Effects Of Various Boundary Conditions Research Articles

Numerical investigation of the effect of nanoparticle aggregation on the performance of concentrated photovoltaic-solar thermal collectors with spectral filtering

Solar energy, particularly solar thermal technology, has gained popularity as a possible long-term replacement to fossil fuels. The application of concentrated photovoltaic-solar thermal (CPV/T) collectors, which are improved by spectral filter fluids (SFF) and nanotechnology, has the potential to provide both higher thermal power for heating and cooling as well as improved electrical power generation. This work contributes new insight by quantifying the influence of nanoparticle agglomeration on collector performance and highlighting the challenges associated with the heterogeneous distribution of nanoparticles in CPV/T systems. The study employed coupled Eulerian multiphase modeling and discrete ordinate (DO) radiation modeling to examine slip velocity, nanoparticle diameter (including agglomeration), and suspension concentration. Population balance modeling (PBM) was utilized to determine the nanoparticle size distribution, and the obtained results were validated through comparison with experimental and numerical studies. When neglecting the effect of agglomeration and breakage of the non-solar participating media, the maximum error for this configuration was found to be 3.58% when compared to experimental work. From the solar participating study, in terms of electrical energy production, the best performance obtained was 16.64% with a volume fraction of 0.005% when considering agglomeration and breakage. It was also found that the Sauter diameter increases with volume fraction as the tendency for nanoparticle agglomeration increases. This study provides a broader view of the application of multiphase modeling in solar participating and non-solar participating media and, additionally, provides insight on the effect of various boundary conditions on the key system performance indicators. To extend this work, the flow Reynolds number can be increased in addition to varying the type of working fluid.

Mathematical modelling of passive displacement dual cooling coil (PDDCC) system in a tropical climate

Unlike the conventional displacement ventilation (DV) systems, the Passive Displacement Dual Cooling Coil (PDDCC) system generates airflow in indoor environments based on natural convection and eliminates the necessity of mechanical ventilation to meet the thermal comfort and indoor air quality requirements. Investigations on such PDDCC systems, though, have been largely limited and its performance capacity and fluid flow behaviour are not fully understood. A mathematical model was, hence, developed in the current study to explore the effects of various boundary conditions on the performance of the PDDCC system. Results obtained from the mathematical model were, first, compared and validated against the measurement readings gathered from an experimental investigation conducted on the PDDCC system in a controlled test environment. The validated mathematical model was then applied to a parametric evaluation where the effects of chilled water supply (CHWS) temperature, flow rate, and return air temperature on the PDDCC system performance were examined. The varying effect of the latent and sensible cooling load was observed at the different boundary conditions applied to the PDDCC model. Slightly more than 32% of rise in total cooling load was predicted by reducing the CHWS temperature which established a much more significant contribution in comparison to the CHWS flow rate which generated approximately 5% rise in the total cooling load. Findings were supported by examining the sensible heat ratio (SHR) and the ratio of Latent cooling load: Sensible cooling load which was then was attributed to the temperature difference between the supply and return air temperature. By ensuring the maximum temperature difference, the total cooling load performance of the PDDCC system can be maximised. The contribution of both the CHWS temperature and flowrate was essential to achieve the maximum cooling load, hence, improving the total cooling performance of the PDDCC as a result.

Fast performance prediction and field reconstruction of gas turbine using supervised graph learning approaches

Accurately and rapidly predicting the multi-conditions characteristics of turbines is fundamental for realizing efficient energy conversion and optimal layout schemes. Based on supervised graph learning approaches, this work is dedicated to establishing a fast multidisciplinary prediction model for gas turbines. The research target is a gas turbine blade with complex cooling channels. An Aerodynamic Strength Prediction Graph neural network (ASP-GNN) is proposed to predict the aerodynamic-strength characteristics and temperature field under different boundary conditions. The superiority of our approach is demonstrated by prediction precision and time cost. The generalizability of the network is also investigated by adopting different training set sizes, and the ASP-GNN can achieve satisfactory accuracy with a limited number of training samples. Based on the established model, the effects of various boundary conditions on aerodynamic and strength performance are quantified. The unsteady characteristic of performance and temperature field are also obtained conveniently. The proposed model could serve as a fast analysis approach to aid the design and analysis of turbomachinery. It may relieve the workload of numerical simulations for complex engineering analysis.

