To understand the structural dynamics of a complex mechanical assembly, it is often advantageous to study the dynamics of the individual components within the system. This has been utilized in numerical models for decades. An alternative is to represent the dynamics of these substructures using test data. Combining models based on vibrational test data with analytical/numerical models is known as experimental dynamic substructuring.

The Society of Experimental Mechanics’ (SEM’s) Technical Division on Dynamic Substructuring recognized a need for a geometrically simple yet conceptually challenging benchmark structure. A four-unit frame structure was designed to form its base. The substructuring collaboration was initially focused on linear substructuring but recent developments have led to an interesting nonlinear challenge problem.

Joints between substructures often cause nonlinear behavior in built-up systems; typical underlying physics including dry friction, varying contact areas, and other tribomechadynamic phenomena. Other causes are material nonlinearities, large deformation and contact in gaps/clearances. To include well-defined nonlinearities in the benchmark structure, the team from Sandia National Laboratories designed and manufactured a set of nonlinear subcomponents that serve as baseline examples. The design utilizes the four-unit frame as a basis and introduces wings with midspan lap joints as well as underwing pylons. The two pylon designs, the Gap Pylon (GP) and the Radius Pylon (RP), differ in the shape of the mounting blocks. The RP contains a smoothly varying contact with a metal strip while the GP features an abrupt change in the contact. 

This study utilizes the four-unit Frame and rectangular jointed wing with attached RPs. Experimental dynamic substructuring is used to form a representation of the isolated nonlinear dynamics of the wing assembly by decoupling the dynamics of the Frame subsystem from the full structure. This process is completed at a range of excitation levels to characterize the nonlinear dynamics of the wing with two pylons as a function of response level. To avoid nonlinearities other than the one introduced by the RP, washers are inserted between the fuselage and the wing, between the wing parts in the lap joints, and between the wing and the upper pylon part. This work seeks to extend the boundaries of what is achievable with dynamic substructuring and demonstrate the process on a challenging use case.

Research focus on experimental dynamic substructuring has grown in recent years in both academic and industrial interests. Progress continues for both component mode synthesis and frequency based substructuring methods with a heightened interest around the nonlinearities that come about in interfaces often found in dynamic substructuring examples. Many examples of substructuring decouple structures at the interface where sources of nonlinear damping and stiffness may occur, and some, like the transmission simulator method, instead mass-load the interface. A clear path to incorporate these interface nonlinearities is a true challenge for the substructuring community. In recent years, the Society of Experimental Mechanics’ (SEM’s) Technical Division on Dynamic Substructuring recognized a need for a simple yet challenging benchmark structure for experimental-analytical substructuring collaborations as compared to previous benchmark structures (Mayes, An introduction to the SEM substructures focus group test bed – The Ampair 600 Wind Turbine. In topics in experimental dynamics substructuring & wind turbine dynamics, Jacksonville, FL, 2012; Harvie and Avitable, Comparison of some wind turbine blade tests in various configurations. In Proceedings from the 30th International Modal Analysis Conference, Orlando, FL, 2012; Roettgen and Mayes, Ampair 600 wind turbine 3-bladed assembly substructuring using the transmission simulator method. In Proceedings from the XXXIII IMAC Conference, Orlando, FL, 2015). A team with members from many research institutes set out from several desirable properties and a unit-frame structure was designed as a benchmark for current collaborative efforts detailed in (Roettgen and Linderholt, Planning of a black-box benchmark structure for dynamic substructuring. In International Modal Analysis Conference 37, 2019). The benchmark structure is built up by a frame with threaded inserts that is bolted to plates of varying thickness and materials. When assembled, this structure can span a diverse application space of substructuring techniques. Previous endeavors with this benchmark have been focused on testing different methods of linear substructuring as well as collaborating in the development of different methods. The next steps in this challenge aim to direct the community at different nonlinear substructuring challenges that can be studied using the four-unit frame from the benchmark structure. This abstract highlights three potential nonlinear adaptations of the benchmark structure, where drawings and data for these options will be made available on the dynamic substructuring Wiki prior to the IMAC conference.

