Rectangular Aspect Ratio Research Articles

New aeroelastic studies for a morphing wing

For this study, the upper surface of a rectangular finite aspect ratio wing, with a laminar airfoil cross-section, was made of a carbon-Kevlar composite material flexible skin. This flexible skin was morphed by use of Shape Memory Alloy actuators for 35 test cases characterized by combinations of Mach numbers, Reynolds numbers and angles of attack. The Mach numbers varied from 0.2 to 0.3 and the angles of attack ranged between -1° and 2°. The optimized airfoils were determined by use of the CFD XFoil code. The purpose of this aeroelastic study was to determine the flutter conditions to be avoided during wind tunnel tests. These studies show that aeroelastic instabilities for the morphing configurations considered appeared at Mach number 0.55, which was higher than the wind tunnel Mach number limit speed of 0.3. The wind tunnel tests could thus be performed safely in the 6'×9' wind tunnel at the Institute for Aerospace Research at the National Research Council Canada (IAR/NRC), where the new aeroelastic studies, applied on morphing wings, were validated.

Solid-state recycling of aluminium alloy swarf through cold profile extrusion and cold rolling

In this study, the possibility of solid-state recycling of aluminium alloy machining swarf using cold extrusion and a subsequent cold rolling process is investigated. Cast Al–Si alloy swarf was cold compacted into billets and successfully profile-extruded into square bars with a rectangular cross-sectional aspect ratio of 1:1.8 under an extrusion ratio of 4 or more. After annealing, the extruded bars underwent multi-pass cold rolling into 1-mm thick strips with a total rolling reduction of 85%. Optical microscopy demonstrated that in material recycled using only an extrusion process, coarse residual voids existed in regions where insufficient plastic strain was introduced, causing a visible expansion of the material during heat treatment. However, uniaxial tensile tests showed that extrusion-recycled material had a higher mechanical strength than the original aluminium alloy, implying sufficient bonding among the individual pieces of machining swarf. It was also found that the strength and density of material recycled through extrusion and an additional rolling process were superior to material recycled using extrusion only. Moreover, it was observed that the ductility of the recycled materials was inferior to that of the original aluminium alloy.

Equivalent Rectangular Active Region and SPICE Macro Model for Split-Drain MAGFETs

This work presents an analytical methodology to estimate the equivalent rectangular aspect ratio of the active region of a Split-Drain MAGFET (SD-MAGFET) by combining known active regions. With this result, a SPICE Macro Model (SMM) for SD-MAGFETs is proposed associating each drain to a MOSFET. The effect of the magnetic flux density is introduced through the substrate-source voltage of each MOSFET, in opposite sense from each other, establishing different channel concentration. The total DC drain current of the equivalent rectangular MOSFET obtained in HSPICE has an error <15% with respect to results experimenttally measured for SD-MAGFETs of W=10µm and different L (2µm, 5µm and 15µm). The drain current imbalance obtained in HSPICE using the proposed SMM has an error <1,6% with respect to results experimentally measured with a SD-MAGFET of W/L=10µm/2µm.

Real Time Morphing Wing Optimization Validation Using Wind-Tunnel Tests

In this paper, wind-tunnel results of a real time optimization of a morphing wing in the wind tunnel for delaying the transition toward the trailing edge are presented. A morphing rectangular finite aspect ratio wing, having a wind tunnel experimental airfoil reference airfoil cross section, was considered, with its upper surface made of a flexible composite material and instrumented with Kulite pressure sensors and two smart memory alloys actuators. Several wind-tunnel test runs for various Mach numbers, angles of attack, and Reynolds numbers were performed in the 6' x 9' wind tunnel at the Institute for Aerospace Research at the National Research Council Canada. Unsteady pressure signals were recorded and used as feedback in real time control while the morphing wing was requested to reproduce various optimized airfoils by changing automatically the two actuators' strokes. This paper shows the optimization method implemented into the control software code that allows the morphing wing to adjust its shape to an optimum configuration under the wind-tunnel airflow conditions.

