

Impact of spatially correlated heterogeneity and boundary on techno-economic performance of CO2-circulated geothermal harvest

Depleted oil/gas reservoirs are excellent candidates to apply CO2 Plume Geothermal (CPG) production, a promising CO2 storage and utilization technique. However, most oil/gas reservoirs are separated into geological blocks by faults, and the impact of boundary conditions and formation heterogeneity on CPG performance is still challenging. This study evaluates a CPG system's optimal configuration with various heterogeneous formations and boundaries. Six CPG scenarios with spatially correlated heterogeneous porosity, permeability, and open/close lateral boundaries are designed and simulated. For each scenario, well space and injection overpressure are sampled in their ranges to generate a suite of CPG models. Net present values (NPV) are calculated from the simulation results and used as the objective function. A meta-model-based optimization framework is developed to find the optimal well space and overpressure to maximize NPV for each scenario. The comparative analyses between the six scenarios find that high heterogeneity variance and long geologic continuity in the flow direction cause an early breakthrough. Long well space can enhance NPV, but no longer if it is larger than the correlation length in the flow direction. CO2 storage and electricity revenues are essential to profit for a closed system, but CO2 storage income is the primary source of profit in an open system.

Continuum modeling of soft glassy materials under shear

Soft Glassy Materials (SGM) consist in dense amorphous assemblies of colloidal particles of multiple shapes, elasticity, and interactions, which confer upon them solid-like properties at rest. They are ubiquitously encountered in modern engineering, including additive manufacturing, semi-solid flow cells, dip coating, adhesive locomotion, where they are subjected to complex mechanical histories. Such processes often include a solid-to-liquid transition induced by large enough shear, which results in complex transient phenomena such as non-monotonic stress responses, i.e., stress overshoot, and spatially heterogeneous flows, e.g., shear banding or brittle failure. In the present article, we propose a pedagogical introduction to a continuum model based on a spatially resolved fluidity approach that we recently introduced to rationalize shear-induced yielding in SGMs. Our model, which relies upon non-local effects, quantitatively captures salient features associated with such complex flows, including the rate dependence of the stress overshoot, as well as transient shear-banded flows together with non-trivial scaling laws for fluidization times. This approach offers a versatile framework to account for subtle effects, such as avalanche-like phenomena, or the impact of boundary conditions, which we illustrate by including in our model the elasto-hydrodynamic slippage of soft particles compressed against solid surfaces.

Vibration analysis of cracked beam based on Reddy beam theory by finite element method

The lateral vibration of cracked isotropic thick beams is investigated. Generally, the analysis of thick beam based on line elements can be undertaken using either Timoshenko beam theory or a third order beam theory (TSDT) such as Reddy beam theory. TSDT is superior to Timoshenko beam theory, as it eliminates the need for a shear correction coefficient. However, there is no available solution for a cracked beam based on Reddy beam theory which is the main focus of this paper. The investigated beam is divided into several elements where their stiffness and mass matrices are derived using Reddy beam theory. Each element has two nodes with 3 degrees of freedom (1 lateral and 2 rotational) at each node. The crack was modeled using two rotating springs with stiffnesses that varied with crack depth. These elements are used to connect the adjacent beam elements. The impact of boundary conditions, slenderness ratio, crack location, and crack depth are investigated. In addition, experimental and finite element analyses of cracked steel beams is undertaken to validate the results of the present model. The results show that the maximum deviation between the analytical and the experimental results is less than 3% up to the third mode shape.

Impact of Boundary Condition and Kinetic Parameter Uncertainties on NOx Predictions in Methane–Air Stagnation Flame Experiments

Abstract A comprehensive understanding of uncertainty sources in experimental measurements is required to develop robust thermochemical models for use in industrial applications. Due to the complexity of the combustion process in gas turbine engines, simpler flames are generally used to study fundamental combustion properties and measure concentrations of important species to validate and improve modeling. Stable, laminar flames have increasingly been used to study nitrogen oxide (NOx) formation in lean-to-rich compositions in low-to-high pressures to assess model predictions and improve accuracy to help develop future low-emissions systems. They allow for nonintrusive diagnostics to measure sub-ppm concentrations of pollutant molecules, as well as important precursors, and provide well-defined boundary conditions to directly compare experiments with simulations. The uncertainties of experimentally measured boundary conditions and the inherent kinetic uncertainties in the nitrogen chemistry are propagated through one-dimensional stagnation flame simulations to quantify the relative importance of the two sources and estimate their impact on predictions. Measurements in lean, stoichiometric, and rich methane–air flames are used to investigate the production pathways active in those conditions. Various spectral expansions are used to develop surrogate models with different levels of accuracy to perform the uncertainty analysis for 15 important reactions in the nitrogen chemistry and the six boundary conditions (ϕ, Tin, uin, du/dzin, Tsurf, P) simultaneously. After estimating the individual parametric contributions, the uncertainty of the boundary conditions are shown to have a relatively small impact on the prediction of NOx compared to kinetic uncertainties in these laboratory experiments. These results show that properly calibrated laminar flame experiments can, not only, provide validation targets for modeling, but also accurate indirect measurements that can later be used to infer individual kinetic rates to improve thermochemical models.

