Length Scale Factor Research Articles

Poroelastic size dependent dynamics of viscoelastic microbeams connected via a viscoelastic layer

This article aims to investigate the dynamics of clamped-clamped porous viscoelastic double microbeams interconnected via a viscoelastic layer within the framework of the modified couple stress theory (MCST). Different types of porosity distributions are considered to examine the material imperfection effects on the dynamics of the double microbeam. A closed-cell porosity model is employed to model the variation of the material properties in the thickness plane. The coupled longitudinal and lateral equations of motion are derived using Hamilton’s principle. The governing equations of motion are solved using the modal decomposition method. The equations of motion are verified against the literature for simplified cases (i.e., a non-porous single viscoelastic microbeam and a porous single microbeam resting on a viscoelastic foundation). The numerical results are validated for simpler versions of the system using the finite element method and against the existing literature for a simplified case of a uniformly distributed porous double macrobeam connected via an elastic layer. Influences of viscoelasticity in the double microbeam, viscoelastic layer, porosity, and small-scale influences on the dynamics of the viscoelastic double microbeams are studied. It was found that increasing the material length-scale factor causes the complex fundamental lateral vibrational frequencies to increase for all the porosity patterns.

The impacts of variable nonlocal, length-scale factors and surface energy on hygro-thermo-mechanical vibration and buckling behaviors of viscoelastic FGP nanosheet on viscoelastic medium

The impacts of variable nonlocal, length-scale factors and surface energy on hygro-thermo-mechanical vibration and buckling behaviors of viscoelastic FGP nanosheet on viscoelastic medium

Degradation of signal-to-noise ratio due to turbulence in various biological tissues

When a biological tissue is excited by an optical beam, the presence of turbulence in the tissue causes the signal-to-noise ratio (SNR) to degrade. This degradation is in reference to the SNR value in the absence of tissue turbulence. The effect of tissue turbulence in reducing the SNR is examined. SNR reductions are examined for various types of biological tissues such as liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human). Also, SNR reductions in the turbulent tissue are evaluated against the changes in the strength coefficient of the refractive-index fluctuations, fractal dimension, characteristic length of heterogeneity, small length-scale factor, tissue length, wavelength and the source size.

Electroelastic wave dispersion in the rotary piezoelectric NEMS sensors/actuators via nonlocal strain gradient theory

This article introduces a computational means for investigating the electroelastic nonlinear wave dispersion traits of the nano-dimension sandwich pipe, which is composed of a core formed of a bi-directional functionally graded (Bi-FG) material, together with a piezoelectric sensor/actuator. A combination of Hamilton’s principle, first-order shear deformation, along with Von-Karman nonlinearity, is used for modeling and obtaining the nonlinear governing equations of the nano-sized sandwich pipe connected to a piezoelectric part. The nonlinear governing equations to obtain the nonlinear phase velocity of the current system are determined using a combination of analytical and multiple scales approaches. Due to some computational cost for choosing the precise values of both the nonlocality factor and length scale of the nanopipe in the laboratory, for the first time in this research, with the aid of COMSOL multi-physics finite element simulation, the results are verified, and new outcomes for obtaining the exact functions for nonlocal and length scale factors is presented. In addition, an artificial neural network (ANN) is utilized in this study for the prediction of the results. The mathematical and finite element results were used to train the ANN. A newly presented optimization algorithm is exploited for the first time for optimizing the ANN parameters concluding higher accuracy of the ANN predictions. Consequently, to explore the influences of the location of the piezoelectric patch, nonlocality and length scale factors, and applied voltage parameter on the phase velocity characteristics of the nano-dimension sandwich pipe made of a Bi-FG core and electrically patch, an effort is performed. As an applicable result that can be useful in the related nano-industries, the current work presents exact nonlocal and length scale functions for different conditions.

