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| 2. |
- Adiels, Emil, 1989, et al.
(författare)
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The use of virtual work for the formfinding of fabric, shell and gridshell structures
- 2018
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Ingår i: Proceedings of the Advances in Architectural Geometry conference 2018. - 9783903015135 ; , s. 286-315
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Konferensbidrag (refereegranskat)abstract
- The use of the virtual work theorem enables one to derive the equations of static equilibrium of fabric, shell and gridshell structures from the compatibility equations linking the rate of deformation of a surface to variations in its velocity. If the structure is treated as a continuum there is no need to consider its micro-structure provided that the grid is fine compared to the overall geometry. Thus we can include fabrics, ribbed shells, corrugated shells and gridshells with a fine grid, such as the Mannheim Multihalle. The equilibrium equations are almost identical to those obtained by assuming that a shell is thin and of uniform thickness, but are more general in their application. Our formulation introduces the concept of geodesic bending moments which are relevant to gridshell structures with continuous laths. The virtual work theorem is more general than the energy theorems, which it in- cludes as a special case. Hence it can be applied to surfaces which admit some form of potential, including minimal surfaces and hanging fabrics. We can then use the calculus of variations for the minimization of a surface integral to define the form of a structure. Many existing formfinding techniques can be rewritten in this way, but we concen- trate on surfaces which minimize the surface integral of the mean curvature subject to a constraint on the enclosed volume, producing a surface of constant Gaussian curvature. This naturally leads to the more general study of conjugate stress and curvature directions, and hence to quadrilateral mesh gridshells with flat cladding panels and no bending moments in the structural members under own weight.
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| 3. |
- Andersson, Mats, et al.
(författare)
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Road Friction Estimation
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This project is part of the Swedish IVSS program. The aim of IVSS is to stimulate research and development for the road safety of the future. Road conditions with low friction have been identified as a frequent cause of traffic accidents. Therefore, technology to automaticallydetect changes in road conditions and alert the driver or take proper actions with active driver support systems would be a key contribution to increased road safety.The aim of this project was to investigate the possibilities to estimate the tire to road friction.Three different approaches have been developed and evaluated, from concept to early prototypes in test vehicles. In the first method, the estimation of the coefficient of friction is based on the forces and torques that are produced at the front tires at cornering maneuvers.The second method is based on a physical model of the tire behavior and estimates road friction from information on the forces that are produced at straight driving. The third method is based on an optical sensor that classifies the road surface ahead of the vehicle.The three methods have been successfully evaluated in proving ground and public road tests in summer and winter conditions with different tires, and have been compared with reference measurements. The conclusion is that all three methods can be used for tire to road frictionestimation and are recommended for further development and industrialization.
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| 4. |
- Blomdell, Anders, et al.
(författare)
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Extending an Industrial Robot Controller-Implementation and Applications of a Fast Open Sensor Interface
- 2005
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Ingår i: IEEE Robotics & Automation Magazine. - 1070-9932. ; 12:3, s. 85-94
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Tidskriftsartikel (refereegranskat)abstract
- Many promising robotics research results were obtained during the late 1970s and early 1980s. Some examples include Cartesian force control and advanced motion planning. Now, 20 years and many research projects later, many technologies still have not reached industrial usage. An important question to consider is how this situation can be improved for future deployment of necessary technologies. Today, modern robot control systems used in industry provide highly optimized motion control that works well in a variety of standard applications. To this end, computationally intensive, model-based robot motion control techniques have become standard during the last decade. While the principles employed have been known for many years, deployment in products required affordable computing power, efficientengineering tools, customer needs for productivity/performance, and improved end-user competence in the utilization of performance features. However, applications that are considered nonstandard today motivate a variety of research efforts and system development to package results in a usable form. Actually, robots are not useful for many manufacturing tasks today, in particular those found in small and medium enterprises (SMEs). Reasonsinclude complex configuration, nonintuitive (for the shop floor) programming, and difficulties instructing robots to deal with variations in their environment. The latter challenge includes both task definitions and definition of motion control utilizing external sensors. The key word here is flexibility, and flexible motion control is particularly difficult since the user or system integrator needs to influence the core real-time software functions that are critical for the performance and safe operation of the system. We must find techniques that permit real-time motion controllers to be extended for new, demanding application areas.
