Submarine Body Research Articles

COUPLING A HIGH FIDELITY NEAR SURFACE EFFECTS MODEL INTO PARAMARINE S4

When a submarine is operating at depths typical of those required when using the periscope, snorting during the period of recharging the batteries or, in some cases, at slow to zero speed whilst hovering, the submarine can experience complex oscillatory motion due to higher order sea loads. The second order vertical plane loads can manifest themselves as a mean and time varying suction force effectively causing the submarine to be drawn to the surface risking broaching and increasing the possibility of detection. Current methodologies for modelling near surface effects tend to utilize coefficientbased methods to represent the first and second order wave forces on a submarine body. These empirical methods may be suitable for some applications but are not able to capture all the effects of the submarine operating close to the free surface. As the body approaches the free surface, the flow field around the submarine is modified by the gravitational wave effects, changing the pressure distribution across the body and hence the forces and moments. This change in force is dependent upon the shape of the body and the environment and, therefore, it is impractical that a coefficients-based approach could cover all these scenarios to any great level of fidelity. This paper presents a potential flow method for quantifying the hydrodynamic loads on a fully appended submarine when in proximity and under the influence of surface waves. The paper presents some validation of the method and describes its integration with the Paramarine S4 submarine manoeuvring software.

전산 소음 해석 기법을 이용한 잠수함 표면 처리에 따른 소음 효과 관찰

Submarine has been performed for national defense activities representatively as a multi-purpose underwater vehicle. Underwater Radiated Noise (URN) which emitted during underwater vehicle operation is directly related to the survivability of the underwater vehicle. This study focused on examining the effects of surface treatment on noise aspects in whole submarine body for the first time. Prior to the acoustic analysis on the submarine model, the acoustic analysis procedure using commercial CFD software was verified using a 2D cylinder model. Acoustic analysis on submarine model was conducted for two cases: smooth surface as a reference case, and a few micrometers of V-type applied riblet case. To solve the incompressible fluid flow passing the submarine, the Reynolds-averaged Navier-Stokes (RANS) equation coupled with the k-ω SST turbulence model was used. For acoustic analysis, the Ffowcs Williams and Hawkings acoustic analogy, which calculates flow-induced noise by designating a physical wall as a noise source, was used. The noise effects according to the surface treatment on submarine shape were examined by comparing overall sound pressure level (OASPL) between smooth and riblet case and the results indicate that noise around submarine shape was reduced about 4.3 dB in maximum on surface-treated area. However, when calculating OASPL excluding noise below 20 Hz, which is a frequency range where noise does not propagate, the noise tends to increased due to riblet shape. This study provides established procedure in acoustic analysis on whole submarine body and a new perspective that underwater radiation noise should be considered when designing surface treatment on submarine.

Numerical investigation of tip-vortex cavitation noise of submarine propellers using hybrid computational hydro-acoustic approach

In this study, the hybrid computational hydro-acoustics (CHA) method is applied to predict hydrodynamic noise due to tip vortex cavitation (TVC) of underwater submarine propellers. The hybrid CHA approach consists of two sequential methods: Delayed Detached Eddy Simulation (DDES) technique with adaptive mesh refinement method and the Ffowcs Williams and Hawkings (FW–H) equation. The former is utilized for accurate prediction of TVC of underwater propellers, and the latter is used for efficient prediction of hydro-acoustic pressure due to cavitating flow. The target submarine and propeller are the DARPA suboff submarine and two high skew propellers with skew angles of 17 and 38°. The propellers are designed to investigate the effects of skew angle on TVC and its noise. The corresponding experiments are performed in the Large Cavitation Tunnel (LCT) of the Korea Research Institute of Ships and Ocean Engineering (KRISO). The two preliminary simulations are carried out to confirm the close reproduction of the experimental conditions in the main simulations. First, the flow through the LCT test section is simulated to confirm the accurate reproduction of the wall boundary layer. Its validity is confirmed by comparing the predicted boundary layer profiles with the measured results. Second, the flow over the DARPA suboff submarine without a propeller in the LCT test section is simulated to confirm the accurate prediction of the inflow distortion originating from the boundary layer flow of the submarine body. Its validity is also confirmed by comparing the predicted nominal wake field with the measured one. After the close reproduction of these two effects is confirmed, the cavitating flow of the propellers installed to the DARPA suboff submarine body is simulated by using the DDES technique combined with adaptive mesh refinement, and the TVC noise is predicted by applying the quadrupole-corrected FW-H equation to the surfaces enclosing the propellers. The predicted TVC of the propeller closely follows the measured one. The numerical and experimental results capture the TVC induced by the wake flows due to the submarine body's rudders and sail. The predicted hydro-acoustic pressure spectra due to the propellers' cavitating flow also show excellent agreements with the predicted ones. Besides, both the numerical and experimental results confirm that the lower noise is generated by the propeller with a higher skew angle.

