Rigid Conditions Research Articles

Analysis of Driver Departure and Damage in Frontal 100% Overlap Rigid Barrier Crash Conditions with AEB Intervention.

A braking robot and an in-vehicle HD camera were used to study the influence of emergency braking systems on the passive safety of vehicles, to conduct real vehicle tests on volunteers. The dynamic responses of 18 groups of volunteers under different braking deceleration speeds and different test speeds were collected, and the change rule of the driver’s forward tilt displacement during AEB braking was analyzed. The x-direction displacement of the head and shoulder of the volunteers increased with the increase of the braking deceleration speed, and there was no obvious correlation with the initial speed. Madymo was used to build a restraint system model, verified against the real vehicle crash test data. The maximum off-position state of the volunteer’s real car test was input into the restraint system model. The injury of drivers in frontal 100% overlap rigid barrier crash conditions with or without AEB effect was analyzed through simulation and comparison. It was concluded that AEB interventions do not increase the damage value with the existing passive safety development strategy.

Value analysis with blockchain-based information transparency system to eliminate information distortion

Information distortion is common in supply chains, especially demand information distortion. An easily-thought way of eliminating information distortion is information sharing. Although there exist many information sharing mechanisms that can coordinate the supply chains, they are not easy to implement due to their rigid implementation conditions. Consequently, many upstream manufacturers in reality commonly buy data from downstream retailers to eliminate demand information distortion, or may build a blockchain-based information transparency system (BITS), which is an alternative way proposed in this paper. The main purpose of this paper is to investigate how the two alternative ways perform in eliminating demand information distortion within supply chains. In specific, we study a two-echelon supply chain consisting of one manufacturer and one retailer under three scenarios: benchmark scenario with demand distortion, demand distortion elimination through data buying and through constructing BITS. Our findings are the following (Babich and Hilary, 2020): Eliminating demand distortion by BITS can always bring the manufacturer additional value, but a higher information transparency of BITS is not always better to the manufacturer, and the manufacturer chooses a fully transparent BITS to eliminate demand distortion only when the demand distortion is relatively large (Carley and Lin, 1997); The data purchase way of eliminating demand distortion can bring additional value to the manufacturer only when the data-buying cost is not very large (Chen and Huang, 2007); As compared to the data-buying scenario to eliminate demand distortion, the BITS construction scenario can generate more additional values for the manufacturer if the demand volatility is relatively small, or when the cost coefficient of building BITS is relatively small (CachonGérard and Fisher, 2000); If the retailer bears the BITS construction cost, the retailer prefers to proactively share the BITS construction cost rather than passively bear it completely.

Brinkman–Bénard Convection with Rough Boundaries and Third-Type Thermal Boundary Conditions

The Brinkman–Bénard convection problem is chosen for investigation, along with very general boundary conditions. Using the Maclaurin series, in this paper, we show that it is possible to perform a relatively exact linear stability analysis, as well as a weakly nonlinear stability analysis, as normally performed in the case of a classical free isothermal/free isothermal boundary combination. Starting from a classical linear stability analysis, we ultimately study the chaos in such systems, all conducted with great accuracy. The principle of exchange of stabilities is proven, and the critical Rayleigh number, Rac, and the wave number, ac, are obtained in closed form. An asymptotic analysis is performed, to obtain Rac for the case of adiabatic boundaries, for which ac≃0. A seemingly minimal representation yields a generalized Lorenz model for the general boundary condition used. The symmetry in the three Lorenz equations, their dissipative nature, energy-conserving nature, and bounded solution are observed for the considered general boundary condition. Thus, one may infer that, to obtain the results of various related problems, they can be handled in an integrated manner, and results can be obtained with great accuracy. The effect of increasing the values of the Biot numbers and/or slip Darcy numbers is to increase, not only the value of the critical Rayleigh number, but also the critical wave number. Extreme values of zero and infinity, when assigned to the Biot number, yield the results of an adiabatic and an isothermal boundary, respectively. Likewise, these extreme values assigned to the slip Darcy number yield the effects of free and rigid boundary conditions, respectively. Intermediate values of the Biot and slip Darcy numbers bridge the gap between the extreme cases. The effects of the Biot and slip Darcy numbers on the Hopf–Rayleigh number are, however, opposite to each other. In view of the known analogy between Bénard convection and Taylor–Couette flow in the linear regime, it is imperative that the results of the latter problem, viz., Brinkman–Taylor–Couette flow, become as well known.

