Marine Structures Services
Vipac offers a full range of design analysis and sea trial services in the areas of vibration and acoustics, structural integrity fatigue life, and underwater radiated noise. With over twenty-five years of experience with marine structures, Vipac can provide a comprehensive and efficient service via its offices located throughout Australia as well as Southeast Asia.
Vibration and On-board Acoustics
Vipac has extensive experience in the assessment and control of vibration and acoustics aboard marine structures.
Torsional vibration in diesel propulsion machinery; whirling vibration of line shafting, and axial vibration of thrust blocks are all specific areas of ship design which require special attention to ensure safe and reliable operation. Vipac is able to provide classification society approved design assessments, certification measurements, and specialist investigation techniques to solve operational problems.
Using techniques such as condition monitoring and machine fault diagnosis, Vipac is able to diagnose problems quickly and accurately and recommend corrective actions. Extended time between overhauls and component replacement minimises maintenance costs and avoids catastrophic breakdowns. It allows timely scheduling of overhauls and inventory.
Hull and Structural Vibration
Vipac are able to assess the dynamic characteristics of subsystems, such as engine foundations and surrounding hull, radio masts and funnels, using both Finite Element (FE) techniques and measurements of modal characteristics and response shapes, as well as strain measurements.
Shock isolation helps ship designers deal with effects of loads on equipment and local structure resulting from underwater explosions and wave impact. We undertake shock mount selection, configuration, and/ or assessments through analysis and testing.
Shipboard Noise Control
Many onboard systems, such as the main propulsion engines, induce noise and vibration in accommodation and working areas, e.g. bridge, and contribute to underwater radiated noise. Vipac utilises state-of-the-art methods, such as the AutoSEA software, developed by Vipac, to assess noise and vibration throughout the ship and its environment in order to ensure that specifications are met. Optimal noise abatement measures are included in the design phase. Similar methods, in conjunction with measured data, are used for the design of post production noise and vibration treatments.
Relevant treatments include absorptive materials, damping compounds, floating floors and bulkheads, enclosures, vibration isolation and silencers. In addition, Vipac performs analysis and assessment of noise generated by HVAC systems. This includes the actual HVAC plant, the air handling units and vents.
Vipac engineers are experienced in underwater acoustics with continual extension of that knowledge through projects concerning:
- Hull radiated noise from surface ships and submarines
- Buoyant fibre towed arrays for surveillance and exploration
- Fixed hydrophone arrays for vessel classification
- Hydrodynamic analysis of marine structures and vessels
Using advanced methods, prediction of noise signatures and modelling of underwater radiated noise from ships and submarines to the development of noise reduction measures is provided.
Sea Trials and Testing
In addition to testing associated with noise and vibration, Vipac provides specialised test capabilities including sea trial services.
Shaft Power Measurement
Vipac engineers are able to measure instantaneous torque and RPM on main propulsion or auxiliary machinery. Disputes between ship owners, builders, and engine suppliers over vessel speeds and engine power output can easily and conclusively be resolved.
Vipac maintains an extensive range of instrumentation including sound level meters and intensity probes, hydrophones, strain measurement equipment and multi-channel data acquisition systems and analysers.
Advanced Design and Analysis
- Concept Design (requirements and feasibility)
- Integration & Installation
- Preliminary Design & Specification
- Detailed Design
- Problem Diagnosis & System Identification
- Design Analysis & Development
- Test Requirements
- Synthesis of Analysis and Test
Vipac uses techniques such as finite element modelling to assist in natural frequency calculations and stress analysis of hulls, superstructures and superstructure attachments.
Finite Element Techniques
Vipac has extensive experience with FE analysis of subsystems as well as whole vessels particularly in the field of dynamic modelling.
Still water analysis and traditional trochoidal wave analysis determines overall hull girder bending moments and stresses. Vipac use these analyses for overall design and to validate FE models.
Ship motions and structural stresses due to various sea states and associated wave spectra present the most realistic criteria for ship design.
Vipac has performed advanced analysis based upon the Response Amplitude Operators (RAO’s) for ship motion, using linear strip theory for the excitation by unit sinusoidal waves from various directions. Application of the resulting hydrodynamic and inertia loads to an FE model of the whole vessel allowed calculation of normalised stresses within the structure. These were scaled to se state induced stresses by convolution with sea state spectra.
The analyses provide a powerful and versatile design tool for analysis ships for both static and dynamic sea states and can be used to extract extreme and RMS responses for any quantity, i.e. stress, force, bending moment, etc for any sea state. Dynamic Analysis is particularly suited to the following investigations:
- Evaluation of modification to the existing structure
- Determination of fatigue loading in critical area
- Life extension studies