Preliminary Design Tool Research Articles

Simplified analytical solutions for seismic response on cross section of circular tunnel with composite linings

Simplified analytical solutions are very useful tools for the seismic preliminary design of tunnels and can quickly and easily give seismic responses to structures. This study presents simplified analytical solutions for the stress and deformation of circular composite-lined tunnels subjected to in-plane S-waves. Unlike previous solutions for single-lined tunnels, the proposed analytical solutions are suitable for tunnels with arbitrary numbers of linings. Moreover, tunnel linings are treated as multilayer thick-walled cylinders in the new solutions. Compared with thin shell or beam models used in previous analytical solutions, thick-walled cylinders provide more precise forecasts. In addition, the slippage effect at the lining-lining and ground-lining interface is considered by introducing a spring-type flexibility coefficient into the interaction force–displacement relationship. To verify the proposed analytical solutions, dynamic numerical examples are studied. The proposed solutions have good agreement with the dynamic numerical results and outperform previous analytical solutions. Finally, parameter studies are conducted to investigate the effect of the flexibility coefficient, degraded zone around the outermost lining and steel plate supporting the innermost lining on the seismically induced stresses and deformations. The proposed analytical solutions are applicable for approximately evaluating the seismic responses of circular tunnels with composite linings.

Multi-objective optimization of hybrid PEMFC/Li-ion battery propulsion systems for small and medium size ferries

Hybrid Polymer Electrolyte Membrane Fuel Cells/Lithium-ion battery powertrains are a promising solution for zero-local-emissions marine propulsion. The present study aims to optimize the design and operation of such hybrid powertrain for small-size passenger ferries, taking into account the performance degradation of both fuel cells and batteries. A Mixed-Integer Linear-Programming approach and a hierarchical method are adopted to concurrently minimize the fuel cells degradation, the capital expenditure and the operating expenditure, while constraints are included in the model to limit the battery degradation. The results show that the proposed multi-objective optimization can lead to a reduction of fuel cells degradation by up to 65% compared to a cost-minimization only. However, this can imply an increase in the battery capacity by up to 136%. The proposed method has general validity, and it is a useful tool for both preliminary design and choice of the optimal energy management strategy for ships energy systems.

Climatic Envelope as an Urban Planning Tool to Configure Urban Fabric of Guwahati City to Support Daylight and Natural Ventilation

Over the last decade, as a result of rapid urban growth and increasing human population, Guwahati city is witnessing multilayered transformation owing to socio-economic, geo-political and technological issues. This constant increase of built form is resulting haphazard urban growth pattern in down town city areas sacrificing the access to daylight and solar radiation inside residential buildings. Even though the development pattern of Guwahati is controlled by established GMDA building bye-laws; these building regulations and guidelines are unable to control the organic growth of the city since there is no climate-sensitive approach available in the existing GMDA bye-laws. This paper aims to discuss the likelihood of constructing a composite climatic envelope by using daylight spacing angle and solar elevation angle techniques within the residential zone of Guwahati city. This paper also analyses how climatic envelope technique helps to establish an efficient height-to-width (H/W) ratio in spatial arrangement of residential neighbourhood and ensures a higher levels of daylight factor (DF), permits solar access to the neighboring buildings and also enables better ventilation rate inside every rooms of residential buildings. This paper analyses further to discuss about the performance of natural ventilation inside building envelope and reviews the common energy code of openable window to floor area (WFRop) ratio in urban residential buildings. During this study, an existing urban spatial arrangement of residential neighbourhood under GMDA jurisdiction is studied, discussed and analysed. Results of this study, plotting H/W ratio against average daylight factor and ventilation rate can be used as a preliminary urban design tool to configure the urban fabric especially within the residential zone of GMDA area.

