Showing papers by "University of Architecture, Civil Engineering and Geodesy published in 2017"

Changing climate shifts timing of European floods

Abstract: A warming climate is expected to have an impact on the magnitude and timing of river floods; however, no consistent large-scale climate change signal in observed flood magnitudes has been identified so far. We analyzed the timing of river floods in Europe over the past five decades, using a pan-European database from 4262 observational hydrometric stations, and found clear patterns of change in flood timing. Warmer temperatures have led to earlier spring snowmelt floods throughout northeastern Europe; delayed winter storms associated with polar warming have led to later winter floods around the North Sea and some sectors of the Mediterranean coast; and earlier soil moisture maxima have led to earlier winter floods in western Europe. Our results highlight the existence of a clear climate signal in flood observations at the continental scale.

A simple FSDT-based meshfree method for analysis of functionally graded plates

Abstract: Modeling of mechanical behavior of plates has been accomplished in the past decades, with different numerical strategies including the finite element and meshfree methods, and with a range of plate theories including the first-order shear deformation theory (FSDT). In this paper, we propose an efficient numerical meshfree approach to analyze static bending and free vibration of functionally graded (FG) plates. The kinematics of plates is based on a novel simple FSDT, termed as S-FSDT, which is an effective four-variable refined plate theory. The S-FSDT requires C 1 -continuity that is satisfied with the basis functions based on moving Kriging interpolation. Some major features of the approach can be summarized: (a) it is less computationally expensive due to having fewer unknowns; (b) it is naturally free from shear-locking; (c) it captures the physics of shear-deformation effect present in the conventional FSDT; (d) the essential boundary conditions can straightforwardly be treated, the same as the FEM; and (e) it can deal with both thin and thick plates. All these features will be demonstrated through numerical examples, which are to confirm the accuracy and effectiveness of the proposed method. Additionally, a discussion on other possible choices of correlation functions used in the model is given.

Integrating Spherical Panoramas and Maps for Visualization of Cultural Heritage Objects Using Virtual Reality Technology.

Abstract: Development and virtual representation of 3D models of Cultural Heritage (CH) objects has triggered great interest over the past decade. The main reason for this is the rapid development in the fields of photogrammetry and remote sensing, laser scanning, and computer vision. The advantages of using 3D models for restoration, preservation, and documentation of valuable historical and architectural objects have been numerously demonstrated by scientists in the field. Moreover, 3D model visualization in virtual reality has been recognized as an efficient, fast, and easy way of representing a variety of objects worldwide for present-day users, who have stringent requirements and high expectations. However, the main focus of recent research is the visual, geometric, and textural characteristics of a single concrete object, while integration of large numbers of models with additional information-such as historical overview, detailed description, and location-are missing. Such integrated information can be beneficial, not only for tourism but also for accurate documentation. For that reason, we demonstrate in this paper an integration of high-resolution spherical panoramas, a variety of maps, GNSS, sound, video, and text information for representation of numerous cultural heritage objects. These are then displayed in a web-based portal with an intuitive interface. The users have the opportunity to choose freely from the provided information, and decide for themselves what is interesting to visit. Based on the created web application, we provide suggestions and guidelines for similar studies. We selected objects, which are located in Bulgaria-a country with thousands of years of history and cultural heritage dating back to ancient civilizations. The methods used in this research are applicable for any type of spherical or cylindrical images and can be easily followed and applied in various domains. After a visual and metric assessment of the panoramas and the evaluation of the web-portal, we conclude that this novel approach is a very effective, fast, informative, and accurate way to present, disseminate, and document cultural heritage objects.

Three-dimensional phosphorus-doped graphene as an efficient metal-free electrocatalyst for electrochemical sensing

Abstract: Three-dimensional (3D) porous architecture enables the high exploration of graphene excellent properties, ie large surface area and superior conductivity Additionally, heteroatoms doping can improve the electrocatalytic activity of graphene by creating abundant defective/active sites To combine the prominent advantages of 3D porous structure and heteroatoms doping, we reported the facile synthesis of 3D phosphorus (P)-doped graphene (3D-PG) and evaluated its potential application in electrochemical H2O2 sensing As an efficient metal-free electrocatalyst, 3D-PG modified electrode exhibited exceptional sensing performances for sensitive, selective and stable detection of H2O2, which was ascribed to the synergistic effects of 3D porous structure and P-doping in significantly enhancing the eletrocatalytic activity for H2O2 reduction reaction More importantly, the 3D-PG based sensor could be used for real-time tracking H2O2 released from living HeLa cells, hence making 3D-PG a potential high-performance electrocatalyst for practical electrochemical sensing

