Influence of ice conditions on the effectiveness of the resonant method of breaking ice cover by submarines

This paper describes a numerical model for analyzing the stress-strain state of ice cover which has fractures of various widths caused by hydrodynamic loads due to submarine motion. Calculations and experiments were performed using the model of unbreakable ice, and the results were used to obtain dependences of the amplitude of deflections and stress in ice cover on the width of the ice fracture. The behavior of ice cover under wave loading was studied.     

水下爆炸冲击波载荷作用下冰层破碎特性及其影响因素

水下爆炸破冰是复杂的爆破工程,为了研究冰层在水下爆炸冲击波载荷作用下的破碎特性及规律,利用几何动力分析软件LS-DYNA对水下爆炸破冰的过程进行数值模拟,并将计算结果与实验结果进行对比,误差在8%以内,验证了数值模型的有效性。根据本文中的建模方法及建立的模型,计算不同的实验工况:实验场地环境不变,调整爆距分析不同爆距下冰层破碎特性;调整药量、爆距和冰厚,通过正交设计方法设计9组实验方案,应用灰色系统理论对3种因素进行分析,建立了各个因素与破冰半径之间的灰色关联度系数及灰色关联度。分析结果表明:药量为100 g,冰厚为29 cm,水深为2.9 m,爆距范围为0.3~1.5 m破冰的半径范围为0~1.1 m,最佳爆距范围在0.3~0.45 m之间;根据以上9种工况的分析可知,药量(100、200、300 g)、爆距(0.3、0.6、0.9 m)和冰厚(24、28、32 cm)对破冰半径的影响的主次关系依次为爆距、药量、冰厚。     

Stress-strain state of ice cover during aircraft takeoff and landing

We consider the linear unsteady motion of an IL-76TD aircraft on ice. Water is treated as an ideal incompressible liquid, and the liquid motion is considered potential. Ice cover is modeled by an initially unstressed uniform isotropic elastic plate, and the load exerted by the aircraft on the ice cover with consideration of the wing lift is modeled by regions of distributed pressure of variable intensity, arranged under the aircraft landing gear. The effect of the thickness and elastic modulus of the ice plate, takeoff and landing regimes on stress-strain state of the ice cover used as a runway.     

Ice cover perturbation by a dipole in motion within a liquid

The two-dimensional problem of ice cover perturbation by a dipole starting to move uniformly, rectilinearly, and horizontally in a liquid initially at rest is considered. It is shown that stationary waves of two different types can be established on the liquid/ice interface, depending on the ice thickness and the dipole velocity. Examples of the numerical investigation of these waves are presented.     

Interaction of surface and flexural-gravity waves in ice cover with a vertical wall

The problem of the interaction of surface and flexural-gravity waves with a vertical barrier is solved in a two-dimensional formulation. It is assumed that the fluid is ideal and incompressible, has infinite depth, and is partially covered with ice. The ice cover is modeled by an elastic plate of constant thickness. The eigenfrequencies and eigenmodes of oscillation of the floating elastic ice plate, the deflection and deformation of ice, and the forces acting on the wall are determined.     

Solitary wave packets beneath a compressed ice cover

A family of plane solitary wave packets of a small (but finite) amplitude on the surface of an ideal incompressible fluid of finite depth beneath an ice cover is described. The solitary wave trains correspond to solutions of the two-dimensional system of Euler’s equations of an ideal incompressible fluid of the type of a traveling wave which decreases at infinity and has identical phase and group velocities. The ice cover is simulated by an elastic Kirchhoff-Love plate freely floating on the fluid surface in the compressed state.     

Waves generated on an ice cover by a source pulsating in fluid

A point source of variable intensity located at rest in a plane infinitely deep fluid layer under an ice cover is considered. The general expression for perturbations of the fluid-ice interface is obtained. In the case of the long operation in the pulsating regime the wave established on the ice cover is found.     

Behavior of a semi-infinite ice cover under periodic dynamic impact

Oscillations of a semi-infinite ice cover in an ideal incompressible liquid of finite depth under local time-periodic axisymmetric load are considered. The ice cover is simulated by a thin elastic plate of constant thickness. An analytical solution of the problem is obtained using the Wiener–Hopf method. The asymptotic behavior of the amplitudes of oscillations of the plate and the liquid in the far field is studied. It is shown that the propagation of waves in the far field is uneven: in some directions, the waves propagate with a significantly greater amplitude.     

Hydrodynamic loads acting on an oscillating cylinder submerged in a stratified fluid with ice cover

The two-dimensional problem of steady oscillations of a horizontal cylinder submerged in a linearly stratified fluid layer whose upper boundary is ice cover is considered in a linear treatment using the Boussinesq approximation. The method of mass sources distributed along the body contour is used for the internal wave generation regime, and the integral equation for the disturbed pressure in the fluid is used for the regime of no internal waves. The hydrodynamic load acting on the body was calculated as a function of the oscillation frequency for the case of a continuous ice cover and for special cases (broken ice, free surface, and rigid lid).     

