scholarly journals Study on Slamming Pressure Characteristics of Platform under Freak Wave

2021 ◽  
Vol 9 (11) ◽  
pp. 1266
Author(s):  
Fali Huo ◽  
Hongkun Yang ◽  
Zhi Yao ◽  
Kang An ◽  
Sheng Xu
Keyword(s):  
Three Dimensional ◽  
Experimental Tests ◽  
Air Gap ◽  
Offshore Platform ◽  
Superposition Method ◽  
Linear Superposition ◽  
Freak Wave ◽  
Wave Slamming ◽  
Run Up ◽  
Cfd Method

Freak waves have great peak energy, short duration, great contingency, and strong nonlinear characteristics, and can cause severe damage to ships and marine structures. In this study, numerical simulations in conjunction with experimental tests are applied to study air gap response and wave slamming loads of a semi-submersible offshore platform under a freak wave. A three-dimensional wave tank, which is created based on the computational fluid dynamics (CFD) method, is applied to study the hydrodynamic responses of a semi-submersible platform. The numerical model of the tank and offshore platform system are checked according to the experimental results. A typical freak wave is modelled in numerical wave tanks by the linear superposition method, and its significant wave height is 13.03 m. It is found that the freak wave is closely associated with the wave slamming. The appearance of the freak wave gives rise to a negative air, gap which appears on the side of the back wave surface at the bottom of the deck box, and considerable slamming pressure is generated. Furthermore, the wave run up at the junction of the column and the buoyancy tank is also seen due to the freak wave.

scholarly journals Research on the Water Ridge and Slamming Characteristics of a Semisubmersible Platform under Towing Conditions

2022 ◽  
Vol 10 (1) ◽  
pp. 116
Author(s):  
Fali Huo ◽  
Changdong Wei ◽  
Chenyang Zhu ◽  
Zhaojun Yuan ◽  
Sheng Xu
Keyword(s):  
Numerical Simulations ◽  
Wave Height ◽  
Experimental Tests ◽  
Linear Increase ◽  
Wave Period ◽  
Wave Slamming ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Method ◽  
Rough Sea ◽  
Pressure Analysis

During the towing of semisubmersible platforms, waves impact and superpose in front of the platform to form a ridge shaped “water ridge”, which protrudes near the platform and produces a large slamming pressure. The water ridges occur frequently in the towing conditions of semisubmersible platforms. The wave–slamming on the braces and columns of platform is aggravated due to the water ridges, particularly in rough sea conditions. The effect of water ridges is usually ignored in slamming pressure analysis, which is used to check the structural strengths of the braces and columns. In this paper, the characteristics of the water ridge at the braces of a semisubmersible platform are studied by experimental tests and numerical simulations. In addition, the sensitivity of the water ridge to the wave height and period is studied. The numerical simulations are conducted by a Computational Fluid Dynamics (CFD) method, and their accuracy is validated based on experimental tests. The characteristics of the water ridge and slamming pressure on the braces and columns are studied in different wave conditions based on the validated numerical model. It is found that the wave extrusion is the main reason of water ridge. The wave–slamming pressure caused by the water ridge has an approximately linear increase with the wave height and is sensitive to the wave period. With the increase of the wave period, the wave–slamming pressure on the brace and column of the platform increases first and then decreases. The maximum wave–slamming pressure is found when the wave period is 10 s and the slamming pressure reduces rapidly with an increase of wave period.

scholarly journals Research of freak wave effect on a floating object in seakeeping tank

2021 ◽  
Vol 3 (397) ◽  
pp. 65-74
Author(s):  
V. Maslov ◽  
Keyword(s):  
Physical Modeling ◽  
Wind Waves ◽  
Interaction Process ◽  
Superposition Method ◽  
Floating Structure ◽  
Linear Superposition ◽  
Sea State ◽  
Wave Effect ◽  
Freak Wave ◽  
Acceleration Sensors

