Generation Of Waves Research Articles

Environmental-Sensing and adaptive optimization of wave energy converter based on deep reinforcement learning and computational fluid dynamics

This paper introduces a novel coupled model for real-time control of the point absorber wave energy converter (WEC) using parallelized deep reinforcement learning (DRL), where the WEC is situated within a numerical wave tank (NWT) built with the method of computational fluid dynamics (CFD). An in-house solver is developed to couple with the DRL and CFD to solve the interaction between WEC and the fluid environment. Validations on wave generation, wave-floater interaction, and power take-off (PTO) unit are carried out. Then, neglecting the detailed model for the PTO technologies, the DRL-based strategy dynamically adjusts the PTO force as a function of the wave features and floater motion. Based on the interaction data, the model-free DRL is outstanding in adaptability and robustness. Simulation results reveal that DRL control improves the wave energy absorption in irregular wave environments, resulting in improvement of 107.5 % compared to the resistive control, with better device protection performance than the model predictive control (MPC). An additional analysis of model-free characteristics of DRL demonstrates the optimization ability independent of floater modeling. This work is the first in-depth study of DRL control of WECs in CFD simulation, providing a more accurate simulation and an optimization process closer to the reality.

КОМП'ЮТЕРНЕ МОДЕЛЮВАННЯ НЕСТАЦІОНАРНОГО ПРОЦЕСУ РОЗВИТКУ НАДЗВУКОВОГО ПЕРЕРОЗШИРЕНОГО СТРУМЕНЮ

Questions of numerical simulation of non-stationary process of the development of a supersonic overexpanded jet are considered. Unsteady Reynolds-averaged Navier-Stokes equations (URANS) of compressible flows, written in an arbitrary coordinate system, along with the Spalart-Allmaras one-equation differential turbulence model are applied. The calculations of non-stationary formation of an air cold supersonic jet during the blowing through a conical Laval nozzle (simulation of engine start-up) were made. The physical features of the shock and acoustic waves generation and propagation are discussed. In the stationary phase an overexpanded free supersonic turbulent jet is formed, which includes a Mach disc in its structure. The obtained results were compared with experimental data and calculations by other authors based on the ANSYS Fluent and FloEFD CFD tools.

Effectiveness of Body Armor Against Shock Waves: Preventing Blast Injury in a Confined Space.

Introduction Blast injuries in modern society often occur owing to terrorist attacks in confined spaces, particularly in urban settings, indoors, and in vehicles, leading to significant damage. Therefore, it is important to focus on blast injuries in confined spaces rather than in conventional open-field experiments. Materials and methods We used an air-driven shock wave generator (blast tube) established indoors in 2017 and conducted basic research to potentially save the lives of patients with blast injuries. Under general anesthesia, pigs were divided into with body armor (BA) and without BA groups. The pigs were fixed in the measurement chamber with their dorsal chest directly exposed to the shock wave. The driving pressure was set at 3.0 MPa to achieve a mortality rate of approximately 50%. A generated shock wave was directly applied to the pigs. Comparisons were made between the groups with respect to cardiac arrest and survival, as well as apnea, bradycardia, and hypotension, which are the triad of blast lung. Autopsies were performed to confirm the extent of the organ damage. Statistical analysis was performed using Fisher's exact test, and statistical significance was set at p<0.05. The animal experimentation was conducted according to the protocol reviewed and approved by the Animal Ethics Committee of the National Defense Medical College Hospital (approval number 19041). Results Eight pigs were assigned to the BA group and seven pigs to the non-BA group. In the non-BA group, apnea was observed in four of seven cases, three of which resulted in death. None of the eight pigs in the BA group had respiratory arrest; notably, all survived. Hypotension was observed in some pigs in each group; however, there were no cases of bradycardia in either group. Statistical analysis showed that wearing BA significantly reduced the occurrence of respiratory and cardiac arrest (p=0.026) but not survival (p=0.077). No significant differences were found in other vital signs. Conclusions Wearing BA with adequate neck and chest protection reduced mortality and it was effective to reduce cardiac and respiratory arrest against shock wave exposure. Mortality from shock wave injury appears to be associated with respiratory arrest, and the avoidance of respiratory arrest may lead to survival.

