Enclosure Boundaries Research Articles

Maximum ceiling temperature and longitudinal distribution in a corridor-like enclosure with opening

This paper reports a quantitative study on the effects of a side opening on the transition between the fuel-controlled and the ventilation-controlled condition and temperature distribution in a corridor-like enclosure fire. A side opening was introduced to simulate breakage of glass window in case of fire. Experiments were carried out in a 1/8 model tunnel with the dimensions of 3.14 m×0.42 m×0.368m(length×width×height), including 56 test conditions arising from variations of heat release rates (HRR) and opening sizes. The results showed that the transition was correlated with the fraction of the heat released to the heat convected through the opening and the ratio of the heat lost through enclosure boundary to the heat convected through the opening. The maximum temperature rise in the fuel-controlled condition was positively correlated with the fire heat release rate, but it was negatively correlated with the opening aspect ratio. There were two combustion stages in the ventilation-controlled condition, one with flame oscillation inside the corridor-like enclosure and the other with persistent flame ejection through the opening. The maximum temperature rise in the stage of flame oscillation inside the compartment was positively correlated with the air mass supply through the opening and negatively correlated with the heat loss through the corridor-like enclosure boundary. Non-dimensional correlations between the maximum temperature rise and the heat release rates (HRRs), opening sizes and the heat loss were proposed. Moreover, a piecewise equation was proposed to predict the longitudinal decay along the centerline of the corridor-like enclosure with an opening. All the proposed correlations were found to fit well with the experimental data, which established a basic relationship to quantify the (i) temperature variation, (ii) critical heat release rate and (iii) transition for various opening sizes and HRRs in a corridor-like enclosure fire. These new findings and the proposed non-dimensional model provide the basis for understanding fire growth and temperature distribution inside a corridor-like enclosure with opening.

Transition of thermally induced flow in a square cavity using an iterative predictor–corrector meshfree approach

AbstractThis paper aims to propose a new approach based on meshfree method to solve the dimensionless steady nonlinear natural convection equations. The solution methodology uses the moving least squares (MLS) shape functions to discretize the weak form of the governing equations and the Newton–Raphson algorithm to compute the nonlinear solution. Parametric studies of natural convection concerning closed two‐dimensional (2D) cavity with different operating conditions filled with air is used to assess the impact of the proposed approach on the performance of computed solutions. The cavity is formed by adiabatic and isothermal walls. For that, in all considered cases, the vertical sidewalls of the enclosure are heated differentially and maintained at hot and cold temperatures. The horizontal top and bottom walls are considered thermally insulated. The thermophysical properties of the working fluid are assumed to be constant except the density variations causing a body force term in the momentum equation. No‐slip boundary condition is applied at all enclosure boundaries and all internal body boundaries. The considered cases are described and analyzed in detail to check the validity of the proposed method. A comparison is performed between the results obtained from the present computer code and those available in the literature. The influence of various controlling parameters is analyzed and discussed graphically through the obtained streamlines, isotherms, and (maximum and average) Nusselt number. The numerical results computed by the proposed method are found to be in good agreement with the reference data.

Fluid flow and heat transfer of porous TPMS architected heat sinks in free convection environment

Heat dissipation in electronic devices is challenging due its limited size and cooling space constraint. Implementing Triply Periodic Minimal Surfaces (TPMS)-based cellular structures could enhance the thermal exchange mechanism due to their novel architected, interconnected, and inter wind porous topologies and high surface area to volume ratio. In this study, three novel mathematically-driven TPMS heatsink structures were investigated using computational fluid dynamics (CFD) based models. TPMS heat sinks consisting of seven triply periodic unit cells were examined to investigate their thermal performance and fluid flow behavior in free convection air environment. The thermal performance indicators as convection heat transfer coefficient and surface temperature under parametric variation of applied heat load, fluid enclosure boundary condition, and TPMS structure orientation were determined. Enclosure boundary conditions found to have a significant effect on the thermal behavior of each heat sink structure; including radiation contribution was found to account for approximately 23% of the overall heat transfer in due to the complex TPMS internal structure. Three empirical Nusslet number correlations were then derived for the investigated TPMS structures. The results showed that TPMS-based heat sinks outperform conventional heat sinks by 48–61% owing to the random perturbations of flow and high packing density. This work shows the potential of TPMS porous architectures as very promising heat sinks.

