subject:(dual Doppler)

University of Oklahoma

1. Gebauer, Joshua. Assessing Dual-Doppler Vertical Velocity Retrievals from Rapid-Scan Radar Data.

Degree: PhD, 2020, University of Oklahoma

► Vertical velocity is the most difficult wind component to accurately retrieve from dual- Doppler observations. Typical radar scans are conducted with shallow elevation angles and… (more)

▼ Vertical velocity is the most difficult wind component to accurately retrieve from dual- Doppler observations. Typical radar scans are conducted with shallow elevation angles and therefore, the radial velocity observations poorly constrain the vertical velocity in retrievals. Traditional dual-Doppler analysis (DDA) uses the anelastic mass conservation equation as a constraint to retrieve vertical velocity. However, procedures that integrate the anelastic mass conservation equation can have large errors in the vertical velocities due to missing low-level data, errors in boundary specification, and the compounding of horizontal divergence errors in the integration. In recent years, it has been proposed to use a vertical vorticity equation as a weak constraint in addition to the mass conservation equation in order to improve vertical velocity retrievals. Prior observation simulation experiments have found that the vorticity equation constraint can improve vertical velocity retrievals in situations with missing low-level data and radar volume scan times that are sufficiently short to calculate the vorticity tendency accurately. In this study, the vertical vorticity equation constraint DDA was tested using real observations from rapid-scan radars. A dual-Doppler dataset of a convective storm was collected on 4 Sept 2018 with a maximum volume scan time of 30 seconds. An additional radar was positioned under the storm and conducted near-vertical planned-position indicator scans (PPIs), which were used as a verification dataset. In general, the vorticity equation DDA was able to improve vertical velocity retrievels, but the improvement was dependent on the time between volume scans and the technique used to calculate the vorticity tendency. When the time between volume scans was 30 seconds, a simple centered difference of the vorticity calculated from provisional wind retrievals was sufficient for estimating the vorticity tendency, but with greater time between volume scans this method resulted in significantly degraded vertical velocities. A technique that used advection correction to shorten the time difference in the centered difference improved the vertical velocities of these longer volume scan times, but caused the DDAs with 30 seconds between volume scans to become slightly worse. A new three-dimensional advection correction technique that was developed for the vorticity tendency estimation produced slightly better vertical velocity retrievals than those that used two-dimensional advection correction. One key difference between these results and those of the prior OSSE experiments is that the improvement in the retrieved vertical velocities occurred even though there was not a large data void between the lowest data level and the ground. Additionally, the vorticity equation constraint DDA was more forgiving to radar data errors as it did not produce unphysical vertical velocities in a region of sidelobe contamination that was present in the other DDAs. Considering that observation… Advisors/Committee Members: Shapiro, Alan (advisor), Corey, Potvin (committee member), Palmer, Robert (committee member), Homeyer, Cameron (committee member), Petrov, Nikola (committee member).

Subjects/Keywords: Radar Analysis; Dual-Doppler; Ensemble Kalman Filter

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APA (6^th Edition):

Gebauer, J. (2020). Assessing Dual-Doppler Vertical Velocity Retrievals from Rapid-Scan Radar Data. (Doctoral Dissertation). University of Oklahoma. Retrieved from http://hdl.handle.net/11244/326614

Chicago Manual of Style (16^th Edition):

Gebauer, Joshua. “Assessing Dual-Doppler Vertical Velocity Retrievals from Rapid-Scan Radar Data.” 2020. Doctoral Dissertation, University of Oklahoma. Accessed March 08, 2021. http://hdl.handle.net/11244/326614.

MLA Handbook (7^th Edition):

Gebauer, Joshua. “Assessing Dual-Doppler Vertical Velocity Retrievals from Rapid-Scan Radar Data.” 2020. Web. 08 Mar 2021.

Vancouver:

Gebauer J. Assessing Dual-Doppler Vertical Velocity Retrievals from Rapid-Scan Radar Data. [Internet] [Doctoral dissertation]. University of Oklahoma; 2020. [cited 2021 Mar 08]. Available from: http://hdl.handle.net/11244/326614.

