Journal articles on the topic 'Wall layer model'
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1
Landahl, M. T. "Near-wall model for boundary layer turbulence." Applied Scientific Research 51, no. 1-2 (June 1993): 435–43. http://dx.doi.org/10.1007/bf01082573.
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Gerodimos, G., and R. M. C. So. "Near-Wall Modeling of Plane Turbulent Wall Jets." Journal of Fluids Engineering 119, no. 2 (June 1, 1997): 304–13. http://dx.doi.org/10.1115/1.2819135.
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In most two-dimensional simple turbulent flows, the location of zero shear usually coincides with that of vanishing mean velocity gradient. However, such is not the case for plane turbulent wall jets. This could be due to the fact that the driving potential is the jet exit momentum, which gives rise to an outer region that resembles a free jet and an inner layer that is similar to a boundary layer. The interaction of a free-jet like flow with a boundary-layer type flow distinguishes the plane wall jet from other simple flows. Consequently, in the past, two-equation turbulence models are seldom able to predict the jet spread correctly. The present study investigates the appropriateness of two-equation modeling; particularly the importance of near-wall modeling and the validity of the equilibrium turbulence assumption. An improved near-wall model and three others are analyzed and their predictions are compared with recent measurements of plane wall jets. The jet spread is calculated correctly by the improved model, which is able to replicate the mixing behavior between the outer jet-like and inner wall layer and is asymptotically consistent. Good agreement with other measured quantities is also obtained. However, other near-wall models tested are also capable of reproducing the Reynolds-number effects of plane wall jets, but their predictions of the jet spread are incorrect.
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Jai, John, George S. Springer, Laszlo P. Kollar, and Helmut Krawinkler. "Reinforcing Masonry Walls with Composite Materials-Model." Journal of Composite Materials 34, no. 18 (September 2000): 1548–81. http://dx.doi.org/10.1106/38xx-ggb5-nxc9-tjha.
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In this investigation, a procedure is developed for determining the effectiveness of composite materials in retrofitting masonry buildings to reduce seismic damage. The reinforcement considered is a thin layer of fiber-reinforced composite applied to the wall in a wallpaper-like fashion. Models were developed which predict the behavior of masonry walls reinforced in such a fashion and subjected to static, in-plane normal and shear loads. Solid walls, as well as walls with openings (such as windows and doors), were considered. The models estimate the load-deflection characteristic of the wall, the load set at which the wall fails, and the deflection of the wall at the instant of failure. Numerical results were also generated which indicate that composite reinforcement applied in a wallpaper-like fashion may increase substantially the load carrying capacities of masonry walls.
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Keirsbulck, L., L. Labraga, A. Mazouz, and C. Tournier. "Surface Roughness Effects on Turbulent Boundary Layer Structures." Journal of Fluids Engineering 124, no. 1 (October 15, 2001): 127–35. http://dx.doi.org/10.1115/1.1445141.
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A turbulent boundary layer structure which develop over a k-type rough wall displays several differences with those found on a smooth surface. The magnitude of the wake strength depends on the wall roughness. In the near-wall region, the contribution to the Reynolds shear stress fraction, corresponding to each event, strongly depends on the wall roughness. In the wall region, the diffusion factors are influenced by the wall roughness where the sweep events largely dominate the ejection events. This trend is reversed for the smooth-wall. Particle Image Velocimetry technique (PIV) is used to obtain the fluctuating flow field in the turbulent boundary layer in order to confirm this behavior. The energy budget analysis shows that the main difference between rough- and smooth-walls appears near the wall where the transport terms are larger for smooth-wall. Vertical and longitudinal turbulent flux of the shear stress on both smooth and rough surfaces is compared to those predicted by a turbulence model. The present results confirm that any turbulence model must take into account the effects of the surface roughness.
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Gre´goire, G., M. Favre-Marinet, and F. Julien Saint Amand. "Modeling of Turbulent Fluid Flow Over a Rough Wall With or Without Suction." Journal of Fluids Engineering 125, no. 4 (July 1, 2003): 636–42. http://dx.doi.org/10.1115/1.1593705.
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The turbulent flow close to a wall with two-dimensional roughness is computed with a two-layer zonal model. For an impermeable wall, the classical logarithmic law compares well with the numerical results if the location of the fictitious wall modeling the surface is considered at the top of the rough boundary. The model developed by Wilcox for smooth walls is modified to account for the surface roughness and gives satisfactory results, especially for the friction coefficient, for the case of boundary layer suction.
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Hamdhan, Indra Noer, and Fauziah Fitriani Iskandar. "Analisis Perkuatan Timbunan Di Atas Tanah Lunak Menggunakan Dinding Turap dengan Pendekatan Model Numerik." MEDIA KOMUNIKASI TEKNIK SIPIL 25, no. 1 (August 10, 2019): 48. http://dx.doi.org/10.14710/mkts.v25i1.18006.
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Embankment on soft clay may be affect settlement at subgrade, causing lateral deformation and vertical deformation around embankment. Therefore, reinforcement is needed to overcome the effects caused of the embankment. This research was conducted to find out the influence of sheet pile wall of embankment using PLAXIS 2D program based the finite element method. The analysis was done by varying of two condition, they are installation of sheet pile wall under the embankment and the sheet pile wall outside embankment. Sheet pile wall installation is carried out before embankment construction and length of sheet pile wall in this model is 15 m. The soil layers beneath the embankment consist of 10 m layer of soft clay layer and 5 m of sand layer. The height of embankment in this analysis is 8 m, where the constructing of the embankment was done in stages. The distance of sheet pile wall position under embankment from toe of embankment are -9 m, -6 m, -3 m, 0 m, 3 m dan 6 m. The results of analysis show the effective position for displacement are toe of embankment. The Installation of sheet pile walls below the embankment will reducing deformation up to 78% and the safety factor will increase up to 10%.
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Hultmark, Marcus, Marc Calaf, and Marc B. Parlange. "A New Wall Shear Stress Model for Atmospheric Boundary Layer Simulations." Journal of the Atmospheric Sciences 70, no. 11 (October 31, 2013): 3460–70. http://dx.doi.org/10.1175/jas-d-12-0257.1.
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Abstract A new wall shear stress model to be used as a wall boundary condition for large-eddy simulations of the atmospheric boundary layer is proposed. The new model computes the wall shear stress and the vertical derivatives of the streamwise velocity component by means of a modified, instantaneous, and local law-of-the-wall formulation. By formulating a correction for the modeled shear stress, using experimental findings of a logarithmic region in the streamwise turbulent fluctuations, the need for a filter is eliminated. This allows one to model the wall shear stress locally, and at the same time accurately recover the correct average value. The proposed model has been applied to both unique high Reynolds number experimental data and a suite of large-eddy simulations, and compared to previous models. It is shown that the proposed model performs equally well or better than the previous filtered models. A nonfiltered model, such as the one proposed, is an essential first step in developing a universal wall shear stress model that can be used for flow over heterogeneous surfaces, studies of diurnal cycles, or analyses of flow over complex terrain.