Object and purpose of research. This paper describes physical modeling of interaction process of abnormal wave (freak wave) with a marine floating structure in a seakeeping tank of the Krylov State Research Center. Freak wave is extremely dangerous because of the difference from wind waves by an unusually steep front slope and a gentle trough. Freak wave appears suddenly and collapses rapidly. Research of effect process features is necessary for understanding and analysis of the object behavior at extreme sea conditions. As experiment results it was necessary to obtain empirical data of sea object motions and accelerations at interaction with freak wave on different course angles and speeds. The obtained physical experiment results will be the foundation of theoretical studies and numerical calculation methods. Materials and methods. Physical modeling of the interaction process of freak wave with a marine floating structure was conducted in a deep seakeeping tank. Freak wave was generated by the linear superposition method of four twodimensional unidirectional regular waves with variable steepness in frequency range of 2 to 6 rad/s. To create a control signal was using special software. Wave packets were formed consisting of a sequence of a four harmonicas with a given frequency, height and duration. For parameters registration of freak wave were used string probes installed with a certain step along the length of the tank. A marine floating structure model was fixed by elastic fastening system in a window of a tow cart. For measure the motions of marine floating structure and its accelerations in define points at encounter with freak wave the contactless optic system and two-component acceleration sensors (accelerometers) were used. Cases of structure interaction with freak wave at different course angles and speeds were considered. Main results. As result of physical experimental data of floating structure motions in the interaction with freak wave in conditions of regular sea state at five course angles with speed and without speed were obtained. Dependencies of roll, pitch and heave motions at different course angles and various speeds were built. Similar dependencies of vertical and transverse accelerations on a stem also were built. Comparative analysis of results with data, which were obtained on intensive irregular sea state (spectrum JONSWAP) at identical experiment conditions, and also with foreign results was carried out. Conclusions. The greatest roll and maximum accelerations are registered at alongside position to abnormal wave, but cargo vessel has a sufficient reserve of dynamic stability to withstand such an impulse effect. The values of roll motion and accelerations on irregular sea state are close to the parameters measured at freak wave effect. This similarity is explained by rocking effect of periodic impact of irregular sea state, the proximity of natural period of roll oscillations to average period of waves and sufficiently high waves. In comparison with foreign researches, a wider range of heading angles and speeds is considered, and data about accelerations in a stem are obtained.

scholarly journals Analysis of a Main Cabin Ventilation System in a Jack-Up Offshore Platform Part I: Numerical Modelling

2019 ◽  
Vol 9 (15) ◽  
pp. 3185 ◽  
Author(s):  
Yingchun Xie ◽  
Zepeng Zheng ◽  
Huibin Wang ◽  
Zhen Xu ◽  
Guijie Liu ◽  
...  
Keyword(s):  
Simulation Model ◽  
Ventilation System ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Offshore Platform ◽  
Ansys Fluent ◽  
Computational Fluid Dynamics Cfd ◽  
Ventilation Performance ◽  
Jack Up ◽  
Selection Of

This work aims to measure the thermodynamics of a main cabin ventilation system in a JU-2000E jack-up offshore platform. A three-dimensional (3D) physical model of the ventilation system was established, and the computational fluid dynamics (CFD) software (ANSYS FLUENT) was used to calculate the model thermodynamics. Numerical analysis was performed to investigate the influence mechanisms of the ventilation factors such as ventilation temperature and volume on the ventilation performance. The analysis results demonstrate that (1) top-setting of the exhaust vents is more effective than the side-setting in terms of high temperature reduction, (2) small ventilation temperature and volume can improve the ventilation efficiency, and (3) proper shutdown selection of the backup diesel engine can enhance the ventilation performance. Furthermore, the effect of humidity for the ventilation air was investigated. Lastly, an experimental platform was developed based on the simulation model. Experimental tests were carried out to evaluate the shutdown selection of the backup engine and have shown consistent results to that of the simulation model. The findings of this study provide valuable guidance in designing the ventilation system in the JU-2000E jack-up offshore platform.

scholarly journals Investigation of Pressure Oscillation and Cavitation Characteristics for Submerged Self-Resonating Waterjet

