Design of passive anti-roll tanks for roll stabilization in the nonlinear range

The best way of reducing roll motion is by increasing roll damping. Bilge keels are the most common devices for increasing roll damping. If more control is required, anti-roll tanks and fins are used. Tanks have the advantage of being able to function when the ship is not underway. Our objective is to develop design procedures for passive tanks for roll reduction in rough seas. This paper focuses on the design of passive U-tube tanks. The tank-liquid equation of motion is integrated simultaneously with the six-degree-of-freedom (6DOF) equations of the ship motion. The coupled set of equations is solved by using the Large Amplitude Motion Program ‘LAMP’, which is a three-dimensional time-domain simulation of the motion of ships in waves. The unstabilized and stabilized roll motions of a S60-70 ship with forward speed and beam waves have been analyzed. For high-amplitude waves, the unstabilized roll angle exhibits typical nonlinear phenomena: a shift in the resonance frequency, multi-valued responses, and jumps. The performance of a S60-70 ship with a passive tank is investigated in various sea states with different encounter wave directions. It is found that passive anti-roll tanks tuned in the linear or nonlinear ranges are very effective in reducing the roll motion in the nonlinear range. The effect of the tank damping, frequency, and mass on the tank performance is studied. Also, it is found that passive anti-roll tanks are very effective in reducing the roll motion for ships having a pitch frequency that is nearly twice the roll frequency in sea states 5 and 6.     

Importance of ciliated protozoa in relation to the bacterial and phytoplanktonic biomass in an oligo-mesotrophic lake,during the spring diatom bloom

The abundance and the biomass of bacterial, phytoplanktonic, and ciliate communities were estimated at different depths during the spring planktonic development in an oligo-mesotrophic lake (the Pavin lake).The bacterial population, which consists mainly of free bacteria (94% of the total bacterial abundance), displays only low cell densities (0.6 to 7 × 10⁵ cells · ml^–1) and represents low biomass values (0.9 to 11.5 µgC·l^–1) The bacteria represent from 0.9 to 23.8% (M = 9.7%) of the microplanktonic biomass (with the exclusion of heterotrophic nanoflagellates, i.e. bacteria + phytoplankton + ciliates, size range 0.2–160 µm). The abundance of the phytoplankton varies between 0.5 and 1.8 × 10⁶ cells·l^–1, and the biomass values between 12 and 118 µC·l^–1. The phytoplankton population constitutes the largest part of the microplanktonic biomass (51.9 to 96.6%, M = 80.6%), and the diatomMelosira italica subsp.subarctica is the largely dominant species of this community. The population of ciliates, essentiallyOligotrichida andScuticociliatida, displays densities between 1.3 and 38.3 × 10³ cells·l^–1 (M = 6.7 × 10³ cells·l^–1), and biomass values vary from 0.10 to 16.30 µgC·l^–1 (M = 6.01 µgC·l^–1). The ciliates constitute thus from 0.1 to 26.4% (M = 9.8%) of the microplanktonic biomass. Whereas the oligotrichs are best represented in the euphotic zone, the small-sized scuticociliates dominate in the hypolimnion. Besides, species having symbionts and considered to be mixotrophic (Strobilidium gyrans, Strombidium viride, Stokesia vernalis) develop preferentially in the epilimnion and constitute more than 50% of the total ciliate biomass.     

Strength and compressibility of Abqaiq marl, Saudi Arabia

The increasing number of construction projects and the lack of good quality soil for use in these projects in eastern Saudi Arabia necessitate the use of available marginal soils. Most, if not all, engineering projects use the fine-grained calcareous sediments, known locally as marl, either as a foundation material or as a fill material. The lack of published information on their engineering characteristics and behavior under ambient conditions has resulted in many construction and post-construction problems. This investigation is one of a series to evaluate the geotechnical properties of selected marl soils obtained from different areas in eastern Saudi Arabia. Marl samples, obtained from Abqaiq, were prepared in the laboratory under controlled conditions and subjected to different tests including CBR (soaked and unsoaked), triaxial compression, unconfined compression and one-dimensional compression tests. Samples were prepared at different moisture contents on both the wet and dry sides of optimum. X-ray diffraction analysis indicates that this marl contains high percentages of dolomite and calcite, in addition to other materials. The molding water content significantly affects the engineering properties of this material. Compaction on the dry side of optimum resulted in samples that have some swelling potential and highly compressible characteristics when subjected to a load after inundation.     

Major Ions in the Damietta Branch of the River Nile,Egypt

Major cations and anions were investigated in the Damietta branch of the River Nile. The branch is divided into two different regions; the fresh Nile water (Region A) and the mostly marine environment (Region B). The latter region represents the Damietta estuary. The relative abundance of the major ions in the fresh water system was Na > Ca > Mg > K, HCO₃ > Cl > SO₄ > CO₃, while in the mostly marine area it was Na > Mg > K > Ca, Cl > HCO₃ > SO₄ > CO₃. Regional and monthly variations of the major ions were related to the duration of the Nile discharge and climatic conditions. The major ions -to- chloride ratios for Region A were higher than those in the adjacent Mediterranean waters, while those for the mostly marine region were slightly lower.     

