Richard Loendersloot

Wireless sensor network for helicopter rotor blade vibration monitoring: Requirements definition and technological aspects

The main rotor accounts for the largest vibration source for helicopter fuselage and components. However, accurate blade monitoring has been limited due to the practical restrictions on instrumenting rotating blades. The use of Wireless Sensor Networks (WSNs) for real time vibration monitoring promises to deliver a significant contribution to rotor performance monitoring and blade damage identification. This paper discusses the main technological challenges for wireless sensor networks for vibration monitoring on helicopter rotor blades. The first part introduces the context of vibration monitoring on helicopters. Secondly, an overview of the main failure modes for rotor and blades is presented. Based on the requirements for failure modes monitoring, a proposition for a multipurpose sensor network is presented. The network aims to monitor rotor performance, blade integrity and damage monitoring at three different scales referred to as macro layer, meso layer and micro layer. The final part presents the requirements for WSNs design in relation with sensing, processing, communication and actuation. Finally power supply aspects are discussed.

Power harvesting in a helicopter rotor using a piezo stack in the lag damper

A piezoelectrically augmented helicopter lag damper has been simulated for the purpose of harvesting electrical energy within the rotor of the aircraft. This energy can then be consumed locally for sensing, processing, and transmission of data to the cockpit. An 8.15-m radius rotor is considered, and in-plane rigid lagging motion forms the prime excitation of the damper. The piezoelectric stack is installed within the rod of the damper in such a manner that the stack is submitted to all damper loads. MATLAB and Simulink are used to simulate a simplified blade model. A number of electrical harvesting circuits are investigated, and the piezo stack is optimized for each circuit. Also the effect of nonlinear capacitance of the piezo material is investigated revealing a profound effect. The important design parameters are identified and optimized resulting in a power output of 5.1 W for a steady 130-knot forward flight profile.

Geometrical optimization of a hingeless deployment system for an active rotor blade

Deployment systems for the Gurney flap need to sustain large centrifugal loads and vibrations while maintaining precisely the displacement under aerodynamic loading. Designing such a mechanism relies on both the actuation technology and the link that transmits motion to the control surface. Flexible beams and piezoelectric patch actuators have been chosen as components to design this mechanism. Flexible beams provide a hingeless robust structure onto which the piezoelectric actuators are bonded. A candidate topology is determined by investigating the compliance of a simple wire structure with beam elements. A parameterized finite element model is then built and optimized for displacement and force through surrogate optimization.

Permeability of non-crimp fabric preforms

Abstract: Experimental permeability data of non-crimp fabrics (NCFs) is discussed in this chapter. The chapter starts with a general introduction on permeability, followed by a discussion on experimental permeability data. The influence of geometrical features of the textile architecture, in particular the stitching, is discussed in the third section, whereas the relation between fabric deformation and permeability is addressed in the fourth section. Two types of deformation can be distinguished: compression and in-plane shear. Both are addressed in this section. The chapter ends with concluding remarks, including comments regarding the benchmark project recently initiated and some future developments.

Vibro-acoustic modulation–based damage identification in a composite skin–stiffener structure:

Vibro-acoustic modulation–based damage identification relies on the modulation of a high-frequency carrier signal by an intenser low-frequency vibration signal due to damage-induced structural nonlinearities. A time domain analysis of the vibro-acoustic modulation phenomena was presented at multiple spatial locations in an impact damaged composite skin–stiffener structure. The instantaneous amplitude and frequency of the carrier velocity response were extracted to analyze the intermodulation effects between the two excitation signals. Increased amplitude modulations at the damaged region revealed the presence, location, and length of the skin–stiffener damage. The damage hardly modulated the frequency of the carrier response. This difference in behavior was attributed to the nonlinear skin–stiffener interaction introduced by the periodic opening and closing of the damage, according to earlier research by authors on the same structure. A parametric study showed that the amplitude and phase of the amplitude modulation are dependent on the selected carrier excitation frequency, and hence the high-frequency wave field that is introduced. This work demonstrates not only the potential but also the complexity of the vibro-acoustic modulation based damage identification approach.

