Results Of Numerical Modeling Research Articles

Dynamic Characteristics of a 1950s Heritage Building: A Comparison of Original Design Methods and Modern Techniques

Research on design rules and methods for architectural heritage is an important aspect of conservation practice. Nevertheless, efforts to recover and divulge design methods for Modern Heritage remain limited. This paper is related to the recent structural assessment of a 15-storey heritage building built in 1950, during which a document describing the original seismic analysis of this structure was identified. The methodology employed is of particular interest, as it involves the application of pioneer concepts of dynamic analysis in the design of the first tall buildings in Mexico. The primary aim of this paper is to review the seismic design criteria for the case under study in order to contribute to the state of the art in Modern Heritage. The review includes a comparison between the dynamic characteristics estimated during the design and the results of recent ambient vibration tests and numerical modeling. Several sources of error among the design criteria were identified. Notably, the fundamental period estimated during the design was 38% larger than the experimental value due to an underestimation in stiffness, which introduces significant uncertainty into the design. Overall, the review shows the evolution of seismic analysis over time and provide valuable insights for the study of similar buildings.

Marginal stability analyses for thermochemical convection and its implications for the dynamics of continental lithosphere and core-mantle boundary regions

Summary Significant compositional differences may exist in the lithospheric mantle and above the core-mantle boundary (CMB) relative to the ambient mantle. The intrinsic density differences may affect the development of thermal boundary layer (TBL) instabilities associated with lithospheric delamination and formation of thermochemical plumes. In this study, we explored the instability of two-layer thermochemical fluid using two different techniques: marginal stability analysis with a propagator-matrix method and finite element modeling. We investigated both the instabilities in lithospheric mantle (i.e., lithospheric instability) and the mantle above the CMB (i.e., plume-forming instability) using a background temperature Tbg(z) with the TBL. For lithospheric instability, we found that two-layer fluid with free-slip boundary conditions mainly undergoes the same three different convective modes (i.e., two oscillatory convection modes and one layered convection regime) as that with no-slip boundary condition reported in Jaupart et al., (2007). However, with free-slip boundary conditions, the transitions between these convection modes occur at larger values of buoyancy number B. Free-slip boundary conditions lead to smaller critical Rayleigh number Rac, but larger convective wavelength and oscillation frequency ωc, compared with those with no-slip boundary conditions. Our numerical modeling results demonstrate that Rac and ωc predicted from the classical marginal stability analyses using Tbg(z) with TBL temperature may have significant errors when the oscillatory period is comparable with or larger than the timescale of lithospheric thermal diffusion that causes Tbg(z) to vary with time significantly. In this case, using a more gently sloped background temperature profile ignoring the TBL temperature, the stability analysis predicts more accurate stability conditions, thus presenting an effective remedy to the stability analysis. For plume-forming instability, because of the reduced viscosity in the hot and compositionally dense bottom layer, the transition to the layered convection occurs at significantly smaller B values, and in the oscillatory convection regime, Rac is larger but ωc is smaller, compared with those for lithospheric instability. Finally, our study provides a successful benchmark of numerical models of thermochemical convection by comparing Rac and ωc from numerical models with those from the marginal stability analysis.

The impact of the destruction of the Kakhovka reservoir dam on the oceanographic conditions in the north-western part of the Black Sea according to the results of modeling