2021 ◽  
Vol 11 (15) ◽  
pp. 6972
Author(s):  
Lihua Cui ◽  
Fei Ma ◽  
Tengfei Cai
Keyword(s):  
Sudden Change ◽  
Three Dimensional ◽  
Pressure Oscillation ◽  
Experimental Tests ◽  
Low Pressure ◽  
The Self ◽  
Two Phase ◽  
Cavitation Phenomenon ◽  
Pressure Zone ◽  
Unsteady Characteristics

The cavitation phenomenon of the self-resonating waterjet for the modulation of erosion characteristics is investigated in this paper. A three-dimensional computational fluid dynamics (CFD) model was developed to analyze the unsteady characteristics of the self-resonating jet. The numerical model employs the mixture two-phase model, coupling the realizable turbulence model and Schnerr–Sauer cavitation model. Collected data from experimental tests were used to validate the model. Results of numerical simulations and experimental data frequency bands obtained by the Fast Fourier transform (FFT) method were in very good agreement. For better understanding the physical phenomena, the velocity, the pressure distributions, and the cavitation characteristics were investigated. The obtained results show that the sudden change of the flow velocity at the outlet of the nozzle leads to the forms of the low-pressure zone. When the pressure at the low-pressure zone is lower than the vapor pressure, the cavitation occurs. The flow field structure of the waterjet can be directly perceived through simulation, which can provide theoretical support for realizing the modulation of the erosion characteristics, optimizing nozzle structure.

scholarly journals An Alternative Method for Calculating the Eddy Current Loss in the Sleeve of a Sealless Pump

Actuators ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 78
Author(s):  
Tomislav Strinić ◽  
Bianca Wex ◽  
Gerald Jungmayr ◽  
Thomas Stallinger ◽  
Jörg Frevert ◽  
...  
Keyword(s):  
Eddy Current ◽  
Three Dimensional ◽  
Eddy Current Loss ◽  
Theoretical Background ◽  
Air Gap ◽  
Magnetic Flux Density ◽  
Pump Impeller ◽  
Current Loss ◽  
Faraday’S Law ◽  
Transient Simulations

A sealless pump, also known as a wet rotor pump or a canned pump, requires a stationary sleeve in the air gap to protect the stator from a medium that flows around the rotor and the pump impeller. Since the sleeve is typically made from a non-magnetic electrically conductive material, the time-varying magnetic flux density in the air gap creates an eddy current loss in the sleeve. Precise assessment of this loss is crucial for the design of the pump. This paper presents a method for calculating the eddy current loss in such sleeves by using only a two-dimensional (2D) finite element method (FEM) solver. The basic idea is to use the similar structure of Ampère’s circuital law and Faraday’s law of induction to solve eddy current problems with a magnetostatic solver. The theoretical background behind the proposed method is explained and applied to the sleeve of a sealless pump. Finally, the results obtained by a 2D FEM approach are verified by three-dimensional FEM transient simulations.

scholarly journals An Immunoinformatics Approach for SARS-CoV-2 in Latam Populations and Multi-Epitope Vaccine Candidate Directed Towards the World’s Population

Vaccines ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 581
Author(s):  
Andrés Felipe Cuspoca ◽  
Laura Lorena Díaz ◽  
Alvaro Fernando Acosta ◽  
Marcela Katherine Peñaloza ◽  
Yardany Rafael Méndez ◽  
...  
Keyword(s):  
B Lymphocyte ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Health Crisis ◽  
Public Health Crisis ◽  
Histocompatibility Complex ◽  
Potential Vaccine ◽  
Lymphocyte Responses ◽  
Socioeconomic Consequences ◽  
Epitope Candidate

