CONSOLE: A CAD tandem for optimization-based design interacting with user-supplied simulators

CONSOLE employs a recently developed design methodology (International Journal of Control 43:1693-1721) which provides the designer with a congenial environment to express his problem as a multiple ojective constrained optimization problem and allows him to refine his characterization of optimality when a suboptimal design is approached. To this end, in CONSOLE, the designed formulates the design problem using a high-level language and performs design task and explores tradeoff through a few short and clearly defined commands. The range of problems that can be solved efficiently using a CAD tools depends very much on the ability of this tool to be interfaced with user-supplied simulators. For instance, when designing a control system one makes use of the characteristics of the plant, and therefore, a model of the plant under study has to be made available to the CAD tool. CONSOLE allows for an easy interfacing of almost any simulator the user has available. To date CONSOLE has already been used successfully in many applications, including the design of controllers for a flexible arm and for a robotic manipulator and the solution of a parameter selection problem for a neural network

On-Line Optimization of Chemical Plants Using Steady State Models.

The subject of this dissertation is the on-line optimization of continuous chemical plants that are operated under steady state. For these plants, transient periods are short compared to periods of steady operation, and a steady state optimization (using a steady state nonlinear model) covers the major part of the potential gain that can be made through optimization. Cheaper computer technology and a more competitive market cause an increased industrial interest in this supervisory control technique. The existing literature on applications of on-line optimization using steady state models is discussed. Publications reflect the wide interest in the optimization based technique, but in general the reports are vague, and they do not answer many fundamental questions. Some are even contradictory on issues such as partitioning of the optimization problem or choice of optimization variables. In this dissertation, a modular structure for an on-line optimizer is suggested. In this structure, existing algorithms in model updating, data reconciliation and optimization are combined with new applications. The application of sensitivity analysis is the most important new approach that is presented in this dissertation. Optimization sensitivity analysis is a computationally cheap tool that provides information about the status of an optimization result. That information can be used in an on-line optimizer for use in a sign)ficance test of setpoint changes, and for an online accuracy assessment of the on-line optimizer operation. Sensitivity information is therefore combined with statistical information from e.g. the model updating module. Results from a sensitivity analysis can also be used in short-cut feasibility studies. Also model execution frequency, data reconciliation techniques and particular problems with model updating are discussed, as well as the influence of noise on the performance of on-line optimized plants. Case study results are provided as illustration. The systems studied in these case studies are a distillation column (propane propylene splitter), a boiler network with common header and a simple heat exchanger network

On-Line Optimization Using Steady State Models.

Many sectors of the chemical industry suffer from a production overcapacity. Efficient production strategies are important. This situation combines with dropping computer costs to form an excellent environment for on-line optimization. If the transient periods of an operation are short relative to the steady intervals, a major part of the operation economics is determined by the steady state. Therefore, an optimization limited to the steady state will cover the main part of the attainable profit of the plant. A structure for an on-line optimizer is proposed. The optimization is conceived as a calculation of a set of optimal setpoints for the plant. The on-line optimizer is composed of a number of modules. The most important modules perform the optimization and identify the model. Although steady state models are much morre readily available and accurate than dynamic models, they still are approximate and contain parameters that have to be updated regularly to correct for the plant model mismatch and for slow changes in the plant. Sensitivity analysis of the optimization results and statistical analysis of the model identification results are combined in short-cut feasibility studies and on-line accuracy estimation. Data reconciliation improves the robustness of the application. Two examples serve as illustrations. The first example concerns a propane-propylene splitter. This example shows many of the interesting issues on a system of reduced size. The results are therefore easier to interpret. The second example is a boiler load allocation problem. This example is more involved and shows a realistic application

CFD simulations of the aerodynamic drag of two drafting cyclists, Comput. Fluids 71

Research highlights: High-resolution grids with wall-adjacent cell centres at 15 micrometer from the body surface Validation with wind-tunnel measurements of drag force of single cyclist and two cyclists. CFD simulations and measurements show that drafting provides drag reduction for both cyclists Drag reduction of leading cyclist due to trailing cyclist in his/her wake goes up to 2.6%. The optimum strategy for team time trials should consider drafting effects of every team member. Abstract The aerodynamic drag of two drafting cyclists in upright position (UP), dropped position (DP) and time-trial position (TTP) is analysed by Computational Fluid Dynamics (CFD) simulations supported by wind-tunnel measurements. The CFD simulations are performed on high-resolution grids with grid cells of about 30 micrometer at the cyclist body surface, yielding y* values well below 5. Simulations are made for single cyclists and for two drafting cyclists with bicycle separation distances (d) from 0.01 m to 1 m. Compared to a single (isolated) cyclist and for d = 0.01 m, the drag reduction of the trailing cyclist is 27.1%, 23.1% and 13.8% for UP, DP and TTP, respectively, while the drag reduction of the leading cyclist is 0.8%, 1.7% and 2.6% for UP, DP and TTP, respectively. The drag reductions decrease with increasing separation distance. Apart from the wellknown drag reduction for the trailing cyclist, this study also confirms and quantifies the drag reduction for the leading cyclist. This effect was also confirmed by the wind-tunnel measurements: for DP with d = 0.15 m, the measured drag reduction of the leading cyclist was 1.6% versus 1.3 % by CFD simulation. The CFD simulations are used to explain the aerodynamic drag effects by means of the detailed pressure distribution on and around the cyclists. It is shown that both drafting cyclists significantly influence the pressure distribution on each other's body and the static pressure in the region between them, which governs the drag reduction experienced by each cyclist. These results imply that there is an optimum strategy for team time trials, which should be determined not only based on the power performance but also on the body geometry, rider sequence and the resulting aerodynamic drag of each team member. Similar studies can be performed for other sports such as skating, swimming and running

