Parallel Computing of the Underwater Explosion Cavitation Effects on Full-scale Ship Structures

As well as shock wave and bubble pulse loading, cavitation also has very significant influences on the dynamic response of surface ships and other near-surface marine structures to underwater explosive loadings. In this paper, the acoustic-structure coupling method embedded in ABAQUS is adopted to do numerical analysis of underwater explosion considering cavitation. Both the shape of bulk cavitation region and local cavitation region are obtained, and they are in good agreement with analytical results. The duration of reloading is several times longer than that of a shock wave. In the end, both the single computation and parallel computation of the cavitation effect on the dynamic responses of a full-scale ship are presented, which proved that reloading caused by cavitation is non-ignorable. All these results are helpful in understanding underwater explosion cavitation effects.

A boundary element method for the simulation of non-spherical bubbles and their interactions near a free surface

The basic principle and numerical technique for simulating two three-dimensional bubbles near a free surface are studied in detail by using boundary element method. The singularities of influence coefficient matrix are eliminated using coordinate transformation and so-called 4π rule. The solid angle for the open surface is treated in direct method based on its definition. Several kinds of configurations for the bubbles and free surface have been investigated. The pressure contours during the evolution of bubbles are obtained in our model and can better illuminate the mechanism underlying the motions of bubbles and free surface. The bubble dynamics and their interactions have close relation with the standoff distances, buoyancy parameters and initial sizes of bubbles. Completely different bubble shapes, free surface motions, jetting patterns and pressure distributions under different parameters can be observed in our model, as demon- strated in our calculation results.

Turbulence Model Investigations on the Boundary Layer Flow with Adverse Pressure Gradients

In this paper, a numerical study of flow in the turbulence boundary layer with adverse and pressure gradients （APGs） is conducted by using Reynolds-averaged Navier-Stokes （RANS） equations. This research chooses six typical turbulence models, which are critical to the computing precision, and to evaluating the issue of APGs. Local frictional resistance coefficient is compared between numerical and experimental results. The same comparisons of dimensionless averaged velocity profiles are also performed. It is found that results generated by Wilcox （2006） k-co are most close to the experimental data. Meanwhile, turbulent quantities such as turbulent kinetic energy and Reynolds-stress are also studied.

Numerical Investigation on Two-dimensional Boundary Layer Flow with Transition

As a basic problem in many engineering applications, transition from laminar to turbulence still remains a difficult problem in computational fluid dynamics （CFD）. A numerical study of one transitional flow in two-dimensional is conducted by Reynolds averaged numerical simulation （RANS） in this paper. Turbulence model plays a significant role in the complex flows＇ simulation, and four advanced turbulence models are evaluated. Numerical solution of frictional resistance coefficient is compared with the measured one in the transitional zone, which indicates that Wilcox （2006） k-ω model with correction is the best candidate. Comparisons of numerical and analytical solutions for dimensionless velocity show that averaged streamwise dimensionless velocity profiles correct the shape rapidly in transitional region. Furthermore, turbulence quantities such as turbulence kinetic energy, eddy viscosity, and Reynolds stress are also studied, which are helpful to learn the transition＇s behavior.

Experimental Study on the Configuration Hydrodynamics of Trimaran Ships

This paper presents experimental results on configuration hydrodynamics.Three models are used in the model tests,which are typical of hard,round,and soft chines.Although specific values are different,the influence patterns are similar in the three ship models.A set of different outrigger positions is investigated in calm water and regular waves.A variety of interesting phenomena are observed,among which the splash resistance is the dominant component for a trimaran at high speeds(with Froude number Fr>0.6).If two small outriggers are placed inside Kelvin’s wave systems of the main hull,a strong splash appears,resulting in a significant resistance increase.Moreover,short and long waves cannot be neglected,for they may excite the motions of much smaller outriggers.This condition leads to non-vanishing heaving at high-frequency and non-normalized pitches at low frequencies.Based on the tests,three spectra of optimum configurations for resistance,longitudinal motions,and transverse motions are presented.These results reveal the optimum configurations of a trimaran hull in terms of hydrodynamic performance,thus providing a very powerful tool for optimum design of trimaran ships.

Analysis of the Effect of Different Treatment Schemes on Helicobacter Pylori Infection on Improving the Quality of Life of Patients

Objective:To analyze the effect of different treatment schemes on the quality of life of patients with Helicobacter pylori infection.Methods:From June 2019 to November 2020,96 patients with Helicobacter pylori infection were selected and randomly assigned Combined treatment with omeprazole,amoxicillin and clarithromycin was named group A;Group B was treated with omeprazole,amoxicillin,clarithromycin and colloidal bismuth pectin;Group C was given omeprazole,amoxicillin,clarithromycin and metronidazole.Results:The symptom score and gastroscope score of group B or C were lower than those of group A(P<0.05);The incidence of adverse reactions and HP eradication rate in group C were lower than those in group B,and those in group B were lower than those in group A(P<0.05);The quality of life score of group C was higher than that of group B,and that of group B was higher than that of group A,P<0.05.Conclusions:The sequential therapy of omeprazole,amoxicillin,clarithromycin and metronidazole in patients with Helicobacter pylori infection can improve the HP eradication rate,improve the quality of life of patients,which is safe and efficient.

