Multigrid optimization for space-time discontinuous Galerkin discretizations of advection dominated flows

The goal of this research is to optimize multigrid methods for higher order accurate space-time discontinuous Galerkin discretizations. The main analysis tool is discrete Fourier analysis of two- and three-level multigrid algorithms. This gives the spectral radius of the error transformation operator which predicts the asymptotic rate of convergence of the multigrid algorithm. In the optimization process we therefore choose to minimize the spectral radius of the error transformation operator. We specifically consider optimizing h-multigrid methods with explicit Runge-Kutta type smoothers for second and third order accurate space-time discontinuous Galerkin finite element discretizations of the 2D advection-diffusion equation. The optimized schemes are compared with current h-multigrid techniques employing Runge-Kutta type smoothers. Also, the efficiency of h-, p- and hp-multigrid methods for solving the Euler equations of gas dynamics with a higher order accurate space-time DG method is investigated

Extension of the discontinuous Galerkin finite element method to viscous rotor flow simulations

Heavy vibratory loading of rotorcraft is relevant for many operational aspects of helicopters, such as the structural life span of (rotating) components, op- erational availability, the pilot’s comfort, and the ef- fectiveness of weapon targeting systems. A precise understanding of the source of these vibrational loads has important consequences in these application ar- eas. Moreover, in order to exploit the full poten- tial offered by new vibration reduction technologies, current analysis tools need to be improved with re- spect to the level of physical modeling of flow phe- nomena which contribute to the vibratory loads. In this paper, a computational fluid dynamics tool for rotorcraft simulations based on first-principles flow physics is extended to enable the simulation of vis- cous flows. Viscous effects play a significant role in the aerodynamics of helicopter rotors in high-speed flight. The new model is applied to three-dimensional vortex flow and laminar dynamic stall. The applica- tions clearly demonstrate the capability of the new model to perform on deforming and adaptive meshes. This capability is essential for rotor simulations to accomodate the blade motions and to enhance vor- tex resolution

Space-time discontinuous Galerkin method for the compressible Navier-Stokes equations on deforming meshes

An overview is given of a space-time discontinuous Galerkin finite element method for the compressible Navier-Stokes equations. This method is well suited for problems with moving (free) boundaries which require the use of deforming elements. In addition, due to the local discretization, the space-time discontinuous Galerkin method is well suited for mesh adaptation and parallel computing. The algorithm is demonstrated with computations of the unsteady \ud ow field about a delta wing and a NACA0012 airfoil in rapid pitch up motion

On the design of block preconditioners for maritime engineering

The iterative error can be an important part of the total numerical error of any Com- putational Fluid Dynamics simulation when the iterative convergence stagnates or when loose convergence criteria are used. In the quest for better iterative convergence of CFD simulations, we consider the design of iterative methods for the Reynolds-averaged Navier-Stokes equations, discretized by finite-volume methods with cell-centered, co-located variables. The central point is the approximation of the Schur complement (pressure matrix) in the block factorization of the discrete system of mass and momentum equations. We show particular approximations of these blocks that yield either segregated solvers or block preconditioners for fully coupled solvers. The performance of these solvers are then demonstrated by computing the flow over a flat plate and around a tanker on both structured and unstructured grids. We find that iterative convergence to machine precision is attainable despite the high Reynolds numbers and mesh aspect ratio’s. Improved approximations of the Schur complement do result in improved convergence rates, but do not seem to pay-off in terms of total cost compared to the basic SIMPLE-type approximation

Extension of a discontinuous Galerkin finite element method to viscous rotor flow simulations

Heavy vibratory loading of rotorcraft is relevant for many operational aspects of helicopters, such as the structural life span of (rotating) components, operational availability, the pilot's comfort, and the effectiveness of weapon targeting systems. A precise understanding of the source of these vibrational loads has important consequences in these application areas. Moreover, in order to exploit the full potential offered by new vibration reduction technologies, current analysis tools need to be improved with respect to the level of physical modeling of flow phenomena which contribute to the vibratory loads. In this paper, a computational fluid dynamics tool for rotorcraft simulations based on first-principles flow physics is extended to enable the simulation of viscous flows. Viscous effects play a significant role in the aerodynamics of helicopter rotors in high-speed flight. The new model is applied to three-dimensional vortex flow and laminar dynamic stall. The applications clearly demonstrate the capability of the new model to perform on deforming and adaptive meshes. This capability is essential for rotor simulations to accomodate the blade motions and to enhance vortex resolution

Analysis and evaluation of tillage on an alfisol in a semi-arid tropical region of India

