High-frequency Temperature Fluctuations Research Articles

A global atlas of potential thermal refugia for coral reefs generated by internal gravity waves

Coral reefs are highly threatened by ocean warming and the majority are likely to be lost in less than three decades. A first step in maximizing reef conservation through this period is to identify where coral reefs are more likely to survive rising ocean temperatures, such as locations that experience lower temperatures than surrounding regions, high temperature variability, and high food supply. Such conditions are often the result of naturally occurring internal gravity waves (IGWs), oscillatory subsurface disturbances that can entrain cooler and/or nutrient-rich subsurface waters and cause high frequency temperature fluctuations. These features usually remain undetected because they occur subsurface and at spatial scales of O(1 km) and smaller. To shed light on where IGWs are likely to impact temperature conditions within coral reef regions, we present an analysis of data from the LLC4320, a massive high resolution (1/48˚; < 2.5 km) numerical global ocean simulation. The results highlight strong regional differences in the incidence of IGW-induced temperature variability. The analysis also reveals that thermal refugia are limited to depths where high temperature variability coincides with the actual reef depth and may not persist year-round. Assuming 10-m depth as the nominal reef depth, reef regions likely to benefit from IGW-induced cooling occur in SE Asia and the Coral Triangle, the Galápagos, along the Pacific shelf of Central America, and isolated locations worldwide. Such refugia are rare within the Atlantic reef sector. An interactive global atlas showing the results of this study has been made freely available online at https://ncar.github.io/coral-viz/.

Large-eddy simulation on thermal-mixing experiment at horizontal T-junction with varied flow temperature

In a thermal-mixing pipe-flow close to a mixing tee, where flow streams with different temperatures are mixed, high frequency temperature fluctuations can be created and lead to material damage in the pipe line. Such damage mechanism is denoted as thermal fatigue and constitutes a potential risk to the safety of the piping system in nuclear power plants. At the University of Stuttgart, the Fluid-Structure Interaction (FSI) test facility has been constructed and operated for investigating flow-mixing mechanism causing thermal fatigue at a pipeline T-junction. In previous work, experimental investigation has been performed with high temperature difference between the inlet flow stream (>140 K). It has been found the temperature difference is one of the crucial factors on the damage potential due to thermal fatigue.In this work, numerical simulations have been performed on the previous experiments with the varied flow temperature. Wall-resolved Large-Eddy Simulation (LES) method has been applied in the simulations. Distributions of flow parameters have been reproduced for understanding of mixing behavior at high temperature difference. The simulation results provide a good illustration on the flow region and agree well with the experimental data. Moreover, the new mixing phenomenon, tangential oscillation of thermal stratification, has been identified from the analysis on the previous experimental data. Additional methods have been applied in this work for reproducing this phenomenon. The simulation results have confirmed that the tangential oscillation has been initiated in the thermal-mixing process. The characteristic frequency of this phenomenon can be found in the frequency spectra of the temperature monitor data at several different monitor positions.

Method of calculating the heat and stress-deformed state of the cylinder head of a transport diesel with liquid cooling

In an internal combustion engine (ICE), stresses arise from the action of a variable gas force and from a variable temperature due to the combustion of fuel in the combustion chamber in the cylinder head and piston, while the thermal stresses are much higher than the stresses from the power load. Therefore, at the design stage of a new engine design, they are calculating the durability of heat-stressed parts, since they limit the reliability of a piston engine. The paper discusses the method of selecting source data when calculating the thermal and stress-strain state of the cylinder head of a diesel engine using the finite element method and using the Solid Works software package. The stages of creating and preparing a solid model of a cylinder head to create a finite element model are described using the example of the 8ChN12 / 13 diesel engine (KAMAZ 740.75-440). The main loads acting on the cylinder head during the assembly period are considered: efforts from pressing in valve seats and bushings, as well as from tightening the bolts for fastening the head to the crankcase. The shape of the elements for the finite element model of the cylinder head was chosen from the condition of reducing the estimated time. This condition was suited to the shape of a finite element in the form of a tetrahedron with four nodal points. These elements made it possible to reduce the computational grid in cross sections, for example, stress concentration. It is shown that high-frequency temperature fluctuations that occur as a result of the flow of the working process of a piston engine do not affect the thermal strength of the cylinder head, and high-frequency temperature fluctuations due to changes in the engine operating conditions affect. The changes in the basic characteristics of the aluminum alloy from which the cylinder head is made with temperature and cyclic thermomechanical loading of low frequency are given. It is shown that with increasing temperature, the endurance limit of the material decreases at low frequency loads.

