Wave Blockage Research Articles

Experimental Investigation of Gas Transmission Pipeline Blockage Detection Based on Dynamic Pressure Method

The blockage of natural gas pipelines caused by solid deposits such as hydrates is one of the major safety risks to transmission pipeline systems. The key to effective blockage relief or removal is to determine the location and severity of the blockage. In recent years, the pressure pulse wave method has been considered as a practical detection method due to its fast response time, simplicity of operation, and extended detection distance. Nevertheless, the current implementation of this method in pipelines indicates that the accuracy in detecting blockages is very low. To improve the accuracy of the pressure wave blockage detection technique in our experiments, a series of experiments were carried out to detect and locate hydrate blockages in natural gas pipelines based on the pressure wave method using a separate pipeline system of 22 mm diameter and 106 m length. The experimental results show that the accuracy of the blockage location prediction based on the pressure pulse wave method is within 5%. Still, the blockage’s cross-sectional shape can significantly affect the intensity of the reflected wave, with a maximum prediction error of 35%.

A Bayesian Lasso Logistic Regression Model for Predicting the Probability of Regional Seismic Phase Observation UsingSnin the Middle East and East Asia as Examples

ABSTRACTHigh-frequency seismic wave blockage is often the result of strong attenuation, and the regional phase Sn is particularly prone to blockage in comparison with any of the other regional phases including Lg. As widespread blockage can lead to difficulty in the estimation of source parameters or path attenuation, accurate characterization of efficient regional wave propagation is necessary. We have applied two approaches to map Sn phase blockage: (1) the relatively standardized efficiency tomography and (2) a newly developed Bayesian logistic regression model that is able to predict the likelihood (probability) of phase blockage. As a byproduct of our Bayesian approach, we obtain measures of uncertainty for the probability of blockage. We applied both our methods on simulated efficiency data as well as real efficiency data obtained from earthquakes and stations from the middle east and eastern Asia. Our models successfully predict the probability of blockage zones with relatively high accuracy (>75%). In addition, we observe both low probability of Sn blockage and efficient Sn propagation in tectonically stable continental lithosphere, such as the Arabian plate, the Mediterranean Sea, northeastern Iran, the Ordos plateau, and the Sichuan basin. Regions with a high probability of Sn blockage or inefficient Sn propagation zones are in the tectonically active areas, such as the Tibetan and Iranian plateaus. Our probability of blockage model can also be used to image the regions where SnQ models are likely to be biased due to blocked data.

Numerical investigation on nonlinear wave interaction with partially submerged subsea pipe-valve structures

The dynamic behaviours of subsea pipe-valve structures—the principal components of subsea equipment—are of critical concern for the control of the lowering through the splash zone during installation. Nonlinear interactions between waves and pipe-valve combinations are challenging the investigation of the wave forces acting on large-dimension structures. This paper proposes a numerical model to study the nonlinear hydrodynamic performance of partially submerged pipe-valve structures. A two-dimensional (2D) numerical water tank (NWT) was established to efficiently generate high-accuracy incident waves, and a semi-immersed horizontal cylinder was applied to the numerical simulations of wave-structure interaction (WSI) to study the mesh and time convergence. The numerical model was validated with a comparative analysis of the modelling results with experimental data, other numerical results, and theoretical results. Numerical simulations of the interaction between Stokes-II waves and subsea pipe-valve structures were performed, and the effects of the valve height ratio, valve length ratio, and valve spacing were investigated. The subsea pipe-valve structure is a kind of multi-scale structure, the wave forces exhibited stronger nonlinearity when acting on the partially submerged valves than on the completely submerged pipe. Changes in valve structure and distribution significantly increased the overall change in the wave forces acting on the valves. The stronger nonlinearity was primarily derived from phenomena such as wave reflection, wave blockage, and wave run-up. The numerical results provide references for the structure and strength designs and offshore installations of large subsea equipment like subsea manifolds.

