Transformation of Nonlinear Waves in the Presence of Wind, Current, and Vegetation

Accurate prediction of extreme wave events is crucial for the safe maritime activities and offshore operations. Improved knowledge of wave dissipation mechanisms due to breaking and vegetation leads to accurate wave forecast, protecting life and property along the coast. The scope of the thesis is to examine the wave transformations in the presence of wind, current, and vegetation, using a two-phase flow solver based on the open-source platform OpenFOAM. The Reynolds-Averaged Navier-Stokes (RANS) equations are coupled with a Volume of Fluid (VOF) surface capturing scheme and a turbulence closure model. This RANS-VOF model is adapted to develop a numerical wind-wave-current flume suitable for studying wind-wave, wave-current, and wave-structure interactions. Proper wind/wave/current boundary conditions are devised, two-equation and Shear Stress Transport (SST) turbulence models modified, and new modules capturing fluid-structure interactions are developed. The wind and current effects on the evolution of a two-dimensional dispersive focusing wave group are examined. The model predictions are validated against experimental measurements with and without following wind. The effects of wind-driven current and opposing wind are investigated based on additional model results. The air flow structure above a plunging breaking wave group is examined. The RANS-VOF model is also applied to investigate the phenomenon of wave breaking and blocking due to strong opposing currents on a flat bottom. The geometric and hydrodynamic characteristics, i.e., the breaking criterion, the wave set-down and set-up, the energy dissipation, and the turbulence and vorticity generated in the wave breaking/blocking process are examined. A new coupled wave-vegetation interaction model is developed by coupling the RANS-VOF wave model with a Finite Element Method (FEM) based structure model using an immersed boundary approach. The wave height decay along and wave kinematics within a vegetation patch are examined. The study has contributed to understanding of the wind effects on the extreme wave formation and breaking, the characteristics of current-induced wave breaking/blocking, and the vegetation effect on wave transformations. Insights gained from this study shed some light on the formation mechanism for rogue waves, and the breaking- and vegetation-induced dissipation formulations in the present wave prediction and circulation models

Wind and current effects on extreme wave formation and breaking

AbstractWind and current effects on the evolution of a two-dimensional dispersive focusing wave group are investigated using a two-phase flow model. A Navier–Stokes solver is combined with the Smagorinsky subgrid-scale stress model and volume of fluid (VOF) air–water interface capturing scheme. Model predictions compare well with the experimental data with and without wind. It was found that the following and opposing winds shift the focus point downstream and upstream, respectively. The shift of focus point is mainly due to the action of wind-driven current instead of direct wind forcing. Under strong following/opposing wind forcing, there appears a slight increase/decrease of the extreme wave height at the focus point and an asymmetric/symmetric behavior in the wave focusing and defocusing processes. Under a weak following wind, however, the extreme wave height decreases with increasing wind speed because of the dominant effect of the wind-driven current over direct wind forcing. The vertical shear of the wind-driven current plays an important role in determining the location of and the extreme wave height at the focus point under wind actions. Furthermore, it was found that the thin surface layer current is a better representation of the wind-driven current for its role in wind influences on waves than the depth-uniform current used by previous studies. Airflow structure above a breaking wave group and its link to the energy flux from wind to wave as well as wind influence on breaking are also examined. The flow structure in the presence of a following wind is similar to that over a backward-facing step, while that in the presence of an opposing wind is similar to that over an airfoil at high angles of attack. Both primary and secondary vortices are observed over the breaking wave with and without wind of either direction. Airflow separates over the steep crest and causes a pressure drop in the lee of the crest. The resulting form drag may directly affect the extreme wave height. The wave breaking location and intensity are modified by the following and opposing wind in a different fashion.</jats:p

Numerical Simulations of Spread Characteristics of Toxic Cyanide in the Danjiangkou Reservoir in China under the Effects of Dam Cooperation

Many accidents of releasing toxic pollutants into surface water happen each year in the world. It is believed that dam cooperation can affect flow field in reservoir and then can be applied to avoiding and reducing spread speed of toxic pollutants to drinking water intake mouth. However, few studies investigated the effects of dam cooperation on the spread characteristics of toxic pollutants in reservoir, especially the source reservoir for water diversion with more than one dam. The Danjiangkou Reservoir is the source reservoir of the China’ South-to-North Water Diversion Middle Route Project. The human activities are active within this reservoir basin and cyanide-releasing accident once happened in upstream inflow. In order to simulate the spread characteristics of cyanide in the reservoir in the condition of dam cooperation, a three-dimensional water quality model based on the Environmental Fluid Dynamics Code (EFDC) has been built and put into practice. The results indicated that cooperation of two dams of the Danjiangkou Reservoir could be applied to avoiding and reducing the spread speed of toxic cyanide in the reservoir directing to the water intake mouth for water diversions

Asynchronous vibration response characteristics of connectors with looseness fault and its verification

For the universal phenomenon of the aero-engine connectors with the looseness fault, a single degree of freedom lumped mass model was established and a looseness fault model was introduced. The response of the system was obtained by numerical integration methods and the asynchronous response characteristics were analyzed. The experiments were conducted on the connectors with looseness clearance. It is found that the acceleration response of the mass block after noise reduction has up-down asymmetrical impact characteristics in the waveform, also the pseudo-critical subharmonic resonance and the pseudo-critical ultra-harmonic resonance appear in frequency spectrum. These characteristics are in agreement with the results of the numerical simulation, which can be identified as the characteristics of the looseness fault. The reason leading to the looseness characteristics is that the period of stiffness changes in the period of the rotating speed. When the changing period of stiffness is equivalent to the vibration period, frequency multiplication will appear and the natural frequency of the system will be excited at specific speeds. When the changing period of stiffness is equivalent to n times the vibration period, 1/n frequency division and frequency multiplication will appear and the natural frequency of the system will be excited at specific speeds