Council of Science Editors:

Gebauer J. Assessing Dual-Doppler Vertical Velocity Retrievals from Rapid-Scan Radar Data. [Doctoral Dissertation]. University of Oklahoma; 2020. Available from: http://hdl.handle.net/11244/326614

Virginia Tech

2. White, Trevor Stewart. Dual-Doppler Derived Vorticity as a Predictor of Hail Size in Severe Thunderstorms.

Degree: MS, Geography, 2017, Virginia Tech

URL: http://hdl.handle.net/10919/74927

► One of the primary missions of the National Weather Service (NWS) is to use a network of more than 150 NEXRAD radar installations to monitor… (more)

Subjects/Keywords: hail size; severe thunderstorm; supercell; dual Doppler

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APA (6^th Edition):

White, T. S. (2017). Dual-Doppler Derived Vorticity as a Predictor of Hail Size in Severe Thunderstorms. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/74927

Chicago Manual of Style (16^th Edition):

White, Trevor Stewart. “Dual-Doppler Derived Vorticity as a Predictor of Hail Size in Severe Thunderstorms.” 2017. Masters Thesis, Virginia Tech. Accessed March 08, 2021. http://hdl.handle.net/10919/74927.

MLA Handbook (7^th Edition):

White, Trevor Stewart. “Dual-Doppler Derived Vorticity as a Predictor of Hail Size in Severe Thunderstorms.” 2017. Web. 08 Mar 2021.

Vancouver:

White TS. Dual-Doppler Derived Vorticity as a Predictor of Hail Size in Severe Thunderstorms. [Internet] [Masters thesis]. Virginia Tech; 2017. [cited 2021 Mar 08]. Available from: http://hdl.handle.net/10919/74927.

Council of Science Editors:

White TS. Dual-Doppler Derived Vorticity as a Predictor of Hail Size in Severe Thunderstorms. [Masters Thesis]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/74927

Texas Tech University

3. Hirth, Brian D. Examination of the Coastal Transition Zone in Hurricane Frances (2004).

Degree: 2011, Texas Tech University

URL: http://hdl.handle.net/2346/ETD-TTU-2011-05-1396

► Understanding the structure of the coastal internal boundary layer (IBL) during the landfall of a tropical cyclone has important ramifications on operational forecasting, structural design,… (more)

▼ Understanding the structure of the coastal internal boundary layer (IBL) during the landfall of a tropical cyclone has important ramifications on operational forecasting, structural design, and post-storm damage assessment. Despite these important issues, it is unclear how the structure of the IBL evolves at the coastline on micro- and meso-scales during a landfalling hurricane. Knowledge of the vertical kinematic structure within tropical cyclones over water has improved greatly through aircraft reconnaissance missions and the advent of GPS dropsondes and the Stepped Frequency Microwave Radiometers. Unfortunately, reconnaissance and research aircraft are limited to over-water missions resulting in a poor understanding of vertical kinematic structure near the coastal interface where changes in IBL structure are expected due to changes in coastal geometry and surface roughness. Additionally, IBL structure may evolve due to the passage of convective precipitation and associated downdrafts. A unique observational dataset was collected from the coastal transition zone in the onshore flow region of Hurricane Frances (2004) over Cape Canaveral, FL. Single- and dual-Doppler radar data collected by the Shared Mobile Atmospheric Research and Teaching radars provide the ability to discern horizontal and vertical mean IBL structure over a complex coastal interface while assessing the influence of a variable underlying surface and the passage of transient convective wind gusts. Additional wind speed data were collected by a meso-network of surface towers operated by the Cape Canaveral Air Force Station and Kennedy Space Center along with a portable surface tower deployed by Texas Tech University. Radar and tower data analyses reveal that IBL mean structure over the Cape Canaveral remains quite consistent during the landfall of Hurricane Frances, though IBL growth is suppressed when compared to empirical growth models. Additionally, transient convective gusts commonly perturb the mean structure at the top of the IBL, though the higher momentum associated with these gusts is typically not able to descend to the surface within an established IBL. Advisors/Committee Members: Schroeder, John L. (Committee Chair), Weiss, Christopher C. (committee member), Smith, Douglas A. (committee member).

