scholarly journals TURBULENT OSCILLATORY FLOW OVER RIPPLES AT HIGH REYNOLDS NUMBERS FOR PETA-SCALE SIMULATIONS

2018 ◽  
pp. 95
Author(s):  
Guillermo Oyarzun ◽  
Athanassios Dimas
Keyword(s):  
Coastal Zone ◽  
High Performance ◽  
Oscillatory Flow ◽  
Three Dimensional ◽  
Small Scale ◽  
Poisson Solver ◽  
Execution Model ◽  
High Reynolds ◽  
Wave Induced ◽  
The Impact

Surface waves in the coastal zone induce oscillatory flow motions in the vicinity of the seabed. These wave-induced coastal flows interact with the sandy seabed and modify the bed shape by generating coherent small-scale bed structures, which are generally known as ripples. The presence of ripples in oscillatory flows is important due to the impact they have on the seabed roughness and how they affect the near-bed boundary layer hydrodynamics. Simulations of higher and more real-scale Reynolds number (Re) require the use of supercomputers in order to obtain results in a reasonable amount of time. However, the constant evolution of the computing facilities makes the development of parallel algorithms a rather difficult task. The objective of the proposed research is to advance in the comprehension of coastal processes utilizing high performance computing (HPC) for the numerical simulation of the three-dimensional, turbulent flow, which is induced in the coastal zone by wave propagation. In particular, our CFD code (SimuCoast) has been developed using a hybrid MPI+OpenACC execution model that increases its scalability and allows it to engage the vast majority of high-end supercomputers. Special attention has been paid in the parallelization strategy of the Poisson solver that is the most computational demanding operation.

Turbulent flow between counter-rotating concentric cylinders: a direct numerical simulation study

2008 ◽  
Vol 615 ◽  
pp. 371-399 ◽  
Author(s):  
S. DONG
Keyword(s):  
Turbulent Flow ◽  
Large Scale ◽  
Outer Cylinder ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Taylor Vortex ◽  
Small Scale ◽  
Mean Flow ◽  
Concentric Cylinders ◽  
High Reynolds

We report three-dimensional direct numerical simulations of the turbulent flow between counter-rotating concentric cylinders with a radius ratio 0.5. The inner- and outer-cylinder Reynolds numbers have the same magnitude, which ranges from 500 to 4000 in the simulations. We show that with the increase of Reynolds number, the prevailing structures in the flow are azimuthal vortices with scales much smaller than the cylinder gap. At high Reynolds numbers, while the instantaneous small-scale vortices permeate the entire domain, the large-scale Taylor vortex motions manifested by the time-averaged field do not penetrate a layer of fluid near the outer cylinder. Comparisons between the standard Taylor–Couette system (rotating inner cylinder, fixed outer cylinder) and the counter-rotating system demonstrate the profound effects of the Coriolis force on the mean flow and other statistical quantities. The dynamical and statistical features of the flow have been investigated in detail.

scholarly journals Towards Continuous Production of Shaped Honeycombs

2018 ◽  
Author(s):  
Sam E. Calisch ◽  
Neil A. Gershenfeld
Keyword(s):  
High Performance ◽  
Continuous Production ◽  
Continuous Process ◽  
Three Dimensional ◽  
Sandwich Panels ◽  
Performance Space ◽  
Bending Loads ◽  
Future Work ◽  
The Impact ◽  
Parallel Folding

Honeycomb sandwich panels are widely used for high performance parts subject to bending loads, but their manufacturing costs remain high. In particular, for parts with non-flat, non-uniform geometry, honeycombs must be machined or thermoformed with great care and expense. The ability to produce shaped honeycombs would allow sandwich panels to replace monolithic parts in a number of high performance, space-constrained applications, while also providing new areas of research for structural optimization, distributed sensing and actuation, and on-site production of infrastructure. Previous work has shown methods of directly producing shaped honeycombs by cutting and folding flat sheets of material. This research extends these methods by demonstrating work towards a continuous process for the cutting and folding steps of this process. An algorithm for producing a manufacturable cut-and-fold pattern from a three-dimensional volume is designed, and a machine for automatically performing the required cutting and parallel folding is proposed and prototyped. The accuracy of the creases placed by this machine is characterized and the impact of creasing order is demonstrated. Finally, a prototype part is produced and future work is sketched towards full process automation.

scholarly journals Dimensional Nanofillers in Mixed Matrix Membranes for Pervaporation Separations: A Review

