Response of guyed offshore towers to stochastic loads in the presence of steady current

The validity of the widely used stochastic linearization method for analysing the response of guyed towers to stochastic loads is investigated. The governing equations of a guyed tower have two main sources of nonlinearities, fluid-structure interaction and the restoring force of the cables. In this study, two models are considered. First, a linearized single degree of freedom (SDOF) model of a guyed tower is developed using the stochastic linearization approach. It is solved in the frequency domain, giving the statistical response of the guyed tower to random waves and earthquake loading. The results are compared to the response statistics of a time simulation of a single degree of freedom system that fully incorporates the nonlinearities of the cable system and the fluid-structure interaction. Second, the dynamic response of a multiple degree of freedom (MDOF) model of a guyed offshore tower to stochastic earthquake loads and steady uniform current is investigated. The nonlinear cable stiffness and the fluid-structure interaction were again linearized using the stochastic linearization method. Numerical results for several load cases are presented and discussed. The displacement statistics from the MDOF linear analysis were compared to the statistics of the SDOF time simulation that fully incorporated the nonlinearities of the structure. The increased damping of the structure with increasing current was found to significantly reduce the stochastic forces and moments of the structure. The SDOF model is adequate for predicting statistics of displacements, but a MDOF model is needed to accurately predict statistics of maximum moments in the tower. It is found that the results from the linearized model agree reasonably well with the results from the time simulation of the fully nonlinear system. The computer time using the stochastic linearization approach is several order of magnitude less than for a conventional time simulation method. It is therefore justifiable to use this method in the early design stages of guyed towers

Sugar-stimulated CO2 sequestration by the green microalga Chlorella vulgaris

Post-print (lokagerð höfundar) opið á: https://systemsbiology.hi.is/wp-content/uploads/2018/11/Sugar-stimulated-CO2-sequestration-by-the-green-microalga-Chlorella-vulgaris-draft.pdfTo convert waste CO2 from flue gases of power plants into value-added products, bio-mitigation technologies show promise. In this study, we cultivated a fast-growing species of green microalgae, Chlorella vulgaris, in different sizes of photobioreactors (PBRs) and developed a strategy using small doses of sugars for enhancing CO2 sequestration under light-emitting diode illumination. Glucose supplementation at low levels resulted in an increase of photoautotrophic growth-driven biomass generation as well as CO2 capture by 10% and its enhancement corresponded to an increase of supplied photon flux. The utilization of urea instead of nitrate as the sole nitrogen source increased photoautotrophic growth by 14%, but change of nitrogen source didn't compromise glucose-induced enhancement of photoautotrophic growth. The optimized biomass productivity achieved was 30.4% higher than the initial productivity of purely photoautotrophic culture. The major pigments in the obtained algal biomass were found comparable to its photoautotrophic counterpart and a high neutral lipids productivity of 516.6 mg/(L·day) was achieved after optimization. A techno-economic model was also developed, indicating that LED-based PBRs represent a feasible strategy for converting CO2 into value-added algal biomass.This research was supported by the Icelandic Technology Development Fund, the Geothermal Research Group (GEORG) Fund and NYUAD faculty research funds (AD060).Peer Reviewe

Chemical Mutagenesis and Fluorescence-Based High-Throughput Screening for Enhanced Accumulation of Carotenoids in a Model Marine Diatom Phaeodactylum tricornutum

Publisher's version (útgefin grein)Diatoms are a major group of unicellular algae that are rich in lipids and carotenoids. However, sustained research efforts are needed to improve the strain performance for high product yields towards commercialization. In this study, we generated a number of mutants of the model diatom Phaeodactylum tricornutum, a cosmopolitan species that has also been found in Nordic region, using the chemical mutagens ethyl methanesulfonate (EMS) and N-methyl-N′-nitro-N-nitrosoguanidine (NTG). We found that both chlorophyll a and neutral lipids had a significant correlation with carotenoid content and these correlations were better during exponential growth than in the stationary growth phase. Then, we studied P. tricornutum common metabolic pathways and analyzed correlated enzymatic reactions between fucoxanthin synthesis and pigmentation or lipid metabolism through a genome-scale metabolic model. The integration of the computational results with liquid chromatography-mass spectrometry data revealed key compounds underlying the correlative metabolic pathways. Approximately 1000 strains were screened using fluorescence-based high-throughput method and five mutants selected had 33% or higher total carotenoids than the wild type, in which four strains remained stable in the long term and the top mutant exhibited an increase of 69.3% in fucoxanthin content compared to the wild type. The platform described in this study may be applied to the screening of other high performing diatom strains for industrial applications.This research was supported by the Icelandic Technology Development Fund with Grant No. 163922-0611, Landsvirkjun Energy Research Fund and NYUAD faculty research funds (AD060).Peer Reviewe