Magnetoconvection around an elliptic cylinder placed in a lid‐driven square enclosure subjected to internal heat generation or absorption

AbstractThe impacts of MHD and heat generation/absorption on lid‐driven convective fluid flow occasioned by a lid‐driven square enclosure housing an elliptic cylinder have been investigated numerically. The elliptic cylinder and the horizontal enclosure boundaries were insulated and the left vertical lid‐driven wall was experienced at a fixed hot temperature, and the right wall was exposed to a fixed cold temperature. COMSOL Multiphysics 5.6 software was used to resolve the nondimensional equations governing flow physics. A set of parameters, such as Hartmann number (), Reynolds number (), Grashof number (), heat generation‐absorption parameter (), and elliptical cylinder aspect ratio (AR) () have been investigated. The current study discovered that for low Reynolds number, the adiabatic cylinder AR of 2.0 provided the optimum heat transfer enhancement for the model investigated, also the impact of cylinder size diminishes beyond Gr = 104. But for high Reynolds (Re = 1000), the size of the cylinder with AR = 3.0 offered the highest heat transfer augmentation. The clockwise flow circulation reduces because of an increase in AR, which hinders the flow circulation. In addition, heat absorption supports heat transfer augmentation while heat generation can suppress heat transfer improvement.

Exploiting spatio-temporal spectral features of the indoor acoustic field for sound source localization

The estimation and classification of spectral features of the spatio-temporal acoustic field in a reverberant rectangular enclosure is undertaken with application to localizing sound sources. The field is constructed using an image source model of the impulse response that captures the acoustic properties of the enclosure boundaries. The received field is examined considering linear and randomly distributed array configurations and spectral peaks are characterized to derive a set of features for classification and source identification. The effects of noise generated by the environment and the diffuse field from multiple reflections is distinguished.

Direct Algorithm for Bernstein Enclosure Boundary of Polynomials

Multivariate polynomials of finite degree can be expanded into Bernstein form over a given simplex domain. The minimum and maximum Bernstein control points optimize the polynomial curve over the same domain. In this paper, we address methods for computing these control points in the simplicial case of maximum degree L. To this end, we provide arithmetic operations and properties for obtaining a fast computational method of Bernstein coefficients. Furthermore, we give an algorithm for direct determination of the minimum and maximum Bernstein coefficients (enclosure boundary) in the simplicial multivariate case. Subsequently, the implicit form, monotonicity, and dominance cases are investigated.

Impact of Enclosure Boundary Patterns and Lift-Up Design on Optimization of Summer Pedestrian Wind Environment in High-Density Residential Districts

A comfortable wind environment favors the sustainable development of urban residential districts and public health. However, the rapid growth of high-rise urban residential districts leads to low wind velocity environments in summer. This study examines the influence of enclosure boundary patterns and lift-up design on the wind environment and proposes an optimization strategy to improve the low wind velocity environment in residential districts in summer. A typical residential district in Hangzhou was selected; the average wind velocity, calm wind zone ratio and comfortable wind zone ratio were selected as the evaluation indexes. The wind environment for different enclosure boundary patterns and lift-up designs were obtained via computational fluid dynamics (CFD) simulations. The results indicate that the pedestrian wind environment is greatly improved in residential districts by reducing the height/width of the enclosure boundary, increasing the permeability rate and adopting a lift-up design in all buildings within residential districts. A combination of permeable railings and lift-up design is recommended; this can increase the average wind velocity and the ratio of comfortable wind zones by 70% and 200%, respectively. This study provides practical guidelines for the optimization of a low wind velocity environment in Chinese high-density residential districts in summer.

Interior near-field acoustic holography based on finite elements.

This paper deals with the mathematical framework of near-field acoustic holography based on finite elements in application to the acoustic response of a fluid within a closed cavity to the enclosure boundary conditions. The finite element method is an effective implementation of the modal approach for arbitrary geometries and provides advantages for certain wavenumber intervals in rooms. An inverse implementation of the direct problem can benefit from using generalized coordinates with modally reduced system matrices. A solution can be obtained via singular value decomposition together with Tikhonov regularization. This paper investigates acoustic mode spectrums of acoustic transfer functions, which has a major effect on the reconstruction of particle velocities from given sound pressures in a simple cavity model. It is found that the largest considered modal wavenumber in the acoustic transfer matrix should be twice the maximum excitation wavenumber. Furthermore, the relation between reconstruction errors and the detectability of evanescent waves depending on the wavenumber of excitation is considered. The proposed method is validated experimentally by reconstructing particle velocities on the inner boundaries of an Airbus A400M fuselage based on measurements of the inner pressure field. Results are compared with structural velocities measured with a laser Doppler vibrometer.