Oscillations of a cylindrical body submerged in a fluid with ice cover

The linear plane problem of oscillations of an elliptic cylinder in an ideal incompressible fluid of finite depth in the presence of an ice cover of finite length is solved. The ice cover is modeled by an elastic plate of constant thickness. The hydrodynamic loads acting on the body are determined as functions of the oscillation frequency and the positions of the cylinder and plate.     

Action of periodic surface pressure on an ice cover in the vicinity of a vertical wall

This paper presents the solution of the linear hydroelastic problem for steady forced vibrations of a semi-infinite ice cover under the effect of localized external load. The ice cover is simulated by a viscoelastic thin plate, the thickness of the fluid layer is assumed to be small, and the shallow water theory is used. The fluid is limited by a solid vertical wall, and the rectilinear edge of the elastic plate adjacent to the wall can be both free and clamped. The solution is obtained with the help of the Fourier integral transform. The behavior of the ice cover is studied depending on the frequency of the external load and boundary conditions on the edge of the plate. It is shown that, in the case of a free edge of the plate, there are considerable deflections on the edge, which could be comparable with deflections at the center of the pressure impact region. It is established that, due to the existence of wave movements of the type of edge waves, the external load energy is transferred to larger distances along the free edge, and there are significant bending moments on the edge of the clamped plate, which can lead to fracture of the ice cover with sufficiently great intensity of the external load.     

气垫平台破冰阻力的模型试验研究

通过开展低温拖曳冰水池物理模型试验,测试气垫平台在遭遇平整冰时的破冰过程和破冰阻力.在模型试验中,以一座现役破冰气垫平台为原型,建立了合理的模型试验相似律.依据相似律分别对原型平台的结构框架、气道结构、围裙结构和垫升系统等部分进行了模拟,从而得到一套与原型平台结构型式和垫升机制相似的模型平台.模型平台在试验拖车的拖曳下通过低温冰水池中的模型冰排,分别以垫升高度和航行速度为试验参数,对不同试验工况下气垫平台的破冰过程进行测试.通过对模型试验现象和结果的分析,深入解析了气垫平台的破冰过程,揭示了气垫平台的破冰机理.通过试验发现,非全垫升状态更有利于模型平台的破冰作业.气垫平台破冰的关键机理是在冰排底部形成稳定的气腔,从而促使冰排在结构的下压作用和气腔的上顶压力下发生弯曲破坏.在试验中测试了气垫平台破冰风压随结构姿态的变化,在时频域内对风压的变化情况进行了分析,并讨论了风压随航行速度的变化规律.以此为基础,对气垫平台破冰阻力随垫升高度和航行速度的变化规律进行分析,从而为该类气垫平台的结构设计和操船方法提供必要的基础性数据和参考依据.      

海冰动力学中本构模型研究的若干进展

从20世纪70年代, 人们在不同尺度下建立了一系列的海冰动力学本构模型用于海冰数值模拟和预测. 将目前应用的海冰动力学本构模型分为弹塑性、黏塑性、各向异性和颗粒流体动力学中的黏弹塑性模型4类,并分别讨论了各类模型的特点和适用范围. 尤其对在极区及副极区大、中尺度下广泛应用的黏塑性及其改进的本构模型进行了深入地分析. 最后得出: 在大、中尺度下建立海冰动力学的黏弹塑性本构模型是提高海冰动力学计算精度的有效途径; 将小尺度下采用黏弹塑性本构模型的海冰颗粒流体动力学的计算时效进一步改进后, 可在大、中尺度下对海冰的重叠、堆积特性进行模拟; 进一步开展海冰动力学的尺度效应研究, 进行海冰本构模型的实验验证, 并建立不同尺度模型间的相互联系也应是海冰动力学本构模型研究的重要内容.      

船-冰作用中海冰典型破坏模式的离散元数值模拟

在破冰船破冰过程中,冰排主要表现为挤压与弯曲两种破坏模式.本文基于黏结离散单元法对船-冰作用中的这两种典型破坏模式进行数值模拟.海冰离散元数值试样采用随机排布方式生成,采用单轴压缩试验与三点弯曲试验相结合的方式标定模型中的细观参数.将船-冰碰撞中的挤压和弯曲作用方式简化为直立或倾斜 平板与海冰的作用模式,构建挤压与弯曲...     

