Method For Preliminary Design Research Articles

A New Practical Approach to the Design of Industrial Axial Fans: Tube-Axial Fans With Very Low Hub-to-Tip Ratio

This paper presents a simple but complete design method to obtain arbitrary vortex design tube-axial fans starting from fixed size and rotational speed. The method couples the preliminary design method previously suggested by the authors with an original revised version of well-known blade design methods taken from the literature. The aim of this work is to verify the effectiveness of the method in obtaining high-efficiency industrial fans. To this end, the method has been applied to a 315 mm rotor-only tube-axial fan having the same size and rotational speed, and a slightly higher flow rate coefficient, as another prototype previously designed by the authors, which was demonstrated experimentally to noticeably increase the pressure coefficient of an actual 560 mm industrial fan. In contrast, no constraints are imposed on the hub-to-tip ratio and pressure coefficient. The new design features a hub-to-tip ratio equal to 0.28 and radially stacked blades with aerodynamic load distribution corresponding to a roughly constant swirl at rotor exit. The ISO-5801 experimental tests showed fan efficiency equal to 0.68, which is 6% higher than that of the previous prototype. The pressure coefficient is lower, but still 12% higher than that of the benchmark 560 mm industrial fan.

Technical considerations on the Takoradi–Cairo air route of the Second World War

This paper describes an initiative of the British War Cabinet to procure thousands of aircraft to Egypt during the crucial, central years of the Second World War. The aircraft were sent crated by cargo ships to Takoradi, in the Gold Coast (current Ghana), assembled at an on-purpose facility there, and flown over Nigeria, Chad, Sudan, and Egypt to the Nile Delta, where appropriate Maintenance Units would deliver them later to fighting squadrons. More than 5000 airplanes were dispatched in this way from British harbors, arriving into the Cairo area just a few weeks later. Most aircraft flown in this trans-African route were fighters, which required fully loaded external drop tanks to cover the longest stages, commonly against prevailing trade winds. The convoys were typically formed by a light bomber, as lead aircraft, and six to eight fighters. The aerodynamic characteristics of the fighters have been modelled with first level preliminary airplane design methods, to reconstruct its performances in the route. The results, in terms of range and cruise speed, agree very well with scarce data available from literature.

Sectional strength design of concrete-infilled double steel corrugated-plate walls with T-section

This paper presents the sectional strength design method of concrete-infilled double steel corrugated-plate walls with T-section (T-CDSCWs). The T-CDSCW is composed of flange and web wall elements and concrete-filled steel tubes, where the former are formed by bolt-connected steel corrugated-plates and infilled concrete while the latter behave as vertical boundary elements. Load bearing capacities of T-CDSCWs are significantly improved by the favorable combination effect between bolt-connected steel corrugated-plates and infilled concrete in the wall elements. The failure mechanism and the sectional strength design of T-CDSCWs under combined axial compression and bending moment are focused analytically, experimentally and numerically, with an assumption of no consideration of overall instability of T-CDSCWs and local buckling of the steel corrugated-plates in the wall elements. An experiment of the T-CDSCW for sectional strength prediction was carried out, and a refined finite element (FE) model of the T-CDSCW was validated by the experimental results. Based on the FE model, parametric analyses of T-CDSCWs are performed to further investigate the effects of steel ratio and sectional geometry on the load-bearing capacities. It is found that T-CDSCWs under axial compression have completely different values of load-bearing capacities when they incorporate different bending direction moments. Based on experimental and numerical results, design formulas for predicting the sectional strength of T-CDSCWs under axial compression and bending moments are proposed, providing a preliminary structural design method of T-CDSCWs.

Methods for conceptual and preliminary seismic design of buildings with steel structure

Throughout the last two decades, seismic design standards evolved to ever more comprehensive and detailed prescriptions, stressing out the need for design methods that deal with earthquake effects not as actions, but as a design philosophy. The Eurocode 8 adoption as national law throughout the European Union countries and informally in many parts of Africa, Asia and Latin America is the pretext for the current study. It aims to provide some guidance to the seismic design of steel structures as well as to the Eurocode 8 implementation by the designers.Some lines on the preliminary design of structural systems were written based on several real cases of structures designed taking into account the seismic action. Such a content is, usually, relevant in any design guide, given its value in enhancing the design technical and economical content. However, it is now of utter significance at the current context as an essential tool to facilitate the safety checking of several code requirements.Some of the Eurocode 8 prescriptions are then decoded, explained and justified based on the supportive bibliography. The information is subsequently ordered as a design guide, where some procedures are proposed to cope with the code interrelated prescriptions and one structural solution is proposed in order to overcome a design challenge while complying with the code.One last but not less relevant addressed issue is the fact that some Eurocode 8 prescriptions may be reviewed, in the eyes of a designer, given its practical outcome. Such issues are identified, explained and some slight code adjustments are suggested.

