Feasible Design Options Research Articles

Upgraded one-dimensional code for the design of a micro gas turbine mixed flow compressor stage with various crossover diffuser configurations

Abstract Micro Gas Turbine (MGT) designers often have the need for a design tool, capable of rapidly providing feasible design options. The upgrade of such an existing MATLAB® based mixed flow compressor design application (1D App) is discussed. In MGT engines, diffuser design largely influences the compressor stage performance. Crossover diffusers provide superior efficiency and pressure ratio performance compared to legacy type diffusers, albeit at the expense of operating range. The reduced operating range attributed to single vane crossover diffusers can be alleviated by splitter vane, tandem vane, and combined configurations. Therefore, the 1D App is updated to allow the user the ability to design these additional crossover diffuser configurations. Performance results are verified using Numeca/FINE™ Turbo CFD software. It is shown that the upgraded 1D App provides predicted performance results within 1 % of CFD results for both total-to-total efficiency and pressure ratio.

Life cycle-oriented low-carbon product design based on the constraint satisfaction problem

The design and development of low-carbon products have become a recent global concern due to serious greenhouse gas emissions and climate change. The design phase determines 70 % of the environmental performance of the product, which covers complex life cycle information and diversified constraints, resulting in low efficiency of life cycle modeling and difficulty in realizing design automation. Therefore, this study proposes a life cycle-oriented low-carbon design strategy based on the constraint satisfaction problem to express the association mechanism of life cycle information and constraints and efficiently generate the low-carbon design solution. Specifically, the hierarchical life cycle-oriented low-carbon design model is proposed to manage the associations of life cycle information in terms of function, structure, design feature, and machining feature. On the basis of the model, the constraint-based design space is constructed to explicitly express all the feasible design options and the constraints of the product, which can effectively support the automation of product design. Then, all design options and the constraints for product design are transformed into a constraint satisfaction problem, which can be optimized by the proposed hybrid optimizer algorithm. This algorithm supports the efficient optimization of complex products in large-scale design space, and the low-carbon design solution is effectively generated. An example of the low-carbon design of a wind turbine is given to demonstrate the capability of the suggested method, indicating that they have reduced the carbon emission of the wind turbine nearly by 19.82 % in comparison with the existing design solution, and the material acquisition and manufacturing stages generated the highest carbon emissions, accounting for 47.94 % and 56.42 %, respectively. This work effectively standardizes products’ life cycle design information and various design constraints and provides a targeted strategy for guiding designers to implement low-carbon design through the life cycle.

Multi-objective optimisation for building integrated photovoltaics (BIPV) roof projects in early design phase

Building-integrated photovoltaics (BIPV) is an excellent renewable energy application for building envelopes. In Australia, BIPV roofing is considered to be promising because of recent major concerns about fire risks of façades. However, the integration of PV into building envelope elements is a complicated process which, if not done properly, may lead to failure of the BIPV system. Therefore, feasible BIPV design solutions need to be examined in terms of life-cycle cost and energy performance from the early design phase of a BIPV envelope project. There have been few investigations of the identification of feasible BIPV design options in the early design phase to enable product selection and parametric tests. This study explores a multi-objective optimization method which formulates feasible BIPV envelope design options which have relatively high energy generation and low life cycle costs to informed decision making. The optimisation process has four segments: data inputs, simulator, optimizer and pareto front based optimised BIPV solutions. The proposed multi- objective optimization process is applied in a BIPV roof application using a case study in Australia with roof sheets and skylights. The results demonstrate seven optimum roof sheet BIPV design solutions and fourteen optimum skylight BIPV design solutions to enable design makers to compare and select the most appropriate. The life cycle cost, life cycle energy, CO2 emissions avoided, net present value, payback period, and levelized cost of energy of BIPV solutions vary based on the BIPV modules, tilt angles and placement locations. The proposed optimization method is a helpful guide for BIPV design professionals to identify suitable BIPV design options in the early design phase instead of relying on rule-of-thumb experience.

