Benny Ørtoft Endelt

A MODEL FOR CAVITATION-INDUCED PRIMARY BREAK-UP OF VISCOUS LIQUID SPRAYS

In this paper, a new model for cavitation induced primary break-up is proposed, which is able to map the influence of cavitating nozzle flow on spray formation. The model is applicable for viscous liquid sprays, where the Reynolds number is below 800. For such viscous spray systems, liquid break-up is enhanced when cavitation bubbles burst at the nozzle exit. The proposed model describes the transition from the flow inside the nozzle, modelled using a homogeneous equilibrium model (HEM) method, to the first primary droplets modelled using a Eulerian-Lagrangian method. Thus, providing the boundary conditions for the calculation of the secondary break-up and spray formation. The nozzle exit is divided into a definite number of patches, and liquid momentum and density from each patch are used to initialize the primary droplets. Using this method, the influence of bursting cavitation bubbles and asymmetrical properties of viscous sprays can be identified. The model has been implemented in the open-source CFD software package OpenFOAM and a first validation has been done using high-speed shadowgraphic imaging.

Rheological behaviour of lubrication oils used in two-stroke marine engines

Purpose The purpose of this study is to investigate the rheological behaviour of commercial lubrication oils used for cylinder lubrication in two-stroke marine diesel engines. Furthermore, it is of interest to investigate whether the viscosity of lubrication oils is affected by different levels of alkalinity. Design/methodology/approach Viscosity measurements are performed using both rotational and capillary rheometry. It was possible to measure oil viscosity in the shear rate from 0.1 to 3,000 s−1 using rotational rheometry, whereas capillary rheometry allowed measurements in higher shear rates from 5 × 105 to 1.3 × 106s−1 at 50°C. Findings The viscosity measurements show that the studied lubrication oils behave as a Newtonian fluid and that the viscosities are insensitive to the level of alkalinity. Furthermore, the viscosity/temperature dependency for the lubrication oils was found to fit the Arrhenius model. Originality/value This study presents useful information about the rheological behaviour of lubrication oils, more precisely how the oil properties are affected by shear rate, temperature and level of alkalinity. The value of this research is considered to be important for designing two-stroke diesel engines and cylinder lubrication systems.

Applied state space feedback control of a deep drawing process

This paper presents results from application of discrete state spacebased feedback control of the blank holder force (BHF) magnitude and distribution in the drawing ofa rectangular workpiece. By means of monitoring the flange draw-in during the punch stroke, the controller makes continuousadjustments to the BHF magnitude and distribution by individuallycontrolling the pressure of a hydraulic fluid in a number of cavitiesembedded in the blank holder plate. The adjustments are conducted onlineduring the punch stroke to minimize the deviation of the achieved flange draw-in from a predetermined reference.

Designing a feedback control algorithm for the tube hydroforming process

Tube hydroforming has a broad industrial appeal as the process enables production of geometrically complex parts within a single forming operation. The process is highly flexible with respect to adjustable process parameters (in the present context trajectories for the internal pressure and axial feeding). The objective of the present work is to identify a suitable and representative set of state variables and to develop a feedback algorithm enabling online control of material flow throughout the part using only limited/local information regarding the filling of the tool cavity. The filling of the tool is controlled by the internal pressure and the axial material feeding, and the proposed system operates with a constant axial feeding trajectory and controls the internal pressure based on the filling of the tool geometry. The methodology proves to be stable and flexible with respect to the dynamic behavior of the system and the numerical tests show that it is possible to control the quality and plastic def...

Statistical investigation of a blank holder force distribution system for a multi-step deep drawing process

This paper investigates process control possibilities obtained from a new tool concept for adaptive blank holder force (BHF) distribution. The investigation concerns the concept’s application to a multi-step deep drawing process exemplified by the NUMISHEET2014 benchmark 2: Springback of draw-redraw pan. An actuator system, where several cavities are embedded into the blank holder plate is used. By independently controlling the pressure of hydraulic fluid in these cavities, a controlled deflection of the blank holder plate surface can be achieved whereby the distribution of the BHF can be controlled. Using design of experiments, a full 3-level factorial experiments is conducted with respect to the cavity pressures, and the effects and interactions are evaluated.

Intelligent Shimming for Deep Drawing Processes

This paper demonstrates the use of an intelligent shimming system to compensate for changes in process output due to tool wear. A new tool concept with integrated hydraulic cavities used as actuators in feedback control system is presented. By prescribing a hydraulic pressure in the individual cavities the blank‐holder force distribution can be controlled during the punch stroke.By means of a sequence of numerical simulations abrasive wear is imposed to the deep drawing of a rectangular cup. The abrasive wear is modelled by changing the tool surface geometry using an algorithm based on the sliding energy density.As the tool surfaces are changed the material draw‐in is significantly altered when using conventional open‐loop control of the blank‐holder force. A feed‐back controller is presented which is capable of reducing the draw‐in difference to a certain degree. Further a learning algorithm is introduced to the system, which is able to improve the response of the feed‐back system significantly.

Analytic Differentiation of Barlat's 2D Criteria for Inverse Modeling

The demand for alternative identification schemes for identification of constitutive parameters is getting more pronounced as the complexity of the constitutive equations increases, i.e. the number of parameters subject to identification. A general framework for inverse identification of constitutive parameters associated with sheet metal forming is proposed in the article. The inverse problem is solved, through minimization of the least square error between an experimental punch force sampled from a deep drawing and a predicted punch force produced from a coherent finite element model.

Advanced Gradient Based Optimization Techniques Applied on Sheet Metal Forming

The computational‐costs for finite element simulations of general sheet metal forming processes are considerable, especially measured in time. In combination with optimization, the performance of the optimization algorithm is crucial for the overall performance of the system, i.e. the optimization algorithm should gain as much information about the system in each iteration as possible. Least‐square formulation of the object function is widely applied for solution of inverse problems, due to the superior performance of this formulation.In this work focus will be on small problems which are defined as problems with less than 1000 design parameters; as the majority of real life optimization and inverse problems, represented in literature, can be characterized as small problems, typically with less than 20 design parameters.We will show that the least square formulation is well suited for two classes of inverse problems; identification of constitutive parameters and process optimization.The scalability and ro...

Flexible Aluminum Tubes and a Least Square Multi-objective Non-linear Optimization Scheme

The automotive industry currently uses rubber hoses as the media carrier between e.g. the radiator and the engine, and the basic idea is to replace the rubber hoses with flexible aluminum tubes.A good quality is defined through several quality measurements, i.e. in the current case the key objective is to produce a flexible convolution through optimization of the tool geometry, but the process should also be stable, and the process stability is evaluated through Forming Limit Diagrams. Typically the defined objectives are conflicting, i.e. the optimized configuration represents therefore a trade‐off between the individual objectives, in this case flexibility versus process stability.The optimization problem is solved through iteratively minimizing the object function. A second‐order least square scheme is used for the approximation of the quadratic model, and the change in the design parameters is evaluated through the trust region scheme and box constraints are introduced within the trust region framewor...