Permanent Rotation Research Articles

Effective Stress-Based Numerical Method for Predicting Large-Diameter Monopile Response to Various Lateral Cyclic Loadings

Extreme marine environmental cyclic loading significantly affects the serviceability of monopiles applied for the foundation of offshore wind turbines (OWTs). Existing research has primarily used p-y methods or total stress-based models to investigate the behavior of monopile–marine clay systems, overlooking the pore pressure development in subsea clay. Studies on the effective stress-based behavior of clay under various lateral cyclic loading conditions are limited. This paper presents an effective stress-based 3D finite element numerical method developed to predict key behaviors of pile–clay systems, including permanent pile rotation under cyclic loading, pile bending moment, and the evolution of pore pressure in subsea clay. The model is verified by contrasting the simulations results to centrifuge experimental results. Cyclic lateral loading is divided into average cyclic load and amplitude of cyclic load to investigate their impacts on the pile–clay system response. The research findings offer insights for the design of large-diameter monopiles under complex cyclic loading conditions.

Comparison of methods for enhancing gold recovery from double refractory concentrates using the technology of autoclave oxidation

The study aims to investigate the most efficient method for significant minimization of the impact of organic carbon on gold recovery from double refractory raw materials. We tested three double refractory gold-sulfide concentrates from different deposits with the content of gold from 23.5 to 40.9 g/t and total carbon from 1.2 to 9.5 wt %. Thermal treatment was carried out in a tubular rotary furnace that provided permanent temperature setting and rotation speed in the reactor. The initial concentrate was grinded as pulp in a Fritsch planetary mono mill Pulverisette 6. Autoclave oxidation was performed in Premex and Büchi titanium autoclaves. The technology of autoclave oxidation with the addition of a secondary oxidizer was found to be the most efficient, since it can increase gold recovery up to 97%. Another technology – hightemperature autoclave oxidation – also proved high performance; however, a significant increase in the residence time of the material in the autoclave (up to 120 min) at elevated temperatures is required to achieve this performance. According to the results, thermal treatment in general can provide a small increase in gold recovery (up to 4%). Due to this, it can be used as an additional processing with other methods analyzed in this article rather than as a self-sufficient technological solution. The studies revealed that the preliminary thermal treatment of concentrates entering autoclave oxidation shows a positive effect; high-temperature autoclave oxidation of concentrates with different carbon content provides high gold recovery for high-carbon concentrates; the use of a secondary oxidizer (in the form of nitric acid) also benefits the gold recovery. The high efficiency of the technology for concentrates with different carbon content allows us to recommend it for further research.

Оценка длительного воздействия бессменного выращивания различных сельскохо зяйственных культур на микробные сообщества почвы

The study of soil microbial communities under different agricultural crops (flax, clover, barley, potato, winter rye) grown in permanent cropping and crop rotation was carried out. The effect of permanent cropping and crop rotation on the taxonomic profile of the prokaryotic and fungal components of the soil microbiome was studied. The effect of permanent cropping and crop rotation on the metabolic intensity and stability of soil biota in the absence of mineral and organic fertilisers was assessed. The subject of the research was the long-term experience established in 1912 by Professor A.G. Doyarenko at the Russian State Agrarian University – Moscow Timiryazev Agricultural Academy, founded in 1912 by Professor A.G. Doyarenko. It was shown that the highest OUT (operational taxonomic units) values for fungi were found in soils under fallow and crop rotation. For prokaryotes, however, the crop rotation variant had the lowest number of OTUs. Ascomycetes were found to be the dominant fungal taxon in all samples studied. Prokaryotes were dominated by Proteobacteria and Acidobacteriota, followed by Actinobacteriota and Firmicutes, and Chloroflexi were represented to a lesser extent. Among the archaea, the Crenarcheota phylum was dominant. It was shown that continuous cultivation of crops generally has a negative effect on the functioning of the microbial community. With an optimal metabolic coefficient of 0.2 in monoculture, they reached 0.6. The sustainability of the soil microbial community is reduced by the continuous cultivation of potatoes, flax and clover without organic and mineral fertilizers, as well as by the “perpetual fallow” option. Particularly unfavorable conditions were found in potato monoculture. Continuous cultivation of cereals, especially winter rye, does not lead to a significant decrease in the activity of soil biota and the stability of soil microbial communities. Crop rotation makes it possible to optimize microbiological processes in the soil and to increase the stability of the soil microbial community.

