Determination of the bilinear stress-crack opening curve for normal- and high-strength concrete

An improved version of the method proposed to ACI committee 446 and to RILEM TC 187-SOC to determine the fracture parameters of concrete is applied in this study to several mixtures of normal and high-strength concretes. The results are processed with a C++ program developed by the authors to automatise the mathematical operations required to obtain the bilinear softening curve of concrete from the experimental results. Numerical simulations of the tests are also carried out using finite elements with an embedded cohesive crack. The comparison between numerical and experimental results confirms that the experimental and numerical procedures are appropiate for normalstrength concretes and high-strength concretes

Oil Rig Trainees’ Perspectives on the Influence of Drilling Simulation on Their Learning and Motivation

Low enrollment levels in vocational drilling training programs in the Arabian Gulf area have resulted in a talent gap, with little success in building and retaining national crews. With current simulation technology, it is believed that trainees\u27 learning, motivation, and achievements will increase; however, further study is needed to determine if these conclusions hold. The purpose of this basic qualitative study was to explore how using simulation technologies influences trainees\u27 learning, motivation, and perspectives about completing their education at an oil-field drilling rig’s vocational training facility. Davis’s technology acceptance model concerning user reception of information systems formed the conceptual framework. Semi structured virtual interviews were conducted with 10 purposely sampled drilling crew trainees. Data were transcribed, and manual descriptive coding was used to identify five themes that addressed the research questions. The first three themes reflected the ease and usefulness of teaching drilling application skills using the simulator technology. The other two themes applied to how using the drilling simulator motivated the trainees and made them eager to complete their studies. The study’s findings showed that drilling simulators are an effective teaching tool, creating an easy-to-operate, hands-on-the-job training environment and increasing overall competencies. Results from the study could inform drilling contractor training facilities’ leaders about the importance of increasing drilling simulation practices covering all possible drilling job activities. The use of drilling simulations could promote positive social change at the trainee level, the country’s drilling rig workforce level, and the regional level through better learning and understanding of drilling processes

POLYNOMIAL STATIC OUTPUT FEEDBACK H ∞ CONTROL FOR CONTINUOUS-TIME LINEAR SYSTEMS VIA DESCRIPTOR APPROACH

International audienceThis paper deals with the problem of the robust static output feedback H ∞ control (SOFC) for continuous linear systems with polytopic uncertainties. The controller has been gotten by the use of descriptor redundancy. Under this approach a sufficient condition is provided for the existence of a solution to the problem. Thus, the advantage of this method is to obtain more free matrices in the design condition, also the polynomial approach helps to have a less conservative result. In the end, the performance of the method is shown by several examples

