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Diesel engines are used widely in the world due to their capability of handling high torque and heavy loads efficiently. Fuel injection systems in the diesel engine have different processes that affect the complete burning of fuel in the combustion chamber. These include the primary and secondary breakup of liquid fuel droplets and evaporation. Diesel engines use the air as a working substance only. One of the processes is the evaporation of fuel droplets. Complete evaporation of diesel fuel liquid in the combustion chamber is a prerequisite for complete combustion. Hence evaporation of droplets has an impact on the efficiency of the engine and consequently on the output power and torque. In the present paper evaporation of two different diesel fuels is modeled numerically taking into account the turbulence effects present in the cylinder due to high temperature and pressure using the RANS turbulence model. Evaporation of n-heptane diesel fuel and n-decane is controlled by the numerical model that includes the conservation equations of mass, energy, momentum and species transport. During the evaporation phase heat is transferred to the droplet and due to evaporation from the surface of the droplet, the mass of evaporating droplets is decreased. These two processes are controlled by the equations of the Discrete Phase Model present in the Fluent. Then the results are plotted by varying the droplet diameter and temperature. Results include the decay in droplet diameter, increase in the droplet temperature effect on the velocity of droplet and temperature changes in the cylinder due to evaporation of fuel. There are different parameters which affect the rate of evaporation of fuel droplets inside the engine cylinder of an internal combustion engine. These parameters include the diameter of fuel droplets, initial temperature of fuel droplets, and the temperature inside the cylinder after the compression stroke and surface area of droplets. Small droplets need a short time to evaporate while if the size of droplets is large then evaporation times is also increased. [ABSTRACT FROM AUTHOR]

Correlations for the supersonic jet characteristics, the mean shock cell length and the supersonic core length, have been obtained in terms of the jet parameters. The jet parameters considered in this study are the exit diameter of the nozzle (de), the design Mach number (Me), the nozzle pressure ratio (NPR) and the ratio of specific heats of the medium (γ). The parameters were varied as follows: exit diameters, from 0.5 to 25 mm; Mach number from 1 to 3; the NPR from 2.14 to 35. Initially, working fluid used is cold air and then effect of variation of γ is taken into consideration. The computational model has been validated and then used for all the numerical simulations. A quadratic fit for both characteristics has been obtained which is applicable to any supersonic jet. The correlations developed are valid within the respective ranges of the parameters stated above.

The present study focuses on the feasibility of using fluids, and in particular magnetic fluids, as “Fluid Structures” in designing external appendages for the submerged bodies and propulsive fins as a practical example. After reviewing the literature of the mathematical simulation of magnetic fluids and their applications, the concept of “Fluid Structures” and “Fluid Fins” are briefly introduced. The validation of the numerical solver against analytical solutions is presented and acceptable error of 1.21% up to 2.29% is estimated. Subsequently, the initial shaping of the ferrofluid as an external fluid fin, using three combinations of internal magnetic actuators, is presented which makes the way to the oscillating motion of the obtained fin, by producing a periodically changing magnetic field. It is demonstrated that the shape of the fluid fin is almost the replica of the magnetic field. On the other hand, it is illustrated that a fluid fin with a size under 0.005 m on a circular submerged body of 1cm diameter could produce 0.0158 N force which is a high thrust force relative to the size of the body and the fin. Based on the obtained results, one may conclude that, when a “Fluid Fin” is capable of producing this amount of thrust, other fluid appendages could be scientifically contemplated and practically designed.

Numerical analysis of contact stresses at rotational elements of gerotor pumps with fixed position of shafts axis and with driving rotor acting as internal element, is presented in this paper. The basic characteristics and principles of functioning of this type of pumps are explained and review of researches in the area of numerical methods and developments and design optimizations of those pumps are presented. The basic assumptions, limitation and input values are defined in order to determine maximal stresses, numerical analysis of contact stresses, which are caused by transmitting of torque from internal to external gear. The obtained results of research contact stresses by numerical and analytical method are graphical presentations. The comparisons of results for better understanding of its deviations also were performed.

The investigation of fatigue strength of lotus-type structure with nodular cast iron as a base material using computational model is analysed in present study. The irregular pores distribution in transversal and longitudinal direction, regarding the external loading, is considered in the computational models. The complete fatigue process of analyzed porous structure is then divided into the crack initiation (Ni) and crack propagation (Np) period where the total fatigue life (N) is defined as: N = Ni + Np. The crack initiation period is determined using strain life approach where elastic-plastic numerical analysis is performed to obtain the total strain amplitude in the critical stress fields around the pores. The simplified universal slope method is then used to determine the number of stress cycles, Ni, required for formation of initial cracks. The number of stress cycles, Np, required for crack propagation from initial to the critical crack length is also numerically determined using finite element (FE) models, in the frame of Abaqus computation FEM code. The maximum tensile stress (MTS) criterion is considered when analyzing the crack path inside the porous structure. The performed computational analyses show that stress concentrations around individual pores are higher when external loading is acting in transversal direction in respect to the pore distribution. Therefore, further computational analyses regarding crack initiation and crack propagation period have been done only for pores distribution in transversal direction.

