Design Lifetime Research Articles

Statistical Analysis of the Thermal Performance and Reliability in the Heat Sink With Heat Pipes for the Power Electronics Module

Cooling devices are often used with power electronics systems to allow them to operate stably over long periods of time, they help guarantee not only thermal performance but also reliability. To understand the performance of these cooling devices it is important they are verified by various types of testing, also the test results themselves should be quantified and analyzed using recognized statistical methods. For this paper, we investigated an air-cooled heat sink with heat pipes by conducting heat load, high/low temperature storage limits, accelerated life, and transport vibration tests. The collected experimental data were analyzed by statistical methods such as the independent samples t-test, the paired samples t-test, correlation analysis, process capability analysis, and the tolerance interval analysis. A newly manufactured power conditioning system had one heat sink on which the two power electronics modules were attached while providing a heat load of up to 3.2 kW. It was found that there was no deterioration in the thermal performance of the heat sink due to vibrations while being transported from the Republic of Korea to the United States. If such a heat sink is used over 20 years, it is anticipated that there will be a performance degradation of 6.2% over those years with a 95% confidence level for a B10 life. Based on our accelerated life testing, the heat sink is capable of dealing with a heat load of up to 3.1 kW over the design lifetime of 20 years. Thermal engineers should eventually introduce design margins in consideration of the reduction in quality and reliability that can occur over the lifetime of a cooling device.

Gradient descent algorithm to optimize the offshore scale squeeze treatments

Scale deposition is one of the serious oilfield chemical issues which may lead to a range of downhole and production problems, including the reduction of well productivity index. Scale Inhibitor (SI) squeeze treatments are one of the most common techniques which are applied to prevent downhole scaling in production wells. A treatment typically consists of four stages, (i) a preflush, to condition the rock surface; (ii) a main treatment, where a batch of high concentration inhibitor is bullheaded into the formation; (iii) an overflush, to displace the scale inhibitor slug deeper into the near-well formation, and (iv) a shut-in stage to allow further inhibitor retention before putting the well back on production. During this backflow period, scale inhibitor is released from the rock surface into the produced water, and the scale deposition is prevented if the inhibitor concentration is above some specified Minimum Inhibitor Concentration (MIC). Due to logistic constraints in offshore wells, it is often required that the scale protection afforded by a squeeze treatment should last for some fixed design lifetime until the next treatment becomes available. For example, in the North Sea sector, well operations are often based on an annual treatment design. This paper presents a methodology to optimize the squeeze treatment design for a fixed target lifetime and this is applied for two offshore well squeeze treatments. This approach allows us to account for the operational constraints in the squeeze optimization process to treat a fixed volume of produced water, while minimizing the inhibitor neat volume and the total pumping time. A sensitivity study was performed on the inhibitor concentration, where the results showed that deploying a smaller inhibitor slug but with higher concentration is more effective than a larger slug with lower concentration, assuming a fixed volume of inhibitor and injected water. Therefore, it is recommended that the inhibitor is deployed at the maximum possible concentration, while avoiding the potential for any formation damage. Considering the same inhibitor slug (volume and concentration), this study suggests that the squeeze lifetime continuously increases with the overflush volume. This implies that the lifetime function is differentiable with respect to the overflush, and thus a gradient-based optimization algorithm, specifically the Gradient Descent (GD) may be applied to find the exact overflush volume resulting in the target lifetime. Employing this procedure for a wide range of main treatment volumes allows us to calculate the squeeze “Iso-Lifetime” curve which represents all the possible squeeze designs for the target lifetime. Thereafter, from the iso-lifetime designs, the CPB value (total cost of squeeze per treated barrel of water produced) can be minimized to find the most optimum squeeze design. This approach is shown to result in the optimum scale inhibitor squeeze treatment strategy in the long-term.

