Sea Wave Motion Research Articles

The environmental low-frequency background for macro-calorimeters at the millikelvin scale

Many of the most sensitive physics experiments searching for rare events, like neutrinoless double beta (0νββ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0\ u \\beta \\beta $$\\end{document}) decay, coherent elastic neutrino nucleus scattering and dark matter interactions, rely on cryogenic macro-calorimeters operating at the mK-scale. Located underground at the Gran Sasso National Laboratory (LNGS), in central Italy, CUORE (Cryogenic Underground Observatory for Rare Events) is one of the leading experiments for the search of 0νββ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0\ u \\beta \\beta $$\\end{document} decay, implementing the low-temperature calorimetric technology. We present a novel multi-device analysis to correlate environmental phenomena with the low-frequency noise of low-temperature calorimeters. Indeed, the correlation of marine and seismic data with data from a couple of CUORE detectors indicates that cryogenic detectors are sensitive not only to intense vibrations generated by earthquakes, but also to the much fainter vibrations induced by marine microseisms in the Mediterranean Sea due to the motion of sea waves. Proving that cryogenic macro-calorimeters are sensitive to such environmental sources of noise opens the possibility of studying their impact on the detectors physics-case sensitivity. Moreover, this study could pave the road for technology developments dedicated to the mitigation of the noise induced by marine microseisms, from which the entire community of cryogenic calorimeters can benefit.

Investigation of Electromechanical Characteristics of a Three-Phase Linear Generator

The motion of sea waves can be converted into electrical energy using a three-phase linear generator. This paper investigates the electromechanical characteristics of two types of the three-phase linear generator, namely TPLG-6 and TPLG-18. The electromechanical characteristics such as power, efficiency, torque, d-q axis synchronous inductance, saliency ratio and current are investigated. MATLAB Simulink is used for the simulation. In this study, the d-q synchronous inductance is calculated to investigate the effects of d-q synchronous inductance on the permanent magnet. The Maximum Torque Per Ampere (MTPA) is plotted to determine the torque required to generate the maximum d-q current. The saliency ratio will also be investigated by comparing the d-q synchronous inductance for TPLG-6 and TPLG-18.

Experimental Investigation on Performance of Counter-rotating Impulse Turbine with Middle Vanes for Wave Energy Conversion

In an oscillating water column (OWC) based wave energy device, a water column that oscillates due to the sea wave motion generates a bi-directional airflow in an air chamber, and finally, air turbine driven by the bi-directional airflow converts the pneumatic energy into the mechanical energy. A counter-rotating impulse turbine for bi-directional airflow has been proposed by M. E. McCormick of the United States Naval Academy in 1978. In previous studies by using CFD analysis, the authors investigated the effect of the turbine geometry on the performance of the counter-rotating impulse turbine for bi-directional airflow, and it was clarified that the efficiency of the turbine is higher than that of an impulse turbine with a single rotor for bi-directional airflow in a range of high flow coefficient.On the other hand, this impulse turbine has a disadvantage that the efficiency in a range of low flow coefficient is remarkably low due to the deterioration of the flow between the two rotors. In a previous study, the authros proposed to installed middle vanes between the two rotors in order to overcome the above drawback. And the effect of the middle vanes the turbine performance was investigated by CFD analysis. As a result, it was found that the middle vanes installed to the turbine rectify the flow between the rotors in a range of low flow coefficient and it drastically increases the efficiency.In this study, the middle vanes was actually installed in the counter-rotating impulse turbine for bi-directional airflow, and its performance was elucidated by wind tunnel tests which has the turbine with a inner diameter of 240 mm and a centrifugal fan. It was found from the experiment result that the turbine performance at low flow coefficient is improved and the peak efficiency increases by 1.14 times, by means of the installation of middle vanes to the turbine.

Degradation Mechanism of a Sauce-Glazed Ware of the Song Dynasty Salvaged out of the Water at Dalian Island Wharf: Part I-The Effect of the Surface-Attached Composite Coagula.

