Cross-section Rib Research Articles

A numerical study on the effect of rib size and location on thermo-fluid performance of synthetic jet

A two-dimensional, axisymmetric numerical model is used to study the effect of synthetic jet flow structure and thermal performance, validated with experimental data. The Reynolds number is set at 5473, and orifice-to-surface spacing (z/d) varies (2, 6, 10). Three square cross-section ribs at different radial positions are analyzed. Results show that ribs reduce heat transfer at the stagnation point, with a maximum decrease of 74.37% at z/d=10 for a 5mm×5mm rib at r/d=0.5 and a minimum of 47.70% at z/d=6 for the same rib. Heat transfer increases near the rib's leading edge but drops before and after the rib. No area-averaged heat transfer improvement is observed, with a maximum reduction of 69.24% at z/d=10 for a rib at r/d=2 and a minimum of 2.43% at z/d=6 for a rib at r/d=1. Stagnation pressure increases by 24.42% at z/d=2 and decreases by 15.66% at z/d=10 due to a rib at r/d=2.

Electrical and Thermal Performances of a Single-Pass Double-Flow Photovoltaic-Thermal Collector Coupled with Nonuniform Cross-Section Rib

The air-based photovoltaic-thermal collector (PVTC) is a system that can generate electricity and heated air simultaneously from solar energy. This study investigates the electrical and thermal performances of an air-based single-pass double-flow photovoltaic-thermal collector (SPDFPVTC) coupled with a nonuniform cross-section rib (NUCSR) under various operating conditions. The rib is installed at the rear of the photovoltaic panel to enhance the heat transfer performance between the photovoltaic panel and the flowing air. Based on the energy balance equations, a mathematical model of the proposed SPDFPVTC is established and validated by experimental results. The solar intensity, air mass flow rate, and wind speed are selected as operating conditions. The effects of these operating conditions on the electrical and thermal performance of the SPDFPVTC have been discussed. In addition, this study evaluates the daily performance of SPDFPVTC with and without NUCSR. The average electrical, thermal, and overall efficiency were 17.59%, 43.96%, and 61.55%, respectively, for SPDFPVTC with NUCSR and 16.97%, 38.87%, and 55.83%, respectively, for SPDFPVTC without NUCSR. Consequently, installing NUCSR could enhance the daily electrical, thermal, and overall energy output of SPDFPVTC by 4.33%, 13.23%, and 10.63%, respectively.

Design method of combined stiffened pressure hulls with variable-curvature characteristic

This study presents a combined pressure hull design method with variable-section ribs. This method for determining the length-radius ratio of the pressure hull's bearing unit is derived based on the stiffness-matching characteristic of the shell and stiffener. The bearing mechanism of variable curvature stiffened shell is discussed through theoretical derivation and numerical simulation. The design scheme of variable cross-section and the equal-stiffness rib is proposed to address the limitations of outer envelope size and inner space utilization of the pressure hull. Its buckling load is determined by the energy method. The design approach for a new type of stiffened pressure hull is summarized. In addition, the method is verified by the design example and the experiment. The results revealed that the combined variable curvature shells are a superior pressure hull configuration. Compared to the cylindrical stiffened shell, the buckling load of the pressure hull with variable cross-section ribs can be improved significantly (about 26.7%). At the same time, space utilization remains at the original level. The stiffened design technique described in this research based on elastic buckling theory can accurately determine the length-radius ratio of the bearing unit, relying on the design objective with high feasibility.

Effects of wavy ribs on vortex generation and thermal-hydraulic performance in a rotating rectangular channel

An experimental and numerical study has been conducted to analyze the effects of rib configurations on heat transfer in U-turn rotating rectangular channels with smooth walls. A new model of a wavy rib is studied and compared with traditional ribs in a rectangular cross-section. Heat transfer coefficients for all rib configurations were measured from Reynolds numbers 4000 to 12000, whereas rotation numbers ranged from 0.025 to 0.15. Computational fluid dynamics (CFD) with the k-ω SST turbulence model were utilized to investigate turbulent kinetic energies, Nusselt numbers, flow structure, and thermal performance. The results indicated that the thermal performance factor of wavy ribs was 22.1%–28.7% higher than the rectangular cross-section ribs. The effects of Coriolis and rotational buoyancy result in growth and reduction of heat transfer in the leading and trailing walls. The simulation results are supported by experimental data with a difference of 3 to 10% for all samples, respectively.

