Symmetric Sections Research Articles

Techniques to manage geometry characteristics of hollow-fiber membranes

The process of the dry-wet spinning of asymmetric hollow-fiber membranes has been studied. The set of the parameters of spinning process, which allows the preparation of the smooth, round, and symmetric cross section of a fiber and the given inner and outer diameter so that the hollow-fiber membrane would finally appear as a smooth hollow cylinder, has been determined. The procedure was carried out using the fabrication of hollow fibers from poly(2,6-dimethyl-1,4-phenylene oxide) as an example. The samples with the oxygen permeance Λ/δ (O2) = 400 L/(m2 h bar) and the separation factor corresponding to the properties of material, α(O2/N2) = 4.5, have been obtained. The effective thickness of the selective layer of this membrane is 100 nm. The maximum diameter ratio that has been attained upon dry-wet spinning is 1.4 for the studied polymer solution–internal coagulant system.

A compact wideband harmonic suppressed 10 dB branch line coupler using cascaded symmetric PI sections

This article presents the size-miniaturized, wide-bandwidth, and harmonic-suppressed 10 dB branch line coupler (BLC) using cascaded symmetric PI sections. The complete design equations are derived to obtain the physical parameters of cascaded PI sections. To validate the proposed design, a 10 dB BLC operating at 0.9 GHz is designed, fabricated, and tested. The reported BLC is having dimensions of 0.175 λg × 0.25 λg and is 76.6% smaller than the conventional coupler. The measured results show that the designed coupler fractional bandwidth is >52% and up to 4th harmonic is suppressed with a level better than 20 dB. Good agreement is found between the theoretical predictions and experimental results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1610–1613, 2016

Experimental Studies on Strength and Stiffness Enhancement in CFRP-Strengthened Structural Steel Channel Sections under Flexure

AbstractAn experimental study to investigate the stiffness and strength enhancement in a structural steel channel section strengthened by six different carbon fiber–reinforced polymer (CFRP) wrapping configurations is described in this paper. An approach of transforming the singly symmetric open section such as a channel section to a closed section by CFRP wrapping as a means to increase the stiffness and strength is demonstrated. A total of 21 specimens, both CFRP reinforced and bare steel specimens, were tested in four-point bending. Two different CFRPs, unidirectional and bidirectional fabrics, were used in wrapping the specimen. While the unidirectional layers contribute to the stiffness and strength, the bidirectional layer primarily contributes to confining the former in addition to increasing the resistance to lateral torsional buckling (LTB) of the specimens. The results indicate that the CFRP-strengthened closed sections confined by bidirectional fabrics are effective in enhancing the strength an...

Residual stresses in welded I-shaped sections fabricated from Q460GJ structural steel plates

A new type of high-performance structural steel named by GJ steel, has been widely used in many large scale structures like National Olympic Stadium (Birds Nest), new CCTV Headquarters and Canton Tower in China. However, previous studies on 460MPa GJ steel are very limited. In this study, the residual stresses on eight full scale I-shaped sections welded by flame-cut Q460GJ (“Q” means yield strength) steel plates including five doubly symmetric sections and three singly symmetric sections, were investigated by experimental tests. By using sectioning method, it was found that the deformation of curved strips was one part of circular curve. The results from the circular curve correction method are generally identical to the results from a new curve correction method named by “straightening measurement”. Then the residual stress distributions on Q460GJ welded I-shaped sections were obtained. It was concluded that residual stresses were related to sectional dimensions and flanges and webs were influenced with each other. Compared with the existing residual stress distribution models, the residual stresses on sectional flanges obtained in this study are much smaller, while no significant difference is found for sectional webs. It is also found that the flange tips are all under compression rather than tension, and the average value of the peak tensile residual stresses on flanges is only about 0.5fy. Finally, the residual stress levels at typical locations of I-shaped sections were summarized and suggested.

