9000吨供油船机舱设备选型与热平衡分析外文翻译资料

4.0 MODELING GUIDELINES

4.1 Units (optional)

Consistent units are needed for a finite element model. The recommended units are millimeters,

seconds,Newtons,and 1000 kilograms.Alternate units that may be used are centimeters, seconds, Newtons, and 100 kilograms; or meters, seconds, Newtons, and kilograms.

Alternately, instead of specifying mass in 1000 kg, or 100 kg, mass could be specified in kilograms, but a PARAM WTMASS card with a correct value is needed. For the mm-s-N-kg model the value is .001, and for cm-s-N-kg model .01 is needed. This method is not recommended because of unit consistency problems with other models. This method should be avoided unless absolutely necessary.

SI units are needed for a statistical energy analysis model and energy flow method.

4.2 Contents (optional)

Both direct SEA model and hybrid FEA/EFM/SEA model consist of a fully trimmed vehicle body and the acoustic space inside vehicle cabin. The door and door cavity are also included. The suspension/chassis/powertrain portion is not part of the model. The structure-borne inputs are applied at the attachment points on the body side. The acoustic treatments, including seats, trims,carpet, headliner, dashmat, etc, are modeled into the acoustic subsystems or in the junctions between the panels to the interior acoustic space.

4.3 Coordinate Systems (optional)

The usual car coordinate system is used.

4.4 Modeling Techniques (optional)

AutoSEA is the software used for statistical energy analysis. Using AutoSEA Version 1.5 can generate a direct SEA model for the structure-borne noise.

Due to the limitation of AutoSEA Version 2 on structural representation, it is not suitable for modeling structure-borne noise paths. However, by using finite element analysis and energy flow method, the vehicle panel responses can be calculated. Using the panel response as the input load to the model built by AutoSEA 2, the AutoSEA 2 model is still capable to predict the acoustic responses in the vehicle cabin. In the following paragraphs, these two approaches will be detailed separately.

4.4.1 Direct SEA model by using AutoSEA 1.5

There are three major steps to build a SEA model by using AutoSEA Version 1.5. Step 1 is to create material database, trim database and damping database. Step 2 is to define the subsystems through partition of the vehicle. Step 3 is to connect the subsystems through junction.

4.4.1.1 Database

4.4.1.1.1 Material database

Material database consists of the material type for the vehicle body structures, trim panels and acoustic cavity. For non-porous material, e.g., steel and glass, the material property includes the density, Youngrsquo;s modulus, Poisson ratio, and shear modulus. For porous material, e.g., air, the material property includes density and speed of sound.

In order to model the mass effect of the damped steel panel, the density of the damped steel panel is modeled by increasing the density of the steel to count the added mass and keep the steel panel thickness. However, the stiffness effect of the damped steel panel is not modeled.

4.4.1.1.2 Trim database

Trim database consists of the acoustic treatment in the vehicle, e.g., headliner, dashmat, carpet, absorptive pad behind the trim panel. A plug-in of 5-layer trim modeler is used for modeling fiber based absorptive material. A plug-in of foam modeler is specific for modeling foam. In 5-layer trim modeler, the flow resistivity and thickness of the porous material is needed. The surface density is needed to model the impervious layer. In foam modeler, the thickness, density, Youngrsquo;s modulus, Poisson ratio, damping loss factor, porosity, tortuosity, and flow resistivity of the foam are needed.

4.4.1.1.3 Damping database

Damping database consists of the spectrum for the damping loss factor for the panels and acoustic cavities, and the absorption coefficient for the acoustic treatments. These values can be

generated through testing. By using built-in analysis capability in AutoSEA Version 1.5, the

absorption coefficient of the acoustic treatment detailed in the trim database can be generated.

4.4.1.2 Vehicle partition and subsystem definition

Direct SEA model models trimmed body and acoustic space inside vehicle cabin and the doors. The suspension/chassis/powertrain portion is not modeled. The trimmed body is modeled into two groups, structural frames and panels. The acoustic treatments, including seats, trims, carpet, headliner, dashmat, etc, are modeled into the junction between the panels to the interior acoustic space. The connection line between the panel and the frame is the natural boundary of the panel. For certain large panels, e.g., floor and roof, they can be separated into left side and right side or front portion and rear portion.

The acoustic space inside vehicle cabin is divided into many acoustic subsystems. Laterally, the cabin can be divided into left side, central, and right side. Longitudinally, the cabin can be divided into windshield/IP/toepan, front row seat, 2nd row seat, 3rd row seat, and cargo/trunk space. Vertically, the cabin can be divided into head level, waist level and foot level. The door cavity is also modeled separately. The seat is not modeled as individual subsystem. However, the absorption of the seat is counted in the acoustic subsystems adjacent to it.

4.4.1.2.1 Vehicle structural frame modeling

Most of the structural frames of the vehicle body are modeled as the type of “Cylinder Flexural” due to the natural shape and the minimal effect of in-plane modes. These structural frames include all the rails, cross members, and pillars. The parameter of the “Cylinder Flexural” includes material, damping, length side, included angle, thickness, radius, fluid loading, use modal formulation, and user-defined parameter. Materi

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