Practical Design Tool Research Articles

Validation of simulation model for robotic milking barn design

As milking robots are a recent technological development, there are few precedents and little experience to draw upon when designing robotic milking barns. There is wide diversity among farms, so the optimal layout of the robotic milking barn (RMB) varies accordingly. Using a behaviour-based simulation model, the design focused on optimal facility allocation and its relation with feeding routine, herd size, management practices, etc. This paper applies validation study, compares data on real and simulated RMBs. Measurements from a real robotic farm with 10, 20, and 29 cows are compared with simulation data. The simulation model appears to be a valid, accurate representation of the real system, under commercially feasible conditions. This hypothesis is tested statistically and is not rejected at α=2.5%. So, the conclusion is that the model is a practical design tool, enabling the designer to optimise facility allocation and barn layout.

Monte Carlo simulation of flood frequency curves from rainfall

The currently adopted rainfall-based design flood estimation techniques, for example the Design Event Approach, do not account for the probabilistic nature of the key variables except for the rainfall depth. This arbitrary treatment of key inputs and parameters can lead to inconsistencies and significant bias in flood estimates for a given average recurrence interval. This paper presents a Monte Carlo simulation technique that makes explicit allowance for the probability-distributed nature of the key flood producing variables and the dependencies between them to determine derived flood frequency curves. The proposed approach employs joint probability principles to develop a design flood estimation technique that can incorporate commonly applied rainfall–runoff models and design data. The application of the proposed technique to three catchments in Victoria has shown that the new method provides a relatively precise reproduction of the observed frequency curves. The new technique is relatively easy to apply for catchments with good rainfall data and a limited streamflow record. The technique thus shows a strong potential to become a practical design tool; further work is needed to allow its routine application in a wider range of design situations.

Development and validation of a zonal model — POMA

This paper reports the development of a simplified numerical model, Pressurized zOnal Model with Air-diffuser (POMA), which is able to predict the airflow pattern and thermal distributions within a room. POMA model is based on the conservation of mass and energy. Jet characteristic equations were introduced in the model to generalize its application to mechanically ventilated buildings. POMA's prediction was compared with the experimental results and with the prediction of another zonal model as well as a CFD model. Comparisons were made for both natural and force ventilation cases, and in the case of force ventilation the comparison was done for cross-ventilation and a linear ceiling jet. The good agreements between results of POMA model and those of a CFD model and experimental data demonstrated that POMA model was a practical tool for ventilation system design.

Practical assessment of project performance: the ?potential impact? approach

This article sets out an approach to assessing project performance, using ‘potential impact’ of the project. Its purpose is to assist project design and evaluation. In project design, potential impacts of alternative activities on the project objective are compared, in order to select activities with the greatest impact. In project evaluation, potential and actual impacts of a project are compared. Additional benefits of the approach are that it indicates ‘value for money’ of development assistance invested in projects, and easier tracing of reasons for underachievement in projects to weaknesses in their design or management. Limitations are that it relies on informed judgement of the planners or evaluators and the categories for rating performance may unavoidably be broad. It complements the logical framework approach by providing a practical design and evaluation tool. Copyright © 2000 John Wiley & Sons, Ltd.

Ground movements around excavations in granular soils: a few remarks on the influence of the constitutive assumptions on FE predictions

Two different approaches for modelling soil non-linearity (hardening plasticity and hypoplasticity) are compared with reference to the analysis of soil–structure interaction in an excavation in dense dry sand, supported by a propped diaphragm wall. The analysis focuses on the prediction of wall and soil movements. A commercial FE code has been used for the elastoplastic analyses, in order to assess the performance of a readily available design tool in current geotechnical engineering practice as compared to the predictions of a more advanced research tool. Although obtained for an idealized scheme, the results allow a number of more general conclusions to be drawn on the influence of the constitutive assumptions. Copyright © 2000 John Wiley & Sons, Ltd.

