A wave-based model reduction technique for the description of the dynamic behavior of periodic structures involving arbitrary-shaped substructures and large-sized finite element models

International audienceThe wave finite element (WFE) method is investigated to describe the dynamic behavior of periodic structures like those composed of arbitrary-shaped substruc-tures along a certain straight direction. Emphasis is placed on the analysis of non-academic substructures that are described by means of large-sized finite element (FE) models. A generalized eigenproblem based on the so-called S + S −1 transformation is proposed for accurately computing the wave modes which travel in right and left directions along those periodic structures. Besides, a model reduction technique is proposed which involves partitioning a whole periodic structure into one central structure surrounded by two extra substructures. In doing so, a few wave modes are only required for modeling the central periodic structure. An error indicator is also proposed to determine in an a priori process the number of those wave modes that need to be considered. Their computation hence follows by considering the Lanczos method, which can be achieved in a very fast way. Numerical experiments are carried out to highlight the relevance of the proposed reduction technique. A comprehensive validation of the technique is performed on a 2D periodic structure. Also, its efficiency in terms of CPU time savings is highlighted regarding a 3D periodic structure that exhibits substructures with large-sized FE models

Variable phosphorus uptake rates and allocation across microbial groups in the oligotrophic Gulf of Mexico

Microbial uptake of dissolved phosphorus (P) is an important lever in controlling both microbial production and the fate and cycling of marine P. We investigated the relative role of heterotrophic bacteria and phytoplankton in P cycling by measuring the P uptake rates of individual microbial groups (heterotrophic bacteria and the phytoplankton groups Synechococcus, Prochlorococcus, and picoeukaryotic phytoplankton) in the P-depleted Gulf of Mexico. Phosphorus uptake rates were measured using incubations with radiolabeled phosphate and adenosine triphosphate coupled with cell sorting flow cytometry. We found that heterotrophic bacteria were the dominant consumers of P on both a biomass basis and a population basis. Biovolume normalized heterotrophic bacteria P uptake rate per cell (amol P μm-3 hr-1) was roughly an order of magnitude greater than phytoplankton uptake rates, and heterotrophic bacteria were responsible for generally greater than 50% of total picoplankton P uptake. We hypothesized that this variation in uptake rates reflects variation in cellular P allocation strategies, and found that, indeed, the fraction of cellular P uptake utilized for phospholipid production was significantly higher in heterotrophic bacteria compared to cyanobacterial phytoplankton. These findings indicate that heterotrophic bacteria have a uniquely P-oriented physiology and play a dominant role in cycling dissolved P

A 2D wave finite element-based superelement formulation for acoustic analysis of cavities of arbitrary shapes

International audienceA substructuring technique is proposed which enables fast computation of the acoustic response of arbitrary-shaped 2D cavities subject to different kinds of excitations. It combines rectangular superelements which are modeled by means of the wave finite element (WFE) method, and arbitrary-shaped superelements modeled using component mode synthesis (CMS). Within the WFE framework, the so-called receptance matrices of rectangular superelements — which link the pressure vectors to the acoustic force vectors over the boundaries — can be derived in an efficient way in terms of wave modes, without the need of explicitly condensing the internal degrees of freedom of the systems. A model reduction strategy is proposed which aims at expressing the receptance matrices with a few wave modes only. The proposed strategy involves enclosing each rectangular superelement in a finite element (FE) layer with a small width. In this way, smoothed pressure fields are likely to occur over the WFE superelements, hence enabling these superelements to be described with a few wave modes only. By considering those WFE-based rectangular superelements surrounded by FE layers, this yields the so-called hybrid WFE/FE superelements whose dynamic stiffness matrices can be computed in a very fast way. Modeling a whole arbitrary-shaped acoustic cavity follows from conventional assembly procedure between hybrid WFE/FE superelements, CMS superelements and other FE components. Numerical experiments are carried out to highlight the relevance of the proposed substructuring technique

Multicommodity formulations for the prize collecting vehicle routing problem in the petrol industry