Scale‐dependent spatial patterns in benthic communities around a tropical island seascape

Understanding and predicting patterns of spatial organization across ecological communities is central to the field of landscape ecology, and a similar line of inquiry has begun to evolve sub‐tidally among seascape ecologists. Much of our current understanding of the processes driving marine community patterns, particularly in the tropics, has come from small‐scale, spatially‐discrete data that are often not representative of the broader seascape. Here we expand the spatial extent of seascape ecology studies and combine spatially‐expansive in situ digital imagery, oceanographic measurements, spatial statistics, and predictive modeling to test whether predictable patterns emerge between coral reef benthic competitors across scales in response to intra‐island gradients in physical drivers. We do this around the entire circumference of a remote, uninhabited island in the central Pacific (Jarvis Island) that lacks the confounding effects of direct human impacts. We show, for the first time, that competing benthic groups demonstrate predictable scaling patterns of organization, with positive autocorrelation in the cover of each group at scales < ~1 km. Moreover, we show how gradients in subsurface temperature and surface wave power drive spatially‐abrupt transition points in group dominance, explaining 48–84% of the overall variation in benthic cover around the island. Along the western coast, we documented ten times more sub‐surface cooling‐hours than any other part of the coastline, with events typically resulting in a drop of 1–4°C over a period of < 5 h. These high frequency temperature fluctuations are indicative of upwelling induced by internal waves and here result in localized nitrogen enrichment (NO2 + NO3) that promotes hard coral dominance around 44% of the island's perimeter. Our findings show that, in the absence of confounding direct human impacts, the spatial organization of coral reef benthic competitors are predictable and somewhat bounded across the seascape by concurrent gradients in physical drivers.

Numerical simulation of the transfer of high-frequency temperature fluctuations from hot air flow to the array of thin pyroelectric plates

Pyroelectric energy harvesting is an important option for powering autonomous electronic devices. For the technology to be efficient high-frequency thermal oscillations are needed. Here we suggest a method of creation of thermal oscillations in a pyroelectric plate, based on Karman instability. Vortices, shedding alternatively from the two sides of a heated body, accumulate heat in their cores and transfer it to a pyroelectric plate. The effect is demonstrated by means of numerical simulations. A number of geometries were considered, to optimize the parameters of operation and achieve maximal thermal oscillations in the plate. A prototypical device for waste heat harvesting is presented. It is able of achieving harvested power of 1 W/g for a thin (200 nm) plate of ferroelectric (BaTiO3).

Hot spots become cold spots: coevolution in variable temperature environments.

Antagonistic coevolution between hosts and parasites is a key process in the genesis and maintenance of biological diversity. Whereas coevolutionary dynamics show distinct patterns under favourable environmental conditions, the effects of more realistic, variable conditions are largely unknown. We investigated the impact of a fluctuating environment on antagonistic coevolution in experimental microcosms of Pseudomonas fluorescens SBW25 and lytic phage SBWΦ2. High-frequency temperature fluctuations caused no deviations from typical coevolutionary arms race dynamics. However, coevolution was stalled during periods of high temperature under intermediate- and low-frequency fluctuations, generating temporary coevolutionary cold spots. Temperature variation affected population density, providing evidence that eco-evolutionary feedbacks act through variable bacteria-phage encounter rates. Our study shows that environmental fluctuations can drive antagonistic species interactions into and out of coevolutionary cold and hot spots. Whether coevolution persists or stalls depends on the frequency of change and the environmental optima of both interacting players.

