Numerical simulation of the impact of an integrated renovation project on the Maowei Sea hydrodynamic environment

Integrated renovation projects are important for marine ecological environment protection. Three-dimensional hydrodynamics and water quality models are developed for the Maowei Sea to assess the hydrodynamic environment base on the MIKE3 software with high resolution meshes. The results showed that the flow velocity changed minimally after the project, decreasing by approximately 0.12 m/s in the east of the Maowei Sea area and increasing by approximately 0.01 m/s in the northeast of the Shajing Port. The decrease in tidal prism (~ 2.66 × 106 m3) was attributed to land reclamation, and accounted for just 0.86% of the pre-project level. The water exchange half-life increased by approximately 1 day, implying a slightly reduced water exchange capacity. Siltation occurred mainly in the reclamation and dredging areas, amounting to back-silting of approximately 2 cm/year. Reclamation project is the main factor causing the decrease of tidal volume and weakening the hydrodynamics in Maowei Sea. Adaptive management is necessary for such a comprehensive regulation project. According to the result, we suggest that reclamation works should strictly prohibit and dredging schemes should optimize in the subsequent regulation works.

Spatial and Temporal Vertical Distribution of Chlorophyll in Relation to Submarine Wastewater Effluent Discharges

The vertical distribution of chlorophyll in coastal waters is influenced by a combination of the hydrodynamic environment and different biotic and abiotic processes. The spatial and temporal occurrences of chlorophyll profiles provide a good representation of the changes in the marine environment. The majority of studies in the Adriatic Sea have so far been conducted in areas unaffected by anthropogenic pressure. Our study site is located near two marine outfalls, which are part of the public sewage system. This study aims to characterize the chlorophyll vertical distribution and describe its variability based on the stratification conditions and the presence of a wastewater effluent plume. Based on these conditions, we identified three characteristic scenarios/types of chlorophyll profiles. The first one occurs when the vertical mixing of the water column creates the upwelling of chlorophyll and nutrients to the upper part of the water column. The second and third scenarios occur during stratified conditions and differ by the extent of the effluent plume intrusion. Using modern fluorescence techniques, we identified and described three different vertical chlorophyll profiles, characterizing them according to their physical and biological parameters and processes. For cases with a visible effluent intrusion, we confirmed the importance of the pycnocline formation in keeping the effluent below and maintaining the higher water quality status at the top of the water column.

Change in rheotactic behavior patterns of dinoflagellates in response to different microfluidic environments

Plankton live in dynamic fluid environments. Their ability to change in response to different hydrodynamic cues is critical to their energy allocation and resource uptake. This study used a microfluidic device to evaluate the rheotactic behaviors of a model dinoflagellate species, Karlodinium veneficum, in different flow conditions. Although dinoflagellates experienced forced alignment in strong shear (i.e. “trapping”), fluid straining did not play a decisive role in their rheotactic movements. Moderate hydrodynamic magnitude (20 < |uf| < 40 µm s−1) was found to induce an orientation heading towards an oncoming current (positive rheotaxis), as dinoflagellates switched to cross-flow swimming when flow speed exceeded 50 µm s−1. Near the sidewalls of the main channel, the steric mechanism enabled dinoflagellates to adapt upstream orientation through vertical migration. Under oscillatory flow, however, positive rheotaxis dominated with occasional diversion. The varying flow facilitated upstream exploration with directional controlling, through which dinoflagellates exhibited avoidance of both large-amplitude perturbance and very stagnant zones. In the mixed layer where water is not steady, these rheotactic responses could lead to spatial heterogeneity of dinoflagellates. The outcome of this study helps clarify the interaction between swimming behaviors of dinoflagellates and the hydrodynamic environment they reside in.

