Uniform Temperature Variation Research Articles

Design optimization of continuous fiber composites with thermo-mechanical coupling and load uncertainties

This paper introduces a theoretical framework for the design optimization of continuous fiber composites reinforced with continuous fiber trajectories subject to thermo-mechanical coupling and load uncertainties. Different uniform temperature variations are applied in the structure to investigate the influence of ambient temperature change on the structural performance. To consider the external load uncertainties, a robust design optimization model is proposed where the loads are modeled as hybrid variables, namely magnitudes as random variables and directions as interval variables, with the robust objective determined through a hybrid orthogonal polynomial expansion method. Furthermore, we use a level-set function to represent the structural boundary, with its evolution driven by shape derivatives calculated based on uncertainty analysis. The continuous fiber paths are subsequently determined by the level-set isoline extracted from the structural boundary, which in turn influences the structural mechanical performance due to the material anisotropy of composites. The continuity of continuous fiber and the equal space between adjacent trajectories largely ensure the additive manufacturability of the composites. Three numerical examples are presented to demonstrate the effectiveness of the developed framework. The results show that the ambient temperature variations and load uncertainties largely impact the optimized topology and fiber infill patterns of composites, thus are important to be considered in the design stage. Moreover, the optimized structure can have a 5-fold stiffness per unit mass compared with the initial design thus largely increasing the material efficiency in carrying external uncertain loads.

EFG meshless-ANN approach for free vibration analysis of functionally graded material plates on elastic foundation in thermal environments

This study focuses on free vibration analysis of functionally graded material (FGM) plates supported by Winkler–Pasternak elastic foundation in thermal environment using element-free Galerkin (EFG) meshless method. Plate kinematics depend on first-order shear deformation theory. Uniform, linear, and nonlinear temperature variations through the thickness direction are considered, along with the temperature-dependent material properties. The numerical outcomes obtained from EFG method are compared with those available in the published literature to validate the proposed method’s accuracy. An artificial neural network (ANN) model that can easily predict the natural frequencies of the plate is constructed from the EFG method outcomes. Further, the effect of foundation parameters, power law index, thickness ratio, temperature variations, and different boundary conditions are investigated; results show that these significantly influence the vibration response of FGM plates supported by the elastic foundation. Increasing the temperature of FGM plates supported by the Winkler–Pasternack foundation causes a decrease in the dimensionless fundamental natural frequency, and the uniform temperature influence is greater than that of linear and nonlinear temperature variation. The proposed EFG-ANN prediction model saves approximately 98.80% computation time when predicting the natural frequency with an accuracy of approximately 98.76% compared to that by EFG meshless method alone.

Stochastic FEM-based thermal buckling of SMA fiber-reinforced composite laminated plate using polynomial chaos

This research investigates the statistics in terms of mean and coefficient of variance of thermal buckling temperature of shape memory alloy (SMA) fiber-reinforced composite laminated plate using polynomial chaos (PC). The basic mathematical formulation is adopted based on Co finite element method (FEM) in conjunction with secant function-based shear deformation theory. The uncertain input system properties in material and geometrical parameters are modeled as random variables. The effects of SMA fiber and location, pre-strain, loading, modes, temperature distribution, modulus ratio, fiber orientation, length-to-thickness ratio, aspect ratio, and various boundary conditions on the statistics of critical temperature are analyzed. The small amount of random change in input system parameters significantly affects the variance and reliability of SMA fiber-reinforced composite laminated plate thermal buckling temperature under uniform and non-uniform temperature variations. The present PC simulation’s results are compared with independent Monte Carlo simulation and those existing in the literature.

Comparison of Local Mean Age of Air between Displacement Ventilation System and Mixing Ventilation System in Office Heating Conditions during Winter

A novel displacement ventilation system (DVS) was designed using a four-way cassette fan coil unit (FCU) and air purifiers (APs) for supplying clean air. The proposed DVS in this study involved drawing indoor air through the FCU and diffusers installed in the ceiling, controlling air temperature using the FCU, and then discharging it back into the office through the APs placed on the floor. The comparative ventilation system considered was the typical mixing ventilation system (MVS) that intakes and exhausts indoor air using diffusers installed on the ceiling. The local mean age of air was used as an index to compare indoor air quality between DVS and MVS under winter heating conditions. It was found that the DVS was more effective in improving indoor air quality in winter than the MVS. Moreover, compared to the MVS, utilizing the DVS designed in this study resulted in the advantage of a much more uniform air temperature variation in the office space. Therefore, it is anticipated that modifying the structure of an indoor space with an FCU installed in the ceiling and APs on the floor to use the DVS designed in this study would greatly assist in enhancing indoor air quality.

