The influence of surface tension upon trapped waves and hydraulic falls

We consider steady two-dimensional free-surface flows past submerged obstructions on the bottom of a channel. The flow is assumed to be irrotational, and the fluid inviscid and incompressible. Both the effects of gravity and surface tension are considered. Critical flow solutions with subcritical flow upstream and supercritical flow downstream are sought using fully nonlinear boundary integral equation techniques based on the Cauchy integral formula. When a second submerged obstruction is included further upstream in the flow configuration in the absence of surface tension, solutions which have a train of waves trapped between the two obstacles before the critical flow have already been found (Dias and Vanden-Broeck 2004). We extend this work by including the effects of surface tension. Trapped wave solutions are found upstream for small values of the Bond number, for some values of the Froude number. Other types of trapped waves are found for stronger tension when the second obstruction is placed downstream of the hydraulic fall generated by the first obstacle

Critical control in transcritical shallow-water flow over two obstacles

The nonlinear shallow-water equations are often used to model flow over topography. In this paper we use these equations both analytically and numerically to study flow over two widely separated localised obstacles, and compare the outcome with the corresponding flow over a single localised obstacle. Initially we assume uniform flow with constant water depth, which is then perturbed by the obstacles. The upstream flow can be characterised as subcritical, supercritical and transcritical, respectively. We review the well-known theory for flow over a single localised obstacle, where in the transcritical regime the flow is characterised by a local hydraulic flow over the obstacle, contained between an elevation shock propagating upstream and a depression shock propagating downstream. Classical shock closure conditions are used to determine these shocks. Then we show that the same approach can be used to describe the flow over two widely spaced localised obstacles. The flow development can be characterised by two stages. The first stage is the generation of upstream elevation shock and downstream depression shock from each obstacle alone, isolated from the other obstacle. The second stage is the interaction of two shocks between the two obstacles, followed by an adjustment to a hydraulic flow over both obstacles, with criticality being controlled by the higher of the two obstacles, and by the second obstacle when they have equal heights. This hydraulic flow is terminated by an elevation shock propagating upstream of the first obstacle and a depression shock propagating downstream of the second obstacle. A weakly nonlinear model for sufficiently small obstacles is developed to describe this second stage. The theoretical results are compared with fully nonlinear simulations obtained using a well-balanced finite-volume method. The analytical results agree quite well with the nonlinear simulations for sufficiently small obstacles

Nonlinear free surface flows past a semi-infinite flat plate in water of finite depth

We consider the steady free surface two-dimensional flow past a semi-infinite flat plate in water of a constant finite depth. The fluid is assumed to be inviscid, incompressible and the flow is irrotational; surface tension at the free surface is neglected. Our concern is with the periodic waves generated downstream of the plate edge. These can be characterized by a depth-based Froude number, F, and the depth d (draft) of the depressed plate. For small d and subcritical flows, we may use the linearized problem, combined with conservation of momentum, to obtain some analytical results. These linear results are valid when F is not close to 0 or 1. As F approaches 1, we use a weakly nonlinear longwave analysis, and in particular show that the results can be extended to supercritical flows. For larger d nonlinear effects need to be taken account, and so we solve the fully nonlinear problem numerically using a boundary integral equation method. Here the predicted wavelength from the linear and weakly nonlinear results is used to set the mean depth condition for the nonlinear problem. The results by these three approaches are in good agreement when d is relatively small. For larger d our numerical results are compared with known results for the highest wave.We also find some wave-free solutions, which when compared with the weakly nonlinear results are essentially just one-half of a solitary wave solution

Free surface flow under gravity and surface tension due to an Applied Pressure Distribution II bond number less then one-third

We consider steady free surface two-dimensional flow due to a localized applied pressure distribution under the effects of both gravity and surface tension in water of a constant depth, and in the presence of a uniform stream. The fluid is assumed to be inviscid and incompressible, and the flow is irrotational. The behaviour of the forced nonlinear waves is characterized by three parameters: the Froude number, F, the Bond number, τ < 1/3, and the magnitude and sign of the pressure forcing term ǫ. The fully nonlinear wave problem is solved numerically by using a boundary integral method. For small amplitude waves and F < Fm < 1 where Fm is a certain critical value where the phase and group velocities for linearized waves coincide, linear theory gives a good prediction for the numerical solution of the nonlinear problem in the case of a bifurcation from the uniform flow. As F approaches Fm, however, some nonlinear terms need to be taken in the problem. In this case the forced nonlinear Schr¨odinger equation is found to be an appropriate model to describe bifurcations from an unforced envelope solitary wave. In general, it is found that for given values of F < Fm and τ < 1/3, there exist both elevation and depression waves

Growth and development of Gnathostoma spinigerum (Nematoda: Gnathostomatidae) larvae in Mesocyclops aspericornis (Cyclopoida: Cyclopidae)

