Underwater Pressure Research Articles

PERFORMANCE STUDY OF HYBRID BOLTED-BONDED VERTICAL T- AND L-JOINTS WITH COMPOSITE ADHERENDS SUBJECTED TO UNDERWATER SHOCK PRESSURE

Three-dimensional explicit dynamic simulations are carried out to study the failure of hybrid bolted-bonded vertical T- and L-joints under noncontact underwater explosion shock pressure. In this modelling, adherends are fibrous laminated composites having an orthotropic behavior, while bolts and adhesive layers exhibit an isotropic behavior. It is found that hybrid vertical T- and L-joints display appreciably higher joint resistance to underwater explosion shock pressure than adhesive T- and L-joints.

Underwater implosion pressure pulse interactions with submerged plates

An experimental and analytical investigation is conducted to study the underwater interaction of implosion pressure pulses with large plates. Two plates with stiffnesses significantly apart are investigated experimentally in a large-diameter pressure vessel for their Fluid-Structure Interaction (FSI) phenomena during proximal implosions of thin metallic shells. High-speed photography, in conjunction with 3D Digital Image Correlation (DIC) measurements, is employed to obtain full-field displacements of the plates. Local dynamic pressure histories are also simultaneously recorded to investigate the incident, reflected and transmitted fluid pressures across the plates during dynamic loading. The lesser stiffness plate showed higher deflection, allowed a weaker reflected pressure pulse and allowed a stronger transmitted pressure pulse as compared to the higher stiffness plate. The peak deflections of the plates occurred during the underpressure phase of the implosion event. Four analytical modeling iterations with increasing complexities starting from Taylor's FSI model are considered to assess the response of water backed plates to dynamic pressure pulse loadings. Each iteration is analyzed individually in an experimental context to understand its role as a building block in a final analytical model. The final model developed is based on the classical plate-bending equation and fluid velocity corrected for ‘afterflow’ effects and performed better than Taylor's original model in predicting pressure-time history of the plates’ reflected pressure and transmitted pressure. The plates’ mid-point deflection profiles are also better predicted using this model. Furthermore, the model showed that the response of a plate during a dynamic implosion pressure pulse interaction is weakly dependent on its bending stiffness. Instead, it is observed that for a large plate, its areal mass density is the dominant factor in determining the reflected pressure, the transmitted pressure and the plate mid-point deflection profiles.

Study on dynamic characteristics of underwater pressure compensator considering nonlinearity

Abstract. The external pressure is the biggest problem faced by underwater hydraulic systems. The strength and sealing ability of the structure are facing enormous challenges. For this problem, the common solution is to use pressure compensation technology. The pressure of the seawater is transmitted to the inside of the hydraulic system through a pressure compensator, which equalizes the return pressure of the hydraulic system and the seawater pressure. The structure of the compensation system, the volume and dynamic characteristics of the compensator, and the compensation failure caused by hydraulic oil leakage will all affect the normal operation of the underwater equipment. Therefore, it is necessary to study the pressure compensation system. This paper analyzes the pressure characteristics of the rubber-bellows type compensator. The dynamic characteristic equation of the pressure is established. Due to the strong nonlinear nature of rubber, the finite element method is used to simulate the deformation process of the rubber-bellows type pressure compensator. The relationship between the volume variation and the spring displacement of the rubber-bellows type pressure compensator is calculated by FE simulation. The relationship is brought into the theoretical equation result to obtain the pressure characteristics of the compensator. Through the control variable method, the influence of damping, total mass, effective area and spring stiffness on the internal pressure of the compensator is obtained. According to the analysis result, the damping ratio should be appropriately increased to reduce the overshoot of pressure fluctuations in the design. Since the damping is difficult to control, the total mass of the end cap, the guide post, the rubber bellows and the spring can be minimized. It also reduces the quality of the equipment. The spring stiffness and effective area have a significant influence on the steady-state pressure. A softer spring should be used and the effective area should be increased as much as possible to reduce the final steady-state pressure.