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Badano, Nicolás D., and Angel N. Menéndez. "Accuracy of boundary layer treatments at different Reynolds scales." Open Engineering 10, no. 1 (April 8, 2020): 295–310. http://dx.doi.org/10.1515/eng-2020-0033.
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AbstractResistive forces associated to boundary layers (‘friction’) are usually out of scale in physical models of hydraulic structures, especially in the case of hydraulically smooth walls, generating distortions in the model results known as scale effects, that can be problematic in some relevant engineering problems. These scale effects can be quantified and corrected using suitable numerical models. In this paper the accuracy of using numerical simulation through the Reynolds Averaged Navier-Stokes (RANS) approximation in order to represent the head losses introduced by friction in hydraulically smooth walls is evaluated for a wide range of Reynolds scales. This is performed by comparing the numerical results for fully developed flow on circular pipes and between parallel plates against experimental results, using the most popular wall treatments. The associated numerical errors, mesh requirements and ranges of application are established for each treatment. It is shown that, when properly applied, RANS models are able to simulate the head losses produced by smooth wall friction accurately enough as to quantify the scale effects present in physical models. A methodology for upscaling physical model results to prototype scale, free of scale effects, is proposed.
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Basu B., Mallik, and Garain D.N. "Mathematical Model of Blood Flow through Capillaries to Study Transport of Nanoparticles Using Power Law Fluid Model." International Journal of Zoological Investigations 08, special issue (2022): 275–84. http://dx.doi.org/10.33745/ijzi.2022.v08i0s.034.
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A model of blood capillary flow that is axially symmetric with a peripheral layer and wall slip is provided mathematically in this study. Power law fluid was employed in the core area of suspension of all erythrocytes whereas Newtonian fluid was used in the periphery plasma layer to analyse longitudinal transport of nanoparticles within blood vessels. The capillary walls are impenetrable to nanoparticles in our study, and they are not absorbent. The formulas for the velocity profile, flow rate, mean velocity, and solute concentration were produced, and the findings were discussed using graphs.
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Tang, Yang Yang, Zhi Qiang Li, Yong Wang, Ya Chao Di, Huan Xu, and Qing Yang. "Numerical Investigation of the Compressible Flat-Plate Turbulent Boundary Layer with Extended GAO-YONG Turbulence Model." Applied Mechanics and Materials 444-445 (October 2013): 416–22. http://dx.doi.org/10.4028/www.scientific.net/amm.444-445.416.
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The extended GAO-YONG turbulence model is used to simulate the flow and heat transfer of flat-plate turbulent boundary layer, and the results indicate that GAO-YONG turbulence model may well describe boundary layer flow and heat transfer from near-wall region to far outer area, without using any empirical coefficients and near-wall treatments, such as wall-function or modified low Reynolds number model, which are used widely in all RANS turbulence models.
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Taghavi, S. M. "A two-layer model for buoyant displacement flows in a channel with wall slip." Journal of Fluid Mechanics 852 (August 10, 2018): 602–40. http://dx.doi.org/10.1017/jfm.2018.555.
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We study theoretically buoyant displacement flows of two generalized Newtonian fluids in a two-dimensional (2-D) channel with wall slip. We assume that a pseudo-interface separates two miscible (immiscible) fluids at the limit of negligible molecular diffusion (negligible surface tension). A heavy fluid displaces a light fluid at near-horizontal channel inclinations, implying that a stratified flow assumption is relevant. We develop a classical lubrication approximation model as a semi-analytical framework that includes a number of dimensionless parameters, such as a buoyancy number, the viscosity ratio, the non-Newtonian properties and the upper and lower wall slip coefficients. For specified interface heights and slopes, the reduced model can furnish the flux and velocity functions in displacing and displaced phases. We numerically solve the interface kinematic condition for four different wall slip cases: no slip (Case I), slip at the lower wall (Case II), slip at the upper wall (Case III) and slip at both walls (Case IV). The solutions for these cases deliver the interface propagation in time, for which leading and trailing displacement front heights, shapes and speeds and several key displacement features, such as front characteristic spreading lengths and short time behaviours, can be directly predicted by simplified analyses. The results reveal in detail how the presence of a channel wall slip may significantly affect the overall displacement flow and the interface evolution characteristics, for both Newtonian and non-Newtonian fluids. Regarding the latter, our analysis quantifies in particular the appearance and removal of static residual wall layers of the displaced phase, versus the wall slip cases.
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Bae, Hyunji Jane, Adrián Lozano-Durán, Sanjeeb T. Bose, and Parviz Moin. "Dynamic slip wall model for large-eddy simulation." Journal of Fluid Mechanics 859 (November 16, 2018): 400–432. http://dx.doi.org/10.1017/jfm.2018.838.
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Wall modelling in large-eddy simulation (LES) is necessary to overcome the prohibitive near-wall resolution requirements in high-Reynolds-number turbulent flows. Most existing wall models rely on assumptions about the state of the boundary layer and require a priori prescription of tunable coefficients. They also impose the predicted wall stress by replacing the no-slip boundary condition at the wall with a Neumann boundary condition in the wall-parallel directions while maintaining the no-transpiration condition in the wall-normal direction. In the present study, we first motivate and analyse the Robin (slip) boundary condition with transpiration (non-zero wall-normal velocity) in the context of wall-modelled LES. The effect of the slip boundary condition on the one-point statistics of the flow is investigated in LES of turbulent channel flow and a flat-plate turbulent boundary layer. It is shown that the slip condition provides a framework to compensate for the deficit or excess of mean momentum at the wall. Moreover, the resulting non-zero stress at the wall alleviates the well-known problem of the wall-stress under-estimation by current subgrid-scale (SGS) models (Jiménez & Moser, AIAA J., vol. 38 (4), 2000, pp. 605–612). Second, we discuss the requirements for the slip condition to be used in conjunction with wall models and derive the equation that connects the slip boundary condition with the stress at the wall. Finally, a dynamic procedure for the slip coefficients is formulated, providing a dynamic slip wall model free of a priori specified coefficients. The performance of the proposed dynamic wall model is tested in a series of LES of turbulent channel flow at varying Reynolds numbers, non-equilibrium three-dimensional transient channel flow and a zero-pressure-gradient flat-plate turbulent boundary layer. The results show that the dynamic wall model is able to accurately predict one-point turbulence statistics for various flow configurations, Reynolds numbers and grid resolutions.
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Mercadé-Prieto, Ruben, Colin R. Thomas, and Zhibing Zhang. "Mechanical double layer model for Saccharomyces Cerevisiae cell wall." European Biophysics Journal 42, no. 8 (May 8, 2013): 613–20. http://dx.doi.org/10.1007/s00249-013-0909-x.
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Lei, Guang Yu, Yu Yao Zeng, and Can Guo Jin. "Study on Seismic Performance of Infilled Frame of Underlying Weak Layer." Applied Mechanics and Materials 204-208 (October 2012): 1028–33. http://dx.doi.org/10.4028/www.scientific.net/amm.204-208.1028.