Experimental Study on Thermal Management of Nano-Enhanced Phase Change Material Integrated Battery Pack

Abstract In recent years, lithium-ion batteries (LIBs) have gained attention and popularity due to their extended cycle life and high energy density. A hexagon-shaped 18,650 lithium-ion cylindrical cell battery pack was designed, incorporating paraffin wax (PA) as a phase change material (PCM) and nano-enhanced phase change material (Ne-PCM). However, the low thermal conductivity of the PCM causes a significant challenge to the development of electric vehicles (EVs). The highest temperature in the cylindrical cell battery pack is reached in the midregion, leading to an uneven temperature distribution across the cells. To overcome these challenges and achieve efficient battery module performance, phase change with nanomaterials such as graphene platelet nanopowder (GPN), multiwalled carbon nanotubes (MWCNTs), and graphite-synthetic powder (GSP) was placed in the center of four cells. Studies on the battery module were conducted without cooling, with PCM cooling, and with Ne-PCM cooling. The investigation revealed that the battery pack with Ne-PCM performed well, maintaining the temperature below 50 °C at different discharge rates of 1C, 2C, and 3C, and ensuring a uniform temperature variation within the cells. Ne-PCM decreased the temperature differential between the modules at 1C, 2C, and 3C discharge rates by 85.49%, 91.47%, and 84.21%, respectively, compared to PCM.

Electromechanical analysis of a piezoelectric semiconductor bilayer system with imperfect interface

An electromechanical model of the bilayer structure consisting a piezoelectric semiconductor film and an elastic substrate with imperfect interface is established. The combined effects of piezoelectricity and flexoelectricity are taken into consideration simultaneously. Based on the Newmark model, closed-form expressions for the distributions of electron concentrations and relevant electromechanical fields in the bilayer composite beam system subjected to uniform temperature variation are obtained. The effects of interfacial parameter, flexoelectricity and initial carrier concentration have been discussed respectively. Different from the bilayer structure with perfect interface, it can be found that interfacial parameter plays a significant role in the electromechanical coupling characteristics of the bilayer system. Besides, the effect of flexoelectricity weakens the influence of imperfect interface to some extent. This research offers a new sight and guidance for practical applications of piezoelectric semiconductor multilayer systems.

Thermal buckling and postbuckling of functionally graded multilayer GPL-reinforced composite beams on nonlinear elastic foundations

Under the influence of axial forces and uniform temperature variations, the thermal buckling and postbuckling of composite beams reinforced of functionally graded multilayer graphene platelets (GPLs) resting on nonlinear elastic foundations are examined. The Halpin-Tsai model is used to calculate the elastic modulus of each layer of GPL-reinforced composite (GPLRC). According to the virtual work principle, the nonlinear governing equations for the beam are obtained from the first-order shear deformation beam theory. The impact of axial force and nonlinear elastic foundation on thermal buckling and postbuckling is discussed using the differential quadrature method (DQM), and the analytical expression is given by the two-step perturbation method (TSPM). The effects of axial force, boundary conditions, slenderness ratio, GPL geometry, GPL weight fraction, GPL distribution pattern, and elastic foundation coefficient on thermal buckling and postbuckling are examined through parameter analysis.

Optimizing electrode design to minimize thermal spread in radiofrequency-induced colonic anastomosis

