Similarity Criteria Research Articles

Dynamic similarity criteria for simple cases of buildings and structures aerodynamics

The work concerns dynamic similarity criteria of various phenomena occurring in hydraulics and fluid dynamics originally derived from ratios of forces and forces moments affecting these phenomena. The base of dynamic similarity criteria formulations and considerations is A.Flaga’s method and procedure for determining dynamic similarity criteria in different issues of fluid-solid interactions i.e. at different fluid-solid relative motions. The paper concerns the determination and analysis of dynamic similarity criteria for various practical problems encountered mainly in hydraulics and fluid dynamics at steady, smooth fluid onflow in front of a solid. Moreover, the cases of mechanically induced vibrations of a body in a stationary fluid moving with constant velocity in front of the body have been presented.

Study on Collision Dynamics Similarity of Thickness Distortion Model of Train Five-Hole Thin-Walled Structure

Full-scale train collision tests are rarely carried out because of high cost, but small-scale model tests have good economy and repeatability, providing a new research method for train crashworthiness design. The metal thin-walled tube is a commonly used energy-absorbing structure for trains. Its collision characteristics directly affect the impact resistance and collision behavior evolution process of trains. This paper studies the collision dynamics similarity of the small-scale model of a five-hole thin-walled energy-absorbing structure at the end of a high-speed train. Firstly, the dynamic mechanical behavior and governing equations of high-speed train collision were analyzed, and the applicable similarity criterion was derived by similarity transformation to develop a similarity scale model. According to the simulation, the energy absorption, peak force and other key responses of the full-scale prototype collision were analyzed. Then, the applicability of the thickness distortion scale model of the five-hole energy-absorbing structure in the high-speed train was proved by equation analysis and error analysis. The impact dynamic responses of the complete similarity model and the distortion similarity model were discussed. A correction program with collision deceleration as the dependent variable was proposed for the distortion similarity model, and the fitting relationship between the distortion factor and the correction factor was obtained. The results calculated by the proposed method prove that the peak force-deformation-energy absorption error of the thickness distortion similarity model in predicting the dynamic responses of the prototype collision is less than 8%, which means the thickness distortion scale model has good accuracy in the prediction of full-scale prototype collision dynamics responses.

ANALYSIS OF THE EFFECTS OF SELECTED QUANTITIES ON THE FOULING OF NATURAL GAS COOLER PIPES

In this article, the effects of selected quantities on the thickness of a fouling layer that is formed on the internal surface of the pipes of natural gas (NG) coolers are discussed. Models created by applying an analytical method, a dimensional analysis, and a multiple linear regression were compared. The most complex model was the analytical model with a total of 16 relevant physical quantities. From the practicality point of view, that model was very complicated since it required applying the iterative process. The dimensional model comprised 6 similarity criteria. The difference between the fouling layer thicknesses identified analytically and those identified using a model based on a dimensional analysis did not exceed 3.06 %. Out of the total number of relevant quantities, only those that had the strongest effects on the fouling layer thickness were selected with the use of MinitabX software. Three regression models, containing 6, 5, and 4 variables, were thus created. The difference between the results obtained from the simplest regression model and the values obtained from the dimensional model amounted to a maximum of 3.20 %. The use of the presented regression models in technical practice may be recommended.

New Solutions in Pipe Billet Production

This paper proposes a method for determining the speed of hollow steel billet casting to produce seamless oil and gas pipes. At the same time, the use of hollow billet excludes, in the technological process of pipe production, the piercing of the billet. The results of industrial production modeling were recalculated into natural quantities according to the Fourier number similarity criterion. The calculations determined that the optimal drawing speed and casting speed of a billet with a diameter of 210 mm are 2.01 m/min and 0.273 t/min, respectively. At the same time, productivity increased by 16%, compared to the one when casting a solid billet. To ensure the homogeneity of structure and mechanical properties over the entire cross-section of the hollow billet, the optimum ratio of coolant flow rates into the inner cavity and outside the billet in the secondary cooling zone was determined, considering the area of the cooled surface, which is equal to 1.46.