Natural frequency investigation of graphene oxide powder nanocomposite cylindrical shells surrounded by Winkler/Pasternak/Kerr elastic foundations with a focus on various boundary conditions

For the first time, the present research examines the free vibration responses, Natural Frequencies (NFs), of Graphene Oxide Powder (GOP) nanocomposite cylindrical shells surrounded by three types of elastic foundations considering different Boundary Conditions (BCs). To support this, the effects of various BCs are examined on the NFs related to the GOP Nanocomposite Cylindrical Shells (GOPNCS). In addition, elastic foundations are characterized by three factors: Winkler, Pasternak, and Kerr. Addedly, First-order Shear Deformation Theory (FSDT) and Donnell's shell theory are combined to discover the fundamental formulations related to the GOPNCS structures. Then, the equations of motion related to the GOPNCS are formulated employing Hamilton's principle. In subsequent, the equations associated with the previous step are discretized by implementing the Generalized Differential Quadrature Method (GDQM), counted as the mesh reduction method. Afterward, the standard eigenvalue determination is employed to determine the NFs associated with the GOPNCS. Ultimately, multiple benchmarks are answered to authenticate the scheme recommended for determining the NFs of the GOPNCS. Further, numerous original problems are arranged and highlight the effects of changes in material and geometrical features, various BCs, and three types of elastic foundations on the NFs related to the GOPNCS.

High-Order Accurate Numerical Simulation of Supersonic Flow Using RANS and LES Guided by Turbulence Anisotropy

This paper discusses accuracy improvements to Reynolds-Averaged Navier–Stokes (RANS) modeling of supersonic flow by assessing a wide range of factors for physics capture. Numerical simulations reveal complex flow behavior resulting from shock and expansion waves and so, a supersonic jet emanating from rectangular nozzle is considered. PIV based experimental data for the jet is available from literature and is used for validation purposes. Effect of various boundary conditions and turbulence modeling approaches is assessed qualitatively and quantitatively. Of particular interest are the inlet conditions considering the turbulence intensity and the effect of upstream air supply duct, the effect of nozzle wall surface roughness on nozzle internal flow and downstream, wall y+ sensitivity for boundary layer resolution and laminar to turbulent transition modeling. In addition to mesh sensitivity, domain dependency is conducted to evaluate the appropriate domain size to capture the kinetic energy dissipation downstream of the nozzle. To further improve the flow characteristics, accounting for the anisotropy of Reynolds stresses is also one of the focuses. Therefore, non-linear eddy viscosity-based two-equation model and Reynolds stress transport model are also investigated. Additionally, the results of baseline linear (Boussinesq) RANS are compared. Corresponding comparisons with high-fidelity LES are presented. Jet self-similar behavior resulting from all simulation fidelities is assessed and it appears that turbulent flow in LES becomes self-similar, but not in RANS. Finally, various factors such as the nozzle geometry and numerical modeling choices influencing the anisotropy in jet turbulence are discussed.

Analytical and numerical analysis of functionally graded (FGM) axisymmetric cylinders under thermo-mechanical loadings

This study examines the thermo-mechanical behavior of FGM hollow cylinders subjected to mechanical loading and steady thermal stresses. The distribution of temperature, displacement, and stresses on the cylinder's inside and outside surfaces is considered a function of radius. The analytic solution of the displacement and stress distributions was obtained by solving Navier's second-order differential equation using the integral and differential transform method, derived from the mechanical equilibrium and heat equations. Moreover, numerical models were built using the finite element method with USDFLD and the finite difference method to test the accuracy of the analytical solution. The analytical formulation and numerical simulation predictions have a high level of agreement, indicating that the model is accurate. The effect of inhomogeneity in the FGM thick cylinder was addressed in this study by selecting a non-dimensional parameter β=[−2,2]that may be assigned any value influencing the stresses in the cylinder. It is concluded that by altering the valueβ, the properties of FGM can be altered to achieve the lowest stress levels. It is also shown that the effect of various Boundary Conditions (B.Cs) is significant in stress fields. This present work also observed that the significance of thermal B.C. is more dominant than fixed pressure B.Cs.

Experimental and finite element investigation of statistical energy analysis parameters for idealized subsystems

In the field of acoustic and vibration analysis, statistical energy analysis proven to be an efficient tool for evaluation of the crucial parameters like damping loss factor (DLF), modal density and coupling loss factor of complex structures. In the present study, modal densities and DLFs of idealised subsystems i.e. rectangular plates comprised of different materials were evaluated experimentally and numerically. In addition, the effects of various boundary conditions (BCs) like free-free, simply supported and cantilever on the statistical energy parameters have been studied. The results obtained using both experimental and numerical approaches are in close agreement. In the case of comparison of all the considered materials, the highest modal density was observed for aluminium, whereas the lowest frequency was observed for graphene doped epoxy composite. The highest DLF was observed for GFR epoxy composite, whereas the lowest DLF was observed for stainless steel.

