External Wave Research Articles

Hydrodynamics of a floating liquid-tank barge adjacent to fixed structure in beam waves

Physical experiments are conducted in a wave flume to investigate the hydrodynamic behavior of a liquid-tank barge floating near an identical barge. The two barges are arranged side-by-side and subjected to the action of beam waves. The floating barge is equipped with two liquid tanks and encounters the waves before the second barge. Systematic investigations on the effects of liquid tanks, mooring constraints, and arrangement configurations provide rich findings on the physics of fluids. Mathematical solutions are also derived to interpret the underlying mechanism behind the experimental observations. Our primary findings suggest two essential modes, i.e., trend and oscillatory components, in the motion of the floating barge. Of these, the oscillatory component can be strongly coupled with the liquid sloshing in the tanks. A mean-drift load caused by internal sloshing waves occurs as a result of the second-order nonlinearity, which significantly modulates the mean-drift force induced by external water waves and may change the drift direction of the floating barge. The properties of the mooring constraints effectively determine the trend component. Regardless of the liquid filling level in the tanks, the maximum ratio of the sloshing-wave height to the oscillatory amplitude of the barge always occurs at the fundamental natural sloshing period. The contributions of radiation damping and viscous damping to the barge oscillation are explicitly distinguished. The physical insights revealed in this study will help guarantee the operational safety of side-by-side floating structures.

Reinforcement learning-based optimal fault-tolerant control for offshore platforms

This article investigates a novel reinforcement learning-based fault-tolerant control approach for steel-jacket offshore platforms. In the first step, the dynamic of the steal-jacket offshore platform with an active mass damper is considered, and the equivalent linear time-invariant model is obtained with the actuator fault. In fault-free conditions, an optimal controller is designed to keep the system stable under external wave force. Subsequently, in faulty conditions, the actuator fault is estimated by the fault observer. Next, by inserting the actuator fault estimation into the cost function, the fault-tolerant control problem transforms into the optimal control problem. The online policy iteration is used to minimize the new cost function. Finally, the final control law, which is a mixture of the nominal and the modified control law, stabilizes the offshore platform and improves its performance in the presence of the actuator fault without needing the complete knowledge of the offshore platform. The simulation results show the effectiveness of the proposed method.

Effective terahertz shielding properties of extreme graphene-silver nanowire surfaces investigated by nanoprobing

SummaryIn the terahertz (THz) electromagnetic wave regime, which has recently received great attention in the fields of communication and security, shielding of THz waves is a significant issue. Therefore, carbon-based nanostructures or polymer–carbon nanocomposites have been widely explored. Herein, significantly enhanced THz shielding efficiency is reported for silver nanowires coated with reduced graphene oxide (rGO) and nanoscale THz metamaterials, as compared to the cases without nanoscale metamaterials. Using a nanoslot-patterned metamaterial with strong resonances at certain frequencies, THz transmission in intensity is enhanced up to three orders of magnitude. Enhanced transmission by nanopatterns substantially increases the shielding performance to the external THz waves, even for ultrathin films (several tens of nanometers) produced by a simple spray of rGO (a few nm of flakes) on a complex random nanowire network. Excellent shielding performance is presented and the shielding mechanism is investigated by the nanoprobing configuration at the same time.

An analytical study of sound transmission loss of functionally graded sandwich cylindrical nanoshell integrated with piezoelectric layers

The multidisciplinary nature of piezoelectric (PZ) structures necessitates precise and efficient methods to express their behavior under different conditions. This article extends the general usage of PZ materials by introducing acoustic and fluid loading effects in a way that an unfilled multilayer cylindrical nanoshell with a functionally graded (FG) material core and PZ layers is subjected to preliminary external electric load, acoustic waves and external flow motion. As the properties of a functionally graded material changes along the shell thickness, a power law model is assumed to be governing such variations of desired characteristics. Evidently, this system includes different types of couplings and a comprehensive approach is required to describe the structural response. To this aim, the first-order shear deformation theory (FSDT) is used to define different displacement components. Next, the coupled size-dependent vibroacoustic equations are derived based on in conjunction with nonlocal strain gradient theory (NSGT) with the aid of Hamilton’s variational principle and fluid/structure compatibility conditions. NSGT is complemented with hardening and softening material effects which can greatly enhance the precision of results. It is expected to use the findings of this paper in the optimization of similar systems by selecting suitable FG index, incident angle of sound waves, flow Mach number, nonlocal and strain gradient parameters, starting electric potential and geometric features. One of the important findings of this study is that increasing the electric voltage can obtain better sound insulation at small frequencies, specially prior to the ring frequency.