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After the Wenchuan earthquake, a large number of infilled frame structure of underlying weak layer (the bottom of non-filled walls, the upper wall of clouds filling) of the housing system did not appear "weak beam strong column" of the failure mode. Established pure frame structure of finite element model which considered the quality of in filled wall without taking into account of its stiffness and strength and the frame of finite element model which contains filler wall, and carried out elastic-plastic time-history analysis with established finite element model of two under earthquake, through analysis and comparison understand reasons which infilled frame structure of underlying weak layer did not achieve the "weak beam strong column" ductile failure mechanism, and further explored how to achieve "weak beam strong column" failure mechanism for infilled frame structure of underlying weak layer, raised a number of assurance measures.
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Fang, Jian, Xi Deng, and Zhi X. Chen. "Direct numerical simulation of supersonic internal flow in a model scramjet combustor under a non-reactive condition." Physics of Fluids 35, no. 2 (February 2023): 026103. http://dx.doi.org/10.1063/5.0137884.
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A Mach 1.5 non-reactive flow in a cavity-stabilized combustor of a model scramjet is studied via a direct-numerical simulation approach, and the analysis is focused on the interaction among boundary layer, free shear-layer above the cavity and shock wave. It is found that the impingement of the free shear-layer on the aft wall of the cavity leads to strong turbulence kinetic energy, high local pressure, and a fan of compression waves. The compression waves evolve into an oblique shock, which reflects between the upper and lower walls and interacts with the boundary layers attached to the two walls. The analysis of the turbulence production reveals that the amplification of turbulence in the core of the shear-layer and around the reattachment point is mainly due to the shear production, but the deceleration production mechanism presents a significant impact in the regions above the aft wall of the cavity and around the shock interaction points. The very low frequency commonly observed in shock wave/boundary layer interactions is not observed in the present research, which might be due to the low Reynolds number of the studied case.
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Mukin, Dmitrii, Ekaterina Valdaytseva, and Gleb Turichin. "Analytical Solution of the Non-Stationary Heat Conduction Problem in Thin-Walled Products during the Additive Manufacturing Process." Materials 14, no. 14 (July 20, 2021): 4049. http://dx.doi.org/10.3390/ma14144049.
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The work is devoted to the development of a model for calculating transient quasiperiodic temperature fields arising in the direct deposition process of thin walls with various configurations. The model allows calculating the temperature field, thermal cycles, temperature gradients, and the cooling rate in the wall during the direct deposition process at any time. The temperature field in the deposited wall is determined based on the analytical solution of the non-stationary heat conduction equation for a moving heat source, taking into account heat transfer to the environment. Heat accumulation and temperature change are calculated based on the superposition principle of transient temperature fields resulting from the heat source action at each pass. The proposed method for calculating temperature fields describes the heat-transfer process and heat accumulation in the wall with satisfactory accuracy. This was confirmed by comparisons with experimental thermocouple data. It takes into account the size of the wall and the substrate, the change in power from layer to layer, the pause time between passes, and the heat-source trajectory. In addition, this calculation method is easy to adapt to various additive manufacturing processes that use both laser and arc heat sources.
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Pihler-Puzović, D., and T. J. Pedley. "Flutter in a quasi-one-dimensional model of a collapsible channel." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2166 (June 8, 2014): 20140015. http://dx.doi.org/10.1098/rspa.2014.0015.
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The effects of wall inertia on instabilities in a collapsible channel with a long finite-length flexible wall containing a high Reynolds number flow of incompressible fluid are studied. Using the ideas of interactive boundary layer theory, the system is described by a one-dimensional model that couples inviscid flow outside the boundary layers formed on the channel walls with the deformation of the flexible wall. The observed instability is a form of flutter, which is superposed on the behaviour of the system when the wall mass is neglected. We show that the flutter has a positive growth rate because the fluid loading acts as a negative damping in the system. We discuss these findings in relation to other work on self-excited oscillations in collapsible channels.
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Ni, Shiyuan, Yi Lin, Defei Yao, Guilian Wu, Zehao Wang, and Yan Huang. "Optimal Dispatch of Regional Integrated Heating and Power System Based on Differential Thermal Inertia Model." E3S Web of Conferences 256 (2021): 02018. http://dx.doi.org/10.1051/e3sconf/202125602018.
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As the physical carrier of Energy Internet, regional integrated energy system (RIES) has become an important role for improving comprehensive energy utilization efficiency. First, a subtle thermodynamic model of buildings and water-heating network was constructed based on differential thermal inertia model. Different from the traditional single-layer wall thermal inertial model, this paper constructed multi-layer wall thermal model. Then, an optimization scheme combining electricity and heat was established. The optimization results show that, compared with the traditional single-layer wall thermal inertia model, the proposed multi-layer wall thermal inertia model has better performance. The proposed comprehensive energy optimization scheme can reduce the cost of electricity while maintaining indoor comfort, and can provide a reference for the system operation status for distribution network dispatching.
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Idris, Nurul A., Maketelana Aleamotuʻa, David W. McCurdy, and David A. Collings. "The Orchid Velamen: A Model System for Studying Patterned Secondary Cell Wall Development?" Plants 10, no. 7 (July 2, 2021): 1358. http://dx.doi.org/10.3390/plants10071358.
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Understanding the mechanisms through which plants generate secondary cell walls is of more than academic interest: the physical properties of plant-derived materials, including timber and textiles, all depend upon secondary wall cellulose organization. Processes controlling cellulose in the secondary cell wall and their reliance on microtubules have been documented in recent decades, but this understanding is complicated, as secondary walls normally form in the plant’s interior where live cell imaging is more difficult. We investigated secondary wall formation in the orchid velamen, a multicellular epidermal layer found around orchid roots that consists of dead cells with lignified secondary cell walls. The patterns of cell wall ridges that form within the velamen vary between different orchid species, but immunolabelling demonstrated that wall deposition is controlled by microtubules. As these patterning events occur at the outer surface of the root, and as orchids are adaptable for tissue culture and genetic manipulation, we conclude that the orchid root velamen may indeed be a suitable model system for studying the organization of the plant cell wall. Notably, roots of the commonly grown orchid Laelia anceps appear ideally suited for developing this research.
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Gao, Fa Rong, Xu Gang Xi, Yun Yuan Gao, and Qi Zhong Zhang. "Static Stress Distribution in Microvessel Wall with a Layered Model." Advanced Materials Research 772 (September 2013): 258–63. http://dx.doi.org/10.4028/www.scientific.net/amr.772.258.
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Based on the vascular membrane stress model and the pseudo-elastic vessel model, the combination constitutive model with a layered structure in microvessel is presented in this paper. By using obtained constitutive equations of the current model, the circumferential stress of the membrane intimal (inner) layer and the three-dimensional stress distribution of the structural outer layer are analyzed. Under the initial blood pressure state, the vascular static stress changes with the inner stiffness increase are also discussed. The results show that with inner stiffness increasing, the stress of outer layer is less affected but the circumferential stress of the intimal layer is increased significantly, which may be one potential risk factor for the vascular injury. These analysis methods and its conclusions have some theoretical significance for studying the problems of arteriosclerosis and other diseases, and preventing the occurrence of related diseases.
