Multi-step Simulation Research Articles

Ice Shape Convergence in Multistep Ice Accretion Simulations

Local errors in the geometrical description of the ice front are amplified in multistep simulations over conformal meshes due to the coupling of aerodynamics, water impingement, ice accretion, and grid deformation. Small perturbations in the initial phase of ice formation possibly result in dramatically different ice shapes, which can hinder the stability of the multistep procedure. This problem is analyzed by investigating the combined effects of space and time discretization on the ice growth over airfoils and three-dimensional wings. We propose an automatic procedure for selecting the time interval for the update of the aerodynamics and particle impingement. A local growth limiter λ is introduced here to bound the local ice thickness growth to be comparable to the local grid spacing on the surface, resulting in an automatic adaptive time step to be used in the multistep simulation. Examples are provided for three-dimensional cases under both rime and glaze conditions over straight and swept wings. These examples highlight the different accretion mechanisms of the two ice regimes and preliminarily indicate that ice-shape convergence can be achieved for low values of λ.

Impact of Imperfect Kolsky Bar Experiments Across Different Scales Assessed Using Finite Elements

Abstract Typical Kolsky bars are 10–20 mm in diameter with lengths of each main bar being on the scale of meters. To push 104+ strain rates, smaller systems are needed. As the diameter and mass decrease, the precision of the alignment must increase to maintain the same relative tolerance, and the potential impacts of gravity and friction change. Finite element models are typically generated assuming a perfect experiment with exact alignment and no gravity. Additionally, these simulations tend to take advantage of the radial symmetry of an ideal experiment, which removes any potential for modeling nonsymmetric effects, but has the benefit of reducing computational load. In this work, we discuss results from these fast-running symmetry models to establish a baseline and demonstrate their first-order use case. We then take advantage of high-performance computing techniques to generate half symmetry simulations using Abaqus® to model gravity and misalignment. The imperfection is initially modeled using a static general step followed by a dynamic explicit step to simulate the impact events. This multistep simulation structure can properly investigate the impact of these real-world, nonaxis symmetric effects. These simulations explore the impacts of these experimental realities and are described in detail to allow other researchers to implement a similar finite element (FE) modeling structure to aid in experimentation and diagnostic efforts. It is shown that of the two sizes evaluated, the smaller 3.16-mm system is more sensitive than the larger 12.7 mm system to such imperfections.

Improving fatigue initiation life of open-hole fibre metal laminates by laser shock peening

Although drilling open holes in fibre metal laminates reduces weight, it brings potential crack initiation sites. This paper investigates the effect of laser shock peening (LSP) on fatigue performance of open-hole titanium-based carbon-fibre/epoxy laminates (Ti-CF FMLs). A method based on multi-step simulation was proposed for the reconstruction of LSP induced residual stress field in open-hole Ti-CF FMLs. The results show that the fatigue initiation life of open-hole Ti-CF FMLs is improved by 22.1 %–81.0 % after LSP, depending on the structure of FMLs and the applied fatigue load. The improved fatigue crack initiation life attributes to compressive residual stress generated throughout the entire depth of the hole wall in outer titanium layer in Ti-CF FMLs after LSP. However, LSP leads to the formation of tensile residual stress far from the hole edge, resulting in accelerated propagation of fatigue crack. The fatigue initiation lives of open-hole Ti-CF FMLs before and after LSP were calculated by finite element simulation and theoretical method, showing good consistency.

Research on Dynamic Response of Pipeline under the Reeling Process and Laying Process

During the process of laying submarine pipelines using the R-lay (short for reel-lay) method, the interaction between the pipeline and the laying equipment undergoes continual fluctuations, leading to bending in the pipeline induced by the stochastic dynamics of various external loads. Considering the challenge in forecasting the dynamic behavior of pipeline bending moments and ovality throughout this procedure, we constructed a finite element-based shell element model for a 6-inch pipeline. In this paper, a multi-step simulation approach was used to replicate the pipeline laying process, and the dynamic response in pipeline bending moments and ovality during the winding, unwinding, and straightening processes was analyzed. Additionally, the effects of the pipeline’s diameter–thickness ratio and material properties on the dynamic response process were also studied. The results show that the dynamic response in bending moments and ovality is closely related to the curvature of the pipeline; a brief peak will appear at the critical point where the pipeline deforms, and the peak is related to the different bending stages of the pipeline, with the winding stage having a greater impact on the peak than the unwinding stage. During the unwinding process, a reverse bending moment will occur. The dynamic response of pipeline bending moments and ovality is influenced to some extent by the pipeline’s diameter–thickness ratio and material properties, with the diameter–thickness ratio demonstrating a more conspicuous impact.