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| 5. |
- Olsson, Rolf, 1969-
(författare)
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MANAGING PROJECT UNCERTAINTY BY USING AN ENHANCED RISK MANAGEMENT PROCESS
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An increasing number of companies are focusing their efforts on project management. Project management is frequently used as an enabler for meeting an uncertain and turbulent environment. Consequently, the overall effectiveness of the project management process is essential for long-term profitability. The aim and final effects of project management are to predict the outcome, i.e. cost, time and quality. However, uncertainty is inherent in the objectives of the project itself, as we use assumptions and expectations in defining and realizing the outcome of the project. A project’s ability to identify and react to uncertainty will influence the outcome of the project. Presently, risk management processes exist in several forms and are often used to manage uncertainty. However, it is frequently argued in academia as well as for the practitioner that risk management does not live up to expected results. The overall objective of this research is to improve the process for managing risks and opportunities within a project organization. The research starts from the single project view, followed by the strategic link to business strategy by including the project portfolio management perspective. Finally, the research focuses on opportunities and the ability of a project to realize them. Thus, the research questions addressed concern how risk is conceived in a theoretical global context and how this would assist in developing a methodology for risk management in an international project organization. They also involve how risk management within a project portfolio could be conducted and its effectiveness measured. Finally, the research questions also address how the management of opportunities could be improved. This research includes the development of four methodologies, based on industrial need. A holistic approach with a systems perspective has been used in order to handle the complexity of the research task. Both empirical and theoretical material has been used for developing the proposed methodologies. The developed methodologies for project risk management and the measures of its effectiveness have been tested and improved over a five-year period within the complete case company. Subsequently, two of them were implemented. The developed methodologies show that the risk management process in a single project does not foster learning and is not directly applicable within a portfolio of projects. Furthermore, the risk management process is not able to address all types of uncertainty. The project manager is a major factor in an effective management of uncertainty. When identifying and managing opportunity, having the ability to create a holistic view, to oversee both customer expectations, and to communicate project related information are important factors. Furthermore, the implementation also showed that it is actually possible, through the consistent use of a risk management process, to develop a cultural behavior within an organization that is much more preventive and proactive than before.
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| 6. |
- Henrysson, Erica, 1987, et al.
(författare)
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Conceptual Design and Analysis of Membrane Structures
- 2016
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Ingår i: Proceedings of 29th Nordic Seminar on Computational Mechanics – NSCM29.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this work one approach for formfinding and analysing tension membranestructures is described. Focus has been on the conceptual stage. For this the computersoftware SMART Form has been further developed, enabling the possibility to do real-timeformfinding and analysis of fabric structures. The software is based on a method where theorthotropic membrane is modeled with a triangular mesh, where the mass is lumped on thenodes. As a computational tool dynamic relaxation is used to find the static equilibriumconfiguration for the structure. The advantage with this is that there is no need for formulationand manipulation of matrices common in the finite element method.
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| 7. |
- Olsson, Jens, 1985, et al.
(författare)
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The numerical simulation of standard concrete tests and steel reinforcement using force flux peridynamics
- 2023
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Ingår i: Structural Concrete. - : Wiley. - 1751-7648 .- 1464-4177. ; 24:2, s. 2071-2092
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Tidskriftsartikel (refereegranskat)abstract
- Peridynamics is a numerical particle-based solid mechanics method that enables the simulation of brittle and quasi-brittle materials, as well as ductile materials. It allows cracking to appear spontaneously in the arms joining the particles and can therefore be used to simulate progressive fracture. In this article, we apply our version of peridynamics, which we call force flux peridynamics, to the simulation of concrete where the appearance of cracks plays an important role in the global mechanical properties. It is not difficult to modify the material parameters in peridynamics to achieve a given tensile strength or a given compressive strength. However, it is much more difficult to choose parameters which will model all the strength parameters of a material within the same model. When concrete fails in compression it may split or spall showing a complex relationship between compressive and tensile failure. We therefore set ourselves the simple task of producing a single peridynamics model which can predict the stiffness and strength behavior of concrete in standard compression and tension tests for which we chose the American Society for Testing and Materials standards for the cylinder compression test, the split cylinder test, and the modulus of rupture test. A parameter sensitivity study was performed based on the cylinder compression test to tune the key peridynamics parameters that determine the global material behavior. The compressive and tensile strengths were then determined from the combined simulation data. While the fracture modes, crack branching pattern and also the stress–strain curve show promising results, the maximum tensile strength was found to be significantly larger than physical experiments suggest. This is probably due to imperfections within real concrete at the interface between aggregate particles and cement paste and it shows that the detailed numerical modeling of the failure of concrete is highly complex with a large number of unknown material parameters.
