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Number of results: 9
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Abstract

Geomechnical model testing has been widely applied as a kind of research technique in underground engineering problems. However, during the practical application process, due to the influence of many factors, the desired results cannot be obtained. In order to solve this problem, based on the measurement requirements of the model test, combined with FBG(Fiber Bragg Grating) sensor technology and traditional measurement methods, an FBG monitoring system, Micro-multi-point displacement test system, resistance strain test system and surrounding rock pressure monitoring system are developed. Applying the systems to a model test of the tunnel construction process, the displacement in advance laws of tunnel face, radial displacement distribution laws and surrounding rock pressure laws are obtained. Test results show that a multivariate information monitoring system has the advantage of high precision, stability and strong anti-jamming capability. It lays a solid foundation for the real-time data monitoring of the tunnel construction process model test.
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Abstract

The analysis of changes in the mechanical properties of wooden mining cribs under the influence of different types of exploitation loads is the question for which deals with many domestic and abroad research centers deal with. High The high interest in this subject results from the increase of the conducted depth exploitation, which contributes to the increase in both the vertical pres-sure and the complexity of geological – mining conditions and in- the intensification of natural hazards. Another reason is the tendency of decreasing the thickness of the exploited ores deposits. Wooden crib support is used Both both in underground ore, hard coal and salt mining is used wooden crib support. Mining cribs with various configurations are especially useful for the reinforcement of excavations workings behind the front and for further strengthen of the crossings. In particular, additional reinforcement support in the form of wooden cribs (pile supporting), which shall be left empty or filled with waste rock is applied in the ore mining in places where found extended rooms or drifts are found or in places with degraded roof conditions, applies additional reinforcement support in the form of wooden cribs (pile supporting), which shall be left empty or filled with waste rock. During underground ex-ploitation is produced waste Waste rock, which comes from the access, prepar-atory excavations and from ongoing field of exploitation is produced during underground exploitation. In the case of the underground exploitation of cop-per ore, waste rock is used to fill voids after exploitation as rock stowing. It is also used for filling mining wooden cribs, as an artificial support and for harder transportation roads. This paper presents the results of the laboratory strength tests performed on models of four-point timber cribs, built with beams set horizontally, at the ge-ometrical scale of 1:10. In the laboratory research Research wooden cribs models with size 200 × 200 × 200 mm and 100 × 100 × 100 mm were used in the laboratory. The paper describes the maximum loading capacity of the cribs consisted consisting only of beams and filled with waste rocks. In addition, a vertical and appropriate strain of cribs at maximum force was shown. On the basis of laboratory research it was found that the use of the same number of timbers and the management of waste rocks, the filling of the four-point cribs with the waste rocks allowed several times to increase its support to be increased several times.
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Abstract

The methane hazard is one of the most dangerous phenomena in hard coal mining. In a certain range of concentrations, methane is flammable and explosive. Therefore, in order to maintain the continuity of the production process and the safety of work for the crew, various measures are taken to prevent these concentration levels from being exceeded. A significant role in this process is played by the forecasting of methane concentrations in mine headings. This very problem has been the focus of the present article. Based on discrete measurements of methane concentration in mine headings and ventilation parameters, the distribution of methane concentration levels in these headings was forecasted. This process was performed on the basis of model-based tests using the Computational Fluid Dynamics (CFD). The methodology adopted was used to develop a structural model of the region under analysis, for which boundary conditions were adopted on the basis of the measurements results in real-world conditions. The analyses conducted helped to specify the distributions of methane concentrations in the region at hand and determine the anticipated future values of these concentrations. The results obtained from model-based tests were compared with the results of the measurements in realworld conditions. The methodology using the CFD and the results of the tests offer extensive possibilities of their application for effective diagnosis and forecasting of the methane hazard in mine headings.
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Abstract

This study, describing computer simulation of a glider crash against a non-deformable ground barrier, is a part of a larger glider crash modeling project. The studies were intended to develop a numerical model of the pilot - glider - environment system, whereby the dynamics of the human body and the composite cockpit structure during a crash would make it possible to analyze flight accidents with focus on the pilot's safety. Notwithstanding that accidents involving glider crash against a rigid barrier (a wall, for example) are not common, establishing a simulation model for such event may prove quite useful considering subsequent research projects. First, it is much easier to observe the process of composite cockpit structure destruction if the crash is against a rigid barrier. Furthermore, the use of a non-deformable barrier allows one to avoid the errors that are associated with the modeling of a deformable substrate, which in most cases is quite problematic. Crash test simulation, carried out using a MAYMO package, involved a glider crash against a wall positioned perpendicularly to the object moving at a speed of 77 km/h. Computations allowed for determination of time intervals of the signals that are required to assess the behavior of the cockpit and pilot's body - accelerations and displacements in selected points of the glider's structure and loads applied to the pilot's body: head and chest accelerations, forces at femur, lumbar spine and safety belts. Computational results were compared with the results of a previous experimental test that had been designed to verify the numerical model. The glider's cockpit was completely destroyed in the crash and the loads transferred to the pilot's body were very substantial - way over the permitted levels. Since modeling results are fairly consistent with the experimental test, the numerical model can be used for simulation of plane crashes in the future.
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Abstract

