A Seakeeping Analysis Method for T-Craft

AbstractThe Transformable-Craft (T-Craft) is an innovative vessel serving as a connector between sea base and beachheads. When operatingat seas, the T-Craft is a surface effect ship (SES) with compartmented air cushions. To analysis the seakeeping performance of the T-Craft SES, a high efficient 2D/2.5D analytical model has been developed by combining the one dimensional waveequation for solving aerodynamics of pressurized cushion air with the STF/2.5D method for solving hydrodynamics of demihulls at low/high speeds. To enhance the computational efficiency, the entire model is linearized except the dynamics of air leakage, which is strongly nonlinear and inappropriate for linearization. Results obtained from the proposed seakeeping analysis model show reasonable agreement with experimental data, while the proposed model hascompetitiveness in the computational efficiency as compared with some 3D models from public works

Numerical simulation of nonlinear interaction between structures and steep waves

Responding to great concerns about the interaction between steep waves and structures in naval architecture and offshore engineering, a methodology and corresponding numerical algorithm for computing three-dimensional inviscid flow with a free surface are developed based on a fully nonlinear theory in this thesis. The associated boundary value problem is solved using a finite element method. In order to chose an efficient solver for algebraic equations, a direct method and an iterative method with two different preconditioners are compared to each other, which leads to the suggestion that the conjugate gradient method with an SSOR preconditioner is the most suitable for the problem of concern. Furthermore, the radiation condition at a truncated boundary is imposed with an associated damping coefficient optimised to reduce the reflection of waves. In addition, an analytical solution for transient standing waves in a circular tank is derived using second order theory, which provides a tool to validate the numerical method. The developed numerical method is first utilised in simulating the sloshing wave in a tank generated by initial disturbance on the free surface and by the translational motion of the tank. Numerical results are compared with analytical solutions in several cases, which show that the numerical method can be very accurate. The features of the steep sloshing waves are then examined. In the second application, the interaction between vertical cylinders and waves generated by a wave maker is investigated. The motion of the wavemaker can be specified accordingly, in order to generate monochromatic, bichromatic or irregular progressive waves. The forces on one and two cylinders are obtained and compared with published data. The steep waves and their effects on hydrodynamic loads are analysed. It is concluded that the developed methodology based on the finite element method is a good alternative to the existing techniques for the simulation of steep waves. Its accuracy, flexibility and efficiency demonstrated by various numerical examples appear to be quite favourable

Updated Smoothed Particle Hydrodynamics for Simulating Bending and Compression Failure Progress of Ice

In this paper, an updated Smoothed Particle Hydrodynamics (SPH) method based on the Simplified Finite Difference Interpolation scheme (SPH_SFDI) is presented to simulate the failure process of ice. The Drucker–Prager model is embedded into the SPH code to simulate the four point bending and uniaxial compression failure of ice. The cohesion softening elastic–plastic model is also used in the SPH_SFDI framework. To validate the proposed modeling approach, the numerical results of SPH_SFDI are compared with the standard SPH and the experimental data. The good agreement demonstrated that the proposed SPH_SFDI method including the elastic–plastic cohesion softening Drucker–Prager failure model can provide a useful numerical tool for simulating failure progress of the ice in practical field. It is also shown that the SPH_SFDI can significantly improve the capability and accuracy for simulating ice bending and compression failures as compared with the original SPH scheme

Modelling of Violent Water Wave Propagation and Impact by Incompressible SPH with First-Order Consistent Kernel Interpolation Scheme

The Smoothed Particle Hydrodynamics (SPH) method has proven to have great potential in dealing with the wave–structure interactions since it can deal with the large amplitude and breaking waves and easily captures the free surface. The paper will adopt an incompressible SPH (ISPH) approach to simulate the wave propagation and impact, in which the fluid pressure is solved using a pressure Poisson equation and thus more stable and accurate pressure fields can be obtained. The focus of the study is on comparing three different pressure gradient calculation models in SPH and proposing the most efficient first-order consistent kernel interpolation (C1_KI) numerical scheme for modelling violent wave impact. The improvement of the model is validated by the benchmark dam break flows and laboratory wave propagation and impact experiments

Influence of surface coating on structure and properties of metallic lithium anode for rechargeable Li-O2 battery

Abstract Amorphous lithium phosphorous oxynitride film was coated directly on pre-treated lithium metal as anode of lithium air battery by radio-frequency sputtering technique from a Li 3 PO 4 target. The structure and composition of modified anode was analyzed before and after charge/discharge test in a lithium-air battery, which comprises 0.5 M LiNO 3 /TEGDME as the electrolyte and super P carbon as cathode. Batteries were galvanostatically discharged by an Arbin BT-2000 battery tester between open current voltage and 2.15 V vs. Li + /Li at various current regimes ranging from 0.1–0.4 mA/cm 2 . Compared with fresh lithium, LIPON-coated anode exhibited better electrochemical performance. Good charging efficiency of 90% at a narrower voltage gap with high ionic conductivity of 9.4 × 10 −5 S/cm was achieved through optimizing lithium pre-treated conditions, sputtering N 2 flows and suitable solute for electrolyte

Probability weighted four-point arc imaging algorithm for time-reversed lamb wave damage detection

Damage imaging based on scattering signals of ultrasonic Lamb waves in plate structure is considered as one of the most effective ways for structural health monitoring area. To improve location accuracy and reduce the impact of artifacts, a probability weighted four-point arc imaging algorithm for time reversal Lamb wave damage detection is proposed in this paper. By taking the defect as a secondary wave source, the four-point arc positioning method is used to calculate the propagation time of the signal from transducer to defect. And the amplitude of damage signal corresponding to the time of flight is used for imaging. In order to eliminate the artifacts, a damage probability weighting is combined with four-point circular arc imaging algorithm. The effectiveness of the proposed method is experimentally verified in aluminum plate. Experimental results indicate that damage location accuracy and imaging quality has been improved in both single-flaw and double-flaw samples compared with conventional delay-and-sum method

A modified damage index probability imaging algorithm based on delay-and-sum imaging for synthesizing time-reversed Lamb waves

Imaging for damage in plate structure by Lamb waves is one of the most effective methods in the field of structural health monitoring. In order to improve the accuracy of damage localization, a novel method is proposed to modify damage exponent probability imaging algorithm based on delay-and-sum imaging by using time reversal Lamb waves. A new probability distribution function is introduced to improve the damage index probability method and is combined with delay-and-sum method for damage localization. Experimental results on aluminum plate show that the hybrid algorithm achieves better accuracy of damage location and imaging quality than the conventional delay-and-sum method