On The Effects of Roughness Parameters on Turbulent Boundary Layer Flows

Turbulent boundary layers (TBLs) are a well-known phenomenon in fluid dynamics and are observed in various transport, such as ships and aeroplanes. The majority of wall-bounded flows in engineering applications possess a rough surface, such as the growth of bio-fouling on ship hulls or surface erosion of wind turbine blades. The existence of surface roughness significantly influences the boundary layer flow and affects the heat and momentum transfer. The increase in drag caused by roughness leads to greater fuel consumption and emissions in transportation. Therefore, comprehending the impact of roughness on boundary layer flows is vital for enhancing energy efficiency and decreasing environmental impact across multiple industries. One of the principal objectives of rough wall fluid dynamics research is to determine the drag penalty of surfaces exclusively based on their topographical characteristics. Nevertheless, there is no consensus regarding the most important length scale or roughness parameter that accurately describes a surface in relation to friction drag, and several studies have attempted to identify it. This study investigates the impact of various two-dimensional (2D) and three-dimensional (3D) roughness geometries on turbulence statistics and drag coefficient (Cf ) in a zero pressure gradient (ZPG) turbulent boundary layer (TBL), using single hotwire anemometry (HWA). The research involves the use of three types of 2D roughness elements, namely circular rods, 3D printed triangular ribs, and computerised numerical control (CNC) machined sinewave surfaces with different heights and streamwise spacings. Additionally, three types of 3D sinewave rough- ness are examined, including isotropic 3D sinewave surfaces with equal streamwise and spanwise wavelengths, anisotropic 3D sinewave surfaces with different streamwise and spanwise wave- lengths, and isotropic 3D sinewave surfaces with different roughness skewness values (positive, negative, and zero). The turbulence statistics and drag coefficient are evaluated to determine the effects of the various 2D and 3D roughness geometries in the ZPG-TBL flows. In the fully rough regime, the friction Reynolds number (Reτ ) no longer affects Cf . Compared to smooth wall profiles, all types of roughness cause a downward shift in the wall- unit normalised streamwise mean velocity profile. When the roughness height and streamwise spacing are the same, 2D roughness has higher Cf and roughness functions (∆U +) than 3D roughness. This is due to the larger blockage area imposed by 2D roughness, which forces the fluid to flow over the roughness elements. Conversely, the fluid can flow around and above the roughness elements of 3D roughness. As TBL develops from a transitionally to a fully rough regime, the inner peak of turbulence intensity profiles for 2D surface roughness gradually reduces with increasing Reynolds number. However, the inner peak disappears entirely in the fully rough regime, and the profiles only exhibit an outer peak, located at a wall-normal location of approx- imately y δ ≈ 0.06 where δ represents the boundary layer thickness. These findings suggest that Townsend’s similarity hypothesis for 2D surface roughness is relatively well approximated in the outer region of the flow, as evidenced by the collapse of velocity defect, turbulence intensity, skewness, and flatness distributions when scaled with δ, The streamwise spacing to height ratio (s k) has a greater impact on ∆U + and C than the spanwise spacing to height ratio (sz k) for 3D sinewave roughness. However, sz k substantially affects streamwise turbulence intensities in the log and outer layer. Surfaces with positive roughness skewness (ksk) exhibit higher drag, resulting in a more significant downward shift compared with zero and negative roughness skewness. Cf decreases as ksk decreases. The increase in the percentage of Cf and ∆U + is significantly higher when moving from negative to zero roughness skewness than when moving from zero to positive roughness skewness. The shape factor (H) was identified as a suitable scaling parameter for improving the data collapse of the diagnostic plot for both 2D and 3D roughness. Numerous studies have been conducted to determine the most significant surface pa- rameter in wall-bounded turbulence. The concept of equivalent sand-grain roughness (ks) was introduced by Nikuradse (1933) to standardise different types of roughness and serve as an in- put parameter for predictions of ∆U +. A chronological compilation of roughness correlations is presented, providing details on the parameter ranges and types of roughness used during their development. The research findings indicate that in the fully rough regime, for 2D roughness, the roughness skewness ksk and the streamwise effective slope ESx are significant parameters that influence the drag coefficient Cf . These parameters have been incorporated into a new expression for ks that is normalised with the maximum peak to valley roughness height (kt). Similarly, for 3D roughness in the fully rough regime, a correlation has been developed based on ksk and ESx to predict ks normalised with the root mean square roughness height kq . Despite the fact that this correlation is restricted to 3D surface roughness, which is a more realistic representation, the model demonstrated a high level of accuracy in predicting ks for over 120 distinct rough surfaces, with a coefficient of determination (R2) of 0.96, The R2 value, is a statistical measure that represents the proportion of the variance in the dependent variable that is explained by the independent variable(s) in a regression model. It is a measure of how well the regression line fits the data.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Mechanical Engineering, 202

Robust H∞ Filters for Uncertain Systems with Finite Frequency Specifications

International audienceThis paper deals with H∞ filtering problem of linear discrete-time uncertain systems with finite frequency input signals. The uncertain parameters are supposed to reside in a polytope. By applying the generalized Kalman–Yakubovich–Popov lemma, polynomially parameter-dependentLyapunov function and some key matrices to eliminate the product terms between the filter parameters and the Lyapunov matrices, an improved condition isobtained for analyzing the H∞performance of the filtering error system. Then sufficient condition in terms of linear matrix inequality is established for designing filters with a guaranteed H∞ filtering performance level. Finally, a numerical examples are used to demonstrate the effectiveness of the proposed method

