708 最適化手法を用いた遮音壁の設計に関する研究(機械力学・計測制御II)

Hong Kong is a crowded city where pavements, lanes, hawker areas, trunk roads and highway are closely built. With heavy traffic flow on complex road networks, the noise barriers located in the urban centre usually adjacent to commercial centres and residential buildings. The design of noise barriers is therefore needed to be in harmony with the landscape of the neighbourhood. Different kinds of green noise barrier systems combined with soil and vegetation had been developed across Europe and the USA in recent years. It is believed that an effective controller of noise shall be visually attractive especially for residents who are adjacent to the roads. A number of noise barriers with vegetation were successfully implemented in European Countries. Nevertheless, these engineering techniques cannot be fully applied to Hong Kong due to the over-crowded living environment.
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\nA well-designed green noise barrier system is the critical reason for successful application to sustain the vegetation and to insulate and absorb noise. The objective of this study to investigate different kinds of green noise barriers and come up with some guidelines for design consideration in order to optimize the green noise barriers. The study provides a thorough analysis of the available green noise barrier systems across the world, including a look at all the potentials benefits from environmental and socio-economics perspectives.
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\nThe pilot field measurement was conducted at Yeung Uk Road where green noise barriers located between a heavily travelled main road and residential area in Tsuen Wan, to measure the SPL and Leq noise levels to assess the effectiveness of the green noise barriers. No significant attenuation effect is observed on the green noise barrier which has to be attributed to the median placement and over-crowded urban environment.
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\nOnline questionnaires and interviews are conducted to investigate the effects of vegetation on the perception of green noise barriers. Results show that 78% of the respondents preferred vegetation rather than concrete (0.1%) and other materials. 77% like the aesthetics appearance of vegetation and 86% are willing to bear the cost. In general, 95% of the respondents agreed green noise barriers should be promoted in Hong Kong. The results assured that (1) vegetation on green noise barrier is aesthetically pleasing and mostly preferred; (2) people are willing to pay for green noise barrier for aesthetics; (3) aesthetic or vegetated screen is important in determining human response to noise which improved public perception of traffic noise due to visual and psychological relief.
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\nThe outcome of the study indicated that it is feasible to promote green noise barriers in Hong Kong, with the evidence of the potential benefits, technical experience and public support. It is also suggested that the living wall modular system is the best system which is suitable for the application in Hong Kong.

Aerodynamic impacts of high-speed trains on city-oriented noise barriers: A moving model experiment

The height of a noise barrier required to give a certain insertion loss is strongly dependent on the elevation of the noise source above the ground. Currently, noise barrier design methods assume equivalent point source heights for different types of vehicles, but these have never been substantiated by measurements. This study used a microphone array, with parametric processing, to evaluate the equivalent noise source height of 100 different vehicles. The results give the noise source position as a function of frequency between 200 Hz and 2.5 kHz. The relative importance of engine, stack and tire noise on the source height is apparent. It was found that the equivalent source on heavy trucks is at 1.2 m, medium trucks 0.7 m, and small vehicles 0.6 m, above the ground. [Work sponsored by Florida Department of Transportation.]

The use of a single vertical screen to obstruct the propagation of noise from source to receiver over hard and soft flat ground is well known. However, in addition to considerations of acoustical efficiency, the design of road traffic noise barriers depends on many other factors. Site conditions, planning restraints and visual considerations will affect the final selected design, as will engineering considerations related to the construction materials, the weather loading due to wind and precipitation. The aim of this article is to show both the acoustical benefits and drawbacks of using a screen adjacent to a highway located in a cutting dip in otherwise flat ground topography.

Optimal rigid and porous material distributions for noise barrier by acoustic topology optimization

A shape design sensitivity analysis and optimization procedure is proposed using a meshfree method. A CAD tool connection is established to facilitate the seamless integration of structural modeling, simulation, and design optimization. A new CAD-based method for design velocity computation is proposed, applicable to both the meshfree method and the finite element method. A shape design variable can be chosen among the geometric parameters defined in the CAD model in order to support a concurrent engineering environment. A new CAD-based method for updating the discrete model is proposed, such that the meshfree model is automatically updated in a continuous and consistent way during design optimization. The proposed method is applied to 2D and 3D linear elastic problems, as well as to a large deformation hyperelastic problem.

Noise pollution from construction sites has become a major problem for major cities with the continued rapid development as well as redevelopment of cities. These construction sites, in particular for new subway systems, are often near to residential and commercial buildings. A better understanding and characterization of noise profiles will be required for project management and planning as well as environmental impact assessment. In this study, instead of using the typical type 1 sound level meters for the measurement of noise profiles emitted from construction equipment and processes commonly done in construction industry, we attempt to characterize the noise profiles of common construction equipment at their respective noise source using an Acoustic Array or Acoustic Camera. The study also highlighted the significant presence of low-frequency noise at construction sites for some construction equipment and processes. This may have some implications for the design of noise barriers at construction sites.

