Enhancing the performance and ensuring the long-time reliability of Offshore Wind Turbines (OWTs) requires a comprehensive understanding of OWT system response and interactions between OWT system components under realistic loading conditions. This paper presents Real-Time Hybrid Simulation (RTHS) results for a monopilesupported OWT under normal and extreme loading scenarios, which include aero-hydro-mechanicalgeotechnical-structural component interactions. RTHS divides the OWT into analytical and experimental substructures, with dynamic equilibrium and compatibility maintained at the interfaces between substructures. The analytical substructures model the superstructure of the OWT above the mudline, along with the applied wave and wind loads, and the effects of the power-take-off unit using well-established numerical models, while the experimental substructure is the soil-monopile system that is physically tested in the laboratory. The RTHS results reveal that the OWT exhibits a ratcheting response due to a progressive accumulation of the monopile displacement under cyclic and dynamic loads. In addition, the stiffness and damping characteristics of the soilmonopile system change significantly, where the lateral stiffness increased by more than 100% and the damping ratio decreased by 76% relative to initial values during the RTHS. The results show that the OWT system response is dominated by wave loading and influenced by the soil-monopile response. The 1st fore-aft towermonopile mode frequency was reduced by about 10% relative to a reference case without soil-monopile effects. The study shows that the soil-monopile response must be considered to accurately simulate the response of OWTs to various loading conditions.

The response of geo-structures subjected to static axial loading, cyclic axial loading, or both depends on the shear response at the soil-structure interface. In this research study, the cyclic interface shear test system, an automated interface testing device that was developed by the research team, was used to perform monotonic interface shear tests to fundamentally underon the shear response of cohesive soil-structure interface. The test setup allows for the direct measurements of the shear force and shear displacement curves, in addition to the soil volume change at the interface. In this paper, normally consolidated cohesive soil was prepared in the laboratory and interface shear tests were conducted on surfaces with asperity heights (h) ranging from 0 (smooth, no surface elements) to 1.75 mm, and on surfaces with center-to-center asperity spacing (Sc) ranging from 0 (smooth, no surface elements) to 25.4 mm. The shear resistance increased with height (h) when the soil-plates interface sheared under static axial shearing. Furthermore, it is concluded that the interface shear resistance is controlled by the spacing-to-height (Sc/h) ratio. According to the test findings presented in this research study, a Sc/h ratio ranging between 7 to 9 mobilizes the maximum interface shear resistance for the tested cohesive soil.

The response of Offshore Wind Turbines (OWTs) under loading is influenced by the SoilFoundation Interaction (SFI) and the wide spectrum of excitation frequencies and amplitudes of the wind, wave, and dynamic machine loads. This paper evaluates the Soil-Foundation-Structure Interaction (SFSI) of OWTs under realistic loading conditions using Real-Time Hybrid Simulation (RTHS). RTHS divides the structure (OWT in this case) into analytical and experimental substructures that are dynamically coupled at the shared nodes to investigate the response of the whole OWT system under realistic loads. This paper also provides a brief description of a modified scaling approach for laterally loaded piles in sand. The scaling approach is used to accurately predict the full-scale response using reduced-scale models. The modified scaling approach is implemented in a small-scale RTHS test. The RTHS test is conducted on monopile-supported OWT under normal operation conditions using a small-scale experimental setup. The test results show the importance of the RTHS in evaluating the response of the OWT considering SFSI. The results also indicate that the cyclic response of the various structural components of OWT (e.g., soil-monopile and tower) is governed by the wave loading, while the wind load acts as a static load that continuously pushes the structure in the direction of loading causing an accumulation in the monopile and tower displacements with time.

Renewable energy systems such as Offshore Wind Turbines (OWTs) are subjected to static loads (e.g., structure dead weight), cyclic and dynamic loads (e.g., wind, wave, turbine and power take-off unit loading). These complex loading conditions subject the system (i.e., foundation to turbine blades) to long-term loading cycles with varying directions, amplitudes and frequencies during the service life of the structure. For OWTs, the response exhibits significant sensitivity to the directionally- and time-varying loading cycles due to the strong interactions between the structural elements and the soil-foundation system (i.e., Soil-Foundation-Structure Interaction (SFSI)). Therefore, understanding the SFSI of OWTs is essential to improve the response of these systems under complex environmental and mechanical loading conditions. This paper presents the design and development of a new Large-Scale Multidirectional SFSI Testing Facility at the Advanced Technology for Large Structural Systems (ATLSS) Engineering Research Center in Lehigh University. The new facility has unique multidirectional loading capabilities that allow for simultaneous application of multidirectional multi-axis loading including axial and lateral loads, and overturning moments to a physical model simulating the foundation (e.g., monopile). The paper also summarizes a recently developed Real-Time Hybrid Simulation (RTHS) tool, that allows for investigating the response of the entire structure under realistic wind, wave and machinegenerated loads. Furthermore, this paper discusses a multidirectional loading mechanism, and the kinematic transformations required when a physical model of the foundation is subjected to multidirectional loading. The kinematic transformations are first validated using a small-scale testing setup and subsequently implemented in a large-scale RTHS test.

