Wall Absorption Research Articles

Machine learning aided near-field acoustic holography based on equivalent source method.

In recent times, equivalent source method-based near-field acoustic holography methods have been extensively applied in sound source localization and characterization. The most commonly used equivalent sources are spherical harmonics. In a non-reverberant environment with no reflections, these equivalent sources could be the best choice since spherical harmonics are derived for the Sommerfeld boundary condition. However, these methods are not the best fit for reverberating environments. In such cases, a new relationship can be calculated between the field weights and the measured pressure with enough training examples. The proposed machine learning models include linear regression (LR) with adaptive moment estimation (Adam), LR with limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS), and multi-layer perceptron with one and two hidden layers. These methods are tested for multiple monopoles and vibrating plate simulations in a room with different wall absorption coefficients. The data-driven methods are also studied on loudspeakers numerically and experimentally in a free field environment. The results from these methods are compared with the results of one norm convex optimization (L1CVX). LR with L-BFGS performed the best among all the methods studied and performed better than L1CVX for less absorption coefficient for geometrically separable sources. LR with L-BFGS also has much faster inference times.

Study Of Nanoparticle Dispersion In Capillaries Using Power Law Nanofluid Model

This paper investigates the aspects of dispersion of nanoparticles in blood capillaries linked to nanodrug delivery systems. Nanoparticles are injected intravenously in blood capillaries and the resultant fluid has been identified as nanofluid. The viscosity of nanofluid is modelled using the nanoparticle size dependent viscosity relation. The properties of blood are studied using power law fluid, owing to their physically close simulations. The dispersion model framed here has been solved applying the method used by Sankarsubramanian and Gill for deriving exchange coefficients. The study conducted gives an insight into temperature, velocity and three transport coefficients of nanoparticles dispersed in blood with respect to various parameters like heat source parameter, volume fraction, power law index, size of nanoparticles, Grashof number, Darcy number and slip parameter for small values of wall absorption parameter under steady state conditions. MATLAB software has been used to plot the graphs. The outcomes reveal that physical properties of nanoparticles like size chiefly govern their dispersion. Convergence analysis is also stated for the inhomogeneous Bessel differential equation obtained while solving the problem. The developed mathematical model has useful applications to understand the dispersion of nanodrugs in the treatment of cardio vascular diseases.

Determination and Evaluation of Potentially Toxic Heavy Metals in Some Selected Rivers within Ijebu-North, Nigeria

Human health would be at risk if water which is essential for every human activity is contaminated with carcinogenic substances including heavy metals, this present study evaluated potentially toxic metal concentration in some selected rivers in Ijebu-North of Nigeria to determine the concentration of heavy metals and evaluate the pollution index. Ten (10) rivers were randomly selected for the purpose of this study. Samples were collected using a labelled acid pre-cleaned polyethylene container so as avoid wall absorption, the samples were collected from different points at different locations along the course of the river. The samples were filtered, acidified with HNO3 and analysed for heavy metals using Atomic Absorption Spectrometer (AAS). Concentrations of Pb, Ni, Cr and Cu in all the rivers were higher than the WHO limit. However Hg, Cd, Ag, Al, and Mn values are below the recommended values. The contamination factor (C_f) for the Pb varied from 2.18-4.04, Ni varied from 3.0-14.0, Hg was between 0.00-0.03333, Cd was between 0.16667-0.6667, Cr varied between 8.00-48.40, Cu varied between 4.00-12.00, Ag varied between 0.01-0.02, Se varied from 0.05-1.25, Al varied between 0.12-0.46 and Mn varied from 0.020-0.028, Cu values fall within the range of very severe pollution. The results from this study revealed that some rivers within the study area were polluted and recommended for treatment before they can be used domestically and for other purposes.