Objective: To study temperature distribution in different electrodes and to evaluate thermal spread during colonic anastomosis induced by radiofrequency energy through finite element modeling, aiming to provide the basis for optimizing the design of new electrodes with improved effectiveness of electrosurgical welding. Methods: Three electrodes with the feature of concave-convex (CC), rail coupled concave-convex (rail-CC), and cross rail coupled concave-convex (cross rail-CC) were designed for radiofrequency-induced serosa-to-serosa colonic anastomoses to evaluate the thermal spread process by finite element modeling using COMSOL Multiphysics. Parameters used in the modeling were set with a peak voltage of 45 V, a duty cycle of 10% and a repetition rate of 1 s. Additionally, a three-dimensional finite element model of the cross rail-CC electrode was further constructed to compare temperature variation and distribution when the voltage Fwas applied to ridges of upper electrode alternately. Results: The electrode with CC design produced similar temperature between 'gap' and 'compressed' areas, whereas the electrode with rail-CC design exhibited the highest temperature at 'gap' and 'compressed' areas compared with those with CC and cross rail-CC designs. Moreover, the cross rail-CC electrode, by tightly occluding the upper and lower electrodes, could create uniform compression and temperature variation. When electric voltage was applied to ridges of upper electrode of the cross rail-CC electrode alternately, the temperature at 'gap' was half of that at the 'compressed' section, which was comparable to the temperature at 'compressed' area in the rail-CC electrode (p=0.241). Conclusion: Alternating application of voltage to ridges of upper electrode of the cross rail-CC electrode can potentially produce an optimal fusion zone by reducing thermal damage with low 'gap' temperature while keeping the 'compressed' temperature high.

On the thermal stresses in chiral porous elastic beams

This paper is concerned with the strain gradient theory of porous thermoelastic solids. We study the deformation of isotropic chiral cylinders subjected to a temperature field that is linear in the axial coordinate. It is shown that the solution can be reduced to the study of two-dimensional problems. The results are used to investigate the deformation of a circular cylinder subjected to a uniform temperature variation. In contrast to the case of achiral materials, the thermal field in chiral cylinders produces torsional effects.

Statistical channel modeling of intensity fluctuations in a turbulent underwater wireless optical communication system

Subject of study. The statistical modeling of received intensity fluctuations due to temperature-induced turbulence and the random presence of air bubbles in an underwater wireless optical communication channel is presented. Aim of study. Temperature-induced turbulence and air bubbles induce severe intensity fluctuations in the received optical signal, which degrade the underwater wireless optical communication link performance. Method. Therefore, to characterize the turbulent water channel, an experimental setup has been designed in the laboratory that considers uniform and gradient-based temperature variations along with variable-sized bubble populations. To estimate the effect of these random variations in the water channel, a statistical approach has been followed, which characterizes the nature of the recorded observations. Main results. It is observed that the behavior of random irradiance fluctuations due to uniform and gradient-based temperature variations in the underwater wireless optical communication link follows a single-lobe Gaussian distribution. Moreover, with the incorporation of air bubbles, the received irradiance fluctuations no longer follow a single-lobe Gaussian distribution but follow a multi-lobe Gaussian distribution, i.e., the Gaussian mixture model, which is the weighted sum of the Gaussian distribution. The accuracy of the proposed underwater wireless optical communication link models is verified by conducting the goodness of fit test; the observed confidence interval of 95% authenticates the proposed model. Also, the performance of the Gaussian-mixture-model-based underwater wireless optical communication link has been evaluated in terms of bit error rate, and the acceptable bit error rate levels between 1014 and 1010 have been observed. The proposed underwater wireless optical communication with Gaussian mixture model completely depicts thermally uniform, gradient-based nonuniform, and variable air bubble populations in the ocean. Practical significance. The Gaussian mixture model can further be utilized by the researchers to estimate numerous performance parameters of the turbulent underwater wireless optical communication links using advanced modulation schemes and diversity techniques and paves a valuable way to address the future aspects of research in this area.

Solute dispersion phenomena in a free and forced convective flow with boundary reactions

The applications of solute dispersion in a free and forced convective flow are highly important in the diversified fields of chemical industries, nuclear power plants, etc. In the present work, the dispersion of tracers between two parallel plates in a combined free and force convective flow under the effect of wall absorption and bulk chemical reaction is explored using Mei’s multi-scale homogenization method. A uniform temperature variation is considered along both the plates. The main focus of this study is to investigate the effect of the Grashof number not only on Taylor diffusivity but also on the longitudinal and transverse concentration distribution. The effects of the boundary absorption and bulk chemical reaction in presence of the Grashof number are analyzed. The most interesting fact of this study is that the Taylor dispersivity is equal for both the positive and negative Grashof number i.e. for heating and cooling respectively. Also, the longitudinal concentration of solute reduces when both the process of cooling and heating increases. But the opposite scenario arises in the case of transverse concentration distribution. The results of the present study may be applied to waste management systems in chemical industries.