Experimental study on explosion overpressure and flame propagation characteristics of simulated vertical dome oil tank

In order to study the development law of gasoline-air mixture explosion in vertical dome oil tank, a series of experiments are carried out in simulated oil tank. It is found that the development of overpressure in internal field can be divided into three stages: the overpressure rising stage, the overpressure relief stage and the overpressure oscillation and attenuation stage. The maximum overpressure peak, average overpressure rise rate and maximum overpressure rise rate in internal field all increase first and then decrease with the increase of gasoline vapor volume fraction. However, the formation time of the maximum overpressure peak, the maximum negative overpressure and the average pressure relief rate have opposite numerical trends. All of these peaked at the initial gasoline vapor volume fraction of 1.7%. The external field pressure wave of gasoline-air mixture explosion has a great relationship with spatial azimuth. With the increase of proportional distance, the pressure wave of external field at any angle shows the exponential decay law in form of Pext=kR−α. The relationship among the maximum overpressure peak, distance and direction can be uniformly expressed by a formula. With the increase of gasoline vapor volume fraction, the maximum overpressure peak at the nearest measurement point in the direction of dome opening increases first and then decreases, and the formation time of the maximum overpressure peak changes in the opposite trend, which can be expressed by cubic polynomials. The flame propagation of gasoline-air mixture explosion can be divided into three stages: the in-tank development stage, the vent explosion stage and the free burning stage. In addition, affected by fluid instability during explosion propagation, the positive feedback mechanism makes the development of explosion more and more intense.

Permeability enhancement of the KcsA channel under radiation of a terahertz wave.

Potassium ion channels are essential elements in cellular electrical excitability and help maintain a resting potential in nonexcitable cells. Their universality is based on a unique combination of strong selectivity for K^{+} ions and near-diffusion-limited permeation efficiency. Understanding how the channel regulates the ion conduction would be instructive to the treatment of ion channelopathies. In this work, by means of molecular dynamics simulations, we demonstrate the significantly enhanced permeation of KcsA channel in reaction to an external terahertz wave, due to the effective response of the K^{+} ions in the selectivity filter regions of the channel. Compared to the case without external terahertz wave, a fourfold increase in the ion current through the channel is found.

Dynamics of a fermion with dipole moments in external wave fields

We discuss the motion of a massive fermion spin 1/2 particle in external wave field configurations when the Pauli type non-minimal interaction of the gauge field strengths with particle’s dipole moments is taken into account. The exact solution of the relativistic Dirac-Pauli equation is presented for the case of the plane electromagnetic wave.

Doom-roof steel tanks under external explosion: Dynamic responses and anti-explosion measures