Urban heat island (UHI) effect is a significant problem in urban areas, leading to elevated temperatures, increased energy consumption, and worsening air pollution. One promising solution involves the use of pervious concrete (PC) with lightweight aggregates infused with phase change material (PCM), forming a thermal energy storage system. This system helps regulate temperature in the pavement and surrounding environment. This Comprehensive study focuses on understanding the effect of using lightweight aggregate on the mechanical and thermal properties of pervious concrete. Due to its favourable mechanical and thermal characteristics, this type of concrete is suitable for low-traffic roads, sidewalks, bicycle paths, and urban squares. The study also evaluates the thermal energy storage capacity of various PC mixes. The impact of aggregate type, replacement ratios, water-to-cement (w/c) ratio, and paste-to-aggregate ratio on the mechanical and thermal properties of hardened PC was experimentally examined. The aggregates exhibited a range of crushing resistance: natural coarse aggregate (NWA) had an ACV of 21%, LWA1 had 29%, and LWA2 had 40%. Compressive strength, splitting tensile strength, and elastic modulus decreased linearly with increasing crushing resistance. PC made with LWA2 demonstrated the highest thermal storage capacity, reaching up to 45 MJ/m3.

While dry cooling systems excel in water conservation compared to wet cooling systems, their performance at high ambient temperatures remains subpar. This study explores a novel latent heat storage module, acting as a water-free pre-cooler to lower temperature of ambient air into the dry cooling system. Four module designs were constructed, based on a pervious concrete and a custom-made inorganic phase change material, calcium chloride hexahydrate, with stable latent heat over 1,000 freeze-thaw thermal cycles. This marks the first-time integration of inorganic phase change material into pervious concrete through micro- and macro-encapsulation. A forced-air heat transfer apparatus was used to evaluate the modules' thermal performance and heat transfer characteristics, revealing substantial thermal capacity increases of the modules- from 20.0 to 49.2 kWh/m3 charging and 20.3 to 43.6 kWh/m3 in discharging. The module with highest heat storage capacity investigated in this work is the pervious concrete module with micro-encapsulated phase change material and cast around a metal tube array filled with phase change material, which consistently reduces temperature of the airflow at 35 degrees C and 0.86 m/s by an average of 2 celcius over three hours, showing potential as a pre-cooler in dry cooling applications.

The erosion of the structural backfill behind bridge abutments subjected to water flow conditions representative of extreme and overtopping floods was examined through scaled water tank testing using physical hydraulic models. The erosion behavior of the unreinforced backfill materials, embankment material, and structural backfill was tested. Based on the observed patterns of erosion and embankment failure of these tests, the proposed construction practices, including geosynthetics and riprap, were examined in the laboratory with the objective of reducing erosion and the probability of failure during flood events. The input flow rate, flow velocity, and upstream and downstream waterheads were controlled and measured during the tests. The research results indicated that slope failure before overtopping can be mitigated by using a riprap on the slope. Geosynthetics, including geogrids and geotextiles, effectively prevented global failure during flood events if the reinforced core of the backfill was appropriately wrapped.

This study explores the feasibility of utilizing pervious concrete (PC) incorporating diverse lightweight aggregates (LWAs) integrated with phase change materials (PCM) for applications where forced air cooling would be advantageous. The use of such a component provides latent and sensible heat that can cool forced air applications, offsetting ambient temperature increases that occur during the day. Macro- and microencapsulation techniques were used to incorporate inorganic PCM in the PC. The macro-encapsulation technique involved enclosure of PCM within a stable shell prior to addition into the concrete. The microencapsulation technique involved the impregnation of PCM into porous lightweight aggregate. To overcome the PCM reaction with the concrete constituents, an epoxy coating was utilized. The design of the PCM concrete mix and comprehensive laboratory assessment of porosity, water permeability, PCM absorption capacity, compressive strength, and microstructure of the LWAs are detailed. The test results indicate that LWAs have high PCM impregnation rates ranging from 32 % to 57 % by volume. The compressive strengths of PC using LWAs were reduced by 25 % to 65 % when using microencapsulation. The use of microencapsulation was found to reduce the pressure drop under air flow due to the increase in aggregate size as a result of the coating thickness. PCM-PC with a shell thickness of 100 mm, resulted in a pressure drop of less than 100 Pa at a velocity of 0.35 m/s. The use of macro-encapsulated PCM in PC was sensitive to the phase of the PCM, where the liquid phase reduced the compressive strength by 67 %. The failure occurred within the macro-encapsulated PCM at the liquid phase temperatures and at the interface between the encapsulated PCM at solid phase temperatures. The heat transfer provided by the LWA infused PCM when used in a packed aggregate bed or in PC, was shown to match expected latent and sensible heat estimates based on the thermal properties of the materials. This systematic investigation provides valuable insights into LWAs and PCM performance in pervious concrete, offering a comprehensive understanding of their interaction in cooling applications.