Electronic and structural properties of mixed-cation hybrid perovskites studied using an efficient spin-orbit included DFT-1/2 approach.

Fundamental understanding and optimization of the emerging mixed organic-inorganic hybrid perovskites for solar cells require multiscale modeling starting from ab initio quantum mechanics methods. Particularly, it is important to correctly predict the structural and electronic properties such as phase stability, lattice parameters, band gaps, and band structures. Although density functional theory is the method of choice to address these properties and generate the input for subsequent multiscale, high-throughput, and data-driven approaches, standard exchange correlation functionals fail to reproduce the bandgap, particularly if spin-orbit coupling (SOC) is correctly taken into account. While many SOC-included hybrid functionals suffer from low transferability between different molecular ions and are computationally costly, we propose an efficient multistep simulation protocol based on the DFT-1/2 method. We apply this approach to APbI3 with A: FA, MA, Cs, and systems with mixed cations and show how the choice of the A-cation modifies the Pb-I scaffold and the hydrogen bonding and discuss their interplay with structural stability. Furthermore, band gaps, band structures, Rashba band splitting, Born effective charges as well as partial density of states (PDOS) are compared for different cases w/wo the SOC effect and the DFT-1/2 approach.

Thermomechanical Analysis of a Reactor Pressure Vessel under Pressurized Thermal Shock Caused by Inadvertent Actuation of the Safety Injection System

The damage induced pressurized thermal shock (PTS) may pose to a reactor pressure vessel (RPV) is a critical safety requirement assessed as part of the ageing management programme of pressurized water reactors (PWRs). A number of researches have studied PTS initiated mainly by postulated accidents such as loss of coolant accidents (LOCAs). However, investigations on PTS-induced threat on RPV caused by inadvertent actuation of the safety injection, a frequent anticipated transient, have not been thoroughly studied. In this paper, a simplified multistep analysis method is applied to study the thermomechanical status of a two-loop PWR under PTS loads caused by inadvertent actuation of the safety injection system. A direct-coupling thermomechanical analysis is performed using a three-dimensional (3D) RPV finite element model. A 3D finite element submodel (consisting of the highiest stress concentration area in the RPV) and an assumed crack are then used to perform fracture mechanics analysis. Subsequently, the critical integrity parameter-stress intensity factor (SIF) is estimated based on FRANC3D-M-integral method coupled in the multistep simulation. The material fracture toughness of the vessel is computed based on the master curve method with experimental fracture toughness data. The results obtained from the direct coupling stress analysis in comparison with sequential coupling approach demonstrate the effectiveness of the proposed multistep method. Also, comparing SIF results obtained with that calculated based on the conventional virtual crack-closure technique (VCCT) and extended finite element method (XFEM) show good agreement. This study provides a useful basis for future studies on anticipated transient-induced crack propagation and remaining service life prediction of ageing reactor pressure vessels.

Order reduction method for high-order dynamic analysis of heterogeneous integrated energy systems

The dynamics of heterogeneous integrated energy systems (HIES) coupling of electricity, gas, and heating/cooling subsystems is with high-order characteristics. The complex dynamics, including electromagnetic transients, electromechanical transients, hydraulic and thermal dynamics, exist in different system devices and interacts with others in different time scales. To deal with the difficulty of analysing the multi-time scale dynamics, this paper proposes an order reduction method (ORM) to map high-order modes into a lower dimensional space. Firstly, the complex model of HIES is partitioned and modelled by individuals, and the dynamic characteristics of each unit is revealed. Then modal synthesis is used to obtain feature modes of the system. Similar dynamics of individuals are synthesized whereas different modes are classified in order. When exploring dynamic process of a certain variable, the relevant modes are extracted from the synthesis model, with other modes handled as parametric or algebraic equations. Simulation studies are conducted to investigate dynamic characteristics of a test HIES using the proposed ORM. The results indicate that the proposed method is capable of simulating high-order dynamics of the test system. Furthermore, it has advantages in both computation accuracy and time, compared with equal-step method and conventional subsystem multi-step simulation method.

