Att förutsäga sprickförskjutningar är en av de viktigaste faktorerna i säkerhetsbedöm­ningarna av ett djupt geologiskt slutförvar för använt kärnbränsle och är viktiga för andra anläggningar. Laboratorie- och in situ-experiment används för att uppskatta dessa egenskaper. Trots betydande bidrag under de senaste decennierna har det funnits en kunskaps­lucka kring de mekaniska egenskaperna hos stora sprickor på stora djup under inverkan av bergmassans styvhet (konstant normalstyvhet, CNS) och höga normal­spänningar. Genom POST-projektet har SKB (Sverige), NWMO (Kanada) och Posiva från Finland (endast i fas 1) samarbetat för att studera dessa frågor. Efter rekommend­ationer från projektfas 1 (som var främst inriktad på in situ-experiment och numerisk modellering) har den andra fasen av POST-projektet fokuserat på att ta fram data från normalbelast­nings- och skjuvförsök i kontrollerad laboratoriemiljö för att kunna generera resultat med hög kvalitet. Provningar har genomförts på naturliga och draginducerade sprickor i granitprover i tre storlekar, 35×60 mm, 70×100 mm och 300×500 mm, samt replikor av bergsprickor (70×100 mm), under representativa spänningsförhållanden som råder på stora djup vid kontrollerade laboratorieförhåll­anden. En rad stora experimentella fram­steg har gjorts i projektet. En unik utrustning för direkta skjuvförsök har utvecklats på RISE som kan ta prover upp till 400×600 mm och kan belasta sprickor upp till 20 MPa i normal- och skjuvriktningen under både CNS- och CNL-förhållanden (Constant Normal Load), med möjlighet att skjuva provet upp till 50 mm. Karakteriseringar har genomförts före, under och efter skjuvförsök med hjälp av högupplöst optisk skanning, kontakttrycksmätningar, lokala mätningar av sprickdeformationer med hjälp av Digital Image Correlation (DIC) och akustiska emissionsmätningar under skjuvförsöken.

Skjuvning av bergssprickor är en kritisk felmod som i många fall därför avgör vilken belastning en berganläggning kan motstå. De skjuvmekaniska egenskaperna predikteras genom tillämpning av teoretiska modeller i kombination med data från skjuvförsök. En omdiskuterad frågeställning är om, och i så fall hur, storleken på sprickytan inverkar på de skjuvmekaniska parametrarna, den så kallade skaleffekten. I denna artikel presenteras nya rön från en omfattande experimentell studie där skaleffekten av två viktiga skjuvmekaniska parametrar studerats: skjuvhållfasthet och skjuvstyvhet. Genom att ha utfört flera skjuvförsök för varje parameterkombination, på unika provkroppar för samma material (granit), och i kontrollerad laboratoriemiljö, har osäkerheterna reducerats. Vidare har kunskapen breddats genom att försöken utförts under ej tidigare studerade kombinationer av normalspänning (5 MPa) och sprickstorlekar (21 cm² till 1500 cm²), under randvillkoren konstant normalspänning och konstant normalstyvhet, för både naturliga och spänningsinducerade sprickor. Nya fysikaliskt baserade definitioner för skjuvhållfasthet och skjuvstyvhet presenteras tillsammans med metoder för att fastställa dessa parametrar enligt definitionerna. Vidare diskuteras effekten på skjuvstyvheten av att mäta sprickans skjuvning konventionellt med förskjutningsgivare mellan skjuvboxarna och med optik direkt över sprickan. Slutligen undersöks effekten av sprickstorlek, randvillkor och spricktyp på både skjuvhållfasthet och skjuvstyvhet statistiskt med variansanalys.

Shearing of rock joints is a critical failure mode that in many cases determines the load-bearing capacity of an underground structure. The shear-mechanical properties are predicted through the application of theoretical models combined with data from shear tests. A debated question is whether, and if so how, the size of the joint surface affects the shear-mechanical parameters—the so-called scale effect. This article presents new findings from an extensive experimental study in which the scale effect of two important shear-mechanical parameters has been investigated: shear strength and shear stiffness. By performing multiple shear tests for each parameter combination, on unique specimens of the same material (granite), and under controlled laboratory conditions, uncertainties have been reduced. Furthermore, knowledge has been broadened by conducting tests under previously unstudied combinations of normal stress (5 MPa) and joint sizes (21 cm² to 1500 cm²), under the boundary conditions of constant normal stress and constant normal stiffness, for both natural and tensile stress-induced joints. New physically based definitions of shear strength and shear stiffness are presented together with methods for determining these parameters according to the definitions. In addition, the effect on shear stiffness when measuring joint shear displacement conventionally with displacement sensors between shear boxes versus using optical measurements directly across the joint is discussed. Finally, the effects of joint size, boundary conditions, and joint type on both shear strength and shear stiffness are statistically examined using analysis of variance.

