| 1. |
- Correa, Maicon Ribeiro, et al.
(författare)
-
A transient thermoelastic mathematical model for topology optimization of support structures in additive manufacturing
- 2024
-
Ingår i: Structural and multidisciplinary optimization (Print). - : SPRINGER. - 1615-147X .- 1615-1488. ; 67:3
-
Tidskriftsartikel (refereegranskat)abstract
- This study presents a Topology Optimization (TO) methodology for determining the optimal distribution of support structures in the powder bed fusion Additive Manufacturing (AM) fabrication technology. The support structures enhance thermal dissipation, reducing distortion on overhang surfaces during the build process and improving printability. A novel transient thermoelastic layer-by-layer model simulates the AM process, evaluating temperature and displacement in partially built structures with supports. We propose two new objective functions related to part distortion, perform their adjoint sensitivity analysis, and present a comprehensive set of numerical experiments with different geometries and levels of overhang complexity. The numerical results show non-standard optimal support structures obtained using the proposed TO-AM methodology for different model parameters, including support volume, thermal anisotropy, time discretization method, and building times for each layer.
|
|
| 2. |
- Haveroth, Geovane Augusto, et al.
(författare)
-
A thermal model for topology optimization in additive manufacturing: Design of support structures and geometry orientation
- 2024
-
Ingår i: Computers & structures. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0045-7949 .- 1879-2243. ; 301
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we present an efficient Topology Optimization (TO) approach designed to optimize support structures in metal Additive Manufacturing (AM), with a particular focus on Powder Bed Fusion (PBF) technology. The developed framework uses a purely thermal formulation to identify regions within the design that are susceptible to high heat concentrations. In the proposed modeling of the AM process, we postulate that new material layers are included in a partially built design that has already cooled to a controlled temperature. This aspect provides a layer -by -layer model of AM entirely local, enabling the building process parallelization and resulting in an algorithm with superior computational efficiency. Numerical results show the robustness of the proposed strategy, with the successful incorporation of support structures beneath overhanging surfaces and their effectiveness across a wide range of geometries and orientations. Furthermore, this framework is also applied to optimize the geometry orientation within the build chamber, further enhancing its applicability in the AM context.
|
|
| 3. |
- Gleeson, Daniel, 1988, et al.
(författare)
-
Generating Optimized Trajectories for Robotic Spray Painting
- 2022
-
Ingår i: IEEE Transactions on Automation Science and Engineering. - 1558-3783 .- 1545-5955. ; 19:3, s. 1380-1391
-
Tidskriftsartikel (refereegranskat)abstract
- In the manufacturing industry, spray painting is often an important part of the manufacturing process. Especially in the automotive industry, the perceived quality of the final product is closely linked to the exactness and smoothness of the painting process. For complex products or low batch size production, manual spray painting is often used. But in large scale production with a high degree of automation, the painting is usually performed by industrial robots. There is a need to improve and simplify the generation of robot trajectories used in industrial paint booths. A novel method for spray paint optimization is presented, which can be used to smooth out a generated initial trajectory and minimize paint thickness deviations from a target thickness. The smoothed out trajectory is found by solving, using an interior point solver, a continuous non-linear optimization problem. A two-dimensional reference function of the applied paint thickness is selected by fitting a spline function to experimental data. This applicator footprint profile is then projected to the geometry and used as a paint deposition model. After generating an initial trajectory, the position and duration of each trajectory segment are used as optimization variables. The primary goal of the optimization is to obtain a paint applicator trajectory, which would closely match a target paint thickness when executed. The algorithm has been shown to produce satisfactory results on both a simple 2-dimensional test example, and a non-trivial industrial case of painting a tractor fender. The resulting trajectory is also proven feasible to be executed by an industrial robot.
|
|
| 4. |
- Gleeson, Daniel, 1988, et al.