Based on the results of numerical modelling, characteristic features of distribution of transformed and polluted waters of the Dnieper River in the water area of the north-western part of the Black Sea (NWBS) are determined and analyzed. This pollution of the marine environment resulted from the extremely large man-made flood caused by the destruction of the Kakhovka Reservoir dam by the Russian occupation forces in June 2023. Various types of pollutants, which contained in the Kakhovka Reservoir, in the lower Dnieper River and in the bottom sediments, were carried out into the sea by the flood discharge. A significant amount of pollutants was washed into the sea from the flooded areas of the lower Dnieper basin. Special attention is given to changes in oceanographic conditions in the Dnieper-Bug estuary region (DBR) of the Black Sea, which determine the extent of marine pollution. Sea water salinity was used as an indicator of the degree of infiltration of polluted seawater from the estuary into the sea. It was identified that the least transformed river waters with low salinity correspond to high pollution levels. Delft3D-Flow Flexible Mesh hydrodynamic model, developed by Deltares, was used in this study. The simulation was performed for the time period 01 to 30 June 2023. During the first days after the dam break the desalinated and polluted transitional waters, flowing from the Dnieper-Bug estuary, spread over the entire water column down to 15-20 m depth in the DBR area. In this case, the spreading of transitional waters was atypical, as it usually occurs only within the thin near-surface layer of the sea. By mid-June the flow of transitional water with a salinity of 4-6 ‰ covered the entire water column from surface to bottom near the northern coast of the NWBS and over the Odessa Bank. This was facilitated by the supermassive volumes of transformed Dnieper river waters flowing out over a short period of time due to dam break, as well as by the resulting intense gradient currents and mixing caused by spatial gradients in the velocity of the generated currents. The width of the desalinated water plume and its area in the bottom layer were smaller than in the surface layer. The largest vertical salinity gradients were formed to the south of the Odessa Bank, where salinity was 4-6 ‰ in the surface layer and 14-17 ‰ in the bottom. Dilution of the desalinated water plume in the bottom water layer was much more intensive than in the surface water. The character of water circulation pattern in the northern part of the NWBS in the first days after the inflow of transient waters from the Dnieper-Bug estuary was determined by the runoff gradient currents, which later were replaced by wind-driven currents in the Odessa area and over the Odessa Bank, and by the meandering flow of gradient density currents further south. The findings of this study contribute to a better understanding of the impact of the inflow of transformed river waters from the Dnieper-Bug estuary on the variability of oceanographic characteristics and the ecological state of marine waters in the Dnieper-Bug region of the northwestern Black Sea.

2D discrete element analysis of the footing above excavated circle in soil

The bearing capacity and settlements of surface foundations located on a soil slope are the important issues that have to be considered by geotechnical engineers for the design. The presence of an underground void beneath the footing can affect the foundation stability and can lead to serious structure damages. In this study, the results of two-dimensional (2D) discrete element (DE) and finite element (FE) analyses of a surface footing on a soil slope above a void are presented. To validate the numerical model results, the DE results obtained have been compared with experimental test presented in the previous study. After validation of the DE numerical model, parametric studies were carried out to evaluate the effect of important factors on the surface footing performance. The studied parameters include the horizontal spacing of the void axis relative to the slope edge (SH), the vertical spacing of the void crown relative to the footing base (SV), the horizontal spacing of the footing edge relative to the slope edge (De) and the void diameter (Dv). The effects of these parameters on the pressure-settlement curves and the contact force distributions in the soil slope are presented and discussed. The results showed that the footing bearing pressure increases with an increase of SH, SV and De but decreases when Dv increases. The behavior of a surface footing on a soil slope above a void significantly depends on the SV value.

Simulation of intra-chamber processes in a low-thrust rocket engine with a hydrogen-air mixture and counterflow cooling

The principles and methods of improvement of thrust, efficiency and cooling of rocket engines for space flight safety are of great interest for aerospace industry. The development of reliable and durable low-thrust rocket engines for space missions seems to be one of the important areas of development of the rocket and space industry. Issues related to the implementation of a new direction related to the design of propulsion systems for orientation systems of upper stages of launch vehicles using environmentally friendly fuel components are considered. A mathematical model is developed and numerical modelling of processes in the combustion chamber of a low-thrust rocket engine with gaseous fuel components (hydrogen and oxygen) is carried out. The model takes into account the presence of a cooling jacket. The mathematical model includes the effects of turbulence, combustion of a gaseous fuel mixture, kinetics of hydrogen combustion, and radiation. As a result of calculations, distributions of flow quantities in the combustion chamber and thermal loads on its walls are obtained. The influence of hydrogen mass flow rate on the efficiency of the working process and the dependence of thrust on hydrogen mass flow rate are discussed. The results of numerical modelling are compared with the data of a physical experiment obtained through fire tests of an engine model made of stainless steel on a three-dimensional printer.