Dalian Island is located in the sea area near Pingtan County, Fujian, Southeast China. The sea area used to be the junction of the eastern and western ship routes on the Maritime Silk Road, and is also an important region for underwater archaeology in China. This study focused on a sauce-glazed ware of the Song Dynasty, with serious degradation, which was salvaged out of the water at the Dalian Island Wharf. Optical microscopy, scanning electron microscopy, X-ray diffraction analysis, and micro-Raman spectroscopy were used to comprehensively analyze the composition, phase attributes and microstructure of the ware and the surface-attached coagula. The findings revealed that the sea wave-borne debris scoured the surface of the ware, causing mechanical damage to varying degrees and a significant decrease in its degradation resistance. This was the primary factor accounting for the poor preservation state of the salvaged ceramic ware, and the precondition for the subsequent attachment of marine organisms and the deposition of inorganic pollutants. The calcareous skeletons formed on the surface induced by the bio-mineralization of coralline algae (a type of marine plant) could resist the mechanical action caused by the motion of sea waves, thereby slowing down the ware's degradation process. In other words, the calcareous skeletons played a 'bio-protective' role to a certain degree. In addition, inorganic pollutants represented by iron rusts also participated in the corrosion of the glaze. Some pollutants were directly deposited on the pits and cracks on the surface of the ware, which brought stress to the glaze and glaze/body interface, causing the glaze to further crack and spall. Moreover, iron rusts reacted with the glaze, leading to chemical alteration, accompanied by the formation of iron silicate as the alteration product. Anorthite crystals in the interlayer did not participate in the reaction but remained at the original position. The alteration product gradually replaced the original glass phase of the glaze and entered into the body via pores and cracks. In conclusion, the complex degradation morphology of the salvaged sauce-glazed ware could be attributed to the combined action of mechanical damage, marine bio-fouling, and chemical alteration.

Effect of guide vane on the performance of a sail wing turbine for wave energy conversion

Abstract In an Oscillating Water Column (OWC) based wave energy plant, the sea wave motion is used to drive an air column in an air chamber and that results in a bi-directional airflow. An air turbine for bi-directional airflow is used to convert the pneumatic energy into mechanical energy. The sail wing turbine can be used as an air turbine for wave energy conversion because it has a special structure in which the shape of the sail changes in reciprocating airflow and always can rotate in the same direction. In addition, the sail wing turbine does not experience the stalling effect and can acquire energy at a wide range of rotational speed and flow rate. In our previous studies, the performance of the sail wing turbine for bi-directional airflow has been investigated by using a wind tunnel test. In the present study, in order to further improve the performance of the sail wing turbine, guide vanes were installed, and the effect of the guide vane on the performance was investigated by a wind tunnel test and a computational fluid dynamics (CFD) analysis under a steady flow condition.

A study of counter-rotating impulse turbine for wave energy conversion-effect of middle vane thickness on the performance-

Abstract In an oscillating water column (OWC) based wave energy device, a water column that oscillates due to the sea wave motion generates a bi-directional airflow in an air chamber, and finally, the bi-directional airflow driven air turbine converts the pneumatic energy into mechanical energy. The counter-rotating impulse turbine for bi-directional airflow has been proposed by M. E. McCormick of the United States Naval Academy in 1978. In a previous study, the authors investigated the effect of the turbine geometry on the performance of a counter-rotating impulse turbine for bi-directional airflow, and it was clarified that the efficiency of the turbine is higher than an impulse turbine with a single rotor for bi-directional airflow in a range of high flow coefficient. Moreover, this impulse turbine has a disadvantage that the efficiency in a range of low flow coefficient is remarkably low due to the deterioration of the flow between the two rotors. In this study, in order to make the counter-rotating impulse turbine practically compatible, the thickness of the middle vanes installed between the two rotors was changed, and the effect of the thickness on the turbine performance was investigated by the computational fluid dynamics (CFD) analysis. As a result, it was found that the efficiency of the counter-rotating impulse turbine with middle vanes increases as the thickness of the middle vanes decreased.

Simulation of a Wideband Radar Echo of a Target on a Dynamic Sea Surface

Unlike a generally rough ground surface, the sea surface varies over time. To analyze the impact of the motion of sea waves on the synthetic aperture radar (SAR) image of a target, the wideband echo simulation method based on a frequency domain is used. For the wideband echo, the electromagnetic (EM) scattering properties of the main frequency components are analyzed by the simulation method. Based on the EM scattering properties, the echo can be accurately simulated by using the inverse fast Fourier transformation (IFFT). Combined with the flight path of the radar, the echo of each pulse can be simulated to obtain the SAR image. The correct evaluation of the EM scattering properties is indispensable to the acquisition of an accurate SAR image. For complex targets, such as ships, the multiple scattering effects have a significant influence on the EM scattering properties. Thus, a rectangular wave beam-based geometrical optics and physical optics (GO/PO) method is introduced to calculate the EM scattering properties, which is more efficient than the traditional GO/PO. The GO/PO method is suitable to simulate SAR images in which the EM scattering properties of each pulse need to be calculated. With these methods, the SAR images of the target on the sea surface are simulated. Based on the comparison of the SAR images between a static and dynamic sea surface, it is found that the region corresponding to the target is blurred and the texture of the dynamic sea is blurrier. The impact of multiple scattering and sea wave motion on target recognition are also analyzed with the SAR images that were generated under different conditions. Some strong scattering points appear when multiple scattering effects are considered. It is also found that the texture of the SAR images, corresponding to the sea surface, changes with the synthetic aperture time.

