Numerical Dynamic Analysis Research Articles

Dynamic evolution and numerical analysis of rock deformation under impact failure based on corner correlation method

To fulfill the requirement for deformation measurement within the failure area during rock failure, a newly developed digital image algorithm, known as the corner correlation method, was implemented. A corner correlation measurement system was established by utilizing a Split Hopkinson Pressure Bar (SHPB) and a high-speed camera. The study focused on monitoring the deformation and failure characteristics of sandstone samples under dynamic loading. The results show that the corner correlation method has its unique advantages in rock dynamic mechanics experiments, and can obtain the deformation of the failure region during the rock failure process. Specifically, the initiation, extension, and contraction processes of surface cracks on sandstone were examined. Parameters such as crack width, width propagation rate, and extension shrinkage rate were measured. The entire crack development process was analyzed, including crack width, crack initiation point, crack extension and contraction trajectory, elongation and contraction velocity, width expansion rate, and longitudinal crack penetration, which were obtained at any given time on the surface of the rock sample. Additionally, the attenuation law of stress, characterized by an exponential decay of the stress peak value, was obtained through numerical simulation using a similar model.

Frequency response of the construction of a large-span building with a cylindrical-and-slab roof†

Relevance of the research. Numerical studies of structural frequency response of a large-span building with cylindrical-and-slab roof as a large mechanical system were carried out. Finite element model No. 1 “Superstructure-Fixed-end” . The purpose of the study was to develop the methodology for modal analysis of a large-span building structure with a cylindrical-and-slab roof as a mechanical system with a large number of degrees of freedom . Methods. Numerical analysis of the building dynamics was carried out with the use of the САЕ (Computer-aided engineering) software package Femap NX NASTRAN, which implements the finite element method. Results. The “dangerous” resonant frequencies and forms of harmonic oscillations of the structure were revealed, and the sensitivity of the buildings’ reactions to various structural changes was analyzed. Frequency analysis of harmonic response of the building allowed to obtain dependences of amplitude values of nodal displacements (accelerations) and stresses in finite elements from the frequency of the inducing external force. In the next article, it is proposed to conduct a dynamic analysis of a large-span building with a cylindrical-and-slab roof for seismic effects.

Experimental and numerical study of thermal coupling on catalyst-coated membrane for proton exchange membrane water electrolyzer

During the long-term operation of proton exchange membrane water electrolyzers (PEMWEs), Formation of localized hotspots in the catalyst-coated membrane (CCM) will seriously threaten the safe and efficient operation of the electrolyzer. This paper adopts a combination of dynamic experiments and numerical simulation analysis, aiming to develop the in-situ characterization technology of the thermal characteristics as well as the theoretical analysis of the multiphysics field for the·PEMWE. Based on both experimental and theoretical results, it is concluded that: (1) The high current density leads to an extremely uneven temperature distribution on the surface of the CCM. High temperature difference (as high as 34.04 °C) and high local temperature (up to 98.08 °C) are observed; (2) 30–50% of the electrical energy during the electrolyzer is converted into heat, of which the polarization heat accounts for the major part, followed by proton-conductive Joule heat; (3) The accumulation of gas phase during the transfer process of gas-liquid two phases is the primary cause of the deterioration of heat transfer, which further leads to local overheating. This study provides an experimental and theoretical basis for the safe and efficient operation of proton exchange membrane water electrolysis technology.

Evaluating Earthquake Stability of Solar Module Soundproofing Structure by 3D Numerical Analysis

In this study, dynamic numerical analysis was conducted on the existing sound barrier wall structure and the recently developed double-sided solar-module-integrated sound barrier wall structure using the finite-difference method for numerical modeling. A seismic safety evaluation was performed based on a series of numerical analysis results. Both structures were modeled using a 3D modeling technique with FLAC 3D to account for differences in lateral stiffness. For seismic considerations, the Pohang seismic wave was selected to represent short-period earthquakes in line with Korea’s seismic characteristics. Additionally, the Hachinohe seismic wave was chosen to simulate long-period earthquakes and consider the effects of the seismic period. To calculate the input seismic waves based on the ground response, a site response analysis was conducted for a site designated for demonstrating a double-sided solar module-integrated sound barrier wall structure in Korea. The analysis reveals that the existing structure maintains overall structural integrity and ensures the safety of solar modules even in an earthquake with a return period of 2400 years. However, for a solar module-integrated sound barrier wall structure, stresses exceeding the compressive strength of the solar module occur in earthquakes with a return period exceeding 1000 years, necessitating additional design and reinforcement for preparation.