Ground heat transfer effects on the thermal performance of earth-contact structures

A review of ground heat transfer effects on the thermal performance of earth contact structures is presented. The fundamental heat transfer processes relevant to the problem are described along with methods of determining thermal properties of soils. An overview of the many analytical, semi-analytical and numerical methods available to solve the heat transfer problem is also provided, followed by a brief summary of design guides. The review also considers the influence of changes in ground water content on the heat transfer properties of soils. A description of the processes that give rise to changes in ground water conditions is provided. The bulk thermal conductivity of a soil is shown to be strongly related to its water content. An overview of methods of analysing changes in soil moisture content is then presented. Methods of estimating the relevant hydraulic properties of soils are also considered. The final part of the review provides a brief outline of the theoretical approach required to analyse coupled heat and moisture migration in soils. Notwithstanding the fact that there are many practical design tools available, it appears that further work is necessary to clarify the circumstances in which more sophisticated analysis is warranted. Recent studies indicate that geometric simplification can lead to quite significant errors in heat loss calculation. Full three-dimensional treatment appears to be necessary in some cases. Thermal properties of soils vary according to the properties and proportions of the constituent phases (air/water/solid). Soil moisture content variations occur naturally or as a result of anthropogenic activity. The influence of such variations on the thermal conductivity of the ground is significant. The review outlines some simplified methods of accommodating this feature of the ground heat transfer problem. However, this aspect of the problem appears to need further consideration.

The Clemson Limit Stress Diagram for Ductile Parts Subjected to Positive Mean Fatigue Loading

The Bagci, Gerber, Goodman, quadratic, and Soderberg diagrams are some of the diagrams proposed to serve as practical design tools for the design of ductile metals loaded in fatigue with positive mean and alternating stresses. However, all of these diagrams are either conservative, or have domains containing stress greater than yield strength of material. This paper presents the Clemson diagram, which has the same format as the aforementioned diagrams with the exception that the exponential power order varies with the material property. The Clemson diagram has a great potential to fit the experimental data and appears to better fit the limited data found in the open literature. A good initial approximation of an acceptable design for parts made of ductile ferrous materials can be obtained by using the proposed diagram. [S1050-0472(00)00301-9]

Ground movements around excavations in granular soils: a few remarks on the influence of the constitutive assumptions on FE predictions

Two different approaches for modelling soil non-linearity (hardening plasticity and hypoplasticity) are compared with reference to the analysis of soil–structure interaction in an excavation in dense dry sand, supported by a propped diaphragm wall. The analysis focuses on the prediction of wall and soil movements. A commercial FE code has been used for the elastoplastic analyses, in order to assess the performance of a readily available design tool in current geotechnical engineering practice as compared to the predictions of a more advanced research tool. Although obtained for an idealized scheme, the results allow a number of more general conclusions to be drawn on the influence of the constitutive assumptions. Copyright © 2000 John Wiley & Sons, Ltd.

Thermal stabilization of chemical reactors II. Bifurcation analysis of the Endex CSTR

The steady states of the dynamical Endex CSTR problem are analysed in terms of degenerate bifurcation (singularity) theory. Steady–state analysis is used in two ways: (1) as a device to assist in understanding and predicting complex dynamical behaviour; and (2) as a practical design and operational tool, by applying the concept of quasi–static parameter variation. In the bifurcation analysis, consideration is given to the effects of thermal mismatching, kinetic mismatching, and variations in the thermal exchange, mass flux and heat loss rate parameters, on the structure of the parameter space. The qualitative equivalence of the bifurcation structure of the kinetically matched perfectly coupled adiabatic Endex scheme and the single–reaction adiabatic CSTR is demonstrated, with reference to the role of the reaction enthalpy effects. Numerical analysis shows that either kinetic mismatching of the reactions or imperfect heat exchange may introduce Hopf bifurcations into the adiabatic system. This is a result that is both philosophically and practically important because it shows that limit cycles are not restricted to non–adiabatic thermokinetic systems. The coefficients of thermal exchange, mass flux and heat loss are found to induce distortions of the surface of saddle–node bifurcations (the limit–point shell) through codimension–2 bifurcations. The steady–state and oscillatory–state degeneracies are discussed with reference to the design and operational implications for a working system.

CPT‐Based Liquefaction Evaluation Using Artificial Neural Networks

This article presents various artificial neural network (ANN) models for evaluating liquefaction resistance and potential of sandy soils. Various issues concerning ANN modeling such as data preprocessing, training algorithms, and implementation are discussed. The desired ANN is trained and tested with a large historical database of liquefaction performance at sites where cone penetration test (CPT) measurements are available. The ANN models are found to be effective in predicting liquefaction resistance and potential. The developed ANN models are ported to a spreadsheet for ease of use. A simple procedure for conducting uncertainty analysis to address the issue of parameter and model uncertainties is also presented using the ANN‐based spreadsheet model. This uncertainty analysis is carried out using @Risk, which is an add‐in macro that works well with popular spreadsheet programs such as Microsoft Excel and Lotus 1‐2‐3. The results of the present study show that the developed ANN model has potential as a practical design tool for assessing liquefaction resistance of sandy soils.

