scholarly journals Modelling copepod development: current limitations and a new realistic approach

2008 ◽  
Vol 65 (3) ◽  
pp. 399-413 ◽  
Author(s):  
W. C. Gentleman ◽  
A. B. Neuheimer ◽  
R. G. Campbell
Keyword(s):  
Environmental Variability ◽  
Assimilation Efficiency ◽  
Small Time ◽  
Population Models ◽  
Calanus Finmarchicus ◽  
Age Classes ◽  
Time Step ◽  
Realistic Approach ◽  
Large Numbers ◽  
Copepod Development

Abstract Gentleman, W. C., Neuheimer, A. B., and Campbell, R. G. 2008. Modelling copepod development: current limitations and a new realistic approach. – ICES Journal of Marine Science, 65: 399–413. To predict the influence of environmental variability on copepod dynamics and production, models must account for the effects of temperature and food on stage-dependent time-scales. Here, data for development-time means and variance of Calanus finmarchicus are used to quantify the limitations of existing models. Weight-based individual models are sensitive to uncertain parameters, such as moulting weights, assimilation efficiency, and environmental dependencies, making them highly difficult to calibrate. The accuracy of stage-based population models using ordinary differential equations depends on model structure, with some predicted generation times being incorrect by months. Even when large numbers of age classes are used to reduce modelled variability, it is not possible to make variability consistent with the data. Accuracy of mean times for stage-based population models using difference equations requires a small time-step, which results in large numbers of age classes and modelled variability that is underestimated by orders of magnitude, unless a probabilistic moult fraction is used. We present a new stage-based individual model that avoids the limitations of other models and successfully represents C. finmarchicus mean development timing and associated variability. This approach can be adapted easily for other species, as well as dynamic environmental conditions.

A Numerical Approach in Predicting Flow Field Induced by Randomly Moving Nano Particles

2013 ◽  
Author(s):  
Way Lee Cheng ◽  
Reza Sadr
Keyword(s):  
Flow Field ◽  
Underlying Mechanism ◽  
Numerical Approach ◽  
Small Time ◽  
Nano Particles ◽  
Navier Stokes ◽  
Time Step ◽  
Navier Stokes Equation ◽  
Brownian Particles ◽  
Induced Flow

There have been several reports that suspending nano-particles in a fluid, or nanofluids, can enhance heat transfer properties such as conductivity. However, the extend of the reported enhancement is inconsistent in the literature and the exact mechanisms that govern these observations (or phenomena) are not fully understood. Although the interaction between the fluid and suspended particles is suspected to be the main contributor to this phenomenon, literature shows contradicting conclusions in the underlying mechanism responsible for these effects. This highlights the need for development of computational tools in this area. In this study, a computational approach is developed for simulating the induced flow field by randomly moving particles suspended in a quiescent fluid. Brownian displacement is used to describe the random walk of the particles in the fluid. The steady state movement is described with simplified Navier-Stokes equation to solve for the induced fluid flow around the moving particles with constant velocity at small time steps. The unsteady behavior of the induced flow field is approximated using the velocity profiles obtained from FLUENT. Initial results show that random movements of Brownian particles suspended in the fluid induce a random flow disturbance in the flow field. It is observed that the flow statistics converge asymptotically as time-step reduces. Moreover, inclusion of the transitional movement of the particles significantly affects the results.

Comparison of DDES and URANS for Unsteady Tip Leakage Flow in an Axial Compressor Rotor

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Yangwei Liu ◽  
Luyang Zhong ◽  
Lipeng Lu
Keyword(s):  
Reynolds Stress ◽  
Large Scale ◽  
Turbulence Modeling ◽  
Axial Compressor ◽  
Small Time ◽  
Detached Eddy Simulation ◽  
Tip Leakage Flow ◽  
Time Step ◽  
Tip Leakage ◽  
Eddy Simulation

Tip leakage vortex (TLV) has a large impact on compressor performance and should be accurately predicted by computational fluid dynamics (CFD) methods. New approaches of turbulence modeling, such as delayed detached eddy simulation (DDES), have been proposed, the computational resources of which can be reduced much more than for large eddy simulation (LES). In this paper, the numerical simulations of the rotor in a low-speed large-scale axial compressor based on DDES and unsteady Reynolds-averaged Navier–Stokes (URANS) are performed, thus improving our understanding of the TLV dynamic mechanisms and discrepancy of these two methods. We compared the influence of different time steps in the URANS simulation. The widely used large time-step makes the unsteadiness extremely weak. The small time-step shows a better result close to DDES. The time-step scale is related to the URANS unsteadiness and should be carefully selected. In the time-averaged flow, the TLV in DDES dissipates faster, which has a more similar structure to the experiment. Then, the time-averaged and instantaneous results are compared to divide the TLV into three parts. URANS cannot give the loss of stability and evolution details of TLV. The fluctuation velocity spectra show that the amplitude of high frequencies becomes obvious downstream from the TLV, where it becomes unstable. Last, the anisotropy of the Reynolds stress of these two methods is analyzed through the Lumley triangle to see the distinction between the methods and obtain the Reynolds stress. The results indicate that the TLV latter part in DDES is anisotropic, while in URANS it is isotropic.

