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1.
In diesel common-rail systems, the exact knowledge of the injection pressure is important to accurately control the injected diesel mass and thus the combustion process. This paper focuses on the mathematical modelling of the hydraulic and mechanical components of a common-rail system in order to describe the dynamics of the diesel rail pressure. Based on this model, an average model is derived to reduce the model complexity and to allow for a fast calculation of the mass flow into the rail for different crank shaft revolution speeds and openings of the fuel metering unit. The main purpose of this average model is to serve as a basis for a model-based (non-linear) controller design. The stationary accuracy of the models is validated by means of measurement data. 相似文献
2.
An overview of the state-of-the-art in the performance modelling of computer systems is presented in this paper. The various forms of modelling procedures used in the past are reviewed with a greater emphasis given to new approaches which include queueing networks for mutliple-resource system analysis. Aspects of accuracy and computational efficiency of the algorithms involved are also discussed. 相似文献
3.
The design of a control oriented motorcycle model for the simulation of two-wheeled vehicles is widely recognized to be a very challenging task, as a complete analytical model is not directly available, due to its complexity and its high sensitivity to parameters' variations. Accordingly, a reliable model should be based on multibody modelling tools endowed with automated symbolic manipulation capabilities. This paper presents a simulation model for the dynamic behaviour of a motorcycle based on the object-oriented modelling paradigm developed in Modelica, within the Dymola environment. Specifically, we illustrate the modular approach to motorcycle modelling and discuss the tire-road interaction model, which is the crucial part of the proposed model. The validity of the proposed simulation model is assessed on real data, measured on an instrumented test vehicle. Further, to perform the verification phase a virtual driver model has been implemented, which allows to track both a roll angle and a target speed profile during different maneuvers. In particular, the behaviour of the driver is modelled as an inverse pendulum, with a rotational degree of freedom along the forward axis. This allows accounting for the driver lean angle, which is necessary to fully capture the real driving behaviour and its effects on the overall vehicle dynamics. 相似文献
4.
In this paper a new approach to the modelling of minimal surfaces is described and applied. Rather than use a continuous model, we develop a discrete, n-body model with basic tensile interactions derived from classical molecular force formulae. Computer results are described and discussed. 相似文献
5.
The paper describes the use of the grid-free Smoothed Particle Hydrodynamics (SPH) method to investigate lava flow from volcanic eruptions using real three dimensional topography in the form of Digital Terrain Models (DTM). Heat transfer resulting from conduction and radiation and solidification of the lava modelled via a variable viscosity are coupled to the fluid flow solution. Simulations show that the run-out distance and the nature of the lava flow are affected significantly by the lava viscosity and that this is dependent on the scale of the volcanic eruption, with solidification effects strongest on the smallest scale. SPH appears to be a highly effective technique for predicting lava flow with very good representations of the fluid free surface, close interaction with the complex topography, easy inclusion of the thermal and solidification effects leading to very plausible flow predictions. The pile-up of the lava at the front as it solidifies and the subsequent deceleration of the flow are easily modelled by SPH. 相似文献
7.
We attempt to explore the development of a financial crisis mathematically, constructing and analysing a simple qualitative mathematical model of a progressing crisis. This model brings an insight into the evolution of a crisis and enables us to evaluate the likely outcomes of the possible interventions that can slow the crisis’ progress or ameliorate its consequences. The model also helps to identify the factors and actions that may enhance the global economic security. 相似文献
8.
PLS Path modelling has several interesting advantages compared to other existing approaches traditionally used for structural
modelling. However, the lack of convergence properties of the existing iterative procedures for the computation of the latent
variables, has always been considered as a major drawback. The convergence is stated only in practice. The present paper shows
that when the estimation mode B is chosen for all blocks, the iterative procedure for the computation of latent variables
proposed by Wold (in Encyclopaedia of statistical sciences, vol 6. Wiley, New York, pp. 581–591, 1985) is monotonically convergent. 相似文献
10.
This article proposes a new formalism for the dynamic modelling of cables that can even be applied when they are submitted to cross flow of water or air. An important application is the case of umbilical cables used in remotely operated vehicles. The primary basis for the formulation is to assume that the continuous flexibility is represented by a discrete approach, consisting of rigid links connected by elastic joints, allowing movement in three dimensions. Each elastic joint allows three independent movements, called elevation, azimuth and torsion (twist). A significant contribution of the proposed formalism is the development of a compact equation that allows obtaining the Lagrangian of the system directly and automatically, regardless of the number of links chosen to form a chain of rigid bodies connected by flexible joints to represent the continuous flexibility of the cable. This formulation allows the construction of an algorithm for obtaining the equations of the dynamic model of flexible cables. 相似文献
11.
While the facilitated modelling literature recognises the importance of the group process within facilitated modelling workshops, published empirical research rarely examines their dynamic nature. In this paper, we address this gap in the literature in two ways. First, we propose to locate facilitated modelling workshops as the main focus of investigation, and adopt decision development as the analytical lens. Second, we provide guidance regarding how to implement a research strategy that is informed by such a focus. We start by mapping the different conceptualisations of decision development that seem embedded within the facilitated modelling tradition, and contrast them with theoretical models from the group communication field. Our analysis identifies a number of potentially useful areas for the study of facilitated modelling workshops from a decision development perspective, and articulates a number tentative research questions and testable propositions amenable to empirical research. Central to our proposal are research methods for the study of dynamic group processes. We thus discuss the steps required to extract group process data from facilitated modelling workshops that are usable and open to analysis. This includes a review of issues regarding research design, coding scheme development, data coding and choice of analytical techniques. Finally, we offer conclusions and briefly discuss some feasibility issues related to the implementation of our proposal. 相似文献
12.
