Underwater Vibration Research Articles

Crack-Based Composite Flexible Sensor with Superhydrophobicity to Detect Strain and Vibration.

Vibration sensors are widely applied in the detection of faults and analysis of operational states in engineering machinery and equipment. However, commercial vibration sensors with a feature of high hardness hinder their usage in some practical applications where the measured objects have irregular surfaces that are difficult to install. Moreover, as the operating environments of machinery become increasingly complex, there is a growing demand for sensors capable of working in wet and humid conditions. Here, we present a flexible, superhydrophobic vibration sensor with parallel microcracks. The sensor is fabricated using a femtosecond laser direct writing ablation strategy to create the parallel cracks on a PDMS film, followed by spray-coating with a conductive ink composed of MWCNTs, CB, and PDMS. The results demonstrate that the developed flexible sensor exhibits a high-frequency response of up to 2000 Hz, a high acceleration response of up to 100 m/s2, a water contact angle as high as 159.61°, and a linearity of 0.9812 between the voltage signal and acceleration. The results indicate that the sensor can be employed for underwater vibration, sound recognition, and vibration monitoring in fields such as shield cutters, holding significant potential for mechanical equipment vibration monitoring and speech-based human-machine interaction.

Characterization of Fiber Bragg Grating Accelerometer for Underwater Vibration Detection

In this paper, the results of the characterization of a Fiber Bragg Grating (FBG) Accelerometer for detecting vibrations underwater are reported. The FBG Accelerometer, consisting of three FBGs, is utilized to detect underwater vibrations in three-dimensional directions. A water pump, with positions varied from 0 to 10 cm, is employed as the vibration source. Furthermore, the experimental results are presented in the form of the peak wavelength shift reflected by the FBG (ΔλB) and frequency. From the experiment results, it is shown that with increasing distance, ΔλB decreases linearly with successive gradients of 0.0058 nm/cm; 0.0059 nm/cm; and 0.0045 nm/cm. for FBG X, Y, and Z. It is also shown that with increasing distance, there is a decrease in frequency from 50 Hz for FBGs X, Y, and Z to 39 Hz; 38 Hz; and 40 Hz for FBGs X, Y, and Z respectively.

Underwater Vibration Adhesion by Frequency-Controlled Rigid Disc for Underwater Robotics Grasping

Underwater Vibration Adhesion by Frequency-Controlled Rigid Disc for Underwater Robotics Grasping

Method for vibration and acoustic radiation analysis of underwater stiffened plates with acoustic coatings

Based on the effective medium theory as well as the three-dimensional viscoelastic theory, a semi-analytical model of the three-dimensional underwater vibration and acoustic radiation with cavity-type stiffened plate structures covered with acoustic coatings is established to solve the issues related to underwater vibration and acoustic radiation calculation of the stiffened plate and shell structure with complex acoustic coatings. By comparing the far-field acoustic radiation characteristics of the proposed semi-analytical model and the finite element numerical model, this research verifies the validity and accuracy of the proposed model. On such a basis, this research preliminarily investigates the coupling effect exerted by stiffeners and parent plates in stiffened plates as well as the vibroacoustic characteristics of acoustic coatings, thereby providing a valuable idea for the prediction of vibroacoustic characteristics concerning underwater structures.

Underwater dynamic modeling and experiments of flexible structure with harmonic actuation of macro fiber composites

Flexible structures driven by smart actuators are promising alternatives for aquatic bionic propulsion vehicles. However, the hydrodynamic effects induced by viscous fluids on the dynamic response of flexible structures remain an ongoing challenge. Thus, this article presents a fluid-structure interaction dynamic model of a flexible underwater structure actuated by macro fiber composite actuators, and the underwater multimodal vibration characteristics are studied. The model is based on the extended Hamilton’s principle, which considers the effects of hydrodynamic forces. The segmented mode shape functions of the flexible structure are derived using the assumed mode method. The study shows that the first two mode shapes of the beam predicted by the model agrees with the experimental results. The underwater dynamic responses of the flexible structure in a board band covering the first two resonance frequencies are also investigated at different actuation levels. The underwater results indicate that the first two resonance frequencies are 1.05 and 6.1 Hz respectively, basically consistent with the simulation ones (1.07 and 6.61 Hz). Correspondingly, the maximum transverse deflections at the end of the beam are 4.81 and 1.31 mm respectively, which are slightly lower than the predicted values of 5.75 and 1.62 mm. Therefore, the validity of the proposed coupled dynamic model is verified, which can be utilized to predict the multimodal dynamic responses of underwater flexible structures actuated by MFC or other smart actuators.