A new multiscale Cosserat model for size effect simulation in granular media

The Cosserat continuum, which contains a length scale factor l reported to link with the material’s grain size, is seemingly reasonable to describe the size effect of granular media. However, the physical meaning of l is still unclear, and its potential in describing the size effect is seldom studied. In this work, the performance of the conventional Cosserat model in capturing the size effect of granular media is firstly assessed. A new multiscale Cosserat constitutive model with an additional higher-order internal length scale vector Dq is then proposed based on the conventional Cosserat theory. The advantage of the proposed multiscale Cosserat model in size effect simulation for granular media is discussed through numerical simulations of centrifuge slope experiments and triaxial compression tests. The analysis results denote that the multiscale Cosserat continua are more sensitive to size effect than the conventional Cosserat continua, and the length scale vector Dq is like a symmetry-breaking factor that can trigger asymmetric deformation in structures; the influences of length scale factor l and Dq are seemingly opposite on stress concentration. This subtly improved constitutive model has the potential to simulate the size effect of a wider variety of materials.

Investigation of guided wave propagation in nanoscale layered periodic piezoelectric plates based on Eringen's nonlocal and strain gradient theory

This paper investigates the dynamic propagation behavior of guided waves in nanoscale media composed of alternating layers of piezoelectric phases. The study employs Eringen's nonlocal and strain gradient theories to derive equations for symmetric wave propagation and the scattering relations of guided waves perpendicular to these structures. Dispersion curves are calculated and plotted to compare these theories, considering the influence of nanoscale size-effect, volume ratio of constituent layers, and material length scale. Using the strain gradient theory, the paper explores the impact of length scale parameters on the propagation behavior of horizontally polarized guided waves in an alternating layer structure of nanoscale piezoelectric material, specifically nanoscale piezoelectric laminates. The analysis involves calculating localization factors and dispersion curves to analyze the effects of size-effect and length scale parameters on wave propagation and band structures. Additionally, the study plots and analyzes changes in mechanical displacement and electrical potential, followed by an investigation and discussion of nanoscale size effects and the effects of the material's length scale parameter on dispersion curves and conversion modes within specific regions. The results highlight that the length scale effect parameter significantly impacts the mode conversion zones and band gap structures, more so than the NLPE continuum theory suggests. As the strain gradient parameter increases, these zones shift towards higher wavenumbers and to the right . Furthermore, introducing the length scale factor results in a substantial decrease in both the formation of conversion zones and the density of dispersion curves.

Application of multi-directional FG material to improve natural frequencies of perovskite solar cells under mechanical shock validated by deep-learning approach

In order to generate electricity from sunlight, spacecraft that operate within the inner solar system often utilize photovoltaic solar panels that are controlled by power electronics. For this purpose, the emerging technologies of perovskite solar cells (PSCs) have attracted plenty of attention recently. Improving the stability of this kind of cell is the main purpose of this research. In the current work, for the first time, dynamic stability analysis of the PSCs, including the multi-directional functionally graded (MD-FG) layer as the host layer, is presented. Also, due to the complex situation of solar cells, this kind of system may be under mechanical shock loading. Various types of PSCs, including cylindrical, spherical, and hyperbolic paraboloid solar cells, by changing curvature factors are modeled. For considering the size-dependency of the PSCs, modified couple stress theory (MCST) with one length scale factor on the strain energy is presented. The forced vibration caused by mechanical shock loading is illustrated by inverting the Laplace transform using the fully modified representation of Abate and Dubner’s solution. A deep neural network (DNN) with independent variables, hidden, input, and output layers, intrinsic neural network parameters, activation function, hidden neurons, and loss function is offered to train the current appropriate structure once the results of mathematical modeling have been obtained. Finally, by applying the two-dimensional differential quadrature method (2D-DQM) as an accurate integral operator, the discretized motion equations can be derived from the weak form of the equations. Finally, in the results section, some suggestion for improving the stability and frequency of the PSCs is discussed.

Correlations of multimode optical incidences in a turbulent biological tissue.

