3D MRI measurements of the effects of wind direction on flow characteristics and contaminant dispersion in a model urban canopy

2019 ◽  
Vol 19 (4) ◽  
pp. 851-878 ◽  
Author(s):  
Gawoon Shim ◽  
Dipak Prasad ◽  
Christopher J. Elkins ◽  
John K. Eaton ◽  
Michael J. Benson
Keyword(s):  
Wind Direction ◽  
Flow Characteristics ◽  
Urban Canopy ◽  
3D Mri ◽  
Contaminant Dispersion ◽  
Mri Measurements

Aerodynamic Simulation of Road Vehicle in Steady Crosswind

2013 ◽  
Vol 376 ◽  
pp. 341-344
Author(s):  
Shan Ling Han ◽  
Ru Xing Yu ◽  
Yu Yue Wang ◽  
Gui Shen Wang
Keyword(s):  
Flow Field ◽  
Wind Direction ◽  
Motor Vehicle ◽  
Aerodynamic Force ◽  
Flow Characteristics ◽  
Simulation Method ◽  
Aerodynamic Characteristics ◽  
External Flow ◽  
Slant Angle ◽  
Ahmed Body

Because crosswind affects drivers to control their vehicles safely, the research on flow characteristics in automotive crosswind has a great significance to improve the crosswind stability of the vehicle. By the steady state numerical simulation method, the aerodynamic characteristics of external flow field of Ahmed body in crosswind was investigated. The Ahmed body with 25° slant angle is built in UG NX. The external flow field of the Ahmed body in the wind direction of 0°, 15º, 30° angle is simulated in XFlow software. According to the map of the pressure and velocity distribution, the flow field both before and after, as well as left and right has significant change as the wind direction angle increased, and the trail turbulence intensity also changes. The changes of aerodynamic force and moment affect the driving stability of a motor vehicle.

scholarly journals Three-Dimensional Magnetic Resonance Imaging for Guiding Tibial and Femoral Tunnel Position in Anterior Cruciate Ligament Reconstruction: A Cadaveric Study

2020 ◽  
Vol 8 (3) ◽  
pp. 232596712090991
Author(s):  
Yousef Marwan ◽  
Jens Böttcher ◽  
Carl Laverdière ◽  
Rehana Jaffer ◽  
Mark Burman ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Anterior Cruciate Ligament ◽  
Magnetic Resonance ◽  
Cruciate Ligament ◽  
Resonance Imaging ◽  
3D Mri ◽  
Tunnel Position ◽  
Median Distance ◽  
Anterior Cruciate ◽  
Mri Measurements

Background: Femoral and tibial tunnel malposition for anterior cruciate ligament (ACL) reconstruction (ACLR) is correlated with higher failure rate. Regardless of the surgical technique used to create ACL tunnels, significant mismatches between the native and reconstructed footprints exist. Purpose: To compare the position of tunnels created by a standard technique with the ones created based on preoperative 3-dimensional magnetic resonance imaging (3D MRI) measurements of the ACL anatomic footprint. Study Design: Controlled laboratory study. Methods: Using 3D MRI, the native ACL footprints were identified. Tunnels were created on 16 knees (8 cadavers) arthroscopically. On one knee of a matched pair, the tunnels were created based on 3D MRI measurements that were provided to the surgeon (roadmapped technique), while on the contralateral knee, the tunnels were created based on a standard anatomic ACLR technique. The technique was randomly assigned per set of knees. Postoperatively, the positions of the tunnels were measured using 3D MRI. Results: On the tibial side, the median distance between the center of the native and reconstructed ACL footprints in relation to the root of the anterior horn of the lateral meniscus medially was 1.7 ± 2.2 mm and 1.9 ± 2.8 mm for the standard and roadmapped techniques, respectively ( P = .442), while the median anteroposterior distance was 3.4 ± 2.4 mm and 2.5 ± 2.5 mm for the standard and roadmapped techniques, respectively ( P = .161). On the femoral side, the median distance in relation to the apex of the deep cartilage (ADC) distally was 0.9 ± 2.8 mm and 1.3 ± 2.1 mm for the standard and roadmapped techniques, respectively ( P = .195), while the median distance anteriorly from the ADC was 1.2 ± 1.3 mm and 4.6 ± 4.5 mm for the standard and roadmapped techniques, respectively ( P = .007). Conclusion: Providing precise radiological measurements of the ACL footprints does not improve the surgeon’s ability to position the tunnels. Future studies should continue to attempt to provide tools to improve the tunnel position in ACLR. Clinical Relevance: This cadaveric study indicates that despite the use of 3D MRI in understanding the ACL anatomy, re-creating the native ACL footprints remains a challenge.

