Non-uniform Conditions Research Articles

Thermal analysis for clamped laminated beams with non-uniform temperature boundary conditions

The focus of this study is thermal responses of a clamped composite laminated beam with arbitrary layer numbers under non-uniform temperature boundary conditions. Analytical solutions of temperature, stresses, and displacements are derived based on the theory of thermoelasticity. The temperature distribution in the laminated beam is divided into two parts. The first part is constructed to satisfy the inhomogeneous temperature boundary conditions, while the second part is obtained on the basis of the Fourier law of heat conduction and the temperature environment. On the other hand, the unit pulse function and the Dirac delta function are introduced to translate the clamped support into the simply support with an unknown horizontal stress. According to the continuities at the interface and the state space method, the relationships of displacements and stresses between the top and bottom surfaces of the laminated beam are derived. Finally, the unknown coefficients of displacements and stresses are determined by the mechanical boundary conditions. It can be observed from the numerical results that this method has excellent convergence performance. The accuracy of this method is verified by comparing with the results of the finite element method. Furthermore, the effects of surface temperature, material properties, length-to-thickness ratio and layer numbers on the distributions of temperature, displacements and stresses in the laminated beam are in depth investigated.

Theoretical and Experimental Models to Evaluate the Possibility of Corrosion Resistant Concrete for Coastal Offshore Structures.

This study built theoretical and practical models to evaluate the corrosion resistance of concrete for coastal offshore structures in Vietnam. A mathematical model was developed in the form of a system of nonlinear partial differential equations characterizing the diffusion “free calcium hydroxide” in a solid of a concrete structure. The model describes the process of non-stationary mass conductivity observed in the “concrete structure—marine environment” system under non-uniform arbitrary initial conditions, as well as combined boundary conditions of the second and third kind, taking into account the nonlinear nature of the coefficients of mass conductivity k and mass transfer β. It was shown that the solution of the boundary value problem of non-stationary mass conductivity allows us to conclude about the duration of the service life of a concrete structure, which will be determined by the processes occurring at the interface: in concrete—mass conductivity, depending on the structural and mechanical characteristics of hydraulic structures, and in the liquid phase—mass transfer, determined by the conditions of interaction at the interface of the indicated phases.

Measuring the near-target neutron field of a D–D fusion facility with the novel NCT-WES spectrometer

A new directional neutron spectrometer called NCT-WES (Neutron Capture Therapy Wide Energy Spectrometer) was recently developed within the INFN ENTER_BNCT project. This device constitutes a more compact and portable alternative to state-of-the-art directional neutron spectrometers. The device was used for the first time to characterise the near-target field produced by an accelerator-driven D–D fusion neutron source. NCT-WES operates as a “parallelised” Bonner spheres spectrometer, embedding six semiconductor-based thermal neutron detectors in a cylindrical moderator. Owing on a cylindrical collimating aperture, the device exhibits sharply directional response. To account for the non-uniform irradiation condition experienced in the near-target field, a dedicated NCT-WES response matrix was developed. The neutron spectrum at 0^{circ } from the D–D neutron target, determined by means of the FRUIT unfolding code, is coherent with that previously derived with Bonner spheres. NCT-WES proved to be a promising device for angular spectrometric characterisation of neutron-emitting targets.

Mason–Weaver theory: Revised and extended for a semi-infinite domain

Mason and Weaver developed equations to describe small particles settling under the influence of gravity and Brownian motion, including the limiting case for an infinitely deep suspension. We encountered this common convection–diffusion equation and no-flux boundary conditions in a model for dynamics of adsorbed polymers in dead end pores of a depolymerization catalyst. Close examination reveals that the Mason–Weaver solution is not correct for the infinite domain with a non-uniform initial condition. In this paper, we obtain the time dependent Green’s function for the no flux boundary condition and also for a more general reactive boundary condition. We demonstrate how the results provide solutions, via superposition, which provide solutions for several boundary conditions and all initial conditions.