The Seismicity of Lipari, Aeolian Islands (Italy) From One-Month Recording of the LIPARI Array

Seismic activity in volcanic settings could be the signature of processes that include magma dynamics, hydrothermal activity and geodynamics. The main goal of this study is to analyze the seismicity of Lipari Island (Southern Tyrrhenian Sea) to characterize the dynamic processes such as the interaction between pre-existing structures and hydrothermal processes affecting the Aeolian Islands. We deployed a dense seismic array of 48 autonomous 3-component nodes. For the first time, Lipari and its hydrothermal field are investigated by a seismic array recording continuously for about a month in late 2018 with a 0.1–1.5 km station spacing. We investigate the distribution and evolution of the seismicity over the full time of the experiment using self-organized maps and automatic algorithms. We show that the sea wave motion strongly influences the background seismic noise. Using an automatic template matching approach, we detect and locate a seismic swarm offshore the western coast of Lipari. This swarm, made of transient-like signals also recognized by array and polarization analyses in the time and frequency domains, is possibly associated with the activation of a NE-SW fault. We also found the occurrence of hybrid events close to the onshore Lipari hydrothermal system. These events suggest the involvement of hot hydrothermal fluids moving along pre-existing fractures. Seismological analyses of one month of data detect signals related to the regional tectonics, hydrothermal system and sea dynamics in Lipari Island.

Analysis of Rectangular Flexible Horizontal Piezoelectric Cantilever Beam Base on ANSYS

This paper presents the analysis of energy harvester by using rectangular flexible piezoelectric cantilever beam in which applied on sea wave. The limitation of blade design is it only focus on single direction flow of sea wave motion. The finite element model is constructed by using ANSYS to optimize the blade design to maximize the output power. The analysis of rectangular flexible piezoelectric design shows the ability to generate variable of electric power from minimum 20 µW up to 141.30 µW, with dimension of width, length, height of piezo is 10 mm, 30 mm, 0.10 mm and amplitude of sea wave surface of 1.5 m respectively.

Design optimization and experimental validation of a two-body Wave Energy Converter with adjustable Power Take-Off parameters

Wave energy is extracted from the motion of sea waves. The technologies to convert this energy into electricity have not yet reached maturity and there is no clear dominant design. In this work, a design methodology is proposed for a two-body Wave Energy Converter (WEC) with a novel configurable electromechanical Power-Take-Off (PTO) that allows setting its parameters for optimal power output according to wave conditions. A prototype has been modeled, designed and tested experimentally. It is intended for low power and energy self-sustainable applications, such as in telecommunications and data acquisition. This work addresses the modeling, optimal design, and parameter setting, to obtain maximum power output and efficiency for this class of WEC. A floating body is connected via the PTO to a submerged body in neutral buoyancy. If the PTO parameters are correctly set to match the external frequency of the waves, the system can operate close to resonance condition, which maximizes the generated power. Modeling a WEC can be extremely complex, so a linear mathematical model originally proposed by Falnes was adapted to find optimal PTO parameters for both regular and irregular waves. To validate the design model, tank tests were performed. Optimal PTO parameters in the WEC were determined experimentally. In the experiments, 16 cm high waves and 0.55 Hz of frequency were used to test multiple design parameters searching for optimal power output. Peaks of up to 20 W were generated with these waves. Extrapolating the experimental results, output power in the range of 400–600 W and an efficiency of 48.3% can be expected for 1 m high waves. The design model gives an acceptable prediction for the amplitude of the relative motion between bodies, the optimum damping coefficient of the PTO (c^pto), and the maximum generated power. The design model also makes a good prediction for the optimum stiffness coefficient (k^pto) for smaller values of the mass of the submerged body.