Design and Analysis of a Graded-Index Strained Si<inline-formula> <tex-math notation="LaTeX">$_{1-x}$ </tex-math> </inline-formula>Ge<inline-formula> <tex-math notation="LaTeX">$_x$</tex-math> </inline-formula> Optical PN Phase Shifter

In this paper, a graded-index strained Si $_{1-x}$ Ge $_x$ optical PN phase shifter with multiple strained layers has been proposed for high speed data modulation at 1550 nm with low device footprint. The quasi-vectorial finite difference method, non-local empirical pseudopotential method and the Payne-Lacey model has been used to analyze the proposed device. A phase shift of 122 $^\circ$ /mm, V $_\pi$ L $_\pi$ of 0.74 V.cm, and insertion loss of 4 dB at 5 V reverse bias with a 3-dB modulation bandwidth of 27.5 GHz has been obtained for a 500 nm × 250 nm cross-section rib waveguide with 50 nm slab. A 15 $^\circ$ /mm increase in phase shift and 0.08 V.cm decrease in V $_\pi$ L $_\pi$ has been observed when the junction is shifted by 60 nm towards the N side.

Sources of Variability in Structural Bending Response of Pediatric and Adult Human Ribs in Dynamic Frontal Impacts.

Despite safety advances, thoracic injuries in motor vehicle crashes remain a significant source of morbidity and mortality, and rib fractures are the most prevalent of thoracic injuries. The objective of this study was to explore sources of variation in rib structural properties in order to identify sources of differential risk of rib fracture between vehicle occupants. A hierarchical model was employed to quantify the effects of demographic differences and rib geometry on structural properties including stiffness, force, displacement, and energy at failure and yield. Three-hundred forty-seven mid-level ribs from 182 individual anatomical donors were dynamically (~2 m/s) tested to failure in a simplified bending scenario mimicking a frontal thoracic impact. Individuals ranged in age from 4 - 108 years (mean 53 ± 23 years) and included 59 females and 123 males of diverse body sizes. Age, sex, body size, aBMD, whole rib geometry and cross-sectional geometry were explored as predictors of rib structural properties. Measures of cross-sectional rib size (Tt.Ar), bone quantity (Ct.Ar), and bone distribution (Z) generally explained more variation than any other predictors, and were further improved when normalized by rib length (e.g., robustness and WBSI). Cortical thickness (Ct.Th) was not found to be a useful predictor. Rib level predictors performed better than individual level predictors. These findings moderately explain differential risk for rib fracture and with additional exploration of the rib's role in thoracic response, may be able contribute to ATD and HBM development and alterations in addition to improvements to thoracic injury criteria and scaling methods.

High-throughput refractive index-based microphotonic sensor for enhanced cellular discrimination

This paper presents a novel microphotonic sensor based on silicon technologies for high-throughput single cell measurements. It employs a highly sensitive Fabry-Pérot resonant cavity to extract cellular refractive index information. The integrated large cross-section rib waveguides provide a single-mode like behavior important for resonant cell sensing. Differentiated myeloid cells derived from a promyelocytic leukemia cell line were injected in a microchannel, sheathlessly focused using inertial forces and analyzed while flowing through the resonant cavity volume. Results were compared against a commercial flow cytometer and showed a substantial improvement on cellular discrimination. Thus, this sensor has the ability to discriminate cell populations, usually identified using fluorescent parameters, without any dyes and can reach measurement rate as high as 2000 cells per second. By harnessing the cell's effective volume refractive index, our device offers complementary measurements readily improving actual technologies and thus providing crucial information for research and clinical professionals.

