Application Of Boundary Conditions Research Articles

Performances of the sandwich panel structures under fire accident due to hydrogen leaks: Consideration of structural design and environment factor using FE analysis

Abstract This study presents a comprehensive analysis using the finite element method (FEM) to examine and evaluate the behavior of fuel carrier ship structure. Sandwich panels are effective structures for use in ship structures due to their lightweight yet robust nature. Sandwich panels used in ship structures have various core shapes, such as hexagonal, circular, and square, as needed. The sandwich panel structure can be widely implemented in ship construction, for example, on the deck, hull, and bulkhead of the ship’s cabin. Hydrogen is an alternative fuel that can replace fossil fuels. In this modern era, hydrogen is high valuable energy commodity, so accidents involving carrier ships could have significant consequences. Hydrogen is produced from liquefied natural gas (LNG), so if a leak occurs, for instance, in a storage tank or fuel tank, it has the potential to lead to accidents such as fires. Corrosion is a significant concern for the maritime industry, as it can jeopardize the structural integrity of these vessels and pose substantial safety and environmental risks. In this research, FEM was utilized to model and simulate the effects of corrosion on hydrogen carrier ships when exposed to fire, considering various environmental and operational factors. Through a systematic investigation, it is aimed to gain insights into the impact of corrosion on ship structural components during fires, such as hulls and storage tanks. The result of this study will contribute to improving corrosion and fire mitigation strategies, ensuring the safety and longevity of hydrogen and LNG carrier ships, and supporting the sustainable transportation of hydrogen to meet global energy demands. No research has been conducted on the structural behavior resulting from hydrogen fires and corrosion simultaneously. To achieve this, it is assumed to use the corrosion properties of steel in heavily traveled ship routes such as the Panama Canal Zone, Barent Sea, North Sea, and Suez Canal Zone. This study utilized an approach by modeling corrosion using shell thickness in Abaqus Quasi-Static and applying boundary conditions in the form of temperature increase up to 800°C and subsequent cooling back to the initial temperature. At the maximum temperature, the most significant mid-span displacement occurred in the circular core sandwich panel, with a value of 4 mm. The axial force in the structure was inversely proportional to the mid-span displacement. In the case of the circular core sandwich panel, the axial force was 96 kN. The most resilient core type was hexagonal because it experiences the least deformation when compared to circular and square cores.

Numerical modeling and analysis of fluid-filled truncated conical shells with ring stiffeners

This study uses a hybrid finite element method to predict dynamic behavior of truncated conical shells with ring stiffeners under fluid loading. The proposed approach combines classical shell theory and the finite element method, making use of displacement functions derived from exact solutions of Sanders’ shell equilibrium equations for conical shells. The analysis of the shell-fluid interface involves leveraging the velocity potential, Bernoulli’s equation, and impermeability conditions to determine an explicit expression for fluid pressure. To the best of our knowledge, this paper is the first to compare the methods applied to ring-stiffened shells against other numerical and experimental findings. Our results on conical shells in various conditions, with and without ring stiffeners, are largely consistent with previous findings. This study also explores the influence of geometric parameters, stiffener quantity, cone angle, and applied boundary conditions on the natural frequency of fluid-loaded ring-stiffened conical shells. The paper concludes with a discussion of several useful implications for further research.

Boosting energy levels in graphene magnetic quantum dots through magnetic flux and inhomogeneous gap

We study the effects of a magnetic flux and an inhomogeneous gap on the energy spectrum of graphene magnetic quantum dots (GMQDs). By considering the Dirac equation in the infinite mass framework, we can analytically obtain eigenspinor expressions. By applying boundary conditions, we obtain an energy spectrum equation in terms of system parameters such as radius, magnetic field, energy, flux, and gap. In the infinite limit, we recover Landau levels for graphene in a magnetic field. We show that the energy spectrum increases significantly in the presence of flux and a gap inside the GMQDs, which prolongs the lifetime of the trapped electron states. We show that higher flux also produces new Landau levels of negative angular momentum. Meanwhile, we find that the gap increases the separation between the electron and hole energy bands. As shown in the radial probability analysis, flux and gap emerge as influential factors in controlling electron mobility, affecting confinement, and prolonging the presence of quasi-bound states.

