Cross-Flow Vibrations of a Pipe Close to a Rigid Boundary

1984 ◽  
Vol 106 (4) ◽  
pp. 451-457 ◽  
Author(s):  
V. Jacobsen ◽  
M. B. Bryndum ◽  
R. Nielsen ◽  
S. Fines
Keyword(s):  
Wave Train ◽  
Cross Flow ◽  
Flow Conditions ◽  
Rigid Boundary ◽  
Irregular Wave ◽  
Steady Current ◽  
Sea Bed ◽  
Velocity Flow ◽  
Pipe Segment ◽  
Hydroelastic Vibrations

The paper describes the results of a model test series with the purpose of determining the hydroelastic vibrations of a nearbed pipeline span exposed to flow conditions created by steady current, waves and waves superimposed on steady current. The study has been conducted using a model composed of a spring-mounted rigid pipe segment and a flat plate simulating the sea bed. The hydroelastic cross-flow vibrations of the pipe segment are presented as function of the flow velocity, flow condition (waves and/or steady current) and the relative distance of the pipe to the seabed. A simple approach to analyze the vibrations caused by an irregular wave train is presented.

Study of Turbulent Models in Jet Impingement at Different Cross-Flow Conditions

2017 ◽  
Vol 17 (17th International Conference) ◽  
pp. 1-21
Author(s):  
Abd Elnaby Kabeel ◽  
Medhat Elkelawy ◽  
Hagar Bastawissi ◽  
Ahmed El-Banna
Keyword(s):  
Cross Flow ◽  
Jet Impingement ◽  
Flow Conditions ◽  
Turbulent Models

Alternative Methodologies for Subsea Flexible Strength Analysis

2018 ◽  
Author(s):  
Anskey A. Miranda ◽  
Fred P. Turner ◽  
Nigel Barltrop
Keyword(s):  
Real World ◽  
Wave Train ◽  
Irregular Waves ◽  
Wave Crest ◽  
Strength Analysis ◽  
New Wave ◽  
Regular Wave ◽  
Wave Analysis ◽  
Sea State ◽  
Irregular Wave

This paper presents a study of the analysis methodologies used to predict the most likely response of flexibles in a subsea environment, with the aim of determining an efficient and reliable prediction methodology. The most accurate method involves simulating multiple wave realisations of a real world sea state, i.e. irregular waves, and post-processing the results to determine the most probable maximum (MPM). Due to the computationally intensive nature of this approach, however, regular wave analysis is typically used to determine flexible response. This approach considers the maximum wave within a design storm at a desired period; the choice of periods may leave room for uncertainty in the conservatism of the approach. With proper screening, regular wave analysis can be a valid yet overly conservative approach resulting in over design and additional cost. However, if screened incorrectly, there is a possibility that the choice of periods could give results that are under conservative. In addition to regular wave analysis, the paper presents two alternative methodologies to determine the most likely response, with the focus on reducing the computational resources required. The first alternative is an ‘Irregular Wave Screen’ approach in which the wave train is screened at areas of interest for waves within a user defined threshold of the maximum wave height, in addition to other user defined parameters. Only waves within these parameters are simulated to determine responses. The second alternative is the ‘New Wave’ approach, which models the most probable wave elevation around the maximum wave crest. The calculated new wave is then placed at the desired location to determine responses. The responses of the Regular, Irregular Wave Screen and New Wave methodologies are compared with the Irregular MPM approach to determine their feasibility to predict the response of flexibles in a real world irregular sea state with lower computational requirements.

scholarly journals LABORATORY STUDY ON TWO-DIMENSIONAL BEACH TRANSFORMATION DUE TO IRREGULAR WAVES

1986 ◽  
Vol 1 (20) ◽  
pp. 102 ◽  
Author(s):  
Nubuo Mimura ◽  
Yukinori Otsuka ◽  
Akira Watanabe
Keyword(s):  
Wave Train ◽  
Irregular Waves ◽  
Two Dimensional ◽  
Beach Profile ◽  
Irregular Wave ◽  
Sand Ripple ◽  
Ripple Formation ◽  
Sand Movement ◽  
Incident Waves ◽  
Profile Change