Development of a numerical wave tank of deep ocean engineering basin via high order spectral method

ABSTRACT In this study, we developed a numerical model for simulating wave environments of the deep ocean engineering basin (DOEB) by utilising the high order spectral (HOS) method. The approach employed the pseudospectral basis of the cosine function to automatically account for the tank wall boundary conditions. Additionally, the fast Fourier transform (FFT) algorithm was implemented to maximise the numerical efficiency. For selecting an appropriate wave generation technique for the DOEB, which distinguishes itself as a large-scale facility with controllable depth, in contrast to conventional wave basins, two-dimensional wave generation simulations were executed. These simulations entailed the application and subsequent evaluation of the embedded wave generation technique and the additional potential technique. Of these, the embedded wave generation technique, characterised by its suitability for numerical efficiency and adaptability to variable water depths, was chosen for implementation in the DOEB numerical tanks. The Stroke–source converting procedure was established to transform the stroke time history of the wave maker into the input wave source time history for the embedded wave generation technique, with due consideration to phase correction. In order to validate the developed numerical model, a wave generation experiment was conducted, and its results were compared with the numerical simulations. This comparative analysis revealed a high degree of correspondence between the nonlinear simulations and the experimental wave time history, demonstrating the model’s ability to accurately replicate higher-order wave components, including wave–wave interactions. The resulting numerical model serves as a valuable computer-aided tool, enhancing the efficiency of experiments within the DOEB.

Modulation effect of uniform flow on three-dimensional freak wave generation in arbitrary water depth

In arbitrary water depths, the influence of uniform flow, which includes transverse and longitudinal flows, on the generation of three-dimensional (3D) freak waves is examined. A modified Davey–Stewartson equation is derived using potential flow theory and the multiscale method. This equation describes the evolution of 3D freak wave amplitude under the influence of uniform flow. The relationship between two-dimensional (2D) modulational instability (MI) and the generation of 3D freak waves, as represented by the modified 3D Peregrine Breather solution, is explored. The characteristics of 2D MI depend on the orientation of the longitudinal and transverse perturbations. In shallow waters, the generation of freak waves by MI is challenging due to the minimal orientation difference, and longitudinal flows hardly affect the occurrence of MI. Variations in relative water depth can contribute to forming shallow-water freak waves. In finite-depth waters, oblique modulation leads to MI, whereas in deep and infinite-depth waters, longitudinal modulation gains significance. In environments of finite-depth, deep, and infinite-depth waters, the divergence (convergence) effect of longitudinal favorable (adverse) currents reduces (increases) the MI growth rate and suppresses (facilitates) freak wave generation.

An Earth-fixed observer to ship waves

This work deals with the linear surface waves generated by a vessel advancing at a constant forward speed. These waves, known as ship waves, appear stationary to an observer on the vessel. Rather than exploring the well-studied stationary ship waves, this work delves into the physical properties of ship waves measured at Earth-fixed locations. While it might have been expected that analysing these waves in an Earth-fixed coordinate system would be a straightforward transformation from existing analytical theories in a moving coordinate system, the reality proves to be quite different. The properties of waves measured at fixed locations due to a passing ship turn out to be complex and non-trivial. They exhibit unique characteristics, being notably unsteady and short crested, despite appearing stationary to an observer on the generating vessel. The analytical expressions for the physical properties of these unsteady waves are made available in this work, including the amplitude, frequency, wavenumber, direction of propagation, phase velocity and group velocity. Based on these newly derived expressions and two-point measurements, an inverse method has been presented for determining the advancing speed and the course of motion of the moving ship responsible for the wave generation. The results from this study can be used in a wide range of applications, such as interpreting data from point measurements and assessing the roles of ship waves in transporting ocean particles.