Validation of a Simulation Model for Robotic Sacrocolpopexy.

We sought to validate a simulation model for robotic sacrocolpopexy (RSCP) that includes multiple steps: presacral dissection/mesh attachment, vaginal mesh attachment, and peritoneal closure. An RSCP training model was developed. Female pelvic medicine and reconstructive surgery (FPMRS) experts and current FPMRS fellows were videotaped using the model; sessions were timed and scored using the Global Evaluative Assessment of Robotic Skills (GEARS) by 3 surgeon reviewers masked to participants' identities. Construct validity was measured by comparing performance on the model between experts and trainees. Interrater reliability was determined by calculating intraclass correlation coefficients for total GEARS scores. Face validity was assessed by a postprocedure questionnaire. Experts included 9 board-certified FPMRS physicians experienced in RSCP; trainees were 17 fellows. Experts practiced at 7 different institutions in the United States, and the majority (5/7) taught fellows. Trainees were from 7 institutions and in various years of training: postgraduate year (PGY) 5 (n = 6), PGY 6 (n = 5), and PGY 7 (n = 6). Experts' performances were rated significantly higher for total GEARS scores and for relevant domains of the GEARS scale. Intraclass correlation coefficient for the 3 reviewer pairs (0.96-0.99) indicated high interrater reliability. All participants "agreed/strongly agreed" that the model closely approximated live RSCP surgery and was useful for teaching and learning the procedure, indicating high face validity. This novel, multistep simulation model demonstrated construct validity and high interrater reliability. Face validity was also established. Consequently, this RSCP model could be used for surgical training and assessment of these discrete surgical skill steps.

COMPARISON OF WASTE DUE TO IRRADIATED STEELS IN THE ESFR AND DEMO

For either nuclear fusion or generation IV fission reactors to be viable as a commercial energy source the decommissioning and waste disposal solutions must be considered during the design. A multi-step simulation process combining Monte Carlo Neutron Transport simulations with inventory simulations have been performed to estimate the activation of steels in key reactor components of the European Sodium-cooled fast Reactor (ESFR). Waste classifications based on UK waste disposal regulations have been applied to the key components to estimate the expected masses of low level and intermediate level waste. The use of reduced activation steels, EUROFER and F82H, in reactor components external to the core results in a factor of 10 reduction in the percentage of waste classified as Intermediate Level Waste (ILW). Waste estimates are compared to existing waste estimates for the European Demonstration fusion reactor (DEMO). The ESFR has a lower percentage of ILW per total reactor mass due to irradiated steels compared to DEMO. However, there is no Higher Activity Waste (HAW) associated with DEMO, compared with arisings from the ESFR spent fission fuel.

Experimental-numerical study of laser-shock-peening-induced retardation of fatigue crack propagation in Ti-17 titanium alloy

Residual stresses induced by laser shock peening in Ti-17 titanium specimens were experimentally and numerically investigated to identify the mechanisms and generation conditions of the retardation of fatigue crack propagation (FCP). The retardation was experimentally observed with fatigue life prolonged by 150%. A multi-step simulation strategy for fatigue life prediction is applied, which successfully predicts the experimentally observed FCP behavior. The fractographic observations and numerical simulation indicate that crack closure, as opposed to other microstructural influences, is the dominant effect on retardation. The studies of multi-FCP aspects show that significant retardation occurs in specimens at high values of residual stresses, small peening gap distances, and lower externally applied loads.