scholarly journals Carbohydrates in some marine planktonic animals

1960 ◽  
Vol 39 (2) ◽  
pp. 239-248 ◽  
Author(s):  
J. E. G. Raymont ◽  
S. Krishnaswamy
Keyword(s):  
Chemical Composition ◽  
Dry Weight ◽  
Single Species ◽  
Fat Content ◽  
Carbohydrate Content ◽  
High Protein ◽  
Calanus Finmarchicus ◽  
Large Numbers

There have been few analyses of the fat, protein and carbohydrate fractions in zooplankton, and owing to the difficulty of sorting large numbers of single species, the majority of the earlier determinations were necessarily carried out on mixed zooplankton hauls (Brandt, 1898; Brandt & Raben, 1919; Moberg, 1926; Wimpenny, 1929; Drummond & Gunther, 1934; Vinogradov, 1953). Most of these analyses suggested a relatively high protein and fat content, and this was confirmed by Orr (1934 a), who investigated the chemical composition of a single species, Calanus finmarchicus. Orr's result gave fat, protein and chitin as 20–40,35–50 and 3%, respectively of dry weight. Similar high values were also reported by Orr (1934 b) for Euchaeta norvegica. The carbohydrate content was not, however, estimated in either of Orr's investigations since large numbers of animals would have been required. Brandt (1898), after analysing mixed plankton hauls which were predominantly copepods, suggested a carbohydrate content of ca. 20%.

scholarly journals Thermo-Mechanical Modeling of Abradable Coating Wear in Aircraft Engines

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Florence Nyssen ◽  
Alain Batailly
Keyword(s):  
Numerical Modeling ◽  
Thermal Effects ◽  
Small Time ◽  
Technical Solution ◽  
Contact Interactions ◽  
Time Step ◽  
Element Mesh ◽  
Mechanical Coupling ◽  
Abradable Coating ◽  
The Impact

In modern turbomachine designs, the nominal clearances between rotating bladed-disks and their surrounding casing are reduced to improve aerodynamic performances of the engine. This clearance reduction increases the risk of contacts between components and may lead to hazardous interaction phenomena. A common technical solution to mitigate such interactions consists in the deposition of an abradable coating along the casing inner surface. This enhances the engine efficiency while ensuring operational safety. However, contact interactions between blade tips and an abradable layer may yield unexpected wear removal phenomena. The aim of this work is to investigate the numerical modeling of thermal effects within the abradable layer during contact interactions and compare it with experimental data. A dedicated thermal finite element mesh is employed. At each time-step, a weak thermo-mechanical coupling is assumed: thermal effects affect the mechanics of the system, but the mechanical deformation of the elements has no effect on temperatures. Weak coupling is well appropriated in the case of rapid dynamics using small time-step and explicit resolution schemes. Moreover, only heat transfer by conduction is considered in this work. To reduce computational times, a coarser spatial discretization is used for the thermal mesh comparing to the mechanical one. The time-step used to compute the temperature evolution is larger than the one used for the mechanical iterations since the time constant of thermal effect is larger than contact events. The proposed numerical modeling strategy is applied on an industrial blade to analyze the impact of thermal effects on the blade's dynamics.

Parallel Computation of the Point Neutron Kinetic Equations Using Parallel Revisionist Integral Deferred Correction

2018 ◽  
Author(s):  
Yun Cai ◽  
Xingjie Peng ◽  
Qing Li ◽  
Zhizhu Zhang ◽  
Zhumin Jiang ◽  
...  
Keyword(s):  
Time Integration ◽  
Kinetic Equations ◽  
Accurate Method ◽  
Small Time ◽  
Time Step ◽  
Deferred Correction ◽  
Time Integration Method ◽  
Speed Up ◽  
Point Kinetics ◽  
Reactivity Insertion

The point kinetics is very important to the safety of the reactor operation. However, these equations are stiff and usually solved with very small time step. These equations are solved by Revisionist integral deferred correction (RIDC), which is a parallel time integration method. RIDC is a highly accurate method, and it reduces the error by iteration. Based on C++ and MPI, a four-core fourth-order RIDC is implemented and tested by several cases, such as step, ramp, and sinusoidal reactivity insertion. Compared with other methods, the time step of RIDC in the step reactivity insertion case is smaller, but it’s larger in the case of the sinusoidal reactivity insertion. RIDC can keep high accuracy while the time step is appropriately large. The numerical results also show that the speed-up ratio can achieve 2 when 4 processors are used.

