Hasil untuk "Mechanics of engineering. Applied mechanics"

Zerrouki Moussa, Najib Mohamed Bouaziz

This paper presents a detailed study of the interaction between conduction through a vertical fin and conjugate mixed convection of a nanofluid flowing in a porous medium. The fin model and the primitive partial differential equations governing the nanofluid with boundary conditions are transformed into dimensionless forms. For the nanofluid, fin, and fin-nanofluid interface equations, a second-level nonsimilarity transformation is obtained and solved by the bvp4c solver. A validation of the computational code is ensured by comparing the results to a conventional fluid. It was found that the fin temperature is strongly controllable by the geometrical parameters and thermal conductivity of the fin, while Brownian motion and thermophoresis have a moderate effect on it. In addition, low values of Nr and Ω favor the fin efficiency. An analysis on very different values of the Pr number reveals that the use of nanofluids with a suitable base fluid allows high fin dissipations. A more advantageous thermal design can be achieved by combining a nanofluid in a porous medium with a fin in specific applications. These main results provide valuable information on the necessary optimization of the fin efficiency.

Piaopiao Qiu, Jiaqi Huang, Huasheng Zhang et al.

Abstract Objectives This study aimed to establish a rapid and accurate predictive model for mandibular third molar (MM3) extraction difficulty based on machine learning and multimodal parameters. Methods A dataset was constructed by integrating clinical characteristics with morphological features automatically extracted from cone-beam computed tomography (CBCT) images. Extraction difficulty was determined by three experienced experts using a ten-factor scoring system and clinical judgment. Six machine learning (ML) models were developed: support vector machine (SVM), artificial neural network (ANN), extreme gradient boosting (XGBoost), random forest (RF), k-nearest neighbors (KNN), and logistic regression. Model performance was optimized using grid search and five-fold cross-validation. SHapley Additive exPlanations (SHAP) were used to interpret feature importance, and recursive feature elimination (RFE) was employed for validation. Results The ML models predicted extraction difficulty efficiently, with XGBoost achieving the highest accuracy (88.24%), outperforming junior clinicians (83.53%). SHAP and RFE analyses highlighted the dominant role of morphological features, especially the angulation between adjacent teeth, contact area, and volume of the MM3. Clinical features such as fibrinogen and prothrombin time also contributed to prediction. The ML models demonstrated high accuracy and efficiency. Conclusion Integrating morphological and clinical features significantly improves prediction performance. Adjacent tooth resistance was the most influential factor, followed by bone resistance and mandibular canal-related features.

Himr Daniel, Dokoupil Pavel

There are more possibilities how to control flow rate in a pipeline system. When the flow is provided by pump, it is very economic to use frequency converter to change the pump speed which leads to flow rate change. Another possibility is to change number of running pumps, when pump station contains more than one unit. Control valve is used in systems without pump regulation especially, when the initial costs has to be low. The paper is focused on measurement of control ability of a ball valve. Generally, ball valves are not suitable to fulfil flow control function, but in an emergency case, when the control valve is damaged and the system has to be operated, there is no other possibility, but to use the ball valve.

Hong Yuan, Chang-Pu Sun

To address the observation of Max Born (M. Born 1969) that the Newton's second law can emerge from a purely statistical perspective, we derive the evolution equation about the statistical distribution for dilute gas based solely on statistical principles, without invoking Newtonian mechanics, and then obtain the equations of motion for individual particles. Newton's second law for a single particle naturally emerges when the distribution reaches equilibrium. We demonstrate that the magnitude of an external force, traditionally measured by particle acceleration, can be understood as a measure of distribution inhomogeneity. We further show that the entropic force (utilized in current gravity studies) is equivalent to the statistical force and under non-equilibrium conditions, a deviation arises between the entropic force and the Newtonian force. This framework offers a novel perspective distinct from classical Newtonian mechanics and broadens the potential scope of its application.

Vedran Žanić, Kalman Žiha

The paper presents some aspects of the sensitivity analysis within the multivariate distribution models. The presented procedures are provided for engineering problems based on the Nataf model. The Nataf model involves the marginal distributions of the random variables and the correlation between them. Sensitivities are considered through derivatives with respect to the correlation coefficients. The terms for the derivatives of the Nataf correlation coefficients with respect to the given correlation coefficients are presented. The derivatives of the transformations between the random variables are given next. The Cholesky decomposition and the spectral decomposition are applied. Derivatives of the Cholesky decomposition are obtained in the form of a recursive scheme. Derivatives of the eigenvalues and eigenvectors are obtained using perturbations. In addition, a comprehensive method for derivatives of distances and derivatives of angles between the directions is given. Finally, numerical examples are attached to illustrate the presented procedures.