In a turbulent biological tissue, field correlations at the observation plane are found when a multimode optical incidence is used. For different multimode structures, variations of the multimode field correlations are evaluated against the biological tissue turbulence parameters, i.e.,the strength coefficient of the refractive-index fluctuations, fractal dimension, characteristic length of heterogeneity, and the small length-scale factor. Using a chosen multimode content, for specific biological tissue types of liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human), and deep dermis (mouse), field correlations are evaluated versus the strength coefficient of the refractive-index fluctuations and small length-scale factor. Again, with a chosen multimode content, behavior of the field correlations is studied against the strength coefficient of the refractive-index fluctuations for various diagonal lengths and the transverse coordinate at the observation plane. Finally, the field correlation versus the strength coefficient of the refractive-index fluctuations is reported for different single modes, which are special cases of multimode excitation. This topic is being reported in the literature for the first time, to our knowledge, and the presented results can be employed in many important biological tissue applications.

Data-driven solution for supersonic aerodynamics analysis of Perovskite solar cells considering the velocity of sound and Mach number

Due to the use of Perovskite solar cells (PSC) in aerospace applications, so, in this work for the first time, aerodynamic flutter and vibrational analysis of PSC are presented. For modeling the PSCs aerodynamic motion in the mathematical domain, the variational differential quadrature (VDQ) technique is used as a numerical operator for the discretization of various domains. Also, due to improving the stability of the PSC, carbon nanotubes with various distribution patterns as the reinforcement of the metal layer are presented. In this work for modeling the aerodynamics behavior, we use Krumhaar’s modified supersonic piston theory incorporating curvature influence, to simulate the aerodynamic stiffness and damping matrices. Also, for modeling the size effect, a modified couple stress theory with only one length scale factor is suggested. Data-driven solution with the aid of deep neural network with independent variables, input, hidden, and output layers, activation function, neural network’s intrinsic parameters, loss function, and hidden neurons is presented to solve the current applicable structure. The results show that the stability of the system is substantially impacted by the value of the yaw angle, and the link between Mach number and stability is heavily reliant on the value of the yaw angle. Another important outcome is that designing a spherical PSC and increasing its stability should have special attention to the a/b parameter. Also, future engineering research should have special attention that spherical solar cell has the highest natural frequency than other types of solar cells. Other important outcomes of the innovative PSC are presented in the results section for future handbooks on solar cells as sustainable energy.

Assessment of experimental methods for measurements of the horizontal flow of fluidized solids under bubbling conditions

Dual fluidized bed systems are indispensable for future energy systems that require solids cycling between different atmospheres. However, controlling the residence time of solids in the reactor, which is crucial for controlling the heat and mass transfer of the fuel, is a significant challenge. This study investigates four experimental techniques to quantify the horizontal flow of solids fluidized under bubbling conditions: integral mass accumulation; differential mass accumulation; thermal tracing; and magnetic solids tracing. Integral mass accumulation entails collecting bed material using a defluidized box within a given time period. Differential mass accumulation measures the material accumulation rate in a section of the bed that is monitored using pressure measurements. Thermal tracing calculates the solids flow rate by solving the heat balance to match the temperature field captured by a thermographic camera. Magnetic solids tracing involves injecting a batch of magnetic tracer solids into the reactor and then measuring the residence time distribution using impedance coils.The experiments were conducted under down-scaled conditions that resemble large-scale operations with a length scaling factor of 0.12. For this study, three operational parameters were varied: the fixed bed height; the volumetric flow rate of the conveying air; and the fluidization velocity in the bed. The horizontal solids circulation rates achieved ranged from 1.7×10−4 to 10 kg/m·s, corresponding to 1.2×10−3 to 70 kg/m·s on a hot up-scaled basis, which is a relevant range to indirect biomass gasification in an industrial setting.The three selected operational parameters led to increases in the horizontal solids flow. While all four methods replicated the trends, quantitative variations in the measured circulation rates occurred due to the inherent characteristics of the methods. High circulation rates resulted in a continuous decrease in the solids inventory, leading to an underestimation of the circulation rate when using the integral mass accumulation method. The accuracy of the differential mass accumulation method relied on transient pressure measurements, which were less-effective at low solids flow rates. Conversely, the accumulation time required for pressure measurements was reduced at high circulation rates, resulting in uncertainties in the analysis. The accuracy of the thermal tracing method decreased drastically with higher solids circulation, resulting in an overestimation of the circulation rate. Moreover, low circulation rates adversely affected the accuracy of the magnetic solids tracing by producing barely discernible tracer concentration gradients.

