Wave Disturbances Research Articles

Variability and distribution of nighttime equatorial to mid latitude ionospheric irregularities and vertical plasma drift observed by FORMOSAT-5 Advanced Ionospheric Probe in-situ measurements from 2017 – 2020

Irregularities in ionospheric plasma distribution can result in severe scintillation and disruption to the radio frequencies utilized for satellite communications and navigation. In the low and mid latitudes, these irregularities can include Equatorial Plasma Bubbles (EPBs) and Travelling Ionospheric Disturbances (TIDs). EPBs are irregularities manifesting in low latitude nighttime ionosphere plasma density that can extend along magnetic field lines with zonal scales on the order of 100 km or less, while TIDs are propagating wave disturbances. High frequency in-situ measurements of ionospheric plasma aboard spacecraft in Low Earth Orbit (LEO) are a direct measurement of irregularities in plasma density and are therefore valuable for resolving EPB and TID occurrences, variability, and relation to other ionospheric parameters that are believed to play a driving role in the formation of such irregularities. In this study, we utilize observations taken over a three-year period between 2017 and 2020 by the Advanced Ionospheric Probe (AIP) carried aboard the FORMOSAT-5 satellite to examine the spatial, seasonal, and interannual variability of equatorial to mid latitude ionospheric irregularities and vertical ion drift during this time. AIP provides in-situ measurements of ion density and vertical ion drift in the equatorial to mid latitude ionosphere at approximately 720 km altitude with local times between 22:00 – 23:00 local time. Our global scale results resolve distinct and inter-annually recurrent seasonal patterns in the distribution of nighttime ionospheric irregularities and vertical plasma drift during this time. Elevated occurrences of ion density irregularities are resolved along the Equatorial Ionization Anomaly (EIA) latitudes, while notable occurrences with variability consistent with EPBs also observed along the low and equatorial magnetic latitudes. Zonal variability of equatorial irregularities consistent with the signatures of nonmigrating atmospheric tides are observed. It is also notable that the occurrences and geographic distribution of ion density irregularities showed a considerable level of interannual variability, especially at mid latitudes over the South Atlantic and Southern African sectors, which showed much higher levels of irregularities in 2017–––2018, compared to 2019 and 2020. In comparison, the spatial and interannual variation of the co-located vertical ion drifts were much more consistent during the years examined, indicating that the driver for the observed interannual variability in ion density irregularities cannot be attributed to the vertical ion drift at the same time and location of the observations. This highlights the need for in-situ instruments distributed across multiple satellites in different local time zones.

A sliding mode predictive anti-pitching control for a high-speed multihull

A sliding mode predictive anti-pitching control considering appendages constraints is proposed to improve the wave suppression capability of multihulls while reducing heave and pitch motions. The control method combines the advantages of model predictive control and sliding mode control to both improve the strong robustness of the system and to ensure the optimization and the ability to handle constraints explicitly. The vertical motion model is established for multihull with two types of appendages, T-foils and flaps, to achieve anti-pitching. According to the characteristics of the first-order autoregressive wave disturbance model, a low-complexity disturbance observer is devised to estimate the wave disturbance force and moment online, and combine the estimates with the prediction model to enhance the accuracy of the prediction. On this basis, a prediction model and an objective function are established with the sliding mode states as variables, and the sliding mode terminal stability constraint set is adopted to improve the stability of the closed-loop system. Last, the closed-loop system stability was analyzed based on Lyapunov stability theory. The effectiveness of the designed controller is verified by simulation and experiment, in which the multihull heave displacement is reduced by 52% and the pitch angle is reduced by 58%.

Numerical Investigations of Nonlinearly Generated Disturbance Waves in High-Speed Boundary Layers

In several experimental investigations of hypersonic boundary-layer transition, higher harmonics of the linearly unstable second mode waves as well as low-frequency waves, which are not related to first mode waves, have been observed. It has been conjectured that the higher harmonics are nonlinearly generated by a self-interaction mechanism of the linearly amplified second mode waves. Several hypotheses regarding the origin of the low-frequency waves and their role in the transition process have been put forth. However, a clear understanding of the origin and role of these low-frequency disturbances in the transition process is difficult to attain from experiments and thus still not completely achieved. The nonlinear generation of higher harmonics and low-frequency disturbances is relevant because in high-speed boundary layers, second modes can reach very large amplitudes, which can lead to a considerable stretching of the transitional regime where these nonlinearly generated waves can then reach significant amplitudes and participate in the transition process. To shed light on this unresolved issue, numerical investigations were carried out for a flared cone at Mach 6. These calculations have shown that nonlinear interactions of sufficiently large-amplitude second mode waves can generate low-frequency disturbances. This was confirmed by a theoretical nonlinear interaction model.

