Hasil untuk "Descriptive and experimental mechanics"

Chao Li, Ilia Derevitskii, Sergey Kovalchuk

This paper presents a PDE-based auto-aggregation model for simulating descriptive norm dynamics in autonomous multi-agent systems, capturing convergence and violation through non-local perception kernels and external potential fields. Extending classical transport equations, the framework represents opinion popularity as a continuous distribution, enabling direct interactions without Bayesian guessing of beliefs. Applied to a real-world COVID-19 dataset from a major medical center, the experimental results demonstrate that: when clinical guidelines serve as a top-down constraint mechanism, it effectively generates convergence of novel descriptive norms consistent with the dataset; in the bottom-up experiment, potential field guidance successfully promotes the system's reconstruction of descriptive norms aligned with the dataset through violation-and-recoupling; whereas fully autonomous interaction leads to the emergence of multi-centric normative structures independent of the dataset.

Milan Mihajlović, Juan G. Ramírez, Ildefonso Campos Velarde et al.

Fluidized bed reactors (FBRs) are integral to various industries due to their exceptional capability in facilitating efficient gas–solid interactions, resulting in superior mixing and heat and mass transfer. This research delves into the impact of temperature on fluidization dynamics, particularly focusing on the collisional properties of particles within the bed. The investigation builds upon foundational research, notably Geldart’s classification of fluidization regimes and recent advancements in high-temperature experimental techniques, such as High-Temperature Endoscopic-Laser particle image velocimetry/digital image analysis. To explore these temperature effects, a coupled Discrete Element Method and Computational Fluid Dynamics (<span style="font-variant: small-caps;">cfd–dem</span>) model was employed. This approach enables a detailed examination of gas–particle and particle–particle interactions under varying temperature conditions. The simulations in this study explore the friction coefficient, as well as changes in both tangential and normal restitution coefficients, which affect the fluidization behavior. These changes were systematically analyzed to determine their influence on minimum fluidization velocity and bubble formation. The numerical results are compared with experimental data from high-temperature fluidization studies, highlighting the necessity of incorporating inter-particle forces to fully capture the observed phenomena. The findings underscore the critical role of particle collisional properties in high-temperature fluidization and suggest the potential increasing role of inter-particle forces. Overall, this paper provides new insights into the complex dynamics of fluidized beds at elevated temperatures, emphasizing the need for further experimental–numerical research to enhance the reliability and understanding of these systems in industrial applications.

Mouhsine M. Benmbarek, Samir F. Moujaes

This research investigates the enhancement of heat transfer in a heat exchanger that is made of a corrugated tube which has a twisted plate inserted in it; the corrugation and twisted plate are expected to increase the amount of heat transfer since the plate is acting as a connection between the center of the flow and the edges of the tube. The turbulence will cause an increase in pressure drop along the channel length, so the investigation will try to find the best compromise between the gain in heat transfer and loss of hydraulic energy by using well-established metrics. A positive heat transfer gain is achieved if the metric indicates a value equal to or greater than 1. This CFD research will be compared with the experimental results found in previous studies cited in the text. After validating the CFD results, it is proposed to investigate a new insert geometry to further improve the efficiency of the heat exchanger. The computational fluid dynamics (CFD) simulation was conducted to investigate and validate the CFD model, which evaluates the heat transfer performance in a spirally corrugated tube that has a twisted tape inserted. The heat transfer was then compared to a simple corrugated tube without the twisted tape and to a smooth tube with no corrugations and no twisted tape.

Luca Cocconi, Michalis Chatzittofi, Ramin Golestanian

The study of active solids offers a window into the mechanics and thermodynamics of dense living matter. A key aspect of the non-equilibrium dynamics of such active systems is a mechanistic description of how the underlying mechano-chemical couplings arise, which cannot be resolved in models that are phenomenologically constructed. Here, we follow a bottom-up theoretical approach to develop a thermodynamically consistent active solid (TCAS) model, and uncover a non-trivial cross-talk that naturally ensues between mechanical response and dissipation. In particular, we show that dissipation reaches a maximum at finite stresses, while it is inhibited under large stresses, effectively reverting the system to a passive state. Our findings establish a generic mechanism plausibly responsible for the non-monotonic behaviour observed in recent experimental measurements of entropy production rate in an actomyosin material and enzymatic activity in crowded condensates.