Study of the effect of truncation on the optical and thermal performances of an ICS solar water heater system

The aim of this work is to study the effect of truncation of an integrated solar collector with full CPC reflectors on the optical and thermal performances. The design with untruncated concentrator has a strong connection with a previous study where an old ICS system was designed and experimentally tested and it was already studied in a previous work. The upper part contained two symmetrical parabolic sections with focal axes tilted by θ=48° from the vertical plane. The lower part was constituted by three involute reflectors. Its cylindrical storage tank covered the triangle formed by the three involute parts centers. In order to reduce its size while keeping an acceptable level of the average temperature, minimize its manufacturing cost and facilitate its installation, truncation is suggested. A numerical model based on the detailed geometric characteristics of the full CPC was developed to plot the corresponding profile that was took as reference to switch to a truncated CPC deduced from the latter mathematical equations.A theoretical study was then carried out to predict the optical and thermal behavior of the system and simulate several parameters such as the concentration ratio and the height of the upper concentrating stage. The results are presented and discussed. The developed numerical tool within this work can be considered as important for a future study of the optical performances regarding the angle of acceptance for optimization.

Experimental study of bowing defects in pre-notched channel section products in the cold roll forming process

In this study, the factors influencing bowing defects, which reduce quality in the cold roll forming of pre-notched products, are investigated by conducting experimental cold roll forming tests to produce symmetrical channel sections from pre-notched strips. The input parameters influencing bowing comprise factors that are related to the geometric characteristics of roll-formed products (including the distance between holes, distance between holes and strip edge, hole diameter, web and flange channel width, and strip thickness) and factors that are related to the cold roll forming line (including the forming angle increment or flower pattern, uphill and downhill strategies, horizontal distance between stands, and lubrication condition). Through a non-linear regression method, all the input factors were compared with each other to find the ones that are most and least influential on bowing. The obtained results showed that the forming angle increment and distance between holes had the greatest effects on bowing, so that increasing the number of forming stands from two to six reduced bowing more than five times. The results also showed that compared with other factors, the horizontal distance between stands, lubrication condition, and strip thickness have the least effects on bowing.

Stability and free vibration analyses of orthotropic 3d beam–columns with singly symmetric section including shear effects

A complete beam–column classification and the corresponding characteristic equations for the stability and undamped natural frequencies of 3D orthotropic Timoshenko beam–columns with singly symmetric closed section and with elastic end connections subjected to an eccentric end axial load are presented and derived using three different approaches. The first two approaches are those by Engesser and Haringx that include the shear component of the applied axial force proportional to the slope (du/dx and dv/dx in planes xz and yz, respectively) and to the angle of rotation of the cross-section (θx and θy in planes yz and xz, respectively) along the span of the member, respectively. The third approach is a simplified formulation based on the classical Euler theory that includes the effects of shear deformations but neglects the induced shear component of the applied axial force along the member. The proposed methods and characteristic equations are capable of determining the critical axial loads and undamped natural frequencies of beam–columns with elastic end connections. Four comprehensive examples are included that show the effectiveness and simplicity of the proposed method and the results obtained are compared with experimental results available in the technical literature. It is shown that: (1) the natural frequencies and critical axial loads of beam–columns increase as the shear stiffness GAs, the degrees of fixity and lateral bracings at the ends of the member increase; (2) the natural frequencies calculated using the three approaches are identical to each other when the applied axial load is zero; (3) the critical axial load in compression using the Engesser approach is lower than the one obtained using the Haringx approach; (4) the critical axial loads in compression are highly affected by the degree of flexural fixity at the supports, but those in tension are not affected much; and (5) the Haringx approach is the only one among the three approaches capable of capturing the phenomena of tension buckling observed in seismic isolators.

MICROSONIC RETRIEVABILITY OF INTRACANAL SEPARATED ROTARY NICKEL-TITANIUM INSTRUMENTS HAVING ASYMMETRIC VERSUS SYMMETRIC DESIGNS AND EVALUATION OF REMAINING DENTIN THICKNESS USING CBCT

