Computer Code Research Articles

Experimental Investigation of Transient Flow Phenomena in Rotating Compressor Cavities

Abstract The clearance of compressor blade tips during aero-engine accelerations is an important design issue for next-generation engine architectures. The transient clearance depends on the radial expansion of the compressor discs, which is directly coupled to conjugate heat transfer in co-rotating discs governed by unsteady and unstable buoyancy-induced flow. This paper discusses an experimental and modeling study using the Bath Compressor Cavity Rig, which simulates a generic axial compressor at fluid-dynamically scaled conditions. The rig was specifically designed to generate heat transfer of practical interest to the engine designer and validate computational codes. This work presents the first study of the fundamental fluid dynamic and heat transfer phenomena under transient conditions. The rotating flow structure was seen to be characterized by coherent pairs of cyclonic/anticyclonic vortex pairs; the strength, rotational frequency, stability, and number of these unsteady structures changed with changing rotational Reynolds and Grashof numbers during the transients. These structures, measured by unsteady pressure transducers in the rotating frame of reference, were only present when the flow in the rotating cavity was dominated by buoyancy. Experimental correlations of both Nusselt number and radial mass flowrate in the rotating core were correlated against Grashof number. Remarkably, the experiments revealed a consistent correlation for both steady-state and transient conditions over a wide range of Gr. The results have a practical application to thermo-mechanical models for engine design.

Modeling of tsunami wave height distribution functions along the east coast of Sakhalin Island

The functions of the distribution of tsunami wave heights along the eastern coast of Sakhalin Island from sources located along the Kuril Islands are being studied. Known information about the tsunami on Sakhalin is given. Many of them were modeled numerically, which made it possible to assess the hazard of tsunami waves. The present work focuses on the functions of distributing the heights of tsunami waves, which were not previously calculated for this region at all. To this case, calculations were made of the propagation of tsunami waves from hypothetical strong earthquakes with M = 8.2 located in the regions of the Northern, Middle and Southern Kuril Islands. These calculations were carried out using the NAMI-DANCE computational code, which solves non-linear shallow water equations using nested grids with a minimum grid is about 9 m. Having no reliable coastal topography, the modeling was carried out to a depth of about 3 m. The results of the calculations confirmed that the calculated functions of the distribution of tsunami wave heights along the eastern coast of Sakhalin are well approximated by the lognormal function. The parameters of these distributions depend on the location of the source even with the same earthquake parameters, which once again emphasizes the significant role of seabed bathymetry on the characteristics of a tsunami on the shore.

Does DeFi remove the need for trust? Evidence from a natural experiment in stablecoin lending

Decentralized Finance (DeFi) is built on a fundamentally different paradigm. Rather than trusting individuals and institutions, DeFi participants, in principle, only need to trust computer code enforced by a decentralized network of computers. We examine a natural experiment that exogenously stress-tests this alternative paradigm by revealing the identities of individuals (including a convicted criminal) associated with the Abracadabra lending protocol. The revelation seriously damaged the protocol, indicating that, in practice, DeFi does not (yet) entirely remove the need for trust in individuals. Our findings suggest that smart contracts are incomplete and are subject to protocol-run risk. Thus, individuals’ character and trust remain relevant in this alternative financial system.

Surrogate Modelling of an Industrial Distillation Column Obtained from Statistical Techniques and Machine Learning

Purpose: To study a case of modeling an industrial distillation system, using the Aspen Plus simulator as the mathematical model and subsequently generating surrogate models using Machine Learning techniques in Matlab. Theoretical Framework: Metamodels are reduced models obtained from data generated by rigorous models, replacing them entirely or partially when the computational codes originating from them require excessively large computational effort to be used feasibly. Method/Design/Approach: The simulation of the process was performed in Aspen Plus. Subsequently, the most important variables were selected, and an experimental design was created using Latin Hypercube Sampling in Matlab, generating points to be used in sensitivity analysis in Aspen Plus. The next step was the construction of metamodels using the Statistics and Machine Learning toolbox in Matlab, employing linear regression and Gaussian process regression models. Finally, a statistical analysis was conducted. Results and Conclusion: The distillation system simulation converged, and the obtained metamodels had good regression indicators, especially the Gaussian process regression models, making them the most suitable for representing the rigorous Aspen Plus model. Research Implications: Understanding the multicomponent distillation process integrated with computational tools and data regression models, leading to a reduction in computational effort. Originality/Value: Development of a tool that enables the simulation and evaluation of a distillation process without the need to acquire software with rigorous equation databases.

