Xvib
Xvib performs flow-induced vibration analysis of a single tube in a heat exchanger bundle. The program uses a rigorous structural analysis approach to calculate the tube natural frequencies for various modes and offers flexibility in the geometries it can handle.
Although Xist automatically checks all its cases for vibration, some cases require an in-depth analysis. Xvib is designed to help the expert user analyze these cases. A complete Xvib case can be created directly from the Xist tube layout drawing for a particular tube.
Program Capabilities
Xvib calculates multispan natural frequencies for straight and U-tubes using 3D structural analysis methods. The analysis includes calculation of tube deflections for the first and higher modes to predict potential vibration problems by considering fluidelastic instability and vortex shedding vibration mechanisms.
The analysis can be performed for straight or U-tubes with up to 900 spans. Supports (baffles, DTS™, STS™) can be specified at any location along the tube; the number of supports is limited only by the number of spans that Xvib can handle. For straight tubes, you may choose not to use supports or may select a tubesheet or baffle as an end support. At the U-bend, you may also specify no supports or select a tubesheet or baffle as an end support. Supports may also be placed in the U-bend span. Analysis can be performed for up to fifteen modes, depending on the number of spans being analyzed.
Each span is divided into five elements, for which two-dimensional velocities and shellside densities can be specified. For increased detail in the analysis, the number of elements can be increased by multiples of five by subdividing a span and specifying no supports between the elements. The location of supports in the U-bend is specified by providing the bend curvature radius and the corresponding span angle.
You can transfer support (span) information, as well as crossflow velocities and shellside fluid densities, easily from Xist to Xvib for detailed analysis. Just drag-and-drop any Xist case into Xvib or right-click a tube in the Xist tube layout.
Results
Results of flow-induced vibration analysis for each mode requested include
- natural frequency of the tube
- maximum ratio of fluid gap velocity and critical velocity
- maximum tube deflections due to vibration by vortex shedding
- location of the span with the maximum amplitude due to vortex shedding
Xvib also generates detailed results of the vibration analysis. These include
- ratio of the fluid gap velocity and critical velocity for each node in two directions
- tube deflections due to vortex shedding at each node in three directions
- mode shapes
Graphical output includes
- Plot of mode spaces for each mode calculated
- Plot of in-plane and out-of-plane velocity profiles