scholarly journals Model Experimental Study of Damage Effects of Ship Structures under the Contact Jet Loads of Bubble in a Water Tank

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Hailong Chen ◽  
Baoyu Ni ◽  
Wenjin Hu ◽  
Yanzhuo Xue
Keyword(s):  
High Speed ◽  
Oscillation Amplitude ◽  
Bending Moment ◽  
Oscillation Period ◽  
High Speed Photography ◽  
Beam Model ◽  
Water Tank ◽  
Bending Rigidity ◽  
Ship Structures ◽  
Negative Bending

The damage effects of ship structures under the contact jet loads of bubble are studied by using an electric spark bubble as well as high-speed photography. A series of model experiments of ship structures under contact explosion was carried out in a water tank. On the one hand, we monitored the displacement and period of the oscillation of a hull plate of a ship model with a large bending rigidity. On the other hand, we observed the overall motion of a box-beam model with a small bending rigidity. The results show that when the distance parameter is less than 0.6, the bubble jet will impact on the surface of the structure directly, which is defined as “contact bubble jet” herein. The contact bubble jet causes significant local loads on the ship and induces the “sagging moment” effect. This mainly results from the relatively negative bending moment caused by the bubble attached to the hull. With the increase of detonation distance, this negative bending moment decreases. As a result, the oscillation amplitude of the ship structure decreases sharply and the oscillation period reduces gradually.

scholarly journals Effect of Slam Force Duration on the Vibratory Response of a Lightweight High-Speed Wave-Piercing Catamaran

2015 ◽  
Vol 59 (02) ◽  
pp. 69-84
Author(s):  
Jason John McVicar ◽  
Jason Lavroff ◽  
Michael Richard Davis ◽  
Giles Thomas
Keyword(s):  
High Speed ◽  
Bending Strength ◽  
Experimental Studies ◽  
Bending Moment ◽  
Higher Order ◽  
Acute Angle ◽  
Beam Model ◽  
Higher Order Modes ◽  
Hull Structure ◽  
Vertical Bending Moment

When the surface of a ship meets the water surface at an acute angle with a high relative velocity, significant short-duration forces can act on the hull plating. Such an event is referred to as a slam. Slam loads imparted on ships are generally considered to be of an impulsive nature. As such, slam loads induce vibration in the global hull structure that has implications for both hull girder bending strength and fatigue life of a vessel. A modal method is often used for structural analysis whereby higher order modes are neglected to reduce computational effort. The effect of the slam load temporal distribution on the whipping response and vertical bending moment are investigated here by using a continuous beam model with application to a 112 m INCAT wave-piercing catamaran and correlation to full-scale and model-scale experimental data. Experimental studies have indicated that the vertical bending moment is dominated by the fundamental longitudinal bending mode of the structure. However, it is shown here that although the fundamental mode is dominant in the global structural response, the higher order modes play a significant role in the early stages of the response and may not be readily identifiable if measurements are not taken sufficiently close to the slam location. A relationship between the slam duration and the relative modal response magnitudes is found, which is useful in determining the appropriate truncation of a modal solution.

The role of rapidly compressed gas pockets in the initiation of condensed explosives

1974 ◽  
Vol 340 (1620) ◽  
pp. 113-128 ◽  
Keyword(s):  
High Speed ◽  
Thermal Contact ◽  
Gas Bubbles ◽  
Lead Azide ◽  
High Speed Photography ◽  
Water Tank ◽  
Minimum Volume ◽  
Specific Heats ◽  
Series Of Experiments ◽  
Minimum Volumes