Methods and Criterion for Adaptive Ice Accretion Simulation: Mesh Boundary Merge and Reconstruction

The strong coupling effect of two-phase flow and ice accompanies the ice accretion process of aircraft and wind turbine in damp and cold environment. A method based on the Eulerian two-phase flow, domain discretization of finite volume method (FVM) and finite element method (FEM), and fluid–solid coupling for numerical simulation of ice accretion is presented in this paper. In addition, the icing process of two-dimensional (2D) ice accretion on airfoils is investigated. It is found that the difference between simulation results and experimental data comes from the phase changes of local collection efficiency [Formula: see text], which is a function of local vortex strength and changes with time. Furthermore, with the ice accretion, it is easy to generate a negative or distortion grid because of the inappropriate mesh boundary merge and reconstruction, leading to an inaccurate ice prediction result. Based on the influence region of icing accretion and capturing the complex flow characteristics of the near-wall region, a dynamic and partition adaptive grid reconstruction strategy between macroscopic ice layer and microscopic ice crystal growth process is established. This is then used to build the ice accretion step adjustment strategy for multi-step simulation method under different icing conditions. The droplet collection efficiency distribution is modified by considering the vortex structure in the near-wall region. For verification purposes, multi-step simulation results for ice accretion of NACA0012 airfoil and large camber and strong separation airfoil under specified icing conditions are compared with the corresponding experimental data and some previously predicted results. The results of quantitative comparison of ice shape indicate that the current calculation method has better consistency with the experimental data, especially for glaze ice. The similarity of ice shape is more than 20% higher than the previous prediction results, showing that the time-space adaptive adjustment strategy has good robustness and accuracy for ice prediction.

Atomistic liquid crystalline structures of discotic bent-core-like mesogens formed by hydrogen bonding and interchain interactions

Integrated atomistic and molecular dynamic simulations are used to characterize the role hydrogen bonding and interchain interactions on structures and phase transitions of novel bent-core-like mesogenic materials that exhibit new self-assembly features, attractive to the development of functional materials. Multi-step simulations were carried out to model phase transitions and various spectra of two complex mesogenic materials formed from acid functionalized azo compounds, 4-[2,3,4-tri(octyloxy)phenylazo] benzoic acid and 4-[2,3,4- tri(heptyloxy)phenylazo] benzoic acid. The simulations contain three consecutive steps, involving molecular quantum chemistry, molecular crystal packing, and super cell molecular dynamics calculations. These two mesogens are supposed to form phasmidic molecular conformers. However, simulations point to the formation of complex discotic bent-core-like liquid crystals with tetramer mesogenic assemblies, in very good agreement with experimental observations. The wide range agreements between simulations and experimental results include transitions of crystal structures to columnar and uniaxial nematic phases, x-ray diffraction patterns of columnar phases, the structure of the two-dimensional complex bent-core-like tetramers, molecular Raman spectra, Raman depolarization spectra, and order parameters of nematic phases. The multi-step simulation methodology and its results shed light on this unique behaviour of plasmids with flexible side chains for simulation design of novel bent-core-like mesogenic materials.

Fracture mechanics analyses of a reactor pressure vessel under non-uniform cooling with a combined TRACE-XFEM approach

This paper presents the integrity analyses of a model reactor pressure vessel (RPV) subjected to pressurized thermal shocks (PTS). The analyses are performed with a one-way multi-step strategy that includes the thermo-hydraulics, thermo-mechanical and fracture mechanics analyses to simulate three hypothetical loss of coolant accidents (LOCA). The thermo-hydraulics analyses are performed with the system code TRACE and a three-dimensional (3D) model of the RPV, providing the input for the structural analyses with the finite element code ABAQUS. These employ a sequential use of global model (entire RPV) and submodels (a portion of the RPV containing the crack), where the eXtended Finite Element (XFEM) approach is employed to compute the stress intensity factor (SIF) of a postulated crack in the RPV wall.The results first present a verification of the multi-step strategy with the FAVOR code for uniform temperature distribution in the RPV wall. Under uniform temperature and pressure load, a significant effect of the nozzle geometry on the asymmetric stress distribution is demonstrated. The second part of the results shows that the stresses and the SIFs are also sensitive to the non-uniform temperatures due to the presence of the cooling plumes. It is also confirmed that the analyses with ABAQUS and FAVOR provide very similar results for the medium and large break LOCA transients. For the small break LOCA, the FAVOR code underestimates the SIFs due to the missing nozzle geometry in combination with system pressure. Finally, the paper corroborates that the use of TRACE and XFEM, within the one-way multi-step simulation strategy, reduces the computational costs and the number of assumptions and approximations needed for feasible and relivable 3D fracture mechanics analyses of the RPV with consideration of the cooling plume effect.

