Isosceles Triangular Cross-section Research Articles

Modeling and Analysis of a Large-Scale Double-Level Guyed Mast for Membrane Antennas

This paper proposes a double-level guyed membrane antenna for stiffness improvement of a large-scale tri-prism deployable mast using the collapsible tubular mast (CTM). Initially, the construction of the antenna and the modeling of the CTM boom are illustrated. Afterwards, the central mast with isosceles triangular cross section is mathematically equivalent to a continuum beam, in which the equations of motion and the constitutive relations are derived. Based on the equivalent central beam, the double-level guyed mast for the membrane antenna is modeled as a 2(3-SPS-S) mechanism, and then velocity Jacobian matrices and stiffness matrices of SPS branches are constructed. Additionally, the total stiffness matrix of the equivalent mechanism is derived with the principle of virtual work and then evaluated as an accurate approach. Finally, with the aim to improve the static stiffness of the double-level guyed mast, the numerical analysis using the Genetic Algorithm (GA) is carried out for optimizing the distribution of guys in terms of anchor positions and attachment heights.

Effect of transverse rib on heat transfer between circulating fluidized bed and membrane fins of water wall membrane tubes

Overall heat transfer between circulating fluidized beds (CFB) and the ribbed membrane fins of a water wall tube was investigated experimentally in a cold model circulating fluidized bed riser. The riser had a cross sectional area of 0.1 × 0.2 m2 and the height from the distributor plate to the riser exit was 3.9 m. Three isosceles triangular cross section prisms having a height to base width ratio (e/B) of 0.54 corresponding to the height to riser diameter ratios (e/D) of 0.019, 0.038 and 0.06, respectively were used as ribs. The ribs were installed transversely on the fins with three rib spacings (S) of 0.4 m, 0.5 mand 0.6 m. Local sand having an average diameter of 315 μm was used as the bed material. It was found that the heat transfer coefficients and the cluster solid fractions of the ribbed membrane fins were higher than those of the membrane fin, and varied with the rib spacing and the rib height to diameter ratio in the same manner. In addition, cluster contact time of the ribbed membrane fins was shorter than that for the membrane fin without ribs.

Numerical Study of the Hydrodynamic and Thermal Proprieties of Titanium Dioxide Nanofluids Trapped in a Triangular Geometry

In the present work, we investigate numerically the fluid flow and heat transfer inside an entrapped cavity, which has an isosceles triangular cross-section and is filled with TiO2–water nanofluid. The base wall is maintained at high constant temperature, while the two other sides are kept a lower constant temperature. The length of the cavity is large enough to assume that the flow is two-dimensional. The governing equations are discretized by the finite volume method and solved numerically via the SIMPLER algorithm. In the present work, we investigate the effect of some parameters including the Rayleigh number, the solid volume fraction, the cavity aspect ratio and the inclination angle on both the thermal performance and the flow structure. The obtained results show that the thermal performance of the cavity and the flow structure are most sensitive to Rayleigh number and solid volume fraction. On the other hand, the aspect ratio of the cavity and its inclination also affect considerably the heat transfer and fluid flow pattern. We notice the occurrence of a pitchfork bifurcation phenomenon, which is a function of both Rayleigh number and cavity aspect ratio. Our results provide information that may be useful for design optimization as well as for thermal performance enhancement of energy systems such as solar water heaters.

Scaling of free convection heat transfer in a triangular cavity for Pr > 1

Unsteady natural convection inside a triangular cavity subject to a non-instantaneous heating on the inclined walls in the form of an imposed temperature which increases linearly up to a prescribed steady value over a prescribed time is reported. The development of the flow from start-up to a steady-state has been described based on scaling analyses and direct numerical simulations. The ramp temperature has been chosen in such a way that the boundary layer is reached a quasi-steady mode before the growth of the temperature is completed. In this mode the thermal boundary layer at first grows in thickness, then contracts with increasing time. However, if the imposed wall temperature growth period is sufficiently short, the boundary layer develops differently. It is seen that the shape of many houses are isosceles triangular cross-section. The heat transfer process through the roof of the attic-shaped space should be well understood. Because, in the building energy, one of the most important objectives for design and construction of houses is to provide thermal comfort for occupants. Moreover, in the present energy-conscious society it is also a requirement for houses to be energy efficient, i.e. the energy consumption for heating or air-conditioning houses must be minimized.