Eustasy in the Aptian world: A vision from the eastern margin of the Iberian Plate

Eustatic controls on Early Cretaceous (Aptian) sedimentation in the western Tethys are discerned in outcrops of carbonate platforms that developed in the Maestrat rift basin located at the eastern margin of the Iberian Plate. The relative sea-level fluctuations with a dominant eustatic contribution investigated had estimated magnitudes of between 50 and 60 m in <0.9 My and ≥115 m in <3 My, and occurred respectively during the late early and early late Aptian. The major relative sea-level falls of mainly eustatic nature were recorded as forced regressive sedimentary wedges or as incised valleys carved into highstand carbonate platforms, whereas the subsequent sea-level rises back-filled the incised topographic lows created, or favoured the development of lowstand platforms. The finding of 50–115 m amplitude fluctuations of Aptian age is of relevance in that show magnitudes of relative sea-level fall in the order of that recorded during the last glacial maximum in the late Pleistocene ( c . 120 m). The current knowledge on Cretaceous climate history shows an Earth with non-uniform greenhouse conditions. However, geological evidence of temporary icehouse states with ice-cap magnitudes close to late Pleistocene scales during the Aptian is absent, or at least has not been reported so far. Thus, although falling within the glacio-eustatic domain, the driving processes of these widespread drops and subsequent rises in relative sea level remain a mystery. Finally, this paper is an example of how sequence stratigraphy can be applied to carbonate successions, and of how this methodology indeed permits to unravel ancient relative sea-level fluctuations which controlled carbonate production and accumulation. • Eustatically-driven changes in accommodation deciphered • The Aptian world recorded a strong eustatic signal • Development of incised valleys during the Aptian

Assessment of thermal comfort of frail people in a sitting posture under non-uniform conditions using a thermal manikin

Thermal comfort has gradually become an important research field in the context of sustainable living. Several thermal comfort studies have been conducted in thermally uniform environments, though far fewer are being performed in non-uniform thermal conditions. Recently, the evaluation of thermal responses in non-uniform thermal environments, has come to the attention of researchers. This study aims to evaluate the thermal responses of frail people using a “Newton” thermal manikin and a test chamber. Personalized cooling and heating floor systems were used to produce non-uniform conditions by supplying global cooling air flow and vertical heat flow to the whole manikin body. In this paper, skin temperature, core temperature, and thermal responses were examined and discussed in both males and females. The analysis showed a significant difference in thermal sensation and dynamic thermal sensation between females and males over time, and under the same experimental conditions. On the other hand, the ANOVA analysis revealed a significant difference in the main effect of gender in terms of thermal comfort. Results show that thermal discomfort in frail people originated largely from air temperature. It was found that air temperature increments of 5 °C–30 °C can modify thermal comfort by 1.5 scale units’ in comparison with the thermal sensation.

Prediction of effective properties for multilayered laminated composite with delamination: A multiscale methodology proposal

In the manuscript, piezoelectric composites with non-uniform imperfect contact at the interface are studied. For this, the two-scales asymptotic homogenization method is used to determine the effective properties of said piezocomposite. First, a theoretical framework is offered to determine the effective properties of piezoelectric materials with generalized periodicity. In addition, a method to solve the local problems for the particular case of stratified media with imperfect contact conditions is described. In the second part, the above-described methodology is used to study different numerical examples and compare the results taking into account distinct contact conditions at the interfaces. Examples include wavy composites with uniform imperfect contact, laminate composite with cracks at the interface, and non-uniform imperfect contact conditions elastic and piezoelectric composites. Also, the influence on the average properties of the small geometrical parameter related to the size of the periodic cell in the homogenization is illustrated. To validate the model, some of the results are compared with the values obtained by the finite elements method (FEM).

