A parallel Eulerian–Lagrangian localized adjoint method

We describe an approach to parallelize Eulerian–Lagrangian localized adjoint methods such that no errors are introduced compared to the sequential case. This parallelization approach fully captures the hyperbolic features of the underlying problem. It uses an overlapping domain decomposition technique, and does not involve the introduction of artificial boundary conditions between subdomains. Implementation details on different parallel architectures are discussed.     

Arbitrary Lagrangian Eulerian formulation for soil structure interaction problems

Simulation of soil structure interaction problems becomes more and more the focus of computational engineering in the last decades in the civil engineering community. In many applications in civil engineering, the Lagrangian formulation is the main approach for soil structure interaction problems. For the last decades, various approaches have been investigated in fluid and structure mechanics, to solve fluid structure interaction problems, including Arbitrary Eulerian Lagrangian (ALE) formulation and meshless methods as Smoothing Particle Hydrodynamics (SPH). These two approaches are more common in fluid mechanics than structure and civil engineering, where the classical Lagrangian formulation is still dominant for numerical simulations. The Lagrangian formulation, where the mesh moves with material is mainly used to solve problems in solid mechanics, and civil engineering for soil structure interaction problems. For small deformation, Lagrangian formulation can solve soil structure interface and material boundary accurately; the main limitation of the formulation is high mesh distortion for large deformation and moving structure. One of the commonly used approaches to solve these problems is the ALE formulation which has been used with success in the simulation of fluid structure interaction with large structure motion such as sloshing fuel tank in automotive industry and bird impact in aeronautic industry. In this paper, devoted to ALE formulation for civil engineering problems, the mathematical and numerical implementation of the ALE formulation and the contact algorithm are described. In order to validate the ALE algorithms, and prove its ability for civil engineering applications, we consider two different applications. First we perform the simulation of a shock wave propagation generated by a detonation of an explosive. In the second application, we consider a soil structure coupling problem, using an ALE formulation for the soil which undergoes large mesh deformation, and a Lagrangian formulation for the structure. A contact algorithm is performed at the soil structure interface.     

Lagrangian and Eulerian estimates of circulation in the lee of Kapiti Island,New Zealand

Lagrangian drifters, moored acoustic Doppler current meters and hydrographic observations are combined with wind observations to describe the mean and variable nature of flow around Kapiti Island, New Zealand. Thirteen day-long deployments of up to six Lagrangian drifters show the mean flow is to the southwest, with evidence of stronger flows in the channel separating the island from the mainland, and an island wake in the lee of the island. Vortices in this island wake may be tidally driven. Scaling considerations suggest the flow is strong enough that tidal-generated vortices are shed on each tidal cycle. Both the drifters and mooring data suggest that the d’Urville Current around Kapiti Island has a significant wind-driven component. During north-westerlies, the drifters tend to hug the coast, and south-eastwards flows in the Rauoterangi Channel are accelerated. We suggest the observed correlation is the local expression of a South Taranaki basin scale response to the winds.     

A split operator approach to reactive transport with the forward particle tracking Eulerian Lagrangian localized adjoint method

A forward particle tracking Eulerian Lagrangian localized adjoint method (ELLAM) is applied to the multicomponent reactive transport problem using a split operator approach. Two split operator algorithms are compared, the Strang algorithm and the sequential non-iterative algorithm (SNIA). The reaction equations are integrated using a coupled predictor corrector algorithm with adaptive time stepping. Reaction time steps are adjusted at the inflow boundary to reflect the actual time of transport inside the solution domain.Results show that split operator ELLAM formulations are competitive with direct or fully coupled ELLAM solutions for reactive transport problems. The SNIA algorithm is more accurate than the Strang splitting algorithm when large time steps are used. The reaction algorithm employed dominates computational effort in runs with large time step sizes. To illustrate the use of the method in practical problems, the model is fitted to aerobic aniline degradation data from laboratory scale column experiments. Model inversion is achieved using non-linear regression with a shuffled complex evolution optimization algorithm and parameter uncertainty is assessed using a Bayesian uncertainty analysis procedure.     

