Samoilă Grigoraș Claudia, Ioniță Ion, Niacșu Lilian, Grigoraș Georgel and Blebea-Apostu Ana Maria
Land degradation has been recognized as an important environmental threat in the Moldavian Plateau of eastern Romania. This study was designed to estimate the magnitude of land degradation and to review land management in a small catchment in the Central Moldavian Plateau. Several methods were deployed to estimate soil erosion losses, gully distribution, landslide inventory and reservoir sedimentation rates. Results obtained in the study area of 7,766 ha, of which 31% is arable and 32% native forest, show that the mean value of soil losses by water erosion on agricultural land is 19.0 t ha−1y−1. By adding the woodland contribution, this value significantly decreases to 12.8 t ha−1y−1. Then, a large proportion of land (58%) is covered by landslides. Most of them are shallow and dormant (stable), and the active ones form only ~2% of the total landslide area. Siltation rates determined using 137Cs reflect the impact of land management on deposition patterns in reservoirs. Proper conservation measures were applied over a 20-year time-span from 1970-1990. Since 1991 the contour farming system collapsed and returned to the traditional ‘up-and-down slope’ farming system on very small plots.
Raul-Gabriel Ilea, Cosmina-Andreea Manea and Marina-Aurelia Antonescu
The urban climate is a specific type of topoclimate characteristic to big cities, like Bucharest, which is formed due to the horizontal and vertical expansion of the space, the nature of the materials used for constructions, the pollution, and other side effects of the socio-economic activities. The main objective of this study is the analysis of the variability of four main meteorological elements (air temperature, atmospheric precipitation, relative air humidity, duration of sunshine) in Bucharest and its neighboring area, in relation to the built space evolution. In the last decades, Bucharest has been experiencing an exceptional development, materialized both by territorial expansion, as well as structural-functional and architectural-urbanistic transformations. The fact that the population of the city is increasing, correlated with the expansion of the built space area, suggests the intensity of the urban sprawl phenomena. This has numerous side effects, among which is the creation of a specific topoclimate, different from the one in the periphery. As an example, the results of the meteorological analysis showed that the air temperature is higher inside the city, at the Filaret station, with 0.1ºC, than at the periphery (Baneasa station) and the periurban area (Afumati station).
Lifei Song, Houjing Chen, Wenhao Xiong, Zaopeng Dong, Puxiu Mao, Zuquan Xiang and Kai Hu
The unmanned surface vehicles (USV) are required to perform a dynamic obstacle avoidance during fulfilling a task. This is essential for USV safety in case of an emergency and such action has been proved to be difficult. However, little research has been done in this area. This study proposes an emergency collision avoidance algorithm for unmanned surface vehicles (USVs) based on a motion ability database. The algorithm is aimed to address the inconsistency of the existing algorithm. It is proposed to avoid collision in emergency situations by sharp turning and treating the collision avoidance process as a part of the turning movement of USV. In addition, the rolling safety and effect of speed reduction during the collision avoidance process are considered. First, a USV motion ability database is established by numerical simulation. The database includes maximum rolling angle, velocity vector, position scalar, and steering time data during the turning process. In emergency collision avoidance planning, the expected steering angle is obtained based on the International Regulations for Preventing Collisions at Sea (COLREGs), and the solution space, with initial velocity and rudder angle taken as independent variables, is determined by combining the steering time and rolling angle data. On the basis of this solution space, the objective function is solved by the particle swarm optimization (PSO) algorithm, and the optimal initial velocity and rudder angle are obtained. The position data corresponding to this solution is the emergency collision avoidance trajectory. Then, the collision avoidance parameters were calculated based on the afore mentioned model of motion. With the use of MATLAB and Unity software, a semi-physical simulation platform was established to perform the avoidance simulation experiment under emergency situation. Results show the validity of the algorithm. Hence results of this research can be useful for performing intelligent collision avoidance operations of USV and other autonomous ships
The article presents the development of author’s concept of a diesel/hydraulic propulsion system for inland watercraft. Due to specific nature of vessel navigation on rivers, classical propulsion systems with shaft lines can be effectively replaced by systems with hydraulic power transmission. A solution is also presented of a hybrid design with extra electric port having the form of a pumping system driven from a battery of accumulators. Strong and weak points of the proposed solution are discussed and its energy efficiency is assessed.
The centrifugal magnetic fluid seals have important advantage over the conventional centrifugal seals. They maintain very good sealing capacity at static, medium and high speeds of shaft rotation, with the increased seal lifetime, and minimum torque and static friction. These seals are particularly useful in cases when the angular shaft velocity varies and sometimes decreases to nearly or exactly zero, such as in flywheel applications, ship propeller main shafts, etc. Unique properties of the magnetic fluid give rare opportunities for application in marine design, where perfect sealing together with reliable lubrication are required.
The paper presents a typical design and operation principle of a centrifugal magnetic fluid shaft seal, along with new design solutions. Not only in ocean technology and underwater robotics. Some cases of application of centrifugal magnetic fluid seals in modern sealing technology are included.
