Influence Of Geometrical Parameters Research Articles

ANALYSIS OF SIMULATION DATA OF A SUPERSONIC FLOW IN A SHORT NOZZLE WITH A NOZZLE

In this paper, we analyzed the influence of the geometric parameters of a shortened nozzle when operating under various conditions - at sea level (at Р=1 bar) and upper atmosphere (Р= 0.1 bar). The influence of geometrical parameters of the nozzle, pressure at the inlet, and the environment on the impulse characteristics of the flow are considered. It is shown that the momentum factor decreases with decreasing inlet pressure, but with increasing flight altitude, i.e. a decrease in the pressure of the external environment, the momentum coefficient decreases to a certain value, and then increases again. This character of the dependence is explained by the wave structure of the flow in a shortened nozzle. The study of simulation data can be used to create new types of nozzles for rocket and space technology.

Rigid-Elastic Combined Metamaterial Beam With Tunable Band Gaps for Broadband Vibration Suppression

Abstract Extensive research efforts have been dedicated to exploring the application of metamaterial beams for vibration suppression. However, most existing designs primarily focused on utilizing the translational motion of local resonators to create band gaps. To address this limitation of employing solo motion to induce a relatively narrow band gap, this study proposes a novel design: a rigid-elastic combined metamaterial beam utilizing both translational and rotational motions of local resonators. Theoretical framework development involves extending the transfer matrix method to incorporate rigid bodies, with analytical results validated through finite element simulations and experimental data. Compared to conventional metamaterial beams, the proposed design exhibits an additional wide band gap in the low-frequency region that can be utilized for broadband vibration suppression. A parametric study elucidates the influences of geometric parameters on band gap formation, followed by an exploration of the tunability of the proposed meta-beam through a graded scheme and optimization strategy. In particular, a multiple-objective optimization approach is employed to enlarge the vibration suppression region and enhance vibration suppression ability. The optimized meta-beam demonstrates a remarkable 45% wider dominant suppression region and a 14% lower average transmittance compared to a uniform model.

The Influence of Geometric Parameters for Training an Artificial Neural Network to Predict the Band Structure of 1-D Fishbone Photonic Crystal

With the rising demand for the transmission of large amounts of information over long distances, the development of integrated light circuits is the key to improving this technology, and silicon photonics have been developed with low absorption in the near-infrared range and with sophisticated fabrication techniques. To build devices that work in different functionalities, photonic crystals are one of the most used structures due to their ability to manipulate light. The investigation of photonic crystals requires the calculation of photonic band structures and is usually time-consuming work. To reduce the time spent on calculations, a trained ANN is introduced in this study to directly predict the band structures using only a minimal amount of pre-calculated band structure data. A well-used 1-D fishbone-like photonic crystal in the form of a nanobeam is used as the training target, and the influence of adjusting the geometric parameters is discussed, especially the lattice constant and the thickness of the nanobeam. To train the ANN with very few band structures, each of the mode points in the band structure is considered as a single datapoint to increase the amount of training data. The datasets are composed of various raw band structure data. The optimized ANN is introduced at the end of this manuscript.

Nacre-inspired auxetic interlocking brick-and-mortar composites

We design auxetic 3D interlocking brick-and-mortar composites inspired by nacre - a natural strong and resilient high-performance material. The influences of geometrical parameters and base material properties on their effective elastic properties are systematically investigated by finite element simulations and computational homogenization. The numerical results indicate that the composites exhibit tunable negative Poisson’s ratios by properly tailoring the underlying microstructures. It is revealed that the auxetic behavior therein is attributed to the relative sliding between adjacent bricks with waviness, i.e., the sliding mechanism. These materials, with their auxetic properties and high fracture toughness, are well-suited for a wide range of engineering applications, such as serving as robust auxetic materials.