Numerical and Theoretical Study on Flexural Performance and Reasonable Structural Parameters of New Steel Grating–UHPFRC Composite Bridge Deck in Negative Moment Zone

As the bridge’s structural component is directly subjected to vehicle loads, the stress performance of the bridge deck has a significant impact on the safety, durability, and driving comfort of the bridge. In order to improve the bending performance of the bridge deck in the negative moment zone, a new type of steel grating–UHPFRC composite bridge deck was proposed in this paper. Firstly, structural details and advantages of the new steel grating-UHPFRC composite bridge deck were introduced. Secondly, the finite element program ABAQUS was used to establish a refined solid finite element model of the new bridge deck. The mathematical program MATLAB (PYTHON) was also used to analyze the effects of the structural parameters on bending bearing capacity and put forward reasonable structural parameters of the new bridge deck, considering the technical and economic indexes. Thirdly, the simplified plasticity theory was applied to analyze the bending bearing capacity of the new bridge deck, and the corresponding formula for bending bearing capacity calculation was derived and verified by numerical model results. In addition, the cost–benefit analysis and environmental impact assessment of the new bridge deck were also conducted. The results show that the bending bearing capacity of the new bridge deck in the negative moment zone increases with the increase of the width of the bridge deck, the thickness of the wing plate, and the height of the web plate, with a trend of increasing and then decreasing when the horizontal inclination of the web plate decreases. The bridge deck width does not have a significant effect on improving the bearing capacity. The bearing capacity calculated by theoretical formulas is close to that calculated by numerical models and the maximum relative deviation is 9.1%. The new steel grating-UHPFRC composite bridge deck proposed in this paper is superior to conventional steel-UHPC composite bridge deck in terms of cost-benefit and environmental impact.

Sensitivity of Frequency Domain Near Infrared Spectroscopy for Neurovascular Structure Detection in Biotissue Volume: Numerical Modeling Results.

Through numerical modeling, it has been determined that near infrared spectroscopy with a frequency domain approach can detect neurovascular structures with diameters from 0.5 mm at source-detector distances of 5-8 mm, depending on optical parameters and technical implementation of the method. Among the five classical machine learning methods considered, quadratic discriminant analysis is the most effective for detection. Furthermore, it has been demonstrated that the use of a photomultiplier tube and the registration of both amplitude and phase signal components exhibit the highest sensitivity. Spectroscopy can rival modern ultrasound for detecting arterial vessels. A cross-shaped probe configuration improves sensitivity, and the ratio of reduced scattering coefficient values at different wavelengths is informative for blood-filled vessel detection. These findings are consistent with and significantly extend previous experimental in vivo and in situ studies and could be valuable for intraoperative diagnostic tasks, particularly in neurosurgery.

Impact Craters on Earth with a Diameter of More than 200 km: Numerical Modeling

The three largest impact craters, the remains of which have been found on Earth to date, had diameters of about 200 km immediately after formation. The search for traces of larger impact structures continues. This paper presents the results of numerical modeling of the formation of terrestrial impact craters larger than those already found. It is shown that the inferred geothermal gradient significantly influences the initial geometry of the impact melt region, which may facilitate the search for the remains of deeply eroded ancient impact structures.

Comprehensive Investigation of the Thermal Performance of an Electrically Heated Double-Glazed Window: A Theoretical and Experimental Approach

The thermal performance of windows is an important area of research to reduce the energy consumption of buildings and improve indoor comfort. The application of innovative glazing technologies can improve the energy performance of windows and transparent facades, resulting in significant energy savings. This paper presents research results on the energy performance of electrically heated windows. A comprehensive CFD and experimental analysis of the heat transfer processes in a window space depending on the size, power, and location of an electric heater was performed. The convective gas flows in the gas gaps and in the boundary layer were also analysed, and it is shown that a window with an electric heater can reduce the energy consumption of a room by 10–12%. This study is a pilot study to assess the feasibility and cost-effectiveness of electric local heating of a window or facade to minimise heat loss before full-scale implementation. The results of numerical modelling and experimental studies confirm the potential of the new technologies.