Difference between the Lagrangian trajectories and Eulerian residual velocity fields in the southwestern Yellow Sea

The responses to tidal and/or wind forces of Lagrangian trajectories and Eulerian residual velocity in the southwestern Yellow Sea are investigated using a high-resolution circulation model. The simulated tidal harmonic constants agree well with observations and existing studies. The numerical experiment reproduces the long-range southeastward Eulerian residual current over the sloping bottom around the Yangtze Bank also shown in previous studies. However, the modeled drifters deployed at the northeastern flank of the Yangtze Bank in the simulation move northeastward, crossing over this strong southeastward Eulerian residual current rather than following it. Additional sensitivity experiments reveal that the influence of the Eulerian tidal residual currents on Lagrangian trajectories is relatively weaker than that of the wind driven currents. This result is consistent with the northeastward movement of ARGOS surface drifters actually released in the southwestern Yellow Sea. Further experiments suggest that the quadratic nature of the bottom friction is the crucial factor, in the southwestern Yellow Sea, for the weaker influence of the Eulerian tidal residual currents on the Lagrangian trajectories. This study demonstrates that the Lagrangian trajectories do not follow the Eulerian residual velocity fields in the shallow coastal regions of the southwestern Yellow Sea.     

Experimental methods for river discharge measurements: comparison among tracers and current meter

Abstract

Discharge measurements in natural watercourses are performed in order to determine the value of the surface outflow of a basin, its temporal variability, and the outflow characteristics. The methods conventionally used for these measurements utilize an immersed current meter in different points of a river section, which acquires the mean flow velocity. Using this measurement, the discharge can be calculated. Some experimental problems arise, however, when there is a very high discharge. An important method, valid in such cases, is the artificial tracing method. In particular, the use of chemical tracers for small watercourses is very convenient because they are low cost, easily handled, low impact and provide satisfactory results. In the past, radioactive tracers such as tritium have been used in large rivers, while fluorescent tracers have been commonly exploited in the USA and now elsewhere. However, if the water is turbid, the suspended sediments may easily absorb some tracers. In this paper, the preliminary results of a comparison between current meter and artificial tracer measurements are reported. In particular, field tests in a small tributary have been performed, in order to investigate the behaviour of different tracers.

Citation Tazioli, A. (2011) Experimental methods for river discharge measurements: comparison among tracers and current meter. Hydrol. Sci. J. 56(7), 1314–1324.     

Comparing Eulerian and Lagrangian eddy census for a tide-less,semi-enclosed basin,the Baltic Sea

Ocean Dynamics - Eddies in the global and coastal ocean play a key role in mixing and transport processes. Here, we present an eddy census for the Baltic Sea covering the years 2008–2010. The...     

A new efficient Eulerian–Lagrangian localized adjoint method for solving the advection–dispersion equation on unstructured meshes

A new and high efficient scheme is developed for the Eulerian–Lagrangian Localized Adjoint Method (ELLAM) to solve the Advection–Dispersion transport Equation (ADE) on unstructured triangular meshes. To obtain accurate results, the new method requires a very limited number of integration points (usually 1 per element).     

极区电离层加热的数值模拟与实验对比

大功率无线电波能加热电离层等离子体,可以引起电离层电子温度和密度的扰动,实现电离层的人工变态.从电子的连续性方程、动量方程和能量方程出发,我们给出了地面人工大功率无线电波加热电离层的数值模型.通过对方程的数值求解,计算了极地电离层条件下,电子温度、电子密度的加热效应,讨论了泵波参数对加热效应的影响.研究结果表明,电子温度几乎在整个高度上表现为一致性的幅度增强,且在反射高度附近形成温度增强峰很平缓.电子密度在峰上高度附近形成密度谷,谷两侧存在密度增强.加热效应基本随加热功率的增大而增大,随加热频率的增大而减小.使用我国2008年1月在挪威进行的电离层加热实验的电离层参量作为仿真初值,对6个O波加热时刻进行了数值仿真,仿真结果与实验观测基本保持一致.     