Stereotypic behaviours are heterogeneous in their triggers and treatments in the American mink, Neovison vison, a model carnivore

Stereotypic behaviours (SBs) are common in confined animals including captive Carnivora, which display diverse forms of SB: often whole-body movements (e.g. pacing), but also head-only movements (e.g. head twirling) and ‘scrabbling’ (scratching at enclosure boundaries). Although often pooled together, emerging evidence indicates that SBs are heterogeneous, suggesting that subtypes differ in their causes, triggers, and consequently treatments. In mink, a model carnivore, scrabbling seems to be elicited by neighbouring conspecifics. We tested this hypothesis via three studies of 32 males (individually caged in rows and separated by solid partitions). Study 1 investigated whether neighbour proximity affects the location of any SBs, and Study 2, whether removing neighbours reduces any SBs. Results revealed that although mink typically avoided proximity to their neighbours, scrabbling was uniquely directed towards neighbours who were close to the shared cage partition. It was also the only SB significantly elevated by having all-male neighbours, and reduced by removing neighbours. Study 3 then investigated whether environmental enrichment, a standard SB treatment, would reduce or abolish different SBs equally, to assess whether scrabbling is simply easier to alleviate than other SBs. Enrichment reduced all SB subtypes, but logistic regressions revealed that the odds of complete abolition were higher for whole-body and head-only SBs than for scrabbling. Overall, these naturally solitary carnivores thus seem to avoid conspecific proximity, but they specifically direct their stereotypic scrabbling at neighbours; and their scrabbling is reduced by neighbour removal, while their whole-body and head-only SBs are instead better alleviated with enrichment. Understanding that carnivore SBs are heterogeneous in their triggers and most effective treatments may help zoos, breeding centres and mink farms improve the design of their enclosures and the efficacy of their enrichments.

Modeling high frequency broadband acoustic fields inside rectangular and cylindrical enclosures using an energy-intensity boundary element method

Accurate prediction of high frequency broadband acoustic fields inside enclosures with curved boundaries typically requires time consuming frequency-by-frequency numerical techniques. A quick solution is developed for general enclosure shapes using an energy-intensity boundary element method, previously tested for rectangular geometries and now extended to cylinders with flat or spherical endcaps. Derived from first principles, which are reviewed, the approach uses uncorrelated spreading energy-intensity boundary sources to directly solve for the steady-state mean-square pressures. The enclosure boundary is discretized into radiating panels that account for interior energy transfer and satisfy prescribed reflection and absorption boundary conditions. Half-space orthogonal spherical harmonics serve as basis functions to emulate both diffuse and specular reflections. Panel interactions are calculated by an energy-accurate quadrature technique and studied for curved boundaries. Computationally intensive benchmark solutions are developed for verification. A fully correlated Helmholtz solution is derived for the cylindrical enclosure using a novel internal scattering approach to calculate high frequency pressure, and numerically integrated over a third-octave band. Comparisons between the fully correlated solution and the energy method for enclosures of various aspect ratios reveal excellent agreement. Simulations are also presented contrasting interesting behavioral differences between diffuse and specular reflection fields.

Absorption scaling theory applied to an energy-intensity boundary element method for prediction of broadband acoustic fields in enclosures

Insight into the acoustic energy distribution in enclosures is gained by applying Absorption Scaling Theory. Broadband high-frequency acoustic fields within 3D rectangular enclosures are modeled with an energy-intensity boundary element method (EIBEM) that replaces the enclosure boundary with a distribution of broadband uncorrelated directional intensity sources to simulate either diffuse or specular reflection. Assuming a highly reflective enclosure, the boundary panel strengths are expanded in a power series with the spatially-averaged absorption as a small parameter. For diffuse reflection fields, where the theory is well developed, a matrix formulation is derived for each of the expansion coefficients that must be solved in sequential order. The leading order term in the expansion is inversely proportional to the scaling parameter and estimates the average level inside the enclosure, the next term gives spatial variation independent of average absorption level, while higher order terms account for the spatial variation of energy due to the distribution of absorption and the location of sources. For a highly reflective enclosure, only a few terms are needed to accurately predict the mean-square pressures. Similar behavior is demonstrated for specular reflection using numerical simulations. Applications include theoretical and empirical enclosure design and assessment, and solving the inverse problem.

