Results Of Numerical Prediction Research Articles

SIMULATION OF ELASTOPLASTIC FRACTURE OF A CENTER CRACKED PLATE

The strength of a square plate with a central crack at normal separation was studied within the framework of the Neuber–Novozhilov approach using a modified Leonov–Panasyuk–Dugdale model using an additional parameter, the diameter of the plasticity zone (width of the pre-fracture zone). As a model of a deformable solid body, a model of an ideal elastic-plastic material with a limiting relative elongation was chosen. This class of materials includes, for example, low-alloy steels used in structures operating at temperatures below the cold brittleness threshold. In the presence of a singular feature in the stress field in the vicinity of the crack tip, it is proposed to use a two-parameter discrete integral strength criterion. The deformation fracture criterion is formulated at the tip of a real crack, and the force criterion for normal stresses, taking into account averaging, is formulated at the tip of a model crack. The lengths of real and model cracks differ by the length of the pre-fracture zone. The constitutive equations of the analytical model are analyzed in detail depending on the characteristic linear dimension of the material structure. Simple formulas suitable for verification calculations for the critical breaking load and the length of the pre-fracture zone are obtained. Numerical modeling of the propagation of plasticity zones in square plates under quasi-static loading has been performed. In the numerical model, the updated Lagrangian formulation of the equations of mechanics of a deformable solid body is used, which is most preferable for modeling the deformation of bodies made of an elastic-plastic material at large deformation. The plastic zone in the vicinity of the crack tip is obtained by the finite element method. The results of analytical and numerical prediction of plate fracture under plane deformation are compared. It is shown that the results of numerical experiments are in good agreement with the results of calculations using the analytical model of fracture of materials with a structure under normal separation. Diagrams of quasi-brittle and quasi-ductile fracture of a structured plate are constructed.

High‐performance metallic materials for applications in infrastructure and energy sectors

AbstractHigh performance steels, such as stainless steels, have many desirable characteristics that warrant their use in various sectors, including infrastructure and energy applications. This paper is concerned with two of such applications: (i) the use of stainless steel for large‐scale liquid hydrogen storage tanks, which is a requirement for the future hydrogen energy network, and (ii) the use of stainless steel in steel‐framed buildings to enhance their robustness under extreme loading conditions. The paper begins with a discussion of the technical challenges associated with the material behaviour of stainless steel storage tanks under extreme temperature and pressure conditions. It presents and discusses the results of a pilot experimental programme that investigates the mechanical behaviour of stainless steel 304 L material under cryogenic 20 k hydrogen environment. Next, to demonstrate the benefits of the strategic use of stainless steel in the key connection parts of steel‐framed structures, the paper presents the setup for a new test programme that investigates the behaviour of stainless steel beam‐to‐column connections, using A4‐70 bolts and EN1.4301 plates, under a column removal scenario. The numerical modelling prediction results of the specimens are presented, and comparisons with carbon steel counterparts are made and discussed.

Numerical prediction of surface morphology and roughness in rotary ultrasonic face grinding SiO2f/SiO2 composite

The SiO2f/SiO2 ceramic matrix composite has been applied to fabricate high-performance radar radome because of its good wave transmission and mechanical property. The machined surface morphology and roughness of SiO2f/SiO2 ceramic matrix composite have an important impact on the service performance of radome products. This paper presented a numerical model to predict surface morphology for grinding of SiO2f/SiO2 composite. The prediction model was based on finite element method (FEM). Both conventional face grinding (CFG) and rotary ultrasonic face grinding (RUFG) of SiO2f/SiO2 composite were FEM simulated by integrating the microstructure of SiO2f/SiO2, the constitutive as well as failure mechanism of fiber/matrix, and the coupling grinding effect of multiple abrasive grits. The machined surface morphology was predicted by extracting node coordinates on simulated ground surface. The numerical prediction results were quantitatively validated using experimental results of ground surface roughness Sa. The application of the proposed prediction model not only elucidated the influence law of fiber orientations and machining parameters on ground surface quality but also revealed the different shear failure modes of SiO2 fiber during grinding process. The ground surface of SiO2f/SiO2 was deteriorated by uncut-off debonding fibers and fiber peeling pits. Ultrasonic-assisted vibration was beneficial to improve ground surface quality by force reduction and hammering effect caused by intermittent machining. However, the key prerequisite for the ultrasonic hammering effect to exert its process advantage was that the ultrasonic hammering energy could effectively fracture fibers on the ground surface rather than being absorbed by crack propagation at the fiber–matrix interface.

