Limit Angles Research Articles

Quantitative Analysis of the Subsidence Trough of the Barapukuria Coal Mine, Bangladesh

Subsidence has been an ever-increasing concern of the Barapukuria coal mine for nearly two decades and has indeed called for quantification to predict the expansion of surface subsidence. The study has been undertaken to address this issue. Earlier studies only dealt with the horizontal expansion of the subsidence trough and were calculated based on a rudimentary rule of thumb. On this basis, about 646 acres of land have been acquired and marked as the Influence zone of the mine. However, the extension of the subsidence trough has moved further beyond the Influenced-zone boundary, severely damaging several houses around the mine . This study empirically measures the spatial extension of the subsidence trough identifying mining-induced cracks and joints in 37 affected houses around the mine that emphasized the modification of the rule of thumbs, particularly the angle of draw. It is revealed that the minimum and maximum limit angles are 42o and 60o respectively, and a distance of 378m to 727m (average 552m) must be considered to mark the influenced-zone boundary of the mine while the mining depth is 420m. To precisely quantify and predict the increasing progression of subsidence trough, it is imperative to determine an angle of draw, spatial and areal expansion, and the geotechnical properties for this specific mine.

Mechanical Behaviour and Failure Mode Analysis of Penetrated Mortise–Tenon Joint with Neighbouring Gaps Based on Full-Scale Experiments

The penetrated mortise–tenon joint (PMT) connecting column and beam in traditional timber structures often has neighbouring gaps between connected structural members due to initial manufacture errors and damage accumulated over years. Influences of the neighbouring gaps on the mechanical properties of the PMT joint have been analysed based on a full-scale experimental study. Four typical gap values are determined according to the probability analysis of on-site survey results of a Chinese traditional timber structure. Four full-scale models of PMT joints with varied gap values have been established. Failure modes and deformation characteristics have been studied by quasi-static tests. Results show that the failure modes are the tearing of wood fiber along the grain at variable cross-sections. The loose penetrated mortise–tenon (LPMT) joints all have high deformability. The slip distance of tenon grows as the gap value increases. Limit angles of the loose joints lag with the increasing degree of loosening. The bending bearing capacity and rotational stiffness of LPMT joints decrease as the gap value increases, and the limitation value of the gap is analysed. The resisting capacities of LJ-2, LJ-3 and LJ-4 are much lower than that of LJ-1. The changing ratios are 18.5%, 55.4% and 70.4%, respectively. A three-parameter power function model of the mortise–tenon joint with consideration of the neighboring gap is presented. Research results provide important references on the condition assessments of the existing traditional timber structures.

Study on heat transfer characteristics of single-layer double-row pulsating heat pipe

The structure and inclination angle of a pulsating heat pipe are critical factors influencing the heat transfer performance and operation mode. In this work, a single-layer double-row pulsating heat pipe is designed, and the start-up and heat transfer characteristics of pulsating heat pipe at limit angles (0?, 90?, and 180?) are experimentally investigated. Also, the operation mode and heat transfer characteristics are studied through infrared imager and temperature profiles. The study highlighted that the pulsating heat pipe has excellent operation characteristics in the limit angle. When the inclination angle is 0?, the double-row structure improves the start-up performance and at 90? inclination, the pulsating heat pipe starts the fastest, and the heat transfer resistance keeps the smallest in the whole test. When the inclination angle is 180?, the pulsating heat pipe has the best thermal sensitivity but weak working fluid-flow capacity during operation.

Device for automatic determination of inclination angles of means of mechani-zation of technological processes in agro-industrial complex

The article describes the problem associated with the loss of stability of means of mechanization of agro-industrial processes by machine-tractor units (transport, stealing, automobile and automobile trains, combines, and lifting cranes). It is noted that this circumstance leads to overturns, accidents, injuries, fires, often accompanied by fatalities. In support of the above, information is summarized on the number of injuries among women and men in the country's agro-industrial enterprises (including lethal ones). It is noted that this is due to the fact that these units are not equipped with devices that signal, automatically notify operators operating in conditions of irregularities in the terrain of fields and roads (mountainous areas) about the achievements of maximum inclination angles, the excess of which leads to overturns. In order to eliminate these situations, a device is justified and based on extensive research, automatically signalling and visually and soundly about reaching the limit angles (for a given machine) of stability in order to take measures by the operator to prevent overturning. Equipping these machines with the proposed innovative device will eliminate the possibility of overturns and related accidents, injuries, fires, providing a socio-economic effect.

