Experimental survey on the behaviour of AISI 304 steel sheets subjected to perforation

This paper presents and analyzes the behaviour of AISI 304 steel sheets subjected to perforation under a wide range of impact velocities. The relevance of this steel resides in the potential transformation of austenite into martensite during mechanical loading. This process leads to an increase in strength and ductility of the material. It makes the AISI 304 attractive for many engineering applications, especially for building structural elements responsible for absorbing energy under fast loading. However, this transformation takes place only under determined loading conditions strongly dependent on initial temperature and deformation rate. In order to study the material behaviour under impact loading, perforation tests have been performed at room temperature using both, a drop weight tower and a pneumatic gas gun within the range of impact velocities 2.5 m/s≤V₀≤85 m/s. The results are compared with those reported in [18] and [21] for ES steel and TRIP 1000 steel. The comparison highlights the good performance of the AISI 304 under high loading rates. Martensitic transformation taking place in this steel during perforation is identified responsible for such behaviour.     

Succession of phytoplankton functional groups regulated by monsoonal hydrology in a large canyon-shaped reservoir

Liuxihe reservoir is a deep, monomictic, oligo-mesotrophic canyon-reservoir in the subtropical monsoon climate region of southern China. Phytoplankton functional groups in the reservoir were investigated and a comparison made between the succession observed in 2008, an exceptionally wet year, and 2009, an average year. The reservoir shows strong annual fluctuations in water level caused by monsoon rains and artificial drawdown. Altogether 28 functional groups of phytoplankton were identified, including 79 genera. Twelve of the groups were analyzed in detail using redundancy analysis. Because of the oligo-mesotrophic and P-limited condition of the reservoir, the dominant functional groups were those tolerant of nutrient (phosphorus) deficiency. The predominant functional groups in the succession process were Groups A (Cyclotella with greatest axial linear dimension < 10 μm), B (Cyclotella with greatest axial linear dimension >10 μm), L_O (Peridinium), L_M (Ceratium and Microcystis), E (Dinobryon and Mallomonas), F (Botryococcus), X₁ (Ankistrodesmus, Ankyra, Chlorella and Monoraphidium) and X₂ (Chlamydomonas and Chroomonas). The development of groups A, B and L_O was remarkably seasonal. Group A was dominant during stratification, when characteristic small size and high surface/volume ratio morphology conferred an advantage. Group L_O was dominant during dry stratification, when motility was advantageous. Group B plankton exhibited a high relative biomass during periods of reduced euphotic depth and isothermy. Groups L_M, E, F, X₁ and X₂ occasionally exhibited high relative biomasses attributable to specific environmental events (e.g. drawdown, changes in zooplankton community). A greater diversity of phytoplankton functional groups was apparent during isothermy. This study underscores the usefulness of functional algal groups in studying succession in subtropical impoundments, in which phytoplankton succession can be significantly affected by external factors such as monsoonal hydrology and artificial drawdown, which alter variables such as retention time, mixing regime and thermal structure and influence light and nutrient availability.     

Genetic programming-based formulation for distortional buckling stress of cold-formed steel members

The main purpose of the research is to develop formulations for estimating the Elastic distortional buckling stress (EDBS) of cold-formed steel member under compressive loading using Genetic programming (GP) which has not been applied so far. The required data used for the training and testing is collected from the literature. Two GP-based formulations are proposed to predict the elastic distortional buckling of cold formed steel C sections. The results of proposed GP formulations are compared with experimental and analytical results of different researchers and methods and found to be accurate. The results obtained from the formulas have shown that GP is a promising technique for predicting EDBS of cold-formed steel C sections.     

Driving factors of the phytoplankton functional groups in a deep Mediterranean reservoir

