Dimensionless Model Research Articles

Analytical Investigation of the Differences between Cast-In-Situ and Precast Beam-Column Connections under Seismic Actions

At present, the engineering designers generally design and analyze the precast structural models according to the equivalent cast-in-situ principle, and have a vague understanding of non-identical problems. However, these issues cannot be ignored, especially for high-intensity areas. This paper considers the differences of the hysteretic relationship between two typical precast joints and cast-in-situ (RC) joints, and researches the influence of these differences on the seismic response of frame structures. For the monolithic precast joint, the force mechanism was analyzed based on its assembly form, and the differences with the RC joint in the testing phenomena were explained accordingly. The dimensionless hysteresis models of two types of joints were proposed, and the rationality of the monolithic precast joint model was verified according to the existing experimental results. Different performances of joints were realized by assigning the constitutive models calculated from sectional reinforcement to the spring elements of analysis models. Considering two possible performance deficiencies of each type of precast joint separately, a total of seven structural analysis models were formed. Nonlinear static analysis and dynamic time-history analysis methods were adopted to reveal the differences between precast frames and the RC frame in terms of structural capacity curve, displacement response, ductility demands of components and structural residual deformation. The results showed that under strong seismic excitation, the response differences between precast frames and the RC frame were significant, so it is worthwhile to establish nonlinear models suitable for precast frames in seismic analysis. This study is valuable for understanding and distinguishing the nonlinear response of precast frames and traditional RC frames.

Simulation and experimental implementations of memcapacitor based multi-stable chaotic oscillator and its dynamical analysis

In this work, linear quadratic regulator (LQR) method is proposed for controlling and synchronizing memcapacitor based chaotic system (MMCO). The MMCO is constructed with a charge controller memcapacitor, a resistor, a conductance and two capacitors. The proposed oscillators dimensionless model is derived and considered for analysis. The investigations of the systems are made using nonlinear analyses tools such as bifurcation diagrams, Lyapunov exponents, phase portraits, bifurcation like sequence, time series and frequency spectra. To explore further on coexisting multiple attractors, we have also presented the basin of attraction for the MMCO. As the memcapacitor is not a commercially available component, we have to use a electronic circuit model simulation and realization for the complete dimensionless model of MMCO to confirm the hardware realizability. A LQR based chaos suppression and chaos synchronization algorithm is also proposed. For understanding active controller’s impact on global asymptotic stability of synchronization and control errors, the Lyapunov function is used. Numerical analyses are demonstrated to reveal the effectiveness of applied active control method and the results are discussed.

A Dimensional Analysis of Local Sandy Soil Erosion Induced By Leaky Sewer Pipes

Soil erosion is the most important reason that leads directly to the formation of sinkholes in the roads of urban areas. Soil erosion occurs due to the movement of water from and into the surrounding soil through defects in sewer pipes. In the present study, dimensional analysis of the erosion process was carried out and a dimensionless model was proposed to estimate the rate of erosion for local sandy soil. Model tests were conducted under a varying matrix of influencing parameters including: leak size, soil particle size, initial water content, water flow rate, height of water level above the defect in soil, and number of water flow cycle. The experimental model involved soil exposed to cyclic water flow through leaks located at the bottom of the model. Eroded soil is collected, dried, weighted and sieved for each cycle. From the results, it was found that the proposed dimensional analysis prediction model can reasonably estimate the rate of erosion for the local sandy soil.

