Precise Numerical Simulations Research Articles

Determining Material Data for Welding Simulation of Presshardened Steel

In automotive body-in-white production, presshardened 22MnB5 steel is the most widely used ultra-high-strength steel grade. Welding is the most important faying technique for this steel type, as other faying technologies often cannot deliver the same strength-to-cost ratio. In order to conduct precise numerical simulations of the welding process, flow stress curves and thermophysical properties from room temperature up to the melting point are required. Sheet metal parts made out of 22MnB5 are welded in a presshardened, that is, martensitic state. On the contrary, only flow stress curves for soft annealed or austenitized 22MnB5 are available in the literature. Available physical material data does not cover the required temperature range or is not available at all. This work provides experimentally determined hot-flow stress curves for rapid heating of 22MnB5 from the martensitic state. The data is complemented by a comprehensive set of thermophysical data of 22MnB5 between room temperature and melting. Materials simulation methods as well as a critical literature review were employed to obtain sound thermophysical data. A comparison of the numerically computed nugget growth curve in spot welding with experimental welding results ensures the validity of the hot-flow stress curves and thermophysical data presented.

Unified constitutive model of aluminum alloy 2219 at elevated temperature

Exploring the hot deformation behaviors of materials is essential for the precise numerical simulation of hot forming processes. In this study, the hot tensile deformation behaviors of aluminum alloy 2219-O are studied by uniaxial tensile tests at the temperature range of 473-673K and stain rate range of 0.001-0.1s−1. Mechanism-based unified constitutive equations are developed to model the grain size, recovery and dislocation density. The results show that under the tested deformation conditions, the flow stress decreases with the increase of deformation temperature or the decrease of strain rate. Additionally, the increasing of elongations to fracture in this study indicates that the elevated temperature can improve the plasticity of AA2219-O. Moreover, the flow stresses predicted by the developed unified constitutive model well agree with the experimental data, which indicate that the developed constitutive model is valid.

Pipeline Damage Detection Using Piezoceramic Transducers: Numerical Analyses with Experimental Validation.

This paper aims to set up a finite element model using piezoelectric elements to realize pipeline structure damage identification analysis. Ultrasonic guided wave propagation characteristics and damage identification of pipeline structures are analyzed by the ABAQUS software. The pulse-echo method using an L(0, 2) mode impulse guided wave with a central frequency of 70 kHz is applied to evaluate different size circumferential cracks. An experiment was performed for the validation of the numerical analysis results. Both of the results show that the proposed FEM model with piezoelectric elements can efficiently reveal the dynamic behaviors, which can be used in much more precise numerical simulations than the equivalent dynamic displacement loading method.

Shot Peening Numerical Simulation of Aircraft Aluminum Alloy Structure

After shot peening, the 7050 aluminum alloy has good anti-fatigue and anti-stress corrosion properties. In the shot peening process, the pellet collides with target material randomly, and generated residual stress distribution on the target material surface, which has great significance to improve material property. In this paper, a simplified numerical simulation model of shot peening was established. The influence of pellet collision velocity, pellet collision position and pellet collision time interval on the residual stress of shot peening was studied, which is simulated by the ANSYS/LS-DYNA software. The analysis results show that different velocity, different positions and different time intervals have great influence on the residual stress after shot peening. Comparing with the numerical simulation results based on Kriging model, the accuracy of the simulation results in this paper was verified. This study provides a reference for the optimization of the shot peening process, and makes an effective exploration for the precise shot peening numerical simulation.

Spectra of turbulently advected scalars that have small Schmidt number

Exact statistical equations (ESEs) allow precise direct numerical simulation (DNS) quantification. ESEs reveal quantities determining deviations from asymptotic relationships. Here, ESEs for small Schmidt-number scalar advection, in general and asymptotic cases, are obtained and compared with DNSs.

