28 research outputs found
BARDEX II: Nearshore sediment resuspension and bed morphology
No full textSediment resuspension in the region outside the surf zone is known to contribute to the morphological response of barrier beaches to wave forcing, such as onshore bar migration processes. However, few measurements in this region exist, limiting our ability to quantify its contribution. These processes are complicated by the presence of bedforms in the nearshore, which alter the sand transport processes while modifying bed roughness in a complex feedback mechanism. The Hydralab IV funded BARDEX II experiments, which took place in the Delta Flume in 2012, were used to provide measurements of these processes in the nearshore of a sandy barrier beach (D50 = 0.42mm) under a range of wave conditions (Hs = 0.3 - 0.8 m; Tp = 4 – 2 s) and water levels, through deployment of a suite of acoustic instruments measuring flow velocity, near-bed turbulence, sediment resuspension profiles and bed morphology in cross-section and plan view. Initial findings indicate that sediment suspension in the nearshore appears to be controlled by a combination of near-bed turbulent bursting processes which results in near-instantaneous low concentration suspensions restricted to the bottom boundary layer, and vortex shedding from bedforms which results in higher concentration suspensions which are larger in scale than vertical eddy sizes, and perpetuate outside of the bottom boundary layer
Observations of a tidal intrusion front in a tidal channel
No full textA visible front indicated by a surface colour change, and sometimes associated with foam or debris lines, was observed in a tidal channel during neap tide. This is an example of a tidal intrusion front occurring in the absence of sudden topographical changes or reversing flows, typically reported to be associated with such fronts. Detailed Acoustic Doppler Current Profiler and conductivity/temperature/depth measurements were taken on repeated transects both with fronts apparent and with fronts absent. The results indicated that the front occurred as a result of stratification, which was sustained by the buoyancy flux and the weak tide-induced mixing during neap ebb tide. The stronger tide-induced mixing during spring tide restrained stratification, leading to the absence of a front. The mechanism of the frontogenesis was the density gradient between the stratified water formed during neap ebb tide, and the more mixed seawater during neap flood tide; thus, the water on the landward (southwestern) side of the front was stratified, and that on the seaward side (northeastern) of the front was vertically well mixed. Gradient Richardson number estimates suggest that the flow between the stratified and mixed water was near the threshold 0.25 for shear instability. Meanwhile, the density gradient would provide an initial baroclinic contribution to velocity convergence, which is indicated by the accumulation of buoyant matter such as foam, grass, and debris into a sharply defined line along the surface. The front migrates with the flood current, with a local maximum towards the eastern side of the channel, leading to an asymmetrical shape with the eastern side of the front driven further into the Tiaozhoumen tidal channel
Morphological evolution of creek networks in 10 restored coastal wetlands in the UK
No full textCoastal wetlands provide crucial ecosystem services including flood protection and carbon storage, but are being lost rapidly worldwide to the combined effects of sea-level rise, erosion and coastal urbanisation. Managed Realignment (MR) aims to mitigate for these losses by restoring reclaimed land to tidal influence. Data of creek evolution is critical to assess the performance of design strategies and improve design and implementation practices. This data descriptor provides a dataset of the horizontal morphological evolution of creek systems from various initial conditions in 10 MR schemes across the UK. Using a semi-automated workflow, morphological creek parameters were extracted from 52 lidar datasets at 1 m horizontal resolution spanning 2 to 20 years post-breach. This constitutes the most comprehensive systematic monitoring of MR creek morphology to date. The dataset will assist future MR design and provide baseline morphological information for ecological and biogeochemical surveying
Seasonal mobility of transverse finger bars within a mixed sand-gravel bay measured using X-band Radar
No full textTransverse finger bars have largely been associated with sandy coasts. Here we show that these features persist within a wider mixed sediment environment, adjacent to a shingle cuspate foreland, which has not been previously reported. Details of the bars' characteristics were gleaned from analysis of bathymetry data, whilst weekly migration rates were inferred from remote sensing of the sea surface roughness as a proxy of undulating bedforms, using X-band radar reflectance data. The bars were on average ~380 m long, had wavelengths of ~160 m, amplitudes of approximately 0.2 to 0.6 m and were orientated 30° to shore normal. They were found in water depths between −3.3 and −5.8 m Ordnance Datum. The bars migrated by approximately 150 m over the first ‘winter’ observation period (15/11/2020–02/04/2021) and 70 m in the following winter period (Sept 2021–Feb 2022) but showed virtually no signs of movement during the intervening summer months. Analysis of hydrodynamic conditions suggested the bar mobility was related to the dominant longshore currents resulting from high angle, south westerly waves. Low amplitude rhythmic bedforms were also found in the upper beach, migrating at a similar rate to the nearshore bars, which are thought to be driven by high-angle wave instability
Will the declining sea ice extent in the Arctic cause a reversal of net benthic-pelagic exchange directions?
