Hybrid isolation of structure-borne sound

Interior noise problems become more important due to the tendency to construct lighter vehicles. An important source for interior noise in a vehicle is the engine. The structural vibrations induced by the engine will transmit through the vehicle and will finally result in interior noise elsewhere in the vehicle, so-called structure-borne sound. To reduce the interior noise a solution is sought in a combination of passive and active isolation (hybrid isolation) of the engine. A project has been started to investigate this type of isolation and to develop experimentally validated numerical simulations for the design of hybrid isolation system. \ud This paper focuses on the numerical modelling approach for this type of problems. The model consists of a structural and a bounded acoustic part that are representative for a vehicle. The responses of both parts are determined efficiently with modal superposition. The controller design, necessary for the active part of the isolation, is performed with the optimal control theory that is based on minimization of a cost function. Different cost functions will be compared with each other with emphasis on the performance of the structural related cost functions (e.g. minimization of structural velocities) in comparison with the acoustical cost functions (e.g. minimization of sound pressures)

Numerical modelling of rubber vibration isolators

An important cause for interior noise in vehicles is structure-borne sound from the engine. The vibrations of the source (engine) are transmitted to the receiver structure (the vehicle) causing interior noise in the vehicle. For this reason the engine is supported by rubber isolators for passive isolation in especially the high-frequency region. To make a good judgment of the characteristics of a vibration isolator in the design process, it is useful to use numerical models. In this paper a cylindrical vibration isolator is modelled numerically with the Finite Element package ABAQUS. The investigation is split in two parts: first a nonlinear analysis is performed for different pre-deformations of the mount. After that, a linear harmonic analysis is superimposed on the pre-deformed isolator. The structure-borne sound is transmitted by the isolator by six degrees of freedom, so the harmonic analysis must be performed for different excitations. With the results the behavior of the isolator can be represented by dynamic stiffness matrices as function of the frequency and predeformation. These matrices can be used to model the passive isolation components as part of numerical models of hybrid isolation systems. These isolation systems describe a combination of active and passive isolation to reduce the structure-borne sound transmission to receiver structures

Parsing the heterogeneity of Major Depression:Biological subtyping and other statistical approaches to unravel the causes of Major Depression

Major Depression (MD) is the largest contributor to the global burden of disease. Unfortunately, standard pharmacological treatments are not always effective. Combined with the heterogeneity of the patient population, this indicates that there is likely no biological disturbance (e.g., impaired serotonin) underlying depression in all MD patients. Indeed, many potential risk factors for MD have been identified, ranging from genetic and environmental variables to different types of biological disturbances. The first part of this thesis provided more insight into the etiology of MD by using rich datasets and novel methodology to identify the most important predictors of MD. Family history of depression and anxiety was one of the most important predictors of both onset and recurrence of MD. This thesis also showed that the gender gap in MD prevalence arises early in life and remains stable over the lifetime. The second part of this thesis addressed the heterogeneity of the MD population by investigating if and how well studies based on biological data might enable the discovery of more homogeneous subtypes of MD. The results indicated that although subtyping based on etiology and pathophysiology is a promising research avenue, no definitive conclusions can be drawn as of yet. Importantly, the results showed that this kind of subtyping research is a very complex endeavor that requires elaborate and costly data collection as well as intricate research designs that enable the evaluation of the robustness of the model results

Biological embedding of maternal postpartum depressive symptoms: The potential role of cortisol and telomere length.

Although maternal postpartum depressive symptoms (PDS) are associated with child behavior problems, the underlying biological mechanisms are poorly understood. Thus, the current study focused on 193 healthy mother-child dyads and investigated child cortisol and telomere length as potential mediating factors. At 3 and 6 months postpartum, mothers reported on PDS. At age 6, children provided saliva and buccal swab samples. At age 10, mothers and children reported on child behavior problems. Structural equation modelling revealed (a) no association between PDS and child behavior problems and thus no possibility of mediation, but that (b) lower cortisol forecast more child-reported internalizing problems, and (c) shorter telomere length predicted more child-reported internalizing and externalizing problems. These findings raise mediational questions about the determinants of these biomarkers