A review of the effect of a/W ratio on fracture toughness (Ⅲ)——theoretical analysis

In partⅠandⅡof this series, experimental investigation in both EPFM and LEFM had been discussed. In this part, further theoretical analysis is given. The theoretical development of Two Parameter Fracture Mechanics by Hancock etc, has rationalized our experimental results. This method can be applied to engineering practice, and will allow the advantage of enhanced toughness for specimens with low levels of constraint to be taken into account for defect assessment.     

Study on J-integral with SENB specimensin a condenser material

A series of tests was performed with three-point single-edge-notched-bend (SENB) specimens in a condenser material (Titanium alloy). Results show that the J-integral values of welded joint and HAZ are obviously smaller than those of the base metal. It signifies that the welding process can result in a reduced toughness of Titanium alloy and the effect of crack orientation on toughness value is not negligible for engineering applications. Besides, the J-integral values of L-T direction specimens are much higher than those of LS ones. The J-integral values of rolled ring are: J_(C-R)>J_(C-L)>J_(L-R).     

The effect of plastic constraint on the initiation of ductile tears in shipbuilding structural steels

In this paper, the effect of plastic constraint on the initiation of ductile tears in four different shipbuilding structural steels has been experimentally studied by measuring the J-integral and crack opening displacement COD at initiation in three-point bend specimens with deep and shallow notches. Experimental results of seven groups of different strength alloy steels show that both Si and Ji values of ductile tear from the shallow crack specimens which have less constraint flow field are significantly higher than those of deeply notched specimens. Slip-line-field analysis shows that, for shallow crack, the hydrostatic stress is lower than that from standard deeply cracked bend specimen, which develops a high level of crack tip constraint, provides a lower bound estimate of toughness, and will ensure an unduly conservative approach when applied to structural defects, especially if initiation values of COD and J-integral are used.     

Direct tension and fracture resistance curves of ultra high performance marine composite materials

Fracture behavior is one of the most important, yet still little understood properties of ultra-high performance cementitious composites （UHPCC）, a new marine structural engineering material. Research on the fracture and direct tension behavior of UHPCC was carried out. The constitution law of UHPCC was divided into three phases： pre-partial debonding, partial debonding, and pullout phases. A direct tension constitution law was constructed based on the proposed fiber reinforcing parameter as a function of fiber volume fraction, fiber diameter and length, and fiber bonding strength. With the definition of linear crack shape, the energy release rate of UHPCC was derived and the R-curve equation was calculated from this. Loading tests of UHPCC using a three-point bending beam with an initial notch were carried out. The predictions from the proposed R-curve were in good agreement with the test results, indicating that the proposed R-curve accurately describes the fracture resistance of UHPCC. Introduction of a fiber reinforcement parameter bridges the fracture property R-curve and micro-composites＇ mechanics parameters together. This has laid the foundation for further research into fracture properties based on micro-mechanics. The proposed tension constitution law and R-curve can be references for future UHPCC fracture evaluation.     

AFM试样复合加载下的计算断裂分析(英文)

Fracture processes in ship-building structures are in many cases of a 3-D character.A finite element (FE) model of an all fracture mode (AFM) specimen was built for the study of 3-D mixed mode crack fracture behavior including modes I,II,and III.The stress intensity factors (SIFs) were calculated by the modified virtual crack closure integral (MVCCI) method,and the crack initiation angle assessment was based on a recently developed 3-D fracture criterion––the Richard criterion.It was shown that the FE model of the AFM-specimen is applicable for investigations under general mixed mode loading conditions,and the computational results of crack initiation angles are in agreement with some available experimental findings.Thus,the applicability of the FE model of the AFM-specimen for mixed mode loading conditions and the validity of the Richard criterion can be demonstrated.     

Free transverse vibration analysis of an underwater launcher based on fluid-structure interaction

A pneumatic launcher is theoretically investigated to study its natural transverse vibration in water. Considering the mass effect of the sealing cover, the launcher is simplified as a uniform cantilever beam with a top point mass. By introducing the boundary and continuity conditions into the motion equation, the natural frequency equation and the mode shape function are derived. An iterative calculation method for added mass is also presented using the velocity potential function to account for the mass effect of the fluid on the launcher. The first 2 order natural frequencies and mode shapes are discussed in external flow fields and both external and internal flow fields. The results show good agreement with both natural frequencies and mode shapes between the theoretical analysis and the FEM studies. Also, the added mass is found to decrease with the increase of the mode shape orders of the launcher. And because of the larger added mass in both the external and internal flow fields than that in only the external flow field, the corresponding natural frequencies of the former are relatively smaller.     

