This report reviews the recent advances of the past years in ships and offshore structural testing area including scaling laws, DIC, hydrodynamic of flexible structures, wave-in-deck, hybrid model testing, corrosion testing, iced load measurements, health monitoring model and digital twin model. The following summary and recommendations are made for future work in the area of innovative experimental methods in ships and offshore industry. It is important to also note that as experimental techniques allow for a greater understanding of the underlying material and structural behaviour, and generate extensive data clouds for processing and evaluation. As a result, we recommend that a future chapter in the next committee report focus on data evaluation and statistical approaches; this can provide an in-depth look of state of the art of processes utilized for evaluating the extensive data captured/utilized during experiments. In chapter 2, a review of scaling laws is presented in systematic and recent advancements in structural testing related to ships and offshore structures. General scale modelling methods are provided and described the main characteristics of each method such as dimensional analysis, applied to governing equation, energy method, empirical similarity method through the literature review. Recent application of scale models can be found in field of offshore wind turbine structure and ice testing area. These structures are subjected to complex phenomena such as wave loads and drifting forces may also need to be considered in particular applications, ice flows, continuous winter sea ice, and icebergs. Application DIC in chapter 3, DIC techniques have certainly come into play in many recent experimental evaluations, as the methods allows for elucidating the surface strain behaviour of a component evaluated either in the laboratory and in the field. This chapter has been to give an updated review on applications of DIC techniques in ships and offshore structural tests classifying them by test articles, with a brief insight on commercial instrumentations available on the industry and related to DIC society and a deeper focus on the applied methodologies, providing recent references for those who are interested in this topic. Worth mentioning is that some DIC applications are included in the benchmark study performed by the Committee and reported in section 15. In chapter 4, A large amount of research has focused on better measuring and predicting the hydrodynamic loads, forming several practical hydrodynamic coefficients databases which have been widely used in VIV prediction tools for flexible structure manufacturing industry. Although these databases make great contributions to the field of VIV research, have not been sufficiently modelled in the coefficient database obtained from rigid cylinder experiments. Recently, the phase angle between cross-flow and in-line response had a strong influence on the hydrodynamic coefficients for both rigid and flexible cylinders. And variations of tension and flow velocity were strongly correlated with time-varying hydrodynamic coefficients, therefore, inputs to the prediction of vessel motion induced VIVs, making the prediction possible. Also, the effects of Re numbers and surface roughness on hydrodynamics of VIV and the effect of wake interference on hydrodynamics of a twin-tube submerged floating tunnel (SFT) can be found for can efficient way and requirement in the literature. In chapter 5, based on the challenges remaining in the problem of wave-in-deck impact on offshore structures discussed above, there are several research gaps that can be addressed in future. There is still considerable uncertainty about the magnitude and distribution of wave impact loads on structural deck elements near the free-surface. Effects of the columns of the floating platform on the wave-in-deck forces have not been systematically studied. The measurement, estimation and simulation of local pressures due to wave-in-deck impact events on all types of offshore structures remains challenging. Accurate measurements and prediction of global loads and dynamic response of floating offshore structures due to wave-in-deck impact events is extremely limited. Combined numerical-experimental wave-in-deck investigations on floating offshore structures are not currently available in the open literature. In chapter 6, this chapter focused on hybrid model testing (HMT) combines physical model test and numerical simulations to solve problems that physical model tests alone cannot conveniently or reliably address. In marine model testing, the challenges like ultra-deep water, multi-phase fluids, parameter traversal and so on cannot be avoided. HMT is regarded as the most promising technique to solve these issues. As of today, HMT is still immature, some advanced applications however have been developed. HMT allows researchers to impose mass-spring-damping parameters in virtual space and can artificially adjust and precisely control these critical parameters. It is a very helpful and exciting idea to solve the involved problems. In Chapter 7, a brief reviewed of friction test in terms of two main areas exist where friction is of importance: machineries and mechanical connections, and in cargo/mechanical handling operations. For maritime and offshore applications (e.g. Out-of-Plane Bending), surface conditions and environmental conditions are important parameters. Small and the smaller specimens may be used for screening the theoretical friction coefficients and find trends. Larger or even real size specimens should be used to confirm the actual behaviour. As per the results of literature, friction tests can be split it eh standard, small size specimen standard tests, and the large size, more representative tests. While the standard tests are well covered by standards and guidelines, the larger set-ups are to be tailor made and require goo understanding of the physics as results require interpretation by the experimenter. In chapter 8, the measurement, analysis and mitigation of vibrations in ship and offshore structures is rather well established. Nevertheless, measurement and mitigation methods are still being