Assessment of cyclic superposition approaches for the cyclic design of monopiles supporting offshore wind turbines

One of the key design criteria for the design of monopiles supporting offshore wind turbines is limiting the permanent rotation accumulated through its lifetime (Igoe et al., 2022). In geotechnical design practice, macro-modelling approaches are often used to assess the cyclic accumulated rotation. They requires 4 key components: (1) a static model, (2) a cyclic model for accumulating rotation for a given load package, (3) a superposition model for accumulating rotation between different load packages (4) an unloading model to assess the final permanent accumulated rotation once unloaded. The majority of literature focuses on the cyclic models. This paper assesses the effect of using different cyclic superposition models. A new superposition approach is proposed which matches well with the results from a high-quality field test from the literature. The paper compares the permanent accumulated rotation from four widely used semi-empirical cyclic models (Hettler, 1981, Solcyp, 2017; Leblanc et al., 2010a, Klinkvort and Hededal, 2013) used in conjunction with four different superposition approaches. The results demonstrate that the choice of superposition approach can be as important as the choice of cyclic model, which is often overlooked in the literature but is critical for the estimation of accumulated permanent rotation.

Seismic vulnerability of shield tunnels in interbedded soil deposits: Case study of submarine tunnel in Shantou Bay

This paper presents a numerical approach for deriving seismic fragility curves for a submarine shield tunnel subjected to transverse ground shaking in interbedded soil deposits. To simulate the nonlinear behavior of soils, PM4Sand and HS-small constitutive models were adopted. In contrast, the closed-form elastic design method or elastic–plastic design method was used for modeling the shield tunnel lining considering the effect of joints on the seismic performance of structures. Fully coupled numerical analyses provided a satisfactory interpretation of the seismic responses of soil–structure systems considering the effects of groundwater level and soil–tunnel interaction. Subsequently, free-field peak ground acceleration was selected as the intensity measure. The ratio of maximum bending moment to capacity bending moment or permanent joint rotation of the tunnel lining was selected as the damage measure, combined with incremental dynamic analysis, a series of fragility curves were generated. In this study, one-dimensional equivalent-linear earthquake site response analysis was implemented to validate the nonlinear dynamic analysis under weak earthquakes. However, the analysis overestimates the amplitude periodic vibrations in interbedded soil deposits under strong earthquakes. Additionally, numerical results show that the examined tunnel is prone to slight or moderate damage under ground shaking, and its joints are more vulnerable to damage than its segments. The fragility curves constructed were compared with existing fragility curves, highlighting the significant effects of local soil profiles, groundwater conditions, soil–tunnel interaction, and segmental joints on the seismic vulnerability of shield tunnels in a submarine environment. The developed fragility functions contribute to the prediction of seismic damage to submarine shield tunnels of similar characteristics, enabling the rapid and efficient response of structures to disasters in ocean engineering.

The permanently rotating wind turbines: a new strategy for reliable power system frequency support under low and no wind conditions

The problem of frequency stability becomes more concerning as the presence of converter-interfaced units increases and conventional generators are suppressed. A decrease in total system inertia, inherently delivered by synchronous generators, results in abrupt frequency changes and jeopardizes power system stability. Therefore, securing sufficient flexible resources with frequency support capability is necessary. The rotational masses of wind turbines (WTs) are a significant and economical source of flexibility in power systems. However, the available kinetic energy (KE) of the WTs’ rotational masses depends on wind conditions and can only be exploited when the wind speed is sufficient for their rotation. When the wind speed is low, the WT is stopped and cannot support the frequency recovery. In this paper, a new concept of WT operation is proposed, which enables the permanent rotation of the WT under low and no wind conditions, making them reliable flexible resources that can continuously provide frequency support. Due to its widespread presence, the doubly-fed induction generator (DFIG) type of machine was considered. The variable-speed WT’s converter management allows rotational speed control, fast power injection, and release of the turbine’s stored KE even when no wind energy is available. The estimated accessible KE in the WT justifies the proposed concept, and the energy consumption due to motoring operation under low and no wind conditions is shown to be acceptable. A case study is performed for the South Banat region in Serbia to demonstrate the presented management concept. Additionally, a dynamic simulation was implemented to illustrate the permanent operation strategy’s impact on frequency stability in a low-inertia system under low and no wind conditions. Besides virtual inertia continuous capability, the proposed concept provides reduced wear of the WT mechanical components due to a lower number of on/off events.