Subjects/Keywords: Internal boundary layer; Hurricane; Dual-doppler; Doppler radar; Tower measurements; Roughness length; Wind

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APA (6^th Edition):

Hirth, B. D. (2011). Examination of the Coastal Transition Zone in Hurricane Frances (2004). (Thesis). Texas Tech University. Retrieved from http://hdl.handle.net/2346/ETD-TTU-2011-05-1396

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Hirth, Brian D. “Examination of the Coastal Transition Zone in Hurricane Frances (2004).” 2011. Thesis, Texas Tech University. Accessed March 08, 2021. http://hdl.handle.net/2346/ETD-TTU-2011-05-1396.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Hirth, Brian D. “Examination of the Coastal Transition Zone in Hurricane Frances (2004).” 2011. Web. 08 Mar 2021.

Vancouver:

Hirth BD. Examination of the Coastal Transition Zone in Hurricane Frances (2004). [Internet] [Thesis]. Texas Tech University; 2011. [cited 2021 Mar 08]. Available from: http://hdl.handle.net/2346/ETD-TTU-2011-05-1396.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Hirth BD. Examination of the Coastal Transition Zone in Hurricane Frances (2004). [Thesis]. Texas Tech University; 2011. Available from: http://hdl.handle.net/2346/ETD-TTU-2011-05-1396

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Colorado State University

4. Martinez, Matthew Thomas. Description and evaluation of the CASA dual-Doppler system.

Degree: MS(M.S.), Electrical and Computer Engineering, 2011, Colorado State University

URL: http://hdl.handle.net/10217/47430

► Long range weather surveillance radars are designed for observing weather events for hundreds of kilometers from the radar and operate over a large coverage domain… (more)

▼ Long range weather surveillance radars are designed for observing weather events for hundreds of kilometers from the radar and operate over a large coverage domain independently of weather conditions. As a result a loss in spatial resolution and limited temporal sampling of the weather phenomenon occurs. Due to the curvature of the Earth, long-range weather radars tend to make the majority of their precipitation and wind observations in the middle to upper troposphere, resulting in missed features associates with severe weather occurring in the lowest three kilometers of the troposphere. The spacing of long-range weather radars in the United States limits the feasibility of using dual-Doppler wind retrievals that would provide valuable information on the kinematics of weather events to end-users and researchers. The National Science Foundation Center for Collaborative Adapting Sensing of the Atmosphere (CASA) aims to change the current weather sensing model by increasing coverage of the lowest three kilometers of the troposphere by using densely spaced networked short-range weather radars. CASA has deployed a network of these radars in south-western Oklahoma, known as Integrated Project 1 (IP1). The individual radars are adaptively steered by an automated system known as the Meteorological Command and Control (MCC). The geometry of the IP1 network is such that the coverage domains of the individual radars are overlapping. A dual-Doppler system has been developed for the IP1 network which takes advantage of the overlapping coverage domains. The system is comprised of two subsystems, scan optimization and wind field retrieval. The scan strategy subsystem uses the DCAS model and the number of dual-Doppler pairs in the IP1 network to minimizes the normalized standard deviation in the wind field retrieval. The scan strategy subsystem also minimizes the synchronization error between two radars. The retrieval itself is comprised of two steps, data resampling and the retrieval process. The resampling step map data collected in radar coordinates to a common Cartesian grid. The retrieval process uses the radial velocity measurements to estimate the northward, eastward, and vertical component of the wind. The error in the retrieval is related to the beam crossing angle. The best retrievals occur at beam crossing angles greater than 30 degrees. During operations statistics on the scan strategy and wind field retrievals are collected in real-time. For the scan strategy subsystem statistics on the beam crossing angels, maximum elevation angle, number of elevation angles, maximum observable height, and synchronization time between radars in a pair are collected by the MCC. These statistics are used to evaluate the performance of the scan strategy subsystem. Observations of a strong wind event occurring on April 2, 2010 are used to evaluate the decision process associated with the scan strategy optimization. For the retrieval subsystem, the normalized standard deviation for the wind field retrieval is used to evaluate the quality of… Advisors/Committee Members: Chandra, Chandrasekar V. (advisor), Notaros, Branislav M. (committee member), Mielke, Paul W. (committee member).