Proper Simulation of Chemical-EOR Pilots - A Real Case Study

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 179659, “Proper Simulation of Chemical-EOR Pilots—A Real Case Study,” by Nariman Fathi Najafabadi, SPE, and Adwait Chawathe, SPE, Chevron, prepared for the 2016 SPE Improved Oil Recovery Conference, Tulsa, 11–13 April. The paper has not been peer reviewed. A critical step in proper design and optimization of any chemical-enhanced-oil-recovery (CEOR) process is appropriate and precise numerical simulations. Addition of chemical species to the material-balance equations, along with finer resolution requirements for CEOR simulations compared with waterfloods, often makes it impractical to run full-field CEOR simulations to the required accuracy. Sector models, by their definition, are naturally suited for modeling of pilots. This paper presents a case study for appropriate simulation of a CEOR pilot. Introduction Chemical flooding (polymer flooding, surfactant/polymer flooding, and alkali/surfactant/polymer flooding) has improved significantly over the past decade because of vast research efforts to find practical solutions to specific field applications, improvements in the manufacturing and synthesis of new chemicals, field trials, and implementations by the industry. Because of the complexity of CEOR and the inherent uncertainties regarding success of a particular CEOR process, extensive evaluations are required before decisions about full-field implementation can be made. Numerical simulations are critical in CEOR evaluation and provide a realistic performance estimate, assuming that the underlying Earth model is reliable and appropriately calibrated. Usually, chemical floods are performed on candidate fields with a successful water flood history, but CEOR simulations are more complex and challenging compared with water flood modeling and history matching. Sector-Model Generation For the subject asset, which is a brown-field, the primary requirement in CEOR modeling is a representative, quality-controlled waterflood-history-matched full-field (or sector) model. Such a model should replicate the field performance (pressures and flow rates), at least on an overall basis and, preferentially, on a well-by-well basis. The model used for this study had high well density, was sufficiently reliable, and was used routinely for field development and performance prediction. The paper demonstrates the preparation and use of a sector model from this readily available waterflood full-field model for a polymer-flood pilot area. The area of interest (AOI) for the pilot should be selected during an alternatives-analysis phase by a multifunctional team of field engineers and scientists and CEOR subject-matter experts after a project-framing exercise. In this case, this area is a seven-spot pattern containing a central injector and six surrounding producers. This is a small area compared with the full-field model. A local-grid-refinement (LGR) option was considered to create a sufficiently fine grid for CEOR simulation, but the resulting model was still deemed practically prohibitive.

打撃式油圧さく岩機による穿孔過程

Rock drills were developed about two hundred years ago, and hydraulic percussion rock drills are about half-century old. Performance and efficiency of rock drills have been increased by a number of researchers and engineers. Percussion energy was dramatically increased with changing the power source from pneumatic to hydraulic pressures; rods and rod joints were improved to endure the high percussion energy; carbide button bits were developed for hard rock drilling. This paper reviewed the previous studies and future issues on the drilling processes with hydraulic percussion rock drills. Studies on the stress wave propagation in rods and rod joints were based on theoretical and graphical methods and recently on numerical simulation. Studies on the interaction between a button bit and rock included crack propagation in rock, force-penetration relationship during drilling, and bit wear. Studies on the factors affecting drilling efficiency and drilling rate made a transition from simple to precise numerical simulations. Finally, important future issues were presented for the further progress of hydraulic percussion rock drills.

Effects of the Hygrothermal Conditions on the Fracture Energy of the Concrete

The scenario of a severe accident in the containment building of a nuclear plant results in an increase in pressure, temperature and relative humidity that can reach respectively 5 bars, 140 °C and the saturation of water vapour. As well as the regulatory calculations, accurate knowledge of the thermal and mechanical behaviour of materials and more specifically of concrete is required to carry out more precise numerical simulations. Our study aims to investigate the mechanical behaviour of concrete under homogeneous conditions of moisture and temperature. An experimental apparatus was designed in order to assess the evolutions of the fracture energy of concrete. Different temperature levels up to a maximum of 110 °C and at different values of the controlled moisture content were investigated. The equipment was used to perform DCT (Disk-shape Compact Tension) tests at 30, 90 and 110 °C. Five levels of degree of liquid water saturation (Sw) were investigated for each temperature level.