Membranes ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 193
Author(s):  
Guang Yang ◽  
Zongli Xie ◽  
Marlene Cran ◽  
Chunrui Wu ◽  
Stephen Gray
Keyword(s):  
Polymer Matrix ◽  
High Performance ◽  
Three Dimensional ◽  
Liquid Mixtures ◽  
Mixed Matrix Membranes ◽  
Mixed Matrix ◽  
Inorganic Fillers ◽  
High Flexibility ◽  
The Impact ◽  
Matrix Membranes

Pervaporation (PV) has been an intriguing membrane technology for separating liquid mixtures since its commercialization in the 1980s. The design of highly permselective materials used in this respect has made significant improvements in separation properties, such as selectivity, permeability, and long-term stability. Mixed-matrix membranes (MMMs), featuring inorganic fillers dispersed in a polymer matrix to form an organic–inorganic hybrid, have opened up a new avenue to facilely obtain high-performance PV membranes. The combination of inorganic fillers in a polymer matrix endows high flexibility in designing the required separation properties of the membranes, in which various fillers provide specific functions correlated to the separation process. This review discusses recent advances in the use of nanofillers in PV MMMs categorized by dimensions including zero-, one-, two- and three-dimensional nanomaterials. Furthermore, the impact of the nanofillers on the polymer matrix is described to provide in-depth understanding of the structure–performance relationship. Finally, the applications of nanofillers in MMMs for PV separation are summarized.

Three-dimensional conditional structure of a high-Reynolds-number turbulent boundary layer

2011 ◽  
Vol 673 ◽  
pp. 255-285 ◽  
Author(s):  
N. HUTCHINS ◽  
J. P. MONTY ◽  
B. GANAPATHISUBRAMANI ◽  
H. C. H. NG ◽  
I. MARUSIC
Keyword(s):  
Skin Friction ◽  
High Reynolds Number ◽  
Large Scale ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Small Scale ◽  
Large Scale Structures ◽  
Local Mean ◽  
Scale Structures ◽  
High Reynolds

An array of surface hot-film shear-stress sensors together with a traversing hot-wire probe is used to identify the conditional structure associated with a large-scale skin-friction event in a high-Reynolds-number turbulent boundary layer. It is found that the large-scale skin-friction events convect at a velocity that is much faster than the local mean in the near-wall region (the convection velocity for large-scale skin-friction fluctuations is found to be close to the local mean at the midpoint of the logarithmic region). Instantaneous shear-stress data indicate the presence of large-scale structures at the wall that are comparable in scale and arrangement to the superstructure events that have been previously observed to populate the logarithmic regions of turbulent boundary layers. Conditional averages of streamwise velocity computed based on a low skin-friction footprint at the wall offer a wider three-dimensional view of the average superstructure event. These events consist of highly elongated forward-leaning low-speed structures, flanked on either side by high-speed events of similar general form. An analysis of small-scale energy associated with these large-scale events reveals that the small-scale velocity fluctuations are attenuated near the wall and upstream of a low skin-friction event, while downstream and above the low skin-friction event, the fluctuations are significantly amplified. In general, it is observed that the attenuation and amplification of the small-scale energy seems to approximately align with large-scale regions of streamwise acceleration and deceleration, respectively. Further conditional averaging based on streamwise skin-friction gradients confirms this observation. A conditioning scheme to detect the presence of meandering large-scale structures is also proposed. The large-scale meandering events are shown to be a possible source of the strong streamwise velocity gradients, and as such play a significant role in modulating the small-scale motions.

Computing Acceleration Loads on Free-Fall Lifeboat Occupants: Consequences of Including Nonlinearities in Water Waves and Mother Vessel Motions

2010 ◽  
Author(s):  
Neil Luxcey ◽  
Se´bastien Fouques ◽  
Thomas Sauder
Keyword(s):  
Water Waves ◽  
Three Dimensional ◽  
Free Fall ◽  
Momentum Conservation ◽  
Irregular Waves ◽  
Stokes Waves ◽  
Induced Motion ◽  
Wave Models ◽  
Wave Induced ◽  
The Impact

The safety of occupants in free-fall lifeboats (FFL) launched from a skid is addressed, and the focus is on numerical evaluation of acceleration loads during water impact. This paper investigates the required level of detail when modeling the physics of a lifeboat launch in waves. The first part emphasizes the importance of the non-linearity of the wave surface. Severity of impacts in linear (Airy) waves is compared to impacts in regular Stokes waves of the 5th order. Correspondingly, severity of impacts in irregular waves of the 2nd order is statistically compared to impacts in linear irregular waves. Theory of the two wave models are also briefly presented. The second part discusses the importance of a more detailed modeling of the launching system. This concerns especially cases for which damage to the mother vessel induces major lifeboat heel angles. A three-dimensional skid model is presented, along with validation against experimental measurements. In addition, the wave induced motion of the mother vessel is included. Consequences on the severity of the impact of the lifeboat in regular waves are discussed. This study is based on MARINTEK’s impact simulator for free-fall lifeboats, in which slamming loads are evaluated based on momentum conservation, a long wave approximation, and a von Karman type of approach. It is coupled here to the SIMO software, also developed at MARINTEK. Performance of this coupling is discussed.