Shake table testing and computational framework for seismic response of utility-scale bucket foundation offshore wind turbines

Shake table testing was conducted to document the seismic response of a bucket foundation offshore wind turbine (OWT) system. Salient response of the system's soil-structure interaction effects is presented and discussed. Among the observed response characteristics, excess pore pressure fluctuation within and around the soil-bucket domain is thoroughly addressed, including the strong tendency for the soil dilation excursions driven by the induced cyclic strains. The experimental data is used to calibrate a numerical model with dynamic soil response simulated by a coupled solid-fluid formulation. The calibrated model is extended to investigate seismic response of a prototype utility-scale OWT, with and without added wind loading effects. Overall, the research outcomes indicate that: i) excess pore pressure fluctuations in the vicinity of the bucket play an important role in dictating the extent of potential permanent base rotation, ii) consideration should be given to wind loading that might further exacerbate this base rotation, and iii) it is of importance to model the turbine tower as a system of discrete masses rather than the simplified proposed for practice equivalent top mass idealization.

Production of Summer Vegetables Using Conservation Agriculture Techniques: Experiences from Northern Bangladesh

Poor soil quality and decreasing crop yields brought on by ongoing monocropping in the fields of small-scale farmers in Bangladesh have demanded a search for sustainable production methods that are more resource efficient and environmentally friendly. Conservation agriculture is such a beneficial approach that effectively addresses crop productivity and soil quality enhancements using locally available resources. Therefore, the objective of the study was to determine the impacts of conservation agricultural practices on the growth and yield of summer vegetables cultivated in the northern region of Bangladesh. The study was carried out at farmers field situated in the Chilmari upazila of Kurigram district using the Randomized Complete Block Design (RCBD) with three replications during July to September 2020. The trial vegetables, i.e., Red amaranth, Kangkong and Indian spinach had showed the better yield of 4.95 t/ha, 14.5 t/ha and 19.5 t/ha in compared with traditionally cultivated vegetable cultivated methods in the farmers field, according the conservation agriculture method had enhanced vegetable yield. As part of conservation agriculture practices, soil organic matter content, total nitrogen, phosphorus, and potassium levels, as well as pH for better crop production, were all positively increase with the implications of conservation techniques like, adding organic manure, minimal tillage, permanent crop residues and crop rotation. Therefore, the study came to the conclusion that traditional agriculture would need to adopt conservation agriculture methods in order to produce more food while using fewer resources and doing so in a more efficient manner while having the least possible negative effects on the environment.

Influence of maxillary first molar rotation on the severity of dental class II malocclusion: A cross-sectional study.

The aim of the study was to evaluate and assess the influence of maxillary molar rotation on severity of dental class II malocclusion. The study comprised of 4 different groups namely, 1/4th class II malocclusion, 2/4th class II malocclusion, 3/4th class II malocclusion and full class II malocclusion involving sample size of 20,15,16 and 12. The samples were subjected to digital evaluation of maxillary 1st permanent molar rotation using 4 parameters namely angle of Friel, Ricketts E-Line, angle of Henry and Premolar angle. The results were subjected to statistical analysis using one way ANOVA wherein group IV (Full class II malocclusion) exhibited a greater rotational value. On evaluation, angle of Friel exhibited a mean of 59.6±1.61 degrees, Ricketts E-Line was found to be 12.3±1.77mm while angle of Henry showed a mean of 19±3.19 degrees and premolar angle was 12.5±5.83 degrees. On evaluating molar rotation using angle of Friel, Ricketts E-Line, angle of Henry and premolar angle, full cusp class II malocclusion presented higher degree of mesiopalatal rotation maxillary molar rotation. With increasing mesiopalatal rotation, the severity of molar relation also increased from 1/4th to full class II. Hence the maxillary molar spatial position along the long axis majorly influences the molar relation wherein a full cusp class II molar relation exhibits higher degree of molar rotation.