No full textIn the Arctic, loss of sea ice due to climate change and the northward shift of the Polar Front are predicted to affect many ecosystem processes such as the ecologically important process of particulate and dissolved matter exchange between the seafloor and the water column. In this study, we show for the first time that a change from an ice-covered, Arctic water-dominated system to an Atlantic -dominated ice-free one is likely to reverse seafloor-water exchange directions. A north – south transect across the Barents Sea was studied over two years with differing sea ice cover conditions, recording biological, biogeochemical, hydrographic, geophysical, and oceanographic data. There was a clear difference between the direction and magnitude of key benthic-pelagic fluxes present at Atlantic-dominated environments, and those in Arctic water – dominated ones. Currently, the southern Barents Sea exhibits a net downward flux of dissolved matter and a net upward flux of particulates, while in the northern region solutes fluctuate upwards and particulates downward, making the North a more depositional region that promotes near-surface primary productivity. Broad scale assessments of net fluxes in rapidly changing ecosystems should be employed to monitor impacts of climate change and anthropogenic activities
Transitions in modes of coastal adaptation: addressing blight, engagement and sustainability
No full textCoastal defences have long provided protection from erosion and flooding to cities, towns and villages. In many parts of the world, continued defence is being questioned due to both environmental, sustainability and economic considerations. This is exemplified in England and Wales, where strategic Shoreline Management Plans envisage realignment of many protected coasts, often with low population densities, over the coming decades. The policy transition from protection to realignment is often resisted by affected communities and can have high political costs. Whilst some preparations for such transitions have been made, the communities affected are often not fully aware of the implications of policy change, and this brings the potential for blight. In this paper, we investigate the challenges of implementing transitions in coastal policy within England and Wales. The analysis is based on data obtained from three workshops held in 2019 that were attended by council members, engineers, planners, scientists and other relevant professionals. Five conditions are found to promote contention: (i) policy actors with competing priorities and different decision making time frames (immediate to decadal to a century); (ii) divergence between regulations and ad hoc political decisions (e.g. in relation to the demand for new housing); (iii) limited or non-existent funding to support policy transition; (iv) community expectation that protection is forever; and (v) a disconnection between people and ongoing coastal change. Our research indicates that transitions can be better supported through: (1) integrated multi-scalar preparedness for coastal change; (2) an accessible evidence base and future vision to nurture political confidence in adaptation; and (3) defined, time-bound and accessible diverse funding streams to achieve transitions. Critically, these generic actions need to be embedded within the local political and planning system to facilitate transition to more sustainable coasts and their communities.</p
Pecos County WW I Memorial, close-up of plaque
No full textPecos County WW I Memorial, plaque with names.
PECOS COUNTY'S CONTRIBUTION
1917 - TO THE WORLD WAR - 1919
ABLE, J.D. HOEFS, E.G. PRYOR, IKE T.
ACHTERBERG, ALBERT J. HOLLOWAY, E.H. PYLE, F.B.
ACHTERBERG, GEORGE ISAAC, JOHN J. PYLE, T.H.
BARR, R.E. JACKSON, BARNEY QUINTELA, JOSE
BENNETT, R.A. JACKSON, H.L. RIGGS, STERLING
BRAGG, W.R. JACKSON, JOE RIGGS, WALTER
BROWN, W.L. JACKSON, MARK REDWINE, W.C.
BROYLES, JACK JACKSON, W.C. RIGSBEE, JAMES E.
BROYLES, JAMES JACKSON, O.K. ROONEY, PHILIP
BURKETT, GEORGE JAMESON, W.C. ROONEY, O.A.
CAMP, JO W. JESSUP, D.M. ROONEY, V.L.
CAMPOS, ALBERTO JOHNS, URBAN ROTAN, GARNETTE
CANNON, O.C. JOHNSON, T.W. RIZ, LEANDRO
CASTRO, LIBRO LAKE, J.E. RYAN, B.H.
CHIPMAN, E. LAMBERT, J.E. RYAN, J.W.
COFFEY, W.L. LANG, C.H. SANDERSON, PRYOR
CONNER, J.R. LEWIS, THEODORE SCOTT, WILL
COSTELLO, JOSE LIGON, ASTIN SHARP, J.M.
COWGILL, F. LIGON, LLOYD SHEDD, OWEN
DACY, J. LIGON, E.B. SMITH, B.G.
DAKAN, B.B. LITTLE, R.L. SMITH, L.S.
DALTON, R. LIVINGSTON, H.R. STARNES, W.V.
DAMS, M.A. LYLE, G.C. STONE, FRANCIS
DAVIS, J.A. MAPES, EMMET STONE, L.W.
DEES, A.H. MARINES, JOSE SULLIVAN, J.L.
DUNCAN, F.C. MASON, H.F. SUMMERALL, GILES
DURAN, M. MARTIN, CHARLIE TEN EYCK, ALFRED
ELLIOTT, C.H. MARTIN, W.A. THEN EYCK, WILLIAM E.
FARRIS, C.L. MARTIN, W.L. THOMPSON, C.L.
FLORES, MANUEL McCALLUM, F.A. THOMPSON, C.P.
FORD, S.P. McDOWELL, A.W. THOMPSON, MELVIN
FRY, F.E. McKEE, J.R. TURNEY, M.L.