S-Bend Silicon-On-Insulator (SOI) Large Cross-Section Rib Waveguide for Directional Coupler

S-bend contributes the high losses in the silicon-on-insulator (SOI) large cross-section rib waveguide (LCRW). The objective of this work is to investigate S-bend SOI LCRW with two different single-mode dimensions named symmetrical and asymmetrical. The S-bend SOI LCRW has been simulating using beam propagation method in OptiBPM software. The asymmetrical waveguide with two different dimension arc given the best performance if compared to others dimension with 3 µm of waveguide spacing. It achieved 92.24% and 91.10% of normalized output power (NOP) for 1550 nm and 1480 nm wavelength respectively. Moreover, the minimum of S-bend spacing between the two cores is 0.9 µm for both 1550 nm and 1480 nm. Therefore, asymmetrical waveguide with two different dimension arc and 0.9 µm of S-bend spacing are chosen. This analysis is important to determine the right parameter in order to design the SOI passive devices. However, future work should be done to see the performance by designing the coupler and implement in the real system.

Surface trimming of silicon photonics devices using controlled reactive ion etching chemistry

Surface trimming of rib waveguides fabricated in 5-μm SOI substrate has been carried out successfully without any significant increase of propagation losses. A reactive ion etching chemistry has been optimized for trimming and an empirical model has been developed to obtain the resulting waveguide geometries. This technique has been used to demonstrate smaller footprint devices like multimode interference based power splitters and ring resonators after defining them photolithographically with relatively large cross-section rib waveguides. We have been also successful to fabricate 2D tapered spot-size converter useful for monolithic integration of waveguides with varying heights and widths. The taper length is again precisely controlled by photolithographic definition. Minimum insertion loss of such a spot-size converter integrated between waveguides with 3-μm height difference has been recorded to be ∼2dB. It has been also shown that the overall fiber-to-chip coupling loss can be reduced by >3dB by using such spot-size converters at the input/output side of the waveguides.

CFD (computational fluid dynamics) investigation on Nusselt number and friction factor of solar air heater duct roughened with non-uniform cross-section transverse rib

A 3-dimensional CFD (computational fluid dynamics) investigation has been carried out to study the heat transfer and friction characteristics of solar air heater duct roughened with periodic transverse rib. The selected rib roughness is a new concept; it has non-uniform cross-section in the form of saw-tooth. For comparison, transverse ribs with uniform cross-section of circular, square and trapezoidal have also been investigated. The Nusselt number and friction factor have been determined for Reynolds number range of 3000–15,000. The k-ε turbulence model was selected for analysis. The non-uniform cross-section saw-tooth rib was found to result in higher Nusselt number than uniform cross-section ribs for Reynolds number above 7000 due to reduced low heat transfer area downstream of the rib caused by disruption in re-circulations. The maximum enhancement in Nusselt number for duct roughened with saw-tooth rib and trapezoidal rib was 1.78 and 1.50 respectively. The friction factor was found to be lower for saw-tooth rib as compared to uniform cross-section ribs investigated. The maximum enhancement in friction factor for duct roughened with saw-tooth and trapezoidal rib was 2.49 and 3.58 respectively.

Compressive strength of HPS box girder flanges stiffened with open ribs

This paper presents a set of new strength equations for box girder flanges stiffened with open ribs subjected to uniaxial compression. Tee type and flat-plate type cross-section ribs were considered in the isolated stiffened plate systems that were studied. A total of eighty four hypothetical compression flange panels were modeled with wide ranges of slenderness parameters and then were investigated by nonlinear finite element analysis (FEA). The dimensions of the FEA models were carefully determined to satisfy the major requirements for stiffened flange systems and the longitudinal stiffeners were designed such that stiffener local buckling did not govern the failure of the stiffened flanges. Both conventional and high performance steels (HPS) were investigated in the analysis models by utilizing multi-linear constitutive relationships. Initial imperfections and residual stresses were also considered in the analysis. New design equations to predict the in-plane compressive strengths of the stiffened flanges are proposed based on the FEA results and compared with other design equations specified in Eurocode 3, the Federal Highway Administration (FHWA) design specifications, and the Japanese Road Association (JRA) specifications, and equations previously proposed by other researchers. It has been found that the equations provided in the above design codes underestimate the strengths determined from the HPS models, which may result in an inefficiently conservative strength design.

