1,721,399 research outputs found
Large-scale forcing effects on wind flows in the urban canopy: impact of inflow conditions
Full text linkWind flow modeling in urban areas is usually performed by means of Wind-Tunnel (WT) testing or Computational Fluid Dynamics (CFD) simulations. Results obtained with both techniques can be affected by the boundary conditions. This study aims at investigating how two sets of inflow conditions, termed set 1 and set 2 and calculated respectively using the equations proposed by Richards and Hoxey (1993) and Tominaga et al. (2008), may affect the accuracy of the results in terms of mean wind speed, turbulent kinetic energy, yaw and pitch angles when predicting wind flows in urban areas. 3D steady RANS simulations were performed for a selected urban area (“Quartiere La Venezia” in Livorno, Italy). WT tests on the same urban model were used to validate the CFD simulations. Mean wind profiles at 25 positions in the urban area were compared and the statistical performance was quantified using four metrics for both sets of inflow conditions. The results obtained using the two sets of inflow conditions showed comparable performances in terms of wind flow predictions in the urban canopy, which means that at the building scale there is no need to use more accurate conditions because they are as effective as the simpler ones
Characterization of experimentally produced isolated downburst winds by Large Eddy Simulations
No full textVortex dynamics and radial outflow velocity evolution in downburst-like winds
Full text linkDownbursts can cause severe winds near ground level, potentially damaging buildings and structures. A particular problem is that downburst-induced wind action is not considered in the design stage as it is not included in the building codes. This paper provides an in-depth characterization of a downburst flow field including its vortical structures in both space and time. The analysis is based on Large Eddy Simulations (LES) to reproduce dedicated experiments of a vertical downburst carried out in the test chamber of the WindEEE Dome laboratory. The trajectory of the radial velocity maxima is evaluated, which indicates that the height of the maximum velocity increases with the traveled distance after having produced the strongest wind gusts. The spatial evolution of the convective velocity of the primary vortex across the test chamber is evaluated and three regions are distinguished: the speed-up (up to r/D = 1.25), the slow-down (1.25 < r/D < 2.29) and the deflection region (r/D > 2.29). The analysis indicates that trailing ring vortices produce higher outflow velocities than the primary vortex after a sufficient time span, causing the radial locations between 0.8 and 1.8 r/D to be continuously exposed to strong gusts
Impact of morphological parameters on urban ventilation in compact cities. The case of the Tuscolano-Don Bosco district in Rome
Full text linkAir pollution and heat stress are major concerns associated with the liveability, resilience and sustainability of cities. They directly affect health and comfort and are associated with augmented morbidity and mortality and an increase in the energy demand for building ventilation, air cleaning and cooling. Nevertheless, the detrimental effects of poor air quality may partly be mitigated by increased urban ventilation. This strategy is closely related to the level of urbanization and the urban morphology. Therefore, detailed investigations on the impact of different morphologies on urban ventilation are of paramount importance. Computational Fluid Dynamics simulations have been widely used during the last decades to investigate the effects of the urban morphology on the urban ventilation. However, most of these studies focused on idealized building arrangements, while detailed investigations about the role of real urban morphologies are scarce. This study investigates the ventilation in a compact area in the city of Rome, Italy. 3D steady-state Reynolds-averaged Navier-Stokes simulations are performed to analyze the impact of Morphological Parameters (MP) on the urban ventilation. The results show a considerable worsening of urban ventilation with increasing building density with a reduction in the mean wind velocity up to 62% experienced at the pedestrian level (zp). Correlations between five MPs, e.g., plan area density, area-weighted mean building height, volume density, façade area density, and non-dimensional mean velocity at pedestrian level and at 10 m height are evaluated, and simple models are obtained using linear regression analysis. Among the selected MPs, the building façade area density shows a remarkable correlation with the non-dimensional mean velocity at zp (R2 = 0.82). Such correlations can be valuable tools for practitioners and urban designers, particularly during the first stage of planning, for highlighting areas potentially vulnerable to poor air conditions without running computationally expensive simulations