Optimum sizing of hydrokinetic turbine integrated photovoltaic-battery system incorporating uncertainties of resources

ABSTRACT Hydrokinetic turbines (HKT’s) are used to produce power from the kinetic energy of the river current. A hydrokinetic turbine, when combined with a photovoltaic (PV)-battery system is an excellent option for the electrification of isolated communities residing at the banks of a river or a canal system. A methodology for the optimum sizing of an HKT-PV-battery system for remote electrification incorporating the uncertainty associated with power produced by the PV modules and hydrokinetic turbines is proposed. The entire set of feasible design options known as design space is identified for the HKT-PV-battery system using a deterministic as well as probabilistic approach. For a given load demand an HKT-PV- battery system with two HKT’s is identified as the overall optimum configuration when the deterministic approach is applied. Chance-constrained programming is utilized to incorporate the uncertainty in power from renewable sources. Sizing curves are generated at a specified confidence level by varying the number of hydrokinetic turbines. The lowest cost of energy is observed for an HKT-battery system with three HKTs irrespective of all reliability values considered. The methodology is validated using the Monte Carlo simulation approach with the help of illustrative examples. The optimum configuration at each confidence level is selected based on the cost of energy.

Reliability-based design for lightweight vehicle structures with uncertain manufacturing accuracy

Structural lightweight optimization is one of the key themes to continuously improve vehicle performance. However, most of the studies so far have not considered reliability and manufacturing issues brought about by the uncertainty of tolerances in structural lightweight optimization. In this study, a reliability-based design for lightweight vehicle structures with uncertain manufacturing accuracy is proposed. This method can provide not only the optimal design variables but also the maximum allowable deviation range. The main design variables lacking sample information are regarded as interval variables and other design parameters as probabilistic values. A progressive reliability-based design with uncertain manufacturing accuracy is established for lightweight vehicle structures by employing the transformation method of the interval model and the decoupling strategy of the probabilistic model. Firstly, the general test function is used to analyze the accuracy and efficiency of the reliability decoupling method. Then, lightweight optimization models of a classic cantilever beam and two vehicle structures (parking robot frame, energy absorption box) are established respectively, and the effectiveness of the present optimization method is verified. The optimized design results show that the optimal variables and the corresponding maximum allowable deviation range under acceptable manufacturing requirements can be obtained. The requirements for manufacturing accuracy can be reduced by appropriately increasing the deviation range of the design variables, which may lead to a reduction in manufacturing cost. This study aims to provide feasible design options by optimizing lightweight structures considering uncertain manufacturing accuracy.

Sizing and techno-economic analysis of hydrokinetic turbine based standalone hybrid energy systems

Hydrokinetic turbines (HKT’s) are used to generate power from the kinetic energy of flowing water in canals and rivers. This paper proposes a methodology for the optimum sizing of two types of HKT based hybrid energy systems. An HKT-DG-battery system is proposed for the off-grid isolated villages located near to the river or canal. The entire set of feasible design options known as design space is identified for an HKT-DG-battery system using a MATLAB algorithm involving the time series simulation of the energy sources. Another choice with the HKT is proposed with the HKT-PV-battery system. The procedure is extended to generate the design space of an HKT-PV-battery system. The design space generated can be utilized to choose the appropriate system configuration by optimizing the economic criteria along with location parameters as the constraints. An illustrative example is presented to generate the design space using the energy source data for the site. For the case study, the minimum cost of energy in the case of the HKT-DG-battery system is found to be 11 % less than that of the HKT-PV-battery system. The sensitivity analysis conducted presents the effect of fuel price variation and PV cost on the cost of energy.