Predicting displacement damage for ion irradiation: Origin of the overestimation of vacancy production in SRIM full-cascade calculations

Ion irradiation and implantation have wide applications that demand accurate determination of displacement damage profile and distribution of implanted ion concentration. The prediction of vacancies is especially important to determine displacements per atom (dpa), the standard parameter of primary radiation damage in materials. However, significant discrepancies exist in estimations of vacancies between full-cascade (F-C) and quick calculation (Q-C) options in the popular computer code SRIM. This study inspected the SRIM code and a relatively new code called Iradina, which uses a similar methodology, to develop an understanding of the origin of vacancy overestimation in the F-C options for SRIM and Iradina. We found that the default values of thresholds (namely final energy in SRIM and replacement energy in Iradina) in displacement production calculations results in excessively large number of calculated vacancies and very few replacements. After conducting multiple calculations using SRIM, Iradina, and MARLOWE (all based on the binary collision approximation), a comparison of the results indicates that there is a shortcoming in the SRIM and Iradina F-C methodology for treating near-threshold collisions. This issue is responsible for the deficiency of replacements and excess of calculated vacancies in the SRIM and Iradina F-C results. Drawing on the principles of collision physics, we propose recommendations for modifying the source codes to address these issues.

Theoretical and numerical approaches of a plane, laminar and non-confined, impinging jet

We propose in this paper, a numerical study of a planar impacting jet flow. The flow is assumed isothermal, laminar and unconfined. The developed computer code is based on the finite volume method, which was used to discretize the N-S equations. The code allowed us to simulate the physical phenomenon’s taking place in the jet flow. The work focuses, on the description of the evolution of the jet and the presentation of the different characteristics of the flow, for different values of the Reynolds number and the impacting height. Calculations were made for values of the Reynolds numbers ranging from 0.01 to Re = 2000, i.e. in the limits of laminar flow regime, and for values of the ratio between the height of the outlet nozzle-impact surface of 0.1 to 20. The theoretical and numerical approaches of this work are confronted with the experimental works of Sholtz et al., [2].

Digital distortions and interpretive choices: A cartographic perspective on encoding regulation

Rules as Code (RaC), which encompasses the conversion of legal and regulatory rules into computer code, is gaining traction internationally. This article analyses ‘digital distortions’ in RaC, which refer to disconnects between regulation and code that arise from interpretive choices in the encoding process. We contend that Boaventura de Sousa Santos’ ‘symbolic cartography of law’ provides valuable concepts for understanding digital distortions in encoding regulation. Specifically, we argue that the cartographic concepts of scale, projection, symbolisation and orientation highlight distortions that can arise from choices involving the documentation to code, logics to follow, languages to use and coded outputs to present. We demonstrate how these distortions arose in our attempt to convert the ePayments Code, an Australian voluntary code of conduct for consumer electronic payment transactions, into machine-executable code. The article concludes by underscoring the importance of greater awareness of interpretive coding choices and their implications for diverse users of digitised regulation.

Devanagari CAPTCHA: For the Security in Web

Completely Automated Public Turing Test to Tell Computers and Humans Apart or CAPTCHA is a solution for cyber-attack. CAPTCHA is a small challenge that an internet user has to pass before accessing any online service. The most common type of CAPTCHA is text-based CAPTCHA, in which a small image (contains a random number of alphabets) is presented before the user. The user has to identify and then type the alphabet in a text box. The textual information in the CAPTCHA must not be identified by a bot (computer code). So, artificial noise and distortion are applied in the image. Earlier text-based schemes use English alphabets, but over time non-English language-based text CAPTCHAs also came into the picture. Native language-based text CAPTCHA is very useful for internet users who do not know the English language. This article is an effort towards the current status of the Devanagari script-based CAPTCHAs. We have analyzed 28 unique Devanagari CAPTCHAs from a security and usability point of view. Total 28000 different samples are collected for this experiment. For the success of a text-based CAPTCHA, it must be very secure from the bot and easy for human beings. Devanagari CAPTCHA can be very beneficial for Indian websites. This paper is written by keeping the importance of Devanagari script-based CAPTCHA.