Natural convection of a nanofluid in an enclosure with an inclined local thermal non-equilibrium porous fin considering Buongiorno’s model

ABSTRACTThere is growing interest in application of inclined fins to a cavity wall. As such, this paper focuses on the numerical investigation of laminar free convection flow and heat transfer in an enclosure with an inclined thin local thermal non-equilibrium porous fin and saturated by a nanofluid. The porous medium is assumed to be isotropic and homogenous, the cavity walls are assumed to be impermeable to the nanoparticles, and there is a no-slip boundary condition on the enclosure boundaries. The vertical walls are isothermal and the horizontal ones are adiabatic. Moreover, the influence of indispensable parameters regarding heat and mass transfer, such as Rayleigh number, Darcy number, Prandtl number, porosity, thermophoresis and Brownian parameters, fin length, fin position, and the fin angle on the average Nusselt number, are taken into account. Generally, it is found that the average Nusselt number is an increasing function of Ra, Pr, Da, and porosity (ε). Furthermore, increasing either fin position (Sp) or thermal conductivity ratio (η) produces corresponding decreases in average Nusselt number. Finally, heat transfer shows a different behavior for different values of fin angles and lengths.

Framing the grid: effect of boundaries on grid cells and navigation

Cells in the mammalian hippocampal formation subserve neuronal representations of environmental location and support navigation in familiar environments. Grid cells constitute one of the main cell types in the hippocampal formation and are widely believed to represent a universal metric of space independent of external stimuli. Recent evidence showing that grid symmetry is distorted in non-symmetrical environments suggests that a re-examination of this hypothesis is warranted. In this review we will discuss behavioural and physiological evidence for how environmental shape and in particular enclosure boundaries influence grid cell firing properties. We propose that grid cells encode the geometric layout of enclosures.

Three dimensional numerical analysis of natural convection cooling with an array of discrete heaters embedded in nanofluid filled enclosure

This study deals with the numerical analysis of 3D natural convection equipment cooling with a 3×3 array of isothermal heaters mounted on one vertical wall of the nanofluid filled enclosure. The enclosure is filled with water based nanofluid containing Copper (Cu) or Alumina (Al2O3) nanoparticles. The transport equations are solved by the finite volume method based on the SIMPLE algorithm with power-law scheme. The influence of pertinent parameters such as Rayleigh number (105⩽Ra⩽107), nanoparticle volume fraction (0%⩽ϕ⩽10%) and enclosure side aspect ratio (1.0⩽AS⩽7.5) on the fluid flow and heat transfer characteristics are investigated together with different nanofluids and enclosure boundary conditions. It is observed that Cu–water nanofluid has the greatest effect on the equipment cooling performance compared with Al2O3–water nanofluid. Moreover, the row averaged Nusselt number increases monotonically with increase in both the Rayleigh number and the nanoparticle solid volume fraction.

Sternal Gland Scent-Marking Signals Sex, Age, Rank, and Group Identity in Captive Mandrills.

Mandrills are one of the few Old World primates to show scent-marking. We combined ethological and chemical approaches to improve our understanding of this behavior in 3 zoo-managed groups. We observed the olfactory behavior performed by adults and adolescents (N = 39) for 775h. We investigated the volatile components of sternal scent-marks using gas chromatography-mass spectrometry and compared volatile profiles with traits of the signaler. Males marked more than females and within each sex the frequency of scent-marking was related to age and dominance status, but alpha males scent-marked most frequently and particularly in specific areas at the enclosure boundaries. We identified a total of 77 volatile components of sternal gland secretion, including compounds functioning as male sex pheromones in other mammals, in scent-marks spontaneously released on filter paper by 27 male and 18 female mandrills. We confirmed our previous findings that chemical profiles contain information including sex, male age and rank, and we also found that odor may encode information about group membership in mandrills. Our results support the hypotheses that scent-marking signals the status of the dominant male as well as playing territorial functions but also suggest that it is part of sociosexual communication.

Prediction of broadband high-frequency acoustic reflection and transmission from subcritical membranes and elastic plates

Earlier work has shown that distributed broadband excitation of subcritical membranes and plates can yield surprisingly simple closed-form band-averaged directivity patterns, and that the directivity is closely related to energy flow in the structure. A first principles energy-intensity boundary element method (EIBEM) for sound fields in enclosures has also been developed, and shown to be very accurate for impedance reflection boundary conditions. The present work involves the derivation of more realistic reflection and transmission of models for enclosure boundaries with elastic boundaries. For subcritical panels, reflection, radiation, and transmission properties can be characterized by a limited set of parameters, and fairly simple analytical results are derived for the broadband case. Surface reflection and edge re-radiation are both considered. These results facilitate an energy-intensity reformulation of the structural equations, as well as the acoustic field, allowing for the possibility of formalizing the coupling between energy flows in the acoustic and structural systems. The goal is to develop efficient first principles computational models for more accurate modeling of real enclosures.