Investigation on the hydrodynamic scaling effect of an OWC type wave energy device using experiment and CFD simulation

This paper presents a study of the effect of model scale on the performance of a fixed Oscillating Water Column (OWC) type Wave Energy Converter (WEC). Tank tests at two different scales, including the effect of scaling of the test tanks to minimise the bias introduced by different wave blockage effects. CFD simulations based on Reynolds Average Navier Stokes (RANS) method were then carried out for both scaled OWCs to investigate whether CFD simulation is able to reproduce the scale effect. Comparison between the tank test results and the CFD simulation results suggests that CFD simulation is capable of reproducing the hydrodynamic scaling effect with a good accuracy. Results also suggest that the hydrodynamic scaling effect is mainly introduced by the Reynolds number effect for cases investigated in the current study.

Study of interaction between wave-current and the horizontal cylinder located near the free surface

In this paper, the authors experimentally and numerically study the interaction between wave-current and the horizontal cylinder near the free surface. The experiments are conducted in the Circulating Water Channel with varying axis depths of cylinder. Considering the same wave height and different wave lengths, two regular waves are generated combined with current using a flap-type wave maker. Also, the numerical model based on the RANS equations is solved by the finite volume method, in which the RNG k−ε model is adopted to simulate the turbulence while the VOF method is used to capture the free surface. In this study, the free surface deformation due to wave reflection and blockage is investigated firstly. Then, the typical features of the wave-current force on the cylinder with various axis depths are studied. The peak values of the force are also discussed by comparison with those calculated by the modified Morison’s equation. Besides, the vorticity field around the fully submerged cylinder is discussed in detail. It is found that the wave-current force value is affected by both wave reflection and wave blockage under lower cylinder submergence. To be detailed, the force value increases due to wave reflection while decreases because of wave blockage. With regard to the partially submerged cylinder, wave reflection plays a dominant role compared with wave blockage. Therefore, the measured force value is larger than the theoretical one by modified Morison’s equation. However, for the fully submerged cylinder, its wave blockage is more notable in contrast with dramatically reduced wave reflection, resulting in a lower measured force value compared with theoretical one.

NEARSHORE WAVE DAMPING DUE TO THE EFFECT ON WINDS IN RESPONSE TO OFFSHORE WIND FARMS

Despite the progress that has been made in modeling wind wake interaction between turbines in offshore wind farms, only a handful of studies have quantified the impact of wind turbines or wave farms upon surface waves, and there are even less articles about the wave blockage induced by the whole array of turbines upon wind waves. This hypothetical case study proposes a methodology that takes into account the combined effect of wind wake and wave blockage on wind waves when transforming offshore waves to nearshore in an offshore wind farm scenario.

A computer simulation of grain orientation and aspect ratio that promotes the reflection of a pressure wave by elastic rotational stress

Optimal orientation angles and aspect ratios of a grain are presented for the attenuation of a longitudinal pressure wave by elastic stresses that arise from the rotation of a grain. A computer program in C++ allows the grain to be a two-dimensional ellipse of several orientations with respect to the incoming load. The program also varies the aspect ratio of the grain. The induced elastic stresses from the rotation of the grain are calculated with complex variable methods that do not require meshes and elements. Low aspect ratios of 5/3, 10/7 and 5/4 were particularly effective in halting the stress from the pressure wave when the major axis of the grain was tilted between 15° and 45° and again above 70° with respect to the line of the incoming load. Attenuation was found to be more sensitive to grain orientation than to aspect ratio. The conclusion is supported by numerous switches in the extent of wave blockage over small angular variations in the orientation of the grain.

