Irregular Cross-sectional Shape Research Articles

A hybrid wave and finite element/boundary element method for predicting the vibroacoustic characteristics of finite-width complex structures

This paper presents a hybrid wave and finite element/boundary element method for predicting the vibroacoustic characteristics of complex panels characterised by an irregular cross-sectional shape with a non-flat upper surface. In this approach, the panels are treated as waveguides and only a small segment of the panel is modelled using finite elements. The mass and stiffness matrices of the segment are then post-processed to project the motion onto its cross-sectional boundaries interfacing with the surrounding fluids. The acoustic pressures in the fluids are modelled by applying Fourier transforms to the Helmholtz boundary integral equations in the wavenumber domain. For each wavenumber component, the pressures acting on the segment are transformed into external nodal forces by evaluating the virtual work performed by the surface pressure on the segment. The wave and finite element formulations are subsequently coupled to the discretised boundary integral equations to determine the response of the panel to acoustic wave excitation. The hybrid method for predicting dispersion curves and sound transmission is validated through comparisons with predictions obtained from both an analytical model and a wave-based method found in the literature. To demonstrate the practical utility of the approach, the hybrid method is employed to predict sound transmission through a corrugated sandwich panel, where developing an analytical model is difficult. The method provides accurate predictions at a low computational cost.

Adaptive Helical Rolling of a Snake Robot to a Straight Pipe With Irregular Cross-Sectional Shape

The snake robot, which mimics the mechanism of real snakes, is expected to be used in various environments. This article addresses the challenge of snake robots autonomously adapting to and moving inside and outside pipes having complex shapes using a helical rolling motion. We consider that an irregular helical form can be defined as a combination of three components, namely the axis, cross-sectional shape, and pitch angle, and that it is easier to consider deformations that have compliance only in a specific direction. Our proposed method deforms the cross-sectional shape of the snake robot locally so that it adopts the shape of the pipe accurately. Experiments were conducted using our developed snake robot to verify the effectiveness of the proposed method, and it was demonstrated that the proposed method can be used for a snake robot moving inside and outside of straight pipes and outdoor tree, including those having noncircular and varying cross sections.

An improved procedure for calculating the pore size distribution of filter cloths in capillary flow porometry

Pore size distribution is one of the most important structural characteristics of filter cloths and can, in theory, be used to predict filtration performance. Capillary flow porometry is a common method to determine the pore diameter(s) and the pore size distribution of a porous material. Equipment applying this method has many advantages, but data processing and further calculations still require refining to be fit for purpose in calculations of flow capacity. The present study aims to develop a new procedure for processing volumetric flow rate data and corresponding pressure, which are measured by capillary flow porometry. The processed data are further used to calculate the pore size distribution of textile materials. Six industrial samples of polypropylene filter cloth were examined using scanning electron microscopy and capillary flow porometry. The raw data measured by the capillary flow porometer were processed using the developed method that considers changes in flow regimes as pressure increases. In addition, the nonideality of pores, originating from tortuosity, an irregular cross-sectional shape of the pore, and the number of pores, were considered in calculations by combining all these characteristics in one single parameter. This work shows that pores in a textile material are not ideal cylinders. The standard pore size distribution calculations should consider an imperfect pore structure and, therefore, be corrected.

Deformation Detection of Mining Tunnel Based on Automatic Target Recognition

Mining tunnels have irregular and diverse cross-sectional shapes. Structural deformation detection using mobile laser measurement has some problems, such as the inconvenient positioning of the deformation, difficulties in unifying the multiphase data, and difficulties in solving the section parameters. To address these problems, this paper proposes a mining tunnel deformation detection method based on automatic target recognition. Firstly, a mobile tunnel laser detection scheme combined with the target layout is designed. Secondly, a preview image of the tunnel lining is generated using the mobile laser point cloud data, and the index relationship between the image and point cloud is established. The target recognition accuracy of the You Only Look Once version 4 (YOLOv4) model is optimized by integrating the prediction confidence threshold, target spatial position, and target gray scale rule. Based on target recognition and positioning, the chord length and vault net height of the mining tunnel are calculated using gross error elimination and curve fitting. Finally, the engineering application of the model and algorithm is realized using ML.NET. The research method was verified using the field measurement data of the mining tunnel. The target recognition accuracy reached 100%, and the repeated deviations of the chord length and net height of the arch crown were 1.7 mm and 1.4 mm, respectively, which established the effectiveness and high accuracy of the research method.