Uncertainty and statistics of dislocation-precipitate interactions on creep resistance

To meet the 30,000-h design lifetime of a typical turbine disc, understanding of long-term creep behavior is critical to prevent premature structural failure. The existing creep-life predictions often belittle the importance of multiple dislocation-precipitate interactions, resulting in several-orders-of-magnitude deviations in comparison with experiments. Herein, our experimental observation shows precipitate spatial distribution to yield uncertainty of dislocation-precipitate interactions and precipitate-size lognormal distribution to cause coexistence of climb, cutting, and Orowan mechanisms. Accounting for this physical process, we establish a unified model without adjustment parameters for predicting the stress-sensitive creep rate in precipitate-strengthened alloys. The predicted creep rates show agreement with experimental data, which makes up for the flaw of typical classic models with great deviations. Moreover, the present work reveals the stress-controlled transformation of multiple creep mechanisms and evaluates their weighting of creep-resistance contributions. Thus, our model provides insights for accurate design of high-strength and high-creep-resistant alloys under complex service environments. The model accounts for three-dimensional configuration of precipitates The flaw of typical models with several-orders-of-magnitude deviations has been made up The stress-controlled transformation of multiple creep mechanisms is revealed The weighting of creep-resistance contributions from various mechanisms is evaluated Considering the coexistence and uncertainty of climb, cutting, and Orowan mechanisms during creep processes, Li et al. develop a creep model coupling precipitate-spatial and precipitate-size lognormal distribution to predict accurately creep rate. This finding provides insights to design high-performance alloys under complex service environments.

Hong Kong Zhuhai Macao Bridge-Tunnel project immersed tunnel and artificial islands – From an Owners’ perspective

The Hong Kong Zhuhai Macao Bridge (HZMB) link is currently one of the largest fixed links ever realised. The link comprises various bridges, causeways, artificial islands and tunnels and has a total length of more than 55 km with an investment of about RMB 120billion (approx. €15 billion). The Link accommodates a dual carriageway with three traffic lanes in each direction.The construction of the Link started at the end of 2010 and was opened to traffic in October 2018. The HZMB Link is internationally regarded as one of the most challenging sea crossing projects in China and a demonstration of China's comprehensive breakthrough in technology, scientific research and other related fields.The offshore part of the HZMB Link, crossing the Pearl River Estuary involves one of the world’s longest and deepest immersed tunnels. The tunnel was designed and constructed to meet state-of-the-art requirements and challenging structural, geotechnical and marine/offshore conditions. The HZMB tunnel won the ITA Tunnelling Award Major Project of the Year 2018.This paper presents the project from the Client perspective. The paper will give a general introduction of the project, will provide information regarding the challenging environment in which the tunnel had to be realized and the high demanding design criteria that were applicable. Furthermore, the evaluation of the various technical options will be discussed, ultimately leading to the selection of the immersed tunnel option. The paper will also look into the background of selecting the Design & Build contract approach for this project and the experiences that were built up using this type of contract, new to China on this scale. Finally, the paper introduces how operation and maintenance of the tunnel is planned and executed so as to guarantee the 120-year design lifetime. In Ref. (The Islands and Tunnel Project of HZM Link et al., 2022) more details of the project are discussed from the D&B contractors’ perspective.