This paper provides mathematical modelling for prefabricated timber-framed walls composed of a timber frame and fibre-plaster boards. Because the tensile strength of the fibre-plaster boards is approximately 10-times lower than the compressive one, it is convenient to strengthen the boards in their tensile diagonal direction with carbon fibre-reinforced polymer (CFRP) strips, which are glued to the boards. Based on analysis of experimental research results [M. Premrov, P. Dobrila, B.S. Bedenik, Analysis of timber-framed walls coated with CFRP strips strengthened fibre-plaster boards, Int. J. Solids Struct. 41 (24/25) (2004) 7035–7048] special approximate mathematical models have been developed. The models enable simultaneously to consider the influence of inserted CFRP strips, flexibility of mechanical fasteners in the connecting areas and any appearing of tensile cracks in the coating boards. 相似文献
13.
This paper provides a comparative study of simulation strategies for assessing risk in mortality rate predictions and associated estimates of life expectancy and annuity values in both period and cohort frameworks. 相似文献
14.
In this paper we formulate a dynamic model expressing the human life table data by using the first-passage-time theory for a stochastic process. The model is derived analytically and then is applied to the mortality data in Belgium and France. A stochastic simulation is also performed for the ‘health state function’ proposed and the related stochastic paths. Furthermore the implications of the proposed model and the results derived for pension funds and option theory are discussed. 相似文献
15.
A mathematical model of the solar dryers designed and used in Cuba is presented and discussed. The model consists of a set of ordinary nonlinear differential equations which describe the behaviour of the main parts of the dryer. Using the model, an optimal control problem is formulated and solutions within the class of piecewise constant controls are numerically obtained. It is shown that controls which are constant over intervals of 24 hours have the best properties for application to drying plants. 相似文献
16.
The complexity of biological regulatory networks often defies the intuition of the biologist and calls for the development of proper mathematical methods to model their structures and to delineate their dynamical properties. One qualitative approach consists in modelling regulatory networks in terms of logical equations (using either Boolean or multi-level discretisations). The Petri Net (PN) formalism offers a complementary framework to analyse the dynamical behaviour of large systems, either from a qualitative or from a quantitative point of view. Our proposal consists in articulating the logical approach with the PN formalism. In a previous work, we have already defined a systematic re-writing of Boolean regulatory models into a standard PN formalism. In this paper, we propose a rigorous and systematic mapping of multi-level logical regulatory models into specific standard Petri nets, called Multi-level Regulatory Petri Nets (MRPNs). We further propose some reduction strategies. Consequently, the resulting models become amenable to the algebraic and computational analyses used by the PN community. To illustrate our approach, we apply it to a multi-level logical model of the genetic switch controlling the lysis-lysogeny decision in the lambda bacteriophage. 相似文献
17.
An efficient three-dimensional non-hydrostatic model is applied to simulate free-surface waves interacting with structures. The model employs an implicit Crank–Nicholson scheme to discretize the Navier–Stokes equations under a Cartesian staggered grid framework. An integration method is introduced to account for the full effects of non-hydrostatic pressure at the free-surface layer. A domain decomposition method is proposed to effectively solve the resulting matrix system. The model is first validated by simulating three-dimensional sloshing waves in a container. The model is then applied to simulate waves propagating over two-dimensional and three-dimensional submerged structures, in which the effects of non-linearity and dispersion are important. The model results show that the model using only two vertical layers are in all favorable agreements with experimental data, demonstrating the efficiency and accuracy of the model on simulating surface waves interacting with structures. 相似文献
18.
In this paper, we utilize wavelet transform to obtain dynamical models describing the behaviour of fluid flow in a local spatial region of interest. First, snapshots of the flow are obtained from experiments or from computational fluid dynamics (CFD) simulations of the governing equations. A wavelet family and decomposition level is selected by assessing the reconstruction success under the resulting inverse transform. The flow is then expanded onto a set of basis vectors that are constructed from the wavelet function. The wavelet coefficients associated with the basis vectors capture the time variation of the flow within the spatial region covered by the support of the basis vectors. A dynamical model is established for these coefficients by using subspace identification methods. The approach developed is applied to a sample flow configuration on a square domain where the input affects the system through the boundary conditions. It is observed that there is good agreement between CFD simulation results and the predictions of the dynamical model. A controller is designed based on the dynamical model and is seen to be successful in regulating the velocity of a given point within the region of interest. 相似文献
19.
The limitations of the classic work of Lanchester on non-spatial ordinary differential equations for modelling combat are well known. We present work seeking to more realistically represent troop dynamics and to enable a deeper understanding of the nature of conflict. We extend Lanchesters ODEs, constructing a new physically meaningful system of partial differential equations. Spatial force movement and troop interaction components are represented with both local and non-local terms, expanding upon the swarming behaviour of fish and birds proposed by Mogilner et al. We are able to reproduce crucial behaviour such as the emergence of cohesive density profiles and troop regrouping after suffering losses in both one and two dimensions. 相似文献
20.
In the workplace mathematics and statistics are essential for communication and decision-making. Process workers at lower classifications of skill levels are likely to be confronted with statistical charts and warnings about nonconformity. Mathematics, statistics, and technology education in and for the workplace must take account of the cultural diversity which exists within and between workplaces. The design of generic mathematics, and in some cases statistics, curricula rarely reflect actual workplace practice except at a superficial level. One way of overcoming these problems is for mathematics/statistics educators to work in cooperation with industry, particularly at the local level, in a way that will encourage and support lifelong learning yet remain critical of the uses to which mathematics, statistics, and technology are put. This paper outlines some ways in which to address the challenge of making mathematics, statistics, and technology education take on real meaning within the context of the workplace. 相似文献
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