developed. Measurement’s techniques may also include laser of video techniques. Mitigation measures include devices that cancel vibrations at a low weight penalty, such as absorbing supports or Tuned Mass Dampers. Numerical developments include methods that use sub-structuring or modal shapes to reduce the computational cost. In chapter 9, Material selection for ships and offshore structures exposed to sub-zero temperatures is traditionally based on Charpy and fracture toughness test results of the base materials and its welded connections. In the last years however, fatigue properties have been the focus of a couple of studies due to the acceleration of fatigue crack growth below the so-called fatigue transition temperature, where ductile crack growth is superimposed by cleavage burst. Concluding, fatigue testing at low temperatures demands special attention to the set-up and instrumentation. The testing temperature is normally lower than the application temperature, and liquid nitrogen may be needed to cool down the area of interest to -60 °C. Temperature compensation is required for sensor, either strain gauges or potential drop methods. In chapter 10, The corrosion process and the interpretation of the effect of corrosion on the structural integrity remains an area of uncertainty. In corrosion testing, a large spread may be observed in measured corrosion rates, as is confirmed by industrial thickness measurement. Including the geometrical effects of corrosion damage in a representative manner in numerical simulations requires the use of probabilistic methods, as a precise description would require model with too many details. Hence, simplifications and generalizations are needed. In chapter 11, large scale impact experimentation are unique options to verify developments in structures design, analysis and prediction of failure. In turn, this demands good command of the experimentation techniques, and the use of as many sensors as possible to make possible use of the results. In chapter 12, The chapter present a State-of-the-Art review, to include recent advances and future trends of industry challenge with current standard and out lookout. The wind industry is concerning with the long time-to-marked for future large turbine blades and are interested in ways to shorten the test time. It is a question at which size and when will it stop to make sense to test these long blades according to current standard. Trends of development of more advanced test methods investigated a dual or multi axis test methods to test blades under more representative loading compared to operational loads and ways to speed up the test and challenge with different SN-curves for different materials. Testing parts of blades captured testing with more complex and realistic loading at forced loading, challenges with boundaries, and using subcomponent testing to validate numerical models. In chapter 13, Full scale ice load measurements play a significant role in the design of ships and offshore structures in ice covered waters. Full scale measurements of fixed vertical offshore structure are dis-cussed here. Generalizability of the results can be summarised that as pointed out by Kärnä (2009) it is likely that the experimental data recorded on vertical structures is only applicable for the conditions where the data was record-ed. Thus, data recorded for stiff structures might not be applicable for compliant structures. As discussed before, the compliancy might be one source of the observed rate dependency. The collected data is often incomplete: although local and global ice forces can be recorded during ice action, the ice properties (compressive strength, porosity...) might remain unknown. It is because the ice samples cannot be taken during ice action - when ice is moving. Actual local pressure is challenging to measure. It is known that the ice pressure is concentrated in a small area as shown by Joensuu & Riska (1989). They observed in laboratory scale experiments using PVDF-film that the ice pressure is concentrated on narrow, line like high pressure zones. But, the area of the load panels in full scale of often quite big, in the order of 1 m2. Thus, the actual local pressure exerted to structure is significantly higher than the average pressure measured with the big load panels. But there is no method available for more accurate local pressure measurements in full scale. Although field tests are important and can reveal phenomena that cannot be observed in laboratory scale, there are few things to consider when interpreting the results. In chapter 14, Bridging the relationship between the degradation in the material and the structure is an emerging field of research which requires advanced data fusion, signal processing, AI-based trend detection algorithms and the reliability analysis methods. Data fusion herein refers to combining the data gathered from different SHM sensors by using data fusion algorithms for better damage diagnosis (Eleftheroglou et al., 2018). Other research efforts are recommended for improving the durability of SHM sensors for offshore implementations, inclusion of SHM in the condition monitoring standards and guidelines, addressing big-data issues for developing real-time data collection and analysis frameworks and using the digital twins for real-time reliability assessment. In the Benchmark study, from this relatively simple experiment performed by 6 parties, it is clear that a vast range of choices can be made to carry out the tests. Understanding the effect of the choices on the end result is essential. For instance, a heavy sensor influences the natural frequency a lot. Also, the chosen instrumentation influences the information to be gained from an experiment. Only the natural frequency, by manual excitation, or also damping and higher order modes when using an instrumented hammer. In order to understand the many experiments that are done worldwide, sharing of the results and being transparent on the methodologies of experimentation is very beneficial for making the most of any experiment. Experimental data should be published as is in digital format and not only as a by-product in a publication as figures limiting the use of it.