Material removal characteristics in submerged pulsating air jet polishing process

In this paper, the material removal characteristics and mechanism of submerged pulsating air jet polishing (SPAJP) process are investigated by polishing experiment on K9 glass and computational fluid dynamics simulation. The experimental results show SPAJP can etch almost perfect Gaussian footprints with high stability. Under comparable condition, SPAJP achieves nearly 300 times higher material removal rate (3.0 × 10−3 mm3/min) than that of traditional fluid jet polishing (FJP) (9.9 × 10−6 mm3/min) at the cost of a moderate degradation in processed surface roughness from Sa 3.97 nm by FJP to Sa 20.49 nm by SPAJP. Jet evolution, abrasive behavior and material removal mechanism in SPAJP are clarified by numerical modeling and experimental jet observation. It is found that SPAJP relies on jet instability of the submerged airflow beam to entrain and accelerate abrasive particles in the slurry, achieving stable and efficient polishing removal on the workpiece surface. To explore the potential of the process for deterministic polishing, an array structure surface is then designed and polished by SPAJP. The processing results are consistent with numerical prediction results, indicating that the new process has good material removal controllability which makes it applicable to deterministic polishing. This study highlights the possibility of using SPAJP to produce ultra-precise surfaces in terms of form control or fabricate high precision optical components in a more efficient and convenient manner.

Hybrid Forecasting of Wind for Air Pollution Dispersion over Complex Terrain

In case of an unplanned emission event from a nuclear power plant, the local population can be protected more efficiently when valid atmospheric dispersion model results are available. Atmospheric dispersion models use local meteorological variables as inputs. When atmospheric dispersion in the future is being predicted, a forecast of the local meteorological variables is needed. The most important variable in atmospheric dispersion modelling is wind, and accurately predicting ground level winds presents a challenge to numerical weather prediction models. We therefore develop hybrid models for forecasting local ground level wind at a single location where the terrain is complex and the average wind is weak and fluctuating. Wind speed and direction are modelled as west-east and south-north wind components. Each model is composed of a numerical weather prediction model and a Gaussian process statistical model that uses numerical weather predictions as some of its inputs and is trained on historical data to predict the output component. The most advanced Gaussian process models studied are of Gaussian process nonlinear autoregressive model with exogenous input (GPNARX) type. In addition to numerical weather predictions, they also use local meteorological variables, including the output variable, as their inputs. Numerical weather prediction results based on large scale information and fundamental knowledge of the system are thus supplemented by local measurements that better reflect the effects of local topography and land use. The models are tested by prediction and simulation. The wind components predicted by more advanced models are more accurate than raw or post-processed numerical weather prediction results. As an example, a model predicting 2D wind vector 1.5 h in advance achieves a NRMSE of 0.214 if it uses all the immediately available information. This is better than both the persistence model with NRMSE of 0.188 and post-processed NWP with NRMSE of 0.164. This demonstrates that hybrid modelling provides the best weather information for short-term and medium-term atmospheric dispersion forecasting. While the method is motivated by nuclear emission sources, it could also be applied to other pollution.

Effects of Upstream Step Geometries on Endwall Film Cooling and Phantom Cooling Performances of a Transonic Turbine Vane