Influence of dowel group configuration on the stability of reinforced slopes

Introduction. Slope reinforcement with dowels is the most economical and environmentally friendly method of their stabilization. However, the lack of theoretically substantiated schemes for optimal placement of dowels in groups, confirmed by tests in various conditions, leads to inefficient, often excessive use of the material in the arrangement of engineering protection.Aim. To determine the most effective arrangement of dowels in groups with regard to the overall stability of the reinformed soil mass. To assess quantitatively the stability depending on the spacing and shape of dowels in the group.Materials and methods. A review of international and Russian literature on the problem of assessing the influence of geometric parameters of dowel and anchor groups was carried out. According to the results of the review, primary calculations with the use of numerical simulation in the PLAXIS 3D software package was carried out.Results. The available publications mainly analyze configurations of screw anchor groups, paying insufficient attention the use of dowels of cylindrical cross-section. This fact substantiates further research in this field. The conducted numerical simulation allowed the slope stability provided by five dowel group configurations to be compared. The calculation results show that the slope stability depends on the configuration and the number of dowels in the group. The difference between the stability factors for the polygonal and triangular three-row configuration was 0.072 %, with the polygonal configuration requiring three dowels less. Selection of optimal dowel placement contributes to increased landslide control efficiency and reduced costs.Conclusions. The relevance and importance of studying the effect of dowel group configuration on slope stability, emphasizing the need for more in-depth and comprehensive research in this area.

Multi-band tunable electromagnetically induced transparencies based on active metasurface with polarization-independent property

The analogue of an electromagnetically induced transparency (EIT) spectrum is achieved using a metasurface that consists of an array of cross and L-shaped resonators. The mechanism of the EIT-like phenomenon are analyzed, and the influence of geometrical parameters on the effect is discussed. We achieve a multi-band EIT-like through structure configuration. In particular, polarization-independent EIT is realized. A potential application in sensing is suggested and the sensitivity of 65 GHz RIU−1 is obtained. We also investigate the impact of analyte and substrate on the transmission spectrum. We find that when the analyte thickness is higher than 40 μm, the EIT spectral shift is less affected by the analyte thickness. The thickness insensitive characteristics are beneficial for reducing errors caused by analyte dose, thereby improving the accuracy of sensing. By introducing a phase change material, vanadium dioxide, we obtain active control of the EIT effect. Our results provide valuable insights into the development of multi-band tunable compact devices based on metasurfaces.

Strength and failure assessments of 3D printed PLA single lap joints: Experimental and numerical analysis

In this paper, fused deposition modelling (FDM), is either used exclusively or in conjunction with adhesive bonding to manufacture single lap joints (SLJ). The design aspects of 3D printed SLJs are studied to assess their strength and failure mechanisms. Novel tooth-shaped interface joints are developed, leading to stronger and tougher joints. The uniaxial characteristics of Polylactic acid (PLA) were determined through testing on dog-bone samples. Subsequently, numerical models were developed to simulate the strength and failure modes of SLJs, followed by experimental testing. A parametric study was conducted to establish the influence of geometric parameters of tooth-shaped interface joints on failure load of tailored SLJs. Compared to baseline SLJs produced purely by 3D printing, the best performing tooth-shaped interface SLJs exhibit increased strength, failure strain, and toughness of ≈30%, ≈52%, and ≈130% respectively. Computational and experimental results confirm that SLJs with tooth-shaped interfaces can improve strength and failure strain.