This article presents results of an analysis of impact of a designed discharge of contaminated water into the Dead Vistula (Wisła Martwa) in the region of the Isthmus (Przesmyk) with the aim of determination of a possible effect of the pollution onto protected areas of Natura 2000 (bird habitats and sites, especially the Bird Paradise – Ptasi Raj) nature reserve. The analysis was conducted on the basis of the two-dimensional modelling of unsteady transport of non-degradable dissolved matter. To this end, a numerical model of a section of the Dead Vistula was worked out. Four scenarios of hydro-dynamical conditions (2 – for average weather conditions and 2 – for stormy weather conditions) were selected. To solving the equation of pollution migration the finite volumes method (MOS) was applied. Two localizations of contaminated water discharge outlet were considered, namely: the first from the side of Siennicki Bridge before the Isthmus and the other in the section of the Brave Vistula (Wisła Śmiała) downstream the Isthmus. The obtained results made it possible to assess positively the first localization of the designed discharge outlet. In the other case there is a fear that at unfavourable hydro-meteorological conditions a water pollution may happen over Natura 2000 protected areas.
Tu Tran Ngoc, Do Duc Luu, Thi Hai Ha Nguyen, Thi Thu Quynh Nguyen and Minh Vu Nguyen
The paper presents the results of computational evaluation of the hull-propeller interaction coefficients, also referred to propulsive coefficients, based on the unsteady RANS flow model. To obtain the propulsive coefficients, the ship resistance, the open-water characteristics of the propeller, and the flow past the hull with working propeller were computed. For numerical evaluation of propeller open-water characteristics, the rotating reference frame approach was used, while for self-propulsion simulation, the rigid body motion method was applied. The rotating propeller was modelled with the sliding mesh technique. The dynamic sinkage and trim of the vessel were considered. The free surface effects were included by employing the volume of fluid method (VOF) for multi-phase flows. The self-propulsion point was obtained by performing two runs at constant speed with different revolutions. The well-known Japan Bulk Carrier (JBC) test cases were used to verify and validate the accuracy of the case studies. The solver used in the study was the commercial package Star-CCM+ from SIEMENS.
Bogdan Alexandru Maco, Nicoleta Ionac and George Tudorache
Air pollution is one of the major problems of mankind, transport of pollutants extending far beyond the borders of the countries where they were produced, causing unpredictable, direct and indirect changes of the environment. The main tool for the study of this phenomenon consists of mathematical modeling of complex physical and chemical phenomena involved. In practice, air emissions are estimated on basis of measurements taken from selected sources being representative of the major categories and types. At national level, the Air Quality Evaluation Center (CECA) provides regular reports to the European Environment Agency (EEA) or the European Commission as requirements of Romania’s lawful duties in air quality domain. The registry of emissions TNO/ MACC (Netherlands Organisation for Applied Scientific Research/ Monitoring Atmospheric Composition and Climate) contains emissions inventories which have been homogenized and checked in advance and obtained from emissions officially reported at sectoral level for each country. In this study, for the analysis of the weather numerical dispersion and transport of pollutants, it has been used the numerical air quality model WRF-CHEM version 3.5, centered over Romania, at the spatial resolution of 10 km, using as input data the TNO emission database for 2009. By interpolating values from the regular grid of the TNO database with the WRF-CHEM model 3.5 grid, monthly average values were obtained for each day of the week, for any parameter considered. Preliminary results obtained for different pollutants (for example: PM10, O3) confirm the need to validate these results by implementing and integrating air quality forecasting model by assimilating different types of measurements (data model, gravimetric data observations, etc.).
The paper presents results of numerical simulations of size effect phenomenon in concrete specimens. The behaviour of in-plane geometrically similar notched and unnotched beams under three-point bending is investigated. In total 18 beams are analysed. Concrete beams of four different sizes and five different notch to depth ratios are simulated. Two methods are applied to describe cracks. First, an elasto-plastic constitutive law with a Rankine criterion and an associated flow rule is defined. In order to obtain mesh independent results, an integral non-local theory is used as a regularisation method in the softening regime. Alternatively, cracks are described in a discrete way within Extended Finite Element Method (XFEM). Two softening relationships in the softening regime are studied: a bilinear and an exponential curve. Obtained numerical results are compared with experimental outcomes recently reported in literature. Calculated maximum forces (nominal strengths) are quantitatively verified against experimental values, but the force – displacement curves are also examined. It is shown that both approaches give results consistent with experiments. Moreover, both softening curves with different initial fracture energies can produce similar force-displacement curves.
The lysimeter is most often defined as a box filled with soil with an intact structure for measuring the amount of infiltration and evapotranspiration in natural conditions. At the bottom of the device there is an outflow for atmospheric precipitation water infiltrating to a measuring container. Lysimeter studies are included in the group of dynamic leaching tests in which the leaching solution is added in a specified volume over a specific period of time. Lysimeter studies find applications in, amongst others, agrotechnics, hydrogeology and geochemistry. Lysimeter tests may vary in terms of the type of soil used (anthropogenic soil, natural soil), sample size, leaching solution, duration of the research and the purpose for conducting it. Lysimeter experiments provide more accurate results for leaching tests compared with static leaching tests. Unlike several-day tests, they should last for at least a year. There are about 2,500 lysimeters installed in nearly 200 stations around Europe. The vast majority of these (84%) are non-weighing lysimeters. There are a few challenges for lysimeter research mostly connected with the construction of the lysimeter, estimating leaching results and calibrating numerical transport models with data obtained from lysimeters. This review is devoted to the analysis of the principal types of lysimeters described in the literature within the context of their application. The aim of this study is to highlight the role of lysimeters in leaching studies.