The main purpose of this paper was to develop a selection method of the pneumatic connectors for directional 3/2 valve. The method was established to minimize resistance and loss of pressure in the valve with mounted pneumatic connections for the selected pipe diameters. Directional valve was modeled in 3D CAD software SolidWorks while 3D models of the air connections have been downloaded from the website of one of the leading suppliers of pneumatic. Based on developed solid model the simulation of compressed air flow in the software for computational fluid dynamics Ansys CFX was conducted. The studies using CFD methods helped to determine which air connections best meet the assumptions. Performed numerical tests enable proper selection of items to the newly designed pneumatic systems for a particular group of valves. As a consequence, this translates into a reduction in energy consumption and improve the efficiency of the entire pneumatic complex system.

The present paper reports the results of the study, which was designed to perform a numerical evaluation of dynamic response of a single-storey steel structure model. The experimental model was previously subjected to a number of different earthquake ground motions during an extensive shaking table investigation. The analyzed structure model was considered as a 1-DOF system with lumped parameters, which were determined by conducting free vibration tests. In order to solve the dynamic equation of motion, Newmark's average acceleration method was adopted. The results obtained from the numerical analysis confirm the accuracy in assuming lumped parameters to characterize the analyzed single-storey structure. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing occurred in Hyttejuvet dam in Norway during its first impounding. The water containing soil particle was emerging from the downstream toe of the dam. The water level on the reservoir was then lowered in order to reduce the potential of failure. Further investigation indicated that the clay core configuration was the main caused of the hydraulic fracturing to occur. The clay core material was moraine till soils. Due to the pore water pressure dissipation in the core was very slow, the upstream slope was steepened. This practice increased the arching effect and load transfer between embankment zones. This paper studies the effect of clay core configuration on the rock fill dams against hydraulic fracturing using numerical analysis. The configuration of the Hyttejuvet dam was analyzed using finite element method. Couple analyses between stress & deformation and seepage analyses were used. The stress and deformation during construction was then used as initial stress in the couple analysis with increasing water in the reservoir. When the effective vertical stresses in the upstream face of the clay core was less than the water pressure in the reservoir, hydraulic fracturing will occur. In order to investigate the effects of clay core materials in the analyses, the clay core material was replaced by clay core materials used in 5 major dams in Indonesia The variation of the clay materials were made in the 6 different fine contents. There were 30 variations of the clay core materials were analyzed. The results indicated that hydraulic fracturing was still occurred in the relatively same locations, event the clay core materials were replaced by 30 variations. The analyses results indicated that the configuration of clay core of the rock fill dam strongly influence to the hydraulic fracturing. [ABSTRACT FROM AUTHOR]

The paper presents a practical detailed analysis regarding the use of the classical Preisach hysteresis model, covering all the steps, from measuring the necessary data for the model identification to the implementation in a software code for Computer Aided Design (CAD) in Electrical Engineering. An efficient numerical method is proposed and the hysteresis modeling accuracy is tested on magnetic recording materials. The procedure includes the correction of the experimental data, which are used for the hysteresis model identification, taking into account the demagnetizing effect for the sample that is measured in an open-circuit device (a vibrating sample magnetometer).

The paper discusses deformation of over consolidated soils in Hardening Soil Model in terms of their initial stress state. When carrying out numerical analysis in Plaxis, it has been stated that Hardening Soil Model “remembers” the history of previous loadings. In forming the initial stress state of over consolidated soils with the pre-overburden pressure POP, there occurs the more reliable description of the soil deformation process than with the over consolidation ratio OCR. These findings are valid for odometer conditions and for real geotechnical calculations. [ABSTRACT FROM AUTHOR]

Stability of the unique equilibrium in two mathematical models (based on chemical balance dynamics) of human respiration is examined using numerical methods. Due to the transport delays in the respiratory control system these models are governed by delay differential equations. First, a simplified two-state model with one delay is considered, then a five-state model with four delays (where the application of numerical methods is essential) is investigated. In particular, software is developed to perform linearized stability analysis and simulations of the model equations. Furthermore, the Matlab package DDE-BIFTOOL v.~2.00 is employed to carry out numerical bifurcation analysis. Our main goal is to study the effects of transport delays on the stability of the model equations. Critical values of the transport delays (i.e., where Hopf bifurcations occur) are determined, and stable periodic solutions are found as the delays pass their critical values. The numerical findings are in good agreement with analytic results obtained earlier for the two-state model.