Computational fluid dynamics analysis of drag and convective heat transfer of individual body segments for different cyclist positions

This study aims at investigating drag and convective heat transfer for cyclists at a high spatial resolution. Such an increased spatial resolution, when combined with flow-field data, can increase insight in drag reduction mechanisms and in the thermo-physiological response of cyclists related to heat stress and hygrothermal performance of clothing. Computational fluid dynamics (steady Reynolds-averaged Navier-Stokes) is used to evaluate the drag and convective heat transfer of 19 body segments of a cyclist for three different cyclist positions. The influence of wind speed on the drag is analysed, indicating a pronounced Reynolds number dependency on the drag, where more streamlined positions show a dependency up to higher Reynolds numbers. The drag and convective heat transfer coefficient (CHTC) of the body segments and the entire cyclist are compared for all positions at racing speeds, showing high drag values for the head, legs and arms and high CHTCs for the legs, arms, hands and feet. The drag areas of individual body segments differ markedly for different cyclist positions whereas the convective heat losses of the body segments are found to be less sensitive to the position. CHTC-wind speed correlations are derived, in which the power-law exponent does not differ significantly for the individual body segments for all positions, where an average value of 0.84 is found. Similar CFD studies can be performed to assess drag and CHTCs at a higher spatial resolution for applications in other sport disciplines, bicycle equipment design or to assess convective moisture transfer.status: publishe

Aerodynamic study of different cyclist positions: CFD analysis and full-scale wind-tunnel tests

Three different cyclist positions were evaluated with Computational Fluid Dynamics (CFD) and wind-tunnel experiments were used to provide reliable data to evaluate the accuracy of the CFD simulations. Specific features of this study are: (1) both steady Reynolds-averaged Navier-Stokes (RANS) and unsteady flow modelling, with more advanced turbulence modelling techniques (Large-Eddy Simulation - LES), were evaluated; (2) the boundary layer on the cyclist's surface was resolved entirely with low-Reynolds number modelling, instead of modelling it with wall functions; (3) apart from drag measurements, also surface pressure measurements on the cyclist's body were performed in the wind-tunnel experiment, which provided the basis for a more detailed evaluation of the predicted flow field by CFD. The results show that the simulated and measured drag areas differed about 11% (RANS) and 7% (LES), which is considered to be a close agreement in CFD studies. A fair agreement with wind-tunnel data was obtained for the predicted surface pressures, especially with LES. Despite the higher accuracy of LES, its much higher computational cost could make RANS more attractive for practical use in some situations. CFD is found to be a valuable tool to evaluate the drag of different cyclist positions and to investigate the influence of small adjustments in the cyclist's position. A strong advantage of CFD is that detailed flow field information is obtained, which cannot easily be obtained from wind-tunnel tests. This detailed information allows more insight in the causes of the drag force and provides better guidance for position improvements.status: publishe

Computational fluid dynamics analysis of cyclist aerodynamics: Performance of different turbulence-modelling and boundary-layer modelling approaches

This study aims at assessing the accuracy of computational fluid dynamics (CFD) for applications in sports aerodynamics, for example for drag predictions of swimmers, cyclists or skiers, by evaluating the applied numerical modelling techniques by means of detailed validation experiments. In this study, a wind-tunnel experiment on a scale model of a cyclist (scale 1:2) is presented. Apart from three-component forces and moments, also high-resolution surface pressure measurements on the scale model's surface, i.e. at 115 locations, are performed to provide detailed information on the flow field. These data are used to compare the performance of different turbulence-modelling techniques, such as steady Reynolds-averaged Navier-Stokes (RANS), with several k-epsilon and k-omega turbulence models, and unsteady large-eddy simulation (LES), and also boundary-layer modelling techniques, namely wall functions and low-Reynolds number modelling (LRNM). The commercial CFD code Fluent 6.3 is used for the simulations. The RANS shear-stress transport (SST) k-omega model shows the best overall performance, followed by the more computationally expensive LES. Furthermore, LRNM is clearly preferred over wall functions to model the boundary layer. This study showed that there are more accurate alternatives for evaluating flow around bluff bodies with CFD than the standard k-epsilon model combined with wall functions, which is often used in CFD studies in sports.status: publishe

CONSOLE User's Manual.

The CONSOLE tandem is a tool for optimization-based design of a large class of systems. The essential requirements are that a simulator be available for evaluating the performance of instances of the system under consideration and that the parameters to be optimally adjusted vary over a continuous (as opposed to discrete) set of values. Todate, CONSOLE has been used on problems as diverse as design of a controller for a flexible arm, an aircraft, or a copolymerization reactor. The manual is organized as follows. In Chapter 1, the ideas and principles upon which CONSOLE is constructed are outlined and the design methodology underlying CONSOLE is sketched. Chapter 2 introduces the novice user to CONSOLE by way of a simple tutorial example. This chapter is strongly recommended to new users as it leads them step by step through a CONSOLE session. Chapter 3 is entirely devoted to CONVERT. It includes a thorough description of the different data types, assignments and commands that form the CONVERT syntax. Chapter 4 discusses SOLVE. The essential features of the optimization algorithm are outlined and the operation of SOLVE SOLVE is discussed. Special attention is given to the interactive capabilities of SOLVE, in particuar the Pcomb display. In Chapter 5, the question of using an interface between SOLVE and simulators of the user's choice is discussed. A general structure is given. Finally, Chapter 6 presents two design examples. Appendices A and B consist in reference manuals, for CONVERT and SOLVE respectively