Abstract In gas turbine engines, the endwall misalignment (step geometries with various step heights) commonly exists between the combustor exit and the first nozzle guide vane endwall, due to assembly error, metal corrosion, and thermal expansion. The step geometries affect the secondary flow field near the endwall and coolant flow behavior, thereby leading to a significant variation in endwall film cooling, vane surface phantom cooling, and vane passage aerodynamic performances. This paper presents a detailed experimental and numerical study on endwall film cooling and vane pressure side surface phantom cooling at simulated gas turbine operating conditions (high inlet freestream turbulence level of 16%, exit Mach number of 0.85, and exit Reynolds number of 1.7 × 106). The experimental measurements were conducted at Virginia Tech’s transonic blowdown wind tunnel for two configurations: baseline cascade (HR = 0) and forward-facing step geometry (HR = −0.1). The numerical predictions were performed by solving the steady-state Reynolds-averaged Navier Stokes (RANS) with realizable k–ɛ turbulence model. Based on a double coolant temperature model, a novel numerical method for the predictions of adiabatic wall film cooling effectiveness was proposed. The qualitative and quantitative comparisons between the numerical prediction results and experimental data are provided in this paper. The results indicate that this method can reliably predict endwall film cooling distributions and vane pressure side surface phantom cooling distributions, and significantly reduce (more than 50%) numerical prediction errors. The effects of upstream step geometries were numerically studied at the design flow conditions (BR = 2.5, DR = 1.2), by quantizing the endwall film cooling effectiveness, endwall net heat flux reduction (NHFR), vane pressure side surface phantom cooling effectiveness, and total pressure loss coefficients (TPLC) for various upstream step heights: three forward-facing step heights (HR = −0.16, −0.1, and −0.06), a baseline cascade (HR = 0), and four backward-facing step heights (HR = 0.06, 0.1, 0.136, and 0.2). Results show the upstream forward-facing step geometry is beneficial for enhancing endwall film cooling (maximum enhancement level of 15%), endwall net heat flux reduction (maximum enhancement level of 10%), and vane pressure side surface phantom cooling (maximum enhancement level of 66.7%). Nevertheless, the upstream backward-facing step geometry is pernicious to the endwall film cooling, endwall heat flux reduction, and phantom cooling, and these pernicious effects have sharply deteriorated when the upstream step height is larger than a critical value (HR > 0.136). To be specific, the film cooling effectiveness (from 30% to 80%), net heat flux reduction (up to 78%), and phantom cooling effectiveness (completely disappeared) significantly decrease by introducing an overlarge backward-facing step height HR = 0.2. The upstream step geometries lead to deteriorated aerodynamic performance, though the reduction level may be slight (0.36% at HR = 0.136). These suggest that the overlarge backward-facing misalignment will increase the risk of thermal failure and must be avoided during the component assembly and the operational processes of a gas turbine.

An experimental and numerical investigation of the ballistic penetration behavior and failure mechanism of 3D MWK composites

3D multi-axial warp knit (MWK) composites have been gradually focused on the aeronautics and astronautics fields. This paper carried out ballistic penetration experiment of 3D MWK carbon/epoxy composites with blunt projectile to obtain ballistic penetration behaviors and failure mechanisms. Meanwhile, an elasto-plastic constitutive model was established to predict the damage evolution and absorbed energy, where strain rate effect and interface behavior were considered simultaneously. A sensitivity analysis of ballistic penetration properties to impact velocity was thoroughly analyzed. The experimental data were compared with the numerical prediction results. The results convincingly concluded that the ballistic penetration properties strongly depended on the impact velocity. With the increase of impact velocity, the energy absorption capacity of the composite was strengthened, and yarn breakage and resin plasticization were more severe. The numerical predicted results were well in conjunction with the experimental data, proving that the ballistic penetration behaviors could be accurately predicted.

Online Sequential Extreme Learning Machine-Based Active Interference Activity Prediction for Cognitive Radar

For anti-active-interference-oriented cognitive radar systems, the mismatch between the acquired and actual interference information may result in serious degradation of cognitive anti-active-interference performance. To yield more effective knowledge of the electromagnetic environment and eliminate the mismatch effect, the electromagnetic activity prediction technique, which deduces future electromagnetic behaviors based on current observations, has received increasing attention. However, high computational complexities limit the application of conventional electromagnetic activity prediction methods in dynamic active interference prediction with high real-time requirements. In this paper, the online sequential extreme learning machine (OS-ELM)-based method, which is dedicated to high-efficiency active interference activity prediction, is proposed. The advancement includes two aspects. First, benefiting from the single-hidden-layer network structure and recursive-formula-based output weight updating, the proposed OS-ELM-based frequency prediction (OS-ELM-FP) and OS-ELM-based angle prediction (OS-ELM-AP) models can predict the interference state and update the prediction model parameters with much higher computational efficiency. Second, the better generalization performance enables the proposed method to achieve smaller interference activity prediction errors compared with conventional methods. Numerical examples and prediction results based on measured jamming data demonstrate the advantages of the proposed method.