<p>Abstract</p> <p>Background</p> <p><it>Gnathostoma spinigerum </it>larva is pathogenic, causing gnathostomiasis in humans and certain animals, and is prevalent mainly in Asia. Growth and development of <it>Gnathostoma spinigerum </it>larvae in the cyclopoid copepod <it>Mesocyclops aspericornis</it>, the first intermediate host, were examined.</p> <p>Results</p> <p>When newly hatched, ensheathed second-stage larvae (L2) were ingested by <it>M. aspericornis</it>, they immediately appeared exsheathed in the stomach of <it>M. aspericornis</it>. They then penetrated the stomach wall and entered the body cavity, where they immediately metamorphosed to a stunted form with the body length/width ratio equal to the early third-stage larvae (EL3) up to 2 h after being ingested. During metamorphosis, the anterior spine-like structure of L2 transformed into unequal transparent lips. The larvae moulted into EL3 in the body cavity of the copepod at around day 5-7 post-infection. Minute cuticular striations were seen on the whole body, with prominent single-pointed spines on the anterior part of the body. The head bulb had four rows of hooklets and two lateral trilobed lips. The size of EL3 in copepods continuously increased towards day 12 and showed a negative correlation to their density per copepod (R = -0.881, <it>P </it>< 0.05 for body length, and R = -0.906, <it>P </it>< 0.05 for body width).</p> <p>Conclusions</p> <p>The results revealed for the first time that <it>M. aspericornis</it>, one of the most abundant freshwater copepods in Thailand, is a suitable first intermediate host for <it>G. spinigerum</it>. High susceptibility of <it>M. aspericornis </it>suggests its importance for the maintenance of the life cycle of <it>G. spinigerum </it>in Thailand.</p

Consistent Weighted Average Flux of Well-Balanced TVD-RK Discontinuous Galerkin Method for Shallow Water Flows

A well-balanced scheme with total variation diminishing Runge-Kutta discontinuous Galerkin (TVD-RK DG) method for solving shallow water equations is presented. Generally, the flux function at cell interface in the TVD-RK DG scheme is approximated by using the Harten-Lax-van Leer (HLL) method. Here, we apply the weighted average flux (WAF) which is higher order approximation instead of using the HLL in the TVD-RK DG method. The consistency property is shown. The modified wellbalanced technique for flux gradient and source terms under the WAF approximations is developed. The accuracy of numerical solutions is demonstrated by simulating dam-break flows with the flat bottom. The steady solutions with shock can be captured correctly without spurious oscillations near the shock front. This presents the other flux approximations in the TVD-RK DG method for shallow water simulations

Critical control in transcritical shallow-water flow over two obstacles

This article was published in the Journal of Fluid Mechanics [© Cambridge University Press] and the definitive version is available at: http://dx.doi.org/10.1017/jfm.2015.485The nonlinear shallow-water equations are often used to model flow over topography. In this paper we use these equations both analytically and numerically to study flow over two widely separated localised obstacles, and compare the outcome with the corresponding flow over a single localised obstacle. Initially we assume uniform flow with constant water depth, which is then perturbed by the obstacles. The upstream flow can be characterised as subcritical, supercritical and transcritical, respectively. We review the well-known theory for flow over a single localised obstacle, where in the transcritical regime the flow is characterised by a local hydraulic flow over the obstacle, contained between an elevation shock propagating upstream and a depression shock propagating downstream. Classical shock closure conditions are used to determine these shocks. Then we show that the same approach can be used to describe the flow over two widely spaced localised obstacles. The flow development can be characterised by two stages. The first stage is the generation of upstream elevation shock and downstream depression shock from each obstacle alone, isolated from the other obstacle. The second stage is the interaction of two shocks between the two obstacles, followed by an adjustment to a hydraulic flow over both obstacles, with criticality being controlled by the higher of the two obstacles, and by the second obstacle when they have equal heights. This hydraulic flow is terminated by an elevation shock propagating upstream of the first obstacle and a depression shock propagating downstream of the second obstacle. A weakly nonlinear model for sufficiently small obstacles is developed to describe this second stage. The theoretical results are compared with fully nonlinear simulations obtained using a well-balanced finite-volume method. The analytical results agree quite well with the nonlinear simulations for sufficiently small obstacles

Development of a PCR assay and pyrosequencing for identification of important human fish-borne trematodes and its potential use for detection in fecal specimens

BACKGROUND: Small liver and minute intestinal flukes are highly prevalent in Southeast Asia. Definitive diagnosis of parasite infection is usually achieved parasitologically by finding the fluke eggs in feces. However, their eggs are difficult to differentiate morphologically in fecal samples, even for experienced technicians. The present study developed a PCR assay coupled with DNA pyrosequencing for identification of the fish-borne trematodes (FBT), Opisthorchis viverrini, Clonorchis sinensis, Haplorchis taichui, H. pumilio and Stellantchasmus falcatus, and to evaluate potential detection in fecal specimens, and identification and differentiation of cercarial and metacercarial stages. METHODS: Primers targeting the partial 28S large subunit ribosomal RNA gene were designed and about 46–47 nucleotides were selected as the target region for species identification by a PCR assay coupled with a pyrosequencing technique. RESULTS: The nucleotide variations at 24 positions, which is sufficient for the identification of the five species of FBT were selected. The method could identify O. viverrini and C. sinensis eggs in feces, cercarial and metacercarial stages of O. viverrini, and metacercarial stage of H. pumilio and H. taichui. The detection limit was as little as a single O. viverrini or C. sinensis egg artificially inoculated in 100 mg of non-infected fecal sample (equivalent to 10 eggs per gram), indicating highly sensitivity. The method was found to be superior to the traditional microscopy method and was more rapid than Sanger DNA sequencing. CONCLUSIONS: DNA pyrosequencing-based identification is a valuable tool for differentiating O. viverrini and other Opisthorchis-like eggs, and can be applied to epidemiological studies and for molecular taxonomic investigation of FBT in endemic areas