Preliminary Design Stage Research Articles

A Revision of Empirical Models of Stirling Engine Performance Using Simple Artificial Neural Networks

Stirling engines are currently of interest due to their adaptability to a wide range of energy sources. Since simple tools are needed to guide the sizing of prototypes in preliminary studies, this paper proposes two groups of simple models to estimate the maximum power in Stirling engines with a kinematic drive mechanism. The models are based on regression or ANN techniques, using data from 34 engines over a wide range of operating conditions. To facilitate the generalisation and interpretation of results, all models are expressed by dimensionless variables. The first group models use three input variables and 23 data points for correlation construction or training purposes, while another 66 data points are used for testing. Models in the second group use eight inputs and 18 data points for correlation construction or training, while another 36 data points are used for testing. The three-input models provide estimations of the maximum brake power with an acceptable accuracy for feasibility studies. Using eight-input models, the predictions of the maximum indicated power are very accurate, while those of the maximum brake power are less accurate, but acceptable for the preliminary design stage. In general, the best results are achieved with ANN models, although they only employ one hidden layer.

Effects of binder proportion and curing condition on the mechanical characteristics of volcanic ash- and slag-based geopolymer mortars; machine learning integrated experimental study

Contradicting natures of volcanic ash (VA)- and ground granulated blast furnace slag (GGBFS)- based geopolymers with regard to their need for being exposed to a heating source for conducting alkali-reactions make meaningful differences in the strength and flowability of mortars. To address the impacts of types of the geoploymerizing agent, their proportions, and different curing regimes on their strength and shrinkage behavior, three different curing scenarios including curing at room temperature, RT curing; resting under room temperature for various curing periods, and then hydrothermally curing at an elevated temperature for one day, RO curing; and curing in the oven for one day and then resting at the room temperature, for various curing periods, OR curing, are considered. Based on the flowability, setting time, unconfined compressive strength (UCS), and drying shrinkage tests on eight different mixtures, the effects of binder proportion and curing conditions are evaluated. It was observed that with the substitution of 30% VA with GGBFS, specimens cured at RT condition outperformed OR specimens. This threshold was 45% while comparing RT and RO specimens and with higher slag content, RT specimens gain higher UCS. Also, for GGBFS proportion less than 45%, specimens cured at RO conditions showed higher long-term UCS compared to the OR specimens, and this behavior was reversed for higher GGBFS content. Scanning electron microscopy test results indicated that N-A-S-(H) type gel is the dominant geopolymeric gel in VA-based specimens, and as the amount of slag increases, the gels formed change to N-(C)-A-S-H and with further addition of GGBFS, C-A-S-H type gel is the dominant gel which results in strength development in GGBFS-based specimens. Based on the results of 80 UCS and 140 drying shrinkage tests, different machine learning (ML) algorithms and an evolutionary model were employed to present accurate and cost-effective predictive models as useful and capable methods for practitioners and researchers for the preliminary design stages of projects. A comparative study revealed the superior prediction efficiency of the gradient boosting (GB) model with the R2 score of 95% among 8 different ML algorithms and advanced ensemble models. In addition, evolutionary models with the coefficients of determination of 92% and 95% are, respectively, proposed for the drying shrinkage and the UCS. This study advances the field by assessing VA-GGBFS blend and curing effects on geopolymer mortars and developing ML-based models for compressive strength and drying shrinkage, facilitating efficient optimization in practical applications.

Prediction of Added Resistance of Container Ships in Regular Head Waves Using an Artificial Neural Network

In this paper, an artificial neural network was used to predict the added resistance coefficient for container ships in regular head waves for various speeds. The data used for training the neural network were gathered based on performed numerical calculations using the Boundary Integral Element Method for various hull forms of container ships. The numerically obtained results were validated against the available experimental data for three benchmark container ships. The data were divided into three classes based on the ship length, and the expressions for the prediction of the added resistance coefficient for each container ship class were provided. The performance and generalization properties of the neural network were evaluated based on the normalized value of the root mean square error. The model enables reliable prediction of the added resistance coefficient within the preliminary design stage of a ship based on the ship characteristics and speed.