Performance of an advanced sand constitutive model in modelling soil and soil-structure interaction under seismic excitation

There is a growing number of available advanced soil constitutive models aimed at capturing soil cyclic behaviour and their subsequent use in seismic applications. Nevertheless, detailed validation studies of these soil constitutive models on benchmark experimental works including seismic soil-structure interaction are still rare. This work presents a short validation study of the seismic performance of an advanced elastoplastic sand constitutive model on a boundary value problem including kinematic and inertial soil-structure interaction. The results of the finite element numerical model for the free field and structural responses are compared with the experimental work on a group of piles analysed in a flexible soil container filled with dry sand and subjected to simplified seismic loading. In general, the comparisons show a satisfactory match between the results of the simulations and the experiments, with the exception of the numerical predictions of settlements. The computed results are discussed based on: i) the dominant stress-paths in soil; ii) parametric studies on the settlement evaluation; iii) the origin of the high frequency motion oscillations to simple sinusoidal input motions; all with respect to potential improvements in the formulation of the elastic behaviour of the constitutive model in the future.

Effect of joint-slippage on transmission tower performance with a simplified model of bolted joints

ABSTRACT Bolted joint behaviour is a key parameter in predicting transmission tower performance. Various types of joints are based on the number of bolts and their configuration. However, a few types of these joints were tested or modelled. In the present study, the load-deformation response of transmission tower joints as a joint behaviour was predicted using a simplified numerical model. Then, available experimental load-deformation responses of joints were used to verify the results of the proposed model. In the last step, the joint behaviours of a 400 kV transmission tower were predicted with the proposed numerical model. Then, the evaluation of the tower’s response was done with a numerical model in ABAQUS under testing loading conditions. Lastly, the deformation of a full-scale tested tower was compared with the numerical results. The numerical model results show a good agreement with the experimental results. The ultimate strength and its corresponding displacement at the full-scale model are predicted with an error of about 4%. Moreover, the failure mode of the transmission tower was not affected by the behaviour of the joints.

Modeling of the unsteady aerodynamic characteristics of the NACA 0015 airfoil from the data of numerical calculations of the flow

The possible application of the results of numerical modeling in developing an approximate phenomenological mathematical aerodynamic model applicable in solving the problems of dynamics is studied with reference to the example of the unsteady flow past the NACA 0015 airfoil oscillating in the angle of attackat different frequencies, amplitudes, and mean angles of attack. For this purpose, the Reynolds equations are solved in both steady and unsteady formulations, together with thek–ω-SST turbulence model. The results of the calculations are validated by means of comparing them with the experimental data. The model of the normal force and the longitudinal moment formulated within the frameworkof an approach introducing an internal dynamic variable is identified according to the data of calculations. The results of the modeling are compared with the numerical and experimental data. The comparison with the conventional approach to the modeling based on the linear unsteady model with the use of dynamic derivatives is also carried out.

Exploring the impact of epoxy coated 3D-Printed polymers on surface roughness and mechanical behavior: An experimental and numerical study

The present study used polymers such as PLA and ABS filaments for the 3D printing parts with varying layer thicknesses. The mechanical properties and surface finish of the as-printed and epoxy resin-coated samples were investigated. Noteworthy findings indicate that when the PLA material is printed at a layer thickness of 0.06 mm followed by no coating one can achieve superior tensile strength of approximately 39 MPa as compared to 20 MPa of ABS material. The ultimate tensile strength of the coated materials averaged approximately 15 MPa for both PLA and ABS. The surface roughness of PLA material printed with a 0.06 mm layer thickness showed a 95.13 % reduction after coating. Despite ABS samples being harder than PLA material, the layer thickness emerged as the most influential factor in enhancing the hardness. The dominance of lower layer thickness over other conditions is particularly evident in the modulus of elasticity. In addition to the experimental investigation, a non-linear structural analysis of the uniaxial tensile behaviour of the coated and uncoated 3D prints was also carried out. The fracture modes and deformation behaviours in numerical modelling and experimental results across various parametric conditions were found to be in good agreement. Specifically, the numerical results at lower loading conditions for a layer thickness of 0.06 mm PLA and ABS samples, in the uncoated conditions, mirrored the experimental outcomes.