Experimental investigation of the oscillation threshold to limit state operation of a single branch pulsating heat pipe

The study investigates the characteristics of oscillations and associated thermo-hydrodynamic phenomena for startup, limit state, and intermediate transitional behavior of a pulsating heat pipe (PHP) with the help of its single branch. Experiments are performed on a transparent single branch PHP (SBPHP) at different orientations, evaporator and condenser section temperatures using n-pentane as the working fluid. The entire two-phase flow behavior is recorded with the help of shadowgraph based high speed imaging synchronized in real-time domain with pressure data acquisition at evaporator end. Instability threshold is determined in terms of evaporator temperature at different tube orientations and condenser temperatures. The oscillation startup mechanism along with the associated intermittency is studied in detail. The SBPHP is found to have characteristic variations in oscillation amplitude and frequency as it undergoes a gradual transition from its oscillation threshold to limit state. The mechanism by which the limit state creeps-in and intumesces further is an intrinsic function of liquid-vapor distribution in SBPHP, which in turn depends on the applied boundary conditions. The operational limit is governed by evaporator dryout exceeding permissible limits marked by the steep rise in the dry length of evaporator. As SBPHP approaches or operates at its limit state, evaporator is found to have different regimes across its length, viz., mild convective evaporation combined with subcooled nucleate boiling, saturated nucleate boiling, forced convective boiling, film breakdown and permanent dryout. The liquid film distribution, pressure fluctuations, and heat transfer components in evaporator at the limit state have also been studied.

Enhancing Sensitivity of Double-Walled Carbon Nanotubes with Longitudinal Magnetic Field

In this study, the behavior of double-walled carbon nanotubes (DWCNTs) used as mass sensors is explored under various boundary conditions; particular attention is paid to the crucial topic of resonant nanomechanical mass sensors. In the presented approach, nanotubes are subjected to a distributed transverse magnetic force and supported by an elastic foundation. The impacts of the longitudinal magnetic field, elastic medium, and diverse physical parameters on the responsiveness of the sensors are assessed. Using the energy method, governing equations are formulated to determine the frequency shifts of the mass nanosensors. Our findings reveal significant variations in the frequency shifts due to a longitudinal magnetic field, which depends on the applied boundary conditions. This research holds significance in the design of resonant nanomechanical mass sensors and provides valuable insights into the interplay of factors affecting their performance. Through exploring the intricate dynamics of DWCNTs used as mass sensors and thus contributing to the broader understanding of nanoscale systems, the implications for advancements in sensor design are offered and applications are introduced.

Natural frequencies and modal shapes of folded sandwich plates made of porous core and FG-CNTRC coating layers resting on two parameters elastic foundation

Folded structures hold significant importance in aerospace technology due to their distinct design, effectively reconciling strength with a lightweight framework. Within aerospace applications, these structures fulfill diverse roles, serving as pivotal elements in aircraft wings, fuselage sections, and essential components of spacecraft and satellites. This study delves into the free vibration behavior of folded sandwich plates composed of a porous core and functionally graded carbon nanotube-reinforced composite (FG-CNTRC) coatings, resting on a two-parameter elastic foundation. Leveraging first-order shear deformation plate theory (FSDT), elasto-dynamic equations are established for each individual plate segment. Utilizing the two-dimensional generalized differential quadrature method (2D-GDQM), these equations are discretized. Subsequently, by applying boundary conditions to all six edges, including traditional clamped, simply supported, and free configurations, and incorporating continuity conditions for displacements, forces, and moments at the joint borders, natural frequencies and modal shapes are extracted for the folded plate structure. The validity of the proposed formulation and results is demonstrated by comparing them with numerical examples for both composite flat and folded plates. This comparison provides strong support for the accuracy and reliability of the present study. The study comprehensively examines the influence of various parameters on natural frequencies, including modal shape visualizations under different boundary configurations, plate thickness, crank angle, porosity parameter, core thickness, foundation stiffness, and CNTs distribution type.