An Experimental Investigation on the Stability of Foundation of Composite Vertical Breakwaters

A series of 2D model tests were conducted to assess the foundation stability of composite vertical breakwaters. In this paper, the results from the experimental study are presented conjointly with a formula to estimate the stability number of foundation, which is the most important parameter for evaluation of foundation stability of such structures. The influences of wave height, wave period and the berm width on the stability of composite breakwaters with different armor stone sizes were investigated. Forty-five tests were performed to cover the influences of these parameters. According to the present research, berm width is a significant parameter concerning erosion of armor foundation. As the berm width increases, the amount of berm erosion decreases. Comparisons are made between results of present study and the estimated stability number proposed by Kimura et al.(1994), which is extension of Tanimoto formula. Results show that the later formula underestimates the stability number. However, by applying an enhancement factor about 1.7 meters to Kimura et al. formula, results correlated with the present experimental results..     

Numerical analysis of transient fluid-structure interaction of warship impact damage caused by underwater explosion using the FSLAB北大核心CSCD

［Objectives］This paper aims to address the numerical simulation problems of the dynamic response of ships subject to near-, medium- and far-field underwater explosions by establishing several numerical methods and calculation models. ［Methods］First, load and fluid-structure interaction models are established on the basis of the Eulerian finite element method and acoustic finite element method using the field-split technique, and FSLAB fluid-structure interaction software is developed. Next, near-, medium- and far-field underwater explosions are numerically simulated respectively. The shock wave propagation law, bubble shape and load evolution characteristics of near free-surface and near-wall underwater explosions are obtained, and the shock response characteristics of a spherical shell and ship subject to far-field underwater explosions are analyzed. Finally, the FSLAB software results are compared with the analytical solutions, reference solutions and experimental data. ［Results］The results show that the FSLAB fluid-structure interaction software developed in this paper is effective and accurate in simulating the impact damage of underwater explosions on warships. ［Conclusion］This study can provide a basis and support for the power assessment of underwater anti-explosion and shock design of warships. © 2022 Journal of Clinical Hepatology. All rights reserved.     

Analytical study of magnetohydrodynamic propulsion stability

In this paper an analytical solution for the stability of the fully developed flow drive in a magneto-hydro-dynamic pump with pulsating transverse Eletro-magnetic fields is presented. To do this, a theoretical model of the flow is developed and the analytical results are obtained for both the cylindrical and Cartesian configurations that are proper to use in the propulsion of marine vessels. The governing parabolic momentum PDEs are transformed into an ordinary differential equation using approximate velocity distribution. The numerical results are obtained and asymptotic analyses are built to discover the mathematical behavior of the solutions. The maximum velocity in a magneto-hydro-dynamic pump versus time for various values of the Stuart number, electro-magnetic interaction number, Reynolds number, aspect ratio, as well as the magnetic and electrical angular frequency and the shift of the phase angle is presented. Results show that for a high Stuart number there is a frequency limit for stability of the fluid flow in a certain direction of the flow. This stability frequency is dependent on the geometric parameters of a channel.     

Numerical method of electromagnetic pulse response of conductor with complex load北大核心CSCD

[Objectives]Electromagnetic pulse can seriously affect and even destroy naval shipborne electronic information systems, weapons, equipment and so on. Due to the complexity of the antenna port load circuit, it is necessary to formulate a numerical method which can easily obtain the antenna load current. [Methods]The induced current of the terminal is obtained on the basis of the finite-difference time-domain (FDTD) and Holland model. According to the Thévenin equivalent circuit, the conductor is equivalent to the voltage source to realize decoupling between the conductor and load end, and the load circuit is solved using Simulink software.[Results]Compared with the traditional terminal model, this method is simple and feasible for high-order circuit processing. The effectiveness of the model is verified using non-linear elements and parallel capacitors and resistors as the load respectively. The results show that the calculation results of this method are consistent with those of the traditional methods. Finally, the antenna of the end-connected protect- or is calculated. The results show that the lead inductance caused by the installation of the protector is an important factor affecting the protection performance.[Conclusions]The method proposed in this paper can greatly reduce the simulation complexity of the coupling current of an antenna with a complex load, giving it useful reference value for the field of ship electromagnetic pulse protection design. © 2023 Editorial Department of Chinese Journal of Ship Research. All Rights Reserved.     