Extracting Lagrangian coherent structures in the Kuroshio current system

Ocean Dynamics - In this paper, we propose to extract Lagrangian coherent structures (LCSs) based on MADT data to describe the structure of the Kuroshio Current System, and this method helps study...     

A comparison of EISCAT and Dynasonde measurements of the auroral ionosphere

Incoherent-scatter radar and ionospheric sounding are powerful and complementary techniques in the study of the Earths ionosphere. The work presented here involves the use of the Tromsø Dynasonde as a correlative diagnostic with the EISCAT incoherent-scatter radar. A comparison of electron-density profiles shows how a Dynasonde can be used to calibrate an incoherent-scatter radar and to monitor changes in the system. Sky-maps of the direction of Dynasonde echoes are compared with EISCAT-derived density profiles to illustrate how a Dynasonde can be used to measure the drift velocity of auroral features. Vector velocities fitted to Dynasonde echoes are compared with EISCAT-derived plasma velocities. The results show good agreement when the data are taken during quiet to moderately active conditions and averaged over time scales of 30 min or more.     

A comparison of satellite systems for gravity field measurements

A detailed and accurate Earth gravity field model is important both to geophysical progress and to the precise tracking necessary for interpretation of geophysical experiments. Various satellite techniques which may be used to determine the Earth's gravity field are compared and their ability to recover the long wavelength and short wavelength features of the field are described.A high-low configuration satellite-to-satellite tracking mission is recommended for the determination of the long wavelength portion of the gravity field. Satellite altimetry and satellite gradiometry experiments are recommended for determination of the short wavelength portion of the gravity field.     

A comparison of methods for low streamflow estimation from spot measurements

Low streamflow statistic estimators at ungauged river sites generally have large errors and uncertainties. This can be due to many reasons, including lack of data, complex hydrologic processes, and the inadequate or improper characterization of watershed hydrogeology. One potential solution is to take a small number of streamflow measurements at an ungauged site to either estimate hydrogeologic indices or transfer information from a nearby site using concurrent streamflow measurements. An analysis of four low streamflow estimation techniques, regional regression, regional plus hydrogeologic indices, baseflow correlation, and scaling, was performed within the Apalachicola–Chattahoochee–Flint watershed, a U.S. Geological Survey WaterSMART region in the south‐eastern United States. The latter three methods employ a nominal number of spot measurements at the ungauged site to improve low streamflow estimation. Results indicate that baseflow correlation and scaling methods, which transfer information from a donor site, can produce improved low streamflow estimators when spot measurements are available. Estimation of hydrogeologic indices from spot measurements improves regional regression models, with the baseflow recession constant having more explanatory power than the aquifer time constant, but these models are generally outperformed by baseflow correlation and scaling.     

Validation of joint inversion of direct current and electromagnetic measurements

One of the ways to improve the information content of a set of field data is that of combining the interpretation of disparate data sets. Electromagnetic and direct current resistivity methods suffer from inherent equivalence problem. Application of joint inversion for these measurements can overcome the problem of equivalence very well. In the present work, synthetic data from vertical electrical sounding (VES) and horizontal coplanar low-frequency induction sounding (EMHD) are inverted individually and jointly over different types of 1D earth structures. Global optimization with Monte Carlo Multistart algorithm was used in the calculations. The results obtained from the inversions of synthetic data indicate that the joint inversion significantly improves the solution reducing the ambiguity of the models.     