System-based limit state design criterion for 3D steel frames under wind loads

Advanced nonlinear finite element analysis (FEA) enables the Direct Design Method (DDM) of a frame by computational analysis in place of designing members and connections to codified specific equations. The Direct Design Method has become a feasible design option and attracted increasing attention from the research community, designers and code writers. One of the research challenges of adopting the DDM is to develop a system-based limit state design criterion to ensure a stipulated level of structural reliability, similar to that of member-based design methods. The present paper derives the system resistance factors suitable for the DDM of typical spatial moment-resisting steel frames comprising rigid connections and members of compact sections under wind and gravity loads. The interaction of the system resistance factor and frame reliability is established, which can serve as a basis for the code writers to choose the appropriate system resistance factors for the DDM.

Selectivity Engineering with Hybrid Reactive Distillation Column: Mixtures Containing Inerts and Multi-Azeotropes

Reactive Distillation (RD) which combines reaction and distillation can be effectively used to get desired selectivities in multi-reaction systems. In case of azeotropic systems, nonideal vapor-liquid equilibrium and distillation boundaries are responsible for the contraction of the feasible reactive stage composition region required for the design of hybrid RD column. In the present study, we show that if the mixture contains inert as well then this feasible reactive stage composition region reduced further and thereby decreases the feasible design options of desired selectivity in multireaction systems. Therefore, an attempt is made here, to developed a conceptual design algorithm which is based on combined graphical-simulation approach and attainable region concepts. The developed methodology successfully finds at least one feasible design of hybrid RD column to give desired selectivity. Method gives excellent starting values for rigorous simulations suited to industrial applications.

Development of complex products and production strategies using a multi-objective conceptual design approach

Conceptual design is a fundamental phase for developing optimal product configurations. During conceptual design, the degree of freedom in engineering choices can propose optimal solutions in terms of assembly, manufacturing, cost and material selection. Nevertheless, in current industrial practices, each aspect is analysed independently and a guided decision-making approach based on multi-objective criteria is missing. Multi-objective analysis is a way of combining each production aspect with the aim of choosing the best design option. The goal of this research work is to define a multi-objective design approach for the determination of optimal and feasible design options during the conceptual design phase. The approach is based on the concept of functional basis, module heuristics for defining product modules and the theory of multi-criteria decision-making for mathematical assessment of the best design option. The novelty of this approach lies in making the design process, currently based on company know-how and experience, systematic. A complex product (i.e. tool-holder carousel of a computer numerical control machine tool) is the case study used to assess the economic sustainability of different design options and to validate the proposed design workflow in a real manufacturing context. Different product modules have been re-designed and prototyped for comparing the assemblability, manufacturability and cost of the design solutions.

A Multi-objective Design Approach to Include Material, Manufacturing and Assembly Costs in the Early Design Phase

Conceptual design is a crucial activity in the product development process. The design freedom must consider a trade-off analysis among several aspects such as assembly, manufacturing, and costs. The goal of this approach is to define a multi-objective design approach for the determination of feasible design options. The approach is grounded on the concept of functional basis for the analysis of product modules and the theory of Multi Criteria Decision Making (MCDM) approach for the assessment of the best design option. A complex product (tool-holder carousel of a machine tool) is used as a case study to validate the approach.

The need to balance merits and limitations from different disciplines when considering the stepped wedge cluster randomized trial design.