Геомагнитные эффекты взрывов сибирских метеоров

The geomagnetic effects of falling meteors have been known for a long time, but so far they have not received a complete theoretical explanation. The paper considers the response of the geomagnetic field to the destruction of meteors in Yakutia (March 4, 2014, 21:29 UT) and Khakassia (December 6, 2016) according to the Irkutsk magnetic observatory data of the Institute of Solar-Terrestrial Physics SB RAS. The analysis of variations in the geomagnetic field components showed that the passages and explosions of meteors were accompanied by the appearance of several groups of geomagnetic disturbances in the area of the Irkutsk magnetic observatory. Their appearance can be caused by the propagation of shock, internal gravity and magnetohydrodynamic waves formed as a result of the passages and destructions of meteors. The periods of these wave disturbances and the velocities of their propagation from the generation regions are estimated. It is noted that noticeable wave manifestations in the geomagnetic field give waves with a period of more than 10 minutes, i.e. having gravity modes.

Design of the roll and heel reduction controller on ship’s turning motion

When the ship turns, it will heel and exacerbate the roll triggered by the sea waves, ultimately impacting the safe navigation of the ship. A study was conducted on a design method for a roll and heel reduction controller based on nonlinear feedback to mitigate the ship’s roll and heel during turning motion. A mathematical model was established for a ship with four degrees of freedom. Subsequently, a systematic analysis was conducted on the hydrodynamic force, rudder force, fin force and wave disturbance force of the ship. The ship’s roll and heel motion are reduced by controlling the roll reduction force generated by the fin. The roll and heel reduction controller uses a nonlinear PID controller with parameters that vary with the feedback signal. This effectively enhances the dynamic response characteristics of the system. Simulations were performed to analyze the effect of different rudder angles and different fin angles on the performance of the ship’s turning motion. The nonlinear feedback technique is employed to decrease the output of the fin angle, minimize the mechanical wear of fin stabilizer and save energy without compromising the control performance. The study analyzed the effect of a nonlinear feedback based controller in reducing roll and heel during turning motions of a ship. Simulations were conducted and compared with the classical PID controller method. The results indicated that the nonlinear feedback controller had a better performance in reducing roll and heel, validating the effectiveness of the designed method.

Three-dimensional evolution and interaction of disturbance waves on a gas-sheared liquid film on a horizontal plane near the transition region

Three-dimensional evolution and interaction of disturbance waves on a gas-sheared liquid film on a horizontal plane near the transition region

Stability Analysis of 3D UAV Gimbal using Flexible Body

Unmanned aerial vehicle (UAV) application in visual object tracking requires a gimbal to stabilize the camera in following the object’s movement. External disturbance and gimbal stability are the issues in this application. This study aims to analyze disturbance effects and study the stress and modal analysis on UAV gimbal using flexible body concepts. The three-dimensional (3D) gimbal is modeled using the RecurDyn software consisting of 3 arms and a camera. Each of the arms is connected using a revolute joint and a rotational force to represent a motor. The considered disturbances are step, pulse, ramp, and sine wave input. The PID controller is used to stabilize the gimbal arm from the gravity of the camera and external disturbance. The result shows that the PID controller is robust to step, pulse, and ramp disturbance, but not to the sin wave disturbance. In addition, the second arm of the gimbal is the most stressed component and is prone to vibration.

Effect of wave disturbance on the fluid dynamics of the pump turbine in a seawater pumped storage hydroplant

Compared with conventional pumped-storage hydroplants, seawater pumped-storage hydroplants are constructed in a complex marine environment. The wave disturbance may affect the safety operation of the pump turbine in the seawater pumped hydroplant via affecting the level of the free water surface. To explore the effect of wave disturbance on the operation of the pump turbine in a seawater pumped-storage hydroplant, assuming that the wave disturbance follows a sine function, on the basis of Airy’s micro-amplitude wave theory and the comprehensive characteristic curve of a pump turbine, we use sliding grid technology and the SST k–ω turbulence model to simulate the dynamics of fluid in a full-flow channel. In this study, the unsteady flow field, Q-criterion vorticity, relative pressure pulsation amplitude, and frequency of pressure pulsation are analyzed to determine the internal flow field and pressure pulsation under different wave disturbance conditions and operating loads. The results show that both the pressure pulsation in the pump turbine and its frequency domain are affected by the wave disturbance. In addition, the turbulent flow with a large flow rate tends to produce higher relative pressure pulsation under wave disturbance. Due to the large flow rate and strong static and dynamic interference in the vaneless area, the relative amplitude of the pressure pulsation is significantly affected by wave disturbance. Furthermore, the low-frequency pressure pulsation of the draft tube is superimposed with the wave disturbance frequency.

