Results Of Numerical Modeling Research Articles

3D-Oculography: New Method of Determination of Human Gaze Point Position in Space

INTRODUCTION: Oculography — a method of recording movement of eyeballs of a human or animal by analyzing changes in electrical potentials recorded by two electrodes fixed on skin near the eye socket is used to solve various problems. Among them are the determination of pronounced nystagmus, of characteristic changes of oculomotor reactions in different conditions of observing video images. Of interest is the determination of the position of gaze point (GP) and of the area of increased attention in three-dimensional space. This information is associated with the cognitive system of the observer and is of interest not only to physiologists, but also to specialists of related fields. . AIM: To experimentally prove the effectiveness of the developed method of 3D-oculography providing determination of the GP position in space. MATERIALS AND METHODS: The possibility of restoring GP position based on the analysis of recorded oculograms even in the presence of additive noise induced by the external electromagnetic fields, is proven by the numeric modeling method. Direct experimental studies were conducted with recording oculograms of a human observer on a previously verified equipment. A ZB-2 oculograph was used, the data obtained were verified by the method of average values. RESULTS: The obtained modeling results permitted to determine the maximal values of dispersion of additive noise and amplitude shifts of signals, which make possible satisfactory restoration of the coordinates of the GP and parameters of its movement trajectory. The qualitative correspondence of the experimental results to the results of numerical modeling was proven. The correspondence between trajectories of the observed object moving in space and trajectories of GP movement synthesized from counts of recorded oculograms was confirmed. CONCLUSION: Multichannel record of oculographic signals permits restoring parameters of the GP trajectory. Creating systems for recording these signals requires minimization of the noise level. An increase in dispersion of the noise component of the signal leads to most significant errors in calculating the coordinates of trajectory points.

Aerodynamic and Structural Design Procedures Supported by Fabrication and Flight Testing of a Small Unmanned Helicopter

In this work, typical design, production, and testing procedures for a small unmanned helicopter are explained and performed. In doing so, preliminary sizing of the helicopter and three main disciplines are conducted: aerodynamic analytical and numerical simulations, power calculations, and structure analysis assessment. First, a thorough survey is implemented to obtain the trends for the maximum take-off weight versus some design constraints such as rotor diameter, motor power, payload, and empty weight. Performance calculation results are obtained to figure out all aspects that correspond to the specified mission. The designed rotor geometry along with the aerodynamic characteristics and flight performance variables is then validated using the blade element theory and numerical simulations. Second, based on the power curves obtained for different flight regimes, an electric brushless motor is selected. The numerical simulations (Computational Fluid Dynamics) analysis is used to enhance the selection which implies that the motor power should be greater than 5.4 kW to overcome the drag forces. The motor power selection corresponds to a maximum rotor pitch angle of 15∘ and a maximum rotor speed of 1450 RPM. Then, the aerodynamic loads are used as an input for the structural analysis using one-way coupling of fluid–structure interaction (FSI) and consequently designing the internal structure of the blade. Eventually, the internal structure manufactured using carbon fiber-reinforced polymer (CFRP) by applying a combined technique between wet layup and compression molding. The blade is statically tested compared with numerical finite element model results. The fuselage structure along with hub and tail units is manufactured and assembled with the existing on-shelf components to examine the helicopter lift capability with different payloads up to 9 kg. The results show that the detailed design process is significant for manufacturing such blades and the helicopter is capable of lifting off the ground with various payloads depending on the rotor pitch angles (8∘, 12∘, and 15∘) at a constant rotor speed of 1450 RPM.

Construction of the structure of rural electric networks taking into account the availability of renewable sources of electricity

It is noted that although the share of renewable electricity sources continues to grow and develop rapidly, the industry still faces many challenges, including how to continue to reduce electricity losses and annualized costs, improve operation and maintenance efficiency, maintain grid stability, ensure safety and reliability of the power supply system containing renewable sources of electrical energy. It is shown that an effective solution to these problems is possible only on the basis of the analysis of the prospects for the development of local electric power systems that contain renewable sources of electric energy, the development of technical and organizational support mechanisms that will contribute to the construction of modern system (schematic) solutions. It is proposed to apply the potential surface method for building the optimal structure of the rural electrical network during its design and modernization in the presence of renewable sources of electrical energy, which allows optimizing the structure of the network from the point of view of electrical energy losses and reducing annualized costs. The algorithm for forming the structure of power supply systems is described, which implements the simultaneous solution of the tasks of determining the number of load nodes, distributing electrical receivers between them, determining the design of power sources, taking into account the discreteness of the design of system elements. The results of numerical modeling based on the proposed algorithm are presented on the example of solving the problem of reconstruction of a section of the rural electricity network.