Application of Radar Radial Velocity Data Assimilation in the Forecasts of Typhoon Linfa Based on Different Horizontal Length Scale Factors

In order to explore the improvement of radar radial velocity data assimilation on the initial and forecast fields of typhoons, this study assimilates the quality-controlled radial velocity data in the case of Typhoon Linfa (2015) using the three-dimensional variational data assimilation system of the weather research and forecasting model (WRF-3DVAR), and then conducts several sensitivity experiments with different horizontal length scale factors. The results show that reducing the horizontal length scale factor of the background error covariance can effectively assimilate the micro- and meso-scale information from radar data and improve the forecasting effect of Linfa. Following the optimization of the horizontal length scale factor, the radial velocity data assimilation can improve the typhoon wind field structure, produce reasonable cyclonic wind field increments, and further improve the dynamic and thermal structure of the inner core area of the typhoon. Then, we can obtain a better initial field of model forecasting, and thus typhoon track and intensity forecasting are improved.

Wind characteristics in typhoon boundary layer at coastal areas observed via a Lidar profiler

Information about typhoon wind characteristics provides a basis and is a prerequisite for conducting anti-typhoon studies and practices. Despite the great efforts and active exploration made in the field of typhoon measurements using various equipment over the past decades, how to effectively obtain both the mean and fluctuating components of typhoon wind especially within the atmospheric boundary layer around the inner region of the storm still remains as a challenge. In recent years, Lidar wind profilers have been attracting increasing attention and showing great promise owing to their advantages, such as wide detection range, high sampling frequency, handiness, and flexible layout. However, the results for turbulent wind components using Lidar wind profilers tend to be biased due to the intrinsic spatial average in remote sensing detection. In view of the above, this paper explores the use of the Lidar wind profiler to conduct legitimate measurements of typhoon averages and fluctuating wind field characteristics. Firstly, wind field measurements in the inner regions of two typhoons were successfully captured during their passage with the flexible deployment of equipment in coastal areas. Based on the data obtained, the mean wind field characteristics of the typhoons were examined during different transitional stages and under different exposure conditions, with a focus on the influence of inner boundary layer on the vertical wind speed profile and its key parameters, such as surface roughness and zero-plane displacement. A method based on a wind spectrum model is proposed to correct the typical fluctuating wind field parameters, which include turbulence integral length scale, turbulence intensity, and gust factor. The difference between these wind turbulence parameters before and after the correction was significant, but the corrected results were in better agreement with similar existing results, reflecting the necessity and validity of the correction work. The presented results are expected to be helpful for further understanding of the wind characteristics in the middle and upper portions of typhoon boundary layer, and contribute to the development of using Lidar profiler for observing wind turbulence.

Structure functions for optical waves in a complex medium of turbulent biological tissues.

Although optical wave propagation is investigated based on the absorption and scattering in biological tissues, the turbulence effect can also not be overlooked. Here, the closed-form expressions of the wave structure function (WSF) and phase structure function (PSF) of plane and spherical waves propagating in biological tissue are obtained to help with future research on imaging, intensity, and coherency in turbulent biological tissues. This paper presents the effect of turbulent biological tissue on optical wave propagation to give a perception of the performance of biomedical systems that use optical technologies. The behavior of optical waves in different types of turbulent biological tissues such as a liver parenchyma (mouse), an intestinal epithelium (mouse), a deep dermis (mouse), and an upper dermis (human) are investigated and compared. It is observed that turbulence becomes more effective with an increase in the characteristic length of heterogeneity, propagation distance, and the strength of the refractive index fluctuations. However, an increase in the fractal dimension, wavelength, and small length scale factor has a smaller turbulence effect on the propagating optical wave. We envision that our results may be used to interpret the performance of optical medical systems operating in turbulent biological tissues.