Optimization and Analysis of Drive Shaft Using CAE Tools

Drive shaft or propeller shaft is the essential part of Automobiles. It is used to deliver torque from transmission to the differential and further to the wheel to cause the motion of the vehicle. The drive shaft is used to connect with the transmission shaft with the help of universal joint whose axis intersects and the rotation of one shaft about its own axis results in the rotation of the other shaft about its axis. In present work the model of the drive shaft has been generated in Solid works and further imported in ANSYS workbench. A finite element analysis of the drive shaft has been carried out as a case study. In the present work the static analysis of a drive shaft has been carried out with the new design changes. The results for equivalent von-Mises stress, strain and deformation have been calculated by applying boundary conditions and compared with the existing results.

Numerical Solution of Eighth Order Two Point Boundary Value Problems by Taylor Series Method

A Taylor series method which is taught at undergraduate levels and which has been hitherto used for the solution of initial value problem is successfully used in this work for the solutions of eighth-order two point boundary-value problems. The method is based on successive differentiation of the governing equation to obtain high order derivatives and then evaluated at the boundary point x=a. The solution is expressed inform a Taylor series with the unknown coefficients at a point x=a. By applying boundary conditions at x=b in the Taylor series solution, the system of unknown coefficient is obtained. After solving the system, then unknown coefficient are determined. The procedure is applied on both linear and nonlinear boundary-value problems. A comparison of the results obtained by the present method with results obtained by other methods reveals that the present method is simple, effective and also is in good agreement with the previous result and exact solution as showing in the tables and figures.

Computation of TM Scattered Fields Induced by a Truncated Semi-Elliptic Cavity in a PEC

This study investigated the scattered transverse-magnetic (TM) electromagnetic field from a truncated semi-elliptic embedded in a perfectly electric conducting plane. Boundary value analysis and the region-point-matching technique are employed to address the issues considered. The analyzed region is divided into three sub-regions, after which the tangential fields are expanded in terms of Mathieu functions into two different coordinate systems. By applying boundary conditions at two auxiliary boundaries and using the region-pointmatching technique, several independent equations are constructed and subsequently simplified to generate a system of linear equations. For the validation of the obtained results, the suggested procedure is compared to the method of moment. Finally, the effects of cavity depth and incident angle on the scattering signature are inspected.

Design and performance simulation of a soft artificial heart by using the ANSYS software

Blood is pumped from the heart, a muscular organ, to various body organs via blood arteries. The aim of this paper is to create a temporary device, such as a pump, for individuals with cardiac diseases for whom survival without a transplant is unfeasible. Until a donor heart becomes available, the patient may have ample time with these makeshift devices. This paper uses engineering principles to explore the idea of an artificial heart. Using SOLIDWORKS 18 and ANSYS 21, numerical simulation and examination of the artificial heart were carried out. A Multiphysics static structural model and fluent fluid flow (CFD) analytical techniques were utilized to ascertain the dynamic response and impacts of pressure. SOLIDWORKS was utilized to model the 3D geometries, and ANSYS Design Modeler was used to import the geometries for preprocessing. The solver used throughout the study is ANSYS FLUENT, a tool used to analyze fluid flow troubles, known as Computational Fluid Dynamics (CFD). Next is mesh generation, which means discretization of the domain to solve governing equations at each cell and later specify the boundary zones to apply boundary conditions for this paper. The simulation results showed that at maximum levels of absolute pressure in air pressurized chambers, the performance of the heart remained secure and suitable for comfortable conditions.

Characterizing uncertainty in process-based hydraulic modeling, exemplified in a semiarid Inner Mongolia steppe