A new cohesive crack tip symplectic analytical singular element involving plastic zone length for fatigue crack growth prediction under variable amplitude cyclic loading

Abstract: Modelling fatigue crack growth under variable amplitude cyclic loading (VACL) remains challenging in engineering due to multiple damage/failure mechanisms and the difficulties in capturing stress state around the crack tip. Previous efforts have been devoted to develop appropriate models in which the plastic zone length (PZL) in front of crack was involved. However, the PZL can not be calculated accurately by using the existing numerical approaches. In this study, a new singular finite element which takes into account the fracture process zone (FPZ) located in front of the crack tip by using cohesive zone model (CZM) is introduced to study fatigue crack growth under VACL. The cohesive stresses are converted into nodal force of the singular element, and the PZL can be solved numerically by iteration. A few numerical examples have been worked out to demonstrate the proposed method, and it is shown that the fatigue life under VACL can be predicted accurately by using the developed method.

Effect of laser parameters on microstructure, metallurgical defects and property of AlSi10Mg printed by selective laser melting

Abstract: AlSi10Mg alloy has been widely used in selective laser melting (SLM). However, the formation of metallurgical defects in this material during SLM process has not been studied sufficiently. In this work, different laser parameters were adopted to fabricate the specimens. The effects of volumetric energy density (VED) on the metallurgical defect, densification, phase composition and mechanical property were also comprehensively analyzed. At low VED of 37.39J/mm3, a nearly full dense sample with density of 2.602g/cm3 can be printed. The sample with maximal tensile strength of 475MPa can be printed. While with the increase of VED, the ultimate tensile strength decreases due to the formation of micro-pores. The formation mechanisms of micro-pores including gas pores and keyhole-induced pores were disclosed from the angle of alloy smelting. Better understanding of the influence mechanisms of the laser parameters on the formation of metallurgical defects is beneficial for the production of high performance SLM p...

Tricalcium Phosphate Ceramics Doped with Silver, Copper, Zinc, and Iron (III) Ions in Concentrations of Less Than 0.5 wt.% for Bone Tissue Regeneration

Abstract: Novel materials with a variety of properties, such as biocompatibility, antibacterial activity, interconnected porosity, and functionalities combined in one, are required for regenerative medicine. Porous β-tricalcium phosphate (β-TCP) ceramics doped with Cu2+, Zn2+, Ag+, and Fe3+ ions in the concentrations of less than 0.5 wt.% were synthesized and investigated. The obtained samples were analyzed by the diversity of analytical tools. The structure, solubility, and antimicrobial properties of the porous ceramics are shown to be very sensitive to the presence and the type of the cationic substituent. It opens the way to manage structure and properties of the materials for bone tissue regeneration by co-doping of the initial matrix simultaneously with different types of substituent ions.

Foresight Methods in Pedagogical Design of University Learning Environment

Abstract: Currently, informational-educational environment has become one of the constitutive tendencies in the development of modern education and correlates with IT development in all spheres of human life. The availability of multiple possibilities for using information and communication technologies in education brings about variability in university learning environment design. The authors propose the use of foresight methodology to optimize educational content and structure didactic potential of learning environment. The mechanism of pedagogical design using foresight methodology is based on accommodation of subjective views of stakeholders in the education system, creation of a common vision of the informational and educational environment which involves objective prognostic information and the trends and tendencies in regional education development. The knowledge gained from foresight methodology made it possible to design informational and educational, or learning, environment at the university that is able to ensure the learning process meeting the expectations of all stakeholders as close as it is possible and affect the employment rate of the university graduates.

Evaluation of the CropSyst Model during Wheat-Maize Rotations on the North China Plain for Identifying Soil Evaporation Losses.