(författare)
-
Robot spray painting trajectory optimization
- 2020
-
Ingår i: IEEE International Conference on Automation Science and Engineering. - 2161-8070 .- 2161-8089. ; 2020-August, s. 1135-1140
-
Konferensbidrag (refereegranskat)abstract
- In the manufacturing industry, spray painting is often an important part of the process. Especially in the automotive industry, the perceived quality of the final product is closely linked to the exactness and smoothness of the painting process. For complex products or low batch size production, manual spray painting is often used. But in large scale production with a high degree of automation, the painting is normally performed by industrial robots. There is a need to improve and simplify the generation of robot trajectories used in industrial paint booths. A method for spray paint optimization is presented, which can be used to smooth out an initial trajectory and minimize paint thickness deviations from a target thickness. By fitting a spline function to experimental data, an applicator footprint profile is determined, which is a two-dimensional reference function of the applied paint thickness. This footprint profile is then projected to the geometry and used as a deposition model at each point along the trajectory. The positions and durations of all trajectory segments are used as optimization variables. They are modified with the primary goal to obtain a paint applicator trajectory, which will closely match a target paint thickness when executed. The algorithm is shown to produce satisfactory results on both a simple 2-dimensional test example, and a nontrivial industrial case of painting a tractor render. The final trajectory shows an overall thickness close to the target thickness, and the resulting trajectory is feasible to execute directly on an industrial robot.
|
|
| 5. |
- Kozakevicius, Alice de Jesus, et al.
(författare)
-
Solving a mixture model of two-phase flow with velocity non-equilibrium using WENO wavelet methods
- 2018
-
Ingår i: International Journal of Numerical Methods for Heat and Fluid Flow. - 0961-5539. ; 28:9, s. 2052-2071
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose The purpose of this work is to present the implementation of weighted essentially non-oscillatory (WENO) wavelet methods for solving multiphase flow problems. The particular interest is gas-liquid two-phase mixture with velocity non-equilibrium. Numerical simulations are carried out on different scenarios of one-dimensional Riemann problems for gas-liquid flows. Results are validated and qualitatively compared with solutions provided by other standard numerical methods. Design/methodology/approach This paper extends the framework of WENO wavelet adaptive method to a fully hyperbolic two-phase flow model in a conservative form. The grid adaptivity in each time step is provided by the application of a thresholded interpolating wavelet transform. This facilitates the construction of a small yet effective sparse point representation of the solution. The method of Lax-Friedrich flux splitting is used to resolve the spatial operator in which the flux derivatives are approximated by the WENO scheme. Findings Hyperbolic models of two-phase flow in conservative form are efficiently solved, as shocks and rarefaction waves are precisely captured by the chosen methodology. Substantial computational gains are obtained through the grid reduction feature while maintaining the quality of the solutions. The results indicate that WENO wavelet methods are robust and sufficient to accurately simulate gas-liquid mixtures. Originality/value Resolution of two-phase flows is rarely studied using WENO wavelet methods. It is the first time such a study on the relative velocity is reported in two-phase flows using such methods.
|
|
| 6. |
- Jacobson, Therese, et al.
(författare)
-
Cadmium Causes Misfolding and Aggregation of Cytosolic Proteins in Yeast
- 2017
-
Ingår i: Molecular and Cellular Biology. - : Informa UK Limited. - 0270-7306 .- 1098-5549. ; 37:17
-
Tidskriftsartikel (refereegranskat)abstract
- Cadmium is a highly poisonous metal and is classified as a human carcinogen. While its toxicity is undisputed, the underlying in vivo molecular mechanisms are not fully understood. Here, we demonstrate that cadmium induces aggregation of cytosolic proteins in living Saccharomyces cerevisiae cells. Cadmium primarily targets proteins in the process of synthesis or folding, probably by interacting with exposed thiol groups in not-yet-folded proteins. On the basis of in vitro and in vivo data, we show that cadmium-aggregated proteins form seeds that increase the misfolding of other proteins. Cells that cannot efficiently protect the proteome from cadmium-induced aggregation or clear the cytosol of protein aggregates are sensitized to cadmium. Thus, protein aggregation may contribute to cadmium toxicity. This is the first report on how cadmium causes misfolding and aggregation of cytosolic proteins in vivo. The proposed mechanism might explain not only the molecular basis of the toxic effects of cadmium but also the suggested role of this poisonous metal in the pathogenesis of certain protein-folding disorders.
|
|
| 7. |
- Johnson, Tomas, 1979, et al.
