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- Appiah Mensah, Alex, et al.
(författare)
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Modelling potential yield capacity in conifers using Swedish long-term experiments
- 2022
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 512
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Tidskriftsartikel (refereegranskat)abstract
- Information on forest site productivity is a key component to assess the carbon sequestration potential of boreal forests. While site index (SI) is commonly used to indicate forest site productivity, expressions of SI in the form of yield capacity (potential maximum mean annual volume increment) is desirable since volume yield is central to the economic and ecological analyses of a given species and site. This paper assessed the functional relationship between SI and yield capacity on the basis of yield plot data from long-term experiments measured over several decades for Norway spruce (Picea abies), Scots pine (Pinus sylvestris), Lodgepole pine (Pinus contorta) and Larch (Larix decidua and Larix sibirica) in Sweden. Component models of total basal area and volume yield were also developed. SI was determined by existing height development functions using top height and age, whereas functions for stand-level (m2 ha- 1) basal area development were constructed based on age, SI and initial stand density using difference equations and nonlinear mixed-effects models. The relation between volume yield (m3 ha- 1) and top height was adjusted with total basal area production through nonlinear mixed-effects models. Species-specific parametric regression models were used to construct functional relationships between SI and yield capacity. The root mean square errors of the species-specific models ranged from 2 to 6% and 10-18% of the average values for the basal area and volume equations, respectively. For the yield capacity functions, the explained variations (R2) were within 80-96%. We compared our yield capacity functions to earlier functions of the species and significant differences were observed in both lower and higher SI classes, especially, for Scots pine and Norway spruce. The new functions give better prediction of yield capacity in current growing conditions; hence, they could later be used for comparing tree species' production under similar site and management regimes in Sweden.
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| 2. |
- Dhak, Janice, et al.
(författare)
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Developing a generic method for paper mill optimization
- 2004
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Ingår i: Proceedings of the PAPTAC Control Systems 2004 Conference, (Quebec City, Canada, June 14-18). ; , s. 207-214
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Konferensbidrag (refereegranskat)abstract
- A generic method for formulating pulp and paper optimization problems is presented. Two ongoing projects in the framework of the DOTS project illustrate the method: optimization of sizing quality at a specialty paper mill, and optimization of the water and broke systems at a coated paper mill. Explicit and implicit formulations are compared, and different usages of external simulators in conjunction with optimization are discussed. The problems are solved using MATLAB/TOMLAB. Some results from different optimization algorithms are also presented.
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| 3. |
- Dhak, Janice, et al.
(författare)
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Generic methods for paper mill optimisation
- 2004
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Ingår i: PTS-COST Symposium Simulation and Process Control for the Paper Industry, (Munchen, Germany, March 9-10, 2004).
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Konferensbidrag (refereegranskat)
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| 4. |
- Fransson, C. -M, et al.
(författare)
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Global controller optimization using horowitz bounds
- 2002
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Ingår i: IFAC Proceedings Volumes (IFAC-PapersOnline). ; , s. 247-252
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Konferensbidrag (refereegranskat)abstract
- A procedure for global optimization of PID type controller parameters for SISO plants with model uncertainty is presented. Robustness to the uncertainties is guaranteed by the use of Horowitz bounds, which are used as constraints when low frequency performance is optimized. The basic idea of both the optimization and the parameter tuning is to formulate separate criteria for low, mid and high frequency closed loop properties. The trade-off between stability margins, high frequency robustness and low frequency performance is then elucidated and, hence, the final choice of parameters is facilitated. The optimization problems are non-convex and ill-conditioned and we use a combination of new global and standard local optimization algorithms available in the TOMLAB optimization environment to solve the problem. The method does not rely on a good initial guess and converges fast and robustly. It is applied to a controller structure comparison for a plant with an uncertain mechanical resonance. For a given control activity and stability margin as well as identical tuning parameters it is shown that a PID controller achieves slightly improved low frequency performance compared to an H∞ controller based on loop-shaping. The reason for this somewhat surprising result is the roll-off in the H∞ controller, which adds additional high frequency robustness compared to the PID controller. Computationally, a factor of 10-20 has been gained compared to an earlier, less general, version of the procedure.
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| 8. |
- Holmström, Andreas, 1978, et al.
(författare)
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Efficient Space-time FE for a Simplified Thermo-metallurgical Problem Relevent to Casting
- 2005
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Ingår i: Computational Methods for Coupled Problems in Science and Engineering, COUPLED PROBLEMS 2005 Santorini Island, Greece, May 25-27, 2005. - 8495999714 ; , s. 227-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Solving the non-linear thermo-metallurgical problem such as the thermal cooling of a molten metal or the macro-segregation during a cooling process are problems that needs careful consideration. The strong non-linearities of the problem makes it difficult to solve without having a prohibitive high cost arising from the high spatial and time-domain discretization needed to solve the problem. For the studied application of design optimization of cast components a low computational time is important since a lot of computations are necessary in an optimization.From the first law of thermodynamics we derive a space-timeFE-discretization for a hierarchy of discontinuous Galerkin in time, dG(k) k>=0. This formulation integratesthe stored energy exact. As a special case we regain theenthalpy-method with suitable average of the energygeneration over time.For the macro-segregation, the problem is reformulated so that the phase-transition drives a flow of species. Diffusion is possible throughout the domain in this model. This can then be further rewritten using a potential approach. We can by this aproch arrive in discretizations that guaranties that the balance equation is satisfied and can solve phase-transition problem as a fieldproblem or as a local problem.The coupled problems of cooling-transformation are solved. The possibility of using adaptivity in space-time for the coupled problem is discussed.
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| 10. |
- Holmström, Andreas, 1978, et al.
(författare)
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Optimization of Cast Components in the Development Process
- 2005
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Ingår i: WCSMO6- 6th World Congress on Structural and Multidisciplinary Optimization, Rio de Janeiro, 30 May-3 June, 2005. ; , s. 26-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In structural optimization, we wish to design a component such that we fulfill a set of functional requirements while minimizing, for instance, the cost or weight of a component. Here we focus on the optimization of cast components in trucks. Of the functional requirements, several are related to strength issues. For a cast component, the resulting mechanical behavior depends on the casting process, and it must be taken into account that strong couplings exist between the geometry, the production process and the material properties. As a result, one is faced with a complex multidisciplinary optimization problem.In this contribution, a generic process for optimizing complex multi-physics problems is presented using a succession of more and more complex analyzes. The strategy that we propose is to use low level analyzes to scan a large number of different solutions in order to find the most viable ones. These are then further narrowed down during a chain of analyzes with successively higher level of detail, while trying not to remove good solutions. During the very latest stages of the analysis, only a few solutions are considered, and therefore, more time and resource consuming analyzes can be used in order to fully investigate the properties of the component.A principal problem of a cast component is discussed for a given a set of mechanical load demands and with consideration to the production process in order to exemplify the process and some possible pitfalls. The explicit computational procedure, based on FE-analysis, is applied to a simplified mechanical and thermal problems involved in the casting of a typical load-bearing structural component.
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