A numerical study on the blade–vortex interaction of a two-dimensional Darrieus–Savonius combined vertical axis wind turbine

To investigate power losses of a Darrieus–Savonius combined vertical axis wind turbine (hybrid VAWT) associated with the interaction between blades and wake, it is crucial to understand the flow phenomena around the turbine. This study presents a two-dimensional numerical analysis of vortex dynamics for a hybrid VAWT. The integration of a Savonius rotor in the hybrid VAWT improves self-starting capability but introduces vortices that cause transient load fluctuations on the Darrieus blades. This study attempts to characterize the flow features around the hybrid VAWT and correlate them with the Darrieus blade force variation in one revolution. Results demonstrate the capability of numerical modeling in handling a wide range of operational conditions: the relevant position of Savonius and Darrieus blades (attachment angle γ=0°−90°) and Savonius' tip speed ratio λS (0.2–0.8, varied Savonius' rotational speed). The torque increase in the Darrieus blade in hybrid VAWT (compared to a single Darrieus rotor) due to the appearance of the vortex shedding from the advanced Savonius blade is independent of the attachment angle and tip speed ratio. Apart from start-up and power performances of the hybrid VAWT, the most rapid force fluctuation is identified when the Darrieus blade interacts with Savonius' wake at γ=0° and λS=0.8, which is considered undesirable. Furthermore, attachment angles of 60° and 90° exhibit better power coefficients compared to those of 0° and 30° for the hybrid VAWT. This study contributes to a comprehensive understanding of flow dynamics in hybrid VAWTs, revealing the correlation between torque variation and vortex development.

Numerical simulation analysis of multi-scale computational fluid dynamics on hemodynamic parameters modulated by pulsatile working modes for the centrifugal and axial left ventricular assist devices

Continuous flow (CF) left ventricular assist devices (LVAD) operate at a constant speed mode, which could result in increased risk of adverse events due to reduced vascular pulsatility. Consequently, pump speed modulation algorithms have been proposed to augment vascular pulsatility. However, the quantitative local hemodynamic effects on the aorta when the pump is operating with speed modulation using different types of CF-LVADs are still under investigation. The computational fluid dynamics (CFD) study was conducted to quantitatively elucidate the hemodynamic effects on a clinical patient-specific aortic model under different speed patterns of CF-LVADs. Pressure distribution, wall shear stress (WSS), time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), and velocity were calculated to compare their differences at constant and pulsatile speeds under centrifugal and axial LVAD support. Results showed that pulse pressure on the aorta was significantly larger under pulsatile speed mode than that under constant speed mode for both CF-LVADs, indicating enhanced aorta pulsatility, as well as the higher peak blood flow velocity on some representative slices of aorta. Pulsatile speed modulation enhanced peak WSS compared to constant speed; high TAWSS region appeared near the branch of left common carotid artery and distal aorta regardless of speed modes and CF-LVADs but these regions also had low OSI; RRT was almost the same for all the cases. This study may provide a basis for the scientific and reasonable selection of the pulsatile speed patterns of CF-LVADs for treating heart failure patients.

Dynamic Numerical Analysis of Interactions Between High-Altitude Electromagnetic Pulse and Power Grid

Dynamic Numerical Analysis of Interactions Between High-Altitude Electromagnetic Pulse and Power Grid

A simplified method for the dynamic analysis of structures under column loss

The progressive collapse of buildings as a dynamic phenomenon can be fully understood only within a transient dynamic analysis context considering for damping and inertia effects. The response of a typical beam-column substructure is usually dominated by a single mode of deformation, thus the single-degree-of-freedom (SDOF) modelling assumption provides an accurate representation of the problem. In this study, the dynamic response of an inelastic SDOF system with damping was investigated analytically. Closed form analytical equations of the model were derived that describe the complete dynamic response in the time domain. Moreover, simplified formulae to estimate peak responses and Dynamic Increase Factors (DIFs) were provided. Numerical dynamic analyses in OpenSees were performed to verify the accuracy of the analytical model. The results indicate that the analytical model can trace the full dynamic response accurately while peak displacements can be accurately estimated with the proposed formulas. The estimated DIFs were in agreement with available from the literature results and demonstrate the significant effect of damping and hardening. Application of the analytical methodology on the progressive collapse analysis of a 10-storey steel frame demonstrated the effectiveness and potential of the proposed SDOF system.