Wind-tunnel experiments on cross-ventilative cooling in a generic isolated building with one heated wall: impact of opening size
Full text linkThis paper presents wind-tunnel experiments of cross-ventilative cooling in a generic isolated building with an interior heated side wall. Two different sizes of openings are considered: large and small openings. Particle image velocimetry (PIV) is used to determine velocities in the vertical centerplane. Air temperatures in the vertical centerplane are measured using negative temperature coefficient (NTC) sensors. Surface temperatures on the heated wall are measured using an infrared camera. Surface heat fluxes are obtained using heat flux sensors. In both cases the indoor airflow is dominated by the jet through the openings, with higher velocities in the building with large openings. The air temperatures measured with small openings are up to 7.5 % larger than those with large openings. The surface heat fluxes are up to 20 % higher in the building with large openings. The interior convective heat transfer coefficients vary considerably across the heated wall for both opening sizes and can be very different (up to 5 times higher) from those obtained by existing internal convective heat transfer coefficient correlations. The measurement results give insight into the complexity of ventilative cooling and can be used to validate computational fluid dynamics (CFD) simulations of cross-ventilative cooling
Cross-ventilation in a generic isolated building equipped with louvers: wind-tunnel experiments and CFD simulations
Full text linkNatural ventilation can be used to improve indoor air quality, remove contaminants from spaces and to remove heat from a building during the day, or during the night. In some cases, openings for natural ventilation are equipped with shading devices – such as louvers – to reduce solar heat gains while allowing natural ventilation. This study presents wind-tunnel experiments and computational fluid dynamics (CFD) simulations of a cross-ventilated building equipped with louvers. Four opening positions are studied: (i) openings in the center, (ii) upper or (iii) lower part of the windward and leeward facades or (iv) one opening in the upper part of the windward facade and one opening in the lower part of the leeward facade. The 3D steady Reynolds-averaged Navier-Stokes (RANS) simulations are performed with three turbulence models (RNG k-ε, SST k-ω, RSM) and validated with the wind-tunnel experiments. The experimental results show that the largest velocities occur in a building with openings in the upper part of the facade. The best agreement with experimental data is provided by RSM. In addition, CFD simulations for buildings without louvers are conducted for the same opening positions to evaluate the effect of louvers on the dimensionless volume flow rate, age of air and air exchange efficiency. The highest dimensionless volume flow rate at reduced scale (0.69) is obtained in the building with louvered openings in the upper part of the facade and the highest air exchange efficiency is achieved for a building with louvered openings in the center of the facade (45%)
Advanced Materials and Technologies for Structural Performance Improvement
Full text linkThe development of advanced materials and technologies for
application to new and existing structures, infrastructures,
and equipment, aiming at improving their response to service
and extreme loads, represents an emerging issue both from
an academic and a professional viewpoint. Relevant performance
assessment procedures, based on effective experimental
verification methods [1] and refined numerical simulation
models [2], are quickly evolving as well.
New or improved building materials and innovative protection
technologies offer updated solutions to the constantly
increasing capacity requirements in structural, geotechnical,
plant, and mechanical engineering design and rehabilitation.
At the same time, they open novel and challenging research
and application perspectives.
The objective of this special issue was to provide readers
with a representative outlook of the latest achievements in
this field, including emerging aspects in modelling, testing,
manufacturing, and practical implementation studies. The
response of the scientific community was encouraging, with
over 100manuscripts submitted. The published papers offer a
selected and articulated overview of the examined topics.
Several papers are dedicated to concrete, reinforced
concrete (R/C) members, and cement composites. J. Zhang
and J. Li develop a semi-implicit constitutive integration
algorithm for elastoplastic damage models, specially implemented
for concrete. Literature mechanical tests of reinforced
concrete components are numerically simulated, showing the
effectiveness of the numerical method in history-dependent
energy estimation within this class of nonlinear problems. H.