Traumatic Brain Injury and Conversion Disorder in a Veteran’s Atypical Presentation

IntroductionTraumatic brain injury (TBI) induces cognitive and behavioral changes due to environmental impacts on brain tissue.ObjectivesHighlighting the atypical TBI presentation challenging conventional diagnostics and obscured by conversion disorders.MethodsA 36-year-old male veteran, injured by a sniper rifle in 2011, presented with right ear tinnitus and monthly, unresponsive right hemicranial headaches. Seizures occurred every two weeks with no reported loss of consciousness or sensation. The gunshot wound to the neck in 2011 prompted emergency intervention, with entry and exit wounds located in the posterior lateral neck. Post-injury symptoms comprised hearing loss, tinnitus, restricted neck movement, and weakness in the right arm. Seizures persisted, accompanied by numbness and neck movement. Management included physical therapy, hyperbaric oxygen therapy (improving weakness but not tinnitus), and administration of piracetam (2400 mg/day), sertraline (100 mg/day), and ginkgo biloba (2400 mg/day). Psychiatric consultation suggested a diagnosis of “conversion disorder.”ResultsNeuropsychological Evaluation: Raven Standard Progressive Matrices Test showed borderline impairment. Psychiatric Evaluation noted monotonous mimics, occasional depersonalization, reduced emotional involvement, and slowed psychomotor activity. Elevated trait anxiety was observed per the State-Trait Anxiety Inventory. Neurological Examination identified left arm weakness and impaired resting balance. Imaging Findings: F18-FDG PET/CT Scan at 1 year post-GSW showed hypermetabolism in the right frontal lobe, and at 3.5 years post-GSW demonstrated decreased glucose metabolism in the bilateral cerebellar cortex, temporal lobe, and bilateral parietal lobe.ConclusionsA high-kinetic-energy bullet passed through the right lateral base of the neck without causing apparent brain damage. Proposed is the generation of upward pressure waves in neck tissues through the transmission of kinetic energy, compressing and displacing soft tissues toward the skull. Gunshot injuries create cavities, forming high-pressure waves capable of damaging distant brain regions, leading to TBI such as crush injury, edema, and myelin and axonal damage (Courtney &amp; Courtney, 2007). Microscopic brain damage, undetectable by current imaging, may only surface during autopsy (Yilmaz &amp; Pekdemir, 2007). Rat studies after primary blast injuries reveal brain alterations, highlighting that high-pressure pulses can cause neuronal damage, potentially yielding related symptoms (Cernak et al., 2001). The patient’s atypical symptoms, combined with the initial conversion disorder hypothesis, underscore the need for a diagnostic paradigm shift to differentiate traumatic brain injury from other potential misnomers.Disclosure of InterestNone Declared

On the Global Features of the 10–60‐Min ULF Waves in Jovian Magnetosphere: Juno Observations

AbstractIn the Jovian magnetosphere, quasi‐periodic phenomena, with quasi‐periods on the order of 10–60 min, are frequently identified using different data sets. These pulsations are a branch of ultra‐low frequency (ULF) waves, which are believed to play a crucial role in driving the energy circulation within Jupiter's magnetosphere. In this study, we utilize magnetic field data collected by Juno between 2016 and 2022 to perform a comprehensive global statistical analysis of the spatial distribution and periodic characteristics of ULF waves in the Jovian magnetosphere. Our findings reveal distinct periodic features observed at different latitudes and distances, providing valuable insights into the generation mechanisms of ULF waves. Furthermore, we establish a close relationship between the presence of these ULF wave fluctuations and the magnetospheric state, such as under conditions of solar wind compression. By combining contemporaneous ultraviolet aurora observations from the Hubble Space Telescope (HST) and magnetic field data obtained by Juno, we have discovered that the compressed magnetospheres exhibit more pronounced ULF waves and enhanced auroral activity. These results provide a global picture of the distribution, implying potential generation of ULF waves in the Jovian magnetosphere, and shedding light on the processes behind the 10–60‐min energy releases.

