Results Of Numerical Modeling Research Articles

Experimental and numerical investigation of rectangular labyrinth weirs in an open channel

Labyrinth weirs are commonly used to increase the discharge efficiency in free-overflow discharges. These weirs provide a higher discharge efficiency than conventional linear weirs at the same headwater. In this study, the hydraulic performance of rectangular labyrinth weirs (RLWs) under different geometries and flow conditions was investigated experimentally and numerically. The numerical model was verified and validated using the grid convergence index method and experimental data. Numerical modelling results showed increased performance of the RLW due to the distribution of lateral velocities in the inlet keys, while nappe interference in the downstream keys led to a decrease in performance at high headwater. Within the limitations of 1.5 ≤ L/B ≤ 2.33 and 0.1 < Ho/P < 0.61 (L is the weir crest length, B is the channel width, Ho is the total water head and P is the weir height), a performance increase of 44% on average (maximum increase of 67%) for unit channel width was found for RLWs compared with linear weirs. For these limitations, two new empirical formulas with a high correlation were derived to estimate the discharge coefficients of RLWs based on B and L for Ho/P > 0.1, which are widely used in practice. When compared with some data in the literature, the empirical formulas produced satisfactory results.

Разрешение шумовых сигналов при наличии случайных неоднородностей океанической среды

The formation of a hologram of noise signals in a randomly inhomogeneous oceanic environment is discussed. It is shown that a hologram of signals from several sources appears predominantly as a sum of holograms of signals formed by undisturbed and disturbed fields. A method for clearing a hologram from disturbed fields is described. Criteria for signal resolution are proposed. The results of numerical modeling are presented for resolving two signals and estimating the parameters of sources against the background of intense internal waves causing horizontal refraction of sound field modes.

Peri-Ultrasound Modeling to Investigate the Performance of Different Nonlinear Ultrasonic Techniques for Damage Monitoring in Plate Structures

Abstract Peri-ultrasound modeling which is based on nonlocal peridynamics is found and proven to be effective for modeling nonlinear waves propagating and interacting with damages in structures. This work presents the peri-ultrasound modeling to investigate the performance of three commonly used nonlinear ultrasonic (NLU) techniques—wave mixing, higher harmonic generation (HHG), and sideband peak count-index (or SPC-I) for monitoring damages (or cracks) in three-dimensional (3D) plate structures. Cracks can be defined as “thin cracks” and “thick cracks” according to the horizon size mentioned in peridynamics. Peri-ultrasound modeling results reveal that the SPC-I results are consistent with other reported numerical modeling and experimental results available in the literature. However, the modulation indicator (MI) from the wave mixing model only shows consistent trends for thin cracks but not for thick cracks and its reliability is affected by the initial excitation bandwidth. The relative acoustic nonlinearity factor β from the HHG technique shows consistent trends for thick cracks but not for thin cracks. It can be concluded from the obtained parametric analysis results that the SPC-I technique is more robust and reliable for monitoring damages in engineering structures.

Experimental Investigation of Parameters Influencing the Formation of Dry Bands and Related Electric Field

This paper presents an experimental investigation conducted to determine the influence of parameters such as the ambient temperature, pollution level, and substrate material on the formation of dry bands on polluted layers. To investigate these parameters, we applied a simplified insulator geometry, developed in our previous work, to experimentally control the complex process of dry band formation on a polluted surface. The simple geometry of the experimental model enabled the use of Plexiglas, RTV, and glass as construction substrate materials. RTV and glass were used to simulate a composite and ceramic insulator surface, respectively. Moreover, an electrooptic (EO) probe enabled the measurement of the axial E-field evolution at the surface of the dry band during dry band formation. The results indicated that the substrate material, ambient temperature, and pollution level substantially influence dry band formation. The effects of the first two parameters are directly associated with heat transfer phenomena in the substrate material and at the ambient air/substrate interface. The effect of the third parameter is associated with absorption and evaporation of the pollution layer. In addition, the appearance of the dry band can be clearly identified by a rapid increase in both the pollution layer resistance and the axial E-field in the dry band area. The value of the axial E-field is influenced primarily by the width of the dry band and by the pollution layer resistance, which is directly dependent on the humidification duration. Finally, because most of the results obtained herein were in accordance with those in the literature, we conclude that the proposed experimental model may provide an effective and inexpensive testing method for developing new materials and solutions for improving the dielectric performance of insulators used in polluted environments. Similarly, the simple geometry of the experimental model and the ability to easily control the experimental parameters may enable this tool to validate the results of various numerical models in studies of the thermoelectrical behavior of polluted insulators.