Three-dimensional flow instability in a lid-driven isosceles triangular cavity

Linear three-dimensional modal instability of steady laminar two-dimensional states developing in a lid-driven cavity of isosceles triangular cross-section is investigated theoretically and experimentally for the case in which the equal sides form a rectangular corner. An asymmetric steady two-dimensional motion is driven by the steady motion of one of the equal sides. If the side moves away from the rectangular corner, a stationary three-dimensional instability is found. If the motion is directed towards the corner, the instability is oscillatory. The respective critical Reynolds numbers are identified both theoretically and experimentally. The neutral curves pertinent to the two configurations and the properties of the respective leading eigenmodes are documented and analogies to instabilities in rectangular lid-driven cavities are discussed.

Laminar Natural Convection in Isosceles Triangular Roofs in Wintertime Conditions

In this work, numerical analysis of steady laminar natural convection in a roof with an isosceles triangular cross section has been performed for wintertime conditions. Base angles varying from 15° to 75°, that is, with corresponding aspect ratios between 0.13 and 1.87, have been used for Rayleigh numbers ranging from 103 to 105. The inclined and the base walls are maintained at cold and hot, respectively, representing the wintertime conditions. To perform the computational analysis, the finite-volume method is used for the discretization of the governing equations. The effects of the Rayleigh number and base angle on the flow field and heat transfer are analyzed. The detailed streamline patterns and temperature distributions are presented. The variation in the average convective Nusselt numbers versus Rayleigh numbers and base angles is given. The present study aims to help designers and builders to select the most suitable isosceles triangular roof base angle from an energy-saving point of view. It is found that roofs having low base angles are not suitable for wintertime conditions because of high heat transfer rates from the isosceles triangular attic space of the building.

Experimental investigation on the aerodynamic loads and wake flow features of low aspect-ratio triangular prisms at different wind directions

The results are described of measurements of the mean and fluctuating forces acting on low aspect-ratio triangular prisms placed vertically on a plane, having isosceles triangular cross-section with 60∘ or 90∘ apex angles and aspect ratios ranging from 1.0 to 3.0. The tests are carried out in a wind-tunnel by varying the wind direction, θ, between 0∘ and 180∘, at a Reynolds number Re ≃1.2×105. Furthermore, for the model with apex angle of 60∘ and aspect ratio 3.0, flow visualizations with tufts and hot-wire measurements are performed, which permit to characterize the wake morphology as a function of wind direction and to assess that an alternate vortex shedding always exists, with a frequency that is roughly inversely proportional to the wake width. The force measurements show that large variations in the mean values of the drag and cross-flow forces occur by varying θ, in strict correspondence with changes in wake flow features. The intensity of the fluctuating cross-flow forces, directly connected with vortex shedding, is found to vary significantly with flow orientation and aspect ratio, and to be approximately proportional to the streamwise projection of the body surface immersed in the separated wake. Finally, an increase in vortex shedding frequency is generally found with decreasing aspect ratio.

Three-dimensional vibration analysis of prisms with isosceles triangular cross-section

This paper studies the three-dimensional (3-D) free vibration of uniform prisms with isosceles triangular cross-section, based on the exact, linear and small strain elasticity theory. The actual triangular prismatic domain is first mapped onto a basic cubic domain. Then the Ritz method is applied to derive the eigenfrequency equation from the energy functional of the prism. A set of triplicate Chebyshev polynomial series, multiplied by a boundary function chosen to, a priori, satisfy the geometric boundary conditions of the prism is developed as the admissible functions of each displacement component. The convergence and comparison study demonstrates the high accuracy and numerical robustness of the present method. The effect of length-thickness ratio and apex angle on eigenfrequencies of the prisms is studied in detail and the results are compared with those obtained from the classical one-dimensional theory and the 3-D finite element method. Sets of valuable data known for the first time are reported, which can serve as benchmark values in applying various approximate beam and rod theories.

Efficient calculation of the Green's functions for multilayered shielded cavities with right isosceles-triangular cross-section

An efficient calculation of the Green's functions inside multilayered shielded cavities with right isosceles-triangular cross-section is presented. The method is entirely developed in the spatial domain, and it is based on image theory. The idea is to use the spatial-domain Green's functions inside a multilayered shielded square box, in order to accurately obtain the Green's functions for the right isosceles-triangular cavity. Image theory is then used to enforce the boundary conditions along the non-equal side of the triangle. It is shown that the new algorithm is very robust, with limited computational effort. Resonance frequencies and potential patterns of a triangular cavity have been calculated and compared with those obtained by other techniques, showing very good agreement. Finally, a transversal filter inside a multilayered triangular-shaped cavity is designed, manufactured and tested using the developed technique.

