Wavy Water Surface Research Articles

Numerical Study of Skipping Motion of Blended-Wing–Body Aircraft Ditching on Calm/Wavy Water

The blended-wing–body (BWB) is hoped to be the main configuration of next-generation transport aircraft. However, its large flat belly may cause a violent skipping motion during the ditching on water. In this paper, the skipping motions of a BWB aircraft ditching on calm and wavy water are numerically investigated. The finite volume method with the volume-of-fluid approach is employed to solve the unsteady Reynolds-averaged Navier–Stokes equations. A coupled method between global moving mesh and overset mesh is proposed to avoid a large background domain and improve the prediction accuracy of the free surface, and its accuracy is well validated by predicting the motions of a skipping stone, the hydrodynamic load and pressure on a flat plate in high-speed ditching, and the fifth-order Stokes wave in a dynamic wave tank. At the beginning of every surfing stage, the flat belly of BWB aircraft impacts heavily on the water surface at a smaller pitch angle and larger speed, resulting in the local vertical overload peak, which is much larger than the peak in the porpoising motion. The wavy water surface intensifies the heave and pitch motions and increases the risk of the cockpit diving into the water.

Dynamics of oil slicks on wavy water surfaces

AbstractWe hypothesize that the spread of oil slicks on the water’s surface during oil spills is significantly influenced by water wave motion at the initial or intermediate spreading stages, well before emulsification processes have a substantial impact on the oil film’s state. We demonstrate that the spreading dynamics of an oil slick on the water surface are facilitated by water waves, employing the thin film approximation. It is shown that water wave motion can rapidly deplete any oil slick, reducing the oil layer’s thickness to nearly zero. This mechanism may act as a precursor to emulsification processes, leading to the accelerated depletion of oil spills into a distribution of droplets that form an emulsion.

Study on the Polarization Pattern Induced by Wavy Water Surfaces

In nature, the wavy ocean surface is a common polarizer, which can change the polarization state of incident light by refraction and reflection and form a new polarization pattern different from the atmosphere. In this paper, we establish the polarized optical transmission model of wavy ocean surface reflection and refraction and simulate polarization patterns induced by wavy ocean surfaces. We study the polarization patterns reflected by wavy water surfaces and polarization patterns inside and outside Snell’s window under wavy ocean surfaces. The correctness of the simulation results is verified by qualitative and quantitative analysis. The environmental factors affecting the corresponding polarization patterns are discussed. Through contrastive analysis, we find that polarization patterns induced by wavy water surfaces are predictable and regular, which has great potential for human application. This kind of polarization pattern is influenced by the sun’s position and water surface condition. The study will promote the development of remote sensing, target detection, and polarization navigation.

Water Surface Acoustic Wave Detection by a Millimeter Wave Radar

Feature extraction and recognition of underwater targets are important in military and civilian areas. This paper studied water surface acoustic wave (WSAW) detection by a millimeter wave (mmWave) radar. The mmWave-based endpoint detection method of the WSAW was introduced. Simulated results show that the continuous wavelet transform (CWT) method has a better detection performance. A 77 GHz large aperture antenna mmWave radar sensor and an underwater acoustic transmitter have been applied to conduct laboratory experiments. Still water surface experimental results verify that the CWT method has better detection capability, and the mmWave radar can accurately detect even 155 nm WSAW. Wavy water surface experimental results demonstrate the ability of the mmWave radar to analyze the time-frequency feature of the weak WSAW signal. These works indicate the potential of mmWave radar for the cross-medium detection and recognition of underwater targets.

Effects of underwater swing nodes on water-to-air visible light communication.

In water-to-air visible light communication (W2A-VLC), the dynamics of underwater nodes and a wavy water surface should not be neglected. This paper investigates the link performance by combining the dynamic effects of an underwater light-emitting diode (LED) transmitter with a wavy water surface. Monte Carlo simulation is first adopted to evaluate the underwater LED dynamics. Experimental tests are then conducted to measure and analyze the influence of underwater dynamic parameters on link performance, which shows results consistent with theoretical prediction. It is demonstrated that the swing angle dominates the stability and reliability of the W2A-VLC link under a dynamic water surface, providing some insight into the design of underwater optical transmitters.

