Hasil untuk "Mechanics of engineering. Applied mechanics"

Nawras Thamer, Khattab S. Abdul-Razzaq

Even when applied at midspan, unequal loading is a major driver of deep-beam response and capacity. By contrast, with a central, equal load, the compression-strut paths that carry force from the supports to the loading node(s) are typically symmetric. However, in the present study, the load inequality causes these struts to be asymmetrical. As a result, the strut carrying the larger load failed before the one carrying the smaller load. Therefore, the deep beam fails early. Twenty-one deep beam specimens were analyzed using SAP 2000 software, which is based on the well-known finite element method.  Three patterns of load distribution between three concentrated load points were adopted: 33%-33%-33%, 50%-25%-25%, 25%-50%-25%, 67%-16.5%-16.5%, 16.5%-67%-16.5%, 75%-12.5%-12.5% and 12.5%-75%-12.5%. These load cases were studied using different concrete's compressive strength values of 20, 30, and 40 MPa. Based on these results, load capacity remained essentially unchanged, while midspan deflection and shear stresses decreased by 4.0–4.6% and 3.8–17%, respectively; in contrast, the maximum positive moments increased by 0.55–7%.

Zafar Malikov, Farrukh Nazarov, Sardor Khaydarov

This paper discusses the hot subsonic and near-sonic axisymmetric submerged stationary jets flowing from a nozzle with a radius of 25.4 mm. The Mach number at the nozzle exit is 0.376 for a subsonic jet, and for a near-sonic jet, it is 0.985. The Reynolds number for both problems was equal to 5600. A two-fluid turbulence model was used to study these problems. The numerical results of this model were obtained for both the full elliptic and simplified parabolic systems of equations. The SIMPLE procedure was applied to the numerical implementation of the complete elliptic system of equations. In the parabolic system of equations, the marching method of integrating equations in the longitudinal direction is used. The results of the two-fluid model are compared with the results of other known RANS turbulence models, which were obtained using the COMSOL Multiphysics® package, as well as with the experimental data from the NASA database.

Bahram Javidi, Artur Carnicer, Kavan Ahmadi et al.

In 1994, Javidi and Horner published a paper in Optical Engineering that highlighted the ability of free space optical systems to manipulate sensitive data for authentication purposes. The underlying idea was effective yet surprisingly simple: an optical nonlinear joint transform using a random phase mask in both the input and the reference could produce a correlation peak to indicate whether the input object is authentic or not. This seminal paper fueled the development of this new discipline. After three decades, optical encryption and security have matured into a field that plays a central role in the development of photonics techniques. While the pioneering work was mainly focused on the field of optical information processing, nowadays, a broad spectrum of disciplines are contributing to developing security solutions, including nanotechnology, materials science, quantum information, and deep learning, just to cite a few. The present roadmap paper gathers 28 leading authors in the field from 21 academic institutions across nine different countries. It is organized into 17 sections which discuss the present and future challenges, state-of-the-art technology, and real-world solutions to address the security challenges facing our society.

Yifeng Shi, Yifan Zheng, Xun Xiao et al.

Ion migration presents a formidable obstacle to the stability and performance of perovskite solar cells (PSCs), hindering their progress toward commercial feasibility. Herein, the degradation mechanism of PSCs caused by iodide ion migration, which leads to abnormal changes in photoluminescence transients at the buried interface of perovskite films, is investigated. In light of this problem, a novel strategy is proposed to mitigate ion migration by introducing poly(2‐vinylnaphthalene) into poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] as the hole transport layer with improved ion‐blocking capability. Consequently, this layer effectively reduces defect concentration, suppresses ion migration, and modulates energy level alignment, leading to an impressive efficiency exceeding 23% for doctor‐bladed FAPbI3 PSCs. Moreover, the corresponding unencapsulated devices demonstrate remarkable durability, maintaining over 80% of their initial value after undergoing rigorous stress tests in accordance with the International Electrotechnical Commission 61215 standard for temperature, humidity, and illumination. These tests include 1000 h of thermal cycling and a long‐term operational test lasting 600 h under maximum power point tracking.

Hendrik Fischer, Julian Roth, Ludovic Chamoin et al.

