Physical Modeling Method Research Articles

The biomechanics of concussion for ice hockey head impact events

The purpose of this research was to conduct reconstructions of concussive and non-concussive impacts in ice hockey to determine the biomechanics and thresholds of concussive injury in ice hockey. Videos of concussive and non-concussive impacts in an elite professional ice hockey league in North America were reconstructed using physical and finite element model methods. Eighty concussive and 45 non-concussive events were studied. Logistic regressions indicate significant thresholds for concussion for linear/rotational acceleration and CSDM10%. Impacts in ice hockey were mostly long duration events, longer than 15 ms. These results have significant implications for helmet standards and development to prevent concussion.

An Application of Semi-empirical Physical Model of Tsunami-Bore Pressure on Buildings

Characteristic patterns of tsunami wave pressure on buildings is divided into three types, depending on its vertical profiles and time, which is observed after the tsunami impacted the buildings. The first one is the impulsive pressure, which is observed just after the tsunami impacted the buildings. The second one is the bore pressure, which is observed after the impulsive pressures. The third one is the quasi-steady pressure, which is observed after the bores go away from the buildings. In this study, based on characteristics of bore pressure observed in a hydraulic experiment, a semi-empirical physical model of bore pressure is developed by applying a turbulent bore theory. Also, we present an application method of the semi-empirical physical model to evaluations of bore pressure with usage of numerical results of inundation simulations of two-dimensional nonlinear shallow water equation models. Furthermore, we apply the semi-empirical physical model to evaluations of pressure acting on buildings in an inundation area by carrying out numerical simulations of tsunami inundation.

The study of the process of physic-chemical destruction of coal by the method of physical modeling

One of the possible ways of physic-chemical destruction (PCD) of coal was considered. It is established that condition of the realization of a principle possibility of spontaneous dispersion of coal is to reduce its surface energy by 40-60 J/m2. Laboratory experiments to study the PCD of coal in different liquids were conducted. According to the results, kinetic curves of swelling coal in them transition D-G stamps is presents. It was established that the most intensive physical and chemical destruction of the coal to a particle size from tenths to tens of millimeters occurs in solutions of methylamine and hydrochloric acid. The most severe swelling of the coal was noted in those environment as well. The intensity of swelling is not significantly associated with the characteristics of wetting. The influence of various effects on the PCD parameters of coal was studied by physical simulation. The total time the chemical destruction of coal on the treated area was calculated. It was proposed method PCD for coals occurring in the clay rocks of various stages of catagenesis.

Cavitation in swirling flows of hydraulic spillways

During operation of high-head hydraulic spillway systems, cavitation phenomena often occur, leading to destruction of structural elements of their flow conductor portions. The article is devoted to the study of erosion due to cavitation in the circulation flows of eddy hydraulic spillways, including those equipped with counter-vortex flow energy dissipators. Cavitation destructive effects depend on many factors: intensity consisting in the rate of decrease in the volume or mass of a cavitating body per unit of time, the stage of cavitation, geometric configuration of the streamlined body, the content of air in water, the flow rate, the type of material. The objective of the study consisted in determination of cavitation impacts in circulating (swirling) water flows. The studies were conducted by a method of physical modeling using high-head research installations. Distribution of amplitudes of pulses of shock cavitation impact is obtained according to the frequency of their occurrence depending on the flow velocity, the swirl angle, the height of the cavitating drop wall and the stage of cavitation. The impact energy depending on the stage of cavitation and the flow rate is given for different operating modes of the counter-vortex flow energy dissipators of a hydraulic spillway. In the conclusions, it is noted that cavitation impacts in the circulation flows occur mainly inside the flow, which is a fundamental difference from similar processes in axial flows.

