Comparison Between the Effects of Zero and Non-Zero Flow Acceleration on the Entropy Wave Decay: An Experimental Study

Entropy wave, as the convecting hot spot, is one of the sources of combustion instabilities, which is less explored through the literature. Convecting in a highly turbulent flow of a combustor, entropy waves may experience some levels of dissipation and deformation. In spite of some earlier investigations in the zero acceleration flow, the extent of the wave decay has not been clear yet. Further, there exist no results upon the wave decay in non-zero accelerated flows. This is of crucial importance, as the wave passes through the end nozzle of the combustor or gas turbine stages. The current experiment, therefore, compares the wave decay in both flow of constant and variable bulk velocity, meaning, respectively, a uniform pipe and a convergent nozzle. The comparison will aid the theoretical models to reduce complexity by simplifying the relations of non-zero acceleration flow to those of no acceleration, as followed by the earlier effective-length method. Reynolds number and inlet turbulence intensity are considered as the governing hydrodynamic parameters for both investigated flows. The entropy wave is generated by an electrical heater module and detected using fast-response thermocouples. The results show that the entropy wave variation is point-wise and frequency-dependent. The accelerated flow of the nozzle is generally found to be more dissipative in comparison with the zero acceleration flow.

STUDI PERBANDINGAN STRESS RATIO PADA PORTAL BAJA MENGGUNAKAN BRACING DENGAN EFFECTIVE LENGTH METHOD (ELM) DAN DIRECT ANALISYS METHOD (DAM)

In the design of high and low-rise buildings, structural systems should consider the requirements of strength, stifness, and stability. The addition of bracing affects the stiffness of the structure of the building. In SNI 03-1729-2002 there is an Effective Length Method (ELM) method which only recommends first-order analysis with amplification factor. However, currently there is a new structural design regulation that is SNI 1729: 2015 which refers to the American Institute of Steel Contruction (AISC 2010) where the steel structure stability planning has taken into account the second-order effect directly. This study aims to compare the application of Direct Analysis Method (DAM) and Effective Length Method (ELM) on 2D simple structure, where the comparison of both methods is focused on stress ratio value, which aims to determine more effective and efficient method in designing of braced steel frame structure. The difference values of stress ratio obtained in this study varies from 0.1 to 8.9%, where the value of DAM stress ratio is smaller than ELM. Comparison between the two methods shows that DAM is a more effective method and results in higher profile capacity than ELM.

CONSIDERATIONS ON THE DIFFUSE SEISMICITY ASSUMPTION

Second-order effects were historically included by the effective length method (K concept). All the studies about that methodology have been developed in frame plane, with regular rectangular frames. The new way to include those effects is the use of second-order analysis, direct analysis method or alternative simplified options. This methodology was included in ANSI AISC360 in the 2005 version and in the 2010 version. As before, the studies already developed for DAM analysis are in plane. In this paper, the K concept is revisited by numerical analysis, and extended to the 3D space. Using models of symmetric and non-symmetric industrial steel structures in plane, 3D stability analyses were developed, and the results were compared with plane behavior. Several conclusions and recommendations were exposed, resulting from the analyzed models. Keywords: Second-order analyses, steel structures, irregular 3D frames.

The Overall Stability Calculation Method for Sway Frame

There are three levels in stability calculating for sway frame. The first level is the traditional effective length method. The second level is the effective length method considering interaction of columns in one story and the third level is the effective length method considering inter-story interaction. The traditional effective length method may lead to unsafe design. Using the concept of equivalent negative stiffness, story stiffness to negative stiffness ratio factor and story support factor were proposed. Through the story stiffness to negative stiffness ratio factor, the weak-story and the inter-story support relationship can be found. Then, a formula for calculating the elastic stability capacity of sway frame is proposed, by which the inter-column interaction and inter-story interaction can be considered, and the finite element buckling analysis for stability capacity can be avoided. Through the stability capacity, the column effective length can be calculated. The results show that this simple calculation method has good precision and accuracy, can be used for engineering design and theoretical calculations.

STABILITY AND SIMULATION-BASED DESIGN OF STEEL SCAFFOLDING WITHOUT USING THE EFFECTIVE LENGTH METHOD

A robust computer procedure for the reliable design of scaffolding systems is proposed. The design of scaffolding is not detailed in design codes and considered by many researchers and engineers as intractable. The proposed method is based on the classical stability function, which performs excellently in highly nonlinear problems. The method is employed to predict the ultimate design load capacities of four tested 3-storey steel scaffolding units, and for the design of a 30 m×20 m×1.3 m 3-dimensional scaffolding system. As the approach is based on the rigorous second-order analysis allowing for the P-δ and P-Δ effects and for notional disturbance forces, no assumption of effective length is required. It is superior to the conventional second-order analysis of plotting only the bending moment diagram with allowance for P-Δ effect since it considers both P-Δ and P-δ effects such that section capacity check is adequate for strength and stability checking. The proposed method can be applied to large deflection and stability analysis and design of practical scaffolding systems in place of the conventional and unreliable effective length method which carries the disadvantages of uncertain assumption of effective length factor (L e /L).

Effective lengths of laterally continuous, laterally unsupported steel beams

Laterally unsupported steel beams of sufficient length may fail by elastic or inelastic lateral–torsional buckling. The fundamental equations governing elastic lateral–torsional buckling, taking into account such parameters as the shape of the bending moment diagram, the level of application of the load, and the effect of end restraints to lateral movement and to twist, are reviewed. Provisions in the current CSA Standard CAN3-S16.1-M84 are discussed. The methods currently available for dealing with the interactive lateral–torsional buckling of laterally continuous beams are evaluated statistically. Two new methods for considering this interaction, called the iterated effective length method and the equivalent beam method, are presented. A statistical evaluation of these methods shows that they are in reasonable agreement with available test data. Resistance factors for use in limit-states design are developed for the existing methods discussed as well as for the new methods. Key words: beam, bending moment, buckling, effective lengths, elastic, inelastic, lateral–torsional buckling, laterally continuous, steel.