Field correlations of a partially coherent optical Gaussian wave in tissue turbulence.

For a partially coherent Gaussian optical wave, field correlations in turbulent tissues are examined. Changes in the field correlations are evaluated when the degree of source coherence, diagonal length from the receiver point, transverse receiver coordinate, tissue type, tissue length, source size, characteristic length of heterogeneity, strength coefficient of the refractive-index fluctuations, fractal dimension, and the small length-scale factor of the turbulent tissue vary. Investigated turbulent tissue types are liver parenchyma (mouse), upper dermis (human), intestinal epithelium (mouse), and deep dermis (mouse). For all the examined tissue types, field correlations are found to increase as the degree of source coherence, fractal dimension, and small length-scale factor increase and as the diagonal length from the receiver point, transverse receiver coordinate, tissue length, characteristic length of heterogeneity, and strength coefficient of the refractive-index fluctuations decrease. For the coherent source, an increase in the source size will increase the field correlations; however, for the partially coherent source, this trend is reversed.

Intensity fluctuations in biological tissues at any turbulence strength

This study investigates the intensity fluctuations of the optical plane and spherical waves in biological tissue that experience any strength of turbulence. Biological tissue is a random and complex medium for optical wave propagation, having a power spectrum reflecting the turbulent characteristics that depend on the structural parameters. It is important to accurately determine the strength of turbulence and classify turbulence regimes for the correct modeling of the behavior of the optical wave propagation. To classify weak, moderate and strong turbulent regimes, closed-form expressions of modified Rytov variances are obtained. Based on the modified Rytov variance that involves the large-scale and small-scale variations, the intensity fluctuations specified by the metric of scintillation index, are calculated versus various parameters such as the propagation distance, refractive index, characteristic length of heterogeneity, small length-scale factor, wavelength, fractal dimension and strength of the refractive index fluctuations. Behavior of optical plane and spherical waves in different turbulent regimes and the comparison of intensity fluctuations in different specimens of human and animal tissues are shown.

Design and testing of a model-scale yaw mechanism for an experimental wind turbine model

In this study a new yaw mechanism for a small existing wind turbine model is designed and tested. The special requirement for this yaw device is its compact design due to the small length scaling factor of the model turbine. Such a dense design is crucial in order for the wake of the model turbine not to be influenced by the yaw mechanism. Furthermore, it has to have a fast system response and high accuracy to take into account the time scaling. Different concepts are investigated and a design located at the tower base is realized. To limit its drag, the structure is being concealed in an aerodynamically shaped cover. Wind tunnel measurements confirmed that the wake of the turbine is not influenced by the structure. A system analysis, using a Simulink model of the turbine helps finding the right motor and shows that the device has a fast system response with high accuracy. Consequently, the designed yaw mechanism is suited for the small wind turbine model, which can be used for experimental wake and wind farm control studies in the future.

Adaptive optics correction of beam spread in biological tissues

Beam spread in turbulent biological tissues is examined when the tissue is excited with a collimated Gaussian laser beam. Adaptive optics correction is applied to the beam spread in the form of piston only (P Only), tilt only (T Only), piston+tilt (P+T), and the reduction in the beam spread is evaluated as compared to the no adaptive optics (No AO) corrected beam spread. No AO and adaptive optics corrected beam spread are expressed for various biological tissue types, against the variations in the strength coefficient of the refractive-index fluctuations, source size, small length-scale factor of turbulence, tissue length, fractal dimension, characteristic lengths of heterogeneity and the wavelength. For the examined tissue types of liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human) and deep dermis (mouse), No AO beam spread and the adaptive optics corrected beam spread are found to increase as the strength coefficient of the refractive-index fluctuations, tissue length, fractal dimension, the characteristic lengths of heterogeneity increase, and to decrease as the source size, small length-scale factor, wavelength increase. Reduction ratio of P+T correction is almost the same for all the evaluated cases which is 74%.