Active Power Filter Pre-Selection Tool to Enhance the Power Quality in Oil and Gas Platforms

This paper proposes a preliminary design tool for active power filters’ (APFs) solutions to be applied in offshore oil and gas platforms, where power quality indices are typically low, and reactive power compensation and current harmonic mitigation are often desired. The proposed approach considers that APF selection and rating is a trade-off between performance and size, and that both component and system aspects need to be optimized to achieve a well-tailored solution. As size and weight are critical constraints in offshore applications, possible benefits of using Silicon Carbide (SiC) switches for the APF implementation are investigated. Moreover, different compensation strategies are compared, varying the connection point of the APF between two different voltage levels and assigning the APFs different compensation goals. Improvements in power quality indices, as well as APFs rating, number of components, power losses, and filter size, have been considered for both SiC and Silicon-based solutions to identify the best trade-offs suitable for the considered, energy intensive industrial application.

Analysis, synthesis and modelling of air individual smart rescue system

The morphological approach is a successful analytical tool for development schematic, conceptual and preliminary design of new engineering systems in Aerospace. This investigation used a morphological approach to engineering solutions development as well as to tools for creating promising individual smart rescue system on conceptual design stage. The problem was solved in two stages. At a higher level of the hierarchy, the principle of action in morphological box was chosen. In the second phase, specific engineering solutions were explored. Analysis of engineering systems, solutions and solving technique and systems and their potential opportunities with technique provide correct guidelines to supply the reasonable decisions. Flight simulations, depending on different initial conditions, were performed using the LANE program.

Development of a Throughflow-Based Simulation Tool for Preliminary Compressor Design Considering Blade Geometry in Gas Turbine Engine

Gas turbine engines are highly intricate machines, and every component of them is closely associated with one another. In the traditional engine developing process, vast experiment tests are needed. To reduce unnecessary trials, a whole gas turbine engine simulation is extremely needed. For this purpose, a compressor simulation tool is now developed. Considering the inherent drawbacks of 0D analysis and 3D CFD (Computational Fluid Dynamics) calculation, the 2D throughflow method is an indispensable tool. Based on the circumferential average method (CAM), 3D Navier–Stokes is transformed into a 2D method. One phenomenon arising is that the lack of description about circumferential motion leads to the need for the blade force modeling in compressor simulation. Previous models are based on the assumption that flow passes through the average stream surface without entropy increasing, which is not applicable in the CAM. An improved model is proposed based on the result analysis from CAM and NUMECA method in a linear cascade. Whereafter, the model is applied in a highly loaded and low-speed fan, which has been tested for its performance characteristics. Utilizing the new model, the error of the adiabatic efficiency between CAM and experiment decreases from 4.0% to 1.0% and the accuracy of the mass flow, and pressure ratio remains unchanged. The time involved in the CAM simulation is nearly 70 times faster than that of the 3D simulation.

Analytic Model of Proprotor Forces and Moments at High Incidence

The paper presents an analytical model for estimation of proprotor aerodynamic loads at elevated incidence angles. Previous theories have concentrated on either small incidence angle for aircraft stability analysis or edge-wise flow for helicopter forward flight. This development attempted an engineering method that covers the full incidence angle range from 0 to π/2. Blade element theory was applied to known proprotor geometry, and off-axis loads including normal force and in-plane moment were obtained in closed form based on thrust and torque in axial condition. The model was found to be sufficiently accurate over a broader flight conditions compared to classical models, and computationally more efficient than numerical methods. Hence it could be easily used as a preliminary design and analysis tool for future convertible aircraft proprotors. The paper further discusses a dedicated wind tunnel campaign on proprotor off-axis load measurement. Experimental data from the test campaign was considered in model validation. The results suggested that the model was capable to accurately estimate proprotor performance in nominal flight regimes.