A Numerical study of masonry cracks Part II

Brick walls of ceramic without any mortar covering or paint are used extensively in building façades in Spain. One of the most used masonry wall system is based on non-bearing panels partially supported, about two thirds of the brick width, over the edge beams of the structural skeleton. The edge beam is veneered with special thinner bricks to achieve the visual continuity of the façade. A considerable number of these walls show cracking. In a previous work, finite element simulations were performed in order to gain insight on the causes of cracking. A special finite element, based on the strong discontinuity analysis and the cohesive crack theory is used in the numerical simulations. The results agree with the overall cracking patterns observed but if an imposed displacement is applied in the range allowed by the standards, extensive cracking occurs. This implies that the design displacements are not the actual ones. In this work, an elastic study using the principle of superposition is used to determine the effective deflections under service loading. Then these deflections are applied to the structure and the evolution of cracking is studied. This study shows that the masonry panels of the first and last store have the major probability of cracking. Another parametric study is carried out changing the elastic and tensile properties of the masonry. This study shows that although the cracking of the masonry panels starts at different loads for different tensile properties, the crack patterns are similar for a given panel geometry and loading. This numerical study provides a method of design to determine the crack width for different geometries, loadings and fracture properties. - Las paredes de ladrillo visto de cerámica se utilizan extensivamente en fachadas de edificios en España. Uno de los sistemas más usados de edificación se basa en los paneles apoyados parcialmente, cerca de dos tercios de la anchura del ladrillo, sobre las vigas del borde del esqueleto de la estructural. Las vigas del borde se cubren con ladrillos de tamaño especial para alcanzar la continuidad visual de la fachada. Un número considerable de estas paredes demuestra agrietamiento. En un trabajo anterior, se realizaron simulaciones con elementos finitos para estudiar los problemas de agrietamiento de las fachadas de ladrillo visto. Un elemento finito especial, basado en el análisis de la discontinuidad fuerte y la teoría de la fisura cohesiva se utiliza en las simulaciones numéricas. Los resultados coinciden en general con los patrones de agrietamiento observados, pero si se aplica un desplazamiento impuesto con los valores máximos que permiten las normas, aparecen muchas grietas. Esto implica que los desplazamientos de calculo no son los reales. En este trabajo, se utiliza un estudio elástico basado en el principio de la superposición para determinar las flechas eficaces bajo la carga máxima de servicio. Luego, estas flechas se aplican a las vigas de cada panel por separado y se estudia la evolución del agrietamiento. Este estudio demuestra que los paneles de ladrillo del primero y el ultimo pisos tienen la probabilidad mas alta de agrietarse. Se realiza otro estudio paramétrico cambiando las características elásticas y la resistencia a tracción. Este estudio demuestra que aunque el agrietamiento de los paneles comienza a distintas cargas al cambiar las características de los paneles, los patrones de agrietamiento son similares para una geometría y tipo de carga dados. Este estudio numérico proporciona un método de diseño para controlar la anchura de la grieta para las diversas geometrías, cargas y características de fractura

The Role Of Leadership Styles On Staffs Job Satisfaction In Public Organizations

 Job satisfaction is a very important factor among the employees of Public Universities. Job satisfaction is considered an internal principle created by various elements found within a work environment. Due to the influence of various items on job satisfaction, educational organizations should be conscious of implementing the right leadership styles. However, the lack of attention given to this organizational behavior has led to the rise of abnormal reactions among employees. Thus, the current paper focused on the essential role of leadership styles in improving job satisfaction among the employees of Public Universities. Substantial attention should be dedicated to the precise leadership style practiced in an organization. In the same way, specific leadership styles, as external factors, have an important impact on the job satisfaction of employees at Public Universities, because these styles can improve the employees' commitment to the organizations. This initiative involves enhancing satisfaction among employees and finding an effective leadership style, which is one of the main components of improving educational organizations