Пульсации течения жидкого металла, генерируемые переменным магнитным полем

This paper studies numerically a vortex flow of liquid metal driven by an electromagnetic force, which is generated by the interaction of the alternating magnetic field of a short solenoid with the induced electrical current. A short solenoid is placed coaxially to a cylindrical cell at half of its height. The mathematical model used to describe the process is based on the equations of magnetic hydrodynamics in the induction-free approximation. Calculations, which are carried out by the control volume method using the ANSYS Fluent package, show that the average flow has the form of two toroidal vortices. The calculated velocity fields are indicative of the oscillatory behavior of vortices, accompanied by a change in their sizes. In the examined range of the force parameter, the predominant flow pattern is the single-mode oscillatory flow. The dependences of characteristic frequency and Reynolds number on the force parameter, are obtained using spectral analysis. It has been found that the oscillation period is close to the period of rotation of a large-scale vortex. It has been established that the oscillations are of quasi-periodic character, and a distinct oscillation frequency is observed only in the flow region near the solenoid. The effect of velocity fluctuations is strong and can be detected in laboratory conditions when using gallium eutectic. Such experiment is planned for the near future. The flow rate of gallium eutectic will be measured by an ultrasonic Doppler anemometer. The results of numerical modeling and their verifications can be useful in determining the ways of reducing the intensity of vortex flows during the electromagnetic separation of impurities, which is based on the induction mechanism responsible for the generation of electromagnetic force that displaces particles. The data on the oscillation frequency of the unsteady flow can be used in the development of a non-contact technique for estimating the average electrical conductivity of a two-phase medium, such as a liquid metal with undesirable impurities.

The impact of nuclear reactions on the neutron-star g-mode spectrum

ABSTRACT Mature neutron stars are expected to exhibit gravity g modes due to stratification caused by a varying matter composition. These modes are affected by nuclear reactions, leading to complex (damped) mode frequencies and the suppression of high-order g modes. This is in contrast with the common non-dissipative analysis which leads to an infinite g-mode spectrum. Focusing on the transition between the fast- and slow-reaction regimes, we examine the precise impact of nuclear reactions on the g-mode spectrum. The general framework for the analysis is presented along with sample numerical results for a matter model based on the BSk21 equation of state with a suitable parametrization for the reaction rates.

NUMERICAL JUSTIFICATION OF THE LABORATORY TECHNIQUE FOR TESTING OF FIRE-EXTINGUISHING POWDERS

Improvement of firefighting means and methods for measuring their effectiveness are important tasks in the field of fire safety. The paper presents the results of experimental measurements of the minimum extinguishing concentration of powder mixtures that can be applied as effective explosion-suppressing barriers. Measurements of the minimum extinguishing concentration of the investigated powders were carried out using a laboratory method with their pulsed delivery to a microfire of class B using compressed air. In order to justify and assess possible errors of the mentioned laboratory method for measuring extinguishing efficiency, numerical 3D modeling of the interaction of a multiphase flow with a model combustion focus was performed. The analysis of the numerical modeling results has shown that, for the applied laboratory method, almost the entire portion of the investigated powder enters the combustion zone. Additionally, the numerical calculations indicate that under the specified experimental conditions, the particle size of the powder has no noticeable effect on their loss into the surrounding flame space. Thus, these results justified the use of the mentioned laboratory method for he comparative evaluation of fire-extinguishing powders with a wide range of dispersity. The application of this laboratory method for assessing the effectiveness of the fire-extinguishing powder allowed for the development of an optimal powder composition for explosion suppression, incorporating inert mineral particles as the main component and an additive of a chemically active potassium-containing combustion inhibitor.