This research project focuses upon the wake behind a two-dimensional blunt-trailing-edged body. Data are obtained numerically by means of a Direct Numerical Simulation code. The body has an elliptical nose followed by a straight section that ends in a blunt base. The present paper is dedicated to the analysis of the onset of the shedding process. The effort is certainly worthwhile, because, in contrast to the case of the circular cylinder, the boundary layers’s separation points are defined and fixed. This allows a better assessment of the vital influence of the boundary layers upon the wake, in a controlled way. This is not the case for the circular cylinder, because, in this instance, the separation points oscillate in relation to a mean position. In the present analysis, the relationship between the onset of shedding Reynolds number, RehK , and the aspect ratio, AR, is obtained.To this end, a wide range of aspect ratios between 3 and 25, was investigated. The result represented by this relationship is a novelty in the literature. Values of RehK are strongly influenced by the aspect ratio for the case of the short cylinders — for which AR is low. After AR about 9, the curve flattens and the influence of the aspect ratio upon the shedding Reynolds number is very mild. Besides, the paper discusses another very important aspect; the overall stability of the pre-shedding laminar bubble at the base of the body. It is important to stress that the latter study relies on the fact that the boundary layers separation points are fixed.

A study of natural convection in water-filled square enclosures whose bottom wall is cooled at 0°C, whereas the top wall is partially or entirely heated at a temperature ranging between 10°C and 30°C is performed numerically through a computational code based on the SIMPLE-C algorithm, assuming temperature-dependent physical properties, for cavity widths in the range 1 cm−10 cm, with the main aim to point out the basic heat and momentum transfer features. [ABSTRACT FROM AUTHOR]

This paper investigates rotational effects on secondary flow in rotating flow passages with sudden expansion or contraction. Consideration is given to laminar flow. The governing boundary-layer equations are discretized by means of a finite-difference technique and numerically solved to determine the distributions of velocity vector under the appropriate boundary conditions. The Reynolds number (Re) and rotation rate are varied to determine their effects on the formation ofsecondary flows. It is disclosed from the study that: (i) when laminar flow is introduced into an axially rotating pipe with expansion, the stretch ofthe secondary flow zone is amplified with an increase in the rotation rate and Re, and (ii) in contrast, for axially rotating pipe flows with contraction, the secondary flow region is somewhat suppressed due to pipe rotation, and the change is slightly affected by the rotation rate and Re. Results may find applications in automotive and rotating hydraulic transmission lines.

Approximation models are frequently used in design optimization in order to reduce computational cost. Many new forms of approximation model have appeared recently, but it is difficult to know which one to choose for the problem at hand. This paper investigates a model selection strategy that estimates the accuracy of all the different approximation models under consideration, so that the most accurate one can be chosen. [ABSTRACT FROM AUTHOR]

A simulation model based on finite-element method is presented to simulate the soil ionization phenomenon around the grounding system. The advantage of the methodology proposed in this study against analytical methods is that both simple and complex grounding systems buried in homogeneous or nonhomogeneous soil taking into account soil breakdown process can be modeled. The suggested modeling is validated by comparison of the calculated results, which are laid out for grounding rod and grounding grid, with experimental tests results and simulations results found in literature. The performance of grounding system, considering the soil ionization effect at high-magnitude current, is also compared with the one not considering the soil ionization effect. [ABSTRACT FROM AUTHOR]

Key developments in computational electromagnetics are proposed. Historical highlights are summarized concentrating on the two main approaches of differential and integral methods. This is seen as timely as a retrospective analysis is needed to minimize duplication and to help settle questions of attribution. [ABSTRACT FROM AUTHOR]

Millimeter plasmas were tailored to play a role as dynamic devices of microwave components, that is, to control electromagnetic wave propagation dynamically on a microstrip line. The generation of millimeter plasmas with their relatively long discharge channel (∼3 mm) was in high-pressure (20-200 torr) Ne, and they were successfully arranged near and on the conductor of microstrip lines. When such a plasma was set perpendicularly to the conductor to form a T junction, a significant reduction of electromagnetic wave transmission along the metal conductor was observed. The reduction rate depended on the discharge current and the number of T junctions. These experimental results are compared with the case of 2 MHz launching for crude electron density measurements and the numerical results of propagating electric fields in a two-dimensional model. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the buckling and post-buckling behaviour of unidirectional and cross-ply composite laminated plates with multiple delaminations has been studied. Finite elements analyses have been performed, using a linear buckling model, based on the solution of the eigenvalues problem, and a non-linear one, based on an incremental-iterative method. With non-linear method large displacements have been taken into account and also contact constraints between sublaminates have been added to avoid their interpenetration. It has been found that both delamination length and position and stacking sequence of the plies influence the critical load of the plate; furthermore, linear and non-linear buckling models are not always in perfect agreement. [Copyright &y& Elsevier]