Effective thermal energy storage is key to expanding the use of thermal energy, which plays an important role in mitigating the energy crisis worldwide. Digital construction via additive manufacturing technology, has received an increasing interest over the past decades because it facilitates construction of geometrically complex objects at reduced construction time and cost compared to conventional construction techniques. This study combines these concepts and examines the suitability of concrete components 3D printed by selective binder activation and infused with phase change materials (PCM) for thermal energy storage applications. Immersion and vacuum impregnation techniques were used to incorporate organic and inorganic PCMs. The porosity, water and PCM absorption capacity, compressive strength, and microstructure of the 3D printed components were evaluated. The test results indicate that the base 3D printed concrete has a porosity of 41% which facilitates high PCM absorption. The absorption was most effective using vacuum assistance with the inorganic and organic volumetric absorptions reaching 39–45% and 34–40%, respectively. The compressive strength was impacted by the use of inorganic PCM. The microscopy results indicated delayed cement hydrate formation with minimal formation at early ages. The heat transfer provided by the infused PCM was shown to match expected latent and sensible heat transfer based on the thermal properties of the materials.

An innovative thermosiphon-concrete thermal energy storage system is developed using an enhanced concrete formulation for sensible storage media and thermosiphons for heat exchangers. A finite element analysis approach is established for this cylindrically shaped thermosiphon-concrete thermal energy storage system to assess transient thermal and mechanical performance at different scales and under different operating conditions. Two modules at 10 kWhth and 150 kWhth capacities are modeled and validated against experimental data generated in previous studies by the authors. Parametric evaluation is then conducted to examine their thermomechanical performance with variations in charging/discharging rate, module geometry (slenderness ratio), type of concrete media, and type of heat transfer fluid. The validated simulation approach is demonstrated as an effective numerical tool to provide design guidance for the implementation of the proposed system or other similar thermal energy storage systems.

This study examines the performance of pervious concrete when used for heating and cooling through forced air conditions. The influence of aggregate type, water-cement ratio, and paste volume on the air flow characteristics were examined through experimental evaluation of 10 mixes. The thermal properties and sensible heat energy stored in the pervious concrete were evaluated by measuring temperature changes with hot air flow. The results show that at a velocity of 0.35 m/s, the pressure drop falls within the range of 500 Pa/m to 8000 Pa/m. The pressure drop increases with an increase in the volume of paste to volume of aggregate ratio and decreases in water/cement ratio due to changes in the porosity and interconnected void structure of the pervious concrete. A modified pressure drop formulation based on the porosity, volume of paste to aggregate, and water/cement ratio is developed which provides a reasonable prediction for pervious concrete. The energy stored in the concrete can be accurately estimated based on the measured specific heat of the pervious concrete.

Foundation elements with rough (textured) surfaces mobilize larger interface shear resistance than ones with conventional smooth or random rough surfaces when sheared against soils under monotonic loading. The overall performance of foundation elements such as piles supporting offshore wind turbines, suction caissons supporting tidal energy converters, soil nails, and soil anchors installed in cohesive soils could be enhanced through utilizing rough (textured) surfaces to resist applied static and/or cyclic loading. This paper describes the shear behavior of smooth and rough (textured) surfaces in kaolinite clay and kaolinite clay-sand mixture soils under static and cyclic axial loading. The experimental investigation presented herein consists of a series of interface shear tests performed on 3D printed rough (textured) surfaces and a 3D printed smooth reference surface utilizing the Cyclic Interface Shear Test system. The paper includes a description of the interface testing system components, cohesive soil specimens’ preparation procedure, smooth and rough (textured) surfaces details, testing procedure, and results of static and cyclic tests. Test results indicate that kaolinite clay-sand mixture soil mobilized larger static and post-cyclic interface shear resistance and volume contraction relative to kaolinite clay soil when sheared against the smooth reference surface. When tested against rough (textured) surfaces with variable asperity height, larger shear resistance was mobilized and larger soil dilation greater than that mobilized by the reference untextured surface in both soils. The results also indicate rough (textured) surfaces exhibited a prevalent frictional anisotropy increases with asperity angle and height in cohesive soils, the surfaces mobilized larger shear resistance and volume change in one direction (i.e., against the asperity right-angled side) than the other direction (i.e., along the asperity inclined side).