Investigation of sound absorption on a polymeric acoustic metamaterial using 3D printing process

AbstractThis paper presents the design and characterization of DENORMS (Designs for Noise‐Reducing Materials and Structures) cell‐based acoustic metamaterial developed using a 3D printing technique. The metamaterial's acoustic absorption properties were investigated through experimental testing and numerical simulations. The experimental testing of the acoustic metamaterial was conducted in an impedance tube using a two‐microphone method. The numerical simulations were carried out using a thermoviscous module. The simulations allowed for a deeper understanding of the influence of geometric parameters on the absorption coefficient, providing valuable insights for optimizing the design. It was observed that upon increasing the spherical diameter while maintaining the same cylindrical diameter and cylindrical length resulted in an increase in the absorption coefficient throughout the frequency range. It was also observed that upon increasing the cylindrical diameter, there was a significant decrement of absorption coefficient, and upon increasing the length of the cylinder, there was a shift of response toward lower frequency. The augmentation in cell count from 9 to 24 led to a rise in the absorption coefficient and a shift of the response toward lower frequencies. The findings highlight the significance of photopolymer 3D printing in tailoring complex geometries for enhanced performance of the acoustic metamaterial.Highlights Photopolymeric resin used for DENORMS cell‐based acoustic metamaterial. High cleanability and accuracy of digital light processing 3D printing technique. Usage of thermoviscous model for simulation of sound absorption behavior. Use of two microphone impedance tube to determine sound absorption coefficient. Geometric parameters significantly affect the absorption coefficient.

A novel metamaterial with instantaneously sign-switchable coefficient of thermal expansion and Poisson's ratio

Most materials expand when heated and contract when cooled. In contrast, negative thermal expansion materials exhibit the opposite behavior. In this paper, we present a metamaterial that expands both when heated and cooled. The unit cell configuration is crafted by embedding two isosceles triangular structures composed of high thermal expansion materials within a re-entrant hexagonal honeycomb framework. Initially, the bases of the two isosceles triangles are in contact. The metamaterial exhibits two deformation states under different external loads. Analytical formulas for the equivalent parameters were derived based on classical beam theory within the regime of small deformation. Finite element simulations were conducted to validate the accuracy of these analytical formulas. The influence of geometric parameters on the metamaterial is discussed in detail. The results demonstrate that the metamaterial can exhibit excellent multi-functional properties within a small range of deformation, including instantaneous sign-variable coefficients of thermal expansion and Poisson's ratios, along with significantly distinct tensile and compressive stiffnesses. This metamaterial consistently exhibits expansive characteristics regardless of variations in ambient temperature. Additionally, the material always expands laterally regardless of the sign of uniaxial loads. Based on these properties, the metamaterial can be applied to fasteners in the aerospace industry that require permanent locking, ensuring stability in various temperature and mechanical load conditions.

Application of information technology to create the digital acoustic models of VVER

The IT used to create DAMPS is based on an interdisciplinary approach. DAMNR is presented as a self-oscillatory system, belonging to a special class of nonlinear dissipative systems capable of generating undamped oscillations. The use of DAMNR in the design and operation of NPP makes it possible to identify the sources of occurrence of ASW in the coolant, the conditions for their occurrence and frequency, and determine the influence of geometric parameters and the layout of coolant circuit equipment on the interaction of neutronic-physical, thermal–hydraulic and vibroacoustic processes. The use of DAMNR makes it possible to optimize engineering and design solutions when creating NPP by eliminating the conditions that cause the occurrence of unwanted self-oscillations of the coolant and vibroacoustic resonances in normal and emergency operating modes, as well as under conditions of shock impacts and seismic loads. Universal models and analysis methods were verified at Novovoronezh NPP.

Mechanical logic gate design based on multi-stable metamaterial with multi-step deformation

Mechanical metamaterials exhibit remarkable design versatility, enabling a series of unconventional mechanical properties via structural modifications. However, it is worth noting that many existing mechanical metamaterials either possess a singular deformation path or only multi-step deformation paths without reusability. This study proposes a novel multi-step deformation metamaterial that possesses multiple stable configurations. This metamaterial produces a unique two-step deformation mode under displacement loading, where the curved beams of the unit cells undergo snap-through and the vertical beams buckling. The influence of geometrical parameters on the multistability of the structure is thoroughly examined, and a theoretical prediction model for the buckling load is formulated. To validate the accuracy of the model, experimental tests and finite element simulations are conducted on the two-step deformation mode of periodic array of the unit cell. Additionally, a bi-material design approach for the unit cell is further introduced to enhance the specific energy absorption of the structure while reinforce the negative stiffness effect. Leveraging the multistable characteristics of the structure, mechanical logic gates such as AND, OR, NOT and NAND are conceptualized and experimentally validated. Through the implementation of rational designs and combinatorial connections within the logic gate structure, more complex logic operations can be realized.