Abstract In this work, the space-time MORe DWR (Model Order Reduction with Dual-Weighted Residual error estimates) framework is extended and further developed for single-phase flow problems in porous media. Specifically, our problem statement is the Biot system which consists of vector-valued displacements (geomechanics) coupled to a Darcy flow pressure equation. The MORe DWR method introduces a goal-oriented adaptive incremental proper orthogonal decomposition (POD) based-reduced-order model (ROM). The error in the reduced goal functional is estimated during the simulation, and the POD basis is enriched on-the-fly if the estimate exceeds a given threshold. This results in a reduction of the total number of full-order-model solves for the simulation of the porous medium, a robust estimation of the quantity of interest and well-suited reduced bases for the problem at hand. We apply a space-time Galerkin discretization with Taylor-Hood elements in space and a discontinuous Galerkin method with piecewise constant functions in time. The latter is well-known to be similar to the backward Euler scheme. We demonstrate the efficiency of our method on the well-known two-dimensional Mandel benchmark and a three-dimensional footing problem.

Tao Wang, Yunjie Liu, Renjiang Zhu et al.

Understanding the mechanism of mode-locking in a laser with high-order transverse mode is important for achieving an ultrashort pulses train under more complicated conditions. So far, mode-locking with high-order transverse mode has not been reported in other lasers except the multimode fiber laser. This paper demonstrates robust mode-locking with high-order transverse mode in a Kerr-lens mode-locked vertical-external-cavity surface-emitting laser for the first time, to the best of our knowledge. While the longitudinal modes are locked, continuous mode-locking accompanied by high-order transverse mode up to TEM₄₀ is observed. The threshold of the mode-locking is only a little bigger than that of the lasing. After the laser oscillation is built up, the mode-locked pulse train can be obtained almost immediately and maintained until the thermal rollover of the laser. Output powers of 717 mW under fundamental mode and 666 mW under high-order transverse mode are achieved with a 4.3 ps pulse duration and 1.1 GHz pulses repetition rate, and some phenomenological explanations to the related characteristics of the mode-locked operation of high-order transverse mode in the vertical-external-cavity surface-emitting laser are proposed.

Teerapong Senjuntichai, Barami Phulsawat, Suraparb Keawsawasvong et al.

Geo-materials naturally display a certain degree of anisotropy due to various effects such as deposition. Besides, they are often two-phase materials with a solid skeleton and voids filled with water, and commonly known as poroelastic materials. In the past, despite numerous studies investigating the vibrations of strip foundations, dynamic impedance functions for multiple strip footings bonded to the surface of a multi-layered transversely isotropic poroelastic half-plane have never been reported in the literature. They are first presented in this paper. All strip foundations are assumed to be rigid, fully permeable, and subjected to three types of time-harmonic loadings. The dynamic interaction problem is investigated by using an exact stiffness matrix method and a discretization technique. The flexibility equations are established by enforcing the appropriate rigid body displacement boundary conditions at each footing-layered soil interface. Numerical results for dynamic impedance functions of two-strip system are presented to illustrate the influence of various effects on dynamic responses of multiple rigid strip foundations.

Pei-Yu Chu, Han-Yun Hsieh, Pei-Shan Chung et al.

Summary: The objective of this study is to develop a device to mimic a microfluidic system of human arterial blood vessels. The device combines fluid shear stress (FSS) and cyclic stretch (CS), which are resulting from blood flow and blood pressure, respectively. The device can reveal real-time observation of dynamic morphological change of cells in different flow fields (continuous flow, reciprocating flow and pulsatile flow) and stretch. We observe the effects of FSS and CS on endothelial cells (ECs), including ECs align their cytoskeleton proteins with the fluid flow direction and paxillin redistribution to the cell periphery or the end of stress fibers. Thus, understanding the morphological and functional changes of endothelial cells on physical stimuli can help us to prevent and improve the treatment of cardiovascular diseases.

Zsolt Szabó

In this paper the dynamic behaviour of a continuum inextensible pipe containing fluid flow is investigated. The fluid is considered to be incompressible, frictionless and its velocity relative to the pipe has the same but time-periodic magnitude along the pipe at a certain time instant. The equations of motion are derived via Lagrangian equations and Hamilton's principle. The system is non-conservative, and the amount of energy carried in and out by the flow appears in the model. It is wellknown, that intricate stability problems arise when the flow pulsates and the corresponding mathematical model, a system of ordinary or partial differential equations, becomes time-periodic. The method which constructs the state transition matrix used in Floquet theory in terms of Chebyshev polynomials is especially effective for stability analysis of systems with multi-degree-of-freedom. The stability charts are created w.r.t. the forcing frequency w, the perturbation amplitude l/ and the average flow velocity U.