Optimization of reinforced members for crash safety design of vehicles

CAE technology has been widely applied for the crash safety design of vehicles. Nevertheless, an optimum design approach has not been completed for the crash behavior of the vehicles because of the nonlinearity of the dynamic problem. The authors have proposed a Statistical Design Support System (SDSS), and suggested this is one of the available optimal approaches for nonlinear and dynamic problems such as the vehicles. In this study, the SDSS was applied for the multiobjective optimization design of the main reinforced members of a vehicle. The thicknesses of each member were chosen as the design variables, and the total weight and the deformation of the cabin as the multi-objective functions. It was shown that the SDSS could satisfactorily be used as a practical multi-objective optimization design tool for the crash safety design of vehicles, and the design cycle could be significantly reduced using SDSS. Transactions on the Built Environment vol 37 © 1999 WIT Press, www.witpress.com, ISSN 1743-3509

237 船舶流体シミュレーションの可視化

CFD (Computational Fluid Dynamics) techniques are being used as a practical design tool in ship hydrodynamics. As the techniques are applied to more complicated flow fields such as flows around a maneuvering ship or unsteady turbulent flows, it becomes more important to visualize flow data for understanding flow phenomena. In this paper, visualization results of ship flow simulations are shown.

Numerical analysis of an aperture coupled rectangular dielectric resonator antenna using a surface formulation and the method of moments

A rigorous analysis of an aperture coupled rectangular dielectric resonator antenna (DRA) is presented. The method is based on a surface integral equation approach by which the dielectric resonator (DR) is treated via a set of combined field integral equations (CFIE). The CFIE and associated coupling is then formulated with sets of mixed potential integral equations (MPIE). The coupled integral equations are solved by the method of moments (MoM) in the spatial domain using Galerkin's procedure. Complex images are employed in the calculation to enhance numerical efficiency. Numerical tests have shown that only a relatively small impedance matrix is needed to compute the parameters of the antenna with good accuracy. The numerical model is demonstrated to be a very versatile and practical design tool which can analyse the DRA with minimal computation effort.

Westergaard Curling Solution Reconsidered

An in-depth and systematic examination is presented of the effect of temperature gradients on slab-on-grade pavements. The main objective for the examination was the development of practical design tools for use in a typical engineering office. This has been achieved by a critical reconsideration of the literature, a synthesis of currently available analytical resources, and the implementation of recent technological achievements promulgated in related areas of engineering. Prominent among these are the application of the principles of dimensional analysis, the finite element method, advanced statistical regression analysis, and artificial neural networks (ANN). A number of ANNs have been trained for the curling problem, and in several instances they are found to be more efficient predictive tools than corresponding statistical regression equations. It is found that the most important shortcomings of the Westergaard curling solution are the assumption of continuous contact between slab and subgrade (infinite slab self-weight) and the explicit treatment of only daytime conditions. Although Westergaard’s curling-only predictions are significantly inferior to those from ANN and statistics, his load-plus-curling predictions exhibit approximately the same scatter as those from these two more modern and nominally more sophisticated tools. The case of Westergaard’s curling solution can serve as an example pointing to the usefulness and desirability of theoretical solutions, even when these are achievable only on the basis of considerable abstraction and simplification.

Finite element heat transfer analysis of viscoelastic damper for wind applications

Abstract A finite element approach for analyzing the thermal-structural coupling effects of the viscoelastic dampers subjected to steady-state excitation is presented. Nonlinear viscoelastic properties due to temperature rise in the viscoelastic material are considered in the analysis. Examples given in the paper illustrate that the finite element approach can properly predict the temperature distribution in the damper and can be used as a practical design tool.