Nonuniform input-output criteria for exponential expansiveness of discrete dynamical systems and applications

The aim of this paper is to present a new and complete study based on input-output methods for exponential expansiveness of discrete variational systems, treating both the nonuniform behavior and the uniform one. We continue the line of studies initiated in Dragičević et al. (2020) [19] and Dragičević et al. (2022) [20], providing a new approach in exploring the expansiveness properties. We associate to a discrete variational system a control type system that consists of a family of input-output discrete-time equations defined between two sequence spaces whose norms are translations invariant and we introduce new concepts of exact admissibility that rely on nonuniform local conditions. First, by imposing some minimal hypotheses on the input space or respectively on the output space, we establish connections between the exact admissibilities and the nonuniform exponential expansiveness. Moreover, we give for the first time a complete description of the structure of exactly admissible pairs that can be considered to explore nonuniform expansive behaviors in the discrete variational case. In addition, all the hypotheses on the classes from which we choose the input or the output spaces are motivated by illustrative examples. Next, we present characterizations for uniform exponential expansiveness via certain nonuniform exact admissibilities and we generalize the recent criteria for expansiveness of dynamical systems from Dragičević et al. (2020) [19]. Furthermore, we show via relevant examples that the results are the most general and the working hypotheses cannot be weakened or removed. As application, we give general criteria for uniform exponential expansiveness of skew-product semiflows in terms of nonuniform admissibility properties with sequence spaces invariant under translations.

MIXED REALITY CONTENT ALIGNMENT IN MONUMENTAL ENVIRONMENTS

Abstract. Mixed reality provides on-the-spot and real-time data access capabilities by making virtual models and information more intuitive and accessible. Furthermore, allowing the operator to perceive 3D as holograms would allow for a more natural and straightforward manipulation of the perceived 3D content by permitting the augmentation of real objects with various levels of data. This can be accomplished by appropriately registering and superimposing the presented 3D models with the surrounding environment. This work aims to provide a quantitative evaluation of HoloLens 2 capabilities in registering virtual content inside monumental spaces. Two different methodologies are evaluated: Vuforia image targets and Microsoft World Locking Tools (WLTs). Tests have been performed inside Milan Cathedral's monumental spaces. Here, ambience dimensions, single architectural element repetition and non-uniform lighting conditions push out-of-the-box methods to their limits. Results show that WLTs with their space pins API can correctly reference virtual content keeping deviations in the order of 15 cm coping with the scale error produced from sensors’ drifts.

Potential flow around polygonal shaped cylinders using hypotrochoidal mapping function

In this paper, some investigations on two-dimensional steady potential flow over polygonal shaped cylinders are presented. The polygonal shapes with finite corner radius are obtained using Hypotrochoidal mapping function. The complex potential function derived using Milne-Thompson circle theorem, along with Hypotrochoidal mapping is employed to get various flow parameters over different shaped cylinders. The uniform and non-uniform flow conditions are arrived at, by taking infinite and finite distance of vortex from the cylinder, respectively. The velocity and pressure distribution over various shaped cylinders are presented and some of them are compared with the results from commercial software package (ANSYS) and available literature. Formulas are developed to obtain velocity and pressure distribution around various shaped geometries. Also, the effect of various geometrical parameters on velocity and pressure distribution is studied.

S-duct flow distortion with non-uniform inlet conditions.

Convoluted aero-engine intakes are often required to enable closer integration between engine and airframe. Although the majority of previous research focused on the distortion of S-duct intakes with undistorted inlet conditions, there is a need to investigate the impact of more challenging inlet conditions at which the intake duct is expected to operate. The impact of inlet vortices and total pressure profiles on the inherent unsteady flow distortion of an S-duct intake was assessed with stereo particle image velocimetry. Inlet vortices disrupted the characteristic flow switching mode but had a modest impact on the peak levels and unsteady fluctuations. Non-uniform inlet total pressure profiles increased the peak swirl intensity and its unsteadiness. The frequency of swirl angle fluctuations was sensitive to the azimuthal orientation of the non-uniform total pressure distribution. The modelling of peak distortion with the extreme value theory revealed that although for some inlet configurations the measured peak swirl intensity was similar, the growth rate of the peak values beyond the experimental observations was substantially different and it was related with the measured flow unsteadiness. This highlights the need of unsteady swirl distortion measurements and the use of statistical models to assess the time-invariant peak distortion levels. Overall, the work shows it is vital to include the effect of the inlet flow conditions as it substantially alters the characteristics of the complex intake flow distortion.

