Some researchers have studied crashworthiness characteristics of thin-walled tubes under oblique loading in previous works. Han et al.  for the first time studied the crushing behavior of thin-walled square tubes under oblique loading using LS-DYNA. They showed through numerical study that there is a critical load angle at which a transition takes place from the axial collapse mode to the bending collapse mode. Reyes et al. [7, 8] experimentally and numerically investigated the behavior of square aluminum tubes under quasi-static oblique loading for three different load angles. The square tubes were clamped at one end and oblique loading conditions were realized by applying a force in the upper end, with different angles, relative to the centerline of the tube. Yang et al. , using nonlinear ﬁnite element analysis through LS-DYNA, investigated the crushing behavior a class of axisymmetric thin-walled square
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To study the crushing process of thin-walled structures, in 1984, Abramowicz et al. based on  to make some assumptions, thereby identifying the two basic folding elements shown in Fig. 4 which has been used to predict the static axial progressive buckling of square tubes with a mean width c and a mean wall thickness h. This is also revised in .
In the present numerical study, the response of these materials in a square tube subjected to the energy corresponds to a car accident has been studied. The objective of the work is to analyze the crashworthiness of the square tube in-filled with different aluminum based foams, which is measured in terms of energy absorption during a car accident. In the present work, three dimensional (3D) FEM models of square tubes have been created which is subject to unidirectional compression loading of such an order of magnitude replicating the situation of a 1000 kg weight car moving with a 36km/hr speed. The empty square tubes models of aluminum alloy (Al 2014) and mild steel (MSrst37) shell column materials were studied for its crashworthiness. In other cases, these two shell columns are in-filled with different aluminum foams. The material properties of foams considered in the present study are given in Table 1. Metallic foams having approximately same relative densities are taken from the available literature. The four foams considered in the present study are Aluminum-Magnesium based (ALSi 8 Mg), Aluminum-Silicon Carbide based (CYMAT Al-
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The purpose of this research is to develop a mathematical model of the collapse behaviour of symmetric hexagonal tubes. For that, a finite element analysis procedure was conducted using ABAQUS software to determine the lateral collapse behaviour of symmetric hexagonal of angles, 30°, 45° and 60° and square tubes to compare the results with the cylindrical tube. Then, a new predictive mathematical model of the lateral collapse behaviour for the generalized symmetrical geometric tubes is developed based on rigid, perfectly plastic model and the energy balance method. The newly mathematical model was validated with the simulation method results. It was discovered that symmetric hexagonal and square tubes performed different deformation behaviour than the cylindrical tube. Square and symmetric hexagonal with 15° tubes performed Type II deformation behaviour. Symmetric hexagonal tubes with 30°, 45° and 60° performed Type I with the perfectly plastic collapse behaviour whereas cylindrical tube performed Type I with strain hardening deformation behaviour. The mathematical prediction model had managed to model the deformation behaviour of symmetric hexagonal tubes with 30°, 45° and 60° but failed to model the square and symmetric hexagonal with 15° tubes because it was the perfectly plastic model which suitable for Type I with perfectly plastic deformation behaviour. Keywords: Lateral collapse, symmetric hexagonal tubes, square tube, mathematical model, energy absorption 1. Introduction
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Aside from higher heat transfer performance, keeping pressure drop at a minimum is of interest for reducing the operating cost and saving energy. Figure 12b shows a summary of the pressure drop required for all cases studied. Note that the mass flow rate is kept constant in all cases; hence, it can be used directly to represent the pumping power required. The straight channel requires the lowest pressure drop among all cases; whereas the coiled tube designs require more than double the pres- sure drop of the straight channel. Among the coiled tubes, helical spiral tube needs the highest pressure drop, followed by in-plane spiral and conical spiral tubes. An interesting phenomenon is observed at a nanofluid concentration of 1% when the pressure drop for coiled tubes is slightly lower than that for water. This is due to the fact that at low particle concentra- tions, the particle volumetric concentration affects the nanofluid viscosity negligibly while the effect of tem- perature increases in the nanofluid thermo-physical properties.