3D numerical study of neutral gas dynamics in the DTT particle exhaust using the DSMC method

Recently the design of the divertor tokamak test (DTT) Facility divertor has been modified and consolidated. The new divertor design presents significant geometrical differences compared to the previous ITER-like one, including the presence of a more flattened dome shape. This paper presents a complete 3D numerical analysis of the neutral gas dynamics inside the DTT subdivertor area for the latest divertor design. The analysis has been performed based on the direct simulation Monte Carlo method by applying the DIVGAS simulator code. SOLEDGE2D-EIRENE plasma simulations have been performed for a deuterium plasma scenario at the maximum additional power in partially detached condition achieved by neon impurity seeding and the extracted information about the neutral particles has been imposed as incoming boundary conditions. The pumping efficiency of the DTT divertor is examined by considering various cases with respect to the pumping probability and the effect of the toroidal and poloidal leakages is quantified. The results show that a significant percentage of the incoming flux of neutrals returns back to the plasma site through the entry gaps (60% for deuterium and 40% for neon), and, consequentially, only a small percentage (∼2%–15%) of the incoming flux can be pumped out from the system. The toroidal leakages affect significantly the pumping performance of the divertor causing a significant decrease in the pumped flux (and also in the pressure at the pumping opening) about 37%–47% and 43%–56% for deuterium and neon respectively. It is discussed how many pumping ports are needed depending on the achievable pumping performance per port. The number can be reduced by closing the toroidal gaps. The analysis shows that enlarging the poloidal gaps by a factor of two causes a significant increase in the poloidal flux losses by a factor 1.7. It is also illustrated how the presence of the cooling pipes leads to conductance losses.

Seismic response of deep circular tunnels subjected to P-waves: Axial and transverse compression-extension

Body waves can intersect a tunnel at various angles and thus induce complex structural responses that, at a minimum, require a comprehensive understanding of all modes of tunnel deformation due to both P- and S-waves. The majority of studies in this field have focused on a single S-wave mode, ovaling or racking (where the waves impinge on a tunnel transversely with the direction of particle movement perpendicular to the tunnel axis). Significantly less work has been devoted to the other modes. This study introduces two sets of new analytical solutions, using the soil-structure interaction approach, to predict the P-wave modes of tunnel deformation: axial compression-extension and transverse compression-extension. The solutions account for both drained and undrained loading conditions, with both no-slip and full-slip interface conditions between the tunnel lining and the ground. 2-D and 3-D numerical simulations, both static and dynamic analyses, are performed to verify the analytical solutions and determine their applicable limits. The numerical analyses also provide insights into the effects of dynamic amplification on the tunnel cross section.

Development of fragility functions of low-rise steel moment frame by artificial neural networks and identifying effective parameters using SHAP theory

Estimating analytical fragility functions requires high computational costs due to numerous incremental non-linear dynamic analyses. This study employs a soft computing approach to reduce this process and increase estimation accuracy. Utilized a fragility database of low-rise steel moment structures designed for different versions of Iranian seismic design code, and six feedforward Artificial Neural Networks (ANN) with various architectures were trained to estimate the fragility function’s parameters to determine the most desired architectures. The neural networks used the design parameters (frames story, code edition of design, ductility, soil type, near- and far-field earthquake, and seismic zone factor and importance factor) as inputs. For each of the fragility function’s parameters (Median PGA and βs of damages: slight, moderate, extensive, and complete) as outputs, an ANN was trained. The best architect of ANN was selected based on the accuracy of the models from different statistical indicators and the most balanced of the inputs’ importance on the outputs using SHapley Additive explanations (SHAP) analysis. To demonstrate the accuracy of the selected architect, the coefficient of determination was estimated for all database values, and the fragility functions of four randomly chosen frames were compared. The high R2 value in most cases and the closeness of the predicted fragility curved with the actual one indicates the reliability of the ANN method for predicting the fragility function.