Numerical Investigation of Tip Vortex Cavitation Inception and Noise of Underwater Propellers of Submarine Using Sequential Eulerian–Lagrangian Approaches

In this study, the high-fidelity numerical methods are developed to investigate the tip vortex cavitation (TVC) inception and noise of underwater propellers, namely, Model-A and Model-B, which are designed to investigate the effects of sweep angle on cavitation inception and noise. In addition, the entire body of the DARPA Suboff submarine is included to consider the effects of the inflow distortion originating from the boundary layer flow of the submarine body on the cavitating flow of the propellers. The Eulerian approach consisting of Reynolds-averaged Navier–Stokes (RANS) solver and the vortex model is coupled with the Lagrangian approach using the bubble dynamics equations and the acoustic analogy for nuclei initially distributed in inlet flow. First, three-dimensional incompressible unsteady RANS simulations are performed to predict the hydrodynamic flow field driven by underwater propellers installed on a DARPA Suboff submarine body. The Scully vortex model and dissipation vortex model (DVM) are used to regenerate the tip vortex dissipated by artificial numerical damping and low grid resolution around the vortex core center, which is identified by using minimum λ2-criterion in the swirling flow field originating from the propeller blade tip. Then, tip vortex cavitation inception is simulated by applying the bubble dynamics equations to nuclei initially distributed in the inflow region. The volume and location of each nucleus are obtained by solving the bubble dynamics equations on the flow field obtained using the Eulerian method. Finally, the cavitation noise is predicted by modeling each bubble with a point monopole source whose strength is proportional to its volume acceleration. The validity of the present numerical methods is confirmed by comparing the predicted acoustic pressure spectrum with the measured ones.

Effect of Acoustic Shock on Submarine

The carried-out analysis of the dynamics of a submarine body’s translational motion affected by an acoustic shock in the ideal medium provides for the possibility to evaluate the physical properties of the medium and elastic properties of the external body of the submarine to the value of limited motion of a submersible vehicle. The results of analysis provide for the possibility to conduct a comparative analysis of the submersible vehicle’s translational motion affected by an acoustic shock, taking into account the peculiarities of the motion medium, or rather taking into account the viscosity of the real medium. In this work, evaluative measurements of the features of moving the layout of the submarine were carried out. The limiting values of the displacement of the layout of the submarine are established for the case of the presence of an external artificial diffuse disturbance. A fluid with air bubbles from a compressed air cylinder was used to create an artificial diffuse perturbation. Such conditions are possible with intensive local bombardment or the presence of other high-speed underwater vehicles involved in local underwater operations.

The Generation Mechanism of the Flow-Induced Noise from a Sail Hull on the Scaled Submarine Model

Flow-induced noise from the sail hull, which is induced by the horseshoe vortex, the boundary layer separation and the tail vortex shedding, is a significant problem for the underwater vehicles, while has not been adequately studied. We have performed simulations and experiments to reveal the noise generation mechanism from these flows using the scaled sail hull with part of a submarine body. The large eddy simulation and the wavenumber–frequency spectrum are adopted for simulations. The frequency ranges from 10 Hz to 2000 Hz. The simulation results show that the flow-induced noise with the frequency less than 500 Hz is mainly generated by the horseshoe vortex; the flow-induced noise because of the tail vortex shedding is mainly within the frequency of shedding vortex, which is 595 Hz in the study; the flow-induced noise caused by the boundary layer separation lies in the whole frequency range. Moreover, we have conducted the experiments in a gravity water tunnel, and the experimental results are in good accordance with the simulation results. The results can lay the foundation for the design of flow control devices to suppress and reduce the flow-induced noise from the sail hull.