Unsteady solute dispersion in pulsatile Luo and Kuang blood flow (K - L Model) in a tube with wall reactive absorption

Unsteady solute dispersion in pulsatile non-Newtonian flow in a circular tube has been investigated considering higher order moments using the Aris’s method of moments. The Luo and Kuang(1992) (K - L Model) constitutive relation is used for the non-Newtonian fluid. The axial mean concentration of solute is estimated by considering exchange, convective, dispersion coefficients. In addition, considering the 3rd and 4th central moments, the skewness, and kurtosis in the mean concentration is examined. Variations of these five moments against the absorption parameter, K-L fluid parameters, and Womersley frequency parameter are thoroughly investigated. The increase in the Womersley frequency parameter led to the occurrence of a double frequency period for the dispersion coefficient, which influenced the skewness and kurtosis coefficients that led to the deviation from usual normal distribution of the mean concentration distribution at the starting of the dispersion process. The concentration distribution is skewed towards the central region of the tube. The concentration contours also reveal that the solute convection is more in the central region of the tube. The results for Newtonian, Bingham, and Casson fluid models are retrieved as special cases. The mean concentration has the highest peak for the K-L model and the lowest for the Newtonian fluid model. It is scattered axially more for the Bingham fluid than the Casson fluid. This investigation emphasizes that higher moments provide precise information about the solute dispersion in the flow field and its deviation from the normal distribution at small time scales. • This investigation examining the unsteady axial dispersion of a solute in the non-Newtonian pulsatile flow in a cylindrical tube, considering the impact of an irreversible first-order boundary reaction. Solute dispersion in K-L model has been introduced, which gives the shear thinning and thickening behaviour of blood flow even if yield stress is zero. • The present study initiated skewness and kurtosis analysis for steady/ unsteady, non-pulsatile/ pulsatile and Newtonian/ non-Newtonian fluid flow by using method of moments. Here analytical results for all transport coefficient with skewness and kurtosis has been discussed. • The perturbation and numerical solution of coupled and non-linear equation of shear stress and momentum equation has been obtained to get the velocity profile. A new class of computationally explicit Runge–Kutta (CERK) numerical method (Yadav et. al. (2022)) has been used to solve this stiff problem. A detailed comparison of perturbation and numerical solutions is also given in this manuscript. • The solution of the concentration equation is obtained analytically adopting the Aris0 s method of moments, with fourth-order precision. In the presence of boundary reaction, the transport coefficients are affected not only by time but also by the Womersley frequency parameter, other chemical variables, the wall absorption parameter, the yield stress, the amplitude of the fluctuating pressure component, and plasma viscosity. The non-Gaussian distribution of solute is visible for small time after injection. • The mean concentration as well as the two-dimensional concentration distribution are accurately described. The results for the Bingham model, the Casson model, and the Newtonian model are derived directly from this analysis.

Flexural behavior of hollow interlocking compressed stabilized earth-block masonry walls under out-of-plane loading

The present study aims to investigate the out-of-plane flexural behavior of hollow interlocking compressed stabilized earth block (ICSEB) masonry walls reinforced with bamboo and steel bars. The effect of grouting, channel block and reinforcement layout (vertical and mesh type) was assessed. A total of thirty masonry walls were fabricated using fibre reinforced blocks and categorized into five groups: two groups of ungrouted and grouted (without bamboo or steel reinforcement) masonry wall specimens and three groups of grouted masonry wall specimens reinforced with bamboo splints and steel bars. All the specimens were subjected to a constant pre-compression load while lateral load parallel to bed joints was gradually applied until failure. In addition, the experimental moment capacity of reinforced masonry walls was compared with the MSJC-11 formulations to assess the applicability. A statistical regression analysis was then performed on the test results to predict the ultimate moment and deformation capacity of all wall specimens. Test results suggest that grout alone has significantly contributed to the load carrying capacity of wall specimens but with a marginal improvement in deformability. While, channel blocks has no significant effect on load carrying capacity of reinforced grouted masonry wall specimens. Bamboo splints and steel bars as internal reinforcements are very effective in preventing the sudden failure and also enhancing the flexural resistance of masonry walls. Steel mesh showed the highest load carrying capacity, lateral deformation and energy absorption capacity. The addition of bamboo or steel reinforcement combined with grout improved the ultimate load carrying, deformation capacity and energy absorption of walls by 114.88%–260.55%, 19%–35.52% and 168.25%–489.28% respectively.The MSJC-11 code overestimated the moment capacity of reinforced masonry walls; whereas the regression models developed accurately predicted the moment capacity and lateral deformation of the masonry walls.