Effects of wind on deep convection in Lake Baikal during the autumnal thermal bar

The results of numerical modeling of processes of deep convection in Lake Baikal during the autumnal thermal bar are presented. Analysis of the space—time distributions of temperature under different wind conditions was conducted on an example of the Boldakov River—Maloye More Strait cross-section which is characterised by the great depths. Simulations have shown the effectiveness of wind only in the upper 250 m layers. However, cabbeling instability generated by the thermal bar can lead to convective mixing to a depth of ∼600 m.

Low-noise thermal shielding around the cryogenic payloads in the Einstein Telescope

The Einstein Telescope (ET) is a planned third-generation gravitational-wave detector that includes a low-frequency (LF) and a high-frequency (HF) laser interferometer. Cryogenic operation of ET-LF is imperative for exploiting the full scientific potential of ET, with mirrors operated at temperatures of 10 K to 20 K in order to reduce the thermal noise. Thermal shielding around the optics is essential to support the cooldown process and to decrease the heat load. Additionally in steady-state operation, mechanical vibrations must be kept to an absolute minimum in order to limit noise contributions from scattered light.We present a cooling concept for a thermal shield surrounding the cryogenic optics of ET-LF, which considers rapid cooldown and low vibration in steady-state operation. During cooldown, cooling tubes enable the flow of supercritical helium, driving the shield temperature decrease by forced convection. For steady-state operation, the shield cooling mechanism is converted to static heat conduction in He-II within the same tubes. A first mechanical model is presented that fulfills the thermal and vibrational requirements. Thermal characteristics of the shield are demonstrated by means of analytical and numerical modeling results. Modal and dynamic analyses are performed to obtain natural frequencies and transfer functions.

Physics-informed machine learning of multi-source monitoring data sparsely measured within a 2D vertical cross-section

Conventional machine learning (ML) methods suffer from several limitations, e.g., overreliance on large training datasets and poor performance in extrapolating beyond observations. Geotechnical monitoring data at specific sites are multi-sourced (e.g., settlement and horizontal displacement data). Moreover, each source of monitoring data may vary temporally and be sparsely measured, e.g., within a two-dimensional (2D) geological cross-section. Thus, effectively learning multi-source and limited monitoring data is difficult using existing ML methods. To address this challenge, this study proposes a physics-informed ML method combining geotechnical numerical models (e.g., the finite element model (FEM)) with sparse dictionary learning (SDL) methods. It uses a range of probable numerical model results corresponding to multiple, temporally varying responses in a 2D spatial range to construct a “dictionary” in SDL and employs multi-source and limited monitoring data to identify a few “atoms” from the constructed dictionary to improve model predictions. An engineering project for embankment construction is used to illustrate the proposed approach. Our results indicate that the proposed approach effectively integrates FEM results with multi-source and sparsely measured monitoring data and improves the predictions of multiple spatio-temporally varying geotechnical responses significantly, particularly those at subsequent time steps and unmonitored spatial locations within a 2D vertical cross-section.

Prediction method for the tension force of support ropes in flexible rockfall barriers based on full-scale experiments and numerical analysis

This paper proposes a prediction method for the tension force of support ropes in flexible rockfall barriers. The method is based on two full-scale model tests with an impact energy of 3000 kJ, as well as 36 set numerical models featuring varying lengths and impact energies. From the results of full scale tests and numerical models, it is inferred that the tension force at the end of the support rope is significantly less than that at the point of impact, exhibiting an approximate Gaussian attenuation distribution with propagation distance. To account for the attenuation of tensile forces in support ropes, a tensile attenuation coefficient is defined. Through comparative analysis of data obtained from 36 models with varying impact energies and propagation distances, the average attenuation coefficient for the upper support rope is determined to be approximately 0.7, while the average coefficient for the lower support rope is around 0.8. Utilizing the least squares method, a prediction method for the tension force of support ropes in flexible rockfall barriers is established. This method takes into account both the propagation distance and impact energy, enabling accurate predictions of the tensile behavior of the ropes under different conditions. This prediction model provides valuable insights for engineers in the design and optimization of these flexible barriers for rockfall mitigation.