Influence of seabed profile on the seismic response of monopile-supported offshore wind turbines including dynamic soil-structure interaction

In this article, the seismic response of four different Offshore Wind Turbines (OWTs) from 5 to 15 MW, founded on monopiles embedded in homogeneous and non-homogeneous soil profiles with equivalent shear-wave velocities from 100 to 300 m/s is analysed. Two types of variable soil profiles with a semi-parabolic variation of the shear-wave velocity as depth increases are considered. The system seismic response under ten different accelerograms is computed through a finite element substructuring model in frequency domain. The foundation behaviour is obtained by a continuum model including kinematic and inertial interaction. Several models, in addition to that of rigid base condition, are considered to determine the influence of soil-structure interaction (SSI), as well as the contribution of each kinematic interaction (KI) factor. The seismic response of the OWTs is obtained in terms of maximum shear forces and bending moments at mudline level, as well as the acceleration amplification factor at hub level. It is found that the maximum response is produced when SSI is considered, including both the inertial and kinematic interaction. The differences arising due to the soil profile definition are shown to be mainly related to the rotational KI factor, which significantly affects the second vibration mode of the system. The largest responses are obtained for the homogeneous equivalent profile.

ВИКОРИСТАННЯ СИМЕТРІЇ ДЛЯ РОЗВ’ЯЗУВАННЯ ЗАДАЧ ДЕФОРМУВАННЯ ПЛИТ НА ЖОРСТКІЙ ОСНОВІ

The optimization of the design scheme of deformation of a rectangular multilayer plate with transversally isotropic layers resting on a rigid (non-deformable) foundation is proposed. The essence of optimization is to consider such a design diagram of the plate, in which the stress-strain state (SSS) of plate would be fully described by only one component, namely the unflexural component of symmetrical SSS relative to the middle surface of plate which is bilaterally symmetrically loaded. To do this, instead of the actual design of the multilayer plate, which is deformed without separation from the foundation, it is suggested to consider the design diagram of the plate, which is formed by supplementing it with a symmetric one about the contact surface of the foundation. In this case, the plate will be symmetrically loaded with respect to the middle surface of the plate, and the thickness of the plate will double. On the middle surface, the conditions of sliding contact of the upper and lower parts of the symmetrical plate, i.e. sliding contact of the plate with foundation are fulfilled. To model absolutely rigid contact at the border with the foundation, an additional thin layer of high rigidity ("non-deformable layer") is introduced into the supplemented plate. This does not change the essence of the calculation model of plate. The SSS of plate will be unflexural, which significantly simplifies its modeling. A two-dimensional model of deformation of multilayer rectangular plates on a rigid foundation with isotropic and transversally-isotropic layers is constructed in an elastic formulation for a unflexural SSS, with a high degree of iterative approximation, but three-dimensional by the nature display of the SSS. This model sufficiently takes into account transverse shear deformations and of transverse compression of the plate under transverse loading. The model is continuous, that is, the number of equations and the order of differentiation of the solving system of equations does not depend on the number of layers in the plate. This order of differentiation and the number of solving equations can depend only on the order of iterative approximation of the model. The derivation of the solving differential equations in the generalized forces and displacement functions is given, as well as the boundary conditions are obtained by the variational Lagrange method. The results of the analytical solution of the problem of deformation of homogeneous rectangular plate in sliding contact with a rigid foundation whith Navier-type boundary conditions under the action of a transverse sinusoidal load are given. A comparison of the calculation results with the exact three-dimensional solution ones was made. Keywords: multilayered plate, rigid foundation, transverse shear, transverse compression, continual model

Thermal vibration of perforated nanobeams with deformable boundary conditions via nonlocal strain gradient theory

