Reliable Design Model Research Articles

Strength of Loop Connections between Precast Bridge Decks Loaded in Combined Tension and Bending

The paper presents a study of the load-carrying capacity of loop connections subjected to combined tension and bending. For such connections, the main design challenge in practice is to obtain a load- carrying capacity that is governed by yielding of the looped reinforcing bars (i.e., the U-bars) and not by fracture of the joint concrete. Unfortunately, reliable design models serving this purpose have not yet been published. Therefore, in this paper, a design-oriented plasticity model is proposed for the calculation of the N–M interaction diagram accounting for both failure modes. The work is an extension of a model previously developed by the authors for the case of pure tension. In addition to the theoretical work, test results of connections subjected to combined tension and bending are also presented. Calculations according to the model have been compared with tests. Satisfactory agreements have been found.

Data and design models for military turbo-propeller aircraft

This article presents a comparative and analytic review of present fixed-wing military aircraft equipped with turboprops. The database includes several aircraft types ranging from the training/light attack role to strategic transport. Data concerning masses, wing and tail surfaces, propellers and engines, as well as aerodynamic data and performance figures of 43 military aircraft in current inventories is analysed. The data is compared to conceptual and preliminary design models that are commonly available in the literature for turbo-propeller aircraft. Models from different sources are used concurrently. Departures from those models reveal that purpose built design models for civilian aircraft are not applicable to military aircraft without amendment; while models specifically issued for military turbo-propellers often rely on outdated data. New model coefficients, or new model laws are proposed whenever necessary so that current trends are adequately translated into reliable design models for future military aircraft.

Standardised double-shear test for determining bond of FRP to concrete and corresponding model development

Bond stress – slip characteristics play a major role in the behaviour of EBR FRP strengthened RC beams. These characteristics are normally determined by using experimental data from small-scale bond tests. However, the research community is yet to agree on a unified experimental set-up and testing procedure for these tests. The lack of standard tests leads to high variability in published results and hinders the development of reliable design models. The testing programme presented herein was part of an international Round Robin Test (iRRT) exercise, aimed at assessing the suitability of double shear tests to characterise the bond behaviour of FRP strengthening systems. A total of 20 tests were performed on different FRP plates. Recommendations on how to improve the iRRT methodology are given. Based on the results, an improved capacity model that accounts for concrete surface preparation is proposed and validated against an extensive database of published results. The outcome of the current research is expected to provide engineers with more confidence in designing safely strengthening applications whilst making the best use of the FRP materials.

Alpha Reliable Network Design Problem

Uncertainties are unavoidable in engineering applications. A new model is proposed for designing networks under uncertainty of future demands. The objective is to minimize the total travel time budget required to satisfy the total travel time reliability constraint while considering the route choice behavior of network users. The model adopts the value-at-risk risk measure instead of the utility function to model planner risk preferences. It allows the planners to specify their risk preferences by using a confidence level of alpha on the total travel time reliability. This alpha reliable network design model is formulated as a stochastic bilevel optimization problem. The upper-level subprogram is a variant of the chance-constrained model that minimizes the total travel time budget subject to a chance constraint with a user-specified confidence level, a budget constraint, and design variable constraints; the lower-level subprogram is a user-equilibrium problem under demand uncertainty. A simulation-based genetic algorithm procedure is developed to solve this complex network design problem (NDP). Two numerical examples are presented to illustrate the features of the proposed NDP model.

Conventional and Complex Knitted Mesh Mist Eliminators

Knitted wire mesh mist eliminators have a widespread application in many industrial plants as they assure an optimum cost/performance for many applications compared with other separation devices. Complex mesh pads allow the performance and the range of applications of conventional wire mesh pads to be extended. In recent years, increasing research effort has been dedicated to the experimental investigation of both common and complex mesh pads and to the development of reliable design models that are essential for the design and optimization of complex separation units.