Numerical Analysis of the Transient Capture Dynamics of Ions by Radio Frequency

The radiofrequency imprisoned ion system can isolate the coupling effect between ion and environment, and is helpful to the precise control of ion quantum state, which is an ideal candidate system for new atomic clocks. In this paper, the coupling effect between imprisoned ion and RF potential field is quantitatively studied by using finite element numerical analysis method. The coupling process of ion and RF phase is established, and the unsteady dynamic process of ion capture is analyzed. The influence of radio frequency amplitude on ion trapping ability and the reasonable range of radio frequency parameters conducive to ion stable confinement are studied. This method can be widely used in the study of ion trap structure and electromagnetic field parameter optimization in the fields of imprisoned ion frequency scale and quantum computing, and is helpful to the development of highly coherent quantum systems.

Dynamic numerical simulation method and flow characteristic analysis on the mode transition in variable cycle compression system

Studying the dynamic aerodynamic characteristics and flow field characteristics for the dynamic mode transition in the variable cycle compression system (VCCS) can guarantee that the variable cycle engine (VCE) achieves high performance and stable mode transition. The common quasi-steady state analysis method cannot reflect the transient performance of the dynamic mode transition. Moreover, the dynamic simulation based on the dynamic grid technology will encounter the problem of negative volume grids because the adjustment range of variable components for VCCS is usually very large. To solve the problem, a dynamic simulation method based on real-time variation for geometry and aerodynamic boundaries of the dynamic mode transition in VCCS is first established in this paper. Using this method, the dynamic simulation was completed for the couple adjustment process of the outer bypass valve and variable stators of the dynamic mode transition in VCCS. The results of the dynamic simulation are compared with the quasi-steady state results. The results show that the rotor work ability and stator separation degree are affected by the stator variable angle degree and the mass flow rate (MFR) during the dynamic opening process of the outer bypass valve. For the MFR variation of 14.8%, when the stator variable angle is small (less than 3.3° in this study example), the flow separation on the variable stator blade pressure surface is increased during the dynamic opening process of the outer bypass valve. And the work ability of the downstream rotor is weakened. Therefore, in order to reduce the flow separation of stator blades with a small variable angle during the dynamic opening process of the outer bypass valve, a larger positive incidence angle can be adopted for stators at a small bypass ratio. For the whole dynamic process, the variation trend of the rotor work ability and stator separation state is opposite in the opening and closing process of the outer bypass valve. However, there is a dynamic effect of the flow field variation lagging behind the geometry variation in the opening and closing process. Therefore, the transient flow field in the opening and closing process is different from the quasi-steady state results, and the difference is more significant in the case of a small valve opening. Under a small valve opening, the work ability of the stage before the outer bypass entrance in the open process is significantly smaller than that in the closing process. And the difference in the flow field is mainly that the stator separation state of the stage before the outer bypass entrance in the open process is significantly weaker than that in the closing process. Therefore, the dynamic effect of the opening and closing process is more significant under a small valve opening, and the flow stability problem is more likely to occur during the dynamic mode transition in VCCS.

Organic ternary mixture separation and purification using chromatography: Design, operation, and optimization

BackgroundFrom the improvement of raw material production and process, environmental friendliness has been silently packaged into commodities and integrated into society. Traditional batch chromatography methods are often used for separating succinic acid but incur large wastewater treatment costs and low efficiency. MethodsThe process design of simulated-moving-bed cascades (SMBC) for separating organic ternary mixture is proposed to address environmentally friendly raw material production methods with a more resource-saving process. Through dynamic modeling, numerical analysis, separation theory, and optimization methods, SMBC model is validated and scale-up by using Aspen Chromatography. FindingAccording to the adsorptivity and selectivity of different adsorbents, two scenarios of the SMBC for separating the organic ternary mixture of succinic acid, formic acid, and acetic acid are investigated. The results show that the SMBC using Amberchrom-CG300C and Reillex 425 resins could achieve the purity of each organic acid up to 96.8∼99.9%, and the corresponding recovery ratio is around 97.7∼99.9%.