Guidance for footbridge design: a new simplified method for the accurate evaluation of the structural response in serviceability conditions

This paper proposes a simplified hand-calculation methodology that permits a fast response assessment (both in vertical and lateral direction) under different pedestrian scenarios. This simplified method has the same accuracy than that of very sophisticated numerical nonlinear finite element models including pedestrian inter-variability, interaction among pedestrians in flows, and pedestrian-structure interaction. The method can capture the effects of pedestrian loads in and out of resonance. This methodology is based on a new, and experimentally contrasted, stochastic pedestrian load model derived by the authors implementing a multi-disciplinary state-of-the-art research, and on a large set of sophisticated finite element analyses.There is a significant gap in the literature available for bridge designers. Some current codes do not indicate how the performance for serviceability limit-states should be assessed, in particular for lateral direction. Others define methods that are not based on the latest research in this field and that require the use of dynamic structural analysis software. A very sophisticated load model, such as that described above, and recently proposed by the authors, may not be accessible for most of the design offices, due to time and software constraints. However, an accurate assessment of the serviceability limit state of vibrations during the design stages is paramount. This paper aims to provide designers with an additional simple tool for both preliminary and detailed design for the most typical structural configurations.First, the paper presents the methodology, followed by an evaluation of the impact of its simplifications on the response appraisal. Second, the paper evaluates the validity of the methodology by comparing responses predicted by the method to those experimentally measured at real footbridges. Finally, the paper includes a parametric analysis defining the maximum accelerations expected from pedestrian streams crossing multiple footbridges. This parametric analysis considers different variables such as section type, structural material, span length and traffic-flow characteristics, and shows the sensitivity of the serviceability response to traffic-flow characteristics and span length in particular.

An integrated topology optimization framework for three‐dimensional domains using shell elements

SummaryIn the last decades, topology optimization has been widely investigated as a preliminary design tool to minimize the use of material in a structure. Despite this, applications to realistic three‐dimensional engineering problems are still limited. This study provides the instruments for the definition of a versatile and integrated framework in order to apply topology optimization to large‐scale 3‐D domains for the design of efficient and high‐performing structures. The paper proposes a novel topology optimization strategy to identify the optimal layout of lateral resisting systems for tall buildings through the adoption of Mindlin–Reissner shell elements for the discretization of the continuum design domain. The framework is based on the practical interoperability between MATLAB, Ansys, and computer‐aided design (CAD) environments to incorporate optimization routines in the conceptual design phase of structural systems. Finally, the paper examines a three‐dimensional tall building case study in order to demonstrate the applicability of the proposed procedure to realistic Civil Engineering design problems and its robustness in finding optimal layouts free from mesh‐dependency instabilities.

Morphological methods of searching for new engineering solutions and their use in Industry 4.0

The Innovation techniques as part Industry 4.0 is critical for competitive and economic for new systems and products and thus has been widely debated. This research suggests a morphological approach to innovations development as well as to tools for creating promising engineering solutions of conceptual design stage. The article presents the history of the development of morphological methods. These methods are as techniques for solving multidimensional, multicriterial and non-quantifiable problems under uncertainty conditions. The approach can be a successful analytical tool for development schematic, conceptual and preliminary design, decision making, design development, production management etc. The method is a conceptual tool that can be used to generate solutions space, systematization of knowledge, enhancement application opportunities and achieve the synergistic effects. Analysis of emerging technologies and systems and their potential opportunities with technique provide correct guidelines to supply the reasonable decisions with into account future risks.

A graph-based approach and an interactive tool for preliminary digital prototyping

Design process is usually based on past experiences and best practises which compose the company know-how. The challenge is to identify common patterns in the design solutions generated for different design problems. The present paper focuses on the identification of product patterns by using a graph-based approach. It deals with the designing of automotive gearboxes and with the development of an approach and a software tool aimed to support preliminary design and CAD modelling activities in gearbox designing. The approach is applied to two different architectures of manual transverse gearboxes characterized by two and three shafts. It aims at the identification of common design features through the detection of the directed graphs matching. A Matlab software tool for gearbox preliminary design is implemented according to the detected common features. The proposed approach and the developed software tool provide an effective way to keep and re-use company know-how, especially in the context of large automotive companies.