Abstract Due to nonlocal and strain gradient effects with rigid and deformable boundary conditions, the thermal vibration behavior of perforated nanobeams resting on a Winkler elastic foundation (WEF) is examined in this paper. The Stokes transformation and Fourier series have been used to achieve this goal and to determine the thermal vibration behavior under various boundary conditions, including deformable and non-deformable ones. The perforated nanobeams’ boundary conditions are considered deformable, and the nonlocal strain gradient theory accounts for the size dependency. The problem is modeled as an eigenvalue problem. The effect of parameters such as the number of holes, elastic foundation, nonlocal and strain gradient, deformable boundaries and size on the solution is considered. The effects of various parameters, such as the length of the perforated beam, number of holes, filling ratio, thermal effect parameter, small-scale parameters and foundation parameter, on the thermal vibration behavior of the perforated nanobeam, are then illustrated using a set of numerical examples. As a result of the analysis, it was determined that the vibration frequency of the nanobeam was most affected by the changes in the dimensionless WEF parameter in the first mode and the changes in the internal length parameter when all modes were considered.

Contribution of the rotational kinematic interaction to the seismic response of monopile-supported offshore wind turbines

This paper presents a study on the role of kinematic interaction effects on the seismic response of large monopile-supported offshore wind turbines. For this purpose, a finite element substructuring model is used to analyse the behaviour of three reference wind turbines with rated powers of 5, 10 and 15 MW founded on several soil profiles and subjected to different accelerograms. The foundation response is computed through a continuum model which includes soil–structure interaction. The effects of inertial and kinematic soil–structure interaction on the system seismic response is evaluated also through comparisons with results corresponding to the infinitely rigid base condition. It is found that neglecting kinematic interaction factors could lead to underestimate the seismic response of large monopile-supported offshore wind turbines. The rotational kinematic interaction factor is shown to increase the OWTs seismic response.

A Hybrid Anchoring Technology Composed of Reinforced Flexible Shells for a Knee Unloading Exosuit.

Soft robotic wearables have emerged as an ergonomic alternative to rigid robotic wearables, commonly utilizing tension-based actuation systems. However, their soft structure's natural tendency to buckle limits their use for compression bearing applications. This study presents reinforced flexible shell (RFS) anchoring, a compliant, low-profile, ergonomic wearable platform capable of high compression resistance. RFS anchors are fabricated with soft and semirigid materials that typically buckle under compressive loads. Buckling is overcome using the wearer's leg as a support structure, reinforcing the shells with straps, and minimizing the space between the shells and the wearer's skin-enabling force transmission orders of magnitude larger. RFS anchoring performance was evaluated comparatively by examining the shift-deformation profiles of three identically designed braces fabricated with different materials: rigid, strapped RFS, and unstrapped RFS. The unstrapped RFS severely deformed before 200 N of force could be applied. The strapped RFS successfully supported 200 N of force and exhibited a nearly identical transient shift-deformation profile with the rigid brace condition. RFS anchoring technology was applied to a compression-resistant hybrid exosuit, Exo-Unloader, for knee osteoarthritis. Exo-Unloader utilizes a tendon-driven linear sliding actuation system that unloads the medial and lateral compartments of the knee. Exo-Unloader can deliver 200 N of unloading force without deforming, as indicted by its similar transient shift-deformation profile with a rigid unloader baseline. Although rigid braces effectively withstand and transmit high compressive loads, they lack compliance; RFS anchoring technology expands the application of soft and flexible materials to compression-based wearable assistive systems.