The coronavirus pandemic is a major public health crisis affecting global health systems with dire socioeconomic consequences, especially in vulnerable regions such as Latin America (LATAM). There is an urgent need for a vaccine to help control contagion, reduce mortality and alleviate social costs. In this study, we propose a rational multi-epitope candidate vaccine against SARS-CoV-2. Using bioinformatics, we constructed a library of potential vaccine peptides, based on the affinity of the most common major human histocompatibility complex (HLA) I and II molecules in the LATAM population to predict immunological complexes among antigenic, non-toxic and non-allergenic peptides extracted from the conserved regions of 92 proteomes. Although HLA-C, had the greatest antigenic peptide capacity from SARS-CoV-2, HLA-B and HLA-A, could be more relevant based on COVID-19 risk of infection in LATAM countries. We also used three-dimensional structures of SARS-CoV-2 proteins to identify potential regions for antibody production. The best HLA-I and II predictions (with increased coverage in common alleles and regions evoking B lymphocyte responses) were grouped into an optimized final multi-epitope construct containing the adjuvants Beta defensin-3, TpD, and PADRE, which are recognized for invoking a safe and specific immune response. Finally, we used Molecular Dynamics to identify the multi-epitope construct which may be a stable target for TLR-4/MD-2. This would prove to be safe and provide the physicochemical requirements for conducting experimental tests around the world.

scholarly journals On the Post-Processing of 3D-Printed ABS Parts

Polymers ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1559
Author(s):  
Mohammad Reza Khosravani ◽  
Jonas Schüürmann ◽  
Filippo Berto ◽  
Tamara Reinicke
Keyword(s):  
Surface Treatment ◽  
Fused Deposition Modeling ◽  
Three Dimensional ◽  
Acrylonitrile Butadiene Styrene ◽  
Experimental Tests ◽  
Fracture Load ◽  
Post Processing ◽  
Fused Deposition ◽  
Dog Bone ◽  
3D Printed

Application of Additive Manufacturing (AM) has significantly increased in the past few years. AM also known as three-dimensional (3D) printing has been currently used in fabrication of prototypes and end-use products. Considering the new applications of additively manufactured components, it is necessary to study structural details of these parts. In the current study, influence of a post-processing on the mechanical properties of 3D-printed parts has been investigated. To this aim, Acrylonitrile Butadiene Styrene (ABS) material was used to produce test coupons based on the Fused Deposition Modeling (FDM) process. More in deep, a device was designed and fabricated to fix imperfection and provide smooth surfaces on the 3D-printed ABS specimens. Later, original and treated specimens were subjected to a series of tensile loads, three-point bending tests, and water absorption tests. The experimental tests indicated fracture load in untreated dog-bone shaped specimen was 2026.1 N which was decreased to 1951.7 N after surface treatment. Moreover, the performed surface treatment was lead and decrease in tensile strength from 29.37 MPa to 26.25 MPa. Comparison of the results confirmed effects of the surface modification on the fracture toughness of the examined semi-circular bending components. Moreover, a 3D laser microscope was used for visual investigation of the specimens. The documented results are beneficial for next designs and optimization of finishing processes.

scholarly journals Numerical Analysis of the Perforated Steel Sheets Under Uni-Axial Tensile Force

Metals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 632 ◽  
Author(s):  
Ahmed M. Sayed
Keyword(s):  
Load Capacity ◽  
Tensile Force ◽  
Three Dimensional ◽  
Tensile Load ◽  
Experimental Tests ◽  
Strain Engineering ◽  
Uniaxial Tensile ◽  
Fe Model ◽  
Stress Strain ◽  
Steel Sheets

The perforated steel sheets have many uses, so they should be studied under the influence of the uniaxial tensile load. The presence of these holes in the steel sheets certainly affects the mechanical properties. This paper aims at studying the behavior of the stress-strain engineering relationships of the perforated steel sheets. To achieve this, the three-dimensional finite element (FE) model is mainly designed to investigate the effect of this condition. Experimental tests were carried out on solid specimens to be used in the test of model accuracy of the FE simulation. Simulation testing shows that the FE modeling revealed the ability to calculate the stress-strain engineering relationships of perforated steel sheets. It can be concluded that the effect of a perforated rhombus shape is greater than the others, and perforated square shape has no effect on the stress-strain engineering relationships. The efficiency of the perforated staggered or linearly distribution shapes with the actual net area on the applied loads has the opposite effect, as it reduces the load capacity for all types of perforated shapes. Despite the decrease in load capacity, it improves the properties of the steel sheets.