X-ray-induced acoustic computed tomography for guiding prone stereotactic partial breast irradiation: a simulation study.

The aim of this study is to investigate the feasibility of x-ray-induced acoustic computed tomography (XACT) as an image guidance tool for tracking x-ray beam location and monitoring radiation dose delivered to the patient during stereotactic partial breast irradiation (SPBI). An in-house simulation workflow was developed to assess the ability of XACT to act as an in vivo dosimetry tool for SPBI. To evaluate this simulation workflow, a three-dimensional (3D) digital breast phantom was created by a series of two-dimensional (2D) breast CT slices from a patient. Three different tissue types (skin, adipose tissue, and glandular tissue) were segmented and the postlumpectomy seroma was simulated inside the digital breast phantom. A treatment plan was made with three beam angles to deliver radiation dose to the seroma in breast to simulate SPBI. The three beam angles for 2D simulations were 17°, 90° and 159° (couch angles were 0 degrees) while the angles were 90 degrees (couch angles were 0°, 27°, 90°) in 3D simulation. A multi-step simulation platform capable of modelling XACT was developed. First, the dose distribution was converted to an initial pressure distribution. The propagation of this pressure disturbance in the form of induced acoustic waves was then modeled using the k-wave MATLAB toolbox. The waves were then detected by a hemispherical-shaped ultrasound transducer array (6320 transducer locations distributed on the surface of the breast). Finally, the time-varying pressure signals detected at each transducer location were used to reconstruct an image of the initial pressure distribution using a 3D time-reversal reconstruction algorithm. Finally, the reconstructed XACT images of the radiation beams were overlaid onto the structure breast CT. It was found that XACT was able to reconstruct the dose distribution of SPBI in 3D. In the reconstructed 3D volumetric dose distribution, the average doses in the GTV (Gross Target Volume) and PTV (Planning Target Volume) were 86.15% and 80.89%, respectively. When compared to the treatment plan, the XACT reconstructed dose distribution in the GTV and PTV had a RMSE (root mean square error) of 2.408 % and 2.299 % over all pixels. The 3D breast XACT imaging reconstruction with time-reversal reconstruction algorithm can be finished within several minutes. This work explores the feasibility of using the novel imaging modality of XACT as an in vivo dosimeter for SPBI radiotherapy. It shows that XACT imaging can provide the x-ray beam location and dose information in deep tissue during the treatment in real time in 3D. This study lays the groundwork for a variety of future studies related to the use of XACT as a dosimeter at different cancer sites.

Multi-step Simulation of Vacuum-carburizing Reactor Based on Kinetics Approach

Multi-step Simulation of Vacuum-carburizing Reactor Based on Kinetics Approach

A flexible and effcient microscopic simulation of multiple GEM chamber based on Garfield++

Microscopic simulations may bring a better understanding of the response of gaseous detectors. Such simulations are computationally demanding, due to the modelling of the low energy processes and to the high segmentation required for the 2D/3D field maps. In MPGD such maps can be much more complex than those of traditional multiwire chambers, due to the heterogeneous materials and more involute geometries, which break the simplifying symmetries featured in the latter. In order to investigate the performance of the triple GEM 2-dimensional tracking chambers being developed for high luminosity experiments with the Super BigBite Spectrometer at Jefferson Laboratory, we have set up a flexible and rather effcient multistep simulation processor based on either ANSYS or GMSH+ELMER for 3D CAD and electrostatic field modelling and then combined to Garfield++. Potential systematic effects from the 3D CAD modellers, the mesh generators and the electrostatic field solvers have been estimated with dedicated simulations; once these effects have been assessed, the results of the multistep approach have been compared to a simplified whole GEM chamber model.