Abdominal biofidelity assessment of 5th percentile female ATD responses relative to recently developed belt and bar loading corridors

Objective The objective of this study was the quantitative evaluation and comparison of the responses of the Hybrid III 5th percentile female (HIII-05F) and the 5th percentile female Test Device for Human Occupant Restraint (THOR-05F) anthropomorphic test devices (ATDs) subjected to abdominal loading conditions. Method The HIII-05F and THOR-05F were subjected to 3 different abdominal loading conditions: fixed-back belt pull (low compression), fixed-back belt pull (high compression), and free-back rigid bar impact at 6 m/s. The stroke of the impact was controlled to represent injurious and noninjurious loading conditions as observed in the experiments with postmortem human subjects (PMHS). Quantitative comparisons were made between the ATD abdominal force and compression responses and biofidelity corridors obtained from matched-pair PMHS tests under identical loading conditions, using the most recent version of the NHTSA Biofidelity Ranking System (BRS). Results The overall THOR-05F BRS scores across all tests (BRS score = 1.84) indicated good biofidelity. For the belt loading test conditions, the average BRS scores for both THOR-05F (BRS scores = 1.45 and 1.34) and HIII-05F (BRS scores = 1.42 and 1.01) showed good biofidelity. For the rigid bar loading condition, the THOR-05F (BRS score = 2.74) showed better biofidelity compared to HIII-05F (BRS score = 10.63), with the HIII-05F exhibiting poor performance in this condition. The average pressures recorded by the abdomen pressure twin sensors (APTS) in the current study ranged from 45 to 130 kPa, increasing proportionally with higher stroke and loading rate. Conclusions Overall, the THOR-05F BRS scores were better than the HIII-05F BRS scores, which suggests improved biofidelity of the THOR-05F abdomen. The abdominal insert in the HIII-05F did not provide enough room for compression, leading to higher stiffness and occupant motion as observed in the rigid bar tests. Because of practical challenges in measuring abdomen deflection in a soft ATD abdomen component, use of APTS in THOR-05F provides the ability to measure the restraint loading to the abdomen and assess the risk of abdominal injury. With good BRS scores observed in this study for THOR-05F, pressure and other measurements included in the THOR-05F may be used to develop abdominal injury risk functions in the future.

Fluid-Fluid Interaction Problems at High Reynolds Numbers: Reducing the Modeling Error with LES-C

We consider a fluid-fluid interaction problem, where two flows (with high Reynolds numbers for one or both of these flows) are coupled through a joint interface. A nonlinear coupling equation, known as the rigid lid condition, creates an extra level of difficulty, typical for atmosphere-ocean problems. We propose a novel turbulence model, NS- -C, from the recently introduced family of LES-C (large eddy simulation with correction) models. Combining it with the so-called geometric averaging (GA) partitioning method, we obtain the NS- -C-GA model that is shown to possess several key properties. First, the preexisting solvers for the subdomains can be used, which is critical, e.g., for atmosphere-ocean applications. Second, the LES-C turbulence models use defect correction to efficiently reduce the modeling error of the corresponding LES models; we demonstrate numerically that the NS- -C model outperforms its LES counterpart, the NS- model. It has also been shown recently that it is favorable for an LES model to have the nonfiltered velocity in the interface terms. The NS- -C-GA model possesses this important property; we also show it to be stable and have optimal convergence properties.

An analytic method for vibration analysis of non-uniformly coupled L-shaped plates with arbitrary boundary conditions

L-shaped plates are extensively utilized in practical engineering and plates are uniformly coupled in most previous studies. However, spot welding, riveting or bolting is also employed to link two plates and these connection types lead to non-uniform coupling conditions. In this regard, an analytic model is developed for vibration analysis of L-shaped plates with non-uniform coupling conditions. The system is decomposed into two independent rectangular plates, and both bending and in-plane vibrations are analyzed via the classic plate theory and superposition method. The artificial spring technique is adopted to deal with non-uniform continuity conditions and arbitrary uniform boundary conditions, and these conditions are assembled into the governing equation. Comparisons of natural frequencies of L-shaped plates with different boundary and coupling conditions are firstly made, and high accuracy and wide application of the developed model are demonstrated. Furthermore, influences of boundary conditions, coupling conditions, coupling angle and length of plates are investigated. Results reveal that out-of-plane and in-plane displacements are coupled in every plate of L-shaped plate systems. Uniform distribution of coupling nodes can efficiently increase natural frequencies and a few coupling nodes play the role of uniform rigid coupling conditions. Natural frequencies of L-shaped plates at a right angle are the maximum or very close to maximum one. Besides, present results can be used as benchmarks for future researchers.