Investigation on the band narrowing and shifting effects of micro-perforated panel absorbers.

Micro-perforated panel (MPP) absorbers exhibit multiple resonance bands with increased bandwidth narrowing and shifting in higher frequencies, limiting their effectiveness. This study investigates the effects of narrowing and shifting in higher-order resonance bands of MPP absorbers. First, an acoustic impedance model for MPP absorbers is introduced, and the narrowing and shifting coefficients are defined and modeled to quantify these effects. It is observed that a larger ratio of acoustic resistance to acoustic mass is favorable for reducing the narrowing and shifting effects. Subsequently, the theoretical model is validated using a numerical model, and a parametric study is conducted to explore the influence of geometric parameters on the narrowing and shifting effects. The study reveals that decreasing aperture and panel thickness, while increasing perforation ratio and cavity depth, reduces the narrowing and shifting coefficients. Remarkably, ultra-micro-perforated panels (UMPPs) with an aperture below 0.1 mm and perforation constant below 0.0046, having relatively larger acoustic resistance and smaller acoustic mass, demonstrate near-zero band narrowing and shifting. Finally, UMPPs are fabricated using micro-electro-mechanical systems (MEMS) technology, and their normal absorption coefficients are measured. Results align with theoretical predictions, confirming UMPPs' ability to achieve zero narrowing and shifting compared to ordinary MPPs and verifying the study's findings.

Design and optimization of a hybrid cooling configuration combining PCM and liquid cooling for Li-ion battery using data-based response surface approximation model

Effective thermal management is crucial for safe operation of electric vehicles. This study proposes a novel hybrid cooling system that using phase change material (PCM) and liquid cooling to address issues such as leakage, non-uniform temperatures under high discharge rates. A comprehensive 3D model was developed to analyze the influence of geometric parameters on the cooling system. Response surface approximation modeling was used to optimize the layout parameters of the PCM. The results show that the hybrid cooling outperforms other methods, maintaining the cell temperature with 35 ℃ and the temperature difference within 4 ℃. The thickness of the PCM is a significant factor, as it increases heat storage capacity and reduces temperature; however, exceeding a certain threshold leads to increased thermal resistance. A non-uniform PCM layout can reduce the temperature difference by 26 %. An optimal PCM thickness of 2.5 mm to 3 mm ensures that the maximum temperature remains below 32.5 ℃, with a temperature difference within 2 ℃. The lowest temperature difference is achieved with a vertical layout height of 70 mm and a horizontal layout thickness of 3 mm. These findings are valuable for enhancing the thermal management of lithium-ion battery.

Nonlinear dynamics simulation of the helical gear transmission system for high-speed train

Considering the bending-torsional-axial-coupled vibration of the helical gear transmission system, a 10 degrees of freedom high-speed train gear transmission system model, including motor and load, is established based on the lumped parameter method. In addition, the potential energy method based on the slicing principle is used to accurately calculate the time-varying meshing stiffness of helical gears. Furthermore, the influence of geometric parameters of helical gears on the time-varying meshing stiffness is studied, and the impact of time-varying meshing stiffness on the system is further investigated. Meanwhile, by analyzing the dynamic phenomena of the system under different parameter excitations under different parameter excitations, the influence of internal and external excitation parameters such as gear speed, wheel rail creep force, support stiffness, and support damping on the stability of high-speed train gear transmission system is deeply studied.

