Hydrodynamic Characteristics Research Articles

Hydrodynamic characteristics around offshore pipelines and oscillatory pore pressures in sand beds under combined random wave and current loads

Hydrodynamic characteristics around offshore pipelines and oscillatory pore pressures in sand beds under combined random wave and current loads

Impacts of wind forcing on microplastics kinematic in a sensitive water area.

Microplastics (MPs) have been found in different environmental department globally, and the threat to organisms posed by MPs is also widely recognized. Kinematic characteristics of low-density fiber MPs in Poyang Lake under different due-south wind were calculated by combining hydrodynamic model with particle tracking model in this study. Poyang Lake is divided into north lake and south lake for study based on its topographic and hydrodynamic characteristics, and the results are as follows: the critical wind speeds causing vertical mixing of MPs in the water column ranges from 6 to 9m·s-1 in the north lake, while it is >9m·s-1 in the south lake, and the MPs beaching rate decreases by 7.08%/(m·s-1) as the due-south wind speed increases. The MPs speed is mainly affected by surface current, while the direction of the velocity is more affected by wind. The MPs velocity in the south lake is only 27.10% of that in the north lake, and the direction is more dispersed, so the due-south wind concentrates the direction of MPs velocity more to the north in the south lake. The northern wards movement of MPs resulted in a noticeable decrease in FS in the south lake, with FS decreasing by 0.10 for every 1m·s-1 increase in wind speed, and therefore, the due-south wind reduces the ecological risk posed by MPs through reducing the range of movement and retention time. However, since the FS in the north lake has been close to the minimum value of 1, the reduction of the FS is not significant, and the wind reduces the risk mainly by shortening the retention time of the MPs. Therefore, the ecological risk caused by MPs in Poyang Lake under no or weak wind conditions should be taken into consideration.

Numerical study on hydrodynamic characteristics and heat transfer enhancement of gas-liquid Taylor flow in divergent microchannels

Numerical study on hydrodynamic characteristics and heat transfer enhancement of gas-liquid Taylor flow in divergent microchannels

Numerical study on aerodynamic and hydrodynamic load characteristics of a floating pneumatic wave energy converter under real sea conditions

Numerical study on aerodynamic and hydrodynamic load characteristics of a floating pneumatic wave energy converter under real sea conditions

Characterization of hydrodynamics around plates shaped like dragonfly wings as a sediment reduction measure in a sewer system.

Sediment control is a major concern in sewer management. Early studies focused on the parameters affecting the efficiency of existing dredging facilities, and novel long-term sediment reduction measures have not been developed. Superior sediment reduction performance has been demonstrated for plates folded at 25° placed in a pipe. In this study, flushing experiments are carried out to validate the efficacy of using hydrodynamic characteristics to analyze sediment reduction performance. A detached-eddy simulation is performed to characterize the hydrodynamics around various plates shaped like dragonfly wings placed in pipes to enhance sediment reduction performance. Experimental results indicate that the maximum sediment reduction efficiency occurs in the middle section of the plates for both coarse and fine sediment beds, where the flushing thickness is extended by 1.3 cm and 3.2 cm, respectively. However, the sediment reduction efficiency is maximized for mixed sediment beds downstream, where the flushing thickness is extended by 2.4 cm. The results of numerical simulations indicate that compared with conventional sediment reduction measures, the plates produce less detrimental effects on the streamwise velocities near the pipe bottom at the plate front and increase the time-averaged vertical and transverse velocities as well as the overall turbulent kinetic energy. Therefore, the use of plates shaped like dragonfly wings is an effective sediment reduction measure.

The influence of parameters on the hydrodynamic characteristics of oscillating water column devices: A numerical study