Numerical computation of the tidally induced Lagrangian residual current in a model bay

With a depth-averaged numerical model, the tidally induced Lagrangian residual current in a model bay was studied. To correctly reflect the long-term mass transport, it is appropriate to use the Lagrangian residual velocity (LRV) rather than the Eulerian residual velocity (ERV) or the Eulerian residual transport velocity (ETV) to describe the residual current. The parameter κ, which is defined as the ratio of the typical tidal amplitude at the open boundary to the mean water depth, is considered to be the indicator of the nonlinear effect in the system. It is found that the feasibility of making the mass transport velocity (MTV) approximate the LRV is strongly dependent on κ. The error between the MTV and the LRV tends to increase with a growing κ. An additional error will come from the various initial tidal phases due to the Lagrangian drift velocity (LDV) when κ is no longer small. According to the residual vorticity equation based on the MTV, the Coriolis effect is found to influence the residual vorticity mainly through the curl of the tidal stress. A significant difference in the flow pattern indicates that the LRV is sensitive to the bottom friction in different forms.     

A three-dimensional Eulerian model for transport and deposition of volcanic ashes

Volcanic ash fallout represents a serious threat to people living near active volcanoes because it can produce several undesirable effects such as collapse of roofs by ash loading, respiratory sickness, air traffic disruption, or damage to agriculture. The assessment of such volcanic risk is therefore an issue of vital importance for public safety and its mitigation often requires to evaluate the temporal evolution of the phenomenon through reliable computational models.We develop an Eulerian model, named FALL3D, for the transport and deposition of volcanic ashes. The model is based on the advection–diffusion–sedimentation equation with a turbulent diffusion given by the gradient transport theory, a wind field obtained from a meteorological limited area model (LAM) and the source term derived from by buoyant plume theory. It can be used to forecast either ash concentration in the atmosphere or ash loading on the ground. Model inputs are topography, meteorological data given by a LAM, mass eruption rate, and a particle settling velocity distribution. A test application to the July 2001 Etna eruption is presented.     

Analytical solution for the tidally induced Lagrangian residual current in a narrow bay

In a weakly nonlinear tidal system, the depth-averaged equations for the first-order Lagrangian residual velocity (LRV) are deduced systematically. For the case of a narrow bay, the equations are solved analytically and the results for a specific bottom profile are discussed in detail. According to the pattern of the first-order LRV, the bay can be divided into three parts, namely an inner part, a transitional zone, and an outer part. For the given depth profile, the streamline of the first-order LRV for a shorter bay is a part of that for a longer bay. The first-order LRV depends on a nondimensional parameter that combines the influences of the bottom friction coefficient, the tidal period and the averaged water depth. The form of the bottom friction also has a significant influence on the first-order LRV. The second-order LRV, i.e., the Lagrangian drift, is analytically solved and shows dependence on the initial tidal phase. The LRV differs from the Eulerian residual transport velocity both quantitatively and qualitatively. It is demonstrated that the residual currents obtained according to other definitions may cause misunderstanding of the mass transport in water exchange applications.     

A comparison of veloCity measurements from the CUTLASS Finland radar and the EISCAT UHF system

The CUTLASS Finland radar, which comprises an integral part of the SuperDARN system of HF coherent radars, provides near continuous observations of high-latitude plasma irregularities within a field-of-view which extends over some four million square kilometres. Within the Finland radar field-of-view lie both the EISCAT mainland and EISCAT Svalbard incoherent scatter radar facilities. Since the CUTLASS Finland radar commenced operation, in February 1995, the mainland EISCAT UHF radar has been run in common programme 1 and 2 modes for a total duration exceeding 1000 h. Simultaneous and spatially coincident returns from these two radars over this period provide the basis for a comparison of irregularity drift veloCity and F-region ion veloCity. Initial comparison is limited to velocities from four intervals of simultaneous radar returns; intervals are selected such that they exhibit a variety of veloCity signatures including that characteristic of the convection reversal and a rapidly fluctuating veloCity feature. Subsequent comparison is on a statistical basis. The velocities measured by the two systems demonstrate reasonable correspondence over the veloCity regime encountered during the simultaneous occurrence of coherent and incoherent scatter; differences between the EISCAT UHF measurements of F-region ion drift and the irregularity drift velocities from the Finland radar are explained in terms of a number of contributing factors including contamination of the latter by E-region echoes, a factor which is investigated further, and the potentially deleterious effect of discrepant volume and time sampling intervals.