Numerical Loss Investigation of a Small Scale, Low Specific Speed Supercritical CO2 Radial Inflow Turbine

Radial inflow turbines, characterized by a low specific speed, are a candidate architecture for the supercritical CO2 Brayton cycle at small scale, i.e., less than 5 MW. Prior cycle studies have identified the importance of turbine efficiency to cycle performance; hence, well-designed turbines are key in realizing this new cycle. With operation at high Reynolds numbers, and small scales, the relative importance of loss mechanisms in supercritical CO2 turbines is not known. This paper presents a numerical loss investigation of a 300 kW low specific speed radial inflow turbine operating on supercritical CO2. A combination of steady-state and transient calculations is used to determine the source of loss within the turbine stage. Losses are compared with preliminary design approaches, and geometric variations to address high loss regions of stator and rotor are trialed. Analysis shows stage losses to be dominated by endwall viscous losses in the stator. These losses are more significant than predicted using gas turbine derived preliminary design methods. A reduction in stator–rotor interspace and modification of the blade profile showed a significant improvement in stage efficiency. An investigation into rotor blading shows favorable performance gains through the inclusion of splitter blades. Through these, and other modifications, a stage efficiency of 81% is possible, with an improvement of 7.5 points over the baseline design.

Design and numerical simulation of a clamshell-shaped inlet cover for air-breathing hypersonic vehicles

An efficient clamshell-shaped inlet cover configuration based on a shockwave interference methodology is proposed, which has the advantage of an autonomous opening using the aerodynamic force and moment. A preliminary design method for the inlet cover is introduced and used to produce cover models of two different lengths, with contributions similar to those of cowlings, rocket fairings, shrouds, or false ogives. The clamshell-shaped inlet cover features a practical design with a wide range of applications, including utilization in air-breathing hypersonic vehicles under specific constraints. In this investigation, aerodynamic numerical simulations were conducted to evaluate the extent to which the objectives and design principles are achieved for two typical ballistic separation states. The results show that both configurations can prevent an excessive accumulation of shockwaves in the nose cone area. In addition, the inlet cover generates negative lift, which results in the generation of an opening moment. The calculated heat flux at the leading edge of the clamshell-shaped inlet cover is approximately 13 MW/m2, which is within the limit of the composite material but slightly higher than that of the stagnation point of the nose cone.

Laced steel–concrete composite sandwich system in flexure: Experiments, analysis and design

Steel–concrete sandwich composite system consists of steel skin and concrete core. The aim of this paper is to present methods for analysis and preliminary design of a recently developed new class of sandwich composite system laced steel–concrete composite for flexural loads. In laced steel–concrete composite system, continuous lacings are used in place of discrete shear connectors which are generally welded to the skin of the composite. Specimen laced steel–concrete composite systems were subjected to laboratory-controlled experimental investigations. Subsequently, three analytical methods are formulated for evaluating the moment–curvature relation of laced steel–concrete composite system. All the methods exploit the prismatic nature of the laced steel–concrete composite system to derive the moment–curvature relation and employ virtual work principle to evaluate the deflection of the laced steel–concrete composite system. In the first method, the stress–strain relationship of the steel and concrete in tension and compression is utilized to analyse the cross-section of laced steel–concrete composite system. In the second method, fibre-based analysis is used to obtain the response of laced steel–concrete composite system. The third method is based on equivalent transformed section in which the tensile stress–strain behaviour of concrete is represented by an equivalent area under tension. The methods are validated by comparing the predicted values with those of the two- and multi-point loading experiments carried out on laced steel–concrete composite beam and one-way laced steel–concrete composite slab, respectively. All the three methods are found to satisfactorily predict the response of laced steel–concrete composite system. A limited parametric study is carried out by using these analytical methods to identify the role played by the lip and web of the cover plates, tensile strength of concrete and confinement of concrete on the structural response of the laced steel–concrete composite system. In the end, guidelines and charts which can be used for preliminary design of laced steel–concrete composite system for flexure loads are presented.