Large-scale cylinder storage tank is a kind of typical thin shell space structure, which is widely used in the storage of petrochemical products such as LNG, LPG and so on. The dynamic responses and failure process for steel tank under external explosion shock wave are complex dynamic problems with strong instantaneity, strong non-linearity and strong coupling. In this paper, a coupled analysis model was developed for simulating the dynamic responses of tank under external ground explosion. Compared with experimental datas which were given in existing relevant studies, the validity for numerical model and accuracy for simulation results were verified. Dynamic response for typical cylindrical tank was obtained through coupled numerical simulation, and the influences of scaled distance and tank wall thickness were studied through parameter analysis. Based on the simplified model of explosion loading on tank, the difference of dynamic response between uncoupled model and coupled model was analyzed. The anti-explosion effect for different parameters of anti-explosion bands on tank under external explosion was finally compared. The results show that: 1) The lower two layers tank wall firstly appear inward concave deformation and local plastic state. With the shock wave propagating upward along tank wall, the concave deformation and plastic strain of the front surface of tank wall increase obviously, and the maximum deformation region moves up to the middle part of tank wall, while the maximum plastic region basically remains at the lower part of tank wall. 2) Both the changes of scaled distance and tank wall thickness have significant influences on the deformation and equivalent plastic strain for steel storage tank. The maximum equivalent plastic strain and fracture failure mode generally appears at the lower part of tank wall firstly. The increase of the tank wall thickness is an effective measure to reduce the deformation and plastic strain for tank, and strengthen the anti-explosion performance for tank. 3) Due to the obstacle effect of the anti-explosion bands, the maximum equivalent plastic strain region moves from the bottom part of tank wall to the middle and upper part of tank wall. The displacement and equivalent plastic strain for steel tank decrease with the increase of cross-section and spacing for anti-explosion bands, and the effect of the former (increase height only) is relatively better.

Digital FPGA-based processing of pulses of gas-filled gamma-radiation detector for acoustic noise suppression

Gas-filled proportional detectors of ionizing radiation often contain such elements as thin anode wire, which make them sensitive to external acoustic or vibrational impact. This study investigates such sensitivity for the case of the proportional -radiation detectors filled with high-purity xenon gas. The detector demonstrates a dependence of its signal noise on the external acoustic wave frequency, the character of which most likely depends on the design of the detector, i.e. on such parameters as diameter and tension strength of the anode wire, etc. To suppress the negative impact of acoustic noise on the characteristics of the detector, the detector digital signal is processed in a Field-Programmable Gate Array board. The authors investigate the algorithm of «time windows», which allows separating (filtering) low-frequency noise in the output signal of a gas-filled detector, which arises due to the influence of external sound, from the useful signal, i.e. the ionization pulses. This approach allows performing spectral measurements of -radiation with a significant acoustic noise background, when detectors with a conventional analog spectrometric channel cannot handle the task.

Детектирование субтерагерцевых колебаний на основе гетероструктуры антиферромагнетик/тяжелый металл

We study a model of a detector of subterahertz electromagnetic waves based on an array of heterostructures containing an antiferromagnet and a heavy metal. We show that the operating frequency of the detector can be tuned by a constant magnetic field applied in the direction of the easy magnetization axis of the antiferromagnet. The dependence of the rectified voltage on the frequency of the external electromagnetic wave for different values ​​of the constant magnetic field is resonant in nature, and an increase in the constant magnetic field leads to an increase in the resonance peak. It is shown that the use of an array of antiferromagnets in the form of a comb structure makes it possible to increase the level of the rectified output voltage.

Ship RBF neural network sliding mode PID heading control

In view of the inherent non-linearity, complexity, susceptibility to external wind, wave, and current interference of under-driven ships, and the difficulty of adjusting and adjusting control parameters, to improve the performance of ship’s autopilot, a kind of RBF neural network sliding mode variable structure PID controller is designed. Traditional PID control is sensitive to parameter changes, online tuning is difficult, and easy to overshoot. In order to solve this problem, combining the variable structure characteristics of PID, a differential compensation term is added to the integral term to convert the PID control parameters into three parameters with more obvious physical meanings, and then combined with the RBF neural network learning and identification function to realize online tuning and adaptive control of ship control parameters. Using MATLAB software to simulate the container ship “MV KOTA SEGAR” MMG model shows that the designed RBF neural network sliding mode PID controller can effectively eliminate the ship’s lateral deviation caused by external interference such as wind, waves, currents, etc., with high control accuracy,robustness and strong adaptability.