The Mobile Oil Recovery (MOR) unit is a truck designed to pump marginal oil wells in a petrol field. The MOR optimization Problem (MORP) consists in optimizing both the oil extraction and the travel costs. In this article, we describe several formulations for the MORP using a single vehicle and we propose two formulations to the case where several vehicles are used. We strengthen the proposed formulations by taking advantage of the MORP characteristics, by improving the number of subtour elimination constraints and by using cuts. Computational results are presented for instances close to the reality and optimality is proved for instances with up to 200 nodes

Pathology in Practice

A 1.5-year-old second-parity Large Black X Tamworth cross sow from a well-managed 20-sow, unvaccinated, pasture-raised herd of pigs in upstate New York aborted a litter of 7 variably mummified near-term fetuses and stillborn piglets. This sow had no signs of ill health other than abortion; it was housed in a group with 4 other sows and a 2-year-old Gloucestershire Old Spot boar. One of the stillborn piglets from this litter was submitted to the New York State Animal Health Diagnostic Center for necropsy; no placental tissue was submitted with the piglet. A second sow from this group had aborted a litter at the same late stage of gestation within the preceding 2 weeks; however, none of the fetuses were submitted for diagnostic investigation. No signs of ill health were reported for the rest of the herd. The referring veterinarian indicated that these pigs had access to corn standing in the field and that, because of recent wet weather, there was concern that mycotoxin contamination might be the cause of the abortions

Computational elastoacoustics of uncertain complex systems and experimental validation

Semi-Plenary LectureInternational audienceThe paper deals with the robustness of uncertain computational elastoacoustic models in low- and medium-frequency ranges. The elastoacoustic system is made up of a heterogeneous viscoelastic structure coupled with an internal acoustic cavity filled with a dissipative acoustic fluid. A reduced mean elastoacoustic model is deduced from the mean finite element model by using the modal approach with the structural modes of the structure and the acoustic modes of the acoustic cavity. Data uncertainties and model uncertainties are taken into account by using a nonparametric probabilistic approach for the structure, for the acoustic cavity and for the vibroacoustic coupling interface. The main objectives of this paper are (1) to present experimental validation of the nonparametric probabilistic approach of model uncertainties and to propose methods to perform the experimental identification of the probabilistic model parameters, (2) to analyze the robustness of computational elastoacoustic models with respect to model and data uncertainties, (3) to study uncertainty propagation through complex elastoacoustic systems. Two experimental configurations are analyzed with the stochastic computational elastoacoustic model. The first experimental configuration is made up of a composite sandwich panel coupled with an acoustic cavity constituted of a simple rigid box. Experimental measurements have been performed for 8 manufactured composite panels. The second experimental configuration is a car made up of a complex heterogeneous structure coupled with a complex acoustic cavity. Experimental measurements have been performed for 22 manufactured cars of the same type with optional extra

Spatial and Temporal Dynamics of Inorganic Phosphate and Adenosine-5’-Triphosphate in the North Pacific Ocean

Temporal variability in dissolved inorganic, organic phosphate (Pi, DOP) and particulate phosphorus (PPO4) concentrations, and microbial utilization of Pi and dissolved adenosine-5′-triphosphate (DATP) was studied at Station ALOHA (22.75◦N, 158◦W) in the North Pacific Subtropical Gyre (NPSG) over a multi-year period. Spatial variability of the same properties was investigated along two transects, to and from Hawaii, that traversed the NPSG boundaries to the east (2014) and north (2016). Radiotracer techniques were employed to measure the turnover time of Pi and DATP pools to calculate Pi uptake rates and the Pi hydrolysis rates of DATP. Pi concentrations were more variable, both in time and space, than DOP, ranging two orders of magnitude compared to a factor of two for DOP. The DATP pool, while constituting on average 0.2 μm size class dominating the DATP uptake. Our results indicate that during Pi limiting conditions, regenerated P is rapidly consumed, and that Pi limitation occurs locally and transiently but does not appear to be the predominant condition in the upper water column of the NPSG

High-performance computing for data analytics

One of the main challenges in data analytics is that discovering structures and patterns in complex datasets is a computer-intensive task. Recent advances in high-performance computing provide part of the solution. Multicore systems are now more affordable and more accessible. In this paper, we investigate how this can be used to develop more advanced methods for data analytics. We focus on two specific areas: model-driven analysis and data mining using optimisation techniques