Dimensional Numerical Calculations Research Articles

Optimized designing of generalized electrodes for aluminum/steel resistance spot welding process based on numerical calculation

This work focused on the effects of using different electrode combinations on the welding process and welding quality during aluminum/steel resistance spot welding (RSW) process. The electrodes used during the RSW process can be classified into two catalogues, planar type (P type) and sphere type(S type). An effective two dimensional (2D) numerical calculation model using finite element method (FEM) was developed. In the model, the friction effects between different contact surfaces were seriously considered, and the accuracy and reliability of the model were verified by means of actual welding experiments. Subsequently, the numerical calculation model was used to determine which type of electrode combination was the best one for welding quality by analyzing corresponding RSW processes using four different electrode combination schemes: PP type, SS type, PS type and SP type for upper and lower electrodes. To guarantee scientific nature of the comparisons and analyses, a constant energy regulation method was introduced for each process. The heat energy generation analyses, intermetallic compound formation and growth analyses, and current density analyses were conducted. Combining with actual experiments, the results showed that the welded joint obtained from RSW process using SP type electrode combination scheme had the best comprehensive performance, not only in the double nugget sizes, but also in the deformations of two types of parent metal sheets. In addition, the optimum sizes of the electrodes in this combination were determined through numerical calculations and experiments. Final result showed that the optimum diameter for S type and P type were respectively 9 mm and 60 mm. The work can supply important references for the dissimilar metal RSW process improvement.

Thermal Transmittance around Edge of Vacuum Glazing

The main objective of the calculations thermal performance properties of the edge of vacuum glazing was the quantification of the heat flow around edge of glazing. Additional heat flow around edge of glazing is expressed by means linear thermal transmittance. Linear thermal transmittance of the junction between edge vacuum glazing and wooden frame or wooden-aluminium frame was calculated by using a two dimensional (2D) numerical calculations. Edge sealing of vacuum glazing is assumed by means solder glass with Indium metal strip, so it is metal-based edge seal. In vacuum glazing the edge seal acts as a thermal bridge between the glass sheets. Heat? ows from the glass sheet on the warm side through the edge seal to the sheet on the cold side, not only does it increase the overall thermal performance of the glazing, but also it causes temperature variation (decrease surface temperatures) and stress in the edge region.

Development of one dimensional numerical calculation for unsteady gas-liquid flow in pipes

Development of one dimensional numerical calculation for unsteady gas-liquid flow in pipes

Low temperature delayed recombination and trap tunneling

Delayed recombination of charge carriers at an activator is a significant problem for fast scintillators and is usually associated with thermal effects. However, experimental results have shown that this phenomenon can occur even at the lowest temperatures. We here provide evidence in support of the idea that this is due to quantum tunneling between activator and nearby traps, and provide analytic estimates relating the energy levels and locations of those traps to the observed delayed recombination. Several calculations are devoted to showing that deviations from the simplest estimates in fact do not occur. Moreover, these estimates are consistent with lower dimensional numerical calculations for a physically significant range of trap distances. In two examples involving the activator Pr, the formulas developed are used to give the locations of traps based on likely values of trap energy depth.

Numerical Simulation Analysis of Isolation Pile-Steel Shotcrete Combined Support of Deep Foundation Pit Excavation

The rapid development of deep foundation pit engineering, has become an important part of the urbanization construction, which brings deep excavation support of geotechnical engineering problem research also became a major issue. This paper uses the international well-known geotechnical engineering numerical simulation software FLAC3D, through 3D finite difference numerical calculation and analysis, to better simulation calculation and analysis of deep foundation pit construction site condition, forecast after excavation of the deep foundation pit deformation displacement and dangerous position, analysis of deep foundation pit excavation process isolation pile - steel shotcrete combined support effect. Three dimensional numerical model analysis and calculation in deep foundation pit engineering design and construction scheme optimization with economy is convenient wait for a obvious advantages, can for deep foundation pit excavation of deep foundation pit support design and construction to provide effective basis.

Innovative bi-fluid atomizer inner flow characterization and outer spray diffusion analysis

We developed an atomizer nozzle equipping a medical device used for airborne disinfection of medical rooms. The diffusion technology of the equipment is based on the spraying of fine liquid droplets of disinfectant into the volume to be treated. The liquid phase is expulsed thanks to an air assist atomizer we designed, which originality comes from the geometry we give to the throat of the micro-venturi, inner part of the atomizer nozzle. The micro-venturi throat is deviated of angle of 4° and will permit a homogeneous diffusion.We computed three dimensional numerical calculations of the inner compressible turbulent air flow through the atomizer we designed and compared the results obtained with the ones computed for a symmetrical atomizer. The modeling was done with the CFD codes STARCCM+ and Fluent, choosing the k-omega turbulent model. The modeling has been validated especially by one dimensional analytical calculations and experimental measurements of the mean axial velocity and mass flow rate circulating through the atomizer. Three dimensional numerical calculations show the vertical deviation of the flow at throat level and swirl effect generated by the deviated inner throat of the micro-venturi. These calculations allowed understanding the nature of the spray observed in experimental conditions, and the advantages to use a deviated micro-venturi throat.Indeed, micro bacteriological tests showed that the quality and the effectiveness of the diffusion are enhanced in comparison to equipments with a symmetrical micro-venturi.