Flow prediction and dimensionless feature analysis in orifice microchannels under cavitation conditions based on similarity criteria

A novel set of dimensionless numbers for predicting cavitation flow in gas-liquid flow through a throttling orifice is proposed. Multiple sets of cavitation data are obtained from the literature, and eight dimensionless groups are extracted using dimensional analysis. Subsequently, self-similarity among these groups is established, leading to the proposal of new dimensionless correlations (CfW and CfWd). Investigation results indicate that the established correlations between dimensionless groups can predict cavitation flow in orifices under a wide range of hydrodynamic and geometric conditions. The predictive model is validated using different sets of experimental data, improving accuracy (average relative error decreased by more than 57%) and covering more physical conditions compared to previous correlation predictions. Furthermore, dimensionless parameters with significant influence on the cavitation discharge coefficient are identified by the explanatory machine learning technique SHapley Additive exPlanations (SHAP) and sensitivity analysis. Based on these findings, this investigation contributes to a reduction in the number of variables involved in cavitation experiments or simulations.

A hybrid approach portraying the dynamics of free convection condensation around a circular cylinder

We introduce a hybrid framework to model the fluid dynamics of free convection condensation of saturated steam outside a circular cylinder. The liquid film is modeled analytically, and the adjacent vapor flow field is resolved numerically. The model incorporates temperature-dependent thermophysical properties of the condensate. We explore the subtle role of Jakob number (Ja) and Weber number (We) in the two-phase flow and establish the criteria for dynamic similarity of the flow field with two new dimensionless numbers, viz., free-fall Reynolds number and similarity number. For fixed base Prandtl number of the condensate, the increases in the subcooling rate with Ja and the cylinder's surface area to volume ratio with We cause film thickening. We develop a theoretical correlation to predict the average film thickness (δm). We identify entrainment and bypass zones in the vapor flow field demarcated by a separating streamline. The entrainment zone's streamlines converge to the interface, yielding a net condensate drainage. The bypass streamlines never reach the interface and reduce the condensation efficiency. The results show that the tangential velocity is dominant within the liquid film, the radial velocity is dominant within the vapor flow field, and they are of the same order at the interface. We locate the point of flow separation influenced by a surface tension-induced adverse pressure gradient. The location of the flow separation point shifts upstream, and the separating streamlines become steeper with the increase in We. Our investigation reveals the zone of tangential flow reversal near the interface, promoted with increasing We.

Similarity of scaled-down tests of water entry slamming considering the effects of atmospheric pressure and density

The water entry cavity and load characteristics obtained through scaled-down tests are correlated with the atmospheric pressure and density at the free surface. The evaluation of the influence of the cavitation number and atmospheric density coefficient is highly essential for scale tests to improve the prototype prediction accuracy. Focusing on the similarity criterion simulations and load prediction of the scaled-down tests, this study conducts the simulation tests of the water entry characteristics of the scaled-down model under different environments: normal pressure, reduced pressure, and reduced pressure and heavy gas replacement. Moreover, the influence of the cavitation number and atmospheric density coefficient on the multiphase flow, slamming load, and air cushion effect is discussed. The “air cushion effect” is formed at the top of the vehicle during water entry process, which affects the peak narrow pulse width slamming load. Furthermore, the “air cushion” experiences expansion–stability–rupture–escape with increasing water invasion depth. As the atmospheric pressure decreases, the gas tends to thin and the retention inertia weakens. The decrease in the “air cushion” buffering capacity leads to the increase in the slamming load and the expansion of the cavity scale formed by the liquid. Excessive simulation of the dynamic pressure results in the delayed closure of the cavity surface and the slow fall of the water curtain. As the atmospheric density increases, the retention inertia of gas increases because of the increase in the molecular mass, the slamming load gradually decreases, and the closure time of the cavitation and water curtain decreases. The research results of this paper provide some reference for the similarity transformation of the scaled-down test and the pre-research of the prototype.

