Rib Cross Research Articles

Transmission laser welding of thermoplastics: Influence of welding parameters and rib dimensions on the strength of welded joints

Laser transmission welding of injection moulded thermoplastics is commonly used in industrial applications such as electronic packaging, textiles, biomedical devices, windows, signs, food and medical packaging, visual displays and automotive components due to very precise control of the process parameters, including the amount of energy delivered and its location, which results in high joint quality. In this article, the influence of laser transmission contour welding parameters and geometry of welding rib on joint force is investigated. Velocity with which the laser beam moves on the sample, temperature applied, clamp force, laser beam size and number of laser passes were studied for various dimensions of the rib with rectangular and triangular cross section. Samples of different thermoplastic materials, PMMA and PC/ABS, were produced and then joined by transmission laser welding and after that were subjected to tensile tests, in order to measure strength of the joint between the plastic parts. Initially, optimal welding conditions were found for each studied rib and their influence on the force of the joint was analysed. Afterwards, a comparison between the best results obtained for each rib was performed, in order to define the dimensions of the rib that result in the highest joint force. It was observed that samples with triangular ribs achieved higher joint strength. For both studied geometries of rib cross section, an increase of the width of the ribs improves the joint strength, while an increase of the height worsens it.

Covariation between the shape and mineralized tissues of the rib cross section in Homo sapiens, Pan troglodytes and Sts 14.

Studying rib torsion is crucial for understanding the evolution of the hominid ribcage. Interestingly, there are variables of the rib cross section that could be associated with rib torsion and, consequently, with the morphology of the thorax. The aim of this research is to conduct a comparative study of the shape and mineralized tissues of the rib cross section in different hominids to test for significant differences and, if possible, associate them to different thoracic morphotypes. The sample consists of the rib cross sections at the midshaft taken from 10 Homo sapiens and 10 Pan troglodytes adult individuals, as well as from A. africanus Sts 14. The shape of these rib cross sections was quantified using geometric morphometrics, while the mineralized tissues were evaluated using the compartmentalization index. Subsequently, covariation between both parameters was tested by a Spearman's ρ test, a permutation test and a linear regression. Generally, P. troglodytes individuals exhibit rib cross sections that are rounder and more mineralized compared to those of H. sapiens. However, the covariation between both parameters was only observed in typical ribs (levels 3-10). Although covariation was not found in the rib cross sections of Sts 14, their parameters are closer to P. troglodytes. On the one hand, the differences observed in the rib cross sections between H. sapiens and P. troglodytes might be related to different degrees of rib torsion and, consequently, to different thoracic 3D configurations. These findings can be functionally explained by considering their distinct modes of breathing and locomotion. On the other hand, although the rib cross sections belonging to Sts 14 are more similar to those of P. troglodytes, previous publications determined that their overall morphology is closer to modern humans. This discrepancy could reflect a diversity of post-cranial adaptations in Australopithecus.

Surgical Approaches to Single-Stage Extended Aortic Repair from the Ascending to the Distal Descending Aorta.

Single-stage extended replacement from the ascending to the distal descending aorta or beyond is a formidable operation that should be preserved for those who have no other option or those who are physically fit, and should be performed in the experienced centers. Hybrid operations combining open surgical repair with thoracic endovascular aortic repair through a median sternotomy incision are preferable because these operations are less invasive than the extended open aortic repair and the risk of spinal cord ischemia is lower compared with the frozen elephant trunk operation. However, these operations are associated with the inherent demerits of endovascular aneurysm exclusion. When the underlying aortic pathology necessitates extended open aortic repair in a single stage, approaches such as the anterolateral partial sternotomy, straight incision with rib cross, and extended thoracotomy with sternal transection may be useful to provide sufficient exposure for both aortic reconstruction and organ protection, with less surgical stress to the patients.

Numerical modeling of an innovative arc shape rib based solar air heater

Solar air heating is a solar thermal technology wherein the sun energy is absorbed by an intermediate medium and utilized to heat air. In the present paper, a solar air heater equipped with innovative arc shaped ribs is considered. The heat transfer process in the proposed solar air heater is evaluated numerically for Reynolds numbers between 6000 and 12000. The influences of the rib cross section type, the inter-rib distance, the aspect ratio and the pitch of the ribs on the thermal efficiency of solar air heater are analyzed. Results indicate that firstly, ribs with quadrangular type of cross section exhibit the best coefficient of performance. Moreover, ribs with low pitch (40 mm) and aspect ratio equal to 0.5 show the highest thermal performance. Also, the effect of the distance between the ribs on the thermal efficiency of the considered solar air heater is insignificant. Finally, two correlations are obtained for the average Nusselt number and friction factor based on three dimensionless geometric factors.