Investigating the structure, bonding, and energy decomposition analysis of group 10 transition metal carbonyls with substituted terminal germanium chalcogenides [M(CO)3GeX] (M = Ni, Pd, and Pt; X = O, S, Se, and Te) complexes: insight from first-principles calculations.

This research focused on the theoretical investigation of transition metal carbonyls [M(CO)4] coordinated with terminal germanium chalcogenides complexes [M(CO)3GeX], where M represents Ni, Pd, and Pt and X represents O, S, Se, and Te labeled 1-15. While the notable complexes M(CO)4 (where M = Ni, Pd, Pt) numbered 1, 6, and 11 are of significance, substituting one of the CO ligands in 1, 6, and 11 with a GeX ligand (where X = O, S, Se, or Te) result in substituted complexes (2-5, 7-10, and 11-15). Substituting of the CO ligand slightly alters these bond angles. Specifically, the ∠CMC bond angles for [Ni] complexes range from 111.9° to 112.2°, for [Pd] complexes from 111.4° to 111.7°, and for [Pt] complexes from 112.4° to 112.8°. These findings indicate a minor deviation from the tetrahedral geometry due to the influence of the new GeX ligand. Similarly, there is a slight change in the geometry of the metal complexes, where the ∠GeMC angles for [Ni] complexes are between 106.7° and 106.9°, for [Pd] complexes between 107.2° and 107.5°, and for [Pt] complexes between 105.9° and 106.4°. Comparing among the substituted GeX complexes, those containing GeTe exhibit a higher natural bond orbital (NBO) contribution from the Ge atom compared to the M atom. Consequently, based on the above observations, it can be inferred that GeX acts as an effective sigma donor in contrast to carbonyl compounds. Results of energy decomposition analysis (EDA) for the M-CO bond in 1, 6, and 11 and for the M-GeX bond in the other [M(CO)3(GeX)] complexes where M = Ni, Pd and Pt. The percentage contribution of ΔEelstat and ΔEorb shows a relatively identical behavior for all ligands in case of each metal complexes. Density functional theory (DFT) calculations were conducted using the B3LYP/gen/6-31G*/LanL2DZ level of theory to examine transition metal carbonyls [M(CO)4] coordinated with terminal germanium chalcogenides complexes [M(CO)3GeX], where M represents Ni, Pd, and Pt, and X represents O, S, Se, and Te labeled 1-15 utilized through the use of Gaussian 09W and GaussView 6.0.16 software packages. Post-processing computational code such as multi-wave function was employed for results analysis and visualization.

SIMMER-IV application to safety assessment of severe accident in a small SFR

A sodium-cooled fast reactor (SFR) core has a potential of prompt criticality due to a change of core material distribution during a severe accident, and the resultant energy release has been one of the safety issues of SFRs. In this study, the safety assessment of an unprotected loss-of-flow (ULOF) in a small SFR (SSFR) has been performed using the SIMMER-IV computer code, which couples the models of space- and time-dependent neutronics and multi-component, multi-field thermal hydraulics in three dimensions. The code, therefore, is applicable to the simulations of transient behaviors of extended disrupted core material motion and its reactivity effects during the transition phase (TP) of ULOF, including a potential of prompt-criticality power excursions driven by fuel compaction. Several conservative assumptions are used in the TP analysis by SIMMER-IV. It was found out that one of the important mechanisms that drives the reactivity-inserting fuel motion was sodium vapor pressure resulted from a fuel-coolant interaction (FCI), which itself was non-energetic local phenomenon. The uncertainties relating to FCI is also evaluated in much conservative way in the sensitivity analysis. From this study, the ULOF characteristics in an SSFR have been understood. Occurrence of recriticality events under conservative assumptions are plausible, but their energy releases are limited.