Abstract Silicatein‑α enzyme, which is naturally found in sea sponges, was produced in the laboratory and applied in biomineralization to control the CaCO3 crystal morphology. In this study, silicatein-α enzyme was engineered and expressed in modified Escherichia coli bacteria and then extracted and purified for lab use. Syringe tests were conducted to characterize the morphology and the structure of the CaCO3 precipitates with the guide of silicatein-α enzyme in soils. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to characterize the CaCO3 at the microscale. Spicule (needle-like structures) morphology of CaCO3 precipitates were observed from the syringe tests compared to the cubic morphology of the CaCO3 precipitates treated by Microbial Induced Carbonate Precipitation (MICP) and Enzyme (urease enzyme) Induced Carbonate Precipitation (EICP). The optimized silicatein‑α enzyme treatment protocol including enzyme medium (0.1 M CaCl2, 0.1 M MgCl2, and active silicatein-α enzyme (concentration from 2×10-6 to 6×10-6 M)) and cementation medium, containing 0.2 M (NH4)2CO3 at pH=11 and saturated with CO2 gas, was determined based on the conditions tested in this study. Confined compression tests were also used to investigate the mechanical property of the bio-cemented soil using the silicatein‑α enzyme. The shear modulus of soil was improved after silicatein-α treatment through shear wave velocity measurement, and the silicatein-α enzyme-treated soil (pH value of the cementation medium of 11) was less compressible than the untreated soil but more compressible than MICP and EICP-treated soils. Overall, spicule morphology of CaCO3 precipitates can be created and the mechanical property of the soil can be improved using silicatein‑α enzyme treatment.

A steel pipe assemblage is integrated into a structurally reinforced precast concrete column to demonstrate thermal energy storage (TES) and space heating capabilities. This thermal energy column is heated via hot water at varying flow conditions. The system is used as a thermal storage medium, as a means of reducing the demands on the building heat pump, and for regulating the thermal comfort of the building interior environment. The thermal performance of the energy column is examined experimentally and numerically in both charging and discharging phases. Two examples are used to demonstrate the improvements in the operation of building thermal equipment and in the building thermal environment offered by either passive or active discharging of the energy column. Following the conclusion of thermal evaluation, the structural performance of the column under axial compression was evaluated by loading the system to failure. The experiment was paused for visual observation at both the service level and nominal capacity milestones. The longitudinally embedded steel pipes developed comparable strains to the column longitudinal steel reinforcing bars. The structural capacity of the energy column can be accurately predicted using standard concrete design approaches that account for the mechanical influence of the embedded steel pipe assemblage. It is demonstrated that the developed concrete energy column provides a viable option for improving the building thermal energy efficiency and maintaining structural performance.

Wind, wave, 1P, and 3P loading subject the offshore wind turbine (OWT) structure to multidirectional long-term cyclic loads that have varying amplitudes, frequencies, and patterns. Therefore, studying the soil-foundation-structure interaction (SFSI) under realistic loading is required to understand the response of the entire OWT during the service life of the structure. This paper presents the establishment and capabilities of a new large-scale multidirectional offshore wind SFSI testing facility at the Advanced Technology for Large Structural Systems (ATLSS) research center at Lehigh University. The new testing facility has unique multidirectional loading capabilities that allow for simultaneous application of realistic wind, wave, gravity loads, and their induced moments at the top of the OWT foundations (i.e., mudline). The capabilities of the new testing facility also include large-scale real-time hybrid simulation (RTHS) testing. These capabilities provide the ability to evaluate the response of the whole OWT structure under loading. In addition to presenting the design, concepts, and framework of the facility, this paper presents validation results for the RTHS framework of OWTs using small-scale tests. These small-scale RTHS tests are used as a first step to prepare for conducting large-scale RTHS tests.