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Mizonov, V. Е., A. V. Mitrofanov, E. V. Basova, and E. А. Shuina. "A cell model of heat conduction in multi-layer medium with variable number of the layers." Vestnik IGEU, no. 3 (June 30, 2020): 51–57. http://dx.doi.org/10.17588/2072-2672.2020.3.051-057.
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The heat conduction is an important part of heat transfer processes in power engineering, civil engineering, chemical technologies, etc. Variety of researches is devoted to theoretical and experimental study of the heat transfer by the heat conduction. At present, the considerable attention is concentrated on the heat conduction in media with variable boundaries (the so-called Stephan’s problem). A reason of a boundary motion can be burning-out of material, its wear, its melting with carry-over of a melt, other physic-chemical processes. Analytical solutions to the Stephan’s problem exist only after far-going assumptions, which lead to the loss of their practical value. The development of effective numerical methods of its solution becomes an actual scientific and practical problem. Such methods are to combine universality and physical clearness and convenience for engineering practice. In order to solve the problem, the method of mathematical modeling is used. The model uses the mathematical tools of the theory of Markov chains. It is adapted to the cell model of a medium, in which the number of cells can vary due to this or that mechanism of the edge cells interaction with outside medium. The heat transfer by the heat conduction and the heat interaction with the heat sources are described by the classical heat balance equations. The study of the influence of parameters on the process is performed by numerical methods. A mathematical model that allows describing transient heat processes in a multi-layer medium with variable number of layers is developed. The results of heat process calculation inside a plane wall with the moving boundary form the heat source side due to the boundary thermal distruction at a certain critical temperature are presented. The obtained results are physically consistent and approve the model workability. The principle differences between the heat processes in the walls with immovable and movable boundaries are found. It is shown that the temperature in a wall with moving boundary does not overbalance the critical temperature of the thermal distraction when the wall still exists, and the rate of the wall dimension decrease is growing with its dimension decrease.
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Gong, Xiao Ying, and Jun Wu Dai. "Nonlinear Seismic Analysis of Masonry Infilled RC Frame Structures." Applied Mechanics and Materials 117-119 (October 2011): 288–94. http://dx.doi.org/10.4028/www.scientific.net/amm.117-119.288.
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Many RC frame structures were severely damaged or collapsed in some layer. The phenomenon was significantly different from the expected failure mode in seismic design code. This paper comprehensively sums up the earthquake characteristics of masonry infilled RC frame structures. Based on an investigation of a masonry infilled RC frame structure damaged in the earthquake area, conduct the research on frail-layer caused by infill walls uneven decorated. On the hypothesis of keeping the main load-bearing component invariant, two models were considered, i. e. frame with floor slab, and frame with both floor slab and infill wall. Furthermore, divide them into groups of the bottom, the middle and the top frail-layer to discuss by changing the arrange of infill wall. Time history analyses using three-dimensional sophisticated finite element method were conducted. The major findings are: 1)infill walls may significantly alter the failure mechanism of the RC frames. 2)controlling the initial interlayers lateral stiffness ratio in a reasonable range is an effective method to avoid frail-layer damage. These findings suggest that the effects of infill wall should be considered in seismic design, keep the initial interlayers lateral stiffness ratio less than the paper suggested, and the structural elasto-plastic analysis model should take slabs and infill walls into account.
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Abe, Hisashi, and Ryo Funada. "Review — The Orientation of Cellulose Microfibrils in the cell walls of Tracheids in Conifers." IAWA Journal 26, no. 2 (2005): 161–74. http://dx.doi.org/10.1163/22941932-90000108.
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We examined the orientation of cellulose microfibrils (Mfs) in the cell walls of tracheids in some conifer species by field emission-scanning electron microscopy (FE-SEM) and developed a model on the basis of our observations. Mfs depositing on the primary walls in differentiating tracheids were not well-ordered. The predominant orientation of the Mfs changed from longitudinal to transverse, as the differentiation of tracheids proceeded. The first Mfs to be deposited in the outer layer of the secondary wall (S1 layer) were arranged as an S-helix. Then the orientation of Mfs changed gradually, with rotation in the clockwise direction as viewed from the lumen side of tracheids, from the outermost to the innermost S1 layer. Mfs in the middle layer of the secondary wall (S2 layer) were oriented in a steep Z-helix with a deviation of less than 15° within the layer. The orientation of Mfs in the inner layer of the secondary wall (S3 layer) changed, with rotation in a counterclockwise direction as viewed from the lumen side, from the outermost to the innermost S3 layer. The angle of orientation of Mfs that were deposited on the innermost S3 layer varied among tracheids from 40° in a Z-helix to 20° in an S-helix.
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Khalid, Mahmood, Khalid A. Juhany, and Salah Hafez. "Computational modeling of the flow in a wind tunnel." Aircraft Engineering and Aerospace Technology 90, no. 1 (January 2, 2018): 175–85. http://dx.doi.org/10.1108/aeat-05-2016-0072.
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Purpose The purpose of this paper is to use a computational technique to simulate the flow in a two-dimensional (2D) wind tunnel where the effect of the solid walls facing the model has been addressed using a porous geometry so that interference arriving at the solid walls are duly damped and a flow suction procedure has been adopted at the side wall to minimize the span-wise effect of the growing side wall boundary layer. Design/methodology/approach A CFD procedure based on discretization of the Navier–Stokes equations has been used to model the flow in a rectangular volume with appropriate treatment for solid walls of the confined volume in which the model is placed. The rectangular volume was configured by stacking O-Grid sections in a span-wise direction using geometric growth from the wall. A porous wall condition has been adapted to counter the wall interference signatures and a separate suction procedure has been implemented for reducing the side wall boundary layer effects. Findings It has been shown that through such corrective measures, the flow in a wind tunnel can be adequately simulated using computational modeling. Computed results were compared against experimental measurements obtained from IAR (Institute for Aerospace, Canada) and NAL (National Aeronautical Laboratory, Japan) to show that indeed appropriate corrective means may be adapted to reduce the interference effects. Research limitations/implications The solutions seemed to converge a lot better using relatively coarser grids which placed the shock locations closer to the experimental values. The finer grids were more stiff to converge and resulted in reversed flow with the two equation k-w model in the region where the intention was to draw out the fluid to thin down the boundary layer. The one equation Spalart–Allmaras model gave better result when porosity and wall suction routines were implemented. Practical implications This method could be used by industry to point check the results against certain demanding flow conditions and then used for more routine parametric studies at other conditions. The method would prove to be efficient and economical during early design stages of a configuration. Originality/value The method makes use of an O-grid to represent the confined test section and its dual treatment of wall interference and blockage effects through simultaneous application of porosity and boundary layer suction is believed to be quite original.
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DHANAK, M. R., and C. SI. "On reduction of turbulent wall friction through spanwise wall oscillations." Journal of Fluid Mechanics 383 (March 25, 1999): 175–95. http://dx.doi.org/10.1017/s0022112098003784.