Ozone mass transfer in water treatment: hydrodynamics and mass transfer modeling of ozone bubble columns

Most of the mathematical models that are employed to model the performance of bubble columns are based on the assumption that either plug flow or complete mixing conditions prevail in the liquid phase. Although due to the liquid-phase axial dispersion, the actual flow pattern in bubble columns is usually closer to being mixed flow rather than plug flow, but still not completely mixed flow. Therefore, the back flow cell model (BFCM), that hypothesises both back flow and exchange flow to characterise the liquid-phase axial dispersion, is presented as an alternative approach to describe the hydrodynamics and mass transfer of ozone bubble columns. BFCM is easy to formulate and solve. It is an accurate and reliable design model. Transient BFCM consists of NBFCM ordinary-first-order differential equations in which NBFCM unknowns (Yj) are to be determined. That set of equations was solved numerically as NBFCM linear algebraic equations. Steady-state BFCM consists of 3 × NBFCM non-linear algebraic equations in which 3 × NBFCM unknowns (qG,j, Xj, and Yj) are to be determined. Those non-linear algebraic equations were solved numerically using Newton–Raphson technique. Steady-state BFCM was initially tested using the pilot-scale experimental data of Zhou. BFCM provided excellent predictions of the dissolved ozone profiles under different operating conditions for both counter and co-current flow modes.

Designing Ozone Bubble Columns: A Spreadsheet Approach to Axial Dispersion Model

When designing ozone bubble columns, two major sources of uncertainties usually exist: (1) the measurement techniques and the estimation methods of the various operating parameters; and (2) the application of the pertinent design model. This paper presents a simple and easy-to-use, yet accurate and reliable design model for describing the performance of ozone bubble columns for water and wastewater treatment applications. This mode! is a modified non-isobaric steady-sate one-phase axial dispersion model (1P-ADM). The 1P-ADM is different from the complete axial dispersion model, or referred to as the two-phase axial dispersion model (2P-ADM), in its simple use for practical design and process control of full-scale contacting chambers. The 2P-ADM is represented by a system of two non-linear partial differential equations. In order to solve that system of equations, an elaborate numerical solving technique is needed. On the other hand, die 1P-ADM is composed of a single non-homogeneous linear second-order ordinary differential equation representing the liquid phase. Yet, this liquid-phase differential equation accounts for the countering effects of die gas bubbles' shrinkage and expansion caused by gas depletion and absorption and reduced liquid hydrostatic head. The differential equation was solved analytically by the method of variation of parameters. Expressing the 1P-ADM in terms of dimensionless operating parameters and with the available analytical solution of the differential equation, the model predictions of the dissolved and the gaseous ozone profiles along the column height were examined using a simple spreadsheet approach. Therefore, describing mat analytical solution in terms of a simple spreadsheet program facilitated obtaining the model predictions for any operating conditions represented by the model parameters entered into die spreadsheet program. Consequently, using die 1P-ADM for process design and/or on-line process control becomes very feasible. The 1P-ADM was initially tested to evaluate its predictions of the dissolved ozone profiles for water treatment conditions. The model provided excellent predictions of the dissolved ozone profiles along the bubble column for die counter-current and the co-current flow modes.

Computational fluid dynamics modelling of vertical pneumatic conveying dryers

At present, there are no fully reliable design models for pneumatic conveying dryers. SPS have carried out experiments to find particle velocities, heat transfer and drying rates in a vertical unit, and have developed a model based on stepwise integration up the tube. Results were promising, but drying rates were underpredicted near the feed point. Computational fluid dynamics (CFD) techniques, using the FLOW3D program, were employed to model the feed point region. Particle trajectories, gas velocities and temperatures were calculated. A large dead zone near the feed point was revealed and the hold-up in this was estimated. The model predicted two previously unexplained experimental observations; higher than expected particle velocities up to 0.5 m above the feed point, and ‘dipping’ of solids entering the drying tube. A wide range of further applications for CFD techniques can be envisaged.

Ozone disinfection of primary effluent using a stirred tank reactor

A pilot-scale stirred tank reactor was used to evaluate the efficiency of ozone for disinfecting primary effluent. Total and fecal coliform numbers before and after disinfection were evaluated concomitant with several common wastewater characteristics. A disinfection model was built using the method of linear least squares. The model enables the designer to choose the transferred ozone dose to achieve a given number of indicator bacteria in the effluent when the BOD5 is known. The model was found to be useful for the primary effluent studied but should not be used in other applications without pilot plant investigations. Examination of similar models reported in the literature suggests that weak wastewaters (COD < 25 mg/L) may be described by a regression model using COD and transferred ozone as variables but extrapolation to moderate and strong wastewaters, as was done in this study, introduced gross errors. Further research into the fundamental kinetics of ozone disinfection of wastewater is necessary before a reliable design model is available. Key words: ozone, disinfection, primary eflluent, model, coliforms.