Tillage field experiments were conducted on Alfisols in a semi-arid tropical environment in India. The research was conducted within the framework of the Farming Systems Research Program of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT).To put the experiments into perspective, a general review is given in chapter 2 on the environment of the semi-arid tropics, its problems and the research related to agricultural production. Rainfed agriculture has failed to provide a stable and sufficient food supply for the populations of many developing countries. An important reason is the severe physical constraint to agricultural production imposed by the harsh climate. Water is the key factor and though the average total precipitation appears to be sufficient for cropping, its distribution is highly erratic. Much of the rain falls in high intensity storms, resulting in uncontrolled runoff and erosion. Thus a high proportion of the water is lost for crop use.The majority of as much as 500 million people living in the world's semi-arid tropics, depend on agriculture for income, food and shelter. During the last three decades, populations have doubled in many of the 48 countries which are at least partly located in the semi-arid tropics.Since the indigenous production systems are characterised by stagnant yield levels, hitherto stable forms of agriculture came under immense pressure by the attempt to continue to provide sufficient amounts of food and fiber for the rapidly growing populations. The farmers were compelled increasingly to expand their agricultural activities to more marginal lands.Consequently, the production potential of the resource base is threatened seriously and vast areas already have been damaged permanently further destabilizing agricultural production.To improve a situation of recurrent food shortages, governments tended to concentrate their resources on improving agriculture in water- assured areas. With the advent of high yielding varieties of wheat and rice, this strategy proved succesfull.In India it was realised that continuing such a policy would further widen the gap with dryland farmers, as it creates 'islands of prosperity in a sea of poverty'. Furthermore, there is a physical limit to the area that potentially can be irrigated. A high proportion of the nation's food requirements would still have to be met by rainfed agriculture. So, unless yield levels and stability are improved in this segment of farming, a few poor monsoons in succession would still lead to serious food problems.Therefore, research on dryland agriculture was revived, but met with limited and varying results. Either too much emphasis was given to genetical improvement of the seeds, or major attention was given to soil and crop management aspects. The proposed technologies did not fit well into the farmers traditional cropping systems, in which crop yield security is important.In 1972, ICRISAT started to work on the improvement of dryland crops. From the outset, it was recognized that the lack of a suitable technology for soil and water management and crop production systems, was a primary constraint to agricultural development in rainfed farming. A farming systems research program was developed. A so-called watershed based research program evolved, wit' the underlying filosophy that the only water available to the common farmer comes from rain falling on a limited area. Therefore, small natural watersheds comprising several field-scale units, became the testing ground for promising new technologies.During the first period, attention was focussed on developing improved soil and water conservation and cropping systems suitable for deep Vertisols.In Chapter 3, the role of tillage is described generally , and specifically the zonal-tillage concept.A 'broad bed and furrow' (BBF)-system, based on the zonal-tillage concept, provided a breakthrough for these soils, in which tillage operations are difficult both under wet and dry conditions. The indigenous practice of rainy season fallowing could be replaced by rainy season cropping, as new technology facilitated dry planting at the onset of the monsoon, while primary tillage could be executed after harvest of the second crop. As a result, the rainfall use efficiency increased tremendously and soil erosion was curbed. The BBF-system was fully operable with the use of a multi-purpose tool carrier drawn by a pair of bullocks.Unfortunately, the system was less succesfull on Alfisols. These soils are structurally weak, the surface becoming smooth and sealing readily due to the impact of rain. At the beginning of the rainy season, substantial portions of the precious water run off even from yet unsaturated soil profiles. Plant establishment proved difficult and crusting was believed to cause poor, spotty plant stands.Because the BBF-system features many advantages, it was felt worthwhile not to abandon the system, but to try to improve its performance by adapting the tillage component.In Chapter 4, the experimental setup of the tillage field experiments is described.In Chapter 5, the effects of primary tillage in terms of soil response and its effects on crop growth are discussed. By varying depth and principle of tillage on the beds, infiltration characteristics were expected to be influenced. Different soil surface conditions, in terms of soil surface roughness and storage provided by the increased pore space in the tilled zone, were thus created. In particular, the newly developed tillage treatment (T1) (Fig. 12), in which the whole width of the beds was tilled at the greatest depth, proved