Objective: This study compared retrievability of two rotary nickel Titanium (NiTi) instruments with symmetric versus asymmetric cross sections; ProTaper Universal® and RevoS®, respectively, with reference to the influence of some anatomic factors, as well as evaluated of the remaining minimum dentin thickness after retrieval using cone beam computed tomography (CBCT). Materials and Methods: Thirty six extracted mandibular first molars with curved mesiobuccal canals were used. The apical 4mm of ProTaper Universal rotary NiTi instrument ® (Dentsply Maillefer, Ballaigues, Switzerland) size F3 (n=18) and RevoS rotary NiTi instrument ® (Micro- Mega, Besanc¸on, France) size A35/06 (n=18) were fractured in the apical region of the canal. Fragments were located at apical or apical-middle and their coronal end were before canal curvature, at or beyond it. Microsonic technique was successful when instrument retrieval occurred without mishaps. Post retrieval CBCT was superimposed on preoperative CBCT to determine changes in distal dentin thickness (at coronal end of instrument (C level) and at furcation level (F level) and in canal width. Chi-square test evaluated success incidence between the two instruments types and effects of influencing anatomic factors. Mann-Whitney U test compared quantitative data, significance was set at P<0.05. Results: Overall success rate for removal of fractured fragments was 72.2% with equal incidence in both instruments types. Retrieval of ProTaper instrument was positively affected by being in the apical-middle location, P=0.047. Retrieval of RevoS instrument was positively affected by being before and at the curvature; P = 0.04. CBCT measurements showed overall minimum distal dentin thickness after retrieval to be approximately 0.67±0.14 mm. Percent of dentin removal was significantly higher at F level, P=0.04, while Canal width was higher at C level P=0.052. In ProTaper group, percent of dentin removal at C level was slightly lower than in RevoS group, P=0.28. Strip perforation occurred in 8 samples and secondary fracture in 2 samples. Conclusions: The successful removal of fractured Ni-Ti instruments is more influenced by anatomical factors namely; the position of the instrument within the root canal, the location of the fractured instrument in relation to the root canal curvature and the remaining dentin thickness. Instrument’s design indirectly affects success by requiring greater amount of dentin removal to disengage it.

Geometrical Method for Increasing Precision of Machine Building Parts

Calculation of complex curves with high accuracy is challenging. The curve is approximated by segments of straight lines and carried out smoothing. A new method of analytic geometry to calculate the trajectories of mechatronic systems and CAD/CAM is offered. The theoretical basis of the method is symmetries in the Euclidean plane. The method can accurately calculate the trajectory for the centrally symmetric conic sections and, in some cases, arbitrary differentiable planar curves. The method gives an accurate analytical solution without using radicals. This allows you to find the formulaic dependencies for further calculations. The existence of Lissajous figures allows assuming the presence of a universal method of calculation of complex trajectories based on planar differentiable curves. Some examples of the design of the kinematic mechanisms are presents additionally.

Evaluation of empirical methods for estimating potential evaporation values in northeast France

This study presents and discusses the field monitoring of an experimental embankment divided into two symmetrical sections constructed with two different fine-grained soils in the northeast of France. The field instrumentation included detailed monitoring of volumetric water content, matric suction and temperature within the embankment as well as measurements of meteorological data. The field measurements show that the used instrumentation worked well on monitoring the soil responses to the meteorological changes in the two soils. The study also evaluates different empirical methods for estimating potential evaporation (ET) values based on regional meteorological data. The results show a large variability observed on the ET values for the investigated site calculated by empirical methods or equations based on meteorological local date.

Empirical Modeling of Pressure Spectra in Adverse Pressure Gradient Turbulent Boundary Layers

This study investigated the unsteady aerodynamic forcing that occurs near the trailing edge of airfoils with chordwise Reynolds numbers between 2 and 6 million. Static pressure, unsteady surface pressure, and velocity measurements were made throughout the trailing-edge region of an airfoil model with three interchangeable, symmetric trailing-edge sections. The data of the present study were used to develop a new model for estimation of fluctuating surface pressure autospectra beneath two-dimensional turbulent boundary layer flow experiencing an adverse pressure gradient of variable strength. This new model has been used to compare with data from six separate experimental investigations from literature, and has been compared against a separately developed empirical model of the fluctuating surface pressure. Additional empirical modeling of the coherent extents of the fluctuating pressure field in the longitudinal and lateral directions, as well as the convection velocity, is presented as a function of nondimensional variables dependent on the adverse pressure gradient flow condition.

Thermal catalytic oxidation of octachloronaphthalene over anatase TiO2 nanomaterial and its hypothesized mechanism.