Influence of masonry infill walls on fire-induced collapse mechanisms of steel frames

This paper numerically investigates the influence of masonry infill walls on collapse mechanisms of steel frames under fire scenarios. Three six-story by five-bay steel frames were designed in this study. One of these frames had no infill walls, another one had horizontal infill walls, and the last one had vertical infill walls. Load redistribution and fire resistance were investigated under edge bay fire scenario and central bay fire scenario. The numerical results indicated that masonry infill walls provide alternate load paths in fire conditions, causing significantly large variations of axial forces in surrounding columns. Furthermore, the lateral resistance of the infilled frames is provided by the integral loading resisting system under edge bay fire scenario. The infill walls decrease the buckling temperature and increase the collapse temperature of the heated columns. A series of parametric analyses were performed to investigate the factors influencing the fire resistance of the steel frames. Finally, a preliminary design method was proposed with an aim to prevent the collapse of steel frames with infill walls under fire scenarios.

Preliminary design of centrifugal compressor using multidisciplinary optimization method

Centrifugal compressor is widely used in turbochargers in which the aerodynamic performance and strength are invariable among the important design objectives. As high pressure ratio centrifugal compressor develops, the interaction between multiple disciplines should be involved in the preliminary design process. A strength prediction method was presented and the prediction error was less than 3% compared with the 3D finite element calculation. The preliminary design method was established with consideration of multidisciplinary couplings. Then, a centrifugal compressor with the lowest pressure ratio of 4.4 was designed based on the method. The optimal results showed that the aerodynamic efficiency increases by 2.245% compared with the initial design results. Finally, the 3D validation was carried out including aerodynamic analysis and strength calculation, which showed good agreement with the optimal results of the preliminary design.

Optimal design for hybrid renewable energy system using particle swarm optimization

This paper proposes the Particle Swarm Optimization (PSO) to minimize the Hybrid Renewable Energy System (HRES) Cost of Energy (COE) on different sizing between wind turbines and solar PV modules subjecting to a particular investment constraint. The wind speed and solar irradiation data from a particular site are used to determine the annual energy production (AEP) following the HRES configuration. While the turbine power curve converts the wind speed range to wind power, solar power generation model transforms solar radiation incident on PV modules. The investment cost of the solar PV system is interpolated from a commercial supplier data. However, the wind turbine cost is derived from the turbine component cost model of the National Renewable Energy Laboratory (NREL) and discounted to the present value using the inflation rate. Once a wind turbine and PV modules are configured as HRES, the COE as the objective function would be determined. The minimum COE from this study at 0.1204 $/kWh is in the 95th percentile of the global renewable power generation cost database from IRENA ranging between 0.06 – 0.22 $/kWh for solar energy and 0.04 – 0.10 $/kWh for wind energy but higher than the average value because of the low potential on both solar radiation and wind speed data from the particular site. However, PSO as the preliminary design method could be determined the optimal HRES with minimized COE when compare with the conventional design.

Surrogate model of complex non-linear data for preliminary nacelle design

Most response surface methods typically work on isotropically sampled data to predict a single variable and fitted with the aim of minimizing overall error. This study develops a metamodel for application in preliminary design of aircraft engine nacelles which is fitted to full-factorial data on two of the eight independent variables, and a Latin hypercube sampling on the other six. The specific set of accuracy requirements for the key nacelle aerodynamic performance metrics demand faithful reproduction of parts of the data to allow accurate prediction of gradients of the dependent variable, but permit less accuracy on other parts. The model is used to predict not just the independent variable but also its derivatives, and the Mach number, an independent variable, at which a certain condition is met. A simple Gaussian process model is shown to be unsuitable for this task. The new response surface method meets the requirements by normalizing the input data to exploit self-similarities in the data. It then decomposes the input data to interpolate orthogonal aerodynamic properties of nacelles independently of each other, and uses a set of filters and transformations to focus accuracy on predictions at relevant operating conditions. The new method meets all the requirements and presents a marked improvement over published preliminary nacelle design methods.