Динамика перманентного движения твердого тела в псевдоевклидовом пространстве

The conditions for the existence and properties of the permanent motion of an absolutely rigid body rotating around a fixed pole are studied in the pseudo-Euclidean space. The body is affected by a force vector-moment, which is constant relative to the coordinate system, invariably associated with the body, as well as a system of gyroscopic forces with a resulting vector-moment, which is linear relative to the angular velocity of the body. The first algebraic integrals of a dynamical system are found, as well as the necessary conditions for the existence of a permanent motion of a body. The equations of the moving hodograph of the angular velocity in this motion are obtained. The structural-kinetic properties of the axes of permanent rotation and the geometry of their distribution in space relative to the body are studied.

Bearing behaviour of shallow foundations for wind energy converters on sandy soils under cyclic eccentric loads

ABSTRACT For wind energy converters (WECs), the behaviour under cyclic loading is critical to the operation and lifetime, especially because the cyclic load is associated with eccentricity. In various geotechnical design standards, the eccentricity of shallow foundation for WECs is supposed to be limited. In the German geotechnical design standards, it is specifically required that no gapping shall occur under quasi-static eccentric load. This verification is often decisive in practical design and leads to potential over-dimensioning. The one possible favourable effect of limiting the gapping of WECs on non-cohesive subsoils is to limit the accumulation of permanent rotation under cyclic loads indirectly. In this article, the experimental results of cyclic rotation accumulation of shallow foundation on non-cohesive subsoils from literatures and own medium scale tests are discussed. It is shown that the gapping has no direct influence on the rotation accumulation rate, instead it is the load magnitude relative to the bearing capacity of foundation that is decisive to the cyclic rotation accumulation behaviour. Based on these observations, the verification ‘no gapping under quasi-static eccentric load case’ seems dispensable in the design of WEC shallow foundations on non-cohesive subsoils.

B-SDM: A bounding surface stiffness degradation method for modelling the long-term ratcheting response of offshore wind turbine foundations

Long-term cyclic loading from environmental conditions can lead to excessive permanent rotation of offshore wind turbines (OWTs) due to the ratcheting response of sand.A practical hybrid strain accumulation approach, termed the bounding surface stiffness degradation method (B-SDM), for finite element analysis (FEA)-based design of OWTs under cyclic loading is presented. This method includes a base elastoplastic constitutive model that captures the stress–strain relationship in the first load-unload cycle and a cyclic strain accumulation scheme for modelling the subsequent cycles. The presented approach allows for a versatile overlay scheme that calculates cyclic strain accumulationto be applied to a range of base elastoplastic models. The base constitutive model utilisedis established based on the bounding surface concept and considers strain-hardening and plastic volume change before failure. The method has been validated by single element test data on sand and used in finitesingle-element element modelling of monopile response in cyclic loading. When the monopile response is modelled in 3D FEA, the conventional step-by-step modelling approach is used until the end of the first regular cycle. Strain accumulation in subsequent cycles is modelled using the B-SDM, in which the plastic modulus and dilatancy relationship are scaled based on a strain accumulation law.

Lateral cyclic behavior of OWT tripod suction bucket foundation in clays

Tripod suction bucket foundations are increasingly used to support offshore wind turbines (OWTs) due to their economic advantages and high overturning resistance. In the harsh marine environment, OWT tripod bucket foundations are subjected to long-term lateral cyclic loads from wind, waves and current. However, the response of tripod bucket foundations in clay to cyclic lateral loads is not well covered in the literature. Therefore, a three-dimensional (3D) numerical method is developed for analyzing their lateral cyclic response based on a simplified bounding surface model of clay. The numerical model is validated by comparing its results with scaled model test results available in the literature. The validated model is then used to investigate the rotation mechanism of tripod suction bucket under lateral monotonic and cyclic loading. The ‘bonded contact’ and ‘separable contact’ were set between the soil plug and the inner wall to simulate the upper limit and the lower limit cases of the tensile capacity of the suction bucket. The influences of the bucket-soil contact condition, loading direction and cyclic loading mode (one-way and two-way) on the cyclic behavior were analyzed. It was found that these factors have a significant impact on the cyclic responses, permanent rotation angle and failure mechanism of the tripod bucket foundation. The findings from this study can provide guidance for the design of OWT tripod bucket foundations.