Method of negative pressure analysis for secondary containment of BWR-6 plant

In the analysis of design basis loss of coolant accident (DB LOCA) for BWR, the time it takes the Secondary Containment to reach the negative pressure condition, typically of 0.25 in. wg, is termed positive pressure period (PPP). In accordance with the USNRC regulatory guide, the filtration system can only be credited to reduce the radioactivity released to the environment at the time after PPP. Hence the PPP time is an important input parameter for the dose calculation during the DB LOCA. In view of this, an analysis method used to determine PPP time, based on the transient calculation of the GOTHIC computer code, is developed in the study. The analysis is performed for the Secondary Containment of the Kuosheng BWR-6 plant. A lumped parameter model of GOTHIC is used to model the Secondary Containment. A standby gas treatment system (SGTS) used for drawing the air from the Secondary Containment and discharging it to the ambient is modeled in conjunction with an in-leakage modeling. The results show that the GOTHIC predicts well the pressure and temperature response of the Secondary Containment. The corresponding PPP time thus can be determined appropriately based on the response of the pressure difference between the Secondary Containment and the ambient. Sensitivity study is also performed for the key parameters affecting the PPP time.

Characterizing affect dynamics with a damped linear oscillator model: Theoretical considerations and recommendations for individual-level applications.

People show stable differences in the way their affect fluctuates over time. Within the general framework of dynamical systems, the damped linear oscillator (DLO) model has been proposed as a useful approach to study affect dynamics. The DLO model can be applied to repeated measures provided by a single individual, and the resulting parameters can capture relevant features of the person's affect dynamics. Focusing on negative affect, we provide an accessible interpretation of the DLO model parameters in terms of emotional lability, resilience, and vulnerability. We conducted a Monte Carlo study to test the DLO model performance under different empirically relevant conditions in terms of individual characteristics and sampling scheme. We used state-space models in continuous time. The results show that, under certain conditions, the DLO model is able to accurately and efficiently recover the parameters underlying the affective dynamics of a single individual. We discuss the results and the theoretical and practical implications of using this model, illustrate how to use it for studying psychological phenomena at the individual level, and provide specific recommendations on how to collect data for this purpose. We also provide a tutorial website and computer code in R to implement this approach. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Numerical Simulation of Turbulent Structures Inside Internal Combustion Engines Using Large Eddy Simulation Method

<div>Using two subgrid-scale models of Smagorinsky and its dynamic version, large eddy simulation (LES) approach is applied to develop a 3D computer code simulating the in-cylinder flow during intake and compression strokes in an engine geometry consisting of a pancake-shaped piston with a fixed valve. The results are compared with corresponding experimental data and a standard K-Ɛ turbulence model. LES results generally show better agreement with available experimental data suggesting that LES with dynamic subgrid-scale model is more effective method for accurately predicting the in-cylinder flow field. Representative Fiat engine equipped with moving valve and piston bowl is analyzed as the second case to assess the capability of the method to handle complex geometries and impacts of geometrical parameters such as shape and position of piston bowl together with swirling intake flow pattern on both turbulent structure of in-cylinder flow and engine performance using dynamic version of LES approach over a curvilinear computational meshed geometry. Results indicate that presence of piston bowl leads to eye-catching increment in both turbulent kinematic energy and tumble ratio amounts at the end of compression stroke by around 29% and 33%, respectively. The optimum swirl ratio found to be 4, leading to 67.9% increment in pre-injection turbulent kinetic energy in comparison with non-swirl pattern, whereas 20% eccentricity of cylinder bowl just led to 2% improvement in the pre-injection turbulent kinetic energy, which is not recommended due to small impact compared to noticeable manufacturing expenditures.</div>

Heat transfer enhancement using combined microchannel with vertical rectangular micro fins

