Now showing 1 - 5 of 10
- ItemBiophysical flocculation reduces variability of cohesive sediment settling velocity(Communications Earth & Environment, 2023-04-24) Ye, L.; Penaloza-Giraldo, J. A.; Manning, A. J.; Holyoke, J.; Hsu, T.-J.Biophysical cohesion, introduced predominantly by Extracellular Polymeric Substances (EPS) during mineral flocculation in subaqueous environments, plays important role in morphodynamics, biogeochemical cycles and ecosystem processes. However, the mechanism of how EPS functioning with cohesive particles and affects settling behaviors remain poorly understood. We measure initial flocculation rate, floc size and settling velocity of mineral and artificial EPS (Xanthan gum) mixtures. Combining results from these and previous studies demonstrate coherent intensification of EPS-related flocculation compare with those of pure mineral and oil-mineral mixtures. Importantly, the presence of EPS fundamentally changes floc structure and reduces variability of settling velocity. Measured data shows that ratios of microfloc and macrofloc settling velocity for pure mineral flocs is 3.9 but greatly reduced to a lowest value of 1.6 due to biological EPS addition. The low variability of settling velocity due to EPS participation explains the seemingly inconsistent results previously observed between field and laboratory studies.
- ItemFourth-order stability analysis for capillary-gravity waves on finite-depth currents with constant vorticity(Physics of Fluids, 2023-02-01) Dhar, A. K.; Kirby, James T.We derive a fourth-order nonlinear evolution equation (NLEE) for narrow-banded Stokes wave in finite depth in the presence of surface tension and a mean flow with constant vorticity. The two-dimensional capillary-gravity wave motion on the surface of finite depth is considered here. The analysis is limited to one horizontal dimension, parallel to the direction of wave propagation, in order to take advantage of a formulation using potential flow theory. This evolution equation is then employed to examine the effect of vorticity on the Benjamin–Feir instability (BFI) of the Stokes capillary-gravity wave trains. It is found that the vorticity modifies significantly the modulational instability and in the case of finite depth, the combined effect of vorticity and capillarity is to enhance the instability growth rate influenced by capillarity when the vorticity is negative. The key point is that the present fourth-order analysis exhibits considerable deviations in the stability properties from the third-order analysis and gives better results consistent with the exact numerical results. Furthermore, the influence of linear shear current on Peregrine breather (PB) is studied.
- ItemA surface porosity approach for eliminating artificial ponding in coastal salt marsh simulations(Coastal Engineering, 2022-11-23) Deb, Mithun; Kirby, James T.; Abdolali, Ali; Shi, FengyanHydrodynamic processes over marsh topography are significantly affected by surface defects such as cuts and rills on channel berms and platforms. These meter-scale features are often missing in the model representation due to the spatial resolution available from data sources, as well as incomplete resolution in the model grid itself. To minimize the artificial hydraulic isolation in the numerical models, we propose implementing an effective porosity algorithm on the marsh surface by considering the fine-scale topography over marsh depressions that control the drainage process. The modification is carried out to eliminate artificial ponding effects observed in model simulations in Bombay Hook National Wildlife Refuge, DE, USA using the original FVCOM code. Results from the revised and original FVCOM models are compared with pressure gauge data collected from an isolated depression in the marsh platform. The new implementations for proper wetting and drying are efficient and accurate for hydrodynamic modeling inside a complex salt-marsh system, which constitutes a major breakthrough in the context of increasing need for better understanding of physical and morphological changes in valuable coastal ecosystems.
- ItemMomentum Balance Analysis of Spherical Objects and Long-Term Field Observations of Unexploded Ordnance (UXO) in the Swash Zone(Journal of Marine Science and Engineering, 2023-01-03) Cristaudo, Demetra; Gross, Benedict M.; Puleo, Jack A.Military activity has resulted in unexploded ordnance (UXO) existing in the nearshore. Understanding and predicting UXO behavior is important for object identification, and management. Here, two studies (laboratory and fieldwork) have been conducted to observe UXO surrogates in the swash zone and relate burial and migration to the underlying forcing conditions. A small-scale laboratory dam-break study was conducted to quantify migration of varying density spherical objects at different locations on a sloping, mobile, sandy bed. A moment balance was applied to derive two data-driven relationships to: (1) predict moments from the cross-shore flow velocity with predictions confined within a factor of two; (2) predict upslope or downslope migration from the moment. Fitting coefficients for the upslope and downslope relationships vary as a function of density, initial position, and burial. A field study was also conducted to investigate long-term behavior of eight varieties of UXO surrogates. Of the 129 observations, 56% were mobilized of which 76% were directed offshore. Burial/exposure was mostly related to far-field beach accretion/erosion (67%). However, scouring processes were also observed. Data showed that migration is likely a short-term process and most munitions will ultimately scour into a mobile bed.
- ItemLayout and design optimization of ocean wave energy converters: A scoping review of state-of-the-art canonical, hybrid, cooperative, and combinatorial optimization methods(Energy Reports, 2022-11-23) Golbaz, Danial; Asadi, Rojin; Amini, Erfan; Mehdipour, Hossein; Nasiri, Mahdieh; Etaati, Bahareh; Naeeni, Seyed Taghi Omid; Neshat, Mehdi; Mirjalili, Seyedali; Gandomi, Amir H.Ocean Wave energy is becoming a prominent technology, which is considered a vital renewable energy resource to achieve the Net-zero Emissions Plan by 2050. It is also projected to be commercialized widely and become a part of the industry that alters conventional energy technologies in the near future. However, wave energy technologies are not entirely yet developed and mature enough, so various criteria must be optimized to enter the energy market. In order to maximize the performance of wave energy converters (WECs) components, three challenges are mostly considered: Geometry, Power Take-off (PTO) parameters, and WECs’ layout. As each of such challenges plays a meaningful role in harnessing the maximum power output, this paper systematically reviews applied state-of-the-art optimization techniques, including standard, hybrid, cooperative, bi-level and combinatorial strategies. Due to the importance of fidelity and computational cost in numerical methods, we also discuss approaches to analyzing WECs interactions’ developments. Moreover, the benefits and drawbacks of the popular optimization methods applied to improve WEC parameters’ performance are summarized, briefly discussing their key characteristics. According to the scoping review, using a combination of bio-inspired algorithms and local search as a hybrid algorithm can outperform the other techniques in layout optimization in terms of convergence rate. A review of the geometry of WECs has emphasized the indispensability of optimizing and balancing design parameters with cost issues in multimodal and large-scale problems.