Combined artificial high-silicate medium and LED illumination promote carotenoid accumulation in the marine diatom Phaeodactylum tricornutum

Publisher's version (útgefin grein).Background: Diatoms, which can accumulate large amounts of carotenoids, are a major group of microalgae and the dominant primary producer in marine environments. Phaeodactylum tricornutum, a model diatom species, acquires little silicon for its growth although silicon is known to contribute to gene regulation and play an important role in diatom intracellular metabolism. In this study, we explored the effects of artificial high-silicate medium (i.e. 3.0 mM sodium metasilicate) and LED illumination conditions on the growth rate and pigment accumulation in P.Tricornutum, which is the only known species so far that can grow without silicate. It's well known that light-emitting diodes (LEDs) as novel illuminants are emerging to be superior monochromatic light sources for algal cultivation with defined and efficient red and blue lights. Results: Firstly, we cultivated P.Tricornutum in a synthetic medium supplemented with either 0.3 mM or 3.0 mM silicate. The morphology and size of diatom cells were examined: The proportion of the oval and triradiate cells decreased while the fusiform cells increased with more silicate addition in high-silicate medium; the average length of fusiform cells also slightly changed from 14.33 μm in 0.3 mM silicate medium to 12.20 μm in 3.0 mM silicate medium. Then we cultivated P.Tricornutum under various intensities of red light in combination with the two different levels of silicate in the medium. Higher biomass productivity also achieved in 3.0 mM silicate medium than in 0.3 mM silicate medium under red LED light irradiation at 128 μmol/m2/s or higher light intensity. Increasing silicate reversed the down-regulation of fucoxanthin and chlorophyll a under high red-light illumination (i.e. 255 μmol/m2/s). When doubling the light intensity, fucoxanthin content decreased under red light but increased under combined red and blue (50:50) lights while chlorophyll a content reduced under both conditions. Fucoxanthin accumulation and biomass productivity increased with enhanced red and blue (50:50) lights. Conclusion: High-silicate medium and blue light increased biomass and fucoxanthin production in P.Tricornutum under high light conditions and this strategy may be beneficial for large-scale production of fucoxanthin in diatoms.This research was supported by the Icelandic Technology Development Fund (163922-0611), Landsvirkjun Energy Research Fund and NYU Abu Dhabi faculty research funds (AD060).Peer Reviewe

Photo-Oxidative Stress-Driven Mutagenesis and Adaptive Evolution on the Marine Diatom Phaeodactylum tricornutum for Enhanced Carotenoid Accumulation

Marine diatoms have recently gained much attention as they are expected to be a promising resource for sustainable production of bioactive compounds such as carotenoids and biofuels as a future clean energy solution. To develop photosynthetic cell factories, it is important to improve diatoms for value-added products. In this study, we utilized UVC radiation to induce mutations in the marine diatom Phaeodactylum tricornutum and screened strains with enhanced accumulation of neutral lipids and carotenoids. Adaptive laboratory evolution (ALE) was also used in parallel to develop altered phenotypic and biological functions in P. tricornutum and it was reported for the first time that ALE was successfully applied on diatoms for the enhancement of growth performance and productivity of value-added carotenoids to date. Liquid chromatography-mass spectrometry (LC-MS) was utilized to study the composition of major pigments in the wild type P. tricornutum, UV mutants and ALE strains. UVC radiated strains exhibited higher accumulation of fucoxanthin as well as neutral lipids compared to their wild type counterpart. In addition to UV mutagenesis, P. tricornutum strains developed by ALE also yielded enhanced biomass production and fucoxanthin accumulation under combined red and blue light. In short, both UV mutagenesis and ALE appeared as an effective approach to developing desired phenotypes in the marine diatoms via electromagnetic radiation-induced oxidative stress