Unsteady solute dispersion in non-Newtonian fluid flow in a tube with wall absorption—Deviation from the Gaussianity

Unsteady solute dispersion in a pulsatile Herschel–Bulkley fluid flow in a tube is reinvestigated to examine the significance of the skewness and kurtosis on the concentration distribution using Aris' method of moments considering Hermite polynomials. This study is also an initiation in the direction of solute dispersion in a pulsatile non-Newtonian flow considering the first five moments. This investigation not only brings in the accuracy in the estimation but also measures the deflection and decrease in the axial mean concentration distribution of a solute in a tube. Significant variations in the skewness and kurtosis coefficients against various values of the flow governing parameters, such as the yield stress τy, the wall absorption parameter β, the power law index a, the Womersley frequency parameter α, and the amplitude of fluctuating pressure component e, are presented graphically along with the variations in the mean concentration distribution of the solute in the tube. For larger values of the Womersley frequency parameter, the occurrence of double frequency period for the convection and dispersion coefficients is noticed, which has significant influence on the skewness and kurtosis coefficients. The results for solute dispersion in Newtonian fluid, Bingham fluid, and power law fluid flows are also reported as special cases of this analysis.

Optical analysis of a semi-transparent packed bed of spheres for next-generation volumetric solar receivers

Volumetric solar absorbers are attractive for high-temperature concentrating solar applications because they—theoretically—have lower re-radiation losses than surface absorbers since concentrated radiation penetrates their volume. In practice, however, the incident radiation is predominantly absorbed in the top/frontal surfaces of porous and distributed absorber materials. Another challenge with high-temperature absorbers, generally, is the risk of creating hot spots resulting from a non-uniform temperature distribution. To overcome these limitations, this study reports on a semi-transparent absorber design, enabling the peak temperature to occur within the internal volume. Eight different ‘constant-transmittance’ and ‘variable-transmittance’ combinations of transparent/semi-transparent/opaque spheres were packed into a cylindrical cavity and exposed to a solar simulator for a layer-by-layer transmission test. A 3-D ray-tracing model was also developed to further elucidate the relative optical absorption of the cavity walls and spheres. An optimal variable-transmittance design enabled ∼40% of the rays to penetrate to >70% of the absorber's depth, and ∼56% of the total rays were absorbed within the inner volume. Therefore, the optimal design yields uniform absorption, potentially leading to a uniform temperature distribution and a minimisation of thermal emission losses. This study provides the first experimental proof that a semi-transparent packed bed can significantly outperform an opaque design.

An Improved nongray-wall emissivity-absorptivity model for the Full-Spectrum Correlated K-distribution method

In practical combustion chambers, the emissivity of wall materials in general varies spectrally and inappropriate treatments may lead to significant errors in modeling radiative heat transfer. To reduce the error of the Full-Spectrum Correlated K-distribution (FSCK) method in practical problems involving nongray walls, a nongray-wall model is proposed by reordering the wall emissivity and absorptivity separately, in which the Planck function at the wall temperature and an effective mean temperature is used as the weight function of wall emissivity and absorptivity, respectively. As a result, this new model preserves the wall emission and considers the spectral radiative property of the wall. Radiative heat transfer calculations in 1D and 3D configurations bounded by nongray walls are simulated to evaluate the accuracy of this new model. The results show that this new model is in general more accurate than the recently developed nongray-wall model (Liu et al., Int. J. Heat Mass Transf. 2021), especially in cases where the wall-to-wall radiative heat transfer plays an important role. It is also showed that this new model is less sensitive to the choice of the effective mean temperature and the medium blackbody emission-averaged temperature is recommended.

Effect of ring-source release on dispersion process in Poiseuille flow with wall absorption

The analysis of Taylor dispersion in a fluid flowing through a narrow pipe is of considerable interest among the scientific community. Most of the studies on dispersion primarily considered a transversely uniform release of contaminant at the initial moment, while only a few have addressed the influence of the initial condition on the dispersion process in a tube flow. The present work investigates the transient dispersion process with a ring-source release of solute by means of an unsteady two-dimensional transport model. An irreversible absorptive type of a first-order reaction is also considered. The transport model is solved using the series expansion technique of W. N. Gill [“A note on the solution of transient dispersion problems,” Proc. R. Soc. A 298, 335 (1967)], known as the generalized dispersion technique. The whole transport model is explained using the transport coefficients obtained from the first four terms of Gill's series expansion. Meanwhile, the concept of statistical moments is also used for finding the transport coefficients. The study outcomes are well established, satisfying the result of existing literature under limiting conditions. The inclusion of the ring-source release of solute in the study of dispersion has a significant effect at the initial time. In addition, the view of the cross-sectional distribution of solute concentration gives more detailed information on solute scattering under the proposed model.