A Versatile Methodology for Reactor Pressure Vessel Aging Assessments

The operation of many nuclear pressurized water reactors is being extended beyond their design lifetime threshold. From the perspective of possible further lifetime extension, satisfying safety requirements is a priority. Characterization of the structural integrity of the reactor pressure vessel (RPV) is an important issue as it is a guiding parameter that influences the reactor lifetime. Embrittlement of RPV material is primarily induced by the bombardment of fast neutrons (with energies greater than 1 MeV). Consequently, fast neutron fluence is one of the quantities used by safety authorities to characterize the structural integrity of RPV. However, future RPV aging assessments might lean on new variables with respect to current laws, such as neutron fluence considering the whole neutron spectrum or displacements per atom (dpa) since the latter is more representative of overall damage generated in the RPV. In order to meet these challenges, a versatile calculation scheme for RPV aging assessments is proposed in this paper. The developed methodology allows one to compute (fast and non-fast) neutron fluence as well as dpa rate, using the Norgett-Robinson-Torrens dpa model and the Athermal Recombination Corrected dpa model, for a wide azimuthal and axial range on the RPV and in the capsules of the aging monitoring program (which contain dosimeters and vessel material samples). This methodology is based on a coupling between deterministic (CASMO5 and SIMULATE5) and Monte Carlo (MCNP6) numerical approaches. First, the deterministic approach is used to evaluate the full-core fission neutron source term. Second, Monte Carlo modeling is used to perform the neutron attenuation from the core to sites of interest, such as the RPV. The computational efficiency, accuracy, and potential benefits of the methodology are presented. Moreover, the frequency at which neutron transport calculations should be performed in order to obtain sufficiently accurate time-integrated data over a reactor cycle is discussed. Finally, the validity of the fast neutron fluence as an indicator of RPV aging is compared against the use of dpa.

The Global Satellite Precipitation Constellation: Current Status and Future Requirements

AbstractTo address the need to map precipitation on a global scale, a collection of satellites carrying passive microwave (PMW) radiometers has grown over the last 20 years to form a constellation of about 10–12 sensors at any one time. Over the same period, a broad range of science and user communities has become increasingly dependent on the precipitation products provided by these sensors. The constellation presently consists of both conical and cross-track-scanning precipitation-capable multichannel instruments, many of which are beyond their operational and design lifetime but continue to operate through the cooperation of the responsible agencies. The Group on Earth Observations and the Coordinating Group for Meteorological Satellites (CGMS), among other groups, have raised the issue of how a robust, future precipitation constellation should be constructed. The key issues of current and future requirements for the mapping of global precipitation from satellite sensors can be summarized as providing 1) sufficiently fine spatial resolutions to capture precipitation-scale systems and reduce the beam-filling effects of the observations; 2) a wide channel diversity for each sensor to cover the range of precipitation types, characteristics, and intensities observed across the globe; 3) an observation interval that provides temporal sampling commensurate with the variability of precipitation; and 4) precipitation radars and radiometers in low-inclination orbit to provide a consistent calibration source, as demonstrated by the first two spaceborne radar–radiometer combinations on the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Measurement (GPM) mission Core Observatory. These issues are critical in determining the direction of future constellation requirements while preserving the continuity of the existing constellation necessary for long-term climate-scale studies.

Estimation of Wear and Lifetime for an Improved Turbine Operation

Design, construction and certification of wind turbines (WT) generally target a lifetime of at least twenty years. Depending on the specified design criteria in comparison with the’real’ conditions on site lifetime may fall below or pass over the design lifetime targets. After installation and during operation WT continuously suffer from incremental damage due to loads, fatigue and the continuous exposure to the physical environment and operating conditions. The initially inherent wear reserve of the WT or its components permanently decreases until it finally reaches predefined safety margins or the occurrence of premature component failure. The objective of the work is to identify quantifiable wear-out metrics and to deduce information on lifetime issues in order to optimise WT operation. The method divides into a simplified approach explaining the general concept and its implementation and adaption from design to in-situ conditions. Furthermore, the methodology is transferred to a component-specific level, namely generator windings, in order to evaluate the general suitability for non-mechanical load exposures. Finally, economic issues including an economic optimisation strategy considering previously calculated wear-out figures complete the work.

A Cost-Effective Approach to the Risk Reduction of Cable Fault Triggered by Laying Repeaters of Fiber-Optic Submarine Cable Systems in Deep-Sea

Long-distance submarine cable systems, such as the transoceanic system, generally consist of a series of cables and repeaters. Repeater units are spaced at regular intervals to boost the attenuated optical signal and presently contain optical amplifiers in a pressure vessel made of copper alloy. Since the repeater unit is more massive than the cable, it pulls the cable catenary locally toward the seabed. In the 1990s, several studies numerically simulated cable behavior in the water and showed that the seabed slack runs short, and the seabed cable tension increases just before the repeater reaches the seabed. Therefore, it has been pointed out that an unarmored cable with a polyethylene sheath can be easily damaged. However, no reports have been published regarding the actual situation of cable faults related to the laying of repeaters. This study quantitatively analyzes the mechanism of cable damage related to the laying of repeaters, based on experiments, simulations, maintenance records, and a comparative analysis between the simulation results and actual cable faults. Cost-effective methods to mitigate cable faults triggered by laying a repeater in the deep sea are also explored to ensure mechanical stability during the design lifetime.