Assessing root sources of three uncertainties – parameterization of soil hydraulic characteristics, boundary conditions, and estimation of source/sink terms – is a significant challenge in soil water transport modeling. This study aims to evaluate the uncertainty of three each widely-used parameter estimation methods affecting plot-scale water dynamics. The study employs HYDRUS, a process-based hydrologic model, to incorporate these uncertainties and compare model predictions to measured values in a semiarid Inner Mongolia steppe, China. Soil hydraulic parameters are determined using two direct methods (laboratory-derived approach and evaporation method) and one indirect method (neural network). While each hydraulic parameter method generally simulates soil moisture dynamics, the evaporation method performed better, especially under dry conditions. This suggests that measuring the intensity properties, such as unsaturated hydraulic conductivity, with the evaporation method is crucial for reasonable soil moisture simulation. The study also demonstrates the impact of different applied boundary conditions on simulated soil moisture, specifically the partitioning of reference FAO evapotranspiration via one direct method (soil fraction cover) and two indirect methods (leaf area index and crop height). The partitioning via soil fraction cover reflected a better simulation. Additionally, the study compares the uncertainties of root water uptake function with root growth parameters and constant root depth referenced to grass and pasture, and finds no significant difference among them. Comparing three sources of uncertainty in predicting soil moisture, the study concludes that the input soil hydraulic parameter is more sensitive than evapotranspiration partitioning or representation of root water uptake function. Our study highlights that measuring soil intensity properties can better reflect the effects of land use change, such as compaction, on field water transports.

Numerical study of the vibrational absorption considering the periodic foundation effect in a small structure

The growth of urban areas has led buildings to come closer and closer to road traffic routes, exposing civil buildings to traffic vibrations, causing discomfort for users and damage to structures. Although there are numerical studies on traffic vibrations, effective vibrational isolation techniques are little explored in this research. A promising approach is the use of periodic structures. Although used in several areas of engineering, periodic structures still have limited application in civil engineering, especially to isolate vibrations caused by vehicles rolling on pavement in small buildings. In this context, this research developed three numerical finite element models for a small structure, which represent residential and/or commercial buildings with a number of floors equal to or less than three, in reinforced concrete. The first model involved a periodic block-type structure foundation, while the two comparative models included periodic raft-type foundations and block-type concrete foundations. The objective was to analyze the vibrational absorption of different foundations for forced vibrations arising from road traffic in the 1-50Hz range. In order to compare them and observe how beneficial the use of periodic foundation is, in the context of the study. The methodology used consisted of creating structural models using finite elements, applying boundary conditions to couple the foundation layers and the structure, establishing continuity. The study looked for modal responses, and in the frequency domain, resulting from excitation in the foundation, using the Ansys® software (2023) for all simulations. The results revealed that periodic foundations are capable of reducing amplitude peaks at frequencies above 30 Hz, which is beneficial for attenuating vibrations in this range. With an appropriate design, adjusting the geometric and physical parameters of the materials, it is possible to obtain effective vibrational isolation for structures, minimizing vibrations arising from ground waves in buildings. This suggests that the use of periodic structures would be promising in isolating vibrations caused by traffic in small structures.

A 2D hybrid analytical electromagnetic model of the dual‐stator axial‐field flux‐switching permanent magnet motor

AbstractThe two‐dimensional (2D) analytical model for the calculation of the components of the flux density distribution in the air gap in a dual‐stator axial‐field flux‐switching permanent magnet (PM) motor (DSAFFSPM) is presented. The novelties of this study are deriving a 2D hybrid analytical model and replacing the rotor teeth with some surface currents for the calculation of air‐gap magnetic flux density for the first time in the DSAFFSPM motor. The 2D analytical model for DSAFFSPMs is more challenging due to the doubly salient structure and inner PM of the stator. 1D analytical interior PMs are first transferred to the bore of the stator body using the magnetic equivalent circuit model (MEC). Next, the effects of the rotor teeth are taken into consideration by injecting virtual surface currents for 2D analytical model. Applying boundary conditions and solving the Laplace/Poisson equations, the vertical and tangential flux components of the flux density distribution in the air‐gap DSAFFSPM motor are computed. The verification of the proposed method and the obtained results are validated by the 3D finite element method.