Simulated rhythmic growth of targeted single crystal by polymer phase-field model

The novel phase field model with the “polymer characteristic” was established based on a nonconserved spatiotemporal Ginzburg–Landau equation TDGL model. Especially, we related the parameters of crystal temperature with the TDGL model. Moreover, the diffusion equations were discretized according to the diffusion coefficient of every lattice site in various crystal growth faces, and the shape of lattice was selected based on the real proportion of the unit cell dimensions. Spatiotemporal growth of stripped single crystals during isochronous decoration has been investigated theoretically based on this phase field model. Two dimensional numerical calculations were performed to elucidate the faceted single crystal growth including the stripped lozenge-shaped and hexagonal single crystals. Our simulated patterns were in good agreement with the experimental morphologies, and the physical origin of polymer single crystal growth was discussed.

Movements caused by the excavation of tunnels using face pressurized shields — Analysis of monitoring and numerical modeling results

In this paper, monitoring results of two cross tunnel sections are presented. This underground work has been realized for a subway in an urban area (Lyon, France). By comparison with measurements of other projects, it appears that the face instability and the annular gap identified after the shield release are the main sources of short-term settlements.These observations of vertical and horizontal movements during the tunnel excavation by a slurry pressurized tunnel boring machine are then compared with several numerical approaches. The 2D numerical approach uses the concept of volume loss and is applied to each excavation stage. It simulates approximately the observed movements but requires the use of empirical coefficients to represent in two dimensions the three-dimensional problem. The 3D approach considers more directly the physics of the problem and permits to take into account: the slurry pressure at the tunnel face, the shield conicity, the grout injection in the annular void and the grout consolidation. Three dimensional numerical calculations are the most accurate approaches to simulate all the physical processes occurring during tunneling. However this type of model assumes that all the parameters that control the movements induced by the excavation are well known. Due to the complexity of a tunneling boring machine, it is not necessarily the case.

Spatio-temporal changes in seismic velocity associated with the 2000 activity of Miyakejima volcano as inferred from cross-correlation analyses of ambient noise

Miyakejima volcano, Japan, showed strong and interesting volcanic activities in 2000 with the occurrence of dike intrusions, caldera formation and a large amount of gas emission. To understand temporal changes of the volcanic structure associated with this activity, we apply ambient noise correlation analyses to the seismic records of five seismic stations at Miyakejima volcano from July 1999 to December 2002. We calculate cross-correlation functions (CCFs) for eight available station pairs at frequency bands of 0.4–0.8Hz and 0.8–1.6Hz, and retrieve the Rayleigh waves propagating with a group velocity of about 1.0km/s. Comparing CCFs obtained for each day with the reference CCFs that are calculated from a few months of data, we estimate seismic velocity changes before and after the 2000 activity. Results at the two frequency bands show seismic velocity increase and decrease. Shallow structure at the volcanic edifice on the flanks experienced a seismic velocity increase up to 3.3%. On the other hand, the regions located close to the collapsed caldera show a seismic velocity decrease down to 2.3%. To understand the mechanisms that may introduce these seismic velocity increase and decrease, we examine several possible mechanisms of the velocity changes: stress changes due to volcanic pressure sources and caldera formation, and topographic changes. By using the deflation sources previously determined from GPS data, we calculate the stresses at depths of 0km and 1km at the volcano. The results suggest that the seismic velocity increases observed at seismic paths on the volcanic flank are explained by the compression caused by the deflation sources associated with magma activity in 2000. Stress sensitivities of the seismic velocity changes are estimated to be 1.5×10−2 to 2.2×10−2MPa−1 and 4.6×10−3 to 2.4×10−2MPa−1 at frequency bands of 0.4–0.8Hz and 0.8–1.6Hz, respectively, which are in the range of the previously reported results. Our three dimensional numerical calculations on seismic wave propagation show that the seismic velocity decreases observed at seismic paths crossing the collapsed caldera can be explained by topographic changes introduced by a caldera. We further suggest that the seismic velocity decreases detected around the regions close to the caldera may originate from the dilated regions cause by formation of the caldera.