In the present study, effects of irregular waves on two-dimensional beach transformation and related phenomena were investigated through a series of laboratory experiments. Attempts were made to determine a representative wave of irregular wave trains which controlled individual phenomenon related to the two-dimensional beach profile change. It was found that the representative wave is different for each phenomenon. For the macroscopic beach profile change, it is the mean wave which represents whole incident waves. On the other hand, some of microscopic phenomena, such as initiation of sand movement and sand ripple formation, are controlled by larger waves in the wave train selectively, of which representative wave is the significant wave.

Effect of spark discharge energy scheduling on ignition under quiescent and flow conditions

2020 ◽  
Vol 234 (12) ◽  
pp. 2878-2891
Author(s):  
Zhenyi Yang ◽  
Xiao Yu ◽  
Hua Zhu ◽  
David S-K Ting ◽  
Ming Zheng
Keyword(s):  
Flow Velocity ◽  
High Power ◽  
Cross Flow ◽  
Spark Discharge ◽  
Discharge Process ◽  
Discharge Energy ◽  
Flow Conditions ◽  
Flame Kernel ◽  
Spark Plug ◽  
Spark Energy

The enhancement of the breakdown power during the spark discharge process has been proved to be beneficial for the flame kernel formation process under lean/diluted conditions. Such a strategy is realized by using a conventional transistor coil ignition system with an add-on capacitance in parallel to the spark plug gap in this paper. In practical application, the use of different ceramic material other than aluminum oxide can change the parasitic capacitance of the spark plug, achieving similar effect in terms of rescheduling the discharge energy released during the breakdown phase. Detailed research has been carried out to investigate the effect of the parallel capacitance and the cross flow velocity on the flame kernel formation and propagation process. With the increase in parallel capacitance, more spark energy is delivered during the breakdown phase, while less energy is released during the arc/glow phase. Shadowgraph images of the spark plasma reveal that the high-power spark discharge can generate a larger high-temperature area with enhanced electrically prompted turbulence under quiescent conditions, as compared with that using the conventional transistor coil ignition discharge strategy under the same condition. The breakdown enhanced turbulence of the high-power spark is proved to be beneficial for the flame kernel development, especially with the lean or exhaust gas recirculation diluted combustible mixtures, given that sufficient spark energy is available for the high-power spark strategy to successfully generate the breakdown event. The results of combustion tests under flow conditions reveal that the breakdown enhanced turbulence of the high-power spark tends to be overshadowed by the turbulence generated from the flow field, and both the increase in flow velocity and parallel capacitance contribute to the reduction in discharge duration of the arc/glow phase. Therefore, the benefits brought about by the high-power spark discharge tend to diminish with the intensification of flow velocity.

Jet interaction at supersonic cross flow conditions

Shock Waves ◽  
2003 ◽  
Vol 13 (1) ◽  
pp. 13-23 ◽  
Author(s):  
F. Seiler ◽  
P. Gnemmi ◽  
H. Ende ◽  
M. Schwenzer ◽  
R. Meuer
Keyword(s):  
Cross Flow ◽  
Flow Conditions ◽  
Jet Interaction

The use of turbulence generators to mitigate crystallization fouling under cross flow conditions

Desalination ◽  
2012 ◽  
Vol 288 ◽  
pp. 108-117 ◽  
Author(s):  
Basim O. Hasan ◽  
Graham J. Nathan ◽  
Peter J. Ashman ◽  
Richard A. Craig ◽  
Richard M. Kelso
Keyword(s):  
Cross Flow ◽  
Flow Conditions

Irregular Wave Simulation and Fatigue Damage Evaluation of a Flexible Riser Subjected to Bi-Modal Sea States