Forecasting In-Flight Icing over Greece: Insights from a Low-Pressure System Case Study

Forecasting in-flight icing conditions is crucial for aviation safety, particularly in regions with variable and complex meteorological configurations, such as Greece. Icing accretion onto the aircraft’s surfaces is influenced by the presence of supercooled water in subfreezing environments. This paper outlines a methodology of forecasting icing conditions, with the development of the Icing Potential Algorithm that takes into consideration the meteorological scenarios related to icing accretion, using state-of-the-art Numerical Weather Prediction model results, and forming a fuzzy logic tree based on different membership functions, applied for the first time over Greece. The synoptic situation of an organized low-pressure system passage, with occlusion, cold and warm fronts, over Greece that creates dynamically significant conditions for icing formation was investigated. The sensitivity of the algorithm was revealed upon the precipitation, cloud type and vertical velocity effects. It was shown that the greatest icing intensity is associated with single-layer ice and multi-layer clouds that are comprised of both ice and supercooled water, while convectivity and storm presence lead to also enhancing the icing formation. A qualitative evaluation of the results with satellite, radar and METAR observations was performed, indicating the general agreement of the method mainly with the ground-based observations.

Modeling and Analysis of Kamikaze UAV Design with 3 Different Wing Configurations

Appropriate design parameters need to be determined for unmanned aerial vehicles that can perform kamikaze missions. In this study, a UAV with 3 different wing configurations and a fuselage and tail wings were designed, and the flow around the wing was examined using computational fluid mechanics. Advanced modeling techniques were employed to simulate and analyze the aerodynamic behavior of these configurations. The effect of angle of attack (AoA), wing positioning on the fuselage, and wing configurations were investigated. Due to the effect of the wing sweep angle, high-pressure values in the arrow-angle wing were lower than in rectangular and trapezoidal wings. In a similar situation, the flow separation on the arrow-angle wing is less advanced towards the wing tip. When the wing type and connection location were examined, the highest ${{C}_{l}}/{{C}_{d}}$ ratio was obtained in the trapezoidal model connected to the fuselage in the middle. The results of numerical wing models compared with the theoretical lift coefficient were consistent. Trapezoidal and rectangular wings had a high lift coefficient, but after ${{15}^{\circ }}$ of AoA, the lift coefficient decreased. At angles of attack beyond ${{15}^{\circ }}$, the arrow-angle wing still has an increasing lift coefficient. As the angle of attack increased, the drag coefficient was also enhanced. The lowest drag coefficient occurred in the arrow-angle wing model. Up to ${{5}^{\circ }}$of AoA, all wing models raised the ${{C}_{l}}/{{C}_{d}}$ ratio. The ${{C}_{l}}/{{C}_{d}}$ ratio decreased at higher angles of attack. As a result of the examination, it would be more correct to choose trapezoidal and arrow-angle wings.

Голографический метод обработки гидроакустических сигналов высокочастотного источника в мелком море

The paper presents a method for holographic processing of high-frequency hydroacoustic signals using a vector-scalar receiver in shallow waters. The results of theoretical analysis and numerical modeling are presented. Interferograms and holograms for various components of oscillatory velocity and sound pressure are analyzed. It is shown that noise signals holographic processing using a vector-scalar receiver allows detecting a source and estimating a bearing. The results of the method verification in a numerical experiment are presented.