The mechanism of initiation of explosion by the rapid compression of gas spaces has been studied by means of high-speed photography at framing rates up to 10 7 frames s -1 . Single crystals of silver azide, lead azide and PETN were mounted in a water tank and gas bubbles of chosen composition and size (diameter in the range 50 μm to 1 mm) collapsed on to them by water shocks of strength about 0.1 GPa (1 kbar). The gas bubbles collapsed to minimum volumes in times of the order of 1 μs (depending on the initial bubble size). Initiation of fast reaction occurred in the azides within ca . 5 × 10 -8 s of the bubble reaching minimum volume provided the bubble made thermal contact with the explosive. During the collapse, the bubble involuted to form a jet of velocity of a few 100 ms -1 , and after reaching minimum volume, expanded giving an expansion shock. The importance of these phenomena in the initiation of explosion, as well as possible initiation by shock perturbation, was assessed in a series of experiments designed to separate the various possible mechanisms. The conclusion is that adiabatic heating of the gas in the bubble was the prime cause for initiation. Calculations, and experiments with gases such as argon and helium (high value of γ ; the ratio of the specific heats) and butane (low γ ) supported this conclusion. Finally, the relevance to other explosive situations is discussed.

Study of Scale-Interactions in Strained and Destrained Turbulence

2004 ◽  
Author(s):  
Jun Chen ◽  
Joseph Katz ◽  
Charles Meneveau
Keyword(s):  
High Speed ◽  
High Speed Photography ◽  
Water Tank ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Mean Velocity ◽  
Piv Measurements ◽  
Scale Interactions ◽  
Background Turbulence ◽  
High Reynolds

This paper examines the interactions among different length-scales of turbulence during straining and de-straining of the flow. Understanding scale-interactions is a crucial ingredient in formulating improved subgrid models for Large Eddy Simulations. In this experimental study, planar Particle Image Velocimetry (PIV) measurements are performed in a water tank, in which high Reynolds number turbulence with very low mean velocity is generated by an array of spinning grids. Planar straining and de-straining are applied by pushing or pulling rectangular piston whose width is equal to that of the a rectangular tank towards and away from the bottom. The velocity of the piston is computer controlled and synchronized with the PIV system. The initial background turbulence, characterized by the distributions of rms values and energy spectra, confirms that that the turbulence is nearly isotropic and homogeneous. The applied straining is characterized using high-speed photography of the piston and by PIV measurements of the mean flow. The results consist of the time evolution of several turbulence parameters subjected to a sequence of straining and destraining motions, with particular emphasis on the Reynolds stresses, Sub-grid scale (SGS) stresses, SGS anisotropy and SGS dissipation. The paper also examines the scale dependence of the SGS stress and dissipation, and compares the energy flux between different scales during the straining and destraining parts of the deformation.

The motion of two-dimensional vortex pairs in a ground effect

1977 ◽  
Vol 82 (4) ◽  
pp. 659-671 ◽  
Author(s):  
Steven J. Barker ◽  
Steven C. Crow
Keyword(s):  
High Speed ◽  
Ground Plane ◽  
Vortex Formation ◽  
Ground Effect ◽  
Transition To Turbulence ◽  
High Speed Photography ◽  
Surface Boundary ◽  
Water Tank ◽  
Two Dimensional ◽  
Mean Flow

A new technique for generating a pair of line vortices in the laboratory has been developed. The mean flow of these vortices is highly two-dimensional, although most of the flow field is turbulent. This two-dimensionality permits the study of vortex motions in the absence of the Crow mutual induction instability and other three-dimensional effects. The vortices are generated in a water tank of dimensions 15 × 122 × 244 cm. They propagate vertically and their axes span the 15 cm width of the tank. One wall of the tank is transparent, and the flow is visualized using fluorescein dye. High speed photography is used to study both the transition to turbulence during the vortex formation process and the interaction of the turbulent vortices with a simulated ground plane.Transition occurs first in an annular region surrounding the core of each vortex, starting with a shear-layer instability on the rolled-up vortex sheet. The turbulent region then grows both radially inwards and radially outwards until the entire recirculation cell is turbulent. A ‘relaminarization’ of the vortex core appears to take place somewhat later.The interaction of the vortex pair with the ground plane does not follow the predictions of potential-flow theory for line vortices. Although the total circulation is apparently conserved, the vortices remain at a larger distance from the ground than is expected and eventually ‘rebound’ or move away from the ground. Differences between a free-surface boundary condition and a smooth or rough ground plane are discussed. The ground-plane interaction is qualitatively very similar to that of aircraft trailing vortices observed in recent flight tests.