Álvaro Tejero, Daniel Manzano, Pablo I. Hurtado

The possibility of efficiently converting heat into work at the microscale has triggered an intense research effort to understand quantum heat engines, driven by the hope of quantum superiority over classical counterparts. In this work, we introduce a model featuring an atom-doped optical quantum cavity propelling a classical piston through radiation pressure. The model, based on the Jaynes-Cummings Hamiltonian of quantum electrodynamics, demonstrates the generation of mechanical work through thermal energy injection. We establish the equivalence of the piston expansion work with Alicki's work definition, analytically for quasistatic transformations and numerically for finite time protocols. We further employ the model to construct quantum Otto and Carnot engines, comparing their performance in terms of energetics, work output, efficiency, and power under various conditions. This model thus provides a platform to extract useful work from an open quantum system to generate net motion, and sheds light on the quantum concepts of work and heat.

Ian A. Cosden

The Princeton Research Software Engineering Group has grown rapidly since its inception in late 2016. The group, housed in the central Research Computing Department, comprised of professional Research Software Engineers (RSEs), works directly with researchers to create high quality research software to enable new scientific advances. As the group has matured so has the need for formalizing operational details and procedures. The RSE group uses an RSE partnership model, where Research Software Engineers work long-term with a designated academic department, institute, center, consortium, or individual principal investigator (PI). This article describes the operation of the central Princeton RSE group including funding, partner & project selection, and best practices for defining expectations for a successful partnership with researchers.

Lena Kästner, Markus Langer, Veronika Lazar et al.

Recently, requirements for the explainability of software systems have gained prominence. One of the primary motivators for such requirements is that explainability is expected to facilitate stakeholders' trust in a system. Although this seems intuitively appealing, recent psychological studies indicate that explanations do not necessarily facilitate trust. Thus, explainability requirements might not be suitable for promoting trust. One way to accommodate this finding is, we suggest, to focus on trustworthiness instead of trust. While these two may come apart, we ideally want both: a trustworthy system and the stakeholder's trust. In this paper, we argue that even though trustworthiness does not automatically lead to trust, there are several reasons to engineer primarily for trustworthiness -- and that a system's explainability can crucially contribute to its trustworthiness.

A. C. Umuhire, J. Uwamahoro, K. Sasikumar Raja et al.

Solar radio type II bursts serve as early indicators of incoming geo-effective space weather events such as coronal mass ejections (CMEs). In order to investigate the origin of high-frequency type II bursts (HF type II bursts), we have identified 51 of them (among 180 type II bursts from SWPC reports) that are observed by ground-based Compound Astronomical Low-cost Low-frequency Instrument for Spectroscopy and Transportable Observatory (CALLISTO) spectrometers and whose upper-frequency cutoff (of either fundamental or harmonic emission) lies in between 150 MHz-450 MHz during 2010-2019. We found that 60% of HF type II bursts, whose upper-frequency cutoff $\geq$ 300 MHz originate from the western longitudes. Further, our study finds a good correlation $\sim $ 0.73 between the average shock speed derived from the radio dynamic spectra and the corresponding speed from CME data. Also, we found that analyzed HF type II bursts are associated with wide and fast CMEs located near the solar disk. In addition, we have analyzed the spatio-temporal characteristics of two of these high-frequency type II bursts and compared the derived from radio observations with those derived from multi-spacecraft CME observations from SOHO/LASCO and STEREO coronagraphs.

E. Azinpour, J. P. S. Ferreira, M. P. L. Parente et al.

Abstract In this work, the analogous treatment between coupled temperature–displacement problems and material failure models is explored within the context of a commercial software (Abaqus®). The implicit gradient Lemaitre damage and phase field models are implemented utilizing the software underlying capabilities for coupled temperature–displacement problems. The heat conduction equation is made compatible with the diffusive regularization of such material models and calculations are carried out at the material point level. This bypasses the need to implement explicitly the weak form resultant from the coupling between the momentum conservation and the evolution of the diffusive field. Throughout benchmarking examples, the proposed methodology is assessed and validated by investigating typical issues risen from the considered local inelastic-based deformation models, such as mesh dependency and the difficulties to predict cracked regions.