Numerical parametric study of a sweeping-vortex low-frequency fluidic oscillator

Fluidic oscillators are garnering increasing attention in various fields due to their self-induced oscillation characteristics. This study proposes a novel fluidic oscillator, the sweeping-vortex fluidic oscillator (SVFO), characterized by unique feedback properties. These properties exploit fluid feedback from the side opposite the attached wall and the spin delay of the captive vortex to yield low-frequency oscillating jets. The oscillation characteristics and the influence of main geometric parameters were investigated using computational fluid dynamics approach. Results show that the evolution of the flow field within the SVFO demonstrates an intricately dynamic interacting. The deflection switching of the main jet is primarily controlled by a pair of counter-rotating moving vortexes. Geometric parameters influence the stability of the dynamic evolution of both captive and moving vortexes, thereby altering the signal components of the output performance transmitted to the inlet. The overall width of the oscillator has a pronounced impact on the oscillation frequency, and with an increase in the overall width, a maximum frequency increase of 87 % can be observed. Furthermore, the height of the sweeping chamber and the diameter of the vortex chamber outlet have a noticeable effect on the pressure pulse amplitude. A pressure fluctuation coefficient greater than 1.1 was recorded. The results also suggest that the geometric parameters of the fluidic oscillator need to be designed within a reasonable range; otherwise, the jet oscillator will not function. A more refined optimization of geometric parameters could be obtained with the aim of achieving a stable main jet, feedback flow of appropriate intensity, and optimal attachment conditions. This work reveals the oscillation mechanism and the influence of geometric parameters on SVFOs, providing a theoretical basis for designing related oscillators.

Stacked multi-wedge acoustic black holes for low-frequency attenuation of flexible beams

Machines and other driving components like compressors or fans usually generate vibrations which frequently lead to acoustic noise. Flexible structures equipped with acoustic black holes minimise acoustic radiation by confining structural vibrations locally. One main restriction of its usage in the broad engineering field is its limited effectiveness at low frequencies. Recent investigations shifted the frequency range of attenuation successfully down to 1500 Hz. Moving the existing designs towards an even lower frequency demands a large structure. However, in general, sufficient space is often not available in machines and facilities. We propose a new design that enables a geometrically compact and simultaneously broadband vibration attenuation in the low-frequency below to 100 Hz: stacked wedges. The proposed design is calculated and optimised numerically by combining CAD and finite element calculations. The influence of geometrical parameters on the effectiveness of vibration attenuation is analysed with the help of transfer functions and dispersion curves. Successful designs of multi-stacked wedges at different lengths confirm their effectiveness at low frequency.Graphical abstract

Вплив геометричних параметрів автопоїзда на його аеродинамічні характеристики

In the article, the authors analyzed the relevance of the research topic, defined the goal, task, subject and object of the research. They also provided an analysis of well-known studies related to the study of the peculiarities of the formation of air resistance during the movement of motor vehicles. On the basis of the analysis of known studies on the factors affecting the geometric parameters of road trains on aerodynamic resistance, the relevance of the studies is substantiated, and their purpose and tasks are formulated.The purpose of the article is to determine the influence of geometric parameters of road trains on their aerodynamic characteristics and, as a result, on fuel consumption, and therefore on the cost of transport work. The tool for researching this issue is software, which will be used to conduct a number of experiments. Every year, road trains move millions of kilometers of various goods, and on such a scale, the price of each individual kilometer plays a very important role. Based on the analysis of the power balance equation, it can be concluded that a significant part of the engine power is spent on overcoming air resistance, and the higher the speed of the road train, the greater this resistance.The relevance of research lies in the possibility of reducing costs through the adoption of a number of decisions to reduce the aerodynamic resistance of road trains.The mechanism of air resistance is considered. It has been found that reducing aerodynamic drag is a very important task, as every 2% reduction in vehicle drag results in a 1% improvement in fuel economy. Compared to passenger cars, trucks have a much larger cross-section and more clumsy outlines. This is caused by the specifics of their purpose and use. When creating a universal truck, they try to get as much volume as possible to accommodate cargo with the minimum area occupied by the car on the road, and since part of this area is the engine and cabin, it is natural that the body is high. So, if one of the ways to reduce the aerodynamic resistance of a passenger car is to reduce its cross-section, first of all, its height, then another option should be found for a highway truck or road train.