Multiprobe Planar Near-field Range Antenna Measurement System with Improved Performance

This article presents a novel multiprobe planar near-field range (PNFR) measurement system. The said system simplifies the overall mechanical design, making it simpler than the existing scanning probe PNFR measurements, and also significantly reduces testing time. A dielectric-based probe is introduced to reduce the antenna size, thereby improving resolution. The probe under consideration is an antipodal Vivaldi antenna offering broadband support and ensuring wideband characteristics of aerials. Numerical results for representative X-band antenna models, presented in the Matlab environment, demonstrate robust performance of the developed measurement system.

The thermal conductivity properties of porous materials based on TPMS

In this study, the effective thermal conductivity of materials based on a porous TPMS structure is investigated. The resulting structure is similar to a matrix and consists of identical pore cells that are strictly periodic in all directions. These pores have several characteristic sizes, and by altering them, materials with predictable effective thermal conductivity can be created. This work investigated materials based on Triply Periodic Minimal Surface (TPMS) of Schwarz P, Schoen IWP and Neovius. The calculation of thermophysical properties was performed using the numerical finite element method in the Ansys software package. Heat transfer in the structures was studied both with and without considering air. The empirical coefficient “n” for the Aivazov–Domashnev formula is expressed analytically. This relationship allows for the creation of materials with predictable thermophysical properties, taking into account the thermal conductivity of non-porous materials. The results of numerical modeling are validated by analytical Austin’s models and experimental data. The samples for the experimental study were made using additive technologies from PETG, ABS, PLA plastic and photopolymer resin. The study has scientific and applied significance, since a method is proposed for predicting the thermal conductivity of materials with an ordered structure. Several solid-state samples of elementary cells were made publicly available for designing materials with predictable thermal conductivity. The novelty of the work lies in obtaining the dependence of effective thermal conductivity on the geometric parameters of the ordered structure for materials with thermal conductivity in a wide range from 0.12 to 400 W/(m°C).

The Cyclic Performance and Macro-Simplified Analytical Model of Internal Joints in RC-Assembled Frame Structures Connected by Unbonded Prestressed Strands and Mortise-Tenon Based on Numerical Studies

This paper introduces a novel type of connection that integrates unbonded prestressed strands (UPS) and mortise-tenon in an assembly frame structure (UPS-MTF). First, the damage process and failure modes of the joints under reciprocating horizontal loads were systematically analyzed using refined numerical models. The recommended values of the design parameters of the joints were derived from the parametric analysis results. Refined numerical modeling results reveal the diagonal compression strut mechanism within the core region of the joint. The diagonal compression struts model assists in establishing the theoretical calculation formula for the skeleton curve of shear stress–strain in the core region. Second, a genetic algorithm (GA) parameter was identified for the restoring force model of the core region to determine the parameters of the hysteresis rules. Finally, a macro-simplified analytical model of the joint was created based on the restoring force model of the core region, and parameter analysis was conducted to verify the applicability of this macro-simplified analytical model. The research results prove that the damaged form of the joint proposed in this paper originates from the shear and relative slip damage between the components in the core region. The axial compression ratio significantly affects the hysteretic performance of the joints, and the upper and lower limit values were identified for the axial compression ratio of the joints. The area and initial effective stress of the UPS exert a minimal effect on the hysteretic performance of the joint. Based on the method proposed in this paper for determining the restoring force model in the core region of the joints, the hysteresis curves obtained from the macro-simplified analytical model closely match the refined numerical analysis model results. This correspondence verifies the applicability of the macro-simplified analytical model.