Transient heat transfer analysis of airflow in a thermal water-bearing tunnel considering airflow turbulence and surrounding rock seepage effects

In deep tunnels traversing fractured water-rich strata, surface water descend, heats up at depth, and then rises into the tunnel, resulting in a ‘thermal water-bearing’ tunnel. This paper investigates the transient temperature evolution of such tunnels through laboratory-scale model experiment and numerical simulation, considering the convective heat transfer of thermal water in the surrounding rock. The experimental model was designed using similarity criteria derived from the equation analysis method. The 3D numerical model simulates the interaction between thermal water-saturated surrounding rock and tunnel airflow. The thermal field of the surrounding rock accounts for the coupling effects of the flow field, which follows Darcy's law. The tunnel airflow is governed by the RANS (Reynolds-Averaged Navier-Stokes) equations and the k−ω turbulence model, combined with the LRNM (Low-Reynolds Number Modeling) method for near-wall treatment. This approach is coupled with the energy balance equation to calculate the airflow temperature. The numerical model is validated using monitoring data from experimental measurements of grouted tunnel wall and airflow temperatures. Finally, parameter studies are conducted for both ungrouted and grouted tunnels, demonstrating the effectiveness of grouting in controlling airflow temperature by blocking thermal water.

A weighted knowledge extraction strategy for dynamic multi-objective optimization

Multi-objective evolutionary algorithms suffer from performance degradation when solving dynamic multi-objective optimization problems (DMOPs) with a new conditional configuration from scratch, which motivates the research on knowledge extraction. However, most knowledge extraction strategies only focus on obtaining effective information from a single knowledge source, while ignoring the useful information from other knowledge sources with similar properties. Motivated by this, a weighted multi-source knowledge extraction strategy-based dynamic multiobjective evolutionary algorithm is proposed. First, a similarity criterion based on angle information is constructed to quantify similarity between different source domains and the target domain. Second, a knowledge extraction technique is developed to select a specific number of individuals from each source domain using a distance metric. Third, a generation strategy based on dynamic weighting mechanism is proposed, which generates a certain number of individuals and merges these individuals into the initial population within the new environment. Finally, the comprehensive experiments are conducted on public DMOP benchmarks and demonstrate the devised method significantly outperforms the state-of-the-art competing algorithms.

Experimental study on radiative heat flux from annular pool fires under the cross airflow

This paper investigates the radiative heat flux of annular pool fires under cross airflow (0–5 m/s), a configuration that has been underexplored in fire safety research despite its relevance in industrial fire hazards. Results show that radiative heat flux decreases with increasing distance from the fire source but increases with higher cross airflow speeds and larger annular pool diameters (Din/Dout). Existing models overestimate radiative heat flux in annular pool fires due to the underrepresented hollow flame region. A new modified triangular prism radiation model was developed based on the similarity criterion of annular pool fires. An extensive comparative analysis was further conducted, encompassing a wide array of experimental configurations documented in the literature, characterized by varying diameters spanning from 0.1 m to 0.7 m and cross wind velocity ranges extending from 0 m/s up to 5 m/s. The results of this comprehensive examination reveal a good agreement between the newly established model and the empirical data, thereby substantiating the model’s universal applicability and robust reliability. The new model will effectively assist industrial facilities in enhancing fire safety design, strengthening thermal hazard prevention and control, and ensuring a higher level of fire safety design.

Synthesis and molecular modelling of new donor-π-acceptor benzothiazole-carbazole-pyridine-based fluorescent chromophore

The targeted benzothiazole-carbazole-pyridine dye (ThCzPy) was synthesized using a synthetic approach completed by the condensation of 6-(benzothiazol-2-yl)-3-formyl-9-hexyl-9H-carbazole (4) with 4-aminopyridine (5). The absorption and emission spectra of the chromophore ThCzPy, in DMSO, displayed good Stokes’ shift (Δν¯ = 4653 cm−1). The DFT configuration of the frontier molecular orbits in gas and solvated ground state (So) were compared to the solvated excited state (S1). Furthermore, the new chromophore’s antimicrobial efficacy was evaluated as minimum inhibitory concentration (MIC) against a panel of Gram’s positive, negative, and fungi using ampicillin and fluconazole as reference drugs, where it exhibited comparable activity. The SwissADME study revealed that ThCzPy has a bioavailability score 0.55 and meets Lipinski’s criteria for drug similarity.