Computational Analysis for the Evaluation of Fire Resistance in Constructive Wooden Elements with Protection

Wood is a material whose properties vary depending on different conditions, being particularly vulnerable to changes induced by high temperatures. When exposed to a fire situation, the wood properties suffer degradation, causing a char layer formation. Despite ensuring the protection of the inner core of the wood, the char layer reduces its resistant section. The evaluation of wood behavior under fire conditions is possible through experimental tests, simplified analytical models, and numerical models. To overcome difficulties in the development of experimental tests and in the approximations made to analytical methods, numerical models allow the evaluation of the fire resistance in a parametric way. First, this study will present a numerical model validated with an experimental test, using the finite element method. The validation of the results is based on the evolution of the temperature field, the char layer formation on the wooden elements, and its residual section, as well as the application of the thermal insulation criterion. The second part of the study evaluates the influence of geometric parameters, associated with different wooden constructive models with gypsum board exposed to fire. Different numerical tests are presented to evaluate the thermal and transient analysis of different wooden constructive elements with gypsum board. This type of constructive element presents cavities, making the numerical analysis in the study complex when approaching real models. The methodology applied allowed us to conclude that, at the same time, a smaller distance between wooden centers, a greater dimension of the wooden beam in height and width, as well as a greater thickness of gypsum board guarantee a better performance of the constructive wooden model.

Theoretical, numerical, and experimental investigation on second-order Bezier curve flexure hinges

This paper proposes the second-order Bezier curve flexure hinge. The flexure hinge can obtain different notch profiles by changing the position of the control points. Firstly, the compliance and precision of the flexure hinge are modeled based on the force deformation formula of the cantilever beam in material mechanics. Compared with the simulation data of ANSYS Workbench, the modeling error is less than 7%. Secondly, the influence of geometric parameters on compliance and precision is analyzed. The flexure hinge is compared with circular, elliptical, and parabolic hinges. The results show that the second-order Bezier curve flexure hinges have a higher compliance precision ratio. In addition, the use of second-order Bezier curve flexure hinges provides better performance than the use of traditional circular and elliptical flexure hinges in bridge amplification mechanisms. Finally, a flexure hinge was manufactured and measured. The experimental results show that the error between the experimental and modeling values is 8.76%. Both the simulation and experimental results verified the effectiveness of the model.

Numerical Study of the Effect of Primary Nozzle Geometry on Supersonic Gas-Solid Jet of Bypass Injected Dry Powder Fire Extinguishing Device

A two-way coupled model between polydisperse particle phases with compressible gases and a density-based coupling implicit solution method, combining the third-order MUSCL with QUICK spatial discretization scheme and the second-order temporal discretization scheme, are constructed based on the discrete-phase model (DPM) and the stochastic wander model (DRWM) in the Eulerian–Lagrangian framework in conjunction with a unitary particulate source (PSIC) approach and the SST k-ω turbulence model. The accuracy of the numerical prediction method is verified using previous supersonic nozzle gas-solid two-phase flow experiments. Numerical simulation of a two-phase jet of dry powder extinguishing agent gas with pilot-type supersonic nozzle was performed to analyze the influence of geometrical parameters, such as the length ratio rL and the area ratio rA of the main nozzle on the two-phase flow field, as well as on the jet performance indexes, such as the particle mean velocity vp,a, velocity inhomogeneity Φvp, particle dispersion Ψp, particle mean acceleration ap,a, etc. By analyzing the parameters, we indicate the requirements for the combination of jet performance metrics for different flame types such as penetrating, spreading, and dispersing.