Load Discontinuity and Its Remedy in Step-by-Step Integration

2006 ◽  
Author(s):  
Shuenn-Yih Chang ◽  
Chiu-Li Huang
Keyword(s):  
Numerical Solution ◽  
Small Time ◽  
Step Size ◽  
Time Step ◽  
Integration Procedure ◽  
Amplitude Distortion ◽  
Small Time Step

The discontinuity at the end of an impulse will lead to an extra impulse and thus an extra displacement. Consequently, an amplitude distortion is introduced in the numerical solution. The difficulty arising from the discontinuity at the end of an impulse can be overcome by using a very small time step to perform the step-by-step integration since it reduces the extra impulse and thus extra displacement. However, computational efforts might be significantly increased since the small time step is performed for a complete step-by-step integration procedure. A remedy is devised to computationally efficiently overcome this difficulty by using a very small time step immediately upon termination of the applied impulse. This is because that the extra impulse caused by the discontinuity is almost proportional to the discontinuity value at the end of the impulse and the step size. The feasibility of this proposed remedy is analytically and numerically confirmed herein.

scholarly journals Ambient temperature and algal prey type affect essential fatty acid incorporation and trophic upgrading in a herbivorous marine copepod

2020 ◽  
Vol 375 (1804) ◽  
pp. 20200039 ◽  
Author(s):  
Laura Helenius ◽  
Suzanne M. Budge ◽  
Heather Nadeau ◽  
Catherine L. Johnson
Keyword(s):  
Fatty Acids ◽  
Ambient Temperature ◽  
Environmental Variability ◽  
Essential Fatty Acids ◽  
Prey Type ◽  
Growth Efficiency ◽  
Dietary Fatty Acids ◽  
Calanus Finmarchicus ◽  
Marine Copepod ◽  
Gross Growth Efficiency

The essential fatty acids (EFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are critical nutrients for all organisms, and the temperature sensitivity of their trophic transfer in marine systems is of concern because of rising ocean temperatures. Laboratory-reared copepodites of the marine calanoid Calanus finmarchicus were used to test the effects of temperature (at 6°C, 12°C and increasing temperature stress) and prey type (the dinoflagellate Heterocapsa triquetra and the diatom Thalassiosira weissflogii ) on the extent and efficiency of dietary EPA and DHA incorporation from phytoplankton to copepods in a set of feeding experiments using 13 C labelling. Temperature was a significant determinant of C . finmarchicus copepodites' EFA incorporation and gross growth efficiency, defined as the fraction of ingested EFA retained in copepod tissue. Ingestion and incorporation of both EFA were higher at warmer temperature, except in the case of DHA in copepods feeding on diatoms. DHA-associated growth efficiency was higher at the higher temperature for copepodites consuming the dinoflagellate, but temperature-related variation in algal EFA content was also a predictive factor. Moreover, our results strongly suggest that copepodites are capable of synthesizing EPA when consuming an EPA-depleted diet. Our study implies that the copepod link of marine food webs is resilient in terms of EFA transfer when confronted with alterations of ambient temperature and prey type availability. Measurements presented here are critical for estimating how EFA transfer dynamics respond to intra- and interannual environmental variability. This article is part of the theme issue ‘The next horizons for lipids as ‘trophic biomarkers’: evidence and significance of consumer modification of dietary fatty acids’.

Modeling and Simulation of Cascaded STATCOM Based on RTDS

2014 ◽  
Vol 1008-1009 ◽  
pp. 624-629
Author(s):  
Cheng Jun Xia ◽  
Ji Xue Yan ◽  
Cui Qiong Chen
Keyword(s):  
Closed Loop ◽  
Transient State ◽  
Small Time ◽  
Power Network ◽  
Time Step ◽  
Response Characteristics ◽  
Modeling Technology ◽  
State Response ◽  
Protection Devices ◽  
Real Time Digital Simulator

In 2013, China Southern Power Grid (CSG) installed three ±200Mvar STATCOMs on the 500kV substations which are adjacent to the receiving ends of multiple HVDC lines. Based on the project of STATCOM test in CSG, the ±200Mvar cascaded STATCOM simulation model is established in the real-time digital simulator (RTDS) ,the aim is to study the modeling technology of H Bridge valve group by using small time-step and main control strategy .Amounts of tests has been done to verify the validity of the cascaded STATCOM model in different control modes. The RTDS STATCOM model also tested in the closed-loop CSG power network and the transient state response characteristics has been compared with real STATCOM control and protection devices for engineering prototype to verify the feasibility of the model. The constructed model has been successfully applied on the analysis of impacts on AC/DC paralleled CSG with STATCOM using RTDS.

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