superior in intercepting rainfall. The increased soil roughness was shortlived but the effect on pore space lasted throughout the season. The latter aspect, therefore, seems important with respect to water conservation.Yield increases were positively related to increasing levels of primary tillage, particularly so when soil moisture was limiting. The T1 tillage method performed best in this respect, thereby contributing in stabilizing yields. The limiting moisture supply was partly due to the growth of weeds. Tillage played a pervasive role in weed control throughout the year. The soil-inverting primary tillage methods facilitated seed bed preparation. Weed regrowth after this type of tillage was delayed compared to the non-inverting methods, thereby providing a temporary advantage. By and large, the effect of primary tillage on the amounts of weeds had disappeared during the plant establishment phase. This is not surprising as all tillage methods were essentially at the minimum tillage level.Weed management in the standing crop is essential. Chapter 6 gives a review on the impact of weeds on crop production. It appeared that chemical weed control is not an economically viable option in India for some time to come. Thus, only inter-row cultivation, handweeding and combinations of these were evaluated in the tillage experiments. The potential growth of weeds was tremendous. General weediness levels varied substantially between years and fields, independent from the tillage system. If allowed to grow, the highest measured weediness level at harvest was 6.7 t/ha. Throughout the experiments uncontrolled weeds reduced yields by 10% to 90%. Weed management could greatly reduce weediness levels in the crop. Where inter-row cultivation was practised, inter-row weeds were adequately controlled. However, intra- row weeds developed unchecked and these reduced crop yields considerably, especially in pearl millet. Handweeding proved to be a must for acceptable yields, a supplementary in-the-row weeding after inter-row cultivation being a satisfactory compromise. The effect of weeds on crop yields was partly due to plant population reduction because of competition, but remaining plants also performed less on an individual basis.The toolbar system allows weeding in tall growing crops for a limited time of 4 to 5 weeks after sowing. When weeds develop after the period in which they affect crop yields, a handweeding may still be desirable; certainly when a sequential crop is considered, but also to prevent the weeds from shedding seeds and to facilitate post-harvest tillage.In Chapter 7, plant establishment problems are discussed, as well as various planting method options tested in the field. Poor and uneven stands is one of the major causes of low crop yields in the semi-arid tropics. In Alfisols, crusting was believed an impediment to adequate stands. In the tillage field experiments, plant establishment was given attention but plant establishment was invariably succesfull in all tillage methods. There was no evidence that crusts developed such that crop emergence was hindered. Seed bed compaction by planter press wheels increased crust strength, but apparently it still remained below a harmful] level. In fact, increasing compaction effort increased plant stands and crop yields significantly in a number of cases. An explanation could not be given in terms of improved water supply to germinating seeds and developing seedlings.But it appears that two aspects of the seed bed are extremely important. Firstly, the presence of weeds affect the proper functioning of the planter furrow opener, making seed placement less consistent. When a dry plant establishment period follows, even small amounts of weeds proved to reduce stands considerably. Secondly, the uniformness of the seedbed is important.Evaluation of the consistency of seed placement depth following the various tillage methods revealed a high degree of control. Seed depth was normally distributed with standard deviations of less then 1 cm. The importance of placing the seeds exactly was demonstrated in that seedlings from deeper placed seeds were retarded, even within the narrow depth range achieved. As a consequence, in the field inter-row cultivation must be delayed or part of the smaller seedlings must be sacrificed. Also, competition between crop seedlings may prevent the laggards to become productive.The simulation of the effect of seed placement on emergence showed that the seed bed quality and planting depth have a profound effect not only on total emergence percentage, but also on the uniformity of seedling development.In conclusion, the performance of the BBF-system of cultivation in Alfisols can be improved by increasing soil surface roughness and plow layer storage. A new technique of primary tillage, the T1 tillage method, proved best in this respect. In addition, the method features operational advantages as bigger amounts of crop residue and weeds can be handled without clogging the implements. Seed bed preparation is of crucial importance, particularly freedom from weeds and depth uniformity. Compaction of seed beds by planter press wheels contributes positively to plant stands and crop yields. Crusts did not hinder crop emergence at all.Because none of the evaluated primary tillage methods exceeded the minimum tillage level, weeds developed vigorously soon after planting. For such conditions inter-row cultivation alone proved insufficient to keep weeds in the crop at acceptable levels. Then, supplemental handweeding was absolutely essential for good crop yields.<p/