Study on Solar Radiation and the Extreme Thermal Effect on Concrete Box Girder Bridges

Thermal effect is an essential factor in the durability and safety of concrete bridges. Therefore, this paper mainly studied the concrete bridge box girder temperature distribution and thermal effect under solar radiation and the thermal load. With a concrete rigid frame bridge as the engineering background, the temperature distribution of the box girder on a clear summer day was observed. Then, according to the solar physics and heat transfer theory, the different surfaces of the box girder cross-section are classified based on the heat transfer conditions, and the variation of solar radiation on different surfaces is investigated. The temperature field of the box girder is simulated by ANSYS. To obtain the extreme thermal condition, the meteorological data of the bridge site from 1990 to 2020 are collected. The data are fitted by generalized extreme value distribution to obtain the extreme temperature and average wind factors in the bridge design lifetime. Combined with the solar radiation, temperature, and wind factors, the extreme thermal condition of the concrete box girder is obtained. Lastly, the thermal effect of the box girder under the extreme condition is analyzed, and the thermal stress is compared with the allowable stress in the design code. The results show that the girder temperature difference is closely related to the solar radiation intensity and heat transfer conditions, and the solar radiation intensity is the more critical factor. The tensile stress caused by the extreme thermal load is more significant than the design strength value in the girder cross-section. The results also provide a method to obtain the extreme thermal condition and evaluate the impact of the thermal effect on concrete box girder bridges.

Physical Modelling of Offshore Wind Turbine Foundations for TRL (Technology Readiness Level) Studies

Offshore wind turbines are a complex, dynamically sensitive structure due to their irregular mass and stiffness distribution, and complexity of the loading conditions they need to withstand. There are other challenges in particular locations such as typhoons, hurricanes, earthquakes, sea-bed currents, and tsunami. Because offshore wind turbines have stringent Serviceability Limit State (SLS) requirements and need to be installed in variable and often complex ground conditions, their foundation design is challenging. Foundation design must be robust due to the enormous cost of retrofitting in a challenging environment should any problem occur during the design lifetime. Traditionally, engineers use conventional types of foundation systems, such as shallow gravity-based foundations (GBF), suction caissons, or slender piles or monopiles, based on prior experience with designing such foundations for the oil and gas industry. For offshore wind turbines, however, new types of foundations are being considered for which neither prior experience nor guidelines exist. One of the major challenges is to develop a method to de-risk the life cycle of offshore wind turbines in diverse metocean and geological conditions. The paper, therefore, has the following aims: (a) provide an overview of the complexities and the common SLS performance requirements for offshore wind turbine; (b) discuss the use of physical modelling for verification and validation of innovative design concepts, taking into account all possible angles to de-risk the project; and (c) provide examples of applications in scaled model tests.