The control of phytoplankton growth is mainly related to the availability of light and nutrients. Both may select phytoplankton species, but only if they occur in limiting amounts. During the last decade, the functional groups approach, based on the physiological, morphological and ecological attributes of the species, has proved to be a more efficient way to analyze seasonal changes in phytoplankton biomass. We analysed the dynamics of the phytoplankton functional groups sensu Reynolds, recognising the driving forces (light, mixing regime, and nutrients) in the Sau Reservoir, based on a one-year cycle (monthly surface-water sampling). The Sau Reservoir is a Mediterranean water-supply reservoir with a canyon-shaped basin and a clear and mixed epilimnion layer. The long stratification period and high light availability led to high phytoplankton biomass (110.8 fresh-weight mg L⁻¹) in the epilimnion during summer. The reservoir showed P-limitation for phytoplankton growth in this period. All functional groups included one or more species (X2-Rhodomonas spp.; Y-Cryptomonas spp.; F-Oocystis lacustris; K-Aphanocapsa spp.) selected by resources, especially phosphorus. Species of Cryptomonas (group Y) dominated during the mixing period (winter season) in conditions of low light and relatively high availability of dissolved nutrients. Increases in water-column stability during spring stratification led to phytoplankton biomass increases due to the dominance of small flagellate functional groups (X2 and X3, chrysophyceans). The colonial chlorophycean O. lacustris (group F) peaked during the mid-summer stratification, when the mixed epilimnion was clearly depleted in nutrients, especially SRP. High temperature and increases in nutrient concentration during the end-summer and mid-autumn resulted in a decrease of green algae (group F) and increase of Aphanocapsa spp. (cyanobacteria, group K) and dinoflagellates (group L_o). The study also revealed the important role of physical processes in the seasonal gradient, in selecting phytoplankton functional groups, and consequently in the assessment of ecological status. The Q index (assemblage index) based on functional groups indicated the overall good ecological status of the Sau Reservoir, which varied as a function of the mixing regime. This is the first application of the Assemblage Index to a European water-supply reservoir.     

Numerical modelling of sediment-bacteria interaction processes in surface waters

Faecal bacteria exist in both free-living and attached forms in surface waters. The deposition of sediments can take faecal bacteria out of the water column and to the bed. The sediments can subsequently be re-suspended into the water column, which can then lead to the re-suspension of the faecal bacteria of the attached form back into the water column, where it may desorb from the sediments. Therefore, the fate and transport of faecal bacteria is highly related to the governing sediment transport processes, particularly where these processes are significant. However, little attempt has been made to model such processes in terms of predicting the impact of the sediment fluxes on faecal bacteria levels. Details are given of the refinement of a numerical model of faecal bacteria transport, where the sediment transport processes are significant. This model is based on the model DIVAST (Depth Integrated Velocities And Solute Transport). Analytical solutions for steady and uniform flow conditions were derived and used to test the sediment-bacteria interaction model. After testing the sediment-bacteria interaction model favourably against known results, the model was then set up for idealised case studies to investigate the effects of sediment on bacteria concentrations in the water column. Finally the model was applied to a simplified artificial flooding study to investigate the impact of suspended sediment fluxes on the corresponding bacteria transport processes. The model predictions have proved to be encouraging, with the results being compared to field measurements.     

Isotopenuntersuchungen zur Wechselwirkung von Grund- und Oberflächenwasser in der Entstehungsphase von Bergbauseen

Environmental isotopes such as ³ H, ² H, ¹⁸ O, ³⁴ S and ²²² Rn were applied to characterize relationships within and between ground and surface waters in two developing mining lakes. Using a two-component-model the portion of saline waters ascending through the lake bottom into the lakes was estimated. Similarly the contribution of pyritic sulphur participating in the lake sulfate has been assessed. Locally, the lakes are hydrochemically stratified. Mixing processes are reflected by all isotopes mentioned above. δ ¹³ C _DIC values of the most mineralized lake water did not correspond with those of deep groundwater from Zechstein strata revailing additional effects such as CO ₂ production. ²²² Rn was checked for assessing groundwater fluxes through the lake bottom. ²²² Rn was found in lake water regions with elevated salt contens but being always in an equilibrium with radium (excepting the sediment-lake water interface). Thus, radium must be taken in consideration in order to interprete radon values in saline groundwaters.     

Auffüllversuche in der wassergesättigten und ungesättigten Zone – ein Vergleich unterschiedlicher Verfahren

Permeability tests are used to determine in situ hydraulic conductivity. As different evaluation methods lead to different values a set of unsteady and steady state permeability tests with different evaluation methods was performed on a 100 m ² test site. The field methods used were the USBR method and a method according to Heitfeld et al. (1979). Results show that all values from infiltration tests showed lower hydraulic conductivities than those from grain size analysis. For the unsaturated zone the field method according to Heitfeld et al. (1979) together with the evaluation after Heitfeld et al. (1979) and the USBR field method together with evaluation of Al-Dahir &; Morgenstern (1969) showed consistent results. In the saturated zone the evaluation according to Schuler (1973) and Al-Dahir &; Morgenstern (1969) resembled results with values near the Beyer (1964) values. Unsteady state tests showed more consistent results and are recommended due to higher practicability.     