Rib Structure Optimization of Deployable Umbrella Reflector

In order to reduce the mass of satellite deployable umbrella reflector, a structure optimization model of rib was established by analyzing rib’s structure and forces on it. The minimum mass of rib is calculated by optimizing its structure parameters under given rigidity and loads. Optimized structure parameters were obtained by solving the model with Compound Form method. Comparing the original structure, 50.4% mass was successfully reduced after optimization. It was found that increasing the height of the rib's cross section and using variable section are two effective ways to make rib lighter.

Detached eddy simulation of turbulent flow and heat transfer in cooling channels roughened by variously shaped ribs on one wall

Delayed Detached Eddy Simulations with the k-ω-SST turbulence model were conducted for 8.0 MPa pressurized helium-gas flow in cooling channels with rib arrays on one wall at a Reynolds number of Re = 1.05 × 105. Turbulent flow and heat transfer were determined for arrays of eight variously configured V-shaped and transverse ribs. The relative roughness was e/Dh = 0.0638 and 0.0652 and the rib pitch was p/e = 10. The results showed that for ribs not extended over the total channel width, form drag was reduced and flow stagnation regions with a low heat transfer at the rib corners on the sides disappeared, whereas heat transfer by forced convection increased. Compared to smooth channel flows, the Nusselt numbers were increased by a factor of 1.6–1.8 and 2.2–2.5 for the transverse and V-shaped ribs, respectively. The corresponding friction factors were enhanced by a factor of 2.4–2.9 and 2.8–3.7, respectively. Evaluation of the thermal performance of structured cooling channels in comparison with smooth cooling channels revealed that thermal performance was best for the upstream directed 60° V-shaped ribs. The results showed that secondary flow motion induced by a V-shaped rib configuration caused an outward convective fluid transport within the recirculation region behind the rib. Vortical structures associated with local heat transfer deterioration behind the rib could be eliminated by appropriate designs of rib cross sections. Both lateral convective fluid transport and the elimination of vortical structures deteriorating heat transfer were found to lead to a significant heat transfer enhancement in the leeward rib region for the V-shaped ribs with modified cross section.

Thermal performance augmentation by rib-arrays for helium-gas cooled First Wall applications

Rib-roughening the helium-gas cooling channels in the plasma facing components of DEMO (First Wall, limiters or the divertor) enhances heat transfer and reduces structural material temperatures. In the present study the applicability of six different surface-attached rib-arrays and of two different detached rib-arrays was examined for increasing the thermal performance within the helium-gas First Wall cooling concept. The rib-arrays consisted of transversally oriented or upstream directed 60° (with respect to the centerline) V-shaped ribs with different rib cross section (square, trapezoid, 2mm radius round-edged front- and rear-rib-surface). Turbulent flow and heat transfer for 8MPa pressurized helium-gas with a helium mass flow rate of 0.049kg/s were computed by the Detached-Eddy-Simulation approach. A constant heat flux density of 0.75MW/m2 and 0.08MW/m2 was applied at the plasma-facing and breeding-blanket-facing First Wall structural surface respectively. The results showed that structuring the thermally highly loaded cooling channel surface with rib-arrays of 60° V-shaped ribs provides an efficient heat transfer and increases the cooling performance of the First Wall. The corresponding heat transfer coefficient was in the range from 7.1 to 7.5kW/m2K and from 7.6 to 8.1kW/m2K for the attached and detached V-shaped ribs respectively. Compared to smooth channel flows, only 14–16% of the pumping power is required to obtain an equivalent heat transfer performance or, from another point of view, the heat transfer coefficient can be increased by 168–172% for a constant pumping power.

Numerical Investigation of Channel for Helium Cooled China HCCB-TBM First Wall by Application Enhance Heat Transfer Method

To enhance heat transfer efficiency on first wall (FW) of ITER China Helium-Cooled Ceramic Breeder-Test Blanket Module (HCCB-TBM), CFD numerical simulation method is adopted. On the basis of calculating helium gas cooling scheme of FW smooth channel, FW structural temperature gradient, maximum wall temperature, average heat transfer coefficient, and pressure drop of channel are selected as evaluation indexes. Numerical simulation comparison are performed on heat transfer schemes like placing transversal ribs and V-shaped ribs in the flow channel of front wall and the helium gas turbulence intensity and the heat transfer area are improved through optimizing the distance and angle between V-shaped ribs and other parameters to enhance heat transfer. The optimization scheme of helium-cooled FW for HCCB-TBM through the three dimensional numerical simulation is: V-shaped ribs are placed on the inner surface of front wall, the rib cross section is 1 mm × 1 mm, the distance between rib pitches is 10 mm and the rib angle is 60°. Under the same helium cooling condition, compared with the FW smooth channel, the optimized V-shaped rib scheme enhances the average heat transfer efficiency by about 70 % and the FW maximum temperature drops by 349.3 K. The result provides support for further research on FW helium cooling heat transfer enhancement experiment and engineering design optimization for China HCCB-TBM.