A simplified Johnson-Cook model of TC4T for aeroengine foreign object damage prediction

Foreign object damage (FOD) was one of the major concerns of airworthiness requirements for aeroengines in service and maintenance, which reduced the fatigue life and led to premature failure. In present work, dynamic mechanical properties of a new titanium alloy named TC4T were firstly investigated by using Split-Hopkinson pressure bar (SHPB) tests at high strain rates and quasi-static tensile tests with different triaxiality. Based on experimental data, a simplified Johnson-cook (J-C) model with failure criterion was established to describe the strain-rate dependent constitutive model for TC4T. Finite element (FE) models to simulate SHPB and quasi-static tensile tests were developed and validated by experimental results, respectively, to evaluate the effectiveness of the J-C model. Excellent agreements could be found between numerical prediction and experimental results. Secondly, laboratory simulated FOD tests were carried out by air gun to launch steel spherical projectiles with various diameters impacting the edge of the flat plate specimen made of TC4T at different impact velocities. The corresponding 3D FE model was also developed and predicted FOD profiles were compared with experimental results. Satisfactory agreement could be obtained between numerical predictions and the experimental measurements. Finally, a full-scale 3D FE model of an aeroengine fan blade was established by using the proposed J-C model to predict and evaluate FOD. The effect of the initial stress state and impact position on FOD were investigated and results showed that the initial stress had less influence on the sizes of FOD profiles, while the impact position had a significant effect on FOD.

The passive control on flow and heat transfer with streamwise micro grooves

The flow behavior of smooth channel and channel with streamwise micro grooves are numerically compared at Reynolds number 3000–6000. The numerical prediction results show that the streamwise micro grooves can effectively promote the heat transport in boundary layer. In special cases, the streamwise micro grooves can suppress the ejection and sweep motions of turbulent coherent structure to a certain extent, which is conducive to the improvement of the stability of near-wall flow structure and the reduction in wall shear stress. In addition, 2.16% of drag reduction can be obtained. Furthermore, the streamwise micro grooves increase the number of large-scale vortices and destroy the thermal boundary layer. With the help of the streamwise micro grooves, Nusselt number increases by 8.2% ~ 10.7% in the range of considered Reynolds number.

An improved smoothed particle hydrodynamics method for simulating crack propagation and coalescence in brittle fracture of rock materials

A new meshless numerical method, namely the improved smoothed particle hydrodynamics (ISPH) method, is proposed to simulate the fracture process of rock samples with pre-existing flaws under uniaxial compression. By improving the kernel function of SPH method, the brittle fracture characteristics of materials are presented. In ISPH, a prefabricated node segment (PNS) method is used to generate arbitrarily complex flaws, which avoids the division and distortion of traditional particles. In order to further improve the numerical accuracy, a new solid boundary treatment method called coupled dynamic buffer SBT algorithm is applied to ISPH, which is verified to be effective and robust via two benchmark samples. The effect of the length of a pre-existing flaw on the fracture mode and compressive strength of the rock sample is studied by using the elastic-brittle constitutive model. The numerical prediction results are in good agreement with the experimental observations. In addition, the effect of the unconnected rate on the crack propagation and coalescence mode of a rock sample with two pre-existing flaws under uniaxial compression is also studied. The numerical simulation results are in good agreement with the experimental results, which further verify the accuracy and superiority of the ISPH method.

Анализ опыта метеорологического обеспечения спортивных и культурно-массовых мероприятий

The experience of weather services for international sports and cultural events is analyzed on the basis of the developed Roshydromet concept, which includes a comprehensive system for the development of high-detail weather forecasts based on the application of the results of numerical weather prediction with high spatial and temporal resolution. It is shown that the developed concept is applicable to weather services for Moscow as a megalopolis. The concept is under development and adaptability of use to any outdoor event. Special attention is paid to the diagnosis of severe weather events using remote sensing of the atmosphere and observations at weather stations. The relevance of the results is confirmed by the application of the presented approaches during the preparation of weather services for the 2023 FISU Summer World University Games in Yekaterinburg. Keywords: sports and cultural events, specialized high-detail weather forecast, key factors of weather services, local weather offices, the concept of weather services, integrated weather forecasting system, specialized web interface, high-resolution models.