Numerical study on restrained thermal elongation of cold-formed steel Column subjected to non-uniform thermal loading under transient state

Cold-formed steel (CFS) is extensively used as non-load bearing and load-bearing structural members because of its less weight to strength ratio, transportation economy, and handling ease. Since CFS members are treated as slender sections, they are highly susceptible to buckling under the compression loads at ambient and elevated temperatures. The codes IS801, EN1993–1.3, AS/NZS4600, and BS5950 are used to design the cold-formed steel compression members at ambient temperature, and the code EN1993–1.2 is used to design the CFS member by treating it as a slender member with a limiting temperature of 350 °C. Many researchers have attempted to study the behaviour of CFS members at elevated temperatures, both numerically and experimentally, under uniform thermal loading conditions at steady-state. However, studies on non-uniform thermal loading under transient states are minimal. The present study focuses on the numerical modelling of buckling behaviour of CFS members with restrained thermal elongation under non-uniform temperature conditions. The numerical modelling of the CFS column subjected to non-uniform temperature under a transient state is validated with the past results. The parametric study is carried out by varying the initial load, the member's slenderness ratio, the stiffness of the supporting structure, the width-thickness ratio(w/t), and the temperature difference between flanges.

Transient dynamics of the thermally induced deformation of sands

AbstractCurrently, inconclusive evidence characterizes the thermally induced deformation of sands. In this context, the role of the transient nature of heat diffusion on the thermally induced deformation of sands has remained largely disregarded. This paper presents a theoretical and computational investigation of the transient dynamics characterizing the thermally induced deformation of sands under oedometric conditions. The study shows that heating rates determined by the pore fluid pressure dissipation timescale to ensure drained conditions can cause an important temperature nonuniformity and a breakdown of quasi‐static conditions. Under these dynamic conditions, the differential expansion between the sand and the confining oedometer ring uniquely characterizes the response and is broken down into two characteristic regimes. For slow heating rates and low‐expansion ring materials, a mathematical analysis shows that expansion and only expansion can occur, regardless of relative density and stress level. For fast heating rates and high‐expansion ring materials, a parametric analysis establishes the possibility of a very small initial volumetric contraction for loose materials under high stress levels. In the light of the existing literature, the study shows that the intrinsic volumetric response to heating loads of sand, as a material, is only expansive; volumetric contraction may only be observed under transient conditions. This work supports a conceptual shift in the framework of analysis of thermally induced deformation of sands, from a temperature‐dependent material response to a rate‐dependent response of a finite volume under nonuniform conditions.

Generalized Cost-effective Converter for Solar Street Lighting featuring Averaged State-space Model-based Sensorless MPPT

Decentralized solar street lighting is an economical solution in remote areas. However, non-uniform conditions mandates an efficient maximum power point tracking (MPPT) process. Meanwhile, implementing a less-sophisticated MPPT algorithm on a cost-effective converter is preferable to reduce system cost. In this paper, a current sensorless MPPT approach, based on converter state-space model, is proposed reducing the MPPT controller cost. Moreover, it compromises between tracking accuracy, time and implementation simplicity owing to the applied variable-step perturb and observe algorithm. Regarding the MPPT converter, D1 is selected as it overcomes the discontinuous input current limitation featured by conventional buck/boost converters. Consequently, PV power fluctuations are diminished at minimum converter component-count, enhancing tracking efficiency. Moreover, the large PV output capacitor is eliminated, increasing system reliability. Simulation and experimental results of the developed prototype validate the proposed sensorless approach. Finally, a market-survey verifies the proposed MPPT unit cost-effectiveness when compared to others in literature.