Design of a Bio-inspired Hull Shape for an AUV from Hydrodynamic Stability Point of View through Experiment and Numerical Analysis

The hydrodynamic characteristics and body shape of catfish, Hypostomus, are used to design and develop an Autonomous Underwater Vehicle (AUV) named ZRAUV for subsea pipeline and cable inspection. Among the hydrodynamic characteristics, stability of this bio-inspired AUV, which may be adversely affected by disturbances such as marine currents during inspection process, is taken into consideration and evaluated both numerically and experimentally. Concerning numerical investigation, computational fluid dynamics based on Reynolds Averaged Navier-Stokes equations are applied to compute the hydrodynamic damping derivatives needed for stability analysis. In order to verify the numerical predictions, computations are also performed for the well-known submarine body with a typical axisymmetric hull shape, SUBOFF. Experiments are also carried out for both proposed AUV and a conventional axisymmetric one using self-propulsion tests. Measurements of turning rate in turning circle maneuver are in reasonably good agreement with those of numerical estimations and indicate that the turning rate of conventional bodies like SUBOFF is approximately 3.8 times as great as that of bio-inspired AUV. In other words, the findings reveal that in comparison with common axisymmetric bodies, the proposed AUV with biological hull shape is more stable by about 99%, thus, it is highly suitable for subsea pipeline and cable inspection.

A New Approach of Improving Rain Erosion Resistance of Nanocomposite Sol-Gel Coatings by Optimization Process Factors

Erosion protection nanocomposite sol-gel coatings based on tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxisilane (GPTMS) are prepared and characterized to protect marine structures susceptible to damage caused by liquid impact, e.g., the submarine body. This study focuses on the optimization of compositional and process parameters of transparent hybrid nanocomposite sol-gel coatings resistant to rain erosion by using statistical design of experimental methodology (DoE) based on Taguchi orthogonal design. The impact of compositional and process parameters of the coatings on the erosion protection performance is investigated by five-factor–four-level design methodology. Hybrid coatings were deposited on AA5083 by a dip coating technique. Optimization coatings are analyzed regarding their adhesion (pull-off), flexibility (impact and mandrel bending), hardness (pencil), wear (Taber wear index), and rain erosion resistance (stationary sample erosion test). The surface morphology and roughness were studied by field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The optimization coatings showed excellent flexibility and adhesion to the substrate with smooth nanostructure surface; the RMS surface roughness was 1.85 nm. The evaluation of the result obtained from abrasion shows cohesive and interfacial wear with abrasive and adhesive mechanisms, respectively. Liquid impact results show cohesive failure of the coatings without any sign of delamination.

Preliminary considerations on the potential influence of submarine fans on marine delimitation

The complex issues associated with marine delineation for the outer limit of continental shelf and the boundary delimitation have provoked considerable attention among researchers in a variety of academic circles, particularly in the juristic filed and the geo-science field. In the present contribution, we start from an overview of submarine fans, as one of common types of sediment-deposit bodies in the ocean, and explore the related geological features which may be of relevance to the marine delimitation in accordance with the 1982 United Nations Convention on the Law of the Sea. We carry out a comparative assessment of certain significant geological features of submarine fans, using the Bengal fan as an example, which is the biggest submarine fan in the world and represents an important factor in the maritime boundary dispute between the neighboring states currently. The relationship between the special geological bodies and the international principle in the 1982 United Nations Convention can be established by combining geological and juristic analyses. This preliminary observation on the effect of submarine bodies both on the marine entitlement and boundary delimitation indicates that it is important for the international society to appropriately deal with this problem so that the marine right of any state can be protected.

Modeling of Belt-Pulley and Flexible Coupling Effects on Submarine Driven System Electrical Motors

Nowadays numerous research projects are being conducted in the field of electric motors. Non-modeling of flexible connections such as couplings and the belt-pulley do not show some real behaviors. With an increase in the number of connections and drive factors, these Non-modeled modes become more important. The coupling of two electric motors, instead of one motor, in submarine propeller force is an obvious example which shows that Non-modeled vibration modes caused by flexible connections can disturb controller operation and make undesirable vibrations in the submarine body. In this paper a dynamic model of flexible connections and a completed dynamic model of two different coupled electric models is presented. A robust controller for the completed model is also amended so that the two controlling targets of a desired speed adjustment and an appropriate load division between the two motors with sufficient accuracy are achieved.