Primordial Black Holes in Scalar Field Inflation Coupled to the Gauss–Bonnet Term with Fractional Power-law Potentials

In this study, we investigate the formation of primordial black holes (PBHs) in a scalar field inflationary model coupled to the Gauss–Bonnet term with fractional power-law potentials. The coupling function enhances the curvature perturbations, then results in the generation of PBHs and detectable secondary gravitational waves (GWs). We identify three separate sets of parameters for the potential functions of the form ϕ 1/3, ϕ 2/5, and ϕ 2/3. By adjusting the model parameters, we decelerate the inflaton during the ultra-slow-roll phase and enhance curvature perturbations. Our calculations predict the formation of PBHs with masses of O(10)M⊙ , which are compatible with LIGO-Virgo observational data. Additionally, we find PBHs with masses around O(10−6)M⊙ and O(10−5)M⊙ , which can explain ultra-short-timescale microlensing events in OGLE data. Furthermore, our proposed mechanism could lead to the formation of PBHs in mass scales around O(10−14)M⊙ and O(10−13)M⊙ , contributing to approximately 99% of the dark matter in the Universe. We also study the production of secondary GWs in our model. In all cases of the model, the density parameter of secondary GWs ΩGW0 exhibits peaks that intersect the sensitivity curves of GW detectors, providing a means to verify our findings using data of these detectors. Our numerical results demonstrate a power-law behavior for the spectra of ΩGW0 with respect to frequency, given by ΩGW0(f)∼(f/fc)n . Additionally, in the infrared regime where f ≪ f c , the power index takes a log-dependent form, specifically n=3−2/ln(fc/f) .

Observation of Kinetic Alfvén Waves inside an Interplanetary Coronal Mass Ejection Magnetic Cloud at 1 au

Recent advancements have significantly enhanced our grasp of interplanetary coronal mass ejections (ICMEs) in the heliosphere. These observations have uncovered complex kinematics and structural deformations in ICMEs, hinting at the possible generation of magnetohydrodynamic (MHD) and kinetic-scale waves. While MHD-scale waves in magnetic clouds have been explored, understanding the dynamics of kinetic-scale mode waves remains challenging. This article demonstrates the first in situ observation of kinetic Alfvén waves (KAWs) within an ICME’s magnetic cloud, notably near the heliospheric current sheet–ICME interaction region, close to the reconnection exhaust. Analysis indicates a distinctive negative bump in the estimated normalized magnetic helicity (σ m = −0.38) around the gyrofrequency spread, indicating a right-handed polarization of the wave. Furthermore, examination across flow angle (θ VB) within the frequency domain reveals a specific zone (90°–135°) showcasing negative helicity fluctuations, confirming the presence of KAWs. Moreover, we noted a significant rise in temperature anisotropy in the vicinity, indicating the role of KAWs in plasma heating. Identifying KAW challenges established notions about ordered magnetic clouds and raises questions about energy transfer processes within these structures. This finding opens the door to a deeper understanding of energy transfer mechanisms within traditionally nondissipative regions and invites further exploration of low-beta plasma heating and the interactions between waves and particles in magnetic clouds.

Circuits in the motor cortex explain oscillatory responses to transcranial magnetic stimulation.