Roadside noise barrier helps to reduce downwind pollutant concentrations from vehicle emission. This positive characteristic of the construction feature can be explained by its interaction with flow distribution and species dispersion. In this paper, a three-dimensional numerical model has been developed to simulate highway pollutant dispersion—a realizable k-ε model was employed to model turbulent flow, and a non-reaction species dispersion model was applied to simulate species transport. First, numerical models were validated with experimental data, and good agreement was observed. Then, detailed simulations were conducted to study double barriers’ effects on highway pollutant dispersion under different settings: noise barriers with different heights, noise barriers with and without edge effects, and different atmospheric thermal boundary conditions. Results show that: (1) Noise barriers without edge effects cause bigger downwind velocity and turbulence intensity than noise barriers with edge effects. (2) At ground level, lower downwind pollutant concentration and higher pollutant concentration, near upwind barrier and between barriers, are observed for noise barriers without edge effect cases; higher on-road pollutant concentration can be seen near barrier side edges for cases with edge effect. (3) Downwind velocity and turbulence intensity increase as barrier height increases, which causes reduced downwind pollutant concentration. (4) With the same barrier height, under unstable atmospheric boundary condition, the lowest pollutant concentration can be found for both downwind and between barriers. Overall, these findings will provide valuable inputs to noise barrier design, so as to improve roadside neighborhood air quality.

The one- and two-dimensional inviscid Euler equations are formulated in an integro-differential form for shape design sensitivity analysis and optimization. The principal tool employed to derive the performance derivative sensitivity equations is the variational method, which is a continuous alternative to the discrete sensitivity analysis. Along with the sensitivity equations, the co-state equations and their boundary conditions are derived. Thereafter, based on the modal analysis of Von Neumann theory, the stability limits of the co-state equations are investigated. The stability characteristics of the co-state equations are compared with those of the Euler equations. Finally, using the criteria from the stability analysis of the state and co-state equations, some results of shape design optimization and sensitivity analysis for both quasi one- and two-dimensional Euler equations are presented. Copyright © 1999 John Wiley & Sons, Ltd.

In this paper, neural network- and feature-based approaches are introduced to overcome current shortcomings in the automated integration of topology design and shape optimization. The topology optimization results are reconstructed in terms of features, which consist of attributes required for automation and integration in subsequent applications. Features are defined as cost-efficient simple shapes for manufacturing. A neural network-based image-processing technique is presented to match the arbitrarily shaped holes inside the structure with predefined features. The effectiveness of the proposed approach in integrating topology design and shape optimization is demonstrated with several experimental examples.

Because of their superior mechanical, structural, and electronic properties, graphene sheets (GSs) are supposed to be components of nanoelectromechanical systems (NEMS). In this study, we carry out shape and structural optimization of GSs with topological defects in natural vibration problem to enhance their fundamental frequencies. At first, we model GSs as continuum frame models based on the molecular mechanics method. Then, we carry out shape design optimization of GSs by using a developed free-form optimization method for frame structures. In the shape design optimization, we use the fundamental frequency as objective function and enhance it considering volume constraint and repeated eigenvalues. Next, we derive the optimal atom structures of GSs with topological defects using a combination of the Phase-Field-Crystal method, the Voronoi tessellation method, and molecular dynamics simulation. The numerical results show that the fundamental frequencies of GSs can be significantly increased according to the shape and structural design optimization, and we can get their optimal atom structures with defects, which is helpful for designing GSs as components in NEMS.

Because high noise levels in industrial plants can be injurious to workers and lead not only to psychological but also to physiological ailments, noise control in factories becomes essential. In order to overcome the noise impact emitted from a multi-noise plant, a sound barrier, a popular noise control strategy, has been used in the industrial field for a long time. Yet, the traditional method in the design of a sound barrier is time-consuming. Recently, to economically improve acoustical performance, a new strategy (flexible allocation) is applied; however, the acoustical performance is still insufficient. In order to quickly, efficiently, and economically control the noise level specified by the Environmental Protection Administration, interest in shape optimization of a sound barrier in conjunction with equipment allocation around the plant's boundary is rising. In this paper, the novel technique of simulated annealing (SA) in conjunction with the theoretical sound propagation model and the method of minimized variation square is applied in the following numerical optimizations. Before a sound barrier is optimized, the sound propagation from one single noise is tested and compared with the experimental data for the purpose of accuracy within the mathematical model. Moreover, three kinds of sound barrier systems have been fully discussed and optimally shaped by the SA. The results reveal that the sound barrier can be properly shaped. Consequently, this paper may provide an efficient and rapid methodology in the shape-optimized work for a sound barrier installed in a multi-equipment plant.