Impact Toughness Analysis and Numerical Simulation of Coral Aggregate Concrete at Various Strength Grades: Experimental and Data Investigations

This paper comprehensively investigates the dynamic mechanical properties of concrete by employing a 75 mm diameter Split Hopkinson Pressure Bar (SHPB). To be detailed further, dynamic compression experiments are conducted on coral aggregate seawater concrete (CASC) to unveil the relationship between the toughness ratio, strain rate, and different strength grades. A three-dimensional random convex polyhedral aggregate mesoscopic model is also utilized to simulate the damage modes of concrete and its components under varying strain rates. Additionally, the impact of different aggregate volume rates on the damage modes of CASC is also studied. The results show that strain rate has a significant effect on CASC, and the strength grade influences both the damage mode and toughness index of the concrete. The growth rate of the toughness index exhibits a distinct change when the 28-day compressive strength of CASC ranges between 60 and 80 MPa, with three times an increment in the toughness index of high-strength CASC comparing to low-strength CASC undergoing high strain. The introduction of pre-peak and post-peak toughness highlights the lowest pre-to-post-peak toughness ratio at a strain rate of approximately 80 s−1, which indicates a shift in the concrete’s damage mode. Various damage modes of CASC are under dynamic impact and are consequently defined based on these findings. The LS-DYNA finite element software is employed to analyze the damage morphology of CASC at different strain rates, and the numerical simulation results align with the experimental observations. By comparing the numerical simulation results of different models with varying aggregate volume rates, it is reported that CASC’s failure mode is minimized at an aggregate volume rate of 20%.

Аппроксимация экспериментальных коэффициентов гидродинамических сил крыльевого гидродинамического якоря

The article considers a full-scale comparative experiment conducted in 2020 in the water area of the Novosibirsk reservoir on the simultaneous drift of six marine life rafts with a capacity of 6 people each. Each raft was equipped with one of the developed hydrodynamic anchors (HDA); one raft had a standard parachute floating anchor; one raft had no means of preventing drift. The wing hydrodynamic armature showed good results in reducing the drift velocity. To develop design methods of this kind, hydrodynamic forces were determined in the direct experimental basin of the Siberian State University of Water Transport (SSUWT) by towing with different speeds and angles of attack. According to the tests conducted in the direct experimental pool of the police Department, HDA the coefficients of hydrodynamic forces were obtained. It is noted that the HDA is made in full size, which does not require recalculation according to similarity criteria; the values of the coefficients show an unstable dependence on the towing speed, which is explained by the influence of errors of the experimental method and required averaging of the results. To substantiate the possibility of using the averaging method, the results of numerical modeling of the work of HDA carried out in the Ansys Fluent program are used, which revealed a very weak dependence of the coefficients on the flow rate. On this basis, a decision was made on the possibility of averaging coefficients related to flow velocities v ≥ 0.2 m/s, at which the spread of coefficient values is relatively small. The averaged values of the coefficients obtained in the physical experiment are approximated in their ranges of angles of attack by quadratic polynomials to smooth out the results and facilitate their use in mathematical models of the device operation.

Use of explainable machine learning models in blast load prediction

The effects of blast waves and their consequent damage to structures have been an increasingly popular research topic in the past decade. Various methods are used in blast load prediction on structures, including experimental, semi-empirical and numerical approaches. However, there is a demand for developing time-efficient predictive methods that help various professionals, such as engineering practitioners and first responders, in their regular activities. Machine learning (ML), as a subset of artificial intelligence (AI), has gained significant attention in various engineering applications over the past decades for its ability to aid decision-making. However, a critical gap exists in the comprehensive analysis of these ML models' transparency and interpretability levels. This paper presents a novel approach to employing explainable machine learning (XML) to predict the blast loads generated by high explosives. The primary objective is to assess the validity of utilising a machine learning (ML) framework for blast load predictions, examining the scientific consistency of the model's prediction process. This research utilises XML to interpret the ML model-based blast load prediction framework, marking the first documented use of XML in published literature for blast load prediction. This research study utilised three ML models, namely a) Decision Tree, b) Random Forest, and c) Extreme Gradient Boost (XGB) models, to predict blast loads on rigid structures. Validated numerical model results were used to generate the dataset to train the ML models, and the respective dataset consists of approximately 600 independent blast events. The models were evaluated for their predictability using error metrics: adjusted coefficient of determination (adjusted R2), root mean square error (RMSE), and mean absolute error (MAE). The overall ML model performance evaluation showed that the best-performing model, XGB, could make predictions with 98 % accuracy compared to validated numerical predictions. The XML explanations for the XGB models showcased that the blast load prediction procedure of the models aligns with the blast physics principles, ensuring the credibility of the developed ML models. In summary, these XML predictive models can be considered accurate and reliable for blast load prediction on structures.

