Cezary Graczykowski

Protecting offshore wind turbines against ship impacts by means of adaptive inflatable structures

Collisions with small service ships are serious danger for offshore wind turbines. Installing torus-shaped adaptive inflatable structure that surrounds a wind turbine tower at water level is one method of effective protection. Proposed pneumatic structure contains several separate air chambers equipped with devices for fast inflation and pressure release. The system can be adapted to various impact scenarios by adjusting the level of initial pressure in each chamber and by controlling the release of compressed air during collision. The paper presents finite element simulation of ship collision with wind turbine tower protected by pneumatic structure, conducted using ABAQUS software. Introduced methods of pressure adjustment are aimed at mitigating tower and ship response. The performed feasibility study proves that inflatable structure can effectively protect the wind turbine tower and the ship against serious damage.

On-Line Impact Load Identification

The so-called Adaptive Impact Absorption (AIA) is a research area of safety engineering devoted to problems of shock absorption in various unpredictable scenarios of collisions. It makes use of smart technologies (systems equipped with sensors, controllable dissipaters and specialised tools for signal processing). Examples of engineering applications for AIA systems are protective road barriers, automotive bumpers or adaptive landing gears. One of the most challenging problems for AIA systems is on-line identification of impact loads, which is crucial for introducing the optimum real-time strategy of adaptive impact absorption. This paper presents the concept of an impactometer and develops the methodology able to perform real-time impact load identification. Considered dynamic excitation is generated by a mass M1 impacting with initial velocity V0. An analytical formulation of the problem, supported with numerical simulations and experimental verifications is presented. Two identification algorithms based on measured response of the impacted structure are proposed and discussed. Finally, a concept of the AIA device utilizing the idea of impactometer is briefly presented.

Smart Technologies for Adaptive Impact Absorption

The article presents a review of recent research carried out in the Department of Intelligent Technologies of Institute of Fundamental Technological Research, dedicated to application of systems for adaptive impact absorption to adaptive aircraft landing gears, novel concept of protective MFM structures, flow-control based airbags, maritime applications of inflatable structures, and development of adaptive wind turbine blade – hub connections.

Adaptive Impact Absorption and Applications to Landing Devices

This paper demonstrates progress in Adaptive Impact Absorption (AIA) research field obtained recently in our research group and is based on previously published conference communicates. The monograph (Ref.[1]), under preparation, will present soon more detailed discussion of the considered problems. In contrast to the standard passive systems the proposed AIA approach focuses on active adaptation of energy absorbing structures (equipped with sensor system detecting and identifying impact in real time and controllable semi-active dissipaters, so called structural fuses) with high ability of adaptation to extreme overloading. A semi-active or fully-active solutions can be applied, which depend on constant or time-dependent modifications realized via controllable dissipative devices. Feasible, adaptive dissipative devices under considerations can be based on MR fluids or (hydraulic or pneumatic) piezo-valves. The presentation will be devoted to the following applications of AIA concept: Adaptive Landing Gears (ALG) for mitigation of exploitative aircraft loads and adaptive flow control based airbags for emergency landing of the helicopter.

Adaptive Impact Absorption – The Concept and Potential Applications:

Adaptive Impact Absorption focuses on adaptation of energy absorbing structures to actual dynamic loading by using system of sensors detecting and identifying impact in advance and embedded semi-active dissipaters with controllable mechanical properties. Application of such devices allows to modify dynamic characteristics of the structure during the period of impact and to precisely control the process of energy dissipation. The paper presents an overview of research conducted at the Department of Intelligent Technologies of the Institute of Fundamental Technological Research dedicated to design and applications of various systems of Adaptive Impact Absorption. Wide range of presented examples covers adaptive hydraulic and pneumatic landing gears, skeletal systems equipped with controllable elements and detachable joints as well as adaptive inflatable structures.

Adaptive Self-Protection against Shock and Vibration

This contribution reviews the challenges in adaptive self-protection of structures. A proper semi-active control strategy can significantly increase structural ability to absorb impact-type loads and damp the resulting vibrations. Discussed systems constitute a new class of smart structures capable of a real-time identification of loads and vibration patterns, followed by a low-cost optimum absorption of the energy by structural adaptation. Given the always surging quest for safety, such systems have a great potential for practical applications (in landing gears, road barriers, space structures, etc.). Compared to passive systems, their better performance can be attributed to the paradigm of self-adaptivity, which is ubiquitous in nature, but still sparsely applied in structural engineering. Being in the early stages of development, their ultimate success depends on a concerted effort in facing a number of challenges. This contribution discusses some of the important problems, including these of a conceptual, technological, methodological and software engineering nature.

Controllable Truss-Frame Nodes in Semi-Active Damping of Vibrations

In recent years, vibration damping strategies based on semi-active management of strain energy have attracted a large interest and were proven highly effective. However, most of published research considers simple one degree of freedom systems or study the same basic example (the first vibration mode of a cantilever beam) with the same control strategy. This contribution focuses on truss-frame nodes with controllable moment-bearing ability. It proposes and tests an approach that allows the control strategy to be extended to more complex structures and vibration patterns.

Crashworthiness of Inflatable Thin-Walled Structures for ImpactAbsorption

The paper describes application of innovative, inflatable thin-walled structures for absorption of the impact loading and thoroughly investigates their crash characteristics. The proposed concept assumes inflation of thin-walled structures with compressed gas of appropriately adjusted pressure in order to improve their basic mechanical properties, enhance energy dissipation capabilities, and increase corresponding durability to impact loading. In the first part of the paper the influence of compressed gas on mechanical characteristics of aluminium beverage can is analysed experimentally and by the corresponding numerical simulations. The following section proposes and numerically verifies three diverse engineering applications of inflatable thin-walled structures for impact absorption. Finally, the last part introduces the concept of adaptive inflatable barrier and briefly presents three simple strategies of pressure control. Both the performed basic experiment and the conducted numerical simulations show the advantageous influence of compressed gas and prove the feasibility of using inflatable thin-walled structures for impact absorption.

Force Fields within Michell-Like Cantilevers Transmitting a Point Load to a Straight Support

The paper concerns distribution of the force fields within Michell cantilevers supported on a segment of a straight line. The allowable yield stresses for tension and compression are not necessarily equal. The paper puts emphasis on checking the final results for the optimal weight by computing the weight in two manners: as a virtual work or, alternatively, by finding the force fields, the density of fibres and then by summing up the weights of all the parts of the optimal cantilever, i.e. the weights of the reinforcing bars and the weights of all the fibrous domains. If this duality gap vanishes, the solution is correct.

Constructing Michell Structures in Plane. Single Load Case

This chapter introduces the reader into the methods of construction of the planar frameworks being exact solutions to the Michell problems of optimum design. The layout of bars of these structures follows the trajectories of specific strain fields. The methods of their construction are given in Sects. 4.1–4.4. The simplest Michell structures are composed of straight and circular bars; they are described in Sect. 4.5. The next sections outline the construction of all available nowadays exact solutions of the Michell’s theory; some constructions are checked by the static method. The analytical results are compared with their numerical predictions found by the ground structure method.