Hydrodynamic and sediment transport modelling in the Pearl River Estuary and adjacent Chinese coastal zone during Typhoon Mangkhut

Typhoon Mangkhut, in 2018, was one of the worst typhoons in recent history that has made landfall in the Pearl River Estuary (PRE) China. It swept along the coast of Guangdong Province, causing severe damage to many areas and affecting more than one million people. To study the hydrodynamics and sediment dynamics in different sub-regions of the PRE during the typhoon, we implemented a 3D wave-current-sediment coupled ocean model based on the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM). A series of numerical experiments were conducted to study the variation in suspended sediment concentration (SSC) under different external forcing mechanisms, including tides, waves, river discharges and strong winds. Moderate Resolution Imaging Spectroradiometer (MODIS) images, collected after the typhoon landed, were used to assess the simulation results. We found that in the area where the water depth was shallower than 20 m, the increased total suspended sediment concentration was dominated by the regional erosion of fine sediment which was caused by near-bottom wave orbital velocity and bottom shear stress, especially at the four western outlets and along the western coast of the PRE. For the deeper coastal zone, at depths between 20 and 30 m offshore of the western coast, the high total SSC resulted from the contribution of fine sediment transported from the upper and middle estuaries by southwestward advection. A small amount of sand eroded and migrated locally, owing to the corresponding increase in the bottom shear stress. The variation in SSC during the typhoon had a time lag compared with other dynamic conditions, resulting in a maximum 1 h delayed response after the typhoon made landfall. Based on the results of the sensitivity experiments under the same typhoon conditions, we found that, as a result of wave-enhanced bottom shear stress, the SSC values associated with wave-current interaction were significantly higher, by as much as 1.5 and 1.3 times those of simulations without the waves at the surface and near-bottom layers, respectively. This indicated that the sediment resuspension induced by waves was important during typhoon landfall. However, the strong wind-induced current was weakened owing to the joint effect of wave radiation stress and enhanced bottom stress; thus, considering wave effects, the magnitude of the resulting sediment transport rate was smaller than that without considering wave effects, especially in shallow waters. During the approach, landfall and retreat of Typhoon Mangkhut, Lingding Bay experienced two transitions from a slight state of sediment loss to a relatively high state of sediment gain, followed by an even greater state of sediment loss. During an M2 tidal cycle after Typhoon Mangkhut made landfall, the net seaward suspended load sediment transport in Lingding Bay reached 0.37 megatonnes. For the typhoon period covering three M2 tidal cycles, the overall state of suspended load sediment transport in Lingding Bay was sediment loss, with the magnitude of sediment loss on the west side being larger than that of sediment gain on the east side. The magnitude of the overall sediment loss in Lingding Bay would be enlarged unrealistically by approximately 73% if the wave effects were excluded. In each period, the extent of sediment transport between the two sides of the bay was strengthened by the wave-current interaction under typhoon conditions. We determined that the net effect of wave-current interaction and strong wind-induced currents under typhoon conditions was a key factor for erosion, which resulted in SSC-influenced areas being approximately 8.7 and 4.4 times as large as those under normal weather conditions for the surface and near-bottom layers, respectively. The turbidity maximum moved from the West Shoal of Lingding Bay under normal weather to the Modaomen Estuary, which was the most affected area during the typhoon when wave effects were considered. We also showed that the relative location of the typhoon path with respect to the estuary had a more significant effect on erosion than the intensity of the typhoon.

A model for considering effects of extremely low frequency electromagnetic fields on quail embryonic cells

<abstract> <p>Previous experiments have shown that extremely low frequency electromagnetic fields could cause serious effects on the evolution of cells. We propose a mathematical model which confirms those results. In our model, electromagnetic waves could cause the motions of ions and charges and the emergence of some currents around and in the interior of cells. These currents produce some waves which interact with the DNAs and remove or attach some repressors. Consequently, some genes could be turned on or off, and cells could obtain some properties or lose them. The frequency of the external waves should be close to the frequency of the exchanged waves between the repressors and DNAs or even bigger than them. We test this idea and did some experiments on quail embryonic cells. We connected a sample of these cells to a battery and considered their evolution. We observed that after connecting the battery and the production of electrical current, some rings around the quail embryonic cells emerged. Maybe, these rings are the response of the cells to changes in electromagnetic waves and electrical currents.</p> </abstract>

Motion Responses of a Berthed Tank under Resonance Coupling Effect of Internal Sloshing and Gap Flow