Numerical analysis of laminar natural convection in isosceles triangular enclosures for cold base and hot inclined walls

In this work, a numerical analysis of laminar natural convection in an enclosure of isosceles triangular cross-section has been performed for cold base and hot inclined walls. Base angles varying from 15° to 75° have been used for different Rayleigh numbers ranging from 10 3 to 10 5. Effects of Rayleigh number and aspect ratio on the flow field and heat transfer are analyzed. The streamline patterns and temperature distributions are presented. It is observed that the enclosures with a low aspect ratio have higher heat transfer rates from the bottom surface of the triangular enclosure.

Group-III Nitride P-Ttype Nanowire Heterostructure Field Effect Transistors

A two-step deposition process was developed in a metal organic chemical vapor deposition system to create a defect-free p-type structure consisting of a GaN nanowire (NW) core surrounded by a distinct AlGaN radial shell. The m-plane growth direction yields a nanowire with an isosceles triangular cross section with two identical {-110-1} facets and a third (0001) facet. The AlGaN shell introduces a polarization-induced sheet charge at the AlGaN/GaN interface and may shield the NW from surface-state induced depletion. Transmission electron microscopy confirmed that single-component NWs and sufficiently thin NW heterostructures are free of extended defects. High hole currents and current modulation were demonstrated with back-gated NW transistor structures.

Thermohydraulic performance of a periodic trapezoidal channel with a triangular cross-section

Simulations are performed to study the heat transfer behaviour of an equilateral triangular section duct following a tortuous path for fully-developed laminar flows with Reynolds numbers below 200. The enhancement of heat transfer and the increase in pressure drop are compared with those for ducts of circular, semi-circular and square section following the same serpentine path. For this flow regime, the triangular duct is shown to be the optimum choice (best heat transfer augmentation compared with increased pressure drop) amongst those studied. The effects of changing the path shape, the apex angle for an isosceles triangular cross-section and rounding of a corner of the equilateral triangular duct are also considered.

Galloping instabilities of two-dimensional triangular cross-section bodies

Galloping is a type of aeroelastic instability characterized by large amplitude, low frequency, normal to wind oscillations. It normally appears in bodies with small stiffness and structural damping when they are placed in a flow and the incident velocity is high enough. In this paper a systematic approach for the analysis of galloping of triangular cross-section bodies is reported. Wind tunnel experiments have been conducted aiming at establishing the unstable characteristics of isosceles triangular cross-section bodies when subjected to a uniform flow with angles of attack ranging from 0 to 180°. The results have been summarized in a stability map, where galloping instability zones in the angle of attack—main vertex angle plane—are identified.

Low aspect-ratio triangular prisms in cross-flow: measurements of the wake fluctuating velocity field

Abstract An experimental investigation is carried out to study the characteristics of the fluctuating wake flow field of finite-length prismatic bodies in cross-flow, placed vertically on a plane and having isosceles triangular cross-section with 60° or 90° apex angle orientated in the downstream direction. The wake flow field is studied with hot-wire anemometry for aspect ratios h/w =1.0, 1.5, 2.0 and 3.0 at Re= wU/ν ≅1.2×10 5 , and the velocity signals are analysed by means of procedures based on the wavelet transform. Velocity fluctuations with a clear dominating frequency are found immediately outside the wake along all the models, even if their magnitude decreases at a height corresponding to the free end of the bodies. The wavelet analysis of the phase difference between signals acquired at opposite sides of the wake shows that alternate vortex shedding occurs for all the models. An increase in the phase shift between the fluctuations on the same side of the wake with increasing vertical distance between the probes suggests that the shed vortices are curved. No evidence of symmetrical shedding or of the presence of arch-type vortices is found, even for the models with the smaller aspect ratios.

The torsional stiffness of prismatic beams of isosceles triangular cross section: a survey of methods for small included angles

Six approximate methods of calculating the torsional stiffness of prismatic beams of isosceles triangular cross section are compared with the exact solution for the cross section in the form of a sector of a circle.

Laminar‐turbulent transitional flow phenomena in isosceles triangular cross‐section ducts

AbstractA theoretical analysis of the laminar‐turbulent transition phenomenon is presented for the case of steady, isothermal, fully developed flow of Newtonian fluids in straight ducts of constant isosceles triangular cross section. As a result of this analysis, the simultaneous existence of macroscopically large stable regions of laminar and turbulent flow are predicted to occur during the transition phenomenon. The existence of this special type of flow field, which has not been previously predicted theoretically, is shown to be a consequence of the presence of an asymmetric shear stress distribution. The results of an experimental study are also presented. These data verify the predictions made by the theoretical analysis.