Numerical simulation of micro-bubble drag reduction of an axisymmetric body using OpenFOAM

The two-phase micro-bubble flow over an axisymmetric body is investigated using the OpenFOAM framework.The numerical model consists of an Eulerian-Eulerian two-fluid model with closure relationships for the interfacial momentum transfer to capture the multiphase flow,a standard A:-￡*model for the continuous phase and one turbulence model inside the OpenFOAM for the dispersed phase.The bubble sizes are calculated based on the solution of the transport equation of the interfacial area density.The simulations in this work are carried out with different air injection rates and different flow velocities.The effects of bubble size on drag reduction are analyzed.The numerical results are compared against some available experiments and other numerical simulations.The numerical results indicate that the airflow rate and air volume fraction within the boundary layer near the body play important roles in micro-bubble drag reduction.The frictional drag reduction effect by micro bubbles is larger for lower water speed,and the presence of the micro bubbles can increase the pressure resistance of the body.Drag reduction rates are generally higher when the bubble diameter is smaller.

A numerical study of hydrodynamic influence on collision of brash ice with a structural plate

The ice-structure collision is a transient process, which is further complicated by the presence of the water. It remains unclear how important the hydrodynamic influences are during the collision. This problem is partially investigated in this paper using numerical methods. To simplify the problem as much as possible without loss of generality, a short ice cylinder of circular section is assumed to collide with a vertical large structure plate under a variety of collision scenarios. Among them the most important cases are: (1) the rigid ice cylinder collision with the rigid or elastic structural plate at different collision velocities, (2) the elastic ice cylinder collision with the rigid or elastic structural plate at different collision velocities and (3) the elastoplastic ice cylinder collision with the rigid or elastic structural plate at different collision velocities. The numerical results show that: (1) the hydrodynamic influences are negligible in the first case, (2) the hydrodynamic influences in the second and third cases are not negligible, and become very significant in the third case. The influences are numerically estimated to be in the range of 20%–60% in terms of the momentum change. If the ice response is approximately decomposed into the rigid-body motions and the deformation modes at the instant of the collision with the structure, the previous conclusions show that the hydrodynamic influences on the rigid-body motions of the ice are negligible, but those on the elastic and elastoplastic modes of the ice are significant. Comparison with the case of a submerged ice cylinder (although not a practical case) reveals that the hydrodynamic influences are small in the first case due to the fact that the energy loss is used to produce the water splash and the cavity behind the ice cylinder. Through this study we come into the conclusion that the hydrodynamic influences are not important for the rigid-body motions, but important for the elastic or elastoplastic modes.

Numerical study of air layer drag reduction of an axisymmetric body in oscillatory motions

The air layer drag reduction(ALDR)of an axisymmetric body in oscillatory motions is investigated in this paper with open source toolbox OpenFOAM.The unsteady Reynolds-averaged Navier-Stokes(URANS)equations are used to determine the viscous flow and the volume of fluid(VOF)model is adopted to capture the interface of the air-water two-phase flow.The k-e turbulence model is adopted to simulate the turbulence.The dynamic mesh technique is applied to model the movement of the axisymmetric body.Firstly,the ALDR results are validated by the experimental data.Then,the effects of the movements of the body on the drag reduction during the ALDR state are investigated.Two representative kinds of movements are considered,namely,the pitch and the heave.The numerical results show that the drag reduction varies during the movements and the average drag reduction rates will be reduced.The variation of the drag reduction is related to the morphological change of the air layer.The heave motion is more likely to reduce the effects of the ALDR than the pitch motion.For both oscillatory motions,the large motion amplitude and the low motion period are not conductive to improving the effects of the ALDR.The effects of the oscillatory motion on the ALDR are more sensitive at high water speeds than at low water speeds.Besides,increasing the air flow ratio can be considered as one way to improve the effects of the ALDR.

On the properties of the Rational Function Spectrum describing waves near islands and reefs in South China Sea

On-site measurements show that water waves near islands and reefs in South China Sea exhibit different properties of wave energy distributions with regard to wave frequencies,among which the most prominent factor is the interplay of swells arising from the West Pacific Ocean and the local wind waves.Observations also show that the breaking waves continuously appear,containing more energy in high frequency components,and the nonlinear characteristics of the waves are important in adjusting the energy distribution.These properties may explain the large discrepancies between the well-accepted wave spectra(for example the P-M spectrum,Neumann spectrum,ITTC spectrum etc.)and the measured wave spectra near islands and reefs in South China Sea.Therefore,a new Rational Function Spectrum is proposed in this paper to describe waves near islands and reefs which turns out to show satisfactory accuracy.It well captures wave power distributions in the form of single and double peaks,at low-and high-frequency regions,as well as nonlinear scale power law.Based on the investigation of the measured data near an island in South China Sea,the relation between the parameters used in the Rational Function Spectrum and the statistical parameters of water waves(significant wave height and wave period)is established.It is noted that the wave properties at low-and high-frequencies are controlled by the local wind velocities at the wave growth stage,but remain constant at the wave decay stage.The parameter peak frequency is only dependent on the wave period corresponding to the maximum wave height.The parameter spectral peak is determined from the wave height and the wave period.These relations help to clarify the physical meanings of the parameters used in the Rational Function Spectrum,and thus provide an alternative spectral form to describe random waves near islands and reefs.

The fungal mycobiome:a new hallmark of cancer revealed by pan-cancer analyses

In a recent study published in Cell,1 a group led by Ravid Straussman and Rob Knight characterized fungi across multiple types of cancer and revealed their distribution,relationships with immune cells,and possible prognostic value.Meanwhile,another study led by Anders B.Dohlman and Iliyan D.Iliev2 reported a similar pan-cancer mycobiome analysis of diverse body sites and identified tumor-associated fungi.