Closed-Loop Control Validation of a Morphing Wing Using Wind Tunnel Tests

In this paper a rectangular finite aspect ratio wing, having a wing trailing edge airfoil reference airfoil cross section, was considered. The wing upper surface was made of a flexible composite material and instrumented with Kulite pressure sensors and two smart memory alloys actuators. Unsteady pressure signals were recorded and visualized in real time while the morphing wing was being deformed to reproduce various airfoil shapes by controlling the two actuators displacements. The controlling procedure was performed using two methods which are described in the paper. Several wind-tunnel test runs were performed for various angles of attack and Reynolds numbers in the 6 × 9 foot wind tunnel at the Institute for Aerospace Research at the National Research Council Canada. The Mach number was varied from 0.2 to 0.3, the Reynolds numbers varied between 2.29 and 3.36 x 10 6 , and the angle-of-attack range was within -1 to 2 degrees. Wind-tunnel measurements are presented for airflow boundary layer transition detection using high sampling rate pressure sensors.

Variations in Optical Sensor Pressure Measurements due to Temperature in Wind Tunnel Testing

In this paper, wind-tunnel measurements are presented for the airflow fluctuation detection using pressure optical sensors. Twenty-one wind-tunnel test runs for various Mach numbers, angles of attack, and Reynolds numbers were performed in the 6 x 9 ft 2 wind tunnel at the Institute for Aerospace Research at the National Research Council Canada. A rectangular finite aspect ratio half-wing, having a NACA 4415 cross section, was considered with its upper surface instrumented with pressure taps, pressure optical sensors, and one Kulite transducer. The Mach number was varied from 0.1 to 0.3 and the angle of attack range was within -3 to 3 deg. Unsteady pressure signals were recorded and a thorough comparison, in terms of unsteady and mean pressure coefficients, was performed between the measurements from the three sets of pressure transducers. Temperature corrections were considered in the pressure measurements by optical sensors. Comparisons were also performed against theoretical predictions using the XFoil computational fluid dynamics code, and mean errors smaller than 10% were noticed between the measured and the predicted data.

Energy concentration at the center of large aspect ratio rectangular waveguides at high frequencies

Waveguides in non-destructive evaluation (NDE) applications are commonly of a regular geometry (e.g., circular and ring cross section) for which analytical solutions exist. In this paper, wave propagation in infinitely long strips of large rectangular aspect ratio is discussed. Due to the finite width of strips, a large number of modes exist within the structure. This complicates the analysis and usually discourages the use of strip waveguides in NDE sensors. However, it is shown that among the many modes of a strip, there are some with very desirable properties. This is highlighted by the example of two guided wave modes of a large aspect ratio rectangular strip whose dispersion characteristics approach those of the fundamental modes of an infinitely wide plate at high frequencies. The energy of these modes concentrates in the central region of the strip and decays toward the edges so that the strip waveguide can easily be mechanically attached to other components without influencing the wave propagation. Dispersion curves and mode shapes were derived by using a semianalytical finite element technique and are presented over a range of frequencies. It is shown that selective excitation of both modes is possible in practice and the experimental setup is described.

A novel magnetic tunnel junction structure using the edge of a magnetic film

We propose and demonstrate an edge magnetic tunnel junction (MTJ) structure that uses the edge part of the magnetic thin film and the barrier layer parallel to the edge surface. The shape of an edge MTJ becomes a rectangle whose area is defined as the product of the thickness of one magnetic thin film and the line width of another magnetic film. The thickness of a thin film is reduced in a controlled manner so that the edge junction structure can have a smaller area as well as a smaller variation in area. In the case of the edge junction, a rectangular aspect ratio is enlarged without increasing the area of the cell. An in situ ion milling etching apparatus is connected to the sputtering system in order to avoid the oxidation of the edge surface. In our fabrication process of the edge MTJs, magnetic electrodes are not exposed to water, oxygen plasma, or organic solvent. The edge MTJs consist of CoFeB/MgO/CoFeB. We obtain both a high magnetoresistance ratio (MR) of 71% and a small area of 0.3×0.04 μm in the edge MTJ.