How to Parametrize Urban-Canopy Drag to Reproduce Wind-Direction Effects Within the Canopy

2013 ◽  
Vol 149 (1) ◽  
pp. 43-63 ◽  
Author(s):  
J. L. Santiago ◽  
O. Coceal ◽  
A. Martilli
Keyword(s):  
Wind Direction ◽  
Urban Canopy ◽  
Canopy Drag

scholarly journals Implicit Definition of Flow Patterns in Street Canyons—Recirculation Zone—Using Exploratory Quantitative and Qualitative Methods

Atmosphere ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 794
Author(s):  
Arsenios E. Chatzimichailidis ◽  
Christos D. Argyropoulos ◽  
Marc J. Assael ◽  
Konstantinos E. Kakosimos
Keyword(s):  
Air Pollution ◽  
Wind Direction ◽  
Recirculation Zone ◽  
Health Hazard ◽  
Flow Characteristics ◽  
Width Ratio ◽  
Clustering Methods ◽  
Street Canyons ◽  
Large Eddy Simulation Model ◽  
Implicit Definition

Air pollution is a major health hazard for the population that increasingly lives in cities. Street-scale Air Quality Models (AQMs) are a cheap and efficient way to study air pollution and possibly provide solutions. Having to include all the complex phenomena of wind flow between buildings, AQMs employ several parameterisations, one of which is the recirculation zone. Goal of this study is to derive an implicit or explicit definition for the recirculation zone from the flow in street canyons using computational fluid dynamics (CFD). Therefore, a CFD-Large Eddy Simulation model was employed to investigate street canyons with height to width ratio from 1 to 0.20 under perpendicular wind direction. The developed dataset was analyzed with traditional methods (vortex visualization criteria and pollutant dispersion fields), as well as clustering methods (machine learning). Combining the above analyses, it was possible to extract qualitative features that agree well with literature but most importantly to develop quantitative expressions that describe their topology. The extracted features’ topology depends strongly on the street canyon dimensions and not surprisingly is independent of the wind velocity. The developed expressions describe areas with common flow characteristics inside the canyon and thus they can be characterised as an implicit definition for the recirculation zone. Furthermore, the presented methodology can be further applied to cover more parameters such us oblique wind direction and heated-facades and more methods for data analysis.

scholarly journals NUMERICAL ANALYSIS OF FLIGHT CONDITIONS AT THE ALTA AIRPORT, NORWAY

Aviation ◽  
2014 ◽  
Vol 18 (3) ◽  
pp. 109-119
Author(s):  
Adil Rasheed ◽  
Asif Mushtaq
Keyword(s):  
Numerical Analysis ◽  
Wind Direction ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Mountain Waves ◽  
Atmospheric Flow

In this paper, the results from a numerical study of the atmospheric flow characteristics at the Alta airport, Norway are presented. Experiences of the pilots operating in the region have been used to validate the findings. Further analysis has resulted in the identification of dangerous zones for aviation activities for a particular wind direction. Towards the end an effort has been made to relate the experience of the pilots with the mountain waves generated due to the presence of a small hill close to the airport.

scholarly journals Ventilation and Pollutant Concentration for the Pedestrian Zone, the Near-Wall Zone, and the Canopy Layer at Urban Intersections