Convexity limit angles for isoptics

Given an oval C in the plane, the alpha -isoptic C_alpha of C is the plane curve composed of the points from which C can be seen under the angle pi -alpha . We consider isoptics of ovals parametrized with the support function p(t)=a+cos n t, nin mathbb {N}, and present an example of an oval such that when alpha increases, the alpha -isoptics begin to be convex, then lose their convexity and finally are convex again along a curve intersecting the isoptics orthogonally. Next we give an example of a curve from the same family, for which the curvature of the isoptics changes its sign three times. These changes occur on the symmetry axes of the oval C and coincide with the orthogonal trajectories which start at the points with extremal curvature. Finally, we formulate the hypothesis concerning the general case where we expect n-1 convexity limit angles for the isoptics of an oval parametrized by p(t)=a+cos n t.

Graphical method for determining of limit and permissible values of drawing and friction coefficients, stress, drawing angle and delta-criterion for shape of plastic deformation zone

The maximum and permissible values of the coefficients of drawing and friction, the Delta criterion of the shape of the deformation center, the index of the deformed state, the angle and drawing stress are determined graphically for different models of hardening and values of the anti-tension stress. For the determination, cartesian graphs were used, on the ordinate axis of which the desired indicators are located, and on the abscissa axis the values of the I.L. Per lin safety factor obtained by varying the extraction coefficient. The permissible values of the drawing coefficient and drawing stress decrease with the growth of the safety factor of I.L. Perlin. The dependence of the limit and permissible values of the Delta criterion for the optimal value of the drawing angle on the deformation parameters and the harden ing model is shown. The maximum and permissible values of the coefficient of friction are higher at the optimal value of the drawing angle. For the first time, the possibility of increasing the limit value of the coefficient of friction from the action of anti-gravity is established. The limit and permissible values of the coefficient of friction decrease with the increase in the value of the coefficient of drawing and increase with the increase in the coefficient of hardening k. Curves for the dependences of the safety factor, the stress state indicator and the absolute safety margin Zap on the value of the drawing angle fix small and large values of the limit drawing angle on the abscissa axis. Small limit values of the drawing angle do not differ significantly in value for different values of the drawing and hardening coefficients, in contrast to large limit values of the angle. The action of counter-gravity increases the small limit angles and decreases the large limit angles. Determination of the limit and permissible values of the coefficients of drawing and friction, the Delta criterion, stress and drawing angle contributes to the rational choice of modes of deformation of the wire (bar).

Investigation of milling stability based on a cutting force segmentation model

The chatter vibration is the major limiting factor for higher metal removal rates in milling process. This paper proposed an integral model of cutting force with helical cutter considering the sectional characteristics of cutting force. Based on the model, the variation law of the upper and lower limit angles of the cutting process under different radial cutting depths is analysed. The results show that the shape of cutting force for each tooth has a characteristic of three sections. Moreover, the process dynamic equation of thin-walled parts cutting is constructed based on the model. And, the stability lobe diagram is obtained by semi-discretization method. The time-domain simulations are carried out in different cutting parameters around the stable island to verify the correctness of the prediction method. The results show that the method has good ability to predict the cutting stability of cutters with helix angle.

Improvement in determining the risk of damage to the human lumbar functional spinal unit considering age, height, weight and sex using a combination of FEM and RSM.

Human functional spinal unit (FSU) is comprised of two adjacent vertebrae, the intervertebral disc (IVD), the cartilage endplates and the connecting ligamentous tissues. As humans age, trabecular, cortical bone and IVD change in mechanical properties. These changes influence the movement of the FSU (displacements, rotations and disc bulges). This paper proposes a method to determine the influence of sex, age, weight and height on the movements of the FSU using a combination of the FEM and RSM. The work concentrates on the medium-sized human FSU (L3-L4 lumbar level with standard dimensions of IVD: width = 50mm, depth = 35mm and height = 11mm). Also, the proposed method could be an improvement to the determination of risk of damage based on body mass index (BMI), as well as an alternative method of searching for a healthy weight. The method was developed as follows: First, a three-dimensional parameterized human healthy FSU FE model was generated based on the standard test (for compression, flexion, extension, lateral bending, torsion and shear). The movements of the FSU FE model based on the aforementioned standardized test when the sex, age, weight and height varies in a range for each individual (30-80 years; 70-120 kg; 160-190 cm) were simulated. Quadratic regression models were generated for each standardized test using RSM. An ANOVA test showed that all of the tests have a significant influence on weight and age, whereas height influences only those tests that involve rotation of the FSU (flexion, extension and lateral bending). Normal weight, overweight and obesity BMI classifications were considered in determining the healthy weight with the following constraints: the limit angles of flexion and lateral bending, as well as the maximum posterior bulge limit of the IVD, could not exceed of one-third of the spinal canal. The proposed method concluded that: (1) normal BMI values do not cause damage to the FSU, (2) some overweight BMI values may cause damage to the FSU for a certain range of ages and heights and (3) for BMI obesity values, the risk of damage to the FSU may be imminent.

