scholarly journals Experimental evaluation of the air trapped during the water entry of flexible structures

ACTA IMEKO ◽  
2014 ◽  
Vol 3 (3) ◽  
pp. 63 ◽  
Author(s):  
Riccardo Panciroli ◽  
Giangiacomo Minak
Keyword(s):  
Flexible Structures ◽  
Processing Technique ◽  
Water Entry ◽  
Structural Deformation ◽  
Air Trapping ◽  
Flat Bottom ◽  
Initial Stage ◽  
Entry Velocity ◽  
Bottom Structures ◽  
The Impact

Deformable structures entering the water might experience several fluid-structure interaction (FSI) phenomena; air trapping is one of these. According to its definition, it consists of air bubbles trapped between the structure and the fluid during the initial stage of the impact. These bubbles might reduce the peak impact force. This phenomenon is characteristic for the water entry of flat-bottom structures. Above a deadrise angle of 10°, air trapping is negligible. In this work, we propose a methodology to evaluate the amount of air trapped in the fluid during the water entry. Experiments are performed on wedges with varying stiffness, entry velocity, and deadrise angle. A digital image post- processing technique is developed and utilized to track the air trapping mechanism and its evolution in time. Interesting results are found on the effect of the impact velocity and the structural deformation on the amount of air trapped during the slamming event.

Experimental Investigations of Hydroelastic Effects on Loads During Flat Water Entry

2018 ◽  
Author(s):  
Simon Toedter ◽  
Ould el Moctar ◽  
Jens Neugebauer ◽  
Thomas E. Schellin
Keyword(s):  
High Speed ◽  
Water Entry ◽  
The Other ◽  
Experimental Investigations ◽  
Air Trapping ◽  
Flat Bottom ◽  
Elastic Bottom ◽  
Bottom Structures ◽  
Two Bodies

Extensive water entry experiments were performed to identify the influence of elasticity on impact-induced loads acting of flat bottom structures. Two bodies were tested. One body was fitted with stiffened, rigid bottom plating; the other body, with thin elastic plating. Bottom pressures and forces acting on the flat bottom plating and impact-induced elastic bottom strains were measured. High-speed videos of water entry sequences were evaluated to investigate hydroelastic effects on air trapping.

A Simplified Method of Water Impact on Elastic Plate in Early Stage

2016 ◽  
Author(s):  
Hua Sun ◽  
Deyu Wang
Keyword(s):  
Elastic Plate ◽  
Early Stage ◽  
Impact Loads ◽  
Arbitrary Lagrangian Eulerian ◽  
Water Impact ◽  
Flat Bottom ◽  
Initial Stage ◽  
Simplified Method ◽  
Bottom Structures ◽  
The Impact

For most flat-bottom marine structures, the impact loads are generated by complex transient coupling effects of solid, air and water. However, there are rare simplified forecasting methods to obtain the impact loads and dynamic response of the flat-bottom structures by considering both hydro elastic and air cushion effects. In the paper, a new simplified analysis method of water impact on the elastic plate is proposed referred to Verhagen’s model of the rigid plate. The analysis is focused on the initial stage during which the highest hydrodynamic loads are generated. The method simulates the interaction between the plate, the air and the water. Also, fluid-structure coupling results from the simplified method are compared to numerical results from Arbitrary Lagrangian–Eulerian method and experimental results to validate the feasibility and accuracy of this simplified method.

Experimentally Measured Hydroelastic Effects on Impact-Induced Loads during Flat Water Entry and Related Uncertainties

2019 ◽  
pp. 1-30
Author(s):  
Simon Toedter ◽  
Ould el Moctar ◽  
Jens Neugebauer ◽  
Thomas E. Schellin
Keyword(s):  
High Speed ◽  
Water Entry ◽  
Test Case ◽  
Primary Concern ◽  
Air Trapping ◽  
Flat Bottom ◽  
Benchmark Data ◽  
Elastic Bottom ◽  
Structural Deformations ◽  
Two Bodies

Abstract Extensive water entry experiments were performed to identify uncertainties associated with measured impact-induced loads acting on flat bottom ship structures. Of primary concern was the influence of air trapping on elastic structural deformations. The experimental measurements supplied benchmark data suitable to validate CFD predictions. Two bodies were tested. One body was fitted with stiffened, rigid bottom plating; the other body, with thin elastic plating. A large number of 30 repetitive runs recorded bottom pressures and forces acting on the flat bottom plating and monitored impact-induced elastic bottom strains. For each test case, high-speed videos of water entry sequences were evaluated. The resulting average peak values standard deviations quantified the uncertainty of these measurements.

