Hasil untuk "Descriptive and experimental mechanics"

Zhi Zhang, Haoran Fu, Yang Zhong et al.

Abstract Chinese distilled liquor, known as Baijiu, typically has a relatively high ethanol content (52 or 53% alcohol by volume, ABV) and is characterized by a powerful, heady scent. When its alcohol content is less than 45% ABV, Baijiu loses its flavor and becomes cloudy and tasteless; thus, it is relatively bland and thin. Since this phenomenon has not been reasonably explained, the aim of this study is to determine its underlying mechanism by examining the droplet evaporation. A 1.0 µL of droplets were applied to the substrate surface for evaporation. The results revealed that a reduction in the alcohol content (<45% ABV) triggered the self‐assembly of unique long‐chain fatty acid ethyl esters into various nano‐ or microparticles with sizes ranging from 100 nm to 10 µm within the Baijiu droplets. These particles deposit under the influence of internal flow and exhibit Baijiu‐specific coffee‐ring effects after drying. Interestingly, these particles encapsulated the water‐soluble or insoluble flavor chemicals, resulting in the brightness and aroma/flavor of Baijiu decreased radically; this is the reason that a high alcohol content is needed in Baijiu. These findings offer new insights for the quality control of low‐alcohol Baijiu and Baijiu identification.

Tzu-Hsun Lin, Keh-Chin Chang

The evolution of a coherent structure in a cylindrical wake was studied through observing its energy contribution to the flow field. Analysis using the proper orthogonal decomposition on the PIV data measured at two Reynolds numbers (Re) of 3840 and 9440 was performed. The coherent structure was identified by checking the Fourier power spectrum for each temporal mode coefficient and selecting those whose peak magnitudes were greater than the smallest magnitude of the identified harmonic frequency family as the large-scale organized motions. The energy contribution by the coherent structure is significantly dependent on Re. The evolution of the energy contribution by the coherent structure exhibits a monotonously decaying trend when moving downstream. The coherent structure primarily contains the Kármán vortices in the near wake. The contribution weight of the secondary vortices gradually increases, along with the streamwise distance, except in the very upstream subregions for the case of Re = 9440. The energy contribution by the secondary vortices immediately behind the cylinder (x/d = 0.5–5.5) was 30% for Re = 9440, in comparison with <1% for Re = 3840, but decayed rapidly to the value of <10% in the downstream subranges.

Maria Antonietta Boniforti, Roberto Magini, Tania Orosco Salinas

Flow diverter stents (FDS) are increasingly used for the treatment of complex intracranial aneurysms such as fusiform, giant, or wide-neck aneurysms. The primary goal of these devices is to reconstruct the diseased vascular segment by diverting blood flow from the aneurysm. The resulting intra-aneurysmal flow reduction promotes progressive aneurysm thrombosis and healing of the disease. In the present study, a numerical investigation was performed for modeling blood flow inside a patient-specific intracranial aneurysm virtually treated with FDS. The aim of the study is to investigate the effects of FDS placement prior to the actual endovascular treatment and to compare the effectiveness of devices differing in porosity. Numerical simulations were performed under pulsatile flow conditions, taking into account the non-Newtonian behavior of blood. Two possible post-operative conditions with virtual stent deployment were simulated. Hemodynamic parameters were calculated and compared between the pre-operative (no stent placement) and post-operative (virtual stent placement) aneurysm models. FDS placement significantly reduced intra-aneurysmal flow velocity and increased the Relative Residence Time (RRT) on the aneurysm, thus promoting thrombus formation within the dilatation and aneurysm occlusion. The results highlighted an increase in the effectiveness of FDS as its porosity increased. The proposed analysis provides pre-operative knowledge on the impact of FDS on intracranial hemodynamics, allowing the selection of the most effective treatment for the specific patient.

Hassan Ali Ghazwani, Khairuddin Sanaullah, Vladimir Vladimirovich Sinitsin et al.