Generative learning‐based model for the prediction of 2D stress distribution

AbstractIn this study, we introduce a Generative learning‐based approach to accelerate Finite Element simulations. The aim is to explore the ability of a Generative learning‐based approach to predict the output of Finite Element simulations. Often, the drawback of classical regression models is that they are bound to the distribution of training data and cannot extrapolate outside of the training domain. In the current study, to overcome this, we propose a Generative Adversarial Network (GAN) based approach for learning to infer structural mechanics simulations. GANs have the ability to learn the underlying distribution of data and can efficiently extrapolate outside the training range. We train the proposed network on data obtained from classical Finite Element simulations based on linear elastic and Johnson‐Cook plasticity models. The goal here is to understand the ability of a GAN to replace FEM by incorporating the underlying mechanics knowledge into the network to enhance the generalizing ability of the network for various materials on various loading and boundary conditions. We propose an encoder‐decoder‐like U‐Net generator architecture with activated skip connections and a PatchGAN‐based discriminator that discriminates based on local patches of data leading to a more robust critique for the generator. The advantage of the proposed framework is that it takes inputs such as the nodal information, their corresponding edges, nodal coordinates and the boundary conditions for each particular node from a Finite Element pre‐processor and computes the von Mises stress at each node as output that can be read by a Finite Element post‐processor. Also, the novelty of the proposed GAN is that, unlike the existing literature, it takes nodal values such as applied Boundary conditions and coordinates as inputs instead of images and performs nonlinear regression with Finite Element data and gives von‐Mises stresses at each node as output.

Developing an immersed boundary method for compressible flow

AbstractDevelopment of a 3D sharp interface ghost node immersed boundary method (IBM) within a fluid solver based on the compressible Navier–Stokes equations is underway. The objective of the IBM is to accurately apply boundary conditions at fluid–solid interfaces. The Navier–Stokes solver is currently being verified using various test cases, including the classic cylinder in cross flow. As part of this verification process, particular attention was given to investigating the effects of different lateral boundary conditions. The results demonstrate that extrapolation boundary conditions exhibit better agreement with the literature compared to symmetry conditions, in cases with relatively narrow domains. These findings highlight the potential benefits of extrapolation boundary conditions in reducing confinement effects and removing nonphysical waves in external flow problems.

An analytical method informed by clinical imaging data for estimating outlet boundary conditions in computational fluid dynamics analysis of carotid artery blood flow

Stroke occur mainly due to arterial thrombosis and rupture of cerebral blood vessels. Previous studies showed that blood flow-induced wall shear stress is an essential bio marker for estimating atherogenesis. It is a common practice to use computational fluid dynamics (CFD) simulations to calculate wall shear stress and to quantify blood flow. Reliability of predicted CFD results greatly depends on the accuracy of applied boundary conditions. Previously, the boundary conditions were estimated by varying values so that they matched the clinical data. It is applicable upon the availability of clinical data. Meanwhile, in most cases all that can be accessed are arterial geometry and inflow rate. Consequently, there is a need to devise a tool to estimate boundary values such as resistance and compliance of arteries. This study proposes an analytical framework to estimate the boundary conditions for a carotid artery based on the geometries of the downstream arteries available from clinical images.

Incorporating uncertainty in stress‐strain data acquisition: extended model‐free data‐driven identification

AbstractBased on the increasing ability to collect and store large amounts of data and information, data‐driven methods have recently gained importance in the context of computational mechanics. Compared to the traditional approach of defining a suitable constitutive model and fit the parameters to experimental data, these methods aim to capture complex material behavior without the assumption of a certain material formulation. Distinguished are model‐based data‐driven methods, leading to an approximation of the constitutive material description for example, by neural networks, and model‐free data‐driven methods. The approach of data‐driven computational mechanics (DDCM), introduced by Kirchdoerfer and Ortiz (2016), enables to circumvent any material modeling step by directly incorporating material data into the structural analysis. A basic prerequisite for both types of data‐driven methods is a large amount of data representing the material behavior, in solid mechanics consisting of stresses and strains. Obtaining these databases numerically by multiscale approaches is computationally expensive and requires the definition of lower scale models. In case of an experimental characterization, constitutive descriptions are generally required to compute the stress states corresponding to displacement fields, for example, identified by full‐field measurement techniques, such as digital image correlation (DIC). The method of data‐driven identification (DDI), introduced in Leygue et al. (2018) based on the principles of DDCM, enables the determination of detailed information about the constitutive behavior based on displacement fields and applied boundary conditions without a specific material model. Stresses corresponding to given strains are identified by iteratively clustering and enforcing equilibrium. The algorithm has shown to be applicable to synthetic as well as real data taking linear and non‐linear material behavior into account. Generalized polymorphic uncertainty models, resulting as a combination of aleatoric and epistemic uncertainty models, are utilized to take variability, imprecision, inaccuracy and incompleteness of data into account. The consideration of uncertain material properties by data‐driven simulation approaches leads to the requirement of data sets representing uncertain material behavior. In this contribution, different sources of uncertainty occurring within DDI of stress‐strain relations are addressed and an efficient method for the identification of data sets representing uncertain material behavior based on the concept of DDI is proposed. In order to demonstrate the developed methods, numerical examples are carried out.