An investigation on the stochastic thermal vibration behaviors for laminated combined composite plate systems

The present work aims to study the stationary and nonstationary stochastic thermal vibration properties of the laminated combined plate structures using meshless method. The combined system structure consists of several rigidly connected laminated rectangular plates, where the thermal effect of each subplate is considered according to the thermo-elastic theory. The Hamilton’s principle combined with the first-order shear deformation theory (FSDT) is adopted for generating the vibration formulas of the divided plates. The boundary and rigid compatibility conditions of the combined plates are imposed by massless springs with variable stiffness. The displacement components of the subplate system are approximated by 2D Chebyshev meshfree shape functions and the stochastic acceleration excitation is taken into account by introducing the pseudo excitation method (PEM). The modal behaviors and the stochastic dynamic solutions of laminated combined plates subjected to thermal loads are then successfully obtained. A considerable number of computational examples on the free vibration and random responses of the combined laminated plates are carried out to verify the convergence, accuracy and efficiency of the presented meshless model. Finally, systematic parametric studies are conducted to investigate the effects of thermal factor, acceleration excitations and boundary constraints on the free vibration and random dynamic characteristics of the laminated combined plates.

Diffraction of a Whispering Gallery Mode at a Jumply Straightening of the Boundary

Diffraction of a high-frequency small-number whispering gallery mode running along a concave boundary, which turns into a flat one so that its curvature experiences a jump, is studied. The cases of rigid (Neumann) and soft (Dirichlet) boundary conditions are considered. Within the framework of the parabolic equation method, a mathematically correct scattering problem is obtained which is solved explicitly and investigated asymptotically in detail. Analytic expressions are found for all emerging wavefields. In particular, an edge wave diverging from the point of non-smoothness of the boundary is described. For the rigid condition, its amplitude is proportional to the magnitude of curvature jump, but not for the soft condition.

A study on acoustic performance of dissipative silencer for fluid-filled pipe system according to acoustic models of absorbing material

In many industrial systems involving pipe or duct structures, sound transmission modeling is critical to noise treatment and control. A typical noise treatment method applied to pipe structures is to use a silencer. In particular, a dissipative silencer with a sound absorbing material has a noise control ability to reduce noise through successive sound reflections by impedance mismatch while dissipating incident sound energy as heat. In this study, the acoustic performance of a dissipative silencer lined with multi-layered absorbing materials for fluid-filled pipe system is investigated. Herein, the absorbing materials are modeled applying poroelastic and viscoelastic theories. In the analysis, the eigenvalues and eigenfunctions in the dissipative silencer are determined from the rigid wall boundary condition and the interfaces between the absorbing materials, and then the acoustic performance is compared by obtaining the transmission loss using the mode matching method. Also, a parametric study is conducted to investigate the effect of the number and arrangement of layers on the acoustic performance of the silencer according to the absorbing material properties.

Mathematical simulation of rock mass destruction zones by explosion

Purpose. Improving the parameters of the rock mass destruction zones by a blasting, depending on the pressure of the explosion products in the charging cavity and the physical and mechanical properties of rocks by combining analytical and numerical mathematical simulation. The methodology of research. Using the theory of elasticity and the main provisions of the quasi-static wave hypothesis of the mechanism of destruction of a solid medium under the action of an explosion, an analytical simulation of the parameters of the formation of crush zones and grinding of a rock mass around the charging cavity under its explosive load was carried out. After the change in the stress-strain state of the massif under the action of the explosion, numerical simulation of the crushing zones, intensive grinding and cracking by the finite element method was carried out. To establish the suitability of the obtained analytical models for calculating the radii of the indicated zones, the results of analytical and numerical simulation were compared. Findings. Analytical models have been developed for the radii of the zones of crushing, intense grinding and cracking, which are formed around the charging cavity in the rock mass under its explosive load, taking into account the pressure of the explosion products, the tensile-compressive strength of the rocks, their structural structure, and fracturing. Numerical simulation of the destruction of rocks around the charging cavity established the power-law dependences of the change in the radii of the crushing zones and the grinding of the massif depending on the diameter of the charging cavity, the pressure of the explosion products, and the compressive strength of the rocks. By comparing the results of analytical and numerical simulation for rigid boundary conditions of a homogeneous non-fractured massif, the discrepancy between the radii of the indicated zones is found to be 4, 8 and 6%, respectively. The originality. The radii of the zones of crushing, intense grinding and cracking, established by mathematicalsimulation, formed during the explosive destruction of the rock mass, change according to a power law dependence on the diameter of the explosive charge, the pressure of the explosion products in the charging cavity, the strength of the rocks in tension-compression, the coefficients of the rock structure, structural weakening and compaction, determine the increase in the accuracy of estimating the parameters of the destruction of the rock mass up to 50%. Practical implications. Based on mathematical models of the radii of the zones of crushing, intense grinding and cracking, which are formed in the rock mass around the charging cavity under the action of an explosion, improved parameters of drilling and blasting operations are determined for mine workings, special-purpose cavities and breaking of the massif.

