Experimental investigation of ice loads on vertical and slope offshore structures

An experiment was carried out to study the ice loads of level ice and ridge on the vertical and slope structures. The prototype of the model is the lighthouse Nordströmsgrund, which is a vertical structure and locates in the north Baltic sea. Nevertheless, a conical part was added to the model to study the ice load on slope structures in addition to the study of the ice loads on vertical structures. Three ice sheets with ridges were targeted to design the ice condition around Nordströmsgrund, including the flexural strength, ice thickness, geometrical cross-sectional profile of ridge, etc. Every ice sheet had a constant thickness, ranging from 0.04m to 0.043m in model-scale, but its flexural strength could be changed by using tempering procedure. Eight tests were successfully conducted and the ice loads were measured and recorded with three components divided according to the Cartesian coordinate system. The effect of ice properties and degrees of consolidation were also observed and analyzed with the measured data. The history curve and its envelope were utilized to study the ice loads on structures. The ice loads were decomposed into rubble loads (loads induced by accumulated rubbles) and level ice/consolidated layer loads (loads induced by breaking the level ice/consolidated layer). The upper envelope was assumed to represent the total ice loads and the lower envelope was assumed to represent the rubble loads. Thus, the difference between the upper and lower envelopes could be considered the level ice/consolidated layer loads. Fast Fourier Transform was applied to study the energy distribution of ice loads. The splitting of level ice was observed in front of the ridge at three tests. The histogram and return period are employed to study the distribution of ice loads and affecting parameters. The most important discovery of this research was that the horizontal range of rubbles moved by the structure had stronger influence on the ice ridge loads than the depth of rubble accumulation in front of the structure. Actually, the ridge loads were proportional to the volume of rubble accumulation and the strength of freeze bond in the keel. The zigzag pattern in the curve of horizontal range reflected the process of breaking the keel. This resulted in that the accumulation volume increased with a zigzag pattern in the curve of volume against the structure’s penetration distance into the ridge

A LID APPROACH FOR PREDICTING WAVE INDUCED MOTIONS OF TRIMARAN IN REGULAR WAVES

The wave induced motions of a trimaran sailing in regular head waves were predicted by using the three dimensional boundary integral method. Large wave elevation on the free surface in between the trimaran’s main-hull and the outriggers occurred at some specific frequencies in the numerical model. The large wave elevation also induced large heave and pitch motions of trimaran. However, the large wave elevation and corresponding large motions were not observed during towing tank tests. A lid approach was introduced in this paper by placing lid on the free surface in between hulls to suppress the unrealistically large wave elevation and to correctly predict the induced motions of trimaran. The feasibility and practicability of lid approach were validated against experimental results

Experimental investigation of ice loads on vertical and slope offshore structures

An experiment was carried out to study the ice loads of level ice and ridge on the vertical and slope structures. The prototype of the model is the lighthouse Nordströmsgrund, which is a vertical structure and locates in the north Baltic sea. Nevertheless, a conical part was added to the model to study the ice load on slope structures in addition to the study of the ice loads on vertical structures. Three ice sheets with ridges were targeted to design the ice condition around Nordströmsgrund, including the flexural strength, ice thickness, geometrical cross-sectional profile of ridge, etc. Every ice sheet had a constant thickness, ranging from 0.04m to 0.043m in model-scale, but its flexural strength could be changed by using tempering procedure. Eight tests were successfully conducted and the ice loads were measured and recorded with three components divided according to the Cartesian coordinate system. The effect of ice properties and degrees of consolidation were also observed and analyzed with the measured data. The history curve and its envelope were utilized to study the ice loads on structures. The ice loads were decomposed into rubble loads (loads induced by accumulated rubbles) and level ice/consolidated layer loads (loads induced by breaking the level ice/consolidated layer). The upper envelope was assumed to represent the total ice loads and the lower envelope was assumed to represent the rubble loads. Thus, the difference between the upper and lower envelopes could be considered the level ice/consolidated layer loads. Fast Fourier Transform was applied to study the energy distribution of ice loads. The splitting of level ice was observed in front of the ridge at three tests. The histogram and return period are employed to study the distribution of ice loads and affecting parameters. The most important discovery of this research was that the horizontal range of rubbles moved by the structure had stronger influence on the ice ridge loads than the depth of rubble accumulation in front of the structure. Actually, the ridge loads were proportional to the volume of rubble accumulation and the strength of freeze bond in the keel. The zigzag pattern in the curve of horizontal range reflected the process of breaking the keel. This resulted in that the accumulation volume increased with a zigzag pattern in the curve of volume against the structure’s penetration distance into the ridge