Ambient Noise Measurement System for the Arctic Region

Ayyadurai, T.; Raguraman, G.; Ashokan, M., and Latha, G., 2020. Ambient noise measurement system for the Arctic region. In: Sheela Nair, L.; Prakash, T.N.; Padmalal, D., and Kumar Seelam, J. (eds.), Oceanic and Coastal Processes of the Indian Seas. Journal of Coastal Research, Special Issue No. 89, pp. 67-70. Coconut Creek (Florida), ISSN 0749-0208.Ambient noise measurements in the polar region are challenging due to the ice-covered environment and very low temperature prevailing in the region. The primary aim of this research work is to design and develop a system capable of associated components to withstand harsh environments, such as the Arctic region. This system consists of a hydrophone, a data acquisition system and a battery pack placed in an indigenously developed underwater pressure casing. While the water depth is 190 m, the noise measurement system is placed at a depth of 30 m. The objective of this work is to record the time series of ocean ambient noise in the Kongsfjorden fjord, Arctic region, covering the seasonal cycle and study the sea ice dynamics and biological noise.

Study on influence factors of underwater shockwave sensor dynamic calibration

To test coefficient sensitivity of underwater shockwave pressure sensor, dynamic calibration is conducted using traceable standard bench sensor and PCB913B02 sensor calibration equipment. In the research, silicon oil of different specification was filled into sealed tank in order to study the relations between silicon oil specification and calibration result of pressure sensor. Explosion tests are conducted using explosives of different formulas and underwater shockwave sensors filled with silicon oils of different specifications. The test result shows such principle and the method of calibration mentioned above could ensure the calibration precision, which therefore certifies the accuracy of shockwave pressure test.

Hydrodynamic performance and calculation of lift–drag ratio on underwater glider

The hydrodynamic performance and lift-drag ratio of the underwater glider affected the state of its own operation. Therefore, a three-dimensional physical model and a mathematical model of a certain type of underwater glider are established. According to the principles of aircraft performance characterization, the fluid dynamics method was used to simulate the pressure distribution of the underwater glider pressure field and the overall outflow field, under the attack angle from − 10° to 10° and the gliding speeds were 0.25 m/s, 0.5 m/s, 0.75 m/s, and 1 m/s. Finally, the drag experiment of this type of underwater glider is verified. It is concluded that as the gliding speed increases, the pressure of the high-pressure area of is increases, the pressure of the low-pressure area decreases, and the pressure difference resistance increases continuously. In the case of small attack angle ( 8°), the lift–drag ratio tends to decrease slightly with increase in attack angle. The maximum lift–drag ratio is produced at an attack angle about 8° and the underwater glider can get maximum hydrodynamic efficiency at this attack angle.

Study on the influence of rigid wall surface on the bubble characteristics of underwater explosion

In order to investigate the influence of rigid wall surface on the bubble characteristics of underwater explosion, the underwater explosion experiment under the boundary conditions of free surface and rigid wall surface was carried out on 2.5g cylindrical charge TNT in a 2×2×2m tank. The time history curves of shock wave and bubble pulsation were obtained by underwater pressure sensor, and the bubble pulsation process was observed by high-speed photography. The experimental results show that compared with the free surface underwater explosion, the shock wave peak pressure and the bubble pulse peak pressure in rigid wall surface underwater explosion are increased, and a large cavitation area appeared at the junction of rigid wall and water surface. After the bubbles contacted the rigid wall surface, the bubble morphology changed significantly, the first bubble pulsation period and the maximum radius of bubble expansion became larger. After the first bubble pulsation, the bubble partially collapsed and split into two parts, bubbles continued to pulsate in the direction of the rigid wall and the bottom of the water. Finally, combined with the experimental data of rigid wall surface at different explosion depths, the relationship between the first bubble pulsation period, the maximum bubble expansion radius and the explosion depth of 2.5gTNT under rigid wall conditions is given.

