Publication7

Although durability tests present a different testing challenge compared to the traditional test methods for concrete, the fabrication apparatus and their operation is simple once the mechanisms involved in the tests are properly understood. There can be good cost advantages in making the test set-ups locally. Furthermore, as these test methods involve a number of components. Fabricating the test set-ups locally will give enough flexibility for introducing new modifications. Once a few laboratories get familiar with the design and use of such set-ups, sufficient data can be generated for a number of types of concrete, which would go a long way in establishing appropriate levels of the durability indicators for use in performance specifications.

This paper deals with the resolution of nesting algorithm, known as the irregular packing problem. It focuses on the geometric layer of the nesting algorithm, namely on the implementation of a semi-discrete representation of irregular geometric shapes and on the use of this representation in a nesting algorithm, proposed in previous publications. The proposed geometric scheme combines the features of discrete representation scheme and analytical concepts to quickly represent the geometry of part/sheet in digital form. The uniqueness of the proposed representation scheme lies in representing a part/sheet, of simple to complex geometry, with a series of equidistant vertical lines. These vertical lines not only aid in detecting collision among the parts easily but also assist in effective placement of parts on the sheet with bottom-left placement heuristic. With a view to enhance the speed of nesting, a scheme called Quick Void Skip is proposed to quickly identify the vacant regions on the sheet. For faster and effective nesting of a variety of parts on any geometry of sheet, the distance between the vertical lines, representing the part/sheet geometry, is adaptively chosen. Finally, the effectiveness of the proposed scheme is demonstrated by comparing its performance with that achieved by a semi-discrete approach, proposed in a previous study. © 2013 Copyright Taylor and Francis Group, LLC.

This paper experimentally investigates the far-field turbulent mixing noise from underexpanded triangular and square jets. The investigations are focused on the noise from vertices and edges of these non-circular jets, and in some cases the results are compared with those of circular jets. The jet pressure ratio is varied in the range of 2 to 6, and the acoustic measurements are carried out along the jet axial plane from 37° to 135° (measured from jet exit axis). The experimental results indicate that turbulent mixing noise levels vary linearly with emission angle, notably with two different gradient values along upstream and downstream. These results are ascribed to the two different turbulent scales, viz.; large scales and fine scales, in the jet flow. The turbulent mixing noise from screeching circular jets are found to be higher compared to triangular and square jets. However at higher pressure ratios, as the screech ceases, the turbulent mixing noise from all the jets (circular and other non-circular jets) becomes similar. © S. Hirzel Verlag.

This article proposes a distribution static compensator (DSTATCOM) with interface LCL (inductor-capacitor-inductor) filter for load compensation in threephase four-wire distribution system. DSTATCOM, consisting of voltage source inverter (VSI), is connected in parallel to the load and injects currents corresponding to load reactive, harmonic powers. But this injected current consists of unnecessary high-frequency switching ripple generated by VSI. This LCL filter has superior switching ripple attenuation capability compared to L filter. Moreover, this can be achieved with small value of overall LCL filter inductance than L filter. Thus providing high slew rate for output current to track the desired reference current closely, reducing voltage drop across it, as well as cost and size of filter. However, one major concern with LCL filter is its resonating frequency (determined from its L, C, L values), which can create high-resonance oscillating currents and results in improper load compensation. Therefore, in this study, proper design of LCL filter with high switching ripple attenuation and a current controller with proportional integral (PI) plus harmonic compensation (HC) regulators along with active damping feature of LCL filter in synchronous rotating reference (dq0) frame are presented. HC regulator minimizes the steady-state error in the non-sinusoidal filter currents (fundamental and harmonic) which are tracked by the VSI. Active damping feature (obtained by capacitor current feedback control of LCL filter) is used to overcome resonance oscillations and provides proper control, operation of DSTATCOM under steadystate and dynamic load conditions. Stability studies for designed LCL filter and current controller using Bode and root locus plots are also performed and presented. Extensive simulation study, to understand the compensation performance of LCL filter DSTATCOM with two types of current controllers (PI and PI plus HC) under steady-state and dynamic load conditions, is carried out in PSCAD simulator and the corresponding results along with THDs of various parameters are presented.

Dynamics of magnetic moments near the Mott metal-insulator transition is investigated by a combined slave-rotor and dynamical mean-field theory solution of the Hubbard model with additional fully frustrated random Heisenberg couplings. In the paramagnetic Mott state, the spinon decomposition allows to generate a Sachdev-Ye spin liquid in place of the collection of independent local moments that typically occurs in the absence of magnetic correlations. Cooling down into the spin liquid phase, the onset of deviations from pure Curie behavior in the spin susceptibility is found to be correlated to the temperature scale at which the Mott transition lines experience a marked bending. We also demonstrate a weakening of the effective exchange energy upon approaching the Mott boundary from the Heisenberg limit, due to quantum fluctuations associated to zero and doubly occupied sites. © Copyright EPLA, 2013.