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Kongens Lyngby, Denmark

Hovgaard T.G.,Danfoss A/S | Larsen L.F.S.,Danfoss A/S | Skovrup M.J.,IPU Technology Development | Jorgensen J.B.,Technical University of Denmark
2011 International Symposium on Advanced Control of Industrial Processes, ADCONIP 2011 | Year: 2011

Refrigeration systems consume a substantial amount of energy. Taking for instance supermarket refrigeration systems as an example they can account for up to 50-80% of the total energy consumption in the supermarket. Due to the thermal capacity made up by the refrigerated goods in the system there is a possibility for optimizing the power consumption by utilizing load shifting strategies. This paper describes the dynamics and the modeling of a vapor compression refrigeration system needed for sufficiently realistic estimation of the power consumption and its minimization. This leads to a non-convex function with possibly multiple extrema. Such a function can not directly be optimized by standard methods and a qualitative analysis of the system's constraints is presented. The description of power consumption contains nonlinear terms which are approximated by linear functions in the control variables and the error by doing so is investigated. Finally a minimization procedure for the presented problem is suggested. © 2011 Zhejiang University. Source

Kristiansen M.,University of Aalborg | Villumsen S.,University of Aalborg | Olsen F.O.,IPU Technology Development
Physics Procedia | Year: 2015

Remote fusion cutting (RFC) is an interesting industrial process compared to traditional laser cutting. It is because traditional laser cutting is limiting travel speed and accessibility due to the required positioning of the cutting head just above the workpiece for providing a cutting gas pressure. For RFC this pressure is created by the vapor, which is formed when the laser beam evaporates the cut material. The drawback of RFC compared to traditional laser cutting is a worse cut quality, wide cut kerf and a slower travel speed. The contribution of this paper is an experimental investigation, which determined the process window for RFC in stainless steel with a single mode fiber laser. The process variables: travel speed, focus position, power and sheet thickness were investigated. Based on the results of the experiments and process knowledge the aim of this work was to determine and describe the most important driving mechanisms for understanding and modelling the RFC process. The purpose is to deepen the understanding of the mechanisms in the process and find the factors, which can improve the performance and also determine the limitations. The validation results show that the developed model of the RFC process gives a similar process window as the experimental results for the tested parameters and variation of travel speed and focus position. © 2015 The Authors. Source

Hovgaard T.G.,Danfoss A/S | Hovgaard T.G.,Vestas Inc. | Hovgaard T.G.,Technical University of Denmark | Larsen L.F.S.,Danfoss A/S | And 3 more authors.
Canadian Journal of Chemical Engineering | Year: 2012

Supermarket refrigeration consumes substantial amounts of energy. However, due to the thermal capacity of the refrigerated goods, parts of the cooling capacity delivered can be shifted in time without deteriorating the food quality. In this study, we develop a realistic model for the energy consumption in super market refrigeration systems. This model is used in a Nonlinear Model Predictive Controller (NMPC) to minimise the energy used by operation of a supermarket refrigeration system. The model is non-convex and we develop a computational efficient algorithm tailored to this problem that is somewhat more efficient than general purpose optimisation algorithms for NMPC and still near to optimal. Since the non-convex cost function has multiple extrema, standard methods for optimisation cannot be directly applied. A qualitative analysis of the system's constraints is presented and a unique minimum within the feasible region is identified. Following that finding we propose a tailored minimisation procedure that utilises the nature of the feasible region such that the minimisation can be separated into two linear programs; one for each of the control variables. These subproblems are simple to solve but some iterations might have to be performed in order to comply with the maximum capacity constraint. Finally, a nonlinear solver is used for a small example without separating the optimisation problem, and the results are compared to the outcome of our proposed minimisation procedure for the same conceptual example. The tailored approach is somewhat faster than the general optimisation method and the solutions obtained are almost identical. © 2012 Canadian Society for Chemical Engineering. Source

Tang P.T.,IPU Technology Development
Micro and Nanosystems | Year: 2011

Electroforming is a surprisingly versatile process which is being utilised for production of a number of very different metallic products. The two main reasons for the exploitation of electroforming are the remarkable replication accuracy and the ability to grow seamless metallic products. In this paper the most important types of electroforming processes are discussed, along with the expected properties of the deposits and the challenges associated with selected applications. A special attention will be given to the utilisation of electroforming in the FlexPAET project. © 2011 Bentham Science Publishers. Source

De Chiffre L.,Technical University of Denmark | Carli L.,Technical University of Denmark | Eriksen R.S.,IPU Technology Development
CIRP Annals - Manufacturing Technology | Year: 2011

A novel artefact for calibration of the height in 3D microscopy is presented. The artefact comprises three steps having a common vertical axis, which allows z-coordinate calibration at different magnifications without requiring repositioning. The artefact is suitable for transferring traceability to 3D techniques at the micrometer and nanometer scale, e.g. 3D SEM, confocal microscopes etc. Two different series of samples were fabricated using EDM with three steps of 2-5-7 μm, and 20-50-70 μm, respectively, from a 3 mm diameter carbide wire. The artefact steps were calibrated on a stylus instrument according to ISO 5436 and measured on 3D microscopes. © 2011 CIRP. Source

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