Fish Lateral Line Inspired Flow Sensors and Flow-aided Control: A Review

Any phenomenon in nature is potential to be an inspiration for us to propose new ideas. Lateral line is a typical example which has attracted more interest in recent years. With the aid of lateral line, fish is capable of acquiring fluid information around, which is of great significance for them to survive, communicate and hunt underwater. In this paper, we briefly introduce the morphology and mechanism of the lateral line first. Then we focus on the development of artificial lateral line which typically consists of an array of sensors and can be installed on underwater robots. A series of sensors inspired by the lateral line with different sensing principles have been summarized. And then the applications of artificial lateral line systems in hydrodynamic environment sensing and vortices detection, dipole oscillation source detection, and autonomous control of underwater robots have been reviewed. In addition, the existing problems and future foci in this field have been further discussed in detail. The current works and future foci have demonstrated that artificial lateral line has great potentials of applications and contributes to the development of underwater robots.

Computational fluid dynamics for enhanced tracheal bioreactor design and long-segment graft recellularization

Successful re-epithelialization of de-epithelialized tracheal scaffolds remains a challenge for tracheal graft success. Currently, the lack of understanding of the bioreactor hydrodynamic environment, and its relation to cell seeding outcomes, serve as major obstacles to obtaining viable tracheal grafts. In this work, we used computational fluid dynamics to (a) re-design the fluid delivery system of a trachea bioreactor to promote a spatially uniform hydrodynamic environment, and (b) improve the perfusion cell seeding protocol to promote homogeneous cell deposition. Lagrangian particle-tracking simulations showed that low rates of rotation provide more uniform circumferential and longitudinal patterns of cell deposition, while higher rates of rotation only improve circumferential uniformity but bias cell deposition proximally. Validation experiments with human bronchial epithelial cells confirm that the model accurately predicts cell deposition in low shear stress environments. We used the acquired knowledge from our particle tracking model, as a guide for long-term tracheal repopulation studies. Cell repopulation using conditions resulting in low wall shear stress enabled enhanced re-epithelialization of long segment tracheal grafts. While our work focuses on tracheal regeneration, lessons learned in this study, can be applied to culturing of any tissue engineered tubular scaffold.

Fibrinogen and Fibrin Differentially Regulate the Local Hydrodynamic Environment in Neutrophil–Tumor Cell–Endothelial Cell Adhesion System

As cancer is one of the major fatal diseases for human beings worldwide, the metastasis of tumor cells (TCs) from a blood vessel to an adjacent organ has become a focus of research. A tumor metastasis theory named the “two-step theory” pointed out that polymorphnuclear neutrophils (PMNs) could facilitate TC adhesion on an endothelial monolayer under flow, which was regulated by shear flow and promoted by fibrinogen and fibrin. In order to further understand the role of hydrodynamics played in the “two-step theory”, we improved our side-view micro-particle imaging velocimetry (PIV) system and successfully measured the flow velocity profiles around adherent PMNs and TCs on an endothelial monolayer in the presence of soluble fibrinogen or fibrin under shear flow. Combined with a computational fluid dynamics simulation, we found that: (1) soluble fibrinogen and fibrin influenced the variations of relative shear rates above an adhered PMN and an adherent TC at different PMN-to-TC position states; (2) compared with soluble fibrinogen, soluble fibrin made the curves of relative shear rates above an adherent cell flatter. Soluble fibrin might increase the collision frequency and affect the contact time and contact area between PMNs, TCs, and endothelium cells, resulting in the enhancement of TC adhesion and retention on an endothelial monolayer.

Environmental Assessment of Xinhe Beach Development

The proliferation of beach renovation is affecting the change of the landform of the coast and threatening the ecological environment. Therefore, it is necessary to assess the impact on the environment after the beach is transformed. The survey area is located near the Shipu fishing port in the south of Ningbo City, Zhejiang Province. Based on the Delft-3D grid nesting model and wave-fluid coupling model, the astronomical tide and hydrodynamic environment of the 30 days before the construction were simulated. After the beach was rebuilt and sand was added and the spur dike was added, the astronomical tide and hydrodynamic environment were again simulated. Finally, based on the simulated data, the water level, velocity field, effective wave height distribution, and siltation and siltation of Xinhe Beach were obtained. Xinhe Beach's environmental damage risk indicators can be evaluated based on water level, velocity field, effective wave height direction and sediment erosion and deposition. Artificial sanding and construction of spur dikes will change the hydrodynamics and scouring and siltation of Xinhe Beach, but have little effect on the coastal terrain and ecological environment.