BackgroundVarious papers have addressed pros and cons of the stepped wedge cluster randomized trial design (SWD). However, some issues have not or only limitedly been addressed. Our aim was to provide a comprehensive overview of all merits and limitations of the SWD to assist researchers, reviewers and medical ethics committees when deciding on the appropriateness of the SWD for a particular study.MethodsWe performed an initial search to identify articles with a methodological focus on the SWD, and categorized and discussed all reported advantages and disadvantages of the SWD. Additional aspects were identified during multidisciplinary meetings in which ethicists, biostatisticians, clinical epidemiologists and health economists participated. All aspects of the SWD were compared to the parallel group cluster randomized design. We categorized the merits and limitations of the SWD to distinct phases in the design and conduct of such studies, highlighting that their impact may vary depending on the context of the study or that benefits may be offset by drawbacks across study phases. Furthermore, a real-life illustration is provided.ResultsNew aspects are identified within all disciplines. Examples of newly identified aspects of an SWD are: the possibility to measure a treatment effect in each cluster to examine the (in)consistency in effects across clusters, the detrimental effect of lower than expected inclusion rates, deviation from the ordinary informed consent process and the question whether studies using the SWD are likely to have sufficient social value. Discussions are provided on e.g. clinical equipoise, social value, health economical decision making, number of study arms, and interim analyses.ConclusionsDeciding on the use of the SWD involves aspects and considerations from different disciplines not all of which have been discussed before. Pros and cons of this design should be balanced in comparison to other feasible design options as to choose the optimal design for a particular intervention study.

Using multiobjective optimization for automotive component sizing

This paper shows how a multiobjective problem is formulated and solved in order to size the components of a vehicle with a split hybrid transmission, such as a Toyota Prius. The goal is to explore feasible design options and the trade-offs between fuel economy and vehicle cost. Eight input variables are provided for this optimization, including plant variables such as maximum power ratings for engine, motors, and battery; final drive ratio; and control variables that determine how the battery energy is utilized. Three constraints are used: achievement of the battery charge balance, ability to trace the drive cycle, and ability to achieve a zero to 60 mph acceleration performance within 10 seconds. We describe a multiobjective optimization algorithm that we have implemented in Autonomie, a simulation tool developed at Argonne, and we demonstrate its ability to utilize parallel computing capabilities of Matlab. A parallel/distributed-computing infrastructure is used to simultaneously evaluate multiple combinations of input parameters, over multiple drive cycles, thereby reducing the overall time taken to perform the optimization and hence reduce the total solution time. The optimization produces several design choices, which form a Pareto front. The search algorithm ensures that as the number of iterations increases, more and more points are added on or near the Pareto front. All the points that form the front are relevant design choices, and the front characterizes the balance between conflicting goals such as fuel economy and performance.

Fire-resistance industrial portal frames: design with different mechanical properties steels and 35 meters spans

Various portal frames are studied to establish their fire response over various fire exposure times. The frames were assembled with plain carbon steel (S275) and micro-alloyed fire resistant (FR) steel (with superior fire-resistant properties). An intumescent fire protective paint was also tested to improve the overall fire resistance of the steel structure. In this paper, a dimensioning method is proposed that combines structural calculations with a conventional software package for the calculation of structural stress, in accordance with the geometric and elastic moduli of each complete section of the industrial metallic frame. The structure was sized by selecting the most economical combination and by estimating the stresses in each particular structural element or section of the overall structure. The process was then repeated with these new dimensions to reach the optimal structural design. The key variables analyzed in this study are: six fire-exposure times, seven intumescent paint thicknesses, and eleven price ratios between the FR and the S275 steels. Each structure in this study has a span of 35 m. The main conclusion is that the use of FR steel combined with S275 and an intumescent paint system is the most cost effective and technically feasible design option for industrial portal frames.

Theoretical modelling and experimental investigation of a thermal energy storage refrigerator

Numerical simulations using the computational fluid dynamics (CFD) software ANSYS Fluent were undertaken to characterize the airflow and temperature distribution in a natural convection thermal energy storage refrigerator. The model compared the household refrigerator temperature stability with different phase change materials (PCM) incorporated into the storage compartment. Scenarios investigated included the PCM orientation (vertical or horizontal), PCM temperature (use of water or eutectics) and compartment designs (conventional or drawer type appliance). The results suggested that a horizontal PCM configuration produces lower compartment temperatures than a vertical configuration. The temperature distribution with a horizontal PCM was tested experimentally and the results were in agreement with the CFD predictions. Both the simulation and the experimental results suggest that a eutectic with a phase change temperature below 0 °C must be employed to maintain the compartment temperature within acceptable limits. The model indicated that combining horizontal and vertical PCMs in a full height compartment or dividing the same compartment into two drawers with a horizontal PCM configuration for each drawer are feasible design options for the household thermal storage refrigerator.