A Procedure to Compensate for the Response Drift of a Large Set of Thermistors

AbstractThe drift of temperature measurements by semiconductor negative temperature coefficient thermistors is a well-known problem. This study analyzes the drift characteristics of the thermistors designed and used at the Royal Netherlands Institute for Sea Research for measuring high-frequency temperature fluctuations in the ocean. These thermistors can be calibrated to high precision and accuracy (better than 1 mK) and have very low noise levels. The thermistors can measure independently for long periods of time (more than one year), and the identification and compensation of the drift are thus essential processing steps. A laboratory analysis showing that the drift is similar, in its functional form, to the drift of commercial thermistors described in the literature is presented. An effective procedure to estimate this drift from ocean observations is described and tested using three datasets from the deep Atlantic Ocean. Since the functional form of the drift rate is, with good approximation, universal among different sensors, the procedure could easily be adapted to other datasets and, the authors argue, to measurements from thermistors by other manufacturers too.

Correlation between long-term marine temperature time series from the eastern and western English Channel: Scaling analysis using empirical mode decomposition

High-frequency temperature fluctuations recorded in the English Channel are compared using two long-term autonomous underwater monitoring stations at less than 20-min time resolution. Measurements were taken from 2005 to 2011 from two systems 460 km apart in the western and eastern parts of the English Channel. Spectral analysis reveals similar statistical behaviors, with approximate 5/3 spectra and several forcing frequencies in relation to tidal and daily cycles. A co-spectra study reveals a transition scale of 11 days. The influence of this scale is also visible though Time-Dependent Intrinsic Correlation analysis (TDIC)–a recently introduced cross-correlation analysis based on Empirical mode decomposition. This helps to spatialize high-frequency temporal records at a fixed location.

Fine-scale environmental specialization of reef-building corals might be limiting reef recovery in the Florida Keys.

Despite decades of monitoring global reef decline, we are still largely unable to explain patterns of reef deterioration at local scales, which precludes the development of effective management strategies. Offshore reefs of the Florida Keys, USA, experience milder temperatures and lower nutrient loads in comparison to inshore reefs yet remain considerably more degraded than nearshore patch reefs. A year-long reciprocal transplant experiment of the mustard hill coral (Porites astreoides) involving four source and eight transplant locations reveals that corals adapt and/or acclimatize to their local habitat on a < 10-km scale. Surprisingly, transplantation to putatively similar environmental types (e.g., offshore corals moved to a novel offshore site, or along-shore transplantation) resulted in greater reductions in fitness proxies, such as coral growth, than cross-channel transplantation between inshore and offshore reefs. The only abiotic factor showing significantly greater differences between along-shore sites was daily temperature range extremes (rather than the absolute high or low temperatures reached), providing a possible explanation for this pattern. Offshore-origin corals exhibited significant growth reductions at sites with greater daily temperature ranges, which explained up to 39% of the variation in their mass gain. In contrast, daily temperature range explained at most 9% of growth variation in inshore-origin corals, suggesting that inshore corals are more tolerant of high-frequency temperature fluctuations. Finally, corals incur trade-offs when specializing to their native reef. Across reef locations the coefficient of selection against coral transplants was 0.07 ± 0.02 (mean ± SE). This selection against immigrants could hinder the ability of corals to recolonize devastated reefs, whether through assisted migration efforts or natural recruitment events, providing a unifying explanation for observed patterns of coral decline in this reef system.