A Novel Data-Driven Scheme for the Ship Wake Identification on the 2-D Dynamic Sea Surface

Because the ship wake spreads into an area much larger than that of the ship hull in the sea surface, it has been widely used in the ship detection. However, due to the complex sea wave motion and the high sea state, the ship wake detection is still a challenging task. In this paper, we propose a novel data-driven method based on dynamic mode decomposition (DMD) to detect, reconstruct, and locate the Kelvin wake on the two-dimensional dynamic sea surface. Through the proposed method, the sea's dynamic characteristics including the oscillation frequency and decay/growth rate of ship wakes and the time-varying sea surface can be obtained. Meanwhile, the spatial features of ship wakes can be derived by dynamic modes as well. The proposed method can distinguish the dynamic characteristics between the Kelvin wake and sea background. Then the corresponding modes of the Kelvin wake can be successfully identified. The proposed method is demonstrated by analyzing a 2D sea surface where the Kelvin ship wake is superposed. It is found that our new approach provides an effective and accurate ship detection, even in the case of high sea states. Meanwhile, the extracted mode of the wake shows the ship position clearly with very high resolution.

Monitoring and Analysis of Wave Characteristics during Pipeline End Termination Installation

Pipeline end termination (PLET) installation is an essential part of offshore pipe-laying operation. Pipe-laying operations are sensitive to pipe-laying barge motion and marine environmental conditions. Monitoring the field environment can provide a reasonable basis for planning pipe-laying. Therefore, the measurement and analysis of sea wave motion is helpful for the control and operational safety of the pipeline and vessels. In this study, an environmental monitoring system was established to measure wave motion during PLET operation. Fourier transforms were used to process images that were acquired by ultra-high-frequency X-band marine radar to extract wave parameters. The resulting wave spectra, as measured each minute, were used to simulate real-time wave data and calculate wave characteristics and regressed wave frequency and direction spectrum throughout the PLET operation. The regressed frequency, spectral density, and direction spectra were compared with the theoretical spectra to evaluate their similarity and find the most similar spreading function in the operational area (the South China Sea). Gaussian fitting of real-time wave data was tested while using a classical method. The marginal distribution and joint density of the wave characteristics were estimated and then compared with theoretical distributions to find the most suitable model for improving marine environmental forecasting.

A study of counter-rotating impulse turbine for wave energy conversion - Effect of middle vane on the performance -

In an oscillating water column (OWC) wave energy converter, the oscillating water column caused by the sea wave motion is used to drive an air column in the air chamber. An air turbine for this bi-directional airflow is used to convert the pneumatic energy into the mechanical energy. A counter-rotating impulse turbine for wave energy conversion has been proposed by M. E. McCormick in 1978. In a previous study, authors investigated the effect of turbine geometry on the performance of the counter-rotating impulse turbine and clarified that the efficiency of the turbine is higher than a single rotor impulse turbine in a range of high flow coefficients. However, the counter-rotating impulse turbine has a disadvantage. Its efficiency in a range of low flow coefficients is remarkably lower due to the deterioration of flows between two rotors. In this study, middle vanes were installed between two rotors in order to achieve a further improvement in the performance, and its effect was investigated by using the computation fluid dynamic (CFD) analysis. As a result, it was found that the efficiency of the turbine was greatly improved by installing the middle vanes, and a favourable turbine geometry was clarified.

Coarse Alignment of Marine Strapdown INS Based on the Trajectory Fitting of Gravity Movement in the Inertial Space.

A ship experiences the random motion of sea waves during its travels. Hence, the coarse alignment of the marine strapdown Inertial Navigation System (INS) suffers from rocking disturbances such as pitch and roll. In this paper, a novel approach of marine coarse alignment was proposed for avoiding the resulting loss of accuracy from rocking disturbances. Unlike several current techniques, our alignment scheme is intuitional and concise. Moreover, the coarse alignment can be implemented without any external information. The gravity vector and its derivative expressed within the inertial frame can describe the attitude matrix between an inertial frame and the local geographic frame. We address the challenge of calculating the gravity derivative by the least-squares fitting of the trajectory of the gravity movement in the inertial frame. Meanwhile, the integration of angular rates measured by gyroscopes allows one to compute the attitude matrix between the inertial frame and the body frame. The coarse alignment can be thus accomplished by the combination of the above two attitude matrices. The experimental results show that the coarse alignment is effective with high accuracy and stability for demanding marine applications.

