Stress field around axisymmetric partially supported cavities in elastic continuum-analytical solutions

Lukic, D.,Prokic, A.,Anagnosti, P. Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.35 No.4

The present paper will be concerned to the investigation of the stress-strain field around the cavity that is loaded or partially loaded at the inner surface by the rotationally symmetric loading. The cavity of the spherical, cylindrical or elliptical shape is situated in a stressed elastic continuum, subjected to the gravitation field. As the contribution to the similar investigations, the paper introduces the new function of loading in the form of the infinite sine series. Besides, in this paper the solution of stresses around an oblong ellipsoid cavity, has been obtained using appropriate curvilinear elliptical coordinates. This analytical approach avoids the solutions of the same problem that lead to expressions that contain rather complex integrations. Thus the presented solutions provide the applicable and explicit expressions for stresses and strains developed in infinite series with easily determinable coefficients by the use of contemporary mathematical packages. The numerical examples are also included to confirm the convergence of the obtained solutions.

Stress state around cylindrical cavities in transversally isotropic rock mass

Lukic, Dragan C.,Prokic, Aleksandar D.,Brcic, Stanko V. Techno-Press 2014 Geomechanics & engineering Vol.6 No.3

The present paper is dealing with the investigation of the stress field around the infinitely long cylindrical cavity, of a circular cross section, contained in the transversally isotropic elastic continuum. Investigation is based upon the determination of the stress function that satisfies the biharmonic equation, for the given boundary conditions and for rotationaly symmetric loading. The solution of the partial differential equation of the problem is given in the form of infinite series of Bessel's functions. Determination of the stress-strain field around cavities is a common requirement for estimation of safety of underground rock excavations.

The possibilities for application of STEP-NC in actual production conditions

Dejan Lukic,Sasa Zivanovic,Jovan Vukman,Mijodrag Milosevic,Stevo Borojevic,Aco Antic 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.7

With the rapid advancement of internet technologies (IT) and computer numerical control (CNC) technologies, the production environment has significantly changed in the last two decades. The International Organization for Standardization (ISO) standard 6983 (Gcode), which is still being used as a link between computer aided design/computer aided process planning/computer aided manufacturing (CAD/CAPP/CAM) and CNC system, represents an obstacle for the full integration of design and manufacturing. The result of efforts to eliminate these obstacles and shortcomings of developed standards for data exchange and sharing is the development of (STEP-ISO 10303) standard, as well as its extension to numerical control STEP-NC. This paper shows the current possibility of implementing STEPNC in integration of computer aided technologies CAx and CNC systems in actual production conditions. Two scenarios represent a new approach to programming CNC machine tools using the STEP-NC protocol, which is explained in detail with IDEF0 diagrams, with defining necessary equipment and software. Implementation of the STEP-NC protocol described by the integration definition for function modeling (IDEF0) methodology was experimentally verified on specific examples for both scenarios, with the application of available CAD/CAM systems and the STEP-NC machine software, as well as appropriate virtual and physical CNC machine tools.

Stress field around axisymmetric partially supported cavities in elastic continuum-analytical solutions

D. Lukic,A. Prokic,P. Anagnosti 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.35 No.4

The present paper will be concerned to the investigation of the stress-strain field around the cavity that is loaded or partially loaded at the inner surface by the rotationally symmetric loading. The cavity of the spherical, cylindrical or elliptical shape is situated in a stressed elastic continuum, subjected to the gravitation field. As the contribution to the similar investigations, the paper introduces the new function of loading in the form of the infinite sine series. Besides, in this paper the solution of stresses around an oblong ellipsoid cavity, has been obtained using appropriate curvilinear elliptical coordinates. This analytical approach avoids the solutions of the same problem that lead to expressions that contain rather complex integrations. Thus the presented solutions provide the applicable and explicit expressions for stresses and strains developed in infinite series with easily determinable coefficients by the use of contemporary mathematical packages. The numerical examples are also included to confirm the convergence of the obtained solutions.

Permanent disposal of Cs ions in the form of dense pollucite ceramics having low thermal expansion coefficient

Omerasevic, Mia,Lukic, Miodrag,Savic-Bisercic, Marjetka,Savic, Andrija,Matovic, Ljiljana,Bascarevic, Zvezdana,Bucevac, Dusan Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.1

A promising method for removal of Cs ions from water and their incorporation into stable crystal structure ready for safe and permanent disposal was described. Cs-exchanged X zeolite was hot-pressed at temperature ranging from 800 to 950 ℃ to fabricate dense pollucite ceramics. It was found that the application of external pressure reduced the pollucite formation temperature. The effect of sintering temperature on density, phase composition and mechanical properties was investigated. The highest density of 92.5 %TD and the highest compressive strength of 79 MPa were measured in pollucite hot-pressed at 950 ℃ for 3 h. Heterogeneity of samples obtained at 950 ℃ was determined using scanning electron microscopy. The pollucite hot-pressed at 950 ℃ had low linear thermal expansion coefficient of ~4.67 × 10^-6 K^-1 in the temperature range from 100 to 1000 ℃.