Analytical system for predicting cracks in hydraulic turbines

Today, many hydropower plants face serious problems associated with the sudden appearance of dangerous cracks in key components of hydraulic turbines. This is especially true for large hydraulic units whose design lifetime has already expired. In recent years, hydraulic units have been progressively used under off-design modes of operation, which causes increased loads and stresses in their components, accelerates the appearance and growth of defects, stimulates premature failures, and ultimately can lead to serious accidents with large losses. The currently used diagnostic systems for hydraulic turbines often do not allow tracking the appearance of fatigue cracks in runner blades, guide vanes, shafts, etc. The strong individuality of hydraulic units also excludes the use of any statistical methods for determining the time of cracks initiation. The predictive analytics system is proposed as an additional tool for predicting the appearance and growth of dangerous operational cracks. The system implements an analytical algorithm based on the evaluation of fatigue strength of hydraulic turbine components under frequently changing operating conditions and allows summing up damage from various external loads and in various time ranges. The initial information for this predictive system is the information about the actual operating time at each operating mode and the expected regime parameters for the upcoming period. The output data is information about the exhausted and residual lifetime. All individual features are taken into account by an individual digital model of the matrix type as a combination of equipment responses to external influences. The proposed predictive analysis system not only reduces the frequency of accidents and unplanned shutdowns but is also a way of smart maintenance for hydraulic turbines by developing the most efficient, reasonable, maximum time-saving equipment use strategy.

A statistical model of irradiation hardening induced by non-periodic irradiation defects

Numerous efforts have been made to develop the irradiation hardening models, due to their important role in nuclear reactor design and service lifetime prediction. Most of the models are based on the dislocation line tension approximation, by assuming a periodic array of irradiation defects. The random distribution effect is also generally taken into account from a fully deterministic perspective, such as the well-known Bacon-Kocks-Scattergood model. Different from these previous studies, this work is aimed at developing a statistical irradiation hardening model by systematically coarsening the interaction mechanism between dislocation and non-periodic irradiation defects. The cumulative distribution function of the critical shear stress to overcome the irradiation defect barrier is obtained through the analytical derivation, and is lumped into a 2D Monte Carlo model to predict the mechanical response of irradiated material. The prediction results agree very well with three-dimensional discrete dislocation dynamics results and experimental data.

Failure analysis on rubber universal spherical joints for rail vehicles

Considering the large quantity of passengers in a running rail vehicle, its safety must be paid special attention to, which relies on the reliability of every critical component. Spherical universal joint is widely used in the suspension device of the gearbox in the transmission of railway vehicles for its functions of damping and cushioning. Since it’s commonly made of rubbers rather than the familiar metallic materials, its degradation behaviors and failure mechanisms have not been systematically investigated. In this study, multiple rubber spherical universal joints used in the urban rail transit train were found cracked and sticky during maintenance. Its design lifetime was 5 years, but this kind of failure occurred in <2 years, which posed a threat to the safe operation of the train. In order to identify the root causes of the failure, the physical, chemical, mechanical properties and the surface morphologies of the failed joints were characterized by a series of methods. The results showed that the corrosive solvents introduced during installation was the root cause of the failure, which was further aggravated by the oversizing and segregation of the filler particles in the rubber and the high crosslinking density of the rubber. Based on these failure causes, countermeasures were proposed to prevent the occurrence of similar failure again.

Oil Tanker Simplified Fatigue Assessment with Inspection and Repair Approach and Parameters

The occurrence of cracks in the hull structure of oil tankers is an important concern for the maritime industry because crack propagation will reduce collapse strength of deck-stiffened panels and, consequently, decrease the ultimate hull girder capacity of ship’s structures. Fatigue is an important design criteria for ships to ensure a sufficiently high safety level. Fatigue life predictions of ship’s structural details have traditionally been carried out using S-N approach and the Palmgren-Miner’s rule. The principal objective of such approach is to estimate the time to failure in order to ensure a satisfactory design lifetime of ship’s structural components. Potential cracks are considered to occur in the side shell, in the connections between longitudinal stiffeners and transverse web frame. The main objectives of the present study are to evaluate the fatigue life of vessel’s amidships using the simplified fatigue method, which is based on DNVGL-CG-0129 “Fatigue Assessment of Ship Structures” in order to determine the main cause of the observed cracks on the single skin oil tanker. Fatigue assessment was based on worldwide trade. Longitudinal stiffeners at transverse frames amidships are considered. The results show that fatigue life is generally above 20 years; however, analysis has revealed that the fatigue life of typical stiffener transitions in the side shell is below 20 years. The fatigue lives of side shell longitudinals are regarded as normal for ships built in the period between 1980 and 1990 with extensive use of high tensile steel in the side shell. Inspection and repair proposals of details with fatigue lives below 20 years are advised accordingly. Findings of fatigue analyses provide remaining life assessment, inspection plan definition, determination of repair and modification solutions, and avoiding integrity issues resulting in production downtime and hot work or dry dock.