О РЕАЛИЗАЦИИ КАНАЛА ОБРАТНОЙ СВЯЗИ В СИСТЕМАХ АВТОМАТИЧЕСКОГО УПРАВЛЕНИЯ ОТОПЛЕНИЕМ ЗДАНИЙ

The problem of determining the internal air temperature while constructing feedback control heating systems of buildings is considered. The methods of solving this problem known in the literature are analyzed. It is indicated that neither the method of representative point (points), nor wired and wireless multi-sensor networks, nor the physical model method, nor the temperature ventilation passage method can be considered sufficiently suitable for determining the average internal air temperature of a building. The problem requires further study and development. Fairly simple methods for determining this variable are proposed in the work. The main point of these methods is that the return water temperature contains information about all the variables affecting the heat consumption, including the information about the internal air temperature; therefore, through applying a model of heat exchange, it is possible to estimate the internal air temperature using the return water temperature data. In this case, it is only necessary to properly adjust the heat exchange model to the experimental data (for a specific building). To gain the necessary result, it is necessary to measure the coolant flow mass for the entire heating system, as well as the external air temperature, the direct and return water temperature in one of the cases. In the other case, it is not necessary to measure the external air temperature, since somewhat different heat exchange correlations are considered. An equation adjusted as to the experimental data is produced, which can be used to control the internal air temperature of a building in an automatic control loop. It is shown that the parametric identification quality used to control the heat exchange model is sufficiently high.

Modeling and Simulation of Robot Inverse Dynamics Using LSTM-Based Deep Learning Algorithm for Smart Cities and Factories

In smart cities and factories, robotic applications require high dexterity and security, which requires precise inverse dynamics model. However, the physical modeling methods cannot model the uncertain factors of the manipulator such as flexibility, joint clearance and friction, etc. As an alternative, artificial intelligence (AI) techniques have become increasingly popular in robotics for smart cities and factories. In this paper, deep learning neural network based on LSTM (Long Short-Term Memory) is adopted to predict the manipulator inverse dynamics. This study aims to summarize the influence of the hyper-parameter settings on model performance and to explore the applicability of the LSTM model to joint torque prediction of multiple degrees of freedom series manipulator. Furthermore, the feasibility of using only joint position as input data for torque prediction is verified. Simulation result has shown that, for the proposed deep learning architecture, the effects of the number of maximum epochs on model performance should be prioritized. The effects of the number of hidden nodes on model performance are limited, while prediction accuracy will deteriorate as the number of hidden layers increases. It is proved that it is feasible to predict inverse dynamics when input data is joint position only. The experimental results show that the training time increases with the increase of hidden layers, neurons and epochs.

Determination of rational process-dependent parameters of manufacturing multilayer polymer structures by physical modeling

Abstract The paper researches a very important issue of improving coextrusion technology of secondary polymer materials processing. The paper also presents the results of the research by physical modeling of such process-dependent parameters as preform cooling temperature in the mold and preform secondary deformation pressure, which were not studied enough earlier. Research was carried out using the physical modeling methods. The rational cooling time of the preform in the mold, which ensures its stability of shape, is determined. The rational blowing pressures of tubular preform in the press mold, ensuring the integrity of the end product, are determined.

Methods of physical processes modeling

Methods of physical processes modeling

Analysis of the Stress-Strained State of Billets Processed by Rotary Forging with Special Shape of the Tool

In this paper, we investigated the process of rotary forging of commercially pure copper grade M2 ​​using standard and special-shaped anvils and presented the results of studies obtained by the method of numerical and physical modeling. It is established that the use of anvils with special geometric shapes provides a higher level of accumulated strain and the formation of more dispersed structural states with the same elongation ratio under conditions of multi-cycle processing [1]. The formation of a finer structure in its turn increases the hardness and strength of the material. In addition, the special shape of the anvils provides a positive field of values ​​of the Lode-Nadai coefficient in the cross section of the samples, predominantly in a range of 0.3-0.7 and, correspondingly, a more "comfortable" stress state close to non-uniform all-round compression, which contributes to increasing technological plasticity.

Study on the Evolution Characteristics of Two‐Zone Failure Mode of the Overburden Strata under Shallow Buried Thick Seam Mining

There are risks of water burst and sand inrush in the working face of the Northwest Mining Area in China. Based on the 22407 working face of Halagou coal mine, the evolution characteristics and mechanism of a two‐zone failure mode of the overburden strata in shallow buried thick seam mining were thoroughly analysed using physical modelling, theoretical analysis, on‐site observation, and other research methods. A method to calculate the overburden fissure width was also proposed. The analysis results indicated that the evolution of a two‐zone failure mode of the overburden strata mainly includes four stages: gestation, formation, transformation, and stabilization. In the transformation stage, a fracture zone is transformed into a caving zone. The caving zone and fracture zone are separately transferred to the working face direction based on the structure type of key strata of voussoir beam and cantilever beam after the heights of the two zones stabilize, and the “two‐belt” cracks are mainly composed of inclined and horizontal fissures. Based on this study, the mechanism of the two‐zone failure mode of overburden strata development was analysed according to the mining height and overburden strata key layer structure. This paper serves as a guide for safe and green mining on shallow buried thick seams.