Uncertainty quantification analysis of Reynolds-averaged Navier–Stokes simulation of spray swirling jets undergoing vortex breakdown

The computational fluid dynamics-based design of next-generation aeronautical combustion chambers is challenging due to many geometrical and operational parameters to be optimized and several sources of uncertainty that arise from numerical modeling. The present work highlights the potential benefits of exploiting Bayesian uncertainty quantification at the preliminary design stage. A prototypical configuration of an acetone/air spray swirling jet is investigated through an Eulerian–Lagrangian method under non-reactive conditions. Two direct numerical simulations (DNSs) provide reference data, coping with different vortex breakdown states. Consequently, a set of Reynolds-averaged Navier–Stokes simulations is conducted. Polynomial chaos expansion (PCE) is adopted to propagate the uncertainty associated with the spray dispersion model and the turbulent Schmidt number, delivering confidence intervals and the sensitivity of the output variance to each uncertain input. Consequently, the most significant sources of modeling uncertainty may be identified and eventually removed via a calibration procedure, thus making it possible to carry out a combustion chamber optimization process that is no longer affected by numerical biases. The uncertainty quantification analysis in the current study demonstrates that the spray dispersion model slightly affects the fuel vapor spatial distribution under vortex breakdown flow conditions, compared with the output variance induced by the selection of the turbulent Schmidt number. As a result, additional high-fidelity experimental and numerical campaigns should exclusively address the development of an ad hoc model characterizing the spatial distribution of the latter in the presence of vortex breakdown phenomenology, discarding any effort to improve the spray dispersion formulation.

Weight Assessment of Marine Diesel Main and Auxiliary Engines

During the conceptual and preliminary ship design stages, designers must ensure that the selected principal dimensions and parameters are good enough to deliver a stable ship (statically and dynamically), besides deadweight and speed. To support this, the initial intact stability of the proposed ship must be calculated, and for that, the lightship weight and its detailed breakdown are necessary to be known. After hull (steel) weight, machinery weight, mainly marine diesel propulsion and power generation machinery, plays a vital role in the lightship weight estimate of a ship directly. It also affects the deadweight, displacement, draft, and trim, which finally influence stability. The correct estimation of respective weights improves calculating a ship’s initial stability, typically designed and built. Hence, it would be advantageous for the ship designer to convince the shipowner. Weight control is not easy, especially since its consequences in terms of deadweight and stability could be disastrous. It should start right at the beginning and control throughout the design and construction phases. Marine diesel main engines (MEs) and auxiliary engines (AEs) of various power output (generators output for AEs), engine speed, and cylinder number of different engine manufacturers are collected. These are analyzed and presented in tabular and graphical forms to demonstrate the possible relationship between propulsion engine weight and power generation engine weight, and their respective power, speed, and power–speed ratio. In this article, the authors have attempted to investigate the appraisal behavior of ME weight and AE weight regarding engine power, generator power, engine speed, and power–speed ratio (independent variables). Further attempts have been made to identify those independent variables that influence the weight of the propulsion engine and power generation engine (dependent variables) and their interrelationships. A mathematical model has thus been developed and proposed, as a guiding tool, for the designer to estimate the weight of main and AEs more accurately during the conceptual and preliminary design stages.

Quasi-Periodic Orbit Transfer Design via Whisker Intersection Sets

Impulsive maneuver design between quasi-periodic orbits (QPOs) remains a prevalent problem in astrodynamics. Challenges associated with the higher-dimensional nature of QPOs present difficulties when using existing approaches to design transfers between them. This paper establishes a methodology to abate these issues. Fundamental to the approach is the treatment of orbits as tori and their manifolds as the associated whiskers. Utilizing this formulation, intersection curves, surfaces, or volumes between the manifolds are computed leveraging a robust multiparameter continuation scheme. Intersections are then used to seed a multiple shooting scheme to compute transfer trajectories between a pair of orbits. The approach is applied in the Earth–moon circular restricted three-body problem. Numerical examples demonstrate the benefits of considering QPOs in the preliminary stage of trajectory design, showing that leveraging these higher-dimensional solutions offers reductions in propellant cost and transfer time when compared to their periodic counterparts.

Conceptual design, parameter optimization and performance investigation of a 10MW semi-submersible floating wind turbine in shallow water

There is lacking of floating wind turbine supporting large wind turbine, i.e. 10 MW, aiming at shallow water applications. In this paper, a 10 MW semi-submersible floating wind turbine named OUCwind is proposed for shallow water, and a scale optimization procedure is proposed during the preliminary design stage. It offers an engineering-practical method to determine the main parameters of a new-proposed floater, and critical floater characteristics, such as floater stability, natural period, platform mass etc. are chosen as important design criteria. The hydrodynamic performance with different scale parameters are investigated and it is found that enlarging distance between columns is a cost-effective way to get better stability and hydrodynamic performance. The structural performance of the new-designed OUCwind floater are compared with other two well-known braceless 10 MW platforms, 10 MW-CSC, and OO-star. From the frequency-domain analysis results, the surge linear transfer function, mean drift force and quadratic transfer function near the surge natural frequency of OUCwind is relatively small compared with other two platforms. In the time domain, the new-designed OUCwind also performs better in surge motion and mooring line tension response compared with 10 MW-CSC and OO-star, especially under extreme condition. Nevertheless, for the heave and pitch motions, the wave-frequency response of the OUCwind platform is relatively large under extreme load conditions.