Micromechanical modelling of textile composites using variational principles

The ever increasing use of textile reinforced composite materials for structural applications makes the development of automated and computationally efficient analysis tools a must. In this paper, a micromechanical method for predicting the thermo-mechanical behaviour of textile reinforced (twodimensional woven and braided fabrics) composites is presented. The model considers the shape and type of the yarns, yarn interactions and crimp as well as the matrix distribution. This modelling scheme consists of a multilevel automated geometric decomposition of a representative volume element (unit cell) into smaller elements (block and micro cells) containing yarn and matrix parts. This way, the problem of stress analysis for the whole unit cell is split into a number of subproblems at each level of the decomposition scheme. This top to bottom decomposition is followed by a bottom to top homogenisation scheme in which internal stresses (sub-unit cell level) are linked to external ones (unit cell level). This procedure results in the calculation of the stress-strain field and the prediction of the elastic properties of the composite. To develop this method the complementary variational principle was used. A FORTRAN software programme called TEXCOMP-CEM, has been developed to automate calculation and turn the method into a practical design tool. This program computes stiffness, micro-stress fields and first cell failure. Results obtained are comparable to those obtained experimentally and from finite element modelling. Transactions on Engineering Sciences vol 21, © 1998 WIT Press, www.witpress.com, ISSN 1743-3533

Design of Wood Diaphragms with Openings

The existence of openings in diaphragms causes concentration of shear forces around the openings and the generation of axial forces in the framing. In 1981, the Applied Technology Council developed the only guidelines for designing diaphragms with openings. The procedure for determining the shear around the opening, however, is complicated and has not been experimentally verified. Accordingly, simplified equations for determining the shear forces in diaphragms with openings are derived in this paper. The application of the membrane-to-brace replacement method to diaphragms is also discussed. Horizontal loading tests are conducted on three floor diaphragms designed to the same load. The ultimate loads are almost the same, regardless of the existence of the opening. The observed unit shear around the opening is close to the calculated value. The observed deflection is smaller than the value calculated on the basis of the nominal stiffness for the materials and the fasteners by 14–28%. It can be said from these results that all the methods perform well as a practical design tool.

Wear by surface fatigue on a new foundation part II. particle detachment mechanisms and quantitative aspects

An alternative model of wear produced by surface fatigue (SFW) was suggested. Surface cracks control the process of wear particle generation by SFW. New models of contact mechanics based on material microstructure and its evolution with time type, different from those models based on surface topography, were formulated. During dry sliding, the stress is exerted by pressure spots originated from groupings of harder material. A new quantitative investigation was set up to evaluate the contribution of SFW to the total wear loss produced during dry sliding. It was found that SFW is a major contributor to the overall wear loss generated during dry sliding. For cast irons and ceramic coating. SFW controls the amount of the total wear loss during dry sliding. SFW has a secondary contribution to the total wear loss for ceramic materials and sintered steels. Practical tools for design of materials that withstand SFW were suggested.

Aircraft conceptual design by genetic/gradient-guided optimization

In the present article, which describes the results of a Ph.D. research study (Bos, A.H.W., 1996a. Multidisciplinary Design Optimization of a Second-Generation Supersonic Transport Aircraft using a Hybrid Genetic/Gradient-guided Algorithm., Ph.D. Dissertation, Delft University of Technology, Bos, A.H.W., 1996b. Multidisciplinary Design Optimization of a Supersonic Transport Aircraft using a Hybrid Genetic/Guided-based Algorithm. AIAA 96-4055), a new design procedure based on the combination of a genetic and a gradient-guided optimization algorithm is presented. The procedure was applied to the design of a second-generation supersonic transport aircraft since the interdisciplinary couplings are particularly strong for this kind of aeroplane. Furthermore, since the design space for the defined design problem is extremely small (and even non-existent in cases where all the environmental constraints are imposed) it is very hard—if not impossible—to realize a feasible design by means of classic design procedures. It was established that the method presented here can actually be used as a practical design tool, since it is capable of generating a feasible design from scratch without the necessity to create a baseline design first. The optimization methods minimize constraint violations, and thus actually create a design instead of just adapting a baseline designed according to more traditional methods.

An interactive boundary-layer method for multielement airfoils

A calculation method for the aerodynamic prediction of multielement airfoils based on an interactive boundary-layer approach using an improved Cebeci–Smith eddy viscosity formulation is described. Results are first presented for single airfoils at low and moderate Reynolds numbers in order to demonstrate the need to calculate transition for accurate drag polar prediction and the ability of the improved Cebeci–Smith turbulence model to predict flows with extensive separation, and therefore to predict maximum lift coefficient. Results, in terms of pressure distributions and lift, drag and moment coefficients, are presented for a series of multielement airfoils with flaps and slats. The importance of the compressibility effects and the turbulence model on stall, and, again, the need to calculate the onset of transition, are demonstrated. Finally, recommendations are made for the preferred approach to predicting the aerodynamic performance of multielement airfoils for use as a practical and efficient design tool.