Crack divergence phenomena in tempered glass

2020 ◽  
Vol 13 (3) ◽  
pp. 115-129
Author(s):  
Shin’ichi Aratani
Keyword(s):  
Optimal Design ◽  
High Speed ◽  
Glass Plate ◽  
Acute Angle ◽  
Divergence Angle ◽  
High Speed Photography ◽  
Tempered Glass ◽  
Thick Glass

High speed photography using the Cranz-Schardin camera was performed to study the crack divergence and divergence angle in thermally tempered glass. A tempered 3.5 mm thick glass plate was used as a specimen. It was shown that two types of bifurcation and branching existed as the crack divergence. The divergence angle was smaller than the value calculated from the principle of optimal design and showed an acute angle.

Experimental study of hydrodynamic effects in the inverse water hydrocarbon emulsions flow in microchannels

2016 ◽  
Vol 11 (1) ◽  
pp. 30-37 ◽  
Author(s):  
A.A. Rakhimov ◽  
A.T. Akhmetov
Keyword(s):  
High Speed ◽  
Petroleum Industry ◽  
Chemical Compounds ◽  
High Viscosity ◽  
Blocking Effect ◽  
High Speed Photography ◽  
Simple Chemical ◽  
Reported Study ◽  
Dynamic Blocking ◽  
Hydrodynamic Effects

The paper presents results of hydrodynamic and rheological studies of the inverse water hydrocarbon emulsions. The success of the application of invert emulsions in the petroleum industry due, along with the high viscosity of the emulsion, greatly exceeding the viscosity of the carrier phase, the dynamic blocking effect, which consists in the fact that the rate of flow of emulsions in capillary structures and cracks falls with time to 3-4 orders, despite the permanent pressure drop. The reported study shows an increase in viscosity with increasing concentration or dispersion of emulsion. The increase in dispersion of w/o emulsion leads to an acceleration of the onset of dynamic blocking. The use of microfluidic devices, is made by soft photolithography, along with high-speed photography (10,000 frames/s), allowed us to see in the blocking condition the deformation of the microdroplets of water in inverse emulsion prepared from simple chemical compounds.

scholarly journals Research and Fabrication of Broadband Ring Flextensional Underwater Transducer

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1548
Author(s):  
Jiuling Hu ◽  
Lianjin Hong ◽  
Lili Yin ◽  
Yu Lan ◽  
Hao Sun ◽  
...  
Keyword(s):  
High Speed ◽  
Structural Parameters ◽  
Low Frequency ◽  
Flexural Vibration ◽  
Underwater Acoustic Communication ◽  
Voltage Response ◽  
Water Tank ◽  
Spherical Cap ◽  
Finite Element Software ◽  
Underwater Transducer

At present, high-speed underwater acoustic communication requires underwater transducers with the characteristics of low frequency and broadband. The low-frequency transducers also are expected to be low-frequency directional for realization of point-to-point communication. In order to achieve the above targets, this paper proposes a new type of flextensional transducer which is constructed of double mosaic piezoelectric ceramic rings and spherical cap metal shells. The transducer realizes broadband transmission by means of the coupling between radial vibration of the piezoelectric rings and high-order flexural vibration of the spherical cap metal shells. The low-frequency directional transmission of the transducer is realized by using excitation signals with different amplitude and phase on two mosaic piezoelectric rings. The relationship between transmitting voltage response (TVR), resonance frequency and structural parameters of the transducer is analyzed by finite element software COMSOL. The broadband performance of the transducer is also optimized. On this basis, the low-frequency directivity of the transducer is further analyzed and the ratio of the excitation signals of the two piezoelectric rings is obtained. Finally, a prototype of the broadband ring flextensional underwater transducer is fabricated according to the results of simulation. The electroacoustic performance of the transducer is tested in an anechoic water tank. Experimental results show that the maximum TVR of the transducer is 147.2 dB and the operation bandwidth is 1.5–4 kHz, which means that the transducer has good low-frequency, broadband transmission capability. Meanwhile, cardioid directivity is obtained at 1.4 kHz and low-frequency directivity is realized.

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