The influence of parameters on the hydrodynamic characteristics of OWC (oscillating water column) devices exhibits a coupling phenomenon, which is frequently neglected. To elucidate the comprehensive influence and its mechanism of structure parameters on the hydrodynamic characteristics of offshore OWC devices, a structure with a bottom plate was selected in this study. Through numerical simulation, the hydrodynamic characteristics of the chamber with variations in PTO (power take off) coefficient α, chamber length Bs, internal depth Jn, and under water length of front wall Je with different wave conditions are investigated. The following conclusions are primarily drawn: The research method of using the relative wavelength L/Bs as a non-dimensional parameter and solely varying the wavelength L has its drawbacks. In cases that L/Bs is held constant, the efficiency of chambers differing only in Bs can vary by more than 70%. The influence of each parameter on the effectiveness is interrelated. Chambers with a lower α exhibit a more pronounced impact of Bs. The efficiency of device with a smaller relative wavelength L/Bs is more significantly affected by the Jn. The mechanism by which the parameters affect efficiency is primarily since chambers with shorter Bs or greater Jn exhibit smaller deformations during internal liquid surface oscillation, resembling a more uniform oscillating water column. This allows more energy to be utilized for pushing air in and out of the chamber above, thereby enhancing the energy conversion capability. The results of this research can provide valuable insights for the design of OWC devices.

Structural and hydrodynamic characteristics of hollow cylinder during high-speed water entry

Structural and hydrodynamic characteristics of hollow cylinder during high-speed water entry

Modeling the Underwater Operation Robot Shape and Area of Thrust Surface in Agricultural Ponds Based on CFD Simulation

The underwater operation robot is an effective solution for addressing the inefficiencies and labor-intensive practices of traditional agricultural water management methods. This study aims to enhance efficiency, productivity, and resource utilization in agricultural water management by designing and analyzing an underwater-operated robot. Using SolidWorks software, the robot undergoes comprehensive stress and strain simulations to evaluate structural integrity and propeller performance, while computational fluid dynamics (CFD) simulations assess hydrodynamic performance and flow characteristics. Results from structural analysis at a depth of 3 meters reveal stress values ranging from 3.531e-07 N/m² to 3.076e+05 N/m² on the robot’s body, with minimal displacement (1.000e-30 mm to 4.634e-03 mm) and no material yielding. At 3500 rpm, stress simulations demonstrate rear propeller stress ranging from 1.921e-01 N/m² to 1.139e+05 N/m², with displacement (1.000e-30 mm to 1.9993e-04 mm), ensuring structural safety. Similarly, left and right propellers exhibit stress values from 1.202e-01 N/m² to 1.269e+05 N/m², with displacement (1.000e-30 mm to 1.545e-04 mm), confirming structural integrity. CFD simulations depict velocity (ranging from 0.895 to 3.582 m/s) and pressure (ranging from 98,021.83 to 105,498.84 Pa) variations for different movements, such as forward motion, turning left, and turning right. These simulations offer valuable insights into the robot's performance in agricultural water management. The research presents an underwater-operated robot as a promising solution for agricultural water management, offering enhanced efficiency, automation, and resource optimization, potentially reducing labor costs

Response of Soil Detachment Capacity to Hydrodynamic Characteristics Under Different Slope Gradients

The mechanism of soil detachment on steep slopes is obviously different from that on gentle slopes. However, the slope effect of soil detachment remains unclear. The objective of this study was to quantify the slope effect of soil detachment capacity at the varying hydrodynamic characteristics. In this study, the soil detachment capacity (Dc) on clay loam and hydrodynamic characteristics were measured by conducting the runoff scouring experiments at 10 slope gradients (1.7–57.7%) and 5 unit flow discharges (0.022–0.089 m2·min−1). The results showed that the relationships between Dc and hydrodynamic parameters were affected by slope gradient. Based on the optimal functional relationship, the hydrodynamic characteristics (flow velocity, flow shear stress, stream power, unit stream power, and unit energy) calculated by maximum and minimum Dc in this study changed by 19.91–95138.10%, and the Dc calculated by the maximum and minimum hydrodynamic characteristics could differ by up to nine orders of magnitude. Overall, the power function of hydrodynamic parameters was superior to the linear function in different slope gradients. The stream power was the best predictor for Dc compared with other hydrodynamic parameters. For all combinations of slope gradients, the adjusted coefficient of determination (Adj. R2) of the power relationship between Dc and stream power was 9.41–27.40% higher than it was between Dc and other hydrodynamic parameters. The coefficient and index of power function for different hydrodynamic parameters showed a trend change with increasing slope gradient, indicating that there was a slope effect on Dc. Further analysis found that Dc could be well predicted using a power combination equation of slope gradient, flow velocity, and flow depth (Adj. R2 = 0.96). This study helps to better understand the mechanism of soil detachment and emphasizes that the slope effect should be considered when establishing a soil detachment equation.