An unsteady analysis of two-phase binding of drug in an asymmetric stenosed vessel

In this paper, we investigate endovascular delivery to get a step ahead of the pharmacological limitations it has due to the complexity of dealing with a patient-specific vessel through a mathematical model. We divide the domain of computation into four sub-domains: the lumen, the lumen-tissue interface, the upper tissue and the lower tissue which are extracted from an asymmetric atherosclerotic image derived by the intravascular ultrasound (IVUS) technique. The injected drug at the luminal inlet is transported with the streaming blood which is considered Newtonian. An irreversible uptake kinetics of the injected drug at the lumen-tissue interface from the luminal side to the tissue domains is assumed. Subsequently, the drug is dispersed within the tissue followed by its retention in the extracellular matrix (ECM) and by receptor-mediated binding. The Marker and Cell (MAC) method has been leveraged to get a quantitative insight into the model considered. The effect of the wall absorption parameter on the concentration of all drug forms (free as well as two-phase bound) has been thoroughly investigated, and some other important factors, such as the averaged concentration, the tissue content, the fractional effect, the concentration variance and the effectiveness of drug have been graphically analyzed to gain a clear understanding of endovascular delivery. The simulated results predict that with increasing values of the absorption parameter, the averaged concentrations of all drug forms do decrease. An early saturation of binding sites takes place for smaller values of the absorption parameter, and also rapid saturation of ECM binding sites occurs as compared to receptor binding sites. Results also predict the influence of surface roughness as well as asymmetry of the domain about the centerline on the distribution and retention of drug. A thorough sensitivity analysis has been carried out to determine the influence of some parameters involved.

Absorption of Pulsed Terahertz and Optical Radiation in Earthworm Tissue and Its Heating Effect

The transmission of THz, near-infrared (1030 nm), and green (515 nm) pulses through Eisenia andrei body wall is studied, which consists of epithelial layer and circular and longitudinal muscles. Samples with the full-body cross-section were also investigated. The transmitted power for the green pulses followed the Beer-Lambert law of exponential attenuation for all thicknesses and tissue structures. Different body wall and body center absorption coefficients were found in case of infrared pulses. In the THz range, the body wall absorption coefficient steadily increases from about 80 cm–1 at 0.2 THz to about 273 cm–1 at 2.5 THz. Numerical estimation indicates that THz pulses of 5-μJ energy and 1-kHz repetition rate (5-mW average power) cause only a small temperature increase of about 0.4 K, suggesting that heating has minor contribution to biological effectiveness.

Finite impedance boundary conditions determined in situ for modeling underwater acoustical measurement in laboratory tanks

In underwater acoustics, laboratory tank sound propagation models may be improved using in situ characterization of water tank boundaries. An underwater acoustic tank model is developed with finite impedance boundaries determined in situ from impulse response measurements calculated from the frequency deconvolution of swept-sine signals following techniques commonly used in room acoustics. Impulse responses were used to obtain the acoustic absorption of the acrylic tank walls through reverse Schroeder integration determining the reverberation time and solving the Eyring equation for absorptive effects. This approach improves modeling of sound propagation in water tanks and is validated with numerical test cases and measurements. An improved tank model considering measured finite impedance boundaries will further develop the ability for more realistic data simulation in water tanks which will be used to design machine learning refinement.

Optical Analysis of a Semi-Transparent Packed Bed of Spheres for Next-Generation Volumetric Solar Receivers

Volumetric solar absorbers are attractive for high-temperature concentrating solar applications because they—theoretically—have lower re-radiation losses than surface absorbers since concentrated radiation penetrates their volume. In practice, however, the incident radiation is predominantly absorbed in the top/frontal surfaces of porous and distributed absorber materials. Another challenge with high-temperature absorbers, generally, is the risk of creating hot spots resulting from a non-uniform temperature distribution. To overcome these limitations, this study reports on a semi-transparent absorber design, enabling the peak temperature to occur within the internal volume. Eight different 'constant-transmittance' and 'variable-transmittance' combinations of transparent/semi-transparent/opaque spheres were packed into a cylindrical cavity and exposed to a solar simulator for a layer-by-layer transmission test. A 3-D ray-tracing model was also developed to further elucidate the relative optical absorption of the cavity walls and the spheres. An optimal variable-transmittance design enabled ~40% of the rays to penetrate to >70% of the absorber's depth, and ~56% of the total rays were absorbed within the inner volume. Therefore, the optimal design yields uniform absorption, leading to a uniform temperature distribution and a minimisation of thermal emission losses. This study provides the first experimental proof that a semi-transparent packed bed can significantly outperform an opaque design.