Abstract: The North China Plain (NCP) is a major grain production zone that plays a critical role in ensuring China's food supply. Irrigation is commonly used during grain production; however, the high annual water deficit [precipitation (P) minus evapotranspiration (ET)] in typical irrigated cropland does not support double cropping systems (such as maize and wheat) and this has resulted in the steep decline in the water table (~0.8 m year-1 at the Luancheng station) that has taken place since the 1970s. The current study aimed to adapt and check the ability of the CropSyst model (Suite-4) to simulate actual evapotranspiration (ETa), biomass, and grain yield, and to identify major evaporation (E) losses from winter wheat (WW) and summer maize (SM) rotations. Field experiments were conducted at the Luancheng Agro-ecosystem station, NCP, in 2010-2011 to 2012-2013. The CropSyst model was calibrated on wheat/maize (from weekly leaf area/biomass data available for 2012-2013) and validated onto measured ETa, biomass, and grain yield at the experimental station from 2010-2011 to 2011-2012, by using model calibration parameters. The revalidation was performed with the ETa, biomass, grain yield, and simulated ETa partition for 2008-2009 WW [ETa partition was measured by the Micro-lysimeter (MLM) and isotopes approach available for this year]. For the WW crop, E was 30% of total ETa; but from 2010-11 to 2013, the annual average E was ~40% of ETa for the WW and SM rotation. Furthermore, the WW and SM rotation from 2010-2011 to 2012-2013 was divided into three growth periods; (i) pre-sowing irrigation (PSI; sowing at field capacity) to emergence period (EP), (ii) EP to canopy cover period (CC) and (iii) CC to harvesting period (HP), and E from each growth period was ~10, 60, and 30%, respectively. In general, error statistics such as RMSE, Willmott's d, and NRMSE in the model evaluation for wheat ETa (maize ETa) were 38.3 mm, 0.81, and 9.24% (31.74 mm, 0.73, and 11.89%); for wheat biomass (maize biomass) they were 1.25 Mg ha-1, 0.83, and 9.64% (0.78 Mg ha-1, 0.96, and 7.96%); and for wheat grain yield (maize grain yield) they were 0.65 Mg ha-1, 0.82, and 9.87% (0.2 Mg ha-1, 0.99, and 3.79%). The results showed that CropSyst is a valid model that can be use with a reliable degree of accuracy for optimizing WW and SM grain yield production and water requirement on the NCP.

Wave Propagation Analysis of Piezoelectric Nanoplates Based on the Nonlocal Theory

Abstract: Based on the nonlocal theory, this paper develops the Kirchhoff nanoplate and Mindlin nanoplate models for the wave propagation analysis of piezoelectric nanoplates. The effects of small scale parameter and thermo-electro-mechanical loads are incorporated in the nanoplate models. The Hamilton’s principle is employed to derive the governing equations of the nanoplate, which are solved analytically to obtain the dispersion relation for piezoelectric nanoplates. The results show that the nonlocal parameter, temperature change, mechanical load and external electric potential have significant influence on the wave propagation characteristics of the piezoelectric nanoplates. The cut-off wave number is observed to exist for piezoelectric nanoplates subjected to positive electric potential, axial tensile force and temperature rise.

On Approximation Properties of Phillips Operators Preserving Exponential Functions

Abstract: In the present paper, we study a modification of the Phillips operators, which reproduces constant and the exponential functions. We obtain the moments using the concept of moment-generating function for the Phillips operators. Here we discuss a uniform convergence estimate for this modified forms. Also some direct estimates, which also involve the asymptotic-type result are established.

Outer independent Roman dominating functions in graphs

Abstract: A Roman dominating function (RDF) on a graph G is a function f:V(G)→{0,1,2} satisfying the condition that every vertex u for which f(u)=0 is adjacent to at least one vertex v for which f(v)=2. A function f:V(G)→{0,1,2} is an outer-independent Roman dominating function (OIRDF) on G if f is an RDF and V0 is an independent set. The outer-independent Roman domination number γoiR(G) is the minimum weight of an OIRDF on G. In this paper, we initiate the study of the outer-independent Roman domination number in graphs. We first show that determining the number γoiR(G) is NP-complete for bipartite graphs. Then we present lower and upper bounds on γoiR(G). Moreover, we characterize graphs with small or large outer-independent Roman domination number.

A brief overview of current status of European spatial data infrastructures − relevant developments and perspectives for Bulgaria

Abstract: The paper aims to present a concise overview of the current status of the national spatial data infrastructures (SDI) of the European Union (EU) member states combined with specific peculiarities for Bulgaria. Some major challenges within the progress of the EU SDIs establishing, which is regulated by the European Directive INSPIRE (Infrastructure for spatial information in Europe) toward establishment of a SDI for environmental policies and activities, are marked out. Available comparative analyses of the main indicators for metadata, data-sets, and data services provided by EU member states are briefly discussed as a special attention is given to the Bulgarian progress. Recent achievements on accelerating the process of implementing the recommendations of the INSPIRE Directive in Bulgaria are outlined.

