Asymmetric Cross Section Research Articles

Dynamic Analysis of Composite Wind Turbine Blades as Beams: An Analytical and Numerical Study

This study focuses on the dynamic modelling and analysis of the wind turbine blades made of multiple layers of fibre reinforced composites and core materials. For this purpose, a novel three-dimensional analytical straight beam model for blades is formulated. This model assumes that the beam is made of functionally graded material (FGM) and has a variable and asymmetrical cross section. In this model, the blades are assumed to be thin, slender and long with a relatively straight axis. They have two main parts, namely the core and the shell. The so-called core consists of a lightweight isotropic foam material, which also adds significant damping to the system. The core material is covered by the shell, which is modelled using homogenous and orthotropic material assumptions as the structure is reinforced with continuous fibres. Therefore, the blades are modelled under a straight beam with varying cross-section assumptions, in which the effective elastic properties are acquired by homogenizing the cross section. The beam formulation for modelling the system is performed both analytically and numerically with the finite element method. The results of both methods are in well agreement. The maximum deviation between the results is found below 4%.

An original framework for triply-coupled bending-torsion dynamics of beams

Triply-coupled bending-torsion in beams with asymmetric cross section is an interesting yet challenging problem in dynamics. In this study, a comprehensive framework is introduced to obtain the response in frequency and time domains under arbitrary loads, considering warping effects. First, a Laplace Transform approach provides the dynamic Green’s functions of the beam, which can be used to obtain the frequency response to arbitrary loads by applying simple integration rules of the theory of generalized functions. Next, on deriving suitable orthogonality conditions for the undamped coupled bending-torsion modes, modal impulse and modal frequency response functions are obtained for any load. The solutions are derived under the assumption of proportional damping; they are exact and easy to implement. Finally, the proposed framework is formulated for beams with in-span transversal stiffeners, external supports and is generalized to non-proportional damping including the presence of in-span external dampers.

Morphology and ultrastructure of the spermatozoa of Lonchoptera lutea Panzer, 1809 (Diptera: Lonchopteridae)

Lonchoptera lutea males produce giant spermatozoa that are more than 2000 μm long and 1.4 μm wide. Unlike the typical brachyceran spermatozoon, they have a highly asymmetrical cross-section with only a single, albeit very large, mitochondrial derivative and a pair of massive accessory bodies, one of which extends throughout the entire length of the sperm tail. The accessory bodies consist of an electron-dense matrix in which numerous peculiar electron-lucid substructures are embedded. In the mated female, the giant spermatozoa are found inside two tubular spermathecae which are also extremely long, measuring 4000 μm or more.

On incorporating warping effects due to transverse shear and torsion into the theories of straight elastic bars

By endowing El Fatmi’s theories of bars with first-order warping functions due to torsion and shear, a family of theories of bars, of various applicability ranges, is effectively constructed. The theories thus formed concern bars of arbitrary cross-sections; they are reformulations of the mentioned theories by El Fatmi and theories by Kim and Kim, Librescu and Song, Vlasov and Timoshenko. The Vlasov-like theory thus developed is capable of describing the torsional buckling and lateral buckling phenomena of bars of both solid and thin-walled cross-sections, which reflects the non-trivial correspondence, noted by Wagner and Gruttmann, between the torsional St.Venant’s warping function and the contour-wise defined warping functions proposed by Vlasov. Moreover, the present paper delivers an explicit construction of the constitutive equations of Timoshenko’s theory; the equations linking transverse forces with the measures of transverse shear turn out to be coupled for all bars of asymmetric cross-sections. The modeling is hierarchical: the warping functions are numerically constructed by solving the three underlying 2D scalar elliptic problems, providing the effective characteristics for the 1D models of bars. The 2D and 1D problems are indissolubly bonded, thus forming a unified scientific tool, deeply rooted in the hitherto existing knowledge on elasticity of elastic straight bars.

Flexural-torsional buckling of cold-formed steel columns with arbitrary cross-section under eccentric axial load

In recent years, the use of cold-formed steel sections as load bearing components has increased significantly. These sections are susceptible to a variety of cross-section instabilities, including local, distortional, global or a combination of these buckling modes due to their low thickness, so it is necessary to investigate the buckling behavior of these members. In this paper, the flexural–torsional buckling behavior of cold-formed steel columns with arbitrary asymmetric cross section has investigated. For this purpose, using the exact static stiffness matrix method, the differential equations governing column buckling with arbitrary asymmetric cross section have been extracted under eccentrically axial load. Calculating buckling loads using this method results in a nonlinear eigenvalue problem. For solve this problem, Wittrick- Williams algorithm is used. The extracted formulation is predicted to be used to calculate the critical loads of the types of double symmetric, single symmetric and asymmetric cold-formed sections.