Adaptive path following control for wave gliders in ocean currents and waves

In this paper, a design method is presented for path following control of wave gliders (WGs) subject to velocity and rudder input constraints, as well as marine currents and wave disturbances. The control method integrates an adaptive integral line-of-sight (AILOS) guidance law, an adaptive target-path-switching control and a modified incremental PID heading control for WGs with the multi-straight-line path following, which can extremely overcome the influence of such marine currents interference and guarantee path following accuracy. For the control loop, adaptive adjustments on the parameters of the lookahead distance and the error-circle radius are built to provide a current-influenced position error compensation suitable for the time-varying velocity of the WG. Additionally, an online wave filter using an extended Kalman filter (EKF) is developed to address the issue of wave-induced disturbance influence worked on the position and heading of the WG. Further, simulations and sea trials demonstrate both tracking accuracy and high robustness under ocean disturbances with rudder constraints.

Darcy–Benard convection through a uniformly permeable porous slab

In this article, we study the onset of convection in porous media with through flow based on Darcy formulation. Unlike the impermeable porous medium problems between horizontal two parallel plates frequently accessed in the literature, the thermal instability of convective cells under the influence of a uniform vertical flow is of the prime concern here in an aim to control the thermal instability onset. Three devised thermal boundary constraints representing external heat transfer with isothermal or isoflux lines across the walls are investigated fully taking into account the linear stability equations with small flow/heat wave disturbances with respect to the normal modes. In each case, the neutral stability response of the saturated porous layer separating the stable and unstable perturbation regimes are identified affected by a Peclet number manifesting itself as the through flow strength. The pre-analysis of the analytical solutions of thermal fields proves that the thermal layer thickness is lowered by the opposing through flow, otherwise an assisting through flow enhances the thickness. The critical Darcy–Rayleigh numbers and Benard cell wavenumbers of lateral fluctuating perturbations initiating the convective Darcy–Benard thermal rolls within the porous media for a prescribed Peclet number are ultimately worked out numerically, except an analytical expression is elaborated where the heating is supplied from the walls via varying heat fluxes. The well-documented thresholds of Rayleigh numbers 39.47, 27.09 and 12 with vanishing Peclet number (Barletta, 2019) corresponding to the three studied thermal cases are reproduced successfully. Further results clarified that both opposing and assisting through flows are sources of stabilization when the walls are thermally isothermal. On the other hand, the other thermally conducting porous walls lead to a more unstable convection with the assisting through flow having a thermal layer growth, otherwise stable convection occurs with the opposing through flow.

Nonlinear waves in a composite optical structure containing a dielectric layer between a photorefractive crystal and a medium with an exponential index profile

Three-layered asymmetric structure with different optical properties of the layers is considered. The structure consist of a photorefractive crystal with diffusion nonlinearity and very weak dark intensity, which is separated by optically linear dielectric layer from medium with spatially distributed refractive index according with an exponential profile. The paper objective is a theoretical analysis of wave disturbances arising from the introduction of a dielectric waveguide layer between photorefractive and graded-index media. Waves of new four kinds are described theoretically by exact solutions to the wave equation with spatial inhomogeneous and intensity-dependent refractive index. The waves differ from each other in the distribution profile and the range of existence. Waves with both oscillating and non-oscillating field profiles inside the dielectric layer are obtained. It is found that the dielectric layer significantly affects the main characteristics of the field distribution in the waveguide structure in the direction transverse to the layers. It is shown controlling the values of the characteristics of the layers allows selecting the required field profile, which can be used to suppress oscillations or increase the field intensity in certain regions of a layered structure.