Numerical Analysis of Impact Loads on Subsea Structures During Water Entry in Presence of Waves

2020 ◽  
Author(s):  
Gustavo Garcia Momm ◽  
Ivan Fábio Mota de Menezes
Keyword(s):  
Constant Velocity ◽  
Oil And Gas ◽  
Free Fall ◽  
Water Entry ◽  
Gas Production ◽  
Rigid Bodies ◽  
Bottom Surface ◽  
Impact Loads ◽  
Flat Bottom ◽  
The Impact

Abstract Subsea structures employed on offshore oil and gas production systems are likely to be subject to severe loads during deployment. Lowering these structures through the wave zone is a critical operation and the prediction of the loads associated is complex as it involves accelerations of these bodies induced by the vessel motion and the sea surface displacements. This work presents a numerical approach to assessment of the effect of waves on the impact loads that subsea structures are subject to during water entry. A 2D one degree of freedom model using the SPH method was developed to estimate slamming loads on rigid bodies during water entry considering both calm and wavy surfaces. Initially the model was employed to simulate the water entry of wedge considering both free fall and constant velocity cases, obtaining loads profile similar to experiments and numerical simulations from the literature. Later, the constant velocity model was configured to a flat bottom surface rigid body in order to represent a subsea manifold. A regular waves generator provided different wavelength, height and phase enabling slamming load assessment in various situations.

scholarly journals On the Effect of Cavity Formation during the Water Entry of Flexible Bodies

2018 ◽  
Author(s):  
Riccardo Panciroli ◽  
Tiziano Pagliaroli ◽  
Giangiacomo Minak
Keyword(s):  
Fluid Motion ◽  
Free Fall ◽  
Time Frame ◽  
Water Entry ◽  
The Body ◽  
Structural Deformation ◽  
Cavity Formation ◽  
Experimental Conditions ◽  
Flexible Bodies ◽  
The Impact

Elastic bodies entering the water might experience Fluid-Structure Interaction phenomena introduced by the mutual interaction between the structural deformation and the fluid motion. Cavity formation, often misleadingly named cavitation, is one of these. This work presents the results of an experimental investigation on the water entry of deformable wedges impacting a quiescent water surface with pure vertical velocity in free fall. The experimental campaign is conducted on flexible wedges parametrically varying the flexural stiffness, deadrise angle, and drop height. It is found that under given experimental conditions cavity pockets forms beneath the wedge. Their generation mechanism is found to be ruled by a differential between structural and fluid velocities, which is introduced by the structural vibrations. Results show that the impact force during water entry of stiff bodies is always opposing gravity, while in case of flexible bodies might temporarily reverse its direction, with the body that is being sucked into the water within the time frame between the cavity formation and its collapse. Severe impacts might also generate a series of cavity generation and collapses.

scholarly journals On Air-Cavity Formation during Water Entry of Flexible Wedges

2018 ◽  
Vol 6 (4) ◽  
pp. 155 ◽  
Author(s):  
Riccardo Panciroli ◽  
Tiziano Pagliaroli ◽  
Giangiacomo Minak
Keyword(s):  
Fluid Motion ◽  
Free Fall ◽  
Time Frame ◽  
Water Entry ◽  
The Body ◽  
Structural Deformation ◽  
Cavity Formation ◽  
Experimental Conditions ◽  
Fluid Velocities ◽  
The Impact

Elastic bodies entering water might experience fluid–structure interaction phenomena introduced by the mutual interaction between structural deformation and fluid motion. Cavity formation, often misleadingly named cavitation, is one of these. This work presents the results of an experimental investigation on the water entry of deformable wedges impacting a quiescent water surface with pure vertical velocity in free fall. The experimental campaign is conducted on flexible wedges parametrically varying the flexural stiffness, deadrise angle, and drop height. It is found that, under given experimental conditions, cavity pockets form beneath the wedge. Their generation mechanism might be ascribed to a differential between structural and fluid velocities, which is introduced by structural vibrations. Results show that the impact force during water entry of stiff wedges are always opposing gravity, while, in case flexible wedges temporarily reverse their direction, with the body that is being sucked into the water within the time frame between the cavity formation and its collapse. Severe impact might also generate a series of cavity generation and collapses.

scholarly journals Numerical simulation of cavitation characteristics in high speed water entry of head-jetting underwater vehicle

2021 ◽  
Vol 39 (4) ◽  
pp. 810-817
Author(s):  
Hairui Zhao ◽  
Yao Shi ◽  
Guang Pan
Keyword(s):  
Numerical Simulation ◽  
High Speed ◽  
Impact Load ◽  
Underwater Vehicle ◽  
Water Entry ◽  
Engineering Practice ◽  
Entry Angle ◽  
Air Jet ◽  
Entry Velocity ◽  
The Impact