Evaluation of heat transfer performances of various rib shapes

The heat transfer and friction loss performances of rib-roughened rectangular cooling channels having a variety of cross-sectional rib shapes were analyzed using three-dimensional Reynolds-averaged Navier–Stokes equations. Numerical simulations were conducted for sixteen rib shapes: square, isosceles triangular, fan-shaped, house-shaped, reverse cut-trapezoidal, cut-trapezoidal, reverse boot-shaped, boot-shaped, reverse right-angle triangular, right-angle triangular, reverse pentagonal, pentagonal, reverse right-angle trapezoidal, right-angle trapezoidal, isosceles trapezoidal, and semicircular ribs. The ratios of pitch, height, and width of the rib to hydraulic diameter of the channel were set to 10, 0.047, and 0.047, respectively. The Reynolds stress model was used with the Speziale–Sarkar–Gatski pressure–strain model to analyze the turbulence. The computational results for the area-averaged Nusselt number were validated by comparison with the experimental data under the same conditions. The effects of the Reynolds number and rib pitch-to-width ratio on the performances of various ribs were also investigated for Reynolds numbers of 5000–50,000 and rib pitch-to-width ratios of 5.0–10.0, respectively. The new boot-shaped rib design showed the best heat transfer performance with a pressure drop similar to that of the square rib.

Optical characterization of coupled resonator slow-light rib waveguides

We report on the design, fabrication and optical characterization of a slow light waveguide created using a linear array of coupled resonators in a large cross-section rib waveguide. Structures with as many as 25 high aspect ratio resonators are experimentally investigated. The measured propagation loss, group velocity, and delay-bandwidth product (DBP) are presented. The metric DBP/unit loss is also introduced, with a value 38/dB. Finally we discuss a method for further reducing loss in the slow-light rib waveguide.

Analysis of fluid flow and heat transfer in a rib grit roughened surface solar air heater using CFD

This paper presents the study of fluid flow and heat transfer in a solar air heater by using Computational Fluid Dynamics (CFD) which reduces time and cost. Lower side of collector plate is made rough with metal ribs of circular, square and triangular cross-section, having 60° inclinations to the air flow. The grit rib elements are fixed on the surface in staggered manner to form defined grid. The system and operating parameters studied are: e/ D h = 0.044, p/ e = 17.5 and l/ s = 1.72, for the Reynolds number range 3600–17,000. To validate CFD results, experimental investigations were carried out in the laboratory. It is found that experimental and CFD analysis results give the good agreement. The optimization of rib geometry and its angle of attack is also done. The square cross-section ribs with 58° angle of attack give maximum heat transfer. The percentage enhancement in the heat transfer for square plate over smooth surface is 30%.

Design Rules for Single-Mode and Polarization-Independent Silicon-on-Insulator Rib Waveguides Using Stress Engineering

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> There is a trend towards miniaturization of silicon photonic circuits due to superior performance and small cost. Design rules that must be imposed on the geometry of optical waveguides to make them behave as polarization-independent and single-mode devices are well known for waveguides with relatively large cross sections and for some small cross-sectional rib waveguides with vertical sidewalls and an air top cladding. The influence of the top oxide cover on waveguide birefringence was analyzed recently, but only for relatively large cross-sectional waveguides. This paper reports simulations for both single-mode and polarization-independent behavior for small cross-sectional waveguides with variable rib width, etch depth, top oxide cover thickness, and sidewall angle. The results show that the stress-induced effects must be taken into account to satisfy both requirements. Design rules to maintain birefringence-free operation and to satisfy single-mode behavior for small rib silicon-on-insulator (SOI) waveguides are presented. </para>

