Experiments and numerical simulations are carried out in the upper-level, undergraduate physics laboratory to examine the highly transient startup flow from a small nozzle. The flow is initiated by the rupture of a Mylar R © diaphragm positioned between the nozzle and a pressurized air tank. The studies utilize an approach based on experimental measurements and computational methods. Experimental studies consist of dual-beam heterodyne interferometry and highspeed video (HSV) shadowgraphy. Interferometric measurements at 25 million samples per second relate optical path length changes across the nozzle flow to density variations in the flow. HSV shadowgraphy portrays the initial shock wave and compressible flow features surrounding the nozzle exit at 100,000 frames per second. Finite element computations of the unsteady, axisymmetric, compressible nozzle flow provide a field description of the flow for the full tank-nozzle-exterior domain. The studies show excellent matching between the experimental and computational methods. More importantly, the distinct strengths of the different approaches work together to provide a more comprehensive description of the nozzle flow than can achieved by the individual approaches.
Finite Difference Time Domain Method (FDTDM) is a powerful tool to model electromagnetic propagation; once the medium has been defined by its conductivity (, permittivity ( and permeability (, for each position in the computational volume, is possible to “see” the propagation electromagnetic behavior. We have used FDTDM to model waveguides, slot antennas, field effects over different materials and even propagation effects in nanometric spaces. As obstacles produce reflection, refraction and diffraction phenomena, modifying scattering field in free space zones, knowledge of propagation behavior is very useful to define antenna positions and other system characteristics, for WiFi, cellular telephony and other mobile communication systems. We present in this paper, results of EM propagation modeling inside a building, where furniture, structure, walls and any other obstacle has been defined by their EM constants: Modeling shows how EM field is distributed all over the chosen zone, giving an almost exact quantification of field magnitude in each point. Modeling uses Yee algorithm to transform Differential Maxwell Equations into Finite Difference Equations, capable to be handled by the computer program developed by us. The source we used was a 2.4 GHz WiFi access point, allowing us to compare computational results with direct measurements in the experimental area. Each computational point was a 0.6 cm (per side cube, over a zone of 9x4x3 m. Results are presented in both, as images showing field distribution in representative areas of analysis zone, and linear graphics comparing acquired computational and measurement data, showing a no more than 3 dB difference between them.
A geostatistical solution is presented to assess the acoustic impact of a quarry plant near Rome by drawing acoustic maps all around the selected site.The method utilised to determine the sound pressure level in the area of interest is the Intrinsic Random Function (IRF) Kriging with external drift.This technique allows the value of a regionalized variable to be estimated at a point in which it is unknown through the use of two sets of data.The first one is obtained by carrying out phonometric samples at various points near the site, while the second one is from a deterministic model of sound propagation defined in accordance with norms in force.In order to test the quality of the estimates and especially the contribution of the external drift, acoustic maps on a local scale are drawn up both with and without drift.The quality of the results obtained is tested by means of cross validation.The experimental results demonstrate that, providing it is strongly correlated to the first, the introduction of this secondary information, in a stochastic framework of reference, contributes to a more efficient representation of the spatial variability of sound propagation, and thus to an improvement in the quality of the correlated estimate.In the case study analysed here the introduction of drift permits a reduction of estimate variance, for the same number of available measurements.Again from the cross validation data and estimate variance it was observed that the use of external drift allows loss of information (e.g.due to a reduction in the monitored network) to be compensated for without invalidating the quality of the estimate itself.
The aim of this work was to verify the dynamic behavior of the masonry shell forming the backbone of the Basilica of S. Maria di Collemaggio, in L'Aquila (Italy), and then to compare it with the experimental results related to previous investigations of the ruinous earthquake of April 6 th , 2009.This is with the intention of having an objective indication, in quantitative terms, with respect to the actual damage suffered by the construction and effectiveness of the provisional measures put in place immediately after the earthquake.Another aspect, not to be underestimated, was to envisage a method of investigation based solely on environmental noise as a source of excitation, and to highlight the advantages and potentiality for the experimental study of dynamic artifacts typologically similar to the one in question.In this case, the operational modal analysis can reasonably be defined as the investigation technique for excellence as the most immediate, expeditious and reliable.Future developments and implementations, based on the concept of configurations with transducers at a fixed location, will provide the highest and most effective contribution to the branch of health engineering.