Erik Gustafsson, Magnus Andersson

Physics-informed neural networks (PINNs) are gaining traction as surrogate models for fluid dynamics problems, combining machine learning with physics-based constraints. This study investigates the impact of labeled data on the performance of parameterized physics-informed neural networks (PINNs) for surrogate modeling and design optimization. Different training approaches, including physics-only, data-only, and several combinations of both, are evaluated using fully connected (FCNN) and Fourier neural network (FNN) architectures. The test case focuses on reducing drag over a forward-facing step through optimal placement and sizing of an upstream obstacle. Results demonstrate that the inclusion of labeled data significantly enhances the accuracy and convergence rates of FCNNs, particularly in predicting flow separation and recirculation regions, and improves the stability of design optimization outcomes. Conversely, FNNs exhibit inconsistent responses to parameter changes when trained with labeled data, suggesting limitations in their applicability for certain design optimization tasks. The findings reveal that FCNNs trained with a balanced integration of data and physics constraints outperform both data-only and physics-only models, highlighting the importance of optimizing the training approach based on the specific requirements of fluid mechanics applications.

Allan N. Kaufman, Bruce I. Cohen, Alain J. Brizard

Presented here is a transcription of the lecture notes from Professor Allan N. Kaufman's graduate statistical mechanics course at Berkeley from the 1972-1973 academic year. Part 1 addresses equilibrium statistical mechanics with topics: fundamentals, classical fluids and other systems, chemical equilibrium, and long-range interactions. Part 2 addresses non-equilibrium statistical mechanics with topics: fundamentals, Brownian motion, Liouville and Klimontovich equations, Landau equation, Markov processes and Fokker-Planck equation, linear response and transport theory, and an introduction to non-equilibrium quantum statistical mechanics.

LM Arévalo Aguilar, Rolando Velázquez García

In this work, firstly, we propose how to experimentally demonstrate the single photon steering phenomenon in a simple way. The quantum steering phenomenon was discovered by Erwin Schrodinger, who reason that the laws of quantum mechanics obliges us to admit that by suitable measurements taken on one of two entangled system, then the state of the other system can be determined and steered. On the other hand, the first proposal about the nonlocal property of a single photon focus on showing the Bell nonlocality by using the single-photon path entanglement. Here, we propose a new experimental scheme that, by incorporating and manipulating the internal degree of freedom (IDF) of the photon, easily demonstrate the nonlocal steering phenomenon of single-photon's states. The experimental set-up that we propose differs from those published in the quantum optics' literature to shown the single photon nonlocality, which generally use the path entanglement of photons and homodyne measurements. Secondly, by incorporating its IDF, we show that the single photon steering and the quantum mechanical interaction-free measurement (QM-IFM) are identical phenomena; we will argue that QM-IFM is just a particular instance of the single-photon steering. In short, both the single photon steering and QM-IFM (being identical phenomena) have a common cause: the nonlocality of the wave function. In conclusion, we have demonstrated that it is possible to produce a nonlocal phenomena by manipulating the single photon internal degree of freedom. On the other hand, this unification between steering and QM-IFM could establish a strong support to counterfactual quantum communication and computation.

Simon Zacharias Lahme, Dominik Dorsel, Heidrun Heinke et al.

This exploratory field study investigates the integration of innovative forms of recitation tasks in a first-year introductory mechanics course, focusing on smartphone-based experimental tasks alongside programming and standard recitation tasks. Smartphones, combined with external sensor modules, serve as a gateway enabling students to conduct various low-cost and authentic physics experiments with first-hand data collection outside traditional lab settings. These tasks aim to enhance students' agency in independent physics experimentation and enrich homework assignments by dissolving boundaries between lectures, recitation sessions, and traditional labs, and thereby linking theoretical and experimental aspects of undergraduate physics education. To explore this potential, we implemented and evaluated a sample set of nine smartphone-based experimental tasks and, for comparison, three programming tasks as weekly exercises in a first-year physics course at RWTH Aachen University. We investigated students' perceptions of learning with these new tasks through twelve short surveys involving up to 188 participants. In two additional surveys with 108 and 78 participants, students assessed affective responses to the smartphone-based experimental tasks relative to the programming and standard recitation tasks. Our findings indicate that the smartphone-based experimental tasks were generally well-suited to the students and tended to outperform the programming tasks in terms of perceptions of learning with the tasks and affective responses. Overall, students responded positively to the new experimental tasks, with perceptions comparable to, or only partly below, those of long-established standard recitation tasks. These results suggest that smartphone-based experimental tasks can be successfully integrated into teaching and contribute to refining traditional recitation tasks.