Фізичне моделювання ерозійного руйнування футерівки сталерозливного ковша в процесі експлуатації

The aim of the work is to determine the conditions for reducing the rate of erosion destruction of teeming ladles lining by flows of liquid metal. A concomitant and inherent positive effect is the reduction of steel pollution by the products of lining destruction (exogenous non-metallic inclusions). In the article there have been discussed the mechanisms of destruction of the refractories of teeming ladles. It is observed a significant effect of erosive destruction of the lining during the steel production from the steelmaking unit and in the process of its filling on its life. The authors have proposed a method of physical modeling of erosive destruction of refractories using the basic principles of the similarity theory. Based on the π-theorem, the authors proposed dimensionless similarity numbers, based on which the model scales were determined, in particular, the scale factors for the refractory hardness, fluid density, linear scale of the model and the rate of destruction of refractory. Using the obtained scales, the authors assembled an experimental facility and developed the methodology of an experiment. For the experiment, large-scale models of ladles with standard and developed scheme of lining were used. After carrying out physical modeling, the depth of lining destruction of the ladle model has been measured using a special technique. Based on the results of measurement, a topographic scheme of the lining destruction of the model ladle for the standard and proposed lining has been drown. It has been determined that the developed lining design provided protection for the “impact zone” and reduced the intensity of lining erosion in the area of joint the walls and the bottom of the ladle by the flows of liquid metal. The average rate of destruction of the bottom when using the developed design of the lining is reduced by 18%. The scientific novelty of the work consists in the development of the theoretical foundations of the physical low-temperature modeling of erosive destruction of the ladles lining and other metallurgical units by high-temperature metal melts. The practical significance of the work is the lining design of the teeming ladles, which provides a long life of the teeming ladles with a simultaneous decrease in the level of steel pollution by exogenous nonmetallic inclusions.

Comparative analysis of the efficiency of the application of thermal-hydraulic distributor with classical schemes of connecting subscribers

Analysis of the use of a thermo-hydraulic distributor in district heating schemes showed insufficient study of the mutual influence of the connected circuits, on which the coefficient of hydraulic stability of the heating network depends, and the lack of a comparative analysis of the efficiency of heat supply when using a scheme with a thermo-hydraulic distributor compared to widely used subscriber connection schemes. The purpose of the study is to compare the economic and energy efficiency of the proposed and existing subscriber connection schemes, which is an important task. In laboratory conditions, a wide range of studies have been carried out to study the hydraulic dependence of the contours of the thermo-hydraulic distributor among themselves. Processing of the results was carried out by the method of correlation-regression analysis and mathematical statistics. In a comparative analysis of subscriber connection schemes, methods of physical modeling of thermo-hydraulic modes were used. A comparative analysis showed that the energy efficiency of the scheme with a thermo-hydraulic distributor is higher in heating systems with non-automated subscribers, regardless of the temperature graph of the heating network. When comparing schemes with parallel connection of a hot water heater, it was found that the totality of electricity consumption for coolant circulation and fuel costs for a circuit with a thermo-hydraulic distributor turned out to be less irrespective of the temperature schedule. Statistical research methods confirmed the independence of the circuits and the normal supply of heat to the heating. New solutions have been obtained to increase the hydraulic stability of the centralized heat supply system using a thermo-hydraulic distributor at a heating point – the hydraulic stability coefficient of the heat network during all subscriber operation modes is equal to one. The results of the study can be used in the design of thermal points: the proposed heating system, the consumers of which will provide a stable hydraulic mode; existing heat supply system, the consumers of which must ensure the hydro-stable control of heat.

КЛАССИФИКАЦИЯ МЕТОДОВ ПРОГНОЗИРОВАНИЯ ЧРЕЗВЫЧАЙНЫХ СИТУАЦИЙ

The article discusses the approaches to the prediction emergency situations. The classification for the methods of prediction emergency situations is presented. The possibilities of the application the expert prediction methods, the statistical methods, the methods of physical and mathematical modeling are substantiated. The essence of each method is considered, their advantages and disadvantages are defined.