A Novel Linearization Method of Sin/Cos Sensor Signals Used for Angular Position Determination

Zivanovi, Dragan,Lukic, Jelena,Denic, Dragan The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.4

In this paper a novel method for angular position determination using sensors with sin/cos output and without an excitation signal, is presented. The linearization of the sensor transfer characteristic and digitalization of the measurement results are performed simultaneously with a goal to increase the measurement resolution. This improvement is particularly important for low angular velocities, and can be used to increase the resolution of incremental Hall, magnetic and optical sensors. This method includes two phases of sin/cos signal linearization. In the first linearization phase the pseudo-linear signal is generated. The second linearization phase, executed by the two-stage piecewise linear ADC, is an additional linearization of the pseudo-linear signal. Based on the LabVIEW software simulations of the proposed method, the contribution of each processing phase to a final measurement error is examined. After the proposed method is applied within $2{\pi}$ [rad] range, the maximal nonlinearity is reduced from 0.3307 [rad] ($18.9447^{\circ}$) to $3{\cdot}10^{-4}$ [rad] ($0.0172^{\circ}$).

Automatic analysis of thin-walled laminated composite sections

A. Prokic,D. Lukic,Dj. Ladjinovic 국제구조공학회 2014 Steel and Composite Structures, An International J Vol.16 No.3

In this paper a computer program is developed for the determination of geometrical and material properties of composite thin-walled beams with arbitrary open cross-section and any arbitrary laminate stacking sequence. Theory of thin-walled composite beams is based on assumptions consistent with the Vlasov's beam theory and classical lamination theory. The program is written in Fortran 77. Some numerical examples are given, with complete information about input and output.

Restart Strategy for Scalar Controlled Synchronous Reluctance Machine Driving a High-Inertia Load with a Single DC-link Current Sensor

Kibok Lee,Srdjan M. Lukic 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

This paper proposes an approach for implementing the restart for Synchronous Reluctance Machines (SynRMs) driving a high inertia load. The proposed method uses a simple identification algorithm to estimate the rotor speed and position of the machine so that the appropriate voltage vector can be applied to the machine, thus minimizing the inrush current at the instant of the restart. The novelty is that its implementation only requires nameplate machine parameters and a single DC-link current sensor. The proposed method is suitable for implementation with both high-inertia vector and scalar-controlled SynRMs.

Application of Fuzzy Logic in the Analysis of Surface Roughness of Thin-Walled Aluminum Parts

Jovan Vukman,Dejan Lukic,Stevo Borojevic,Dragan Rodic,Mijodrag Milosevic 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.1

This paper presents the development and application of fuzzy logic in the milling of thin-walled parts for the purpose of analyzing surface roughness. Surface roughness is an important performance indicator of finished components. Depending on conditions such as feed ratio and wall thickness, different machining strategies can be applied. The objective was to analyze and determine the influence of the machining conditions on surface roughness. The model for analyzing and determining surface roughness of the aluminum alloy AL 7075 was trained (design rules) and compared by using the experimental data. The average deviation of the compared data for surface roughness was 12.3%. The effect of the feed ratio, wall thickness and machining strategy as well as their interactions in machining are thoroughly analyzed and presented in this study.

Tuberculosis and other opportunistic infections in tofacitinib-treated patients with rheumatoid arthritis

Winthrop, K L,Park, S-H,Gul, A,Cardiel, M H,Gomez-Reino, J J,Tanaka, Y,Kwok, K,Lukic, T,Mortensen, E,Ponce de Leon, D,Riese, R,Valdez, H BMJ Publishing Group 2016 Annals of the Rheumatic Diseases Vol.75 No.6

<P><B>Objectives</B></P><P>To evaluate the risk of opportunistic infections (OIs) in patients with rheumatoid arthritis (RA) treated with tofacitinib.</P><P><B>Methods</B></P><P>Phase II, III and long-term extension clinical trial data (April 2013 data-cut) from the tofacitinib RA programme were reviewed. OIs defined a priori included mycobacterial and fungal infections, multidermatomal herpes zoster and other viral infections associated with immunosuppression. For OIs, we calculated crude incidence rates (IRs; per 100 patient-years (95% CI)); for tuberculosis (TB) specifically, we calculated rates stratified by patient enrolment region according to background TB IR (per 100 patient-years): low (≤0.01), medium (>0.01 to ≤0.05) and high (>0.05).</P><P><B>Results</B></P><P>We identified 60 OIs among 5671 subjects; all occurred among tofacitinib-treated patients. TB (crude IR 0.21, 95% CI of (0.14 to 0.30)) was the most common OI (n=26); median time between drug start and diagnosis was 64 weeks (range 15–161 weeks). Twenty-one cases (81%) occurred in countries with high background TB IR, and the rate varied with regional background TB IR: low 0.02 (0.003 to 0.15), medium 0.08 (0.03 to 0.21) and high 0.75 (0.49 to 1.15). In Phase III studies, 263 patients diagnosed with latent TB infection were treated with isoniazid and tofacitinib concurrently; none developed TB. For OIs other than TB, 34 events were reported (crude IR 0.25 (95% CI 0.18 to 0.36)).</P><P><B>Conclusions</B></P><P>Within the global tofacitinib RA development programme, TB was the most common OI reported but was rare in regions of low and medium TB incidence. Patients who screen positive for latent TB can be treated with isoniazid during tofacitinib therapy.</P>