НЕЛИНЕЙНЫЙ АНАЛИЗ КИРПИЧНЫХ СВОДЧАТЫХ КОНСТРУКЦИЙ ИСТОРИЧЕСКИХ ЗДАНИЙ

The difficulty in calculating masonry structures lies in taking into account the anisotropic properties of masonry. This problem is particularly acute when analyzing the VAT of historical stone structures during the examination of their technical condition. This article provides an analysis of the vaulted ceiling of the mansion, built in the first half of the XVIII century. For numerical modeling of brickwork, a bilinear model of the material with isotropic hardening can be applied. It is the simplest in practical application, but only one limiting resistance is taken into account in this model. Therefore, for the calculation of stone structures, it was proposed to use a nonlinear Rankine material model, which takes into account the different behavior of masonry under tension and compression, including softening. The article presents the results of numerical modeling of brickwork with different models of materials. The comparison and evaluation of the structural strength were carried out.

NUMERICAL MODELING OF THE SEPARATION OF LIQUID AND GASEOUS PHASES OF HYDROCARBON MIXTURES IN A VORTEX CHAMBER

Analysis of the separation process in a vortex chamber is based on the assumption of phase equilibrium existence in the system. Dynamic processes occurring while phases moving in a vortex chamber contribute to the separation of the liquid and gaseous phases of hydrocarbon mixtures. Thus, the transition of the fluid to a metastable state in the vortex chamber will occur in less time than using the traditional methods.Based on the developed model of a vortex chamber in ANSYS FLUENT a series of numerical experiments were carried out. The influence of various parameters on the amount of removal of liquid and gaseous phases of hydrocarbon mixtures was determined. Indicators of the properties of the liquid phase have the greatest impact on the dynamics of the removal of liquid with gas, while the characteristics of the gas phase can be neglected due to their statistical insignificance.When studying the design of a vortex chamber, the smallest removal is observedwhen the inlet pipe is installed further from the top of the chamber (more recessed into the flow). The H/D ratio has less influence, but the offset decreases monotonically as the H/D parameter increases. The influence of the flow rate and the ratio of phases formed in the nozzles on the amount of carryover indicates that with an increase in the gas phase in the incoming flow, the removal of liquid increases. The inlet rate has a less influence.Statistical processing and regression analysis of the results of numerical modeling were carried out. Empirical equations for calculating the amount of droplet liquid removal from the vortex chamber are obtained. The dispersion value was calculated and the significance of the regression coefficients was checked. Based on the results of assessing homogeneity, reproducibility, and adequacy, a conclusion was made about the suitability of the developed model for calculations.

Assessment of Site Effects and Numerical Modeling of Seismic Ground Motion to Support Seismic Microzonation of Dushanbe City, Tajikistan

In the territory of Dushanbe city, the capital of Tajikistan, detailed geological and geophysical data were collected during geophysical surveys in 2019–2020. The data comprise 5 microtremor array measurements, 9 seismic refraction tomography profiles, seismological data from 5 temporary seismic stations for standard spectral ratio calculations, 60 borehole datasets, and 175 ambient noise measurements. The complete dataset for Dushanbe was used to build a consistent 3D geologic model of the city with a size of 12 × 12 km2. The results of the seismological and geophysical surveys were compared and calibrated with borehole data to define the boundaries of each layer in the study area. The Leapfrog Works software was utilized to create a 3D geomodel. From the 3D geomodel, we extracted six 12 km long 2D geological cross-sections. These 2D geological cross-sections were used for 2D dynamic numerical modeling with the Universal Distinct Element Code software to calculate the local seismic response. Finally, the dynamic numerical modeling results were compared with the amplification functions obtained from the seismological and ambient noise data analysis. The 2D dynamic numerical modeling results allowed a better assessment of the site effects in the study area to support seismic microzonation and the determination of local peak ground acceleration changes in combination with regional seismic hazard maps. In addition, our results confirm the strong seismic amplification effects noted in some previous studies, which are attributed to the influence of local topographic and subsurface characteristics on seismic ground motions.