Extended GTN model for predicting ductile fracture under a broad range of stress states

Continuous damage accumulation resulting from void nucleation, growth, and coalescence leads to the final ductile fracture. The Gurson–Tvergaard–Needleman (GTN) model and its extensions, which model these mechanisms, are famous coupled constitutive models for predicting material failure. In this study, the GTN model was extended by incorporating two different damage variables: void volume fraction and shear damage; this was done to describe damage accumulation and ductile fracture under a wide range of stress states from compression-dominated to tension-dominated ones. The shear damage was composed of the shear void nucleation related to secondary voids and shear deformation damage. In addition, the shear void nucleation and void closure effect resulting from compression deformation were introduced to model the change in void volume under different loading conditions. The Lode angle dependence function was updated to express the various stress states and competition mechanism between two damage variables. Furthermore, the effective damage and its incremental form was used to define the extent of damage accumulation and fracture initiation. Subsequently, the proposed model was implemented in finite element software through user subroutines, and three distinct experiments related to high, low, and negative stress triaxiality were performed to calibrate the model parameters by the inverse analysis method for 1045 steel and 2024-T351 aluminum alloy. The experimental results under proportional and path-changing loading conditions were used to analyze the damage evolution and validate the proposed model. The good agreement between the numerical prediction and experimental results for the displacement and location at fracture, indicates good predictive ability of formulated model under arbitrary loading conditions.

Numerical prediction of dynamic fracture strength of edge-mounted non-symmetric tempered glass panels under steel ball drop impact

Despite the well-known effects of loading rate and specimen size on glass strength, the fracture criterion of products containing tempered glass panels (TGPs) has been established based on the static fracture strength (SFS) of a standard-sized TGP due to procedural difficulties in determining large scale dynamic fracture strength (DFS). This impractical fracture criterion that has universally been adopted in industrial fields results in a use of excessive safety factor in product design and development process. In this work, large scale DFS of full-edge mounted TGPs is numerically predicted using ball drop impact (BDI) simulation, which realize in-service dynamic loading conditions and constraints. The numerical prediction results were verified by a remarkable correlation with a deformation deviation of 1.0–5.0% and stress deviation within about 6.9% comparing to BDI fracture test results. It was found that the average DFS derived in the practical BDI condition was 2.0 times higher than the average SFS derived in standard flexural test condition. We believe this study contributes to setting more efficient fracture criterion when designing or developing products in which TGPs are mounted, with emphasizing difference in glass strength derived from the in-service conditions and the standard test conditions.

Feasibility Study for Well pattern Encryption in Complex Fractured Block Reservoirs--Taking the Liu 90 South Fault Block in the Jidong Oilfield as an example

Jidong oilfield belongs to complex fault block reservoir, and the development has now entered into high water-cut stage. when using Well pattern encryption technology to stabilize production, it is necessary to study the feasibility of Well pattern encryption to ensure a better economic benefit. In this paper, we use theoretical analysis method, consider the influence of oil price on the calculation, improve the economic limit Well pattern density calculation formula, calculate the economic limit Well pattern density under different recovery rates, make recovery rate prediction for different Well pattern density scenarios by combining with Sherkachov's formula, and use the curve intersection method to determine the Well pattern density at the break-even point, so as to determine the economic feasibility of Well pattern encryption. The example calculations show that the use of well network encryption alone does not meet the development requirements of the Liu 90 South block and has no significant economic benefits, so a combination of two-three methods is needed to further improve the recovery rate. Numerical simulation prediction results show that the two-three combination method can improve the recovery rate by 14.54%, accumulate 28.88×104t of oil increase and increase revenue by 678,245,000 yuan.