Underwater Pressure and Temperature Sensor Based on a Special Dual-Mode Optical Fiber

In this paper, an all fiber optic sensor based on a Mach-Zehnder interferometer (MZI) has been proposed for the simultaneous measurement of underwater pressure and temperature, utilizing a dual-mode fiber (DMF) which has been specially designed, and supporting only the LP 01 and LP 02 modes propagating in the fiber. In this design, an in-line MZI sensor that was constructed by splicing a DMF between two pieces of single mode fibers, shows a critical wavelength (CWL) which exists in the transmission spectrum of the LP 01 -LP 02 mode interference. Since the two peaks, located closest to the CWL (and from both lower and higher wavelengths), shift in opposite directions and show different sensitivities under temperature and water pressure variations, the DMF-MZI sensor is capable of measuring both the water pressure and the temperature simultaneously. The CWL-based interference spectrum is stable with the variation of underwater salinity or impurities seen around the fiber surface and independent of the polarization states of the transmission light. As a result, in the operation of the DMF-MZI sensor, underwater pressure and temperature sensitivities increase significantly, when the peak wavelengths are close to that of the CWL. A theoretical analysis has been developed and used to predict that the sensitivities of this specific DMF-MZI structure which can be further improved by increasing the physical length of the DMF and by adjusting the position of the first left/right peak to be closer to the critical wavelength. This co-located, multi-parameter all-fiber sensor developed in this way and showing relatively high sensitivity is easy to implement in the underwater environment. It does not require a complex shell design and the peaks nearest to a CWL are convenient, allowing easy identification and detection, thereby providing a large measurement range to satisfy the requirements of practical marine and fresh water measurements.

Experimental Study on the Creep Characteristics of Cemented Backfill in a Goaf under Water Pressure

As the groundwater environment changes in a goaf, the creep deformation of the backfill underwater pressure is worthy of attention. This paper takes the undercut goaf filling in the Yuzhou section of the middle route of the South‐to‐North Water Transfer Project as an example. Grading loading creep testing of the backfill under different water pressures was carried out using equipment developed by our research team. Based on the experimental results, the following key points were observed: (1) under the same axial stress, the creep strain and steady creep rate increase with increasing water pressure. Under the same water pressure, the creep strain and steady creep rate also increase with increasing axial stress. (2) The long‐term strength of a backfill sample decreases with increasing water pressure and has a nonlinear relationship with water pressure. (3) The increase in water pressure exacerbates the damage of a backfill sample, which is manifested by the secondary crack propagation at the time of failure. Therefore, the increase in water pressure degrades the mechanical properties of the backfill to some extent. The results of this paper provide a reliable theoretical basis for the long‐term stability analysis of goaf filling underwater pressure.

Measurement of small vessel machinery vibration induced acoustic signature levels

Ship vibrations, airborne and underwater noise levels have always been a challenging topic from a performance point of view in ship design, building and operation. The measurement shall help in monitoring the self-noise and the technical state of their machinery mechanism. The vibration levels on the main engine and auxiliary Genset foundation, airborne noise levels of the engine room and underwater self-noise levels of a small mechanized fishing trawler was measured at the jetty in idling condition. The vibration levels on the foundation measured the average value of 0.207 mm/s for the main engine and 1.36 mm/s for auxiliary Genset. The airborne noise levels measured 99 dB (A) in the engine room. The peak underwater sound pressure levels measured 162 dB re 1µPa. The response spectra indicate the peak vibration and noise levels in the lower frequency region <1.2 kHz. The machinery excitation forces transferred to the hull surface as pressure fluctuations which generated the airborne and underwater noise levels. Though the measurement limited to jetty conditions, detailed analysis can be useful for detection, classification, and tracking of small vessels.

Additive manufacturing aboard a moving vessel at sea using passively stabilized stereolithography (SLA) 3D printing

In this paper we investigate the use of passive stabilization to support stereolithography (SLA) printing aboard a moving vessel at sea. 3D printing is a useful technology onboard a seagoing vessel to support engineering development, shipboard maintenance, and other applications when land-based manufacturing resources are unavailable. SLA printed material is particularly suited for underwater applications requiring sealed housings, since SLA printers are capable of producing high-resolution models that are fully solid and impervious to water. Hydrostatic pressure can quickly compromise parts created using standard fused filament fabrication (FFF) 3D printing. However, the dynamic environment onboard a moving vessel could impact the ability of an SLA printer to selectively cure voxels in a liquid resin bath as it undergoes constant motion, and can cause spilling over the walls of the resin tank. Using passive stabilization platforms onboard moving research vessels, we successfully printed a number of parts with no discernable differences from those produced in a traditional land-based laboratory. As a practical demonstration of this capability, we printed at sea underwater pressure housings that remained sealed to 200 m water depth with functional integrated internal electronics. No post-print machining was required to create the sealed housings. This work lays the foundation for lithographic 3D printing in seagoing oceanographic and naval applications, and additionally presents an economical approach for producing custom waterproof pressure housings in the field.