Shearing of rock joints is a critical failure mode in rock masses. The shear strength of rock joints must, therefore, be considered in the design of structures in rock masses. Several criteria for prediction of shear strength have been proposed over the years. However, the possible effect of scale on shear strength is an issue. One possible reason for this is that previous experimental studies on the scale effect contain various sources of uncertainties (mixed test methods, multiple testing of same specimen, application of results to other materials than tested, and omitted handling of statistical dispersion). In this paper, the results from a uniquely comprehensive experimental laboratory program, that handles these uncertainties and also extends the range of previously tested conditions, is presented. 46 direct shear tests on two joint types, natural and tensile induced granite rock joints, have been performed under the constant normal stress and the constant normal stiffness boundary condition at 5 MPa initial normal stress applied over three specimen sizes (35 mm × 60 mm, 70 mm × 100 mm and 300 mm × 500 mm). Analysis of variance shows no effect of the specimen size on the shear strength, whereas the joint type and boundary condition has. Quantitative estimates of the influence of the joint type and boundary condition on the shear strength are presented. A consistent approach for determination of shear strength from the point of time associated with a shear stiffness change of the test system is also presented

A wave energy converter (WEC) comprises many components with distinct functions. The whole WEC system is complicated, as each component is also a complex subsystem. It is challenging to properly model and couple these subsystems to achieve a global simulation of the whole system. This study proposes an FMI-based co-simulation framework to tackle this challenge. Through the use of a co-simulation technique requiring minimal programming effort, a suite of numerical solvers serving for modelling various WEC components is coupled to create a comprehensive system model for a single WEC unit. The modules of the Ansys software, Aqwa and Rigid Dynamics, are employed to model hydrodynamic loads and motion responses. Simulink is utilized to model the power take-off (PTO) system and then integrate all models into a global simulation. The capability and accuracy of the FMI-based co-simulation framework are validated against an experimental heave decay test and verified by cross-comparing a numerical model built in SESAM. Furthermore, the framework is expanded to encompass the modelling of a large-scale wave park that includes multiple WEC units. Based on a novel WEC concept called NoviOcean, two study cases of a single unit and an 18-unit wave park are investigated. Buoy motions and power performance under several regular and irregular sea states are analysed. The hydrodynamic interactions between the units are evaluated quantitatively regarding the power performance. It is found that the interactions improve the power performance, with a maximum increase of up to 36%. 

Ship collisions and groundings are important due to their severe consequences, including exceedance of ultimate strength, loss of stability, and spillage of hazardous cargo and liquids. To mitigate these effects, cost-efficient simulation tools are needed for studying transient flooding and motions of damaged ships with different damage opening characteristics in a wave environment. The objective of this study is to present a validation of a liquid exchange model implemented in the time-domain-based dynamic ship stability simulation code SIMCAP, using experiments presented in the literature. The validated model was then applied in a parametric study of a fully loaded double-hull oil tanker damaged in the inner and outer hulls. Oil outflow, water inflow, and ship motions were analysed for different damage opening positions, shapes, and wave heights. The results showed that the damage location strongly affected the oil outflow. The oil spill rate increased with wave height but was relatively unaffected by heading and wave realization. In conclusion, SIMCAP was reasonably validated qualitatively and quantitatively and is suitable for investigating key physical mechanisms in parametric studies of damaged ships in waves.

In the design of a wave energy converter (WEC) in general, one critical aspect is to develop the power take-off (PTO) system since it has a significant impact on the overall energy harnessing efficiency. Therefore, the modelling of a PTO system should be considered in the simulation of a WEC and carefully tuned with its parameters to guarantee prediction accuracy. However, it is a challenge to model a WEC system with the hydrodynamic system, mooring system and PTO system in a fast and robust way due to various limitations of commercial software and in-house codes. This paper compares four WEC system models, which include either a simplified or a full PTO system model. They also integrate simplified, modified or full hydrodynamic system models. The most complex model considers a complete WEC system with a full hydrodynamic system, full PTO system and mooring system. The study object is the point-absorber WEC WaveEL 3.0 designed by Waves4Power AB. The power performance of the WEC is calculated for six sea states using the four models with different fidelities. The results of the four models are analyzed, and their pros and cons are discussed. Modelling strategies to fulfil different simulation goals are suggested. 