Effect of Shape and Size of a Fire Source on Fire Properties in Vicinity of a Fire Source in a Tunnel

Experiments were performed to investigate the effects of the shape and size of a fire source on fire properties using a tunnel model with a rectangular cross section and aspect ratio of 1:2. Square and rectangular burners were used as the model fire sources. The variations in the heat release rate (HRR) from 4.5 to 36 kW was proportional to the fire size, and the longitudinal ventilation velocity was also varied in the range from 0 to 0.8 m/s. The flame tilt angle, maximum temperature rise of the smoke layer near the ceiling and its position were adopted as the variables that characterise the fire phenomena in the near field of a fire source in the presence of longitudinal ventilation. New empirical formulae considering the effects of the shape and size of a fire source on these variables were developed.

Natural vibration of arbitrary spatially curved rectangular rods with pre-twisted angles

For the natural vibration of rods of pre-twisted rectangular cross-sections with its centerline spatially curved and twisted arbitrarily, a system of non-dimensional ordinary differential equations is obtained in three translation displacements and three rotational angles of the rod. The eigenvalue problem is solved for the natural frequencies of various pre-twisted angles of the rectangular cross-section area, aspect ratios, slenderness ratio, end conditions and functions of varying cross-section area along the rods by using a numerical method of Runge–Kutta integration. The eigenvalues are determined by the vanishing of a rank-six determinant whose column vectors are obtained at the end of six independent numerical integrations. The differential equations of the adjoint operator system for the eigenvalue problem with its associated boundary conditions are also derived and solved for the eigenvalues to check with that of the vibration system. It is found that the effect of increasing pre-twisted angle of the rod is that the lowest natural frequency of an arbitrary curved rod will asymptotically tend to be a constant, in spite of slenderness ratio, aspect ratio of the rectangular cross-section, E / G ratio, types of end conditions, or the functions of the cross-section area along the rod.

Dipolar induced, spatially localized resonance in magnetic antidot arrays

Dipole induced, spatially localized ferromagnetic resonances (at 35 GHz) are observed in micron-sized antidot arrays in permalloy films fabricated with photolithography. All square (3 μm×3 μm) and rectangular (3 μm×4, 5, and 7 μm) array samples exhibit double resonances, with each resonance possessing uniaxial in-plane anisotropy. Interestingly, the easy axes of the two resonances are orthogonal in all cases. The magnitude of the induced dipolar anisotropy decreases with increasing rectangular aspect ratio for one of the resonances, but remains essentially constant for the other. Micromagnetic simulations reveal that the two resonance peaks are the consequence of a dipole field distribution producing two areas with distinctly different demagnetizing field patterns.

Collapse simulation of tubular structures using a finite element limit analysis approach and shell elements

This paper describes the collapse simulation of thin-walled tubular structures using a finite element limit analysis approach and degenerated four-node shell elements. The simulation traces the path of sequential deformation of the structure modelled by considering the strain-hardening effect, which is important for the analysis of collapse behaviour and energy absorption efficiency. The collapse analysis of some square tubes was used to verify the simulation method proposed. Numerical results are compared with experimental observations for sequential collapse loads and deformation modes, showing fairly good coincidence. The collapse analysis of an S-rail was then carried out for sequential collapse loads as well as deformation modes and its results are compared with elasto-plastic analysis results obtained from the explicit dynamic code PAM-CRASH. The energy absorption capacity was studied for a variety of rectangular cross-section aspect ratios. The results show that the energy absorption capacity increases as the height-to-width aspect ratio becomes larger. Results also demonstrate that the finite element limit analysis can predict the plastic collapse load and collapse mode of thin-walled structures efficiently and systematically. The present algorithm with a simple formulation has the advantage of stable convergence, computational efficiency and easy access to strain-hardening materials compared to the incremental rigid–plastic finite element analysis.