Thermal hydraulic issues and challenges for current and new generation FBRs

Pool type sodium cooled fast reactors pose several design challenges and among them, certain thermal hydraulics and structural mechanics issues are special. High frequency temperature fluctuations due to thermal striping, thermal stratifications and sodium free level fluctuations at the liquid–cover gas interfaces are to be investigated carefully to eliminate high cycle thermal fatigue of structures. Solutions to address the core thermal hydraulics call for high power computing. Innovative concepts and methods are developed to carry out plant dynamics and safety studies. Particularly, extensive numerical and experimental simulation techniques are needed for understanding and solving the gas entrainment mechanisms and its effects on core safety. Though decay heat removal through natural convection is achievable in a pool type SFR, demonstration of design solutions conceived in the reactor and performance of diverse systems under all operating conditions, especially over prolonged station blackout situations needs advanced CFD computations and should be validated by relatively large scale simulated experiments. These issues are addressed in this paper under five broad topics: special thermal hydraulic issues to be addressed in SFR, thermal hydraulic design and analysis, plant dynamics studies, safety studies and evolving thermal hydraulic studies for the future FBRs. The 500MWe Prototype Fast Breeder Reactor (PFBR) is taken as the reference design for addressing the issues. Indian fast reactor programme is highlighted in the introduction for the sake of completeness.

Satellite remote sensing reveals coastal upwelling events in the San Matías Gulf—Northern Patagonia

Coastal upwelling events are effective in fluxing nutrients upward to the euphotic layer, thus promoting the growth of marine phytoplankton. Satellite data may provide useful information to detect and characterize upwelling events in regions of sparse in-situ observations. We analyze the coastal upwelling process on the western San Matías Gulf, on the northern continental shelf of Argentina, based on the analysis of remote sensing and in-situ data. Upwelling events are characterized by their frequency of occurrence and magnitude. During the austral summer we found roughly 6 upwelling-favorable wind events per year. Satellite derived sea surface temperature (SST) data provide evidence of upwelling in 85% of the cases between 2000 and 2008. Analysis of specific events provides clues on the wind forcing characteristics required to generate upwelling, and on characteristic space and time scales of the process. On February 2005 SST data reveal a narrow coastal band (~10km) of relative cold water extending ~100km along the west coast of SMG. The SST in this band was 1.5°C lower than further offshore. Near bottom temperature fluctuations from in-situ daily observations collected at two near-shore locations are significantly correlated with along-shore wind stress, suggesting that coastal upwelling is a dominant process controlling high-frequency temperature fluctuations near-shore. A simple quantitative estimate reveals a volume of upwelled water reaching the sea surface of about 1010m3 during one relatively intense upwelling event.

J032012 流体温度変動による配管熱疲労に関する研究 : 合流部温度変動のCFD解析による予測性評価([J032-01]エネルギープラント安全に向けた構造/熱流体/材料の達成問題(1))

CFD simulations based on LES was applied for the thermal striping phenomenon in a T junction pipe. The CFD models of several mesh size were used to evaluate grid convergences for temperature fluctuations. Fluid temperature fluctuations show some grid dependencies, but metal temperature fluctuations show good grid convergences and its order is same as experiments. These results means that high frequency temperature fluctuations induced by local flows like a karman vortex can be represented. Another important issue is to find some signs of low frequency temperature fluctuations by the branch stream swaying. Low temperature frequency fluctuations has possibilities to cause serious thermal fatigue damages in piping. A hypothesis of the mechanism of branch stream swaying was presented.

Nearshore internal bores and turbulent mixing in southern Monterey Bay

We observed transient stratification and mixing events associated with nearshore internal bores in southern Monterey Bay using an array of instruments with high spatial and temporal resolution. The arrival of the bores is characterized by surging masses of dense (cold) water that tend to stratify the water column. The bore is followed by a gradual drop in the temperature throughout the water column over several hours (defined here as the bore period) until a sharp warm‐front relaxation, followed by high frequency temperature fluctuations, returns the column back to nearly its original state (defined here as the mixing period). Mixing periods revealed increased temperature variance at high frequencies (ω &gt; ), as well as a greater percentage of events where dynamic instabilities may be present (Ri&lt; 0.25), suggesting active mixing of the stratified water column. Turbulent dissipation rates in the stratified interior during the mixing period, estimated using the technique of isopycnal slope spectra, revealed mean values the same order of magnitude as near‐bed bottom‐generated turbulence. Observations indicate that local shear‐produced turbulent kinetic energy by the warm front relaxations dominates mixing in the stratified interior. The non‐canonical nature of these bore and relaxation events is also investigated with a numerical model, and the dynamics are shown to depend on the internal Iribarren number. Our results suggest that nearshore internal bores interacting with local bathymetry dramatically alter local dynamics and mixing in the nearshore with important ecological implications.