Practical Calculation of Diaphragm Wall Deflection using Plaxis 3D Software

In this article, the mathematical models within the Plaxis 3D software were used to simulate and assess the deflection of diaphragm walls, comparing with data collected from a real project. This scientific and effective approach is crucial, as analyzing and simulating the excavation stages before constructing diaphragm walls for underground levels becomes essential for controlling wall displacement and preventing potential soil erosion issues in the surrounding deep excavation, which could have serious consequences for neighboring structures. The numerical modeling results demonstrate that the deflection of the diaphragm wall varies inversely with its thickness, but this variation is relatively small and quite compatible with the observed data

Electromagnetic ULF Fields from an Underground Seismic Source on the Earth’s Surface and in the Ionosphere

A theoretical formalism has been developed to calculate the electromagnetic fields generated in the atmosphere–ionosphere system by a finitelength underground horizontal current source. A numerical model with a realistic profile of the ionosphere in a vertical geomagnetic field has been designed based on this theory. It is shown that the apparent impedance of the electromagnetic field created by an underground source on the Earth’s surface is one order of magnitude higher than the Earth’s impedance, which can be used to discriminate perturbations from seismogenic sources. The presented results of numerical modeling allow us to relate perturbations created by a large-scale underground source in the Earth surface magnetic field and in the electric field in the ionosphere. Based on these model estimates it is concluded that many of the ULF electric field perturbations detected in satellite data before earthquakes cannot be attributed to direct emission from seismogenic sources.

Numerical Validation of Fully Coupled Nonlinear Seismic Soil–Pile–Structure Interaction

While many researchers have broadly studied soil–structure interaction (SSI) problems to comprehend SSI effects on the overall system’s behavior, some critical numerical modeling issues have not been sufficiently investigated to achieve the most accurate results. Furthermore, most scholars have not provided detailed explanations of the validation process for their proposed numerical models. Modeling pile foundations in a three-dimensional (3D) continuum system in a fully coupled manner is often challenging for engineers who do not specialize in structural and geotechnical earthquake engineering, as it can be very time-consuming and complicated. Therefore, this work aims to validate a finite element model of seismic soil–pile–structure interaction (SPSI) problems in a continuum soil body by comparing the results of numerical models with those of a centrifuge test and computed numerical simulations available in the literature. In this regard, several newly developed elements in OpenSees (Version 3.6.0) are tested. The results of this work demonstrate a closer alignment with prior experimental research findings. It is believed that providing detailed numerical modeling and validation processes will assist researchers in better understanding crucial issues in modeling soil–pile–structure interaction problems.

Experimental and Numerical Evaluation for Hybrid Reinforced T-Beam with Different Ratios of Recycled Rubberized Concrete

The use of hybrid GFRP and steel bars as main reinforcement increases the flexural capacity of T-section concrete beams and reduces ductility. Adding recycled rubber to the concrete mix would further enhance the ductility of the hybrid system. Evaluation of the concrete's flexural capacity and ductility is the main goal of the current investigation using normal concrete (NC) and rubberized recycled concrete (RRC). Eight T-beams have been experimentally investigated in this research, two beams were reinforced with steel bars and GFRP bars with zero percentage of crumb rubber (C.R). The remaining beams were reinforced with different combinations of GFRP and steel bars with rubberized concrete mixes with partial substitution of sand with recycled crumb rubber by (0%, 7.5%, 10%, and 12.5% replacements by volume) particle size 1.0 to 2.0 mm. The ductility index for the tested hybrid rubberized T-beams (HRTB) BRH1, BRH3a, BRH5, BRH2, BRH4, and BRH6, were higher than BH1 and BH2 by 28.2%, 35.47%, 65.38%, 23.76%, 30.04%, and 56.95% indicating that increasing the percentage of C.R. has a direct effect on increasing the ductility index. The ultimate failure load for the tested HRTB BRH1, BRH3a, and BRH5, decreased by 11.68%, 14.29%, and 17.47% compared to the hybrid T-beam BH1. The energy dissipation decreased for HRTB BRH1, BRH3a, BRH5, BRH2, BRH4 and BRH6 by 7.88%, 12.36%, 17.17%, 8.12%, 12.96%, and 18.28 compared to hybrid T-beams BH1 and BH2. This indicates that the existence of the very weak C.R. was not able to dissipate the energy properly within the concrete matrix. Good agreement was found between the numerical model and experimental results in terms of crack pattern, ultimate loads and deflections.

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.