The Volume Loss: Real Estimation and Its Effect on Surface Settlements Due to Excavation of Tabriz Metro Tunnel

A case study including monitoring data of surface settlements induced by tunneling in Tabriz metro line 2 is presented. This study focuses on about 4.6 km EPB-TBM tunneling works from west depot to S5 Station, where the tunnel was being excavated in sandy and fine grained alluvial, generally below the water table. Although volume loss (VL) has an important effect in estimating the ground movements, the prediction of optimum VL relies on the data from previous case studies with similar ground condition. Realizing unavailability of VL data based on Tabriz geological conditions, from the actual occurred settlements, VL was back-calculates by Gaussian empirical equation to get the VL percentage. Also a back-analysis was done to obtain settlement trough width constant K in both longitudinal and transverse sections. Furthermore, face support and tail grouting pressures were monitored, and compared with COB method. Likewise, a 3D finite element multi-step simulation was carried out by ABAQUS to predict surface settlements. There was concluded that, in longitudinal sections, numerical simulation is not capable of reproducing the recorded Smax, applying Mohr–Coulomb model. Smax can be estimated accurately by Gaussian curves, but the distribution of longitudinal surface settlement doesn’t match with these curves. The obtained VL varies from 0.13 to 1.35%, with an average value of 0.46%. The range of the VL increases significantly with the decrease of the tunnel depth. For the studied case, in shallow tunnels (C/D ≃ 1) high values of VL are occurred despite good control of face and grout injection pressures.

Multi-step simulation of multi-coated tool wear using the coupled approach XFEM/multi-Level-set

A multi-step modelling approach has been proposed to identify the tool/workpiece contact parameters (local friction coefficient, thermal contact conductance) and the flank wear for coated cutting tools. Three main steps constitute this approach: (i) the simulation of the machining process using the ALE approach, (ii) the transient thermal analysis of the cutting tool with multi-layer coatings and (iii) the prediction of flank wear. The combination of the XFEM and Level-set techniques has been done to model the thin layer of coatings. The enrichment functions in the XFEM formulation allowed to avoid in one hand the mesh refinement at the coating/substrate interface and on the other hand the mesh distortion during the evolution of the worn tool profile.

Crack closure mechanisms in residual stress fields generated by laser shock peening: A combined experimental-numerical approach

Laser shock peening (LSP) is successfully applied to retard fatigue cracks in metallic lightweight structures by introducing specific, in particular compressive, residual stress fields. In this work, experiments and a multi-step simulation strategy are used to explain the fatigue crack retarding and accelerating mechanisms within these LSP-induced residual stress fields. Crack face contact is identified as main mechanism to retard the fatigue crack as the stress distribution changes and the stress intensity factor range decreases. Crack face contact is experimentally detected by load vs. crack opening displacement (COD) curves and scanning electron microscopy (SEM) of the crack faces, as well as during numerical simulations. The convincing agreement between experiment and simulation, especially regarding the specific crack face contact areas, allowed the proper evaluation of the stress intensity factors depending on the crack length. It is found that crack closure is indeed one of the main reasons for the efficient application of LSP for fatigue crack retardation. Furthermore, the occurrence of crack closure does not indicate a zero value stress intensity factor in complex residual stress fields, as the areas of crack face contact depend strongly on the LSP-induced compressive residual stresses.

A generalised fuzzy cognitive mapping approach for modelling complex systems

Fuzzy Cognitive Maps (FCMs) were developed as a tool for capturing and modelling the behaviour of qualitative system dynamics. However, several drawbacks have been identified that limit FCMs ability in simulating the behaviour of qualitative system. This paper addresses the limitations of FCMs in modelling complex qualitative system dynamics and proposes a generalised Fuzzy Cognitive Mapping (FCM) approach that is able to overcome those limitations. This approach uses fuzzy rules to represent the dynamics of concepts and relations, including time dynamics of relations and introduces a multistep simulation approach that can use several single layer perceptrons to simulate the dynamics of concepts and relations overtime. This approach also incorporates the fuzziness and ambiguity widely associated with expert knowledge when representing and simulating the dynamics of concepts and relations. In this paper, the design of the proposed generalised FCM approach is explained and demonstrated for a real-world case of the consequences of high intensity rainfall in Kampala City, Uganda. This generalised FCM approach creates a new perspective and an alternative approach to model the behaviour of complex qualitative system dynamics using FCMs.