Numerical analyses are presented for two generations of a floating heaving point absorber wave energy converter (WEC) installed with different farm array layouts. The wave farm configurations are based on WECs developed by Waves4Power. The numerical models are developed in the DNV software package, Sesam. Parametric studies of the isolated WEC configurations and farm array layouts are conducted under typical environmental conditions and various incident wave directions to understand the hydrodynamic power performance and the levelised cost of energy (LCoE). Hexagonal layouts are proposed for deploying the WEC units and compared with a 10-unit layout termed StarBuoy, which has been reported in previous work. The results of the present study confirm that the interactions between arrayed units in a farm can have either positive or negative effects on the LCoE, which is dependent on the array layout and environmental conditions. The hexagonal array layouts lead to lower LCoE owing to constructive interaction effects. 

The production of renewable energy is key to satisfying the increasing demand for energy without further increasing pollution. Harnessing ocean energy from waves has attracted attention due to its high energy density. This study compares two generations of floating heaving point absorber WEC, WaveEL 3.0 and WaveEL 4.0, regarding their power performance and mooring line fatigue characteristics, which are essential in, e.g., LCoE calculations. The main differences between the two WECs are the principal dimensions and minor differences in their geometries. The DNV software SESAM was used for simulations and analyses of these WECs in terms of buoy heave motion resonances for maximising energy harvesting, motion characteristics, mooring line forces, fatigue of mooring lines, and hydrodynamic power production. The first part of the study presents results from simulations of unit WEC in the frequency domain and in the time domain for regular wave and irregular sea state conditions. A verification of the two WECs’ motion responses and axial mooring line forces is made against measurement data from a full-scale installation. In the second part of the study, the influence of interaction effects is investigated when the WECs are installed in wave parks. The wave park simulations used a fully-coupled non-linear method in SESAM that calculates the motions of the WECs and the mooring line forces simultaneously in the time domain. The amount of fatigue damage accumulated in the mooring lines was calculated using a relative tension-based fatigue analysis method and the rainflow counting method. Several factors that influence the power performance of the wave park and the accumulated fatigue damage of the mooring lines, for example, the WEC distance of the wave park, the sea state conditions, and the direction of incoming waves, are simulated and discussed. The study's main conclusion is that WaveEL 4.0, which has a longer tube than WaveEL 3.0, absorbs more hydrodynamic energy due to larger heave motions and more efficient power production. At the same time, the accumulated fatigue damage in the moorings is lower compared to WaveEL 3.0 if the distance between the WECs in the wave park is not too short. Its motions in the horizontal plane are larger, which may require a larger distance between the WEC units in a wave park to avoid losing efficiency due to hydrodynamic interaction effects.

Since each rock joint is unique by nature, the utilization of replicas in direct shear testing is required to carry out experimental parameter studies. However, information about the ability of the replicas to simulate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking. With the aim to facilitate generation of high-quality direct shear test data from replicas, a novel component in the testing procedure is introduced by presenting two parameters for geometric quality assurance. The parameters are derived from surface comparisons of three-dimensional (3D) scanning data of the rock joint and its replicas. The first parameter, σmf, captures morphological deviations between the replica and the rock joint surfaces. σmf is derived as the standard deviation of the deviations between the coordinate points of the replica and the rock joint. Four sources of errors introduced in the replica manufacturing process employed in this study could be identified. These errors could be minimized, yielding replicas with σmf ≤ 0.06 mm. The second parameter is a vector, VHp100, which describes deviations with respect to the shear direction. It is the projection of the 100 mm long normal vector of the best-fit plane of the replica joint surface to the corresponding plane of the rock joint. |VHp100| was found to be less than or equal to 0.36 mm in this study. Application of these two geometric quality assurance parameters demonstrates that it is possible to manufacture replicas with high geometric similarity to the rock joint. In a subsequent paper (part 2), σmf and VHp100 are incorporated in a novel quality assurance method, in which the parameters shall be evaluated prior to direct shear testing. Replicas having parameter values below established thresholds shall have a known and narrow dispersion and imitate the shear mechanical behavior of the rock joint.

Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies. However, a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking. In this study, a novel method is presented for geometric quality assurance of replicas. The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results. In Part 1 of this study, two quality assurance parameters, σmf and VHp100, are derived and their usefulness for evaluation of geometric deviations, i.e. geometric reproducibility, is shown. In Part 2, the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior, which qualifies the parameters for usage in the quality assurance method. Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σmf < 0.06 mm and < 0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength. The wear in these replicas, which have similar morphology as the rock joint, is in the same areas as in the rock joint. The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties, possibly from differences in toughness. It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics, which makes them useful in parameter studies.