Optimization of the Uniformity Index Performance in the Selective Catalytic Reduction System Using a Metamodel

The significance of the selective catalytic reduction system in vehicles increases in line with the high standards of emission control and enhanced selective catalytic reduction efficiency. This study aims to improve the performance of the selective catalytic reduction system through an optimization method using a metamodel. The objective function is defined as the ammonia uniformity index, and the design parameters are defined in relation to the pipe length and mixer related to the chemical reaction of the urea solution. The range of design parameters has been designated by a trial-and-error method in order to maintain the overall design drawings of the selective catalytic reduction system and prevent modeling errors. Three algorithms, namely, ensemble decision tree, Kriging, and radial basis function, are employed to develop the metamodel. The accuracy of the metamodel is verified based on three indicators: the normalized root mean square error, root mean square error, and maximum absolute error. The metamodel is generated using the Kriging model, which has the highest accuracy among the algorithms, and optimization is also performed. The predicted optimization results are confirmed by computational fluid dynamics numerical analysis with a 99.83% match. The ammonia uniformity index is improved by 1.38% compared to the base model, and it can be said that the NOx purification efficiency is improved by 30.95%. Consequently, optimizing the uniformity index performance through structural optimization is of utmost importance. Furthermore, this study reveals that the design variables related to the mixer play a crucial role in the performance. Therefore, using the metamodel to optimize the selectively catalytic reduction system’s structure should be considered significant. Finally, in the future, the analysis model can be validated using test equipment based on the findings of this study.

Experimental and numerical analysis of the pyrolysis dynamics of a single wood particle: presentation of the radiographic technique

Pyrolysis is an oxygen-free process for the thermal decomposition of raw materials. The heat conduction and flow of pyrolysis products (i.e., the gas fraction and liquid vapour generated during pyrolysis) influence the process and products. In this work, the influence of the orientation of wooden particle fibres with respect to the direction of the heat source on the dynamics of the process was investigated, where there were two particle sizes oriented along or across the heat source. The novelty of this work lies in the use of a radiographic technique for analysing the influence of wooden fibres' orientation on the degradation process. The research showed that during pyrolysis, the mass loss rate in the particles with fibres oriented across the heat source and along the heat source was different. A similar tendency was characteristic for the drying process. The dynamics of pyrolysis of a single wood particle depends on many factors—particle size, process parameters, arrangement of fibres in wood, etc. The analysis of the dynamics presented in the publications is based on the analysis of the dynamics of mass loss, which is a very large simplification. The publication contains experimental analysis and mathematical calculations of the pyrolysis process for samples of various sizes and samples with different fibre arrangement. The result of the research is the determination of trends regarding the shape of the particle and the arrangement of fibres on the process, which provides knowledge that can be translated into industrial pyrolysis processes.

On the performance-based seismic design of yielding retaining structures

This work summarises recent research on the seismic behaviour of displacing or yielding retaining structures, i.e., structures that can undergo permanent displacements during strong earthquakes without failing. For these systems, energy dissipation on shaking, leading to reduced inertia forces, can be achieved by allowing the activation of ductile plastic mechanisms. These must be correctly identified to guarantee the desired strength hierarchy, and depend on the specific retaining structure under examination. It is shown that the critical acceleration, or the smallest value of acceleration corresponding to the activation of the critical plastic mechanism, is the key ingredient for the performance-based design of yielding retaining structures. In fact, the critical acceleration controls both the maximum internal forces in the structural elements and the magnitude and trend of post-seismic permanent displacements and rotations, required for quantitative serviceability and post-earthquake operability assessment of infrastructures. Based on a clear understanding of the physical mechanisms governing the dynamic behaviour of these systems, pseudostatic limit equilibrium solutions and simplified dynamic methods can be developed for their seismic design. Theoretical predictions are validated against data from reduced scale centrifuge models and results of pseudo-static and fully dynamic numerical analyses. Finally, all the results presented in the paper, including experimental, numerical and theoretical findings, are used to provide suggestions for the performance-based design of retaining structures.