Subjects/Keywords: dual-Doppler; volume targets; signal processing; networked radar

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APA (6^th Edition):

Martinez, M. T. (2011). Description and evaluation of the CASA dual-Doppler system. (Masters Thesis). Colorado State University. Retrieved from http://hdl.handle.net/10217/47430

Chicago Manual of Style (16^th Edition):

Martinez, Matthew Thomas. “Description and evaluation of the CASA dual-Doppler system.” 2011. Masters Thesis, Colorado State University. Accessed March 08, 2021. http://hdl.handle.net/10217/47430.

MLA Handbook (7^th Edition):

Martinez, Matthew Thomas. “Description and evaluation of the CASA dual-Doppler system.” 2011. Web. 08 Mar 2021.

Vancouver:

Martinez MT. Description and evaluation of the CASA dual-Doppler system. [Internet] [Masters thesis]. Colorado State University; 2011. [cited 2021 Mar 08]. Available from: http://hdl.handle.net/10217/47430.

Council of Science Editors:

Martinez MT. Description and evaluation of the CASA dual-Doppler system. [Masters Thesis]. Colorado State University; 2011. Available from: http://hdl.handle.net/10217/47430

Uppsala University

5. Simon, Elliot. Determination of an Optimum Sector Size for Plan Position Indicator Measurements using a Long Range Coherent Scanning Atmospheric Doppler LiDAR.

Degree: Earth Sciences, 2015, Uppsala University

URL: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-295081

►

As wind energy plants continue to grow in size and complexity, advanced measurement technologies such as scanning Doppler LiDAR are essential for assessing site… (more)

▼

As wind energy plants continue to grow in size and complexity, advanced measurement technologies such as scanning Doppler LiDAR are essential for assessing site conditions and prospecting new development areas. The RUNE project was initiated to determine best practices for the use of scanning LiDARs in resource assessments for near shore wind farms. The purpose of this thesis is to determine the optimum configuration for the plan position indicator (PPI) scan type of a scanning LiDAR. A task specific Automated Analysis Software (AAS) is created, and the sensitivity of the integrated velocity azimuth process (iVAP) reconstruction algorithm is examined using sector sizes ranging from 4 to 60 degrees. Further, a comparison to simultaneous dual Doppler measurement is presented in order to determine the necessity of deploying two LiDARs rather than one. DTU has developed a coordinated long range coherent scanning multi-LiDAR array (the WindScanner system) based on modified Leosphere WindCube 200S devices and an application specific software framework and communication protocol. The long range WindScanner system was deployed at DTU’s test station in Høvsøre, Denmark and measurement data was collected over a period of 7 days. One WindScanner was performing 60 degree sector scans, while two others were placed in staring dual Doppler mode. All three beams were configured to converge atop a 116.5m instrumented meteorological mast. A significant result was discovered which indicates that the accuracy of the reconstructed measurements do not differ significantly between sector sizes of 30 and 60 degrees. Using the smallest sector size which does not introduce systematic error has numerous benefits including: increasing the scan speed, measurement distance and angular resolution. When comparing collocated dual Doppler, sector scan and in-situ met-mast instrumentation, we find very good agreement between all techniques. Dual Doppler is able to measure wind speeds within 0.1%, and 60 degree sector scan within 0.2% on average of the reference values. For retrieval of wind direction, the sector scan approach performs particularly well. This is likely attributable to lower errors introduced by the assumption of flow field homogeneity over the scanned area, in contract to wind direction which tends to be more non-uniform. For applications such as site resource assessments, where generally accurate 10 minute wind speed and direction values are required, a scanning LiDAR performing PPI scans with a sector size of between 30 and 38 degrees is recommended. The laser’s line of sight path should be directed parallel to the predominant wind direction and at the lowest elevation angle possible.