Energy management strategy for hybrid power ships based on nonlinear model predictive control

How to achieve energy saving and emissions reduction is a critical issue of great concern to all countries. The development of marine hybrid power technology provides a new research direction for rational energy distribution and utilization. In this paper, an energy management strategy for real-time regulation of internal combustion engines and motor torque is designed to solve the optimal energy management problem of parallel hybrid power ships. A nonlinear model predictive control method is used as the core, aided by a machine learning technique and an unscented Kalman filter. Machine learning techniques are used to extract representative test cycles and apply them to the testing and evaluation of design strategies. The effect of random waves on propeller load torque is observed using an unscented Kalman filter, which is used as a disturbance variable to participate in establishing the prediction model. Furthermore, a trade-off coefficient is designed to further demonstrate the balance between fuel consumption and carbon emission optimization. To verify the performance of the designed energy management strategy, NMPC is compared with the conventional intelligent optimization algorithm and dynamic programming algorithm, and the fuel consumption and carbon emission trade-off parameterization of the strategy is investigated. The results show that the strategy can resist random wave disturbances and follow the reference data of the ship’s internal combustion engine speed extracted by machine learning. The energy distribution is also performed according to the variation of the trade-off coefficients to achieve the optimal trade-off energy management under the required constraints.

AUV 3D docking control using deep reinforcement learning

Autonomous docking can enable AUV to have long endurance, so it is necessary to consider the issue of robust docking control under current and wave disturbances. In this work, based on the proximal policy optimization (PPO) algorithm, we developed a model-free docking controller to complete three-dimensional docking tasks under disturbances. To improve the performance of PPO, two mechanisms are proposed, including adaptive rollback clipping and self-generated demonstration replay. A simulation environment is constructed, including fuzzy hydrodynamic parameters, ocean current and wave disturbance model. Simulation results demonstrate that our proposed method has faster learning speed, higher robustness, and can control AUV to achieve 3D docking tasks in complex environments with a high success rate.

Finite-time control for USV path tracking under input saturation with random disturbances

In this paper, a finite-time path tracking control method for unmanned surface vessel (USVs) subject to random disturbances and input saturation is proposed. A class of noise may be non-white one is employed to describe wave disturbance more accurately for real sea conditions. The constraints are considered to describe the limited output force of USVs. A finite-time control strategy is introduced to ensure that the requirements of tracking the desired position and heading within finite time. The noise-to-state stability in probability (NSS-P) within finite time, under an asymptotic gain in probability (AG-P) of state signals, is proved via the theoretical framework of random differential equations (RDEs). Finally, simulation results are presented to show the effectiveness of the designed finite-time path tracking control scheme.

ELIMINATION OF THE INFLUENCE OF WIND-WAVE DISTURBANCES ON THE MOVEMENT OF THE UNDERWATER VEHICLE USING LOW-FREQUENCY FILTERING

The article is devoted to the problem of the influence of wind-wave disturbances on the quality of control of an uninhabited underwater vehicle. The problem is urgent, since as a result of such an impact, there is an increase in the cost of electricity for the operation of the engine, which pumps and pumps water into the ballast chamber of the underwater vehicle to maintain it at a given depth, which generally affects the reduction of the time the device stays underwater. In the course of the study, the influence of the wind wave disturbance was assessed depending on its score, and a means was proposed to eliminate excessive energy costs in the form of low-frequency filtration.

Surface plasmon resonance of nanoparticles in two-dimensional elastic system

In this paper we demonstrate the surface plasmon resonance of nanoparticles in a two-dimensional elastic system. We use the layer potential technique related to the elastic equations and make an asymptotic expansion of the disturbed elastic wave field about the size of nanoparticles. The principal term in the asymptotic expansion mentioned earlier is related to the Neumann-Poincáre operator in the elastic system. Finally, the surface plasmon resonance is investigated by the spectral properties of the Neumann-Poincáre operator.

Numerical modeling of wave penetration inside a harbor

Wave penetration analysis is typically performed to ensure that the coastal structure at the harbour provides adequate shelter from waves and currents for ship berthing. Generally, wave penetration inside a harbour occurs through the entrance. The type of coastal protection (usually a breakwater) also has an impact on wave agitation within the harbour. In this research, wave penetration analysis has been done, mainly, by using MIKE 3 Wave FM software to model seven different scenarios as individual cases. From the seven different cases, the mean wave disturbance coefficient and mean significant wave height in the berthing area are determined. The model results showed that the wave penetration on the turning circle in the navigation channel is relatively unaffected by the wave disturbance in all seven cases. It is observed that 80 % of the time the significant wave height in the berthing area was less than or equal to 0.1 meters. The wave climate in the berthing area is therefore classified as good. Consequently, it can be concluded that the breakwaters are achieving their goal of reducing the impact of wave action and currents within the harbour.