Artificial neural network-based nonlinear algebraic models for large eddy simulation of turbulence

In this work, artificial neural network-based nonlinear algebraic models (ANN-NAMs) are developed for the subgrid-scale (SGS) stress in large eddy simulation (LES) of turbulence at the Taylor Reynolds number Reλ ranging from 180 to 250. An ANN architecture is applied to construct the coefficients of the general NAM for the SGS anisotropy stress. It is shown that the ANN-NAMs can reconstruct the SGS stress accurately in the a priori test. Furthermore, the ANN-NAMs are analyzed by calculating the average, root mean square values, and probability density functions of dimensionless model coefficients. In an a posteriori analysis, we compared the performance of the dynamic Smagorinsky model (DSM), dynamic mixed model (DMM), and ANN-NAM. The ANN-NAM yields good agreement with a filtered direct numerical simulation dataset for the spectrum, structure functions, and other statistics of velocity. Besides, the ANN-NAM predicts the instantaneous spatial structures of SGS anisotropy stress much better than the DSM and DMM. The NAM based on the ANN is a promising approach to deepen our understanding of SGS modeling in LES of turbulence.

Development a new methodology for measuring deep drawing forces based on dimensionless evaluation

In this research work, dimensionless models based on geometric parameters have been developed for the deep drawing process of rectangular cups to reduce the manufacturing costs on a large scale of application in a noticeable way. In the following, geometric parameters were given in dimensionless form by the Π-Buckingham dimensional analysis method and a series of dimensionless groups were found for both circular and rectangular initial blank. To find the best group of dimensionless geometric parameters, different cup scales 1:1, 2:1, 4:1 and 5:1 are evaluated numerically by ABAQUS Finite Element (FE) software, validated by experimental work. After all effective geometric parameters have been analyzed, the best fitting relational model of dimensionless parameters is found for rectangular and circular blank separately. Various thicknesses of St12 sheet metals were used for experimental validation, which were formed at room temperature. Also, results and response parameters were compared in the simulation process, experimental tests and dimensionless models. By looking at the outcomes, it is demonstrated that the geometric qualities of a large scale can be predicted by a small scale, utilizing the proposed dimensionless model. A comparison of the outcomes for dimensionless models and experimental tests shows that proposed dimensionless models have a high degree of precision in determining geometrical parameters and the prediction of drawing force. Furthermore, the dimensionless analysis was generalized to ensure high precision estimation of geometric values for large geometric scales.

Double exothermic reaction of viscous dissipative Oldroyd 8-constant fluid and thermal ignition in a channel

The theoretical study of double exothermic combustible reaction and thermal ignition of viscous dissipative Oldroyd 8-constant liquid is examined in a channel. Without consumption of material, the fully developed two-step combustible reaction for the non-Newtonian fluid occurred in a bounded medium. The flow is propelled by reaction activation energy, upper wall motion and pre-exponential chemical kinetics that stimulates internal temperature. The overall solutions for the dimensionless viscoelastic exothermic reaction model is obtained by integrating collocation weighted residual techniques. In graphical and tabular form, the solution results are presented for the fluid flow rate, energy field and the branch-chain bifurcation.

Experimental investigation on the performance of Electrical Submersible Pump (ESP) operating with unstable water/oil emulsions

Electrical Submersible Pump (ESP) is one of the most commonly used artificial lift methods in petroleum production, due to its capacity to operate in several conditions with two or three-phase flows. When the ESP operates with emulsion flow, its performance is degraded, and operational instabilities occur. Therefore, this paper aims to carefully investigate phase inversion and to present, by the first time, the effective viscosity of unstable mineral oil/water emulsions, within the ESP. The first part of this work analyzes the phase inversion phenomenon for two oil types in three viscosities, five ESP rotational speeds, and three mixture flow rates. Logistic functions were fitted using the dimensionless head as a water cut function to determine the phase inversion within the ESP. The continuous phase inversion model, developed for emulsion pipe flow, did not present a satisfactory agreement to flow conditions tested. An indirect method to determine the emulsion effective viscosity within the ESP was proposed, which was obtained from the water/oil emulsion performance curves. The viscous performance data were used to determine the parameters of a dimensionless head empirical model for the tested ESP. Thus, the calculated values were compared with the effective viscosity obtained with oil and water emulsions, as well as the ESP performance, operating with emulsion and oil, which provides similar values for low rotational speeds. The different behavior of the effective viscosity between the pipeline flow and within the ESP was observed for water-in-oil emulsions and may be related to the high centrifugal field in the ESP.