Transient Deformation of an Anisotropic Cylindrical Shell with Structural Features

In this work, a new transient function of normal displacements is obtained in a thin elastic anisotropic cylindrical shell of constant thickness with structural features. Structural features form of two sequences in angular direction of weld spots or rivets. Structural features are mathematically described by point boundary conditions of rigid pinching or point boundary conditions of hinge support, accordingly. A load with time variable amplitude and impact boundaries influences on the outer surface of the shell along the normal. Such movement of the shell is considered in the cylindrical coordinate system as connected with the shell axis. Kirchhoff–Love hypothesis are confirmed as a shell model. The solution of this problem can be formed with the help of Green function method and lift compensation method. The required function of transient normal displacements is represented as the sum of integral operators of Green convolution for an infinite shell with functions of current transient load and compensating loads out of point boundary conditions. Compensating loads satisfying to boundary conditions can be found based on the solution of Volterra integral equations of the first kind with the difference kernel. Green function is such kernel. The system solution can be executed including preliminary discretization of compensating time loads. The convolution integrals can be taken numerically with the help of quadrature formula by the method of rectangles. The verification of the method is represented by comparing the solution of specific case with the known solution for a hinged isotropic cylindrical shell.

The Specific Behavior of Economic Agents with Heterogeneous Expectations in the New Keynesian Model with Rigid Prices and Wages

The purpose and scientific novelty of this work is to analyze the changes and features of economic agents’ behavior when incorporating wage rigidity into a new Keynesian model under cognitive constraints of agents. The working hypothesis is the assumption that the forecasting of the output gap, inflation of prices and wages occurs with the help of fundamentalist and extrapolation rules. The first rule is based on forecasting the variables under study on the basis of their stationary values. The second rule is based on extrapolation of the latest available data on inflation and the output gap. The weight shares of agents applying these heuristic rules change endogenously, which is the source of endogenous waves of optimism and pessimism. An analysis of the impulse responses of interest rate and technology shocks suggests that a more flexible economy (an economy with flexible wages and rigid prices) is less prone to a spike in the economic cycle caused by waves of optimism and pessimism than a more rigid economy (an economy with rigid prices and wages) due to the inability of agents to respond immediately to exogenous disturbances in rigid conditions. Thus, these shocks cause wave effects in the economy, i.e., cyclical movements, i.e., a rigid economy will be more prone to booms and busts caused by alternating optimism and pessimism than a flexible economy. The model with an imperfect labor market is characterized by an increased concentration of vital forces at the values of 0 and 1, as well as in the mid-distribution compared to the base model. This feature provides a key explanation for the abnormal dynamics of the evolution of variables in this model. It is concluded that the difference between the degree of optimism and pessimism in the base model and in the model with rigid wages and prices is the full trust of agents in the central bank in targeting wage inflation in the absence of the stabilization of this inflation by the bank.