An equivalent modelling approach for vibroacoustic characteristics analysis of railway aluminium extrusion

For railway carbody structures with irregular cross-sectional shapes and great longitudinal lengths, it is difficult to obtain their vibroacoustic characteristics using traditional computational methods. Moreover, traditional methods are time intensive and not conducive to the optimisation design of such complex and large structures. This study introduces an equivalent modelling approach for vibroacoustic analysis, i.e., sound transmission loss and sound radiation analysis, of railway aluminium extrusion. The aluminium extrusion is equivalent to a homogeneous orthotropic plate, and the equivalent mechanical properties of the plate are obtained via static analysis based on the small-deflection theory. The vibroacoustic characteristics are obtained using the hybrid method of finite element and statistical energy analysis. First, the equivalent modelling approach is validated using the results of a detailed prediction model and experimental test. Subsequently, the applicability of the equivalent approach is analysed by comparing it to the predicted results of the detailed model with different dimensions and boundary conditions. Ultimately, the minimum longitudinal length that needs to be considered for the analysis of railway aluminium extrusion is discussed using the equivalent approach and the computational efficiency is compared. The results reveal that the equivalent approach can effectively simulate the vibroacoustic performances of the aluminium extrusion in 1/3 octave bands centred below 1000 Hz and reduce the calculation time by 90% compared with the detailed prediction models of aluminium extrusion, which provided a foundation for vibroacoustic optimisation design of railway carbody structures.

Extending the Gutowski model to kidney-bean and elliptically shaped fibers

Efforts by manufacturers to produce more cost-effective carbon fibers have resulted in fibers with irregular cross-section often referred to as kidney-bean shaped fibers. In this research, compaction experiments were performed with a modified laser light section method to evaluate the compaction behavior of kidney-bean shaped carbon fibers. The kidney-bean shaped fibers followed a different compaction behavior compared to the Gutowski model for circular fibers. Additionally, these fibers required an order of magnitude larger force to compact than circular fibers to achieve similar fiber volume fraction, which has implications in infiltration and consolidation efficiency for composites manufacturing. A shape correction factor based on the fiber cross-sectional aspect ratio was proposed to extend the Gutowski model to fibers with irregular cross-sectional shapes. The modified Gutowski model provided an appropriate order of magnitude fit for the kidney-bean fibers. Furthermore, this modification to the Gutowski model recovered the original solution for circular fibers (cross-sectional aspect ratio = 1).

Numerically Modeling the Effect of Flexibility on Flow around Marine Engineering Structures: Using the Shape of the Saguaro Cactus

Lin, J.; Zhao, D.; Guo, C.; Zhang, Z., and Su, Y., 2020. Numerically modeling the effect of flexibility on flow around marine engineering structures: Using the shape of the saguaro cactus. Journal of Coastal Research, 36(3), 628–635. Coconut Creek (Florida), ISSN 0749-0208.The cylinder is an essential infrastructure with a wide range of applications in the engineering fields of shipping, aviation, and construction. The study of the hydrodynamic performance of a cylinder is a current research focus that can provide a more direct reference for the optimized design of its structure. In this study, the principles of bionics and flexible materials are applied to the research of marine structures, and the shape of the saguaro cactus is used as a reference. Considering the influence of flexible materials, a numerical simulation that provides a new route for the research and design of cylinders in the engineering field is performed. Based on the morphological characteristics of the cactus, a three-dimensional model and its fluid-solid control domain are established. Numerical simulations of the flow around rigid and flexible models with different Reynolds numbers are carried out. The lift, drag, flow field characteristics, and structural deformation are obtained. A turbulent vortex street is created by the flow around the cylinder. Vortex-induced vibration is generated, which demonstrates apparent three-dimensional characteristics. In a majority of the cases, flexible materials and irregular cross-sectional shapes have a clear influence on the flow around the cylinder.