Analytical model for lateral depth-averaged velocity distributions in curved channels

The distribution of depth-averaged velocity is crucial to many engineering problems. This paper presents an analytical solution for the lateral depth-averaged velocity distribution in a 120° curved channel with asymmetric trapezoidal cross-sections in which the curved flow is not fully developed. The proposed analytical model was derived from the streamwise depth-integrated Reynolds-averaged Navier–Stokes equation, which considers the bed stress, Reynolds stress, secondary flow and local flow acceleration. In addition, practical boundary conditions are proposed to consider the trapezoidal cross-sections with linearly varying side beds and the flow separation at the inner bank near the bend entrance. The analytical solutions using the proposed model were found to be in good agreement with measured data. The main contributions of this study are the development of a conventional analytical model for sophisticated circumstances and the proposal of practical boundary conditions that consider flow separation.

Closed form solutions for shear deformable thin-walled beams including global and through-thickness warping effects

The present study develops a theory for the static analysis of thin-walled members with general asymmetric cross-sections. The theory captures global and through-thickness warping, in addition to shear deformation effects. Starting with the principle of stationary potential energy, the governing equilibrium equations are developed along with the possible boundary conditions. The theory leads to seven field equations in the axial displacement, lateral and transverse displacements, bending rotation angles, angle of twist, and warping deformation. Unlike conventional non-shear deformable thin-walled beams which predict a torsional response that is uncoupled from the flexural responses, the differential equations obtained herein are fully coupled when applied to beams with asymmetric cross-sections. Closed-form solutions are formulated for beams with asymmetric, monosymmetric, point symmetric, and doubly symmetric cross-sections. Comparisons with the predictions of previous thin-walled beam theories/finite elements and shell finite element solutions verify the validity of the present theory and quantify the effects of shear deformation, through-thickness warping, and the coupling arising from to shear deformation. Numerical examples illustrate the partial coupling effects arising in the special cases of monosymmetric, point symmetric, and doubly symmetric sections.

Experimental and Analytical Study of the Responses of Nanoscale Devices to Neutrons Impinging at Various Incident Angles

In harsh radiation environments, it is well known that the angle of incidence of impinging particles against the surface of the operating devices has significant effects on their sensitivity. This article discusses the sensitivity underestimations that are made if particle isotropy is not taken into account, by means of an analytical study made with a single-event upset predictive platform. To achieve this goal, experimental results carried out with a commercial-off-the-shelf (COTS) bulk 130-nm nonvolatile static random access memory (SRAM) for various incident angles on 14.2 MeV neutrons are first discussed. Then, a modeling tool called multiscales single-event phenomena predictive platform (MUSCA-SEP3) is used to predict the sensitivity of this memory under the same environmental conditions. Predictions and experimental results will be cross-checked, and therefore, the feasibility of this tool will be demonstrated for testing any other incident angle. Finally, an isotropic environment and an XY SRAM array will be emulated with MUSCA in order to demonstrate that the asymmetrical cross sections that were observed experimentally for various incidence angles are due to the underlying asymmetry of the metalization/passivation layers within the device with respect to its active silicon. Conclusions will finally be drawn as for the importance of taking into account particle isotropy in radiation-ground tests.

Inverse design of a single-step-etched ultracompact silicon polarization rotator.

We propose and experimentally demonstrate a novel ultracompact silicon polarization rotator based on equivalent asymmetric waveguide cross section in only single-step etching procedure for densely integrated on-chip mode-division multiplexing system. In the conventional mode hybridization scheme, the asymmetric waveguide cross section is employed to excite the hybridized modes to realize high performance polarization rotator with compact footprint and high polarization extinction ratio. However, the fabrication complexity severely restricts the potential application of asymmetric waveguide cross section. We use inverse-designed photonic-crystal-like subwavelength structure to realize an equivalent asymmetric waveguide cross section, which can be fabricated in only single-step etching process. Besides, a theory-assisted inverse design method based on a manually-set initial pattern is employed to optimize the device to improve design efficiency and device perform. The fabricated device exhibited high performance with a compact footprint of only 1.2 × 7.2 µm2, high extinction ratio (> 19 dB) and low insertion loss (< 0.7 dB) from 1530 to 1590 nm.

