219 research outputs found
A multi-model incremental adaptive strategy to accelerate partitioned fluid-structure algorithms using space-mapping
High fidelity analysis of fluid-structure interaction systems is often too timeconsuming
when a large number of model evaluations are required. The choice for a
solution procedure depends often on the efficiency of the method and the possibility of
reusing existing field solvers. Aggressive Space-Mapping, a technique originally developed
for multi-fidelity optimization, is applied to accelerate the partitioned solution procedure
of a high fidelity fluid-structure interaction model. The method supports software modularity.
Aggressive Space-Mapping (ASM) is applied to an academic testcase and the
results are compared with the corresponding Incremental Quasi-Newton (IQN) method.
An efficiency metric is defined to facilitate the comparison. The ASM method is found
to be more efficient than the corresponding IQN method for the testcases considered.
The efficiency of space-mapping increases with increasing fluid-to-structure mass ratio,
indicating that the method is especially useful for strongly coupled problems
Rosenbrock time integration for unsteady flow simulations
This contribution compares the efficiency of Rosenbrock time integration
schemes with ESDIRK schemes, applicable to unsteady flow and fluid-structure interaction
simulations. Compared to non-linear ESDIRK schemes, the linear implicit Rosenbrock-
Wanner schemes require subsequent solution of the same linear systems with different
right hand sides. By solving the linear systems with the iterative solver GMRES, the preconditioner
can be reused for the subsequent stages of the Rosenbrock-Wanner scheme.
Unsteady flow simulations show a gain in computational efficiency of approximately factor
three to five in comparison with ESDIRK
Estimation of Dynamic Gaussian Processes
Gaussian processes provide a compact representation for modeling and
estimating an unknown function, that can be updated as new measurements of the
function are obtained. This paper extends this powerful framework to the case
where the unknown function dynamically changes over time. Specifically, we
assume that the function evolves according to an integro-difference equation
and that the measurements are obtained locally in a spatial sense. In this
setting, we will provide the expressions for the conditional mean and
covariance of the process given the measurements, which results in a
generalized estimation framework, for which we coined the term Dynamic Gaussian
Process (DGP) estimation. This new framework generalizes both Gaussian process
regression and Kalman filtering. For a broad class of kernels, described by a
set of basis functions, fast implementations are provided. We illustrate the
results on a numerical example, demonstrating that the method can accurately
estimate an evolving continuous function, even in the presence of noisy
measurements and disturbances.Comment: 6 pages, 3 figures, to be presented at 62nd IEEE Conference on
Decision and Control, CDC 2023, Singapore, Singapor
The degree of joint range of motion limitations after burn injuries during recovery
Introduction: The aim of this study was to determine the degree of ROM limitations of extremities, joints and planes of motion after burns and its prevalence over time. Method: The database of a longitudinal multicenter cohort study in the Netherlands (2011–2012) was used. From patients with acute burns involving the neck, shoulder, elbow, wrist, hip, knee and ankle joints that had surgery, ROM of 17 planes of motion was assessed by goniometry at 3, 6 weeks, 3–6–9 and 12 months after burns and at discharge. Results: At 12 months after injury, 12 out of 17 planes of motion demonstrated persistent joint limitations. The five unlimited planes of motion were all of the lower extremity. The most severely limited joints at 12 months were the neck, ankle, wrist and shoulder. The lower extremity was more severely limited in the early phase of recovery whereas at 12 months the upper extremity was more severely limited. Conclusion: The degree of ROM limitations and prevalence varied over time between extremities, joints and planes of motion. This study showed which joints and planes of motion should be watched specifically concerning the development of scar contracture
A biomechanical mathematical model for the collagen bundle distribution-dependent contraction and subsequent retraction of healing dermal wounds
A continuum hypothesis-based, biomechanical model is presented for the simulation of the collagen bundle distribution-dependent contraction and subsequent retraction of healing dermal wounds that cover a large surface area. Since wound contraction mainly takes place in the dermal layer of the skin, solely a portion of this layer is included explicitly into the model. This portion of dermal layer is modeled as a heterogeneous, orthotropic continuous solid with bulk mechanical properties that are locally dependent on both the local concentration and the local geometrical arrangement of the collagen bundles. With respect to the dynamic regulation of the geometrical arrangement of the collagen bundles, it is assumed that a portion of the collagen molecules are deposited and reoriented in the direction of movement of (myo)fibroblasts. The remainder of the newly secreted collagen molecules are deposited by ratio in the direction of the present collagen bundles. Simulation results show that the distribution of the collagen bundles influences the evolution over time of both the shape of the wounded area and the degree of overall contraction of the wounded area. Interestingly, these effects are solely a consequence of alterations in the initial overall distribution of the collagen bundles, and not a consequence of alterations in the evolution over time of the different cell densities and concentrations of the modeled constituents. In accordance with experimental observations, simulation results show furthermore that ultimately the majority of the collagen molecules ends up permanently oriented toward the center of the wound and in the plane that runs parallel to the surface of the skin