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Final deformations of the square tube for various impact velocities are shown in Figs. 5–8. Strain distributions in buckling region are shown in Figs. 9 and 10. Strain-time curve in buckling region is shown in Figs. 11 and 12. In the case of 1 mm thickness tube, shown in Figs. 5 and 6, the irregular pattern on the surface of the tube is a concave- convex pattern on the adjoining surface. When the impact velocity is high, the second buckling is generated in the adjacency part in the ﬁrst buckling. As seen in Fig. 9, compressive strain near the corner of the tube is large compared to that of the other part of the tube. In the case of 1 mm thickness tube, Face A has a convex surface and Face B has a concave surface. As seen in Fig. 11, strain near the corner of the tube in the beginning of the deformation is small
Studies conducted on thin-walled tubes under oblique loads are shown in Figure 7. The analysis conducted by Han and Park (1999) relates to the behaviour for gentle square steel columns that were subjected to oblique loading. Here, the oblique loading affected the columns on rigid walls that were rejected without friction. Also, different angles were studied, in which the reactions are divided into three parts, namely broken axes, broken bends and transitional zones. An empirical angular expression is also given in this study. Further, this foam-filled structure was examined using a thin- walled aluminium extrusion subjected to oblique loading. The type of oblique loading such as the reaction to the square structure of aluminium extrusion (Reyes et al. 2002) has been investigated on empty tube and foam-filled square tubes (Reyes et al. 2003) and aluminium circular tubes (Borvik et al. 2003) using quasi-static experiments. Whereas for other structures, Ahmad et al. (2010) explored the ad-vantages of using foam-cone tubes under oblique loading. Here, cone foam filled were found to have effective energy absorption structures given they were able to withstand the oblique load impact effectively. The cone tubes were able to effectively withstand the oblique load impacts and even the minimum reduction in energy absorption due to the increased load angle. Figure 7 illustrates a foam-filled structure subjected to oblique loading.
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Abstract. An experimental investigation was conducted to compare the crush characteristics and energy absorption capacity of circular and square tubes with located through-hole crush initiator. Circular through-holes were fabricated at three different configurations based on location into steel tubes which had a length of 200 mm. Furthermore, two different side configurations along the tube were considered for introducing the crush initiators. The results found that adding crush initiator onto the tubes effectively reduced the initial peak force of a thin-walled circular and square tubes under axial quasi-static loading. The peak crush force was reduced within a range 3-10% and 5-16% for circular and square tubes, respectively when compared with corresponding tubes without crush initiator. Moreover, the energy absorption capacity of the tubes was independent with the incorporation of through-hole crush initiators. However, the energy absorption of circular and square tubes slightly decreases when compared with the tubes fabricated four sided crush initiation and tubes without crush initiator. Overall, the effect of location and number of crush initiation significantly influenced the initial peak forces while maintain the energy absorbed.
Significant efforts have been taken to study the thin- walled tubes under axial crushing. The crushing of circu- lar tubes was found to develop a diamond mode or a con- certina mode or a mixture of the two, which depends on its material and geometry (Alexander, 1960; Wierzbicki et al., 1992; Guillow et al., 2001). Similarly, the crushing of square tubes features three types of failure modes, i.e., the sym- metric mode, asymmetric mode A and asymmetric mode B (Wierzbicki and Abramowicz, 1983; Abramowicz and Jones, 1984; Abramowicz and Jones, 1986). To estimate the en- ergy absorption of square tubes, Wierzbicki and Abramow- icz (1983) proposed a super folding element theory. Later, this theory was further improved by taking the effective
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Post-buckling behaviour of aluminium alloy extruded polygon section tubes under dynamic axial crushing has been investigated by Rossi et al. (2005). The analysis was performed explicitly by using the LS-DYNA finite element software. The analysis was divided into two stages. In the first stage, the numerical parameters and all the numerical results associated with thin-walled aluminium extruded square tubes were validated with existing published experimental data. In the second stage, the post-buckling behaviour such as extensional, symmetric and asymmetric deformation modes were examined. The numerical simulations revealed that the polygon with more number of walls or flanges had higher axial deformation load and reduced the permanent displacement parameters. For an example, hexagonal tube section increased the deformation load by 11% and reduced the permanent displacement by 10% compared to square tubes. Furthermore, the specimens with the thinnest nominal wall thickness also increased the deformation load and reduced the permanent displacement parameters by 27% and 20% respectively. Figure 2.13 illustrates the final post-buckling deformation state of a hexagonal sectioned model.