Ultralight and Very Light Helicopter Rotor Data

Abstract In recent years, a significant number of one- and two-seat lightweight helicopters have come into existence, and this makes it possible to analyse parameters and determine dependencies for this class of helicopters. the knowledge of such dependencies is necessary at the preliminary design stage. the analysis performed in this paper and its comparison with the statistical data of all categories of helicopters made it possible to determine the necessary corrections in the methods of determining the parameters of the helicopter’s rotor systems.

Behavior of single pile subject to oblique uplift load in sandy soil under global scouring

Soil scouring is one of the most dangerous causes of geotechnical collapse, which can result in catastrophic disasters. An experimental scaled laboratory model was used to investigate the effects of lowering the embedded length of tension pile owing to surface scouring and varying relative densities of sand soil for vertical and angled uplift force. The designs for the uplift piles beneath the concentric oblique loads exposed to surface soil scouring have not been made known up until this point. The lateral and vertical responses of the uplift piles in sandy soil were examined in a series of 1-g experimental tests that included secondary characteristics such as soil relative density, the inclination angle of the uplift load, and various applied uplift loads. By applying statistical analysis to the experimental data, it was found that global scour caused reductions in overall pile capacity where the sum of the applied uplift load ratio and the scour depth ratio was equal to 0.70. Idealized P-y curves for piles with axially vertical, horizontal, or oblique uplift loads were developed, and they can be utilized to calculate the ultimate uplift capacity at the preliminary design stage.

EVOLUTIONARY POLYNOMIAL REGRESSION FOR PREDICTING THE UNCONFINED COMPRESSIVE STRENGTH OF LIME-STABILIZED

Peat has a lack of strength, making it unsuitable for foundations or road construction. The results of 104 unconfined compressive strength (UCS) on peat stabilized with various lime percentages are presented in this article. The strength performance of peat soils stabilized with lime in soaked and unsoaked conditions was also evaluated. Evolutionary Polynomial Regression (EPR) models are constructed to predict the UCS values using the data obtained from the tests. After evaluating the various functions, the EPR model with a hyperbolic tangent function is the best model for predicting the UCS. The proposed EPR models may benefit practitioners when determining the optimal amount of stabilizers to utilize in soft-ground improvement projects. In this section, we show and expand on applying the suggested models to the design of soft ground mixing. Additionally, by applying the created relationships to a new instance, the comprehensiveness of the established relationships is shown, as is the practicality of the suggested relationships for usage during the preliminary design stage. The findings of this study have important implications for estimating the quantity of lime required in ground peat improvement work.

Aerodynamic Aspects in the Formation of the Appearance of Mainline Aircraft at the Preliminary Design Stage

Aerodynamic Aspects in the Formation of the Appearance of Mainline Aircraft at the Preliminary Design Stage

Multiobjective optimization of a staggered-rotor octocopter design based on a surrogate model

When designing a novel double-layer staggered-rotor octocopter with improved aerodynamic performance, the aerodynamic performance and structural parameters will have a complex coupling relationship that should be considered in the overall design process. A surrogate-model-based multiobjective optimization method is proposed in this study to optimize novel octocopter structural design schemes considering total thrust, the weight of the propeller and fuselage, the storage volume, and the fuselage volume. This approximation and optimization approach effectively reduces the cost of a large amount of computational fluid dynamics (CFD) calculations in octocopter design and provides a global prediction of octocopter performance. According to the verified optimal solution through CFD simulation, we can see that the surrogate model offers excellent predictive ability, and the prediction accuracy of thrust exceeds 95%. Compared with the initial optimum data, the optimal solution calculated from the optimization could generate 76.74% more thrust, the objective function y is improved by 11.48%, and the objective function a is improved by 322.06%. These results show that the aerodynamic/structural parameter optimization design method considering the influence of aerodynamic interference for multirotor aircraft proposed in this paper is feasible and exhibits good performance. The methodology proposed in this work could provide guidelines for structural parameter design optimization for double-deck multiple-rotor aircraft design at the preliminary design stage, as well as copter structural design considering multiple-rotor interference effects.