The Russian Arctic zone includes nine regions. These regions are rich in natural resources including fish, timber, and minerals. This distant periphery of Russia is a huge territory and poorly developed. These regions are characterized by the highest gross regional product per capita in the country. In some regions, the industrial sector is powerful, but the social infrastructure is poorly developed. Agriculture is almost absent. In this paper the economic growth in the regions of the Russian Arctic is modeled and factors affecting the economic growth are analyzed. The gross regional product of all nine regions of the Russian Arctic as a percentage of Russia’s gross domestic product is used as dependent variable (endogenous variable) in the model. The value of the dependent variable in the current period can be influenced by both its value in the past periods and current and lagged values of exogenous factors. Considering the process of economic growth and analysis of the factors affecting economic growth in regions of the Russian Arctic, autoregressive distributed lag model is used. Using ordinary least squares the coefficients of the model are estimated and findings about the impact of each of the five exogenous factors on the dependent variable are presented.
The control of dynamic objects inside the locked loop with negative feedback is now widely used in automation and robotics.This ensures greater precision under the action of uncontrolled disturbances.Usually, for controlling the single output value of the object only one input action on the object is sufficient.But there are cases where it is advisable to apply two or more feedback control actions to the object for a single output value controlling.Such a case occurs when the structure of the mathematical model of the object allow the influence to the output value in different ways, every of which corresponds to different mathematical models.Each of these models has their own speed limits on the maximum value of the actions of limited frequency band, and so on.Joint use of the multiple control channels can simultaneously provide both high speed control and a large range of controlled changes in the output value of the object.This requires the use of multiple regulators, jointly acting on the object.Coordination of dynamic and static properties of these regulators has been discussed theoretically using transfer functions.But it does not take into account such a limitation of the control channels of the object as a dynamic non-linearity.This article discusses these limitations one of the channels.It uses mathematical modeling for transient processes and to optimize the regulators.Advantages of using this method are investigated by examples.It is for the first time in this paper that the mathematical modeling and numerical optimization for finding the best values of the coefficients of the various regulators in such a structure were used.The simulation showed the advantages of this method and its limitations for use.The paper is illustrated with the graphs obtained transient processes in the locked system.
The paper deals with an analysis of curved wire antennas. The formulation is based on the Pocklington integro-differential equations for curved wires which is solved via the Galerkin-Bubnov scheme of the Indirect Boundary Element method (GB-IBEM). Some illustrative computational examples related to thin wire loop antenna and various helical antenna types are given in the paper.
The aim of this paper is to describe the influence of the composition of refractory composites on their response to gradual thermal loading.Aluminous cement binder system was modified by metakaolin additive which is produced by calcination and grinding of natural clay.Studied aluminous additive is often used for production of high strength composites with increased mechanical and durability properties.The fundamental problem of these composites is their brittle rupture which is why studied composites were reinforced by very short ceramic fibers.Studied aluminate binder system in combination with natural basalt fine aggregates ensures sufficient resistance to high temperature exposure.The influence of composition changes was evaluated by the results of physical and mechanical testing -compressive and flexural strength and bulk density were determined on the different levels of temperature loading.Application of ceramic fibers brought an expected linear increase of mechanical parameters of studied composites just up to dose of 4% by volume.Metakaolin replacement showed the optimal dose just about 20% of aluminous cement weight.The extensive application of cement supplementary materials has an important motivation because of high energy consumption of aluminous cement based refractory composites.It was experimentally verified that the appropriate combination of aluminous cement with metakaolin additive and natural crushed basalt aggregates ensure sufficient properties for practical utilization of proposed composites.
This paper briefly describes the numerical models for the simulation of fluid-structure coupled problems. The applied models are primarily intended to simulate the fluid-structure dynamic interaction in seismic conditions. Models can simulate the most important non-linear effects of plane and spatial structures that are in direct contact with fluid. Some of models' possibilities are illustrated in numerical analyses of the seismic behavior for several practical examples.
The safe exploitation of the post-buckling region of CFRP panels in aerospace applications is of prime interest here.Due to the long computational time of finite element analysis for the post-buckling response of CFRP panels, there is a need to devise some efficient procedures.Skin/stringer debonding is primarily responsible for the collapse of the stiffened panels under compressive loading.In this study a simplified approach based on a single-stringer compression specimen (SSCS) has been employed to gain an insight into the post-buckling behaviour of CFRP panels under axial compression.A progressive damage model is used to get more accurate numerical results of the post-buckling response of SSCS.The outcomes of the study are compared with the published results and a fair agreement is found.In addition, a comparative study of open-and closed-section stringer stiffened panels based on a global-local approach for predicting pre-buckling, post-buckling and mode shapes is carried out.As the simplified model is used in this study so detailed damage models can be constructed to account for all damage modes: matrix cracking, fibre kinking, fibre fracture, and delamination.The study can be employed as a global-local approach to get the post-buckling response of CFRP stiffened panels.Furthermore, it also provides an efficient mean for the design optimization of CFRP structures in the post-buckling regime.