COMMITTEE V.2 EXPERIMENTAL METHODS
Rizzo C.;
2022-01-01
Abstract
This report reviews the recent advances of the past years in ships and offshore structural testing area including scaling laws, DIC, hydrodynamic of flexible structures, wave-in-deck, hybrid model testing, corrosion testing, iced load measurements, health monitoring model and digital twin model. The following summary and recommendations are made for future work in the area of innovative experimental methods in ships and offshore industry. It is important to also note that as experimental techniques allow for a greater understanding of the underlying material and structural behaviour, and generate extensive data clouds for processing and evaluation. As a result, we recommend that a future chapter in the next committee report focus on data evaluation and statistical approaches; this can provide an in-depth look of state of the art of processes utilized for evaluating the extensive data captured/utilized during experiments. In chapter 2, a review of scaling laws is presented in systematic and recent advancements in structural testing related to ships and offshore structures. General scale modelling methods are provided and described the main characteristics of each method such as dimensional analysis, applied to governing equation, energy method, empirical similarity method through the literature review. Recent application of scale models can be found in field of offshore wind turbine structure and ice testing area. These structures are subjected to complex phenomena such as wave loads and drifting forces may also need to be considered in particular applications, ice flows, continuous winter sea ice, and icebergs. Application DIC in chapter 3, DIC techniques have certainly come into play in many recent experimental evaluations, as the methods allows for elucidating the surface strain behaviour of a component evaluated either in the laboratory and in the field. This chapter has been to give an updated review on applications of DIC techniques in ships and offshore structural tests classifying them by test articles, with a brief insight on commercial instrumentations available on the industry and related to DIC society and a deeper focus on the applied methodologies, providing recent references for those who are interested in this topic. Worth mentioning is that some DIC applications are included in the benchmark study performed by the Committee and reported in section 15. In chapter 4, A large amount of research has focused on better measuring and predicting the hydrodynamic loads, forming several practical hydrodynamic coefficients databases which have been widely used in VIV prediction tools for flexible structure manufacturing industry. Although these databases make great contributions to the field of VIV research, have not been sufficiently modelled in the coefficient database obtained from rigid cylinder experiments. Recently, the phase angle between cross-flow and in-line response had a strong influence on the hydrodynamic coefficients for both rigid and flexible cylinders. And variations of tension and flow velocity were strongly correlated with time-varying hydrodynamic coefficients, therefore, inputs to the prediction of vessel motion induced VIVs, making the prediction possible. Also, the effects of Re numbers and surface roughness on hydrodynamics of VIV and the effect of wake interference on hydrodynamics of a twin-tube submerged floating tunnel (SFT) can be found for can efficient way and requirement in the literature. In chapter 5, based on the challenges remaining in the problem of wave-in-deck impact on offshore structures discussed above, there are several research gaps that can be addressed in future. There is still considerable uncertainty about the magnitude and distribution of wave impact loads on structural deck elements near the free-surface. Effects of the columns of the floating platform on the wave-in-deck forces have not been systematically studied. The measurement, estimation and simulation of local pressures due to wave-in-deck impact events on all types of offshore structures remains challenging. Accurate measurements and prediction of global loads and dynamic response of floating offshore structures due to wave-in-deck impact events is extremely limited. Combined numerical-experimental wave-in-deck investigations on floating offshore structures are not currently available in the open literature. In chapter 6, this chapter focused on hybrid model testing (HMT) combines physical model test and numerical simulations to solve problems that physical model tests alone cannot conveniently or reliably address. In marine model testing, the challenges like ultra-deep water, multi-phase fluids, parameter traversal and so on cannot be avoided. HMT is regarded as the most promising technique to solve these issues. As of today, HMT is still immature, some advanced applications however have been developed. HMT allows researchers to impose mass-spring-damping parameters in virtual space and can artificially adjust and precisely control these critical parameters. It is a very helpful and exciting idea to solve the involved problems. In Chapter 7, a brief reviewed of friction test in terms of two main areas exist where friction is of importance: machineries and mechanical connections, and in cargo/mechanical handling operations. For maritime and offshore applications (e.g. Out-of-Plane Bending), surface conditions and environmental conditions are important parameters. Small and the smaller specimens may be used for screening the theoretical friction coefficients and find trends. Larger or even real size specimens should be used to confirm the actual behaviour. As per the results of literature, friction tests can be split it eh standard, small size specimen standard tests, and the large size, more representative tests. While the standard tests are well covered by standards and guidelines, the larger set-ups are to be tailor made and require goo understanding of the physics as results require interpretation by the experimenter. In chapter 8, the measurement, analysis and mitigation of vibrations in ship and offshore structures is rather well established. Nevertheless, measurement and mitigation methods are still being developed. Measurement’s