scholarly journals Assessing the Impact of the Tropopause on Mountain Waves and Orographic Precipitation Using Linear Theory and Numerical Simulations

2015 ◽  
Vol 72 (2) ◽  
pp. 803-820 ◽  
Author(s):  
Nicholas Siler ◽  
Dale Durran
Keyword(s):  
Numerical Simulations ◽  
Linear Theory ◽  
Three Dimensional ◽  
Orographic Precipitation ◽  
Two Dimensional ◽  
Tropopause Height ◽  
Atmospheric Conditions ◽  
Mountain Waves ◽  
Wave Induced ◽  
The Impact

Abstract The partial reflection of mountain waves at the tropopause has been studied extensively for its contribution to downslope windstorms, but its impact on orographic precipitation has not been addressed. Here linear theory and numerical simulations are used to investigate how the tropopause affects the vertical structure of mountain waves and, in turn, orographic precipitation. Relative to the no-tropopause case, wave-induced ascent above the windward slope of a two-dimensional ridge is found to be enhanced or diminished depending on the ratio of the tropopause height to the vertical wavelength of the mountain waves—defined here as the “nondimensional tropopause height” . In idealized simulations of flow over both two-dimensional and three-dimensional ridges, variations in are found to modulate the precipitation rate by roughly a factor of 2 under typical atmospheric conditions. The sensitivity of precipitation to is related primarily to the depth of windward ascent but also to the location and strength of leeside descent, with significant impacts on the distribution of precipitation across the range (i.e., the rain-shadow effect). Using a modified version of Smith and Barstad’s orographic precipitation model, variations in are found to produce significant rain-shadow variability in the Washington Cascades, perhaps explaining some of the variability in rain-shadow strength observed among Cascade storms.

Apparent impact sound insulation performance of cross laminated timber floors with floating concrete toppings

2021 ◽  
Vol 263 (1) ◽  
pp. 5203-5215
Author(s):  
Jianhui Zhou ◽  
Zijian Zhao
Keyword(s):  
High Performance ◽  
Dynamic Stiffness ◽  
Steel Structures ◽  
Bending Stiffness ◽  
Sound Insulation ◽  
Small Scale ◽  
Cross Laminated Timber ◽  
Mass Timber ◽  
The Impact ◽  
Insulation Performance

Mass timber buildings are gaining increasing popularity as a sustainable alternative to concrete and steel structures. Mass timber panels, especially cross-laminated timber (CLT), are often used as floors due to their dry and fast construction. CLT has poor impact sound insulation performance due to its lightweight and relatively high bending stiffness. Floating concrete toppings are often applied to increase both the airborne and impact sound insulation performance. However, the impact sound insulation performance of floating concrete toppings on CLT structural floors is affected by both the concrete thickness and resilient interlayer. This study investigated the efficiency of both continuous and discrete floating floor assemblies through mock-up building tests using small-scale concrete toppings according to ASTM E1007-16. It was found that the improvements by continuous floating floor assemblies are dependent on the concrete thicknesses and dynamic stiffness of resilient interlayers. The improvements cannot be well predicted by the equations developed for concrete structural floors. The highest apparent impact sound insulation class (AIIC) achieved with continuous floating floor assemblies in this study was 53 dBA, while that of the discrete floating floor assemblies was up to 62 dBA. The discrete floating floor solution showed great potential for use in mass timber buildings due to the high performance with thinner concrete toppings.

New thermal-hydraulic correlations for printed circuit heat exchangers (PCHEs) with zigzag channels under high Reynolds numbers

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Carolina P. Naveira-Cotta ◽  
Jian Su ◽  
Paulo Lucena Kreppel Paes ◽  
Philippe R. Egmont ◽  
Rodrigo P. M. Moreira ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Design Parameters ◽  
Channel Diameter ◽  
Content Type ◽  
Printed Circuit ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
The Impact

Purpose The purpose of this paper is to investigate the impact of semi-circular zigzag-channel printed circuit heat exchanger (PCHE) design parameters on heat transfer and pressure drop of flows under high Reynolds numbers and provide new thermal-hydraulic correlations relevant to conditions encountered in natural gas processing plants. Design/methodology/approach The correlations were developed using three-dimensional steady-state computational fluid dynamics simulations with varying semicircular channel diameter (from 1 to 5 mm), zigzag angle (from 15° to 45°) and Reynolds number (from 40,000 to 100,000). The simulation results were validated by comparison with experimental results and existing correlations. Findings The results revealed that the thermal-hydraulic performance was mostly affected by the zigzag angle, followed by the ratio of the zigzag channel length to the hydraulic diameter. Overall, smaller zigzag angles favored heat transfer intensification while keeping reasonably low pressure drops. Originality/value This study is, to date, the only one providing thermal-hydraulic correlations for PCHEs with zigzag channels under high Reynolds numbers. Besides, the broad range of parameters considered makes the proposed correlations valuable PCHE design tools.