This paper focuses on the numerical optimisation of a combined hybrid microchannel heat sink with rectangular solid fins. The axial length and volume are fixed, and external structure is allowed to vary. The simulation was performed on an elemental unit cell of the microchannel heat sink . The purpose of the optimisation is to discover an optimal geometric arrangement in internal and external configurations that minimises peak temperature in the microchannel heat sink. A high-density uniform heat flux of 250 W/cm2 is assumed to be dissipated on the bottom wall of the unit cell by microelectronics circuit boards devices. Computational fluid dynamic code was used to discretized the fluid domain and solve a set of governing equations. The influence of hydraulic diameter, external structural shape and fluid velocity on peak temperature and global thermal resistance, is discussed. Coolant or water of Reynolds number range 400 to 500 in a forced convection laminar flow is introduced through the inlet of the computational domain to remove the heat at the bottom of the rectangular block microchannel. The results show that when the fluid velocity is increased from 9.8 to 12.3 m/s across the axial length of the micro heat sink, more heat is removed from the bottom of the combined heat sink. The results revealed that the pump power increased by 37.1% in combined microchannels with fins and from by 27.2% in finless micro heat sink. The result of the study is validated with what is documented in open literature for a traditional micro heat sink with circular flow channel and the trends agree.

On symbolic computation of C.P. Okeke functional equations using Python programming language

This present paper is inspired by one of the questions posed by Okeke (Results Math 78(96):1-30, 2023, see Remark 2.10b). In particular, we aim to develop a robust computer code based on the theoretical results obtained in Okeke (2023), which determines the polynomial solutions of the following functional equation, 0.1∑i=1nγiF(aix+biy)=∑j=1m(αjx+βjy)f(cjx+djy),\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\begin{aligned} \ extstyle \\sum \\limits _{i=1}^n \\gamma _i F(a_i x + b_i y)=\ extstyle \\sum \\limits _{j=1}^m(\\alpha _j x + \\beta _j y) f(c_j x + d_j y), \\end{aligned}$$\\end{document}for all x,y∈R\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$x,y\\in \\mathbb {R}$$\\end{document}, γi,αj,βj∈R,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma _i,\\alpha _j,\\beta _j \\in \\mathbb {R},$$\\end{document} and ai,bi,cj,dj∈Q,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$a_i,b_i,c_j,d_j \\in \\mathbb {Q},$$\\end{document} and their special forms. The primary motivation for writing such a computer code is that solving even simple equations belonging to class (0.1) needs long and tiresome calculations. Therefore, one of the advantages of such a computer code is that it allows us to solve complicated problems quickly, easily, and efficiently. Additionally, the computer code will significantly improve the level of accuracy in calculations. Along with that, there is also the factor of speed. We point out that the computer code will operate with symbolic calculations provided by the programming language Python, which means that it does not contain any numerical or approximate methods, and it yields the exact solutions of the equations considered.

Counter-checking uncertainty calculations in Bayesian operational modal analysis with EM techniques

Bayesian operational modal analysis makes inference about the modal properties (e.g., natural frequency, damping ratio) of a structure using ‘output-only’ ambient vibration data. With sufficient data in applications, the posterior probability density function (PDF) of modal properties can be approximated by a Gaussian PDF, whose covariance matrix is given by the inverse of the Hessian of negative log-likelihood function (NLLF) at the most probable value. Existing methodologies for computing the Hessian are based on semi-analytical formulae that offer an efficient and reliable means for applications. Inevitably, their computer coding can be involved, e.g., a mix of variables with different sensitivities, singularity of Hessian due to constraints. In the absence of analytical or numerically ‘exact’ result for benchmarking, computer code verification during development stage is also non-trivial. Currently, finite difference method is often used as the only and last resort for verification, although there are also difficulties in, e.g., the choice of step size, and criterion for comparison/convergence. Motivated by these, this work explores an identity in the theory of Expectation-Maximisation (EM) algorithm to provide an alternative means for evaluating the Hessian of NLLF. Such identity allows one to evaluate the Hessian by means of Monte Carlo simulation, averaging over random samples of hidden variables. While the existing semi-analytical approach is still preferred for Hessian calculations in applications for its high definitive accuracy and speed, the proposed Monte Carlo solution offers a convenient means for counter-checking during code development. Theoretical implications of the identity will be discussed and numerical examples will be given to illustrate implementation aspects.