Multiple myeloma with cardiac amyloidosis and secondary adrenal cortical dysfunction: a case report

Multiple myeloma is a malignant proliferative disease of plasma cells, and some patients may develop systemic amyloidosis. Cardiac amyloidosis is a common cause of death in these patients. Secondary adrenal insufficiency is caused by dysfunction of the hypothalamus and/or the pituitary gland, and multiple myeloma cases combined with secondary adrenal cortical dysfunction have been rarely reported in China. The patient, 55-year-old, male, was admitted to the Emergency Department of Shenzhen Luohu People's Hospital on June 5, 2018 due to "repeated chest tightness and fatigue for 7 months, and fainting for 1 hour". Later, he was transferred to Department of Hematology and was diagnosed as having multiple myeloma (λ light chain type) with systemic amyloidosis through bone marrow puncture and other examinations. The first course regimen of chemotherapy was bortezomib, cyclophosphamide, and dexamethasone. After the course, the patient was infected with a mixture of bacteria and fungi in the lung and had improvement after treatment. Then the regimen was adjusted to bortezomib and dexamethasone from the second course. After the fourth course, the patient achieved complete remission of multiple myeloma. After the fifth course, the patient experienced severe pulmonary-mixed infection again, which was improved after treatment. Thereafter, the patient presented with refractory hypotension, and decreased levels of cortisol and adrenocorticotropic hormone (ACTH), which was diagnosed as secondary adrenal cortical dysfunction. Hydrocortisone replacement therapy was administered. After 9 courses of chemotherapy, the patient received maintenance treatment with ixazomib. Multiple myeloma was evaluated as a stringent complete response. Cardiac amyloidosis was evaluated as a very good partial response, and secondary adrenal cortical dysfunction was treated with hydrocortisone maintenance therapy and with the cortisol level in the normal range

Underlying burning resistant mechanisms for titanium alloy

The "titanium fire" as produced during high pressure and friction is the major failure scenario for aero-engines. To alleviate this issue, Ti-V-Cr and Ti-Cu-Al series burn resistant titanium alloys have been developed. However, which burn resistant alloy exhibit better property with reasonable cost needs to be evaluated. This work unveils the burning mechanisms of these alloys and discusses whether burn resistance of Cr and V can be replaced by Cu, on which thorough exploration is lacking. Two representative burn resistant alloys are considered, including Ti14(Ti-13Cu-1Al-0.2Si) and Ti40(Ti-25V-15Cr-0.2Si)alloys. Compared with the commercial non-burn resistant titanium alloy, i.e., TC4(Ti-6Al-4V)alloy, it has been found that both Ti14 and Ti40 alloys form "protective" shields during the burning process. Specifically, for Ti14 alloy, a clear Cu-rich layer is formed at the interface between burning product zone and heat affected zone, which consumes oxygen by producing Cu-O compounds and impedes the reaction with Ti-matrix. This work has established a fundamental understanding of burning resistant mechanisms for titanium alloys. Importantly, it is found that Cu could endow titanium alloys with similar burn resistant capability as that of V or Cr, which opens a cost-effective avenue to design burn resistant titanium alloys.Comment: 6 figure

Stability of copper acetate at high P-T and the role of organic acids and CO2 in metallic mineralization

Many metal deposits were formed by carbonic fluids (rich in CO2) as indicated by fluid inclusions in minerals, but the precise role of CO2 in metal mineralization remains unclear. The main components in fluid inclusions, i.e. H2O and CO2, correspond to the decomposed products of organic acids, which lead us to consider that in the mineralization process the organic acids transport and then discharge metals when they are stable and unstable, respectively. Here we show that the thermal stability of copper acetate solution at 15–350 °C (0.1–830 MPa) provides insight as to the role of organic acids in metal transport. Results show that the copper acetate solution is stable at high P-T conditions under low geothermal gradient of <19 °C/km, with an isochore of P = 1.89 T + 128.58, verifying the possibility of copper transportation as acetate solution. Increasing geothermal gradient leads to thermal dissociation of copper acetate in the way of 4Cu(CH3 COO)2 + 2H2O = 4Cu + 2CO2 + 7CH3COOH. The experimental results and inferences in this contribution agree well with the frequently observed fluid inclusions and wall-rock alterations of carbonate, sericite and quartz in hydrothermal deposits, and provide a new dimension in the understanding of the role of CO2 during mineralization

Porous chitosan by crosslinking with tricarboxylic acid and tuneable release

Chitosan hydrogels crosslinked with 1,3,5-benzene tricarboxylic acid (BTC) are readily prepared at room temperature by adding aqueous chitosan solution dropwise into BTC-ethanol solution. Highly interconnected porous chitosan materials are subsequently prepared by freeze-drying the chitosan hydrogels. These chitosan materials show porous structures with smaller pores than conventionally prepared chitosan hydrogels via crosslinking with NaOH, genipin or sodium triphosphate. This method of forming chitosan hydrogels with BTC provides the advantage of facile encapsulation of both hydrophobic and hydrophilic compounds, as demonstrated with the model dyes (Oil Red O and Rhodamine B). The release of the hydrophilic dye from the chitosan hydrogels is demonstrated and can be tuned by BTC/chitosan concentrations and the hydrogel drying methods. However, the release of encapsulated hydrophobic dye is negligible