Prediction of High-Speed Planing Hull Resistance and Running Attitude - A Numerical Study Using Computational Fluid Dynamics

Accurate predictions of the resistance and running attitude are key steps in the process of hull design and manufacturing. The predictions have traditionally relied on model testing, but this technique is both expensive and time consuming. In this study, the performance of CFD simulations of planing hulls is evaluated using two commercial software: ANSYS FLUENT, developed by ANSYS, Inc., and STAR-CCM+, developed by CD-adapco. This was done by predicting the steady resistance, sinkage and trim angle of one semi-planing and one planing hull in calm, unrestricted water. The Reynolds averaged Navier-Stokes equations with the SST k-! turbulence model was used along with the volume of fluid method to describe the two-phase flow of water and air around the hull. Furthermore, a two degrees of freedom solver was used together with dynamic mesh techniques to describe the fluid-structure interaction. The simulations were performed with both fixed and free sinkage and trim to make careful comparisons of the software and with experimental data. The results from the fixed sinkage and trim simulations of the planing hull in FLUENT and STAR-CCM+ show a good consistency. However, there is a significant difference in the pressure resistance obtained from the two codes that could not be explained. The free sinkage and trim simulations were mainly conducted in STAR-CCM+ due to problems with obtaining a stable solution in FLUENT. Froude numbers between 0.447 and 1.79 were simulated and the results follow the same trends as what is seen in the experimental data. The calculated resistance, sinkage and trim angle show good correspondence to experimental data in the planing region, where the errors of the predicted values are below 10%

Mandatory audit : Auditors perspective on how high accounting quality in smaller companies can be maintained without auditing as it is designed today

Bakgrund: Idag pågår en debatt om huruvida gränsvärdena för revisionsplikt ska höjas eller sänkas. FAR, enda branschorganisationen för revisorer, hävdar att revisionsplikten i de minsta aktiebolagen borde återinföras. Som stöd för detta har de en rapport från Riksrevisionen som visar att effekterna av intentionerna med avskaffandet av revisionsplikten för de minsta aktiebolagen i stort har uteblivit och att det istället fått negativa konsekvenser. Samtidigt hävdar flera bransch- och företagarorganisationer att Sverige kan hantera småföretagens redovisning utan att återinföra revisionsplikten och anser snarare att gränsvärdena bör höjas. Eftersom nästan alla Sveriges företag är småföretag med färre än tio anställda där ägare och ledning är samma person menar de att behovet av en oberoende kontrollfunktion som revision saknas. Det är tydligt att nuvarande situation inte är önskvärd. De mindre företagen har behov av tjänster som möjliggör att de kan utnyttja sina resurser på bästa sätt samtidigt som staten har behov av att säkerställa att lagar efterföljs, att skatt inte undandras och att ekonomisk brottslighet förhindras. Frågan kvarstår hur dessa båda behov bemöts på bästa sätt. Syfte: Syftet med denna studie är att beskriva yrkesverksamma revisorers syn för att identifiera hur hög redovisningskvalitet kan upprätthållas utan revision och revisionsplikt som den är utformad idag, så att redovisningen fortfarande blir tillförlitlig. På så sätt syftar vi till att öka lagstiftares och standardsättares förståelse för hur lagar och standarder ska utformas så att detta kan uppnås. Metod: I studien har en kvalitativ metod använts med utgångspunkt i en abduktiv forskningsansats. För att kunna besvara studiens frågeställningar har semistrukturerade intervjuer av åtta stycken yrkesverksamma revisorer på både större och mindre revisionsbyråer i Skaraborg genomförts. Slutsats: Studien visar att någon form av granskning/kontroll kan behövas i mindre företag för att hög redovisningskvalitet ska kunna upprätthållas utan revision. I de allra minsta företagen verkar behovet av rådgivning och fokus på att redovisningen är rätt gjord kunna vara mer viktig än en helt oberoende revision. Denna uppfattning är mest framträdande bland revisorer från mindre revisionsbyråer. Befintlig revisionsstandard resulterar i för mycket dokumentation och checklistebaserat fokus i de mindre företagen varvid större fokus borde läggas på revisorns professionella omdöme, för att revisionen ska bli kostnadseffektiv.Background: There is an ongoing debate whether or not the thresholds for mandatory audit in Sweden should be increased or decreased. FAR, the only trade association for auditors claims that the mandatory audit for the smallest companies should be reinstated. In support of their positions, they have a report from the Swedish National Audit Office which shows that the effects of the intentions with the abolition of the mandatory audit for the smallest companies have failed in general, and that it instead has had negative consequences. At the same time, several trade associations claim that Sweden can handle the small companies accounting without reinstating the mandatory audit and rather that the mandatory audit thresholds should be increased. Since most of Sweden’s companies are small companies with fewer than ten employees where the owner and management is the same person, they claim that there is no need for an independent control function as the audit. It is clear that the current situation is not desirable. Small companies need services which enable them to utilize the resources in the best possible way, whereas the government needs to ensure that laws are followed, tax is not avoided and that economic crime is prevented. The question remains how these two needs are best addressed.        Purpose: The purpose of this study is to describe professional auditors’ view in order to identify how high accounting quality can be maintained without the audit and the mandatory audit in its current form and still maintain the reliability of the accounting. In this way we aim to increase legislators’ and standard setters’ understanding on how laws and standards should be designed in order to achieve this. Method: In this study, a qualitative method based on an abductive research approach has been used. In order to answer the research questions of the study, semi structured interviews of eight professional auditors in Skaraborg, Sweden have been conducted at both smaller and larger audit firms.    Conclusion: The study shows that some form of review/control may be needed in smaller companies in order to maintain high accounting quality without auditing. In the smallest companies the need for advice and focus on that the accounting is done correctly seems to be more important than a completely independent audit. This view is most prominent among auditors from smaller auditing firms. Existing auditing standard results in too much documentation and checklist-based focus in smaller companies, wherein greater emphasis should be placed on the auditor’s professional judgment in order for the audit to be cost-efficient

Impact of laminate cracks under solder pads on the fatigue lives of ball grid array solder joints

This paper reports how the solder joint fatigue lives of three types of lead free plastic BGA components were affected by cracks formed in the printed PCB laminate during a thermal cycling test. The investigation showed that cracks were formed in the laminate for all three tested components. For one of the components having a large chip with solder joints located under the chip, very large cracks were formed in the PCB laminate beneath some solder pads.For lead-free solder joints to BGA components consisting of near eutectic solders based on tin, silver and copper, a large fraction of the solder joints may consist of one single tin grain. Due to anisotropy of tin grains, each solder joint to a BGA component will experience a unique stress condition which will make laminate cracking more likely under certain solder joints.The laminate cracks increased the flexibility of the joints and thereby improved the fatigue lives of the solder joints. Therefore, an estimation of the fatigue lives of solder joints to BGA components based on the results from a thermal cycling test may lead to an overestimation of the fatigue lives if products will be exposed to smaller temperature changes in the field than in the test.If cracks are not formed in the PCB laminate, or if the extent of cracking is small, single-grained solder joints can be expected to result in a high spread in failure distribution with some quite early failures