Advanced design of Close-Proximity (CPX) trailer enclosure acoustics on tyre/road noise measurement

The PolyU Mark II Twin-wheeled CPX trailer was developed for the measurement of tyre/road noise in Hong Kong urban environment according to a standard methodology (ISO/CD 11819-2) - the Close-Proximity (CPX) method. Numerical simulations of the acoustics of PolyU Mark II CPX enclosure were conducted and a good agreement between numerical and experimental results was obtained. In order to extend the capacity of the Mark II CPX trailer and enhance the acoustic performance within the enclosure for future tyre/road noise studies, the validated numerical simulations were carried on to design the next generation of the PolyU CPX system. Through analyzing the acoustic performance within the enclosures of different dimensions and the distributions of sound pressure level (SPL) inside the anechoic chamber, the geometry of the PolyU Mark III CPX enclosure was finally determined. With newly designed enhanced interior wall absorption, the new PolyU Mark III CPX enclosure design was delivered into numerical simulations for acoustic analysis. Fewer room modes and high uniformity of SPL distributions were observed within the new enclosure design. The PolyU Mark III CPX enclosure was fabricated based on the corresponding dimensions and the specific absorption layers. Great consistency was achieved between the numerical and measured results of the Mark III CPX enclosure. In addition, the PolyU Mark III CPX enclosure shows an improved acoustic property with a lower background noise level during road tests than Mark II CPX enclosure. The outcome of this study firmly establishes the feasibility of designing advanced CPX enclosure with numerical simulations with results that can be realized in realistic CPX measurement.

Solute dispersion in transient Casson fluid flow through stenotic tube with exchange between phases

A mathematical study on solute dispersion has been carried out in a stenotic tube having an absorptive wall—a study relevant to arterial pharmacokinetics. The rheology of blood is represented by Casson model and the solute is introduced at a point that is uniformly distributed over the cross section. The two-dimensional fluid flow is considered in this study. The governing equations of motion for the flow of Casson fluid, for the transport of solute in the lumen as well as in the tissue along with appropriate initial and boundary conditions, are numerically solved by leveraging the Marker and Cell method and the immersed boundary method in staggered grids formulation. Following the introduction of solute, we provide a comprehensive investigation of the influence of the wall absorption parameter (κ), yield stress (τy), and the severity of the stenosis (ξ) on the three transport coefficients, namely, the fraction of solute remaining in the fluid phase, the apparent convection velocity, and the dispersion coefficient. Simulated results predict the diminishing magnitudes of the transport coefficients with the increase in the values of yield stress and absorption parameter. Moreover, the transport coefficients and the axial mean concentration get significantly perturbed by the severity of the stenosis. Obtained results presented graphically concur with existing steady-state results in the literature. The present study would certainly be of some use in the case of targeted drug delivery and in treatment related to microvascular disease.

Dispersion with wall absorption in non-Newtonian fluid flow subjected to external body acceleration

Dispersion with wall absorption in non-Newtonian fluid flow subjected to external body acceleration

Shear augmented microvascular solute transport with a two-phase model: Application in nanoparticle assisted drug delivery

Solutal dispersion phenomena are associated with the nanoparticle-based drug delivery in the cardiovascular system to cure cardiovascular disorder. In the present problem, we explored the solutal transport for an unsteady blood flow through a microvessel with wall absorption. The rheology of blood is characterized by a two-fluid model similar to three-layer flow, namely, the core region, the intermediate region, and the peripheral region. The nature of the blood is considered as Casson fluid near the axis of the microvessel and Newtonian fluid close to the wall of the microvessel (at the intermediate and peripheral region). The peripheral region and the wall of the microvessel are permeable, and the permeability of the microvessel wall is defined by the Darcy–Brinkman model. The permeability of the inner surface of the microvessel is subjected to a slip condition at the surface. The stress-jump condition acts at the interface of the intermediate and peripheral region. The impact of the absorption parameter, velocity slip, yield stress, stress jump constant, nanoparticle volume fraction, and permeability on the velocity, exchange coefficient, convection coefficient, dispersion coefficient, and mean concentration is shown. It observed that the mean concentration boosts by the yield stress, nanoparticle volume fraction, and absorption parameters. The stress jump constant and permeability boost the convection coefficient, while the dispersion coefficient is restricted by the yield stress and absorption parameter.