Surajit Kumar Paul

In many engineering structural applications, including car body structures, sheet metal formed components are used. A systematic investigation of the impact of forming strain on fatigue life is necessary for an accurate prediction of a formed component's fatigue life. The present work aims to determine the impact of diverse types of tensile pre-straining on high cycle fatigue (HCF), low cycle fatigue (LCF) and notch fatigue performance of automotive grade dual phase steels. In all examined pre-straining conditions, HCF life improves, LCF life deteriorates, and little change in notch fatigue life are observed. The most significant improvement in HCF life and deterioration in LCF life are observed for equi-biaxial and orthogonal tensile pre-straining conditions due to the rotation of maximum shear stress plane and the rotation of the deformation concentrated region around the hard martensite. As the strength improves during pre-straining, there is a corresponding increase in stress concentration around a notch, and as a result, no significant change in notch fatigue life is observed.

Naoto Mitsume

Abstract This study presents a novel wave–structure interaction model, which is a compatible interface wave–structure interaction model that is based on mesh-free particle methods for free-surface flow analysis; the FEM for structural analysis. We adopt the explicitly represented polygon (ERP) wall boundary model, which is a polygon wall boundary model for mesh-free particle methods, to express the fluid–structure interfaces. The fluid–structure interfaces in the proposed model are geometrically compatible because the ERP model has advantages in dealing with complex-shaped and moving boundaries and it enables the direct use of surface meshes and shape functions given by finite element models of structures. This allows the automatic generation of polygons for free-surface flow analysis from finite elements, and therefore, it greatly increases the flexibility of the analysis. Based on the compatible interface between the polygons and finite elements, we propose a strong coupling algorithm based on an iterative partitioned scheme that defines the interacting models between the fluid and the structure. We model the force exerted by fluid particles on structures such that the kinetic boundary condition on the fluid–structure interface is satisfied. We perform the verification and validation tests of the proposed model by solving two benchmark problems.

Frank Ihlenburg, Ivo Babuška

The numerical solution of Helmholtz' equation at large wavenumber is very expensive if attempted by "traditional" discretisation methods (FDM, standard Galerkin FEM). For reliable results, the mesh has to be very fine. The bad performance of the traditional FEM for Helmholtz problems can be related to the deterioration of stability of the Helmholtz differential operator at high wavenumber. As an alternative, several non-standard FEM have been proposed in the literature. In these methods, stabilisation is either attempted directly by modification of the differential operator or indirectly, via improvement of approximability by the incorporation of particular solutions into the trial space of the FEM. It can be shown that the increase in approximability can make up for the stability loss, thus improving significantly the convergence behavior of the knowledge based FEM compared to the standard approach. In our paper, we refer recent results on stability and convergence of h- and h-p-Galerkin ("standard") FEM for Helmholtz problems. We then review, under the label of "knowledge-based" FEM, several approaches of stabilised FEM as well as high-approximation methods like the Partition of Unity and the Trefftz method. The performance of the methods is compared on a two-dimensional model problem.

Vignesh Sekar, Se Yong Eh Noum, Azma Putra et al.

Synthetic fiber is still considered the best sound absorptive material. However, due to the health concern of synthetic fiber usage, researchers are trying to find another viable alternative. A microperforated panel (MPP) is a promising alternative that relies on the concept of a Helmholtz resonator for sound absorption. MPP possessed excellent acoustic resistance and a considerable range of absorption bandwidth. In this paper, MPP made of natural fiber composite was fabricated and its acoustic absorption was measured using a two-microphone impedance tube method as per ISO 10534-2 standard. Later, the tensile strength of the fabricated acoustic absorbers was measured using an Instron Universal Testing Machine as per ASTM D638. The idea of employing additive manufacturing, better known as the 3D printing technique, is proposed to produce lightweight MPP. The 3D printing technique provides design freedom and is less tedious in creating complex and light structures. The 3D printing technique has various important parameters, and infill density is one of the parameters. It was found that the reduction of infill density leads to a decrease of the MPP’s mass and thus, slightly affects the resonance frequency of the MPP, still within the mid-frequency spectrum. It was also noted that the increment of air gap thickness leads to the shifting of MPP’s resonance frequency to a lower frequency range. The tensile strength of the 3D printed samples decreases with a decrease in infill density. A sample with an infill density of 100% has the highest tensile strength of 22 MPa, and a sample with an infill density of 20% has the lowest tensile strength of 12 MPa.