Flow field and fire characteristics inside a tunnel under the influence of canyon cross wind

A series of scale model tests were conducted to investigate the influence of canyon cross wind on burning and flame characteristics of ethanol pool fires inside a tunnel, considering pool size and fire location. At the same time, the characteristics of the flow field inside the tunnel were investigated by Fire Dynamics Simulator (FDS). Results show that an uneven three-dimensional flow field structure will be formed inside the tunnel with the effect of canyon cross wind, which can be divided into three zones, including the negative pressure zone, the transition zone and the unidirectional flow zone. Furtherly, the burning rates and flame shapes of pool fires with different fire locations will be varied. When pool fires are located in the negative pressure zone and the transition zone, the burning rates enhance linearly with the increase of canyon cross wind speed, and the flames appear with a fluctuation phenomenon. When pool fires are located in the unidirectional flow zone, the pool fires show a highly stable burning phenomenon and both the burning rates of the two pool sizes experience three stages with the increase of canyon cross wind speed. A new dimensionless flame length prediction model of pool fire is established based on the previous model proposed by Thomas, considering the effect of cross air flow on the burning rate. Findings of current study are helpful to enrich the tunnel fire research with external air flow.

Usando a altura do ponto de inflexão no perfil do vento para a obtenção de perfis adimensionais acima da floresta amazônica

The most turbulent vortices that populate the forest-atmosphere interface have canopy height length scales. These vortices are mainly responsible for turbulent exchanges between inside and above canopy region. Thus, we used the vertical wind profiles obtained by 10 anemometers installed inside and above the forest canopy of the Rebio-Jarú experimental site, in the Amazon Rainforest. A third degree polynomial function was developed to better fit the wind profile and therefore estimate the inflection point height of the vertical wind profile (zi) a length scale associated with wind shear (Ls), and the wind speed at height zi. These length and velocity scales were used to obtain better fits for the dimensional wind profiles and turbulence statistical moments. Three dimensionless profile models were compared using friction velocity, wind velocity in zi and wind velocity at canopy height. It was observed that the dimensionless profiles using the velocity and shear calculated at zi provided support for the elaboration of more realistic parameterization of the turbulent exchange processes that occur both at the forest-atmosphere interface and inside the canopy.

Free convection MHD flow of viscous fluid by means of damped shear and thermal flux in a vertical circular tube

The main concern of the article is to study the hydromagnetic, free convection, and incompressible viscous fluid flow with generalized boundary conditions. The movement of the fluid is taken into account through a vertical circular tube. We built up a fractional model with the assistance of the constitutive shear stress equation and generalized type of Fourier’s Law. We’ve received closed-form solutions of the dimensionless fractional model by the way of Laplace and finite Hankel transform approach and received results are stated relating the G–function of Lorenzo and Hartley and in the generalized form of Mittag-Leffler. Graphically, the impacts of a choice of fractional and material variables are plotted by the use of Mathcad. The velocity is expanded by expanding the values of fractional factors and The boundary layer difference increment as time is expanded. The boundary layer difference and velocity are expanding by decreasing the value of the magnetic field.

Dimensionless parameter-based numerical model for double conical dielectric elastomer actuators