Transcranial magnetic stimulation (TMS) is a popular method used to investigate brain function. Stimulation over the motor cortex evokes muscle contractions known as motor evoked potentials (MEPs) and also high-frequency volleys of electrical activity measured in the cervical spinal cord. The physiological mechanisms of these experimentally derived responses remain unclear, but it is thought that the connections between circuits of excitatory and inhibitory neurons play a vital role. Using a spiking neural network model of the motor cortex, we explained the generation of waves of activity, so called 'I-waves', following cortical stimulation. The model reproduces a number of experimentally known responses including direction of TMS, increased inhibition, and changes in strength. Using populations of thousands of neurons in a model of cortical circuitry we showed that the cortex generated transient oscillatory responses without any tuning, and that neuron parameters such as refractory period and delays influenced the pattern and timing of those oscillations. By comparing our network with simpler, previously proposed circuits, we explored the contributions of specific connections and found that recurrent inhibitory connections are vital in producing later waves that significantly impact the production of motor evoked potentials in downstream muscles (Thickbroom, 2011). This model builds on previous work to increase our understanding of how complex circuitry of the cortex is involved in the generation of I-waves.

Characteristic and mechanism of pollution by laser cleaning high-value vehicle parts with a complex structure in remanufacturing industry

Remanufacturing high-value vehicle parts is of substantial significance for the circular economy because it provides a second service life and reduces solid waste generation. Laser cleaning is a promising method in the remanufacturing industry owing to its high energy, precision, and efficiency. However, the pollution caused by laser cleaning remains unknown and has rarely been reported, limiting the application of this method. In this study, pollution removal and conversion using a high-energy laser were explored, and environmental life cycle and health risk assessments were conducted. The results showed that high-energy lasers might induce new organic pollutants, such as olefins, alkynes, and aldehydes. During laser cleaning, thermal elastic expansion and shock wave generation were the main mechanisms of rust removal, and evaporation and small-scope boiling were used for waste oil removal. The mean concentration of PM10 was above 7000 µg/m3 in laser rust removal, and the total concentration of volatile organic compounds (VOCs) was the highest in laser oil removal (∼ 2568 µg/m3). Particulate matter contained high amounts of Fe, Al, and Mn. An environmental life cycle assessment indicated that laser cleaning for stain removal significantly reduced the total environmental impact compared with that of traditional solvent-ultrasonic cleaning (∼ 40.0%) and sandblasting (∼ 83.3%). This study provides an environmental protection basis for increasing the use of laser cleaning in the remanufacturing industry.

Rayleigh–Plesset-based Eulerian mixture model for cavitating flows

The homogeneous mixture model (HMM) is widely in use for simulation of cavitating flows. The mass transfer is typically ruled by simplified models whose efficiency is strictly dependent on the empirical choice of vaporization/condensation constants. In the present paper, we formulate a physically based mass-transfer model relying on the solution of the complete Rayleigh–Plesset (RP) equation. The latter can model the elasticity of the bubbles and non-linear interaction with the external pressure field. The model is tested in different configurations, also considering comparisons with the Schnerr–Sauer model (SSm) and the linearized version of the RP equation. The preliminary simplified tests show that the SS model responds statically to pressure variations and thus in not able to reproduce the actual dynamics of cavitation, under certain circumstances. On the other hand, the linearized RP model (RPl), although dynamically responsive to pressure variations, produces unrealistic small-amplitude bubble fluctuations, whereas the complete RP model (RPc) gives more realistic results. Tests on the performance of the SSm and RP models were carried out considering the turbulent flow in a convergent–divergent Venturi channel, already tested in numerical and experimental reference research. Here, we use the incompressible HMM. The study highlights various crucial aspects of the RPc model, emphasizing its own ability in replicating the shedding cycle as a three-dimensional, and non-stationary phenomenon. On the other hand, the SSm model results as a valid approximation for initial growth stages but fails to capture complex dynamics during the collapse phase. The results are consistent with recent literature findings, and refinements in grid resolution enhance accuracy in capturing the non-stationary sheet-to-cloud vapor dynamics. Neglecting compressibility may account for disparities between numerical and experimental outcomes, especially concerning shock waves generation and propagation. The RPc model emerges as a good candidate in reproducing bubble cloud dynamics and, in the next future, can be implemented in compressible HMM.