A line-based flash heating method for numerical modeling and prediction of directed energy deposition manufacturing process

The part-scale directed energy deposition (DED) process is often accompanied by sizeable thermal stress and deformation. It is of great significance to predict the residual deformation and stress of the large component produced by DED. In this paper, a line-based flash heating (LFH) method was proposed and used as the multi-scale law in the thermo-mechanical model of the DED process. The building parameters of the DED process, such as bead dimensions, overlap, and scanning strategies, can be well considered. A series of experimental validation was carried out. Model sensitives and essential resolution, including length scaling factor and bead scaling factor, were identified and characterized. The whole processes of depositing two part-scale samples with different scanning strategies were simulated. Different scaling strategies, including the hybrid scaling strategy, were used in the simulation for the 60-layer model. The results between the simulation and experiments are in good agreement. The recommended critical values of length scaling factor and bead scaling factor are 312 and 0.2, respectively, when defining the critical value of prediction error as 10%. For the two part-scale models, the prediction error of the maximum residual deformation is less than 10% when using the bead scaling strategy with recommended scaling factors. Compared with the layer scaling technique, the hybrid scaling strategy improves the accuracy of prediction and controls the cost of calculation. This work provides a flexible multi-resolution framework for modeling the DED process and an important tool for further understanding the complex thermo-mechanical behaviors in the large DED component.

Signal intensity of the random freeze beam in the biological turbulent tissue

Developing the signal intensity model for random freeze beams, which is an absorption- and diffraction-resistance beam, in the biological turbulent tissue, we investigate the signal intensity evolution of the random freeze beam as the function of the number of the superposition beam, beam waist, the topological charge of vortex modes, the fractal dimension, small length-scale factor, characteristic length of heterogeneity and the constant of refractive-index fluctuation of the tissue. The biological turbulent tissues include frozen human liver sections and the oxygenated (>99%) blood. The results are as follows: the signal transmittance of RF beam is greater than that of the BG beam. The impact of fractal dimension, the constant of refractive-index fluctuation, small length-scale factor and the natural length of heterogeneity on random freeze beam in the oxygenated (>99%) blood is similar to those in frozen human liver sections. The higher the number of superposition sub-beam, the larger the beam waist and the smaller the topological charge can efficiently improve the propagation performance of random freeze beams.

A new nonlinear finite element model for transient dynamic response of a micro composite plate embedded with micro SMA wires considering the size effects

In this research, a nonlinear dynamic analysis of micro plate containing micro shape memory alloy (SMA) wires, taking into account the material and geometric nonlinear effects and also considering the instantaneous changes of martensitic volume fraction (MVF) in different points of the micro plate, has been investigated. In this study, using the first-order shear deformation theory (FSDT) and applying Hamilton's principle, the governing equations of micro plate are extracted such the kinematic equations of micro SMA wires are coupled with governing equations. In this regard, von Karman nonlinear strain-displacement relation is used to consider large displacements and the model proposed by Hernandez and Lagoudas is employed to model the pseudoelastic behavior and also to capture the size effect of the SMA wires at micro scale. The modified couple stress theory is also employed to consider the size effect on the matrix material of micro plate. In addition, it is assumed that the micro wires are arranged in FG forms in the direction of the thickness of the micro plate. Using the return mapping algorithm and nonlinear finite element method, the governing equations of motion, are solved. In the results section, the study of parameters such as size effects, different boundary conditions, taking into account nonlinear strain field, diameter change and type of arrangement of micro SMA wires, length scale factor and thickness of micro plate, have been implemented. To evaluate the validity of the present work, some of the results are compared with the articles available in the literature. New results show that the bigger diameter of the micro SMA wires (considering the total volume fraction constant) and the smaller length scale factor, the higher damping ratio of the micro plate is obtained. Also, the vibration damping ratio increases when more micro SMA wires are arranged in form.