MIP-based heuristics for combinatorial design of reconfigurable rotary transfer machines for production of multiple parts

This paper deals with a problem of the optimal configuration of a rotary transfer machine with turrets for machining multiple parts. This is a hard combinatorial optimization problem appearing at the preliminary machine design stage. Such machines are multi-positional, i.e. parts are sequentially machined on several working positions. At each working position, several machining modules (spindle heads) can be installed to process the tasks assigned to this position. Machining modules are activated sequentially or simultaneously. Sequential activation is realized by the use of turrets. Simultaneous activation is possible if machining modules are related to the different sides of the part, and if they can work in parallel. There are horizontal and vertical spindle heads, and turrets to access different sides of the parts on a working position. At the preliminary design stage, the following decisions must be made: the choice of orientations of the parts on the rotary table; the partitioning of the given set of tasks into positions and their assignment to machining modules (selection or design of machining modules to use), and the choice of cutting modes for each spindle head and turret. The objective is to minimize the total cost of equipment used. The number of possible solutions for this combinatorial design problem increases exponentially with the number of part types to be produced, and this represents a computational burden for decision-makers (usually process engineers). In this paper, in order to help decision makers deal efficiently with the manufacturing of multiple batches of parts, we develop a powerful heuristic framework which can be used in real life industrial cases. We test the developed methodology on the real-life cases provided by one of our industrial partners and demonstrate its efficiency. The proposed model and algorithms allow to minimize the cost of designed machines.

Establishment of a design study for comprehensive hydrodynamic optimisation in the preliminary stage of the ship design

ABSTRACT An automated practical multi-objective optimisation scheme is proposed for ship hull modification. A shift transformation and a self-blending method are sequentially performed based on resistance objectives at multi-design speeds. The Lackenby variation alters hull forms and produces initial designs. Subsequently, self-blending method combines obtained ships to cover design space. All processes are automated by MATLAB coding that connects the ©Maxsurf modeller and ©Maxsurf Resistance in the case of panel method resistance calculation. After whole shape optimisation, the platform defines ship portions in the stern and bow regions. Particularly, an approximation modelling Least-Square approach is investigated to construct a surrogate model. Optimisation results indicate 11.26% cost function reduction contributes to 16.23% resistance reduction at lower speed and 6.12% resistance reduction at higher speed for a passenger catamaran boat. Thus, the developed in-house optimisation code provides an optimal and cost-effective solution for hydrodynamic optimisation in the preliminary stage of ship design.

Approximation method of the axial forces on network of connectors for modular hexagonal floating structures

Modular floating structures are normally made up of modules which are connected using network of connectors. These connectors are prone to heavy load due to facing the open sea wave. Previous studies have examined simple module configuration such as two rectangular form arranged linearly or three or seven hexagonal form arranged in an oblique pattern experimentally or using CFD and FE packages. Two challenges persist afterward; firstly, on applying the current findings to topology made up of a bigger number of modules and secondly on estimating the axial load values of connector at the preliminary design stage. This study developed an approximation method of axial force at the connector based on basic module configuration of hexagonal modular floating structure and axial load values determined by earlier studies. Four approximation methods vary with number of modules, arrangement and connectors facing 900 wave direction were proposed. Early analysis of the proposed method revealed that the axial force of the hexagonal modular connector is affected by the overall structure type and configuration such that hexagonal module-to-module connection requires higher axial load as compared to hexagonal modular cluster-to-cluster linkage due to load distribution amongst the connectors.

Novel Multiphysics Design Methodology for Coreless Axial Flux Permanent Magnet Machines

This work is devoted to multiphysics design of coreless axial flux permanent magnet machines with concentrated coils. Recently, these machines have been proposed for the propulsion of civil miniature electric unmanned aerial vehicles, which need very high torque and power densities. Such requirements tend to be in contrast with other important features such as high efficiency and resilience, making the design quite challenging. Among the various geometrical parameters, the rotor poles to stator coils ratio plays a key role in their performance. The main contribution of this paper is the development of an original design method hinging upon the said ratio. The 2D electromagnetic model at the heart of the approach is derived at the average radius and accounts for multi-layer and axially thick stator coils. Additional contributions include the concurrent use of thermal modelling in the preliminary design stage and mechanical analyses in the design refinement stage aimed at optimizing torque density and guaranteeing rotor integrity at maximum speed. Comprehensive experimental tests on a full-scale prototype are reported and help build confidence in the proposed methodology.