Justification of Safe Operation of Rolling Stock by the Lifetime of Its Bearing Structures

The problem of providing strength and reliability of rolling stock bearing structures which include welded and cast parts of bogie frames and bodies of cars and locomotives, as well as brackets and attachment points for their equipment and traction drive units, is one of the most important in the design, construction and operation. The development of high-speed and heavy-haul traffic, as well as the introduction of requirements for determining the design service life and life time of railway transport facilities, make the above task even more urgent. The influence of the operational loading characteristics of the object on the safety factor of fatigue strength and its depletion: amplitudes of cyclic stresses, frequencies of their change, parameters characterizing the intensity of the rolling stock operation (number of loading cycles, speed of movement, average daily mileage) is shown based on the results of computational and experimental studies carried out with running dynamic and strength tests of locomotives at all operating speeds of their movement in operation.

Wind turbine blade material in the United States: Quantities, costs, and end-of-life options

Wind energy has experienced enormous growth in the past few decades; as a result, there are thousands of wind turbines around the world that will reach the end of their design lifetimes in the coming years. Much of the material in those turbines can be recycled using conventional processes, but the composite material that is the main component of the blades is more challenging to recycle. In the United States, turbine blades may be disposed of in landfills, adding a new solid waste stream to the material already being landfilled. This paper presents a spatially resolved estimate of the mass and volume of wind turbine blade waste in each state by 2050 and compares these amounts to estimates of the remaining landfill capacity by state. We estimate costs for each stage of the disposal process to indicate cost levels for alternatives. Assuming a 20-year turbine lifetime, the cumulative blade waste in 2050 is approximately 2.2 million tons. This value represents approximately 1% of remaining landfill capacity by volume, or 0.2% by mass. We also find that the current cost of disposing of blades in large segments or through grinding is relatively low in comparison to the overall life-cycle cost of energy. Based on these findings, landfill space constraints and disposal costs appear unlikely to motivate a change in waste handling strategies under current policy conditions. Instead, more profound shifts in recycling technologies, blade materials, or policy may be needed to move towards a circular economy for wind turbine blades.

Regression analysis in predicting coating application lifetime on asset integrity project

The Asset Integrity project is one of the strategic priorities in maintenance to ensure the functional lifetime of an asset is well maintained to support the nickel processing. The coating protection application is one of the asset integrity strategy to maintain the structural lifetime, however the corrosive environment of nickel processing plant influences the lifetime of the coating design differently on each facility due to different process in the processing line. The objective of this study is to predict the coating design lifetime on Dryer, KILN, Furnace, and Converter facilities. The analysis used regression method for coating lifetime on each facility by considering the independent variables, i.e. SO2 Intensity, stack emission, NOx emission, rainfall intensity, and underfilm condition. By using regression model, coating design lifetime in Dryer area is 4.95 years, KILN is 5.73 years, Furnace is 6.23 years, and Converter is 6.73 years. Process plant area which having the most significant impact of corrosive environment is Dryer area, causing the coating lifetime in this area is the lowest than other area in the Process Plant area. This result can be used to set maintenance strategy for coating design lifetime lifecycle for the next Asset Integrity project.