A simplified method for estimating the permanent accumulated rotation of an offshore wind turbine monopile throughout its design life

The permanent accumulated rotation is of great importance to the design of monopile foundations for offshore wind turbines because it is critical to the final dimensions of the monopile as well as its cost. Although design specifications require that the permanent accumulated rotation meet tolerances, they do not provide engineers with an appropriate method to calculate this value. This paper proposes a simplified method for estimating the permanent accumulated rotation of a monopile throughout its design life. To establish this method, a series of 1-g model tests were conducted in medium-dense sand to investigate the accumulative tendency of monopile rotation under typhoon and non-typhoon conditions. The results showed that the total accumulated rotation was mainly caused by typhoon events, further indicating that the static rotation generated by the maximum load magnitude among typhoon load sequences may maintain a certain proportional relationship with it. Then, the procedure for determining the two parameters in the method was illustrated by an NREL 5 MW wind turbine mounted on a monopile at a water depth of 28 m in the northern South China Sea. This method can provide a convenient tool for calculating the permanent rotation of a monopile foundation throughout its design life.

Experimental investigation of the seismic performance of caisson foundations supporting bridge piers

Allowing the transitory attainment of bearing capacity of caisson foundations supporting bridge piers during strong seismic events can lead to substantial optimisation in their design and major cost savings. If the approach of capacity design is applied to geotechnical systems, the temporary triggering of plastic mechanisms may be permitted if the resulting permanent displacements are smaller than given threshold values. To validate this design approach, the seismic performance of caisson foundations was assessed through dynamic centrifuge testing on reduced-scale models. This paper presents the results of two tests in which a caisson–pier–deck system was embedded in a typical alluvial deposit and subjected to a series of earthquakes of different intensities. The caissons were founded on soft and very soft clay, to either avoid or induce the attainment of plastic soil behaviour under the same seismic inputs. It is shown that both yielding and failure of the layer of very soft clay limit inertial forces transmitted to the superstructure, validating the design approach and some useful empirical relations available in the literature. In contrast, inelastic soil behaviour implies accumulation of permanent rotation and settlement of the system, which must be carefully evaluated to check for fulfilment of performance requirements.

Numerical modelling of the effects of foundation scour on the response of a bridge pier

Foundation scour can have a detrimental effect on the performance of bridge piers, inducing a significant reduction of the lateral capacity of the footing and accumulation of permanent settlement and rotation. Although the hydraulic processes responsible for foundation scour are nowadays well known, predicting their mechanical consequences is still challenging. Indeed, its impact on the failure mechanisms developing around the foundation has not been fully investigated. In this paper, numerical simulations are performed to study the vertical and lateral response of a scoured bridge pier founded on a cylindrical caisson foundation embedded in a layer of dense sand. The sand stress–strain behaviour is reproduced by employing the Severn-Trent model. The constitutive model is firstly calibrated on a set of soil element tests, including drained and undrained monotonic triaxial tests and resonant column tests. The calibration procedure is implemented considering the stress and strain nonuniformities within the samples, by simulating the laboratory tests as boundary value problems. The numerical model is then validated against the results of centrifuge tests. The results of the simulations are in good agreement with the experimental results in terms of foundation capacity and settlement accumulation. Moreover, the model can predict the effects of local and general scour. The numerical analyses also highlight the impact of scouring on the failure mechanisms, revealing that the soil resistance depends on the hydraulic scenario.