Numerical simulation and control of horseshoe vortex around an appendage–body junction

The horseshoe vortex generated around the appendage–body junction of submarines strongly influences the non-uniformity of submarine wakes at the propeller discs. The flow characteristics around the appended submarine body are numerically simulated and analyzed, and a new method on the vortex control baffle is presented. Then, the influence of the vortex control baffle on the horseshoe vortex generated at the sail–body junction is numerically studied, and the flow phenomena caused by the vortex control baffle with different transverse positions is investigated further. Results show that the vortex control baffle can induce a kind of attached vortex in a rotational direction opposite to the horseshoe vortex; these two kinds of vortices undermine each other. Furthermore, when the transverse position of the vortex control baffle is close to the horseshoe vortex, the state of the horseshoe vortex is directly affected, and the flow structure becomes even more complex. We adapt the vortex control baffle for the horseshoe vortex generated at the stern foil–body junction. Results from the numerical simulation of the flow around the fully appended submarine model indicate that the effect of the vortex control baffle greatly improves the performance of the submarine wake. The circumferential non-uniformity of the axial, tangential, and radial velocity components are decreased markedly. The engineering applicability of the vortex control baffle has been well presented.

Hydroelastic dynamic characteristics of a slender axis-symmetric body

The slender axis-symmetric submarine body moving in the vertical plane is the object of our investigation. A coupling model is developed where displacements of a solid body as a Euler beam (consisting of rigid motions and elastic deformations) and fluid pressures are employed as basic independent variables, including the interaction between hydrodynamic forces and structure dynamic forces. Firstly the hydrodynamic forces, depending on and conversely influencing body motions, are taken into account as the governing equations. The expressions of fluid pressure are derived based on the potential theory. The characteristics of fluid pressure, including its components, distribution and effect on structure dynamics, are analyzed. Then the coupling model is solved numerically by means of a finite element method (FEM). This avoids the complicacy, combining CFD (fluid) and FEM (structure), of direct numerical simulation, and allows the body with a non-strict ideal shape so as to be more suitable for practical engineering. An illustrative example is given in which the hydroelastic dynamic characteristics, natural frequencies and modes of a submarine body are analyzed and compared with experimental results. Satisfactory agreement is observed and the model presented in this paper is shown to be valid.

Influence of turbulence closure models on the vortical flow field around a submarine body undergoing steady drift

Manoeuvring underwater vehicles experience complex three-dimensional flow. Features include stagnation and boundary layer separation along a convex surface. The resulting free vortex sheet rolls up to form a pair of streamwise body vortices. The track and strength of the body vortex pair results in a nonlinear increase in lift as body incidence increases. Consequently, accurate capture of the body vortex pair is essential if the flow field around a manoeuvring submarine and the resulting hydrodynamic loading is to be correctly found. This work highlights the importance of both grid convergence and turbulence closure models (TCMs) to the strength and path of the crossflow-induced body vortices experienced by the DOR submarine model at an incidence angle of 15°. Five TCMs are considered; Spalart–Allmaras, k-e, k-ω, shear stress transport, and the SSG Reynolds stress model. The SSG Reynolds stress model shows potential improvements in predicting both the path and strength of the body vortex over standard one- and two-equation TCMs based on an eddy viscosity approach.

LXXXVI. A letter from James Parsons, M. D. F. R. S. to the Rev. Mr. Birch, Secr. R. S. concerning the formation of corals, corallines, &c

Sir, The several ingenious opinions of some of this learned Society, upon what M. Peyssonnel has advanced, concerning the formation of some of the submarine bodies by animals, have occasion’d the following conjectures; which I lay before you, not at all presuming absolutely to decide a question of so difficult a nature, but only to endeavour at throwing a little more light upon the subject, in general, by such further observations, as I thought would be most conducive at least, to come to a little more certainty about it.