Use of Ritz technique to investigate the sensitivity of the postbuckling response of FG microplates to geometric imperfections

The present study examines the postbuckling behavior of imperfect microplates made from functionally graded (FG) materials using modified strain gradient theory (MSGT) and modified couple stress theory (MCST). Geometric nonlinearity is incorporated by using von-Karman’s assumptions, and the first-order shear deformation theory is used for modeling the microplates. Modified strain gradient theory defines three length scale parameters, and modified couple stress theory (MCST) reduces it to one parameter. To approximate the unknown displacement fields of the problems, the Ritz technique with Legendre polynomials is employed. The solution is derived by minimizing the total potential energy and solving the nonlinear system of equations using the Newton–Raphson technique. The nonlinear postbuckling response of imperfect FG microplates is investigated by considering the effects of various boundary conditions, different values of initial imperfection, material gradient index.

Experimental testing on nonstructural continuous plasterboard suspended ceiling systems under shake table-generated motions

Three different continuous plasterboard suspended ceiling systems were experimentally investigated through shake table-generated motions: (1) vertical strut ceiling system with all edges fixed, (2) vertical strut and lateral brace ceiling system with all edges free, and (3) vertical strut ceiling system with all edges free. Dynamic behavior and performance of these ceiling systems were evaluated to understand the effect of various boundary conditions and lateral force-resisting mechanisms at increasing intensity levels of input motion. All the ceiling systems performed well up to floor accelerations ranging from 1.4 to 1.6 g without any visible damage. However, under sinusoidal excitation at the natural frequency of the ceiling systems, the strut system with free boundaries proved vulnerable as it slipped from the perimeter channel leading to major damage. This suggests that the vertical strut system with free edges is vulnerable for multistory buildings located in any seismic zone due to its poor performance observed under large acceleration demands.

Gravity‐Controlled and Boundary‐Constrained High‐Throughput Fabrication of Polymeric Miniature Lens Arrays

AbstractThis paper reports a facile and high‐throughput method for the controllable fabrication of polymeric miniature lens arrays. Through filling the miniature holes in an additively manufactured template, the curved lenslets are formed in each hole in s steady state, in which the gravity and surface tension of the liquid resin are balanced. Both shapes and curvatures can be controlled by tuning the gravity force and the boundary condition for the resin in each hole. Taking the circular holes for example, the relationship between the formed curvature and the gravity force is described by both analytical and finite element‐based numerical models. Experimentally, the curvature variation and the effect of various boundary conditions on the lenslet surface shapes are also verified, and further examination on the optical features of the spherical miniature lens arrays including the imaging and focus properties demonstrates the effectiveness of the developed fabrication method.

Multi-Objective Optimization of Laminated Functionally Graded Carbon Nanotube-Reinforced Composite Plates Using Deep Feedforward Neural Networks-NSGAII Algorithm

This paper proposes a novel and efficient DNN-NSGAII approach which is an integration of the deep feedforward neural network (DNN) and the nondominated sorting genetic algorithm II (NSGAII) to solve multi-objective optimization (MOO) problems of laminated functionally graded carbon nanotube-reinforced composite (FG-CNTRC) quadrilateral plates. The core idea of the proposed approach is to use the DNN as an analyzer to evaluate the objective and constraint functions instead of using the time-consuming finite element analysis methods (FEAMs) during the optimization process, while the NSGAII is employed to find a set of Pareto-optimal solutions of the MOO problems. Accordingly, the proposed DNN-NSGAII remarkably saves the computational cost, but still provides a high accurate optimal solution. The precision, efficiency, and capability of the proposed method are demonstrated through two different MOO problems of the FG-CNTRC quadrilateral plates. Obtained results of the DNN-NSGAII are compared with those of other methods to investigate the reliability and efficiency of proposed method. Moreover, the effects of various boundary conditions and carbon nanotube (CNT) distributions on the Pareto-optimal solutions of MOO problems are also examined.

Free vibration analysis of elastically connected composite laminated double-plate system with arbitrary boundary conditions by using meshfree method

In this paper, the meshfree method is adopted for the first time to study the free vibration of a composite laminated double-plate system (CLDPS). The first order shear deformation theory is used to analyze the free vibration of the CLDPS, and the artificial elastic spring technique is utilized to generalize its boundary conditions. All of the displacement functions including the boundary conditions are approximated by a meshfree shape function. The reliability and accuracy of the proposed technique are verified through the comparison with the results in the previous literature and by the finite element method. The effects of various boundary conditions, material properties, and geometries of the CLDPS on its natural frequencies are considered in detail.