Reynolds-number effect on flow past a rectangular cylinder in the presence of a free surface

Rectangular cylinders are insensitive to the Reynolds number (Re) due to the geometrically restricted flow separation. The introduction of asymmetry, e.g., inclination, asymmetric cross-section and asymmetric boundary, in the flow can signify the role of Re. To date, the effect of Re on rectangular cylinders near a free surface has not been comprehensively investigated. In this study, multiphase simulations of a square located at four depth-to-length ratios (0.3, 0.7, 1.0 and 4.5) over the Re range from 2.0 × 104 to 9.9 × 104 were conducted. Strong Reynolds-number effect on the flow was observed at the shallow and moderate depths. The surface jet, forming as the result of surface curvature when Re increases, is related to the local Froude number (Fr). The critical Re values for the surface jet formation at the three depth-to-length ratios, i.e., 0.3, 0.7 and 1.0, are 3.0 × 104, 4.0 × 104 and 4.5 × 104, respectively. The suppression of vortex shedding at the shallow depths is explained as the detachment of shear layers together with the modifications of vorticity fluxes. The restoration of vortex shedding when Re is high is due to the surface jet interference which forces the recontact of the shear layers across the sharp corners to couple with each other.

Stability Evaluation of the Transmission Line by using Galloping Simulation

Galloping phenomenon is one of the vibrations caused by icing. If galloping phenomenon continues, short-circuit or ground fault may occur, so analysis of galloping phenomenon through research on transmission line stability is necessary. The DenHartog method, which is frequently used for the galloping stability determination of the transmission line, considers only the vertical movement of the transmission line. In this study, we analyze the motion of multi-degree-of-freedom objects, using a computer aided engineering program. We modeled transmission lines as a multi mass-spring-damper systems using RecurDyn, which is a multibody commercial dynamics analysis program to analyze the galloping phenomenon dynamically. Damping inside transmission line derived from the Rayleigh damping theory through the free vibration experiment of transmission line. ANSYS Fluent, a flow analysis program, was used to derive the aerodynamic coefficients for transmission line with asymmetric cross-section. Using the derived aerodynamic coefficient, we confirmed the galloping occurrence condition of DenHartog method and modeled the wind load acting on the transmission line to conduct galloping simulation. Through the analysis of the motion of a multi-degree-of-freedom transmission line, the occurrence of galloping was classified into ovoid and vertical trajectories, and the case of no galloping was defined as regular trajectory, and the range of angle of attack that causes the instability of transmission lines was defined.

Mechanical and vibrational characteristics of functionally graded Cu–Ni nanowire: A molecular dynamics study

Functionally graded material (FGM) is a class of advanced materials, consisting of two (or more) different constituents, that possesses a continuously varying composition profile. With the advancement of nanotechnology, applications of FGMs have shifted from their conventional usage towards sophisticated micro and nanoscale electronics and energy conversion devices. Therefore, the study of mechanical and vibrational properties of different FGM nanostructures is crucial in exploring their feasibility for different applications. In this study, for the first time, we employed molecular dynamics (MD) simulations to investigate the mechanical and vibrational properties of radially graded Cu–Ni FGM nanowires (NW). Distribution of Cu and Ni along the radial direction follows power-law, exponential and sigmoid functions for FGM NWs under consideration. Our results demonstrate that distribution function parameters play an important role in modulating the mechanical (elastic modulus and ultimate tensile strength) and vibrational (natural frequency and quality factor) properties of FGM NWs. The study also suggests that elastic moduli of FGM NWs can be predicted with relatively good accuracy using Tamura and Reuss micromechanical models, regardless of NW diameter. We found that Euler-Bernoulli beam theory under-predicts the natural frequencies of FGM NWs, whereas He-Lilley model closely approximates the MD results. Interestingly, FGM NWs are always found to exhibit beat vibration because of their asymmetrical cross sections. Finally, this is the first atomistic scale study of FGMs that directly compares MD simulations with continuum theories and micromechanical models to understand the underlying mechanisms that govern the mechanical and vibrational properties of FGM NWs in nanoscale.