Prabowo Aditya Rio, Sohn Jung Min, Bae Dong Myung et al.

During ship collision, hull crashworthiness is an important data which needs to be assessed as rapid development of hull structure has taken into consideration since several notable dangerous events. After catastrophic accidents cause both tragic loss of life and destruction of maritime environment, double skin system is applied for almost all ships, including RoRo passengers. This work aimed to assess effects of selected internal parameters to crashworthiness criteria, considering a passenger vessel as the target of a series of impact loads. A set of collision scenario was numerically designed using finite element (FE) method by involving single and double skin structures, target location and material grade to obtained estimation of hull crashworthiness. Assessment was focussed on the energy absorption, crushing force, stress level and failure strain of the target ship after experiencing side collisions. It was obtained from the analyses regarding role of the inner skin on tendency of the energy absorption. Failure progress on the proposed structures was successfully quantified based on stress expansion. Minimum value of material strength was concluded in final discussion to reduce more massive failure.

Olga V. VISHNEVSKAYA

An approach to the provision of enterprise economic security with crisis management mechanisms is described. The approach is based on the following - the identification of the enterprise financial condition according to its development focus; selection of the anti-crisis mechanisms groups; planning anti-crisis balance of the structural elements of the individual assets and their sources; choice of the specific managerial measures taking into account business environment of the enterprise.

Elena A. Midler, Natalya M. Ovanesyan, Igor V. Boguslavskiy

The innovation transfer system in terms of the integration of its disjoint infrastructural elements is considered. The establishing technique of the innovative brokerage institute as the most effective innovat ion management tool is considered. The local specificity and organization of the innovation infrastructure in case of the R ostov region are analyzed.

Roman Frigg, Charlotte Werndl

Gibbsian statistical mechanics (GSM) is the most widely used version of statistical mechanics among working physicists. Yet a closer look at GSM reveals that it is unclear what the theory actually says and how it bears on experimental practice. The root cause of the difficulties is the status of the Averaging Principle, the proposition that what we observe in an experiment is the ensemble average of a phase function. We review different stances toward this principle, and eventually present a coherent interpretation of GSM that provides an account of the status and scope of the principle.

Pranesh R., Hemanathan M., Babu Kiran K.M. et al.

The airframe of any flying vehicle comprises structural members such as stringers and stiffeners made of sheet metal members, joined by riveted lap joints. Although different joining techniques exist, the rivet type of fastening still stands efficient. Numerous such rivets are required to join the skin completely. The mechanical loading due to the pressurization and depressurization of the fuselage, which occurs once in every flight and the air loads during the cruising flight causes the concentrated stress at the rivet joints which results in the failure of joints . The main objective of this research paper is to improve the strength of the riveted joints using Fiber Metal Laminate (FML) as the reinforcing material between the riveted joints. The tensile testing of the specimens with and without reinforcement are carried out and from the results it is concluded that due to the presence of reinforcement between the riveted joints the overall mechanical strength of the riveted joints is improved.

David M. Rogers

The question of deriving general force/flux relationships that apply out of the linear response regime is a central topic of theories for nonequilibrium statistical mechanics. This work applies an information theory perspective to compute approximate force/flux relations and compares the result with traditional alternatives. If it can be said that there is a consensus on the form of response theories in driven, nonequilibrium transient dynamics, then that consensus is consistent with maximizing the entropy of a distribution over transition space. This agreement requires the problem of force/flux relationships to be described entirely in terms of such transition distributions, rather than steady-state properties (such as near-equilibrium works) or distributions over trajectory space (such as maximum caliber). Within the transition space paradigm, it is actually simpler to work in the fully nonlinear regime without relying on any assumptions about the steady-state or long-time properties. Our results are compared to extensive numerical simulations of two very different systems. The first is a the periodic Lorentz gas under constant external force, extended with angular velocity and physically realistic inelastic scattering. The second is an $α$-Fermi-Pasta-Ulam chain, extended with a Langevin thermostat that couples only to individual harmonic modes. Although we simulate both starting from transient initial conditions, the maximum entropy structure of the transition distribution is clearly evident on both atomistic and intermediate size scales. The result encourages further development of empirical laws for nonequilibrium statistical mechanics by employing analogies with standard maximum entropy techniques -- even in cases where large deviation principles cannot be rigorously proven.