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| 8. |
- Olsson, Erik, et al.
(författare)
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Fault Diagnosis of Industrial Robots using Acoustic Signals and Case-Based Reasoning
- 2004
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Ingår i: Case-Based Reasoning. ECCBR 2004. Lecture Notes in Computer Science, vol 3155. - Berlin, Heidelberg : Springer Berlin Heidelberg. ; , s. 686-701
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Konferensbidrag (refereegranskat)abstract
- In industrial manufacturing rigorous testing is used to ensure that the delivered products meet their specifications. Mechanical maladjustment or faults often show their presence as deviations compared to a normal sound pro-file. This is the case in robot assembly, the selected application domain for the system. Manual diagnosis based on sound requires extensive experience, and the experience is often acquired through costly mistakes and reduced production efficiency or quality loss caused by missed faults. The acquired experience is also difficult to preserve and transfer, and often lost if personnel leave the task of testing and fault diagnosis. We propose a Case-Based Reasoning approach to collect and preserve experience. The solution enables fast experience transfer and leads to less experienced personnel required to make more reliable and informed testing. Sounds from normal and faulty equipment are recorded and stored in a case library together with a diagnosis. Addition of new validated sound profiles continuously improves the system’s performance. The system can preserve and transfer experience between technicians, reducing overall fault identification time and increases quality by reduced number of missed faults. The original sound recordings are stored in form of the extracted features to-gether with other experience, e.g. instructions, additional tests, advice, user feedback etc.
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| 9. |
- Ander, Mats, 1964, et al.
(författare)
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A building of unlimited height
- 2019
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Ingår i: IASS Symposium 2019 - 60th Anniversary Symposium of the International Association for Shell and Spatial Structures; Structural Membranes 2019 - 9th International Conference on Textile Composites and Inflatable Structures, FORM and FORCE. - 9788412110104 ; , s. 1465-1472
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Konferensbidrag (refereegranskat)abstract
- We consider the overall buckling under own weight of a thin-walled column of circular cross-section and a radius that is a hyperbolic sine function of distance from the top of the column. The maximum stress is limited to a given value, but there is no limit to the height of the column. The wall thickness is determined by consideration of local buckling. It can be made to represent a building by adjusting the own weight of the column to include the weight of the floors, finishes, cladding and imposed load.
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| 10. |
- Olsson, Jens, 1985, et al.
(författare)
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Adaptive bone re-modelling for optimization of porous structural components
- 2022
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Ingår i: Proceedings of the IASS Annual Symposium 2022 and APCS 2022.
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Konferensbidrag (refereegranskat)abstract
- This paper presents a speculative application of adaptive bone-remodelling to generate porous structures for building components using a numerical meshless method. We hypothesize that such porous structures could then be 3d printed to achieve light weight and material efficient building components. The meshless model is built up of particles that are connected by arms to their neighbours within a distance called a horizon. The re-modelling adaption is then based on the ratio of arms strain over average arm strain which is mapped to a third-order polynomial function and used to scale the arm stiffness in a way that mimics the resorption and densification of bone tissue. The method is shown to work rather well in the recreation of the structural patterns found in cross section of a femur bone. The translation to a geometry which can be manufactured with additive techniques is not tackled specifically and suggest a direction for further work.
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