30,916 research outputs found
Two-stage optimization method for efficient power converter design including light load operation
Power converter efficiency is always a hot topic for switch mode power supplies. Nowadays, high efficiency is required over a wide load range, e.g., 20%, 50% and 100% load. Computer-aided design optimization is developed in this research work, to optimize off-line power converter efficiency from light load to full load. A two-stage optimization method to optimize power converter
efficiency from light load to full load is proposed. The optimization procedure first breaks the converter design variables into many switching frequency loops. In each fixed switching frequency loop, the optimal designs for 20%, 50% and 100% load are derived separately in the first stage, and an objective function using the optimization results in the first stage is formed in the second stage to consider optimizing efficiency at 20%, 50% and 100% load. Component efficiency models are also established to serve as the objective functions of optimizations. Prototypes 400V to 12V/25A 300W two-FET forward converters
are built to verify the optimization results
Working Notes from the 1992 AAAI Workshop on Automating Software Design. Theme: Domain Specific Software Design
The goal of this workshop is to identify different architectural approaches to building domain-specific software design systems and to explore issues unique to domain-specific (vs. general-purpose) software design. Some general issues that cut across the particular software design domain include: (1) knowledge representation, acquisition, and maintenance; (2) specialized software design techniques; and (3) user interaction and user interface
Template-based reverse engineering of parametric CAD models from point clouds
openEven if many Reverse Engineering techniques exist to reconstruct real objects in 3D, very few are able to deal directly and efficiently with the reconstruction of editable CAD models of assemblies of mechanical parts that can be used in the stages of Product Development Processes (PDP). In the absence of suitable segmentation tools, these approaches struggle to identify and reconstruct model the different parts that make up the assembly. The thesis aims to develop a new Reverse Engineering technique for the reconstruction of editable CAD models of mechanical parts’ assemblies. The originality lies in the use of a Simulated Annealing-based fitting technique optimization process that leverages a two-level filtering able to capture and manage the boundaries of the parts’ geometries inside the overall point cloud to allow for interface detection and local fitting of a part template to the point cloud. The proposed method uses various types of data (e.g. clouds of points, CAD models possibly stored in database together with the associated best parameter configurations for the fitting process). The approach is modular and integrates a sensitivity analysis to characterize the impact of the variations of the parameters of a CAD model on the evolution of the deviation between the CAD model itself and the point cloud to be fitted. The evaluation of the proposed approach is performed using both real scanned point clouds and as-scanned virtually generated point clouds which incorporate several artifacts that could appear with a real scanner. Results cover several Industry 4.0 related application scenarios, ranging from the global fitting of a single part to the update of a complete Digital Mock-Up embedding assembly constraints. The proposed approach presents good capacities to help maintaining the coherence between a product/system and its digital twin.openXXXIII CICLO - INGEGNERIA MECCANICA, ENERGETICA E GESTIONALE - Meccanica, misure e robotica01/A3 - ANALISI MATEMATICA, PROBABILITA' E STATISTICA MATEMATICA01/B1 - INFORMATICA09/B2 - IMPIANTI INDUSTRIALI MECCANICIShah, GHAZANFAR AL
CP4 miracle: shaping Yukawa sector with CP symmetry of order four
We explore the phenomenology of a unique three-Higgs-doublet model based on
the single CP symmetry of order 4 (CP4) without any accidental symmetries. The
CP4 symmetry is imposed on the scalar potential and Yukawa interactions,
strongly shaping both sectors of the model and leading to a very characteristic
phenomenology. The scalar sector is analyzed in detail, and in the Yukawa
sector we list all possible CP4-symmetric structures which do not run into
immediate conflict with experiment, namely, do not lead to massless or
mass-degenerate quarks nor to insufficient mixing or CP-violation in the CKM
matrix. We show that the parameter space of the model, although very
constrained by CP4, is large enough to comply with the electroweak precision
data and the LHC results for the 125 GeV Higgs boson phenomenology, as well as
to perfectly reproduce all fermion masses, mixing, and CP violation. Despite
the presence of flavor changing neutral currents mediated by heavy Higgs
scalars, we find through a parameter space scan many points which accurately
reproduce the kaon CP-violating parameter as well as oscillation
parameters in K and mesons. Thus, CP4 offers a novel minimalistic
framework for building models with very few assumptions, sufficient predictive
power, and rich phenomenology yet to be explored.Comment: 39 pages, 8 figures, 1 table; v2: expanded discussion, extra
references, matches published versio
Nanomechanical and topographical imaging of living cells by Atomic Force Microscopy with colloidal probes
Atomic Force Microscopy (AFM) has a great potential as a tool to characterize
mechanical and morphological properties of living cells; these properties have
been shown to correlate with cells' fate and patho-physiological state in view
of the development of novel early-diagnostic strategies. Although several
reports have described experimental and technical approaches for the
characterization of cell elasticity by means of AFM, a robust and commonly
accepted methodology is still lacking. Here we show that micrometric spherical
probes (also known as colloidal probes) are well suited for performing a
combined topographic and mechanical analysis of living cells, with spatial
resolution suitable for a complete and accurate mapping of cell morphological
and elastic properties, and superior reliability and accuracy in the mechanical
measurements with respect to conventional and widely used sharp AFM tips. We
address a number of issues concerning the nanomechanical analysis, including
the applicability of contact mechanical models and the impact of a constrained
contact geometry on the measured elastic modulus (the finite-thickness effect).