The national total expenditure of a country is precipitated on several factors of which revenue generated could be one and very significant. This paper therefore examines the contribution of some selected sources of Nigerian government revenue to total national expenditure. Statistical and econometric techniques used for the data analysis are unit root test, cointegration test, combined estimators’ analysis, the error correction model (ECM) and the feasible generalized linear (FGLS) estimators. Results showed that the variables are non stationary but are stationary at first difference. The long-run relationship of total expenditure on oil revenue, non-oil revenue, federation account and federal retained revenue revealed that the variables are co-integrated and required the use of combined estimators. The effect of non-oil revenue and federal retained revenue is very significant. Investigations on the short-run modeling necessitated the use of FGLS estimators. The effect of ECM and federal retained revenue is very significant. Consequently, other sources of revenue apart from federal retained revenue need to be enhanced and tailored towards improving economic growth and development through national expenditure.
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Abstract

Effects of mixing on the course of fast chemical reactions are relatively well understood, especially in homogeneous systems. This enables to design and operate chemical reactors with the goal to achieve a high yield of a desired product and use systems of complex reactions as a chemical probe (chemical test reactions) to identify progress of mixing and quality of mixture. Recently, a number of studies have focused on the application of chemical test reactions to identify energy efficiency of mixing, being a convenient way of comparing mixers and reactors in terms of their mixing efficiency. This review offers a presentation of chemical test reactions available in the literature and methods of applications of test reactions to identify the energy efficiency of mixing. Also methods to assess the extent of micromixing by measuring product distribution or segregation index, and to determine the time constant for mixing are presented for single phase homogeneous systems and two-phase liquid-liquid systems.
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Abstract

The paper presents the results of investigating the effect of increase of observation correlations on detectability and identifiability of a single gross error, the outlier test sensitivity and also the response-based measures of internal reliability of networks. To reduce in a research a practically incomputable number of possible test options when considering all the non-diagonal elements of the correlation matrix as variables, its simplest representation was used being a matrix with all non-diagonal elements of equal values, termed uniform correlation. By raising the common correlation value incrementally, a sequence of matrix configurations could be obtained corresponding to the increasing level of observation correlations. For each of the measures characterizing the above mentioned features of network reliability the effect is presented in a diagram form as a function of the increasing level of observation correlations. The influence of observation correlations on sensitivity of the w -test for correlated observations (Förstner 1983,Teunissen 2006) is investigated in comparison with the original Baarda’s w -test designated for uncorrelated observations, to determine the character of expected sensitivity degradation of the latter when used for correlated observations. The correlation effects obtained for different reliability measures exhibit mutual consistency in a satisfactory extent. As a by-product of the analyses, a simple formula valid for any arbitrary correlation matrix is proposed for transforming the Baarda’s w -test statistics into the w -test statistics for correlated observations.
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Abstract

The aim of this paper is analysis of the possibility of determining the internal structure of the fibrous composite material by estimating its thermal diffusivity. A thermal diffusivity of the composite material was determined by applying inverse heat conduction method and measurement data. The idea of the proposed method depends on measuring the timedependent temperature distribution at selected points of the sample and identification of the thermal diffusivity by solving a transient inverse heat conduction problem. The investigated system which was used for the identification of thermal parameters consists of two cylindrical samples, in which transient temperature field is forced by the electric heater located between them. The temperature response of the system is measured in the chosen point of sample. One dimensional discrete mathematical model of the transient heat conduction within the investigated sample has been formulated based on the control volume method. The optimal dynamic filtration method as solution of the inverse problem has been applied to identify unknown diffusivity of multi-layered fibrous composite material. Next using this thermal diffusivity of the composite material its internal structure was determined. The chosen results have been presented in the paper.
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Abstract

Rising technical standards of customers, legal requirements and the trend to minimize maintenance effort raise the thermal, mechanical and tribological loads on components of combustion engines. In this regard, emphasis is laid on improving the piston ring - cylinder liner tribosystem, one with the highest energy losses. An efficient performance has to be guaranteed during its lifetime. Tribological investigations could be carried out on engine test benches, but they are highly cost-intensive and time-consuming. Therefore, a damage-equivalent test methodology was developed with the analogous tribological model, "ring-on-liner". The research was carried out under two characteristic operating conditions. One with a "standard" operating system, modelled in line with ideal lubrication conditions, and the other "extreme abrasive" operating system, typical to a system running on a lubricant contaminated by abrasive particles. To optimize the tribological loading capacity of the cylinder liner, with focus on these two operating conditions, numerous nitride coatings have been investigated. The key aspects being seizure resistance, running-in characteristics and long term wear behaviour.
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