The growth of global energy transportation has promoted the rapid increase of large-scale LNG (liquefied natural gas) carriers, and concerns around the safety of LNG ships has attracted significant attention. Such a floating structure is affected by the external wave excitation and internal liquid sloshing. The interaction between the structure’s motion and the internal sloshing under wave actions may lead to the ship experiencing an unexpected accident. In this research, a hydrodynamic experiment is conducted to investigate the motion responses of a floating tank mooring, both close to and away from a dock. The resonance coupling effect of the internal sloshing and gap flow on the tank’s motion is considered. Based on the measured motion trajectory of the floating tank, the stability and safety of the floating tank are estimated. The results show that the sloshing resonance and narrow gap resonance are beneficial to the stability of the ship. This is helpful for controlling the motion of a berthed ship under wave action with a reasonable selection of the gap distance and the liquid level.

Numerical modelling and dynamic response analysis of a 10 MW semi-submersible floating offshore wind turbine subjected to ship collision loads

The number of installed offshore wind turbines is continuously growing worldwide in recent years. Offshore wind farms are generally located near the coast close to traffic lanes and are exposed to the risk of collisions from visiting and passing ships. Potential consequences of collisions may vary from local structural damage to the detachment of turbine nacelles and rotors, and even tower collapse and capsizing of the turbine platform, causing significant economic loss and fatalities.This paper investigates ship collision responses of a semi-submersible floating offshore wind turbine (FOWT), i.e. the OO-STAR floater with the DTU 10 MW blades, using the nonlinear finite element code USFOS. The OO-STAR floater is made of post-tensioned concrete designed by Dr. techn. Olav Olsen. The striking ships are selected to be a modern supply vessel of 7500 tons and a shuttle tanker of 150,000 tons, representing respectively service/coastal merchant vessels and large passing vessels. Modelling of the FOWT in USFOS is described in detail including the OO-STAR floater, the DTU 10 MW turbine blade, the turbine tower, and the mooring system. The modelled hydrodynamic loads include buoyancy loads and motion induced radiation loads using the Morrison equation. The effects of external waves and currents are assumed to be small and ignored in all directions. Eigenmode analysis of the turbine model is performed to verify the established model.Global collision response analyses of the FOWT were performed in both parked and operating conditions. The ship resistance is modelled as nonlinear springs in USFOS containing force displacement curves simulated in LS-DYNA. In operating conditions, wind loads are introduced including wind thrust loads and wind induced torque to rotate the turbine blades. The changes of upstream wind speeds and rotor/wake interactions during collisions are neglected. The results are discussed with respect to energy absorption of the ship and the FOWT, and structural responses of the FOWT including global motions, nacelle accelerations, tower clearance, tower vibrations, and responses of the mooring system.

An MHD Study of Large-Amplitude Oscillations in Solar Filaments

Quiescent filaments are usually affected by internal and/or external perturbations triggering oscillations of different kinds. In particular, external large-scale coronal waves can perturb remote quiescent filaments leading to large-amplitude oscillations. Observational reports have indicated that the activation time of oscillations coincides with the passage of a large-scale coronal wavefront through the filament, although the disturbing wave is not always easily detected. Aiming to contribute to understand how -- and to what extent -- coronal waves are able to excite filament oscillations, here we modelled with 2.5 MHD simulations a filament floating in a gravitationally stratified corona disturbed by a coronal shock wave. This simplified scenario results in a two-coupled oscillation pattern of the filament which is damped in a few cycles, enabling a detailed analysis. A parametric study was accomplished varying parameters of the scenario such as height, size and mass of the filament. An oscillatory analysis reveals a general tendency where periods of oscillations, amplitudes and damping times increase with height, whereas filaments of larger radius exhibit shorter periods and smaller amplitudes. The calculation of forces exerted on the filament shows that the main restoring force is the magnetic tension.

Mitigation of the supermode noise in a harmonically mode-locked ring fiber laser using optical injection.