Superabsorbing metamaterial wormhole: Physical modeling and wave interaction effects

Conjugate-impedance matched superabsorbers are metamaterial bodies whose effective absorption cross section greatly exceeds their physical dimension. Such objects are able to receive radiation when it is not directly incident on their surface. Here, we develop methods of physical modeling of such structures and investigate interactions of the superabsorbers with passing electromagnetic radiation. The particular superabsorbing structure under study is a wormhole comprised of meshes of loaded transmission lines. A theory of electromagnetic wave propagation and absorption in such metamaterial structures is developed. At the frequency of operation, the structure exhibits greatly enhanced absorption as compared to the black body-type absorber of the same size. Peculiar wave absorption effects such as trapping of nearby passing beams of electromagnetic radiation are demonstrated by numerical simulations. Possible modifications of the wormhole structure under the goal of optimizing absorption while minimizing complexity of the involved metamaterials are discussed. Conjugate-impedance matched superabsorbers may find applications as efficient harvesters of electromagnetic radiation, novel antennas, and sensors.

Microstructure construction of polypropylene-based hollow fiber membranes with bimodal microporous structure for water flux enhancement and rejection performance retention

The low porosity, low pore connectivity and poor hydrophilicity of polypropylene hollow fiber membranes (PPHFMs) reduced membrane performance and limited its application in water treatment. Hence, the bimodal microporous structure including two different grades and independent pore size distributions was constructed in hydrophilic polypropylene (PP)/poly(ethylene-co-vinyl alcohol) (EVOH)/maleic anhydride grafted polypropylene (PP-g-MAH) hollow fiber membrane (PP/EVOH/MAH-HFM) via melt blending combining with melt-spinning and stretching (MS-S). The addition of PP-g-MAH formed compatible interfaces to optimize the bimodal microporous structure in PP/EVOH/MAH-HFM. The porosity and pure water flux of PP/EVOH/MAH-HFM with stretching ratio of 200% respectively increased to 81.5% and 322.7 L/(m2·h), which respectively increased by 27.3% and 118.0% compared to PPHFM with stretching ratio of 200% due to the large micropores in bimodal microporous structure. The rejection performance of PP/EVOH/MAH-HFM was also retained due to the small micropores in bimodal microporous structure. The reactive groups in EVOH and PP-g-MAH significantly improved the hydrophilicity of PP/EVOH/MAH-HFM, while also improving the antifouling property of membrane. Moreover, the formation mechanism of bimodal microporous structure was systematically investigated in combination with physical modeling and FESEM method. This work supplied a new membrane structure and provides a new perspective for the fabrication of high performance polypropylene-based hollow fiber membranes by MS-S.

COVERED KARST LANDFORMS: COMPLEXIFICATION OF METHODS TO ESTIMATION OF MORPHOMETRIC PARAMETERS IN ENGINEERING PURPOSES

The research is aimed to search of optimal solution in integration of various methods for predicting the sizes of karst-suffosion deformations on the ground surface or at the base of shallow foundations. Necessity of integration is dictated by engineering-geological conditionsof the karst areas and the complexity of their reliable study with using modern approaches (drilling, geophysics etc.). From this point of view increasing of authenticity of the final forecast is in direct dependency from completeness of investigation of sizes of observed surface karstforms and features of behavior soils massif above the karst cavity. The mechanism of the karst process in the soils thickness is defined, first of all, by geological structure (thickness and interleaving of different soil layers), hydrogeological conditions and the physical-mechanicalproperties of soils. At the present day are known three basic mechanisms of soil deformation over karst cavity: karst-collapse, karst-suffosion and karst-suffosion-collapse mechanism. Even in the conditions of one site these mechanisms can be interleave during the year, which makesthe karst formation process hard-to-predict in part of diameters of sinkholes and subsidence zones. Today are known and applicable next four methods to estimations of possible sizes of karst-suffosion deformations: 1) method of analogy, 2) probabilistic method, 3) deterministic(calculated) method, 4) laboratory physical modeling method. Each of four methods for predicting the sizes of karst-suffosion deformations has its own advantages and disadvantages, which limit the possibility of using any one of them in different natural environments of karstdevelopment. To improve objectivity and reach necessity accuracy of estimation of diameters and depths of surface karst deformations in engineering-geological purposes a block-scheme of integrations of different forecasting methods is recommended. This scheme is based on the data about surface karst area, the depth of occurrence of karst rocks and level of responsibility of the projecting object.