Experimental and numerical investigation on vibro-acoustic performance of a submerged stiffened cylindrical shell under multiple excitations

The underwater vibro-acoustic characteristics of a stiffened cylindrical shell have been investigated using experimental and numerical methods. A numerical analysis model is developed to capture the behavior of the cylindrical shell structure, and the validity of the model is verified based on experimental data. Experimental measurements are conducted in an anechoic tank to assess the vibration and acoustic radiation characteristics of the stiffened cylindrical shell under white noise excitations. Additionally, the disparities in underwater vibration noise characteristics of the stiffened cylindrical shell under both single excitation and multiple excitations are explored by numerical method. The experimental and numerical findings reveal that, within the frequency range of 10–2000 Hz, the stiffened cylindrical shell exhibits a rapid augmentation of low-frequency vibration noise followed by a gradual stabilization trend. This behavior can be attributed to the high density of low-frequency modes embedded within the structure. Furthermore, it is noteworthy that the underwater vibration noise of the cylindrical shell under multiple excitations arises not solely as a result of individual excitations being superimposed, but rather as a consequence of the intricate coupling effects induced by multiple excitations.

A robust biomass superhydrophobic sensor for Re-healing and underwater vibration detection

Robust functional superhydrophobic materials integrating self-healing ability, degradability, and conductivity assume pivotal roles across a wide variety of emerging fields while limited by environmental issues. Herein, an ultra-robust fully bio-based superhydrophobic sensor (FBSS) was constructed using modified multi-walled carbon nanotubes and bio-based epoxy resin. The FBSS exhibited sustained superhydrophobicity and retained its surface characteristics even after being exposed to air for 70 days or enduring 100 abrasion cycles, which took advantage of its inherent chemical stability and self-similar structure. Thanks to the presence of ester bonds within the system, the FBSS could undergo bond exchange reaction enabling micro-configuration healing ability along with excellent repairing repeatability (> 4 times). Furthermore, capitalizing on the heightened wave sensitivity of the meniscus shape, the conductive FBSS was applied to monitor vibrations generated by stirring, weight falling, velocity variation, blowing, and human activities. This finding provides guidance for fabricating green and sustainable superhydrophobic materials while shedding light on the rational design of underwater sensors.

Design, simulation, and experimental investigation on a novel robot fish driven by piezoelectric bimorphs

The efficient swimming performance of fish is a miracle of nature, and the bionic robot fish powered by smart materials can replicate the movement pattern of fish to a greater extent. To achieve a simple, flexible, and controllable underwater robot, a novel robot fish driven by piezoelectric bimorphs is proposed in this study, which has similar swimming patterns to the body and/or caudal fin propulsion swimming mode and can achieve straight travel and steering underwater. The validity and feasibility of the principles were verified by wet mode simulation. A prototype is manufactured and tested for underwater vibration characteristics to confirm the motion pattern of the caudal fin of the robot fish. It weighs 13.3 g, a length of 150 mm. The maximum uniform speed of the robot fish prototype is 53 mm s−1, the thrust is 2.213 mN, and its maximum efficiency is 0.864%.

Innovative hybrid analysis for underwater MEMS sensor imitating veterinary cilia optimum structure

Veterinary species cilia sense mechanical vibrations and movements in air as well as in water. They allow fish to locate predators and find prey. Cilium participates in detection of sound vibration phonons and determines underwater pathways. In this paper a hybrid software tool packages are used to study, analyze, and determine optimum dimensions of MEMS sensor imitating fish cilia.The availability of powerful Finite-element software such as COMSOL and the new software generations of computer make it possible to investigate the performance of different types of sensor structures and to propose new ones. MEMS Piezoresistive Vector Hydrophone (MPVH) is one of the recent generations of underwater vibration detection and surveillance devices. In this paper basic design structure of MPVH that is found in many research works is modeled and investigated from points of view of sensor parameters, namely sensor sensitivity, frequency response and linearity. A hybrid optimization technique is deduced to attain sensor's best element dimension and performance.