Semi-analytical model development for preliminary study of 3D woven Composite/Metallic flange bolted assemblies

This research deals with the development of a new semi-analytical model for composite-metal eccentric tensile bolted joints of casing structures. The model is based on a direct stiffness method considering structural elements, where flanges are modeled with axisymmetric shell elements, the bolt with a beam element and contact behavior with a specific number of compressive linear springs, identified by means of convergence tests. A hybrid element is added in order to set the link between flange and bolt. Since the model is intended for the preliminary design of bolted joints including composite materials, we propose an extension of the stiffness matrix formulation of isotropic axisymmetric shell elements to orthotropic ones. This formulation is validated with respect to a 2D FE axisymmetric model. Then, a semi-analytical model is established for a casing assembly approximately corresponding to a real casing of an aircraft engine. Design criteria such as normal stress on the bolt, bending moment and axial load at a specific section of the composite flange, given by the semi-analytical model are compared to a 3D FE computation. Results are in very good agreement and the semi-analytical model offers considerable time saving where the computation time was 120 times faster than the 3D FE model. Moreover, relative error does not exceed 2% for normal stress of the bolt and 9% for the flange bending moment which is satisfactory in a preliminary design approach. However, due to the formulation of hybrid element, less accurate results were observed for axial displacement of the composite flange and it would be advisable to consider a new formulation. This will be detailed in future work. Finally, a parametric study showed the ability of the semi-analytical model to predict the physical behavior of joints and proved its usability for running optimization studies and its reliability as a preliminary design tool.

Mean-Line Design of a Supercritical CO2 Micro Axial Turbine

Supercritical carbon dioxide (sCO2) power cycles are promising candidates for concentrated-solar power and waste-heat recovery applications, having advantages of compact turbomachinery and high cycle efficiencies at heat-source temperature in the range of 400 to 800 ∘C. However, for distributed-scale systems (0.1–1.0 MW) the choice of turbomachinery type is unclear. Radial turbines are known to be an effective machine for micro-scale applications. Alternatively, feasible single-stage axial turbine designs could be achieved allowing for better heat transfer control and improved bearing life. Thus, the aim of this study is to investigate the design of a single-stage 100 kW sCO2 axial turbine through the identification of optimal turbine design parameters from both mechanical and aerodynamic performance perspectives. For this purpose, a preliminary design tool has been developed and refined by accounting for passage losses using loss models that are widely used for the design of turbomachinery operating with fluids such as air or steam. The designs were assessed for a turbine that runs at inlet conditions of 923 K, 170 bar, expansion ratio of 3 and shaft speeds of 150k, 200k and 250k RPM respectively. It was found that feasible single-stage designs could be achieved if the turbine is designed with a high loading coefficient and low flow coefficient. Moreover, a turbine with the lowest degree of reaction, over a specified range from 0 to 0.5, was found to achieve the highest efficiency and highest inlet rotor angles.

Multidisciplinary mission and system design tool for a reusable electric propulsion space tug

According to the Global Exploration Roadmap, a Getaway in the lunar vicinity will enable the human exploration of the Moon, paving the way toward Mars and further in the deep space. A reusable transportation system, the Lunar Space Tug (LST), can be a key support transportation system to achieve a continuous and sustainable connection between the Earth and the orbital lunar outpost. Exploiting an electrical propulsion technology consisting in Hall Thrusters (HTs), this reusable space cargo system can maximize the delivered payload, with a lower propellant consumption with respect to a chemical-based platform. This significant improvement comes with two main throwbacks: a long transfer time between Earth and Moon and a complex multidisciplinary design of the overall LST. The first issue can be overcome with good mission planning in order to reduce the layover times and maximize the use of the LST. However, the peculiarities of the adopted propulsion technology shape the overall mass and power distribution of the space tug, as well as its transfer trajectory. The design complexity introduced by this subsystem can be effectively investigated if the mission analysis, trajectory generation and subsystem sizing are merged together in one software. In fact, the low-thrust transfer trajectories are highly affected by orbital perturbation and eclipse periods. At the same time, the high demand in power of the propulsion system puts constraints on the mass breakdown and power allocations of the LST, therefore on the reachable thrust level. The trajectory and subsystems sizing limitations call for a particular accurate mission analysis in order to succeed. Only combining all those elements, it is possible to define feasible design boundaries without performing countless simulations trying to optimize each element as a stand-alone part.Politecnico di Torino, in collaboration with the European Space Research and Technology Centre (ESTEC), developed a MatLab-based preliminary design tool for electric propulsion space tug missions, called MultidisciplinAry desiGN Electric Tug tOol (MAGNETO). Starting from the mission analysis of the lunar space tug, the tool building blocks and capabilities are presented. Moreover, the build-in trajectory module will be analysed in-depth. The potentiality of the trajectory generation tool in MAGNETO enables a refined design of the initial design envelope of the LST. For this reason, the improved results will be confronted with the previous LST design tool developed by Politecnico di Torino.