Theoretical and experimental aspects of the project were conducted to investigate the effect of the mixing of a swirling steam jet into cross-flowing water. It was observed that based on the theoretical adiabatic estimations for the equilibrium temperature of steam–water mixing and by varying P_steam = 1–3 bar, P_water = 1 bar and RPM = 60–300 around 97% (experimentally compared to the area it has at initial condition) and 85% (CFD study compared to the area it has at initial condition), an increase in the area under the influence of perfect adiabatic mixing was found. A virtual cover over the steam duct was seen. The area of this virtual cover based on the void fraction of swirling steam had a weak relationship with the total area of the region, inhibiting the perfect mixing for which an analytical relationship had been developed. The effect of mixing on the stability of swirling steam–water cross-flows was overall more than twice that of the effect on the area under the influence of the stability profile protrusions. Thus, an overall rise in inlet pressure contributed to improper mixing, whereas a rise in the RPM contributed to proper mixing inside a fixed window of observations. The effect of spatial scaling of a swirling steam trajectory on mixing in cross-flowing water was also investigated across the vertical plane. Also, the scaling of the vertical trajectories of the swirling steam jets under all operating conditions resulted in merging the regions of perfect mixing to some extent. Thus, the area under the influence of perfect mixing was reduced to around 3–4.7% under all operating conditions with scaling. This type of scaling has enormous potential for the characterization of larger fluid domains in environmental and process engineering studies.

Bernardo Leite, Frederico Afonso, Afzal Suleman

Hypersonic flight has been the subject of numerous research studies during the last eight decades. This work aims to optimize the aerodynamic performance of a two-dimensional baseline airfoil (NACA0012) at distinct flight regimes from subsonic to hypersonic speeds. A mission profile has been defined, where four points representing the subsonic, transonic, supersonic, and hypersonic flow conditions have been selected. A framework has been implemented based on high-fidelity RANS computational fluid dynamics simulations. Gradient-based optimizations have been conducted with the objective of minimizing the drag. The optimization results show an overall improvement in aerodynamic performance, including a decrease in the drag coefficient of up to 79.2% when compared to the baseline airfoil. In the end, a morphing strategy has been laid out based on the optimal shapes produced by the optimization.

Marc Haussmann, Peter Reinshaus, Stephan Simonis et al.

In this paper, we use a fluid–structure interaction (FSI) approach to simulate a Coriolis mass flowmeter (CMF). The fluid dynamics is calculated by the open-source framework OpenLB, based on the lattice Boltzmann method (LBM). For the structural dynamics we employ the open-source software Elmer, an implementation of the finite element method (FEM). A staggered coupling approach between the two software packages is presented. The finite element mesh is created by the mesh generator Gmsh to ensure a complete open source workflow. The Eigenmodes of the CMF, which are calculated by modal analysis, are compared with measurement data. Using the estimated excitation frequency, a fully coupled, partitioned, FSI simulation is applied to simulate the phase shift of the investigated CMF design. The calculated phase shift values are in good agreement to the measurement data and verify the suitability of the model to numerically describe the working principle of a CMF.

Nguyen Viet Khoa, Dao Thi Bich Thao

This paper establishes the exact receptance function of a clamped-clamped beam carrying concentrated masses. The derivation of exact receptance and the numerical simulations are provided. The proposed receptance function can be used as a convenient tool for predicting the dynamic response at arbitrary point of the beam acted by a harmonic force applied at arbitrary point. The influence of the concentrated masses on the receptance is investigated. The numerical simulations show that peak in the receptance will decrease when there is a mass located close to that peak position. The numerical results have been compared to the experimental results to justify the theory.