Multi-objective optimization of comprehensive performance enhancement for proton exchange membrane fuel cell based on machine learning

The comprehensive performance of proton exchange membrane fuel cells depends on operating conditions. This paper innovatively uses the Pearson correlation coefficient to screen the optimization objectives (uniformity index of oxygen, standard deviation of temperature, net power density), and obtains the optimal operating conditions of the proton exchange membrane fuel cell through a multi-objective optimization method. The optimized dataset comes from the simulation results of the three-dimensional numerical model, and the regression model is established through the response surface method. Moreover, the non-dominated sorting genetic algorithm-II is used for processing to obtain the Pareto front solution set, and the optimal operating conditions are obtained from it through the Technique for order preference by similarity to an ideal solution. The analysis of variance result shows that the influence of cathode operating conditions on the comprehensive performance is greater than that of anode, especially the influence of cathode stoichiometry ratio is the most significant. The optimal solution obtained 1.0981 %, 10.5845 %, and 1.0376 % enhancement compared to the optimal values in the simulation results. The differences between the three optimization objectives are only 0.8190 %, 1.0315 %, and 0.8789 % as verified by numerical simulation, thus the machine learning results are reliable and accurate.

An Analytical Adhesion Model for Elastic Contact Electrification

Abstract Contact electrification is a universal phenomenon that commonly occurs in almost every solid–solid contact pair. The tribo-charges deposited on two surfaces by contact electrification can significantly affect adhesion; however, contact electrification is often overlooked in the study of adhesive contact. Here, we develop an analytical model to investigate electroadhesion during the contact phase between two initially uncharged dielectric surfaces, namely, an elastic parabolic surface and a rigid flat. A system of nonlinear equations is derived to describe the relationship between the indentation, normal load, radius of contact area, and radius of the charged zone using the Barthel–Maugis–Dugdale model (Barthel, 1999, “Modelling the Adhesion of Spheres: When the Form of the Interaction Is Complex, Colloids. Surf., A., 149, pp. 99105.). The analytical results show good agreement with the numerical results of the full self-consistent contact model. When contact electrification leads to a higher tribo-charge density and a larger charged zone, it has a greater impact on the normal traction, interfacial gap, force-approach curves, jump-out, and dissipated energy. The analytical model developed in this study serves as the foundation for advances in rough surface electroadhesive contact and electroadhesion testing, and it sheds light on the usage of adhesive joints in ultra-high vacuum environments and outer space, where contact electrification has a significant impact.

Cyclic loading experiments and numerical analysis of laterally loaded piles constructed in marine soil

This study aims to thoroughly analyze the lateral loads that impact tubular steel piles, which are extensively employed in the construction of coastal structures. The ASTM D 3966 standard was followed for conducting field tests on test piles installed at the Mersin International Port. The “time-displacement” and “load-displacement” curves were obtained from the cyclic loading test of the laterally loaded piles at the construction site. The finite elements models of the tests conducted on the construction site with the same parameters was built to perform numerical analysis. At the end of the analysis, it was determined that the numerical model's results were highly consistent with those obtained from the field test. After verifying the field experiments with numerical models, a parametric study was conducted. Parametric studies were conducted to compare the lateral displacements of tubular steel piles with variations in pile diameter, wall thickness, and load application height effect. The relationship between pile head displacements and these parameters appears to be almost linear. It is noteworthy that a change of approximately 10 percent in these parameters shows a correlation with changes of up to 3 percent in deformations.

NUMERICAL-ANALYTICAL DELAY MODEL BASED ON QS WITHOPERATIONAL SHIFT OF DISTRIBUTION PRINCIPLES

This article demonstrates results for a queuing system formed by right-shifting an Erlang distribution and a second-order hyperexponential distribution. As is known, the first distribution provides a coefficient of variation less than one, and the second one – more than one. From the general queuing theory, it is known that the average delay of requests in the queue in the QS G/G/1 is related to the coefficients of variation of arrival intervals and service times by a quadratic dependence, and the system we are considering belongs precisely to this type. An operational shift in the distribution laws leads to a multiple reduction in delay compared to a conventional system, and this value depends on the value of the shift parameter. To construct a mathematical model of the delay, the method of spectral solution of the Lindley integral equation for the system under consideration was applied. For the practical application of the obtained results, the standard method of oprobability theory moments is used. The obtained results of numerical and analytical modeling in Mathcad clearly confirm the adequacy of the proposed mathematical delay model.