The costs of phenotypic adaptation to repeatedly fluctuating temperatures in a soil arthropod

Costs of phenotypic adaptation to changing environments have often been studied in morphological structures. Such structures typically are irreversible for at least some stage in the organism's life. In this study we investigated whether recurrent and reversible adaptation to changes in the thermal environment incurs a cost in terms of some key life-history traits in the collembolan Orchesella cincta. We exposed juvenile O. cincta to two treatments differing in the frequency of temperature fluctuation but with equal total temperature sums. In the high frequency treatment temperature fluctuated daily between 10 and 20 °C, while in the low frequency treatment temperature fluctuated on a weekly schedule. During the treatments we measured juvenile growth rate and juvenile mortality, and after six weeks the animals were transferred to constant 15 °C and adult starvation resistance was assessed. We found no significant differences between the treatments in juvenile growth rate or juvenile survival. Also, adults that had grown up under high frequency temperature fluctuations did not suffer from reduced starvation resistance compared to animals growing under low frequency temperature fluctuations. This finding supports the hypothesis that selection minimizes the production costs of inducible phenotypes and suggests that the development of optimal phenotypes and evolution of temperature reaction norms are not constrained by such costs.

Lithium line radiation in turbulent edge plasmas: Effects of low and high frequency temperature fluctuations

In lithium-wall-conditioned tokamaks, the line radiation due to the intrinsic impurities (Li/Li+/Li++) plays a significant role on the power balance. Calculations of the radiation losses are usually performed using a stationary collisional–radiative model, assuming constant values for the plasma parameters (Ne, Te,…). Such an approach is not suitable for turbulent plasmas where the various parameters are time-dependent. This is critical especially for the edge region, where the fluctuation rates can reach several tens of percents [e.g. J.A. Boedo, J. Nucl. Mater. 390–391 (2009) 29–37]. In this work, the role of turbulence on the radiated power is investigated with a statistical formalism. A special emphasis is devoted to the role of temperature fluctuations, successively for low-frequency fluctuations and in the general case where the characteristic turbulence frequencies can be comparable to the collisional and radiative rates.

The impact of relaxation on the damping of high-frequency temperature fluctuations arising in tungsten under periodic pulsed laser heating

The possibility is considered of employing periodic pulsed lasers for the investigation of relaxation processes in solids. Results are given of measurements of temperature dependence of the coefficient of damping of high-frequency temperature oscillation in thin tungsten samples.

Fine-wire thermometer to correct CO 2 fluxes by open-path analyzers for artificial density fluctuations

A fine-wire thermometer was applied to measure high-frequency air temperature fluctuations averaged over the length of the optical path of an LI-7500 open-path gas analyzer that was used for CO 2 flux measurements over a forest clear-cut in Sweden. Heat fluxes derived by the fine-wire temperature data were used to correct the CO 2 fluxes for density fluctuations within the optical path. As this method incorporates both natural heat fluxes, accounted for in the conventional Webb–Pearman–Leuning term, and heat fluxes caused by analyzer surface heating, it provides a means to minimize or eliminate the bias in open-path fluxes that could lead to apparent CO 2-uptake in ecosystems during the off-season period, and to a general underestimation of carbon losses in other periods. The proposed technique was compared to two other methods: the conventional WPL-correction and a theoretical correction for the instrument surface heating with empirically estimated instrument surface temperatures. All methods were referenced to a closed-path LI-6262 system because high frequency temperature fluctuations in that system were attenuated by the long intake tube. Measurements demonstrated that the fine-wire correction yielded integrated fluxes that were within 4% of the LI-6262-derived fluxes. The theoretical correction with empirically estimated temperatures led to integrated fluxes being within 6% of those measured using the LI-6262. For the same time period, the conventional WPL-correction underestimated CO 2 losses by 19%. During another period with external heating applied to the LI-7500, the conventional WPL-correction led to an underestimation of the CO 2 efflux by 66%, while the PRT-correction yielded fluxes within 8% of the LI-6262. The experiment confirmed that the bias in the open-path CO 2 flux measurements is mostly caused by instrument surface heating, and that such heat should be accounted for in the density corrections. The experiment also demonstrated that a fine-wire thermometer provided a reliable instrumental solution for the open-path heating phenomenon, and could give adequate corrections on a half-hourly and seasonal basis even when external heat was applied to the open-path analyzer.