Max Quissek, Thomas Lauer

The understanding of impingement processes is crucial for optimizing automotive selective catalytic reduction (SCR) systems. An accurate description of this behavior helps design exhaust systems and increases the validity of modeling approaches. A component test bench was set up, featuring a droplet chain generator for producing droplet sizes typically found in the urea–water solution sprays of SCR systems. A heatable impingement plate with an interchangeable surface enabled investigation of the influence of surface roughness. Data were acquired using a high-speed camera and image postprocessing. The droplet–wall interaction could be described using different regimes. An approach to characterizing impingement behavior based on weighted-regime superposition enabled gradual transitions between regimes, instead of step-like changes. It was observed that the surface roughness increased the droplet–solid contact area and generated thermal-induced secondary droplets at lower temperatures. A region of enhanced mechanical disintegration of the droplet was found, caused by peaks of the surface shearing off parts of the droplet. The probability of a droplet rebounding from the wall was reduced on a rough surface, due to the interference of the surface spikes with the droplet’s spreading and contracting motion. Additionally, the influence of surface topography was investigated using a shot-peened surface. Caused by this surface’s reduced root mean square slope, the aforementioned enhancement of mechanical disintegration was not observed.

Lucas Wansner, Ned J H Wontner

The axiom of countable choice for reals is one of the most basic fragments of the axiom of choice needed in many parts of mathematics. Descriptive choice principles are a further stratification of this fragment by the descriptive complexity of the sets. In this paper, we provide a separation technique for descriptive choice principles based on Jensen forcing. Our results generalise a theorem by Kanovei.

Lalida Wiboonwachara, Sasima Charubusp

In an EFL context, writing in English is often considered challenging for second language learners. Previous studies (Khumphee & Yodkamlue, 2017; Owu-Ewie & Williams, 2017; Richard & Renandya, 2002) suggest that a lack of sufficient cognitive and rhetorical skills for generating ideas and producing coherent compositions can be one of the challenges faced by learners. The transformation of education in this digital era means that learners ought to master their own learning path while dealing with many learning distractions. A ‘Genre-Based Self-Regulated Instruction’ (GBSRI) may therefore help language learners, particularly those with limited language proficiency, to accumulate competency in language, which in turn may encourage them to pursue independent writing and learning. This is due to GBSRI’s distinguishing features pertaining to genre-based writing instructions (Derewianka, 2003; Hyland, 2004; Macken-Horarik, 2002) and the practice of self-regulated learning (Schmitz & Wiese, 2006; Schunk & Zimmerman, 2007; Zimmerman, 2013). The objectives of this study were: (1) to examine the English writing ability of Thai undergraduate students by exploiting language features, text organization, and writing mechanics with a particular focus on two genres, namely: procedural writing and descriptive writing; and (2) to investigate Thai undergraduate students’ opinions as it related to GBRSI. The sample group in this study consisted of 32 Thai undergraduate students. For the purposes of the investigation, a one-group pre-test and post-test quasi-experimental design was utilized. The research instruments included: (1) pre-test and post-test paragraph writing, (2) a GBSRI questionnaire, and (3) semi-structured interviews. The results of the pre-test and post-test revealed that the ability of the participants’ paragraph writing was significantly improved subsequent to participating in GBSRI. Moreover, the qualitative data from the questionnaires and the semi-structured interviews indicated that most students expressed satisfaction with GBSRI and acknowledged its benefits. Furthermore, they stated that both their writing ability and self-regulation in learning had improved after participating in GBSRI, especially in explicit instruction, collaborative learning, and self-regulated writing activities. This study also showcases other considerations regarding the implementation of GBRI in different contexts.

Thomas Höhne, Sören Kliem

The development, verification, and validation of Computational Fluid Dynamics (CFD) codes in reference to nuclear power plant (NPP) safety has been a focus of many research organizations over the last few decades. Therefore, a collection of Rossendorf Coolant Mixing Test Facility (ROCOM) CFD-grade experiments was made obtainable to line up a global International Atomic Energy Agency (IAEA) benchmark regarding Pressurized Thermal Shock (PTS) situations. The benchmark experiment describes the complicated flow structures in mixed convection zones of the RPV during PTS events. The experiments were utilized to validate CFD codes. Additionally, an experiment with no buoyancy forces was elite to point out the influence of density variations. Compared to earlier studies, the turbulence models of the CFD code improved a lot. The turbulence modeling approach shows a respectable agreement with the experimental data.