Modeling analysis of combustion instability in an annular combustor equipped with circumferentially segmented perforated liner

Hazardous azimuthal thermoacoustic modes often occur in lean-premixed annular combustors. One practical control method is the application of perforated liners with bias flow. However, circumferentially uniform perforated liners are not competent to control them, because the perforated plate covered by a single azimuthally uniform backing cavity cannot provide sufficient acoustic pressure difference across the perforated plate to bring in adequate acoustic damping. In this work, we developed a three-dimensional thermoacoustic model to consider the effects of a novel passive control damper of the circumferentially segmented perforated liner. Emphasis is placed on the effects of the segmented liner on controlling the azimuthal modes. It is found that the azimuthal mode in the premixed annular combustor can be either plenum-dominant or combustor-dominant, with the frequency of the latter one larger than the former. The stabilities of the two kinds of modes behave differently with the change of time delay. The results of the lined combustor cases indicate that the circumferentially segmented perforated liner generally improves the control effectiveness compared with the circumferentially uniform perforated liner thanks to the rigid plates inserted in the backing cavity. At the locally inserted position, the rigid plate enforces a rigid boundary condition that changes the azimuthal pressure mode shape in the backing cavity. As a result, more acoustic damping through the pressure difference across the plate is produced. Symmetry-breaking effects are found if the segmentation is asymmetric or two-fold symmetric. The behavior of the splitting frequencies caused by the segmented liner is also studied, and the symmetric segmented liner turns out to be a better choice because the resulting azimuthal mode is degenerate with two equivalent suppressed growth rates. In order to further enhance the control effect, one significant effective measure is to increase the depth of the backing cavity.

Analysis and Control of Acoustic Modes in Cylindrical Cavities with application to Direct Field Acoustic Noise (DFAN) Testing.

It is well known that acoustic cavities have frequencies at which certain free-response 'modes' of propagation respond especially strongly. In the absence of significant damping, these cause peaks of high SPL in the frequency response as well as spatial non-uniformity and temporal ringing. The spatial non-uniformity is especially problematic since it means the room cannot be 'EQ'd' to compensate, since the SPL is different in different positions. This phenomenon has been studied extensively in the room acoustics literature and various strategies for mitigation proposed. Many of these make use of the theoretical mode shapes for a cuboid with a rigid boundary condition, since this is a common shape of room and a reasonable approximation for a solidly constructed wall. But modes exist for other shape spaces too. Of particular interest is the cylindrical cavity that is formed when large enclosing arrays of loudspeakers are used to perform high-intensity acoustic tests on space hardware. These possess problematic modes that can cause over-testing in some positions and under-testing in others. In this work, it is investigated how a simple FEM simulation can compute Q-factors for these modes and identify which will be problematic. How this might inform control system design is discussed.

Investigation of Electromagnetic Sub-Modeling Procedure for the Breeding Blanket System

The outcome of the electromagnetic (EM) analyses carried out during the DEMO pre-conceptual phase demonstrated that EM loads are relevant for the structural assessment of the breeding blanket (BB) and, in particular, for the definition of the boundary conditions at the attachment system with the vacuum vessel. However, within the scope of the previous campaign, the results obtained using simplified models only give a rough estimation of the EM loads inside the BB structure. This kind of data has been considered suitable for a preliminary assessment of the BB segments, but it is not considered representative as input for structural analysis in which a detailed BB internal structure (that considers cooling channels, thin plates, etc.) is analyzed. Indeed, mesh dimensions and computational time usually limit EM models that simulate a whole DEMO sector. In many cases, these constraints lead to a strong homogenization of the BB structure, not allowing the calculation of the EM loads on the internal structure with high precision. To overcome such limitations, an EM sub-modeling procedure was investigated using ANSYS EMAG. The sub-modeling feasibility is studied using the rigid boundary condition method. This method consists of running a global “coarse” mesh, including all the conducting structures that can have some impact on the component under investigation and inputting the obtained results on the detailed sub-model of the structure of interest as time-varying boundary conditions. The procedure was tested on the BB internal structure, taking as reference a DEMO 2017 baseline sector and the helium cooled pebble bed (HCPB) concept with its complex internal structure made by pins. The obtained results show that the method is also reliable in the presence of non-linear magnetic behaviour. The methodology is proposed for application in future BB system assessments.