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A model for turbulent skin friction, proposed by Orlandi & Jimenez, involving consideration of quasi-streamwise vortices in the cross-stream plane, is used to study the effect on the skin friction of oscillating the surface beneath the boundary layer in the spanwise direction. Using an exact solution of the Navier–Stokes equations, it is shown that the interaction between evolving, axially stretched, streamwise vortices and a modified Stokes layer on the oscillating surface beneath, leads to reduction in the skin friction, the Reynolds stress and the rate of production of kinetic energy, consistent with predictions based on experiments and direct numerical simulations.
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Ikeda, Ryosaku, and Hiroyuki Kusaka. "Proposing the Simplification of the Multilayer Urban Canopy Model: Intercomparison Study of Four Models." Journal of Applied Meteorology and Climatology 49, no. 5 (May 1, 2010): 902–19. http://dx.doi.org/10.1175/2009jamc2336.1.
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Abstract The study proposes the simplification of the multilayer urban canopy model. Four types of multilayer urban canopy models—level 4, level 3, level 2, and level 1—are developed to reduce the computational load of the heat budget calculations at the wall surface. The level 4 model, which accounts for the wall directions and the vertical layer, is simplified in three ways: the level 3 model only accounts for the vertical layers, the level 2 model accounts for the wall directions, and the level 1 model accounts for neither the wall directions nor the vertical layer. From the simplification, compared to the level 4 model, the memory is reduced by 57%, 65%, and 72% for the level 3–level 1 models, respectively, when the vertical canopy layer is seven. At the same time, the CPU time is reduced by 67%, 70%, and 78% for the level 3–level 1 models. Then, each canopy model is compared with observations in Tokyo. The results show that the simulations from the four models are close to the observed ones, and the differences among the four models are very small. An additional model intercomparison study based on idealized simulations indicates that the level 3 model can be used instead of the level 4 model in any condition, whereas the level 2 and level 1 models are proposed to be used under conditions with a large sky view factor.
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Zhu, Yalin, Renyi Chen, Liming Wu, Qian Xu, and Zijian Zhan. "Reinforcement placement on mechanics and deformation of stepped reinforced retaining wall experimental study of characteristics." Applied Rheology 32, no. 1 (January 1, 2022): 155–65. http://dx.doi.org/10.1515/arh-2022-0131.
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Abstract Three sets of indoor model tests of reinforced retaining walls were conducted to study the effects of reinforcing material placement on the displacement of reinforced retaining walls, wall top settlement, earth pressure distribution, and potential failure surface. The test results show that under different reinforcement laying conditions, the maximum horizontal displacement of the lower wall panel appears at the top of the lower retaining wall, and the maximum horizontal displacement of the upper wall panel appears at 0.6H. The settlement of the top of the wall decreases by about 9.1% when the reinforcement is laid in the lower layer. Under the condition of 160 kPa, the maximum horizontal and vertical earth pressures increase by about 19.2 and 12.4%, respectively, and the position of the potential fracture surface of the lower wall moves up to the back of the wall with the position of the reinforcement laying. When the reinforcement is laid in the upper layer, the fracture surface of the upper wall is furthest away from the panel.
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Wang, Dan, and Hui Ren Bai. "Life Cycle Model of Ultra High Toughness Cementitious Composites Exterior Walls." Applied Mechanics and Materials 638-640 (September 2014): 1512–15. http://dx.doi.org/10.4028/www.scientific.net/amm.638-640.1512.
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In order to research ultra high toughness cementitious composites (UHTCC) economic rationality, this paper chooses the ultra high toughness cementitious composites thermal insulation wall as the research object, uses the study of life cycle method. Establish full life-cycle model with basic life-cycle economic evaluation principle. Evaluate its economic rationality. The results show that ultra high toughness cementitious composites facade has a longer life cycle than ordinary concrete wall. And their local repair costs are all the same, but their maintain frequencies are different. UHTCC facades facing layer does not require maintenance. The calculated models of the two walls are different.
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Su, Zhi Bin, Tao Han, and Sheng Nan Sun. "Nonlinear Static Pushover Analysis for Shear Wall Structures in SAP2000 Program." Applied Mechanics and Materials 470 (December 2013): 1007–10. http://dx.doi.org/10.4028/www.scientific.net/amm.470.1007.
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To study the nonlinear mechanical characteristics of reinforced concrete shear wall structures under rare earthquakes, a single reinforced concrete shear wall model is established in SAP2000 program, which is simulated by nonlinear multi-layer shell element. Nonlinear static pushover analysis of the model is presented by uniform acceleration lateral load pattern and inverted triangle lateral load pattern. The relationship curve between base shear and top displacement of shear wall, and the stress distribution diagrams of the concrete layer and rebar layer are obtained. It may be concluded that, the yielding of rebar layer and the cracking of the concrete layer may be observed by stress distribution diagrams. SAP2000 program is feasible to nonlinear simulation of shear wall structures.
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Naire, Shailesh, and Oliver E. Jensen. "Epithelial cell deformation during surfactant-mediated airway reopening: a theoretical model." Journal of Applied Physiology 99, no. 2 (August 2005): 458–71. http://dx.doi.org/10.1152/japplphysiol.00796.2004.
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A theoretical model is presented describing the reopening by an advancing air bubble of an initially liquid-filled collapsed airway lined with deformable epithelial cells. The model integrates descriptions of flow-structure interaction (accounting for nonlinear deformation of the airway wall and viscous resistance of the airway liquid flow), surfactant transport around the bubble tip (incorporating physicochemical parameters appropriate for Infasurf), and cell deformation (due to stretching of the airway wall and airway liquid flows). It is shown how the pressure required to drive a bubble into a flooded airway, peeling apart the wet airway walls, can be reduced substantially by surfactant, although the effectiveness of Infasurf is limited by slow adsorption at high concentrations. The model demonstrates how the addition of surfactant can lead to the spontaneous reopening of a collapsed airway, depending on the degree of initial airway collapse. The effective elastic modulus of the epithelial layer is shown to be a key determinant of the relative magnitude of strains generated by flow-induced shear stresses and by airway wall stretch. The model also shows how epithelial-layer compressibility can mediate strains arising from flow-induced normal stresses and stress gradients.
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ZHANG, L. X. "PHYSICS OF COHERENT STRUCTURES OF TURBULENT FLOW IN NEAR-WALL REGION OF A VIBRATING PLATE." Modern Physics Letters B 24, no. 13 (May 30, 2010): 1433–36. http://dx.doi.org/10.1142/s0217984910023803.
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The focus of this paper is on physics of coherent structures in boundary layer flow in near-wall region of a vibrating plate. A dynamical model is developed based on Galerkin projection of the governing equation of the wall layer flow onto a subspace spanned by the orthogonal divergence-free Fourier basis functions. The interactive physics of the coherent structures with the wall vibration is studied with the established model truncated at any order. The compared results show that the prevailing coherent structures in the layer flow near a vibrating wall region are captured.
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Caudwell, T., J. B. Flór, and M. E. Negretti. "Convection at an isothermal wall in an enclosure and establishment of stratification." Journal of Fluid Mechanics 799 (June 23, 2016): 448–75. http://dx.doi.org/10.1017/jfm.2016.360.