First-order feasibility analysis of a space suit radiator concept based on estimation of water mass sublimation using Apollo mission data

Thermal control of a space suit during extravehicular activity (EVA) is typically accomplished by sublimating water to provide system cooling. Spacecraft, on the other hand, primarily rely on radiators to dissipate heat. Integrating a radiator into a space suit has been proposed as an alternative design that does not require mass consumption for heat transfer. While providing cooling without water loss offers potential benefits for EVA application, it is not currently practical to rely on a directional, fixed-emissivity radiator to maintain thermal equilibrium of a spacesuit where the radiator orientation, environmental temperature, and crew member metabolic heat load fluctuate unpredictably. One approach that might make this feasible, however, is the use of electrochromic devices that are capable of infrared emissivity modulation and can be actively controlled across the entire suit surface to regulate net heat flux for the system. Integrating these devices onto the irregular, compliant space suit material requires that they be fabricated on a flexible substrate, such as Kapton film. An initial assessment of whether or not this candidate technology presents a feasible design option was conducted by first characterizing the mass of water loss from sublimation that could theoretically be saved if an electrochromic suit radiator was employed for thermal control. This is particularly important for lunar surface exploration, where the expense of transporting water from Earth is excessive, but the technology is potentially beneficial for other space missions as well. In order to define a baseline for this analysis by comparison to actual data, historical documents from the Apollo missions were mined for comprehensive, detailed metabolic data from each lunar surface outing, and related data from NASA’s more recent “Advanced Lunar Walkback” tests were also analyzed. This metabolic database was then used to validate estimates for sublimator water consumption during surface EVAs, and solar elevation angles were added to predict the performance of an electrochromic space suit radiator under Apollo conditions. Then, using these actual data sets, the hypothetical water mass savings that would be expected had this technology been employed were calculated. The results indicate that electrochromic suit radiators would have reduced sublimator water consumption by 69.0% across the entire Apollo program, for a total mass savings of 68.5 kg to the lunar surface. Further analysis is needed to determine the net impact as a function of the complete system, taking into account both suit components and consumable mass, but the water mass reduction found in this study suggests a favorable system trade is likely.

On the Existence of Non-Convexities in the Design Space of Isolated Wind-Battery Systems

A set of all feasible design options depicted graphically on a diagram with system design variables is known as the design space. For an isolated wind-battery system, the design space is depicted on a rotor diameter vs. generator rating diagram with battery bank size as a parameter. Design space representation enables the distinction between the feasible and infeasible combinations of design variables. It forms a basis to understand the inter-relation between different design variables outlining the tradeoffs in design. In certain cases, it is observed that the feasible solution set may lead to a non-convex design space. Non-convexities in the design space imply that intuitive selection or arbitrary over sizing of design parameter(s) may lead to non-compliance with respect to overall reliability requirement. Through an illustrative example, it is shown that the primary reasons leading to design space non-convexity are the uneven distribution of wind speed standard deviation in the time horizon, high overall system reliability requirement and the wind regime of the site under consideration. From a graph of system reliability vs. coefficient of variation of wind speed (COV), it is observed that non-convexity in design space is most likely to occur for particular combinations of system reliability requirement and COV of wind speed. This representation facilitates predicting the occurrence of non-convexity in the design envelope prior to detailed system design and optimization; thus providing valuable insight to the system designer and preventing a possible failure of performance and loss of investment.