Preparation and properties of bottle-recycled polyethylene terephthalate (PET) filaments

Bottle-recycled polyethylene terephthalate (R-PET) fibers were fabricated by the melt spinning method. Based on characteristics of R-PET chips, this study involved a primary exploration of the spinning parameters, including spinning temperature, spinning speed and spinneret plate. The properties of R-PET and original PET (O-PET) fibers were compared using scanning electron microscopy (SEM), tensile testing, sonic orientation, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). Apparent morphological observation displays an irregular cross-sectional shape and a scattered diameter distribution for R-PET fibers. Compared with O-PET fibers, R-PET fibers demonstrate a greater breaking strength and smaller elongation at break, resulting from the lower crystallinity and higher degree of orientation. Furthermore, the R-PET fibers have the same chemical structure as that of O-PET fibers demonstrated by FTIR spectroscopy, but TGA results show that thermal stability of R-PET fibers is significantly inferior to that of O-PET fibers, as a result of too many impurities and oligomers during the recycling process.

Effect of performance method of sand compaction piles on the mechanical behavior of reinforced soft clay

Sand Compaction Piles (SCPs) are constructed by feeding and compacting sand into soft clay ground. Sand piles have been installed with irregular cross-sectional shapes, and mixtures of both sand and clay, which violate the design requirement of circular shape according to the replacement area ratio due to various factors, including side flow pressure. Therefore, design assumptions cannot be satisfied according to the conditions of the ground and construction and the replacement area ratio. Two case histories were collected, examined, and interpreted in order to study the effect of the shape of SCPs. The effects of the distortion of SCP shape and the mixture of sand and clay were studied with the results of large direct shear tests. The design internal friction angle was secured with the irregular cross-sectional sand piles regardless of the replacement area ratio. The design internal friction angle was secured regardless of mixed condition when the mixture of sand and clay was higher than the replacement area ratio of 65%. Therefore, systematic construction management is recommended with a replacement area ratio below 65%.

The twist-to-bend compliance of the Rheum rhabarbarum petiole: integrated computations and experiments

Plant petioles can be considered as hierarchical cellular structures, displaying geometric features defined at multiple length scales. Their macroscopic mechanical properties are the cumulative outcome of structural properties attained at each level of the structural hierarchy. This work appraises the compliance of a rhubarb stalk by determining the stalk’s bending and torsional stiffness both computationally and experimentally. In our model, the irregular cross-sectional shape of the petiole and the layers of the constituent tissues are considered to evaluate the stiffness properties at the structural level. The arbitrary shape contour of the petiole is generated with reasonable accuracy by the Gielis superformula. The stiffness and architecture of the constituent layered tissues are modeled by using the concept of shape transformers so as to obtain the computational twist-to-bend ratio for the petiole. The rhubarb stalk exhibits a ratio of flexural to torsional stiffness 4.04 (computational) and 3.83 (experimental) in comparison with 1.5 for isotropic, incompressible, circular cylinders, values that demonstrate the relative structural compliance to flexure and torsion.