Effect of surface heat exchange on phase change materials melting with thermocapillary flow in microgravity

This paper presents a numerical analysis of the melting dynamics of n-octadecane in microgravity. The phase change material (PCM) is held in a rectangular container of aspect ratio Γ=L/H=1.5, and the upper boundary is open to a layer of air, which both exchanges heat with the PCM and generates thermocapillary convection in the liquid phase via the Marangoni effect. This study extends the analysis conducted by Martinez et al. [“Effect of surface heat exchange on phase change materials melting with thermocapillary flow in microgravity,” Phys. Fluids 33, 083611 (2021)] in which the air temperature was assumed to vary linearly between the temperatures applied at the lateral walls. Two different scenarios are analyzed here. In the first case, the air temperature is assumed to be homogeneous and equal to the mean value of the temperatures applied at the lateral walls throughout the melting process. In the second case, the air temperature is similarly taken to be constant but with a value of 23 °C, which is representative of a laboratory environment, including many microgravity platforms. The investigation reveals the effect of key dimensionless parameters, including the Marangoni number (Ma), which quantifies the heat transport due to the thermocapillary flow, and the Biot number (Bi), which characterizes the heat exchanged across the PCM/air interface. In contrast to previous analyses of pattern selection, only oscillatory standing (pulsating) waves are observed under these boundary conditions. The results in each case are presented via stability maps in terms of Bi and Ma.

Comparative Study on NACA-9405, NACA-9503 and NACA-9506 Airfoil Profiled Blade Open-Channel Flow Cross-Flow Turbine

Several agricultural areas in Indonesia are classified as underdeveloped rural areas, and challenging to acquire electricity from the primary grid. On the other hand, some pico hydropower potentials can be found in agriculture, especially at the irrigation dam spillway flows. However, no such technology can convert the energy inside the water open-channel flow through dam spillways into electricity. Crossflow turbines (CFT) are expected to utilize dam spillways’ power due to their ability to convert the kinetic energy of water. Prior studies found that airfoil profile could slightly increase CFT efficiency and affect the interaction between water and turbine. Using planar two-dimensional computational fluid dynamics (CFD) numerical simulation analysis, the current study investigated the energy conversion phenomenon inside different open-channel CFT blade profiles. This study simulates CFT working at 3 meters of total head and 0.04 m3/s of water discharge put into the dam spillway’s downstream. The turbine blade profiled with the National Advisory Committee of Aeronautics (NACA) standard airfoil numbered 9405, 9503, and 9506 are being compared and investigated in the present study. CFD numerical analysis results show that the forward direction NACA airfoil profiled blades deliver better efficiency than the reversed one. These findings contradict the prior study’s results which tested airfoil profiled CFT working as usual with nozzle. This phenomenon indicated differences in the energy transfer process between open channel CFT and the ordinary CFT with a nozzle. Furthermore, current work finds that forward NACA-9503 CFT has a higher efficiency than other tested airfoil profiles, with 57.05% efficiency. In addition, the present study finds that the NACA-95XX airfoil has a more suitable chamber curve with the original CFT blade’s curve than the NACA-94XX airfoil by velocity triangle analysis. Then, the NACA-9503 profile is thinner than the NACA-9506 profile, which eases water flowing through the turbine blades.

Numerical Study of the Robustness of Steel Frames with Bolted End-Plate Joints Subjected to Sudden and Gradual Internal Column Loss

The research project was carried out to estimate the robustness of flat steel-framed structures in a selected accidental situation. For this purpose, a multistage approach based on experimental tests and numerical analysis was performed. As the main objective of the work, a numerical dynamic analysis of the steel frames was performed under a sudden and gradual internal column loss scenario. FEA models were created in Abaqus software using solid and shell elements. Computer analyzes were carried out in a number of different cases, taking into account the size of the structure, the type of joints, and the method of removing the column from the structure. Detailed results on the axial forces and rotation of the joints under analysis are presented, and the robustness of the structures is estimated. In all cases of frames with flush end-plate joints, an insufficient level of robustness was observed and failures of the structures were obtained. In the cases of application of extended end-plate joints in frame analysis, the required level of robustness was reached in all cases and the stop of collapse was obtained. Finally, practical recommendations for designing robust joints and the whole frame structure are presented.