Self-powered angle-resolved triboelectric nanogenerator for underwater vibration localization

Precise locating in underwater environment is essential for marine engineering and national security. However, the current technologies usually suffer from energy and complexity issues. Here, a self-powered angle-resolved triboelectric nanogenerator (AR-TENG) is proposed for underwater vibration detecting and locating in a simple and energy-effective fashion. The AR-TENG is made of metal balls and an inverted conical unit consisting of fluorinated ethylene propylene film and multiple sector-like electrodes, where each electrode corresponding to one sensing channel. Each channel of AR-TENG can respond to low-frequency variations with linear electrical outputs and a maximum power density of 1.28 μW·cm−2 at a load resistance of 200 MΩ. Most importantly, the output voltage ratio of two adjacent channels is only related to the vibration direction, endowing AR-TENG with the capability of vibration direction recognition with an angle resolution of 15°. As a result, the underwater vibration locating can be realized by simply intersecting the vibration directions respectively determined by two AR-TENGs arranged in parallel, performing a locating accuracy of >95 %, assisted with a simple trigonometric function and geometric relation. This new scheme is simple, effective and energy-autonomous, holding great potential for various underwater applications.

Flexible and Stretchable Elastomer Composites Based on Lightweight Liquid Metal Foam Spheres with Pod-like Contacts

Liquid metal (LM) is increasingly employed as a conductive filler in soft and flexible elastomer composites owing to its favorable conductivity and liquid fluidity. However, the high density of LM inevitably increases the weight of composites, which brings limitations in large-area and weight-sensitive applications. This work reports a flexible and stretchable elastomer composite composed of pod-like contacting lightweight LM foam spheres and polydimethylsiloxane matrix (LMS/PDMS). The lightweight LMS reduces the amount of LM used in the preparation process while imparting good electrical conductivity and deformability to the composite. The different contact modes of LMS endow the final composites with diverse strain sensitivity. The mechanism of interfacial contact conduction between the LMS with different melting points has been systematically studied, and the result shows that the liquid-solid contact mode of LMS further improves the strain sensitivity of the composite. Moreover, the composite also has satisfactory electrothermal properties and the temperature can quickly reach 70 °C within 30 s, showing good applicability in electric heating. Finally, the composites containing LMS with different contact modes can be developed as multifunctional sensors to detect human activities, temperature variation, and even underwater vibration, demonstrating the great potential in next-generation sensors and electronics.

Vibration based adhesion for underwater robotic operation

In the face of underwater non-magnetic wall environments, the existing underwater adsorption mechanisms are difficult to achieve continuous adhesion without destroying the surface, and the combination of vibration and underwater adsorption will help to solve this problem. The underwater vibration adhesion mechanism of rigid body proposed in this paper uses vibration to form adhesion on the surface of the object, and explores the influence of vibration frequency, driving current and driving disc radius from the perspective of displacement change, and tests the application: A stainless steel disc with a thickness of 0.5 mm and a radius of 50 mm can continuously adhere to a mass load of 1 Kg at a frequency of 150 Hz, and can adhere to the surface of seashells at a frequency of 100 Hz. The underwater vibration adhesion of rigid body is a new adhesion technology, which can be used in the fields of underwater wall climbing robots and underwater object grasping.

A novel structural–functional integration piezoelectric thruster for miniature unmanned underwater vehicles

Unmanned underwater vehicles (UUVs) play a vital role in marine exploration, and can achieve an extension of human hands and eyes to help researchers reach inaccessible and complex underwater spaces. However, the developed UUVs are driven by electromagnetic motors that also make it difficult to miniaturize due to the existence of the transmission system. Additionally, electromagnetic motors need to be protected to against water intrusion, especially in the deep sea. Therefore, in order to solve the above-mentioned problems, a novel structure-functional integration piezoelectric thruster for miniature UUVs is proposed in this study. Based on the converse piezoelectric effect and the direct friction drive principle, rudders and propellers can be alternately driven by a piezoelectric actuator, constructing the thrust unit and the steering unit of the piezoelectric thruster, respectively. Therefore, this makes the structure and function of the piezoelectric thruster integrated. Finite element simulations are first conducted to determine the geometrical sizes of the proposed actuator. The efficiency of the designed piezoelectric actuator is then confirmed using an underwater vibration measurement. Finally, experimental evaluations of the output performance of the piezoelectric thruster are performed. In the propulsion mode, the maximum rotation speed and thrust of the positive and negative propeller of the prototype with an excitation voltage of 600 Vpp were 404 rpm/0.10 N and 413 rpm/0.11 N, respectively. In the cooperative working mode, 20.00 kHz was used as the driving frequency, and the yaw and pitch rudders had the maximum average angle velocities of 92 deg s−1 and 90 deg s−1 for an excitation voltage of 600 Vpp, respectively. The maximum rotation speed and thrust of the positive and negative propellers of the prototype with an excitation voltage of 600 Vpp were 133 rpm/0.01 N and 132 rpm/0.01 N, respectively. According to experimental findings, the prototype piezoelectric thruster exhibits excellent mechanical properties.