RUNE

Subjects/Keywords: LiDAR; WindScanner; PPI; Sector Scan; Dual Doppler; Remote Sensing; Wind Measurement; Energy Systems; Energisystem; Remote Sensing; Fjärranalysteknik

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APA (6^th Edition):

Simon, E. (2015). Determination of an Optimum Sector Size for Plan Position Indicator Measurements using a Long Range Coherent Scanning Atmospheric Doppler LiDAR. (Thesis). Uppsala University. Retrieved from http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-295081

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Simon, Elliot. “Determination of an Optimum Sector Size for Plan Position Indicator Measurements using a Long Range Coherent Scanning Atmospheric Doppler LiDAR.” 2015. Thesis, Uppsala University. Accessed March 08, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-295081.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Simon, Elliot. “Determination of an Optimum Sector Size for Plan Position Indicator Measurements using a Long Range Coherent Scanning Atmospheric Doppler LiDAR.” 2015. Web. 08 Mar 2021.

Vancouver:

Simon E. Determination of an Optimum Sector Size for Plan Position Indicator Measurements using a Long Range Coherent Scanning Atmospheric Doppler LiDAR. [Internet] [Thesis]. Uppsala University; 2015. [cited 2021 Mar 08]. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-295081.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Simon E. Determination of an Optimum Sector Size for Plan Position Indicator Measurements using a Long Range Coherent Scanning Atmospheric Doppler LiDAR. [Thesis]. Uppsala University; 2015. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-295081

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

6. Vega, Manuel A. Multi-frequency dual-polarized platform for validation of satellite precipitation measurements.

Degree: PhD, Electrical and Computer Engineering, 2017, Colorado State University

URL: http://hdl.handle.net/10217/183894

► Satellite missions such as the Tropical Rainfall Measuring Mission (TRMM) and the Global Precipitation Measurement (GPM) mission have demonstrated the value of rainfall measurements at… (more)

Subjects/Keywords: dual-polarized; radar; multi-frequency; Doppler

…L IST OF TABLES 4.1 Specifications of the Dual-frequency, Dual-polarized, Doppler Radar… …designed as one. 1.3. R ESEARCH Q UESTIONS The Dual-frequency Dual-polarized Doppler Radar (… …signals received in a dual-polarized Doppler weather radar and their statistical properties. The… …the Dual-frequency Dual-polarized Doppler Radar (D3R) system. 2.4.3. Doppler… …Doppler velocities, (e) and (f) show differential reflectivities, finally…

10 more images…

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Vega, M. A. (2017). Multi-frequency dual-polarized platform for validation of satellite precipitation measurements. (Doctoral Dissertation). Colorado State University. Retrieved from http://hdl.handle.net/10217/183894

Chicago Manual of Style (16^th Edition):

Vega, Manuel A. “Multi-frequency dual-polarized platform for validation of satellite precipitation measurements.” 2017. Doctoral Dissertation, Colorado State University. Accessed March 08, 2021. http://hdl.handle.net/10217/183894.

MLA Handbook (7^th Edition):

Vega, Manuel A. “Multi-frequency dual-polarized platform for validation of satellite precipitation measurements.” 2017. Web. 08 Mar 2021.

Vancouver:

Vega MA. Multi-frequency dual-polarized platform for validation of satellite precipitation measurements. [Internet] [Doctoral dissertation]. Colorado State University; 2017. [cited 2021 Mar 08]. Available from: http://hdl.handle.net/10217/183894.