The Impact of Boundary Conditions on the Relationship Between Value Creation and Appropriation

Value creation and value appropriation are two crucial issues in strategy, marketing, and supply chain management. Although value creation and value appropriation are two sides of the same coin, most prior studies focus on one or the other. Some empirical works examine value creation and value appropriation simultaneously, but the results remain mixed. This investigation contributes to the current literature by answering the following questions: Does more value creation lead to more value appropriation? Why can a supplier appropriate more value than others in a buyer-supplier relationship? The empirical results from 150 publicly listed firms that play the role of suppliers indicated that suppliers can benefit from their value creation. Partnership, the spillover effect of collaboration, and suppliers’ bargaining power can strengthen the positive relationship between value creation and value appropriation. Our findings and conclusions can have significant implications for research on value creation and value appropriation.

Numerical investigation of laminar burning velocity for methane-hydrogen-air mixtures at wider boundary conditions

To extend the study related to laminar burning velocity (LBV) of methane mixed with hydrogen under different boundary conditions, the FFCM-MECH was selected for chemical kinetic analysis. The influencing mechanisms of LBV of methane mixed with hydrogen were investigated under similar operating conditions for the internal combustion engine, e.g., higher temperatures, higher pressures, CO2 dilution ratios and larger extent of equivalence ratios. The impact of boundary conditions on the concentration of important reactive radicals and the flame structure was also discussed. The results and findings are summarized as follows. The LBV increases as the hydrogen addition ratio and initial temperature increase, but showing opposite trends when the initial pressure and CO2 dilution ratio rise. Moreover, it shows an increasing trend followed by a decreasing trend as equivalence ratio increases. LBV is highly dependent on the concentration of some important radicals in the system, the higher the concentration of radicals, the faster the LBV. Methane mixed with hydrogen has a small rise in adiabatic temperature and an outstanding reduction in carbon dioxide and carbon monoxide content, which can significantly reduce the emission of harmful gases and greenhouse gases. This study not only gives a reference for the design on power machinery, but also is conducive to promoting the development of natural gas engines.

Impact of boundary conditions in a microclimate model on mitigation strategies affecting temperature, relative humidity, and wind speed in a Mediterranean city

This paper investigates several mitigation strategies to detect which has the biggest effect on thermal comfort parameters, namely temperature, relative humidity, and wind speed in a neighborhood in Beirut, the capital city of Lebanon. The strategies include changing the ground surface albedo, replacing old buildings with new ones, and adding vegetation. The simulations, conducted on ENVI-met V4 software, were run on the 20th of January and August representing the two major seasons in the country, winter and summer, respectively. The simulations were carried out on a 200 x 200 x 46-m domain at a resolution of 2 m, which permits the study of small-scale interfaces between buildings, surfaces, and vegetation. The paper then represents various types of lateral boundary conditions (LBC) and illustrates the effects of expanding the area of buildings surrounding the field of interest. The present study will allow urban planners to determine the policies required to ameliorate the urban living environment in cities like Beirut. The simulation exhibits that the greatest impact on thermal comfort parameters is vegetation. It was eminent that the occupancy of vegetation is the most effective mitigation strategy given its capability of enhancing the thermal comfort conditions at the pedestrian's pathway sidewalks. The maximum decrease in air temperature was 2.4 °C at 17:00 on August 20th, while the maximum decrease in the mean radiant temperature was 10.5 °C at 12 at noon on the 20th of August.

Thermal modeling of a Swiss urban aquifer and implications for geothermal heat pump systems

The progressive electrification of the building conditioning sector in recent years has greatly contributed to reducing greenhouse gas emissions by using renewable energy sources, particularly shallow geothermal energy. This energy can be exploited through open and closed shallow geothermal systems (SGS), and their performances greatly depend on the ground/groundwater temperature, which can be affected by both natural and anthropogenic phenomena. The present study proposes an approach to characterize aquifers affected by high SGS exploitation (not simulated in this work). Characterization of the potential hydro/thermogeological natural state is necessary to understand the regional flow and heat transport, and to identify local thermal anomalies. Passive microseismic and groundwater monitoring were used to assess the shape and thermal status of the aquifer; numerical modeling in both steady-state and transient conditions allowed understanding of the flow and heat transport patterns. Two significant thermal anomalies were detected in a fluvio-glacial aquifer in southern Switzerland, one created by river water exfiltration and one of anthropogenic nature. A favorable time lag of 110 days between river and groundwater temperature and an urban hot plume produced by underground structures were observed. These thermal anomalies greatly affect the local thermal status of the aquifer and consequently the design and efficiency of current and future SGS. Results show that the correct characterization of the natural thermo-hydrogeological status of an aquifer is a fundamental basis for determining the impact of boundary conditions and to provide initial conditions required to perform reliable local thermal sustainability assessments, especially where high SGS exploitation occurs.

Design of a 720-mm Square Direct Shear Box and Investigation of the Impact of Boundary Conditions on Large-Scale Measured Strength

Large-scale direct-shear equipment is described and experimental results are presented showing the influence of test boundary conditions on direct shear strength. The equipment was constructed at the University of Newcastle in 2013 for testing square samples up to 720 mm and applying vertical loads up to 4 MPa. Its boundary conditions were modified in 2017 to better comply with the testing philosophy in standards. The main modifications introduced include full compensation for normal load eccentricity induced in the original arrangement and the introduction of a system that would allow the installation of a seamless gap between shear box halves before shearing. Additional modifications considered the restriction of unwanted carriage spinning during lateral displacement and reduction of frictional force between the specimen and the vertical walls of the box. After the modifications were introduced, implementing a careful method for sample construction, repeatability of the friction angle at large displacement in the range of 1° was achieved among single tests. Further equipment improvement strategies were identified.