Superposition Modulation for Physical Layer Security in Water-to-Air Visible Light Communication Systems

In this paper, we propose a physical layer security (PLS) scheme based on superposition modulation for water-to-air (W2A) visible light communication (VLC) systems. We characterize the high correlation between W2A and air-to-water (A2W) link gains from ray tracing simulation and experiments. The proposed scheme selects the modulation order and superposition parameter based on the high correlation between the W2A and A2W link gains. The scheme performance is studied by exploring its immunity against different types of attacks. The symbol error rates (SERs) are analyzed for both random and correlated attacks. Based on the link gains from real measurements, it is shown that under random attack Eve's SER exceeds 0.77 when Eve's signal-to-noise ratio (SNR) varies from 5 dB to 30 dB, and under correlated attack Eve's SER decreases only for a high correlation coefficient when Eve is close enough to Bob, which is unrealistic for eavesdropping. In addition, the entropy of potential set under post-processing attack is derived and the complexity of successful cracking increases with the modulation set size. For intelligent attack, two unsupervised algorithms, namely K-means clustering and expectation maximization (EM) algorithm, are adopted for modulation identification. The distributions of Eve' SER under all four attacks are investigated based on the measured link gains in the laboratory environment, which demonstrates that intelligent attack with K-means clustering possesses the highest eavesdropping capability. However, more numerical results show that for intelligent attack with K-means clustering under wavy water surface, the proportion of the case where Eve has a higher SER than Bob is lower than 0.5 only when Eve lies between Alice and Bob with small horizontal distance, which is unrealistic for eavesdropping operation.

Anti error and erasure coding for water-to-air visible light communication through wavy water surface with wave height up to 0.6 meters.

Considering large dynamic optical intensity range in a water-to-air (W2A) channel, we propose two promising channel coding schemes, namely the concatenated Reed Solomon-Low Density Parity Check (RS-LDPC) code and Raptor code, for W2A visible light communication (VLC). We establish a W2A-VLC link to verify the performance under different wavy water environments and different water depths with a green light emitting diode (LED). A wave generator is adopted to emulate the wavy water surface with wave height up to 0.6 m. The receiver is fixed 3.2 m above the water, and the transmitter varies from 2.5 m to 4.0 m under the water through a up-down-moveable platform. We test the coding schemes with different code lengths and code rates under 5 MSym/s air-interface symbol rate. Experimental results show that both schemes can reduce the bit error ratio (BER) and frame error rate (FER) of a W2A-VLC system, and thus can improve the reliability. Via comparing the two codes with the same overhead and approximately the same code length, it is demonstrated that Raptor code can generally outperform the concatenated RS-LDPC code. Our research provides promising channel coding methods without feedback for a W2A-VLC system.

Wing-in-ground craft longitudinal modeling and simulation based on a moving wavy ground test

Compared with the static wavy ground tests and moving flat ground tests, the moving wavy ground test eliminates the effect of the boundary layer and generates more accurate test results of the aerodynamics in the wave environment. This paper introduces a wind tunnel test of a wing-in-ground (WIG) effect craft with moving wavy ground. The wavy ground is made of elastic material and installed on a moving belt to simulate the relative motion of the WIG craft and the wavy water surface. The test focuses on the relationship between aerodynamics and the waves and indicates that longitudinal aerodynamics is affected not only by wave height but also by wave height change rate, while the lateral and directional aerodynamic characteristics are less affected by the ground effect. The longitudinal aerodynamics and flight dynamics model considering the wave height change rate are established based on the test results. The waves adopted in the dynamics model are random waves to simulate the natural wave environment better. An H∞ controller is designed to deal with the more complicated wave disturbance. The simulation results show that the aerodynamics and flight dynamics model can reasonably simulate the flight of the WIG craft in the wave environment, and the H∞ controller can effectively deal with the wave disturbance and generate a smooth flight.

Experimental Investigation of the Effects of Intermediate Gravity Waves on the Water Evaporation Rate

Abstract A perfectly still water surface is an ideal hypothesis that is rarely encountered in real-world applications. It is impossible to find an open surface of water without any disturbance or waves, as well as an occupied closed water surface, such as a swimming pool. This experiment was done to predict the evaporation rate from the wavy water surface under the different convection regimes (free, forced, and mixed) at turbulent airflow conditions over a wide range of the ratio (Gr/Re2). The evaporation rate from the wavy water surface is strongly affected by combinations between wave steepness and main airflow velocity above the wavy water surface. Experimental results show that no pattern can be followed for which combinations of evaporation rate will increase. Thus, only two facts can be noticed: the evaporation rate is larger than that measured under the same airflow velocity conditions with no waves existing on evaporated water surface because the airflow is smooth and attached along the still water surface and when increasing the wave steepness (H/L,H/T), airflow will separate at the lee side of the wave crest near the bottom of the wave trough. Thus, the vortex will be generated in the airflow separation region. These vortexes are unstable and cause an increase in turbulence, reducing the water surface's resistance to vertical transport water vapor and increasing the evaporation rate. Also, experimental results show that the evaporation rates are somewhat less than that measured under the same airflow velocity with smaller wave steepness due to the air trapped region observed at the leeside of the wave crest near the bottom of the wave trough. Also, the result shows the evaporation rate increases with increased airflow velocity under the same convection regime. The current study implemented the particle image velocimetry (PIV) technique to analyze the airflow structure above the evaporated wavy water surface.