Об одном подходе к групповой навигации необитаемых подводных аппаратов

A method for the group navigation support of autonomous underwater vehicles performing a common mission in shallow waters, which includes a leader underwater vehicle with high-precision navigation tools, is described. The operation of all devices is synchronized and involves information interaction between them. The determination for coordinates of the vehicles is based on measuring the distances between them and the leader device. An algorithm for estimating the location of individual devices is considered. The results of numerical modeling are presented, confirming the operability and required accuracy of the considered algorithm.

STUDY OF THE EFFICIENCY OF THE FUNCTIONING PROCESS OF THE MECHATRONIC SYSTEM OF ENSURING THE MICROCLIMATE OF ANIMAL PREMISES

The development of the livestock industry is the basis of Ukraine's food security. One of the ways to solve this problem is to improve the conditions of keeping animals, including improving the microclimate of livestock and poultry premises. Modern animal husbandry technologies make high demands on the microclimate in livestock premises. According to scientists, animal husbandry specialists and technologists, animal productivity is determined by 50...60% feed, 15...20% by care, and 10...30% by the microclimate in the livestock premises. Deviation of the microclimate parameters from the established optimal limits leads to a decrease in milk yield by 10...20%, an increase in live weight – by 20...35%, an increase in the departure of young animals to 5...40%, and a decrease in laying hens – by 30%...35%, costs of an additional amount of feed, shortening the service life of equipment, machines and the buildings themselves, reducing the resistance of animals to diseases, negatively affecting the service personnel. The article presents a structural and technological scheme of a mechatronic system for ensuring a normative microclimate of livestock premises, which allows to increase the efficiency of ensuring a normative microclimate of livestock premises by using a mechatronic system for controlling the process of air disinfection using ultraviolet radiation of bactericidal lamps. According to the results of numerical modeling of the air heat exchanger of the indirect-evaporative type, the distribution of the temperature field, vector field of velocities and absolute air humidity in channels of different shapes (square, equilateral triangle, circle) was established. The calculated coefficient of thermal efficiency of the heat exchanger with triangular shaped channels is the whitest in contrast to square and round shapes. A comparative analysis of humidity distribution in channels of different shapes confirms that the absolute humidity of the thermal air flow decreases earlier in the indirect-evaporative type heat exchanger with triangular channels.

SIMULATION OF THE STRESSED-DEFORMED STATE OF THE ELASTIC DISCTOR RACK WITH A STIFFNESS REGULATOR

The paper involves the physical-mathematical modeling of the stress-strain state of an elastic stand of a developed disc harrow equipped with a stiffness regulator. The use of disc tools with individual attachment to elastic stands contributes to improving the quality and reducing the energy consumption of soil processing. This is due to the formation of oscillatory motion of the discs caused by the uneven resistance of the soil in the direction of the unit's movement. The goal of theoretical research is three-dimensional modeling of the stress-strain state of the elastic stand of the disc harrow with a stiffness regulator and substantiation of the range of its rational design parameters. To evaluate the interaction process between elastic working elements and the soil, a harmonic analysis was performed to determine the peak response of the system in a steady state to harmonic loads. In each step of the solution, all applied loads and base excitations have the same frequency, and the values are determined by the corresponding frequency curves. Using the SOLIDWORKS Simulation software package, the relevant physical-mathematical apparatus was compiled. On the basis of this approach, already at the stage of designing disk working bodies on elastic risers, it is possible to conclude about the possibility of them performing specific technological tasks, when by changing the parameters of the risers and conducting repeated studies, it is possible to obtain the corresponding dependencies in the form of regression equations. The results of numerical modeling provide visualization of the change in stress distribution over time in the stand. The dynamics of the change in maximum stress, located on the bend of the stand (R2) and the stiffness regulator (R1), were determined as the stress changes according to the law of damped oscillation with a specified natural frequency. In order to ensure the best working conditions of the elastic riser, it is necessary to ensure the greatest deformation of the riser at the place of attachment of the disc ΔL1 and, at the same time, the smallest value of the deformation of the tool frame ΔL2, by solving the trade-off problem in the Wolfram Cloud software package by maximizing the multiplicative function, the rational geometric dimensions of the diskator riser and constructive parameters of its placement in space.