ქ. რუსთავის და მიმდებარე ტერიტორიის ატმოსფეროში PM2.5-ის გავრცელების გამოკვლევა

The distribution of PM2.5 in the atmosphere of the city of Rustavi and its environs was studied under eastern background light air, gentle and fresh breeze. It has been established that the maximum concentrations of PM2.5 in the atmosphere of Rustavi are almost always higher than the corresponding maximum allowable concentrations. The trend of hourly changes in concentrations showed that during the day the concentration of microparticles reaches its maximum in the various period of the day. Numerical modeling of the local distribution of microparticles carried out in the city of Rustavi during background easterly light air, gentle and fresh breeze showed us that the change in the daily regime of relief and temperature with eastern light air in Rustavi for 12 hours leads to a complex and significant change in the wind speed directed to land. It forms on the territory of Kvemo Kartli the opposite current of the background wind, which corresponds to the horizontal circular wind circulation. The value of circulation gradually decreases with increasing height and in the boundary layer of the atmosphere (600 m above the earth's surface) has the form of a wave disturbance. the picture obtained with an average background east wind is qualitatively similar to the field obtained with a background light air, and with a fresh breeze, in contrast to the case of a light air and gentle breeze, the pollution zone covers most of the simulation zone.

Numerical Study of the Internal Fluid Dynamics of Draft Tube in Seawater Pumped Storage Hydropower Plant

Pumped storage hydropower plants are renewable energy systems that are effective in saving energy and solving electricity peak-on shortage. Seawater pumped storage hydropower plants are a novel type of pumped storage hydropower plant specifically supplying electric power for ocean islands with the support of solar energy and wind energy. Compared with traditional pumped storage hydropower plants that are constructed on the mainland, seawater pumped storage hydropower plants should take the influence of the complex marine environment, such as extreme waves and winds, into consideration. Taking the characteristics of waves near islands in the East China Sea as an example, we explored the transient hydraulic characteristics in the draft tube of a pump turbine under wave disturbance using a sliding grid interface and the detached eddy simulation (DES) turbulence model. By analyzing the characteristics of unsteady flow in the draft tube, the vortex characteristics under the Q criterion, the frequency characteristics of the pressure pulsation, the evolution law of the internal fluid, and the propagation law of the pressure pulsation were explored. For the situation without wave disturbance, an obvious eccentric vortex in the straight cone section of the draft tube was observed in the case where the opening of the guide vane was small. With the increase in the opening of the guide vane, the eccentric vortex gradually dissipated. For the situation with wave disturbance, the main frequency of the draft tube equaled the frequency of the wave disturbance, the maximum pressure pulsation at the selected monitoring points increased 5 to 15 times, and the superposition of the wave pressure pulsation signals and the draft tube pressure pulsation produced more low-frequency, high-amplitude pressure pulsation signals. Even though the pressure pulsation frequency spectrum varied a lot, the frequency domain of the pressure pulsation without wave disturbance still existed. In addition, the wave disturbance merely varied with the pressure of the draft tube. The influence of wave disturbance on the pressure distribution in the draft tube was relatively small. The results can provide a reference for the operation of seawater pumped storage hydropower plants.

Developing a Simulation Model to Numerically Estimate Energy Parameters and Wave Energy Converter Efficiency of a Floating Wave Power Plant

The significance of coastal zone object protection using wave electrical energy complexes (WEECs) is dealt with. The authors suggest using a floating wave power plant (FWPP), which comprises electrical energy functions and provides coastal zone protection. Features of simulating FWPP in computational fluid dynamics (CFD) modules are considered. The main simulation stages, construction order, the necessary initial and boundary conditions, calculation objectives and results are described and analyzed. Analysis and adjustment of input parameters (wave amplitude, wave disturbance frequency, FWPP geometric parameters) determining the FWPP fluid flow output parameters (dynamic, total pressure, flow rate, flow velocity) were carried out. Calculation process optimization was carried out by comparing the data obtained using a 2-D solver. The main stages of wave disturbances-with-FWPP-structure interaction have been determined. Epures of flow velocity, pressure, flow path and volume flow rate were constructed and analyzed.