Influence of uniform temperature variations on hybrid bonded joints with a circular or tubular cross-sectional area

The use of lightweight structures is a current concern in several engineering domains. To obtain such types of structures, the bonding technique using Carbon Fibre-Reinforced Polymers (CFRP) has been most recently considered a primary option. If CFRP is known to have a high strength-to-weight ratio or high corrosion resistance, the bonding technique does not need to add other fixation components and it also prevents stress concentrations. However, when combined with, e.g. a metallic surface, the high difference between the thermal expansion coefficient of the CFRP composite and the metallic material may raise some issues when the adhesively bonded structure is subjected to thermal loading. Therefore, the present work presents an analytical model that facilitates the comprehension of the impact of temperature on a hybrid bonded joint with a circular or tubular cross-sectional area. The full debonding process of a double but bonded joint with a regular curvature is discussed thoroughly. Due to the susceptibility of current adhesives to lose their mechanical properties for relatively high temperatures, the vitreous transition temperature of the adhesives and their influence on the local adhesive model is considered in a deeper analysis. The Finite Element Method (FEM) was used to validate all the derived analytical equations, which were achieved due to the close predictions obtained from both ways, i.e. from the numerical simulations and the proposed closed-form solutions.

Multi-Material Topology Optimization of Thermo-Elastic Structures with Stress Constraint

This paper proposes a multi-material topology optimization formulation for thermo-elastic structures considering coupled mechanical and uniform thermal loads. The ordered-SIMP multiple materials interpolation model is introduced, combined with examples considering structural volume minimization under stress constraints. The p-norm function with the adjusted coefficient was adopted to measure the global maximum stress. The adjoint variable method is presented to discuss the sensitivity of stress constraints, and the method of moving asymptotes (MMA) is utilized to update the design variables. The results demonstrate that clear topologies are obtained for complicated multiple material combinations with various temperature values. Meanwhile, the optimized configuration with stress constraints has clear sensitivity to uniform temperature variations. Therefore, the proposed model demonstrates the necessity of a thermo-elastic model influenced by temperature in optimization.

Forced vibration characteristics of sandwich panel with GRPC faces and titanium core under thermal environment

In this paper forced vibration characteristics of a graphene reinforced polymer composite face sheet sandwich panel with a homogeneous core exposed to non-uniform temperature variation is studied. Carbon based materials are highly used in aerospace applications. Further these materials are exposed to different environmental conditions which alters it dynamic characteristics. So, in this paper thermal buckling and forced vibration behavior are studied for different grading patterns, temperature dependent properties and non uniform temperature variation. Here, uniform temperature profile, decreasing temperature profile - heating at one edge, decreasing and increasing temperature profile - heating at two edges, increasing and decreasing temperature profile - heating at middle and camel hump temperature - heating at Centre location of the panels are considered. From the results, it is observed that the temperature distribution at 95% of buckling temperature has reduced the natural frequencies significantly and in the forced vibration response, the sandwich panel in this condition shifts its response curve to the left irrespective of the grading pattern. Further, it is noticed that the velocity response curve of FG-X grading pattern has shifted more compare to UD and FG-O grading pattern.

Flexural wave dispersion characteristics of imperfect Ti-6Al-4V foam circular cylindrical shells in a thermal environment

The present paper is mainly focused on analyzing the flexural wave dispersion of imperfect Ti-6Al-4V foam circular cylindrical shells in a thermal environment. The pores were supposed to be distributed across the thickness (z-direction) in the form of three different patterns as follows: symmetric porosity distribution (SPD), asymmetric porosity distribution (ASPD) and uniform porosity distribution (UPD). Besides, various kinds of temperature variations, including sinusoidal, linear and uniform temperature variations, were studied. The strain-displacement relationship of the shell was derived based on the first-order shear deformable theory (FSDT) of shells. Hamilton’s principle was also applied to obtain the governing equations of metal foam shells which were then solved using an analytical method. Finally, influences of different parameters including circumferential wave number, different kinds of temperature variation, temperature change, radius to thickness ratio , types of porosity distribution across the thickness, porosity coefficient and mode number on the variations of phase velocity and wave frequency were investigated and the results were illustrated and discussed.