Experimental Investigation on Vibro-Acoustic Characteristics of Stiffened Plate Structures with Different Welding Parameters

Varied welding process parameters result in different welding energy inputs and welding residual stresses, significantly impacting the vibro-acoustic characteristics. This work investigated the influence of different welding energy inputs on the vibro-acoustic characteristics of the stiffened plate structure. Several experiments on the stiffened plate structure with different welding energy inputs were conducted regarding modal, underwater vibration, and acoustic radiation. The results revealed that welding energy input had the most significant impact on the first-order natural frequency, and the impact first becomes higher and subsequently decreases as welding energy input increases. The welding energy input had relatively little effect on the peak point distribution of vibration and acoustic radiation curves but could affect the peak point amplitude. With the increase in welding energy input, the overall vibration acceleration level and sound radiation level in each frequency band decreased and then increased. The best result was obtained when the welding energy input was 167 J/cm with a welding current of 200 A, a welding voltage of 25 V, and a welding speed of 3.02–3.06 mm/s. Based on construction technology, this research can provide some instructive insights for enhancing the acoustic stealth performance of ships and marine structures.

Experimental investigation of the hydrodynamic damping of a vibrating hydrofoil in cavitating flow

To understand how cavitation affects underwater structure's vibration characteristics, an experiment on a vibrating hydrofoil is designed to quantitatively measure the flow-induced vibration, added mass, and hydrodynamic damping ratio in cavitating flow. The reliability of the experimental devices was verified, and the maximum cavity length and cavitation Strouhal number were in agreement with previously published experimental results. Regarding the flow-induced vibration, the resonance amplitude decreases with the cavitation development. Especially for the cavitation inception, the resonance amplitude decreases by 74% relative to that without cavitation. For the add mass coefficient, the linear relationship between it and maximum cavity length is established and is found to be independent of flow velocity, attack angle, and cavitation number. However, the effects of cavitation on the hydrodynamic damping are highly related to the flow condition. In particular, the hydrodynamic damping ratio decreases with increasing maximum cavity length when the velocity is above the resonance velocity, and the reduction reaches 39% if cavitation covers the hydrofoil completely. But this trend is inversed in the lock-in region. In addition, the hydrodynamic damping almost keeps constant when the velocity is below the resonance velocity.

A comprehensive investigation on bending stiffness of composite grid-stiffened and functional foams sandwich beam

This paper investigates the bending stiffness of composite grid-reinforced sandwich beams with functional foam cores by a combination of analysis, simulation, and experiment. First, the sandwich layer composed of stiffeners and foam cores is homogenized, and the equivalent mechanical parameters of the sandwich layer are proposed. Then, based on the first-order shear deformation theory, the three-point bending deflection of the beam is derived and verified by tests and simulations. Finally, the factors affecting the bending stiffness are investigated, such as the elastic modulus of the foam cores, the thickness of the stiffeners, the longitudinal and transverse spacing of the stiffeners, and the fiber lay-up angle of the stiffeners. The results of this paper are of great significance to the stiffness design and parameter optimization of composite grid-stiffened sandwich structures with foams for underwater vibration and noise reduction.

Internet Cable Reveals the Source of Underwater Vibrations

A novel use of an existing fiber-optic cable off the coast of Spain has clued scientists in to how seismic noise is generated in the ocean.

Underwater sound absorption performance of exponential gradient anechoic coating

In this paper, the gradient anechoic coating whose density changes exponentially along direction of thickness is investigated. A numerical model is established by finite element method (FEM) to analyze the underwater sound absorption performance under different density distribution. The calculation results show that the exponential anechoic coating has better sound absorption performance compared with the homogeneous medium and linear anechoic coating. In addition, a discrete layered method is proposed to achieve gradient characteristics. In order to change the equivalent density of each layer, periodically distributed semi-cylindrical steel scatterers with different diameters are embedded in each layer. Therefore, the density function of the whole coating changes in exponential gradient with stepped function. Based on the sound absorption mechanism of multiple scattering and waveform conversion, the sound absorption is improved in low-frequency band from 0 Hz to 1000 Hz. The exponential gradient anechoic coating has potential applications in underwater sound absorption and vibration control.