The drive for improved flexibility and reusability in satellite launch systems has brought a resurgence in the popularity of scramjet-powered access-to-space launch vehicle concepts. A challenge in scramjet-powered accelerator vehicles is achieving positive thrust margins at the high-speed end of their flight envelopes. As a consequence, scramjet-powered vehicles typically rely on highly integrated airframe-engine configurations. However, due to the tight integration, the geometries and the flow physics are complex. An automated optimisation method seems an excellent candidate approach to explore the complex design space of hypersonic vehicles. This thesis focuses on the development and application of a particular optimisation method, adjoint-based optimisation, to aid in efficient aerodynamic design in hypersonic flows.Shape optimisation of scramjet-powered vehicles requires many design parameters to capture the geometric detail, and, since the flow physics is complex, the fidelity of Reynolds-Averaged Navier-Stokes (RANS) analyses is desirable. The combination of many design parameters and an expensive objective function evaluation drives the need for gradient evaluation methods that scale well with the number of design variables. An advantage of the adjoint method is that all shape sensitivities for an objective function are evaluated at the cost of only one flow solution and one adjoint solution. As a result of its efficiency, the adjoint method has become widely used for aircraft design, evolving to the design optimisation of full configurations. Despite the wide use of adjoint methods in aircraft optimisation, there has been very little application to hypersonic vehicle design.Several high-speed adjoint solvers have been reported in the literature, however, a majority of these works have only verified the adjoint sensitivities, few have followed on to demonstrate the method for use in design optimisation. The contribution of this work is the description and application of a discrete adjoint solver in high-speed compressible flow optimisation.What is unique in this work is a demonstration that complex-step differentiation works well to linearise a second-order spatially accurate unstructured RANS solver. In particular, the approach presented in this work utilises the k − ω turbulence model in high-speed ducted flow configurations.As part of this work, to provide flow analysis with a rapid turn-around, an unstructured steady-state RANS solver driven by a Jacobian-Free Newton-Krylov method was developed. Turbulence is modelled using the two-equation k − ω turbulence model. The Newton method is globalised by using the pseudo-transient approach. A restarted GMRES method is used to solve the system of linear equations arising when solving for the Newton steps. Evaluation of the matrix-vector products required in the GMRES algorithm is accomplished by Frechet derivatives using imaginary perturbations in the complex plane. This is necessary to achieve robust convergence of the types of turbulent hypersonic flows considered in this work. Equation scaling ensures that the linear solver provides an adequate solution of the linear system, especially for turbulent flows, where the flow and turbulence variables differ by several orders of magnitude. Incomplete lower-upper preconditioning with zero-fill is used to accelerate linear system convergence. To achieve adequate residual convergence for flows with embedded shocks, limiter freezing is required to prevent early stall. The developed flow solver is verified using several methods, including the Method of Manufactured Solutions.Several validation cases from the literature are presented to establish the appropriateness of the implemented physical models for design analysis in high-speed flow.An accompanying discrete adjoint solver was developed to provide efficient computation of the required shape sensitivities. The primary complication of linearising the flow solver routines is handled via a complex-step derivative approach. Targeted differentiation is employed to provide an efficient means of constructing the adjoint operator. The adjoint gradients are verified against a complex variable direct-differentiation method.The flow and adjoint solvers are coupled to the open-source optimisation library, DAKOTA, to perform design optimisation in high-speed flows. Design surfaces are parameterised using Bezier curves and mesh deformation is achieved by the inverse distance weighting method. Two optimisation applications are presented here as a demonstration of the development work: (a) wave drag minimisation of an axisymmetric body; and (b) hypersonic inlet design optimisation. For the case of axisymmetric bodies, the optimal shape determined by this work compares favourably to several minimum-drag power-law bodies published in the literature. The second application is the redesign of the P2 hypersonic inlet. The chosen objective function aimed at removing the reflected cowl shock whilst obtaining the desired compression ratio. The results presented show that the optimiser has removed the reflected shock while achieving the desired compression ratio, at no cost to the inlet performance metrics.The conclusions are that the developed discrete adjoint-based optimisation framework does work well in a hypersonic flow context and that the use of complex-step differentiation is a key enabler in the implementation. In particular, the inlet example presented in this work demonstrates the efficiency, accuracy, and applicability of discrete adjoint-based optimisation to design analysis in turbulent high-speed flow.

This project created a framework for efficient, accurate, and scalable deep neural network representations of design optimization problem solutions. The inputs to these DNN representations are the vector of design requirement parameters, the outputs are the optimal design variables, and the goal is to learn the map from inputs to outputs (i.e., inverse design). The team addressed the problem of the optimal shape design of aerodynamic lifting surfaces—in particular aircraft wings—using a Reynolds-Average Navier Stokes model to govern the CFD-based aerodynamic shape optimization. The inverse design map for such problems is very complex and high-dimensional, involving inputs and outputs on the order of 1000s. To approximate this inverse design map, the team developed algorithms to construct parsimonious DNN architectures, which automatically identify low-dimensional manifolds in which design requirements affect optimal shape parameters, and trained these architectures with multifidelity optimization methods. The resulting methodology accurately and automatically designs optimal aerodynamic lifting surfaces with very high accuracy (99%) at interactive speeds, of the order of milliseconds, resulting in factors of one million or more speedup relative to CFD-based design optimization.

Finite Element analysis is the most widely used computer based analysis method. Design optimization algorithms recently integrated into finite element analysis programs provide iteration capabilities not available with manual methods. In the automated optimization, the model is created and the loads are specified. Optimal characteristics such as weight, shape and design are selected. The optimization program checks the design and updates the model until it converges on a best solution to meet the optimal characteristics and design criteria. This paper reviews the optimization algorithms currently used in design optimization for weight, shape, and structural response.