Remaining useful life prediction of aviation circular electrical connectors using vibration-induced physical model and particle filtering method

The reliability of electrical connectors has a critical impact on electrical systems. Traditionally, this has been characterized by the failure-rate prediction value according to MIL-HDBK-217 in engineering practice. Owing to the limitations and misleading results provided by this approach, a new remaining useful life (RUL) prediction method is presented. This method is aimed at the mechanism of increasing oxide film thickness induced by vibration, which leads to an increase in contact resistance. Moreover, the prediction method is based on failure mechanisms and particle filters, which realizes the combination of a physical model and data-driven method. The particle filters can abundantly employ degradation data and avoid ignoring the failure mechanism. Accelerated degradation testing (ADT) is proposed for effectively assessing the proposed prediction method, in which the random vibration is selected as the accelerated stress. Moreover, the differences in manufacturing processes are considered in the testing. The RULs of circular electrical connectors in two manufacturing processes are obtained under high vibration stress through ADT and data gained from tests. The prediction results are compared with other methods to verify the accuracy and effectiveness of the proposed prediction method.

Research of gas-dynamic processes of motion of combustion products of blast-air heaters

The article deals with the methods of physical modeling of gas-dynamic processes and the calculation of aerodynamic resistance in the motion of combustion products on the exhaust system. The analysis of echoing methods for increasing the diversion of combustion products of hot stoves has been carried out and their main disadvantages have been identified. The basic principles of creation of mathematical models of flue gas flow on an exhaust system are considered and an estimation of their adaptability to the really conditions. The main reasons for the reduction of traction in the exhaust system of the blast-furnace shop of Dneprovsky DMZ are revealed. The research of the state of refractory lining was conducted and the main reasons of a short period of its work were revealed. The ejection and injection phenomena on the basis of which several ways of increasing traction in the chimney tract are considered. Investigations of the level of pressure of combustion products at the exit from the combustion chamber on the existing air heaters have been carried out. The influence of taking blast furnace on draft through air heaters on the duration of service life of refractories of exhaust system and the degree of mixing of combustion products during tangential feeding to common forests is revealed. The calculation of pressure losses in the smoke boron under the conditions of the blast-furnace shop of Dneprovsky DMZ is carried out. Considered ways to increase the value of traction for effective smoke removal from blast air heaters. During the experiments, the distribution of flows between the ejector and around the nozzle was detected. Conclusions are made on the necessity of using some methods for increasing traction in smoke boron and the correspondence of some coefficients of local resistance to experimental data. It is suggested to conduct further physical experiments to specify the coefficients of local resistance.

Modern methods of modeling hydrodynamic processes in CCM tundish

A theoretical analysis of the motion of liquid metal in a tundish CCM during scavenging by an inert gas was carried out. The hydrodynamic parameters of the flow of liquid metal in the confined area of CCM under scavenging by argon are determined by methods of physical and mathematical modeling. Adjustable parameters of a purge are considered by lance distance from the center of a ladle and an angle of its slope to a vertical.

Assessment of embankment dams breaching using large scale physical modeling and statistical methods

Understanding the failure mechanisms of embankment dams due to overtopping is essential for the design of flood mitigation, flood mapping, and flood warning systems. The breach process in embankment dams can be characterized using breach parameters such as breach opening dimensions, time of breach formation, and peak breach outflow. The main objective of this study is to derive new set of statistical equations to predict the target breach parameters. A database of 126 events of embankment failure was collected and then multiple nonlinear regression analysis is used to derive the new set of equations and the uncertainty in the computed parameters was quantified. Finally, five large-scale overtopping failure tests were conducted on cohesive and non-cohesive soils embankments. The derived breach parameters equations showed good agreement with the results of the physical models for non-cohesive soil embankments, while the failure of cohesive soil embankments varied significantly with soil properties; indicating that breach parameters in cohesive soil embankment should be computed based on not only embankment dimensions but soil properties as well.