Gravitational waveforms from binary neutron star mergers with high-order weighted-essentially-nonoscillatory schemes in numerical relativity

The theoretical modeling of gravitational waveforms from binary neutron star mergers requires precise numerical relativity simulations. Assessing convergence of the numerical data and building the error budget is currently challenging due to the low accuracy of general-relativistic hydrodynamics schemes and to the grid resolutions that can be employed in $(3+1)$-dimensional simulations. In this work, we explore the use of high-order weighted-essentially-nonoscillatory (WENO) schemes in neutron star merger simulations and investigate the accuracy of the waveforms obtained with such methods. We find that high-order WENO schemes can be robustly employed for simulating the inspiral-merger phase and they significantly improve the assessment of the waveform's error budget with respect to finite-volume methods. High-order WENO schemes can be thus efficiently used for high-quality waveforms production, also in future large-scale investigations of the binary parameter space.

Analytical model for transverse mode conversion at all-optically induced, transient long-period gratings: from continuous-wave to ultrafast

Transverse mode conversion at an index grating, all-optically induced by multi-mode interference and the optical Kerr effect, is commonly studied by numerical simulations relying on either multi-mode implementations of the generalized nonlinear Schrodinger equation or beam propagation methods. Here, we present and discuss an analytical model describing the directed energy exchange between two probe modes moderated by two control modes. The analytical model can be derived in a four-wave mixing representation as well as in a material representation in analogy to the different numerical approaches demonstrating their equivalence. The analytical nature of the model is used to provide general insight into the conversion process in dependence on phase mismatch as well as induced coupling strength. While being a continuous-wave model, the applicability of the model for mode conversion using ultrashort pulses is discussed and guidelines for using the model as a first estimate for experiments or for more precise but time-consuming numerical simulations are given.

Investigation of the Anisotropic Strain Rate Dependency of AA5182-O and DC04 for Different Stress States

A more precise numerical simulation of sheet metal forming processes leads to a demand for more detailed material characterisation. Hence, it is advisable to consider the strain rate reliant and anisotropic material characteristics. There are various common sheet metals that have beside of an anisotropic a more or less distinct strain rate dependent material behaviour. With regard to these material characteristics, for a more detailed numerical prediction of a sheet metal forming process, it is necessary to include the aspect of deformation velocity. A characterisation of the strain rate dependent hardening behaviour for the two common sheet metals DC04 and AA5182-O is performed under tensile as well as shear load and their behaviour is compared after v. Mises equivalent stress and strain. The two strain rate models from Norton-Hoff and Tanimura are calibrated on basis of the experimental data and their applicability for the investigated materials is evaluated. The calibration of the strain rate sensitive models showed for both materials a very good comparability, respectively.

High-energy electromagnetic cascades in extragalactic space: Physics and features

Using the analytic modeling of the electromagnetic cascades compared with more precise numerical simulations we describe the physical properties of electromagnetic cascades developing in the universe on CMB and EBL background radiations. A cascade is initiated by very high energy photon or electron and the remnant photons at large distance have two-component energy spectrum, $\propto E^{-2}$ ($\propto E^{-1.9}$ in numerical simulations) produced at cascade multiplication stage, and $\propto E^{-3/2}$ from Inverse Compton electron cooling at low energies. The most noticeable property of the cascade spectrum in analytic modeling is 'strong universality', which includes the standard energy spectrum and the energy density of the cascade $\omega_{\rm cas}$ as its only numerical parameter. Using numerical simulations of the cascade spectrum and comparing it with recent Fermi LAT spectrum we obtained the upper limit on $\omega_{\rm cas}$ stronger than in previous works. The new feature of the analysis is "$E_{\max}$ rule". We investigate the dependence of $\omega_{\rm cas}$ on the distribution of sources, distinguishing two cases of universality: the strong and weak ones.