A review of computational models for underwater acoustic radiation induced by structural vibration in the shallowmarine environment

<p indent="0mm">The vibration and acoustic performance of underwater structures have always been a research hotspot in the field of ocean engineering. The acoustic stealth technology of submarines and the marine hydroacoustic detection technology are based on the accurate prediction and effective control of the underwater structural vibration and acoustic behavior in the marine environment. For vibration and acoustic analysis in the marine environment, most of the early studies regarded the marine environment as an infinite fluid region, or a semi-infinite fluid region with a free sea surface. These two marine models simplify the simulation process of underwater acoustic radiation and propagation by ignoring the impact of the seabed. Underwater acoustic radiation and propagation caused by structural vibrations in the shallow marine environment will be greatly affected by the reflection and refraction effects at the sea surface and seabed. Moreover, the sound velocity in the shallow marine environment usually shows different profiles due to the influences of the water pressure and temperature, which affects the vibration and acoustic behavior of underwater structures. To accurately characterize the coupling effect of underwater structures and shallow marine environments, many researchers have devoted their particular efforts to the analysis of vibration and acoustic radiation of underwater structures in the shallow marine environment, and have developed a variety of numerical computational models, such as the finite element method, finite element-boundary element method, finite element-wave superposition method, finite element-singular boundary method, finite element-parabolic equation method and finite element-normal mode method, and so on. This paper focuses on deterministic computational models for vibration and acoustic analysis of underwater structures in the mid-low frequency range, and discusses two analytical schemes: Wet modal analysis and dry modal analysis. The development and application status of the computational models for the vibration and acoustics of underwater structures in the shallow marine environment are reviewed from the aspects of underwater acoustic models and numerical algorithms. Among those computational models, the finite element method combined with absorbing boundary layers is a common and efficient computational model, which is suitable for the analysis of near-field acoustic radiation induced by structural vibrations in the shallow marine environment. By contrast, the boundary discretization schemes, such as the boundary element method, wave superposition method and singular boundary method, avoid the special truncated treatment of marine domains by using the Green’s function derived from the mirror virtual source method and the normal mode model. Therefore, the hybrid computational solvers, such as the finite element-boundary element method, finite element-wave superposition method and finite element-singular boundary method, can be applied to the analysis of vibration and acoustic behaviors of the near- and far-field vibration and acoustic analysis. On the other hand, based on the wet modal analysis, the finite element-wave superposition method, finite element-parabolic equation method and finite element-normal mode method have higher computational efficiency in far-field acoustic propagation problems induced by vibration of underwater structures. Finally, the future development and application prospect of computational models for vibration and acoustic analysis of underwater structures in the shallow marine environment are discussed. Most of the existing computational models are based on the shallow marine environment of the horizontal sea surface and seabed. In future development, it is necessary to broaden the application scope of computational models, improve the computational efficiency of numerical algorithms, introduce the efficient optimization algorithm to develop a high-performance computational model for the optimal design of vibration and noise reduction of underwater structures in the typical and complex shallow marine environment.

Acoustic impact studies and assessments by Bureau of Ocean Energy Management on offshore wind development

The U.S. Bureau of Ocean Energy Management (BOEM) manages the exploration and development of offshore energy resources, including offshore wind development, on the U.S. Outer Continental Shelf. Construction, operation, and decommissioning of offshore wind facilities generate intense or long-lasting underwater sounds and vibrations that may be detrimental to marine life. This presentation will provide an overview of the activities that BOEM is in engaging in to address these impacts. BOEM’s Environmental Studies Program (ESP) has been developing funding and managing numerous studies to understand sound field characteristics and sound propagation from pile driving and geophysical surveys related to offshore wind development, as well as marine species responses to these activities. In addition, BOEM established the Center for Marine Acoustics (CMA) to strengthen its role as a driving force within the regulatory community on sound in the marine environment and provides acoustical expertise within the environmental permitting process. The CMA continues to provide guidance on the development of best practices for the use of acoustics in the evaluating the effects of offshore wind on marine fauna. This presentation will highlight the relevant acoustic studies and explain how BOEM is using the science to better manage noise impacts on the ocean environment.