Council of Science Editors:

Vega MA. Multi-frequency dual-polarized platform for validation of satellite precipitation measurements. [Doctoral Dissertation]. Colorado State University; 2017. Available from: http://hdl.handle.net/10217/183894

Texas Tech University

7. Gunter, William. Observations of convective cells in an outer rainband of Hurricane Frances (2004).

Degree: Geosciences, 2010, Texas Tech University

URL: http://hdl.handle.net/2346/ETD-TTU-2010-12-1117

► As Hurricane Frances made landfall on the eastern coast of Florida on 5 September 2004, Texas Tech University’s Hurricane Research Team deployed two mobile Doppler… (more)

Subjects/Keywords: Rainbands; Miniature supercells; Shear features; Hurricane rainband changes at landfall; Dual-doppler

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APA (6^th Edition):

Gunter, W. (2010). Observations of convective cells in an outer rainband of Hurricane Frances (2004). (Thesis). Texas Tech University. Retrieved from http://hdl.handle.net/2346/ETD-TTU-2010-12-1117

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Gunter, William. “Observations of convective cells in an outer rainband of Hurricane Frances (2004).” 2010. Thesis, Texas Tech University. Accessed March 08, 2021. http://hdl.handle.net/2346/ETD-TTU-2010-12-1117.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Gunter, William. “Observations of convective cells in an outer rainband of Hurricane Frances (2004).” 2010. Web. 08 Mar 2021.

Vancouver:

Gunter W. Observations of convective cells in an outer rainband of Hurricane Frances (2004). [Internet] [Thesis]. Texas Tech University; 2010. [cited 2021 Mar 08]. Available from: http://hdl.handle.net/2346/ETD-TTU-2010-12-1117.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Gunter W. Observations of convective cells in an outer rainband of Hurricane Frances (2004). [Thesis]. Texas Tech University; 2010. Available from: http://hdl.handle.net/2346/ETD-TTU-2010-12-1117

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of Waterloo

8. Morton, Christopher R. Experimental and Numerical Investigations of the Flow Development over Circular Cylinders with Stepwise Discontinuities in Diameter.

Degree: 2010, University of Waterloo

URL: http://hdl.handle.net/10012/5470

► Flow past circular cylinders with stepwise discontinuities in diameter was investigated experimentally and numerically for the diameter ratio D/d = 2 and three Reynolds numbers,… (more)

▼ Flow past circular cylinders with stepwise discontinuities in diameter was investigated experimentally and numerically for the diameter ratio D/d = 2 and three Reynolds numbers, Re = 150, 300, and 1050. The investigation was focused on the vortex shedding phenomena occurring in the wake of the cylinders. In the first series of experimental and numerical studies, the flow development past a single step cylinder was investigated. The single step cylinder model is comprised of a small diameter cylinder (d) attached coaxially to a large diameter cylinder (D). The results show that three distinct spanwise vortex cells form in the step cylinder wake: a single vortex shedding cell in the wake of the small cylinder (the S-cell) and two vortex shedding cells in the wake of the large cylinder, one in the region downstream of the step (the N-cell) and the other away from the step (the L-cell). Due to the differences in vortex shedding frequencies between the three cells, complex vortex connections occur in two vortex-interaction regions located between the adjacent cells. The region at the boundary between the S-cell and the N-cell is relatively narrow and its spanwise extent does not fluctuate significantly. In this region, vortex dislocations manifested as half-loop connections between two S-cell vortices of opposite sign. In contrast, the region at the boundary between the N-cell and the L-cell exhibits a transient behavior, with large scale vortex dislocations causing cyclic variation in the extent of N-cell vortices. For Re = 300 and 1050, small scale streamwise vortices forming in the wake complicate the vortex dynamics within the adjacent S-cell and L-cell. There is no significant Reynolds number effect on the average spanwise extent of the vortex cells and the two transition regions between neighboring cells. Finally, formation of N-cell vortices is linked to downwash fluctuations near the step. The flow development past a dual step cylinder was studied experimentally for Re = 1050. The dual step cylinder model is comprised of a small diameter cylinder (d) and a large diameter cylinder (D) mounted at the mid-span of the small cylinder. The experiments were completed for a range of large cylinder aspect ratios 0.2 ≤ L/D ≤ 17. The flow development is highly dependent on the aspect ratio of the large cylinder, L/D. The results identify four distinct flow regimes: (i) for L/D = 17, three vortex shedding cells form in the wake of the large cylinder, one central cell and two cells of lower frequency extending over about 4.5D from the large cylinder ends, (ii) for 7 < L/D ≤ 14, a single vortex shedding cell forms in the wake of the large cylinder, whose shedding frequency decreases with decreasing L/D, (iii) for 2 ≤ L/D ≤ 7, vortex shedding in the wake of the large cylinder is highly three-dimensional, with vortices deforming in the near wake, (iv) for 0.2 ≤ L/D ≤ 1, only small cylinder vortices are shed in the wake and can form vortex connections across the wake of the large cylinder.