Some study on the potential energy extraction from solar-assisted solid waste for produce electricity in Adama city in Ethiopia

The present work aimed to show (explore) Adama city’s economic and environmental opportunities for solid waste incineration with energy recovery, also known as Waste to Energy. The current waste management system in Adama consists of landfills in the cities and open burning. Environmentally, this is an imperfect solution, and although there are plans for change, no specific strategy has been presented. This is a growing problem, both environmentally and logistically. Another important thing is that Waste to Energy is the additional way of getting energy for Adama city. Data was collected from Adama with four kebele and different literature review. From the collected data, waste-to-energy systems were simulated in CYCLEPAD, PYTHON, and MECH IN EXCEL. The simulations show that a system using waste incineration would be the best solution for Adama city. This study shows that implementing a waste incineration plant in the Adama city energy system is economically and environmentally feasible compared to the current conditions. The chosen system is designed to handle 50,000 tons of waste annually collected from Adama city. The system will provide 118.5 GW hours of electric energy annually. The system investment cost is around 149.5 MUSD, and it is expected to generate an annual profit of 4.71 MUSD. This study clearly shows that there is both economic and environmental potential for waste-to-energy technologies in the region. By implementing waste-to-energy technology, the supplied waste can be seen as a resource instead of a problem. This would give incentives for further actions and investments regarding waste management. Compared with the city’s current solution with landfills and fossil fuel turbines, the present work also develops a significant environmental improvement. During the plant’s design lifetime, greenhouse gas emissions are small, assuming that only a portion of the waste's carbon content is of fossil origin.

TanDEM-X: 10 Years of Formation Flying Bistatic SAR Interferometry

On June 21, 2010, the TanDEM-X mission was launched and opened a new era in spaceborne radar remote sensing. The first formation flying radar system was built by extending the TerraSAR-X synthetic aperture radar (SAR) mission by a second, TerraSAR-X-like satellite TanDEM-X. The resulting large single-pass SAR interferometer features flexible baseline selection, enabling the acquisition of highly accurate cross-track interferograms not impacted by temporal decorrelation and atmospheric disturbances. The primary objective of the mission was the generation of a global Digital Elevation Model (DEM) with unprecedented accuracy (12-m horizontal resolution and 2-m relative height accuracy). The main mission phase for DEM data acquisition has been finished in 2014; the processing of the global TanDEM-X DEM was concluded in September 2016. The final DEM product is well within specifications and features an extremely low percentage of void areas. It is of fundamental importance for a wide range of commercial and scientific applications. But the scientific exploitation of TanDEM-X is not limited to the DEM. TanDEM-X has unique capabilities, including along-track interferometry, and new bistatic and multistatic SAR techniques, that support numerous secondary mission objectives. Indeed, some of these experiments were directly performed during the DEM acquisition phase, when suitable satellite formation geometries were available. Moreover, regular acquisitions over selected super test sites enabled multitemporal analyses. A dedicated science phase after the DEM acquisitions included up to 4 km cross-track baselines, operation in the so-called Dual-Receive Antenna mode, as well as a period in pursuit monostatic flight formation. Comparisons of the TanDEM-X DEM with that of SRTM, or among multitemporal TanDEM-X data, revealed dramatic, ongoing, changes in Earth's topography, especially over ice and forests. In the last 3.5 years the mission has further acquired data for a global change layer showing the height changes relative to the first global DEM dataset. The so-called “Change DEM” is planned for release in 2021. Despite being well beyond their design lifetime, both satellites are still fully functional and have enough consumables for several additional years. Therefore, bistatic operations continue with a focus on changes in the cryosphere, biosphere, and densely populated urban areas.

Efficient identification of random fields coupling Bayesian inference and PGD reduced order model for damage localization

AbstractOne of the main challenges regarding our civil infrastructure is the efficient operation over their complete design lifetime while complying with standards and safety regulations. Thus, costs for maintenance or replacements must be optimized while still ensuring specified safety levels. This requires an accurate estimate of the current state as well as a prognosis for the remaining useful life. Currently, this is often done by regular manual or visual inspections within constant intervals. However, the critical sections are often not directly accessible or impossible to be instrumented at all. Model‐based approaches can be used where a digital twin of the structure is set up. For these approaches, a key challenge is the calibration and validation of the numerical model based on uncertain measurement data.The aim of this contribution is to increase the efficiency of model updating by using the advantage of model reduction (Proper Generalized Decomposition, PGD) and applying the derived method for efficient model identification of a random stiffness field of a real bridge.