Marco Martins Afonso, Philippe Meliga, Eric Serre

With the aim of providing a first step in the quest for a reduction of the aerodynamic drag on the rear-end of a car, we study the phenomena of separation and reattachment of an incompressible flow by focusing on a specific aerodynamic geometry, namely a backward-slanted step at 25<inline-formula> <math display="inline"> <semantics> <msup> <mrow></mrow> <mo>∘</mo> </msup> </semantics> </math> </inline-formula> of inclination. The ensuing recirculation bubble provides the basis for an analytical and numerical investigation of streamwise-streak generation, lift-up effect, and turbulent-wake and Kelvin&#8315;Helmholtz instabilities. A linear stability analysis is performed, and an optimal control problem with a steady volumic forcing is tackled by means of a variational formulation, adjoint methods, penalization schemes, and an orthogonalization algorithm. Dealing with the transient growth of spanwise-periodic perturbations, and inspired by the need of physically-realizable disturbances, we finally provide a procedure attaining a kinetic-energy maximal gain on the order of <inline-formula> <math display="inline"> <semantics> <msup> <mn>10</mn> <mn>6</mn> </msup> </semantics> </math> </inline-formula>, with respect to the power introduced by the external forcing.

K. Venugopal Reddy, M. Gnaneswara Reddy

N. D. Anh, V. L. Zakovorotny, D. N. Hao

A new technique is proposed to investigate the response of Van der Pol-Duffing (V-D for short) oscillator to a combination of harmonic and random excitations in the primary resonant frequency region. The analytical approach is based on the stochastic averaging method and equivalent linearization method. The stochastic averaging is applied to the original equation transformed into Cartesian coordinates. Then the resulting nonlinear averaged equations are linearized by the equivalent linearization method so that the equations obtained can be solved exactly by the technique of auxiliary function. Numerical results show that the proposed approximate technique is an effective approach to solving the V-D equation. Although the technique has been used for the V-D equation in the paper, however, it can also be used to solve many other nonlinear oscillators.

Nguyen Thoi Trung, Nguyen Xuan Hung

An alpha finite element method (\(\alpha\)FEM) has been recently proposed to compute nearly exact solution in strain energy for solid mechanics problems using three-node triangular (\(\alpha\)FEM-T3) and four-node tetrahedral (\(\alpha\)FEM-T4) elements. In the \(\alpha\)FEM, a scale factor \(\alpha \in [0, 1]\) is used to combine the standard fully compatible model of the FEM with a quasi-equilibrium model of the node-based smoothed FEM (NS-FEM). This novel combination of the FEM and NS-FEM makes the best use of the upper bound property of the NS-FEM and the lower bound property of the standard FEM. This paper concentrates on applying directly the \(\alpha\)FEM for solid mechanics to obtain the very accurate solutions with a suitable computational cost by using \(\alpha = 0.6\) for 2D problems and \(\alpha = 0.7\) for 3D problems.

Hoang Van Da, Tran Dinh Son, Nguyen Duc Tinh

In the present paper, the authors have constructed an asymptotic solution of the high order equation with partial derivatives by means of the asymptotic method for the high order systems. The improved first approximation of the solution of the given boundary value problem is determined

Dang Huu Chung

In this paper a 3D model (FSUM) on tidal flows with sediment transport and bed morphology process taking into account the temperature-salinity exchange in estuaries and coastal zones is introduced in more detail. The implicit finite difference method based on semi-Lagrange splitting is used. The software is coded with FORTRAN 90/95. The open boundary condition kinds together source/sink terms are well treated so that it can be applied to every computing domain with the complicated geometry. The software is validated and applied for many different cases and shows the ability of application in practice.

C. A. N. Dias

The exact solution for the problem of damped, steady state response, of in-plane Timoshenko frames subjected to harmonically time varying external forces is here described. The solution is obtained by using the classical dynamic stiffness matrix (DSM), which is non-linear and transcendental in respect to the excitation frequency, and by performing the harmonic analysis using the Laplace transform. As an original contribution, the partial differential coupled governing equations, combining displacements and forces, are directly subjected to Laplace transforms, leading to the member DSM and to the equivalent load vector formulations. Additionally, the members may have rigid bodies attached at any of their ends where, optionally, internal forces can be released. The member matrices are then used to establish the global matrices that represent the dynamic equilibrium of the overall framed structure, preserving close similarity to the finite element method. Several application examples prove the certainty of the proposed method by comparing the model results with the ones available in the literature or with finite element analyses.