Large net-shape deployable antenna reflectors are currently a perfect configuration type for large satellites, and the shape precision affects the performance of antennas greatly.The calculation of the temperature field is fundamental to an analysis of the shape precision.This paper presents a method for calculating the on-orbit temperature field for large net-shape deployable antennas, and gets the temperature by using a numerical calculation.The results support and give a certain reference for an analysis of its shape precision and the antenna thermal testing design.
The results of simulation of mold filling by a highly viscous fluid are presented in this paper.The process of injection molding using a polymer melt is simulated.The mold has a rectangular shape and can have a coaxially placed rod.Evolving flow is characterized by a free surface undergoing significant deformations during the whole process.The indirect boundary element method for two-dimensional Stokes flows was used for calculations.Numerical procedures required for the boundary remeshing are described.Calculations were performed for both cases: top-down filling (gate at the top of the mold) and bottom-up filling (gate at the bottom of the mold).Differences in flow behavior are demonstrated for both variants.Comparison of material distribution in filled molds is performed.For this purpose interfaces between portions of fluid were marked and tracked up to the completion of filling process.The fountain flow regime is predominant for bottom-up mold filling.In the case of top-down mold filling, jet flow and film flow take place.Flow regimes leading to gas entrainments and welding which are considered unacceptable and cause product defects were shown.
The paper deals with the evaluation of transmitted electric field in the ground due to the GPR dipole antenna.The frequency domain formulation is based on the integro-differential equation of the Pocklington type.The influence of the earthair interface is taken into account via the simplified reflection/transmission coefficient arising from the Modified Image Theory (MIT).The space-frequency Pocklington equation is solved via the Galerkin-Bubnov variant of the Indirect Boundary Element Method (GB-IBEM) and the corresponding transmitted field is obtained by numerically computing field integrals.Some preliminary results for the electric field transmitted into material media are presented.
This paper deals with the fluid-structure interaction analysis of a shell partially filled with a liquid.The shell is considered to be thin and the Kirghoff-Lave linear theory hypotheses are applied.The liquid is ideal and incompressible.The problem of analysing the dynamics of shells of revolution partially filled with an ideal incompressible liquid was reduced to solving the system of singular integral equations.The solution was obtained by using a coupled BEM and FEM in-house solver.The tank structure is modelled by the FEM and the liquid sloshing in the fluid domain is described by the BEM.The shell vibrations coupled with liquid sloshing under the force of gravity were considered.The shell and sloshing modes were analysed simultaneously.The free vibration analysis of the elastic cylindrical shell was carried out using the proposed techniques.
The paper concerns potential of numerical simulation for assessment of characteristics of tagged neutron device.The CERN Geant4 code and TPT2 (Toolkit for Particle Transport) code developed in VNIIA were used to simulate the γ-neutron transport in components of the tagged neutron device and recording of ionizing radiation by the scintillation detector.The numerical simulation was corrected and validated by experimentations with the model of the device of the same geometry, type of detector, materials.At first, we obtained a spectral response of LYSO scintillator under γ-and neutron radiation and satisfied that it was close to the measured data.Using the detector response, the instrumental spectra of the tagged neutron device including the neutron generator, LYSO scintillating detector and tetryl/sugar as an object of interrogation were calculated.A good agreement of coefficients of decomposition of experimental and calculated spectra let us validate that Geant4 and TPT2 codes can be used for the reliable numerical simulation of various configurations of the tagged neutron device.
It is well known that the patch test is required for the finite element method (FEM). We may wonder whether we need any special test for the boundary element method (BEM). A sufficient and necessary boundary integral equation method (BIEM) to ensure a unique solution is our concern. In this paper, we revisit this issue for the interior two-dimensional (2-D) elasticity problem and investigate the equivalence of the solution space between the integral equation and the partial differential equation. Based on the degenerate kernel and the eigenfunction expansion, the range deficiency of the integral operator for the solution space in the degenerate-scale problem for the 2-D elasticity in the BIEM is analytically studied. According to the Fichera׳s idea, we enrich the conventional BIEM by adding constants and corresponding constraints. In addition, we introduce the concept of modal participation factor (MPF) to examine whether the adding term of rotation is required for interior simply-connected problems. Finally, two simple examples of degenerate-scale problems containing circular and elliptical boundaries subjected to various boundary conditions of the rigid body translation and rotation for 2-D elasticity problems are demonstrated by using the necessary and sufficient BIEM.