A mathematical model for the simulation of the contraction of burns
A continuum hypothesis-based model is developed for the simulation of the contraction of burns in order to gain new insights into which elements of the healing response might have a substantial influence on this process. Tissue is modeled as a neo-Hookean solid. Furthermore, (myo)fibroblasts, collagen molecules, and a generic signaling molecule are selected as model components. An overview of the custom-made numerical algorithm is presented. Subsequently, good agreement is demonstrated with respect to variability in the evolution of the surface area of burns over time between the outcomes of computer simulations and measurements obtained in an experimental study. In the model this variability is caused by varying the values for some of its parameters simultaneously. A factorial design combined with a regression analysis are used to quantify the individual contributions of these parameter value variations to the dispersion in the surface area of healing burns. The analysis shows that almost all variability in the surface area can be explained by variability in the value for the myofibroblast apoptosis rate and, to a lesser extent, the value for the collagen molecule secretion rate. This suggests that most of the variability in the evolution of the surface area of burns over time in the experimental study might be attributed to variability in these two rates. Finally, a probabili
Outcomes that matter most to burn patients:A national multicentre survey study in the Netherlands
Background: The use of patient-reported outcomes to improve burn care increases. Little is known on burn patients’ views on what outcomes are most important, and about preferences regarding online Patient Reported Outcome Measures (PROMs). Therefore, this study assessed what outcomes matter most to patients, and gained insights into patient preferences towards the use of online PROMs. Methods: Adult patients (≥18 years old), 3–36 months after injury completed a survey measuring importance of outcomes, separately for three time periods: during admission, short-term (<6 months) and long-term (6–24 months) after burn injury. Both open and closed-ended questions were used. Furthermore, preferences regarding the use of patient-reported outcome measures in burn care were queried. Results: A total of 140 patients were included (response rate: 27%). ‘Not having pain’ and ‘good wound healing’ were identified as very important outcomes. Also, ‘physical functioning at pre-injury level’, ‘being independent’ and ‘taking care of yourself’ were considered very important outcomes. The top-ten of most important outcomes largely overlapped in all three time periods. Most patients (84%) had no problems with online questionnaires, and many (67%) indicated that it should take up to 15 minutes. Patients’ opinions differed widely on the preferred frequency of follow-up. Conclusions: Not having pain and good wound healing were considered very important during the whole recovery of burns; in addition, physical functioning at pre-injury level, being independent, and taking care of yourself were deemed very important in the short and long-term. These outcomes are recommended to be used in burn care and research, although careful selection of outcomes remains crucial as patients prefer online questionnaires up to 15 minutes.</p
Stromal vascular fraction-enriched fat grafting as treatment of adherent scars:study design of a non-randomized early phase trial
BACKGROUND: In the last decades, autologous fat grafting has been used to treat adherent dermal scars. The observed regenerative and scar-reducing properties have been mainly ascribed to the tissue-derived stromal vascular fraction (tSVF) in adipose tissue. Adipose tissue's components augment local angiogenesis and mitosis in resident tissue cells. Moreover, it promotes collagen remodeling. We hypothesize that tSVF potentiates fat grafting-based treatment of adherent scars. Therefore, this study aims to investigate the effect of tSVF-enriched fat grafting on scar pliability over a 12-month period.METHODS AND DESIGN: A clinical multicenter non-randomized early phase trial will be conducted in two dedicated Dutch Burn Centers (Red Cross Hospital, Beverwijk, and Martini Hospital, Groningen). After informed consent, 46 patients (≥18 years) with adherent scars caused by burns, necrotic fasciitis, or degloving injury who have an indication for fat grafting will receive a sub-cicatricic tSVF-enriched fat graft. The primary outcome is the change in scar pliability measured by the Cutometer between pre- and 12 months post-grafting. Secondary outcomes are scar pliability (after 3 months), scar erythema, and melanin measured by the DSM II Colormeter; scar quality assessed by the patient and observer scales of the Patient and Observer Scar Assessment Scale (POSAS) 2.0; and histological analysis of scar biopsies (voluntary) and tSVF quality and composition. This study has been approved by the Dutch Central Committee for Clinical Research (CCMO), NL72094.000.20.CONCLUSION: This study will test the clinical efficacy of tSVF-enriched fat grafting to treat dermal scars while the underlying working mechanism will be probed into too.TRIAL REGISTRATION: Dutch Trial Register NL 8461. Registered on 16 March 2020.</p
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