Scale-model ridges and interaction with narrow structures, Part 1 Overview and scaling

publishedVersio

Arvioidaan hydrodynaamisten vaikutusten merkitystä jääkuormitukseen aluksen ja jään liukukosketuksessa: Meriaaltojen ja hydrodynaamisten vuorovaikutusten roolit

With climate change increasing accessibility to polar maritime routes, understanding ice loads on ship hull has become crucial for safe navigation. Traditional methods for evaluating ice loads, such as the Popov method, often simplify the geometry of ships and ice floes, and neglect the complex hydrodynamic interactions and waves that significantly influence ice loads. These simplifications can lead to inaccurate predictions of ice loads, especially in the Marginal Ice Zone (MIZ), where ships and small to medium-sized ice floes are dynamically affected by sea waves. This research aims to fill this gap by developing a comprehensive model that incorporates these factors to enhance the precision of energy-based ice load evaluations. To address these shortcomings, this research proposes a novel approach using the Boundary Element Method (BEM) to assess the hydrodynamic interaction between an advancing ship and an ice floe. This approach incorporates the linear superposition principle to combine the radiation potentials of both bodies and the encounter frequency method to account for the ship's speed. This results in a detailed calculation of added mass and damping coefficients, which are critical for understanding the hydrodynamic interactions between the ship and ice. Further, a Computational Fluid Dynamics (CFD) model is developed to investigate the hydrodynamic coefficients under the interaction between side-by-side structures, focusing on how the surrounding fluid flows affect the hydrodynamic coefficients. The CFD model helps understand the physical significance of specific subsections of the hydrodynamic coefficient matrix, essential for accurate ice load evaluations. The research integrates these findings into an extended energy-based model for ice load evaluation, considering effects of waves and hydrodynamic interactions. This model is illustrated through a case study involving an ice-class ship and ice floes of varying sizes. Key findings of this thesis include the realization that traditional ice load evaluation methods may underestimate ice loads by not accounting for sea waves and hydrodynamic interactions. The novel BEM approach developed in this research provides a more accurate representation of these interactions, leading to better predictions of ice loads. The study also reveals that the impact of wave-induced motions is more pronounced than that of added mass. This research makes significant contributions to maritime engineering by uncovering the influence of hydrodynamics on ice load evaluations. It provides valuable insights for the design and operation of ice-going ships, ensuring safer navigationin ice-infested waters.Ilmastonmuutoksen lisätessä arktisten merireittien saavutettavuutta on laivan runkoon kohdistuvien jääkuormien ymmärtäminen tullut kriittiseksi turvallisen navigoinnin kannalta. Perinteiset menetelmät, kuten Popovin menetelmä, yksinkertaistavat usein alusten ja jäälauttojen geometrian ja jättävät huomiotta monimutkaiset hydrodynaamiset vuorovaikutukset ja aallot, jotka merkittävästi vaikuttavat jääkuormiin. Nämä yksinkertaistukset voivat johtaa epätarkkoihin jääkuorma-arvioihin erityisesti marginaalijäävyöhykkeellä (MIZ), missä alukset ja pienet ja keskikokoiset jäälautat ovat meren aaltojen vaikutuksen alaisina. Tämä työ pyrkii täyttämään tämän aukon kehittämällä kattavan mallin, joka sisällyttää nämä tekijät energian säilymiseen perustuvan jääkuorma-arvion tarkkuuden parantamiseksi. Näiden puutteiden korjaamiseksi tutkimuksessa ehdotetaan uutta lähestymistapaa, joka käyttää reunaelementtimenetelmää (BEM) arvioimaan hydrodynaamista vuorovaikutusta etenevän aluksen ja jäälautan välillä. Tämä menetelmä yhdistää lineaarisen superpositioperiaatteen avulla molempien kappaleiden säteilypotentiaalit, sekä huomioi aluksen nopeuden kohtaamistaajuusmenetelmän perusteella. Tämän seurauksena saadaan yksityiskohtaiset lisätyn massan ja vaimennuskertoimien laskelmat, jotka ovat tärkeitä aluksen ja jään hydrodynaamisten vuorovaikutusten ymmärtämisessä. Lisäksi työssä kehitetään laskennallisen virtausmekaniikan (CFD) malli tutkimaan hydrodynaamisia kertoimia rakenteiden välisen vuorovaikutuksen yhteydessä, joka keskittyy määrittämään ympäröivän nesteen virtauksen vaikutusta hydrodynaamisiin kertoimiin. CFD-malli auttaa ymmärtämään hydrodynaamisen kerroinmatriisin tiettyjen alaosioiden fysikaalista merkitystä, mikä on olennaista tarkkojen jääkuorma-arviointien kannalta. Työssä integroitiin nämä havainnot laajennettuun energian säilymiseen perustuvaan jääkuorman arviointi malliin huomioiden aaltojen ja hydrodynaamisten vuorovaikutusten vaikutukset. Mallia havainnollistetaan tapaustutkimuksella, joka käsittää jääluokan omaavan aluksen ja erikokoisia jäälauttoja. Työn keskeinen havainnot on, että perinteiset jääkuormien arviointimenetelmät voivat aliarvioida kuormia, koska ne eivät huomioi aaltoja ja hydrodynaamisia vuorovaikutuksia. Tässä työssä kehitetty uusi BEM-lähestymistapa tarjoaa tarkemman kuvan näistä vuorovaikutuksista, johtaen parempiin jääkuorma-arviointeihin. Tutkimus osoittaa myös, että aaltojen aiheuttamien liikkeiden vaikutus kuormiin on suurempi kuin lisätyn massan. Tämä työ tuo merkittävää uutta tietoa arktiseen meritekniikkaan paljastaen hydrodynamiikan vaikutuksen laivan runkoon kohdistuviin jääkuormiin. Se tarjoaa arvokasta tietoa jäävahvistettujen alusten suunnitteluun ja käyttöön turvallisemman merenkulun takaamiseksi jääpeitteisillä vesillä