Analytical study on pretensioned bolt-cable combined support of large cross-section tunnel

To study the mechanical responses of large cross-section tunnel reinforced by pretensioned rock bolts and anchor cables, an analytical model is proposed. Considering the interaction between rock mass and bolt-cable support, the strain softening characteristic of rock mass, the elastic-plastic characteristic of bolt-cable support, and the delay effect of installation are considered in the model. To solve the different mechanical cases of tunneling reinforced by bolt-cable support, an analytical approach has been put forward to get the solutions of stress and displacement associated with tunneling. The proposed analytical model is verified by numerical simulation. Moreover, parametric analysis is performed to study the effects of pretension force, cross-section area, length, and supporting density of bolt-cable support on tunnel reinforcement, which can provide references for determining these parameters in tunnel design. Based on the analytical model, a new Ground Response Curve (GRC) considering the reinforcement of bolt-cable support is obtained, which shows the pretension forces and the timely installation are important in bolt-cable support. In addition, the proposed model is applied to the analysis of the Great Wall Station Tunnel, a high-speed railway tunnel with a super large cross-section, which shows that the analytical model of bolt-cable support was a useful tool for preliminary design of large cross-section tunnel.

Evaluation of optimal lateral resisting systems for tall buildings subject to horizontal loads

The tendency of modern designs towards optimal structures often leads to the lightest and best performing choice among a large set of design alternatives. In a similar scenario, the introduction of automated tools to further guide designers in achieving efficient solutions has been a recurrent topic for mechanical and structural engineers, over the past decades. Nowadays, topology optimization is considered a powerful preliminary design tool to determine the optimal material distribution in a design domain, i.e. the most effective configuration that satisfies a given set of prescribed constraints while reducing the consumption of structural material. Among different applications in the field of Civil Engineering, this work focuses on the definition of optimal layouts of lateral resisting systems for multi-storey steel building frameworks subject to lateral loads using topology optimization techniques. The objective of the research is to illustrate the benefits deriving from the introduction of automated routines within the preliminary design stage and establish reliable guidelines for performing accurate and objective optimization procedures. Since the optimal material distribution follows the load flow within the structure, optimal topologies are especially sensitive to the alteration of support and loading conditions: different loading scenarios naturally lead to distinct optimal layouts. In order to avoid the loss of objectivity and preserve the optimality of the results, the effects that preliminary modelling and loading assumptions produce on final layouts are investigated. Numerical applications to high-rise building models are presented and discussed.

Noise evaluation of battery powered small aircraft

Preliminary assessments of battery powered aircraft designs show potential for noise reduction. However, profound analyses estimating this noise reduction potential using white-sheet preliminary aircraft designs are missing so far. Additionally, an investigation on the sensitivity of crucial aircraft design parameters impacting both aircraft performance and noise emissions could be utilized to derive design recommendations for quieter battery powered aircraft without a considerable performance decrease. Feasible preliminary aircraft designs are derived using the multidisciplinary preliminary aircraft design and optimization tool MICADO. The derived preliminary aircraft designs are subsequently evaluated towards their noise emission. Because the propeller represents the dominant noise source, the noise evaluation is focused on the propeller as only source. The noise is evaluated at an observation point situated beneath the flight path on the ground 2500 m away from the brake-release point. Three different aircraft configurations are assessed employing one, two and four electric engines. Besides electric engines, a piston engine aircraft with one engine is assessed for proper baseline values. The design maximum propeller tip Mach number is varied for each configuration resulting in 22 different preliminary aircraft designs. Results substantiate that single electric engine aircraft compared to an analogous single engine piston aircraft, within the actual technology and in terms of propeller noise, produces a higher noise annoyance. Despite this result, important noise reduction potential for electric aircraft can be achieved. When increasing the number of electric engines from one to four, while reducing the design maximum propeller tip Mach number, a max OASPL reduction of 23.8 dBA can be observed for the given TLARs.