Mostafa Mousivand, Ehsan Roohi

This study examined rarefied thermally-driven flow in a square cavity (Case 1) and rectangular bend (Case 2), with various uniform wall temperatures in two dimensions. We employed the direct simulation Monte Carlo (DSMC) to solve problems with a wide range of Knudsen numbers Kn = 0.01 to 10, and the discrete unified gas kinetic scheme (DUGKS) solver was used at Kn = 0.01. The scenario was that, in case 1, the bottom side and its opposite were set hot, and the other sides were set cold. Diffuse reflector boundary conditions were set for all walls. The imposed temperature differences created four primary vortices. The results of the continuum set of equations of the slow non-isothermal flow (SNIT) solver proved that the primary vortices in the square cavity were caused by nonlinear thermal stress effects, and other smaller vortices appearing at Kn = 0.01, 0.1 were brought about by thermal creep processes. As the Kn increased, vortices generated by thermal creep disappeared, and eddies created by nonlinear thermal stress occupied the cavity. In case 2, i.e., a rectangular bend, two sides were set cold, and the others were hot. Two primary vortices were formed, which were caused by nonlinear thermal stress effects. The direction of streamlines in the two main vortices was opposite, from the warm to the cold zone, as some eddies on the left were counterclockwise, and others were clockwise.

Shadi Ansari, David S. Nobes

The passage of a bubble and the required energy for its motion through a confining pore can potentially be affected by the surface roughness and geometry of the pore. The motion of an isolated bubble passing through four different pore geometries (three circular pores, a smooth pore and 2 with different roughness, and a sharp triangular pore) is investigated. The shape of the deformed bubble passing these geometries was evaluated to determine the pressure drop across the bubble and hence the driving force to cause motion. The results of investigating the motion of the bubbles and the change in the pressure and velocity of the bubbles showed that the pore shape and surface roughness have a significant effect on the passage of the isolated phase. The motion of the bubble entering the entrance of the circular pores was similar for all circular cases. On exiting, however, a clear difference between the cases due to the presence of the peaks of the roughness was observed. These results indicate that, in addition to the critical pressure at the entrance of the pore, extra resistance will be introduced due to bubble phase pinning at the exit caused by roughness of the pore.

Mikhailo Sukach

Проведено шосту міжнародну науково-практичну конференцію Transfer of Innovative Technologies 2020, присвячену 90-річчю від дня заснування Київського національного університету будівництва і архітектури. Особливістю цьогорічного форуму було те, що він відбувався дистанційно на платформі Cisco Webex за участі науковців з Польщі, Франції, Австралії, Іраку, Лівії, Бразилії, Китаю. Фахівці в галузях будівництва і архітектури, інженерії та екології, інформаційних технологій та ін. традиційно ділились своїм досвідом. Роботу було спрямовано на інтеграцію українських і закордонних фахівців і наукових шкіл у розробці теорії проведення досліджень, створення нових методів і техніки, практичне застосування енергоощадних, екологічно безпечних технологій та засобів. Мета конференції – спілкуваня з фахівцями різних галузей для вирішення глобальних проблем ресурсного та енергетичного забезпечення виробництва, передачі інноваційних технологій у різні сфери людської діяльності. Офіційними мовами конференції є українська, російська, англійська, польська і французька. Було отримано понад сотню заявок від 140 учасників з наукових та освітніх закладів, промисловості, недержавних установ, студентів, магістрантів та аспірантів. Було представлено понад три десятки інноваційних проектів в галузях архітектури, інженерії споруд, інформаційних технологій, кібербезпеки тощо. Обговорено результати дослідження двох докторських та кількох кандидатських дисертацій. За результатами оголошенних конкурсів в номінаціях Інноваційний проект, Презентація, Публікація визначено переможців 2020 року, які були нагороджені дипломи. Найактивніші учасники з числа фахівців та студентської молоді отримали Подяки і Сертифікати. Результати роботи та препринти найкращих презентацій авторів опубліковано у Збірнику матеріалів конференції (online) та журналі Transfer of Innovative Technologies. КНУБА налагодив співпрацю зі спеціалістами Університету науки і техніки Цзянсу (Китай), Університету прикладних наук та мистецтв (Fachhochschule Dortmund, Germany), IT університету Астани (Казахстан) у галузях досліджень досліджень та видавничої справи. Учасники конференції підтримали Петицію керівництва Міжнародного центру інтегральної екології CEI Laudato Si (Варшава) до Папи Римського і Президента США про антропогенний вплив на світове середовище і захист від академічного насилля та тиску.