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In this experimental–theoretical investigation, we consider a turbulent plume generated by an isothermal wall in a closed cavity and the formation of heat stratification in the interior. The buoyancy of the plume near the wall and the temperature stratification are measured across a vertical plane with the temperature laser induced fluorescence method, which is shown to be accurate and efficient (precision of $0.2\,^{\circ }$C) for experimental studies on convection. The simultaneous measurement of the velocity field with particle image velocimetry allows for the calculation of the flow characteristics such as the Richardson number and Reynolds stress. This enables us to give a refined description of the wall plume, as well as the circulation and evolution of the stratification in the interior. The wall plume is found to have an inner layer close to the heated boundary with a laminar transport of hardly mixed fluid which causes a relatively warm top layer and an outer layer with a transition from laminar to turbulent at a considerable height. The measured entrainment coefficient is found to be dramatically influenced by the increase in stratification of the ambient fluid. To model the flow, the entrainment model of Morton, Taylor & Turner (Proc. R. Soc. Lond. A, vol. 234 (1196), 1956, pp. 1–23) has first been adapted to the case of an isothermal wall. Differences due to their boundary condition of a constant buoyancy flux, modelled with salt by Cooper & Hunt (J. Fluid Mech., vol. 646, 2010, pp. 39–58), turn out to be small. Next, to include the laminar–turbulent transition of the boundary layer, a hybrid model is constructed which is based on the similarity solutions reported by Worster & Leitch (J. Fluid Mech., vol. 156, 1985, pp. 301–319) for the laminar part and the entrainment model for the turbulent part. Finally, the observed variation of the global entrainment coefficient, which is due to the increased presence of an upper stratified layer with a relatively low entrainment coefficient, is incorporated into both models. All models show reasonable agreement with experimental measurements for the volume, momentum and buoyancy fluxes as well as for the evolution of the stratification in the interior. In particular, the introduction of the variable entrainment coefficient improves all models significantly.
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Klimes, Lubomir, Pavel Charvát, and Josef Stetina. "Mathematical Model of Multi-Layer Wall with Phase Change Material and its Use in Optimal Design." Advanced Materials Research 649 (January 2013): 295–98. http://dx.doi.org/10.4028/www.scientific.net/amr.649.295.
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The paper deals with the mathematical model of the multi-layer wall containing the phase change material (PCM). The model utilizes the effective heat capacity method for modeling the latent heat of phase change and the control volume method is used for the discretization of the model. The utilization of the model is then demonstrated on the problem of the optimal design of the multi-layer wall with the PCM. The TMY2 data for the city of Brno were used in simulations as operational conditions. The main attention is aimed at the determination of the optimal thickness of the PCM layer for the multi-layer wall design with various thicknesses of the masonry.
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Chu, C. C., and R. E. Falco. "Vortex ring/viscous wall layer interaction model of the turbulence production process near walls." Experiments in Fluids 6, no. 5 (1988): 305–15. http://dx.doi.org/10.1007/bf00538821.
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Walker, J. D. A., D. E. Abbott, R. K. Scharnhorst, and Gilbert G. Weigand. "Wall-layer model for the velocity profile in turbulent flows." AIAA Journal 27, no. 2 (February 1989): 140–49. http://dx.doi.org/10.2514/3.10075.
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AHN, B. K., W. R. GRAHAM, and S. A. RIZZI. "A structure-based model for turbulent-boundary-layer wall pressures." Journal of Fluid Mechanics 650 (March 16, 2010): 443–78. http://dx.doi.org/10.1017/s0022112009993727.
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Practical prediction of structural vibrations due to a turbulent boundary layer currently depends on empirical representations of the unsteady wall pressures. Improvements in these representations would be greatly facilitated if a simple, physically based model were available to test ad hoc assumptions and provide rigorous interpolation of experimental data. A possible candidate is the attached-eddy model, developed from Townsend's initial ideas by Perry and co-workers in the context of turbulence velocity spectra. This approach employs the superposition of contributions from individual ‘eddies’, of varying size, to yield its predictions. It is shown here that the same methodology can be applied for wall pressures, once the field due to an eddy has been obtained via solution of the governing Poisson equation. Comparisons with large-eddy simulation and experimental data, spanning a two-decade Reynolds number range, show remarkably good agreement, given the simplicity of the model. It is concluded that this approach has the potential to provide useful physical insight and, subject to its extension to a time-resolved form, improvements to existing empirical formulations.
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NAKAMURA, T., K. SAKON, A. YAMAMOTO, and T. MINESHITA. "Double wall layer model of biofluids flowing in a capillary." Biorheology 33, no. 1 (January 1996): 79. http://dx.doi.org/10.1016/0006-355x(96)86752-7.
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Pourriahi, Vahid, Mohammad Heidari-Rarani, and Amir Torabpour Isfahani. "Influence of geometric parameters on free vibration behavior of an aluminum honeycomb core sandwich beam using experimentally validated finite element models." Journal of Sandwich Structures & Materials 24, no. 2 (December 10, 2021): 1449–69. http://dx.doi.org/10.1177/10996362211053633.
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The hexagonal honeycomb core sandwich panels used in the satellite structure are subjected to severe vibration during launch. Therefore, the amounts of natural frequencies of these panels are of great importance for design engineers. Three-dimensional finite element modeling of the core considering all geometric parameters (i.e., a high-fidelity model) to achieve accurate results is not cost-effective. The honeycomb core is traditionally equivalent to a homogenized continuum core (i.e., a low-fidelity model) using simple analytical relations with ignoring the adhesive layer at the double cell-walls and radius of inclined cell-wall curvature. In this study, analytical formulations are first presented for the prediction of the equivalent elastic properties of a hexagonal aluminum honeycomb with considering all geometric parameters including adhesive layer thickness, cell-wall thickness, inclined cell-wall length, radius of inclined cell-wall curvature at the intersection, internal cell-wall angle, and honeycomb height. Then, two aluminum honeycomb core sandwich beams with free-free boundary conditions are modeled and analyzed in Abaqus finite element software, one with 3D high-fidelity core and the other with 3D low-fidelity core. In order to validate the results of the equivalent model, the modal analysis test was performed and the experimental natural frequencies were compared. The obtained results show a good agreement between the 3D low-fidelity and high-fidelity finite element models and experimental results. In addition, the influence of the above-mentioned geometric parameters has been investigated on the natural frequencies of a sandwich beam. [Formula: see text]
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Rodi, W., N. N. Mansour, and V. Michelassi. "One-Equation Near-Wall Turbulence Modeling With the Aid of Direct Simulation Data." Journal of Fluids Engineering 115, no. 2 (June 1, 1993): 196–205. http://dx.doi.org/10.1115/1.2910124.