Numerical investigation of mooring line damping and the drag coefficients of studless chain links

The chain/wire rope/chain combination is a commonchoice for mooring offshore floating platforms. However, data ofthe drag coefficients of chain links are rather limited, resulting inuncertainties with the calculations of the drag force, and hence thedamping of the mooring system. In this paper, the importance of theselection of the drag coefficient is first investigated. Thecomputational fluid dynamics （CFD） method is then used todetermine the drag coefficients of a studless chain under steadyflows. Numerical model validation is first completed by simulatinga smooth circular cylinder under steady flows. In particular, theperformance of different turbulence models is assessed through thecomparisons between the calculations and the experimental results.The large eddy simulation （LES） model is finally selected for thesimulation of steady flows past a chain. The effects of the Reynoldsnumber on the drag coefficient of a stud-less chain is also studied.The results show that the calculated drag coefficients of a stud-lesschain are fairly consistent with the available experimental data.     

Experimental Research on Flash Boiling Spray of Dimethyl Ether

The high-speed digital imaging technique is applied to observe the developing process of flash boiling spray of dimethyl ether at low ambient pressure, and the effects of nozzle opening pressure and nozzle hole diameter on the spray shape, spray tip penetration and spray angle during the injection are investigated. The experimental results show that the time when the vortex ring structure of flash boiling spray forms and its developing process are determined by the combined action of the bubble growth and breakup in the spray and the air drag on the leading end of spray; with the enhancement of nozzle opening pressure, the spray tip penetration increases and the spray angle decreases. The influence of nozzle hole diameter on the spray tip penetration is relatively complicated, the spray tip penetration is longer with a smaller nozzle hole diameter at the early stage of injection, while the situation is just opposite at the later stage of injection. This paper establishes that the variation of spray angle is consistent with that of nozzle hole diameter.     

Analysis of ultimate uniaxial compressive strength of stiffened panel considering influence of shear load北大核心CSCD

［Objective］This study aims to explore the law of the critical compression stress of stiffened panels under the influence of in-plane shear load, and whether in-plane shear load combined with lateral pressure will introduce a strong coupling effect. ［Method ］ To this end, nonlinear finite element (FE) software ABAQUS is used to perform numerical simulation analysis under combined loads on a group of FE models. A limit state equation/curve is then derived from the dimensionless calculation results based on the minimum square error method. ［Results］The results show that the influence law of in-plane shear load on the critical compression stress of stiffened panels is clarified, and a limit state equation of stiffened panels that considers the effect of shear load is obtained. ［Conclusion］The limit state equation in this paper can provide references for modifying the ultimate strength of stiffened panels under the influence of in-plane shear load. © 2023 Chinese Journal of Ship Research. All rights reserved.     

五体船非对称侧体的干扰阻力（英文）

An experimental investigation is performed to assess the relation of interference performance on the total resistance of a pentamaran model advancing in calm water. For this motivation, the total drag of the ship is performed for several values of asymmetric outrigger configuration and hull separation, altering the Froude number in the range 0.3–0.9. Our results indicate that remarkable changes in resistance require notable changes in transverse distance values(hull separation) when wave interference may occur. In addition, there is no single configuration that consistently outperforms the other configurations across the entire speed range and the optimum interference factor-0.2 appears at a Froude number of 0.45 in S/L=0.33 with the outrigger outer position: asymmetric outboard for A3 configuration.     

A review of the Effect of a/W ratio on fracture toughness (II)—experimental investigation in LEFM

1 INTRODUCTIONThe linear elastic fracture mechanics provides auseful means of determining a material’s toughness.However, deeply cracked standard laboratory speci-mens those have high level of constraint may not alwaysbe representative of those found in structural compo-nents. Structural components often exhibit compara-tively shallowand surface-breaking.We have previously shown that shallow crackshave greater COD andJ-integral values at initiationthan deeply cracked specimens in EPFM…     

一种水翼空化的被动控制方法（英文）

This paper introduces a new idea of controlling cavitation around a hydrofoil through a passive cavitation controller called artificial cavitation bubble generator(ACG). Cyclic processes, namely, growth and implosion of bubbles around an immersed body, are the main reasons for the destruction and erosion of the said body. This paper aims to create a condition in which the cavitation bubbles reach a steady-state situation and prevent the occurrence of the cyclic processes. For this purpose, the ACG is placed on the surface of an immersed body, in particular, the suction surface of a 2 D hydrofoil. A simulation was performed with an implicit finite volume scheme based on a SIMPLE algorithm associated with the multiphase and cavitation model. The modified k-ε RNG turbulence model equipped with a modification of the turbulent viscosity was applied to overcome the turbulence closure problem. Numerical simulation of water flow over the hydrofoil equipped with the ACG shows that a low-pressure recirculation area is produced behind the ACG and artificially generates stationary cavitation bubbles. The location, shape, and size of this ACG are the crucial parameters in creating a proper control. Results show that the cavitation bubble is controlled well with a well-designed ACG.     