A ranking-based strategy to prune variable selection ensembles

Abstract: Ensemble pruning techniques are introduced in the context of variable selection.A ranking-based strategy is devised to prune a variable selection ensemble.The ensemble members are sorted by the prediction error of their associated models.Higher selection accuracy is gained by fusing fewer members ranked ahead.The superiority of the novel method over some other methods is validated. Ensemble learning has attracted significant interest in the literature of variable selection due to its great potential to reduce false discovery rate and to stabilize selection results. In this paper, a novel ensemble pruning technique called PST2E (i.e., pruned ST2E) is introduced to obtain smaller but stronger variable selection ensembles. For the ensemble members generated by the ST2E algorithm [3], we sort them in descending order according to the prediction errors associated with their determined models. Subsequently, only a desired number of members ranked ahead are integrated to compose a subensemble. On the basis of the average importance measures produced by the pruned ensemble, all candidate variables are then ranked and decided to be important or not. In the context of linear and logistic regression models, the experiments conducted with both simulated and real-world data illustrate that PST2E significantly outperforms several other popular techniques in most cases when evaluating them with multiple measures. Another advantage of PST2E is that it admits easy implementation. As a result, PST2E can be deemed as an attractive alternative to tackle variable selection tasks in real applications.

A frozen soil creep model with strength attenuation

Abstract: A frozen soil creep model with shear strength attenuation was proposed based on a soft soil creep model. K 0 compression and triaxial shear tests were conducted to obtain the model parameters. With triaxial creep tests, the performance of soft soil creep model was verified at first. It was shown that different creep stages can only be described separately, which was due to a constant failure line used in the model. After incorporating strength attenuation into the original model, relative position between stress point and failure line is time dependent, and the progressive development of creep strain from primary to tertiary stage can be captured reasonably.

Function and effect of the inner vortex on the performance of cyclone separators

Abstract: The inner vortex plays a key role in the performance of cyclone separators. To explore the function and effect of the inner vortex in cyclone separators, a series of metal rods and metal blades are inserted in the typical Lapple cyclone separator to reduce the intensity of the inner vortex. First, the changes in general performance of cyclones are measured by experimental methods after insertion of the metal rods and metal blades. The flow field and particle motion are then simulated, respectively, by means of a Reynolds stress model (RSM) and a Lagrangian particle tracking (LPT) model. The results show that when the length of the metal blades is less than the boundary between the inner and outer vortexes, that is, the outer vortex remains unchanged and the inner vortex is destroyed partly, the separation efficiency remains constant and the pressure drop significantly decreases. When the length of the metal blades exceeds the boundary, the inner vortex is completely destroyed, and the outer vortex is significantly damaged, which results in sharp decrease of both the separation efficiency and pressure drop. The results indicate that the inner vortex has a notable effect on the pressure drop and virtually none on the separation efficiency. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4508–4518, 2017

Characterising deep vadose zone water movement and solute transport under typical irrigated cropland in the North China Plain

Abstract: Understanding the dynamics and mechanisms of soil water movement and solute transport is essential for accurately estimating recharge rates and evaluating the impacts of agricultural activities on groundwater resources. In a thick vadose zone (0-15 m) under irrigated cropland in the piedmont region of the North China Plain, soil water content, matric potential and solute concentrations were measured. Based on these data, the dynamics of soil water and solutes were analysed to investigate the mechanisms of soil water and solute transport. The study showed that the 0-15 m vadose zone can be divided into three layers: an infiltration and evaporation layer (0-2 m), an unsteady infiltration layer (2-6 m) and a quasi-steady infiltration layer (6-15 m). The chloride, nitrate and sulphate concentrations all showed greater variations in the upper soil layer (0-1 m) compared to values in the deep vadose zone (below 2 m). The average concentrations of these three anions in the deep vadose zone varied insignificantly with depth and approached values of 125, 242 and 116 mg/L. The accumulated chloride, sulphate and nitrate was 2179 ± 113, 1760 ± 383 and 4074 ± 421 kg/ha, respectively. The soil water potential and solute concentrations indicated that uniform flow and preferential flow both occurred in the deep vadose zone, and uniform flow was the dominant mechanism of soil water movement in this study. The piston-like flow velocity of solute transport was 1.14 m/yr, and the average value of calculated leached nitrate nitrogen was 107 kg/ha∙yr below the root zone. The results can be used to better understand recharge processes and improve groundwater resources management. This article is protected by copyright. All rights reserved.