Response of offshore wind turbine tripod suction bucket foundation to seismic and environmental loading

Tripod suction buckets offer many advantages as foundations for offshore wind turbines including fast and economic installation and high overturning resistance. In this application, tripod suction buckets are subjected to dynamic loads such as wind and waves as well as earthquakes. However, their dynamic and seismic performance characteristics in cohesive soils are not well covered in the literature. This study investigates the dynamic behavior of tripod foundation installed in clay employing advanced three-dimensional nonlinear finite element analysis. Its rotation mechanism is analyzed considering different load cases including environmental loads, seismic load or combined action of seismic and environmental loads. The dynamic response was evaluated considering ground motions with varying intensity and frequency content, and environmental loads with varying magnitudes. It was found that even though the OWTs system may not experience instability failure due to the combined action of seismic and environmental loads, it is likely to fail to meet the requirements of SLS due to large permanent rotation associated with large settlement of the leeward bucket compared to that of the windward bucket. It was found that the frequency content of the ground motion has a significant effect on dynamic response of tripod foundation; larger permanent rotation can occur when the seismic predominant frequency is close to the frequency ranges of 1p and 3p for the wind turbine structure. The rotation angle of wind turbine structure depends on both the predominant frequency and intensity of the ground motion. These observations should be considered in the seismic design of tripod foundations of OWTs.

Predictive factors associated with adjacent teeth root resorption of palatally impacted canines in Arabian population: a cone-beam computed tomography analysis

BackgroundThis study aimed to evaluate three-dimensionally the factors associated with adjacent teeth root resorption of palatally impacted canines.MethodsIn this retrospective cross-sectional study, one-hundred and fourteen cone beam computed tomography scans with palatally impacted maxillary canines were evaluated for the presence of adjacent root resorption. Seven parameters were analyzed: alignment of maxillary incisors, presence of deciduous canines, first premolars’ roots configuration, impacted canines rotation, angulation of impacted canine to the midline, contact relationship, and area of contact with adjacent teeth. The association between dependent and independent qualitative and quantitative variables was analyzed using chi-square and independent student’s t-test, respectively. The multivariate analysis was performed using regression analysis. The significant value was set at P ≤ 0.05.ResultsThe overall incidence of vertical, horizontal impaction and adjacent root resorption were 92, 8 and 77.2%, respectively. The apical third was the most involved area (57%); resorption of a single tooth was found in 21.9% of the total sample. The most common resorbed teeth were lateral first premolars (24.6%), followed by central lateral incisors (20.2%), and lateral incisors (15.8%) of the total sample. The severity of resorption was highest in grade I (31.5%) and lowest in grade III (7.6%). Three variables showed significant differences between resorption and non-resorption groups namely; canine rotation (P < 0.013), contact relationship (P < 0.001), and area of contact with adjacent teeth (P < 0.001). Regression analysis revealed an association between adjacent root resorption and permanent canine rotation, adjacent premolars’ roots configuration, contact relationship, and area of contact (P < 0.05).ConclusionTwo-thirds of impacted maxillary canines showed a form of root resorption. The most commonly resorbed tooth was the lateral incisors while the least affected one was the central incisors with apical one-third being of the highest risk. The predisposing factors including the canine rotation, premolar with separated roots, contact relationship, and area of contact with adjacent teeth are to be considered for any interceptive treatment.

Adoption of the no-tillage system in Paraná State: A (re)view

The concept of a no-tillage system (NTS), or “Sistema Plantio Direto,” was established in Brazil from the evolution of no-tillage (NT) or “Plantio Direto,” given the edaphoclimatic conditions and the need to promote chemical, physical and biological improvements in cultivated soils. While “Plantio Direto” is a conservationist practice, “Sistema Plantio Direto” presents itself as an agricultural production system based on the simultaneous adoption of minimum soil disturbance, maintenance of permanent soil cover and crop rotation. This study reviews the [...]

Analytical research of the Hopf bifurcation in the problem of motion of the rattleback

We consider the classical problem of the nonholonomic system dynamics — the problem of motion of a heavy rigid body on an perfectly rough horizontal plane. The effect of loss of stability of permanent rotation of a body at a certain critical value of its angular velocity is discussed. It is proved that this effect is accompanied by the occurrence of periodic motions of the body with a frequency close to the critical value, that is, the Hopf bifurcation takes place. It is proved by direct calculation of the first Lyapunov coefficient that the corresponding periodic motions are unstable.