Development of a methodology and design of a device for determining the Mach number of a supersonic flow

The paper presents the developed methodology and designed a device for determining the Mach number during supersonic gas outflow. An analysis of various methods for determining the Mach number was carried out, including measuring the pressure at the flow boundary, the use of shock waves, and the use of optical methods. A comparison was made of the accuracy of the readings when using the considered methods. Based on the results obtained, a technique for high-precision determination of the Mach number has been developed, including a combination of several independent measurement methods. A device has been designed that implements this measurement technique, and the results of experimental tests in a wind tunnel have been reviewed, including instrument readings, graphs and tables confirming the accuracy and reliability of the data obtained. Their accuracy and reliability are analyzed. Using the analysis, it is possible to ensure the selection of the most rational method for determining the Mach number at the initial stage of designing aircraft, such as airplanes, missiles, fighters, and UAVs. Accurate knowledge of the Mach number allows engineers to optimize the aerodynamic characteristics of the aircraft, ensure flight safety, improve engine efficiency and overall air transport performance. In addition, the Mach number is the most important criterion of similarity when modeling in aerodynamic research, which makes the developed methodology and device relevant not only for the design of aircraft, but also for a wide range of scientific and engineering research in the field of aeronautical technology. It is emphasized that the presence of a reliable method for determining the Mach number can significantly reduce the time and resources spent on testing and improving aircraft, and also contributes to the development of innovative technologies in the field of aviation and astronautics.

Identification of bioactive compounds with popular single-atom modifications: Comprehensive analysis and implications for compound design

The extensive bioactivity data available in public databases, such as ChEMBL, has facilitated in-depth structure-activity relationship (SAR) analysis, which are essential for understanding the impact of molecular modifications on biological activity in a comprehensive manner. A central strategy in SAR analysis is the assessment of molecular similarity. Several approaches preferred by medicinal chemists have been developed to efficiently capture structurally related compounds on a large scale. Represented as a popular molecular editing strategy in hit-to-lead and lead optimization processes, we previously introduced four types of single-atom modifications (SAMs) as chemical similarity criterion and conducted a systematic analysis of their application in compound design. In this study, we expanded the analysis to cover 10 common SAMs, including carbon-nitrogen (N↔C), O↔C, N↔O, S↔O, as well as simpler modifications such as OH↔H, CH3↔H, and halogen-hydrogen (F, Cl, Br, I↔H) exchanges. Leveraging high-confidence bioactivity data from ChEMBL (version 34), we assembled a comprehensive dataset comprising 374,979 SAM pairs. Following an evaluation of the frequency of these SAM types in medicinal chemistry efforts, we focused on SAM-induced activity cliffs (ACs), yielding over 7400 ACs, substantially expanding the current knowledgebase of ACs associated with single-atom changes. Furthermore, structural analysis of these ACs, supported by experimental data, provides critical insights into the role of single-atom modifications in modulating compound activity, offering practical guidance for the structure-based optimization of molecular properties in drug development. As a result, we are providing open access to all identified ACs along with their associated structural information.

Digitalization, Management, and Synthesis of Thermal-Hydraulic Legacy Data Using the Dynamical System Scaling