The Society of Experimental Mechanics’ (SEM’s) Technical Division (TD) on Dynamic Substructuring recognized a need for a simpler yet challenging benchmark structure for experimental-numerical substructuring exercises. Some years ago, representatives from several research institutes formed a group that defined several desirable properties for the new benchmark structure. The outcome is a frame structure together with different plates. Together, they can represent various structures such as automotive frames, wing-fuselage structures, and building floors. The frame is made as a one-piece structure with many 10/32 tapped holes that can be used to attach other components, sensors, or excitation devices. Sandia National Labs has manufactured the benchmark structure’s components, an aluminum frame together with two rectangular aluminum wings. An exercise/challenge has been formulated. The components have been shipped to the ones that have shown interest in participating in the exercise. The idea of the exercise is to compare different strategies to tackle an experimental substructuring task, containing both decoupling and coupling, thereby learning from each other. In the exercise, the participants start with an assembly built up by the frame and the thinner of the rectangular wings. That wing should then be numerically decoupled from the fuselage. To that numerical representation of the fuselage, the thicker wing should be coupled numerically. These decoupling and coupling operations render in a numerical representation of the thicker wing attached to the fuselage—a representation which output should be compared with test data stemming from the real structure counterpart. The success of the decoupling and coupling exercises is dependent on the quality of the models of the components that are subtracted and added. Here, models of finite element representing components building up the Technical Division’s Substructuring Benchmark structure are developed. Their convergences are studied, and they are validated by test data stemming from vibration tests of the models’ hardware counterparts.

Understanding the structural dynamics of built-up systems is essential to engineering design. A recent research focus that has steadily grown in both academic and industrial settings is experimental dynamic substructuring, which involves the combination of numerical and experimental models to predict the response of an assembled structure. An international team of dynamic substructuring researchers identified the need for a simple benchmark structure for the community to compare, collaborate, and improve dynamic substructuring techniques. Several nonlinear attachments for this structure have been designed and manufactured to explore aspects of dynamic substructuring in the presence of different nonlinearities. To provide insight to dynamic substructuring researchers participating in this benchmark challenge, this work documents the design of these nonlinear components and demonstrates the degree of nonlinearity encountered via experimental dynamic testing of the assembled structure.

Some years ago, the Society of Experimental Mechanics’ (SEM’s) Technical Division (TD) on Dynamic Substructuring recognized a need for a simpler yet challenging benchmark structure for experimental-numerical substructuring exercises. That structure should replace the modified version of an Ampair 600 wind turbine as the common test object within the TD. Representatives from several research institutes formed a group that defined several desirable properties for the new benchmark structure. The outcome is a frame structure together with a differnt plates. Together, they can represent various structures such as automotive frames, wing-fuselage structures and building floors. The frame is made as a one-piece structure with many 10/32 tapped holes that can be used to attach other components, sensors or excitation devices.Sandia National Labs has manufactured the benchmark structure’s components, an aluminum frame together with two aluminum rectangular wings. An exercise/challenge has been formulated. The components have been shipped to the ones that have shown interest in participating in the exercise. The idea of the exercise is to compare different strategies to tackle an experimental substructuring task, containing both decoupling and coupling, thereby learning from each other.In the exercise, the participants start with an assembly built up by the frame and the thinner of the rectangular wings. That wing should then be numerically decoupled from the fuselage. To that numerical representation of the fuselage, the thicker wing should be coupled numerically. These decoupling and coupling operations render in a numerical representation of the thicker wing attached to the fuselage; a representation which output is compared with test data stemming from the real structure counterpart.Here, virtual points are used in the decoupling and coupling operations. Four attachment points, e.g., four screws, are used. In addition, washers between the fuselage and the wings are used in the connections. The purpose is to avoid too challenging non-linearities to start with. The Component Mode Synthesis (CMS), technique is used.