Zones ofT-wave excitation in the NE Indian ocean mapped using variations in backazimuth over time obtained from multi-channel correlation of IMS hydrophone triplet data

Ground‐coupled hydro‐acoustic waves (so called T waves) observed at International Monitoring System (IMS) hydrophone triplet stations in the Indian ocean were analysed for backazimuth and apparent wave speed by applying a progressive multi‐channel correlation method (PMCC). For T waves, which propagate along topographically unblocked geodesic paths, the three triplet channels generally show good signal correlation over sliding windows and various frequency bands. A characteristic change in backazimuth over time, in some cases combined with signs of dispersion, is observed for many T waves generated by earthquakes from the margin of the Indo‐Australian Plate between the Sunda Islands to the southeast and the Andaman Islands to the northwest. Backazimuths and arrival times of those PMCC detections are used to map point‐by‐point the areas where ground‐to‐water coupling takes place. Such areas are mostly linked to large gradients in the bathymetry, predominantly at approximately the depth of the axis of the SOund Fixing And Ranging (SOFAR) channel, along island arcs, edges of continental shelves and at comparatively small features like isolated islands or sea mountains. Six examples are discussed in this paper. For the strongest events, the area of detectable ground‐to‐water coupling often spans distances of more than 15°, in one case even more than 26°, and a range in backazimuths of up to 35°. Information on the accuracy of backazimuth determination, on the average hydro‐acoustic wave speed along the wave path and on topographic blockage of waves can also be inferred from the results owing to the consistency and great detail of the mapped coupling zones. For the study area, it can be shown that it is predominantly seismic energy from P and/or Pn waves that couples efficiently into the SOFAR channel. Particularly for deep focus events, the backazimuths determined for the highest amplitude segments of the signals can deviate considerably from the great‐circle azimuth between source and receiver, and may therefore lead to inaccurate epicentre locations based on backazimuth measurements of T waves. In some cases, laterally reflected T waves are observed.

Electrochemical Waves on Patterned Surfaces: Propagation through Narrow Gaps and Channels

The dissolution and corrosion of iron and certain types of steel can involve the propagation of electrochemical waves. Low-carbon steel plates covered by nitric acid solutions self-organize pseudo-two-dimensional wave patterns which share many features with reaction−diffusion waves in excitable systems. Here, we investigate the dynamics of these electrodissolution waves in the presence of geometrical constraints. A simple procedure for the preparation of insulating, millimeter-scale obstacles is presented, which allows the controlled, local protection of the metal surface. This method is used in the measurement of the material consumption rate per wave [(850 ± 50) nm/wave or 6−7 g/(m2 wave)] as well as for the study of front propagation through narrow gaps and long channels. In channels, the wave velocity decreases with decreasing width from 10 to 4 mm/s. Propagation failures occur within the channel if its width is smaller than 0.2−0.4 mm. These results indicate that the obstacles have sink-like boundaries. For the estimation of the critical nucleation size in this system, we prepared short and narrow gaps that induce wave blockage for openings smaller than 0.65 ± 0.1 mm.

Spherical wave blockage in reflector antennas

The effects of the spherical wave blockage in reflector antennas is investigated. This problem is likely to occur in axially symmetrical feed antennas of single- and dual-reflector type in both single- and dual-reflector configurations, owing to the presence of primary feeds and their supports including struts that are normally placed between the primary source and the main reflector. The main reflector blockage due to large obstacles is estimated by the well-known null-field technique that employs flat polygonal plate models of the masking structures to define the obscured area. Although this same approach may be used to predict the spherical wave blockage due to the struts, a more rigorous but yet efficient technique is also employed, which consists of superimposing to the primary field the high-frequency scattered field from the struts. This field is calculated by using scattering coefficients that are derived by locally approximating the actual structure, by an infinite circular cylinder. This latter formulation is compared with the null-field technique and validated by an experimental campaign. The measurement setup is particularly useful for isolating spherical wave-blockage effects. It consists of a single-reflector offset antenna where a single strut is mounted with its axis parallel to that of the focusing parabola, thus, practically enforcing the plane wave blockage to vanish. Comparisons with the measurements have shown that the null-field approach is adequate for predicting the secondary pattern for large polygonal obstacle, but it is unsatisfactory to treat the strut blockage. It is found that this latter can be successfully described with the more rigorous high-frequency approach.