Layer-adapted meshes for solute dispersion in a steady flow through an annulus with wall absorption: Application to a catheterized artery

This paper describes the longitudinal dispersion of passive tracer molecules injected in a steady, fully developed, viscous, incompressible, laminar flow through an annular pipe with a first order heterogeneous boundary absorption at the outer wall, numerically using layer-adapted meshes. The model is based on steady advection-diffusion equation with Dirichlet and Robin boundary conditions. The solutions are discussed in the form of iso-concentration contours of the tracer molecules in the vertical plane. An artanh transformation is used to convert the infinite domain into a finite one. A combination of central finite difference and 2-point upwind scheme is adopted to solve the governing advection-diffusion equation. It is shown that how the mixing of tracers is affected by the shear flow, aspect ratio and the first-order boundary absorption. When the flow becomes convection dominated, the monotone finite difference on a uniform mesh does not work properly, so a layer-adapted mesh, namely a “Shishkin” mesh, is used to capture the layer phenomena at the different downstream stations. The present results are compared with existing experimental and numerical data and we have earned an excellent agreement with them. It is observed that, due to the use of layer adapted mesh, we have achieved a better agreement with the experimental data than some other previous results available in the literature, especially in the closest downstream location. The results of this study are likely to be of interest to understand the basic mechanism of dispersion process of solute in blood through a catheterized artery with an absorptive arterial wall.

Slotsuppression of Scattering Loss in the Side Wall of Bent Slot Waveguide

With the higher requirements of advanced integrated circuit technology, waveguides can propagate electromagnetic waves with higher frequencies, such as millimeter waves and centimeter waves, and have a large power capacity, which makes waveguides a common transmission line in the microwave band. In this experiment, based on the research of the curved slot waveguide, the method of suppressing the scattering loss of the side wall is studied. The wave optics module is used to model the optical waveguide, and the mode of the designed curved slot waveguide is analyzed, and the thickness of each layer of the optical waveguide is optimized according to the material characteristics to reduce the influence of the high refractive index substrate and reduce the curvature of the side wall Absorption of scattering loss to avoid the influence of resonance. The curved slot waveguide curved microring resonator and the curved slot waveguide racetrack microring resonator are studied, and the device performance parameters are simulated and analyzed. In view of the above-mentioned shortcomings of the prior art, the purpose of the utility model is to provide a sidewall scattering loss based on a curved slot waveguide and a preparation method. The side scattering characteristics of the waveguide multilayer memory are experimentally studied. The results show that the distribution of the scattered light intensity from the side of the waveguide along the propagation direction of the guided light exhibits an exponential decay law, and its attenuation constant is proportional to the information symbol density, and the curved slot used for recording information increases and grows.

Analysis of factors influencing actual absorption of solar energy by building walls

The reduced heat loss of a solid wall caused by solar radiation is the solar energy actually absorbed by the solid wall (SEW). The absorbed solar energy calculated by using the radiation absorption coefficient of the wall surface is thus not the SEW. This study analyzes the parameters that may affect the SEW, including the heat accumulation coefficient of the wall (S), the heat-transfer coefficient of the south wall’s outer surface (h), the radiation intensity (I), the consecutive sunny days (D), and the outdoor air temperature (T). These influential factors on the solar absorptance of the south-facing wall (εwall) were synthetically evaluated with multiple nonlinear regression analysis. The results indicate that εwall is significantly affected by three parameters (i.e., S, h, D): εwall is high when S is large or h is small or D is small. I and T have little impact on εwall. A prediction model of εwall was further developed by using multivariate nonlinear regression, which can greatly improve the efficiency of building energy consumption analysis. The prediction model can also efficiently determine the effect of wind speed and direction on εwall in winter for optimizing building orientation and layout.