PREDICTION OF OIL PRODUCTION USING PHYSICS-INFORMED NEURAL NETWORKS

In recent years, modern information technologies have been actively used in various industries. The oil industry is no exception, since high-performance computing technologies, artificial intelligence algorithms, methods of collecting, processing and storing information are actively used to solve the problems of increasing oil recovery. Deep learning has made remarkable strides in a variety of applications, but its use for solving partial differential equations has only recently emerged. In particular, you can replace traditional numerical methods with a neural network that approximates the solution to a partial differential equation. Physically Informed Neural Networks (PINNs) embed partial differential equations into the neural network loss function using automatic differentiation. A numerical algorithm and PINN have been developed for solving the one-dimensional pressure equation from the Buckley-Leverett mathematical model. The results of numerical solution and prediction of the PINN neural network for solving the pressure equation are obtained.

Welding distortion prediction and mitigation in thick steel plate structures on ships

ABSTRACT In the ship fabrication process, welding distortion will affect the dimension accuracy. In this paper, an industrialisation prediction method for thick steel plate structures on ships is proposed based on a combination of thermal-elastic-plastic finite element method and inherent deformation theory to reduce the welding distortion in the design stage, and its applicability is verified through a comparison of measurements in the shipyard and numerical simulations. The thick plate models produced by multi-pass welding technology are selected to analyse the welding distortion. The results show that the numerical prediction results are in good agreement with the measurement on site. The transverse bending distortion is the main factor that affects the fabrication accuracy. To mitigate welding distortion, the influence of welding sequence and flame heating is examined. This research may provide a macro concept for understanding the distribution characteristics of welding distortion and serve as a mitigation reference for manufacturing engineers.

A plasticity-based dynamic constitutive model for ultra high toughness cementitious composites

Ultra high toughness cementitious composites (UHTCC) have a wide range of application prospects in various protective structures. At present, various concrete material models have been frequently used to simulate the mechanical response of such materials subjected to high-speed impact and explosive loads. However, none of these models can accurately describe the tensile ductility, strain rate effect, and shear expansion effect of UHTCC, which may lead to inaccurate numerical simulation results. In this study, a dynamic constitutive model of UHTCC was established, which comprehensively considered damage evolution, shear expansion, strain rate, strain hardening and strain softening of such materials. It was implemented into LS-DYNA software through a user-defined interface. Then comprehensive element tests were conducted and compared with the commonly used concrete models. Finally, a set of experimental tests of the UHTCC subjected to high-speed impact and contact blast loads were simulated. It was found that the numerical prediction results were in good agreement with the experimental results.

Investigation on the ultimate uplift capacity for asteroid exploration in drilling anchoring process: Numerical modelling and DEM simulation

Due to the microgravity environment on the asteroid surface, the asteroid probe can not stay on the asteroid surface for a long time for in situ exploration. Therefore, an anchoring device is required to provide enough ultimate uplift capacity to hold the asteroid probe on the asteroid’s surface. In this work, based on the circular arc failure surface hypothesis, a numerical model is proposed to predict the ultimate uplift capacity of the anchor rod of the anchoring devices during the anchoring process. The discrete element method (DEM) simulation is adopted to calculate the ultimate uplift capacity and analyze the geomaterial behavior. To accurately simulate material properties, the parameters of three typical geomaterials are calibrated by the calibration tests. The anchoring experiment verifies the DEM simulation results, and the error between the anchoring experiment results and DEM simulation results is less than 14%. The distribution of loaded particle forces in the geomaterials under various anchoring angles(30°–60°) and the anchoring depths(20 mm–40 mm) in the simulation are compared and analyzed. Compared with the DEM simulation results, the ultimate uplift capacity’s numerical model prediction results have an error of 5%. This work provides a new approach to predict the ultimate uplift capacity of the anchor rod of the anchoring devices during the asteroid exploration process.

Numerical simulation and model prediction of complex wind-turbine wakes

ABSTRACT An accurate description of incoming wind condition is supposed to be a prerequisite for reliable wake simulations. Taking into account the presence of wind shear effect and the vertical profiles of flow quantities in the atmospheric boundary layer flow, a numerical simulation of complex wind-turbine wakes is conducted by solving the Reynolds-averaged Navier–Stokes equations, with a simple actuator disc model implemented for the rotor effects. The Reynolds Stress Model is introduced to account for the anisotropy of atmospheric turbulence. In addition to the computational fluid dynamics means, a three-dimensional analytical wake model is developed for wake prediction. The results of both numerical simulation and model prediction are applied for validations through several cases, and proved to be of good accuracy in wind-turbine wake modeling.