Electrostatic Assembly of a Titanium Dioxide@Hydrophilic Poly(phenylene sulfide) Porous Membrane with Enhanced Wetting Selectivity for Separation of Strongly Corrosive Oil-Water Emulsions.

The efficient treatment of oil-water emulsions in extreme environments, such as strongly acidic and alkaline media, remains a widespread concern. Poly(phenylene sulfide) (PPS)-based porous membranes with excellent resistance to chemicals and solvents are promising for settling this challenge. However, the limited hydrophilicity and the poor hydrated ability of the hydrophilic PPS (h-PPS) membranes reported in the literature prevents them from separating oil-water emulsions with high efficiency, large fluxes, and good antifouling performances. In this study, a firm rough TiO2 layer is constructed on a h-PPS membrane via electrostatic assembly to improve the surface hydrophilization. The introduction of the TiO2 layer increases the wetting selectivity and decreases the oil adhesion, which makes it capable to efficiently treat oil-in-water emulsions (efficiency > 98%). Most importantly, the underwater critical oil intrusion pressure almost doubled after the incorporation of the TiO2 layer, which allows the membrane to withstand pressurized filtration, achieving a high flux of ∼4000 L m-2 h-1. This is more than 2 orders of magnitude larger than the flux of the reported h-PPS. Furthermore, the TiO2@h-PPS membrane displays long-term stability in separating oil-water emulsions in strong acid and strong alkali, showing a promising prospect for the treatment of strongly corrosive emulsions.

Buckling of Cassini Oval Pressure Hulls Subjected to External Pressure

The paper focuses on Cassini oval pressure hulls under uniform external pressure. The Cassini oval pressure hull is proposed based on the shape index of Cassini oval. The buckling of a series of Cassini oval pressure hulls with the shape index of 0.09–0.30 and one spherical pressure hull with the diameter of 2 m is devoted. Such hulls are numerically studied in the case of constant volume, material properties, and wall thickness. The results show that Cassini oval pressure hulls with the shape index of 0.10–0.11 can resist about 4% more external pressure than the spherical one. This deviates from the classical mechanics conclusion that spherical shell is the optimal shape for underwater pressure resistant structures.

Underwater Robot Detection System Based on Fish’s Lateral Line

This paper introduces the near-field detection system of an underwater robot based on the fish lateral line. Inspired by the perception mechanism of fish’s lateral line, the aim is to add near-field detection functionality to an underwater vehicle. To mimic the fish’s lateral line, an array of pressure sensors is developed and installed on the surface of the underwater vehicle. A vibrating sphere is simulated as an underwater pressure source, and the moving mechanism is built to drive the sphere to vibrate at a certain frequency near the lateral line. The calculation of the near-field pressure generated by the vibrating sphere is derived by linearizing the kinematics and dynamics conditions of the free surface wave equation. Structurally, the geometry shape of the detection system is printed by a 3D printer. The pressure data are sent to the computer and analyzed immediately to obtain information of the pressure source. Through the experiment, the variation law of the pressure is generated when the source vibrates near the body, and is consistent with the simulation results of the derived pressure calculation formula. It is found that the direction of the near-field pressure source can distinguished. The pressure amplitude of the sampled signals are extracted to be prepared for the next step to estimate the vertical distance between the center of the pressure source and the lateral line.