Subjects/Keywords: vortex shedding; flow visualization; computational fluid dynamics; numerical simulation; laser induced fluorescence; laser doppler velocimetry; circular cylinder; finned cylinder; step cylinder; dual step cylinder

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APA (6^th Edition):

Morton, C. R. (2010). Experimental and Numerical Investigations of the Flow Development over Circular Cylinders with Stepwise Discontinuities in Diameter. (Thesis). University of Waterloo. Retrieved from http://hdl.handle.net/10012/5470

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Morton, Christopher R. “Experimental and Numerical Investigations of the Flow Development over Circular Cylinders with Stepwise Discontinuities in Diameter.” 2010. Thesis, University of Waterloo. Accessed March 08, 2021. http://hdl.handle.net/10012/5470.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Morton, Christopher R. “Experimental and Numerical Investigations of the Flow Development over Circular Cylinders with Stepwise Discontinuities in Diameter.” 2010. Web. 08 Mar 2021.

Vancouver:

Morton CR. Experimental and Numerical Investigations of the Flow Development over Circular Cylinders with Stepwise Discontinuities in Diameter. [Internet] [Thesis]. University of Waterloo; 2010. [cited 2021 Mar 08]. Available from: http://hdl.handle.net/10012/5470.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Morton CR. Experimental and Numerical Investigations of the Flow Development over Circular Cylinders with Stepwise Discontinuities in Diameter. [Thesis]. University of Waterloo; 2010. Available from: http://hdl.handle.net/10012/5470

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of Dundee

9. Kokkalis, Efstratios. Fluid dynamic assessments of spiral flow induced by vascular grafts.

Degree: PhD, 2014, University of Dundee

URL: https://discovery.dundee.ac.uk/en/studentTheses/5b96492f-983f-4baa-8e48-20da6939e65c ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633772

► Peripheral vascular grafts are used for the treatment of peripheral arterial disease and arteriovenous grafts for vascular access in end stage renal disease. The development… (more)