As an environmentally-green technology, thermal catalytic oxidation of octachloronaphthalene (CN-75) over anatase TiO2 nanomaterials was investigated at 300 °C. A wide range of oxidation intermediates, which were investigated using various techniques, could be of three types: naphthalene-ring, single-benzene-ring, and completely ring-opened products. Reactive oxygen species on anatase TiO2 surface, such as O2−• and O2−, contributed to oxidative degradation. Based on these findings, a novel oxidation degradation mechanism was proposed. The reaction at (101) surface of anatase TiO2 was used as a model. The naphthalene-ring oxidative products with chloronaphthols and hydroxyl-pentachloronaphthalene-dione, could be formed via attacking the carbon of naphthalene ring at one or more positions by nucleophilic O2−. Lateral cleavage of the naphthalene ring at different C1-C10 and C4-C9, C1-C2 and C4-C9, C1-C2 or and C3-C4 bond positions by electrophilic O2−• could occur. This will lead to the formation of tetrachlorophenol, tetrachloro-benzoic acid, tetrachloro-phthalaldehyde, and tetrachloro-acrolein-benzoic acid, partially with further transformation into tetrachlorobenzene-dihydrodiol and tetrachloro-salicylic acid. Unexpectedly, the symmetric half section of CN-75 could be completely remained with generating the intricate oxidative intermediates characteristically containing tetrachlorobenzene structure. Complete cleavage of naphthalene ring could produce the ring-opened products, such as formic and acetic acids.

Experimental and numerical study of bowing defects in cold roll-formed, U-channel sections

Because the cold roll forming process has been developed such that it is now widely used in profile production, the importance of improved product quality is felt more keenly now than in the past. In order to improve the quality of cold-roll-formed products, it is necessary to investigate how defects that may occur during production can be reduced. This paper experimentally and numerically studies profile bowing, because such bowing is one of the most common defects caused by the cold roll formation of symmetrical U-channel sections. To this end, the influence of various factors associated with profile geometry and the cold roll-forming line is investigated and discussed. These parameters include strip thickness, radius of bend, flange width, bend angle increment at each stand, and inter-distance between two successive stands. Then, a curve fitting based on the linear regression method is used to compare the effects of the different input parameters on product bowing, which is used as the output parameter. Results show that the most important parameters to profile bowing are the bending angle increment at each stand, the flange width, and the strip thickness. Conversely, the effects of the inter-distance between successive stands and the radius of bend on the bowing defect are negligible.

An analytical study on the bending of prismatic SMA beams

In this study, an analytical solution is presented for pure bending of shape memory alloy (SMA) beams with symmetric cross section as well as symmetric behavior in tension and compression. To this end, a three-dimensional constitutive equation is reduced to one-dimensional form and employed to study the bending response of SMA beams at high (pseudo-elasticity) and low (shape memory effect) temperatures. An analytical expression for bending stress as well as polynomial approximation for shear stress and deflection are obtained. Derived equations for bending are employed to analyze an SMA beam with rectangular cross section and results are compared with those of the finite element method. The results of this work show good agreement when compared with experimental data and finite element results. Furthermore, the existence of several zero-stress fibers during unloading of SMA beams at low temperature is demonstrated.

Ediacaran skeletal metazoan interpreted as a lophophorate.

While many skeletal biomineralized genera are described from Ediacaran (635–541 million years ago, Ma) strata, none have been suggested to have an affinity above the Porifera–Cnidaria metazoan grade. Here, we reinterpret the widespread terminal Ediacaran (approx. 550–541 Ma) sessile goblet-shaped Namacalathus as a triploblastic eumetazoan. Namacalathus has a stalked cup with radially symmetrical cross section, multiple lateral lumens and a central opening. We show that the skeleton of Namacalathus is composed of a calcareous foliated ultrastructure displaying regular concordant columnar inflections, with a possible inner organic-rich layer. These features point to an accretionary growth style of the skeleton and an affinity with the Lophotrochozoa, more specifically within the Lophophorata (Brachiopoda and Bryozoa). Additionally, we present evidence for asexual reproduction as expressed by regular budding in a bilateral pattern. The interpretation of Namacalathus as an Ediacaran total group lophophorate is consistent with an early radiation of the Lophophorata, as known early Cambrian representatives were sessile, mostly stalked forms, and in addition, the oldest known calcareous Brachiopoda (early Cambrian Obolellida) and Bryozoa (Ordovician Stenolaemata) possessed foliated ultrastructures.