Dynamic Treatment Response of Olive Mills Wastewater Using Series of Adsorption Steps

Olive mills wastewater (OMW) is a critical environmental problem in the Mediterranean area due to its extremely high levels of COD and phenols. In this study, a group of adsorption experiments were conducted to investigate the dynamic response of the pH, COD, phenols, TSS, TDS, and TS concentrations of pretreated OMW, using different concentrations of activated carbon as adsorbent. The pretreatment included sedimentation and filtration of OMW. The pretreated OMW was then subjected to adsorption. A series of adsorption steps in stirred batch vessels were studied, namely, one stage, two‐stage countercurrent, and three‐stage countercurrent adsorption systems. A combined two‐ two‐stage countercurrent adsorption steps were also studied. Experimental results showed that such treatment protocols were promising. For example, a treatment protocol composed of a three‐stage countercurrent adsorption process using activated carbon of concentration of 24 g/L of OMW was able to reduce the COD from 60 000 mg/L down to 22 300 mg/L, while phenols were reduced from 450 to 15 mg/L.     

Relation between a function of the right ascension and the angular distance to the vertex for Hyades stars

In this paper, relation was developed for Hyades stars between a function of the right ascensions and the angular distances from the vertex. The precision criteria of this relation are very satisfactory and a correlation coefficient value of ? 1 was found which proves that the attributes are completely related linearly. The importance of this relation was illustrated through its usages as:

?a criterion for membership of the cluster,

?a generating function for evaluating some parameters of the cluster,

?a generating function for the initial values of the vertex equatorial coordinates which could then be improved iteratively using the procedure of differential corrections.

     

The energy-dependent radiation transfer in a homogeneous finite sphere

Radiation transfer problem in the slowing-down region is solved for a spherical geometry. Modelled kernels are used to represent the slowing-down kernel. Calculations are performed for the radiation flux at the boundary of the sphere for two cases: (i) in the presence of internal source, (ii) if the radiation is incident on the sphere. Numerical results are obtained by using the Padé approximant technique.     

Long-term landscape evolution and post-rift reactivation in the southeastern Brazilian passive continental margin: Taubaté basin

Zircon (ZFT) and apatite (AFT) fission-track low-temperature thermochronology was applied at the Brazilian passive continental margin in order to understand and reconstruct the post-rift evolution since the breakup of southwestern Gondwana. The thermochronological data obtained from samples of both the Precambrian basement and the Paleogene to Neogene sedimentary rocks from the continental rift of southeastern Brazil provided ZFT ages between 148 (15) and 64 (6) Ma, and AFT ages of 81 (8)–29 (3) Ma. These data clearly indicate syn- and post-rift reactivations during the Early Cretaceous, with great emphasis on Paleogene to Neogene times. Integrating the results of older thermochronological studies, the reactivation of the southeastern Brazilian margin can be described in three main phases related to the rift to post-rift evolution of SE Brazil. In general, ZFT and AFT data yield spread values that become younger as samples are closer to the reactivated Neoproterozoic shear zones and might reflect source area exhumation. The analysis of ZFT and AFT data allowed interpretations regarding the main phases that occurred in the study area related to the thermotectonic and tectono-stratigraphic evolution in southeastern Brazil.     

Geochemical assessment of groundwater contamination with special emphasizes on fluoride,a case study from Midyan Basin,northwestern Saudi Arabia

Water samples for chemical analyses were collected in January 2012. A total of 72 samples of groundwater were collected from 72 boreholes in the Midyan Basin, northwestern Saudi Arabia. Samples were collected in polyethylene bottles and preserved and the used analytical techniques were in accordance with the standard methods from American public health association. Geochemical analyses of the groundwater samples from Midyan Basin reveal the concentration of fluoride (F) between 0.98 and 2.1 mg/l. Other parameters, e.g, pH, EC, TDS, HCO₃, SO₄, NO₃, Cl, K, Na, Mg, and Ca have been found in a variable proportion. Among them, the concentration of EC, HCO₃, K, Na and Mg is higher than the permissible limits. According to thermodynamical considerations, most of the analysed samples are graded under-saturated with respect to calcite and fluoride, while saturation has been observed in some samples. The under-saturation could probably be attributed to low concentration of calcite and fluoride in the studied wells. Fluoride concentration shows weak positive correlation with EC, TDS, Na, Cl, and SO₄. Factors controlling the concentration of fluoride (F) in the studied samples are the area climate, water chemistry and the presence of accessory minerals in the rocks through which groundwater is circulating, besides the anthropogenic activities in the area.     

Surface soil assessment in the Ubhur area,north of Jeddah,western Saudi Arabia,using a multichannel analysis of surface waves method

Ten boreholes drilled in Ubhur area up to the depth of bedrock indicted the shallow depth of bedrock where the average depth ranges between 10 and 15 m. The standard penetration test N-values of these boreholes were measured and averaged. Based on N-values to the depth of bedrock, Ubhur area can be classified as site class C and D. Multichannel analysis of surface waves technique has been applied along seventy six profiles using 24-channel geophone array and 4.5Hz vertical geophones with 1m geophone spacing and sledgehammer and/or weight drop as seismic energy sources. Values of shear wave velocity to 30 m are calculated and then averaged (Vs30) where it ranges between 310.08 m/s and 1139.8 m/s. Therefore, Ubhur area can be classified into site class B, C and D based on site classification of the national earthquake hazards reduction program (NEHRP) recommendations. Accordingly, the greatest part of the study area falls in site class C while class B and D covered limited areas in the western and the eastern parts respectively. Depending on the shallow depth of bedrock in the study area, the Vs30 parameter is not applicable in the study area so the average values of Vs for the soil thickness, excluding the bedrock, have been calculated and mapped for site class C and D only. So Vs30 approach is not applicable for areas with shallow depth of bedrock which gives higher classification.