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The length scales appearing in the relations for the eddy viscosity and dissipation rate in one-equation models were evaluated from direct numerical (DNS) simulation data for developed channel and boundary-layer flow at two Reynolds numbers each. To prepare the ground for the evaluation, the distribution of the most relevant mean-flow and turbulence quantities is presented and discussed, also with respect to Reynolds-number influence and to differences between channel and boundary-layer flow. An alternative model is examined in which (v′2)1/2 is used as velocity scale instead of k1/2. With this velocity scale, the length scales now appearing in the model follow closely a linear relationship near the wall. The resulting length-scale relations together with a DNS based relation between v′2/k and y* = k1/2y/v form a new one-equation model for use in near-wall regions. The new model was tested as near wall component of a two-layer model by application to developed-channel, boundary-layer and backward-facing-step flows.
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Durbin, P. A., G. Medic, J. M. Seo, J. K. Eaton, and S. Song. "Rough Wall Modification of Two-Layer k−ε." Journal of Fluids Engineering 123, no. 1 (November 17, 2000): 16–21. http://dx.doi.org/10.1115/1.1343086.
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A formulation is developed to apply the two-layer k−ε model to rough surfaces. The approach involves modifying the lν formula and the boundary condition on k. A hydrodynamic roughness length is introduced and related to the geometrical roughness through a calibration procedure. An experiment has been conducted to test the model. It provides data on flow over a ramp with and without surface roughness.
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Mu, Haochen, Joseph Polden, Yuxing Li, Fengyang He, Chunyang Xia, and Zengxi Pan. "Layer-by-layer model-based adaptive control for wire arc additive manufacturing of thin-wall structures." Journal of Intelligent Manufacturing 33, no. 4 (March 10, 2022): 1165–80. http://dx.doi.org/10.1007/s10845-022-01920-5.
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AbstractImproving the geometric accuracy of the deposited component is essential for the wider adoption of wire arc additive manufacturing (WAAM) in industries. This paper introduces an online layer-by-layer controller that operates robustly under various welding conditions to improve the deposition accuracy of the WAAM process. Two control strategies are proposed and evaluated in this work: A PID algorithm and a multi-input multi-output model-predictive control (MPC) algorithm. After each layer of deposition, the deposited geometry is measured using a laser scanner. These measurements are compared against the CAD model, and geometric errors are then compensated by the controller, which generates a new set of welding parameters for the next layer. The MPC algorithm, combined with a linear autoregressive (ARX) modelling process, updates welding parameters between successive layers by minimizing a cost function based on sequences of input variables and predicted responses. Weighting coefficients of the ARX model are trained iteratively throughout the manufacturing process. The performance of the designed control architecture is investigated through both simulation and experiments. Results show that the real-time control performance is improved by increasing the complexity of implemented control algorithm: controlled geometric fluctuations in the test component were reduced by 200% whilst maintaining fluctuations within a 3 mm limit under various welding conditions. In addition, the adaptiveness of designed control strategy is verified by accurately controlling the fabrication of a part with complex geometry.
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Zhou, Zhong-yi, and Wanlin Cao. "Experimental study on seismic performance of low-rise recycled aggregate concrete shear wall with single-layer reinforcement." Advances in Structural Engineering 20, no. 10 (December 26, 2016): 1493–511. http://dx.doi.org/10.1177/1369433216682504.
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A total of four full-scale low-rise recycled aggregate concrete shear wall specimens were tested adopting a quasi-static loading method to analyze the seismic performance. The low-rise shear walls consisted of recycled aggregate concrete, single-layer reinforcements, concealed special-shaped columns, and expanded polystyrene thermal insulation modules. Based on the experimental results, the seismic performance and failure characteristic of the specimens were comparatively analyzed. The factors affecting the seismic performance of the low-rise shear wall were also analyzed. The shear bearing capacity calculation model and formula of the walls were proposed based on the softened strut-and-tie model. A comparison of the calculated results and the experimental results shows that they are in good agreement. The results show that the load bearing capacity and deformation capacity can be significantly improved by expanded polystyrene thermal insulation modules, and that the shear wall specimens with higher recycled aggregate concrete strength and larger reinforcement ratio of the shear wall exhibit better seismic performance.
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Mogilevich, L. I., V. S. Popov, A. A. Popova, and A. V. Khristoforova. "Mathematical Simulation of Nonlinear Vibrations of a Channel Wall Interacting with a Vibrating die Via Viscous Liquid Layer." Herald of the Bauman Moscow State Technical University. Series Instrument Engineering, no. 2 (139) (June 2022): 26–41. http://dx.doi.org/10.18698/0236-3933-2022-2-26-41.
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The article considers the developed mathematical model and investigates the dynamics of the interaction of a channel wall supported by a nonlinear spring with a vibrating opposite wall through a viscous fluid layer filling the channel. A flat slotted channel formed by two absolutely rigid rectangular walls, parallel to each other was investigated. One of the channel dimensions in the plan was much larger than the other, which leads to the transition to a plane problem. The bottom channel wall rested on a spring with a cubic nonlinear characteristic, and the upper wall was a die oscillating according to a given law. The gap between the walls was assumed to be much smaller than the channel longitudinal dimension, and the amplitudes of wall vibrations were much less than the channel gap. The movement of the viscous fluid in the channel was considered to be creeping. The mathematical model of the channel under consideration consisted of an equation of the dynamics of a single-mass system with a spring having a cubic nonlinearity, as well as the Navier --- Stokes and continuity equations, supple-mented by the boundary conditions for fluid nonslip on the channel walls and its free outflow at the ends. The steady-state nonlinear vibrations of the bottom channel wall at the fundamental frequency were studied, and its hydroelastic response was determined. The proposed model can be used to study nonlinear vibrations of elastically fixed elements that are in contact with liquid and are parts of modern devices and assemblies
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Bhave, Ashish, and Knut Möller. "Comparison of a histology based multi layer artery model to its simplified axisymmetric model." Current Directions in Biomedical Engineering 7, no. 2 (October 1, 2021): 590–93. http://dx.doi.org/10.1515/cdbme-2021-2150.
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Abstract Arteries are vessel structures that serve vital function of transportation of blood to different parts of the body. Researchers have experimented with some approaches to model the arterial behaviour and to analyse its biomechanical properties. To analyse the in-vivo arterial properties, at Furtwangen University an inflatable sensoractuator system is being developed, which provides the basis for a decision support system for vascular surgeons. The capabilities of this sensor shall be evaluated in simulations which requires appropriate modelling of the arteries. The inverse problem, i.e. how to efficiently identify arterial wall properties from sensor readings is targeted. A histology motivated 3D artery model was implemented in FEM using COMSOL (v5.5). The geometry of one model was based on a cross section of a real artery. The second model was axisymmetric and of equal dimensions with respect to volume, layer thickness etc. A biomechanical pressure-stretch analysis was performed applying an inflating pressure inside the walls of the vessels. Stretch in different areas of the first model was evaluated and the circumferential strain was compared to the axisymmetric model. The results show variation of strains within the segments of the first model of upto 10 percent. In addition, its outer wall circumferential stretch was found to be 10 percent lower compared to the axisymmetric setup. This comparison sheds light upon whether a simplification of arterial models is possible, without loss of accuracy in the context of the novel sensor evaluation. It provides useful information whether e.g. standardizing vessel structures to axisymmetric models will still provide results within allowable tolerance limits. Simulations proved useful to evaluate different vessel model formulations in the context of arterial diagnostics.