Herkunft der Salinität in Tiefenwässern des Grundgebirges – unter besonderer Berücksichtigung der Kristallinwässer des Schwarzwaldes

Deep groundwater in fractured crystalline basement has been reported from deep mines and scientific wells. Highly saline brines have been described from several km depth in the continental basement worldwide. The origin of salinity is unknown and many different possibilities have been presented ( Emmermann et al. 1995, Pauwels et al. 1993, Edmunds &;: Savage 1991, Frape &;: Fritz 1987, Kozlovsky 1984, Banks et al. 1996, Stober 1986, 1995, Kanz 1987, Stober &; Bucher 1999). We compare the compositional evolution of deep waters in the Black Forest basements, SW-Germany, with those of other deep crystalline waters and use the halogen systematics (e. g. Cl/Br ratios) and other parameters of the waters to deduce the origin of their salinity. In teh Black Forest the composition of deep thermal waters results from chemical interaction of surface water with the rock matrix and from mixing of the reacted water with stagnant saline deep water of marine origin.     

Wirkung von Gasen auf den reaktiven Stofftransport im Mehrphasensystem Untergrund

The subsurface is a multi-phase system. The mix-phase soil-gas is beside the aqueous and the non aqueous liquid-phases the third fluid capable to occupy the pore space of the solid matrix and to flow through it. The transfer of matter between the mixphase soil-gas and the two liquid mixphases is hereby the key process of the impact of reactive gases on matter-transport in the vadose and groundwater zone. Remediation techniques – as the in situ sparging, stripping and venting – are based on these transfer-reactions. Central are hereby the reactive gases O ₂ , O ₃ , CH ₄ , NH ₃ , PH ₃ , H ₂ , CO ₂ , SO _x and NO _x acting as electron or as proton acceptors or donars, respectively, and as structural elements of cell synthesis in the subsurface. Their application during remediating the contaminated subsurface or by formating bubbler gas walls capable to clean contaminated groundwater flowing through them is of special interest. The Dresden testsite was built up to investigate problems inherent to this subject using hereby pilot-seal test equipment in in- and out-door facilities.     

Abschätzung der Subsidenz im Einflussbereich Geothermischer Anlagen

The estimate of possibly occurring subsidence within the vicinity of geothermal heating plants is indispensable for the judgement of their operational safety and environmental impact. In this study exploitation of a sandstone aquifer using a production and re-injection well was examined with the groundwater simulation program MODFLOW ( Harbaugh &; McDonald 1996) and the accompanying Interbed-Storage-Package ( Leake &; Prudic 1991). Parameter studies of a typical northern German geothermal aquifer showed that the hydraulic characteristics of the clay stone layer, which is sensitive to subsidence, have little influence on the absolute values of the subsidence. In contrast thereto, the hydraulic characteristics of the geothermally used sandstone layer have great impact on the subsidence. Subsidence will be on no account within the magnitude of meters, but most likely in the range of centimeters (2–3 cm), for both the production and the re-injection well. The results are in agreement with field observations.     

Erkundung der regionalen Grundwasserströmung im Muschelkalk Mittelwürttembergs mit stabilen Umweltisotopen

In the city of Stuttgart, several artesian springs discharge carbonic acid enriched mineral water of variable total mineralization at a rate of about 500 l/s. The springs are part of the regional aquifer system in the karstified Upper Muschelkalk. To clarify their genesis and origin, measurements of the stable isotopes δ ¹⁸ O and δ ² H were used. They allow conclusions on the regional groundwater flow system and on the geochemical evolution of the mineral water. Mainly responsible for contrasts in isotope measurements of the 4500 km ² area is the altitude effect. It was determined for δ ¹⁸ O with a depletion of about ?0.4‰ per 100 m increasing altitude. Similar isotope values in western parts of the Fildergraben (recharge area) and in Stuttgart are explained with a low mineralized groundwater flow. The higher mineralized water which is strongly depleted in δ ¹⁸ O is a result of a mixing process with other aquifers in the discharge area.     