Flow and its distribution in wide meandering compound channels

A new stage discharge relationship is suggested for wide meandering streams (ratio of floodplain width and that of main channel in excess of 5.5 and up to 30) with overbank flow. The boundary shear data obtained from various data series with specified range of width ratio and channel sinuosity are analysed. By regression technique, new empirical relationships are derived between the channel dimensions and amount of shear generated for different flow conditions. These new boundary shear models are then used to obtain the stage discharge relation in channels with given roughness characteristics. The present method is then validated for its usefulness by applying the same to a number of data series of small scale and large scale flume experiments of other research projects from the literature. The errors (%) in discharge estimation are within limits for such methods as per practice (i.e. around ±10% for both smooth and rough meandering channels). The method is also compared with a number of other methods from the literature by application to different data series. The RMSE (root mean squared error) value for all the data series validated is estimated as 9.6% and the method is found to be ranked third among all the methods. The method is also able to predict satisfactorily the flow distribution in case of a number of homogeneously smooth and non homogeneously roughened meandering channels of varying sinuosity with overbank flow for large scale flume experimental data sets. The mean error for three available data series is estimated as −3.4% while the RMSE error is 10.68%. Due to its ease of application and simple approach, this 1D method may serve as a preliminary design tool for assessing stage discharge curve for wide two stage channels in field conditions for application in flood estimation and flood warning cum relief measures. Such a preliminary study might better decide the need for further refinement through any exhaustive deep study; the more robust and expensive 2D or 3D analysis.

Shortcut modeling of natural gas supersonic separation

Supersonic separation combines concepts from aerodynamics, thermodynamics, physical separation and fluid-dynamics resulting in an innovative gas conditioning process. It is used to condition the gas by removing condensable vapors and natural gas liquids. In the supersonic separation process, undesired components form liquid condensates, as a result of temperature drop, that are centrifugally removed through side collection streams. This article presents a shortcut one-dimensional numerical model that presents great potential as a fast and accurate tool that enables the simulation of supersonic separators. This model would best fit the category of preliminary conceptual design tools. The developed model is validated through several cases with air, 3-component natural gas and 13-component natural gas mixtures as working fluids at different conditions and nozzle area ratios. Tests included nozzles with and without side streams. Computational loads were decreased by reducing the number of locations tested in the diverging nozzle to locate the side streams and the shockwave. Simulation time and number of locations tested in the nozzle are reduced by 75%–97%. depending on the nozzle geometry and conditions.

On the acoustic response of a generic gas turbine fuel injector passage

A current trend in the design of modern aero engines is the transition towards leaner combustion as a solution to satisfy increasingly stringent emission regulations. Lean combustion systems are often more susceptible to thermoacoustic instability and the fuel injector can play a critical role. This paper presents an analytical study on the unsteady air flow through a generic injector passage in response to incident acoustic waves. The injector passage is represented by a simplified geometry which comprises the main geometrical passage features. The unsteady flow through the passage is obtained by combining the elemental solutions for different parts of the passage. This enables the transfer impedance of the injector passage to be determined and the effects of different design parameters on the sensitivity of the air flow to acoustic perturbations to be examined. The convective wave associated with the unsteady swirl vane wakes is also visited and compared with the results from the numerical simulations obtained in previous works. In addition to helping derive design practices for injector passages from the perspective of thermoacoustic instability, the current analysis can also be applied as a preliminary design tool to assess the acoustic characteristics for an injector passage of the axial swirler type.