Thermal analysis of thermal barrier coating systems under transient and time harmonic thermal loads

In this study, the temperature fields in a thermal barrier coating system (TBC) under various types of thermal loadings, including steady and transient thermal loads, is investigated. TBCs are exposed to a variety of harsh thermal loadings, including thermal shock and periodic thermal loads. Therefore, the need to achieve the temperature distribution in different positions of the TBCs, especially in the protective coating is very crucial. Non-uniform Thermal boundary conditions are considered for both external temperature and heat flux distributions. The coating and substrate are not stationary at the onset of transient thermal load. Using the solution of steady-state problem as initial condition, the transient temperature fields within the coating-substrate system is obtained. The dual-phase lag (DPL) heat conduction is utilized to scrutinize the transient response of the TBC system. Fourier and Laplace integral transforms have been used to solve the temperature field equations. The effect of concentrated thermal shock and steady harmonic thermal load on the temperature fields of coating and substrate is investigated. The results demonstrate that the steady state and transient temperature fields strongly depend on the type of thermal load, the thickness and thermal properties of the coating, and the loading parameters. The results indicate that the effect of concentrated thermal shock is felt after at least 8.33 s at distance 1.2 cm far from the top surface of ceramic coating. The effect of concentrated thermal shock is eminent adjacent to point (x=0,y=0) of the free boundary of coating, but after a longitudinal distance of 2 cm drastically reduced. The ceramic coating is able to relieve the amplitude of temperature oscillations up to 1280C at a vertical distance of 3mm from the free boundary of coating.

On the Accuracy of Particle Image Velocimetry with Citizen Videos—Five Typical Case Studies

The application of image velocimetry to measure surface streamflow velocities requires meticulous preparation, including surveying and securing both the existence of floating features on the water surface, and, as in every hydrometry method, appropriate hydraulic conditions (e.g., uniform flow, turbulent velocity profile, etc.). Though these requirements can be easily satisfied when all stages involved in image velocimetry are prepared and executed by specialists, this is not guaranteed when the video footage is recorded by citizens. This kind of spontaneously obtained data are frequently the only available information of extreme flood events; therefore, and despite their non-scientific origin and standardization, these data are very important for hydrology. In this study, we evaluate image velocimetry under a variety of conditions, including conditions resembling citizen videos. Furthermore, we conclude on the manual analysis as a means of verification of the accuracy of the velocity estimations. An interesting finding from the case study with non-uniform flow conditions was that the surface velocities occurring at the middle section of the river, estimated using large-scale particle image velocimetry algorithms, exhibited a significant error, whereas the manual estimation was more accurate. This finding calls for further investigation and a more careful approach in similar conditions.

Modelling concrete slabs subjected to localised fire action with OpenSees

PurposeReinforced concrete slabs in fire have been heavily studied over the last three decades. However, most experimental and numerical work focuses on long-duration uniform exposure to standard fire. Considerably less effort has been put into investigating the response to localised fires that result in planarly non-uniform temperature distribution in the exposed elements.Design/methodology/approachIn this paper, the OpenSees for Fire framework for modelling slabs under non-uniform fire exposure is presented, verified against numerical predictions by Abaqus and then validated against experimental tests. The thermal wrapper developed within OpenSees for Fire is then utilised to apply localised fire exposure to the validated slab models using the parameters of an experimentally observed localised fire. The effect of the smoke layer is also considered in this model and shown to significantly contribute to the thermal and thus thermo-mechanical response of slabs. Finally, the effect of localised fire heat release rate (HRR) and boundary conditions are studied.FindingsThe analysis showed that boundary conditions are very important for the response of slabs subject to localised fire, and expansive strains may be accommodated as deflections without severely damaging the slab by considering the lateral restraint.Originality/valueThis work demonstrates the capabilities of OpenSees for Fire in modelling structural behaviours subjected to non-uniform fire conditions and investigates the damage pattens of flat slabs exposed to localised fires. It is an advancing step towards understanding structural responses to realistic fires.