R.E.S. Ismail, A.S. Fahmy, A.M. Khalifa et al.

Abstract Bolted end-plate steel connections have become more popular due to ease of fabrication. This paper presents a three dimension Finite Element Model (FEM), using the multi-purpose software ABAQUS, to study the effect of different geometrical parameters on the ultimate behavior of the connection. The proposed model takes into account material and geometrical non-linearities, initial imperfection, contact between adjacent surfaces and the pretension force in the bolts. The Finite Element results are calibrated with published experimental results ''briefly reviewed in this paper'' and verified that the numerical model can simulate and analyze the overall and detailed behavior of different types of bolted end-plate steel connections. Using verified FEM, parametric study is then carried out to study the ultimate behavior with variations in: bolt diameter, end-plate thickness, length of column stiffener, angle of rib stiffener. The results are examined with respect to the failure modes, the evolution of the resistance, the initial stiffness, and the rotation capacity. Finally, the ultimate behavior of the bolted end-plate steel connection is discussed in detail, and recommendations for the design purpose are made.

Pham Chi Vinh

None

Luiz Leite da Silva, Vladimir S. Ribeiro, Denis H. Bianchi Scaldaferri et al.

Abstract Residual stresses are present in materials or structural component in the absence of external loads or changes in temperatures. The most common causes of residual stresses being present are the manufacturing or assembling processes. All manufacturing processes, such as casting, welding, machining, moulding, heat treatment, etc, introduces residual stresses into the manufactured object. The residual stresses effects could be beneficial or detrimental, depending on its distribution related to the component or structure, its load service and if they are compressive or tensile. In order to do the studies of residual stresses inside pipes, where the fatigue cracks normally initiate, an equipment that allows applying the Hole-Drilling Method was developed. The equipment efficacy was confirmed in this work by using it to detect residual strains inside a Mock-up that simulates the relief and security nozzle of Angra 1 Nuclear Power Plant (NPP) pressuriser.

Mohammad Arefi

Abstract This research develops nonlinear electromechanical stability of a circular functionally graded plate integrated with functionally graded piezoelectric layers under compressive radial force. Geometric nonlinearity is considered in the strain-displacement relation using Von-Karman relation. The structure is loaded under mechanical and electrical loads. Distribution of electric potential is considered along the radial and thickness direction. The top and bottom of both piezoelectric layers is short-circuited. The effect of various values of non homogenous index for both functionally graded (FG) and functionally graded piezoelectric (FGP) layers can be considered on the responses of the system. Furthermore, a comprehensive study for evaluation of geometric parameters can be performed on the critical loads of the structure.

Eliene Pires Carvalho, Efigênia Guariento Ferreira, José Celso da Cunha et al.

Abstract The steel-concrete bond is a fundamental property in reinforced concrete structures. Although there are several studies on the steel-concrete bond, few of them have evaluated the performance of reinforcing bars with diameters less than 10.0 mm, which includes 5.0, 6.3, and 8.0 mm diameters, which are normally used in reinforced-concrete elements. This study experimentally evaluates the bond between thin steel bars and concrete of 25MPa compression strength. Three types of methods of testing the bond-strength were performed: confined bar test, pull-out test and beam test. It was compared the adequacy of the tests to calculate the conformation coefficient of the bars. The results of the confined bars tests show that this test may be inadequate to determine the surface conformation coefficient of reinforcing bars thinner than 10 mm, especially for notched (CA-60) steel bars. The pull-out test resulted in better results in terms of evaluating the bond behavior. Regarding the specimens for the pull-out tests, a modified model with an anchorage length equal to 10 times the bar diameter is suggested. Therefore, the main contribution of this study, based on the results obtained and the methodology used, is to present a proposal for the evaluation of steel-concrete bond for thin rebars.

Nguyen Van Dao

In this paper, oscillations and stability of nonlinear oscillators with time delay are studied by means of the asymptotic method of nonlinear mechanics. Harmonic, super harmonic, subharmonic and parametric resonances of a Duffing's oscillator are analyzed. Analytical method in combination with a computer is used.