Effect of exchange and dipolar interlayer interactions on the magnonic band structure of dense Fe/Cu/Py nanowires with symmetric and asymmetric layer widths

We present a systematic experimental and theoretical investigation of the magnonic band structure in dense arrays of both asymmetric and symmetric cross-section trilayered Fe(10 nm)/Cu( $t$)/Py(10 nm) nanowires (NWs). The Cu spacer thickness ($t$) is varied in the range between 0 and 10 nm. The frequency dispersion of collective spin-wave excitations in the above trilayered NW arrays has been studied by the Brillouin light-scattering technique while sweeping the wave vector perpendicularly to the nanowire length over four Brillouin zones of the reciprocal space. The experimental results have been quantitatively reproduced by an original numerical model that includes a two-dimensional Green's function description of the dipole field of the dynamic magnetization and exchange coupling between the layers. We found that, depending on $t$, the Py and Fe magnetic layers within the same nanowire are coupled by either the interlayer exchange or dipolar interactions. This has an impact on both the magnetization reversal and the collective dynamical properties of the artificial crystal. In particular, it is possible to stabilize a magnetization configuration where the layer magnetization vectors point in the same or in the opposite direction over a field range that varies with the Cu thickness. In addition, several modes are detected whose propagation properties (i.e., stationary or dispersive) through the array depend on static magnetization configuration as well as on the relative phase (in-phase or out-of-phase) of dynamic magnetizations between the two layers within the same nanowire.

New method for assessing lateral distribution of energy gradient in curved channels

The energy gradient is a fundamental physical quantity of flow motion. To date, many studies have concentrated on uniform flow or fully developed curved flow, with the energy gradient approximated as the bed slope. This paper presents a new method to assess the lateral distribution of the apparent energy gradient in curved channels when curved flow is not fully developed. A dimensionless apparent energy gradient (K) is presented. An expression for K is explicitly formulated based on the Reynolds-averaged Navier–Stokes (RANS) equations and the lateral distribution of K is derived from measured velocity data. The method was applied in a 120° curved flume with asymmetric trapezoidal cross-sections. The results showed a bilinear distribution of K; that is, K remained nearly constant in the central region of the channel while, in the inner bank region, K increased linearly as the inner bank was approached. These results were derived for specific cases for curved channels with a side-slope, but the method for deriving K can be applied to other cases, thus providing a new way to study energy loss in curved channels to contribute to river management, such as estimation of discharge capacity and navigation improvement.

Motion of an Elastic Capsule in a Trapezoidal Microchannel Under Stokes Flow Conditions.

Even though the research interest in the last decades has been mainly focused on the capsule dynamics in cylindrical or rectangular ducts, channels with asymmetric cross-sections may also be desirable especially for capsule migration and sorting. Therefore, in the present study we investigate computationally the motion of an elastic spherical capsule in an isosceles trapezoidal microchannel at low and moderate flow rates under the Stokes regime. The steady-state capsule location is quite close to the location where the single-phase velocity of the surrounding fluid is maximized. Owing to the asymmetry of the trapezoidal channel, the capsule’s steady-state shape is asymmetric while its membrane slowly tank-treads. In addition, our investigation reveals that tall trapezoidal channels with low base ratios produce significant off-center migration for large capsules compared to that for smaller capsules for a given channel length. Thus, we propose a microdevice for the sorting of artificial and physiological capsules based on their size, by utilizing tall trapezoidal microchannels with low base ratios. The proposed sorting microdevice can be readily produced via glass fabrication or as a microfluidic device via micromilling, while the required flow conditions do not cause membrane rupture.

Forecasting Increase of Quality of Large-Sized Forgings Used for Stamping, Piercing, and Rolling of High-Duty Products

When utilizing current combined systems of manufacturing large-sized shaft forgings, there is a tendency towards using an integrated approach, which consists in optimizing the shape of forged ingots and methods of their forging, intensifying shear strains in the axial zone of the ingots during their plastic deformation, and eliminating asymmetry of external forces at various points along the cross section of the ingot being deformed. This paper presents the results of the comparative analysis of quality of shaft forgings when forging ingots with a three-beam symmetric and asymmetric cross-section, as well as with the traditional octahedral cross-section, are used for the manufacture of shaft forgings. It has been shown that the use of forging ingots with a three-beam symmetrical and asymmetrical cross section provided an increase of KCU by an average of 4.3% and 13.1%, and of density by 17.5% and 21.0%, respectively, in the absence and presence of inert gas (argon) blowdown of the melt in the casting ladle before casting it into ingot molds. Their use also contributes to an increase in the number of forgings, suitable for ultrasonic testing, according to the C/c class with a permissible equivalent discontinuity diameter of ≤ 3 mm.