As the development of soft actuators progresses, new methods for more agile actuator control are required. While there are hardware technologies that can provide such agility (e.g. field-programmable-gate-array electronics), mathematical models tend to slow the controlling processes. For the case of double conical dielectric elastomer actuators (DCDEAs), complex material and physical models are often utilized; however, such models require extended computational time which limits real-time control and prediction, especially in small, portable applications. The foregoing problem is augmented, if agile applications require reprogramming on the fly. In this work, a parameter-based dimensionless model applicable to DCDEAs was developed. The proposed model: (a) relates a dimensionless displacement with a characteristic dimensionless voltage via a power-law equation; (b) is robust enough to accurately describe 5-Degree-of-Freedom motion; (c) is scalable (at least within the range of geometries and parameters used in this study); (d) due to its mathematical simplicity, it could be used for more agile controls. For the development of the model, multiple DCDEAs were manufactured by varying design parameters such as pre-stretch, thickness, dielectric constant, shear modulus, electrode area, and inner and outer radii. By applying the Levenberg-Marquardt best-fit algorithm to experimental data sets containing voltage and (translational and rotational) displacements, a general relationship was found between parameter-based dimensionless quantities and a general dimensionless displacement. The relationship was further simplified via a single dimensionless number related to the actuator design. The model was found to be accurately predictive for VHB4910 and VHB4905. The resulting model is simple and has potential to be used for a wide range of dielectric-elastomer materials.

Analytical and experimental investigation of the centrifugal softening and stiffening effects in rotational energy harvesting

Depending on its mounting orientation, the rotational piezoelectric harvester can be subjected to the centrifugal softening or stiffening effects, which may pose a positive or negative influence on the energy harvesting performance. This paper firstly presents the comprehensive comparison of the centrifugal softening and stiffening harvesters with a unified dimensionless analytical model. The analytical expressions of the optimum short-circuit and open-circuit rotational frequencies, the optimum resistances and the optimum centrifugal coefficients are derived to reveal the influence mechanism of the centrifugal effects. The proposed model is validated experimentally and used for case studies to compare the centrifugal softening and stiffening harvesters. Results illustrate that the centrifugal softening harvester has a superior energy harvesting performance at low rotational frequencies while the centrifugal stiffening harvester is better at high rotational frequencies. Furthermore, the peak power of the centrifugal softening harvester is higher while the frequency bandwidth of the centrifugal stiffening harvester is wider. In addition, it is found that the centrifugal stiffening harvester is more sensitive to the centrifugal coefficient. Based on the centrifugal stiffening effect, the self-tuning harvester can be achieved with a wide frequency bandwidth. Meanwhile, this requires that the centrifugal coefficient is precisely determined, and the fundamental natural frequency of the harvester without the centrifugal force should be low enough when operating at low rotational frequencies. Compared with the centrifugal stiffening effect, the centrifugal softening effect may be more suitable to be used in MEMS/NEMS applications since it can reduce the fundamental resonant frequency of the harvester during the rotation.

Start-Up Electroosmotic Flow of Multi-Layer Immiscible Maxwell Fluids in a Slit Microchannel.

In this investigation, the transient electroosmotic flow of multi-layer immiscible viscoelastic fluids in a slit microchannel is studied. Through an appropriate combination of the momentum equation with the rheological model for Maxwell fluids, an hyperbolic partial differential equation is obtained and semi-analytically solved by using the Laplace transform method to describe the velocity field. In the solution process, different electrostatic conditions and electro-viscous stresses have to be considered in the liquid-liquid interfaces due to the transported fluids content buffer solutions based on symmetrical electrolytes. By adopting a dimensionless mathematical model for the governing and constitutive equations, certain dimensionless parameters that control the start-up of electroosmotic flow appear, as the viscosity ratios, dielectric permittivity ratios, the density ratios, the relaxation times, the electrokinetic parameters and the potential differences. In the results, it is shown that the velocity exhibits an oscillatory behavior in the transient regime as a consequence of the competition between the viscous and elastic forces; also, the flow field is affected by the electrostatic conditions at the liquid-liquid interfaces, producing steep velocity gradients, and finally, the time to reach the steady-state is strongly dependent on the relaxation times, viscosity ratios and the number of fluid layers.