A numerical study of particle deposition in ribbed duct flow with different rib shapes

The effects of surface rib shapes on particle deposition in turbulent duct air flows were numerically studied based on the Reynolds stresses model (RSM) with UDF code correction and the discrete particle model (DPM). The shapes of the rib cross sections were square, triangular and circular. The ratios of rib height to duct diameter e/D were 0.1. The present air velocity distributions for both smooth and ribbed ducts as well as particle deposition velocity in a smooth duct are all in good agreement with previous related study data. An efficiency ratio has been defined to evaluate the particle deposition enhancement ratio together with the increase of flow drag. It is found that the square ribs have the maximum enhancement efficiency on particle deposition, compared with the other rib shapes. The maximum efficiency ratio can reach about 400 for small particles (τp+<1) but only about 2 for large particles (τp+>1) when the rib shape is square. Moreover, the mechanisms of particle deposition enhancement for different rib shapes were investigated and analyzed.

Structural–acoustic optimization of a pressurized, ribbed aircraft panel

A method to reduce the noise radiated by a ribbed, aircraft panel excited by turbulent boundary layer flow is presented. To compute the structural-acoustic response, a modal approach based on finite element/boundary element analysis was coupled to a turbulent boundary flow forcing function. A static pressure load was also applied to the panel to simulate cabin pressurization during flight. The radiated sound power was then minimized by optimizing the horizontal and vertical rib location and rib cross section using an evolutionary search algorithm. Nearly 10 dB of reduction was achieved by pushing the ribs to the edge of the panel, thus lowering the modal amplitudes excited by the forcing function. A static constraint was then included in the procedure using a low-frequency dynamic calculation to approximate the static response. The constraint limited the amount of reduction that was achieved by the optimizer.

Stiff lattices with zero thermal expansion and enhanced stiffness via rib cross section optimization

For engineering applications that are subject to large fluctuations in temperature, yet dimensional stability is essential, low or even zero thermal expansion materials are desirable. In addition to providing minimal thermal expansion care must be taken to ensure reductions in mechanical stiffness are mitigated. This can be achieved be designing structurally hierarchical materials composed of carefully chosen lattice structures. Within this manuscript honeycombs with thermal expansion coefficients equal to zero are developed analytically. The two dimensional lattice microstructure designs described are made of positive expansion materials. Zero expansion is attained with the use of curved, bi-material rib elements that by the use of thermally induced bending achieves zero overall thermal expansion. This work builds upon previous results, and provides further analysis into creating an optimal rib cross section to increase mechanical stiffness. The design of ribs with Tee shaped and I shaped cross sections is developed. Analytical equations are derived for the overall mechanical stiffness and overall thermal expansion coefficients of the lattices. The behavior of these lattices is compared with that of triangular and regular hexagonal honeycombs having non-zero thermal expansion as well as prior zero expansion lattices with rectangular rib cross sections in a modulus-density map. Lattice relative stiffness is improved by as much as a factor of 2.4 when compared with a curved, triangular, zero thermal expansion lattice with ribs of rectangular section. Thermal shear stress at the material interface is calculated and found to be small.

Random Seismic Response Analysis of Leaning-Type Arch Bridge

With an example of steel pipe concrete leaning-type arch bridge, space truss system Finite Element Analysis model is constructed using the Ruiz-Penzien random seismic vibration power spectrum model. The impact of inclined arch rib angle and the number of cross brace between main and stable arch ribs on the seismic internal force response under lateral random seismic excitation is also studied in this research. Research finding shows, the in-plane bending moment of main arch rib gradually increases with increasing stable arch rib angle and cross brace, whereas the out-of-plane bending moment and axial force display a decreasing trend. In general, this indicates that increasing stable arch rib angle and number of cross brace improves the lateral aseismatic performance of leaning-type arch bridge.