Comparison of Single-Phase Mathematical Models for Solid-State Packed Beds for Thermal Energy Storage

This article presents an analytical solution for the evaluation of the thermal performance of packed bed sensible heat storage. The numerical model developed was tested for four different solid storage mediums. The thermal energy equation is solved numerically by deploying the finite difference method. The presented analytical solution is based on a novel mathematical approach. The numerical model was validated using the computer simulation package Comsol Multiphysics v5.3. Our numerical model results are in good agreement with the published experimental data, with an overall difference of ~10%. Hence, the numerical model is an efficient way of evaluating the thermal performance of packed bed thermal energy storage systems compared to other numerical strategies or computer simulation techniques. This proves that the novel analytical model has shown to be a reliable and broadly accurate approach to acquire the thermal performance of sensible heat storage.

Effect of patient-specific factors on regeneration in lumbar spine at healthy disc and total disc replacement. Computer simulation

Background and ObjectiveDegenerative diseases of the spine have a negative impact on the quality of life of patients. This study presents the results of numerical modelling of the mechanical behaviour of the lumbar spine with patient-specific conditions at physiological loads. This paper aims to numerically study the influence of degenerative changes in the spine and the presence of an endoprosthesis on the creation of conditions for tissue regeneration. MethodsA numerical model of the mechanical behaviour of lumbar spine at healthy and after total disc replacement under low-energy impacts equivalent to physiological loads is presented. The model is based on the movable cellular automaton method (discrete elements), where the mechanical behaviour of bone tissue is described using the Biot poroelasticity accounting for the presence and transfer of interstitial biological fluid. The nutritional pathways of the intervertebral disc in cases of healthy and osteoporotic bone tissues were predicted based on the analysis of the simulation results according to the mechanobiological principles. ResultsSimulation of total disc replacement showed that osseointegration of the artificial disc plates occurs only in healthy bone tissue. With total disc replacement in a patient with osteoporosis, there is an area of increased risk of bone resorption in the near-contact area, approximately 1 mm wide, around the fixators. Dynamic loads may improve the osseointegration of the implant in pathological conditions of the bone tissue. ConclusionsThe results obtained in the case of healthy spine and osteoporotic bone tissues correspond to the experimental data on biomechanics and possible methods of IVD regeneration from the position of mechanobiological principles. The results obtained with an artificial disc (with keel-type fixation) showed that the use of this type of endoprosthesis in healthy bone tissues allows to reproduce the function of the natural intervertebral disc and does not contribute to the development of neoplastic processes. In the case of an artificial disc with osteoporosis of bone tissues, there is a zone with increased risk of tissue resorption and development of neoplastic processes in the area near the contact of the implant attachment. This circumstance can be compensated by increasing the loading level.

Comparative Analysis of the Characteristics of Asynchro- nous Drives with Vector Control and Direct Torque Control

Active development of electric drive theory in recent decades has led to the emergence of various methods for asynchronous three-phase motors control, promoted by leading drive development companies, the competition between which inevitably gives rise to false preconceptions about the real capabilities and characteristics of these methods. Additionally, literary sources often bypass positional drives, focusing on speed control, and the same can be said about the preference for synchronous drives over asynchronous ones. This study solves the problem of a comprehensive comparison of the characteristics of classical vector control based drives and direct torque control schemes at the levels of theoretical description and computer simulation. To solve this problem mathematical descriptions and functional diagrams of asynchronous motors with indicated control systems are given and analyzed and models of considered systems are developed in the Simulink environment of the Matlab program, considering flexibility of mechanical transmission and various resistance moments and allowing to form a quantitative assessment of considered characteristics. The results of numerical modeling are presented on example of a specific induction motor with a squirrel-cage rotor DMChTs 80-2-8OM2 for each system variant in several operating modes, which are of interest for various options of such drives practical application and identifying considered control methods individual features. Advantages and disadvantages formulated as a result, as well as recommendations for the use of the compared drive systems, are quite universal and can be used in design of various drives with both asynchro-nous and synchronous motors.