Seasonal water balance of a sandy soil in Niger cropped with pearl millet, based on profile moisture measurements

In the Sahel, calculation of the field water balance from neutron-probe measurements is often difficult for pearl millet (Pennisetum glaucum (L.) R. Br.), which is due to the rapid drainage (D) of the sandy soils, on which it is typically grown. We present a simple method of calculating D in these soils from weekly neutron-probe data. The method divides the water balance into two phases. In the first, applicable early in the season, water flux across the maximum depth of probe measurement (Zm) is assumed negligible, and evapotranspiration (E) and D are calculated from the change in soil water content (θ) between the bottom of the rootzone (Zr) and Zm, thus allowing calculation of unsaturated hydraulic conductivity, K(θ), from the flux across Zr. In the second phase, when soil water starts to percolate across Zm, D is calculated from K(θ), assuming a hydraulic head gradient of −1. The method is used to calculate a one-dimensional water balance of a pearl-millet crop grown in a deep sandy soil at two fertility levels during a season of normal rainfall. Results show that the calculated K(θ) functions compare well with those based on laboratory measurements. An acceptable estimate of drainage, and therefore E could be made. Mean cumulative E and D were, respectively, 211 and 207 mm for the unfertilized crop, and 268 and 148 mm for the fertilized crop with 440 mm of rainfall received during the crop cycle. The fertilized millet crop water balance was simulated, which compared to the calculation method resulted in an about 10% higher seasonal E and a 10% lower seasonal D. Our study shows that E can be corrected for D using a simple but accurate method, and consistent with other studies in the region indicates that rainfall is usually not the primary limiting factor to pearl-millet productio

Regulation of inhibin production in the rat testis

The testis is composed of two compartments: the seminiferous tubules. in which spennatogenesis takes place, and the interstitium, which is composed of blood vessels, nerve fibres, macrophages, endothelial cells, and also contains Leydig cells, which are the steroid-producing cells of the testis. The seminiferous tubules consist of spennatogenic epithelium formed by Sertoli cells and developing genn cells, surrounded by peri tubular myoid cells. Sertoli cells are important for physical support of the developing germ cells. Furthermore, adjacent Se.10li cells form tight junctions, thus fonning a barrier (the so-called Sertoli cell barrier or blood-testis barrier; Dym and Fawcett, 1970; Setchell et aI., 1988), which provides the developing germ cells behind tIlis barrier WitIl a separate environment. Spermatogonia are found outside the blood-testis barrier, in the basal compartment, whereas leptotene spennatocytes start to migrate through the Sertoli cell barrier; the adluminal compartment contains more advanced spematocytes and spermatids (Dym alld Fawcett, 1970). In order to reach cells in the adluminal compartment, substal,ces must pass through Sertoli cells, which thereby determine the composition of the spermatogenic micro-environment. Moreover, Sertoli cells produce a number of factors, which are important for germinal cells

Guillain-Barré Syndrome-related campylobacter jejuni in Bangladesh: ganglioside mimicry and cross-reactive antibodies

BACKGROUND: &lt;br/&gt; Campylobacter jejuni is the predominant antecedent infection in Guillain-Barré syndrome (GBS). Molecular mimicry and cross-reactive immune responses to C. jejuni lipo-oligosaccharides (LOS) precipitate the development of GBS, although this mechanism has not been established in patients from developing countries. We determined the carbohydrate mimicry between C. jejuni LOS and gangliosides, and the cross-reactive antibody response in patients with GBS in Bangladesh.&lt;br/&gt; METHODOLOGY:&lt;br/&gt; Sera from 97 GBS patients, and 120 neurological and family controls were tested for antibody reactivity against LOS from C. jejuni isolates from GBS patients in Bangladesh (BD-07, BD-39, BD-10, BD-67 and BD-94) by enzyme-linked immunosorbent assay (ELISA). Cross-reactivity to LOS was determined by ELISA. The LOS outer core structures of C. jejuni strains associated with GBS/MFS were determined by mass spectrometry.&lt;br/&gt; PRINCIPLE FINDINGS:&lt;br/&gt; IgG antibodies to LOS from C. jejuni BD-07, BD-39, BD-10, and BD-67 IgG antibodies were found in serum from 56%, 58%, 14% and 15% of GBS patients respectively, as compared to very low frequency (&#60;3%) in controls (p&#60;0.001). Monoclonal antibodies specific for GM1 and GD1a reacted strongly with LOS from the C. jejuni strains (BD-07 and BD-39). Mass spectrometry analysis confirmed the presence of GM1 and GD1a carbohydrate mimics in the LOS from C. jejuni BD-07 and BD-39. Both BD-10 and BD-67 express the same LOS outer core, which appears to be a novel structure displaying GA2 and GD3 mimicry. Up to 90-100% of serum reactivity to gangliosides in two patients (DK-07 and DK-39) was inhibited by 50 µg/ml of LOS from the autologous C. jejuni isolates. However, patient DK-07 developed an anti-GD1a immune response while patient DK-39 developed an anti-GM1 immune response.&lt;br/&gt; CONCLUSION:&lt;br/&gt; Carbohydrate mimicry between C. jejuni LOS and gangliosides, and cross-reactive serum antibody precipitate the majority of GBS cases in Bangladesh