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Chen, Yanlong, Aihong Lu, Xianbiao Mao, Ming Li, and Lianying Zhang. "Nonlinear Dynamics Mechanism of Rock Burst Induced by the Instability of the Layer-Crack Plate Structure in the Coal Wall in Deep Coal Mining." Shock and Vibration 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/4051967.
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The instability of layer-crack plate structure in coal wall is one of the causes of rock burst. In the present paper, we investigate the formation and instability processes of layer-crack plate structure in coal wall by experiments and theoretical analysis. The results reveal that layer-crack plate structure formed near the free surface of the coal wall during the loading. During the formation of the layer-crack plate structure, the lateral displacement curve of the coal wall experiences a jagged variation, which suggests the nonlinear instability failure of the coal wall with a sudden release of the elastic energy. Then, a dynamic model for the stability analysis of the layer-crack plate structure was proposed, which takes consideration of the dynamic disturbance factor. Based on the dynamic model, the criterion for dynamic instability of the layer-crack plate structure was determined and demonstrated by an example. According to the analytical results, some control methods of dynamic stability of the layer-crack plate structure was put forward.
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Huo, Yunlong, Xuefeng Zhao, Yana Cheng, Xiao Lu, and Ghassan S. Kassab. "Two-layer model of coronary artery vasoactivity." Journal of Applied Physiology 114, no. 10 (May 15, 2013): 1451–59. http://dx.doi.org/10.1152/japplphysiol.01237.2012.
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Since vascular tone is regulated by smooth muscle cells in the media layer, a multilayer mechanical model is required for blood vessels. Here, we performed biaxial mechanical tests in the intima-media layer of right coronary artery to determine the passive and active properties in conjunction with the passive properties of adventitia for a full vessel wall model. A two-layer (intima-media and adventitia) model was developed to determine the transmural stress and stretch across the vessel wall. The mean ± SE values of the outer diameters of intima-media layers at transmural pressure of 60 mmHg in active state were 3.17 ± 0.16 and 3.07 ± 0.18 mm at axial stretch ratio of 1.2 and 1.3, respectively, which were significantly smaller than those in passive state (i.e., 3.62 ± 0.19 and 3.49 ± 0.22 mm, respectively, P < 0.05). The inner and outer diameters in no-load state of intima-media layers were 1.17 ± 0.09 and 2.08 ± 0.09 mm, respectively. The opening angles in zero-stress state had values of 159 ± 21° for intima-media layers and 98 ± 15° for adventitia layers, which suggests a residual strain between the two layers. There were slightly decreased active circumferential stresses (<10%), but significantly decreased active axial stresses (>25%) in the intima-media layer compared with those in the intact vessel. This suggests that the adventitia layer affects vascular contraction. The two-layer analysis showed that the intima-media layer bears the majority of circumferential tensions, in contrast to the adventitia layer, while contraction results in decreased stress and stretch in both layers.
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Homicz, G. F., and N. Gerber. "Numerical Model for Fluid Spin-Up From Rest in a Partially Filled Cylinder." Journal of Fluids Engineering 109, no. 2 (June 1, 1987): 194–97. http://dx.doi.org/10.1115/1.3242643.
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A numerical investigation is presented for the axisymmetric spin-up of fluid in a partially filled cylindrical cavity. It is an extension of earlier analyses to those cases where the liquid free surface intersects one or both endwalls. Previous models of the laminar Ekman layer pumping are modified heuristically for situations where the layer(s) no longer covers the entire wall. Numerical results for a range of Reynolds number, Froude number, and fill ratio have been obtained. They clearly demonstrae that it is the bottom wall Ekman layer which is primarily responsible for spin-up.
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Yang, Shaohua, Wei Long, and Fangwei Ning. "Analysis of velocity slipping at wall boundary under rarefied gas condition based on the effect of viscosity." Industrial Lubrication and Tribology 70, no. 8 (November 12, 2018): 1509–15. http://dx.doi.org/10.1108/ilt-03-2017-0080.
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Purpose Velocity slipping model, based on the stratification theory (the film in inflatable support area of aerostatic guide way was divided into near wall layer, thin layer and continuous flow layer in the direction of height), was established, and the model was combined with viscosity changes in each layer. Design/methodology/approach Simulated and analyzed by LAMMPS and two-dimensional molecular dynamics method, some relevant conclusions were drawn. Findings At a high temperature, viscosity is low, velocity slipping is large and velocity gaps in near-wall layer and thin layer are large. When the temperature is constant, the dimensionless slipping length and Kn number are linear. Research limitations/implications The effect of the equivalent viscosity on gas slipping model is proposed. viscosity is smaller, gas velocity slipping is greater, temperature is higher, gas velocity slipping is greater, velocity gap of near wall layer and thin layer is larger. When the temperature is constant, the dimensionless slipping length ls and Kn number are linear. Originality/value The global model of lubricating film velocity slipping between plates was established, and mathematical expression of slipping model in each layer, based on the stratification theory, was presented.
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Friedman, M. H. "Arterial Fluid Mechanics and Biological Response." Applied Mechanics Reviews 43, no. 5S (May 1, 1990): S103—S108. http://dx.doi.org/10.1115/1.3120788.
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To better understand the response of the arterial wall to the adjacent blood flow, corresponding hemodynamic and histomorphometric data are obtained at multiple sites in human arteries. The hemodynamic data are obtained by perfusing realistically compliant flow-through casts of vascular segments with physiologically realistic pulsatile flows and measuring near-wall velocities by laser Doppler velocimetry. The hemodynamic and histologic data in combination suggest that the thickening response of the innermost layer of the vessel wall, which may precede atherosclerosis at the site, varies with time and wall shear: at early times, sites exposed to relatively high and unidirectional shears are thicker, while at later times, their thickness is exceeded by that at sites exposed to relatively low or oscillatory shear forces. A biologically plausible mathematical model of the thickening process supports the hypothesis that this behavior can be the consequence of multiple shear-dependent processes in the vessel wall.
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Yang, Fang, Lin Zhu Sun, and Zi Ling Xie. "Theoretical Study on Optimal Design of Thermal Performance of Aerated Concrete-Based Composite Thermal Insulation Wall." Advanced Materials Research 450-451 (January 2012): 663–66. http://dx.doi.org/10.4028/www.scientific.net/amr.450-451.663.
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A wall of aerated concrete only can hardly meet the requirements for energy-saving architectural design. If both sides of the wall are provided with thermal insulation mortar to form a composite wall, the heat transfer performance of the wall will be significantly improved. In this Paper, we established an optimization model for the thermal economy of a thermal insulation composite wall according to heat transfer theory and in consideration of the depreciation and maintenance costs of the wall during use, and took the average heat transfer coefficient and index of thermal inertia of the wall as restricted conditions to calculate and analyze the economical thickness of the thermal insulation layer. We expect the optimization model be valuable reference in promoting the application of aerated concrete-based composite thermal insulation walls.