An Experimental Study on Reinforcing Rock Columns Using Heated Polymeric Ties

Load-bearing rock column and pillar reinforcing without a permanent visual change is an important advantage for applications in both historical and modern sites. One of the most widely seen column reinforcement methods is using steel collars which can cause a visual change on rock surfaces because of its corrosion problem and hardness. Steel collars are mostly used to reinforce rock columns with regular cross-sectional shapes, but not suitable for being used to reinforce rock columns with irregular crosssectional shapes because of their high stiffness which prevents them from being shaped by the column body. Rock column reinforcement method can be divided into two groups: active and passive reinforcement methods (Moghaddam et al. 2010; Bieniewski et al. 1969; Komurlu et al. 2013; Spencer and Gardner 2003). In passive reinforcement method, confinement pressure is supplied as a reaction to the deformation of the rock surface in contact with the reinforcing devices. On the other hand, active reinforcement pressure can increase the load-bearing capacity without a deformation of columns/pillars (Holmes et al. 2014; Windsor 1987; Kovari et al. 1983). Polymers can be divided into two groups: thermoplastics and thermosets, according to their reaction to being heated (Wigley 1971; McCrum et al. 1997; Komurlu and Kesimal 2014). Thermosets cannot be softened and extended easily by heating. Generally, their polymerization process transforms the liquid components into a plastic or rubber by cross-linking. Thermosets are not able to be remolded by heating after their initial formation (Pascault et al. 2002; Tadlaoui et al. 1993; Ebewele 2000). Therefore, thermosets are generally polymerized in molds. In case of heating with high temperatures, cross-links of thermosets are broken without melting. On the other hand, thermoplastics, also called as thermosoftening plastics, can be deformed easily and shaped by heating. Thermoplastics harden and strengthen by cooling, which can preserve the original length or shape after cooling from a temperature level depending on the type of product (Akay and Barkley 1985; Komurlu and Kesimal 2012). Therefore, the use of thermoplastics should be considered for the aim of active reinforcement pressure applied on rock columns encircled with heated ties. Polymer materials are used for different reasons varying within a large range. An important percentage of polymer usage is because of their good chemical resistivity as in applications of food packing, transport of drinking water, hot water or gases (RTMSTI 2010; Ohtomo and Ohnuma 2014; Castagnet and Grandidier 2006; Siracusa et al. 2011). Polymer materials used considering their strength values are generally engineering polymers which have better mechanical properties in comparison to most of the other polymeric materials (Troughton 2008; Komurlu 2012; Komurlu and Kesimal 2011). Also, the chemical resistance of the engineering polymers is an important reason, making them convenient to be used as an alternative to conventional engineering materials. & Eren Komurlu erenkomurlu@gmail.com; ekomurlu@ktu.edu.tr

Morphological, Thermal, and Mechanical Characterization of Sansevieria trifasciata Fibers

Sansevieria trifasciata is a common perennial plant which freely grows and widely found in homes, parks, and woodlands. In this research, we studied the morphology using Scanning Electron Microscope and Fourier Transform Infrared (FTIR); thermal properties using Thermogravimetric (TGA) and Differential Scanning Calorimetric (DSC) analyses; mechanical behavior through tensile tests of Sansevieria trifasciata fiber (STF) obtained from Butaleja in Eastern Uganda. Findings show that the fiber has an irregular cross-sectional shape with lumens in the center, the fiber diameter was between 80 and 120 μm. TGA tests showed that the fiber is stable below 200°C with maximum cellulose decomposition temperature of 315°C. DSC showed that the fiber’s crystallization temperature was 310.5°C and lignin decomposition temperature of 372.7°C. The surface functional groups were majorly of cellulose, hemicelluloses, and lignin in direct correlation with research elsewhere on natural fibers.

2P2-2 Polygonal Buffer Rods Having Irregular Cross-Sectional Shapes for Improving the SNR in Ultrasonic Pulse-Echo Measurements(Poster Session)

2P2-2 Polygonal Buffer Rods Having Irregular Cross-Sectional Shapes for Improving the SNR in Ultrasonic Pulse-Echo Measurements(Poster Session)

Study of Metallic Nanowires with Arbitrary Cross-Sectional Shapes for Negative Refraction in Visible Regime