A unique attribute of the nuclear industry is the extent by which designers, developers, operators, and regulators pay attention to demonstrating the safety case. Nuclear installation resiliency or safety takes overriding priority over function and performance. The preparation of the safety case heavily relies on extensive experimental campaigns that challenge the target design under a spectrum of postulated accident scenarios. For safety reasons, these experiments, typically conducted in subscale test apparatuses intended to reproduce the postulated accident scenarios and event sequences realistically, but subject to proven similarity criteria, are often referred to as scaling analyses. Since the dawn of the nuclear industry, significant resources have been committed to the construction and operation of such test facilities, and a massive amount of data has been generated. Such test data have been and are still used to validate the fundamental assumptions of nuclear power plant phenomena. As we move into the digital world, capturing this multiple decades worth of information in a transparent, easily accessible, and usable manner for the public and industry stakeholders is of paramount importance. Over the last few years, FPoliSolutions has been actively developing an enterprise digital data ontology platform (OGMA) intended to do just that. The goal is to help designers use experimental data to assess their safety case evaluation models. The platform or application programming interface (API) was designed to ontologically organize the experimental data, as well guide the user in the complex analytics associated with the interpretation and use of such test results. The OGMA API supports the user in accessing a library of sophisticated mathematical procedures for performing scaling analyses. For this purpose, the dynamical system scaling (DSS) procedure invented by Dr. Jose’ Reyes was formulated as one of the services in the digital platform. These methods have been demonstrated to provide an excelled mathematical apparatus to identify similarity criteria or quantify distortions between measured data and the target prototypical conditions. Moreover, DSS can provide a level of synthesis across separate effect tests and integral effect tests that has the promise of yielding efficiency in the evaluation code assessment activities, as setting up evaluation models that support the safety case of current and future nuclear power plants is often a daunting and expensive task.

Predictions of windage heating and flow characteristics in a high-speed rotating seal of aero-engine

The labyrinth seal plays a crucial role within the secondary air system of an aeroengine, significantly impacting its safety and reliability. This paper presents a comprehensive evaluation of the complex windage heating phenomenon within a high-speed rotating labyrinth seal system. Employing similarity criteria and dimensional analysis, the multifactorial influences on the seal system are thoroughly characterized. A dedicated high-speed rotating labyrinth seal test rig was constructed to conduct an experimental investigation into the windage heating characteristics of a four-tooth, stepped-slanted labyrinth seal. The results demonstrate a peak windage heating of 11.8 K and windage heating coefficient of 1.14 when the inlet temperature rose from ambient to 100 °C, under the rotating Mach number of 0.418 and pressure ratio of 1.1. Conversely, as the seal clearance increased from 0.2 mm to 0.6 mm, with a rotating Mach number of 0.487 and a pressure ratio of 2.0, the windage heating coefficient decreased to 0.57. Furthermore, five dimensionless operating cases were analyzed using similarity principles to elucidate the correlation between system performance and the combined effects of strong rotating flow and windage heating characteristics. The analysis revealed that the windage heating coefficient exhibited a decreasing trend with increasing flow Reynolds number, effective pressure ratio, inlet swirl ratio, and dimensionless clearance, as the effective pressure ratio increase from 1.1 to 5.0, with the rotating Mach number of 0.624 and flowing Reynolds number of 9600, the windage heating coefficient decrease from 1.831 to 0.797, representing a 56 % reduction. Conversely, the windage heating coefficient increased with a rising rotating Mach number, while the flowing Reynolds number demonstrated a minor influence.

A rapid fingerprint positioning method based on deep convolutional neural network for MIMO-OFDM systems

The combination of fingerprint positioning and 5G (the 5th Generation Mobile Communication Technology) offers broader application prospects for indoor positioning technology, but also brings challenges in real-time performance. In this paper, we propose a fingerprint positioning method based on a deep convolutional neural network (DCNN) using a classification approach in a single-base station scenario for massive multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems. We introduce an angle-delay domain fingerprint matrix that simplifies the computation process and increases the location differentiation. The cosine distance is chosen as the fingerprint similarity criterion due to its sensitivity to angular differences. First, the DCNN model is used to determine the sub-area to which the mobile terminal belongs, and then the weighted K-nearest neighbor (WKNN) matching algorithm is used to estimate the position within the sub-area. The positioning performance is simulated in a DeepMIMO indoor environment, showing that the classification DCNN method reduces the positioning time by 77.05% compared to the non-classification method, with only a 1.08% increase in average positioning error.