Study on microscopic origin of spin excitation in TmFeO3 by time-resolved multicolor optical pump-probe spectroscopy

Spin dynamics of TmFeO3, mainly induced by two different mechanisms, were investigated by time-resolved multicolor pump-probe spectroscopy using femtosecond laser pulses. The spin dynamics, caused either by spin-reorientation phase transition or optical polarization-dependent effect, were distinguished by investigating their dependencies on external magnetic field and optical polarization. Spectral-dependent magneto-optic studies of the spin phase transition-induced spin dynamics revealed that laser-induced nonthermal exchange interaction between the electron states of iron (Fe3+) and thulium (Tm3+) ions is crucial for subsequent spin dynamics. This exchange interaction is influenced by the population change of the 4f electron states of Tm3+ ions, making the spin wave generation highly dependent on crystal temperature. However, spectroscopic studies of the polarization-dependent spin dynamics show that they are only related to the 3d electrons of Fe3+ ions, therefore, the spin dynamics appear to be a universal effect over a wide temperature range. Our observation can be further applied to study extended orthoferrite systems with other rare earth atoms.

Improved detection of nonlinear waves in thin solid materials using a pulse-echo method based on nonlinear modeling of wave fields

The nonlinearity parameter is a powerful tool for nondestructive evaluation, as it provides a measure of the state of damage of structural components. When carrying out nonlinearity parameter measurements of solid structures, the pulse-echo method is more suitable than the through-transmission method; however, a planar stress-free boundary is known to destructively alter the nonlinear wave generation process, including the second harmonic component, meaning that the pulse-echo nonlinear method is limited for practical applications, especially for thin solids. In this work, an improved detection method is proposed for the enhancement of nonlinear wave measurement in thin solids using a pulse-echo method with a dual-element transducer consisting of an outer ring transmitter and an inner disk receiver. A multi-Gaussian beam model is developed for the ring transmitter to fast simulate the pulse-echo nonlinear wave fields, and based on the results, improvements for the received nonlinear waves are achieved by optimizing the driving frequency. The advantages of the proposed method are that solid samples with different thicknesses can be evaluated using a dual-element transducer, and a high measurement accuracy can also be achieved for thin solid samples. Experiments are performed to investigate the harmonic waves measured in fatigue-damaged thin steel samples, and the results verify the effectiveness of the proposed method.

Compressibility effects on cavity dynamics and shock waves in high-speed water entry

The importance of high-speed water entry is acknowledged within the defense industry. This study numerically investigates the water entry of a high-speed rectangle projectile, focusing on cavity dynamics and shock wave generation. A computational model is employed to accurately simulate the intricate fluid dynamics of compressible multiphase flows. This model integrates a dual-phase flow algorithm with a thermally sensitive Tait equation of state for the liquid phase. The primary focus lies in understanding the effects of fluid compressibility on cavity evolution and shock wave propagation across different Froude numbers. The findings reveal that compressibility induces changes in cavity formation size, leading to significant variations in phase composition within the cavity. Furthermore, compressibility enhances the air cushion effect upon surface impact, resulting in delayed water entry and concurrent reduction in projectile drag. Moreover, a prognostic model is proposed, correlating shock pressure with propagation distance, thereby validating theoretical hypotheses advanced by Lee et al. [J. Fluid Struct., 11, 819–844 (1997)].

An Eulerian–Lagrangian particle method for weakly compressible viscous flows using peridynamic differential operator

This study proposes a peridynamic differential operator (PDDO)-based Eulerian–Lagrangian hybrid particle method for weakly compressible viscous flows. The PDDO is utilized to transform the governing partial differential equations into their integral form; hence, the issue of local non-differentiability is eliminated. Both the Eulerian and Lagrangian formulations of particle methods for solving the governing integral equations are derived and then combined to propose the hybrid method. In the proposed method, the Eulerian and Lagrangian formulation is utilized to solve the governing equations in the inner computational domain and in areas with free surfaces, respectively. The results of these two domains are then merged to arrive at the solution. In such a way, the hybrid particle method effectively balances the computational demands and applicability. The numerical stability and interpolation consistency of the proposed method are shown by introducing the laminar viscosity model. A detailed numerical procedure is provided involving the boundary conditions and time-stepping strategy. The proposed method is validated by several benchmark problems. Furthermore, the method was applied to several benchmark problems including the hydrostatic test, Taylor–Green vortex, and numerical wave generation. The results of these numerical examples suggest that the proposed method is computationally less demanding while maintaining accuracy.