2021 ◽  
Vol 18 (21) ◽  
pp. 11080
Author(s):  
Mingjie Zhang ◽  
Zhi Gao ◽  
Xin Guo ◽  
Jialei Shen
Keyword(s):  
Wind Direction ◽  
Flow Characteristics ◽  
Volumetric Flow Rate ◽  
Pollutant Concentration ◽  
Canopy Layer ◽  
Cross Sectional ◽  
Significant Difference ◽  
Wall Zone ◽  
The Impact ◽  
Near Wall

To gain further insight into the ventilation at urban street intersections, this study conducted 3D simulations of the ventilation at right- and oblique-angled intersections under eight wind directions by using the Reynolds-averaged Navier–Stokes (RANS) κ-ε turbulence model. The divergent responses of ventilation and pollution concentration for the pedestrian zone (ped), the near-wall zone (nwz), and the canopy layer to the change in intersection typology and wind direction were investigated. The flow characteristics of the intersections, taken as the air flow hub, were explored by employing indices such as the minimum flow ratio (β) between horizontal openings. The results show that oblique wind directions lead to a lower total volumetric flow rate (Qtotal) but a higher β value for right-angled intersections. For T-shaped intersections, a larger cross-sectional area for the outflow helps to increase Qtotal. Oblique-angled intersections, for example, the X-shaped intersection, experience a more significant difference in Qtotal but a steady value of β when the wind direction changes. The vertical air-exchange rate for the intersection was particularly significant when the wind directions were parallel to the street orientation or when there was no opening in the inflow direction. The spatially averaged normalized pollutant concentration and age of air (τ*¯) for the pedestrian zone and the canopy layer showed similar changing trends for most of the cases, while in some cases, only the τped*¯ or τnwz*¯ changed obviously. These findings reveal the impact mechanism of intersection configuration on urban local ventilation and pollutant diffusion.

Time consumption and quality of an automated fusion tool for SPECT and MRI images of the brain

2003 ◽  
Vol 42 (05) ◽  
pp. 215-219
Author(s):  
G. Platsch ◽  
A. Schwarz ◽  
K. Schmiedehausen ◽  
B. Tomandl ◽  
W. Huk ◽  
...  
Keyword(s):  
Data Sets ◽  
3D Mri ◽  
Clinical Routine ◽  
Fusion Procedure ◽  
3D Data ◽  
Mri Scans ◽  
2D Data ◽  
Time Required ◽  
The Brain ◽  
Manual Correction

Summary: Aim: Although the fusion of images from different modalities may improve diagnostic accuracy, it is rarely used in clinical routine work due to logistic problems. Therefore we evaluated performance and time needed for fusing MRI and SPECT images using a semiautomated dedicated software. Patients, material and Method: In 32 patients regional cerebral blood flow was measured using 99mTc ethylcystein dimer (ECD) and the three-headed SPECT camera MultiSPECT 3. MRI scans of the brain were performed using either a 0,2 T Open or a 1,5 T Sonata. Twelve of the MRI data sets were acquired using a 3D-T1w MPRAGE sequence, 20 with a 2D acquisition technique and different echo sequences. Image fusion was performed on a Syngo workstation using an entropy minimizing algorithm by an experienced user of the software. The fusion results were classified. We measured the time needed for the automated fusion procedure and in case of need that for manual realignment after automated, but insufficient fusion. Results: The mean time of the automated fusion procedure was 123 s. It was for the 2D significantly shorter than for the 3D MRI datasets. For four of the 2D data sets and two of the 3D data sets an optimal fit was reached using the automated approach. The remaining 26 data sets required manual correction. The sum of the time required for automated fusion and that needed for manual correction averaged 320 s (50-886 s). Conclusion: The fusion of 3D MRI data sets lasted significantly longer than that of the 2D MRI data. The automated fusion tool delivered in 20% an optimal fit, in 80% manual correction was necessary. Nevertheless, each of the 32 SPECT data sets could be merged in less than 15 min with the corresponding MRI data, which seems acceptable for clinical routine use.

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