축류 압축기 팁 누설 유동의 비정상 특성에 관한 연구

Three dimensional unsteady numerical calculations were performed to investigate unsteadiness of the tip leakage flow in an axial compressor. The first stage of the four-stage low-speed research axial compressor was examined. Since this compressor has a relatively large tip clearance, the unsteadiness of the tip leakage flow is induced. Through the results from the unsteady calculations, the process of the induced unsteady tip leakage flow was investigated. It was shown that the leakage flow that occurred at a rotor blade tip clearance affected the pressure distribution on the pressure side near the tip of the adjacent blade, thus caused the fluctuation of the pressure difference between the pressure side and suction side. Consequently, the unsteady tip leakage flow was induced at the adjacent rotor blade. The unsteady feature of the tip leakage flow was changed as the operating point was moved. The interface between the tip leakage flow and the main flow only affected the trailing edge region at the design point whereas the interface influenced up to the leading edge at the low flow rate point. As the flow rate decreased, additionally, it was seen that the vortex size of the tip leakage flow increased and the relatively large length scale disturbance occurred. On the other hand, using frequency analysis, it was shown that the unsteadiness was not associated with the rotor speed and was about 40% of the blade passing frequency. This feature was explained in the rotor relative frame of reference, and the frequency decreased as the flow rate decreased.

Coupled Three Dimensional Numerical Calculation of Forces and Stresses on the End Windings of Large Turbo Generators via Integral Formulation

A novel numerical approach to calculate the time evolution of the three dimensional distribution of the magnetic field and forces in the end winding regions of large turbine generators is presented. The proposed approach is based on an integral formulation for nonlinear magnetostatic problems. Its main advantage is the reduction of the discretization to only the conductors and magnetic materials. In this paper the solution of a coupled magnetostructural problem consisting in the calculation of the mechanical stresses and deformations caused by the electrodynamic forces is presented. The analysis is based on a time stepping simulation where the currents are derived from the integration of a lumped parameter model.

Modeling Low Dose Rate Effects in Shallow Trench Isolation Oxides

Low dose rate experiments on field-oxide-field-effect-transistors (FOXFETs) fabricated in a 90 nm CMOS technology indicate that there is a dose rate enhancement factor (EF) associated with radiation-induced degradation. One dimensional (1-D) numerical calculations are used to investigate the key mechanisms responsible for the dose rate dependent buildup of radiation-induced defects in shallow trench isolation (STI) oxides. Calculations of damage EF indicate that oxide thickness, distribution of hole traps and hole capture cross-section affect dose rate sensitivity. The dose rate sensitivity of STI oxides is compared with the sensitivity of bipolar base oxides using model calculations.

OPTIMIZING NANO-OPTICAL ANTENNA FOR THE ENHANCEMENT OF SPONTANEOUS EMISSION

We study the characteristics of nano-optical antenna made of two gold nano-particles by three dimensional numerical calculations in visible and near infrared bands. To carry the computational burden and guarantee the precision and speed of a three dimensional FDTD calculation, adaptive mesh reflnement technology is used. In this paper, we flrst highlight the concrete way of controlling the emitter position and orientation to fulflll the requirements of larger spontaneous emission enhancement. Then, we analyze the far fleld distribution and flnd that the far fleld directivity is strongly in∞uenced by surface plasmon polaritons (SPPs). Choosing the incident wavelength of 600nm, we compute the decay rates and radiant e-ciency as a function of antenna geometry limitations. Next, the particle aspect ratio is optimized, and we obtain that L=R = 4 is the best for our optical-antenna. Furthermore, we present a spectrum analysis. Around 5000 fold spontaneous emission enhancement is successfully achieved. Finally, we flnd a piecewise linearity relationship between the particle length and resonant wavelength.

Simulated morphological landscape of polymer single crystals by phase field model

The novel phase field model with the "polymer characteristic" was established based on a nonconserved spatiotemporal Ginzburg-Landau equation (TDGL model A). Especially, we relate the diffusion equation with the crystal growth faces of polymer single crystals. Namely, the diffusion equations are discretized according to the diffusion coefficient of every lattice site in various crystal growth faces and the shape of lattice is selected based on the real proportion of the unit cell dimensions. Spatiotemporal growth of syndiotactic polypropylene single crystals during isothermal crystallization has been investigated theoretically based on this phase field model. Two dimensional numerical calculations are performed to elucidate the faceted single crystal growth including square, rectangular, lozenge-shaped, and hexagonal single crystals. Our simulated patterns are in good agreement with the experimental morphologies, and the physical origin of polymer single crystal growth is discussed.