Preliminary Design Method for Dense-Gas Supersonic Axial Turbine Stages

A fast preliminary design methodology for supersonic organic Rankine cycle (ORC) stator and rotor axial turbine blades with low degree of reaction is presented. First, the stator and rotor blade mean-line profiles are designed by using the two-dimensional (2D) method of characteristics (MOC), extended to gases governed by general equations of state (EOS). We focus more specifically on working fluids with medium to high molecular complexity, operating at thermodynamic conditions such that the fundamental derivative of gas dynamics Γ is lower than one in a significant portion of the flow field. For rotor blades, MOC is combined with a free-vortex method to achieve a smooth deflection of the supersonic incoming flow. A numerical approach is developed for solving the unique incidence problem in the case of gases governed by general EOS. Both stator and rotor blade geometries designed according to the inviscid MOC model are subsequently corrected to account for the development of viscous boundary layers by solving the compressible integral boundary layer equations extended to dense gases. The resulting blade designs are assessed by means of computational fluid dynamics (CFD) simulations based on a high-order finite volume solver equipped with advanced thermodynamic and transport-property models. Properly accounting for dense gas and viscous effects at an early design stage is found to improve the expected performance of ORC turbine rows significantly and delivers valuable baseline profiles for any further optimization.

A Simple Mathematical Method for Optimal Preliminary Design of Tall Buildings with Peak Lateral Deflection Constraint

The classic methods of structural design based on trial-and-error are generally highly iterative and computationally intensive, especially in a tall building consisting of thousands of structural members. This paper presents a closed-form solution for a minimum weight design problem which may be used at the early-stage design of a high-rise and slender structure. Before considering the weight-based problem, an intervening optimization formulation is introduced in advance which for a fixed amount of material presents an optimal pattern for its distribution. The obtained pattern is then used in the main problem, in which the total weight is considered as the objective function while satisfying the peak lateral deflection constraint and some practical requirements. The flexural stiffness in its general form is selected here as the design variable, so the proposed method is not restricted to a particular system, and any structural system may be addressed. A braced-tube 61-storey building example is presented to be designed based on the proposed technique to illustrate the effectiveness and practicality of the method.

Wave Rotor Design Method With Three Steps Including Experimental Validation

This paper adapted and extended the preliminary two-step wave rotor design method with another step of experimental validation so that it became a self-validating wave rotor design method with three steps. First, the analytic design based on unsteady pressure wave models was elucidated and adapted to a design function. It was quick and convenient for a first prediction of the wave rotor. Second, the computational fluid dynamics (CFD) simulation was adapted so that it helped to adjust the first prediction. It provided detailed information of the wave rotor inner flow. Thirdly, an experimental method was proposed to complement the validation of the wave rotor design. This experimental method realized tracing the pressure waves and the flows in the wave rotor with measurement on pressure and temperature distributions. The critical point of the experiment is that the essential flow characteristics in the rotor were reflected by the measurements in the static ports. In all, the three steps compensated for each other in a global design procedure, and formed an applicable design method for generic cases.

Cantilever beam analogy for modal analysis of rocking core-moment frames

Unlike conventional seismic resisting systems, rocking core-moment frame (RCMF) combinations as low-damage assemblies are being developed to mitigate, or even eliminate structural damage and residual deformations following a severe earthquake. Despite extensive studies on the performance of specific rocking cores, dynamic characteristics and strength demands of a generic RCMF have not been addressed. By utilizing cantilever beam analogy, the current article proposes a modal analysis method to formulate RCMF demands. The proposed model and obtained analytical charts provide a manual method for rapid study and preliminary design of low- to mid-rise RCMFs with relatively uniform properties over the height. An extensive parametric study investigates the effects of rocking core base-fixity and frame-to-core stiffness on demand values. An independent computer analysis verifies the validity and accuracy of the proposed formulas. Findings show significant higher-mode effects in several RCMF combinations.

Multi-criteria decision-making methods for preliminary design of sustainable facades

The current design and construction trends toward sustainable development have led to increased attention on designing high performance building structures, especially emphasizing reductions in energy consumption and CO2 emissions. Facades have the potential to drastically affect building energy performance and the comfort level of occupants; therefore, more attention and effort needs to be given to their design than at present. However, the involvement of various interdisciplinary professionals and the need for satisfying different design criteria makes the design process considerably complicated. This complexity is related to the required integration and provision for balance between all necessary functions of a façade system, which can be conflicting with each other. Consequently, most designers still tend to use conventional design methods that lack consideration of all required criteria. Multi-Criteria Decision Making (MCDM) analysis is a useful tool to assist designers with this integration, by generating the best solutions for achieving conflicting and multiple objectives. MCDM methods have been extensively used in management and optimization fields; however, their application to building technology, especially in façade design, is relatively recent. Currently there are many MCDM methods available, each with related benefits and drawbacks. Nevertheless, not all MCDM methods are appropriate for providing solutions to the façade design problem. This paper reviews and compares the most common MCDM methods for façade design. Accordingly, the most efficient methods for sustainable façade design are introduced and used in a decision-making process to examine their efficiency in façade design.