FRY, S. McQUARTERS, R.B. UNKEFER, C.R.
FUENTES, R. MENDEL, H.D. WALDO, A.W.
FULCHER, A.W. METZGAR, R.H. WALKER, K.B.
FREET, A.T. METCALF, CONDREY WALKER, L.R.
FLETCHER, BOB MOFFETT, J.D. WATSON, E.L.
GARCIA, S.R. MOORE, JOHN WHEELER, HENRY
GILMAN, C.E. MOORE, W.L. WESTERMAN, W.B.
GIRVIN, E.R. MUSGRAVE, W.W. WEVER, RALPH
GIVEN, R.A. NEAL, J.R. WILBANK, W.H.
GLENN, W.D. NIMON, E.J. WILBURN, C.A.
GRABLE, H.M. ONSURES, SEBERO WILEY, J.B.
GRAEFF, WALTER PASCHAL, J.H. WILLIAMS, C.W.
HALLFORD, E.W. PINA, SOTERO WILLIAMS, E.R.
HALLFORD, JOE PENA, MANUEL WILLIAMS, J.C.
MANSEN, JESS PERRY, L.N. WILLIAMSON, D.D.
HARKEY, J.R. PERRY, W.A. WINN, J.H.
HINDE, A.C. PITTAWAY, H.R. WOODRUFF, E.F.
HIRGT, E.K. POOLE, PRICE WOODWARD, FONNIE
HODGES, H.E. POWELL, W.L. YATES, J.O.
HODGES, H.L. PRIMERA, SERAPIO YEAMAN, J.O
Bonding between silicones and thermoplastics using 3D printed mechanical interlocking
No full textSilicones have desirable properties such as skin-safety, high temperature-resistance, and flexibility. Many applications require the presence of a hard body connected to the silicone. Traditionally, it has been difficult to create strong bonding between silicones and hard materials. In this study, a technique is presented to control the bonding strength between silicones and thermoplastics through mechanical interlocking. This is realized through a hybrid fabrication method where silicone is cast onto a 3D-printed mold and interlocking structure. The influence of the structure's design parameters on the bonding strength is explored through theoretical modeling and physical testing, while the manufacturability of the 3D-printed structure is ensured. A CAD tool is developed to automatically apply the interlocking structure to product surfaces. The user interface visualizes the theoretical strength of the cells as the designer adjusts the cell parameters, allowing the designer to iteratively optimize the structure to the product's load case. The bonding strength of the presented mechanical interlocking structure is more than 5.5 times higher than can be achieved with a commercially available primer. The presented technique enables custom digital design and manufacturing of durable free-form parts. This is demonstrated through application of the technique in over-molded products, airtight seals, and soft pneumatic actuators.Materials and ManufacturingMechatronic Desig
Memory-Efficient Modeling and Slicing of Large-Scale Adaptive Lattice Structures
No full textLattice structures have been widely used in various applications of additive manufacturing due to its superior physical properties. If modeled by triangular meshes, a lattice structure with huge number of struts would consume massive memory. This hinders the use of lattice structures in large-scale applications (e.g., to design the interior structure of a solid with spatially graded material properties). To solve this issue, we propose a memory-efficient method for the modeling and slicing of adaptive lattice structures. A lattice structure is represented by a weighted graph where the edge weights store the struts' radii. When slicing the structure, its solid model is locally evaluated through convolution surfaces in a streaming manner. As such, only limited memory is needed to generate the toolpaths of fabrication. Also, the use of convolution surfaces leads to natural blending at intersections of struts, which can avoid the stress concentration at these regions. We also present a computational framework for optimizing supporting structures and adapting lattice structures with prescribed density distributions. The presented methods have been validated by a series of case studies with large number (up to 100 M) of struts to demonstrate its applicability to large-scale lattice structures.</p
A Framework for Adaptive Width Control of Dense Contour-Parallel Toolpaths in Fused Deposition Modeling
No full text3D printing techniques such as Fused Deposition Modeling (FDM) have enabled the fabrication of complex geometry quickly and cheaply. Objects are produced by filling (a portion of) the 2D polygons of consecutive layers with contour-parallel extrusion toolpaths. Uniform width toolpaths consisting of inward offsets from the outline polygons produce over- and underfill regions in the center of the shape, which are especially detrimental to the mechanical performance of thin parts. In order to fill shapes with arbitrary diameter densely the toolpaths require adaptive width. Existing approaches for generating toolpaths with adaptive width result in a large variation in widths, which for some hardware systems is difficult to realize accurately. In this paper we present a framework which supports multiple schemes to generate toolpaths with adaptive width, by employing a function to decide the number of beads and their widths. Furthermore, we propose a novel scheme which reduces extreme bead widths, while limiting the number of altered toolpaths. We statistically validate the effectiveness of our framework and this novel scheme on a data set of representative 3D models, and physically validate it by developing a technique, called back pressure compensation, for off-the-shelf FDM systems to effectively realize adaptive width.Materials and ManufacturingMechatronic Desig