Numerical modeling of ice behavior under high velocity impacts

In this work a constitutive relation for ice at high strain rates and an algorithm for its numerical integration are developed. This model is based on the Drucker–Prager plasticity criteria, which allows a different behavior in tension and in compression. In addition a failure criteria, based on pressure cut-offs, is implemented to describe the ice damage. In order to validate the constitutive model, numerical simulations were compared with experimental results, in which ice cylinders were impacted against a steel plate, allowing the measurement of the contact load. Three different numerical solvers are used in order to analyze its performance to appropriately modeling the ice behavior.     

海上风机动冰力模型试验相似律研究

相似律在模型试验中发挥着非常重要的作用,虽然目前静冰力模型试验的研究比较全面,但还没有一个完整适用的动冰力相似律作为动冰力模型试验基础.本文针对冰激结构振动中动冰力模型试验相似律,基于弹性相似与柯西(Cauchy)相似的联合相似准则,提出了两种动冰力相似律.建立并改进了能够反映冰与结构水平相互作用的相互作用系数.以NR...     

Modeling ocean wave propagation under sea ice covers

Operational ocean wave models need to work globally, yet current ocean wave models can only treat ice covered regions crudely. The purpose of this paper is to provide a brief overview of ice effects on wave propagation and different research methodology used in studying these effects. Based on its proximity to land or sea, sea ice can be classified as: landfast ice zone, shear zone, and the marginal ice zone. All ice covers attenuate wave energy. Only long swells can penetrate deep into an ice cover. Being closest to open water, wave propagation in the marginal ice zone is the most complex to model. The physical appearance of sea ice in the marginal ice zone varies. Grease ice, pancake ice,brash ice, floe aggregates, and continuous ice sheet may be found in this zone at different times and locations. These types of ice are formed under different thermal-mechanical forcing. There are three classic models that describe wave propagation through an idealized ice cover: mass loading,thin elastic plate, and viscous layer models. From physical arguments we may conjecture that mass loading model is suitable for disjoint aggregates of ice floes much smaller than the wavelength, thin elastic plate model is suitable for a continuous ice sheet, and the viscous layer model is suitable for grease ice. For different sea ice types we may need different wave ice interaction models. A recently proposed viscoelastic model is able to synthesize all three classic models into one. Under suitable limiting conditions it converges to the three previous models. The complete theoretical framework for evaluating wave propagation through various ice covers need to be implemented in the operational ocean wave models. In this review, we introduce the sea ice types, previous wave ice interaction models, wave attenuation mechanisms,the methods to calculate wave reflection and transmission between different ice covers, and the effect of ice floe breaking on shaping the sea ice morphology. Laboratory experiments,field measurements and numerical simulations supporting the fundamental research in wave-ice interaction models are discussed. We conclude with some outlook of future research needs in this field.     

Dynamic ice loads on conical structures

Two series of model tests were performed to observe the dynamic ice loads on conical structures. The variable testing parameters include the water line diameter of the model cone and ice parameters. During small water line diameter tests, two-time breaking is found to be the typical failure of ice on steep conical structure, and also be controlled by other factors, such as ice speed and the cone angle. During big water line diameter tests, the ice sheet failed nonsimultaneously around the cone. Several independent zones of bending were found in the nonsimultaneous failure process of ice. With the increase of the ratio of D/h and the number of independent zones, the total ice force was found being gradually reduced.     

Water wave propagation over multiple porous barriers with variable porosity in the presence of an ice cover

Meccanica - A semi-analytical method is applied to investigate the propagation of flexural wave over multiple bottom-standing porous barriers with variable porosity beneath an ice cover under the...     

基于多介质、多尺度离散元方法的冰载荷数值冰水池

极地船舶与海洋工程结构冰载荷的确定是其结构抗冰设计、冰区安全运行和结构完整性管理的重要研究内容. 当前快速发展的高性能计算技术和多介质、多尺度数值方法为准确、高效地计算结构冰载荷提供了有效的途径, 其中以离散元方法为代表的数值方法取得了出色的研究成果. 为此, 本文针对目前极地船舶与海洋工程结构对冰载荷及力学响应的工程需求, 同时考虑国内外对海冰、工程结构与流体相互耦合的多介质、多尺度数值方法研究现状, 对极地船舶与海洋工程数值冰水池的概念、框架、开发技术以及基于离散元方法的软件实现与工程应用进行了论述. 数值冰水池在船舶与海洋工程结构冰载荷确定方面具有可靠性、经济性、快速性、扩展性和情景化等显著优势. 本文工作借鉴数值水池的研究思路, 以典型船舶和海洋平台结构冰载荷及结构力学响应的离散元计算为例, 探讨了数值冰水池研究的可行性和工程应用前景, 阐述其与理论分析、现场测量和模型试验研究相结合的必要性. 以上研究有益于中国在极地船舶与海洋工程领域形成具有独立知识产权的数值计算分析平台, 对中国极地海洋强国的战略实施具有很好的启发和指导意义.