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During the second voltage/time procedure the voltage was maintained at 6 V while the time period ranged from 30 s to 5 min. After 30 s in the electrochemical cell, tubes could be seen forming over the entire substrate surface as seen in Figure 4 (a). In addition to the tubular features was the presence of numerous ACP plate-like particles. The plate-like features had mean diameters of around 5 µm and a thickness of around 1.5 µm and were covering the surface between the tubules as seen in Figure 4 (b). Also present was surface cracks, which were seen earlier in the variable voltage procedure for voltages above 4 V. One minute into the electrochemical procedure saw a significant increase in hydrogen evolution and an increase in size and number of tubules being formed as seen Figure 4 (c). Three minutes into the procedure saw a dramatic increase in the size and depth of cracks in the surface coating, which exposed more of the underling Mg substrate to the electrolyte, Figure (d). Also noticeable during this period was the reduced rate in new tubules being formed as indicated graphically in Figure 4 (f). At this point in time it is believed that most of the gas being formed was exiting the coating via the extensive network of large cracks covering the surface.
In this work we investigate the three-dimensional laminar ﬂow of Newtonian and viscoelastic ﬂuids through square–square expansions. The experimental results obtained in this simple geometry provide useful data for benchmarking purposes in complex three-dimensional ﬂows. Visualizations of the ﬂow patterns were performed using streak photography, the velocity ﬁeld of the ﬂow was measured in detail using particle image velocimetry and additionally, pressure drop measurements were carried out. The Newtonian ﬂuid ﬂow was investigated for the expansion ratios of 1:2.4, 1:4 and 1:8 and the experimental results were compared with numerical predictions. For all expansion ratios studied, a corner vortex is observed downstream of the expansion and an increase of the ﬂow inertia leads to an enhancement of the vortex size. Good agreement is found between experimental and numerical results. The ﬂow of the two non-Newtonian ﬂuids was investigated experimentally for expansion ratios of 1:2.4, 1:4, 1:8 and 1:12, and compared with numerical simulations using the Oldroyd-B, FENE-MCR and sPTT constitutive equations. For both the Boger and shear-thinning viscoelastic ﬂuids, a corner vortex appears downstream of the expansion, which decreases in size and strength when the elasticity of the ﬂow is increased. For all ﬂuids and expansion ratios studied, the recirculations that are formed downstream of the square–square expansion exhibit a three-dimensional structure evidenced by a helical ﬂow, which is also predicted in the numerical simulations.
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consisted of two circular aluminium tubes which was filled with kagome lattice shaped cells (see Figure 2.9). A numerical method was utilised to study several properties of the composite structure such as the interaction effect, deformation mode and energy absorption capacity. It was observed that during the collapse mode, the kagome lattices buckled ﬁrst causing the outer and inner skin tubes to fold locally and enhanced the plastic deformation region. The application of double layer tubes had reinforced the buckling capacity of kagome cell. In addition, the collapse of the honeycomb cell was being delayed by the wrinkled mechanism of the tube walls which intruded into the gap of the honeycomb cell. Hence, the contact effects between the honeycomb and column walls had significantly enhanced the energy absorption efficiency.
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Collection of patient samples in Parasep tubes containing Al- corfix in tandem with collection of patient samples in Parasep tubes containing PVA-formalin represented a significant chal- lenge to the study. ARUP Laboratories serves hospitals in 49 of 50 states in the United States, each of which can submit O&P samples to ARUP Laboratories in fixatives of their choice, though the fix- atives supplied by ARUP Laboratories are PVA with copper and 10% formalin, and specimens in these fixatives represent the ma- jority of submissions that ARUP Laboratories receives. At the time of this study, no hospitals that ARUP Laboratories serves were using Parasep tubes. In order to effectively attain cocollection in our standard collection tubes as well as the Parasep tubes, we issued both collection tubes in a standard stool collection kit to the University of Utah Hospital and Clinics, for which ARUP Labo- ratories serves as the primary/on-site microbiology laboratory. The University of Utah Hospital and Clinics primarily serve the greater Salt Lake Valley of northern Utah, for which the geography is high desert, chaparral, and mountainous terrain with little groundwater and very low humidity (relative humidity, ⬃10 to 20%). As expected, the rate of local parasite acquisition is very low on the basis of historic O&P and stool antigen positivity rates in the laboratory (8; unpublished data). Despite these inherent lim- itations and poor patient compliance with full-volume stool col- lection, 3 of the 26 specimens submitted over the course of the study were positive for protozoa representing four different gen- era of protozoal parasites (Endolimax nana, Entamoeba coli, Blas- tocystis hominis, and Giardia lamblia), each with distinct morpho- logical traits that are necessary for accurate identification. Each of the organisms was identified in each fixative by the testing tech- nologists, and they largely had very comparable morphologies and staining qualities by the two methods. The specimen containing TABLE 3 Work flow comparison for SpinCon versus Mini Parasep SF concentration method
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Several types of brass tubes can be used to manufacture Cupro Braze heat exchangers. These tubes are uniformly made from strip because thin gauges are required for lightness and efficient heat exchange. Tube fabrication requires that the edges of the strip are reliably bonded together. The tube seams can be sealed during the brazing process or they can be welded prior to the brazing process.Tubes for use in the Cupro Braze process should be specified with a crown that is higher compared to the crowns of tubes for use in a soldering process. The crown should be 0.4mm to 0.8mm for tube widths 12mm to 25mm. A higher crown results in a more consistent bond between tube and fin.