Free subgroups in almost subnormal subgroups of general skew linear groups

Abstract: Let $D$ be a weakly locally finite division ring and $n$ a positive integer. In this paper, we investigate the problem on the existence of non-cyclic free subgroups in non-central almost subnormal subgroups of the general linear group ${\rm GL}_n(D)$. Further, some applications of this fact are also investigated. In particular, all infinite finitely generated almost subnormal subgroups of ${\rm GL}_n(D)$ are described.

Properties of Portland cement pastes enriched with addition of calcined marl

Abstract: Increasing global production of Portland cement and the necessity to reduce CO 2 emissions have resulted in the need to increase the production and application of blended cements enriched with supplementary cementitious materials (SCMs). Recently, polymineral clays, which are abundantly available across the globe, have gained attention as promising raw materials for the production of SCMs. In this study, the effect of marl on the properties of hardened Portland cement was investigated. The Portland cement pastes enriched with marl (5–20%) calcined at 400–800 °C and ground up to 250–800 m 2 /kg showed better physical-mechanical properties than those enriched with metakaolin. This study demonstrates the potential of calcined marl to be used as an effective pozzolan additive for Portland cement.

Necessary and sufficient KKT optimality conditions in non-convex optimization

Abstract: We study the optimization problems $$\min _\mathbf{x }\left\{ f(\mathbf{x }):g_j(\mathbf{x })\le 0, j=1,\ldots ,m\right\} $$ where Slater’s condition holds without the convexity of the feasible set and of the functions $$f,~ g_j$$ . At a feasible point $$\mathbf{x }$$ under question the functions $$g_j$$ are assumed to satisfy a non-degeneracy assumption, necessary and sufficient KKT optimality conditions are then considered in relation to the convexity of the level sets of f.

Postbuckling Behavior of Compressed Rods in an Elastic Medium

Abstract: The postbuckling of rods loaded by a compressive force P in an elastic medium is considered. The resolving nonlinear equation is obtained, and a method for solving this equation is given. It is shown that, for large lengths, in contrast to the case without elastic medium, the deflection increases as the force P decreases after the loss of stability. Several simple finite-element models, namely, the problems of compression of multilink rods with links connected by springs, are considered to confirm this effect.

Pareto optimal generalized H 2 -control and vibroprotection problems

Abstract: We consider a novel multi-objective control problem where the criteria are generalized H 2-norms of transfer matrices of individual channels from the disturbance input to various objective outputs. We obtain necessary conditions for Pareto optimality. We show that synthesis of Pareto optimal controls can be done in terms of linear matrix inequalities based on optimizing Germeier’s convolution, which also turns out to be the generalized H 2-norm of the closed-loop system with output composed of the objective outputs multiplied by scalars. As applications we consider multi-objective problems of vibration isolation and oscillation suppression with new types of criteria.

Delamination fracture in a functionally graded multilayered beam with material nonlinearity

Abstract: The present paper describes a theoretical study of delamination fracture in the functionally graded multilayered Crack Lap Shear (CLS) beam configuration with taking into account the nonlinear material behaviour. The fracture was analysed in terms of the strain energy release rate. The analytical solution derived is applicable for CLS with an arbitrary number of layers. Also, the delamination crack may be located arbitrary along the beam height. The mechanical behaviour of beam layers was modelled by a power-law stress–strain relation. It was assumed that the material in each layer is functionally graded along the thickness. Also, the material properties may be different in each layer. An analytical solution of the J-integral was derived in order to verify the nonlinear strain energy release rate analysis. The effects were evaluated of material gradient, crack location along the beam height and material nonlinearity on the strain energy release rate. It was shown that the analysis developed is a useful tool for the understanding of delamination fracture behaviour of functionally graded multilayered CLS beam configurations with material nonlinearity.

Phosphorus recovery potential in Sofia WWTP in view of the national sludge management strategy

Abstract: In view of the vital importance of phosphorus and its increasing scarcity as a natural resource, phosphorus recovery has recently gained significant scientific and technical interest. The aim of this study is to support the implementation of the Bulgarian national sludge management strategy, particularly its objective to achieve more efficient resource management of phosphorus in waste water treatment plants (WWTPs). The study estimates the potential for phosphorus recovery from the municipal WWTP at Sofia, the largest in Bulgaria, serving some 14% of the Bulgarian population. The phosphorus content of five process streams (thickener supernatant, dewatering centrate, sludge before digestion, sludge after digestion and ash) is analysed on the basis of one year of measurements. It is estimated that 170–250 t phosphorus could be recovered annually from the WWTP from digested sludge or ash, depending on the phosphorus recovery technology used.