We present a new method for solving asset pricing models, which yields an analytic price-dividend function of one state variable. To illustrate our method we give a detailed analysis of Abel's asset pricing model. A function is analytic in an open interval if it can be represented as a convergent power series near every point of that interval. In addition to allowing us to solve for the exact equilibrium price-dividend function, the analyticity property also lets us assess the accuracy of any numerical solution procedure used in the asset pricing literature. [ABSTRACT FROM AUTHOR]

We analyze the error in typical moment method scattering solutions for smooth cylindrical geometries and TM-polarized fields. We consider the magnetic field integral equation (MFIE), electric field integral equation (EFIE), and combined field integral equation. To quantify the impact of mesh element size, approximate integration of moment matrix elements, and geometrical discretization error on the accuracy of computed surface currents and scattering amplitudes, we derive error estimates analytically for the circular cylinder. For pulse functions and point testing, current and scattering amplitude errors are generally second order in the mesh element width. The convergence rate worsens to first order if low-order numerical quadrature is used to evaluate moment matrix elements with the EFIE formulation, or if a flat-facet mesh is employed with the MFIE formulation. Third-order convergence is also possible in some special cases. These results for the circular cylinder are empirically compared to computed error values for other smooth scatterer geometries. Convergence rates with respect to mesh refinement agree, but scatterers with regions of high curvature exhibit increased absolute error. [ABSTRACT FROM AUTHOR]

A numerical method is proposed to analyze the electromagnetic behavior of systems that include high-temperature superconductors. The algorithm uses the finite-element method and the critical-state model, and it solves two-dimensional and axially symmetric problems that include superconductors and other materials. The main advantages of the algorithm are its speed, its robustness, and its ease of coupling with circuit equations. This method is used to analyze two different systems: 1) Magnet-Superconductor levitation system--the levitation forces are calculated. In order to validate the model, experimental results of such a system are obtained and compared with simulation results. 2) Nine-wire superconducting cable. Parallel and series-type configurations of the current driven in the wires are analyzed. Hysteresis ac losses are also calculated and compared for both scenarios. [ABSTRACT FROM AUTHOR]

We consider the solution of the time-harmonic Maxwell's equations inside a bounded domain on the boundary of which various conditions are prescribed, including a perfectly matched layer (PML) termination. This problem arises when, e.g., the electromagnetic fields scattered from an inhomogeneous penetrable structure are computed by using a hybrid finite element (FE) and integral equation method in conjunction with a domain decomposition technique. In each of the subdomains, the discretization process leads to a linear system, and an iterative solver may be advantageously utilized when the number of unknowns is large. In this case, the number of iterations and, hence, the computational time required to achieve a given numerical accuracy are known to increase with the condition number κ of the FE matrix. In this paper, we attempt to draw the rules that govern the behavior of κ. To this effect, an eigenmodes technique is proposed that allows to dissociate the influence of the FE mesh and FE basis functions from the one of the actual physical cavity. Numerical examples are provided for one- and three-dimensional problems that illustrate the results so obtained. [ABSTRACT FROM AUTHOR]

A high-order locally corrected Nyström (LCN) method employing the mixed-order basis functions proposed by Çaltşkan and Peterson is presented for the electromagnetic scattering by targets composed of both dielectric and conducting bodies An integral operator based on a combined field formulation for conducting surfaces and a Muller formulation for dielectric surfaces is used. It is found that for general scattering objects, mixed-order basis functions accelerate the convergence of the LCN solution, can eliminate spurious charges, and can significantly reduce the condition number of the impedance matrix. [ABSTRACT FROM AUTHOR]

This paper describes a three-dimensional integral method that models electromagnetic phenomena taking place during inductive melting. The method is well suited to inductive systems undergoing sinusoidal excitation at midrange or high frequencies. Under these conditions, only the surfaces of the conductors need to be meshed. The unknowns of the model are current density and scalar electrical potential. Power density, electromagnetic forces, and electrical impedance can easily be derived. Comparisons between numerical results and measurements confirm the accuracy of the model. [ABSTRACT FROM AUTHOR]