Optimal configuration of a piezoelectric patch for vibrationcontrol of isotropic rectangular plates

This technical note presents the optimal position and orientation of apiezoelectric patch actuator for improving the controllability of isotropicplates against vibration. The main focus is on controlling the first fivemodes either individually or simultaneously. Four rectangular aluminum platesof different aspect ratios and of either simply-supported or cantileveredboundary condition are considered. A formula incorporating results fromfinite-element analyses is developed to predict the steady-state responses of platesdriven by a single piezoelectric patch. Simulation results show that, ingeneral, the controllability of plates is insensitive to patch orientation asfar as the present investigation is concerned. For the simply-supportedplates, the optimal patch positions coincide exactly with anti-nodes of thevibration modes being considered. This, however, is only true for specificmodes of the cantilevered plates.

Effect of rectangular array aspect ratio on the transverse modulus of undirectional fiber composites

Effect of rectangular array aspect ratio on the transverse modulus of undirectional fiber composites

Numerical calculation of fully developed turbulent flow in curved channels: An extended algebraic Reynolds-stress model

The primary objective of the paper is to extend an algebraic Reynolds-stress model including a new expression for the turbulent shear stress, in order to describe the negative production of turbulent kinetic energy appearing in curved channel flows in a region between the points of maximum velocity and vanishing shear stress. This so-called energy reversal cannot be captured by the majority of turbulence models with conventional eddy-viscosity formulation. Computations are made for fully developed flows in channels of rectangular cross section and large aspect ratio with mild and strong curvature. The results are compared with different model predictions and experimental data reported in the literature. In the cases considered, the accuracy of present model predictions is comparable to that of a Reynolds-stress model. The latter, however, requires much more computing time and is thus more costly than the model here proposed.

L'adhérence des jets d'air froid au plafond des locaux climatisés

A jet of cold air is denser than ambient air, but it adheres to the ceiling of the room into which it is blown. This is a paradoxical phenomenon and is not sufficiently known, both in terms of mechanism and quantitative effects. The first objective of this work is to try to provide a qualitative explanation, using an analysis based on certain hypotheses. These assumptions will then be validated by comparison with the results of numerical simulations obtained by using Navier-Stokes equations associated with a turbulence model. In this work, a parametric study was carried out by varying the most significant variables. The results show how the adherence length of the plane wall jet is related to these parameters. This dependence is given as a function of Froude and Reynolds numbers. This result was then extended to the case of the 3-dimensional air jet, thereby highlighting the influence of the rectangular opening aspect ratio. The study leads to some correlations that may have practical use in air conditioning.

Relationship Between Kernel Size Features and Test Weight in Triticum durum

ABSTRACTTest weight or bulk density in durum wheat is a physical quality characteristic considered by semolina millers. High test weight values are desirable because they positively influence market grade and price. This study reports data on kernel size features, determined on a sample size of only 25 kernels, replicated three‐times, of 16 commercial durum wheat cultivars grown in two locations in southern Italy, to ascertain whether some kernel traits could be related to test weight. For each year and cultivar, the analysis of variance for all of characteristics showed that sample size effect was not significant, enabling the use such a small sample for further investigations. The kernel trait with the highest variation for year was kernel width. The absolute variation of 1994 with respect to 1993 growing season was 30.9%. While kernel weight or volume did not correlate with test weight, a negative association with kernel length (r = ‐0.61, P = 0.05) and perimeter (r = ‐0.57, P = 0.05) was found. The kernel shape factors, rectangular aspect ratio (RAR) and circularity shape factor (CSF), showed a positive correlation with test weight (r = 0.51, P = 0.05 and r = 0.59, P = 0.05, respectively). The shape factors were negatively correlated both with kernel length and perimeter and positively with kernel width. A predictive model for test weight (TW = 38.7 + 5.1·ETW, where the estimated test weight [ETW] was computed as individual kernel weight/estimated kernel volume [EKV] ratio), was highly correlated with actual test weight values (r = 0.82, P = 0.001). The effectiveness of the linear model was confirmed when a set of 10 advanced lines of durum wheat were considered, although a slightly lower correlation (r = 0.73, P = 0.05) between actual and predicted test weight values was found. Because the extent of predictability of this approach might be more effective in early‐generation lines, the application of the findings in a durum wheat breeding program would be advisable.