A coupled nonlinear plate finite element for thermal buckling and postbuckling of piezoelectric composite plates including thermo-electro-mechanical effects

This paper investigates the thermo-electro-mechanical effects in the nonlinear response of piezoelectric laminated plates exposed to thermal and/or mechanical fields. The mechanics incorporate a) the direct piezoelectric effect through the coupling between electric-mechanical fields, b) the pyroelectric effect through the coupling between electric-thermal fields, and c) the geometric nonlinear effects due to large rotations and initial stresses. Building upon the nonlinear multifield mechanics an eight-node plate finite element is developed to discretize the generalized coupled nonlinear equations, which are subsequently linearized and iteratively solved, using the Newton-Raphson technique. Numerical evaluations demonstrate the capability of the present model to capture both of direct piezoelectric and pyroelectric effects in the nonlinear electromechanical response of piezoelectric composite plates, exposed to thermal and/or mechanical fields. The influence of direct piezoelectric and pyroelectric effects on thermal buckling and postbuckling response of various piezocomposite plates, is investigated. The possibility of pyroelectric effect to promote thermal buckling of piezocomposite plates with attached sensor patches is also quantified. The influence of thermo-electro-mechanical effects on the nonlinear response of smart composite plates, subject to either uniform or gradient temperature variations is finally illustrated.

RETRACTED: Thermal mechanical coupling analysis of two-dimensional decagonal quasicrystals with elastic elliptical inclusion

In this paper, the thermal mechanical coupling problem of an infinite two-dimensional decagonal quasicrystal matrix containing elastic elliptic inclusion is studied under remote uniform loading and linear temperature variation. Combining with the theory of the sectional holomorphic function, conformal transformation, singularity analysis, Cauchy-type integral and Riemann boundary value problem, the analytic relations among the sectional functions are obtained, and the problem is transformed into a basic complex potential function equation. The closed form solutions of the temperature field and thermo-elastic field in the matrix and inclusion are obtained. The solutions demonstrate that the uniform temperature and remote uniform stresses will induce an internal uniform stress field. Numerical examples show the effects of the thermal conductivity coefficient ratio, the heat flow direction angle and the elastic modulus on the interface stresses. The results provide a valuable reference for the design and application of reinforced quasicrystal materials.

Post-buckling nonlinear analysis of sandwich laminated composite plate

Thermal post-buckling analysis of sandwich composite plates has been presented with the incorporation of shape memory alloy (SMA) under uniform temperature distribution by higher order shear deformation theory (HSDT) with von Karman nonlinear kinematics by finite element method (FEM) in MATLAB environment. The validity of the present utilized model is checked by performing validation study also convergence study has been done to select the mesh size to compute the results without affecting the results. Study clearly defines effect of layer variation, layup sequence, uniform temperature variation, and aspect ratio under different boundary conditions (BC) over nondimensional critical buckling temperature (NCBT). Study also clearly indicate the effect of the SMA volume fraction under different ply sequence over NCBT of sandwich composite plate.

Wave propagation analysis of thermoelastic functionally graded nanotube conveying nanoflow

As a hollow cylindrical structure, a nanotube has potential to convey nanoflow, which has opened up a field of research. Functionally graded nanotube as a designable structure with continuous variation of material properties can perform better than uniform nanotube, especially in physical field without introducing large stress concentration. In this article, we take the thermal effect into account and investigated the wave propagation characteristics of functionally graded material nanotube conveying nanoflow. In particular, we compared the effects of different kinds of volume fraction function and also the cases of uniform and nonuniform temperature variation. According to the numerical results, we can conclude that as we decrease the exponent n of the volume fraction function, the system is enhanced and larger enhancement can be observed in the case of the power volume fraction function. In addition, there is a positive correlation between the stability and both the temperature variation and the nonuniformity of temperature variation.

Flexoelectric effects on dynamic response characteristics of nonlocal piezoelectric material beam

Flexoelectric effect has a major role on mechanical responses of piezoelectric materials when their dimensions become submicron. Applying differential quadrature (DQ) method, the present article studies dynamic characteristics of a small scale beam made of piezoelectric material considering flexoelectric effect. In order to capture scale-dependency of such piezoelectric beams, nonlocal elasticity theory is utilized and also surface effects are included for better structural modeling. Governing equations have been derived by utilizing Hamilton's rule with the assumption that the scale-dependent beam is subjected to thermal environment leading to uniform temperature variation across the thickness. Obtained results based on DQ method are in good agreement with previous data on pizo-flexoelectric beams. Finally, it would be indicated that dynamic response characteristics and vibration frequencies of the nano-size beam depends on the existence of flexoelectric influence and the magnitude of scale factors.