Theoretical study on slamming and transition stages of normal impacts of symmetrical bodies on calm and wavy water surfaces

Wave impact problems attract extensive attention and have a wide range of applications in the marine field. There is an increasing need to propose a general theoretical solution for the impacts of bodies on both calm and wavy water surfaces. In this paper, the slamming and transition stages of the high-speed normal impacts of two-dimensional (2D) symmetrical bodies on calm and wavy water surfaces are studied theoretically, where the body surfaces can be linear, concave or convex. The fluid is assumed to be incompressible, inviscid, and weightless and to have a negligible surface tension effect, and the flow is assumed to be irrotational. For the slamming stage of a wave impact, a modified Wagner model (MWM) is proposed to accurately predict the wetted length of bodies and the pressure distribution on the body surface. The MWM has a better prediction performance than the modified Logvinovich model (MLM) compared with the similarity solution for the impacts of linear wedges on the linear incident wave. For the transition stage of the normal impact of wedges on calm and wavy water surfaces, a curved fictitious body continuation (FBC) is proposed to extend the MWM from the slamming stage to the transition stage. The MWM with a curved FBC can better predict the force than the linear FBC compared with the CFD results.

Numerical Study on Airfoil Aerodynamics in Proximity to Wavy Water Surface for Various Amplitudes

Wing–in–ground crafts will face waves with different amplitudes when flying over the ocean, and the high amplitude situations are especially lack of exploration. Hence, the aerodynamic characteristics of the NACA 4412 airfoil in proximity to the wavy water surface for various wave amplitudes are inspected in this paper. By solving Navier–Stokes equations, the lift coefficients of the airfoil when the angle of attack ranges from 0° to 4° are obtained. The results show that the fluctuation amplitudes of aerodynamic coefficients increase remarkably with successive increases in the wave amplitude and might threaten flight safety. The flow fields at 0° with low and high wave amplitudes are investigated. It is revealed that the upward movement of the water surface is the critical factor for the change of aerodynamics, and the mechanism varies with different wave amplitudes. Comparison of the flow fields at 0° and 2° further indicates that the influence of high amplitude waves depends on the distance between the leading edge of the airfoil and the water surface. This study discovers the reasons for the different aerodynamic characteristics under various wave amplitudes and angles of attack, and is of great value for the design of wing–in–ground crafts.

Preliminary Characterization of Coverage for Water-to-Air Visible Light Communication Through Wavy Water Surface

In this paper, we establish a water-to-air (W2A) visible light communication (VLC) link using green light emitting diode (LED), and investigate the coverage characteristics of the designed W2A-VLC link under calm and wavy water conditions. By transmitting a high-frequency sinusoid signal, we extract the variation of link gain. Based on the received signals of an experimental W2A-VLC system, we obtain the real link gains at different receiver points and analyze the channel temporal properties in good link conditions (called link “on” state). It is seen that the mean channel gain under wavy water surface condition can be larger than that under calm water surface condition, especially when the transmitter and receiver are not perfectly aligned, due to the random spatial modulation effect of wavy water surface. Moreover, the “on” state duration and interval can be well fitted by a shifted exponential distribution and a shifted lognormal distribution, respectively. Bit error rate (BER) results reveal the effect of expanded link gain variation under wavy water surface condition. This work provides significant guidance for future works on the communication protocol design and related performance analysis.

CFD Study on Penetration of Sonic Boom Applying a Wavy-Water Model

The penetration of sonic booms into the ocean and an estimation of the extent of their influence are important topics for supersonic and hypersonic aviation. Most prior studies were conducted assuming a flat-water surface. However, it is known that the effect of the surface waviness is not negligible in the case of real ocean environments. In the present study, the numerical method analyzes the two-dimensional flow field of sonic boom propagation across the air and water is proposed. When the flight Mach number of an aircraft is higher than 4.4, the underwater flow field becomes supersonic, and a sonic boom is generated there. The numerical results show that, in the underwater subsonic regime, the penetrating waves have the form of evanescent waves under either flat or wavy water surface, but the waviness-induced ripples with the smaller decay rate are responsible for deeper penetration. In contrast, in the supersonic underwater flow, the surface waviness hardly affects the penetration depth of underwater sonic booms, although it can slightly weaken the boom intensity. The effect of the amplitude of surface waviness on the underwater penetrating wave was also investigated.