Controlling Cherenkov angles with resonance transition radiation

Cherenkov radiation provides a valuable way to identify high energy particles in a wide momentum range, through the relation between the particle velocity and the Cherenkov angle. However, since the Cherenkov angle depends only on material's permittivity, the material unavoidably sets a fundamental limit to the momentum coverage and sensitivity of Cherenkov detectors. For example, Ring Imaging Cherenkov detectors must employ materials transparent to the frequency of interest as well as possessing permittivities close to unity to identify particles in the multi GeV range, and thus are often limited to large gas chambers. It would be extremely important albeit challenging to lift this fundamental limit and control Cherenkov angles as preferred. Here we propose a new mechanism that uses constructive interference of resonance transition radiation from photonic crystals to generate both forward and backward Cherenkov radiation. This mechanism can control Cherenkov angles in a flexible way with high sensitivity to any desired range of velocities. Photonic crystals thus overcome the severe material limit for Cherenkov detectors, enabling the use of transparent materials with arbitrary values of permittivity, and provide a promising option suited for identification of particles at high energy with enhanced sensitivity.

Long-term time-dependent consolidation analysis by numerical modelling to determine subsidence effect area induced by longwall top coal caving method

Longwall top coal caving (LTCC) is one of the mining methods used in thick coal seams. Large subsidence occurs over the coal mines, where this method is utilised for production. The area affected by subsidence differs due to varying limit angles of the geological formations in the overburden. However, subsidence does not occur instantly, it is a phenomenon which progresses in time. It is especially important to perform time-dependent analyses of mines in the neighbourhood of residential areas, agricultural zones, or any kind of man-made structures. In this study, the long-term development of a subsidence due to production in an underground coal mine in Manisa-Soma-Eynez was examined using time-dependent numerical modelling technique. 750 days after the end of production, the effects of subsidence were examined in place, measurements were taken from the field and they were compared with the results of the time dependent numerical modelling analyses. [Received: November 15, 2014; Accepted: October 6, 2015]

Limit shaping formed sections on grading machines

A mathematical model of a smooth transition zone extent, which allows to determine the limit angles hem, to establish continuity technology and perform calculations when designing interstand distance nomenklatura-based grading equipment.

Dyakonov hybrid surface waves at the isotropic-biaxial media interface.

Dyakonov surface waves (DSWs) at the interface of an isotropic dielectric material and a biaxial dielectric crystal were considered in the case in which two principal axes of the biaxial crystal lie in the plane of the interface. Both x-cut and y-cut biaxial crystals were considered, and all permittivity scalars were assumed to be real and positive. A rather simple expression to relate the components of the wave vector of a DSW was derived, and analytical expressions for the limit angles at which the DSWs can propagate and the Poynting vector components of the DSWs were obtained. These expressions were numerically investigated for several biaxial materials. Different conditions for the relative permittivity scalars at which the DSWs can exist were identified. As an example, DSWs can exist not only for the positive, but also for the negative y-cut biaxial crystals.

Elastic Limits in Torsion of Reciprocating Nickel-Titanium Instruments

IntroductionReciprocating angle and torsional load at the superelastic limit were investigated for nickel-titanium (NiTi) instruments used with reciprocating movements. MethodsTwo reciprocating NiTi instruments (Reciproc R25 [VDW, Munich, Germany] and WaveOne Primary [Dentsply Maillefer, Ballaigues, Switzerland]) and ProTaper F2 (Dentsply Maillefer) were tested for 2 torsional conditions using a custom-designed testing device. Rotational angles were applied, and generated torque values were recorded. The first test condition fixed the files at 5 mm and repetitively rotated them with gradually increasing angles up to 250° (n = 10). The second test subjected the files to a single continuous rotation until fracture (n = 10). The superelastic limits of the instruments were determined from their torque-rotation curves. Statistical analysis was performed (Kruskal-Wallis) at a 95% significance level. The tested specimens were examined under a scanning electron microscope. ResultsIt was found that the angle at the superelastic limit was higher for R25 and Primary files than the ProTaper file (P < .05). Repetitive torsional loading with a gradually increasing rotational angle reduced the torsional resistance compared with the single rotation motion. At the 5-mm fixation level all files had superelastic limit angles higher than the 170° set in the dedicated reciprocating motor. The scanning electron microscopic analysis showed features of torsional failure. ConclusionsUnder the conditions of this study, the 170° set angle of dedicated motors for reciprocating file systems is safe at the 5-mm level. Reuse of reciprocating systems, even with the movements within the elastic limit, may cause deterioration of the instruments.