Three-dimensional underwater sound pressure sensitivity in oceanic environments

Physical oceanographic processes, marine geological features, sub-bottom geoacoustic structure, sea surface disturbances, etc., can either individually or jointly affect underwater sound propagation in the ocean and cause significant temporal and spatial variability in the sound pressure field. The primary goal of this study is to develop a numerical scheme to determine the sound pressure sensitivity in response to variations of index of refraction due to changes of environmental conditions. This sensitivity analysis is an exention of the Born approximation which assumes perturbations at infinitesimal points. To handle disturbance within a finite volume, an improved sensitivity kernel is derived from a higher-order parabolic-equation (PE) approximation. With this sensitivity kernel, we can analyze the spatial distribution and the temporal evolution of the acoustic sensitivity field in complex oceanic environments. This paper will present numerical examples of three-dimensional (3D) sound propagation in continental slopes, submarine canyons, and nonlinear internal wave fields. Discussions on other applications, including uncertainty quantification of transmission loss prediction and adjoint models for 3D acoustic inversions, will also be provided. [Work supported by the Office of Naval Research.]

Research on Calibration Method of Underwater Shock Wave Pressure Measurement Sensor Systemt

Underwater explosions are distinguished from explosions in the air, and their environment is complex, making sensor systems more difficult to calibrate. In this paper, the calibration method of underwater shock wave pressure sensor system is studied. The dynamic pressure calibration method based on water shock tube is proposed to calibrate the system. The propagation characteristics of the pulse pressure signal in the water shock tube are studied. The water shock tube device suitable for the calibration of the underwater shock wave pressure sensor system is designed. In the end, the advantages of the water shock tube in measuring the underwater shock wave pressure are summarized.

Low frequency absolute calibration of complex sensitivity of vector receivers in free-field

Three-transducers spherical wave reciprocity method in free-field is demonstrated effectively for absolute calibration of the complex sensitivity of underwater sound pressure gradient of vector receiver in the frequency range 250 Hz to 4 kHz. The regularity of underwater sound pressure gradient distribution in the spherical wave, the theory of three-transducers reciprocity calibration method and the technique of complex moving weighted average (CMWA) are studied and reviewed. The VHS90 vector receiver manufactured by Hangzhou Applied Acoustics Research Institute (HAARI) is calibrated using underwater sound pressure gradient calibration facility in a 50 m×15 m×10 m anechoic tank. To verify the results of measurements, the VHS90 vector receiver is also calibrated using low frequency vector receiver calibration facility and the underwater sound pressure calibration facility. The calibration results and the comparisons with these facilities prove the accuracy of the calibration method and facilities described in this paper. The max deviation of modulus of complex sensitivity is 0.7 dB and max deviation of phase congruency of three channels is 1.6°.

A new bioinspired method for pressure and flow sensing based on the underwater air-retaining surface of the backswimmer Notonecta.

In technical systems, static pressure and pressure changes are usually measured with piezoelectric materials or solid membranes. In this paper, we suggest a new biomimetic principle based on thin air layers that can be used to measure underwater pressure changes. Submerged backswimmers (Notonecta sp.) are well known for their ability to retain air layers on the surface of their forewings (hemelytra). While analyzing the hemelytra of Notonecta, we found that the air layer on the hemelytra, in combination with various types of mechanosensitive hairs (clubs and pins), most likely serve a sensory function. We suggest that this predatory aquatic insect can detect pressure changes and water movements by sensing volume changes of the air layer under water. In the present study, we used a variety of microscopy techniques to investigate the fine structure of the hemelytra. Furthermore, we provide a biomimetic proof of principle to validate our hypothesis. The suggested sensory principle has never been documented before and is not only of interest for sensory biologists but can also be used for the development of highly sensitive underwater acoustic or seismographic sensory systems.

Fiber Bragg Grating Technology to Construct the Strain Variation Sensing System of an Underwater Pressure Vessel

Fiber Bragg Grating Technology to Construct the Strain Variation Sensing System of an Underwater Pressure Vessel

Mechanical simulation approach in underwater high pressure acting on ships hull

The industry of shipbuilding is a segment that faces many problems caused by flexible environment. We will try to determine the stresses and strain caused by an underwater explosion, which acts on a ship’s hull. The numerical simulation for ship plate is done with commercial software ANSYS using water pressure from other measured sources.