Sheet metal plate design: a structured approach to product optimization in the presence of technological constraints

Geometrical optimization of structural components is a topic of high interest for engineers involved with design activities mainly related to mass reduction. The study described in these pages focuses on the optimization of plates subjected to bending for which stiffness is obtained by a pattern of ribs. Although stiffening by means of ribs is a well-known and old technique, the design of ribs for maximum stiffness is often based on practice and experience. Classical optimization methods such as topological, topographical and parametric optimization fail to give an efficient design with a reasonable programming effort, especially when dealing with many and complex constraints. These constraints are both technical and technological. A most promising technique to obtain optimal rib patterns was to define a set of feasible rib trajectories and then to select the subset with the most efficient combinations. The result is not unique and a method to select the optimal patterns is required. In fact, the stiffening effect increases with increasing rib length, but at a greater cost. A trade-off must be found between structural performance and cost: The tools to guide this selection process is the main objective of the paper, with particular attention in evaluating the stiffening due to the presence of beads on the plate with a close link with the production system and possible technological constraints which can occur during manufacturing processes, such as minimum rib distance or the presence of discontinuities or the presence of holes or other elements on the plate. A special tool with enforced rib cross section is considered, and optimal rib deployment has to be found. Numerical examples attached show the methodology and obtainable results.

Predictions of Young's modulus and negative Poisson's ratio of auxetic foams

AbstractAuxetic foams possess negative Poisson's ratio, exhibiting unique mechanical properties. A modified model based on the quasi‐three‐dimensional model of Choi and Lakes is developed for auxetic foams and the formula of the volumetric compression ratio is also corrected in this study. Three deformation mechanisms of all cell ribs (i.e. stretching, shearing and bending) are incorporated. By applying the newly modified model, the theoretical results of Young's modulus and Poisson's ratio depend on the folded angle of the bent ribs, the relative density, the shape of the rib cross section and the Young's modulus and Poisson's ratio of the virgin material. The predicted values of the effective Young's modulus and Poisson's ratio of auxetic foams compare favourably with experimental data. In addition, a finite element analysis model is proposed to predict the value of Poisson's ratio in this study. The two models can be reduced to predict the mechanical properties of conventional foams, and exhibit the process of the conversion of conventional foams into auxetic foams.

Dependence of bone yield (volume of bone formed per unit of cement surface area) on resorption cavity size during osteonal remodeling in human rib: implications for osteoblast function and the pathogenesis of age-related bone loss

It is both a necessary and a sufficient condition for bone to be lost with age at any surface location that during remodeling the replacement of resorbed bone is incomplete. In both the ilium and the rib, the degree of such focal imbalance is smaller on the intracortical than on the endocortical or cancellous surfaces that are adjacent to bone marrow. The reason for this difference is unknown. To further examine this question, we measured various geometric variables in 1263 osteons in rib cross sections from 65 persons, including both sexes and age ranges 20 to 30 years and 60 to 70 years (four groups). Haversian canal (HC) area did not differ significantly between sexes or age groups. Percent osteonal refilling was close to 95% in all groups and did not differ between sexes but fell slightly with age. There was a very highly significant linear relationship between osteon bone area and (osteon area + HC area) in all groups, with coefficients of determination (r2) greater than 0.98. The regression slopes declined slightly with age in women but not in men. There was a very highly significant quadratic relationship between osteon bone area and osteon perimeter in all groups, with r2 values greater than 0.97. The ratio osteon bone area:osteon perimeter, an index of bone yield—the volume of bone deposited on each unit area of cement surface—was strongly related to osteon area and did not differ between sexes but was slightly less in the older groups. We conclude the following: (1) The high efficiency of intracortical remodeling in the rib is confirmed, with only trivial effects of age. (2) For HC area to be maintained within narrow limits and bone balance preserved, either initial osteoblast density or osteoblast capacity (the two determinants of bone yield) or, most likely, both must increase progressively with the size of the resorption cavity, suggesting that osteoblast recruitment (relative to available surface) and osteoblast lifespan increase with the volume of bone resorbed. (3) Intracortical remodeling in the rib is more efficient than marrow-adjacent remodeling at any site, possibly because of the different relationships to the circulation. In osteonal remodeling, all molecules released from resorbed bone must travel past the sites of osteoblast recruitment and operation, but in hemiosteonal remodeling, some molecules may not be subject to this constraint. (4) If marrow-adjacent remodeling became as efficient as rib intracortical remodeling, age-related bone loss would cease to be an important medical problem. © 2010 American Society for Bone and Mineral Research

Dispersion characteristics of nanometer-scaled silicon rib waveguides

We investigate the dispersion properties of nanometer-scaled silicon waveguides with channel and rib cross section around the optical fiber communication wavelength and systematically study their relationship with the key structural parameters of the waveguide. The simulation results show that the introduction of an extra degree of freedom in the rib depth enables the rib waveguide more flexible in engineering the group velocity dispersion (GVD) compared with the channel waveguide. Besides, we get the structural parameters of the waveguides that can realize zero-GVD at 1550 nm.