Ding et al. examine the failure criteria and the constitutive
relation of early-age concrete,with the aimof providing a theoretical
basis for a novel strategy in early dismantling formwork
construction of floors, aimed at accelerating formwork
recycling as well as at reducing construction costs. Y. Shen
et al. propose a paper spool-inspired anchoring method and
a pretension procedure for carbon fiber reinforced polymer
(CFRP) sheets, for themanufacturing of prestressed concrete
flat slabs. Laboratory flexural tests confirm the feasibility of
this novel reinforcement technique, showing that uniformity
of the fiber stress during tensioning is a key aspect for the successful
application of prestress. Improved flexural calculation
models for R/C members built with ultrahigh performance
concrete (i.e., with cubic compressive strength exceeding
200MPa) are presented by B.-I. Bae et al., who revise the
normal stress distribution schemes adopted for standard concrete
classes. The models are verified and validated by means
Hindawi Publishing Corporation
Advances in Materials Science and Engineering
Volume 2016, Article ID 1854839, 3 pages
http://dx.doi.org/10.1155/2016/1854839
2 Advances in Materials Science and Engineering
of laboratory flexural tests on representative specimens in
this case too. High strength concrete materials, with cubic
compressive strength ranging fromabout 80MPa to 110MPa,
are examined in the paper of L. Zeng et al., as constituting
materials of R/C beam-to-column joints encasing I-shaped
hot-rolled steel profiles. An extensive campaign of cyclic
tests on half-scale weak-type joints allows evaluating the
beneficial influence of the adopted concrete classes in terms
of strength and at the same time a minimal decrease in
ductility, as compared to the cyclic performance of similar
joints cast with standard concretes. Composite concretesteel
tubular columns are the topic of the article by S.
Jayaganesh et al. An experimental programme is carried out
to evaluate the effects of the partial compression of square and
circular cross sections, highlighting a reduction in strength
in comparison to full compression, more accentuated in the
case of the square shape. The correlation of the test results
with the predictions of the analytical models proposed in the
literature to account for these effects seems rather satisfactory.
Another experimental activity is reported in the paper by J.
Deng et al., dedicated to a campaign of pseudostatic cyclic
tests of one-fifth scale prototype R/C bridge piers, damaged
and repaired by means of a steel-tube jacketing traditional
technique, or by wrapping interventions based on the use
of CFRP or basalt fiber reinforced polymer (BFRP) sheets.
The results attest satisfactory performance in all cases, with a
significant increase in lateral stiffness and strength provided
by jacketing as compared to the original response capacity,
and its complete restoration in the case of the two FRP-based
retrofitmeasures.The advantages of the lattermethod consist
in lower physical intrusion and quicker installation times.
The postprocessing study of an experimental programme
carried out by the pseudodynamic method on a set of 13 R/C
shear walls is presented in the article of F. J. Molina et al.,
where the results of the seismic tests are elaborated by an
innovative strategy that allows deriving a capacity-linemodel.
With this approach it is possible to understand better the
different safety margins that are observed in the experiments
depending on the assigned eigenfrequency in relation to the
earthquake response spectra. The effects of the amount of
reinforcement and normal load are also assessed. Enhanced
cement composite materials are investigated in the articles
by H. Choi et al. and J. Lai et al. The former deals with
the experimental characterization of an innovative Portland
cement mortar, prepared by incorporating multiwalled carbon
nanotubes in the mixture.The experimentally measured
compressive strength is greater than the one offered by
standard Portland mortars, as a consequence of the bridging
action of the nanotubes, which prevents the progression of
microcracks and helps reducing the space between the voids
in the hydration material. In J. Lay et al.’s paper, cement fly ash
gravel is examined as constituting material of pile composite
foundations, for their updated use in saturated tailing dams.
A finite element analysis of the settlements of this type
of foundation, calibrated on the experimental investigation
carried out by other authors, assesses a stable and rather
homogeneous response under the design embankment loads.
Three articles are dedicated to advanced seismic protection
technologies. In the paper byM. Ismail et al., a numerical
study of a base isolation system incorporating Roll-in-Cage
devices recently developed by the authors is carried out
by simulating its incorporation in a three-span prestressed
R/C box girder-type bridge. The results show a remarkable
global performance of the system, also in comparison with
other seismic isolation solutions, highlighting its benefits in
the potential application to bridge structures. The article of
F. Mazza and A. Vulcano reports a shaking table testing
programme developed on a one-third scale base-isolated steel
frame structure equipped with an in-parallel combination of
steel-PTFE sliders and elastomeric bearings (HDRBs). The
experimental response confirms the high level of protection
offered by the isolation technology and establishes a
database for a refined numericalmodelling of the constituting
devices. J. W. Hu and M.-H. Noh present a study on selfcentering
friction dissipative steel braces including special
components fabricated with shape-memory alloy wires and
friction-type dampers. A numerical investigation carried
out on single-degree-of-freedom models allows formulating
a design methodology aimed at mutually optimising the
recentering and energy dissipation capacities of the passive
protection system, with a view to its practical implementation.