Considering the nanofabrication errors, the real fabricated metallic nanowires may have irregular cross-sectional shapes. In this work, the metallic nanowires array with arbitrary cross-sectional shapes for negative refraction in visible regime was studied theoretically. To fully understand the evolution process of the negative refraction of the metallic wires with irregular cross-sectional shapes, the effective refractive index, effective mass, and effective radius of the wires were put forth and studied. The nanowire array with arbitrary cross-sectional shapes with different geometrical parameters was investigated in detail by means of computational numerical calculation on the basis of finite difference and time–domain algorithm. The influence of geometrical parameters of the nanowires on negative refraction was systematically analyzed. The calculated results indicate that the irregular shape can play a positive role for the negative refraction-based imaging application.

Study on the manufacturing process of precision linear guide rail through shape rolling and shape drawing

Guide rails are one of the most important components in terms of equipment because the quality of the linear rail in-fluences on the precision linear motion. For long rails used in the guide rail, high dimensional accuracy as well as a cross-sectional shape is required. As a production method of guide rail, drawing process is mainly used. But, the shape rolling process is open used for the pre-process of the other metal forming process such as forging, extrusion, and shape drawing. The shape rolling process is one of the most effective processes which can make long products with constant irregular cross-sectional shape. Therefore, the tool shape is a very important process variable to obtain the required final product. The objective of this paper is the design of roll shape of the rolling process to produce the initial material with irregular cross sectional shape for shape drawing. Also, the die shape of the drawing process is determined to satisfy the dimensional accuracy of the final product. In this study, FE-analysis and artificial neural network (ANN) were applied to achieve the objective. Further, shape rolling and shape drawing experiments were performed to verify the result of FE-analysis. From results, it was possible to design the roll shape of shape rolling process effectively.

Automatic determination of refractive index profile of fibers having regular and/or irregular transverse sections considering the refraction of light rays by the fiber

A new model, using non-destructive two- and/or multiple-beam interferometric techniques, is suggested for measuring the refractive index profile of fibers having regular and/or irregular cross-sectional shape taking into consideration the refraction of the light rays by the fiber. The proposed model is applied for three different fibers having different cross-sectional shapes and different refractive index profiles. These fibers are PPT, homogeneous fiber, with circular cross-section, graded index optical fiber of circular cross-sectional shape and Dralon fiber of irregular cross-section. To validate the proposed model it is used, firstly, to calculate the index profile for a standard PPT fiber. Secondly, the calculated results for the irregular Dralon fiber and GR-IN optical fiber are compared with that calculated using other conventional method. From this comparison, we recommend that the refraction must be taken into account to obtain accurate results especially for birefringent fibers and graded index optical fibers.

Late Triassic gastrochaenid and lithophaginid borings (Mollusca: Bivalvia) from Nevada (USA) and Austria

The endolithic life habit has evolved several times in the Bivalvia, e.g., in the superfamilies Modiolopsoidea (family Modiolopsidae), Mytiloidea (family Mytilidae, subfamily Lithophaginae), Arcoidea (family Arcidae), Cardioidea (family Tridacnidae), Veneroidea (family Petricolidae), Gastrochaenoidea, Myoidea (family Myidae), Hiatelloidea, and Pholadoidea (families Pholadidae and Teredinidae) (Otter, 1937; Yonge, 1963; Cox, 1969; Carter, 1978; Kleemann, 1980). The oldest known definite bivalve borings are Ordovician slotlike depressions in stromatoporoids, made by the facultative nestler/borer modiolopsidCorallidomusWhitfield, 1893 [1895] (Pojeta and Palmer, 1976; Wilson and Palmer, 1988). Pojeta and Palmer (1976) and Morton (1990) citedCorallidomusas the ancestor of the Lithophaginae. However, lithophaginids more likely evolved from modiolinid mytilids, which in turn evolved from modiolopsids (Fang and Morris, 1997; Fang, 1998; Carter et al., 2000).Lithophaga-like shells are known from the Carboniferous and Permian, but these Upper Paleozoic examples are not known to have been endolithic (Kleemann, 1983, 1990, table 2). Wilson and Palmer (1998) attributed certain borings without associated shells in Upper Carboniferous limestone cobbles to lithophaginids because the borings are widest near their anterior end and they lack a constricted neck. However, if, as Wilson and Palmer suggested, these borings are not posteriorly truncated, then their openings are relatively much wider than typical lithophaginid borings. One boring illustrated by Wilson and Palmer (1998, fig. 4) has an irregular anterior cross-sectional shape that is unlike lithophaginid and gastrochaenid borings. This irregularity recalls the Early Ordovician ichnospeciesGastrochaenolites oelandicusEkdale and Bromley, 2001, which is similarly vase-shaped. Ekdale and Bromley (2001) noted that the latter boring predates known endolithic bivalves, so they attributed it to an unknown invertebrate.

