Numerical simulation of liquid sloshing using a fully nonlinear potential flow model in the non-inertial coordinate system

Liquid sloshing has been one of the primary concerns in ocean and offshore engineering due to its significant effects on ship stability and structure integrity. To investigate sloshing flow problems, a 3-dimensional Finite Volume Method based Fully Nonlinear Potential Flow (FNPF) model in the noninertial coordinate system is developed in the present study. In this model, the Laplace equation is spatially discretised and solved using a second-order accurate finite volume method from the open source computational fluid dynamics software OpenFOAM. For the fully nonlinear free surface problems, both kinematic and dynamic boundary conditions at the free surface are implemented in the mixed-Eulerian-Lagrangian (MEL) form to update the free surface elevation and velocity potential respectively. The FNPF sloshing model is validated against a number of available experimental measurements and numerical results for test cases under different external excitations. Finally, the conclusions in terms of model accuracy and applicability are summarised based on the validation and application results. It is found that the proposed FVM based sloshing FNPF model is able to simulate fully nonlinear liquid sloshing process in the non-inertial coordinate system

Investigations on the effects of internal liquid sloshing of semi-submersible floating offshore wind turbines

Originally developed for civil engineering applications, the tuned liquid column damper (TLCD) has been applied not only on tall buildings but also on floating offshore wind turbines (FOWTs) to minimize structural vibrations. This concept has also been adopted widely in navel architecture to reduce the roll motion. However, whether the damper will bring positive effects on mitigating the dynamic motions of FOWTs remains unknown. To this end, the paper studies the star-like three columns tuned liquid multi-column damper (TLMCD) impacts on the dynamic motions of a semi-submersible FOWT. The modelling is achieved by using a high-fidelity computational fluid dynamic (CFD) solver based on OpenFOAM. After the verification of the numerical model for the TLMCD system, it is extended to the modelling of the internal sloshing of TLMCD under prescribed pitch motions. A fully coupled floating-sloshing modelling is then conducted to simulate a semi-submersible FOWT with an integrated TLMCD under regular wave conditions. The study indicates that the passive-control TLMCD system has nearly no influence on the translational motions such as surge and heave. However, the pitch motions can be reduced significantly when the incident wave frequency is close to the natural pitch frequency of the platform. Apart from the natural pitch frequency, the TLMCD has a minor effect at other incident wave frequencies

A stable free-surface boundary solution method for fully nonlinear potential flow models

This paper presents a stable method for solving the kinematic boundary condition equation (KBC) in fully nonlinear potential flow (FNPF) models. The method is motivated by a total variation diminishing (TVD) approach, which makes it especially applicable to advection-dominated partial differential equations such as the KBC. It is also simple, and can be easily implemented in existing finite volume-based FNPF models for wave hydrodynamics. The method is systematically assessed through a series of test cases: the propagation of second and fifth-order Stokes waves; focused wave propagation; and wave shoaling in both 2 and 3-D. It was found that the method stabilised the computation in every instance: it successfully eliminated the sawtooth instability, which commonly arises in FNPF models, without a reduction in computational efficiency. Consequently, we avoided the use of undesirable stabilisation techniques that involve artificial dissipation such as low-order smoothing. The method is also accurate: it produced satisfactory numerical solutions that agreed well with experimental, analytical and other published numerical results. It was also found that the method is superior than classical schemes in terms of energy conservation, applicability, and efficiency—all salient features that are essential for large-scale and long-time simulations

CCP-WSI Blind Test Series 3: OpenFOAM Simulation of Focused Wave Interaction with a Simplified Wave Energy Converter

This paper presents a numerical study of a simplified wave energy converter (WEC) with and without a moon-pool under focused wave conditions and the work presented corresponds to a contribution to the CCP-WSI Blind Test Series 3. The numerical model applies the overset mesh technique in order to deal with large amplitude motions induced by the focused wave groups. The generation of the incident wave group is first examined through a mesh convergence test and by comparing with the experimental data. Simulations are then carried out with the presence of the WEC. In total three wave conditions are considered, each with the same wave period but different wave height. Non-linear effects on the WEC motion are clearly shown when the wave steepness increases and wave over-topping occurs. Furthermore, the effects of the moon pool on the dynamics and kinematics of the WEC including the damping effects on pitch response are also discussed, where the WEC motion is compared for the case with and without a moon-pool under the same wave conditions