Radial Joints Behavior of a Precast Asymmetric Underpass Induced by Long-Term Loads of Ground Vehicles

With the rapid development of the urbanization, many underpasses are designed and constructed in big cities to alleviate the huge traffic pressure. The construction method has been changed from traditional on-site concrete pouring technology to prefabricated assembly technology. However, this change will inevitably bring out some new problems to be studied such as the behaviour of the radial joints. In this study, the numerical simulation model of Moziqiao precast and assemble underpass with large asymmetric cross section was constructed by using the ABAQUS software to study the transient response of the underpass induced by ground surface dynamic load. Based on the similarity theory a 1/10 scaled model test was carried out to study the long-term radial joint behaviour of the underpass considering the prestress loss during the 2000 000 loading cycles. The results transient dynamic response from computed and tested was compared in terms of acceleration. The comparison showed that the transient response accelerations have good consistency. The results of the physical model test were analysed in terms of joint opening, closure, and slipping. The accumulative joint opening was closely correlated to the prestress level, and the joint opening at different prestress levels increased with the loss of the prestress. The joints closure decreased with the increase of the previous accumulative color value. The joint slipping mainly attributed to the slipping of the top segment. Both the opening and slipping of the joints at RJ 1 were larger than that of RJ3 due to the wider span of RJ1, which reflected an asymmetric effect. This study revealed the long-term accumulative behaviour of the radial joints, which convinced us that the long-term accumulative deformation of the joints should be taken into consideration during the design stage for similar projects.

Hybrid flat sheet cellulose acetate/silicon dioxide ultrafiltration membranes for uremic blood purification

Monophasic hybrid cellulose acetate/silica (CASiO2) integrally skinned membranes with tailored hemocompatible surfaces and permeation properties that assure the kidney metabolic functions of preferential permeation of urea and the retention of albumin were synthesized by an innovative method which combines the phase inversion and sol–gel techniques. The morphological and topographical characterization of the hybrid CASiO2 membranes with silica contents between 5 and 18 wt% was performed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Static contact angles were measured through the sessile drop method and permeation experiments were performed to determine the hydraulic permeability and rejection coefficients to reference solutes pertaining to the metabolic functions of the kidney. SEM confirmed asymmetric membrane cross-section structures and AFM showed that the introduction of silica reduced the submicron surface roughness at least 3 times when compared to the pure CA membrane, reaching a roughness mean value below 2.5 nm. Contact angles revealed that the wettability increased for membranes containing 11 and 18 wt%. Permeation studies show that the integration of silica into CA membranes increased the hydraulic permeability of the hybrid CASiO2 membranes by a factor of ~ 2 and that all hybrid membranes fully permeated urea and completely rejected albumin. In terms of hemocompatibility, all CASiO2 membranes were non-hemolytic, low thrombogenic and did not promote the highest stages of platelet activation.

Three-dimensional stress analysis of variable angle tow composite laminate using hybrid brick elements

Abstract Variable angle tow (VAT) composites manufactured using continuous tow shearing (CTS) technique exhibits smooth thickness variation across the plane of the laminate as a function of fiber angle variation. These VAT laminates have a flat surface on one side and a curved surface on the other side resulting in asymmetric cross-section about the mid-surface of the laminate. Mostly shell-based finite elements have been used for modeling the VAT panels, and they neglect the thickness variation introduced by manufacturing in the stress analysis of laminates. In this work, the use of hybrid brick elements for three-dimensional stress analysis of VAT laminates manufactured using CTS technique is studied. A user-defined element subroutine is written for the 8-node and 27-node hybrid brick elements in the ABAQUS finite element software. The numerical performance of the hybrid brick elements in computing the stress solution of composite laminates is evaluated by studying benchmark problems and the results are compared with the displacement brick element. The influence of mesh distortion, shear locking and boundary layer effect in the stress solution evaluated by hybrid elements are studied. VAT laminate with thickness variation is modeled using the hybrid brick elements and the effect of asymmetric cross-section on the through-thickness stress field is investigated. The influence of the fiber angle distribution as well as thickness variation on the phenomenon of stress redistribution across the plane of the laminate for different VAT configuration is studied. Further, the numerical results of VAT laminate with thickness variation obtained using hybrid brick elements are compared with the experimental results available in the literature. The results from this numerical study will help the engineer in designing efficient VAT laminates fabricated using CTS technique.

Atmospheric-pressure microwave line plasma with an asymmetric cross-section waveguide for long-scale N2 plasma production

Production of N2 atmospheric-pressure microwave line plasma (AP-MLP) along a long slot of ∼1 m is demonstrated with an asymmetric cross-section waveguide. Configuration of a waveguide cross-section is modified from a rectangular to an asymmetric one, using a computer simulation to enhance surface conduction current at a position where the slot is supposed. Based on the simulation results, Ar AP-MLPs produced using waveguides with the rectangular and the asymmetric cross-section are compared and 1 m length plasma production at a microwave power of 500 W is realized after the waveguide modification. Using the new waveguide, N2 AP-MLP at a length of 0.7 m is also successfully produced.