Autonomous underwater vehicle will be subjected to a huge impact load during high speed water entry, which will damage the structure and the internal instruments of the vehicle. Therefore, it is of great significance to study the buffer mechanism of the vehicle during the process of water-entry. In this paper, a kind of head-jetting device with disk cavitation is used. The complex cavitation forms, under the three-phase coupling of gas, liquid and solid, in the water entry process of the vehicle on which the device is installed. In this paper, the numerical simulation of high-speed water entry of the vehicle equipped with head jet device is carried out. Through the analysis of water entry cavitation under typical working conditions, the following conclusions are obtained. After the installation of head jet device, the water entry cavity of the vehicle changes gradually from cone to spindle shape. The air jet, compared with that without jet, can promote the formation of water inlet supercavitation, decrease the interaction area between the vehicle and water, and reduce the impact load during water entry. At the same water entry depth, the diameter of cavitation increases with the amount of air jet. The water entry velocity has a great influence on the difference of cavitation shape. The water entry depth closure phenomenon, when the water entry velocity is less than 100 m/s, can be observed in the depth of 3.5 times of the projectile length. The water entry angle has a significant effect on the cavitation shape. The cavity shows obvious asymmetry when the vehicle slants into the water, and the diameter and length of the bubbles decrease with the increase of the water entry angle. The research content of this paper provides technical support for the engineering practice of high-speed water entry and load reduction, and the conclusions are of great significance in related fields.

scholarly journals Technology Entrepreneurship and the Performance of Enterprises in the Conditions of Covid-19 Pandemic: The Fuzzy Set Analysis of Waste to Energy Enterprises in Poland

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3891
Author(s):  
Piotr Kordel ◽  
Radosław Wolniak
Keyword(s):  
Fuzzy Set ◽  
High Performance ◽  
Qualitative Comparative Analysis ◽  
Flexible Structures ◽  
Implementation Strategies ◽  
Waste To Energy ◽  
Energy Industry ◽  
Technology Entrepreneurship ◽  
Research Results ◽  
The Impact

This article’s aim is to explain the impact of technology entrepreneurship phenomenon on waste management enterprise performance in the conditions of COVID-19 pandemic. The concept of technology entrepreneurship according to the configuration approach and the category of high-performance organization are the theoretical bases of empirical investigation. For the implementation of empirical research, Fuzzy set Qualitative Comparative Analysis (FsQCA) was adopted. The research sample included a group of producers of Refused Derived Fuel (RDF) as a central part of the waste to energy industry located in Poland. The research results showed that the waste to energy sector is highly immune to pandemic threats. While during COVID-19, the basic economic parameters (i.e., sales, profitability and employment) of the entire industry in Poland clearly decreased, the same parameters in the case of the waste to energy industry remained at the same level. The research results allow the formulation of two high-performance models of technology entrepreneurship in the waste to energy industry under COVID-19 conditions. The first model is based on traditional technologies and hierarchical organizational structures, and the second is using innovative technologies and flexible structures. Both technology entrepreneurship models are determined by their emergence as complementary to implementation strategies and the opportunity-oriented allocation of resources within business model portfolios.

scholarly journals Monitoring of the Impact of Lithium Nitrate on the Alkali–aggregate Reaction Using Acoustic Emission Methods

Materials ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 20
Author(s):  
Justyna Zapała-Sławeta ◽  
Grzegorz Świt
Keyword(s):  
Acoustic Emission ◽  
Initial Reaction ◽  
Lithium Nitrate ◽  
Acoustic Emission Method ◽  
Emission Method ◽  
Acoustic Activity ◽  
Initial Stage ◽  
Chemical Admixture ◽  
Different Characteristics ◽  
The Impact

The study analyzed the possibility of using the acoustic emission method to analyse the reaction of alkali with aggregate in the presence of lithium nitrate. Lithium nitrate is a chemical admixture used to reduce adverse effects of corrosion. The tests were carried out using mortars with reactive opal aggregate, stored under the conditions defined by ASTM C227. The acoustic activity of mortars with a corrosion inhibitor was referred to linear changes and microstructure of specimens in the initial reaction stages. The study found a low acoustic activity of mortars with lithium nitrate. Analysis of characteristic parameters of acoustic emission signals, combined with the observation of changes in the microstructure, made it possible to describe the corrosion processes. As the reaction progressed, signals with different characteristics were recorded, indicating aggregate cracking at the initial stage of the reaction, followed by cracking of the cement paste. The results, which were referred to the acoustic activity of reference mortars, confirmed that the reaction of opal aggregate with alkali was mitigated in mortars with lithium nitrate, and the applied acoustic emission method enabled the detection and monitoring of ASR progress.

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