Internal tidal bore warm fronts and settlement of invertebrates in central Chile

We studied the occurrence of large high frequency temperature fluctuations and their potential association with settlement of intertidal invertebrates during the spring/summer period 1999/2000 at Las Cruces, on the coast of central Chile. Our results showed the existence of internal tidal bores, characterized by sharp drops in water temperature at the surface and near the bottom, and subsequent temperature increases, which occurred with a semidiurnal periodicity. Measured currents support the hypothesis of alternating onshore and offshore movement of warm-water fronts. The frequency of the events varied through the summer and their amplitude seems to be modulated by onshore winds. The strongest events were observed when strong onshore winds occurred in late afternoon hours and the entire water column showed a semidiurnal temperature signal. Highest values of chlorophyll concentration in the intertidal zone and daily settlement of bivalves, gastropods and crustaceans were observed at times when conditions were favorable for occurrence of internal tidal bores. Results suggest that internal tidal bore warm fronts could play an important role in the transport of neustonic larval invertebrates and the delivery of phytoplankton to at least some intertidal sites along the coast of Chile.

Effects of tidally driven temperature fluctuations on shallow-water acoustic communications at 18 kHz

A communications experiment was conducted to investigate the effects of oceanographic fluctuations on high-frequency acoustic transmissions. Source transmissions containing broadband channel probes and phase-shift-keyed (PSK) communication sequences were carried out in 100-m water depth using a stationary 18-kHz source and a stationary 64-hydrophone receive array. Thermistor string data indicate the presence of high-frequency temperature fluctuations generated by the internal tide as it progresses along the continental shelf. Data are analyzed from three periods when the thermal activity is: (1) absent; (2) confined to the lower water column; and (3) confined to the mid-water column. Because of a downward refracting profile, ray paths are most dense near the bottom, which maximizes wavefront interaction with the fluctuating temperature field during period 2. Statistics of the individual ray paths indicate a strong dependence of the temporal correlation on the presence and location of the thermal activity. Ray paths interacting strongly with the portion of the water column exhibiting rapid temperature fluctuations have coherence times of a few tens of seconds, whereas the correlation remain high over the 60-s observation window when the temperature structure is stable. Because of calm sea surface conditions, surface interacting rays are also highly correlated over this time. Spatial coherence estimates and eigenvalue analysis of the array cross-spectral density matrix further indicate that the thermal activity decorrelates the signal in space. Binary PSK (BPSK) data are processed for each of the three periods using two receiver structures: (1) a multichannel decision feedback equalizer and (2) a single-channel decision feedback equalizer preceded by an eigenvector beamformer which projects the data onto the first empirical orthogonal function. Performance of the two receivers is comparable except during period 2. During this period, the eigenvector beamformer performance suffers due to the spatial decorrelation of the signal imposed by the temperature fluctuations.

Development of the evaluation method for crack propagation due to thermal striping

The evaluation code “THERST” was developed to estimate the fatigue crack propagation behavior under thermal stresses due to high-frequency temperature fluctuations, called “thermal striping”. This paper presents fundamental formulations of the evaluation method and verifications of the evaluation method by FEM analyses. Experimental data were obtained in high cycle thermal fatigue tests and the effect of a multiple crack which is characteristic for a crack under thermal stress is discussed in addition to the results of the FEM analyses. A modification of the evaluation method was performed to take multiple crack effects into account.