A Simple Parametric Model for the Analysis of Cooled Gas Turbines

A natural gas fired gas turbine combined cycle power plant is the most efficient option for fossil fuel based electric power generation that is commercially available. Trade publications report that currently available technology is rated near 60% thermal efficiency. Research and development efforts are in place targeting even higher efficiencies in the next two decades. In the face of diminishing natural resources and increasing carbon dioxide emissions, leading to greenhouse gas effect and global warming, these efforts are even more critical today than in the last century. The main performance driver in a combined cycle power plant is the gas turbine. The basic thermodynamics of the gas turbine, described by the well-known Brayton cycle, dictates that the key design parameters that determine the gas turbine performance are the cycle pressure ratio and maximum cycle temperature at the turbine inlet. While performance calculations for an ideal gas turbine are straightforward with compact mathematical formulations, detailed engineering analysis of real machines with turbine hot gas path cooling requires complex models. Such models, requisite for detailed engineering design work, involve highly empirical heat transfer formulations embedded in a complex system of equations that are amenable only to numerical solutions. A cooled turbine modeling system incorporating all pertinent physical phenomena into compact formulations is developed and presented in this paper. The model is fully physics-based and amenable to simple spreadsheet calculations while illustrating the basic principles with sufficient accuracy and extreme qualitative rigor. This model is valuable not only as a teaching and training tool, it is also suitable to preliminary gas turbine combined cycle design calculations in narrowing down the field of feasible design options.

An analysis of beta type Stirling engine with rhombic drive mechanism

Stirling engine system is one of the options for electrifying a remote community not serviceable by the grid, which can operate on energy input in the form of heat. Major hurdle for the wide-spread usage of rhombic drive beta type Stirling engine is complexity of the drive and requirement of tight tolerances for its proper functioning. However, if the operating and geometrical constraints of the system are accounted for, different feasible design options can be identified. In the present work, various aspects that need to be considered at different decision making stages of the design and development of a Stirling engine are addressed. The proposed design methodology can generate and evaluate a range of possible design alternatives which can speed up the decision making process and also provide a clear understanding of the system design considerations. The present work is mainly about the design methodology for beta type Stirling engine and the optimization of phase angle, considering the effect of overlapping volume between compression and expansion spaces. It is also noticed that variation of compression space volume with phase angle remains sinusoidal for any phase difference. The aim of the present work is to find a feasible solution which should lead to a design of a single cylinder, beta type Stirling engine of 1.5 kW e capacity for rural electrification.

Optimum sizing of wind-battery systems incorporating resource uncertainty

Abstract The inherent uncertainty of the wind is a major impediment for successful implementation of wind based power generation technology. A methodology has been proposed in this paper to incorporate wind speed uncertainty in sizing wind-battery system for isolated applications. The uncertainty associated with the wind speed is incorporated using chance constraint programming approach. For a pre-specified reliability requirement, a deterministic equivalent energy balance equation may be derived from the chance constraint that allows time series simulation of the entire system. This results in a generation of the entire set of feasible design options, satisfying different system level constraints, on a battery capacity vs. generator rating diagram, also known as the design space. The proposed methodology highlights the trade-offs between the wind turbine rating, rotor diameter and the battery size for a given reliability of power supply. The optimum configuration is chosen on the basis of the minimum cost of energy (US$/kWh). It is shown with the help of illustrative examples that the proposed methodology is generic and flexible to incorporate alternate sub-component models.

Application of design space methodology for optimum sizing of wind–battery systems

A methodology for optimum sizing of different components (i.e., rotor diameter, electrical generator rating, and battery capacity) of a standalone wind–battery system is proposed in this paper. On the basis of time series simulation of the system performance along with different design constraints, the entire set of feasible design options, also known as the design space, has been identified on a rotor diameter vs. rated power diagram. The design space of a standalone wind–battery system identifies the entire envelope within which a feasible system may be designed. The optimum configuration of the standalone system is identified on the basis of minimum cost of energy (US$/kWh). It is observed that the cost of energy is sensitive to the magnitude of average demand and the wind regime. Sensitivity of the capital cost on the minimum cost of energy is also studied.