Fully resolved simulation of dense suspensions of freely evolving buoyant particles using an improved immersed boundary method

Fully resolved simulation of flows with buoyant particles is a challenging problem since buoyant particles are lighter than the surrounding fluid, and as a result, the two phases are strongly coupled together. In this work, the virtual force stabilization technique introduced by Schwarz et al. [Schwarz, S., Kempe, T., & Fröhlich, J. (2015). A temporal discretization scheme to compute the motion of light particles in viscous flows by an immersed boundary method. J. Comput. Phys., 281, 591–613] is extended to simulate buoyant particle suspensions with high volume fractions (up to 40%). It is concluded that the dimensionless numerical model constant Cv in the virtual force technique should increase with volume fraction. The behavior of a single rising particle, two in-line rising particles, and buoyant particle suspensions are studied. In each case, results are compared with experimental works on bubbly flows to highlight the differences and similarities between buoyant particles and bubbles. Finally, the drag coefficient is extracted from simulations of buoyant particle suspensions at different volume fractions, and based on that a drag correlation is presented.

Influence of periodic pressure on dendritic morphology and sidebranching

The influence of periodic pressure with low and high frequencies on microstructure and dendritic sidebranching was studied by using 3-D phase field method. In both low and high frequency cases, the variation trend of SDAS (secondary dendritic arm spacing) with increasing pressure frequency is opposite to that of sidebranching frequency, while the variation trend of the average length of secondary arms is consistent with that of sidebranching frequency. The high sidebranching frequency indicates that more secondary arms share the whole driving force of dendrite growth, resulting in lower driving force for each one and leading to less developed secondary arms. The smallest SDAS is obtained when perturbed by the periodic pressure with the frequency of 0.157/τ0 (τ0 is the physical unit of time in the dimensionless phase field model) and 2.200/τ0 in low and high frequency cases, respectively. Comparisons of dendritic morphology and secondary arms are made between the low and high frequency cases. Firstly, in the low frequency case, secondary arms are luxuriant especially when pressure frequency is low, with many high-order side branches stretching out. Secondly, the average length of secondary arms in primary dendrite is longer in the low frequency case than that without pressure, and much longer than that in the high frequency case. Thirdly, the dendrite tip without side branches in the high frequency case is much longer than that in the low frequency case. All of the differences in dendritic morphology and sidebranching in the two cases can be attributed to the different modulation mechanism. In the low frequency case, periodic pressure determines tip velocity and then modulates sidebranching directly. While in the high frequency case, periodic pressure cannot determine sidebranching directly, but via modulating tiny protuberances in dendrite tip, part of which evolves into side branch. In this case, the tiny protuberances take part of the whole driving force, leading to less developed secondary arms.

Thermodynamic second law analysis of magneto-micropolar fluid flow past nonlinear porous media with non-uniform heat source

This study analyzes the second law of thermodynamic for entropy generation in an irreversible hydromagneto-micropolar flow system with non-homogenous heat generation. The non-symmetric microstructure fluid flow past a stretching sheet with saturated porous non-linear media under magnetic field influence. Ignoring the fluid particle deformation, the microstructure is assumed rigid with the viscous suspended medium. The reduced dimensionless nonlinear formulated model is computationally coded and solved to obtain solutions for the entropy volumetric production, Bejan number and heat transfer magneto-micropolar fluid. The parameter dependent solutions for the flow characteristics and irreversibility processes are plotted and discussed. It is revealed from the study that minimization of entropy generation in a magneto-micropolar flow system is possible by improving the thermodynamic equilibrium with low material variables, viscosity and hysteresis magnetic. Also, it is seen that the terms that encourage internal heat generation reduces the micropolar fluid viscosity in the system.

Prediction of Salmonella inactivation in sliced tomato subject to high pressure processing and trans-cinnamaldehyde treatment using selective and non-selective growth media for survival evaluations