Traditionally, the various forms of compactly supported polynomial based schemes such as finite difference, element, and volume methods were used in the numerical solution of ordinary and partial differential equations (ODEs and PDEs) as well as integral equations (IEs).The primitive computers had limited memory and processing speed.As time progressed, spectral and pseudo-spectral methods that possess exponential or spectral convergence that use tensor products of global expansions of one-dimensional orthonormal functions were used to solve ODEs, PDEs, and IEs.In the past 25 years, radial basis functions (RBFs) that can be either compactly supported or global gained in importance.However, those global RBFs that are C ∞ with shape parameters enjoy exponential convergence.The solution accuracy can be increased by either the spatial resolution or increasing the shape parameters.The performance of C ∞ RBFs has been demonstrated in a wide variety of linear and nonlinear elliptic, hyperbolic and parabolic PDEs and IE applications.Both well posed and ill-posed problems can be solved as well as with defined arithmetic and fuzzy arithmetic, problems with fractional derivatives, etc. Computers with the standard 32 bit chips limit the inherent power of the global RBFs by giving rise to potentially severely ill-conditioned systems.However, procedures using preconditioning and domain decomposition can be used to overcome this limitation.Recently, fast extended precision software enables the use of large shape parameters outperforming compactly supported finite elements and other methods.Also, the Galperin-Zheng weak formulation allows treatment of both well posed and ill-posed problems because it looks for solutions with global, rather than local minima.Presently, meshfree C ∞ RBFs appear to have the potential of solving many important scientific problems in higher dimensions.
For a roll gap of continuous plastic forming, the determination of mechanical parameters of a rolling processing involves a multi-body elasto-plastic frictional contact problem.As one of the three important numerical analytic methods, the Boundary Element Method (BEM) is suitable for the solution of contact problems, and it shows superiority to the Finite Element Method (FEM) and Finite Difference Method (FDM) in these cases.However, when the contact objects become very complicated and large-scale discrete nodes are generated, there are inherent difficulties for the BEM, such as time-consuming problem, low efficiency, and so on.To solve these problems, a kind of Fast Multi-pole Boundary Element Method (FM-BEM) is proposed.Combining the Fast Multipole Method (FMM) with BEM opens up a new computational situation, especially when a high efficient solver named Generalized Minimal Residual Algorithm (GMRES (m)) is introduced.Then a node-to-surface frictional contact model and a programming-iteration algorithm are developed.On a PVM network parallel platform, the cold rolling process of 2030 four-high mill with a width-tothickness ratio reaching 1850 is successfully simulated.The total freedom is 18414 and the CPU time is 42 hours and 24 minutes.For this rolling problem, both the high precision and the high computational efficiency are impossible for other numerical analytic methods.
Wave analysis in rocks is widely used in earthquake engineering and geophysical exploration.Rocks under the ground include pores and cracks which are saturated with pore fluid.Waves which propagate in the rocks are affected by these cracks and pore fluid.Therefore, in the numerical simulation of the rocks, it is necessary to consider the effects of both anisotropy and pore fluid.Biot has been proposed as a mechanical model for describing the behavior of such a rock, and this model forms a foundation for wave analysis of general anisotropic fluid-saturated porous solids.This study aims to develop a boundary element method for wave scattering in general anisotropic fluid-saturated porous solids.Formulation is based on the following two kinds of boundary integral equations: one is those for displacement of the solid skeleton and the other is for fluid pressure.Green's function for wave analysis in general anisotropic fluid-saturated porous solids is derived by using Radon and Fourier transforms in space.Some numerical examples show the validity of our proposed method.
The authors present the formulation of the indirect boundary element method (IBEM) for an axisymmetric Stokes flow with a free surface in the presence of gravity.The formulae of the fundamental solutions of the Stokes equations are found for velocities and tractions in the axisymmetric case.These expressions are written in the cylindrical coordinate system and contain the elliptic integrals of the first and second kind.For the integral equations discretization the constant elements are used.The necessary integrals are evaluated numerically except for the singular ones.The analytical formulae are obtained for them.Two boundaryvalue problems with mixed conditions are considered.The problem of the Poiseuille flow of a viscous fluid in a round tube with the exact solution was calculated to verify the IBEM algorithm and to demonstrate its approximation convergence.Another problem of the cylindrical tube filling by a viscous fluid with a free surface was calculated to prove the IBEM in the case of a moving boundary.The simulation in a steady-state formulation showed that the stationary advancing front shapes exist in both cases when the gravity acts against the flow (Stokes number St<0) and aids the flow (0
