Load capacity of the board grillage with two stringers under ice loading

Снизить повреждаемость бортовых перекрытий при ледовых нагрузках можно за счет совершенствования расчетных зависимостей по оценке их несущей способности. Далеко не всегда такие зависимости, приводимые в справочных изданиях, дают верные рекомендации из-за не вполне ясного характера распределения нагрузок в сложных статически неопределимых системах. В справочнике по СМК приводится расчетная зависимость, позволяющая определить несущую способность регулярного перекрытия с двумя стрингерами при действиии локально распределенной нагрузки в пределах прямоугольника. Цель данной работы заключалась в оценке несущей способности реального бортового перекрытия ледокола типа Wind с помощью МКЭ при параметрах ледовой нагрузки, определяемой рекомендациями Морского Регистра РФ, и последующем сравнении полученных результатов с расчетами по теоретической зависимости, приведенной в справочнике. Полученные данные показали, что зависимость в справочнике для оценки несущей способности перекрытия дает удовлетворительно согласующиеся с МКЭ результаты после соответствующего уменьшения числового коэффициента в ней. При анализе несущей способности перекрытия варьировались шпация, толщина обшивки, высота стенок стрингеров и площадь приложения нагрузки. Установлено, что текучесть наблюдается в опорных сечениях шпангоутов и посредине их пролета, а из-за большой ширины присоединенного пояска обшивка у контура перекрытия практически никогда не течет. Полученные МКЭ результаты показали наличие обратно пропорциональной зависимости между предельной нагрузкой и шпацией при фиксированной площади нагружения. Отмечено, что увеличение толщины обшивки несущественно влияет на величину предельной нагрузки при остальных неизменных параметрах перекрытия. Выполненные расчеты позволяют кроме предельной нагрузки оценить также и величины прогибов при упругопластическом деформировании перекрытий, которые затруднительно подсчитать аналитически. To low damage of the board grillages under ice loading is possible by improving analytical relations on estimation of their load capacity. Not always such relations, bringing in manuals, give true recommendations because of complex character of the loads distribution in static indeterminate systems. Im manual on ship structural mechanics is giving analytical relation for determination of load capacity of regular grillage with two stringers under action of localy distributed load in rectangular area. Purpose of this study is to estimate load capacity of real board grillage of icebreaker of type Wind with help of FEM under parameters of ice load recommended in Maritime Register of RF, and following comparison of obtained results with calculation on analytical relation, given in manual. Obtained results show that relation in manual for estimation of load capacity of grillage give satisfactory results corresponding to FEM only after corresponding reducing of numerical coefficient in it. Under analysis of load capacity of grillage, it was changing frame space, thickness of plating, depth of stringers and area of application of load. It was estimated that most loaded zones of frames are their sections near supports and in the mid-span. Because of big width of associated plate the plating near contour of grillage is never yielding practically. Results obtained by FEM show existence of inversely proportional relation between the limit load and space framing under fixed area of loading. It was noticed that increasing of the plating thickness influent not essentially on value of the limit load under all other parameters of grillage unchangeable. Performed calculations allow to estimate limit load and value of deflections under elasto-plastic deformation of grillage, which is difficult to calculate analytically,

Numerical Simulation of the Ice Breaking Process for Hovercraft

A hovercraft can adapt to an ice area, open water, land and other environments, owing to its unique hull structure. It also plays an important role in transporting supplies, rescuing people, breaking ice and conducting other tasks. Ice load prediction is very important for structural safety and navigation of a polar ship, especially in design of air cushion icebreakers or ice breaking platforms. In this paper, based on a simplified circumferential icebreaking pattern, the icebreaking force of the hovercraft operating on the ice sheet at low speed is simulated in a numerical way. Numerical analysis of the icebreaking process with different ice thicknesses and bending strengths are performed. The numerical results are compared with model test data in a time domain for three operating cases. By analyzing the average ice force, the errors between numerical simulation results and model test measurements are less than 30%. The present study is significant for the preliminary design of new icebreaking hovercraft and it assists the operation possibility for existing hovercraft.

The Ice-resistant Performance Analysis of Cable Pipe for Offshore Booster Station

In order to verify the ice-resistant performance of offshore booster station and its cable pipe. Taking a wind farm in Bohai as an an example, the response of offshore booster station and its cable pipe under the condition of sea ice once in 100 years is analyzed by numerical simulation. The results show that the platform and its cable pipe of the booster station have certain anti ice performance, but under extreme ice load, the vibration response of the upper part of the platform is large, so the safety operation of the facilities and cable pipes should be protected.

Structural Pruning in Callery Pear Does Not Change Apparent Branch Union Strength in Seventh Year Static Load Field Testing

Callery pear (Pyrus calleryana) is a tree notorious for poor branch union and breakage during storms. Structural pruning is a pruning technique that can be practiced on young trees to strengthen tree branch attachment. Callery pear (Pyrus calleryana ‘Redspire’) was structurally pruned and allowed to grow for 7 years and compared to an unpruned control. A breaking device was used to determine branch strength by providing a static load to simulate a snow or ice load. Branches from pruned and unpruned trees were pulled to failure to observe any difference from pruning. Regardless of the structural pruning treatment, trees that were unpruned were larger in diameter at breast height (DBH) and width at the end of the test. No differences were found in testing branch union strength for either pruned or unpruned trees, suggesting that more time is needed to determine the long-term benefits of structural pruning. Branch tissue moisture content was greater than trunk tissue both in immediate post-harvest testing and in samples over time. Also, branch moisture content observations suggested the time available for field testing branch union strength could be as much as 5 to 9 days after harvest.