High pressure processing (HPP) is an effective non-thermal food operation means to reduce foodborne illness risks. Trans-cinnamaldehyde (TC) is a GRAS compound widely used in food applications for flavoring and recently found the potential to enhance microbial inactivation with HPP. For the first time, this study investigated combination effects of relatively low hydrostatic pressure level (i.e. 150, 200 and 250 MPa), operation time (i.e. 4, 8 and 12 min) and TC concentration (i.e. 200, 400 and 600 ppm) on Salmonella inactivation in sliced tomato by using both selective (i.e. XLT4 agar plates) and non-selective (i.e. Aerobic Petrifilms™) growth media for microbial survival evaluations. Linear and dimensionless non-linear regression models were developed, evaluated and validated for providing comparative information for descriptions and predictions of the inactivation effects. The results showed that a strong synergistic inactivation effect between hydrostatic pressure and TC was observed, which could explain for the great inactivation effects of the combination treatments (maximum reduction > 6 log CFU/g). The inactivation of Salmonella in XLT4 agar plate counts was significantly larger (up to 1.96 log CFU/g) than in Aerobic Petrifilm™ counts (p < 0.05), suggesting using non-selective growth media could be a more conservative choice than selective growth media, ensuring a higher microbial safety level. According to the novel 4-dimensional response surface plots of developed models, hydrostatic pressure level played the most important role in the inactivation. This study provides valuable reference information to the current HPP manufacturers dealing with tomato products.

Numerical Exploratory Analysis of Dynamics and Control of an Atomic Force Microscopy in Tapping Mode with Fractional Order

In this paper, we investigate the mechanism of atomic force microscopy in tapping mode (AFM-TM) under the Casimir and van der Waals (VdW) forces. The dynamic behavior of the system is analyzed through a nonlinear dimensionless mathematical model. Numerical tools as Poincaré maps, Lyapunov exponents, and bifurcation diagrams are accounted for the analysis of the system. With that, the regions in which the system presents chaotic and periodic behaviors are obtained and investigated. Moreover, the fractional calculus is introduced into the mathematical model, employing the Riemann-Liouville kernel discretization in the viscoelastic term of the system. The 0-1 test is implemented to analyze the new dynamics of the system, allowing the identification of the chaotic and periodic regimes of the AFM system. The dynamic results of the conventional (integer derivative) and fractional models reveal the need for the application of control techniques such as Optimum Linear Feedback Control (OLFC), State-Dependent Riccati Equations (SDRE) by using feedback control, and the Time-Delayed Feedback Control. The results of the control techniques are efficient with and without the fractional-order derivative.

Heat transport in CNTs based nanomaterial flow of non-Newtonian fluid having electro magnetize plate

In this study, heat transfer of CNTs base micropolar fluid flow over a Riga plate. The effects of thermal slip and velocity slip considred to analyze at Riga plate. The compatible model to deals with the impacts of two nanoparticles like SWCNT and MWCNT within the base fluid pure water. Under the considrertion, we developed the mathematical model and applied the boundary layer approximation on the Navier Stokes equations. the dimensionless model have been solve through numerical methos via Maple Software. The involving dimensionless parameters effects are presented in the form of tables and graphs. Surpringly, the best achievement in the heat transfer rate and boundary layer thickness gain by MWCNT as compared to SWCNT.

Investigation of Thermal Transport in Multi-Shaped Cu Nanomaterial-Based Nanofluids.

The unsteady flow of H2O saturated by tiny nanosized particles with various shapes (platelets, blades, cylinders, and bricks) over a thin slit is reported. For this novel analysis, the influences of the magnetic field and heat generation/absorption are incorporated into the governing model. The dimensionless nanofluid model is attained after the successful implementation of similarity transformations. Then, Runge-Kutta and homotopy analysis algorithms are implemented for mathematical analysis, and the results are obtained by varying the main flow parameters. A decrease in nanofluid motion is observed for a stronger magnetic field (M). Additionally, nanofluid temperature β(η) increases for higher values of M. Decreasing trends in the shear stresses Rex0.5CFx are observed for the unsteadiness parameter S, and this declines with stronger M. Similarly, the local heat transfer rate Rex−0.5Nux rises with the unsteady behavior of the fluid. It is observed that the nanofluid motion drops for variable thickness () of the slit, whereas the motion becomes slower with stronger magnetic field effects (M).