Rücker Andreas, Rief Jona, Fottner Johannes

Automated storage and retrieval systems (AS-RS) are commonly used in intralogistic facilities and are often operated by stacker cranes. These stacker cranes are used in high-bay warehouses to move small load carriers, pallets and special load carriers. This paper presents an approach for the determination of the mean energy demand of stacker cranes, using a reference cycle. The examination of the reference cycles is based on a large scale simulation experiment with randomly generated stacker crane and rack configurations and operation tasks. The results permitted an analysis of the correlations between various parameters e.g. energy demand and performance of stacker cranes. Subsequently, three different reference cycles which allow an easy and fast calculation of the mean energy demand are developed and evaluated.

Canan CIMSIT

Absorption refrigeration cycles, the developed as an alternative to vapour-compression refrigeration cycles they are not effective at low temperatures. When the absorption and vapour compression cycles are combined as cascade the consumed compressor work can be reduced considerably, but it requires the use of heat energy at low temperature (solar energy, geothermal energy, waste heat). In this study, the absorption part has been designed to improve the performance of absorption-vapour compression cascade cycle as serial flow double effect. The detailed thermodynamic analysis has been made of the double effect absorption-vapour compression cascade refrigeration cycle. For the novel cycle working fluid used R-134a for vapour compression section and LiBr-H2O for absorption section. This cycle has been compared with single effect absorption-vapour compression cascade cycle and one stage vapour compression refrigeration cycle. The results indicate that the electrical energy consumption in the novel cycle is 73% lower than the one stage vapour compression refrigeration cycle. Also, the thermal energy consumption in the cascade cycle is 38% lower than the single effect absorption-vapour compression cascade refrigeration cycle. It is found that the the minimum and maximum exergy efficiency occurs in the cooling set and the low pressure generator (LPG) as 21.85% and 99.58%, respectively.

Grúňová Zuzana, Holešová Michaela

Oval and elliptic spaces are one group of central plans, used mainly in sacral architecture and palaces. Paper deals with geometrical analysis of one of the smaller representatives of the neoclassical sacral architecture with oval plan - Palesch family chapel of Virgin Mary in village Kľačno in Western Slovakia. Oval and elliptic forms are not so often used in Slovak historical architecture and they are almost always connected with foreign influence and knowledge brought form Vienna, Paris, Pest, Eger and other education and praxis localities of the builder or architect. This uncommon oval form used in the small chapel is therefore certainly of interest from the point of view of architecture and geometry.

Yu YAMAMOTO, Yoshihiro TAGUCHI, Yuji NAGASAKA

We propose a novel patterning method for self-assembled monolayers (SAMs) using near-field photothermal desorption (NPTD). This paper reports the patterning principle and the study on optimum heating conditions. The proposed method utilizes the thermal desorption of constituent molecules of a SAM through the irradiation with near-field light, which can make noncontact and noncontaminating patterning of the SAMs at the nanoscale. In order to verify the validity of the proposed patterning method for SAMs, the preliminary patterning of a SAM by irradiating with a laser beam was performed. The results suggested that the constituent molecules were thermally desorbed and the subsequent modification of another kind of a SAM was successfully carried out. The numerical analysis of the temperature distribution after heating with near-field light was demonstrated by using the finite element method to investigate the heating condition of NPTD. The simulation results of laser heating well agreed with the preliminary experimental results, therefore, the applicability of the proposed analytical model was confirmed. Furthermore, the analytical results of the temperature distribution indicated that the local heating at the nanoscale with sufficient temperature increase for NPTD could be induced by the irradiation with near-field light generated by using an apertured fiber probe coated with Ag. As a result, the validity of the patterning principle and the optimal heating conditions were verified, and therefore, the possibility of the nanoscale patterning of SAMs using NPTD was confirmed.