Precision comparison of the power spectrum in the EFTofLSS with simulations

We study the prediction of the dark matter power spectrum at two-loop order in the Effective Field Theory of Large Scale Structures (EFTofLSS) using high precision numerical simulations. In our universe, short distance non-linear fluctuations, not under perturbative control, affect long distance fluctuations through an effective stress tensor that needs to be parametrized in terms of counterterms that are functions of the long distance fluctuating fields. We find that at two-loop order it is necessary to include three counterterms: a linear term in the overdensity, δ, a quadratic term, δ2, and a higher derivative term, ∂2δ. After the inclusion of these three terms, the EFTofLSS at two-loop order matches simulation data up to k ≃ 0.34 h Mpc−1 at redshift z = 0, up to k ≃ 0.55 h Mpc−1 at z = 1, and up to k ≃ 1.1 h Mpc−1 at z = 2. At these wavenumbers, the cosmic variance of the simulation is at least as small as 10−3, providing for the first time a high precision comparison between theory and data. The actual reach of the theory is affected by theoretical uncertainties associated to not having included higher order terms in perturbation theory, for which we provide an estimate, and by potentially overfitting the data, which we also try to address. Since in the EFTofLSS the coupling constants associated with the counterterms are unknown functions of time, we show how a simple parametrization gives a sensible description of their time-dependence. Overall, the k-reach of the EFTofLSS is much larger than previous analytical techniques, showing that the amount of cosmological information amenable to high-precision analytical control might be much larger than previously believed.

Comment on ‘Absolute negative mobility in a one-dimensional overdamped system’

Recently Ru-Yin Chen et al. (Phys. Lett. A 379 (2015) 2169–2173) presented results on the absolute negative mobility (ANM) in a one-dimensional overdamped system and claimed that a new minimal model of ANM was proposed. We suggest that the authors introduced a mistake in their calculations. Then we perform a precise numerical simulation of the corresponding Langevin equation to show that the ANM phenomenon does not occur in the considered system.

Fundamental mechanical behaviors of dental restorative materials resin composites due to compressive and flexural loading and internal damage evaluation

Development of internal damage within resin composites was evaluated under compressive loading in order to predict crack initiation and fracture. Moreover, three-point bending tests were also carried out in order to clarify mechanical behavior and fracture under tensile stress state in comparison with those under compressive stress state. Both of them were conducted for the purpose of obtaining data to formulate constitutive equations for resin composites and to implement precise numerical simulation. Columnar specimens for compression tests and square pole specimens for three-point bending tests were prepared by using clinical resin composites. In compression tests, loading–unloading (or –reloading) was given to columnar specimens and Young’s modulus was evaluated by the gradient of stress–strain curves under unloading. Internal damage was evaluated from the variation of Young’s modulus as a scalar damage variable based on the continuum damage mechanics. The variation of apparent density and residual strain at vanished stress were also discussed in association with the development of internal damage. Accumulation of internal damage was found on the stress–strain curve under loading–unloading–reloading in comparison with the curve under monotonic loading. On the other hand, in three-point bending tests, dependence of stress–strain curves on light curing time and strain rate was clarified. Since compression tests have been carried out under similar experimental conditions by authors so far, mechanical behaviors of resin composites under tensile stress state were discussed in comparison with those under compressive stress state. Brittleness under tensile stress state was indicated in comparison with compressive stress state.