We have tested our protocol by imaging living PC12 and MDA-MB-231 cells, in
order to demonstrate the importance of the correction of the finite-thickness
effect and the change in cell elasticity induced by the action of a
cytoskeleton-targeting drug.Comment: 51 pages, 12 figures, 3 table
Engineering simulations for cancer systems biology
Computer simulation can be used to inform in vivo and in vitro experimentation, enabling rapid, low-cost hypothesis generation and directing experimental design in order to test those hypotheses. In this way, in silico models become a scientific instrument for investigation, and so should be developed to high standards, be carefully calibrated and their findings presented in such that they may be reproduced. Here, we outline a framework that supports developing simulations as scientific instruments, and we select cancer systems biology as an exemplar domain, with a particular focus on cellular signalling models. We consider the challenges of lack of data, incomplete knowledge and modelling in the context of a rapidly changing knowledge base. Our framework comprises a process to clearly separate scientific and engineering concerns in model and simulation development, and an argumentation approach to documenting models for rigorous way of recording assumptions and knowledge gaps. We propose interactive, dynamic visualisation tools to enable the biological community to interact with cellular signalling models directly for experimental design. There is a mismatch in scale between these cellular models and tissue structures that are affected by tumours, and bridging this gap requires substantial computational resource. We present concurrent programming as a technology to link scales without losing important details through model simplification. We discuss the value of combining this technology, interactive visualisation, argumentation and model separation to support development of multi-scale models that represent biologically plausible cells arranged in biologically plausible structures that model cell behaviour, interactions and response to therapeutic interventions
Computational Techniques to Predict Orthopaedic Implant Alignment and Fit in Bone
Among the broad palette of surgical techniques employed in the current orthopaedic practice, joint replacement represents one of the most difficult and costliest surgical procedures. While numerous recent advances suggest that computer assistance can dramatically improve the precision and long term outcomes of joint arthroplasty even in the hands of experienced surgeons, many of the joint replacement protocols continue to rely almost exclusively on an empirical basis that often entail a succession of trial and error maneuvers that can only be performed intraoperatively. Although the surgeon is generally unable to accurately and reliably predict a priori what the final malalignment will be or even what implant size should be used for a certain patient, the overarching goal of all arthroplastic procedures is to ensure that an appropriate match exists between the native and prosthetic axes of the articulation.
To address this relative lack of knowledge, the main objective of this thesis was to develop a comprehensive library of numerical techniques capable to: 1) accurately reconstruct the outer and inner geometry of the bone to be implanted; 2) determine the location of the native articular axis to be replicated by the implant; 3) assess the insertability of a certain implant within the endosteal canal of the bone to be implanted; 4) propose customized implant geometries capable to ensure minimal malalignments between native and prosthetic axes. The accuracy of the developed algorithms was validated through comparisons performed against conventional methods involving either contact-acquired data or navigated implantation approaches, while various customized implant designs proposed were tested with an original numerical implantation method.
It is anticipated that the proposed computer-based approaches will eliminate or at least diminish the need for undesirable trial and error implantation procedures in a sense that present error-prone intraoperative implant insertion decisions will be at least augmented if not even replaced by optimal computer-based solutions to offer reliable virtual “previews” of the future surgical procedure. While the entire thesis is focused on the elbow as the most challenging joint replacement surgery, many of the developed approaches are equally applicable to other upper or lower limb articulations
Nonlocal hydrodynamic influence on the dynamic contact angle: Slip models versus experiment
Experiments reported by Blake et al. [Phys. Fluids. 11, 1995 (1999)] suggest that the dynamic contact angle formed between the free surface of a liquid and a moving solid boundary at a fixed contact-line speed depends on the flow field/geometry near the moving contact line. The present paper examines quantitatively whether or not it is possible to attribute this effect to bending of the free surface due to hydrodynamic stresses acting upon it and hence interpret the results in terms of the so-called ``apparent'' contact angle. It is shown that this is not the case. Numerical analysis of the problem demonstrates that, at the spatial
resolution reported in the experiments, the variations of the ``apparent'' contact angle (defined in two different ways) caused by variations in the flow field, at a fixed contact-line speed, are too small to account for the observed effect. The results clearly indicate that the actual (macroscopic) dynamic contact angle, i.e.\ the one used in fluid mechanics as a boundary condition for the equation determining the free surface shape, must be regarded as dependent not only on the contact-line speed but also on the flow field/geometry in the vicinity of the moving contact line
FITTING A PARAMETRIC MODEL TO A CLOUD OF POINTS VIA OPTIMIZATION METHODS
Computer Aided Design (CAD) is a powerful tool for designing
parametric geometry. However, many CAD models of current
configurations are constructed in previous generations of CAD
systems, which represent the configuration simply as a collection of
surfaces instead of as a parametrized solid model. But since many
modern analysis techniques take advantage of a parametrization, one
often has to re-engineer the configuration into a parametric
model. The objective here is to generate an efficient, robust, and
accurate method for fitting parametric models to a cloud of
points. The process uses a gradient-based optimization technique,
which is applied to the whole cloud, without the need to segment or
classify the points in the cloud a priori.
First, for the points associated with any component, a variant of
the Levenberg-Marquardt gradient-based optimization method (ILM) is
used to find the set of model parameters that minimizes the
least-square errors between the model and the points. The
efficiency of the ILM algorithm is greatly improved through the use
of analytic geometric sensitivities and sparse matrix techniques.
Second, for cases in which one does not know a priori the
correspondences between points in the cloud and the geometry model\u27s
components, an efficient initialization and classification algorithm
is introduced. While this technique works well once the
configuration is close enough, it occasionally fails when the
initial parametrized configuration is too far from the cloud of
points. To circumvent this problem, the objective function is
modified, which has yielded good results for all cases tested.
This technique is applied to a series of increasingly complex
configurations. The final configuration represents a full transport
aircraft configuration, with a wing, fuselage, empennage, and
engines. Although only applied to aerospace applications, the
technique is general enough to be applicable in any domain for which
basic parametrized models are available
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