The Effect of Adding Coconut Coir Fiber on Compressive Strength, Tensile Strength, and Concrete Flexural Strength in Eco-Friendly Tetrapod Planning in Coastal Areas of IKN Supporting Cities

Beaches often experience erosion or abrasion problems caused by various factors, such as climate change which triggers rising sea levels, high waves, human activities such as beach reclamation, and infrastructure construction that is not environmentally friendly, triggering erosion on the coast. In the coastal area of the city that supports IKN, which is located in the Balikpapan area, Manggar Beach, also experiences abrasion which causes land to narrow in that area. The abrasion that occurs erodes the coastal area around 7-8 meters every year. To produce environmentally friendly infrastructure, this research carried out the addition of coconut fiber waste components to tetrapod concrete used for breakwater construction. In this research, variations in the addition of coir used were 0%, 1%, 2%, 3%, 4% and 5%. The aim was to find out how much influence the addition of coconut coir waste to the concrete mixture had on the compressive strength, tensile strength and flexural strength of the concrete in tetrapods. and produce concrete that uses coconut fiber waste as an alternative material for tetrapod concrete as breakwater armor. Based on the analysis results, the quality of the concrete was 23 Mpa. This value was determined based on wave generation analysis. In addition, it is known that variations in coconut fiber affect the slump, compressive strength, flexural and split tensile test values of concrete. Based on the slump test results, it was found that the greater the variation of coconut fiber in the concrete, the lower the resulting slump test value. In testing the compressive, flexural and split tensile strength, it was found that the optimal composition for adding coconut fiber was 3%, in this composition the amount of coconut fiber fiber was able to improve the mechanical properties of tetrapod concrete compared to other compositions.

Exploring the surge current degradation of natural ester oil-based nanofluids

The surge endurance of natural ester oil-based nanofluids against surge events is investigated experimentally. The focus of this work is the examination, through dielectric spectroscopy measurements, of the alteration of the real and imaginary parts of the complex relative permittivity of iron oxide nanofluids as a result of an accelerated degradation test employing a sequence of repetitive current impulses produced via a 12 kV/6 kA combination wave generator. The target is the exploration of a possible implementation of nanofluids as multipurpose liquids that act, in addition to insulation and coolants, as surge absorption media. Promising experimental results are discussed and compared with those of mineral oil that is widely used as a conventional insulating liquid in power transformers.

Bridge pier under coupled earthquake and wave - Current actions: Numerical model establishing, optimization and structural response analysis

Bridges located in earthquake-prone areas may be subjected to earthquake, wave and current actions simultaneously. Current investigations on bridge piers under these complex loading conditions were generally performed through underwater shaking table (UST) tests, which required advanced test setups and great expenses. With the aim of eliminating these limits and developing a comprehensive understanding of the performance of deep-water bridge piers under coupled earthquake and wave-current actions, the present study carried out systematic numerical investigations. Wave generation and propagation were first simulated, for which thorough sensitivity analysis was conducted to obtain the optimal parameters, including mesh size, time step intervals, damping zone length and damping coefficients. Numerical models which are able to simulate nonlinear wave-current interactions were then established and validated. Following this, structural responses of bridge piers under wave, wave-current and coupled earthquake and wave-current actions were numerically simulated and validated by test results. Finally, parametric analysis was conducted on a pile of a practical deep-water bridge in China using the validated model with consideration of various water depth levels, diverse wave heights, different current velocities, varied earthquakes and different peak ground accelerations to reveal the influence of different excitation parameters on structural responses.