Virtual Design Methodology Research Articles

CFD simulation-based predesign of an advanced gas-diesel combustion concept

The greenhouse gas saving potential of using gaseous fuels with high methane content (e.g. natural gas) in internal combustion engines instead of conventional liquid fossil fuels (e.g. petrol, diesel) is considerable due to the comparatively low emission of carbon dioxide resulting from the low C/H ratio of methane. However, to fully exploit this potential, it is of utmost importance to keep methane slip at a very low level. In contrast to mixture aspirated gas engines and diesel-gas engines, the gas-diesel combustion concept avoids methane slip nearly completely since the gaseous fuel is directly injected into the combustion chamber at the end of the high-pressure phase of the engine cycle, resulting in mixing-controlled combustion with low emission of unburned hydrocarbons. An advanced high-speed large engine concept based on the gas-diesel combustion process was developed. An effective and reliable virtual design methodology was applied during the development of the concept. The methodology comprehensively combines 3D CFD and 1D simulation tools in the combustion concept predesign phase with experiments on a single-cylinder research engine in the concept validation phase. A major challenge in the virtual design of this dual fuel combustion process is the large number of degrees of freedom that result in particular from the use of a fully flexible combined gas/diesel injector. This paper describes in detail the role of 3D CFD simulation in this approach, which allows precise prediction of the optimal geometries and operating strategies for high-efficiency and low-emission engine operation.

Virtual Design Method for Controlled Failure in Foldcore Sandwich Panels

For certification, novel fuselage concepts have to prove equivalent crashworthiness standards compared to the existing metal reference design. Due to the brittle failure behaviour of CFRP this requirement can only be fulfilled by a controlled progressive crash kinematics. Experiments showed that the failure of a twin-walled fuselage panel can be controlled by a local modification of the core through-thickness compression strength. For folded cores the required change in core properties can be integrated by a modification of the fold pattern. However, the complexity of folded cores requires a virtual design methodology for tailoring the fold pattern according to all static and crash relevant requirements. In this context a foldcore micromodel simulation method is presented to identify the structural response of a twin-walled fuselage panels with folded core under crash relevant loading condition. The simulations showed that a high degree of correlation is required before simulation can replace expensive testing. In the presented studies, the necessary correlation quality could only be obtained by including imperfections of the core material in the micromodel simulation approach.

Validation of the computational fluid–structure interaction simulation at real-scale tests of a flexible 29 m umbrella in natural wind flow

The sensitivity of membrane structures to wind loads due to their flexibility and small inertial masses raises the question of their behavior under natural wind conditions. Particularly transient wind loads could lead to dynamic amplification of the structural response. The assessment of the dynamic response of membrane structures is complex due to their special load carrying behavior, their material properties, and their distinct structural interaction with flow induced effects. Computationally intensive fluid–structure interaction simulation could overcome simplifications and limitations of existing approaches, especially small scale wind tunnel tests, and allow the assessment of all relevant structural and fluid phenomena. This paper outlines a virtual design methodology for lightweight flexible membrane structures under the impact of fluctuating wind loads and provides results on the unique validation of the method at real-scale tests of a highly flexible 29 m umbrella.

Virtual Design Methodology for Lightweight Structures — Aerodynamic Response of Membrane Structures

This paper presents the current application of numerical Fluid-Structure Interaction (FSI) simulation to the architectural and structural design of large umbrella structures and the work on generating atmospheric wind inflow conditions for numerical simulations. This article outlines a virtual design methodology for structures under the impact of fluctuating wind loads and provides results on worked examples

Design for ‘X’-abilities of RTM Products - A Graph Theoretic Approach

The resin transfer molding (RTM) process has been widely accepted for fabricating automobile, aircraft, and spacecraft components with high strength and stiffness to weight ratios of the composite products. This process is widely acceptable in various industries, i.e., wherever low manufacturing cost with high mass production is required compared to other processes like compression molding and hand lay-up. Designing the composite products requires a lot of skill with multidisciplinary knowledge. Considering the design and the manufacturing strategies as well as the product development, every aspect of the design is to be considered in a single approach without losing any information. The present approach gives a new methodology for combining all the design aspects together in concurrent design methodology, which finally leads to the achievement of the six-sigma limits i.e., almost defect-free products from the RTM technology. The present paper utilizes the advantages of the graph theoretic approach to considering all the design aspects together in a single methodology with the help of matrix algebra and permanents. It is basically a virtual design methodology, which decides the process, the product strength, and the weakness with the help of a multinomial defined by using the matrix algebra. The design index, developed using the proposed methodology, really decides if the overall design is acceptable or not by considering all the aspects of the design related to the product, process, environment, etc. Finally, a step-by-step procedure is proposed to help generate a new algorithm for software coding.

Acoustic control in a tractor cabin using two optimally designed Helmholtz resonators

A virtual design methodology is developed to minimize the noise in enclosures with optimally designed, passive, 20 acoustic absorbers (Helmholtz resonators). A series expansion of eigenfunctions is used to represent the acoustic=20 absorbers as external volume velocities, eliminating the need for a solution of large matrix eigenvalue problems. A determination of this type (efficient model/reevaluation approach) significantly increases the design possibilities when optimization techniques are implemented. As a full-scale demonstration, the acoustic response from 90–190 Hz of a tractor cabin was investigated. The lowest cabin mode proposes a significant challenge to a noise control engineer since its anti-node is located near the head of the operator and often generates unacceptable sound-pressure levels. Exploiting the low-frequency capability of Helmholtz resonators, lumped parameter models of these resonators were coupled to the enclosure via an experimentally determined acoustic model of the tractor cabin. The virtual design methodology uses gradient optimization techniques as a post-processor for the modeling and analysis of the unmodified acoustic interior to determine optimal resonator characteristics. Using two optimally designed Helmholtz resonators, potential energy was experimentally reduced by 3.4 and 10.3 dB at 117 and 167 Hz, respectively.