Panagiotis Koutsogiannakis, Davide Bigoni, Francesco Dal Corso

A highly deformable rod, modelled as the extensible elastica, is connected to a movable clamp at one end and to a pin sliding along a frictionless curved profile at the other. Bifurcation analysis shows that axial compliance provides a stabilizing effect in compression, but unstabilizing in tension. Moreover, with varying the constraint's curvature at the origin and the axial vs bending rod's stiffness, in addition to possible buckling in tension, the structure displays none, two, or even four bifurcation loads, the last two associated only to the first buckling mode in compression. Therefore, the straight configuration may lose and recover stability one or two times, thus evidencing single and double restabilization, a feature never observed before. By means of the closed-form solution for the extensible elastica, the quasi-static behaviour of the structure is analytically described under large rotations and axial strain. The presented solution is exploited, together with an {\it ad hoc} developed optimization algorithm, to design the shape of the constraint's profile necessary to obtain a desired force-displacement curve, so to realize a force-limiter or a mechanical device capable of delivering a complex force response upon application of a continuous displacement in both positive and negative direction.

Mohamed El Ouafa, Stephane Vincent, Vincent Le Chenadec

In this paper, we investigate the accuracy and robustness of three classes of methods for solving two-phase incompressible flows on a staggered grid. Here, the unsteady two-phase flow equations are simulated by finite volumes and penalty methods using implicit and monolithic approaches (such as the augmented Lagrangian and the fully coupled methods), where all velocity components and pressure variables are solved simultaneously (as opposed to segregated methods). The interface tracking is performed with a Volume-of-Fluid (VOF) method, using the Piecewise Linear Interface Construction (PLIC) technique. The home code Fugu is used for implementing the various methods. Our target application is the simulation of two-phase flows at high density and viscosity ratios, which are known to be challenging to simulate. The resulting strategies of monolithic approaches will be proven to be considerably better suited for these two-phase cases, they also allow to use larger time step than segregated methods.

Pornthep Pattanavanitkul, Watit Pakdee

A numerical analysis of unsteady fluid and heat transport of compressible Helium–Xenon binary gas through a rectangular porous channel subjected to a transverse magnetic field is herein presented. The binary gas mixture consists of Helium (He) and Xenon (Xe). In addition, the compressible gas properties are temperature-dependent. The set of governing equations are nondimensionalized via appropriate dimensionless parameters. The dimensionless equations involve a number of dimensionless groups employed for detailed parametric study. Consequently, the set of equations is discretized using a compact finite difference scheme and solved by using the 3rd-order Runge–Kutta method. The model’s computed results are compared with data from past literature, and very favorable agreement is achieved. The results show that the magnetic field, compressibility and variable fluid properties profoundly affect heat and fluid transport. Variations of density with temperature as well as pressure result in an asymmetric mass flow profile. Furthermore, the friction coefficient is greater for the upper wall than for the lower wall due to larger velocity gradients along the top wall.

Valeriia G. Melnikova, Andrey S. Epikhin, Matvey V. Kraposhin

This paper presents the Eulerian–Lagrangian approach for numerical modeling of high-speed gas-droplet flows and aeroacoustics. The proposed hybrid approach is implemented using the OpenFOAM library and two different methods. The first method is based on a hybrid convective terms approximation method employing a Kurganov–Tadmor and PIMPLE scheme. The second method employs the regularized or quasi-gas dynamic equations. The Lagrangian part of the flow description uses the OpenFOAM cloud model. Within this model, the injected droplets are simulated as packages (parcels) of particles with constant mass and diameter within each parcel. According to this model, parcels moving in the gas flow could undergo deceleration, heating, evaporation, and breakup due to hydrodynamic instabilities. The far-field acoustic noise is predicted using Ffowcs Williams and Hawking’s analogy. The Lagrangian model is verified using the cases with droplet evaporation and motion. Numerical investigation of water microjet injection into the hot ideally expanded jet allowed studying acoustic properties and flow structures, which emerged due to the interaction of gas and liquid. Simulation results showed that water injection with a mass flow rate equal to 13% of the gas jet mass flow rate reduced the noise by approximately 2 dB. This result was in good coincidence with the experimental observations, where maximum noise reduction was about 1.6 dB.

Sergey Denisikhin, Vladislav Emelyanov, Konstantin Volkov

A numerical simulation of the gas-dynamic processes in the thrust vectorable nozzle of the solid rocket motor is considered. Construction of a geometric model and a generation of computational mesh, and reconstruction of model and mesh at each time step are discussed. Calculations of the flowfield of combustion products in the pre-nozzle chamber and nozzle block are carried out for various angles of nozzle rotation. The distributions of the gas dynamic quantities in the pre-nozzle volume corresponding to the outflow of the combustion products from the cylindrical channel and star-shaped channel are compared, as well as the solutions of the problem obtained with quasi-stationary and unsteady formulations. The effects of the channel shape on the distribution of flow quantities and formation of a vortical flow structure in the nozzle block are discussed.