(författare)
-
A finite volume method for electrostatic three species negative corona discharge simulations with application to externally charged powder bells
- 2015
-
Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886. ; 74, s. 27-36
-
Tidskriftsartikel (refereegranskat)abstract
- A three species model for steady-state negative corona discharge is studied. Ionization, attachment, and recombination reactions are modeled. A novel unstructured finite volume algorithm to solve the equations is presented, using the secondary emission of electrons from the cathode to set boundary values for the electrons.To show the usefulness of the method for industrial applications it is used to characterize the electrostatic properties of an externally charged rotary powder bell used in the automotive industry. Experimental current density profiles are reconstructed with good accuracy, which validates the model and the method with real experimental data.
|
|
| 8. |
- Svedung Wettervik, Benjamin, 1990, et al.
(författare)
-
A domain decomposition method for three species modeling of multielectrode negative corona discharge with applications to electrostatic precipitators
- 2015
-
Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886. ; 77, s. 139-146
-
Tidskriftsartikel (refereegranskat)abstract
- The negative corona discharge problem for multi-electrode geometries is modeled by a three speciesmodel. The equations are solved using domain decomposition, by recognizing that multiple species areonly present in a small part of the domain, and hence only need to be incorporated locally in the model.The method is applied to an industrially relevant three wire electrostatic precipitator geometry. Thecalculated current density is in good agreement with experimental data. To further illustrate applicationsof the three species solution, it is used for coupled particle, fluid, and electrostatic simulations to analyzeparticle collection properties.
|
|
| 9. |
- Jakobsson, Stefan, 1970, et al.
(författare)
-
A time domain beam propagation method for chirped signals
- 2014
-
Ingår i: XXXV Congresso Nacional de Matemática Aplicada e Computacional, 8-12 September 2014, Natal, Brazil.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Chirped pulses are used in time stretch analog-to-digital converters to stretch high speed electric signals so that they can be measured with conventional detectors. Here a time domain beam propagation method for strongly chirped signals propagating along a specified direction is presented. By examining the propagation of chirped pulses in waveguides we derive a phase factor which captures the rapidly oscillating part of the chirped pulse. We then solve for the slowly varying envelope with respect to this phase factor in a time window moving with the pulse. The new method is applied to simulation of electro-optical modulators for chirped pulses with promising results.
|
|
| 10. |
- Shirvany, Yazdan, 1980, et al.
(författare)
-
Particle Swarm Optimization Applied to EEG Source Localization of Somatosensory Evoked Potentials
- 2014
-
Ingår i: IEEE Transactions on Neural Systems and Rehabilitation Engineering. - 1558-0210 .- 1534-4320. ; 22:1, s. 11-20
-
Tidskriftsartikel (refereegranskat)abstract
- One of the most important steps in presurgical diagnosis of medically intractable epilepsy is to find the precise location of the epileptogenic foci. Electroencephalography (EEG) is a noninvasive tool commonly used at epilepsy surgery centers for presurgical diagnosis. In this paper, a modified particle swarm optimization (MPSO) method is used to solve the EEG source localization problem. The method is applied to noninvasive EEG recording of somatosensory evoked potentials (SEPs) for a healthy subject. A 1 mm hexahedra finite element volume conductor model of the subject's head was generated using T1-weighted magnetic resonance imaging data. Special consideration was made to accurately model the skull and cerebrospinal fluid. An exhaustive search pattern and the MPSO method were then applied to the peak of the averaged SEP data and both identified the same region of the somatosensory cortex as the location of the SEP source. A clinical expert independently identified the expected source location, further corroborating the source analysis methods. The MPSO converged to the global minima with significantly lower computational complexity compared to the exhaustive search method that required almost 3700 times more evaluations.
|
|