Heat transfer enhancement in a channel with a built-in rectangular cylinder

A two dimensional numerical investigation of the unsteady laminar flow pattern and forced convective heat transfer in a channel with a built-in rectangular cylinder is presented. The channel in the entrance region has a length to plate spacing of ten. The computations were made for several Reynolds number and two rectangular cylinder aspect ratios. Hydrodynamic behavior and heat transfer results are obtained by solution of the complete Navier-Stokes and energy equation. The results show that these flow exhibits laminar self-sustained oscillations for Reynolds numbers above the critical one. This study show that oscillatory separated flows result in a significant heat transfer enhancement but also in a significant pressure drop increase.

Transient conjugated heat transfer from a rectangular hot film

A numerical calculation is carried out for the transient response of a flush-mounted hot-film sensor in a gas flow heated by a step change in the hot-film output flux. The numerical method used is called the unsteady surface element method. This calculation is part of a study of unsteady behavior of hot-film anemometers that involve substrate effects. The numerical results show that the early-time film temperature agrees well with an analytical solution, and the steady-state Nusselt number agrees with an existing numerical solution. The spatial average film temperature vs time is presented for several values of the rectangular hot-film aspect ratio. Nomenclature a = streamwise half-length of the hot film, m b = span wise half-length of the hot film, m K = thermal conductivity, W/(mK) — streamwise length of the yth surface element, m = spanwise length of the yth surface element, m M = number of time steps N = number of surface elements Np = flow parameter, Eq. (16) Nu = Nusselt number P = hot-film output flux, W/m2 Pe = Peclet number, p(2a)2/af q = heat flux, W/m2 qQ = hot-film output, W/m2 T = temperature Tav = spatial average hot-film temperature TQ = initial temperature T- = (T - TQ)l(qQalKs) t+ = ast/a2 x = streamwise coordinate x+ = x/a Xj = center of the yth surface element y = spanwise coordinate y+ = yla yj = center of the ;th surface element z = coordinate normal to the interface a = thermal diffusivity, m2/s /3 = velocity gradient, s1 F( ) = gamma function Ai/r = influence function, Eq. (13) TJ = dummy space variable in the spanwise direction A = dummy time variable //,( ) = unit step function f = dummy space variable in the streamwise direction $ = fundamental solution, defined in Appendix A

Secondary flow of the second kind in rectangular ducts with one rough wall

A study was made to clarify experimentally the influences of a rough wall in a rectangular duct on secondary flow of the second kind and to obtain fundamental data on flow characteristics. Measurements were conducted on turbulent air flows through a square duct and a rectangular (aspect ratio 2:1) duct having one rough wall using hot-wire anemometers. The secondary flow patterrn in the roughened ducts was remarkably different from that in the smooth ducts. In the roughened ducts, only one large longitudinal vortex appeared near the smooth wall on each side, and the secondary currents in the core region proceeded downward from the top smooth wall to the bottom rough wall along the midplate of the duct. The secondary flow was considerably intensified by the existence of the rough wall. The vorticity balance was examined by evaluating the production and convection terms in the vorticity transport equation using the measured turbulent stresses. The two terms almost balanced near the corner bisector of the smooth ducts. However, in the rough ducts, they did not necessarily balance near the corner region formed by the smooth and rough walls.