Research focus on experimental dynamic substructuring has grown in recent years in bothacademic and industrial interests. Methods to couple and decouple in the modal domain, i.e., usingComponent Mode Synthesis (CMS), the frequency domain, i.e., Frequency Based Substructuring(FBS), and the state-space domain have been developed to high pedigree. In addition, the use ofvirtual point transformations in substructuring exercises has opened new opportunities for thedefinition of substructuring constraints. The Society of Experimental Mechanics’ (SEM’s)Technical Division on Dynamic Substructuring recognized a need for a simple, yet challengingbenchmark structure for experimental-analytical substructuring collaborations as compared toprevious benchmark structures [1] [2] [3]. A team with members from many research institutes setout from several desirable properties and a unit-frame structure was designed as a benchmark forcurrent collaborative efforts detailed in [4]. The benchmark structure is built up by a frame withthreaded inserts that is bolted to plates of varying thickness and materials. When assembled thisstructure can span a diverse application space of substructuring techniques including automotiveframes, wing-fuselage structures, and structural frames and floors. The frame is made as a onepiecestructure; it consists of four units cells and includes 10/32 tapped holes that can be used toattach other components. In addition, 10/32 tapped holes are made on the side of the frame toattach impedance heads or force transducers.Substructuring is often used to connect test and finite element (FE) based subassembly models.Each model can play to its strengths with FE models containing high fidelity spatial density andexperimental models capturing difficult to model pieces of an assembly, i.e., joint mechanics. Inthis work the benchmark structure’s components, an aluminum frame together with a rectangularwing manufactured by Sandia National Labs, are combined with swept steel wings manufacturedby Linnaeus University. The study combines a test-based model of the assembled frame andrectangular wing with FE models representing wing subcomponents. The rectangular wing isnumerically decoupled from the fuselage by the use of an FE model representing the wing and theswept wing is then numerically coupled to the frame using an FE model. The modal substructuringpredictions are then compared with results from measurements on the assembly.

Wind-induced dynamic excitation is a governing design action determining size and shape of modern Tall Timber Buildings (TTBs). The wind actions generate dynamic loading, causing discomfort or annoyance for occupants due to the perceived horizontal sway, i.e. vibration serviceability problem. Although some TTBs have been instrumented and measured to estimate their key dynamic properties (eigenfrequencies, mode shapes and damping), no systematic evaluation of dynamic performance pertinent to wind loading had been performed for the new and evolving construction technologies used in TTBs. The DynaTTB project, funded by the ForestValue research program, mixed on site measurements on existing buildings excited by mass inertia shakers (forced vibration) and/or the wind loads (ambient vibration), for identification of the structural system, with laboratory identification of building elements mechanical features, coupled with numerical modelling of timber structures. The goal is to identify and quantify the causes of vibration energy dissipation in modern TTBs and provide key elements to finite element models. This paper presents an overview of the results of the project and the proposed Guidelines for design of TTBs in relation to their dynamic properties.

Forced vibration tests have been conducted on the seven-storey timber building Eken in Mariestad inSweden. The main objective is to estimate the building’s dynamic properties from test data. The eigenfrequencies, modeshapes and their scaling are useful to calibrate numerical models. However, the most important outcomes are the estimatesof the modal damping values. The reason is that the damping impacts the acceleration, and thus the serviceability of thebuilding, and at the same time, it is very hard to model damping. So, during the design phase, one must rely on previoustest data (of which very few exist for taller timber buildings) or rule of thumbs. It is therefore important to gain knowledgeabout the damping for timber buildings in order to enable good designs of future and taller timber buildings. The test datashows that the modal damping is roughly equal to 2% of the critical viscous ones for the eigenmodes extracted. The testcampaign on Eken is made as a part of the project Dyna-TTB in which vibrational tests have been performed on eighthigh-rise timber buildings, in Europe, of which Eken is one.