Numerical approach based design of centrifugal pump volute

Centrifugal pumps are widely used in many industrial sectors. However the experimental characterisation processus of pumps is very complex and expensive task due to the large number of geometrical parameters in consideration. The complexity is increased due to their elaboration by molding process dicted by the pump components (volute, wheel, and rotor). It is then worthful to minimizing the costs associated to design and manufacturing processes of pumps. Ever though the tremendous efforts made in this domain the experimentation does not represent the most reliable solution. A precise numerical simulation of complex liquid flow in centrifugal pump can be rapid and reliable solution for improving the pump performance. A large number of numerical or experimental researches are focussed on rotor dimensurring of radial volute. In this study three different forms of tangential volutes (circular, Bezier and trapezoidal) with same dimensions and the same rotor are used. The behaviour of the fluid either Newtonian or Non-Newtonian is taken into consideration. The objective of the study is to know the effect of the form of the volute and nature of the fluid on the properties of the internal fluid flow. Finite volume method (FVM) is used under the commercial code Ansys-CFX. The numerical simulation is carried out to study the velocity distribution and pressure field distribution in the three volutes. The nature of Non-Newtonian fluid behaviour is integrated in the code via a subprogram. The turbulence of flows in the centrifugal pump is taken into account using k-Ɛ model. The obtain results show that the form of the volute and the nature of fluid flow have a sensitive effects on the velocity, the pressure as well as on the shear stress. DOI: http://dx.doi.org/10.5755/j01.mech.21.4.8930

Optimizing Tire Vertical Stiffness Based on Ride, Handling, Performance, and Fuel Consumption Criteria

Researchers mostly focus on the role of suspension system characteristics on vehicle dynamics. However tire characteristics are also influential on the vehicle dynamics behavior. In this paper, the effects of tire vertical stiffness on the ride, handling, accelerating/braking performance, and fuel consumption of a vehicle are analytically investigated. Furthermore, a method for determining the optimum vertical stiffness of tires is presented. For these purposes, first an appropriate mathematical criterion for the ride, handling, accelerating/braking performance, and fuel consumption is developed. Next, to achieve the optimum tire characteristic, a performance index, which contains all of the above-mentioned criteria, is defined and optimized. In the proposed performance index, the tire vertical stiffness is a design variable and its optimization provides a compromise among ride, handling, accelerating/braking performance, and fuel consumption of the vehicle. Last, the analytical optimization results are confirmed by performing precise numerical simulations.

The Present Situation and Developing Trends of Hot Closed-Die Forging

Due to its advantages including high quality of the forging parts and low production costs,hot closed-die forging (HCDF) play an essential role in the machine building industry. However, in recent decades, the pace of its development is gradually slowing down. In the hope of drawing up some new ideas about future development of the HCDF, this paper presents a brief overview of it. This study roughly prospects several potential research issues of the HCDF. Some new research fields such as precision forging, combined forging and numerical simulation have been shown. Challenges and possible response to them have been discussed.

Asymmetric Lévy flights in the presence of absorbing boundaries

We consider a one-dimensional asymmetric random walk whose jumps are identical, independent and drawn from a distribution ϕ(η) displaying asymmetric power-law tails (i.e. ϕ(η) ∼ c/ηα+1 for large positive jumps and ϕ(η) ∼ c/(γ|η|α+1) for large negative jumps, with 0 < α < 2). In the absence of boundaries and after a large number of steps n, the probability density function (PDF) of the walker position, xn, converges to an asymmetric Lévy stable law of stability index α and skewness parameter β = (γ − 1)/(γ + 1). In particular, the right tail of this PDF decays as . Much less is known when the walker is confined, or partially confined, in a region of the space. In this paper we first study the case of a walker constrained to move on the positive semi-axis and absorbed once it changes sign. In this case, the persistence exponent θ+, which characterizes the algebraic large time decay of the survival probability, can be computed exactly and we show that, if θ+ < 1, the tail of the PDF of the walker position decays as . This last result can be generalized in higher dimensions such as a two-dimensional random walker performing Lévy stable jumps and confined in a wedge with absorbing walls. Our results are corroborated by precise numerical simulations.

Finite-Temperature Behavior of Glueballs in Lattice Gauge Theories

We propose a new method to compute glueball masses in finite temperature lattice gauge theory which at low temperature is fully compatible with the known zero temperature results and as the temperature increases leads to a glueball spectrum which vanishes at the deconfinement transition. We show that this definition is consistent with the Isgur-Paton model and with the expected contribution of the glueball spectrum to various thermodynamic quantities at finite temperature. We test our proposal with a set of high precision numerical simulations in the 3D gauge Ising model and find a good agreement with our predictions.