One-Dimensional Photonic Crystal Rib Waveguides

We analyze an optical waveguide that consists of a 1D photonic crystal (PC) embedded in a large cross-sectional rib waveguide. The PC provides control over the dispersion properties of the waveguide, while the rib geometry provides a low loss and versatile mechanism for confining light. The structure is analyzed using the 3D finite-difference time-domain method. The simulation results indicate that extremely low-loss waveguiding is possible over a defect band. Moreover, the PC has a complete 1D photonic band gap with a gap-midgap ratio (Deltaomega/omega <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mid</sub> ) of 0.913, which is one of the largest ratios ever reported for a PC.

Performance Analysis of Rib Waveguide with Arbitrary Shape of Cross Section

A method to analysis the performance of arbitrary cross section rib waveguide is proposed in this paper. In this method, effective-index method (EIM) and transfer matrix method are used and the results are precision but the process are simple and convenient.

Design and fabrication of multimode interference coupler with strong confinement structure on silicon-on-insulator

A 1x8 multimode interference coupler with a strong confinement structure in the multimode region was proposed and fabricated on silicon-on-insulator material. In the multimode region, the waveguide was etched to the buried silica layer so as to realize the strong confinement and obtain better resolution of the self-imaging effect, while in the input/output ports, the rib waveguides with the large cross-section rib structure were designed to satisfy the single-mode condition, with which the device could be efficiently coupled with single-mode fibers or other waveguide devices. The fabrication process was also specially designed to eliminate the photolithography alignment error.

Fluoride glass planar waveguides for active applications

To help develop an efficient planar optical amplifier, the single mode behaviour of large cross-section rib optical waveguide structures (15 μm high and up to 19 μm wide) made of fluoride glasses have been investigated numerically. Wet chemical etching offers a simple and cheap solution for the fabrication of rib patterns in fluoride glasses, we present measurement of the lateral rib roughness left by this process as well as calculation of consequent scattering losses. We show that such large cross-section rib waveguides show a better tolerance to the rib roughness than standard semiconductor waveguides. This is of practical importance in order to make use of the full benefit of the amplification.

Variable Property and Temperature Ratio Effects on Nusselt Numbers in a Rectangular Channel With 45 Deg Angled Rib Turbulators

Measured local and spatially-averaged Nusselt numbers and friction factors (all time-averaged) are presented which show the effects of temperature ratio and variable properties in a rectangular channel with rib turbulators, and an aspect ratio of 4. The ratio of air inlet stagnation temperature to local surface temperature Toi/Tw varies from 0.66 to 0.95, and Reynolds numbers based on channel height range from 10,000 to 83,700. The square cross-section ribs are placed on two opposite surfaces, and are oriented at angles of +45 deg and −45 deg, respectively, with respect to the bulk flow direction. The ratio of rib height to channel hydraulic diameter is 0.078, the rib pitch-to-height ratio is 10, and the ribs block 25 percent of the channel cross-sectional area. Ratios of globally-averaged rib Nusselt numbers to baseline, constant property Nusselt numbers, Nu̿/Nuo,cp, increase from 2.69 to 3.10 as the temperature ratio Toi/Tw decreases from 0.95 to 0.66 (provided Reynolds number ReH is approximately constant). Friction factor ratios f/fo,cp then decrease as Toi/Tw decreases over this same range of values. In each case, a correlation equation is given which matches the measured global variations. Such global changes are a result of local Nusselt number ratio increases with temperature ratio, which are especially pronounced on the flat surfaces just upstream and just downstream of individual ribs. Thermal performance parameters are also given, which are somewhat lower in the ribbed channel than in channels with dimples and/or protrusions mostly because of higher rib form drag and friction factors.