Leakage and rotordynamic coefficients of labyrinth-scallop seals

Reducing leakages and improving the rotor-dynamic damping characteristics of annular seals is an essential problem of sealing technology. A whole range of damping seals are used to seal the shafts of turbomachines, such as honeycomb, hole pattern, pocket, and scallop seals. To reduce the cost and production time, the scallop seals are increasingly used. They showed quite good dynamic and leakage characteristics in the modernization of compressors in the chemical industry. Some designs of scallop seals are able not only to increase dynamic performance (additional use of swirl brakes in the form of semi-open scallops at the inlet) but also thanks to the hybrid design of the scallop and labyrinth seal made of PEEK material, which ensures a minimum clearance between the seal and the shaft, reduce leakages of pumped fluid. This paper presents the results of calculating the rotordynamic and flow rate characteristics of scallop and labyrinth-scallop seals depending on the operating parameters using computational fluid dynamics (CFD) methods. The CFD was used to calculate the hydrodynamic and rotordynamic characteristics of the seal with shaft whirl. The rotordynamic coefficients were obtained using the frequency excitation method. The obtained characteristics were compared with experimental data available from the literature for annular and labyrinth seals. The study confirmed the relatively low leakages, the high dynamic characteristics of the labyrinth-scallop seals, and the frequency dependence of the stiffness and damping coefficients. It has been confirmed that sickle-shaped scallops create obstacles to the circumferential flow of the working medium. Reducing the circumferential gas flow increases the hydraulic resistance in the grooves and simultaneously minimizes the circulation forces that create shaft whirl, increasing vibration

Numerical Simulation Analysis of an Offshore Multi-Row Arrangement Longline Aquaculture Facility with Lantern Nets Under Environmental Loads

The structural hydrodynamic response of longline aquaculture facilities under the influence of waves and currents is complex. Studying the hydrodynamic characteristics of this aquaculture structure in complex sea environments can contribute to sustainable offshore aquaculture solutions. Thus, we established a numerical model using AquaSim2.18, a proven and effective finite element hydrodynamic software for analyzing the maximum tension in mooring lines and main lines, the displacement of the main lines, and the forces on the lantern nets under waves and currents. The results showed that positioning the system in the direction of incidence of waves and currents minimizes tension in both mooring and main lines, making a downstream arrangement optimal; compared with a single row, the maximum reduction in the tension of the mooring lines is 3.3% and 1.8% for five-row and row-row lines, respectively, and the shadow effects reduced the downstream mooring force. Additionally, line tension increased with wave height and current velocity, whereas wave periods had variable effects due to the period range; the lantern net forces increased with wave height and decreased with wave period. Wave height was also shown to influence the horizontal displacement of main lines. The findings can provide a reference for the hydrodynamic characteristics of different components of the structure.

Slow Steaming as a Sustainable Measure for Low-Carbon Maritime Transport

Reducing greenhouse gas (GHG) emissions is essential across all sectors, including the maritime transport industry. Speed reduction is a key short-term operational measure for lowering GHG emissions from ships, and its implementation has already begun. While speed reduction offers significant benefits, particularly in terms of GHG emissions reduction potential, there are concerns about its application, including increased voyage times, an increase in the number of ships required, and the fact that ships may operate in conditions quite different from those for which they were designed and optimized. This study investigates the impact of speed reduction on ship performance in calm water, using a post-Panamax container ship as an example. Numerical simulations of resistance, open-water, and self-propulsion tests were conducted for a full-scale ship and propeller, and the results were validated against extrapolated towing tank data. Hydrodynamic characteristics, fuel consumption, and carbon dioxide emissions at various speeds were then estimated. The results indicated that when constant transport work was maintained, yearly CO2 emissions decreased by −16.89% with a 10% speed reduction, −21.97% with a 20% speed reduction, and −25.74% with a 30% speed reduction. This study demonstrates that the classical cubic law for fuel oil consumption and speed dependence is not valid, as the speed exponent is lower than 3. The potential benefits and drawbacks of implementing slow steaming are discussed. Finally, this research contributes to the existing literature by evaluating the CO2 emissions reduction potential of slow steaming.