The fully plastic behaviour of monosymmetric steel sections

The behaviour of monosymmetric steel sections when they become fully plastic under the action of an axial force P and a bending moment M applied in the plane of symmetry is considered. Attention is focused on the cross sectional strength, the possibility of local buckling occurring being ignored. The interaction curve that relates the co-existing values of P and M when the section becomes fully plastic is derived. The conditions that this curve must satisfy are established and a procedure for obtaining the curve is given. Interaction curves available for some T-sections are discussed; some anomalies are found in these curves. These are investigated and it is found that they exist because of the procedure used to obtain these curves; they disappear when the procedure proposed in this paper is used instead. If the procedure used previously in the analysis of monosymmetric sections is used to analyse eccentrically loaded doubly symmetric sections, the same anomalies are encountered; these also disappear when the proposed procedure is used.

Experimental study of stainless steel angles and channels in bending

Substantial research has been conducted in recent years into the structural response of stainless steel components, with the focus being primarily on doubly symmetric cross-sections. Limited experimental data exist on non-doubly symmetric stainless steel sections in compression, while there is an absence of such data in bending, despite these sections being widely used in the construction industry as wind posts, lintels and so on. To address this limitation, and to bring an improved understanding of the behaviour of these sections, an experimental study into the flexural response of stainless steel channels bent about their minor axis and angles bent about their stronger geometric axis is described herein. In total, 16 bending tests on austenitic stainless steel beams have been conducted and the obtained results, including the full load-deformation history and observed failure modes have been described. Auxiliary tests on tensile coupons extracted from the tested sections and initial geometric imperfection measurements have also been performed and are reported in detail. The influence of the spread of plasticity and strain hardening on the shift of the neutral axis and the ultimate load carrying capacity is also examined. Based on the obtained test results, the current design provisions of EN 1993-1-4 [1] for these types of cross-sections were assessed and found to be unduly conservative. The effect of strain hardening on the structural response of stocky stainless steel sections and the need to account for it in design has been highlighted.

On the existence and stability of minimizers in ferromagnetic nanowires

We study static 180 degree domain walls in infinite magnetic wires with bounded, C1 and rotationally symmetric cross sections. We prove an existence of global minimizers for the energy of micromagnetics for any bounded C1 cross sections. Under some asymmetry of cross sections we prove a stability result for the minimizers, namely, we show that vectors of micromagnetics having an energy close to the minimal one, must be H1 close to the actual minimizer, which is itself close to the minimizer of the limit energy up to a rotation and a translation.

Out-of-Plane Buckling of Beams Having In-Plane Elastic Restraints under Gradient Thermal Action

AbstractWhen a beam is subjected to an in-plane linear temperature gradient field, the thermal effects of the temperature gradient field tend to change the curvature of the beam in the transverse direction and to expand the beam in the axial direction. The rotation and expansion of the ends of the beam may be restrained elastically by its supports or by adjacent members such as columns. The restrained thermal actions will produce bending moments and compressive forces in the beam, and when these actions reach critical values the elastically restrained beam may bifurcate from its primary in-plane equilibrium configuration to an out-of-plane buckled equilibrium configuration. This paper investigates the thermoelastic out-of-plane buckling of an elastically restrained beam with a doubly symmetric cross section that is subjected to an in-plane linear temperature gradient field. The analytical solution for the critical temperature gradient for thermoelastic out-of-plane buckling of the beam is derived. It is f...

Numerical simulations and experimental validations of force coefficients and flutter derivatives of a bridge deck

This paper presents the results of the application of the large eddy simulation (LES) numerical method with the aim of investigating static coefficients and nonstationary flutter derivatives for a common symmetric bridge deck section. The results are compared with those of the unsteady Reynolds-averaged Navier–Stokes (URANS) study. The results of the investigated numerical simulations are validated by force and pressure measurements from wind tunnel experiments. In addition to the commonly used representation of flutter derivatives based on the integrated forces, the paper uses cross-sectional representation by tracking the contributions of nonstationary coefficients around the bridge deck section. Besides providing a better insight into the physical mechanism, the cross-sectional representation seems to be a powerful tool for identifying deficiencies in visualizing the impact of flow separations on flutter derivatives.