Damage Assessment in Composite Structures Based on Acousto-Ultrasonics - Evaluation of Performance

This work focuses on the damage detection and assessment of barely visible impact damages that occur after impacting a composite stiffened structure through the acousto-ultrasonics technique. Delaminations and debondings have been introduced in two stiffened panels and afterwards interrogated with an integrated structural health monitoring (SHM) network within the project. In order to perform the damage assessment, a methodology for the identification of damages along with a graphical user interface is developed. The performance of the developed methodology is evaluated and a damage assessment based on several damage indices and actuation frequencies is carried out. The most suitable parameters for the given structure and damage types are finally reported.

A Methodology Based on Pulse-Velocity Measurements to Quantify the Chemical Degradation Levels in Thin Mortar Specimens

In this research, ultrasonic pulse echo measurements are used to quantify through thickness chemical degradation in thin mortar specimens. The degradation level is predicted using the time of travel of the acoustic wave through the thickness of the structure. The front and back wall interaction reflections are used to obtain additional information from very early stage degradation. The pulse-velocity of sound waves as a function of the thickness of the layers within the structure is described. With knowledge of the pulse-velocity in pristine and fully degraded conditions, it is possible to determine the complete range of degradation length over the layer thickness. The method is applicable for leaching of calcium and acidic attack. The acoustic measurements were verified with destructive testing. The correlation between the acoustic and non-acoustic experiments agree with the described pulse-velocity and degraded depth function. The method based on ultrasonic measurements can be implemented in other thin-layered structures.

Modal Strain Energy Based Structural Health Monitoring Validation on Rib Stiffened Composite Panels

Structural Health Monitoring (SHM) techniques are emerging more and more in aerospace composite structure applications. Validation of the SHM techniques is one of the issues to be addressed yet. Moreover, cost-efficient and reproducible ways to compare SHM methods can be attractive for researchers and end users. NLR has recently developed ways for automated production of rib-stiffened composite panels using an Automated Fibre Placement (AFP) machine. Without human interference and a fully automated manufacturing process, multiple panels can be cost-effectively laid-up with limited quality variation. In this paper, Modal Strain Energy Damage Index (MSE-DI) method is applied on two impact-damaged panels manufactured in this new way. The results show that the panels have slightly deviating natural frequencies even though the C-scan revealed no major quality variation. Secondly, the presence of the impact damage can be successfully detected by the MSE-DI algorithm, but the localization was inaccurate, contradicting the expectations. This is attributed to the specific characteristics of the panel and indicates a dependency of the performance of algorithms on structure to which they are applied. Future work will include a further exploration of this dependency.

Development of an inline water mains inspection tech nology

The condition of a great part of the drinking water network in the Netherlands is unknown. In order to efficiently identify the assets that are close to their lifetime expectancy, a non-destructive evaluation method was developed based on ultrasonic testing. The water network is composed mostly by polyvinyl chloride (~50%) and cement-based (~30%) pipes. In this work, the degradation due to acidic attack in cement-based drinking water pipes was investigated. Mortar blocks were manufactured and degraded in a hydrochloric acid solution. The amount of degradation was derived by measuring the overall ultrasonic pulse velocity in the specimen. Moreover, two factors played a vital role in the detection of acid induced damage: the high damping of the piezoelectric element, resulting in low resonance and the processing algorithm. A 0.5 MHz central frequency transducer is found to be the most suitable to detect acidic damage in cement-based structures.

Accuracy and multi domain piezoelectric power harvesting model using VHDL-AMS and SPICE

This paper presents a piezoelectric power harvesting model including both the mechanical and electrical domain. It includes a mechanical system, electrical interface, storage capacitor and load. Bridge rectifier, Parallel Synchronized Switch Harvesting on Inductor (P-SSHI) and Synchronous Electric Charge Extraction (SECE) circuits are analyzed as electrical interface. A mechanical system and control signals are implemented in VHDL-AMS and electronics components in SPICE. Simulation results and experimental data are compared to show the accuracy of the proposed model.