techniques may also include laser of video techniques. Mitigation measures include devices that cancel vibrations at a low weight penalty, such as absorbing supports or Tuned Mass Dampers. Numerical developments include methods that use sub-structuring or modal shapes to reduce the computational cost. In chapter 9, Material selection for ships and offshore structures exposed to sub-zero temperatures is traditionally based on Charpy and fracture toughness test results of the base materials and its welded connections. In the last years however, fatigue properties have been the focus of a couple of studies due to the acceleration of fatigue crack growth below the so-called fatigue transition temperature, where ductile crack growth is superimposed by cleavage burst. Concluding, fatigue testing at low temperatures demands special attention to the set-up and instrumentation. The testing temperature is normally lower than the application temperature, and liquid nitrogen may be needed to cool down the area of interest to -60 °C. Temperature compensation is required for sensor, either strain gauges or potential drop methods. In chapter 10, The corrosion process and the interpretation of the effect of corrosion on the structural integrity remains an area of uncertainty. In corrosion testing, a large spread may be observed in measured corrosion rates, as is confirmed by industrial thickness measurement. Including the geometrical effects of corrosion damage in a representative manner in numerical simulations requires the use of probabilistic methods, as a precise description would require model with too many details. Hence, simplifications and generalizations are needed. In chapter 11, large scale impact experimentation are unique options to verify developments in structures design, analysis and prediction of failure. In turn, this demands good command of the experimentation techniques, and the use of as many sensors as possible to make possible use of the results. In chapter 12, The chapter present a State-of-the-Art review, to include recent advances and future trends of industry challenge with current standard and out lookout. The wind industry is concerning with the long time-to-marked for future large turbine blades and are interested in ways to shorten the test time. It is a question at which size and when will it stop to make sense to test these long blades according to current standard. Trends of development of more advanced test methods investigated a dual or multi axis test methods to test blades under more representative loading compared to operational loads and ways to speed up the test and challenge with different SN-curves for different materials. Testing parts of blades captured testing with more complex and realistic loading at forced loading, challenges with boundaries, and using subcomponent testing to validate numerical models. In chapter 13, Full scale ice load measurements play a significant role in the design of ships and offshore structures in ice covered waters. Full scale measurements of fixed vertical offshore structure are dis-cussed here. Generalizability of the results can be summarised that as pointed out by Kärnä (2009) it is likely that the experimental data recorded on vertical structures is only applicable for the conditions where the data was record-ed. Thus, data recorded for stiff structures might not be applicable for compliant structures. As discussed before, the compliancy might be one source of the observed rate dependency. The collected data is often incomplete: although local and global ice forces can be recorded during ice action, the ice properties (compressive strength, porosity...) might remain unknown. It is because the ice samples cannot be taken during ice action - when ice is moving. Actual local pressure is challenging to measure. It is known that the ice pressure is concentrated in a small area as shown by Joensuu & Riska (1989). They observed in laboratory scale experiments using PVDF-film that the ice pressure is concentrated on narrow, line like high pressure zones. But, the area of the load panels in full scale of often quite big, in the order of 1 m2. Thus, the actual local pressure exerted to structure is significantly higher than the average pressure measured with the big load panels. But there is no method available for more accurate local pressure measurements in full scale. Although field tests are important and can reveal phenomena that cannot be observed in laboratory scale, there are few things to consider when interpreting the results. In chapter 14, Bridging the relationship between the degradation in the material and the structure is an emerging field of research which requires advanced data fusion, signal processing, AI-based trend detection algorithms and the reliability analysis methods. Data fusion herein refers to combining the data gathered from different SHM sensors by using data fusion algorithms for better damage diagnosis (Eleftheroglou et al., 2018). Other research efforts are recommended for improving the durability of SHM sensors for offshore implementations, inclusion of SHM in the condition monitoring standards and guidelines, addressing big-data issues for developing real-time data collection and analysis frameworks and using the digital twins for real-time reliability assessment. In the Benchmark study, from this relatively simple experiment performed by 6 parties, it is clear that a vast range of choices can be made to carry out the tests. Understanding the effect of the choices on the end result is essential. For instance, a heavy sensor influences the natural frequency a lot. Also, the chosen instrumentation influences the information to be gained from an experiment. Only the natural frequency, by manual excitation, or also damping and higher order modes when using an instrumented hammer. In order to understand the many experiments that are done worldwide, sharing of the results and being transparent on the methodologies of experimentation is very beneficial for making the most of any experiment. Experimental data should be published as is in digital format and not only as a by-product in a publication as figures limiting the use of it.File | Dimensione | Formato | |
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