scholarly journals Run-Up Simulation of a Semi-Floating Ring Supported Turbocharger Rotor Considering Thrust Bearing and Mass-Conserving Cavitation

Lubricants ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 44
Author(s):  
Christian Ziese ◽  
Cornelius Irmscher ◽  
Steffen Nitzschke ◽  
Christian Daniel ◽  
Elmar Woschke
Keyword(s):  
Reynolds Equation ◽  
Energy Equation ◽  
Thrust Bearing ◽  
Three Dimensional ◽  
Reliable Prediction ◽  
Two Phase ◽  
Hydrodynamic Bearings ◽  
Thrust Bearings ◽  
Run Up ◽  
The Impact

The vibration behaviour of turbocharger rotors is influenced by the acting loads as well as by the type and arrangement of the hydrodynamic bearings and their operating condition. Due to the highly non-linear bearing behaviour, lubricant film-induced excitations can occur, which lead to sub-synchronous rotor vibrations. A significant impact on the oscillation behaviour is attributed to the pressure distribution in the hydrodynamic bearings, which is influenced by the thermo-hydrodynamic conditions and the occurrence of outgassing processes. This contribution investigates the vibration behaviour of a floating ring supported turbocharger rotor. For detailed modelling of the bearings, the Reynolds equation with mass-conserving cavitation, the three-dimensional energy equation and the heat conduction equation are solved. To examine the impact of outgassing processes and thrust bearing on the occurrence of sub-synchronous rotor vibrations separately, a variation of the bearing model is made. This includes run-up simulations considering or neglecting thrust bearings and two-phase flow in the lubrication gap. It is shown that, for a reliable prediction of sub-synchronous vibrations, both the modelling of outgassing processes in hydrodynamic bearings and the consideration of thrust bearing are necessary.

Three-Dimensional Green’s Functions in Anisotropic Elastic Bimaterials With Imperfect Interfaces

2003 ◽  
Vol 70 (2) ◽  
pp. 180-190 ◽  
Author(s):  
E. Pan
Keyword(s):  
Green's Functions ◽  
Green’S Functions ◽  
Three Dimensional ◽  
Imperfect Interface ◽  
Boundary Integral ◽  
Stress Fields ◽  
Superposition Method ◽  
Interface Conditions ◽  
Complementary Part ◽  
Anisotropic Elastic

In this paper, three-dimensional Green’s functions in anisotropic elastic bimaterials with imperfect interface conditions are derived based on the extended Stroh formalism and the Mindlin’s superposition method. Four different interface models are considered: perfect-bond, smooth-bond, dislocation-like, and force-like. While the first one is for a perfect interface, other three models are for imperfect ones. By introducing certain modified eigenmatrices, it is shown that the bimaterial Green’s functions for the three imperfect interface conditions have mathematically similar concise expressions as those for the perfect-bond interface. That is, the physical-domain bimaterial Green’s functions can be obtained as a sum of a homogeneous full-space Green’s function in an explicit form and a complementary part in terms of simple line-integrals over [0,π] suitable for standard numerical integration. Furthermore, the corresponding two-dimensional bimaterial Green’s functions have been also derived analytically for the three imperfect interface conditions. Based on the bimaterial Green’s functions, the effects of different interface conditions on the displacement and stress fields are discussed. It is shown that only the complementary part of the solution contributes to the difference of the displacement and stress fields due to different interface conditions. Numerical examples are given for the Green’s functions in the bimaterials made of two anisotropic half-spaces. It is observed that different interface conditions can produce substantially different results for some Green’s stress components in the vicinity of the interface, which should be of great interest to the design of interface. Finally, we remark that these bimaterial Green’s functions can be implemented into the boundary integral formulation for the analysis of layered structures where imperfect bond may exist.

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