To share the construction and maintenance cost, an asymmetric oscillating water column (OWC) device integrated with a pile-fixed box-typed offshore breakwater is considered experimentally and numerically. A fully nonlinear numerical wave tank is established and validated with the open source solver OpenFOAM. The effects of the width and draft of rear box, and the incident wave height on the wave energy conversion efficiency, reflection and transmission coefficients, and energy dissipation coefficient are examined. In addition, the superiority of the present coupling system, compared to the traditional box-type breakwater, is discussed. With well comparisons, the results show that the existence of the rear breakwater is beneficial for the formation of partial standing waves and further wave energy conversion. In the range of wave heights tested, the higher the incident wave height, the larger the energy absorption efficiency except for the short-wave regimes. Moreover, the OWC-breakwater coupling system can obtain a similar wave blocking ability to the traditional one, and simultaneously extract wave energy and decrease wave reflection.

This study presents numerical and experimental investigations on an oscillating water column (OWC) wave energy device integrated into a sloping breakwater. Regular waves were generated in a physical wave tank to investigate the hydrodynamic performance and extraction efficiency of the small-scale nested OWC device. Simultaneously, to complement various scenarios, numerical simulations were conducted using the open-source computational fluid dynamics platform OpenFOAM. The volume of fluid (VOF) method was employed to capture the complex evolution of the air–water interface, and an artificial source term (Forchheimer flow region) was introduced into the Navier–Stokes equations to replace the power take-off (PTO) system. By analyzing wave reflection properties, energy absorption efficiency, and wave run-up, the hydrodynamic characteristics of the inclined OWC device were explored. The comparison between the numerical and experimental results indicate a good consistence. A smaller front wall draft broadens the high-efficiency frequency bandwidth. For relatively long waves, increasing the air chamber width enhances energy conversion efficiency and reduces wave run-up. The optimal configuration was achieved with the following dimensionless parameters: front wall draft $a/h=1/3$, air chamber width $d_1/h=2/9$, and slope $i=2$. Due to the sloped structure, when compared with a vertical OWC, long waves can more easily enter the chamber. This causes the efficient frequency bandwidth to shift towards the low frequency range, allowing more wave energy to be converted into pneumatic energy. As a result, wave run-up is reduced, enhancing the protective function of the breakwater.

Vertical distribution processes of sediment contaminants in water were studied by flume experiments. Experimental results show that settling velocity of sediment particles and turbulence characteristics are the major hydrodynamic factors impacting distribution of pollutants, especially near the bottom where particle diameter is similar in size to vortex structure. Sediment distribution was uniform along the distance, while contaminant distribution slightly lagged behind the sediment. The smaller the initial sediment concentration was, the more time it took to achieve a uniform concentration distribution for suspended sediment. A contaminants transportation equation was established depending on mass conservation equations. Two mathematical estimation models of pollutant distribution in the overlying water considering adsorption and desorption were devised based on vertical distribution of suspended sediment: equilibrium partition model and dynamic micro-diffusion model. The ratio of time scale between the sediment movement and sorption can be used as the index of the models. When this ratio was large, the equilibrium assumption was reasonable, but when it was small, it might require dynamic micro-diffusion model.

Controllable shock wave (CWS) parameters such as amplitude, operating area and number of operations are easy to control and have received extensive attention as a potential new technology for reservoir permeability enhancement. Based on the continuous-discontinuous element method (CDEM) and considering the coupling mechanism of reservoir deformation, failure, pore seepage and fracture flow, a multiphysical field coupling model of reservoir permeability enhancement under CWS is proposed. Under the fluid–solid coupling condition, the formation and development dynamic process of reservoir fractures are obtained, and the change of reservoir permeability is also obtained. The compression fracture zone, tensile fracture zone and undamaged zone are formed around the wellbore. After repeated impact, the number of fractures is more sensitive to tectonic stress, the fracture aperture is more sensitive to reservoir strength. Different from hydraulic fracturing, a large number of fractures in different directions will appear around the main fracture after repeated impact, forming a complex fracture network similar to spider web, which may be beneficial to improve reservoir permeability. The permeability of reservoirs with different tectonic stresses and strengths increases nonlinearly and monotonicly with repeated impacts. Based on CDEM, the change of reservoir permeability with tectonic stress, strength and impact times is obtained, which is a nonlinear monotonic three-dimensional relationship. Based on that relationship, the parameters of CWS can be controlled to predict the change of reservoir permeability, such as peak pressure, duration, impact times, etc. Therefore, it can optimize the reservoir fracturing scheme and improve the reservoir fracturing efficiency, which has considerable practical significance in engineering.

A floating structure integrated with dual oscillating water column (OWC) wave energy converters is numerically investigated using OpenFOAM and waves2Foam to explore its potential for simultaneous wave energy harvesting and motion mitigation. The volume of fluid method for interface capturing, the six-degree-of-freedom dynamic mesh solver waveDyFoam for motion responses and the porous media layer method for power take-off (PTO) damping are adopted to systematically analyze the influence of OWCs' relative chamber width, wall draft depth, and PTO settings on integrated floating structure's motion suppression and energy capture performance under regular waves. The results show that integrating dual OWC devices substantially alters the peak values of the floating structure's motions while shifting the resonant frequency. Optimal pitch motion suppression in the investigated cases occurs at a relative chamber width of 1/6, relative wall draft depth of 1/1, and PTO orifice ratio of e = 0.25%, achieving amplitude reductions of 63.68%, 63.68%, and 80.61%, respectively. A larger chamber width and smaller wall draft depth enhance wave energy conversion efficiency, notably broadening the high-efficiency frequency bandwidth. The optimal energy conversion efficiency is highly sensitive to PTO parameters, with the configuration e = 0.5% yielding the best performance. Transient flow field analysis elucidates the evolution of the floating structure's dynamic response.

The permeability of low-permeability cores is generally measured using a pulse decay method. The core of low-permeability rocks, such as shale, often has a layered structure. The applicability of pulse decay testing for layered cores is not clear. In this study, the performance of the pulse decay method on layered cores was comprehensively investigated. Numerical simulations were conducted to investigate the influence of the interlayer permeability ratio, storativity ratio, layer thickness, interlayer location, and number of layers on the pulse decay pressure and pressure derivative curves, as well as the permeability obtained from pulse decay testing. The results revealed that the pressure curves of layered cores exhibit distinct differences from those of homogeneous cores if the upstream permeability is larger than the downstream one. The pressure derivative curve shows more inclined or horizontal straight-line segments than in the homogeneous case. The shapes of the pressure and pressure derivative curves are affected by the upstream and downstream positions of the core, but the tested permeability is not affected. The tested permeability differs from the equivalent model permeability, with an error of up to 22%. If the number of layers is not less than 10, the permeability obtained from the pulse decay test is consistent with that of the equivalent model. These differences are influenced by the interlayer permeability ratio, storativity ratio, layer thickness, interlayer location, and number of layers. To improve the accuracy of permeability analysis in pulse decay testing for layered cores, curve fitting using the characteristics of the pressure derivative curve can be employed.