Benjamin Hancock, Aparna Baskaran

Starting from a microscopic model of self-propelled hard spheres we use tools of non-equilibrium statistical mechanics and the kinetic theory of hard spheres to derive a Smoluchowski equation for interacting Active Brownian particles. We illustrate the utility of the statistical mechanics framework developed with two applications. First, we derive the steady state pressure of the hard sphere active fluid in terms of the microscopic parameters and second, we identify the critical density for the onset of motility-induced phase separation in this system. We show that both these quantities agree well with overdamped simulations of active Brownian particles with excluded volume interactions given by steeply repulsive potentials. The results presented here can be used to incorporate excluded volume effects in diverse models of self-propelled particles.

Ruijin WANG, Jiayou DU, Zefei ZHU

Heat transfer enhancement with nanofluid appears to be an attractive work in recent years. In present work, a numerical formulation based on the Buongiorno model for convective heat transfer using Al2O3-water nanofluid accounted for the effects of Brownian motions and thermophoresis of nanoparticles, slip velocity and jump temperature at solid-fluid interface. Numerical investigations for laminar forced convection flows in a rectangle channel subjected to a uniform wall heat flux have been conducted. The numerical results show us that, the slip velocity can augment the heat transfer enhancement significantly due to the increase of the convection near the solid-fluid interface. Inversely, the jump temperature is not beneficial to the convective heat transfer because of the increased thermal resistance. The thermophoresis of particles affects heat transfer enhancement by changing local density, local viscosity, and local thermal conductivity. The thermophoresis of particles influences the skin friction coefficient also. The Nusselt number increases with the Reynolds number and particle volume fraction. The impact on the Nusselt number of Reynolds number will be receded in some extent because the thermophoresis velocity will be greater when the Reynolds number increasing. These numerical results help us to design micro-devices and understand the mechanism of heat transfer enhancement by adding nanoparticles in a microchannel.

Jamal A. Hameed

This paper presents the design of a simple real-time simulator to protection electrical power system tests, whose the operation principle is based on closed feedback in the loop. The hardware system has a series results from scientific projects carried out at the Protection and Control Laboratory of electrical power system. Models interface supports MATLAB / Simulink control system, and LabVIEW interface, and others. This gives not only Simulink, but also provides full support for any test software in real time, which uses the same interface. To run in the Hardware-in-the-Loop (HIL) simulation and the model has a measurement of the variables of the devices, whose receive the calculated variables in the form of mathematics. Testing has an integral part of modern controller development. Hardware-in-the-Loop (HIL) simulation plays a prominent role as test method. In HIL, the implemented controller is tested against a computer model of the process. Besides the communication between simulation and controller, HIL requires their synchronization.Besides the communication between simulation and controller, the program is based on the MATLAB / Simulink package including libraries, while the hardware installed measuring cards segment consists in PC computers, amplifier CMS 156 dedicated and matching circuit.The last section of this article and a brief description of possible improvements expected for simulation in the future.  The study involves xPC Target as a real time operating system in charge of executing a control task is focusing on the built in control and simulation capabilities. We will try to see how accurate and how fit xPC Target is for multiple Targets control, here the xPC Target is used as an operating environment for real time simulation in electrical power sub stations system.

P. Mafra, M. Kalinowski, D. Méndez Fernández et al.

Context] Problems in Requirements Engineering (RE) can lead to serious consequences during the software development lifecycle. [Goal] The goal of this paper is to propose empirically-based guidelines that can be used by different types of organisations according to their size (small, medium or large) and process model (agile or plan-driven) to help them in preventing such problems. [Method] We analysed data from a survey on RE problems answered by 228 organisations in 10 different countries. [Results] We identified the most critical RE problems, their causes and mitigation actions, organizing this information by clusters of size and process model. Finally, we analysed the causes and mitigation actions of the critical problems of each cluster to get further insights into how to prevent them. [Conclusions] Based on our results, we suggest preliminary guidelines for preventing critical RE problems in response to context characteristics of the companies.