▼ Peripheral vascular grafts are used for the treatment of peripheral arterial disease and arteriovenous grafts for vascular access in end stage renal disease. The development of neo-intimal hyperplasia and thrombosis in the distal anastomosis remains the main reason for occlusion in that region. The local haemodynamics produced by a graft in the host vessel is believed to significantly affect endothelial function. Single spiral flow is a normal feature in medium and large sized vessels and it is induced by the anatomical structure and physiological function of the cardiovascular system. Grafts designed to generate a single spiral flow in the distal anastomosis have been introduced in clinical practice and are known as spiral grafts. In this work, spiral peripheral vascular and arteriovenous grafts were compared with conventional grafts using ultrasound and computational methods to identify their haemodynamic differences. Vascular-graft flow phantoms were developed to house the grafts in different surgical configurations. Mimicking components, with appropriate acoustic properties, were chosen to minimise ultrasound beam refraction and distortion. A dual-beam two-dimensional vector Doppler technique was developed to visualise and quantify vortical structures downstream of each graft outflow in the cross-flow direction. Vorticity mapping and measurements of circulation were acquired based on the vector Doppler data. The flow within the vascular-graft models was simulated with computed tomography based image-guided modelling for further understanding of secondary flow motions and comparison with the experimental results. The computational assessments provided a three-dimensional velocity field in the lumen of the models allowing a range of fluid dynamic parameters to be predicted. Single- or double-spiral flow patterns consisting of a dominant and a smaller vortex were detected in the outflow of the spiral grafts. A double- triple- or tetra-spiral flow pattern was found in the outflow of the conventional graft, depending on model configuration and Reynolds number. These multiple-spiral patterns were associated with increased flow stagnation, separation and instability, which are known to be detrimental for endothelial behaviour. Increased in-plane mixing and wall shear stress, which are considered atheroprotective in normal vessels, were found in the outflow of the spiral devices. The results from the experimental approach were in agreement with those from the computational approach. This study applied ultrasound and computational methods to vascular-graft phantoms in order to characterise the flow field induced by spiral and conventional peripheral vascular and arteriovenous grafts. The results suggest that spiral grafts are associated with advanced local haemodynamics that may protect endothelial function and thereby may prevent their outflow anastomosis from neo-intimal hyperplasia and thrombosis. Consequently this work supports the hypothesis that spiral grafts may decrease outflow stenosis and hence improve patency…

Subjects/Keywords: 617.4; Spiral flow; Disturbed flow; Double spiral flow; Dean flow; Multiple spiral flow; Secondary flow motions; Flow stagnation; Flow separation; Flow instability; Peripheral arterial disease; End stage renal disease; Haemodialysis; Haemodynamics; Vascular graft; Prosthetic graft; Bypass graft; Arteriovenous graft; Peripheral vascular graft; AV graft; PV graft; Spiral flow graft; Spiral graft; Flow modification graft; Doppler ultrasound; Colour Doppler; Vector Doppler ultrasound; Flow phantom; Fluid dynamics; Fluid mechanics; Computational fluid dynamics; 31. Polyvinyl alcohol cryogel; Vessel mimic; Vessel mimicking tubing; Tissue mimic; Tissue mimicking material; Blood mimic; Blood mimicking material; Dual beam vector Doppler; Vorticity; Circulation; Velocity; Tangential velocity; Perpendicular velocity; In-plane velocity; Neo-intimal hyperplasia; Thrombosis; Vortical structures; Flow mixing; In-plane mixing; Image guided modelling; Wall shear stress; Helicity; Pressure drop

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APA (6^th Edition):

Kokkalis, E. (2014). Fluid dynamic assessments of spiral flow induced by vascular grafts. (Doctoral Dissertation). University of Dundee. Retrieved from https://discovery.dundee.ac.uk/en/studentTheses/5b96492f-983f-4baa-8e48-20da6939e65c ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633772

Chicago Manual of Style (16^th Edition):

Kokkalis, Efstratios. “Fluid dynamic assessments of spiral flow induced by vascular grafts.” 2014. Doctoral Dissertation, University of Dundee. Accessed March 08, 2021. https://discovery.dundee.ac.uk/en/studentTheses/5b96492f-983f-4baa-8e48-20da6939e65c ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633772.

MLA Handbook (7^th Edition):

Kokkalis, Efstratios. “Fluid dynamic assessments of spiral flow induced by vascular grafts.” 2014. Web. 08 Mar 2021.

Vancouver:

Kokkalis E. Fluid dynamic assessments of spiral flow induced by vascular grafts. [Internet] [Doctoral dissertation]. University of Dundee; 2014. [cited 2021 Mar 08]. Available from: https://discovery.dundee.ac.uk/en/studentTheses/5b96492f-983f-4baa-8e48-20da6939e65c ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633772.

Council of Science Editors:

Kokkalis E. Fluid dynamic assessments of spiral flow induced by vascular grafts. [Doctoral Dissertation]. University of Dundee; 2014. Available from: https://discovery.dundee.ac.uk/en/studentTheses/5b96492f-983f-4baa-8e48-20da6939e65c ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633772

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