Constructal design of tree-shaped microchannel disc heat sink with wavy walls北大核心CSCD

［Objective］To meet the efficient thermal management needs of electronic devices such as ships and underwater vehicles, this study focuses on the constructal design of a tree-shaped microchannel disc heat sink with wavy walls. ［Method］A design prototype of the heat sink with wavy walls is first proposed. Based on constructal theory, the amplitude and wavelength of the wavy walls are designed under the constraints of fixed heat sink volume and fixed microchannel volume by maximizing the comprehensive performance evaluation criteria (PEC) while considering both heat transfer and flow pressure drop. ［Results］The results show that the wavy walls increase the heat transfer surface areas and generate vortices in their cavities, effectively reducing the maximum temperature. When the inlet Reynolds number is fixed at 700, 900 or 1100 respectively, the maximum temperature is reduced by 13.5 K by increasing the amplitude of the wavy walls, while the pressure drop increases significantly; and the maximum temperature is reduced by 4.7 K by reducing the wavelength of the wavy walls, while the pressure drop increases slightly. There are optimal amplitudes that raise the comprehensive performance evaluation criteria to extreme values for given larger wavelengths, while the comprehensive performance evaluation criteria increase monotonously as the amplitude increases for given smaller wavelengths. ［Conclusion］Wavy walls can significantly improve the thermal performance of tree-shaped microchannel disc heat sinks, and the use of constructal design can realize optimal geometric constructs with optimal comprehensive performance evaluation criteria. © 2023 Authors. All rights reserved.     

Fatigue crack growth rates of rotor steel at elevated temperatures

Low fatigue samples were obtained from the outer edges of rotor steel （30CrlMolV） which had operated under different temperatures conditions. Based on this data, the effects of temperature on fatigue crack growth rates were investigated. This paper presents a derivation of the superposition expression of two natural logarithms governing crack growth rates and also discusses the relationship between a material’s constants and temperature. These results can provide experimental and theoretical references for fatigue life design of rotor steel in steam turbines.     

舵几何参数对桨舵系统水动力性能的分析(英文)

In order to study the effects of geometric parameters of the rudder on the hydrodynamic performance of the propeller-rudder system,the surface panel method is used to build the numerical model of the steady interaction between the propeller and rudder to analyze the relevant factors.The interaction between the propeller and rudder is considered through the induced velocities,which are circumferentially averaged,so the unsteady problem is translated to steady state.An iterative calculation method is used until the hydrodynamic performance converges.Firstly,the hydrodynamic performance of the chosen propeller-rudder system is calculated,and the comparison between the calculated results and the experimental data indicates that the calculation program is reliable.Then,the variable parameters of rudder are investigated,and the calculation results show that the propeller-rudder spacing has a negative relationship with the efficiency of the propeller-rudder system,and the rudder span has an optimal match range with the propeller diameter.Futhermore,the rudder chord and thickness both have a positive correlation with the hydrodynamic performance of the propeller-rudder system.     

Influence of slip boundary on flow separation and drag of flow past bluff body at high Reynolds numbers北大核心CSCD

［Objectives］Flow separation increases the drag and noise of underwater vehicles, and influences the controllability of their control surfaces. Therefore, the influence of slip caused by superhydrophobic surfaces on drag reduction and flow separation is studied. ［Methods］A partial slip boundary condition is developed, and the flow around a circular cylinder and foil with a slip boundary at high Reynolds numbers are numerically simulated. ［Results］The results show that the when the slip length increases, the flow around the cylinder goes through three stages: the turbulent Kármán vortex street, laminar Kármán vortex street and non-separation Stokes flow. The drag coefficient increases first and then decreases, and the vortex shedding frequency increases. For flow around a foil, the separation position moves downstream until the separation region disappears when the slip length increases, and the drag coefficient decreases while the lift coefficient increases. ［Conclusions］The results of this study show that for flow past bluff body at high Reynolds number, the slip boundary can control flow separation and reduce drag effectively, providing technical support for the application of superhydrophobic surfaces for the flow control of underwater vehicle appendages. © 2022 Journal of Clinical Hepatology. All rights reserved.