Petter Krus

Fast pipeline models for simulation of hydraulic systems

In most cases it is justified to regard pipelines as lumped capacitances when hydraulic systems are simulated. In some cases, however, when the system is widely distributed the wave propagation effects in lines may become important and there exists very good models today to simulate these effects. The price to be paid is that of a much larger computational effort. In this paper, a numerically highly efficient model is presented which is just slightly more demanding than a model to represent a pure capacitance, yet it captures all the essential characteristics of a line, the finite wave propagation speed and the distributed frequency dependent friction. The model only calculates state variables at the ends of a line and not in any internal nodes as most models do. Despite this, the model gives good results both in the time and frequency domain which compared to more elaborate models. If for some reason internal state variables are wanted they can be obtained by representing a line with several line elements. The model is integrated in the library of the HOPSAN simulation package and has been used successfully for simulation of oil hydraulic systems as well as the human cardiovascular system.

Flexible and robust CAD models for design automation

This paper explores novel methodologies for enabling Multidisciplinary Design Optimization (MDO) of complex engineering products. To realize MDO, Knowledge Based Engineering (KBE) is adopted with the aim of achieving design reuse and automation. The aim of the ongoing research at Linkoping University is to shift from manual modeling of disposable geometries to Computer Aided Design (CAD) automation by introducing generic high level geometry templates. Instead of repeatedly modeling similar instances of objects, engineers should be able to create more general models that can represent entire classes of objects. The proposed methodology enables utilization of commercial design tools, hence taking industrial feasibility into consideration. The concept of High Level CAD templates (HLCt) will be proposed and discussed as the building blocks of flexible and robust CAD models, which in turn enables high fidelity geometry in the MDO loop. Furthermore, quantification of the terms flexibility and robustness are presented, providing a means to measure the quality of the geometry models. Finally, application examples are presented in which the outlined framework is evaluated. The applications have been chosen from three ongoing research projects aimed at automating the design of transport aircraft, industrial robots, and micro air vehicles.

Optimizing Optimization for Design Optimization

Design optimization is becoming and increasingly important tool for design. In order to have an impact on the product development process it must permeate all levels of the design in such a way that a holistic view is maintained through all stages of the design. One important area is in the case of optimization based on simulation, which generally requires non-gradient methods and as a consequence direct-search methods is a natural choice. The idea in this paper is to use the design optimization approach in the optimization algorithm itself in order to produce an efficient and robust optimization algorithm. The result is a single performance index to measure the effectiveness of an optimization algorithm, and the COMPLEX-RF optimization algorithm, with optimized parameters.Copyright

Modeling of mechanical systems using rigid bodies and transmission line joints

Dynamic simulation of systems, where the differential equations of the system are solved numerically, is a very important tool for analysis of the detailed behavior of a system. The main problem when dealing with large complex systems is that most simulation packages rely on centralized integration algorithms. For large scale systems, however, it is an advantage if if the system can be partitioned in such a way that the parts can be evaluated with only a minimum of interaction. Using transmission line models, with distributed parameters, physically motivated pure time delays are introduced in the communication between components. These models can be used to represent both lines in a hydraulic system and springs in mechanical systems. As a result, components and subsystems can be simulated more independently of each other. In this paper it is shown how flexible joints based on transmission line modeling (TLM) with distributed parameters can be used to simplify modeling of large mechanical link systems interconnected with other physical domains. Furthermore, it provides a straightforward formulation for parallel processing.

A Web Service Approach for Model Integration in Computational Design

When today’s engineering design process involves information generated by a wide range of computational tools it is necessary to find tools and methods to integrate this information efficiently. Recent advances in the standardization of distributed application development give new potential to deal with this issue. The programming interfaces made available for this communication are referred to as Web Services and implies a straightforward way to exchange design data between engineers, simulation tools and other distributed information resources. The paper illustrates how simulation models and tools can be deployed as web services and how functionality and design data can be exchanged between these tools and accessed from standard desktop applications. An integration framework is presented where distributed services are integrated and the computational process is explicitly defined and executed. This model integration service also enables design optimization using the COMPLEX algorithm and Monte-Carlo simulation for probabilistic analysis of the design. The presented framework is built on open standards and gives new potential to already existing tools. By wrapping computational tools into a web service they can be integrated and accessed by any other application supporting web-service communication regardless of computer platform or operating system.Copyright

Validation of Models for Small Scale Electric Propulsion Systems

At Linkoping University work has been carried out towards having an automated designand manufacturing process of Micro Air Vehicles (MAV). A dedicated design optimizationframework has been develope ...

Flow versus pressure control of pumps in mobile hydraulic systems

This work studies an innovative working hydraulic system design for mobile applications, referred to as flow control. The fundamental difference compared to load-sensing systems is that the pump is controlled based on the operator’s command signals rather than feedback signals from the loads. This control approach enables higher energy efficiency since the pressure difference between pump and load is given by the system resistance rather than a prescribed pump pressure margin. Furthermore, load-sensing systems suffer from poor dynamic characteristics since the pump is operated in a closed-loop control mode. This might result in an oscillatory behaviour. Flow control systems have no stability issues attached to the load pressure feedback since there is none. This allows the pump to be designed to meet the response requirements without considering system stability. Pressure compensators are key components in flow control systems. This study addresses the flow matching problem which occurs when using traditional compensators in combination with a flow-controlled pump. Flow sharing pressure compensators solve this problem since the pump flow will be distributed between all active functions. Simulation results and measurements on a wheel loader application demonstrate the energy-saving potentials and the dynamic improvements for the flow control system.

Methods for Discrete Design Optimization

One area in design optimization is component based design where the designer has to choose between many different discrete alternatives. These types of problems have discrete character and in order ...

Using CAD-Tools and Aerodynamic Codes in a Distributed Conceptual Design Framework

Aircraft design is an inherently multi-disciplinary activity that requires different models and tools for various aspects of the design. At Linkoping University a novel design framework is being developed to support the initial conceptual design phase of a new aircraft. Different modules are included, each one addressed to analyze and evaluate different aspects of the airplane, such as its aerodynamics, its weight and structure, its sub systems and its performances. All modules are easily accessible from a user-friendly interface based on an Excel spreadsheet. The link between all modules is based on Service Oriented Architecture (SOA) and allows both distribution and integration of all functions. This paper will present the framework, give an overview of its development status and give an indication on the future work.

Distributed Aircraft Analysis Using Web Service Technology

The design of modern aircraft requires the integration of multidisciplinary mouels for analysis in the early design phase to increase the chances of a successful project. In this paper, a framework ...