The Cyclic Interface Shear Test (CIST) device was recently developed to evaluate the response of soil–structure interfaces subjected to monotonic or cyclic loading. Numerical models of the CIST have not been documented. Such simulations may be beneficial to help guide the design of experiments, interpret results, and inform the development of further experimental device modifications. In the present paper, a series of interface shear tests utilizing the CIST system on a cohesive soil under monotonic loadings were simulated using a proposed three-dimensional model in the commercial finite element analysis software ABAQUS/Standard. Comparisons of simulations with experimental results are presented for the Mohr–Coulomb and hypoplasticity models for cohesive soils. It is found that (i) the clay-based hypoplasticity model outperformed the simpler Mohr–Coulomb model in terms of predicting the interface shear stress evolution and the soil volume change and (ii) the clay-based hypoplasticity model allows for identification of trends in shear response as a function of normal confining pressures at the soil–structure interface (e.g. soil–structure interface shear zone thickness). Neither of these capabilities have previously been documented or experimentally validated for cohesive soil–structure interface simulations using clay-based hypoplasticity models.

Real -time hybrid simulation (RTHS) divides a structural system into an analytical and experimental substructure. The former is based on a well-established analytical model while the latter consists of a physical model in the laboratory, for which there is not a well-established analytical model. This paper extends real -time hybrid simulation to monopile-type Offshore Wind Turbines (OWTs) to enable the investigation of their behavior considering the response of pile foundations under operational and more severe conditions. The embedded foundation and surrounding soil of the OWT are modeled physically in a soil box in the laboratory while the remaining parts of the system and loading are modeled analytically. The program OpenFAST, developed by the National Renewable Energy Laboratory (NREL), is linked to the RTHS coordinator to determine the hydrodynamic and aerodynamic loads acting on the OWT, along with modeling the dynamics of the electric power generation equipment and associated controller for the OWT. The RTHS framework along with its initial implementation and validation are described in this paper. RTHSs of a 5 MW OWT subjected to operational and more severe conditions are performed to experimentally validate the framework. The framework offers a realistic approach to investigate the behavior of OWT structures supported on monopiles. This approach accounts for the coupled response of the OWT structure with its foundation, while experimentally capturing the nonlinearities of the soil-foundation interaction in real -time.

The load-carrying capacity of geotechnical systems (e.g., foundations supporting offshore wind turbines) subjected to static and/or cyclic axial loading could be enhanced using engineered or idealized textured surfaces (or surface elements). The use of surface elements may allow for the development of passive wedges during axial loading, which result in an additional interface resistance to the total load-carrying capacity. To investigate the effects of surface pattern and asperity height on the static and post-cyclic interface shear response, the cyclic interface shear test (CIST) device, which was developed by the research team, was used. To achieve this, a smooth plate representing the surface condition of commonly used steel piles and four engineered textured plates (i.e., rough plates) of different level of roughness (i.e., asperity height of 0.35, 0.65, 1.25, and 1.75 mm) were 3D printed, and then the soil-plate interface was subjected to monotonic and cyclic axial loading. The interface shear tests were performed in a normally consolidated sand-kaolinite mixture. In this paper, the experimental setup (i.e., CIST), sample preparation, and results of a series of static and displacement-controlled cyclic interface shear tests on smooth and textured (rough) plates are summarized and compared to the static and post-cyclic soil-smooth shear strength (no surface elements). For static tests, the interface shear strength increased with asperity height, and this increase ranged from similar to 55% to 105% of the soil-smooth interface shear strength. Similarly, the post-cyclic interface shear strength increased with asperity height, and this increase ranged from similar to 167% to 266% of the soil-smooth interface shear strength. The preliminary test results included in this paper also show that the interface shear resistance of surfaces with structured elements is controlled by asperity height (h) and asperity spacing to height ratio (Sc/h ratio).

The wind erosion resistance of the microbial-induced carbonate precipitation (MICP)-treated soil was investigated in this study using wind tunnel experiments. A wind tunnel was calibrated to simulate the atmospheric boundary layer (ABL). The erosion modes of the soil samples with increasing and cyclic wind loading were analyzed using digital imaging techniques. The calcium carbonate content and its uniformity in treated soils were determined using an atomic absorption spectrometer. The effect of soil relative density, soil type, MICP treatment protocol, and wind loads on wind erosion mitigation was evaluated. Based on the testing conditions, a MICP treatment protocol using 0.25 pore volume of bacteria medium (Sporosarcina pasteurii, ATCC 11859) followed by 0.25 pore volume of 0.3 M cementation medium was determined as the optimal treatment for increasing wind load resistance. A calcium content of 0.28% for the soil surface layer was the minimum calcium carbonate content necessary to mitigate wind erosion for the increasing wind loading condition. For the cyclic wind loading condition, a MICP treatment protocol to achieve a minimum calcium carbonate content of 0.68% was determined as the optimum treatment protocol.