Arc discharge technique has been rumored for manufacturing carbon nanotubes.During this technique,as shown in fig 2 , two nanotubes square measure made through arc vaporization of 2 carbon rods placed end to finish with a distance of 1mm in Associate in Nursing environment of argon like element, argon at pressure between fifty to 700 mbar.Carbon rods square measure gaseous by a right way, a current of fifty to a hundred amps driven by 20v which will produce warm temperature discharge between 2 electrodes.due to this, anode can get gaseous and rodshaped tubes are going to be deposited on cathode.Bulk Protection of CNT'S depends on uniformity of plasma arc and temperature of deposition.
Abstract: The brass tubes with foam cores of AlSi7SiC3, AlSi7SiC3Fe1 and AlSi7SiC3Fe3 were produced as the crush-boxes with circle and square cross-section. Then axial compressive behavior and energy absorption capability of the foam-filled tubes were investigated during the quasi-static progressive plastic buckling. The uniaxial compressive stress–strain curves of the foam-filled brass tubes exhibited that the compressive stress enhanced smoothly with the increase of the strain and no stress oscillations occurred in the plastic deformation region throughout the tests. The yield stress and the elastic modulus of the foam-filled brass tubes slightly decreased with the increase of Fe wt. % in the foam cores. Moreover, with the increase of Fe powder from 1wt. % to 3wt. %, the absorption energy of the foam-filled brass tubes decreased slightly dependent on the tubes cross- section. The strain-hardening exponent of the tubes with the Al7Si -3SiC-(+Fe) foam cores were found to be lower than the tubes with the Al7Si-3SiC foam cores without Fe. However, the increase of Fe powder from 1wt. % to 3wt. % caused the approximate elimination of strain- hardening and the plastic deformation behavior tends to be approximated to an ideal-plastic behavior up to the densification strain. The results indicate that all of the compression responses are due to the Micro and Macro-defects within the foams cellular structure as well as the tubes cross-section geometry.
Abstract- In fired heaters, heat is released by combustion of fuels into an open space and transferred to process fluids inside tubes. The tubes are ranged along the walls and roof of the combustion chamber. The heat is transferred by direct radiation and convection and also by reflection from refractory walls lining the chamber. The design and rating of a fired heater is a moderately complex operation. Here forced draft fired heater, which is fired by fuel gas, has been treated. For that all required equations and generalizations are listed from different fired heater design methods as per requirement. A fired heater design calculations are performed using Microsoft Excel Programming software.
Concrete filled Fiber reinforced polymer tubes (CFFTs) (Mirmiran and shahawy 1997; Fam and Rizkalla 2001a, b) are combination of the concrete and the FRP sheets along with the epoxy in which concrete is filled in the pre- fabricated FRP tube. Those tubes can be made with varying thickness depending on the requirement of the strength of the column. Several methods can be adopted for the fabrication of the FRP tube. But the most feasible and simple way of the fabrication is Hand Layup process for the in-situ fabrication and filament winding process for the machine fabrication. FRP Tube provides lateral confinement to the concrete under compression. This lateral confinement from the FRP Tube can significantly increase both the strength and the ductility of the concrete (B. Zhang, T. Yu and J. G. Teng 2014), because of this advantages, FRP tubes are good for use where the structure is supposed to face harsh environments such as freezing or thawing or the corrosive environment like near see shore.
For helical tubes of square cross section there exists insignificant flow perturbation in intra- tube space and low rate of flow whirl. The flow structure is close to the case of plain tubes, which lead to achievement of low values of friction factor. Helical tubes of oval cross section provide good flow whirl along the total length of heat exchanger, thus facilitating increase in heat efficiency, though, hydraulic resistance increases both in tubes, and in intra-tube space.