Maximization of photo-voltaic array power output through Lo Sho Square shade dispersion technique based re-configuration scheme

Non-homogenous irradiation levels across the solar PV array reduces the overall power yield of solar PV plant. Therefore, it is essential to decrease mismatch power loss incurred under non-homogenous conditions. For this purpose, ‘Lo Sho Square’ shade dispersion technique based re-configuration of solar PV modules is investigated in the present research work. Proposed ‘Lo Sho Square’ shade dispersion technique effectively scatters the non-homogenous irradiation across the reconfigured solar PV array, rather than concentrated on one location. Performance of the proposed re-configuration technique is studied by subjecting the 9 × 9 sized solar PV array under five different categories of non-uniform irradiation conditions. Efficacy of the proposed re-configuration is justified to be superior by comparing the simulation results obtained from proposed ‘Lo Sho Square’ technique with those obtained for Total-Cross-Tied interconnection and four recently reported ‘Normal SU-DO-KU’, ‘Optimized SU-DO-KU’, ‘Improved SU-DO-KU’ and ‘Modified SU-DO-KU’ shade dispersion techniques. The simulation results indicate that the proposed re-configuration scheme with values of 20%, 12.5%, 12.5%, 16.13% and 12.5% under five categories of typical non-homogenous conditions, has the lowest mismatch power loss relatively compared to that of literature reported four shade dispersion techniques. In addition, the proposed ‘Lo Sho Square’ technique based re-configuration with the efficiency values of 14.18%, 15.12%, 15.12%, 14.65% and 15.12% under five categories of typical non-homogenous conditions, has highest efficiency relatively compared to literature reported four shade dispersion techniques. Based on the comparative analysis of results obtained upon five typical non-homogeneous conditions, it is concluded that proposed ‘Lo Sho Square’ shade dispersion technique provides a relatively superior output performance compared to that of ‘Normal SU-DO-KU’, ‘Optimized SU-DO-KU’, ‘Improved SU-DO-KU’ and ‘Modified SU-DO-KU’ techniques.

Experimental Study on the Mechanism of Pinching in Cold‐Rolling Processes

Herein, an experimental investigation into the occurrence of “pinching” defects during cold‐rolling of thin metal sheets is presented. Pinched strips are typically characterized by repetitive ripples and local ruptures, which can cause strip breaks. Even though pinches are a widely experienced phenomenon in both hot‐ and cold‐rolling of steel strips, no previous studies are known that have investigated the underlying mechanism for pinching during continuous rolling processes. Therefore, a set of rolling experiments is performed in a single‐stand pilot mill to create pinches by applying sudden perturbations in the process conditions. For the rolling settings chosen in the performed experiments, it is found that disruptions in the lubrication state are a powerful approach to induce shape defects, which develop as pinches. Herein, a first extensive description of the pinching mechanism is provided, as observed during the trials, by monitoring the strip's behavior and analyzing the damaged sheets. It is shown that ripples in these pinched strips are the result of folds, which form in the roll bite. The folds originate from the waviness of the strip upstream of the bite, being created by nonuniform conditions over the width of the strip.

Implementation of a real-time star centroid extraction algorithm with high speed and superior denoising ability.

Star tracker is the most precise attitude measuring device, and its advantages include a high resolution and high update rate. Star centroid extraction, which is a very time-consuming process, has great influence on the attitude update rate. This paper proposes a real-time star centroid extraction algorithm based on a field programmable gate array. First, a 1D top-hat filter is used for star segmentation, which is suitable for both uniform and nonuniform background conditions. Second, multichannel image data is reorganized together into a complete frame through image stitching, which prevents the star spots on the channel boundary from being divided into different parts. Finally, star coordinates are extracted by the center-of-mass algorithm. For an image sensor with a resolution of 2048×2048 pixels, simulation results conducted by a ModelSim simulator show that the star centroid processing time of a single frame is roughly 5.2 ms. Real night experiments demonstrate that the standard deviation of a star centroid error is within 10-2 pixel and the standard deviation of attitude is (2.6 2.2 12.0) arcseconds, which proves that the proposed star centroid extraction algorithm can work continuously and stably.