Two more papers deal with the application of innovative
FRP composite materials in various fields of engineering.
N. B. Baba et al. examine the mechanical and physical
behaviour of a hybrid glass FRP (GFRP) fabricated with three
different types of glass fibers—3D, woven, and chopped—
combined with a mixture of polyester resin and hardener.
Fiber arrangement and volume are varied to evaluate the
combination capable of providing the best performance in
terms of tensile strength and water absorption, which is
identified by means of the characterisation test developed
in the study. In the article by M. E. Tas¸delen et al. the
torsional behaviour of novel braided sleeve composite shafts
consisting of carbon and glass fibers is investigated. Vacuum
assisted resin transfer molding and vacuum bagging
are adopted as manufacturing methods. The results of the
experimental programme and the relevant finite element
simulations underline that, for the same configuration of layup
sequences, the highest torque and tensile strengths are
obtained for test specimens manufactured with the former
method. Furthermore, hybrid carbon-glass solutions strike
the best balance between strength performance and costs.
Special issues are dealt with in the remaining three articles.
By considering the growing applications of piezoelectric
structures in innovative technical areas, L. M. Zhou et al.
implement a mixed cell-based smoothed/extended finite element
method for a careful electromechanical crack analysis of
the constituting material. The case study examples presented
in the paper show that this mixed method is more accurate
and quickly converging than a standard finite element
calculation, also bypassing the mapping process inherent to
the latter, which significantly increases the complexity of the
calculation. J.Chen et al. report an on-site experimental study
of the cooling effect of crushed rock-based embankments on
slope wetlands situated along a railway line. A monitoring
system installed in an embankment of notable dimensions
allows reconstructing the temperature fields and the freezing
Advances in Materials Science and Engineering 3
history with time. The surveyed data show that only the
embankment shady side can be effectively cooled down
in a warm permafrost region, and the crushed rock-based
embankment can cool the entire embankment in a cold
permafrost region. Finally, in the paper by Y. Ou et al.
an innovative self-propagating high-temperature synthesis
(SHS) process to prepare amorphous boron powder, which
is an attractive material in several enhanced engineering
applications, is discussed. The new technique proposed
in this study consists in combining the SHS process and
the traditional magnesium thermal reduction method. The
effectiveness of the resulting technique suggests its possible
industrial application and adoption as a common approach
to prepare various inorganic materials.JRC.E.4 - Safety and Security of Building
New initiative : "ten questions" paper series in building and environment
No full text1. Brief description of the initiative Building & Environment is launching a new initiative for a series of "Ten Questions" papers, to be published in a pre-described format. "Ten Questions" papers should deal with a well-defined topic and should be centered around a selection of ten relevant and topical questions. Submissions are based on invitation only by the Editor of the Special Initiative (SI), Prof. Bert Blocken. Papers will be recruited in a way that ensures balanced coverage of all topics in the scope of Building and Environment. The papers should be (co-)authored by established researchers in the field with proven expertise on the topic, typically by an extensive track record of previously published books and/or peer-reviewed journal papers. The questions are selected and answered by the author(s). The questions should be such that the paper is visionary, authoritative and can provide younger researchers directions for future research
Impact of Disc Wheel Geometry on Aerodynamic Performance: A Computational Fluid Dynamics Investigation
Full text linksponsorship: During the work on this paper the first author has been employed sequentially by KU Leuven in Belgium and by Eindhoven University of Technology (TU/e) in The Netherlands. He expresses his gratitude to both hosting institutions. The authors acknowledge the partnership with ANSYS CFD. This work was also sponsored by NWO Exact and Natural Sciences for the use of supercomputer facilities. The authors are also very grateful to the anonymous reviewers for their very valuable and constructive comments on this paper. (NWO Exact and Natural Sciences)status: Publishe
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