PIV Study of Shallow Open Channel Flow Over d- and k-Type Transverse Ribs

A particle image velocimetry was used to study shallow open channel turbulent flow over d-type and k-type transverse ribs of square, circular, and semi-circular cross sections. The ratio of boundary layer thickness to depth of flow varied from 50% to 90%. The mean velocities and turbulent quantities were evaluated at the top plane of the ribs to characterize interaction between the cavities and overlying boundary layer. It was found that the overlying boundary layer interacts more strongly with k-type cavities than observed for d-type cavities. The profiles of the mean velocities and turbulent statistics were then spatially averaged over a pitch, and these profiles were used to study the effects of rib type and cross section on the flow field. The mean velocity gradients were found to be non-negligible across the boundary layer, and the implications of this observation for momentum transport, eddy viscosity, and mixing length distributions are discussed. The results show that the skin friction coefficient, Reynolds stresses and mixing length distributions are independent of rib cross section for d-type. For the k-type ribs, significant variations in skin friction coefficient values, mean flow, and turbulence fields are observed between square ribs and circular/semi-circular ribs.

Numerical Analysis of Turbulent Heat Transfer in a Square Duct with Different Rib Shapes

Numerical analysis has been performed for three-dimensional developed turbulent flow in a square duct with rib-roughened walls. Special attention pays for the prediction of turbulent heat transfer with roughened wall. Roughened wall is composed of small ribs which are located periodically on bottom wall of square duct. In order to clarify the influence of rib cross sectional shape on flow and temperature fields, three kinds of ribs, that are square, triangular and elliptical cross section, is examined from the point of heat transfer. In numerical calculation, algebraic Reynolds stress model is selected for flow field in order to predict anisotropic turbulent flow precisely and zero equation model assuming constant Prandtl number is applied for temperature field to make clear whether such simple model is able to evaluate Nusselt number correctly. Periodic boundary condition has been used for this flow to save computational time. Calculated results of temperature field are compared with the experimental data in order to examine the validity of the presented numerical method. As a result of this calculation, it has been found out that the present method could predict temperature contour lines and Nusselt number qualitatively although agreement is certainly not perfect in all detail. Adding to this, turbulent structure is affected by rib cross section shape, although rib height is small compared with side length of square. Especially, elliptical cross section promotes the production of vertical fluctuating velocity and shear stress which leads to generate the secondary flow of the second kind more actively than the other rib shapes. At the same time, calculated results suggest that heat transfer is enhanced by the elliptical cross section.

Forced convective heat transfer and pressure drop of air flowing in a rectangle duct with cross-ribs on the opposite walls

Experiments were conducted to investigate the forced convective heat transfer and flow friction of turbulent airflow in a rectangular duct with cross-ribs attached at the two principal walls in the Reynolds number range from 5000 to 40000. The effect of the rib cross angle (45°, 60°, 75°) and the height (4 mm, 5 mm) of the cross-ribs on the forced convection and flow friction were tested. Non-dimensional correlations for the duct average Nusselt number and friction factor of cross-ribs duct were developed from the test data. Experiments were also conducted for the corresponding parallel ribs to compare their relative performance. The experimental results show that both of the convective heat transfer coefficient and friction factor were increased with cross-ribs, with 45° cross-ribs being the best. Compared with parallel ribs normal to the flow direction under identical flow rate and identical pumping power constraints, the cross-ribs can enhance heat transfer in the lower Reynolds number region, while in the high Reynolds number region, the heat transfer performance of the parallel ribs seems better.

Unistructure—A New Concept for Light Weight Integrally Stiffened Skin Structure

Unistructure is a new concept for lightweight integral rib‐reinforced skin structures that is readily adaptable to many configurations. The rib cross sections are a form of I beam. The rib reinforcing patterns considered here are isogrid and waffle, (i.e. triangular and rectangular constructions) but any desirable form can be produced. This paper provides an over‐view of the methods of fabrication and the structural performance features of Unistructure. Comparisons are made with honeycomb, skin/stringer, and integral‐machined structures. These comparisons indicate that the combined ease‐of‐fabrication and performance advantages of Unistructure warrant its consideration in many applications.