Dynamic maneuver loads calculations for a sailplane and comparison with flight test

This work presents the results of dynamic maneuver simulations of a sailplane and the comparison with flight test data. The goal of the effort is to extend and validate an in-house toolbox used for loads analysis of free-flying flexible aircraft in the time domain. The underlying aerodynamic theories are the steady vortex lattice and the doublet lattice method with a rational function approximation for the unsteady simulations in the time domain. The structural model comprises a beam model to represent the stiffness properties and a lumped mass model, both are developed using preliminary design methods. Steady aeroelastic trim simulations are performed and used as initial condition for the time simulation of the unsteady maneuvers in which the pilot’s commands, which were recorded during flight test, are prescribed at the control surfaces. Two vertical maneuvers with elevator excitation, two rolling maneuvers with aileron excitation and three aileron sweeps are simulated. The validation focuses on the comparison of interesting quantities such as section loads, structural accelerations and the rigid body motion. Good agreement between simulation and flight test data is demonstrated for all three kinds of maneuvers, confirming the quality of the models developed by the preliminary design methods.

A New Approach for Centrifugal Impeller Preliminary Design and Aerothermal Analysis

This paper introduces a new approach for the preliminary design and aerothermal analysis of centrifugal impellers using a relative diffusion effectiveness parameter. The relative diffusion effectiveness is defined as the ratio of the achieved diffusion to the maximum available diffusion in an impeller. It represents the quality of the relative diffusion process in an impeller. This parameter is used to evaluate impeller performance by correlating the relative diffusion effectiveness with the impeller isentropic efficiency using the experimental data acquired on a single-stage centrifugal compressor (SSCC). By including slip, which is appropriate considering it is an inviscid effect that should be included in the determination of maximum available diffusion in the impeller, a linear correlation between impeller efficiency and relative diffusion effectiveness resulted for all operating conditions. Additionally, a new method for impeller preliminary design was introduced using the relative diffusion effectiveness parameter, in which the optimal design is selected to maximize relative diffusion effectiveness. While traditional preliminary design methods are based on empirical loss models or empirical knowledge for selection of diffusion factor (DF) in the impeller, the new method does not require any such models, and it also provides an analytical approach for the selection of DF that gives optimal impeller performance. Validation of the method was performed using three classic impeller designs available in the open literature, and very good agreement was achieved. Furthermore, a sensitivity study shows that the method is robust in that the resulting flow angles at the impeller inlet and exit are insensitive to a wide range of blockage factors and various slip models.

Drag Reduction by Laminar Flow Control

The Energy System Transition in Aviation research project of the Aeronautics Research Center Niedersachsen (NFL) searches for potentially game-changing technologies to reduce the carbon footprint of aviation by promoting and enabling new propulsion and drag reduction technologies. The greatest potential for aerodynamic drag reduction is seen in laminar flow control by boundary layer suction. While most of the research so far has been on partial laminarization by application of Natural Laminar Flow (NLF) and Hybrid Laminar Flow Control (HLFC) to wings, complete laminarization of wings, tails and fuselages promises much higher gains. The potential drag reduction and suction requirements, including the necessary compressor power, are calculated on component level using a flow solver with viscid/inviscid coupling and a 3D Reynolds-Averaged Navier-Stokes (RANS) solver. The effect on total aircraft drag is estimated for a state-of-the-art mid-range aircraft configuration using preliminary aircraft design methods, showing that total cruise drag can be halved compared to today’s turbulent aircraft.

A Local Design Method for Pile Foundations

The work at hand attempts to propose a local pile design method based on pile load test results for a reference site. Such LPDM is simply based on the identification of three dimensionless quantities, such as the capacity ratio CR, the stiffness ratio SR, and the group settlement ratio Rs. To prove the LPDM reliability, experimental data collected during years in the Neapolitan area (Italy) have been used to obtain the abovementioned coefficients. Then, LPDM has been applied, as a preliminary design method, to three well‐documented case histories applying capacity and settlement‐based design (CBD and SBD) approaches. The satisfactory agreement between the geometry in the original design of piles and the one obtained by applying the LPDM proves that the proposed methodology may be very helpful for preliminary design, allowing for reasonable accuracy while requiring few hand calculations.