NEW INSIGHT INTO SHORT-WAVELENGTH SOLAR WIND FLUCTUATIONS FROM VLASOV THEORY

The nature of solar wind (SW) turbulence below the proton gyroscale is a topic that is being investigated extensively nowadays. Although recent observations gave evidence of the dominance of Kinetic Alfv\'en Waves (KAW) at sub-ion scales with $\omega<{\omega_{ci}}$, other studies suggest that the KAW mode cannot carry the turbulence cascade down to electron scales and that the whistler mode (i.e., $\omega>\omega_{ci}$) is more relevant. Here, we propose to study key properties of the short wavelength plasma modes under realistic SW conditions, typically $\beta_i\gtrsim \beta_e\sim 1$ and for high oblique angles of propagation $80^\circ\leq \Theta_{\bf kB}<90^\circ$ as observed from the Cluster data. The linear properties of the plasma modes under these conditions are poorly known, which contrasts with the well-documented cold plasma limit and/or moderate oblique angles of propagation ($\Theta_{\bf kB} <80^\circ$). Based on linear solutions of the Vlasov kinetic theory, we discuss the relevance of each plasma mode (fast, Bernstein, KAW, whistler) in carrying the energy cascade down to electron scales. We show, in particular, that the shear Alfv\'en mode extends at scales $k\rho_i\gtrsim1$ following either a whistler mode ($\omega>\omega_{ci}$) or a KAW mode (with $\omega<\omega_{ci}$) depending on the anisotropy $k_\parallel/ k_\perp$. This contrasts with the well-accepted idea that the whistler branch develops as a continuation at high frequencies of the fast magnetosonic mode. We show, furthermore, that the whistler branch is more damped than the KAW one, which makes the latter a more relevant candidate to carry the energy cascade down to electron scales. We discuss how these new findings may facilitate resolution of the controversy concerning the nature of the small scale turbulence, and we discuss the implications for present and future spacecraft wave measurements in the SW.

Determination of actual limit angles to the surface and their comparison with the empirical values in the Upper Silesian Basin (Czech Republic)

This study deals with the determination of the actual limit angles in the long-term formed subsidence basin in the Czech part of the Upper Silesian Basin (the remaining part lays in Poland). Here there was the most extensive underground exploitation of black coal in the north-east of the Czech Republic. A limit angle is absolutely decisive in the determination of deep mining influences in relation to the current and future utilisation of this territory. The two CSM and Paskov mine localities on the edge of the subsidence basin were selected for this study, since they could not have been affected by mining in neighbouring mines. On the grounds of the long-term levelling monitoring of points on the surface which started prior to mining, the horizontal distance between the mined out area and the undisturbed ground surface was identified. The impact of limit angle on the surface was calculated by means of the horizontal distance and the established mining depth. Such identified actual limit angles reached the values of 36° at the CSM Mine and 25° for the Paskov Mine. The calculated values are significantly lower when compared with the currently applied empirical values of 57° for the CSM Mine and 56° for the Paskov Mine. This means that the extent of the undermining effects is unambiguously wider by 611 m at the CSM Mine and by 883 m at the Paskov Mine. This study thus establishes the existence of a significantly vaster area influenced by coal deep mining than previously expected. The identified facts lead to the conclusion that regular revisions and follow-up updates of the empirically determined parameters are recommended.

Optimal Design of 6-UPU Parallel Mechanism

The methodology of the optimal design for the 6-UPU parallel mechanism (PM) is presented based on genetic algorithms. The optimal index which expressed by Jacobian matrix of the PM is first deduced. An optimal model is established, in which the kinematic dexterity of a parallel mechanism is considered as the objective function. The design space, the limiting length of the electric actuators and the limit angles of universal joints are taken as constraints. The real-encoding genetic algorithm is applied to the optimal design of a parallel mechanism, which is proved the validity and advantage for the optimal design of a similar mechanism.