Experimentelle Untersuchungen zur Barytübersättigung einer Thermalsole

On the basis of thermodynamical modelling it was proves that pressure and temperature variations may induce precipitation of barite, anhydrite/gypsum and celestite in geothermyl power plants. The precipitation dynamics of earth-alkaline sulfates has been investigated in a column experiment simulating in-situ conditions for pressure, temperature, and salinity (216 g/l). In this paper we describe the experimental setup for simulating pressures up to 250 bar and high temperatures in a sandstone core. Additional precipitation experiments confirmed the expected second-orer reaction for the precipitation of barite at a medium rate of 2.5 · 10 ^?4 l · mg ^?1 · h ^?1 . The experiments show that the solubility of barite (2.5 mg/l Ba and 450 mg/ISO ₄ ) is higher than the model forecast. Precipitation of celestite and anhydrite/gypsum was not observed. During the column experiments with a sandstone core under in-situ conditions no precipitation of barite, anhydrite/gypsum and celestite took place.     

Hydrogeologie des Oberen Muschelkalks im Bereich hoher Keuperüberdeckung – Modell Schwäbisch-Fränkische Waldberge

A numerical groundwater model was developed for the aquifer of the Upper Muschelkalk between the rivers Neckar, Kocher and Murr. The investigation shoudl mainly serve a better understanding of the hydrogeological situation of this aquifer below the thick Keuper sediments of the Schwäbisch-Fränkischen Waldberge. Here we observe a general groundwater discharge in direction of the rivers with an average hydraulic gradient of 1%. The groundwater recharge from precipitation is estimated at 0.001 m ³ /s for the region below the Keuper mountains, which covers an area of 730 km ² , and 1 m ³ /s for the foreland with an area of 670 km ² . Similar conditions are found comparing the mean pore velocities of both areas (0.4 respectively 200 m/year) and the mean residence time (20000 respectively 20 years) of the groundwater. Thus, the aquifer of the Upper Muschelkalk below the Schwäbisch-Fränkischen Waldberge can be characerized as a fractured non karstified aquifer of low conductivity.     

Grundwasseranbindung von alten Tagebaurestseen im Niederlausitzer Braunkohlentagebaugebiet

Groundwater with high acidity often leads to strongly acidic residual lakes in the vicinity of abandoned open pit lignite mines. Residual lake 77 (RL77) in Lower Lusatia (Germany) belongs to a sequence of residual lakes accomplishing groundwater drainage. A two-part high resolution three-dimensional groundwater model was set-up for the estimation of groundwater discharge into RL77. The objective of the simulations was to quantify the hydraulic component of the mass balance of the lake. The calculated total discharge could be distinguished with respect to water entering from the dump areas (11.3 l s ^?1 ) and from the undisturbed sediments (3.1 l s ^?1 ). The discharge was further distinguished with respect to the vertical entrance location into the temporarily stratified lake. It showed that groundwater discharged into the epilimnion of the lake at a rate of 9.7 l s ^?1 and into the hypolimnion at a rate of 4.7 l s ^?1 . Both the large fraction of water from the dump areas and the preferential entrance into the oxygen rich epilimnion of the lake have an adverse effect on lake water quality.     

Grundwasser- und Bodenluftuntersuchungen im Testfeld Süd

Within the framework of a current DFG (German Research Foundation) program natural attenuation processes of BTEX have been investigated in a Quaternary porous aquifer below a manufactured gas plant in Southwest Germany. Seasonal and regional variations of the BTEX plume have been registered since 1996 by detailed hydrochemical monitoring and frequent soil gas investigations. Taking into account that degradation of organic compounds results in O ₂ decrease and CO ₂ increase in soil air, the measured soil gas CO ₂ -anomalies correspond quite well with the observed contamination pattern of the groundwater. Although soil-gas surveying is usually applicable to the most volatile organic compounds, at the test site only very low concentrations of VOCs have been detected in the soil gas above the contaminated groundwater. In order to understand the results of the field investigations, physical, chemical and microbial processes determining the VOC concentrations have been investigated in detail laboratory scale.     

