Free surface flow and wave impact at complex solid structures

Hydrodynamic wave loading at structures is a complex phenomenon to quantify. The design of structures to resist wave loading has been historically and predominantly achieved through empirical and experimental observations. This is due to the challenging understanding and quantification of wave impact energy transfer processes with air entrainment at solid structures. This paper investigates wave loading on such structures with effects of air entrapment. Specifically, it focuses on predicting the multi-modal oscillatory wave impact pressure signals which result from transient waves impinging upon a solid wall. A large dataset of compressible (and incompressible) numerical modelling scenarios have been generated to investigate these processes. The modelling simulation data are verified through a grid scaling analysis and validated against previous studies. Air bubble entrapment oscillatory pressure response trends are observed in the compressible simulation during wave impact. A frequency domain analysis of the impact pressure response is undertaken. The numerical modelling results are found in good agreement with theoretical and experimental observation data. These findings provide good confidence on the robustness of our numerical model foundations particularly for investigating the air bubbles formation, their mechanics and adjusted resonance frequency modes at impact with solid wall

Herbivory by a Phloem-Feeding Insect Inhibits Floral Volatile Production

There is extensive knowledge on the effects of insect herbivory on volatile emission from vegetative tissue, but little is known about its impact on floral volatiles. We show that herbivory by phloem-feeding aphids inhibits floral volatile emission in white mustard Sinapis alba measured by gas chromatographic analysis of headspace volatiles. The effect of the Brassica specialist aphid Lipaphis erysimi was stronger than the generalist aphid Myzus persicae and feeding by chewing larvae of the moth Plutella xylostella caused no reduction in floral volatile emission. Field observations showed no effect of L. erysimi-mediated floral volatile emission on the total number of flower visits by pollinators. Olfactory bioassays suggested that although two aphid natural enemies could detect aphid inhibition of floral volatiles, their olfactory orientation to infested plants was not disrupted. This is the first demonstration that phloem-feeding herbivory can affect floral volatile emission, and that the outcome of interaction between herbivory and floral chemistry may differ depending on the herbivore's feeding mode and degree of specialisation. The findings provide new insights into interactions between insect herbivores and plant chemistry

Investigation of wave impacts on porous structures for coastal defences

There is great scientific interest in further understanding the underlying wave impact dynamics on solid and/or permeable structures for coastal defences. The accurate and validated simulation of the dynamics of the flow at microsecond temporal scale prior to, at, and after impact is an outstanding and challenging numerical problem in CFD. More advanced numerical models of free surface flow processes which include entrapment of large air pockets is required. These models will yield more insight into the trends of pulse-like forces involved at impact with solid and/or porous material and will enable the understanding of the mechanical stability and integrity of defence structures. Furthermore, the development of advanced numerical models for solving such problems will need to be made accessible as information systems to a wider community of civil engineers in order to achieve integrated design of structural defences (coastal, offshore oil and gas, hydraulic dams etc.). This research is on the development of free surface flow simulations, flow visualisation, analyses of forces of impact, and analyses of the integrity of offshore structures in an information system environment. A large dataset of compressible (and incompressible) numerical models have been generated to simulate waves impacting at solid and porous structures. Initial studies focus on the behaviour of wave impacts with a solid structure in a 2 dimensional domain. The simulations data are verified through a grid independence study. Numerical results are validated against two sets of experimental data. Air bubble entrapment and consequential multi-modal oscillatory pressure response trends are observed in the compressible simulations during wave impact. Frequency domain analyses of the oscillatory impact pressure responses are undertaken. The numerical model data sets are compared with results generated from analytic methods and experimental data with good agreement. These initial findings confirm the robustness of our numerical model predictions concerning the simulated air bubble formations when compared with theories on air bubbles at impact and their resonance frequency modes. The compressible numerical model is extended to a 3 dimensional simulation. A range of porous structure morphologies are incorporated into the domain to replace solid wall impact interface. A brief overview of previous research on the subject of fluid flow in porous media is presented. The characterisation of the porous model morphologies is examined. Various permeability flow models are discussed in detail. The methods for the generation of the various porous structures and their integration into the CFD model are described. The results from a soliton wave impact at the porous structure morphologies both with and without air entrainment effects at the free surface is investigated in detail.Finally future work to develop an experimentation specification for the analysis of fluid flow thorough a porous structure is discussed. It is envisioned that this experimental work with have dual outcomes. Firstly it will serve to validate the numerical models created over the course of this study and secondly the potential for clean, renewable energy harvesting from oscillatory pressures through the incorporation of smart sensor hardware within the porous structure will be investigated

Evaluation of angular and linear spring systems linked to a dual baffle against the sloshing phenomenon

This paper presents a numerical model for predicting sloshing loads on a rectangular tank with a dual baffle having different lengths and locations. The developed model is validated in comparison with the available experimental data. Two types of dual-movable baffles, including linear spring devices and angular spring devices are compared with the dual-fixed baffle. The dual-movable baffles are observed to mitigate the sloshing force exerted on the side wall by about 30–35% when compared with the case of a tank without baffles

Hydrodynamic Investigation on a Land-Fixed OWC Wave Energy Device under Irregular Waves

The hydrodynamic response of a land-based oscillating water column (OWC) wave energy converter under various irregular wave conditions is investigated numerically. Based on the potential flow theory, a two-dimensional fully nonlinear numerical wave flume (NWF) is developed to model the hydrodynamic characteristics using the time-domain higher-order boundary element method (HOBEM). The inner-domain sources method and JONSWAP energy spectrum is used to generate the irregular incident waves, and a linear pneumatic model is used to determine the pneumatic pressure inside the chamber. The free surface elevations at the chamber centre and the oscillatory pneumatic pressures induced by the vertical motion of the water column are recorded. The influence of irregular waves on the hydrodynamic characteristics of the OWC device is carried out by comparison with the regular waves, and a number of significant wave heights and peak wave periods are considered. The hydrodynamic efficiency of the OWC device in irregular wave conditions is observed to be lower than that in regular waves for most wave frequencies, especially near the resonant frequency

Analysis of fluid flow impact oscillatory pressures with air entrapment at structures

Hydrodynamic wave loading at coastal structures is a complex phenomenon to quantify. The chaotic nature of the fluid flow field as waves break against such structures has presented many challenges to Scientists and Engineers for the design of coastal defences. The provision of installations such as breakwaters to resist wave loading and protect coastal areas has evolved predominantly through empirical and experimental observations. This is due to the challenging understanding and quantification of wave impact energy transfer processes with air entrainment at these structures. This paper presents a numerical investigation on wave loading at porous formations including the effects of air entrapment. Porous morphologies generated from cubic packed spheres with varying characteristics representing a breakwater structure are incorporated into the numerical model at the impact interface and the effect on the pressure field is investigated as the wave breaks. We focus on analysing the impulse impact pressure as a surging flow front impacts a porous wall. Thereafter we investigate the multi-modal oscillatory wave impact pressure signals which result from a transient plunging breaker wave impinging upon a modelled porous coastal protective structure. The high frequency oscillatory pressure effects resulting from air entrapment are clearly observed in the simulations. A frequency domain analysis of the impact pressure responses is undertaken. We show that the structural morphology of the porous assembly influences the pressure response signal recorded during the impact event. The findings provide good confidence on the robustness of our numerical model particularly for investigating the air bubbles formation and their mechanics at impact with porous wall