Improved SPIF performance through dynamic local heating

The limited accuracy of the single point incremental forming process [J. Jeswiet, F. Micari, G. Hirt, A. Bramley, J. Duflou, J. Allwood, Asymmetric single point incremental forming of sheet metal, Annals of CIRP 54(2) (2005) 623–650] has been identified as its major deficiency [J.M. Allwood, G.F. King, J. Duflou, A structured search for applications of the Incremental Sheet Forming process by product segmentation, Proceedings of the Institute of Mechanical Engineers, Part B, Journal of Engineering Manufacture 219(2) (2005) 239–244]. Improving the process by introducing either fixed [J.R. Duflou, B. Lauwers, J. Verbert, F. Gelaude, Y. Tunckol, Medical application of single point incremental forming: cranial plate manufacturing, in: Proceedings of the VRAP 2006 Conference, Leiria, September 2006, pp. 161–166] or programmable support structures [J.M. Allwood, N.E. Houghton, K.P. Jackson, The design of an incremental sheet forming machine, in: Proceedings of the Shemet 2005 Conference, Erlangen, April 2005, pp. 471–478; H. Meier, O. Dewald, J. Zhang, incremental forming of sheet metal by two industrial robots, in: AMST’05 Advanced Manufacturing Systems and Technology 2005, vol. 486, Springer, Wien, New York, pp. 437–444], tends to reduce the flexibility of the process and increases the complexity of the control system. In the presented research, the authors have opted for an alternative approach in which the material properties are differentiated by localised temperature variations. In this way, different zones can be created in the sheet metal part being processed. By means of a dynamic heat, input in the direct vicinity of the stylus, a ductile area with low-yield strength is generated. By synchronising the movement of the heat source over the sheet metal surface with the stylus feed rate and direction, and by using appropriate cooling of the surrounding area, a temperature gradient can be assured between this area and the workpiece zone where no deformation is envisaged. Effects of such strategy are reduced forces on the stylus and, in consequence, a better localised deformation and thus a higher precision. Furthermore, higher forming limit angles have been demonstrated for materials with low strainability at room temperature. An experimental setup has been built to test this dynamic, local heating principle and is described in the paper. The effects on the process performance are demonstrated by means of experimental results.

Développement de guides chirurgicaux personnalisés, par prototypage, pour l’installation de vis pédiculaires

Spinal instrumentation surgeries frequently use pedicle screws to fix a corrective rod on the spine. Misplacement of a screw can lead to intra- and postoperative complications. The goal of this study is to develop personalized templates, using prototyping, to ensure accurate placement of the screw in a pedicle. From a CT-scan of a L3 non pathologic vertebra, a 3D model is reconstructed with a CAD software (Catia). Drilling direction and limit angles are computed from an inverse projection of the limits of the pedicle on transverse and sagittal planes. The first template design uses a surface-to-surface registration method and was constructed by subtracting the vertebra from a rectangular prism and a cylinder with the proper orientation. This template and the vertebra were built using rapid prototyping. The second design uses a point-to-surface (6 points) registration method and has an adjustable orientation support device. A mechanism was designed to hold it in place on the spinal process. A virtual prototype was build with Catia software, and a kinematic analysis was done to ensure that the guide does not interfere with the upper and lower vertebrae. During the operation, the surgeon put the template on patient’s vertebra until a perfect match is obtained before drilling. The second design seems better than the first one because it can be reused on different patients and is less sensitive to registration errors. The next step is to build the second design and make experimental and simulations tests to evaluate the benefits of this template during a real operation.

Angular distribution of incident sound energy for estimating the sound transmission loss of multilayered panels

The sound transmission coefficient in the diffuse field depends on the angular distribution of the incident sound energy. Although the field incidence formula has suggested that instead of the random incidence formula, the determination of the limit angle near the grazing incidence is very empirical and various limit angles have been defined by many researchers until now. This angle is especially important when dealing with the sound transmission loss of multilayered panel systems. In order to find the angular energy distribution of the incident sound in the actual test situation, a numerical simulation by using ray tracing is performed for the bounding surfaces of a sphere and a reverberation chamber. The results show that the sound energy distribution of the incidence angle on a bounding surface may be approximated to the Gaussian distribution. Sound transmission losses are predicted by utilizing the concept of the Gaussian distribution of the incidence energy for various single and multilayered panels and they agree very well with experimental results.

Influence of overburden mass behavioural properties on subsidence limit characteristics

An analytical calculation model for the angle of draw is introduced in this paper on the supposition that the roof is considered as an elastic beam. This model indicates the importance of the main factors which control the extent of subsidence produced on the surface, and also provides some appreciation of the influence of overburden strength on the angle of draw. A finite element model has been developed for application to subsidence-related rock mechanics problems. By the use of this model, the authors have investigated the effects rock mass behavioural properties on the limit angle, and also the effects of a distinct bed (strong or weak) in the overburden on the subsidence affected area at the surface. Relevant U.K. data from monitored sites for determining the three limit angles' variation with the dip of seam are discussed. The trend of the limit angle from the north of England to the Midland coalfields is also discussed in the paper. It has been found that the results from the data are in good agreement with numerical model results.