Nitrogen, Phosphorus, and Potassium Flows through the Manure Management Chain in China

The largest livestock production and greatest fertilizer use in the world occurs in China. However, quantification of the nutrient flows through the manure management chain and their interactions with management-related measures is lacking. Herein, we present a detailed analysis of the nutrient flows and losses in the “feed intake–excretion–housing–storage–treatment–application” manure chain, while considering differences among livestock production systems. We estimated the environmental loss from the manure chain in 2010 to be up to 78% of the excreted nitrogen and over 50% of the excreted phosphorus and potassium. The greatest losses occurred from housing and storage stages through NH₃ emissions (39% of total nitrogen losses) and direct discharge of manure into water bodies or landfill (30–73% of total nutrient losses). There are large differences among animal production systems, where the landless system has the lowest manure recycling. Scenario analyses for the year 2020 suggest that significant reductions of fertilizer use (27–100%) and nutrient losses (27–56%) can be achieved through a combination of prohibiting manure discharge, improving manure collection and storages infrastructures, and improving manure application to cropland. We recommend that current policies and subsidies targeted at the fertilizer industry should shift to reduce the costs of manure storage, transport, and application

Primary culture of human blood-retinal barrier cells and preliminary study of APOBEC3 expression

PURPOSE. To develop methods for primary culture of human blood-retinal barrier (BRB) cells and to explore the expression of APOBEC3 (apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3) family gene, novel host-defense factors to HIV-1. METHODS. Cellular components of human BRB (human retinal capillary endothelial cells [HRCECs], human retinal capillary pericytes, and human retinal pigment epithelial cells) were isolated separately and subjected to primary culture according to procedures modified in our laboratory. Immunocytochemistry and immunofluorescence were used to identify specific markers of the primary cells and to analyze their purity by flow cytometry. RNA of the three different cells was isolated, and primers were designed to probe expression of the APOBEC3 gene by reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR. For further confirmation, APOBEC3F and APOBEC3G proteins were detected in the cultured cells and fresh retina tissue through Western blot analysis. In the end, HRCECs were treated with IFN-␥, and change of APOBEC3G expression was displayed. RESULTS. Pure BRB cells (Ͼ95% purity) were primary cultured according to procedures modified in our laboratory. Qualitative test of RT-PCR and semiquantitative examination of realtime PCR demonstrated the presence of APOBEC3B, -3C, -3F, and -3G genes and the absence of APOBEC3A and -3D genes in all cellular components of the BRB. Finding of the APOBEC3G and APOBEC3F proteins expressed in the three primary cultured cells and different layers of retinal tissue by Western blot analysis further confirmed the PCR results. Moreover, IFN-␥ could upregulate the expression of APOBEC3G in HRCECs. CONCLUSIONS. Major cellular components of human BRB could be primary cultured in vitro according to procedures optimized in our laboratory. Different expression of APOBEC3 in human blood-retinal barrier gives a clue to further research in intrinsic antiviral immunity in HIV-1-related retinopathy. (Invest Ophthalmol Vis Sci. 2009;50:4436 -4443

Differential vascular cell adhesion molecule-1 expression and superoxide production in simulated microgravity rat vasculature

Exposure to microgravity leads to orthostatic intolerance in astronauts and differential vascular structural and functional adaptations have been implicated in its occurrence. The present study tended to clarify the characteristics of vascular inflammation and oxidative stress in hindlimb unweighting (HU) rat vasculature. Male Sprague-Dawley rats were randomly divided into control (CON) and hindlimb unweighting (HU) groups. Three weeks later, immunohistochemistry was used to localize the expression of vascular cell adhesion molecule-1 (VCAM-1) and laser scanning confocal microscope were used to detect superoxide production. Immunohistochemical results revealed positive staining of VCAM-1 on endothelial cells in HU rat basilar and carotid arteries compared with CON, but not in abdominal aorta and femoral arteries. Meanwhile, HU increased O2·- levels in all the layers of basilar and carotid arteries from HU rat but not in abdominal aorta and femoral arteries from HU rat. These data suggested that differential expression of VCAM-1 and O2- production were concomitant with the vascular adaptations to simulated microgravity and whether they participate in vascular structure and function remodeling merits further investigation