An equivalent model of horizontal vibratory finishing process: Model construction and analysis based on similarity theory

The manufacturing cost of parts and experimental equipment seriously limits the development of experimental research on mass finishing. To tackle this issue, an equivalent model construction method was proposed based on similarity theory. First, the similarity criterion of relevant physical quantities in horizontal vibratory finishing was determined, and the calculation formula of the distortion coefficient was derived to correct the prediction results. Second, the effects of vibration parameters on the characteristics and similarities of particle velocity and normal force were analyzed by DEM simulation. Finally, the validity of the equivalent model was proved by PIV and force tests. The results show that the equivalent model can be used to reflect the variation of the actual model and anticipate the particle velocity and normal force. And the prediction accuracy can reach 99.56 % and 97.46 %, respectively. The research results provide a new efficient and low-cost method for researching the mass finishing process.

Private hospitals in low- and middle-income countries: a typology using the cluster method, the case of Morocco

BackgroundThe private healthcare sector has become an essential component of healthcare systems globally. This interest has increased with the universal health coverage agenda. However, in most low- and middle-income countries, few classificatory studies of the private hospital sector were carried out.MethodsThis study describes the private hospital sector in a developing country setup and propose a typology that could facilitate the identification of its categories and the understanding of its organizational and strategic characteristics.ResultsAll private hospitals in Morocco as of December 31, 2021 including 397 facilities are included. Most hospitals are for-profit, poly-disciplinary, independent, commercial societies, have fewer than 30 beds or between 30 and 99 beds and are located in urban areas. Private hospitals have a median turnover of 9.8 million MAD and a median capital value of 2 million MAD. The clustering method identifies three main categories of private hospitals: for-profit hospitals with medium size and turnover, spread across the country but with a high concentration in large regions; not-for-profit hospitals, with medium to large size, high turnover, located in large regions and including university hospitals; and small for-profit hospitals with low turnover, independent ownership and wide distribution over the country. Three criteria have the most significant discriminatory power: ownership, size (beds, turnover) and mode of governance.ConclusionsPrivate hospitals in Morocco are organized into three types according to three similarity criteria including ownership, size and governance. These criteria might be used as the basis for a common typology of private hospitals in Morocco and possibly in other low- and middle-income countries with similar contexts.

Similarity joins and clustering for SPARQL

The SPARQL standard provides operators to retrieve exact matches on data, such as graph patterns, filters and grouping. This work proposes and evaluates two new algebraic operators for SPARQL 1.1 that return similarity-based results instead of exact results. First, a similarity join operator is presented, which brings together similar mappings from two sets of solution mappings. Second, a clustering solution modifier is introduced, which instead of grouping solution mappings according to exact values, brings them together by using similarity criteria. For both cases, a variety of algorithms are proposed and analysed, and use-case queries that showcase the relevance and usefulness of the novel operators are presented. For similarity joins, experimental results are provided by comparing different physical operators over a set of real world queries, as well as comparing our implementation to the closest work found in the literature, DBSimJoin, a PostgreSQL extension that supports similarity joins. For clustering, synthetic queries are designed in order to measure the performance of the different algorithms implemented.

Analysis of the impact of key similarity criteria numbers of TBCC inlet during the mode transition

Abstract A simplified configuration was developed to facilitate the mode transition process within an over-under Turbine-Based Combined Cycle (TBCC) inlet. Leveraging dynamic mesh technology, an unsteady numerical simulation of the mode transition was conducted, emphasising the flow characteristics of the mode transition and the impact of key similarity criteria numbers. The findings indicate that at an incoming Mach number of 2.0, the mode transition is paired with a continuous alteration in the capture mass flow of the high-speed duct. This continual change instigates the inlet unstarting, with subsequent flow characteristics being contingent on the historical effect, exhibiting a degree of hysteresis characteristics. When the scale effect is considered, it is observed that a larger model scale results in higher Reynolds (Re) and Strouhal (St) numbers. This directly contributes to a notable delay in the unstart moment, a decrease in the unstart interval, and an enlargement of the hysteresis loop. An examination of control variables reveals that the Re number marginally influences mode transition characteristics, while the St number’s effect constitutes approximately 90% of the scale effect. This conclusively demonstrates that the St number is the predominant similarity criterion number in the mode transition process.