Identification of the angles of attack of a hydrodynamic anchor in comparison of numerical and physical experiments

The article is devoted to the urgent task of increasing the effectiveness of rescue operations for the protection of human life at sea by maximizing the drift of rescue vehicles using a hydrodynamic anchor. The paper defines the hydrodynamic characteristics of a hydrodynamic anchor by two different methods: numerical hydrodynamic modeling and physical experiment in a direct experimental pool by pulling a full-scale hydrodynamic anchor with fixed speeds. The identification of the angles of attack of the hydrodynamic armature was carried out in comparison of numerical and physical experiments and the results of calculations of the angles of the working stroke were shown. The angles of installation of the hydrodynamic armature for the angles of attack of the wing, as well as the angles of attack for idling were determined.

Numerical and Experimental Study on the Hydrodynamic Performance of a Sloping OWC Wave Energy Converter Device Integrated into Breakwater

This study presents numerical and experimental investigations on an oscillating water column (OWC) wave energy device integrated into a sloping breakwater. Regular waves were generated in a physical wave tank to investigate the hydrodynamic performance and extraction efficiency of the small-scale nested OWC device. Simultaneously, to complement various scenarios, numerical simulations were conducted using the open-source computational fluid dynamics platform OpenFOAM. The volume of fluid (VOF) method was employed to capture the complex evolution of the air–water interface, and an artificial source term (Forchheimer flow region) was introduced into the Navier–Stokes equations to replace the power take-off (PTO) system. By analyzing wave reflection properties, energy absorption efficiency, and wave run-up, the hydrodynamic characteristics of the inclined OWC device were explored. The comparison between the numerical and experimental results indicate a good consistence. A smaller front wall draft broadens the high-efficiency frequency bandwidth. For relatively long waves, increasing the air chamber width enhances energy conversion efficiency and reduces wave run-up. The optimal configuration was achieved with the following dimensionless parameters: front wall draft a/h=1/3, air chamber width d1/h=2/9, and slope i=2. Due to the sloped structure, when compared with a vertical OWC, long waves can more easily enter the chamber. This causes the efficient frequency bandwidth to shift towards the low frequency range, allowing more wave energy to be converted into pneumatic energy. As a result, wave run-up is reduced, enhancing the protective function of the breakwater.

A Brief Review of Hydrodynamic Circulation in the Mediterranean Gulfs

In this paper, a brief review regarding the hydrodynamic circulation of the Mediterranean gulfs is presented. Studies concerning the hydrodynamics of the Mediterranean gulfs with significant environmental and commercial importance were gathered as an initial insight of studies in the Mediterranean microtidal environment. Numerical models, field measurements, and satellite images are the methods used by the investigators for the description and prediction of the circulation in the gulfs. The basic hydrodynamic characteristics of the gulfs are mainly defined by the wind action and less by tide and baroclinicity. Most of the gulfs are characterized by a cyclonic wind-driven circulation, since the tidal effect remains weak in the Mediterranean basin. However, tidal resonance and strong currents are evident in the shallow coastal areas as well as in the wider area of straits. Basic gulfs’ characteristics are summarized in a table that gives an overview of the main Mediterranean gulfs, which can be especially useful for young researchers or new hydroenvironmental studies in the Mediterranean marine and coastal environment.

Investigation of hydrodynamic characteristics of a stationary Taylor bubble at different velocities of a downward liquid flow

Investigation of hydrodynamic characteristics of a stationary Taylor bubble at different velocities of a downward liquid flow

Numerical Simulation of Hydrodynamic Performance of an Offshore Oscillating Water Column Wave Energy Converter Device