New approach to estimate temperatures in pre-flashover fires: Lumped heat case

This paper presents a model for estimating temperatures in pre-flashover fires where the fire enclosure boundaries are assumed to have lumped heat capacity. That is, thermal inertia is concentrated to one layer with uniform temperature and insulating materials are considered purely by their heat transfer resistance. The model yields a good understanding of the heat balance in a fire enclosure and was used to predict temperatures in insulated and non-insulated steel-bounded enclosures. Comparisons were made with full scale experiments and with other predictive methods, including CFD modeling with FDS and the so called MQH relationship. Input parameter values to the model were then taken from well-known literature and the heat release rates were provided from the experiments. The fire temperature predictions of the model matched very well with experimental data. So did the FDS predictions while the original MQH relationship gave unrealistic results for the problems studied. Major benefits of using the model in comparison with CFD modeling are its readiness and simplicity as well as the negligible computation times needed. An Excel application of the presented pre-flashover fire model is available on request from the author.

Convection of a heat-generating fluid in a rotating horizontal cylinder

Thermal convection of a fluid in a horizontal cylinder rotating about its own axis with uniformly volume-distributed internal heat sources is experimentally investigated. The enclosure boundary temperature was kept constant. The threshold of the excitation of convective flows and their structure are studied as functions of the heat-release intensity and the rotation velocity. The experiments are performed with water and water-glycerin solutions. It is shown that rapidly rotating fluid is in a stable quasiequilibrium state, namely, the temperature distribution is axisymmetric and has a maximum at the center of the enclosure. It is found that with decrease in the rotation velocity a convective flow arises thresholdwise, in the form of vortex cells periodically arranged along the axis. The thermal convection in the rotating enclosure is shown to be determined by the effects of two different mechanisms. One of these is due to the centrifugal force of inertia and plays the stabilizing role, while the other, thermovibrational mechanism is connected with nonisothermal fluid oscillations under the action of gravity in the enclosure-fitted reference frame and is responsible for the occurrence of mean thermal convection. The boundaries of the convection generation are plotted in the plane of the governing dimensionless parameters and the heat transfer in the supercritical region is studied.

Eliminative Behavior of Captive Numbats, Myrmecobius fasciatus (Mammalia; Marsupialia): Pattern and Identification of Fecal Deposits

This study examined the spatial defecation patterns of numbats within captivity and tested the efficacy of a food colorant as a fecal marker in this species. Rather than randomly distributing scats throughout their environment, the numbats aggregated their feces at specific sites forming latrines. It is unclear whether the strong inclination for latrine formation was due to this species' inherent behavior or is a direct result of captivity. Males were found to have a higher daily defecation rate, different defecation time, larger number of latrines, and greater number of scats per quadrant, as compared to females. In this study, the majority of scats were deposited along enclosure boundaries and for both sexes there was a higher probability of latrines being placed along enclosure fencing shared with a female neighbor. The high concentration of latrines along boundaries suggests that they may play a role in territorial defense. The results also indicated that captive numbats tend to choose defecation points away from food and refuge sites. Transit and total retention time of the marker through the GIT was ≤3 hr and between 24 and 27 hr, respectively. A marker dose of 3 gtts feed(-1) × 2 feeds day(-1) was required to reach a steady and detectable state of marker output, which enabled accurate identification of individual samples during the breeding season. Reliable labeling was obtained using blue and red colored food dye, and there was no evidence that incorporation of the marker into the diet had any negative effects on food intake.

Rigorous Enclosures of a Slow Manifold

Slow-fast dynamical systems have two time scales and an explicit parameter representing the ratio of these time scales. Locally invariant slow manifolds along which motion occurs on the slow time scale are a prominent feature of slow-fast systems. This paper introduces a rigorous numerical method to compute enclosures of the slow manifold of a slow-fast system with one fast and two slow variables. A triangulated first order approximation to the two dimensional invariant manifold is computed “algebraically.” Two translations of the computed manifold in the fast direction that are transverse to the vector field are computed as the boundaries of an initial enclosure. The enclosures are refined to bring them closer to each other by moving vertices of the enclosure boundaries one at a time. As an application we use the method to prove the existence of tangencies of invariant manifolds in the problem of singular Hopf bifurcation and to give bounds on the location of one such tangency.