Light scattering by a periodically time-modulated object of arbitrary shape: the extended boundary condition method

A proper generalization of the extended boundary condition method to calculate the transition matrix, T, for electromagnetic scattering from a homogeneous and isotropic body of arbitrary shape, characterized by a periodically time-varying electric permittivity, is presented. The application of the method on a specific example of a spheroidal dielectric particle confirms that time modulation induces strong inelastic scattering, accompanied by energy transfer between the scatterer and the light field, when the difference of the incident wave frequency to a particle optical resonance matches an integer multiple of the modulation frequency. Moreover, it is shown that, for nonspherical scatterers, these effects can be selectively tuned by external means such as the polarization and the propagation direction of the incident light beam. The method is readily implementable in available dynamic multiple-scattering computer codes, and, because of its versatility and computational efficiency, it can offer new opportunities for studying more complex time-varying photonic structures.

Method for screening paired metal hydrides with appropriate phase change material for a thermochemical energy storage system

Thermochemical energy storage (TES) systems using coupled metal hydrides (MHs) have long been recognized as an option for sustainable energy systems such as solar power plants. The MHs-TES system consists of two linked MH beds (energy storage bed and hydrogen storage bed) that exchange hydrogen during the heat storage/release cycles. The heat reaction of the hydrogen storage bed is stored in a PCM as latent heat, which is recovered during the heat release step. One of the main issues of the MHs-TES system is selecting the best-suited combination of MHs and compatible PCM to satisfy application requirements. Herein, an approach is proposed for screening the right pairs of hydrides and the suitable PCM. To assess this procedure's effectiveness, a 2D-mathematical model is developed, and a computer code is established. In addition, using this code, the dynamic behavior of the MHs-TES system and the effect of the hydrogen storage bed temperature on the system's performance are examined. The Mg2Fe alloy as HTMH bed, and two LTMH beds as LTMH (LaNi4.25Al0.75 at medium temperature and LaNi5 at low temperature) are used. With an efficiency of 86.5%, the results show that Mg2Fe/LaNi5 is a viable MHs combination for a thermal storage system.

The effect of upstream soil type on the amount of catchments sediment

ABSTRACT Mud filled by upstream surface runoff is one of the problems in maintaining the reservoir and dam. The material of upstream bed has a significant effect on the filling of reservoirs. In the present work, the filling rate of the reservoir from the upstream movable bed is investigated by using the Herschel–Bulkley model in both shear-thickening and shear-thinning modes. For this, a two-phase Newtonian-non Newtonian SPH code was developed that has special capabilities such as turbulence effects, surface tension, free surface, and particle displacement. This computational code is then evaluated by the experimental results in addition to finally used to investigate the main problem mentioned above. Five different models of movable beds with are considered, and the filling rate of the downstream tank with these materials is discussed. The results show that among the parameters of the Herschel–Bulkley model, the yield stress is more effective than other factors.

Sensitivity analysis of GTN damage parameters: Application to notched plate ductile fracture simulation

The evolution of preexisting voids causes damage to metal structures with large plastic deformation. In the ABAQUS-Explicit computer code, the damage by the Gurson–Tvergaard–Needleman model (GTN model) is included in the porous failure criteria law. The numerical predictions using the GTN model are very sensitive to the calibrations of these parameters of the experimental results. This model describes until the damage, the mechanism of the evolution of the voids, which begins with their growth and their nucleation with the particles until the coalescence of these voids of a critical level, which causes the damage to the structure. This analysis uses Voce’s hardening model and von Mises’ equivalent stress flow theory. After validation with experimental results, this work aims to analyze the sensitivity of these GTN parameters to the response to damage and to the evolution of the gaps. This objective is applied on a plate notch.