Modified shear lag model for fibers and fillers with irregular cross-sectional shapes

For fibers with irregular cross sections such as ultrahigh modulus polyethylene (UHMPE) fibers and ribbon-like carbon fibers, the original shear lag model would not provide accurate calculations for interfacial shear stress because it assumes a circular fiber cross section. In this study, a modified shear lag model is proposed to calculate the interfacial shear stress that reflects the change of fiber cross-sectional shape. Microbond test on a UHMPE fiber/epoxy system was used for verification of the model. The difference between the interfacial shear strength (IFSS) calculated using the modified model and that using the original model assuming an equivalent fiber diameter was found to be as high as 15% and it linearly increased as the irregularity of the cross-sectional shape increased. When the irregularity constant exceeds 1.12, the error in IFSS involved in using the original shear lag model and an equivalent fiber diameter is greater than 10%.

A NUMERICAL STUDY OF LAMINAR FORCED CONVECTION IN SINUSOIDAL DUCTS WITH ARC LOWER BOUNDARIES UNDER UNIFORM WALL TEMPERATURE

Laminar flow in ducts of irregular cross-sectional shapes is of importance to heat recovery heat exchangers. In this article, heat trasfer and pressure drop characteristics in corrugated sinusoidal ducts with arc lower boundaries are studied for a hydrodynamically fully developed, thermally developing flow under uniform temperature conditions. The numerical method is of high-order accuracy, is numerically implicit, and is unconditionally stable. The cross-derivative term is treated as a source term and is solved by iterations in which a varying axial step size ensures a fast convergence without sacrificing details near the inlet of the thermal entry region. This method allows for the simulation of unevenly distributed nodes on boundaries, in combination with the transformation of the special duct geometry to a rectangular computational domain. The detailed finite difference discretization of the governing momentum and energy equations is provided. The values of (f · Re) and local and mean Nusselt numbers are calculated for different aspect and bending ratios. The velocity and temperature profiles are plotted. The results would be helpful to estimate the performances of honeycomb-type regenerative wheels.

Quantitative phase analysis by X-ray diffraction of martensite and austenite in strongly oriented orthodontic stainless steel wires

A method is described for measuring the volume fractions and textures of martensite and austenite in strongly textured stainless steel orthodontic wires using a conventional X-ray diffractometer. These wires display a classic fibre texture with the 〈111〉 of the FCC austenite phase and the 〈110〉 of the BCC martensite phase aligned parallel to the wire axis. The samples analysed consisted of wire cross-sections bundled together and chemically polished in an epoxy disc. In this form the dominant lines in the XRD patterns are the austenite (111) and the martensite (110). On the basis of X-ray diffraction results from these two lines only, procedures are described for, (a) correcting the X-ray intensity data for both the finite size and irregular cross-sectional shape of the specimens in relation to the X-ray beam footprint, (b) separately measuring the texture of the austenite and martensite phases and, (c) correcting the 111 and 110 integrated intensities for texture. These procedures are illustrated using X-ray data from four different orthodontic wires. The factors limiting the accuracy of the phase analysis are discussed.