An artificial generation of a few specific wave conditions: New simulator design and experimental performance

In recent years, an amplified global awareness has led to a reawakening of interest in renewable energy technology. In an effort to reduce the worldwide dependence on fossil fuels, cleaner power generation methods are being sought in the field of solar, biomass, wind and wave energy. The importance of wave energy is increased in particular in some countries like UK, Portugal, Spain and Japan. A considerable progress has already been achieved in this field but the available technical designs are not adequate to develop reliable wave energy converters. Wave energy is the most available energy associated in water seas and oceans. Simultaneously, the wave energy has consisted of two types of energies: potential and kinetic energy. Therefore, many attempts have been applied to capture these energies. In the present work, a wave generator device has been designed and manufactured to simulate and generate the heaving motion of sea waves with different specification. A PC based electro-pneumatic control system was designed and implemented to individually control wave height, these heights are 3, 8, 16, 18 and 20 cm and different frequencies to generate these regular and irregular waves.

On microseisms recorded near the Ligurian coast (Italy) and their relationship with sea wave height

S U M M A R Y In this study, microseism recordings from a near coast seismic station and concurrent significant sea wave heights (H 1 3 ) are analysed to calibrate an empirical relation for predicting sea wave height in the Ligurian Sea. The study stems from the investigation of the damaging sea storms occurred in the Ligurian Sea between 2008 October and November. Analysing data collected in this time frame allows identification of two types of microseism signal, one associated to the local sea wave motion and one attributable to a remote source area. The former is dominated by frequencies greater than 0.2 Hz and the latter by frequencies between 0.07 and 0.14 Hz. Moreover, comparison of microseism spectrogram and significant sea wave heights reveals a strong correlation in that the spectral energy content of microseism results proportional to the sea wave height observed in the same time window. Hence, an extended data set including also observations from January to December 2011 is used to calibrate an empirical predictive relation for sea wave height whose functional form is a modified version of the classical definition of H 1 3 . By means of a Markov chain Monte Carlo algorithm we set up a procedure to investigate the inverse problem and to find a set of parameter values for predicting sea wave heights from microseism.

Multihull vessel excitations in stochastic formulation

Multihull vessel excitations in stochastic formulation The article analyses excitations of a multihull vessel using stochastic formulation. The excitations which make the vessel move come from the motion of sea waves and the action of wind. The sea undulation has most frequently the form of irregular waves, and that is why it is assumed in many studies of sea-going vessel dynamics that the undulation process has probabilistic nature. In the article the dynamics of a multihull vessel is analysed using a linear model on which an irregular wave acts. It was assumed that the examined object interacts with the head sea, and for this wave a set of state equations was derived. The head sea provokes symmetric movements of the object, i.e. surge, heave and pitch.

Modelling and Control of a Hydraulically Actuated Two-Degree-of-Freedom Inertial Platform

This paper investigates modelling and control issues associated with a two-degree-of-freedom inertial platform for naval applications. In the modelling part, the dynamics of the system are physically characterized and then experimentally identified. It is found that due to the inverted-pendulum structure and the use of hydraulic actuators, the system is open-loop unstable and exhibits different frequency responses when the amplitude of the input signal changes. Moreover, the identification experiment reveals that the inclinometer used has a major resonant peak that will limit the control system performance. Therefore, a complimentary filter scheme is proposed to condition the sensor signals so as to produce a more acceptable absolute-angle measurement. In the control part, two proportional-integral-derivative (PID) controllers, whose control parameters are computed using a non-linear optimization scheme to achieve optimal disturbance rejection with reasonable robustness and noise sensitivity properties, are respectively designed for the pitch and the roll subsystems. Experimental results indicate that when the platform's base frame encounters a biaxial sea-wave motion, the resulted control system can attenuate the vibration to within 10 per cent.

Investigation of the electromagnetic fields induced by sea wave motion

This paper discusses a theoretical model of the electromagnetic field induced by internal waves of baric origin. Comparison of thein situ data on the differences between the horizontal electrical field potentials conditioned by internal waves in some Black Sea and tropical Atlantic areas and of the results of calculations of the model electrical field's intensity in those areas shows their good agreement. The dependences of the electromagnetic field component amplitudes on the internal waves parameters and sea-bed rock conductivity are considered.

Use of offshore mooring platform for sea wave motion analysis

An offshore mooring platform for supertankers may often turn out to be an ideal solution for the problem of installing a meteorological station. Its location may be particularly desirable for the purpose of recording and analysing sea wave motion in deep water or in the intermediate zone between shallow and deep water. We are reporting the preliminary results obtained through the operation of a subsurface sensor at the mooring platform off the harbour of Genoa.