Isotopenverhältnisse der Schwefel- und Kohlenstoffspezies aus Sedimenten und tiefen Grundwässern der Niederrheinischen Bucht

Combined hydrochemical, geochemical and isotopic investigations of solid and dissolved sulphur- and carbon-species from different aquifer levels allow to distinguish two geochemical cycles: The first one is represented by the sedimentary pyrites which have been formed during the Tertiary by bacterial sulplate reduction. These pyrites are characterized by strongly depleted δ ¹⁴ S-signatures. In accordance with a recent origin, the groundwater composition reflects the current sulphur- and carbon-cycling representing the second one. The activity of sulphate reducing bacterian can be deduced from a decrease of the sulphate concentration with depth and a simultaneous increase in δ ¹⁴ S- and δ ¹⁸ O-values as well as increasing hydrogen sulphide concentrations. Dissolved organic carbon, the substrate and electron-donor for the bacterial sulphate reduction, appears to be the limiting factor as its average concentration reaches only 1.6 mg/l. The concentration of dissolved inorganic carbon is slightly higher in the deeper groundwater levels. Due to its clearly negative carbon-isotope signature it can be identified as a product of biogenic oxidation of organic material.     

Sickerwassertransport von Kolloiden und Schwermetallen in Bergbaufolgelandschaften – Felduntersuchungen und Laborversuche

The influence of colloids on the transport of heavy metals at a former lignite mining site investigated. A three-dimensional hydrochemical mapping allows a view into the disposal revealing the stratigraphy within the water body. A SEM/EDX based single-particle method for the characterization of aquatic colloids was developed. Within a size range from 30 nm to 1 μm mostly inorganic silica and salt colloids were be detected, whereas the size fraction below 30 nm was predominated by organic colloids. Although some heavy metals, mainly Co and Cu, were associated to colloids, the total amount of heavy metal colloids was neglectable. Silica colloids were chosen for batch and column investigations. Though the sorption coefficients suggested that the colloids should be a sink for heavy metals, no significant changes of the transport behaviour due to the presence of colloids was observed. Instead, the colloids were filtered by the sediment. The results of teh field and laboratory work indicate clearly that there is no significant enhancement of heavy metal transport at the Kanena landfill site by inorganic colloids.     

Bedeutung des Speichersystems Lohsa II für die wasserhaushaltliche Sanierung im Spreegebiet

Within the framework of the mining remidiation the residual holes of the former brown coal opencast mines “Lohsa”, “Dreiweibern” and “Burghammer” will be connected with each other in order to form the retaining system “Lohsa II”. Including the neighbouring residual hole “Bärwalde” they will provide a storage capacity of more than 90 millions m ³ (118.421 millions cu yards). Considering the water economy the project is expected to be completely ready for operation in the year 2005. Up to 13 m ³ /s (16.9 cu yards per second) of water are to be supplied during dry spells. This will sustain the draining function of the river Spree which has been damaged by lignite mining. At the same time the ecological requirements of the biosphere reserve “Spreewald” and the demands of the conurbation Berlin – concerning its water supply and water storage – will be fulfilled     

Untersuchung von Cyaniden im Grundwasser des Testfeldes Süd

Cyanide contents in groundwater samples of a former manufactured gas plant site, the so-called Testfeld Süd, have been studied for a period of about 1 1/2 year. Non-toxic and highly toxic cyanide species were distinguished by quantifying operational parameters called strong acid dissociable (SAD) and weak acid dissociable (WAD) cyanide according to German standard method DIN 38 405 D14. SAD values reached up to 4.5 mg/l, WAD values up to 34 μg/l. Calculating the species distribution with help of PHREEQC ( Parkhurst &; Appelo 2001), applying site specific geochemical parameters, led to the assumption that a measurement artefact may cause underestimation of the toxic species. The spatial and temporal trend of cyanide values indicated that cyanide is retarded in the observed aquifer. Regarding the geochemical environment and composition of the aquifer material precipitation and adsorption are most likely to be the regarding processes.     

Sanierungsforschung in regional kontaminierten Aquiferen (SAFIRA) – 2. Projektüberblick und Pilotanlage

The joint research project SAFIRA, which is supported by the Federal Ministry of Science and Education (BMBF), deals with the development of innovative technologies for the in situ remediation of heavily contaminated groundwater at the in situ pilot facility in Bitterfeld. In order to evaluate the new promising technological approaches comprehensively, methodological tools are developed to comparatively address economical, ecological as well as a environmental issues of related remediation scenarios. The design period for innovative technologies can hardly be forecasted and/or its success be guaranteed. To prove a long-term stability as well as to reach a sound economical and ecological evaluation for new approaches an on site operation over extended periods of time is needed. Therefore a variety of technologies are tested and optimized simultaneously, in order to achieve a thorough comparison of technologies at the end of the project.