FEM‐based dual length‐scale simulation of hydrothermal ore‐forming systems involving convective flow in fluid‐saturated porous media

AbstractHydrothermal ore‐forming systems usually involve coupled processes among pore‐fluid flow, heat transfer, mass transport and chemical reactions in fluid‐saturated porous media. The finite element method (FEM) has provided a powerful tool to solve hydrothermal ore‐forming problems associated with pore‐fluid convective flow. Depending on different interests of research, a hydrothermal ore‐forming system may be simulated at two different length‐scale models, such as a regional (i.e., large length‐scale) model or a deposit (i.e., small length‐scale) model. However, there is an unsolved issue to guarantee the consistency between the applied boundary conditions to a deposit model and the predicted results, at exactly the same location as the boundary of the deposit model, from using the regional model. This paper proposes a FEM‐based dual length‐scale simulation procedure to address this issue. In the proposed procedure, a regional model of coarse mesh is first simulated by the FEM. Since a deposit model is located within the regional model, the applied boundary conditions to the deposit model of fine mesh can be determined from the simulation results of the regional model, so that the consistency can be guaranteed at the common boundary between the deposit model and the regional model. Main outcomes of this study have demonstrated that: (1) the proposed FEM‐based dual length‐scale simulation procedure is suitable and applicable for solving coupled problems involving pore‐fluid flow, heat transfer, mass transport and chemical reactions in fluid‐saturated porous media; (2) the proposed procedure is predictive because it is unnecessary to know the location of an ore deposit prior to the simulation of a hydrothermal ore‐forming system; (3) the boundary condition of a deposit model of fine mesh is consistent with the simulation results obtained from the regional model of coarse mesh, so that the reliability of the simulation results obtained from the deposit model can be ensured.

Solution of a Half-Space in Generalized Thermoelastic Problem in the Context of Two Models Using the Homotopy Perturbation Method

This paper estimated the problem of one-dimensional generalized thermoelastic half-space in medium considering two models: the Lord and Shulman (LS) model and the Dual-Phase-Lag (DPL) model. We assumed that the surface of the half-space was free from traction force and under an exponentially varying external heat source at the boundary with time. The technique of homotopy perturbation has been applied to find the approximate solution for the interactions of thermoelasticity with the applied boundary condition. The effect of a heat source that varies with the time and the free traction force are investigated for the temperature, displacement, and stress. The numerical results obtained are presented graphically to show the influence of the new external parameters. The results obtained illustrate the strong impacts on the displacement, temperature, and stress with the variations in the two models as well as the relaxation time parameter. The results show the agreement between the present results and the previous obtained results of the phenomenon and applicable, especially in biology, acoustics, engineering, and geophysics.

Stream laws in analog tectonic-landscape models

Abstract. The interplay between tectonics and surface processes defines the evolution of mountain belts. However, correlating these processes through the evolution of natural orogens represents a scientific challenge. Analog models can be used for analyzing and interpreting the effect of such interaction. To fulfill this purpose it is necessary to understand how the imposed boundary conditions affect analog models' evolution in time and space. We use nine analog models characterized by different combinations of imposed regional slope and rainfall rates to investigate how surface processes respond to the presence of tectonically built topography (imposed slope) under different climatic conditions (rainfall rate). We show how the combination of these parameters controls the development of drainage networks and erosional processes. We quantify the morphological differences between experimental landscapes in terms of a proposed Se/R ratio, accounting for both observables and boundary conditions. We find few differences between analog models and natural prototypes in terms of parametrization of the detachment-limited stream power law. We observe a threshold in the development of channelization, modulated by a tradeoff between applied boundary conditions.