Studies of the thermal protective performance of fabrics under fire exposure: from small-scale to hexagon tests

2017 ◽  
Vol 88 (20) ◽  
pp. 2339-2352 ◽  
Author(s):  
Sumit Mandal ◽  
Simon Annaheim ◽  
Thomas Pitts ◽  
Martin Camenzind ◽  
René M Rossi
Keyword(s):  
Heat Transfer ◽  
High Performance ◽  
Radiant Heat ◽  
Air Permeability ◽  
Small Scale ◽  
Fire Exposure ◽  
Thermal Protective Performance ◽  
Flash Fire ◽  
Protective Performance ◽  
The Impact

This study aims to investigate the thermal protective performance of fabrics used in firefighters' clothing under high-intensity fire exposure. The performance of thermal protective fabric systems with different physical properties was evaluated under laboratory simulated fire exposure. Additionally, the influence of the configuration of the fire exposure tests and modes of heat transfer through the fabrics was also thoroughly investigated. The protective performance was evaluated using the standard small-scale flame [International Organization for Standardization (ISO) 9151:1995] and radiant heat (ISO 6942:2002) exposure tests. Additionally, the protective performance was evaluated under flash-fire exposure using a newly developed hexagon test. The protective performance values obtained from the small-scale (flame and radiant heat) and hexagon (flash fire) tests were compared and discussed. It has been found that a multi-layered fabric with high weight, thickness, and thermal resistance can significantly and positively affect the protective performance. If the air permeability of this fabric is high, it can show a lower protective performance; however, the impact of air permeability on the protective performance is insignificant especially in the case of the hexagon test. Notably, the protective performance can differ under two types of small-scale tests − flame and radiant heat. Also, this protective performance value is generally higher in the case of hexagon test in comparison with the small-scale tests. These differences in protective performance are mainly due to the unique configurations of these tests and/or different modes of heat transfer through the tested fabrics. The findings from this study will guide textile or materials engineers in the design and selection of materials for high performance thermal protective clothing; in turn, it will improve the occupational health and safety for firefighters.

scholarly journals Hyperelastic modelling of yarn structures for dynamic applications

2018 ◽  
Vol 183 ◽  
pp. 01031
Author(s):  
Pietro del Sorbo ◽  
Jeremie Girardot ◽  
Frederic Dau ◽  
Ivan Iordanoff
Keyword(s):  
High Performance ◽  
Three Dimensional ◽  
Weight Ratio ◽  
High Strength ◽  
Material Model ◽  
Linear Elastic ◽  
Mesoscopic Models ◽  
First Results ◽  
Hyperelastic Model ◽  
The Impact

Dry fabrics comprised of high performance polymeric fibers have been widely used as protection layers in structures submitted to high velocity impacts (HVI). Their outstanding impact energy dissipation ability combined with an high strength-to-weight ratio make them a preferable choice in different applications such as bullet vests or blade containment systems over standard materials. Among the different approaches adopted to study these structures numerical methods assume a central role. Thanks to their reduced costs and the related possibility of evaluating the effects of single phenomena, they are often used to predict the structure ballistic limits or to study the physical events which occur during the penetration. Among the different strategies adopted to model a fabric, mesoscopic models have been largely adopted by different authors. These models assume the yarns as a continuum body while the fabric geometry is explicitly described. Nowadays yarn material models are universally assumed to be linear elastic and orthotropic. This modelling approach mostly focuses on the longitudinal behaviour of the yarn, however fiber-scale analyses and experimental results shows the importance of three-dimensional stress state on the ballistic limit. In order to obtain a three-dimensional description of the yarn strain state during the impact, a novel hyperelastic model for yarn structures here is developed. In a first step, fiber-level preliminary analyses have been performed to obtain the effective behaviour of these structure under the projectile collision. In the second step, the hyperelastic model has been implemented and identified thanks to microscopic elementary tests. Finally, a continuum model of the yarn have been performed. First results show the relevance of the hyperelastic model compared to the fiber-level observation and enhance the limit of the classical linear elastic material model.

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