We report on a new, to the best of our knowledge, technique enabling mitigation of the supermode noise (and timing jitter) in a soliton harmonically mode-locked (HML) fiber laser built on the nonlinear polarization evolution (NPE). An optical injection of an external continuous wave (CW) into the HML laser cavity results in an increase of the supermode noise suppression level (SSL) by a two-three order of magnitude for harmonics between 25th and 135th. The operation mechanism involves phase-locking between the injected light and soliton pulses and exhibits strong resonant dependence on the CW laser wavelength. Our findings offer important insights into the HML laser dynamics associated with an interaction between solitons and CW background in the laser cavity.

Pulse repetition rate tuning of a harmonically mode-locked ring fiber laser using resonant optical injection.

We report on a new, to the best of our knowledge, technique enabling fine-tuning of the pulse repetition rate (PRR) of a soliton harmonically mode-locked (HML) fiber laser built on the nonlinear polarization evolution (NPE). Optical injection of an external continuous wave (CW) into the HML laser cavity is used for this purpose enabling precise PRR tuning with the elementary step equal to the fundamental PRR one-by-one. The effect exhibits strong resonance dependence on the CW laser wavelength and available in both positive and negative directions. Our findings offer important insights into the HML laser dynamics associated with the birth and annihilation of solitons in the cavity.

Modeling Marsh Dynamics Using a 3-D Coupled Wave-Flow-Sediment Model

Salt marshes are dynamic biogeomorphic systems that respond to external physical factors, including tides, sediment transport, and waves, as well as internal processes such as autochthonous soil formation. Predicting the fate of marshes requires a modeling framework that accounts for these processes in a coupled fashion. In this study, we implement two new marsh dynamic processes in the 3-D COAWST (coupled-ocean-atmosphere-wave sediment transport) model. The processes added are the erosion of the marsh edge scarp caused by lateral wave thrust from surface waves and vertical accretion driven by biomass production on the marsh platform. The sediment released from the marsh during edge erosion causes a change in bathymetry, thereby modifying the wave-energy reaching the marsh edge. Marsh vertical accretion due to biomass production is considered for a single vegetation species and is determined by the hydroperiod parameters (tidal datums) and the elevation of the marsh cells. Tidal datums are stored at user-defined intervals as a hindcast (on the order of days) and used to update the vertical growth formulation. Idealized domains are utilized to verify the lateral wave thrust formulation and show the dynamics of lateral wave erosion leading to horizontal retreat of marsh edge. The simulations of Reedy and Dinner Creeks within the Barnegat Bay estuary system demonstrate the model capability to account for both lateral wave erosion and vertical accretion due to biomass production in a realistic marsh complex. The simulations show that vertical accretion is dominated by organic deposition in the marsh interior, whereas deposition of mineral estuarine sediments occurs predominantly along the channel edges. The ability of the model to capture the fate of the sediment can be extended to model to simulate the impacts of future storms and relative sea-level rise (RSLR) scenarios on salt-marsh ecomorphodynamics.

Ultrasound-Mediated Cancer Therapeutics Delivery using Micelles and Liposomes: A Review.

Existing cancer treatment methods have many undesirable side effects that greatly reduce the quality of life of cancer patients. This review will focus on the use of ultrasound-responsive liposomes and polymeric micelles in cancer therapy. This review presents a survey of the literature regarding ultrasound-triggered micelles and liposomes using articles recently published in various journals, as well as some new patents in this field. Nanoparticles have proven promising as cancer theranostic tools. Nanoparticles are selective in nature, have reduced toxicity, and controllable drug release patterns making them ideal carriers for anticancer drugs. Numerous nanocarriers have been designed to combat malignancies, including liposomes, micelles, dendrimers, solid nanoparticles, quantum dots, gold nanoparticles, and, more recently, metal-organic frameworks. The temporal and spatial release of therapeutic agents from these nanostructures can be controlled using internal and external triggers, including pH, enzymes, redox, temperature, magnetic and electromagnetic waves, and ultrasound. Ultrasound is an attractive modality because it is non-invasive, can be focused on the diseased site, and has a synergistic effect with anticancer drugs. The functionalization of micellar and liposomal surfaces with targeting moieties and the use of ultrasound as a triggering mechanism can help improve the selectivity and enable the spatiotemporal control of drug release from nanocarriers.