Effect of Honeycomb Core on Free Vibration Analysis of Fiber Metal Laminate (FML) Beams Compared to Conventional Composites

According to the different higher-order deformation beam theories, the current survey is related to the fundamental frequency analysis of composite beams using the Rayleigh-Ritz method. Different types of materials, including isotropic, fiber-reinforced orthotropic composites, and FML hybrid composites in the presence and the absence of honeycomb core, have been selected. In this theory, the material property as well as the thickness of each layer can be changed, and the effect of various boundary conditions, lay-up configurations, and slenderness ratios of the beams have been discussed. To verify the obtained theoretical results, the FML beam with [Al/0/90/90/0/Al] lay-up pattern was fabricated by hand lay-up technique and subjected to Clamped-Free boundary condition. Accordingly, the free vibration experimental data confirmed the results which were obtained by the different theories. The results show that by changing the reinforced composite beam to the FML beam, the natural frequencies experience a drop by 37%, 43%, and 43% for slenderness ratios of 5, 20, and 100, respectively. This level of descent for transferring from reinforced composite sandwich beam to the FML sandwich beam is about 24%, 37%, and 37.5%, respectively.

Bubble Complex Finite Strip Method in the Stability and Vibration Analysis of Orthotropic Laminated Composite Plates

In this study, a bubble complex finite strip method (BCFSM) with the higher-order zigzag theory is formulated for mechanical buckling and free vibration analysis of laminated composite plates, including cross-ply and angle-ply laminates. Few studies have been done to obtain the analytical solutions for clamped and free boundary conditions in the longitudinal and transverse edges. Therefore, this study, for the first time, investigates the effects of various boundary conditions on the stability and vibration results of laminated composite plates subjected to axial or pure shear forces with the use of higher-order zigzag theory and BCFSM. Following this, both the interlaminar continuity conditions of transverse shear stresses and the shear-free surface conditions are satisfied by applying a cubic displacement and a zigzag linear varying displacement with the same number of unknowns as the first-order shear deformation theories. Moreover, the effects of width-to-thickness ratio, fiber orientation, number of modes, different dimensional ratios of the plate, and finally, the number of layers are investigated through numerical examples. The bubble shape functions are exploited in the transverse direction to improve the convergence of the method. Finally, the shearing and axial interaction diagrams of composite laminated plates are presented for various types of boundary conditions.

The effect of various boundary conditions on the nonlinear dynamics of slightly curved pipes under thermal loading

Slightly curved pipes are prevalent in many industries including oil installations especially in the Delta regions of the world. The aim of this paper therefore is to investigate the nonlinear dynamics of these pipes conveying fluids under the influence of thermal loadings. These investigations are for three different boundary conditions, namely simply supported ends, clamped-clamped ends and clamped-simply supported ends respectively. To derive the governing equations, small strains of initial curvature, temperature, tension, pressure, longitudinal and transverse strains are considered. Furthermore, strains due to curvature change during bending which are hitherto neglected in most of the previous works on slightly curved pipes are added. The strain due to initial curvature accounts for the geometric imperfection. Two coupled nonlinear differential equations in both longitudinal and transverse directions are obtained and solved using eigenfunction expansion method, up to four modes. Linear natural frequencies were obtained, and is shown that for various boundary conditions, it increases as the initial curvature increases and decreases as thermal loading increases. The nonlinear results obtained show that the amplitude of the pipe motion becomes larger due to the obvious effect of thermal loading. Nonlinear results for both vanishing and non-vanishing longitudinal displacements are presented.

Novel Semi-Analytical Solutions for the Transient Behaviors of Functionally Graded Material Plates in the Thermal Environment.

The primary objective of this article is to present a semi-analytical algorithm for the transient behaviors of Functionally Graded Materials plates (FGM plates) considering both the influence of in-plane displacements and the influence of temperature changes. Based on the classical plate theory considering the effect of in-plane displacements, the equilibrium equations of the motion system are derived by Hamilton’s principle. Here, we propose a novel, accurate, and efficient semi-analytical method that incorporates the Fourier series expansion, the Laplace transforms, and its numerical inversion and the Differential Quadrature Method (DQM) to simulate the transient behaviors. This paper validates the proposed method by comparisons with semi-analytical natural frequency results and those from the literature. Expressly, the results of dynamic response also agree well with those generated by the Navier’s method and Finite Element Method (FEM). A convergence study that utilizes the different numbers of sampling points shows that the process can converge quickly, and a few sampling points can achieve high accuracy. The effects of various boundary conditions at the ends, material graded index, and temperature change are further investigated. From the detailed parametric study, it is seen that the peak displacement increases as the edge degrees of freedom, the gradient index of the material, and temperature change increase.