A comparison of zero-profile anchored spacer (ROI-C) and plate fixation in 2-level noncontiguous anterior cervical discectomy and fusion- a retrospective study

Abstract Background Anterior cervical discectomy and fusion (ACDF) is the classic surgical treatment for symptomatic cervical degenerative disc disease (CDDD). However, there is controversy over the best surgical management in patients with two noncontiguous symptomatic levels of CDDD. Methods From April 2011 to May 2014, 44 patients with two noncontiguous symptomatic levels of CDDD underwent skip-level ACDFs. In Group NoPlate, 23 cases underwent 2 noncontiguous levels of ACDF using zero-profile anchored spacer; and in Group Plate, 21 cases underwent 2 noncontiguous levels of ACDF using cages and plates. Operation-related paraeters for each group were recorded and compared. Japanese Orthopedic Association (JOA) scores and Neck Disability Index (NDI) scores at preoperation and postoperation were compared with at least a 2-year follow-up. Cervical lordosis was analyzed before surgery, 1 month after surgery, 3 months after surgery, and at final follow-up. Results Mean follow-up was 35.4 ± 6.5 (range 24–48) months. Significant improvement on the JOA, NDI scores and cervical lordosis was noted in each group (p  0.05). The operation time in Group NoPlate was significantly shorter than in Group Plate (p < 0.05), and the incidence of dysphagia and adjacent segment degeneration in Group NoPlate was significantly lower than in Group Plate (p < 0.05). Conclusions ROI-C and cages with plate fixation were both effective in two-level noncontiguous ACDF, and there were no significant difference in clinical outcomes, fusion rate, and cervical lordosis. However, ROI-C was associated with shorter operative time, lower incidence of dysphagia and adjacent segment degeneration

The Effect of Yoga Meditation Practice on Young Adults’ Inhibitory Control: An fNIRS Study

Objectives: The present study aimed to test the effect of yoga meditation (YoMed) practice on inhibitory control of young adults.Methods: A total of 50 participants (23 male, 21–28 years old) from a university in Jinan, Shandong Province were enrolled in this study. Participants were randomly assigned to a YoMed group or a Control group. Participants’ basic information, physical activity, and inhibitory control were measured. A multi-channel continuous-wave near-infrared spectrometer was used to monitor the brain’s hemodynamic responses.Results: After the intervention, we found significant differences in Flanker tasks between the YoMed group and Control group. The accuracy in the YoMed group was higher than those in the Control group (p &amp;lt; 0.05). Analysis of fNIRS data showed that oxyhemoglobin (oxy-Hb) levels in the prefrontal cortex (PFC) increased in the YoMed group during the Flanker tasks after the YoMed intervention.Conclusion: YoMed has a temporarily promoting effect on the brain activation of young adults. It is an effective and appropriate exercise to improve the inhibitory control of young adults.</jats:p