Performance Tests of the Subcooling System for the LHD Helical Coils

Performance tests of the subcooling system for the helical coils in the large helical device (LHD) have been performed. For the performance of the system, it is necessary to supply the helical coils with a subcooled helium mass flow of 50 g/s at 3.2 K. From the test results, the performance was able to fulfill the design requirements of the system. Additionally, the coil temperature has been evaluated with the quasi-one dimensional numerical calculation, in which the numerical model simplifying the helical coil configuration is used. The coil temperature would be 3.6 K under a steady heat load of 100 W from outside of the coil case in the system which maintains the above performance, as the result of the calculation.

On the Migration of Protogiant Solid Cores

The increase of computational resources has recently allowed high resolution, three dimensional calculations of planets embedded in gaseous protoplanetary disks. They provide estimates of the planet migration timescale that can be compared to analytical predictions. While these predictions can result in extremely short migration timescales for cores of a few Earth masses, recent numerical calculations have given an unexpected outcome: the torque acting on planets with masses between 5 M_Earth and 20 M_Earth is considerably smaller than the analytic, linear estimate. These findings motivated the present work, which investigates existence and origin of this discrepancy or ``offset'', as we shall call it, by means of two and three dimensional numerical calculations. We show that the offset is indeed physical and arises from the coorbital corotation torque, since (i) it scales with the disk vortensity gradient, (ii) its asymptotic value depends on the disk viscosity, (iii) it is associated to an excess of the horseshoe zone width. We show that the offset corresponds to the onset of non-linearities of the flow around the planet, which alter the streamline topology as the planet mass increases: at low mass the flow non-linearities are confined to the planet's Bondi sphere whereas at larger mass the streamlines display a classical picture reminiscent of the restricted three body problem, with a prograde circumplanetary disk inside a ``Roche lobe''. This behavior is of particular importance for the sub-critical solid cores (M <~ 15 M_Earth) in thin (H/r <~0.06) protoplanetary disks. Their migration could be significantly slowed down, or reversed, in disks with shallow surface density profiles.

Occupation number and fluctuations in the finite-temperature Bose-Hubbard model

We study the occupation numbers and number fluctuations of ultra-cold atoms in deep optical lattices for finite temperatures within the Bose-Hubbard model. Simple analytical expressions for the mean occupation number and number fluctuations are obtained in the weak-hopping regime using an interpolation between results from different perturbation approaches in the Mott-insulator and superfluid phases. These analytical results are compared to exact one dimensional numerical calculations using a finite temperature variant of the Density-Matrix Renormalisation Group (DMRG) method and found to have a high degree of accuracy. We also find very good agreement in the crossover ``thermal'' region. With the present approach the magnitude of number fluctuations under realistic experimental conditions can be estimated and the properties of the finite temperature phase diagram can be studied.

Numerical predictions for the HT-7U divertor

HT-7U is a superconducting tokamak under construction in China. Its magnetically balanced double-null divertor is designed to accommodate the heat load due to a total heating power of 7.5 MW. In order to increase the degree of closure, the divertor structure is designed to consist of vertical targets, tightly fitting side baffles and dome baffles. To predict the details of the scrape-off layer and divertor plasma in different operational regimes and to assess the effects of the divertor geometry, two dimensional numerical calculations with the B2-EIRENE code package have been performed taking into account the real geometry of the HT-7U divertor. The results of the numerical predictions for the HT-7U divertor are to be described in this paper.

Validation of the Eulerian pollution transport model PolTran on the Kincaid data set

The study represents the first performance of the model PolTran on the Kincaid data set. PolTran is a typical representative of the Eulerian models: two dimensional Eulerian advection scheme and numerical calculation of the vertical diffusion. The meteorological pre-processor uses the Kincaid measurements of wind and temperature at 10, 50 and 100 m and provides the dispersion model with wind and turbulence exchange profiles. The model performance is comparable to other models applied to the Model Validation Kit, that could be considered as a good result for a local scale application of a model of Eulerian type.

Magnetohydrodynamic study of electromagnetic separation of nonmetallic inclusions from aluminum melt

Magnetohydrodynamic flow around the nonmetallic inclusions in aluminum melt and the force exerted on the inclusions were explored by dimensional analysis and numerical calculations. Dimensional analysis shows that the invariant \(A = {{JB\rho _f d_p^3 } \over {\mu _f^2 }}\) characterizes the force exerted on the inclusions and the flow intensity of the melt. The physical significance of A is represented as a modified particle Reynolds number that reflects the effects of electromagnetic force. The fluid flow around the particle becomes unstable when A>2×103. It is shown that the neglect of the inertial terms has little effect on the force exerted on the inclusions in the range of A≤1×106. However, the analytical solution of the maximum velocity inside the melt does not apply due to the appearance of turbulent flow in the case of A>2×103.