Small scale and spin effects on free transverse vibration of size-dependent nano-scale beams

This study aims to investigate the transverse vibration of size-dependent nano-beam which spins about its longitudinal axis. To this end, nano-beams are modeled based on the Euler–Bernoulli and Timoshenko theories. To consider the size dependency of the nano-beams, the nonlocal elasticity theory is used. By using an exact analytical solution, the governing equations of motions are solved. Comprehensive results are presented to show the effects of various boundary conditions, nonlocal scale parameter, rotational speed, and geometrical parameters on natural frequencies and critical speeds of spinning nano-beam. As spinning nano-beams are the main part of any rotary nano-machines, conclusions of present analysis promote researcher’s information about the vibrational behavior of spinning nano-beams.

An assessment of blast modelling techniques for injury biomechanics research.

Blast-induced traumatic brain injury (TBI) has been affecting combatants and civilians. The blast pressure wave is thought to have a significant contribution to blast-related TBI. Due to the limitations and difficulties of conducting blast tests on surrogates, computational modelling has been used as a key method for exploring this field. However, the blast wave modelling methods reported in current literature have drawbacks. They either cannot generate the desirable blast pressure wave history or they are unable to accurately simulate the blast wave/structure interaction. In addition, boundary conditions, which can have significant effects on model predictions, have not been described adequately. Here, we critically assess the commonly used methods for simulating blast wave propagation in air (open-field blast) and its interaction with the human body. We investigate the predicted blast wave time history, blast wave transmission, and the effects of various boundary conditions in three-dimensional (3D) models of blast prediction. We propose a suitable meshing topology, which enables accurate prediction of blast wave propagation and interaction with the human head and significantly decreases the computational cost in 3D simulations. Finally, we predict strain and strain rate in the human brain during blast wave exposure and show the influence of the blast wave modelling methods on the brain response. The findings presented here can serve as guidelines for accurately modelling blast wave generation and interaction with the human body for injury biomechanics studies and design of prevention systems.

An analytical solution for static stability of multi-scale hybrid nanocomposite plates

An analytical answer to the buckling problem of a composite plate consisted of multi-scale hybrid nanocomposites is presented here for the first time. In other words, the constituent material of the structure is made of an epoxy matrix which is reinforced by both macro- and nanosize reinforcements, namely, carbon fiber (CF) and carbon nanotube (CNT). The effective material properties such as Young’s modulus or density are derived utilizing a micromechanical scheme incorporated with the Halpin–Tsai model. To present a more realistic problem, the plate is placed on a two-parameter elastic substrate. Then, on the basis of an energy-based Hamiltonian approach, the equations of motion are derived using the classical theory of plates. Finally, the governing equations are solved analytically to obtain the critical buckling load of the system. Afterward, the normalized form of the results is presented to emphasize the impact of each parameter on the dimensionless buckling load of composite plates. It is worth mentioning that the effects of various boundary conditions are covered, too. To show the efficiency of presented modeling, the results of this article are compared to those of former attempts.

Vibration analysis of multi-scale hybrid nanocomposite plates based on a Halpin-Tsai homogenization model

An analytical answer to the natural vibration problem of a composite plate consisted of multi-scale hybrid nanocomposites, is presented here for the first time. In this paper, the constituent material of the structure is made of an epoxy matrix which is reinforced by both macro- and nano-size reinforcements, namely carbon fiber (CF) and carbon nanotube (CNT). The effective material properties like Young's modulus or density are derived utilizing a micromechanical scheme incorporated with the Halpin-Tsai model. To present a more realistic problem, the plate is placed on a two-parameter elastic substrate. Then, on the basis of an energy-based Hamiltonian approach, the equations of motion are derived using the classical theory of plates. Finally, the governing equations will be solved analytically to obtain the natural frequency of the system's oscillation. Afterward, the normalized form of the results will be presented to put emphasis on the impact of each parameter on the dimensionless frequency of nanocomposite plates. It is worth mentioning that the effects of various boundary conditions on the frequency of the plate are covered, too. To show the efficiency of presented modeling, the results of this article are compared to those of former attempts. Numerical results declare that plates fabricated from the hybrid nanocomposites can endure higher frequencies compared with those consisted of conventional composites.