2012 ◽  
Author(s):  
Zhimin Tan ◽  
Yucheng Hou ◽  
John Zhang ◽  
Terry Sheldrake
Keyword(s):  
Fatigue Damage ◽  
Wave Train ◽  
Time History ◽  
Regular Wave ◽  
Flexible Riser ◽  
Single Wave ◽  
Irregular Wave ◽  
Wave Approach ◽  
Wave Simulation ◽  
Wind Sea

This paper presents the fatigue evaluation of a flexible riser subjected to bi-modal sea states, where the local wind and swell conditions act simultaneously, and is observed in many offshore regions including Brazil and West Africa. Due to the irregularity of the riser responses, the traditional, regular wave approach for assessing the fatigue damage of a flexible pipe cannot be applied without significant simplifications. A typical deviation would be to treat the combined swell and wind conditions at sea as two sets of separate cases. The regular wave approach can then be applied and the summation of the damage of both cases defined as the final damage of the pipe. As an alternative, this paper presents a more theoretically accurate irregular wave approach. The entire irregular wave simulation was first performed using the commercial software, OrcaFlex™, together with a tensile wire stress model developed in-house. The model implements the pipe bending hysteresis behavior during dynamic excitation, producing corresponding time history stress results, which are used to assess the fatigue damage using a rain-flow counting method. Two case studies are presented, the first being a dynamic simulation performed with two wave trains generated based respectively on the given swell and wind sea spectrums. In the second case study, a single wave train is generated based on the combined spectrum of the swell and wind sea states. Both results are compared with those obtained by the traditional regular wave approach and a preferred analysis method is recommended based on the conservatism and time efficiency.

Experimental Study of Near-Field Entrainment of Moderately Overpressured Jets

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Stephen A. Solovitz ◽  
Larry G. Mastin ◽  
Farhad Saffaraval
Keyword(s):  
High Speed ◽  
Near Field ◽  
Flow Region ◽  
Flow Conditions ◽  
Entrainment Ratio ◽  
One Dimensional ◽  
Column Collapse ◽  
Developing Flow ◽  
Image Velocimetry ◽  
Velocity Flow

Particle image velocimetry (PIV) experiments have been conducted to study the velocity flow fields in the developing flow region of high-speed jets. These velocity distributions were examined to determine the entrained mass flow over a range of geometric and flow conditions, including overpressured cases up to an overpressure ratio of 2.83. In the region near the jet exit, all measured flows exhibited the same entrainment up until the location of the first shock when overpressured. Beyond this location, the entrainment was reduced with increasing overpressure ratio, falling to approximately 60% of the magnitudes seen when subsonic. Since entrainment ratios based on lower speed, subsonic results are typically used in one-dimensional volcanological models of plume development, the current analytical methods will underestimate the likelihood of column collapse. In addition, the concept of the entrainment ratio normalization is examined in detail, as several key assumptions in this methodology do not apply when overpressured.

The Optimization of Blade Pitch Settings of an Air Turbine Using Self-Pitch-Controlled Blades For Wave Power Conversion

2001 ◽  
Vol 123 (4) ◽  
pp. 382-386 ◽  
Author(s):  
T. H. Kim ◽  
T. Setoguchi ◽  
K. Kaneko ◽  
M. Takao
Keyword(s):  
Oscillating Water Column ◽  
Flow Conditions ◽  
Irregular Wave ◽  
Turbine Performance ◽  
Air Chamber ◽  
Air Turbine ◽  
Wave Power Conversion ◽  
Wave Conditions ◽  
Starting Characteristics ◽  
Blade Pitch Angle

This work investigated an air turbine with self-pitch-controlled blades operating in the airflow generated by an oscillating water column (OWC) under irregular wave conditions to determine turbine performance and identify the optimum blade pitch angle setting. Rotor models with fixed blades were tested under steady flow conditions. The running and starting characteristics of the turbine under irregular wave conditions were determined from a computer simulation that modeled both the turbine and the air chamber. The performance of the air turbine was evaluated and the optimum rotor blade limit was found to be about 10°.

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