Wave energy, as a renewable energy source, plays a significant role in sustainable energy development. This study focuses on a dual-chamber offshore oscillating water column (OWC) wave energy device and performs numerical simulations to analyze the influence of chamber geometry on hydrodynamic characteristics and wave energy conversion efficiency. Unlike existing studies primarily focused on single-chamber configurations, the hydrodynamic characteristics of dual-chamber OWCs are relatively underexplored, especially regarding the impact of critical design parameters on performance. In this study, STAR-CCM+ V2302 software (Version 2410, Siemens Digital Industrial Software, Plano, TX, USA) is utilized to systematically evaluate the effects of key design parameters (including turbine configuration, mid-wall draught depth, and wall angles) on the hydrodynamic performance, wave energy capture efficiency, and wave reflection and loading characteristics of the device. The findings aim to provide a reference framework for the optimal design of dual-chamber OWC systems. The results show that the dual-chamber, dual-turbine (2C2T) configuration offers a 31.32% improvement in efficiency compared to the single-chamber, single-turbine (1C1T) configuration at low wave frequencies. In terms of reducing wave reflection and transmission, the 2C2T configuration outperforms the dual-chamber, single-turbine configuration. When the wall angle increases from 0° to 40°, the total efficiency increases by 166.37%, and the horizontal load decreases by 20.05%. Additionally, optimizing the mid-wall draught depth results in a 9.6% improvement in efficiency and a reduction of vertical load by 11.69%.

Research on water flow characteristics and stress around bridges during floods

ABSTRACT Due to the frequent threat of floods to structures and engineering construction in rivers, in order to study the impact characteristics of river hydrodynamics on structures under excessive flow during floods, this study takes Jiefang Bridge as an example and uses the fluid volume two-phase flow model (VOF) in computational fluid dynamics (CFD), combined with advanced geometric reconstruction techniques such as iso Advector method, to simulate the dynamic changes of gas-liquid interface in the river. On the premise of guaranteeing the independence of the grid, the high precision structure grid is used for numerical simulation. The results indicate that when a flood contacts a bridge, the force on the bridge rapidly increases and fluctuates, reaching a significant peak of over 6,000,000 N. Bridge piers have a significant hindering effect on floods, and their impact gradually expands over time. Vorticity and turbulence energy analysis indicate the presence of strong flow disturbances around the bridge pier. In addition, the characteristics of the contact surface between water flow and bridges also significantly affect the stress and flow characteristics of bridges. Especially at a 45° angle of attack, the force on the bridge decreases, but the wake velocity increases.

The Sea of Azov’s Hydrodynamic Response to Different Atmospheric Forcing Resolutions

This article is devoted to the analysis of the simulated meteorological and hydrodynamic characteristics of the Sea of Azov using the WRF (Weather Research and Forecasting) model and INMOM (Institute of Numerical Mathematics Ocean Model). The goal is to investigate the sea’s response to atmospheric forcing using two different horizontal resolutions. A comparison of the atmospheric simulation results with available meteorological in situ data from the land-based hydrometeorological stations (HMSs) did not reveal any significant differences between the simulations with different atmospheric forcing resolutions. A spatiotemporal analysis of the WRF model and INMOM results showed the most prominent differences along the entire coastal zone, especially in Taganrog Bay, along the spits in the north part of the sea, and in the Kerch Strait. Here, the wind speed obtained at a high spatial resolution (3.3 km) was ~10–15% higher than that obtained at a coarse resolution (10 km), and the surface and bottom currents were up to ~40% and ~15% higher. In marine coastal zones, the greatest differences were noted in a band of ~5 km, and differences in the rest of the Sea of Azov were negligible. An analysis of the bottom current speed revealed the presence of a counter-current flowing into Taganrog Bay. This shows the necessity of using three-dimensional marine circulation models to study the Sea of Azov’s dynamics.

Experimental Study of Submarine Pipeline with Geotextile and Stone Cover Protection Under the Superposition of Waves and Currents

Submarine pipelines are the main transport carriers of marine resources. In order to protect these pipelines, geotextile and stone covering measures are adopted in this paper and the protective effect is studied. A sequence of physical model tests was conducted to carry out the research. The hydrodynamic characteristics and seabed oscillation response of the seabed surrounding the pipeline were analyzed with or without geotextile and stone cover protection, and it was found that they were affected by waves (and currents). The experimental results show the following: (1) comparing the regular wave and current with the regular wave alone, it is found that forward current promotes wave propagation and reverse current inhibits wave propagation; (2) the protective effect of geotextile and stone covering measures on different positions of the pipeline (the front, the bottom, and the back of the pipe) is basically same; (3) in the case of waves with large wave heights and long wave periods superimposed with ocean currents, the protective effect of geotextile and stone coverings on the hydrodynamic and seabed pore pressure around the pipeline is more significant.