Airfoil Aerodynamics in Proximity to Wavy Water Surface

AbstractThe aerodynamics of the airfoil National Advisory Committee for Aeronautics (NACA) 4412 moving in proximity to a wavy water surface are investigated using numerical methods, and the conditi...

Using Remote Laser Technique in Measuring Oil Film Thickness on Water Surface in the Eye-Safe Spectral Range

Possibilities were studied of using a remote laser spectrophotometric method in measuring thickness of oil films on a wavy water surface with utilization of discretely tunable laser source operating at eye-safe narrow spectral range around ~ 2.1 μm. Laser spectrophotometric method is based on measuring reflection coefficient of the water surface on five probing wavelengths and finding thickness of the oil film by the quasisolution search method. It is proposed to use an optical parametric generator tunable along a wavelength in the 1.5--2.6 μm spectral range as a radiation source. Results of mathematical simulation are provided for the optical characteristics of typical oil and pure sea water with a mean square value of measurement noise of 1, 2 and 3 %. Results of mathematical simulation demonstrate that remote laser spectrophotometric method based on the quasisolution selection technique makes it possible to measure oil films with a thickness from several micrometers to ~ 130 μm with an error of no more than 30 % for measurements with noise mean sguare error of 1--3 %

Numerical Study on the Extreme Impact Load of Wavy-Water Ditching

In this paper, numerical method is used study the extreme impact load and its physical causes during the wavy aircraft ditching. the finite volume method and VOF method are used to capture the free surface, six degrees of freedom model and global motion mesh to deal with the relative motion between water and aircraft. and simulate the forced landing process of the aircraft. By choosing the place with the largest vertical velocity relative to the water as the impact position, the extreme impact load on the fuselage is predicted. In this paper, during the impact stage of the wavy water surface, the fuselage encountered an impact peak which is unforeseen on the calm water surface, and the magnitude of the impact peak was related to the sinking speed of the aircraft relative to the water surface. This paper also compares the movement attitude and overload history of aircraft ditching under five sea conditions with different wave height, and gives the influence rules of wave height on the extreme impact load and the peak values of other parameters, which provides a reference for the design of aircraft load distribution.

天空光主导的波浪水面下偏振分布模型仿真

天空光主导的波浪水面下偏振分布模型仿真

A Semi-phenomenological Model for Wind-Induced Drift Currents

Some data of the drift current, Ud, measured on a wavy surface of water in a laboratory and the field, are briefly described. Empirical formulas for Ud are given, and their incompleteness is noted, regarding to absence of the drift current dependence on surface-wave parameters. With the purpose of theoretical justification of empirical formulas, a semi-phenomenological model of the phenomenon is constructed. It is basing on the known theoretical and empirical data about the three-layer structure of the air-water interface: 1) the air boundary layer, 2) the wave-zone, and 3) the water upper layer. It is shown that a presence of linear drift-current profile in the wave-zone, U(z), makes it possible to obtain a general formula for the drift current on the wavy water surface, Ud. This model is based on the balance equation for the momentum-flux and current-gradient, taking place in the wave-zone. The proposed approach allows us to give an interpretation of the empirical results, and indicate the direction of their further detailed specification.

К вопросу о физической природе рассеяния микроволнового излучения Ка-диапазона на взволнованной водной поверхности

К вопросу о физической природе рассеяния микроволнового излучения Ка-диапазона на взволнованной водной поверхности

Analyzing Visible Light Communication Through Air–Water Interface

In underwater wireless networks (UWNs), conventionally there is no direct communication between an underwater node and a remote command center. A floating base-station is often used to serve as an interface to a UWN; such a base-station would typically have both acoustic and radio modems to communicate with underwater nodes and off-shore centers, respectively. Although employing an airborne base-station would avoid the logistically-complicated surface nodes deployment, communication across the air-water interface becomes the main challenge since it involves two mediums. This paper promotes a novel way to interconnect UWNs to airborne base-stations through visible light communication (VLC) links. The paper analyzes the viability of VLC across the air-water interface by determining the coverage area and intensity inside the water for a light transmitter placed in the air. We show that enough intensity can be achieved for VLC communication even in the presence of a wavy water surface. We then provide guidelines for using single and multiple light sources to establish robust VLC links under rough environmental conditions like high water current and turbidity. Our approach is validated using simulation and a lab experiment is done to validate the simulation result for flat water surfaces.