Voltage Divider based on Switched Capacitors for MEM Generators

Simulation results of the operation of voltage dividers based on switched capacitors with diode and transistor-diode switching for microelectromechanical (MEM) generators are presented. It has been established that for a divider with diode-switched capacitors, the voltage division factor doesn't remain when the load resistance changes, and for higher load resistances, the value of the load voltage asymptotically approaches to V0, but not to V0/N. At the same time, a divider with transistor-diode switching of capacitors at higher load resistances makes it possible to obtain an output voltage Vl, which is N times lower than the voltage of the primary power source V0. Analytical expressions have been obtained for estimating the parameters of dividers with diode switching, which allow calculating the characteristics of the divider at the stage of preliminary design of MEM generators with diode-capacitor voltage dividers. It is shown that the simulation of the operation of a diode-capacitor voltage divider must be carried out taking into account the dynamic current-voltage characteristic of diodes. It is established that when using a bipolar transistor as a charging switch, the ripple coefficient of the output voltage is less than when using a reed relay

A discrete adjoint full potential formulation for fast aerostructural optimization in preliminary aircraft design

Preliminary aircraft design is often carried out with the help of multidisciplinary optimization processes. Because there is a strong coupling between the flow and the structure of the aircraft, and because new composite materials have a unique capability of being designed for anisotropic directional stiffness and strength, these processes must model the aeroelastic behavior of the aircraft in order to be effective. Since many design variables are involved during the preliminary design stage, the optimization problems, formulated using high or medium fidelity models, can be solved using the adjoint method. Moreover, the level of fidelity of the fluid model and the associated simulation technique must also be selected with care, as they tend to be the main contributors to the computational cost. The novel contribution of the present work is twofold. Firstly, the discretized gradients of the full potential flow equation, which is a medium-fidelity model, are derived analytically so that they can be used in adjoint optimization problems. Moreover, the full potential flow solution and the computation of the gradients are implemented in an open-source and readily available finite element code. Secondly, aerodynamic shape and aerostructural optimization calculations are carried out on example wings to demonstrate the effectiveness and the computational efficiency of the proposed method. Overall, the results show that the newly implemented discrete adjoint nonlinear potential flow formulation is able to quickly optimize both the shape and the structural parameters of a typical wing. More specifically, the twist distribution along the wingspan is adapted to reduce the induced drag, the airfoils become more supercritical so that the shock strength and the associated wave drag are reduced, and the thickness of the structural elements is tailored to the loads to reduce the internal stresses. The present methodology is therefore able to deliver results at a low computational cost which are sufficiently accurate for the early design stages. Furthermore, the results obtained using the proposed methodology could be used as a starting point for the optimization calculations performed in later design stages.

Construction and application of numerical diagram for high-skew propeller based on machine learning

The field of machine learning has experienced rapid growth, and it has introduced a new methodology for constructing propeller diagrams. To meet the high demand for designing high-skew propellers, a series of high-skew propeller schemes are generated, utilizing the INSEAN E1619 as the parent propeller. The Computational Fluid Dynamics (CFD) method was validated using the E1619 test results and was subsequently employed to perform virtual open water tests for all the series schemes. This effort produced 819 open water performance data of 42 propellers. The study trained and validated the traditional multivariate polynomial regression model and five conventional machine learning regression models based on the CFD calculation data. The analysis of the model prediction accuracy indicated that the Support Vector Machine (SVM) model had the least error among them for the digital expression of diagram hydrodynamic data. The prediction error of KT, KQ, and η decreased by over 20% compared to the LM model. The study subsequently developed a high-skew propeller diagram design program using the SVM regression model and applied it to a specific underwater vehicle's propeller design. The design results demonstrated that, compared to the B-series propeller, the design scheme provided by this numerical diagram had a comparable efficiency and a 6% smaller optimum diameter under unlimited diameter and a 7% higher efficiency under limited diameter for this case. Consequently, the developed numerical diagram in this paper provides a new tool for the propulsion performance evaluation and parameter selection of the propulsion system in the preliminary design stage for the high-skew propeller.

Electrodynamic Withstand of Power Transformers to Short-Circuit Currents

The analysis of simplified expressions allows us to estimate the electrodynamic withstand of power transformers to short-circuit currents on power electrical station and substation. Examples of calculations of magnetic field induction, mechanical forces and pressures that determine the electrodynamic withstand of electrical equipment are given. Simplified qualitative calculations allow us to assess the impact of key parameters on the selection of appropriate elements and the possible range of their changes during the design, operation and modernization at the preliminary design stage.